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Sample records for early holocene monsoon

  1. Reconstruction of Last Glacial to early Holocene monsoon variability from relict lake sediments of the Higher Central Himalaya, Uttrakhand, India

    DEFF Research Database (Denmark)

    Juyal, N.; Pant, R.K.; Basavaiah, N.

    2009-01-01

    Proglacial lake sediments at Goting in the Higher Central Himalaya were analyzed to reconstruct the summer monsoon variability during the Last Glacial to early Holocene. Sedimentary structures, high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced...... fluctuating monsoonal conditions. Optically stimulated luminescence (OSL) dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka. During this period, Goting basin witnessed moderate to strengthened monsoon conditions around 25 ka, 23.5 ka–22.5 ka, 22 ka–18 ka, 17 ka–16...... correspondence at the millennial scale between our data and that of continental and marine records from the Indian sub-continent suggests that Goting basin responded to periods of strengthened monsoon during the Last Glacial to early Holocene. We attribute the millennial scale monsoon variability to climatic...

  2. East Asian monsoon variation and climate changes in Jeju Island, Korea, during the latest Pleistocene to early Holocene

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    Lee, Seung Hyoun; Lee, Yong Il; Yoon, Ho Il; Yoo, Kyu-Cheul

    2008-09-01

    A 4.96-m-long sediment core from the Hanon paleo-maar in Jeju Island, Korea was studied to investigate the paleoclimatic change and East Asian monsoon variations during the latest Pleistocene to early Holocene (23,000-9000 cal yr BP). High-resolution TOC content, magnetic susceptibility, and major element composition data indicate that Jeju Island experienced the coldest climate around 18,000 cal yr BP, which corresponds to the last glacial maximum (LGM). Further, these multi-proxy data show an abrupt shift in climatic regime from cold and arid to warm and humid conditions at around 14,000 cal yr BP, which represents the commencement of the last major deglaciation. After the last major deglaciation, the TOC content decreased from 13,300 to 12,000 cal yr BP and from 11,500 to 9800 cal yr BP, thereby reflecting the weakening of the summer monsoon. The LGM in Jeju Island occurred later in comparison with the Chinese Loess Plateau. Such a disparity in climatic change events between central China and Jeju Island appears to be caused by the asynchrony between the coldest temperature event and the minimum precipitation event in central China and by the buffering effect of the Pacific Ocean.

  3. Wetlands sediment record from the upper Yarlung Tsangpo valley, southwest Tibetan Plateau, reveals mid-Holocene Epipaleolithic human occupation coincident with increased early and mid-Holocene wetness driven by enhanced Indian Monsoon rainfall

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    Hudson, A. M.; Olsen, J. W.; Quade, J.; Lei, G.; Huth, T.; Zhang, H.; Perreault, C.

    2016-12-01

    The headwaters of the Yarlung Tsangpo river valley, located in the southwestern Tibetan Plateau, are characterized by a cold and dry climate, but contain abundant river-marginal wetlands environments, which fluctuate in extent in response to changes in local water table elevation. This region receives 80% of precipitation from the Indian Monsoon, which forms the dominant control on moisture availability, and hence wetlands extent. Our paleowetlands record, based on 14C dating of organic-rich paleowetlands deposits, provides a novel record of Holocene monsoon intensity. The wetlands deposits consist of four sedimentary units that indicate decreasing wetlands extent and monsoon intensity since 10.4 ka BP. Wet conditions occurred at ˜10.4 ka BP, ˜9.6 ka BP and ˜7.9-4.8 ka BP, with similar-to-modern conditions from ˜4.6-2.0 ka BP, and drier-than-modern conditions from ˜2.0 ka BP to present. Wetland changes correlate with monsoon intensity changes identified in nearby records, with weak monsoon intervals corresponding to desiccation and erosion of wetlands deposits. Dating of in situ ceramic and microlithic artifacts in wetlands sediments at multiple sites indicates Epipaleolithic human occupation of the YT valley after 6.6 ka BP. Artifact typology study reveals a similar microlithic technology was employed across the high plateau interior, but XRF obsidian provenance reveals separate northeast and southwest lithic conveyance zones. This indicates widespread colonization of the high, arid Tibetan Plateau interior by one or more highly mobile human populations during the early and mid-Holocene, coincident with favorable warm, wet climate conditions.

  4. Abrupt Holocene changes of the Asian monsoon at millen-nial- and centennial-scales:Evidence from lake sediment document in Minqin Basin,NW China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Considerable research is now focusing on abrupt Holocene changes at millennial- and centennial-scales all over the world. This study shows that the changes in the Holocene summer monsoon can be divided into two main periods, based on climatic proxy records of lake sediments from the Sanjiaocheng section located at the NW boundary of the summer monsoon, Gansu Province. The early and middle Holocene was humid with stronger summer monsoon, while the late Holocene is dry with weak summer monsoon. Detailed results also show a series of millennial- and centennial-scale changes in the intensity of the summer monsoon, with a periodicity of 1600 years during the whole Holocene, and with a periodicity of 800 years during the early Holocene. Ten dry events during the Holocene are associated with the weakening of the summer monsoon. These rapid climatic changes may be representative of a global climatic change pattern during the Holocene.

  5. Coherent tropical-subtropical Holocene see-saw moisture patterns in the Eastern Hemisphere monsoon systems

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    Wang, Yongbo; Bekeschus, Benjamin; Handorf, Dörthe; Liu, Xingqi; Dallmeyer, Anne; Herzschuh, Ulrike

    2017-08-01

    The concept of a Global Monsoon (GM) has been proposed based on modern precipitation observations, but its application over a wide range of temporal scales is still under debate. Here, we present a synthesis of 268 continental paleo-moisture records collected from monsoonal systems in the Eastern Hemisphere, including the East Asian Monsoon (EAsM), the Indian Monsoon (IM), the East African Monsoon (EAfM), and the Australian Monsoon (AuM) covering the last 18,000 years. The overall pattern of late Glacial to Holocene moisture change is consistent with those inferred from ice cores and marine records. With respect to the last 10,000 years (10 ka), i.e. a period that has high spatial coverage, a Fuzzy c-Means clustering analysis of the moisture index records together with ;Xie-Beni; index reveals four clusters of our data set. The paleoclimatic meaning of each cluster is interpreted considering the temporal evolution and spatial distribution patterns. The major trend in the tropical AuM, EAfM, and IM regions is a gradual decrease in moisture conditions since the early Holocene. Moisture changes in the EAsM regions show maximum index values between 8 and 6 ka. However, records located in nearby subtropical areas, i.e. in regions not influenced by the intertropical convergence zone, show an opposite trend compared to the tropical monsoon regions (AuM, EAfM and IM), i.e. a gradual increase. Analyses of modern meteorological data reveal the same spatial patterns as in the paleoclimate records such that, in times of overall monsoon strengthening, lower precipitation rates are observed in the nearby subtropical areas. We explain this pattern as the effect of a strong monsoon circulation suppressing air uplift in nearby subtropical areas, and hence hindering precipitation. By analogy to the modern system, this would mean that during the early Holocene strong monsoon period, the intensified ascending airflows within the monsoon domains led to relatively weaker ascending or

  6. Causes of early Holocene desertification in arid central Asia

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Liya [Lanzhou University, Key Laboratory of Western China' s Environmental System, Lanzhou, Gansu (China); University of Kiel, Institute of Geosciences, Kiel (Germany); Chen, Fahu [Lanzhou University, Key Laboratory of Western China' s Environmental System, Lanzhou, Gansu (China); Morrill, Carrie [University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO (United States); NOAA' s National Climatic Data Center, Paleoclimatology Branch, Boulder, CO (United States); Otto-Bliesner, Bette L.; Rosenbloom, Nan [National Center for Atmospheric Research, Climate and Global Dynamics Division, Boulder, CO (United States)

    2012-04-15

    Paleoclimate records of effective moisture (precipitation minus evaporation, or P-E) show a dry (low effective moisture) period in mid-latitude arid/semi-arid central Asia during the early Holocene (11,000-8,000 years ago) relative to the middle and late Holocene, in contrast to evidence for greater-than-present precipitation at the same time in the south and east Asian monsoonal areas. To investigate the spatial differences in climate response over mid-latitude central Asia and monsoonal Asia we conducted a series of simulations with the Community Climate System Model version 3 coupled climate model for the early, middle and late Holocene. The simulations test the climatic impact of all important forcings for the early Holocene, including changes in orbital parameters, the presence of the remnant Laurentide ice sheet and deglacial freshening of the North Atlantic. Model results clearly show the early Holocene patterns indicated by proxy records, including both the decreased effective moisture in arid central Asia, which occurs in the model primarily during the winter months, and the increase in summer monsoon precipitation in south and east Asia. The model results suggest that dry conditions in the early Holocene in central Asia are closely related to decreased water vapor advection due to reduced westerly wind speed and less evaporation upstream from the Mediterranean, Black, and Caspian Seas in boreal winter. As an extra forcing to the early Holocene climate system, the Laurentide ice sheet and meltwater fluxes have a substantial cooling effect over high latitudes, especially just over and downstream of the ice sheets, but contribute only to a small degree to the early Holocene aridity in central Asia. Instead, most of the effective moisture signal can be explained by orbital forcing decreasing the early Holocene latitudinal temperature gradient and wintertime surface temperature. We find little evidence for regional subsidence related to a stronger summer Asian

  7. Holocene South Asian Monsoon Climate Change - Potential Mechanisms and Effects on Past Civilizations

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    Staubwasser, M.; Sirocko, F.; Grootes, P. M.; Erlenkeuser, H.; Segl, M.

    2002-12-01

    Planktonic oxygen isotope ratios from the laminated sediment core 63KA off the river Indus delta dated with 80 AMS radiocarbon ages reveal significant climate changes in the south Asian monsoon system throughout the Holocene. The most prominent event of the early-mid Holocene occurred after 8.4 ka BP and is within dating error of the GISP/GRIP event centered at 8.2 ka BP. The late Holocene is generally more variable, and shows non-periodic cycles in the multi-centennial frequency band. The largest change of the entire Holocene occurred at 4.2 ka BP and is concordant with the end of urban Harappan civilization in the Indus valley. Opposing isotopic trends across the northern Arabian Sea surface indicate a reduction in Indus river discharge at that time. Consequently, sustained drought may have initiated the archaeologically recorded interval of southeastward habitat tracking within the Harappan cultural domain. The hemispheric significance of the 4.2 ka BP event is evident from concordant climate change in the eastern Mediterranean and the Middle East. The late Holocene cycles in South Asia, which most likely represent drought cycles, vary between 250 and 800 years and are coherent with the evolution of cosmogenic radiocarbon production rates in the atmosphere. This suggests that solar variability is the fundamental cause behind late Holocene rainfall changes at least over south Asia.

  8. High-resolution peat records for Holocene monsoon history in the eastern Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    YU; Xuefeng; ZHOU; Weijian; Lars; G.Franzen; XIAN; Feng; CHENG; Peng; A.J.; Tim; Jull

    2006-01-01

    The variations of summer and winter monsoons during the Holocene in the eastern Tibetan Plateau are shown to follow two basic models based on the reliable dating and high-resolution monsoon proxies determinations, one being a synchronous model in that both summer and winter monsoons are strengthening or decreasing, and the other to form a complementary pattern. These two different patterns evenly interact with each other on different time scales and together compose a complicated monsoon climatic model in this region. The climatic condition integrated by winter and summer monsoons is synchronous to the global pattern, which also shows the instability of the Holocene climate on centennial-millennial timescale. The abrupt monsoon event in about 6.2 ka cal.BP is much more severe than that in ca. 8.0 ka cal. BP, which indicates the regional character of the Asian monsoon and that the Asian monsoon climate is indeed a window on the global climate system.

  9. Seasonal Transitions and the Westerly Jet in the Holocene East Asian Summer Monsoon

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    Kong, W.; Chiang, J. C. H.

    2015-12-01

    The Holocene East Asian Summer Monsoon (EASM) was characterized by a trend to weaker monsoon intensity paced by orbital insolation. Here, we attribute the stronger EASM intensity in the early-mid Holocene to changes in the timing of the transition between the EASM seasonal stages - Spring, pre Mei- Yu, Mei-Yu, and Summer - during that time. Following the recent 'jet transition hypothesis' (Chiang et al., 2015), we explore the role of north-south displacement of the westerlies relative to the Tibetan Plateau that is hypothesized to control the downstream EASM seasonality changes across the Holocene. To this end, we analyze model simulations of the Holocene EASM, compare the simulated Holocene climate with the paleodata observations, and examine the role of atmospheric circulation and specifically the westerlies in modulating the East Asia summer climate. The PMIP3 climate model simulations suggest that, compared to the pre-industrial, the Mei-Yu onset and the transition from Mei-Yu to Summer rainfall occur earlier in the mid-Holocene. The advanced seasonal rainfall transition is accompanied by the weakened and northward-shifted upstream westerlies. In our atmospheric general circulation model (coupled to a slab ocean) simulations of various time periods across the Holocene (9ka, 6ka, 3ka, and pre-industrial), we quantitatively show that the timing and the length of each rainfall stage are closely related to the jet position over East Asia. We also show that the simulated changes in the maximum annual rainfall band and dust emission over East Asia largely agree with the paleo-proxy observations. In addition, we find that changes to the seasonal rainfall transitions, latitudinal westerly position, and stationary eddy activity over East Asia co-vary across the Holocene. In particular, we argue that the changes in the rainfall seasonal transitions are tied to an altered stationary wave pattern, resembling today's the so-called 'Silk Road Pattern', riding along the

  10. Rocky Mountain hydroclimate: Holocene variability and the role of insolation, ENSO, and the North American Monsoon

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    Anderson, Lesleigh

    2012-01-01

    Over the period of instrumental records, precipitation maximum in the headwaters of the Colorado Rocky Mountains has been dominated by winter snow, with a substantial degree of interannual variability linked to Pacific ocean–atmosphere dynamics. High-elevation snowpack is an important water storage that is carefully observed in order to meet increasing water demands in the greater semi-arid region. The purpose here is to consider Rocky Mountain water trends during the Holocene when known changes in earth's energy balance were caused by precession-driven insolation variability. Changes in solar insolation are thought to have influenced the variability and intensity of the El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and North American Monsoon and the seasonal precipitation balance between rain and snow at upper elevations. Holocene records are presented from two high elevation lakes located in northwest Colorado that document decade-to-century scale precipitation seasonality for the past ~ 7000 years. Comparisons with sub-tropical records of ENSO indicate that the snowfall-dominated precipitation maxima developed ~ 3000 and 4000 years ago, coincident with evidence for enhanced ENSO/PDO dynamics. During the early-to-mid Holocene the records suggest a more monsoon affected precipitation regime with reduced snowpack, more rainfall, and net moisture deficits that were more severe than recent droughts. The Holocene perspective of precipitation indicates a far broader range of variability than that of the past century and highlights the non-linear character of hydroclimate in the U.S. west.

  11. Monsoonal response to mid-holocene orbital forcing in a high resolution GCM

    NARCIS (Netherlands)

    Bosmans, J.H.C.; Drijfhout, S.S.; Tuenter, E.; Lourens, L.J.; Hilgen, F.J.; Weber, S.L.

    2012-01-01

    In this study, we use a sophisticated high-resolution atmosphere-ocean coupled climate model, EC-Earth, to investigate the effect of Mid-Holocene orbital forcing on summer monsoons on both hemispheres. During the Mid-Holocene (6 ka), there was more summer insolation on the Northern Hemisphere than

  12. Monsoonal response to mid-holocene orbital forcing in a high resolution GCM

    NARCIS (Netherlands)

    Bosmans, J.H.C.; Drijfhout, S.S.; Tuenter, E.; Lourens, L.J.; Hilgen, F.J.; Weber, S.L.

    2012-01-01

    In this study, we use a sophisticated high-resolution atmosphere-ocean coupled climate model, EC-Earth, to investigate the effect of Mid-Holocene orbital forcing on summer monsoons on both hemispheres. During the Mid-Holocene (6 ka), there was more summer insolation on the Northern Hemisphere than t

  13. A Holocene East Asian winter monsoon record at the southern edge of the Gobi Desert and its comparison with a transient simulation

    Science.gov (United States)

    Li, Yu; Morrill, Carrie

    2015-09-01

    The East Asian winter monsoon (EAWM) exhibits significant variability on intraseasonal, interannual, and interdecadal time scales and the variability can be extended to Holocene centennial and millennial scales. Previous Holocene EAWM proxy data records, which were mostly located in Central, Eastern and Southern China, did not show a consistent Holocene EAWM history. Therefore, it is difficult to provide insights into mechanisms of the long-term winter monsoon variability on the basis of the records. Eolian sediments at the southern edge of the Gobi Desert, Western China, are sensitive to the EAWM changes and less affected by the East Asian summer monsoon due to an obstruction of the Qinghai-Tibet Plateau. This paper presents a comparison between a well-dated Holocene EAWM record and coupled climate model simulations, so as to explore physical processes and influencing factors of the Holocene EAWM. Sediment samples from two Holocene eolian sedimentary sections [Huangyanghe (a) and Huangyanghe (b)] were acquired at the southern edge of the Gobi Desert. Chronologies were established based on twenty bulk organic matter AMS 14C ages and five pollen concentrates AMS 14C ages. Proxy data, including grain-size, total organic carbon, magnetic susceptibility and carbonate content were obtained from the two eolian sections. The grain-size standard deviation model was applied to determine components sensitive to variability of the Holocene EAWM. After a comparison of environmentally-sensitive grain-size components and proxy data, the 20-200 μm component at the Huangyanghe (a) and the 20-159 μm component at the Huangyanghe (b) section were selected as indicators of the Holocene EAWM, which show a strong early Holocene winter monsoon and a decline of the winter monsoon since the mid-Holocene. We also present equilibrium and transient simulations of the climate evolution for the Holocene using a state-of-art coupled climate model: the Community Climate System Model version 3

  14. Centennial to millennial climate variability in the far northwestern Pacific (off Kamchatka and its linkage to the East Asian monsoon and North Atlantic from the Last Glacial Maximum to the early Holocene

    Directory of Open Access Journals (Sweden)

    S. A. Gorbarenko

    2017-08-01

    Full Text Available High-resolution reconstructions based on productivity proxies and magnetic properties of core LV63-41-2 (off Kamchatka reveal prevailing centennial productivity/climate variability in the northwestern (NW Pacific from the Last Glacial Maximum (LGM to the early Holocene (EH. The age model of the core is established by AMS 14C dating and by projections of AMS 14C data of the nearby core SO-201-12KL through correlation of the productivity proxies and relative paleomagnetic intensity. The resulting sequence of centennial productivity increases/climate warming events in the NW Pacific occurred synchronously with the East Asian summer monsoon (EASM sub-interstadials during the LGM (four events, Heinrich Event 1 (HE1 (four events, Bølling–Allerød (B/A warming (four events, and over the EH (four events. Remarkable similarity of the sequence of the NW Pacific increased-productivity events with the EASM sub-interstadials over the LGM-HE1 implies that the Siberian High is a strong and common driver. The comparison with the δ18O record from Antarctica suggests that another mechanism associated with the temperature gradient in the Southern Hemisphere may also be responsible for the EASM/NW Pacific centennial events over the LGM-HE1. During the B/A warming and resumption of the Atlantic Meridional Overturning Circulation (AMOC, clear synchronicity between the NW Pacific, EASM and Greenland sub-interstadials was mainly controlled by changes in the atmospheric circulation. During the EH the linkages between solar forcing, ocean circulation, and climate changes likely control the synchronicity of abrupt climate changes in the NW Pacific and North Atlantic. The sequence of centennial events recorded in this study is a persistent regional feature during the LGM-EH, which may serve as a template in high-resolution paleoceanography and sediment stratigraphy in the NW Pacific.

  15. Monsoonal response to mid-holocene orbital forcing in a high resolution GCM

    Directory of Open Access Journals (Sweden)

    J. H. C. Bosmans

    2012-04-01

    Full Text Available In this study, we use a sophisticated high-resolution atmosphere-ocean coupled climate model, EC-Earth, to investigate the effect of Mid-Holocene orbital forcing on summer monsoons on both hemispheres. During the Mid-Holocene (6 ka, there was more summer insolation on the Northern Hemisphere than today, which intensified the meridional temperature and pressure gradients. Over North Africa, monsoonal precipitation is intensified through increased landward monsoon winds and moisture advection as well as decreased moisture convergence over the oceans and more convergence over land compared to the pre-industrial simulation. Precipitation also extends further north as the ITCZ shifts northward in response to the stronger poleward gradient of insolation. This increase and poleward extent is stronger than in most previous ocean-atmosphere GCM simulations. In north-westernmost Africa, precipitation extends up to 35° N. Over tropical Africa, internal feedbacks completely overcome the direct warming effect of increased insolation. We also find a weakened African Easterly Jet. Over Asia, monsoonal precipitation during the Mid-Holocene is increased as well, but the response is different than over North-Africa. There is more convection over land at the expense of convection over the ocean, but precipitation does not extend further northward, monsoon winds over the ocean are weaker and the surrounding ocean does not provide more moisture. On the Southern Hemisphere, summer insolation and the poleward insolation gradient were weaker during the Mid-Holocene, resulting in a reduced South American monsoon through decreased monsoon winds and less convection, as well as an equatorward shift in the ITCZ. This study corroborates the findings of paleodata research as well as previous model studies, while giving a more detailed account of Mid-Holocene monsoons.

  16. Late Pleistocene-Holocene vegetation and Indian summer monsoon record from the Lahaul, Northwest Himalaya, India

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    Rawat, Suman; Gupta, Anil K.; Sangode, S. J.; Srivastava, Priyeshu; Nainwal, H. C.

    2015-04-01

    The high resolution Holocene paleomonsoon records from Northwest (NW) Himalaya are limited. The carbon isotope (δ13C), Total organic carbon (TOC) and pollen analysis were therefore carried out from a peat-lake sediment sequence developed in alpine meadows of the Chandra valley, Lahaul, NW Himalaya, in order to reconstruct centennial to millennial scale vegetational changes and Indian summer monsoon (ISM) variability during the Holocene. The chronology of peat-lake sediments is constrained with 9 AMS 14C dates. The recovered non-arboreal pollen (NAP) suggested that during Holocene alpine desert-steppe, meadows and shrubs growing along the stream had developed in the Lahaul valley whereas arboreal pollens (AP) e.g. Pinus, Quercus, Cedrus and Ulmus presently growing in the southern hill slopes of Pir Panjal range indicated moisture carrying monsoonal air flow from the South. The increased δ13C and low TOC values between ∼12,880 and 11,640 calibrated years before present (cal yr BP) suggested weakening of ISM and low organic carbon production corresponding to the Younger Dryas (YD) cold event. The gradual depletion in carbon isotope ratio from ∼11,640 to 8810 cal yr BP indicated enhanced precipitation in the Chandra valley in response of increased ISM strength in early Holocene. The short spell of cold and dry climate with gradual decrease in ISM intensity between ca 10,398 and 9778 cal yr BP is closely linked with Bond event-7. The other prominent cold-dry events recorded in present study are (i) ∼8810 to 8117 cal yr BP roughly corresponding to global 8.2 ka cold event, (ii) ∼4808 to 4327 cal yr BP closely preceding the global 4.2 ka cold-arid period, and (iii) ∼1303 to 1609 cal AD corresponding to Little Ice Age (LIA) event. The expansion of thermophillous broad leaved taxa viz. Betula utilis, Alnus nepalensis, Quercus semicarpifolia and Juglans regia and effective growth of meadow vegetation such as grasses, Caryophyllaceae and Artemisia along with

  17. Holocene moisture and East Asian summer monsoon evolution in the northeastern Tibetan Plateau recorded by Lake Qinghai and its environs: A review of conflicting proxies

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    Chen, Fahu; Wu, Duo; Chen, Jianhui; Zhou, Aifeng; Yu, Junqing; Shen, Ji; Wang, Sumin; Huang, Xiaozhong

    2016-12-01

    Climatic and environmental changes in the northeastern Tibetan Plateau are controlled by the Asian summer monsoon (ASM) and the westerlies, two key circulation components of the global climate system which directly affect a large human population and associated ecosystems in eastern Asia. During the past few decades, a series of Holocene palaeoclimatic records have been obtained from sediment cores from Lake Qinghai and from various other geological archives in the surrounding area of the northeastern Tibetan Plateau. However, because of uncertainties regarding the sediment chronologies and the climatic significance of the proxies used, the nature of Holocene climatic changes in the region remains unclear and even controversial. Here we review all major classes of the published data from drilled cores from Lake Qinghai, as well as other evidence from lakes and aeolian deposits from surrounding areas, in order to reconstruct changes in moisture patterns and possible summer monsoon evolution in the area during the Holocene. Combining the results of moisture and precipitation proxies such as vegetation history, pollen-based precipitation reconstruction, aeolian activity, lake water depth/lake level changes, salinity and sediment redness, we conclude that moisture and precipitation began to increase in the early Holocene, reached their maximum during the middle Holocene, and decreased during the late Holocene - similar to the pattern of the East Asian summer monsoon (EASM) in northern China. It is clear that the region experienced a relatively dry climate and weak EASM during the early Holocene, as indicated by relatively low tree pollen percentages and fluctuating pollen concentrations; generally low lake levels of Lake Qinghai and the adjacent Lake Hurleg and Lake Toson in the Qaidam Basin; and widely distributed aeolian sand deposition in the Lake Qinghai Basin and the nearby Gonghe Basin to the south, and in the eastern Qaidam Basin to the west. We argue that the

  18. South Asian climate change at the end of urban Harappan (Indus valley) civilization and mechanisms of Holocene monsoon variability

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    Staubwasser, M.; Sirocko, F.; Erlenkeuser, H.; Grootes, P. M.; Segl, M.

    2003-04-01

    Planktonic oxygen isotope ratios from the well-dated laminated sediment core 63KA off the river Indus delta are presented. The record reveals significant climate changes in the south Asian monsoon system throughout the Holocene. The most prominent event of the early-mid Holocene occurred after 8.4 ka BP and is within dating error of the GISP/GRIP event centered at 8.2 ka BP. The late Holocene is generally more variable and the largest change of the entire Holocene occurred at 4.2 ka BP. This event is concordant with the end of urban Harappan civilization in the Indus valley. Opposing isotopic trends across the northern Arabian Sea surface indicate a reduction in Indus river discharge at that time. Consequently, sustained drought may have initiated the archaeologically recorded interval of southeastward habitat tracking within the Harappan cultural domain. The hemispheric significance of the 4.2 ka BP event is evident from concordant climate change in the eastern Mediterranean and the Middle East. The remainder of the late Holocene shows drought cycles of approximately 700 years that are coherent with the evolution of cosmogenic radiocarbon production rates in the atmosphere. This suggests that solar variability is one fundamental cause behind late Holocene rainfall changes over south Asia.

  19. Interconnections between the Asian monsoon, ENSO, and high northern latitude climate during the Holocene

    Institute of Scientific and Technical Information of China (English)

    HONG Bing; LIN Qinghua; HONG Yetang

    2006-01-01

    The article emphatically reviews the research progress in interconnections between the East Asian and Indian Ocean summer monsoons, between the Asian monsoon and the El Nino-Southern Oscillation (ENSO) activity, and between the monsoon, ENSO and the changing of the North Atlantic climate during the Holocene. According to the studies of recent years, it is found that the intensity variations of the East Asian and Indian Ocean summer monsoons show an opposite relationship, which may be closely related to the phenomena of ENSO in the equatorial Pacific Ocean and the variation of the deep-water formation of the North Atlantic Ocean on the interannual to orbital time scales. The 4k and 8k events occurring at around 4200 and 8200 a BP, respectively, might be the two in a series of severe paleo-El Nino events during the Holocene, strongly reflecting the interactions and influences of the monsoons, ENSO and the North Atlantic climate. In order to better understand the relationships between these paleoclimatic phenomena, scientists need to strengthen the research work on the Asian monsoon division and the comparison between monsoon proxy records, and the study on the proxy record of sea surface temperature with high time-resolution in the equatorial Pacific Ocean and the simulation research of paleoclimate condition.

  20. Transient coupling relationships of the Holocene Australian monsoon

    CERN Document Server

    McRobie, Fiona H; Wyrwoll, Karl-Heinz

    2015-01-01

    The modern-day northwest Australian summer monsoon is dynamically coupled to other regional monsoon systems and inflows from the Indian Ocean, however, the nature of these relationships over longer time scales is uncertain. Previous attempts to evaluate how proxy records from the Indonesian-Australian monsoon region correspond to other records from the Indian and East Asian monsoon regions, as well as to El Ni\\~no-related proxy records, has been qualitative, relying on `curve-fitting' methods. Here, we seek a quantitative approach for identifying coupling relationships between paleoclimate proxy records, employing statistical techniques to compute the interdependence of two paleoclimate time series. We verify the use of complex networks to identify coupling relationships between modern climate indices which correspond to physically-based mechanisms. This method is then extended to a set of paleoclimate proxy records from the Asian, Australasian and South American regions spanning the past 9,000 years. The res...

  1. Prolonged monsoon droughts and links to Indo-Pacific warm pool: A Holocene record from Lonar Lake, central India

    Science.gov (United States)

    Prasad, Sushma; Anoop, A.; Riedel, N.; Sarkar, S.; Menzel, P.; Basavaiah, N.; Krishnan, R.; Fuller, D.; Plessen, B.; Gaye, B.; Röhl, U.; Wilkes, H.; Sachse, D.; Sawant, R.; Wiesner, M. G.; Stebich, M.

    2014-04-01

    Concerns about the regional impact of global climate change in a warming scenario have highlighted the gaps in our understanding of the Indian Summer Monsoon (ISM, also referred to as the Indian Ocean summer monsoon) and the absence of long term palaeoclimate data from the central Indian core monsoon zone (CMZ). Here we present the first high resolution, well-dated, multiproxy reconstruction of Holocene palaeoclimate from a 10 m long sediment core raised from the Lonar Lake in central India. We show that while the early Holocene onset of intensified monsoon in the CMZ is similar to that reported from other ISM records, the Lonar data shows two prolonged droughts (PD, multidecadal to centennial periods of weaker monsoon) between 4.6-3.9 and 2-0.6 cal ka. A comparison of our record with available data from other ISM influenced sites shows that the impact of these PD was observed in varying degrees throughout the ISM realm and coincides with intervals of higher solar irradiance. We demonstrate that (i) the regional warming in the Indo-Pacific Warm Pool (IPWP) plays an important role in causing ISM PD through changes in meridional overturning circulation and position of the anomalous Walker cell; (ii) the long term influence of conditions like El Niño-Southern Oscillation (ENSO) on the ISM began only ca. 2 cal ka BP and is coincident with the warming of the southern IPWP; (iii) the first settlements in central India coincided with the onset of the first PD and agricultural populations flourished between the two PD, highlighting the significance of natural climate variability and PD as major environmental factors affecting human settlements.

  2. Multi-scale Holocene Asian monsoon variability deduced from a twin-stalagmite record in southwestern China

    Science.gov (United States)

    Huang, Wei; Wang, Yongjin; Cheng, Hai; Edwards, Richard Lawrence; Shen, Chuan-Chou; Liu, Dianbing; Shao, Qingfeng; Deng, Chao; Zhang, Zhenqiu; Wang, Quan

    2016-07-01

    We present two isotopic (δ18O and δ13C) sequences of a twin-stalagmite from Zhuliuping Cave, southwestern China, with 230Th dates from 14.6 to 4.6 ka. The stalagmite δ18O record characterizes orbital- to decadal-scale variability of Asian summer monsoon (ASM) intensity, with the Holocene optimum period (HOP) between 9.8 and 6.8 ka BP which is reinforced by its co-varying δ13C data. The large multi-decadal scale amplitude of the cave δ18O indicates its high sensitivity to climate change. Four centennial-scale weak ASM events during the early Holocene are centered at 11.2, 10.8, 9.1 and 8.2 ka. They can be correlated to cold periods in the northern high latitudes, possibly resulting from rapid dynamics of atmospheric circulation associated with North Atlantic cooling. The 8.2 ka event has an amplitude more than two-thirds that of the Younger Dryas (YD), and is significantly stronger than other cave records in the Asia monsoon region, likely indicating a more severe dry climate condition at the cave site. At the end of the YD event, the δ13C record lags the δ18O record by 300-500 yr, suggesting a multi-centennial slow response of vegetation and soil processes to monsoon enhancement.

  3. The East Asian summer monsoon at mid-Holocene: results from PMIP3 simulations

    Directory of Open Access Journals (Sweden)

    W. Zheng

    2012-08-01

    Full Text Available Ten Coupled General Circulation Models (CGCMs participating the third phase of Paleoclimate Modeling Intercomparison project (PMIP3 are assessed for the simulations of East Asian Summer Monsoon (EASM at both the present climate and mid-Holocene. Results show that the PMIP3 model median well captures the characteristics of the EASM, including the two distinct features of the Meiyu Front and the stepwise meridional displacement of the monsoon rainbelt. At mid-Holocene, the enhanced EASM is simulated by the PMIP3 models. The model median shows that the changes of surface air temperature and precipitation are within the range as indicated by the proxy data over the eastern China. Both the changes of monsoonal circulation and the water vapor content favor the increasing of summer precipitation. Regional features can be identified between models because of their different simulations of the above changes. The model spread for the surface air temperature (TAS is relatively smaller when compared with that of PMIP2 models in both the Northern Hemisphere and the eastern China. However, the model spread of summer precipitation is larger among PMIP3 models, particularly in the lower reaches of Yangzi River. The TAS over Tibetan Plateau has a positive relationship with the precipitation in the lower reaches of Yangzi River, yet this relationship does not apply for those PMIP3 models in which the monsoonal precipitation is more sensitive to the changes of large-scale circulation.

  4. Pattern of Holocene glaciation in the monsoon-dominated Kosa Valley, central Himalaya, Uttarakhand, India

    Science.gov (United States)

    Bisht, Pinkey; Nawaz Ali, S.; Rana, Naresh; Singh, Sunil; Poonam; Sundriyal, Y. P.; Bagri, D. S.; Juyal, Navin

    2017-05-01

    Reconstruction based on the geomorphology, lateral moraine stratigraphy, and limited optical chronology indicate that the monsoon-dominated Kosa Valley experienced four glacial advances during the late glacial to late Holocene. The oldest and most extensive glaciation, which is termed as Raj Bank Stage-1 (RBS-1), is represented by the degraded moraine ridge. This glaciation remains undated; however, the chronology of outwash terrace gravel dated to 12.7 ± 1.3 ka indicates that the RBS-1 probably represents the Last Glacial Maximum (LGM). The second glacial advance (RBS-2) is preserved as a curvilinear lateral moraine and is dated to 6.1 ± 0.4 ka. The third glacial advance viz. RBS-3 is bracketed between 5.0 ± 0.5 and 4.0 ± 0.4 ka. Following this, the glacier receded in pulses that are represented by two distinct recessional moraines (RBS-3a and b). The forth glacial stage (RBS-4), which is dated between 2.2 ± 0.2 and 1.6 ± 0.2 ka, shows a pulsating recession and is represented by a prominent recessional moraine (RBS-4a). Whereas, presence of unconsolidated, poorly defined moraine mounds proximal to the glacier snout are ascribed as neoglacial advance corresponding to the Little Ice Age (LIA). With the limited chronometric data, we speculated that the glaciation was driven during the weak to moderate Indian Summer Monsoon (ISM) aided by lowered temperature. Presence of recessional moraines associated with mid-Holocene glacial phase indicate that the monsoon-dominated glaciers respond sensitively to minor (sub-millennial scale) changes in temperature and precipitation conditions. The observations are broadly in accordance with the studies carried out in other monsoon-dominated valleys in the central Himalaya, implying that in ISM dominated regions, lowered temperature seems to be the major driver of glaciations during the late glacial to late Holocene.

  5. Contribution of oceanic and vegetation feedbacks to Holocene climate change in monsoonal Asia

    Directory of Open Access Journals (Sweden)

    A. Dallmeyer

    2010-04-01

    Full Text Available The impact of vegetation-atmosphere and ocean-atmosphere interactions on the mid- to late Holocene climate change as well as their synergy is studied for different parts of the Asian monsoon region, giving consideration to the large climatic and topographical heterogeneity in that area. We concentrate on temperature and precipitation changes as the main parameters describing monsoonal influenced climates. For our purpose, we analyse a set of coupled numerical experiments, performed with the comprehensive Earth system model ECHAM5/JSBACH-MPIOM under present-day and mid-Holocene (6 k orbital configurations (Otto et al., 2009b. The temperature change caused by the insolation forcing reveals an enhanced seasonal cycle, with a pronounced warming in summer (0.58 K and autumn (1.29 K and a cooling in the other seasons (spring: -1.32 K; winter: -0.97 K. Most of this change can be attributed to the direct response of the atmosphere, but the ocean, whose reaction has a lagged seasonal cycle (warming in autumn and winter, cooling in the other seasons, strongly modifies the signal. The simulated contribution of dynamic vegetation is small and most effective in winter, where it slightly warms the near-surface atmosphere (approx. 0.03 K. The temperature difference attributed to the synergy is on average positive, but also small. Concerning the precipitation, the most remarkable change is the postponement and enhancement of the Asian monsoon (0.46 mm/day in summer, 0.53 mm/day in autumn, mainly related to the direct atmospheric response. On regional average, the interactive ocean (ca. 0.18 mm/day amplifies the direct effect, but tends to weaken the East Asian summer monsoon and strongly increases the Indian summer monsoon rainfall rate (0.68 mm/day. The influence of dynamic vegetation on precipitation is comparatively small (<0.04 mm/day. The synergy effect has no influence, on average.

  6. The East Asian Summer Monsoon at mid-Holocene: results from PMIP3 simulations

    Directory of Open Access Journals (Sweden)

    W. Zheng

    2013-02-01

    Full Text Available Ten Coupled General Circulation Models (CGCMs participated in the third phase of Paleoclimate Modelling Intercomparison Project (PMIP3 are assessed for the East Asian Summer Monsoon (EASM in both the pre-Industrial (PI, 0 ka and mid-Holocene (MH, 6 ka simulations. Results show that the PMIP3 model median captures well the large-scale characteristics of the EASM, including the two distinct features of the Meiyu rainbelt and the stepwise meridional displacement of the monsoonal rainbelt. At mid-Holocene, the PMIP3 model median shows significant warming (cooling during boreal summer (winter over Eurasia continent that are dominated by the changes of insolation. However, the PMIP3 models fail to simulate a warmer annual mean and winter surface air temperature (TAS over eastern China as derived from proxy records. The EASM at MH are featured by the changes of large-scale circulation over Eastern China while the changes of precipitation are not significant over its sub-domains of the Southern China and the lower reaches of Yangzi River. The inter-model differences for the monsoon precipitation can be associated with different configurations of the changes in large-scale circulation and the water vapour content, of which the former determines the sign of precipitation changes. The large model spread for the TAS over Tibetan Plateau has a positive relationship with the precipitation in the lower reaches of Yangzi River, yet this relationship does not apply to those PMIP3 models in which the monsoonal precipitation is more sensitive to the changes of large-scale circulation. Except that the PMIP3 model median captured the warming of annual mean TAS over Tibetan Plateau, no significant improvements can be concluded when compared with the PMIP2 models results.

  7. Long-term trend and abrupt events of the Holocene Asian monsoon inferred from a stalagmite δ18O record from Shennongjia in Central China

    Institute of Scientific and Technical Information of China (English)

    SHAO Xiaohua; WANG Yongjin; CHENG Hai; KONG Xinggong; WU Jiangying; EDWARDS R. Lawrence

    2006-01-01

    A high-resolution oxygen-isotope record from a thorium-uranium-dated stalagmite from Shanbao Cave at Shennongjia reflects variations in the amount of monsoon precipitation for the period from 11.5 to 2.1 ka (1 ka = 1000 cal aBP). Between 11.5 and 9.3 ka, a sharp decrease in δ18O indicates a rapid increase in monsoon precipitation. An interval of generally high monsoon precipitation is observed between 9.3 and 4.4 ka. An arid period has prevailed between 4.4 and 2.1 ka. The long-term trend of Shanbao record appears to follow summer insolation at 33°N latitude. An abrupt decrease in monsoon precipitation around 4.3 ka is synchronous with the collapse of Neolithic culture in central China. This abrupt change could have resulted from the amplification of the gradually decreased summer insolation by the positive vegetation-atmosphere-aerosol feedback. The weakened Asian monsoon events were in concert with decreased Greenland temperature during the early Holocene, centered at 8.2, 8.6, 9.3, 10.2 and 11.0 ka. This correlation suggests that changes in low-latitude monsoon are connected with climate change in high-latitude polar region.

  8. The influence of land cover change in the Asian monsoon region on present-day and mid-Holocene climate

    Directory of Open Access Journals (Sweden)

    A. Dallmeyer

    2011-02-01

    Full Text Available Using the general circulation model ECHAM5/JSBACH, we investigate the biogeophysical effect of large-scale afforestation and deforestation in the Asian monsoon domain on present-day and mid-Holocene climate. We demonstrate that the applied land cover change does not only modify the local climate but also change the climate in North Africa and the Middle East via teleconnections. Deforestation in the Asian monsoon domain enhances the rainfall in North Africa. In parts of the Sahara summer precipitation is more than doubled. In contrast, afforestation strongly decreases summer rainfall in the Middle East and even leads to the cessation of the rainfall-activity in some parts of this region.

    Regarding the local climate, deforestation results in a reduction of precipitation and a cooler climate as grass mostly has a higher albedo than forests. However, in the core region of the Asian monsoon the decrease of evaporative cooling in the monsoon season overcompensates this signal and results in a net warming. Afforestation has mainly the opposite effect, although the pattern of change is less clear. It leads to more precipitation in most parts of the Asian monsoon domain and a warmer climate except for the southern regions where a stronger evaporation decreases near-surface temperatures in the monsoon season.

    When prescribing mid-Holocene insolation, the pattern of local precipitation change differs. Afforestation particularly increases monsoon rainfall in the region along the Yellow River which was the settlement area of major prehistoric cultures. In this region, the effect of land cover change on precipitation is half as large as the orbitally-induced precipitation change. Thus, our model results reveal that mid- to late-Holocene land cover change could strongly have contributed to the decreasing Asian monsoon precipitation during the Holocene known from reconstructions.

  9. The influence of land cover change in the Asian monsoon region on present-day and mid-Holocene climate

    Science.gov (United States)

    Dallmeyer, A.; Claussen, M.

    2011-06-01

    Using the general circulation model ECHAM5/JSBACH, we investigate the biogeophysical effect of large-scale afforestation and deforestation in the Asian monsoon domain on present-day and mid-Holocene climate. We demonstrate that the applied land cover change does not only modify the local climate but also change the climate in North Africa and the Middle East via teleconnections. Deforestation in the Asian monsoon domain enhances the rainfall in North Africa. In parts of the Sahara summer precipitation is more than doubled. In contrast, afforestation strongly decreases summer rainfall in the Middle East and even leads to the cessation of the rainfall-activity in some parts of this region. Regarding the local climate, deforestation results in a reduction of precipitation and a cooler climate as grass mostly has a higher albedo than forests. However, in the core region of the Asian monsoon the decrease in evaporative cooling in the monsoon season overcompensates this signal and results in a net warming. Afforestation has mainly the opposite effect, although the pattern of change is less clear. It leads to more precipitation in most parts of the Asian monsoon domain and a warmer climate except for the southern regions where a stronger evaporation decreases near-surface temperatures in the monsoon season. When prescribing mid-Holocene insolation, the pattern of local precipitation change differs. Afforestation particularly increases monsoon rainfall in the region along the Yellow River which was the settlement area of major prehistoric cultures. In this region, the effect of land cover change on precipitation is half as large as the orbitally-induced precipitation change. Thus, our model results reveal that mid- to late-Holocene land cover change could strongly have contributed to the decreasing Asian monsoon precipitation during the Holocene known from reconstructions.

  10. Indian monsoon variations during three contrasting climatic periods: the Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

    Science.gov (United States)

    Zorzi, Coralie; Fernanda Sanchez Goñi, Maria; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

    2016-04-01

    In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4,200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4,200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric

  11. Inverse relation between summer and winter monsoon strength during late Holocene: continental molecular isotopic record from the Indian subcontinent

    Science.gov (United States)

    Sanyal, P.; Basu, S.; Pillai, A.; Singh, P.; Ratnam, J.; Sankaran, M.; Amibili, A.

    2015-12-01

    The Indian monsoon shapes the livelihood of ca. 40% of world's population. Despite dedicated efforts, comprehensive picture of monsoon variability has proved elusive largely due to the absence of long-term qualitative high-resolution record from key climatic zones and variability of monsoon with respect to various forcing mechanisms (e.g., solar insolation) and teleconnections (e.g., El Niño-Southern Oscillation, Indian Ocean Dipole). In this study, high-resolution molecular (n-alkane) isotopic (δD and δ13C ratios) reconstruction of mid-late Holocene (~5.0 cal ka) climate has been undertaken using lacustrine sediments from two climatically sensitive regions; (i) Arid Banni grasslands, western India with dominant moisture source derived from Indian summer monsoon (June-September) and (ii) Semi-arid Ennamangalam lake, south India with significant fraction of rainfall received during winter period (October to December) from Northeast (NE) monsoon. The climate reconstruction from western India based on δDn-alkane values shows prevalence of intensified monsoon until ca. 3 cal ka followed by gradual decrease in the precipitation. In contrast, climate reconstruction from south India is characterized by more negative δDn-alkane (intensified precipitation) values during late Holocene (~2.5 cal ka). The compilation of paleoclimate records shows that the precipitation pattern in Banni region responded linearly to gradually changing insolation and additionally amplified by climate systems like ENSO. However, intensified monsoon in South India shows strengthened NE monsoonal precipitation during late Holocene. The spatial inhomogeneity in the palaeohydrological record can be attributed to the persistence of inverse relationship between summer and winter monsoon. In addition, strong positive correlation between δDn-alkane and δ13Cn-alkane values from both region shows that the relative abundance of C3-C4 plants in the contemporary ecosystems are governed by rainfall

  12. Across an early Holocene humid phase in western Sahara:Pollen and isotope stratigraphy

    Science.gov (United States)

    Lézine, Anne-Marie; Casanova, Joël; Hillaire-Marcel, Claude

    1990-03-01

    Paleohydrology and paleoecology of the region around the Chemchane sabkha (Mauritania) are reconstructed from the comparative analyses of mineralogy, stable isotope ratios of bulk carbonates, and palynology from sediment cores. The age of the section is from ca. 13.5 ka to the middle Holocene. Maximum lake expansion between about 8.3 and 6.5 ka is recorded in a girdle of stromatolite carbonates. These document a lower-salinity lake concomitant with a general establishment of Sahel-Sudan vegetation. The Chemchane area is the northernmost (lat 21°N) occurrence of humid- phase elements that are related to maximum intensity of monsoon activity during the early Holocene.

  13. Early warnings and missed alarms for abrupt monsoon transitions

    OpenAIRE

    Z. A. Thomas; Kwasniok, F.; C. A. Boulton; Cox, P.M.; Jones, R. T.; Lenton, T. M.; C. S. M. Turney

    2015-01-01

    Palaeo-records from China demonstrate that the East Asian Summer Monsoon (EASM) is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesized that over these timescales, the EASM exhibits two stable states with bifurcation-type tipping points between them. Here we test this hypothesis by looking for early warning signals of past bifurcations in speleothem δ18O records fro...

  14. Mid-Holocene Climate Variations Recorded by Palaeolake in Marginal Area of East Asian Monsoon: A Multi-proxy Study

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Traditionally, the mid-Holocene in most parts of China was thought to be warmer with higher precipitation,resulting from a strong Asian summer monsoon. However, some recent researches have proposed a mid-Holocene drought interval of millennial-scale in East Asian monsoon margin areas. Thus whether mid-Holocene was dry or humid remains an open issue. Here, Zhuyeze palaeolake, the terminal lake of the Shiyang River Drainage lying in Asian monsoon marginal areas, was selected for reconstructing the details of climate variations during the Holocene, especially mid-Holocene,on the basis ora sedimentological analysis. Qingtu Lake (QTL) section of 6.92m depth was taken from Zhuyeze palaeolake. Multi-proxy analysis of QTL section, including grain size, carbonate, TOC, C/N and δ13C of organic matter, was used to document regional climatic changes during 9-3 cal ka B.P. The record shows a major environmental change at 9.0-7.8 cal ka B.P., attributed to a climate trend towards warmth and humidity. This event was followed by a typical regional drought event which occurred during 7.8-7.5 cal ka B.P. And a warm and humid climate prevailed from 7.5 to 5.0 cal ka B.P., attributed to the warm/humid Holocene Optimum in this region. After that, the climate gradually became drier.Moreover, comparison of the climate record from this paper with the summer insolation at 30°N indicates that the climate pattern reflecting the Asian monsoon changes was caused by insolation change.

  15. Investigating extreme flood response to Holocene palaeoclimate in the Chinese monsoonal zone: A palaeoflood case study from the Hanjiang River

    Science.gov (United States)

    Guo, Yongqiang; Huang, Chun Chang; Pang, Jiangli; Zha, Xiaochun; Zhou, Yali; Wang, Longsheng; Zhang, Yuzhu; Hu, Guiming

    2015-06-01

    Palaeoflood events recorded by slackwater deposits (SWDs) were investigated extensively by sedimentological criteria of palaeohydrology along the upper Hanjiang River valley. Modern flood SWDs were collected for comparison with palaeoflood SWD in the same reaches. Three typical palaeoflood SWDs were observed within Holocene loess-soil blanket on the first river terrace land. The grain size distributions of palaeoflood SWDs are similar to modern flood SWDs, whereas they are different from eolian loess and soil. Palaeoflood SWD lies in three major pedo-stratigraphic boundaries (TS/L0, L0/S0, and S0/Lt) in the Holocene loess-soil profiles. The chronology of three palaeoflood episodes was established by OSL dating and pedo-stratigraphic correlation with the well-dated Holocene loess-soil profiles in the upper Hanjiang River basin. Holocene palaeoflood events were dated to 9500-8500, 3200-2800, and 1800-1700 a B.P., respectively. Palaeoflood discharges were estimated by the palaeoflood model (i.e., slope-area method and step-backwater method). The highest discharges are 51,680-53,950 m3 s- 1 at the 11,500-time scale in the Xunyang reach of the upper Hanjiang River valley. Holocene extraordinary hydroclimatic events in the Hanjiang River often result from abnormal atmospheric circulations from Southwest monsoons in the Chinese monsoonal zone. These results provide a regional expression of extreme flood response to Holocene palaeoclimate to understand the effects of global climatic variations on the river system dynamics.

  16. Climate implications of major geochemical elements in the Holocene sediments of the North and East China monsoonal regions

    Institute of Scientific and Technical Information of China (English)

    Qianli SUN; Zhanghua WANG; Jing CHEN; Wu FENG

    2009-01-01

    Two Holocene sediment cores were retrieved respectively from the enclosed Lake Daihai in the monsoon/arid transition zone of North China and the Taihu Lake coast in the monsoonal area of the Yangtze delta, Eastern China. Distribution of major geochemical elements and their ratios were employed to reveal the characteristics of Holocene climate and associated envir-onmental implications in the two regions. It is suggested that the temporal distribution of major elements serve as a useful indicator to denote the variations of monsoon effective precipitation for the enclosed lake area. High values of resistant elements such as Al2O3, SiO2, TiO2, (FeO + Fe2O3), MnO in the lake sediments correspond to the depressed chemical weathering and weakened mon-soon effective precipitation, while the highs of mobile and easy soluble elements such as MgO, CaO, Na2O reflect the enhanced chemical weathering and increased monsoon effective precipitation in the lake basin. In comparison, the behaviors of the major elements in sediments of the Taihu Lake coast were largely controlled by the changes both in sea transgression in the different Holocene time periods and the monsoon precipitation. The relatively highs of Al2O3, TiO2, (FeO + Fe2O3), in marine-influenced sedi-ments suggest relatively strong coastal hydrodynamics and chemical weathering, and vice versa. Meanwhile, the lows of SiO2, Na2O and CaO in the non-marine-influenced sediments also denote relatively strong hydrodynamics and chemical weathering due to enhanced monsoon precipita-tion, and vice versa. Sedimentary environment should be taken into account when achieving a full understanding of their climate implications.

  17. Understanding the mechanisms behind the West African Monsoon northward extension during Mid-Holocene

    Science.gov (United States)

    Gaetani, Marco; Messori, Gabriele; Zhang, Qiong; Flamant, Cyrille; Evan, Amato T.; Pausata, Francesco S. R.

    2016-04-01

    Understanding the West African monsoon (WAM) dynamics in the mid-Holocene (MH) is a crucial issue in climate modelling, because numerical models typically fail to reproduce the extensive precipitation suggested by proxy evidence. This discrepancy is largely due to unrealistic imposed land surface cover and aerosols. Numerical experiments are conducted by imposing a "green Sahara", along with a reduced dust concentration in the atmosphere, coherently with the MH environment in the region, and the atmospheric dynamics response and impact on precipitation are investigated. The response of the WAM system to the imposed conditions shows a dramatic augmentation of the precipitation across West Africa up to the Mediterranean coast. This follows a substantial reorganization of the regional circulation, with some monsoonal circulation features (Saharan heat low, African easterly jet, African easterly waves) weakened in favour of deep convection development over land. The simulated response is dominated by land cover changes, and the reduction in dust concentration further enhances the changes induced by the "green Sahara". The intensity and meridional extent of the WAM is fully consistent with proxy evidence. The results for the MH WAM present important implications for understanding future climate scenarios in the region, in the perspective of projected wetter conditions in West Africa.

  18. Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

    Science.gov (United States)

    Miriyala, Pavan; Sukumaran, N. P.; Nath, B. Nagender; Ramamurty, P. B.; Sijinkumar, A. V.; Vijayagopal, B.; Ramaswamy, V.; Sebastian, Tyson

    2017-01-01

    Chemical weathering and the ensuing atmospheric carbon dioxide consumption has long been considered to work on geological time periods until recently when some modelling and natural records have shown that the weathering-related CO2 consumption can change at century to glacial-interglacial time scale. Last glacial to interglacial transition period is a best test case to understand the interplay between Pco2-temperature-chemical weathering when a pulse of rapid chemical weathering was initiated. Here we show, from a high resolution 54 ka record from the Andaman Sea in the northern Indian Ocean, that the chemical weathering responds to deglacial to mid-Holocene summer monsoon intensification in the Myanmar watersheds. The multi-proxy data (Al/K, CIA, Rb/Sr, 87Sr/86Sr for degree of weathering and 143Nd/144Nd for provenance) reveal an increase in silicate weathering with initiation of interglacial warm climate at ~17.7 ka followed by a major change at 15.5 ka. Inferred changes in chemical weathering have varied in tandem with the regional monsoonal proxies (δ18Osw-salinity changes of Northern Indian Ocean, effective Asian moisture content and δ18O records of Chinese caves) and are synchronous with changes in summer insolation at 30°N and δ18O of GISP2 implying that chemical weathering was not a later amplifier but worked in tandem with global climate change. PMID:28303943

  19. Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

    Science.gov (United States)

    Miriyala, Pavan; Sukumaran, N. P.; Nath, B. Nagender; Ramamurty, P. B.; Sijinkumar, A. V.; Vijayagopal, B.; Ramaswamy, V.; Sebastian, Tyson

    2017-03-01

    Chemical weathering and the ensuing atmospheric carbon dioxide consumption has long been considered to work on geological time periods until recently when some modelling and natural records have shown that the weathering-related CO2 consumption can change at century to glacial-interglacial time scale. Last glacial to interglacial transition period is a best test case to understand the interplay between Pco2-temperature-chemical weathering when a pulse of rapid chemical weathering was initiated. Here we show, from a high resolution 54 ka record from the Andaman Sea in the northern Indian Ocean, that the chemical weathering responds to deglacial to mid-Holocene summer monsoon intensification in the Myanmar watersheds. The multi-proxy data (Al/K, CIA, Rb/Sr, 87Sr/86Sr for degree of weathering and 143Nd/144Nd for provenance) reveal an increase in silicate weathering with initiation of interglacial warm climate at ~17.7 ka followed by a major change at 15.5 ka. Inferred changes in chemical weathering have varied in tandem with the regional monsoonal proxies (δ18Osw-salinity changes of Northern Indian Ocean, effective Asian moisture content and δ18O records of Chinese caves) and are synchronous with changes in summer insolation at 30°N and δ18O of GISP2 implying that chemical weathering was not a later amplifier but worked in tandem with global climate change.

  20. Early forecasting of Indian Summer Monsoon: case study 2016

    Science.gov (United States)

    Surovyatkina, Elena; Stolbova, Veronika; Kurths, Jurgen

    2017-04-01

    forecasted the monsoon withdrawal from the Eastern Ghats on the 5th of October with a deviation of +/-5 days. We delivered this prediction on July 27-th, 2016 [3], namely 70 days in advance. The date of the actual start of monsoon withdrawal was October 10th. In this day relative humidity began to decrease. Then it passed the 80 percent threshold, and a transition back to a monsoon became impossible, meteorological stations registered it also. We emphasize that our forecasts of the monsoon onset and withdrawal were delivered for 40 and 70 days in advance respectively, and both of our forecasts lie within our prediction interval. Hence, this year we proved that such early prediction of the monsoon timing is possible. [1] Stolbova, V., E. Surovyatkina, B. Bookhagen, and J. Kurths (2016): Tipping elements of the Indian monsoon: Prediction of onset and withdrawal. Geophys. Res. Lett., 43, 1-9 [doi:10.1002/2016GL068392] [2]https://www.pik-potsdam.de/news/press-releases/indian-monsoon-novel-approach-allows-early-forecasting?set_language=en [3] https://www.pik-potsdam.de/kontakt/pressebuero/fotos/monsoon-withdrawal/view

  1. Similar speleothem δ18O signals indicating diverging climate variations in inland central Asia and monsoonal south Asia during the Holocene

    Science.gov (United States)

    Jin, Liya; Zhang, Xiaojian

    2017-04-01

    High-resolution and precisely dated speleothem oxygen isotope (δ18O) records from Asia have provided key evidence for past monsoonal changes. It is found that δ18O records of stalagmites from Kesang Cave (42°52'N, 81°45'E, Xinjiang, China) in inland central Asia were very similar to those from Qunf Cave (17°10'N, 54°18'E, southern Oman) in South Asia, shifting from light to heavy throughout the Holocene, which was regarded as a signal that strong Asian summer monsoon (ASM) may have intruded into the Kesang Cave site and/or adjacent areas in inland central Asia to produce heavy rainfall during the high insolation times (e.g. the early Holocene). However, this is in contrast to conclusions based on other Holocene proxy records and modeling simulations, showing a persistent wetting trend in arid central Asia during the Holocene with a dryer condition in the early Holocene and the wettest condition in the late Holocene. With an analysis of model-proxy data comparison, we revealed a possible physical mechanism responsible for the Holocene evolution of moisture/precipitation in Asian summer monsoon (ASM)-dominated regions and that in the inland central Asia. It is revealed that a recurrent circumglobal teleconnection (CGT) pattern in the summertime mid-latitude circulation of the Northern Hemisphere was closely related to the ASM and the climate of inland central Asia, acting as a bridge linking the ASM to insolation, high-latitude forcing (North Atlantic sea surface temperature (SST)), and low-latitude forcing (tropical Ocean SST). Also, the CGT influence speleothem δ18O values in South Asia via its effect on the amount of precipitation. In addition, the moisture source from the Indian Ocean is associated with relatively high δ18O values compared with that from the North Atlantic Ocean, leading to increased precipitation δ18O values. Hence, the CGT has probably been the key factor responsible for the in-phase relationship in speleothem δ18O values (Kesang Cave

  2. Vegetation response and landscape dynamics of Indian Summer Monsoon variations during Holocene: an eco-geomorphological appraisal of tropical evergreen forest subfossil logs.

    Directory of Open Access Journals (Sweden)

    Navnith K P Kumaran

    Full Text Available The high rainfall and low sea level during Early Holocene had a significant impact on the development and sustenance of dense forest and swamp-marsh cover along the southwest coast of India. This heavy rainfall flooded the coastal plains, forest flourishing in the abandoned river channels and other low-lying areas in midland.The coastline and other areas in lowland of southwestern India supply sufficient evidence of tree trunks of wet evergreen forests getting buried during the Holocene period under varying thickness of clay, silty-clay and even in sand sequences. This preserved subfossil log assemblage forms an excellent proxy for eco-geomorphological and palaeoclimate appraisal reported hitherto from Indian subcontinent, and complements the available palynological data. The bulk of the subfossil logs and partially carbonized wood remains have yielded age prior to the Holocene transgression of 6.5 k yrs BP, suggesting therein that flooding due to heavy rainfall drowned the forest cover, even extending to parts of the present shelf. These preserved logs represent a unique palaeoenvironmental database as they contain observable cellular structure. Some of them can even be compared to modern analogues. As these woods belong to the Late Pleistocene and Holocene, they form a valuable source of climate data that alleviates the lack of contemporaneous meteorological records. These palaeoforests along with pollen proxies depict the warmer environment in this region, which is consistent with a Mid Holocene Thermal Maximum often referred to as Holocene Climate Optimum. Thus, the subfossil logs of tropical evergreen forests constitute new indices of Asian palaeomonsoon, while their occurrence and preservation are attributed to eco-geomorphology and hydrological regimes associated with the intensified Asian Summer Monsoon, as recorded elsewhere.

  3. Early warnings and missed alarms for abrupt monsoon transitions

    Science.gov (United States)

    Thomas, Z. A.; Kwasniok, F.; Boulton, C. A.; Cox, P. M.; Jones, R. T.; Lenton, T. M.; Turney, C. S. M.

    2015-12-01

    Palaeo-records from China demonstrate that the East Asian Summer Monsoon (EASM) is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesized that over these timescales, the EASM exhibits two stable states with bifurcation-type tipping points between them. Here we test this hypothesis by looking for early warning signals of past bifurcations in speleothem δ18O records from Sanbao Cave and Hulu Cave, China, spanning the penultimate glacial cycle. We find that although there are increases in both autocorrelation and variance preceding some of the monsoon transitions during this period, it is only immediately prior to the abrupt monsoon shift at the penultimate deglaciation (Termination II) that statistically significant increases are detected. To supplement our data analysis, we produce and analyse multiple model simulations that we derive from these data. We find hysteresis behaviour in our model simulations with transitions directly forced by solar insolation. However, signals of critical slowing down, which occur on the approach to a bifurcation, are only detectable in the model simulations when the change in system stability is sufficiently slow to be detected by the sampling resolution of the data set. This raises the possibility that the early warning "alarms" were missed in the speleothem data over the period 224-150 kyr and it was only at the monsoon termination that the change in the system stability was sufficiently slow to detect early warning signals.

  4. The early Holocene optimum inferred from a high-resolution pollen record of Huguangyan Maar Lake in southern China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that (i) pollen percentage of trees and shrubs reached 56% during the early Holocene (11600―7800 cal a BP), of which the pollen percentage of tropical trees reached a maximum at 9500―8000 cal a BP, reflecting a hot and wet environment; (ii) during the mid-Holocene (7800―4200 cal a BP), the pollen percentage of montane coniferous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indicating lower temperature and humidity; (iii) in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500―8000 cal a BP in southern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer monsoon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.

  5. Role of Atmospheric Circulation and Westerly Jet Changes in the mid-Holocene East Asian Summer Monsoon

    Science.gov (United States)

    Kong, W.; Chiang, J. C. H.

    2014-12-01

    The East Asian Summer Monsoon (EASM) varies on inter-decadal to interglacial-glacial timescales. The EASM is stronger in the mid-Holocene than today, and these changes can be readily explained by orbitally-driven insolation increase during the boreal summer. However, a detailed understanding of the altered seasonal evolution of the EASM during this time is still lacking. In particular, previous work has suggested a close link between seasonal migration of the EASM and that of the mid-latitude westerlies impinging on the Tibetan Plateau. In this study, we explore, this problem in PMIP3 climate model simulations of the mid-Holocene, focusing on the role of atmospheric circulation and in particular how the westerly jet modulates the East Asia summer climate on paleoclimate timescales. Analysis of the model simulations suggests that, compared to the preindustrial simulations, the transition from Mei-Yu to deep summer rainfall occurs earlier in the mid-Holocene. This is accompanied by an earlier weakening and northward shift of westerly jet away from the Tibetan Plateau. The variation in the strength and the 3-D structure of the westerly jet in the mid-Holocene is summarized. We find that changes to the monsoonal rainfall, westerly jet and meridional circulation covary on paleoclimate timescales. Meridional wind changes in particular are tied to an altered stationary wave pattern, resembling today's the so-called 'Silk Road' teleconnection pattern, riding along the westerly jet. Diagnostic analysis also reveals changes in moist static energy and eddy energy fluxes associated with the earlier seasonal transition of the EASM. Our analyses suggest that the westerly jet is critical to the altered dynamics of the East Asian summer monsoon during the mid-Holocene.

  6. A Possible Impact of Cooling over the Tibetan Plateau on the Mid-Holocene East Asian Monsoon Climate

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    By using a 9-level global atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP9L-AGCM) under the Chinese Academy of Sciences, the authors investigated the response of the East Asian monsoon climate to changes both in orbital forcing and the snow and glaciers over the Tibetan Plateau at the mid-Holocene, about 6000 calendar years before the present (6kyr BP). With the Earth's orbital parameters appropriate for the mid-Holocene, the IAP9L-AGCM computed warmer and wetter conditions in boreal summer than for the present day. Under the precondition of continental snow and glacier cover existing over part of the Tibetan Plateau at the mid-Holocene, the authors examined the regional climate response to the Tibetan Plateau cooling. The simulations indicated that climate changes in South Asia and parts of central Asia as well as in East Asia are sensitive to the Tibetan Plateau cooling at the mid-Holocene, showing a significant decrease in precipitation in northern India, northern China and southern Mongolia and an increase in Southeast Asia during boreal summer.The latter seems to correspond to the weakening, southeastward shift of the Asian summer monsoon system resulting from reduced heat contrast between the Eurasian continent and the Pacific and Indian Oceans when a cooling over the Tibetan Plateau was imposed. The simulation results suggest that the snow and glacier environment over the Tibetan Plateau is an important factor for mid-Holocene climate change in the areas highly influenced by the Asian monsoon.

  7. Changes in mid to late Holocene monsoon strength in eastern Mexico inferred from high-resolution maar lake sediments

    Science.gov (United States)

    Bhattacharya, T.; Byrne, R.; Wogau, K.; Bohnel, H.

    2013-12-01

    Understanding the Holocene variation in central Mexico's summer precipitation can help identify the processes responsible for climatic change and clarify the role of climate in Mesoamerican cultural change. We present proxy results from Aljojuca, a maar lake in the Oriental-Serdan Basin in Mexico's Trans-Mexican Volcanic Belt. The 12 m sediment core from Aljojuca features a laminated, high-resolution proxy archive. A chronology established via radiocarbon dating shows a basal date of 6,200 cal. years B.P. We use fluctuations in pollen, elemental geochemistry, and the stable isotope ratios of authigenic carbonates to reconstruct the timing and duration of mid to late Holocene droughts in central Mexico. We compare these results with geochemical analyses of maar wall rocks and palynological analyses of modern moss polsters to strengthen our interpretations of proxy results. We interpret periods of aridity as periods of reduced summer precipitation and therefore decreased summer monsoon strength. Our results reveal evidence of a gradual decrease in monsoon strength from the mid to late Holocene. We also identify a multi-century dry period between 1,150 and 800 cal yr. BP, coinciding with the abandonment of the nearby fortified city of Cantona. Spatiotemporal analysis of this and other paleoclimatic records reveals region-wide evidence of this ';Terminal Classic' drought, although its timing is spatially heterogeneous. Our results represent one of the only high-resolution mid-Holocene records from the eastern Trans-Mexican Volcanic Belt.

  8. High-resolution Holocene South American monsoon history recorded by a speleothem from Botuverá Cave, Brazil

    Science.gov (United States)

    Bernal, J. P.; Cruz, Francisco W.; Stríkis, Nicolás M.; Wang, Xianfeng; Deininger, Michael; Catunda, Maria Carolina A.; Ortega-Obregón, C.; Cheng, Hai; Edwards, R. Lawrence; Auler, Augusto S.

    2016-09-01

    A Holocene stalagmite from Botuverá Cave, southeastern Brazil was analyzed by LA-ICPMS for Mg/Ca, Sr/Ca, Ba/Ca. The observed variability in the record was demonstrated to be modulated by prior calcite precipitation, and, thus, is interpreted to reflect monsoon intensity. We find that the calcite δ18O is strongly correlated with Sr/Ca, indicating that atmospheric circulation over South America and monsoon intensity have been tightly correlated throughout most of the Holocene, both directly responding to solar precession. Comparison with other contemporaneous high-resolution hydroclimate records reveals that SAMS has shown a degree of complexity during the Holocene not previously detected, with periods where the South American Convergence Zone (SACZ) expanded to cover most of the South American sub-continent, and coincident with periods of low-SST in the north Atlantic. We also detect periods where rainfall amount in northeastern and southeastern Brazil are markedly anti-phased, suggesting a north-south migration of SACZ, which it appears to be mediated by solar irradiance. The high-resolution nature of our record allow us to examine the effect that Holocene climate anomalies had upon SAMS dynamics and hydroclimate in southeastern Brazil, in particular the 8.2 ka event and the Little Ice Age. In addition to confirm the internal structure of the events, we also detect the possible consequences of the climatic anomalies upon ocean-atmosphere interactions through its effects upon SAMS.

  9. The Holocene history of the North American Monsoon: 'known knowns' and 'known unknowns' in understanding its spatial and temporal complexity

    Science.gov (United States)

    Metcalfe, Sarah E.; Barron, John A.; Davies, Sarah J.

    2015-01-01

    Evidence for climatic change across the North American Monsoon (NAM) and adjacent areas is reviewed, drawing on continental and marine records and the application of climate models. Patterns of change at 12,000, 9000, 6000 and 4000 cal yr BP are presented to capture the nature of change from the Younger Dryas (YD) and through the mid-Holocene. At the YD, conditions were cooler overall, wetter in the north and drier in the south, while moving into the Holocene wetter conditions became established in the south and then spread north as the NAM strengthened. Until c. 8000 cal yr BP, the Laurentide Ice Sheet influenced precipitation in the north by pushing the Bermuda High further south. The peak extent of the NAM seems to have occurred around 6000 cal yr BP. 4000 cal yr BP marks the start of important changes across the NAM region, with drying in the north and the establishment of the clear differences between the summer-rain dominated south and central areas and the north, where winter rain is more important. This differentiation between south and north is crucial to understanding many climate responses across the NAM. This increasing variability is coincident with the declining influence of orbital forcing. 4000 cal yr BP also marks the onset of significant anthropogenic activity in many areas. For the last 2000 years, the focus is on higher temporal resolution change, with strong variations across the region. The Medieval Climate Anomaly (MCA) is characterised by centennial scale ‘megadrought’ across the southwest USA, associated with cooler tropical Pacific SSTs and persistent La Niña type conditions. Proxy data from southern Mexico, Central America and the Caribbean reveal generally wetter conditions, whereas records from the highlands of central Mexico and much of the Yucatan are typified by long -term drought. The Little Ice Age (LIA), in the north, was characterised by cooler, wetter winter conditions that have been linked with increased

  10. Mid- to late Holocene Indian Ocean Monsoon variability recorded in four speleothems from Socotra Island, Yemen

    Science.gov (United States)

    Van Rampelbergh, Maïté; Fleitmann, Dominik; Verheyden, Sophie; Cheng, Hai; Edwards, Lawrence; De Geest, Peter; De Vleeschouwer, David; Burns, Stephen J.; Matter, Albert; Claeys, Philippe; Keppens, Eddy

    2013-04-01

    Four stalagmites covering the last 7.0 ka were sampled on Socotra, an island in the northern Indian Ocean to investigate the evolution of the northeast Indian Ocean Monsoon (IOM) since the mid Holocene. On Socotra, rain is delivered at the start of the southwest IOM in May-June and at the start of the northeast IOM from September to December. The Haggeher Mountains act as a barrier forcing precipitation brought by the northeast winds to fall preferentially on the eastern side of the island, where the studied caves are located. δ18O and δ13C and Mg/Ca and Sr/Ca signals in the stalagmites reflect precipitation amounts brought by the northeast winds. For stalagmite STM6, this amount effect is amplified by kinetic effects during calcite deposition. Combined interpretation of the stalagmites' signals suggest a weakening of the northeast precipitation between 6.0 and 3.8 ka. After 3.8 ka precipitation intensities remain constant with two superimposed drier periods, between 0 and 0.6 ka and from 2.2 to 3.8 ka. No link can be established with Greenland ice cores and with the summer IOM variability. In contrast to the stable northeast rainy season suggested by the records in this study, speleothem records from western Socotra indicate a wettening of the southwest rainy season on Socotra after 4.4 ka. The local wettening of western Socotra could relate to a more southerly path (more over the Indian Ocean) taken by the southwest winds. Stalagmite STM5, sampled at the fringe between both rain areas displays intermediate δ18O values. After 6.2 ka, similar precipitation changes are seen between eastern Socotra and northern Oman indicating that both regions are affected similarly by the monsoon. Different palaeoclimatologic records from the Arabian Peninsula currently located outside the ITCZ migration pathway display an abrupt drying around 6 ka due to their disconnection from the southwest rain influence. Records that are nowadays still receiving rain by the southwest winds

  11. A Continuous Record of Indian Summer Monsoon Variability through the Holocene from Lake Sediments in Yunnan, China

    Science.gov (United States)

    Hillman, A. L.; Abbott, M. B.; Yu, J.

    2015-12-01

    Continuous terrestrial archives of the Indian Summer Monsoon through the Holocene are lacking, yet critical to providing a long-term perspective of hydroclimate variability. Here we present an 8,000 year sediment record from Xing Yun Lake in Yunnan, China that provides a semi-quantitative estimate of lake level change using stable isotopes of authigenic calcite as well as within-lake productivity using stable isotopes of organic matter. Substantial drops in lake level occur at 6,600 years BP, consistent with previous studies of a weaker monsoon system in the mid-Holocene due to declining summer insolation. Lake levels stabilize at 4,700 years BP and remain steady due to the topography surrounding the lake. From 5,600 to 5,100 and from 4,600 to 4,000 years BP, primary productivity decreases and is coincident with significant regional aridity as well as cooler Western Tropical Pacific sea surface temperatures. Variability in the stable isotopes of both calcite and organic matter after 1,500 years BP is primarily controlled by human activities. This study shows broad agreement with previous work on the Tibetan Plateau and provides one of the first continuous records of lake hydrologic balance from a crucial region affected by the Indian Summer Monsoon.

  12. The 9.2 ka event in Asian summer monsoon area: the strongest millennial scale collapse of the monsoon during the Holocene

    Science.gov (United States)

    Zhang, Wenchao; Yan, Hong; Dodson, John; Cheng, Peng; Liu, Chengcheng; Li, Jianyong; Lu, Fengyan; Zhou, Weijian; An, Zhisheng

    2017-06-01

    Numerous Holocene paleo-proxy records exhibit a series of centennial-millennial scale rapid climatic events. Unlike the widely acknowledged 8.2 ka climate anomaly, the likelihood of a significant climate excursion at around 9.2 cal ka BP, which has been notably recognized in some studies, remains to be fully clarified in terms of its magnitude and intensity, as well as its characteristics and spatial distributions in a range of paleoclimatic records. In this study, a peat sediment profile from the Dajiuhu Basin in central China was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9.2 cal ka BP. The results show that the peat development was interrupted abruptly at around 9.2 cal ka BP, when the chemical weathering strength decreased and the tree-pollen declined. This suggests that a strong drier regional climatic event occurred at around 9.2 cal ka BP in central China, which was, in turn, probably connected to the rapid 9.2 ka climate event co-developing worldwide. In addition, based on the synthesis of our peat records and the other Holocene hydrological records from Asian summer monsoon (ASM) region, we further found that the 9.2 ka event probably constituted the strongest abrupt collapse of the Asian monsoon system during the full Holocene interval. The correlations between ASM and the atmospheric 14C production rate, the North Atlantic drift ice records and Greenland temperature indicated that the weakened ASM event at around 9.2 cal ka BP could be interpreted by the co-influence of external and internal factors, related to the changes of the solar activity and the Atlantic Meridional Overturning Circulation (AMOC).

  13. Holocene changes in monsoon precipitation in the Andes of NE Peru based on δ18O speleothem records

    Science.gov (United States)

    Bustamante, M. G.; Cruz, F. W.; Vuille, M.; Apaéstegui, J.; Strikis, N.; Panizo, G.; Novello, F. V.; Deininger, M.; Sifeddine, A.; Cheng, H.; Moquet, J. S.; Guyot, J. L.; Santos, R. V.; Segura, H.; Edwards, R. L.

    2016-08-01

    Two well-dated δ18O-speleothem records from Shatuca cave, situated on the northeastern flank of the Peruvian Andes (1960 m asl) were used to reconstruct high-resolution changes in precipitation during the Holocene in the South American Summer Monsoon region (SASM). The records show that precipitation increased gradually throughout the Holocene in parallel with the austral summer insolation trend modulated by the precession cycle. Additionally the Shatuca speleothem record shows several hydroclimatic changes on both longer- and shorter-term time scales, some of which have not been described in previous paleoclimatic reconstructions from the Andean region. Such climate episodes, marked by negative excursions in the Shatuca δ18O record were logged at 9.7-9.5, 9.2, 8.4, 8.1, 5.0, 4.1, 3.5, 3.0, 2.5, 2.1 and 1.5 ka b2k, and related to abrupt multi-decadal events in the SASM. Some of these events were likely associated with changes in sea surface temperatures (SST) during Bond events in the North Atlantic region. On longer time scales, the low δ18O values reported between 5.1-5.0, 3.5-3.0 and 1.5 ka b2k were contemporaneous with periods of increased sediment influx at Lake Pallcacocha in the Andes of Ecuador, suggesting that the late Holocene intensification of the monsoon recorded at Shatuca site may also have affected high altitudes of the equatorial Andes further north. Numerous episodes of low SASM intensity (dry events) were recorded by the Shatuca record during the Holocene, in particular at 10.2, 9.8, 9.3, 6.5, 5.1, 4.9, 2.5 and 2.3 ka b2k, some of them were synchronous with dry periods in previous Andean records.

  14. The sharp decline of East Asian summer monsoon at mid-Holocene indicated by the lake-wetland transition in the Sanjiang Plain, northeastern China

    Directory of Open Access Journals (Sweden)

    Z. Q. Zhang

    2014-12-01

    Full Text Available The timing of the waxing and wining of the East Asian summer monsoon during the Holocene is still under debate. In present study, we present the high-resolution grain-size and LOI records from a well-dated mud/peat profile to reveal the lake-wetland transition in the Sanjiang Plain and discuss its significance to Holocene monsoon evolutions. The results show that the shallow-water lakes have developed in low-lying areas of the plain before 4600 yr BP, corresponding to the Holocene monsoon maximum. Thereafter, the wetlands began to initiate with the extinction of the paleolakes, marking a lake-shrinking stage with the relative dry climate. Considering the prevalent monsoon climate in the Sanjiang Plain, we suggest the lake-wetland transition at 4600 yr BP indicate a sharp decline of the summer monsoon rather than the basin infilling process. Such a remarkable monsoon weakening event has been widely documented in northern China, and we associated it with the ocean–atmosphere interacting processes in low-latitude regions.

  15. A Possible Role of Solar Radiation and Ocean in the Mid-Holocene East Asian Monsoon Climate

    Institute of Scientific and Technical Information of China (English)

    魏江峰; 王会军

    2004-01-01

    An atmospheric general circulation model (AGCM) and an oceanic general circulation model (OGCM) are asynchronously coupled to simulate the climate of the mid-Holocene period.The role of the solarradiation and ocean in the mid-Holocene East Asian monsoon climate is analyzed and some mechanisms are revealed.At the forcing of changed solar radiation induced by the changed orbital parameters and the changed SST simulated by the OGCM,compared with when there is orbital forcing alone,there is more precipitation and the monsoon is stronger in the summer of East Asia,and the winter temperature increases over China.These agree better with the reconstructed data.It is revealed that the change of solar radiation can displace northward the ITCZ and the East Asia subtropical jet,which bring more precipitation over the south of Tibet and North and Northeast China.By analyzing the summer meridional latent heat transport,it is found that the influence of solar radiation change is mainly to increase the convergence of atmosphere toward the land,and the influence of SST change is mainly to transport more moisture to the sea surface atmosphere.Their synergistic effect on East Asian precipitation is much stronger than the sum of their respective effects.

  16. Early warnings and missed alarms for abrupt monsoon transitions

    Directory of Open Access Journals (Sweden)

    Z. A. Thomas

    2015-04-01

    Full Text Available Palaeo-records from China (Cheng et al., 2009; Wang et al., 2008, 2001 demonstrate the East Asian Summer Monsoon (EASM is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesised that over these timescales, the EASM exhibits two stable states with bifurcation-type tipping points between them (Schewe et al., 2012. Here we test this hypothesis by looking for early warning signals of past bifurcations in speleothem records from Sanbao Cave and Hulu Cave, China (Wang et al., 2008, 2001, spanning the penultimate glacial cycle, and in multiple model simulations derived from the data. We find hysteresis behaviour in our model simulations with transitions directly forced by solar insolation. We detect critical slowing down prior to an abrupt monsoon shift during the penultimate deglaciation consistent with long-term orbital forcing. However, such signals are only detectable when the change in system stability is sufficiently slow to be detected by the sampling resolution of the dataset, raising the possibility that the alarm was missed and a similar forcing drove earlier EASM shifts.

  17. See-saw relationship of the Holocene East Asian-Australian summer monsoon

    Science.gov (United States)

    Eroglu, Deniz; McRobie, Fiona H.; Ozken, Ibrahim; Stemler, Thomas; Wyrwoll, Karl-Heinz; Breitenbach, Sebastian F. M.; Marwan, Norbert; Kurths, Jürgen

    2016-09-01

    The East Asian-Indonesian-Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian-Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could `lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see-saw relationship over the last 9,000 years--with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial- to millennial-scale relationships within the wider EAIASM regime.

  18. See–saw relationship of the Holocene East Asian–Australian summer monsoon

    Science.gov (United States)

    Eroglu, Deniz; McRobie, Fiona H.; Ozken, Ibrahim; Stemler, Thomas; Wyrwoll, Karl-Heinz; Breitenbach, Sebastian F. M.; Marwan, Norbert; Kurths, Jürgen

    2016-01-01

    The East Asian–Indonesian–Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian–Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could ‘lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see–saw relationship over the last 9,000 years—with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial- to millennial-scale relationships within the wider EAIASM regime. PMID:27666662

  19. See-saw relationship of the Holocene East Asian-Australian summer monsoon.

    Science.gov (United States)

    Eroglu, Deniz; McRobie, Fiona H; Ozken, Ibrahim; Stemler, Thomas; Wyrwoll, Karl-Heinz; Breitenbach, Sebastian F M; Marwan, Norbert; Kurths, Jürgen

    2016-09-26

    The East Asian-Indonesian-Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian-Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could 'lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see-saw relationship over the last 9,000 years-with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial- to millennial-scale relationships within the wider EAIASM regime.

  20. Progress in studies of the climate of humid period and the impacts of changing precession in early-mid Holocene

    Institute of Scientific and Technical Information of China (English)

    Jianbin Huang; Shaowu Wang; Xinyu Wen; Bao Yang

    2008-01-01

    Studies on the climate of humid period and the impacts of changing precession in the early-mid Holocene are reviewed in this paper.High-resolution proxy data indicated that the African Humid Period,strong summer monsoon from the Arabian Sea to South Asia,northward migration of ITCZ (Intertropical Convergence Zone) over the northern South America,and the humid period of China appeared in 10.5-5.5 kaBP,10.0-6.0 kaBP,10.5-5.4 kaBP,and 11.0-8.0 kaBP,respectively.Modeling studies proved that summer inso-lation over the Northern Hemisphere increased following the changes of precession in the early Holocene,which increased the land-sea temperature contrasts,intensified the summer monsoon circulation in the Northern Hemisphere,and finally induced a humid climate over the area under the influence of summer monsoon.However,modeling results underestimated the increase of precipitation and the degree of northward extension of monsoon rain belt compared with palaeo-environmental data.These discrepancies between the modeling results and the palaeo-environmental data may be associated with the changes of North Atlantic circulation,sea ice and veg-etation covers.Moreover,climate of the humid period was not stable,in which several droughts were inlaid on centennial scale.In this review,perspectives for further studies of the climate change of the humid period in the early-mid Holocene are also proposed.

  1. Last Glacial to Holocene history of the Indian Monsoon recorded in Andaman Sea sediments

    Science.gov (United States)

    Hathorne, E. C.; Yirgaw, D. G.; Ali, S.; Giosan, L.; Collett, T. S.; Nath, B.; Frank, M.

    2013-12-01

    Over 3 billion people live in the area influenced by the Asian monsoon, the rains of which provide vital water resources while posing a risk to human life through flooding. Despite the importance to so many the monsoon is difficult to predict and model, making its future development in a changing global climate uncertain. To help improve models and predictions, histories of monsoon variability beyond the instrumental record are required. The past variability of the Indian Monsoon is mostly known from records of monsoon wind strength over the Arabian Sea. This study uses a unique long sediment core obtained by the drill ship JOIDES Resolution in the Andaman Sea to examine the past variability of Indian Monsoon precipitation on the Indian sub-continent and directly over the ocean. Here we present multi-proxy data examining variations during the last glacial and deglaciation. The radiogenic Sr, Nd, and Pb isotopic composition of the clay fraction (fresh water. References: Antonov, J. I., D. Seidov, T. P. Boyer, R. A. Locarnini, A. V. Mishonov, and H. E. Garcia (2010). World Ocean Atlas 2009 Volume 2: Salinity. S. Levitus, Ed., NOAA Atlas NESDIS 69, U.S. Government Printing Office, Washington, D.C., 184 pp.

  2. Cyclicity in the Late Holocene monsoonal changes from the western Bay of Bengal: Foraminiferal approach.

    Digital Repository Service at National Institute of Oceanography (India)

    Rana, S.S.; Nigam, R.

    of Paleogene aerobic/ anaerobic benthic foraminifera and deep sea circulation. Palaeogeography Palaeoclimatology Palaeoecology 83: 65-85. Lamy, F., Hebblin, D., Rohl, U., Wefer, G. 2001. Holocene rainfall variability in southern Chile: a marine record...

  3. Late Quaternary (Holocene) landscape evolution of a monsoon-influenced high Himalayan valley, Gori Ganga, Nanda Devi, NE Garhwal

    Science.gov (United States)

    Barnard, Patrick L.; Owen, Lewis A.; Sharma, Milap C.; Finkel, Robert C.

    2004-07-01

    The Garhwal Himalaya provides an excellent natural laboratory in which to examine landscape evolution in a monsoon-influenced high mountain environment. Geomorphic and sedimentological analysis and 10Be cosmogenic radionuclide (CRN) surface exposure dating of moraines, fans, and river and strath terraces in the Gori Ganga Valley of Nanda Devi, NE Garhwal, indicate that fans and river terraces developed rapidly by debris flow and flood processes during periods of deglaciation. These phases of high sediment transfer occurred at ˜1-2, ˜4-5, and ˜7-8 ka. Fan incision rates, subsequent to major times of resedimentation after each glacial advance, are between ˜19 and 57 mm/year. This contrasts with bedrock incision rates, based on mid-Holocene strath terraces, of ˜5 mm/year. These rates indicate that despite episodes of rapid denudation and resedimentation linked to glacial activity in this region, the background rates of denudation are similar to those for other regions of the Himalaya, averaging several millimeters per year. Furthermore, these data show the importance of climatic controls on landscape evolution and suggest a strong monsoonal control on the dynamics of earth surface processes in this region.

  4. Recently studied sedimentary records from the eastern Arabian Sea: Implications to Holocene monsoonal variability

    Digital Repository Service at National Institute of Oceanography (India)

    Agnihotri, R.; Kurian, S.

    in an attempt to comprehend past monsoonal variability in Indian as well as global context are reviewed. We also focus upon different proxies used so far in the Arabian Sea, their fidelity, limitations and future scope of using novel proxies for a better...

  5. The Preboreal-like Asian monsoon climate in the early last interglacial period recorded from the Dark Cave, Southwest China

    Science.gov (United States)

    Jiang, Xiuyang; He, Yaoqi; Wang, Xiaoyan; Sun, Xiaoshuang; Hong, Hui; Liu, Juan; Yu, Tsai-Luen; Li, Zhizhong; Shen, Chuan-Chou

    2017-08-01

    Transitions of glacial-interglacial cycles are critical periods for Quaternary climate shifts. Here, we present new, decadal resolution Asian summer monsoon (ASM) record from three stalagmites obtained from the Dark Cave in southwestern China over 130-114 thousand years ago (ka, before CE 1950). Chronology was anchored by 28 230Th dates with typical uncertainties of ±0.3-1.0 kyr, allowing an assessment of timing and transition of climate changes during the onset and end of the last interglacial. An agreement between this new and previous stalagmite δ18O records supports that summer insolation predominates orbital-scale ASM evolution. A 2-3 kyr-long gradually increasing ASM period, analogous to the classical Preboreal episode in the early Holocene, follows the termination of a weak monsoon interval at 129.0 ± 0.8 ka. This finding suggests a strong influence of high-latitude ice-sheet dynamics on Asian monsoonal conditions during the early interglacial period. An abrupt end of the marine isotope stage 5e at 118.8 ± 0.6 ka was probably caused by the internal climate system threshold effects.

  6. Reorganization of the North Atlantic Oscillation during early Holocene deglaciation

    Science.gov (United States)

    Wassenburg, Jasper A.; Dietrich, Stephan; Fietzke, Jan; Fohlmeister, Jens; Jochum, Klaus Peter; Scholz, Denis; Richter, Detlev K.; Sabaoui, Abdellah; Spötl, Christoph; Lohmann, Gerrit; Andreae, Meinrat O.; Immenhauser, Adrian

    2016-08-01

    The North Atlantic Oscillation is the dominant atmospheric pressure mode in the North Atlantic region and affects winter temperature and precipitation in the Mediterranean, northwest Europe, Greenland, and Asia. The index that describes the sea-level pressure difference between Iceland and the Azores is correlated with a dipole precipitation pattern over northwest Europe and northwest Africa. How the North Atlantic Oscillation will develop as the Greenland ice sheet melts is unclear. A potential past analogue is the early Holocene, during which melting ice sheets around the North Atlantic freshened surface waters, affecting the strength of the meridional overturning circulation. Here we present a Holocene rainfall record from northwest Africa based on speleothem δ18O and compare it against a speleothem-based rainfall record from Europe. The two records are positively correlated during the early Holocene, followed by a shift to an anti-correlation, similar to the modern record, during the mid-Holocene. On the basis of our simulations with an Earth system model, we suggest the shift to the anti-correlation reflects a large-scale atmospheric and oceanic reorganization in response to the demise of the Laurentide ice sheet and a strong reduction of meltwater flux to the North Atlantic, pointing to a potential sensitivity of the North Atlantic Oscillation to the melting of ice sheets.

  7. A late Holocene winter monsoon record inferred from the palaeo-aeolian sand dune in the southeastern Mu Us Desert, northern China

    Institute of Scientific and Technical Information of China (English)

    Bing Liu; HeLing Jin; Fan Yang

    2016-01-01

    The variation of the Asian winter monsoonal strength has seriously affected the climate and environmental conditions in the Asian monsoonal region, and even in marginal islands and the ocean in the East Asian region. However, relevant under-standing remains unclear due to the lack of suitable geological materials and effective proxies in the key study areas. Here, we present a grain-size record derived from the palaeo-aeolian sand dune in the southeastern Mu Us Desert, together with other proxies and OSL dating, which reflect a relatively detailed history of the winter monsoon and abrupt environmental events during the past 4.2 ka. Our grain-size standard deviation model indicated that>224μm content can be considered as an indicator of the intensity of Asian winter monsoon, and it shows declined around 4.2–2.1 ka, enhanced but unstable in 2.1–0.9 ka, and obviously stronger since then. In addition, several typical climate events were also documented, forced by the periodic variation of winter monsoonal intensity. These include the cold intervals of 4.2, 2.8, 1.4 ka, and the Little Ice Age (LIA), and relatively warm sub-phases around 3.0, 2.1, 1.8 ka, and the Medieval Warm Period (MWP), which were roughly accordant with the records of the aeolian materials, peat, stalagmites, ice cores, and sea sediments in various lat-itudes of the Northern Hemisphere. Combined with the previous progresses of the Asian summer monsoon, we prelimi-narily confirmed a millennial-scale anti-correlation of Asian winter and summer monsoons in the Late Holocene epoch. This study suggests that the evolution of the palaeo-aeolian sand dune has the potential for comprehending the history of Asian monsoon across the desert regions of the modern Asian monsoonal margin in northern China.

  8. Monsoon response to changes in Earth's orbital parameters: comparisons between simulations of the Eemian and of the Holocene

    Directory of Open Access Journals (Sweden)

    P. Braconnot

    2008-04-01

    Full Text Available Monsoon is the major manifestation of the seasonal cycle in the tropical regions, and there is a wide range of evidence from marine and terrestrial data that monsoon characteristics are affected by changes in the Earth's orbital parameters. We consider 3 periods in the Eemian and in the Holocene that present some analogy in the Earth's orbital configuration in terms of obliquity and precession. Simulations with the IPSL_CM4 ocean-atmosphere coupled model allow us to discuss the response of the Indian and African monsoon in terms of amplitude and response to the insolation forcing. Results show that precession plays a large role in shaping the seasonal timing of the monsoon system. Differences are found in the response of the two sub-systems. They result from the phase relationship between the insolation forcing and the seasonal characteristics of each sub-system. Also the response of the Indian Ocean is very different in terms of temperature and salinity when the change in insolation occurs at the summer solstice or later in the year. Monsoon has a large contribution to heat and water transports. It is shown that the relative importance of monsoon on the change in the energetic of the tropical regions also vary with precession.

  9. Monsoon response to changes in Earth's orbital parameters: comparisons between simulations of the Eemian and of the Holocene

    Directory of Open Access Journals (Sweden)

    P. Braconnot

    2008-11-01

    Full Text Available Monsoon is the major manifestation of the seasonal cycle in the tropical regions, and there is a wide range of evidence from marine and terrestrial data that monsoon characteristics are affected by changes in the Earth's orbital parameters. We consider 3 periods in the Eemian and 3 in the Holocene that present some analogy in the Earth's orbital configuration in terms of obliquity and precession. Simulations with the IPSL_CM4 ocean-atmosphere coupled model allow us to discuss the response of the Indian and African monsoon in terms of amplitude and response to the insolation forcing. Results show that precession plays a large role in shaping the seasonal timing of the monsoon system. Differences are found in the response of the two sub-systems. They result from the phase relationship between the insolation forcing and the seasonal characteristics of each sub-system. Also the response of the Indian Ocean is very different in terms of temperature and salinity when the change in insolation occurs at the summer solstice or later in the year. Monsoon has a large contribution to heat and water transports. It is shown that the relative importance of monsoon on the change in the energetic of the tropical regions also vary with precession.

  10. Qualitative assessment of PMIP3 rainfall simulations across the eastern African monsoon domains during the mid-Holocene and the Last Glacial Maximum

    Science.gov (United States)

    Chevalier, Manuel; Brewer, Simon; Chase, Brian M.

    2017-01-01

    In this paper we compare a compilation of multiproxy records spanning the eastern African margin with general circulation model simulations of seasonal precipitation fields for the mid-Holocene and the Last Glacial Maximum (LGM) carried out as part of the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). Results show good agreement during the mid-Holocene (the '6K experiment'), with palaeodata and model outputs correlating well and indicating that changes in insolation drove a stronger northern African monsoon (north of ∼0-5°S) during the terminal "African Humid Period" and a weaker southeast African monsoon. For the LGM (the '21K experiment'), however, significant discrepancies exist both between model simulations, and between existing palaeodata and simulated conditions, both in terms of direction and amplitude of change. None of the PMIP3 simulations reflect the pattern inferred from the palaeodata. Two major discrepancies have been identified to explain this: 1) the limited sensitivity of the southern monsoon domain to the colder temperatures of the Indian Ocean (-2 °C), and 2) the absence of changes in the dynamic of the Indian Ocean Walker circulation over the entire basin, despite the exposure of the Sahul and Sunda shelves that weakened convection over the Indo-Pacific Warm Pool during the LGM. These results indicate that some major features of the atmospheric and oceanic teleconnections between the different monsoon regions require further consideration as models evolve.

  11. Early warnings and missed alarms for abrupt monsoon transitions

    OpenAIRE

    Z. A. Thomas; Kwasniok, F.; C. A. Boulton; Cox, P.M.; Jones, R. T.; Lenton, T. M.; C. S. M. Turney

    2015-01-01

    Palaeo-records from China (Cheng et al., 2009; Wang et al., 2008, 2001) demonstrate the East Asian Summer Monsoon (EASM) is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesised that over these timescales, the EASM exhibits two stable states with bifurcation-type tipping points between them (Schewe et al., 2012). Here we test this hypothesis by looki...

  12. Early Holocene chicken domestication in northern China.

    Science.gov (United States)

    Xiang, Hai; Gao, Jianqiang; Yu, Baoquan; Zhou, Hui; Cai, Dawei; Zhang, Youwen; Chen, Xiaoyong; Wang, Xi; Hofreiter, Michael; Zhao, Xingbo

    2014-12-01

    Chickens represent by far the most important poultry species, yet the number, locations, and timings of their domestication have remained controversial for more than a century. Here we report ancient mitochondrial DNA sequences from the earliest archaeological chicken bones from China, dating back to ∼ 10,000 B.P. The results clearly show that all investigated bones, including the oldest from the Nanzhuangtou site, are derived from the genus Gallus, rather than any other related genus, such as Phasianus. Our analyses also suggest that northern China represents one region of the earliest chicken domestication, possibly dating as early as 10,000 y B.P. Similar to the evidence from pig domestication, our results suggest that these early domesticated chickens contributed to the gene pool of modern chicken populations. Moreover, our results support the idea that multiple members of the genus Gallus, specifically Gallus gallus and Gallus sonneratii contributed to the gene pool of the modern domestic chicken. Our results provide further support for the growing evidence of an early mixed agricultural complex in northern China.

  13. Early Holocene groundwater table fluctuations in relation to rice domestication in the middle Yangtze River basin, China

    Science.gov (United States)

    Liu, Tao; Liu, Yan; Sun, Qianli; Zong, Yongqiang; Finlayson, Brian; Chen, Zhongyuan

    2017-01-01

    The early Holocene environmental amelioration stimulated the trajectory of Neolithic farming cultures and specific geographic settings played a role in determining the nature of these cultures. Using microfossil evidence, the present study reveals that the fluctuations of the groundwater table substantially influenced rice domestication in the Dongting Lake area of the middle Yangtze River basin in the early Holocene. Our 14C-dated sediment core taken from the Bashidang (BSD) Neolithic site contains evidence that the site was a floodplain prior to human occupation ca. 8600 years ago. Poaceae, which contained wild rice (Oryza sp.) as indicated by combined pollen and phytolith evidence, and low counts of freshwater algae indicated a moist site condition. The area then gradually evolved into wetlands as the water table rose, in response to the increasing monsoon precipitation during the early Holocene. This favored rice domestication, assisted by firing and clearing, that continued to flourish for several hundred years. Finally, rice domestication declined during the late stage of the Pengtoushan culture, accompanied by evidence of the expansion of wetlands reflecting the effects of a rising groundwater table that had caused the cessation of rice farming at the Bashidang site after ca. 8000-7900 cal yr BP. This study shows that there are local effects at particular sites that may differ from the trend at the regional scale, necessitating a careful interpretation of the available evidence.

  14. Early Holocene hydrology and environments of the Ner River (Poland)

    Science.gov (United States)

    Kittel, Piotr; Płóciennik, Mateusz; Borówka, Ryszard K.; Okupny, Daniel; Pawłowski, Dominik; Peyron, Odille; Stachowicz-Rybka, Renata; Obremska, Milena; Cywa, Katarzyna

    2016-03-01

    The Ner River valley (central Poland) underwent substantial transformation during the Weichselian-Holocene transition as a result of fluvial processes and climate changes, resulting in the establishment of its present shape in the Holocene. A multiproxy study based on organic deposits from a palaeochannel fill (Lutomiersk-Koziówki) shows that after the channel was cut off during the late glacial termination, it became a shallow oxbow, fed by local springs. In the Boreal period, the oxbow lake was also fed by precipitation and became a telmatic environment overgrown by rush and swamp vegetation. Finally, it was covered by overbank deposits. The first flooding phase (9900-9600 cal. BP) was followed by the accumulation of overbank sediments (after 9500 cal. BP) and flooding increased after ca. 9300-9000 cal. BP. Pollen data provide information on the regional vegetation context for local and regional changes. In the Atlantic period, an increase in both summer and winter temperatures is inferred from the pollen data, corresponding to an expansion of thermophilous deciduous forests. While in general, flooding phases of the Early Holocene are poorly recognised in Eastern Europe, the Lutomiersk-Koziówki site may be considered as one of the reference points for this phenomenon in the region.

  15. Early Holocene climate oscillations recorded in three Greenland ice cores

    DEFF Research Database (Denmark)

    Rasmussen, Sune Olander; Vinther, Bo Møllesøe; Clausen, Henrik Brink;

    2007-01-01

    A new ice core chronology for the Greenland DYE-3, GRIP, and NGRIP ice cores has been constructed, making it possible to compare the d18O and accumulation signals recorded in the three cores on an almost annual scale throughout the Holocene. We here introduce the new time scale and investigate d18O...... and accumulation anomalies that are common to the three cores in the Early Holocene (7.9–11.7 ka before present). Three time periods with significant and synchronous anomalies in the d18O and accumulation signals stand out: the well-known 8.2 ka event, an event of shorter duration but of almost similar amplitude...... around 9.3 ka before present, and the Preboreal Oscillation during the first centuries of the Holocene. For each of these sections, we present a d18O anomaly curve and a common accumulation signal that represents regional changes in the accumulation rate over the Greenland ice cap....

  16. Stratigraphic evidence for an early Holocene earthquake in Aceh, Indonesia

    Science.gov (United States)

    Grand Pre, Candace A.; Horton, Benjamin P.; Kelsey, Harvey M.; Rubin, Charles M.; Hawkes, Andrea D.; Daryono, Mudrik R.; Rosenberg, Gary; Culver, Stephen J.

    2012-10-01

    The Holocene stratigraphy of the coastal plain of the Aceh Province of Sumatra contains 6 m of sediment with three regionally consistent buried soils above pre-Quaternary bedrock or pre-Holocene unconsolidated sediment. Litho-, bio-, and chronostratigraphic analyses of the lower buried soil reveals a rapid change in relative sea-level caused by coseismic subsidence during an early Holocene megathrust earthquake. Evidence for paleoseismic subsidence is preserved as a buried mangrove soil, dominated by a pollen assemblage of Rhizophora and/or Bruguiera/Ceriops taxa. The soil is abruptly overlain by a thin tsunami sand. The sand contains mixed pollen and abraded foraminiferal assemblages of both offshore and onshore environments. The tsunami sand grades upward into mud that contains both well-preserved foraminifera of intertidal origin and individuals of the gastropod Cerithidea cingulata. Radiocarbon ages from the pre- and post-seismic sedimentary sequences constrain the paleoearthquake to 6500-7000 cal. yrs. BP. We use micro-and macrofossil data to determine the local paleoenvironment before and after the earthquake. We estimate coseismic subsidence to be 0.45 ± 0.30 m, which is comparable to the 0.6 m of subsidence observed during the 2004 Aceh-Andaman earthquake on Aceh's west coast.

  17. Mid-Holocene variability of the East Asian monsoon based on bulk organic δ13C and C/N records from the Pearl River estuary, southern China

    Science.gov (United States)

    Yu, F.; Zong, Y.; Lloyd, J. M.; Leng, M. J.; Switzer, A. D.; Yim, W. W.; Huang, G.

    2012-12-01

    Understanding the mid-Holocene dynamics of the East Asian monsoon (EAM) is integral to modelling the Holocene development of the global climate system (Webster et al., 1998). Thus the mid-Holocene EAM history was reconstructed using bulk organic carbon isotopes (δ13C), total carbon to total nitrogen (C/N) ratios and total organic carbon (TOC) from a sediment core (UV1), at a mean resolution of 7-10 years, from the Pearl River estuary, southern China. Sedimentary δ13C, C/N and TOC from the Pearl River estuary is a good indicator of changes in monsoonal precipitation strength (Zong et al., 2006; Yang et al., 2010; Yu et al., 2010), eg sediments buried during a period of high precipitation exhibit a high proportion of terrigenous sediments, and have low δ13C and high C/N, and vice versa (Yu et al., 2010). Results suggest a general decreasing trend in monsoonal precipitation from 6650 to 2215 cal yr BP because of the weakening Northern Hemisphere insolation most likely related to the current precession circle (An, 2000). Superimposed on this trend are apparent dry-wet oscillations at centennial to millennial timescales most likely in response to solar activity. Mismatch between δ13C and results from the Dongge Cave in southern China at millennial-timescale oscillations (Wang et al., 2005), may indicate that the δ13C from the Pearl River estuary reveals changes in precipitation in a broader area than the δ18O from Dongge Cave does. Reference An Z (2000) The history and variability of the East Asian paleomonsoon climate. Quaternary Science Reviews 19: 171-187. Wang Y, Cheng H, Edwards RL, He Y, Kong X, An Z, Wu J, Kelly MJ, Dykoski CA and Li X (2005) The Holocene Asian Monsoon: Links to Solar Changes and North Atlantic Climate. Science 308: 854-857. Webster PJ, Magaña VO, Palmer TN, Shukla J and Tomas RA (1998) Monsoons: Processes, predictability, and the prospects for prediction. Journal of Geophysical Research 103(C7): 14451-14510. Yang S, Tang M, Yim WWS, Zong

  18. Phytolith evidence for early Holocene Cucurbita domestication in southwest Ecuador.

    Science.gov (United States)

    Piperno, Dolores R; Stothert, Karen E

    2003-02-14

    Cucurbita (squash and gourd) phytoliths recovered from two early Holocene archaeological sites in southwestern Ecuador and directly dated to 10,130 to 9320 carbon-14 years before the present (about 12,000 to 10,000 calendar years ago) are identified as derived from domesticated plants because they are considerably larger than those from modern wild taxa. The beginnings of plant husbandry appear to have been preceded by the exploitation of a wild species of Cucurbita during the terminal Pleistocene. These data provide evidence for an independent emergence of plant food production in lowland South America that was contemporaneous with or slightly before that in highland Mesoamerica.

  19. Early Holocene environmental change, the presence and disappearance of early Mesolithic habitation near Zutphen (The Netherlands)

    NARCIS (Netherlands)

    Bos, J.A.A.; Geel, B. van; Groenewoudt, B.J.; Lauwerier, R.C.G.M

    2005-01-01

    The Early Holocene landscape near Zutphen (The Netherlands) is reconstructed by means of microfossil, macroremain and bone analyses. In this area early Mesolithic sites were found on a river dune along a former river channel. AMS14C dating provided a detailed chronology for the sites and river chann

  20. Late Holocene (~ 2 ka) East Asian Monsoon variations inferred from river discharge and climate interrelationships in the Pearl River Estuary

    Digital Repository Service at National Institute of Oceanography (India)

    Nan, Q.; Li, T.; Chen, J.; Nigam, R.

    -size distributions, TOC contents, and δ13Corg variations appear to be directly related to monsoon precipitation in the sediment source area. An increased East Asian summer monsoon rainfall (EASM) and/or an enhanced East Asian winter monsoon rainfall could...

  1. The middle Holocene climatic records from Arabia: Reassessing lacustrine environments, shift of ITCZ in Arabian Sea, and impacts of the southwest Indian and African monsoons

    Science.gov (United States)

    Enzel, Yehouda; Kushnir, Yochanan; Quade, Jay

    2015-06-01

    A dramatic increase in regional summer rainfall amount has been proposed for the Arabian Peninsula during the middle Holocene (ca. 9-5 ka BP) based on lacustrine sediments, inferred lake levels, speleothems, and pollen. This rainfall increase is considered primarily the result of an intensified Indian summer monsoon as part of the insolation-driven, northward shift of the boreal summer position of the Inter-Tropical Convergence Zone (ITCZ) to over the deserts of North Africa, Arabia, and northwest India. We examine the basis for the proposed drastic climate change in Arabia and the shifts in the summer monsoon rains, by reviewing paleohydrologic lacustrine records from Arabia. We evaluate and reinterpret individual lake-basin status regarding their lacustrine-like deposits, physiography, shorelines, fauna and flora, and conclude that these basins were not occupied by lakes, but by shallow marsh environments. Rainfall increase required to support such restricted wetlands is much smaller than needed to form and maintain highly evaporating lakes and we suggest that rainfall changes occurred primarily at the elevated edges of southwestern, southern, and southeastern Arabian Peninsula. These relatively small changes in rainfall amounts and local are also supported by pollen and speleothems from the region. The changes do not require a northward shift of the Northern Hemisphere summer ITCZ and intensification of the Indian monsoon rainfall. We propose that (a) latitudinal and slight inland expansion of the North African summer monsoon rains across the Red Sea, and (b) uplifted moist air of this monsoon to southwestern Arabia highlands, rather than rains associated with intensification of Indian summer monsoon, as proposed before, increased rains in that region; these African monsoon rains produced the modest paleo-wetlands in downstream hyperarid basins. Furthermore, we postulate that as in present-day, the ITCZ in the Indian Ocean remained at or near the equator all

  2. Holocene climate changes in the mid-high-latitude-monsoon margin reflected by the pollen record from Hulun Lake, northeastern Inner Mongolia

    Science.gov (United States)

    Wen, Ruilin; Xiao, Jule; Chang, Zhigang; Zhai, Dayou; Xu, Qinghai; Li, Yuecong; Itoh, Shigeru; Lomtatidze, Zaur

    2010-03-01

    Pollen-assemblage data from a sediment core from Hulun Lake in northeastern Inner Mongolia describe the changes in the vegetation and climate of the East Asian monsoon margin during the Holocene. Dry steppe dominated the lake basin from ca. 11,000 to 8000 cal yr BP, suggesting a warm and dry climate. Grasses and birch forests expanded 8000 to 6400 cal yr BP, implying a remarkable increase in the monsoon precipitation. From 6400 to 4400 cal yr BP, the climate became cooler and drier. Chenopodiaceae dominated the interval from 4400 to 3350 cal yr BP, marking extremely dry condition. Artemisia recovered 3350-2050 cal yr BP, denoting an amelioration of climatic conditions. Both temperature and precipitation decreased 2050 to 1000 cal yr BP as indicated by decreased Artemisia and the development of pine forests. During the last 1000 yr, human activities might have had a significant influence on the environment of the lake region. We suggest that the East Asian summer monsoon did not become intensified until 8000 cal yr BP due to the existence of remnant ice sheets in the Northern Hemisphere. Changes in the monsoon precipitation on millennial to centennial scales would be related to ocean-atmosphere interactions in the tropical Pacific.

  3. Early Holocene lake ecosystem development in the southern Baltic lowlands

    Science.gov (United States)

    Słowiński, Michał; Ott, Florian; Kramkowski, Mateusz; Noryśkiewicz, Agnieszka M.; Zawiska, Izabela; Dräger, Nadine; Theuerkauf, Martin; Hass, Christoph; Obremska, Milena; Błaszkiewicz, Mirosław; Kordowski, Jarosław; Tjallingii, Rik; Rzodkiewicz, Monika; Schwab, Markus; Brauer, Achim

    2016-04-01

    The first millennia of the Holocene are characterized by gradual and rapid environmental changes following the warming at the beginning of the Holocene superimposed by short-term climatic instability. Landscape evolution during this period occurred at different time scales due to specific response times of landscape compartments like vegetation succession, soil formation and permafrost thawing. As a consequence, a spatiotemporally heterogeneous pattern of changes occurred particularly in regions close to the margins of the continental ice sheets like the Baltic region. Regional atmospheric circulation patterns were affected by cold catabatic winds from the remains of the Fennoscandian ice sheet. The ongoing deglaciation further influenced the regional climate through meltwater release and related changes in the North Atlantic thermohaline circulation. Both effects declined with the progressive ice sheet melt down. Additionally, the land-sea distribution in the North Sea changed drastically during the final melting phase of the glacial ice sheets. The Baltic Sea development is even more complex due to the strong glacio-isostatic adjustments effects that resulted in open and closed water stages affecting the entire Baltic realm. Consequently, the early Holocene interval of sediment records from the southern Baltic lowlands are not considered as straightforward palaeoclimate archives but need to be interpreted in a broader context. We present five partly varved lake records from northern Poland all including an intriguing highly organic-rich interval interrupting biochemical calcite precipitation at about the same time between 10.5 and 10.2 cal kyr BP. These sediment records have been correlated by independent age models based on varve counting, AMS 14C dating, biostratigraphy and tephrochronology. We present multi-proxy records of early Holocene sediments and our preliminary interpretation suggests hydrological processes as the main reason for the intriguing shifts

  4. Mangrove forest degradation indicated by mangrove-derived organic matter in the Qinzhou Bay, Guangxi, China, and its response to the Asian monsoon during the Holocene climatic optimum

    Institute of Scientific and Technical Information of China (English)

    MENG Xianwei; XIA Peng; LI Zhen; LIU Lejun

    2016-01-01

    The response of mangrove ecosystems to the Asian monsoon in the future global warming can be understood by reconstructing the development of mangrove forests during the Holocene climatic optimum (HCO), using proxies preserved in coastal sediments. The total organic matter in sediments of a segmented core, with calibrated age ranges between 5.6 and 7.7 cal. ka BP and corresponding to the HCO, from the Qinzhou Bay in Guangxi, China, is quantitatively partitioned into three end-members according to their sources: mangrove-derived, terrigenous, and marine phytoplanktonic, using a three-end-member model depicted by organic carbon isotope (δ13Corg) and the molar ratio of total organic carbon to total nitrogen (C/N). The percentage of mangrove-derived organic matter (MOM) contribution is used as a proxy for mangrove development. Three visible drops in MOM contribution occurred at ca. 7.3, ca. 6.9, and ca. 6.2 cal. ka BP, respectively, are recognized against a relatively stable and higher MOM contribution level, indicating that three distinct mangrove forest degradations occurred in the Qinzhou Bay during the HCO. The three mangrove forest degradations approximately correspond to the time of the strengthened/weakened Asian winter/summer monsoon. This indicates that even during a period favorable for the mangrove development, such as the HCO, climatic extremes, such as cold and dry events driven by the strengthened/weakened Asian winter/summer monsoon, can trigger the degradation of mangrove forests.

  5. Evolution of the North American Monsoon from the middle Holocene to the present recorded in marine sediments from low Gulf of California

    Science.gov (United States)

    Nava, Cinthya; Herguera, Juan Carlos

    2016-04-01

    New results of a reconstruction of the summer precipitation in the North American Monsoon area, which is the largest atmospheric circulation feature over much of northwest Mexico, and the southwest the USA. This regime results from the interplay between sea surface temperatures (SSTs) in the northeast tropical Pacific, solar variability, continental topography, land snow cover and soil moisture over the western North America as well as patterns of atmospheric pressure. The links between these factors and the monsoonal variability appear to be of variable importance during the short instrumental record. This hampers any prediction on the future evolution of the climatic regime in a warming climate. We produce an X-Ray Fluorescence record of the relative abundances of Si and Al in high resolution laminated sediments obtained from the Pescadero basin (24N, 108W) as semi-quantitative index of terrigenous input. This record links the transport of terrigenous materials by summer precipitation in the North American Monsoon region, in mountain range Sierra Madre NW Mexico. The record was constructed from XRF scan measurements of a composite core (260cm long) based on several box and Kasten cores, the age model is based on 8 14C AMS ages, producing a record with a mean temporal resolution of 0.5 yr. The variability of the NAM shows a decreasing trend between the middle Holocene to the present. This general trend is parallel to many other records like speleothems, ice cores, pollen fossil, and elemental content in marine and lake sediments. Spectral and cross-spectral analysis were made in order to search for some similarities with other climatic features on global scale, and thus evaluate possible links between the low and high latitudes climate variability. In addition, we compare the last century precipitation with the past few thousand years and explore some possible effect of climate change in the North American Monsoon behaviour.

  6. Coastal rainforest boundary dynamics during the late Holocene in monsoonal Australia: evidence from radiocarbon dates of abandoned nests of Orange-footed Scrubfowl

    Energy Technology Data Exchange (ETDEWEB)

    Bowman, D.M.J.S.; Panton, W.J. [Parks and Wildlife Commission of the Northern Territory, Darwin, NT (Australia); Head, J. [Australian National Univ, Canberra, ACT (Australia). Quaternary Dating Research Centre

    1997-12-31

    The late Holocene history of monsoon rainforest retreat was explored by radiocarbon dating abandoned Orange-footed Scrubfowl (Megapodius reinwardt Gaimard) nests in coastal savannas in the Northern Territory of Australia. Previous work has demonstrated that in savanna environments this rainforest bird can not build nor maintain the large heaps of soil and leaf litter that it uses for nests. Excavations of two earthen mounds in a savanna habitat verified that they were abandoned Scrubfowl nests, and not Aboriginal middens, given their lack of stratigraphy, non-sequential dating of charcoal in a vertical profile, and absence of archaeological material. Radiocarbon dates of material taken from the surface of abandoned nests were determined for three sites on the coast of the Northern Territory. These analyses revealed that for all three sites, rainforests have contracted within the last 1800 years BP. On Elcho Island an abandoned nest was found to contain the land snail Xanthomelon spheroidea Le Guillou (known to prefer rainforest habitat) with a modern radiocarbon age, suggesting recent contraction of rainforest. The results of this study further weaken the theory that Aboriginal burning was a major cause of rain forest fragmentation in the monsoon tropics, and possibly elsewhere in Australia.

  7. Indian summer monsoon variability during the Holocene as recorded in sediments of the Arabian Sea: Timing and implications

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Kawahata, H.; Rao, V.P.

    , representing the nearly complete Holocene succession, having seven AMS 14 C dating points (Table 1; Fig. 2). An age model was then obtained by ap- plying a reservoir age correction of 541 ± 58 (∆R 165 ± 57) years to the 14 C dates, based on the available 14... C measurements on bivalves collected from a very nearby location (Southon et al., 2002). Although Staubwasser et al. (2002) reported changing reservoir ages during the Holocene in a core off Pakistan, this may not be signifi- cant our study region...

  8. Modeling sensitivity study of the possible impact of snow and glaciers developing over Tibetan Plateau on Holocene African-Asian summer monsoon climate

    Directory of Open Access Journals (Sweden)

    L. Jin

    2008-12-01

    Full Text Available The impacts of various scenarios of snow and glaciers developing over the Tibetan Plateau on climate change in Afro-Asian monsoon region and other regions during the Holocene (9 kyr BP–0 kyr BP are studied by using the coupled climate model of intermediate complexity, CLIMBER-2. The simulations show that the imposed snow and glaciers over the Tibetan Plateau in the mid-Holocene induce global summer temperature decreases, especially in the northern parts of Europe, Asia, and North America. At the same time, with the imposed snow and glaciers, summer precipitation decreases strongly in North Africa and South Asia as well as northeastern China, while it increases in Southeast Asia and the Mediterranean. For the whole period of Holocene (9 kyr BP–0 kyr BP, the response of vegetation cover to the imposed snow and glaciers cover over the Tibetan Plateau is not synchronous in South Asia and in North Africa, showing an earlier and a more rapid decrease in vegetation cover in North Africa from 9 to 6 kyr BP while it has only minor influence on that in South Asia until 5 kyr BP. Imposed gradually increased snow and glacier cover over the Tibetan Plateau causes temperature increases in South Asia and it decreases in North Africa and Southeast Asia during 6 kyr BP to 0 kyr BP. The precipitation decreases rapidly in North Africa and South Asia while it decreases slowly or unchanged during 6 kyr BP to 0 kyr BP with imposed snow and glacier cover over the Tibetan Plateau. The different scenarios of snow and glacier developing over the Tibetan Plateau would result in differences in variation of temperature, precipitation and vegetation cover in North Africa, South Asia and Southeast Asia. The model results show that the response of climate change in African-Asian monsoon region to snow and glacier cover over the Tibetan Plateau is in the way that the snow and glaciers amplify the effect of vegetation feedback and, hence, further amplify orbital forcing.

  9. Late holocene primary productivity and sea surface temperature variations in the northeastern Arabian Sea: Implications for winter monsoon variability.

    Digital Repository Service at National Institute of Oceanography (India)

    Boll, A.; Luckge, A.; Munz, P.; Forke, S.; Schulz, H.; Ramaswamy, V.; Rixen, T.; Gaye, B.; Emeis, K.-C.

    ., B. Kromer, J. Beer, R. Muscheler, M. N. Evans, W. Showers, S. Hoffmann, R. Lotti-Bond, I. Hajdas, and G. Bonani (2001), Persistent Solar Influence on North Atlantic Climate During the Holocene., Science, 294, 2130-2136, doi:10.1126/science.1065680...

  10. The Drangajökull ice cap, northwest Iceland, persisted into the early-mid Holocene

    Science.gov (United States)

    Schomacker, Anders; Brynjólfsson, Skafti; Andreassen, Julie M.; Gudmundsdóttir, Esther Ruth; Olsen, Jesper; Odgaard, Bent V.; Håkansson, Lena; Ingólfsson, Ólafur; Larsen, Nicolaj K.

    2016-09-01

    Most glaciers and ice caps in Iceland experienced rapid deglaciation in the early Holocene, reaching a minimum extent during the Holocene Thermal Maximum. Here we present evidence of the Holocene glacial history from lake sediment cores retrieved from seven threshold lakes around the Drangajökull ice cap in the Vestfirðir peninsula, NW Iceland. The sediment cores show on/off signals of glacial meltwater activity, as minerogenic material deposited from glacial meltwater alternates with organic-rich material (gyttja) deposited without glacial meltwater. We base the chronology of the sediment cores on 14C ages and geochemical identification of key tephra layers with known ages. A 25-cm thick layer of the Saksunarvatn tephra in Lake Skorarvatn indicates that the northern part of the ice cap had reached a similar size as today or was smaller already by 10.2 cal kyr BP. However, 14C ages of lake sediment cores from the highlands southeast of Drangajökull suggest that this part of the ice cap was larger than today until 7.8-7.2 cal kyr BP. Even today, the Drangajökull ice cap has a different behavior than the main ice caps in Iceland, characterized by a very low glaciation limit. Because palaeoclimatic proxies show an early-mid Holocene temperature optimum in this part of Iceland, we suggest that the persistence of Drangajökull into the early Holocene and, possibly, also the entire Holocene was due to high winter precipitation.

  11. Late Pleistocene-early Holocene karst features, Laguna Madre, south Texas: A record of climate change

    Energy Technology Data Exchange (ETDEWEB)

    Prouty, J.S. [Texas A& M Univ., Corpus Christi, TX (United States)

    1996-09-01

    A Pleistocene coquina bordering Laguna Madre, south Texas, contains well-developed late Pleistocene-early Holocene karst features (solution pipes and caliche crusts) unknown elsewhere from coastal Texas. The coquina accumulated in a localized zone of converging longshore Gulf currents along a Gulf beach. The crusts yield {sup 14}C dates of 16,660 to 7630 B.P., with dates of individual crust horizons becoming younger upwards. The karst features provide evidence of regional late Pleistocene-early Holocene climate changes. Following the latest Wisconsinan lowstand 18,000 B.P. the regional climate was more humid and promoted karst weathering. Partial dissolution and reprecipitation of the coquina formed initial caliche crust horizons; the crust later thickened through accretion of additional carbonate laminae. With the commencement of the Holocene approximately 11,000 B.P. the regional climate became more arid. This inhibited karstification of the coquina, and caliche crust formation finally ceased about 7000 B.P.

  12. Early and late Holocene glacial fluctuations and tephrostratigraphy, Cabin Lake, Alaska

    Science.gov (United States)

    Zander, Paul D.; Kaufman, Darrell S.; Kuehn, Stephen C.; Wallace, Kristi L.; Anderson, R. Scott

    2013-01-01

    Marked changes in sediment types deposited in Cabin Lake, near Cordova, Alaska, represent environmental shifts during the early and late Holocene, including fluctuations in the terminal position of Sheridan Glacier. Cabin Lake is situated to receive meltwater during periods when the outwash plain of the advancing Sheridan Glacier had aggraded. A brief early Holocene advance from 11.2 to 11.0 cal ka is represented by glacial rock flour near the base of the sediment core. Non-glacial lake conditions were restored for about 1000 years before the water level in Cabin Lake lowered and the core site became a fen. The fen indicates drier-than-present conditions leading up to the Holocene thermal maximum. An unconformity spanning 5400 years during the mid-Holocene is overlain by peat until 1110 CE when meltwater from Sheridan Glacier returned to the basin. Three intervals of an advanced Sheridan Glacier are recorded in the Cabin Lake sediments during the late Holocene: 1110–1180, 1260–1540 and 1610–1780 CE. The sedimentary sequence also contains the first five reported tephra deposits from the Copper River delta region, and their geochemical signatures suggest that the sources are the Cook Inlet volcanoes Redoubt, Augustine and Crater Peak, and possibly Mt Churchill in the Wrangell Volcanic field.

  13. Early Holocene pecan, Carya illinoensis, in the Mississippi River Valley near Muscatine, Iowa*1

    Science.gov (United States)

    Bettis, E. Arthur; Baker, Richard G.; Nations, Brenda K.; Benn, David W.

    1990-01-01

    A fossil pecan, Carya illinoensis (Wang.) K. Koch, from floodplain sediments of the Mississippi River near Muscatine, Iowa, was accelerator-dated at 7280 ± 120 yr B.P. This discovery indicates that pecan was at or near its present northern limit by that time. Carya pollen profiles from the Mississippi River Trench indicate that hickory pollen percentages were much higher in the valley than at upland locations during the early Holocene. Pecan, the hickory with the most restricted riparian habitat, is the likely candidate for producing these peaks in Carya pollen percentages. Therefore, pecan may have reached its northern limit as early as 10,300 yr B.P. Its abundance in Early Archaic archaeological sites and the co-occurrence of early Holocene Carya pollen peaks with the arrival of the Dalton artifact complex in the Upper Mississippi Valley suggest that humans may have played a role in the early dispersal of pecan.

  14. Early Holocene pecan, Carya illinoensis, in the Mississippi River Valley near Muscatine, Iowa

    Science.gov (United States)

    Bettis, E. Arthur; Baker, R.G.; Nations, B.K.; Benn, D.W.

    1990-01-01

    A fossil pecan, Carya illinoensis (Wang.) K. Koch, from floodplain sediments of the Mississippi River near Muscatine, Iowa, was accelerator-dated at 7280 ?? 120 yr B.P. This discovery indicates that pecan was at or near its present northern limit by that time. Carya pollen profiles from the Mississippi River Trench indicate that hickory pollen percentages were much higher in the valley than at upland locations during the early Holocene. Pecan, the hickory with the most restricted riparian habitat, is the likely candidate for producing these peaks in Carya pollen percentages. Therefore, pecan may have reached its northern limit as early as 10,300 yr B.P. Its abundance in Early Archaic archaeological sites and the co-occurrence of early Holocene Carya pollen peaks with the arrival of the Dalton artifact complex in the Upper Mississippi Valley suggest that humans may have played a role in the early dispersal of pecan. ?? 1990.

  15. Early and Middle Holocene Hunter-Gatherer Occupations in Western Amazonia: The Hidden Shell Middens

    Science.gov (United States)

    Lombardo, Umberto; Szabo, Katherine; Capriles, José M.; May, Jan-Hendrik; Amelung, Wulf; Hutterer, Rainer; Lehndorff, Eva; Plotzki, Anna; Veit, Heinz

    2013-01-01

    We report on previously unknown early archaeological sites in the Bolivian lowlands, demonstrating for the first time early and middle Holocene human presence in western Amazonia. Multidisciplinary research in forest islands situated in seasonally-inundated savannahs has revealed stratified shell middens produced by human foragers as early as 10,000 years ago, making them the oldest archaeological sites in the region. The absence of stone resources and partial burial by recent alluvial sediments has meant that these kinds of deposits have, until now, remained unidentified. We conducted core sampling, archaeological excavations and an interdisciplinary study of the stratigraphy and recovered materials from three shell midden mounds. Based on multiple lines of evidence, including radiocarbon dating, sedimentary proxies (elements, steroids and black carbon), micromorphology and faunal analysis, we demonstrate the anthropogenic origin and antiquity of these sites. In a tropical and geomorphologically active landscape often considered challenging both for early human occupation and for the preservation of hunter-gatherer sites, the newly discovered shell middens provide evidence for early to middle Holocene occupation and illustrate the potential for identifying and interpreting early open-air archaeological sites in western Amazonia. The existence of early hunter-gatherer sites in the Bolivian lowlands sheds new light on the region’s past and offers a new context within which the late Holocene “Earthmovers” of the Llanos de Moxos could have emerged. PMID:24013964

  16. Early and middle holocene hunter-gatherer occupations in western Amazonia: the hidden shell middens.

    Science.gov (United States)

    Lombardo, Umberto; Szabo, Katherine; Capriles, José M; May, Jan-Hendrik; Amelung, Wulf; Hutterer, Rainer; Lehndorff, Eva; Plotzki, Anna; Veit, Heinz

    2013-01-01

    We report on previously unknown early archaeological sites in the Bolivian lowlands, demonstrating for the first time early and middle Holocene human presence in western Amazonia. Multidisciplinary research in forest islands situated in seasonally-inundated savannahs has revealed stratified shell middens produced by human foragers as early as 10,000 years ago, making them the oldest archaeological sites in the region. The absence of stone resources and partial burial by recent alluvial sediments has meant that these kinds of deposits have, until now, remained unidentified. We conducted core sampling, archaeological excavations and an interdisciplinary study of the stratigraphy and recovered materials from three shell midden mounds. Based on multiple lines of evidence, including radiocarbon dating, sedimentary proxies (elements, steroids and black carbon), micromorphology and faunal analysis, we demonstrate the anthropogenic origin and antiquity of these sites. In a tropical and geomorphologically active landscape often considered challenging both for early human occupation and for the preservation of hunter-gatherer sites, the newly discovered shell middens provide evidence for early to middle Holocene occupation and illustrate the potential for identifying and interpreting early open-air archaeological sites in western Amazonia. The existence of early hunter-gatherer sites in the Bolivian lowlands sheds new light on the region's past and offers a new context within which the late Holocene "Earthmovers" of the Llanos de Moxos could have emerged.

  17. Centennial-scale environmental and climatic changes during the early Holocene in the Middle Atlas, Morocco

    Science.gov (United States)

    Fletcher, W.; Joannin, S.; Zielhofer, C.; Mischke, S.; Mikdad, A.

    2013-12-01

    Mountain regions of North Africa and the Mediterranean represent one of the hotspots of current climate change, where increasing temperatures and drought stress may lead to significant changes in hydrological, ecological and geomorphological systems. Palaeoecological records can provide insights into the responses of montane systems to climate changes, with the impacts of rapid (centennial-scale) responses being of particular relevance. Here, we present the first results of high resolution (~40-50 yr) palynological and charcoal analyses as part of a multiproxy palaeoecological and palaeolimnological study of new lake sediment cores recovered from Lake Sidi Ali in the Middle Atlas mountains, Morocco (33° 03 N, 05° 00 W; 2,080 m a.s.l.). Focusing on the relatively poorly known early Holocene and early to mid-Holocene transition, we provide evidence for pseudo-cyclic centennial-scale changes in vegetation cover and composition, superimposed on the long-term transition from oak (Quercus spp.) dominated early Holocene vegetation to cedar (Cedrus atlantica) forest of the mid-Holocene. In the context of the intermediate position of the Middle Atlas mountains with respect to the influence of mid-latitude, moisture-bearing air-masses and low-latitude, southerly, Saharan air-masses, this early Holocene variability in vegetation cover is interpreted in terms of dynamics shifts in prevailing atmospheric circulation over this montane region of Northwest Africa. The geographical position of the record is ideal for testing patterns of climate variability previously detected in western Mediterranean marine sequences, and for evaluating linkages between mid- and low-latitude climate dynamics.

  18. Tracking Nile Delta vulnerability to Holocene change.

    Directory of Open Access Journals (Sweden)

    Nick Marriner

    Full Text Available Understanding deltaic resilience in the face of Holocene climate change and human impacts is an important challenge for the earth sciences in characterizing the full range of present and future wetland responses to global warming. Here, we report an 8000-year mass balance record from the Nile Delta to reconstruct when and how this sedimentary basin has responded to past hydrological shifts. In a global Holocene context, the long-term decrease in Nile Delta accretion rates is consistent with insolation-driven changes in the 'monsoon pacemaker', attested throughout the mid-latitude tropics. Following the early to mid-Holocene growth of the Nile's deltaic plain, sediment losses and pronounced erosion are first recorded after ~4000 years ago, the corollaries of falling sediment supply and an intensification of anthropogenic impacts from the Pharaonic period onwards. Against the backcloth of the Saharan 'depeopling', reduced river flow underpinned by a weakening of monsoonal precipitation appears to have been particularly conducive to the expansion of human activities on the delta by exposing productive floodplain lands for occupation and irrigation agriculture. The reconstruction suggests that the Nile Delta has a particularly long history of vulnerability to extreme events (e.g. floods and storms and sea-level rise, although the present sediment-starved system does not have a direct Holocene analogue. This study highlights the importance of the world's deltas as sensitive archives to investigate Holocene geosystem responses to climate change, risks and hazards, and societal interaction.

  19. Long-term forest dynamics at Gribskov, eastern Denmark with early-Holocene evidence for thermophilous broadleaved tree species

    DEFF Research Database (Denmark)

    Overballe-Petersen, Mette V; Nielsen, Anne Birgitte; Hannon, Gina E.

    2012-01-01

    We report on a full-Holocene pollen, charcoal and macrofossil record from a small forest hollow in Gribskov, eastern Denmark. The Fagus sylvatica pollen record suggests the establishment of a small Fagus population at Gribskov in the early Holocene together with early establishment of other...... thermophilous broadleaved trees, including Quercus sp., Tilia sp. and Ulmus sp. The macrofossils contribute to the vegetation reconstruction with evidence for local presence of species with low pollen productivity or easily degraded pollen types such as Populus. The charcoal record shows frequent burning during...... two periods of the early Holocene and from c. 3000 cal. BP to present. The early-Holocene part of the record indicates a highly disturbed forest ecosystem with frequent fires and abundant macrofossils of particularly Betula sp. and Populus sp. The sediment stratigraphy and age–depth relationships give...

  20. Morphological and genetic evidence for early Holocene cattle management in northeastern China

    DEFF Research Database (Denmark)

    Zhang, Hucai; Paijmans, Johanna L A; Chang, Fengqin

    2013-01-01

    The domestication of cattle is generally accepted to have taken place in two independent centres: around 10,500 years ago in the Near East, giving rise to modern taurine cattle, and two millennia later in southern Asia, giving rise to zebu cattle. Here we provide firmly dated morphological...... and genetic evidence for early Holocene management of taurine cattle in northeastern China. We describe conjoining mandibles from this region that show evidence of oral stereotypy, dated to the early Holocene by two independent (14)C dates. Using Illumina high-throughput sequencing coupled with DNA...... hybridization capture, we characterize 15,406 bp of the mitogenome with on average 16.7-fold coverage. Phylogenetic analyses reveal a hitherto unknown mitochondrial haplogroup that falls outside the known taurine diversity. Our data suggest that the first attempts to manage cattle in northern China predate...

  1. Pine nut use in the Early Holocene and beyond: The danger cave archaeobotanical record

    Science.gov (United States)

    Rhode, D.; Madsen, D.B.

    1998-01-01

    Nuts of limber pine (Pinus flexilis) from Early Holocene strata in Danger Cave, Utah, are distinguishable by seed-coat sculpturing from pine nuts of single-needled pinyon (Pinus monophylla), which occur in strata dating nuts in archaeological sites, but the morphology of the pine nuts in Danger Cave strongly indicate they were deposited by human foragers who brought small quantities with them for food for at least the last 7500 years. Large-scale transport of pine nuts to Danger Cave from distant hinterlands is unlikely, however. The seamless transition from limber pine to pinyon pine nuts in the Danger Cave record suggests that foragers who had utilized limber pine as a food resource easily switched to using pinyon pine nuts when pinyon pine migrated into the region at the close of the Early Holocene.

  2. Pipeline geo-hazard prediction and early warning during summer monsoon based on GIS technology

    Energy Technology Data Exchange (ETDEWEB)

    Jia, Shaohui [PetroChina Pipeline RandD Center, Langfang, Hebei (China)

    2010-07-01

    PetroChina Pipeline Company operates over 12 000 kilometers of pipelines with crude oil, gas, and refined oil. The pipelines have been in operation for over 40 years. Geo-hazard is a serious threat for pipeline operators, especially during summer monsoon; monsoon geo-hazards account for 70% to 80% of the annual incidents and financial losses. There is an urgent need of prediction and early warning systems. GIS technology provides an advanced tool for such analysis. Many years of research and experience with PetroChina's prediction model finally established an important link between geo-hazard and rainfall. Spatial analysis is performed with GIS technology, using the predicted rainfall data for the next 24 hours and the data of pipeline geo-hazard susceptibility. Then the severity of pipeline damage expected is predicted. Researchers, while they try to forecast rainfall, try to forecast debris flow at the same time to minimize human casualties and property losses caused by geo-hazards.

  3. Monsoon Country

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Heavy rains have battered areas of south China this year,causing death and destruction For most areas south of the Yangtze River,this year’s monsoon season has come early, with heavy rains triggering floods,damaging crops,threatening reservoirs and causing deaths.

  4. Early and mid-Holocene age for the Tempanos moraines, Laguna San Rafael, Patagonian Chile

    Science.gov (United States)

    Harrison, Stephan; Glasser, Neil F.; Duller, Geoff A. T.; Jansson, Krister N.

    2012-01-01

    Data about the nature and timing of Holocene events from the Southern Hemisphere, especially in southern South America, are required to provide insight into the extent and nature of past climate change in a region where land-based records are restricted. Here we present the first use of single grain Optically Stimulated Luminescence (OSL) dating of a moraine sequence recording glacial advance along the western side of the Patagonian Icefields. Dates from the Tempanos moraines at Laguna San Rafael (LSR) show that the San Rafael Glacier (SRG) advanced to maximum Holocene positions during the period 9.3 to 9.7 ka and at 5.7 ka. Outwash lying beneath the moraine in its northern portion, dated to 7.7 ka, indicates that the glacier front was also advanced at this time. Since these advances span both the regional early Holocene warm-dry phase (11.5 ka to 7.8 ka) and the subsequent cooling and rise in precipitation in the mid-late Holocene (since 6.6 ka) we infer that the advances of the SRG are not simply climate-driven, but that the glacier has also probably responded strongly to non-climatic stimuli such as internal ice dynamics and the transition between calving and non-calving. Many westwards-flowing glaciers in Patagonia were probably calving during much of the Late Pleistocene and Holocene, so we conclude that establishing robust glacial chronologies where climatic and non-climatic factors cannot be distinguished is likely to remain a challenge.

  5. An Early Holocene Eruptive Period at Mount Rainier, Washington

    Science.gov (United States)

    Byman, J.; Vallance, J. W.

    2001-12-01

    Tephrochronologic studies indicate that the Cowlitz Park eruptive period at Mount Rainier began about 7500 years ago and continued intermittently until about 6800 years ago. Stratigraphic evidence suggests that Cowlitz Park time comprises four distinct eruptive episodes, each of which occurred during a relatively brief interval. The eruptions produced subplinian falls, several small ash falls, pyroclastic flows, and lahars, the largest of which swept down the White River valley to Puget Sound lowland. Tephra layers are of two types: vesicle rich (chiefly pumice lapilli, scoria, and ash) and vesicle poor (chiefly fine-grained glass and lithic fragments). Pumice and glass shards in vesicle-rich deposits are microlite-poor and derive from larger explosive eruptions. Glass shards in vesicle-poor ashes have variable microlite contents and derive from smaller explosions, or from ash clouds that billow up from block-and-ash pyroclastic flows. Although the Pleistocene record indicates considerable effusive activity at Mount Rainier, no record remains of lavas that might have erupted during Cowlitz Park time. The oldest eruption, ca 7500 cal yr BP, produced vesicular tephra "A," distributed to the east, with a volume of 5 x 106 m3. Layer A is pumiceous, but fine-grained, glassy layers, suggestive of ash-clouds derived from pyroclastic flows, bracket it stratigraphically. About 7300 cal yr BP, within a short interval of time, a more complex eruptive episode occurred that produced a subplinian fall, at least 3 minor ash layers and an avalanche of hydrothermally altered rock on the south flank of the volcano that generated a lahar. The subplinian layer, "L," was among the most voluminous in the Holocene 30 x 106 m3 at Mount Rainier. This tephra occurs to the southeast and chiefly contains pumice along with subordinate, juvenile, lithic clasts. Related fine-to-coarse-grained ash layers derive from small explosions that occurred shortly before and after the eruption of layer L

  6. Early Holocene deglaciation of Drangajökull, Vestfirðir, Iceland

    Science.gov (United States)

    Harning, David J.; Geirsdóttir, Áslaug; Miller, Gifford H.; Zalzal, Kate

    2016-12-01

    The status of Icelandic ice caps during the early Holocene provides important constraints on North Atlantic climate and the mechanisms behind natural climate variability. A recent study postulates that Drangajökull on Vestfirðir, Iceland, persisted through the Holocene Thermal Maximum (HTM, 7.9-5.5 ka) and may be a relic from the last glacial period. We test this hypothesis with a suite of sediment cores from threshold lakes both proximal and distal to the ice cap's modern margin. Distal lakes document rapid early Holocene deglaciation from the coast and across the highlands south of the glacier. Sediment from Skorarvatn, a lake to the north of Drangajökull, shows that the northern margin of the ice cap reached a size comparable to its contemporary limit by ∼10.3 ka. Two southeastern lakes with catchments extending well beneath modern Drangajökull confirm that by ∼9.2 ka, the ice cap was reduced to ∼20% of its current area. A continuous 10.3ka record of biological productivity from Skorarvatn's sediment indicates local peak warmth occurred between 9 and 6.9 ka. The combination of warm and dry summers on Vestfirðir suggests that Drangajökull very likely melted completely shortly after 9.2 ka, similar to most other Icelandic ice caps.

  7. Impact of a drier Early-Mid-Holocene climate upon Amazonian forests.

    Science.gov (United States)

    Mayle, Francis E; Power, Mitchell J

    2008-05-27

    This paper uses a palaeoecological approach to examine the impact of drier climatic conditions of the Early-Mid-Holocene (ca 8000-4000 years ago) upon Amazonia's forests and their fire regimes. Palaeovegetation (pollen data) and palaeofire (charcoal) records are synthesized from 20 sites within the present tropical forest biome, and the underlying causes of any emergent patterns or changes are explored by reference to independent palaeoclimate data and present-day patterns of precipitation, forest cover and fire activity across Amazonia. During the Early-Mid-Holocene, Andean cloud forest taxa were replaced by lowland tree taxa as the cloud base rose while lowland ecotonal areas, which are presently covered by evergreen rainforest, were instead dominated by savannahs and/or semi-deciduous dry forests. Elsewhere in the Amazon Basin there is considerable spatial and temporal variation in patterns of vegetation disturbance and fire, which probably reflects the complex heterogeneous patterns in precipitation and seasonality across the basin, and the interactions between climate change, drought- and fire susceptibility of the forests, and Palaeo-Indian land use. Our analysis shows that the forest biome in most parts of Amazonia appears to have been remarkably resilient to climatic conditions significantly drier than those of today, despite widespread evidence of forest burning. Only in ecotonal areas is there evidence of biome replacement in the Holocene. From this palaeoecological perspective, we argue against the Amazon forest 'dieback' scenario simulated for the future.

  8. New radiocarbon dates for terminal Pleistocene and early Holocene settlements in West Turkana, northern Kenya

    Science.gov (United States)

    Beyin, Amanuel; Prendergast, Mary E.; Grillo, Katherine M.; Wang, Hong

    2017-07-01

    The Turkana Basin in northern Kenya is located in an environmentally sensitive region along the eastern African Rift system. Lake Turkana's sensitivity to fluctuations in precipitation makes this an ideal place to study prehistoric human adaptations during key climatic transitions. Here we present eleven radiocarbon dates from two recently excavated sites in West Turkana, Kokito 01 and Kokito 02. The sites span the Pleistocene-Holocene transition, a time of fluctuating lake levels and novel cultural responses within the region. Several scenarios are laid out for the interpretation of site chronologies, and these are discussed with reference to the terminal Pleistocene and early Holocene chronological record for the region. Given the paucity of well-dated sites from this timespan in the Turkana Basin, the new radiocarbon dates are an important step toward establishing human settlement history and associated cultural developments in the region.

  9. Early Holocene thermal maximum in western North America: New evidence from Castle Peak, British Columbia

    Science.gov (United States)

    Clague, John J.; Mathewes, R. W.

    1989-03-01

    Conifer logs and branches of early Holocene age are common on the surface and in sediments above timberline at Castle Peak in the southeastern Coast Mountains of British Columbia. A study of this wood and associated peat and colluvium has shown that local timberline from 9.1 to 8.2 ka was at least 60 m, and perhaps more than 130 m, higher than today. Mean growing-season temperature at Castle Peak during this period thus may have been 0.4-0.8°C warmer than at present. This is consistent with theoretical considerations based on Milankovitch forcing of climatic change and is supported by other paleoecological data from the southern Canadian Cordillera and adjacent northwestern United States. A generally warm climate may have persisted until about 5-6 ka, followed by late Holocene cooling.

  10. East Asian Monsoon and EL NIÑO-SOUTHERN Oscillation Activities Since the Mid-Holocene Evidences from Massive Corals in the the Central Vietnamese Coast, Western South China Sea

    Science.gov (United States)

    Nguyen, A. D.; Zhao, J.; Feng, Y.; Yu, K.; Gasparon, M.; U-Series Dating Technique Team

    2011-12-01

    The climate of the Vietnamese coast, western South China Sea (SCS), is driven by the annually reversing East Asian Monsoon (EAM) system which is also related to the El Niño-Southern Oscillation (ENSO) through teleconnection. Our understanding of EAM activity and its connection with global climate is not fully established. In this study high resolution Sr/Ca and δ18O records derived from four fossil Porites sp. corals with U-series ages ranging from ~7000 to 1800 years (yrs) were used to characterise the EAM-ENSO activities since the mid-Holocene. The results show that both the summer and winter monsoons were stronger than present ~ 7000 yrs ago, as evidenced by the higher-than-present amplitudes of annual cycles in SST (9.1 °C) and seawater δ18O (1.4%). The strengthened summer monsoon is considered to result from higher Northern Hemispheric insolation during the mid-Holocene, while the enhanced winter monsoon could be attributed to a reduction/shutdown of North Atlantic Meridional Overturning (NAMOC), leading to a prevailing "cold tongue" off the Vietnamese coast, and an amplified east-west SST gradient in the northern SCS. The EAM was weakened ca. 4200 yrs ago, as reflected by the lower amplitude of SST (4.3 °C) and seawater δ18O (0.57%) annual cycles. The downturn of the EAM is correlated in timing with the cold phase or the Bond event of the high-latitude climate, the Neolithic cultural collapse in China, and the strengthened ENSO in the Pacific. After this downturn, the EAM was slightly strengthened ~3600 and 1800 yrs ago as shown by larger amplitudes of SST (~ 5 °C) and seawater δ18O (1.0-1.2%) annual cycles. The enhanced EAM at these times are out of phase with the high-latitude climate, but are consistent with evidence from historical documents in Vietnam and China. The waxing/waning of the EAM appear to match with the waning/waxing of the ENSO intensity throughout the records since the mid-Holocene. The changes in EAM activity were accompanied by

  11. Reconstruction of early Holocene paleoclimate and environment in the SW Kola region, Russian Arctic

    Science.gov (United States)

    Grekov, Ivan; Kolka, Vasiliy; Syrykh, Liudmila; Nazarova, Larisa

    2016-04-01

    In the current period of the global climate change it becomes necessary to have a clear understanding of not only the changes taking place in the components of the natural environment, but also to understand development of all interactions between those components. Quaternary terrigenic sediments and lakes of the Kola Peninsula store information about the development of the region in the Late Glacial and Holocene: movements of the glacier, neotectonic activity, post-glacial rebound, formation and development of natural environments after deglaciation. Multi-proxy study of landscapes evolution of the Kola Peninsula in the Late Quaternary will help to establish a detailed reconstruction of climatic and environmental changes of this poor studied sector of the Arctic. Quaternary history on the Kola Peninsula is represented mainly by Late Pleistocene and Holocene sediments covering the Baltic Shield (Lavrova, 1960; Evzerov, 2015). Several palaeolimnological investigations in the Baltic Shield area have been performed earlier (Donner et al., 1977; Anundsen, 1985; Berglund, 2004). Studies of the southern coast of the Kola Peninsula have shown that marine transgression took place in the Late Pleistocene that was then replaced by a regression with variable speed. The slowdown of the uplift of the area took place between 8800 - 6800 BP (cal. years) and corresponded to the time of the Tapes transgression of the Arctic Ocean (Evzerov et al. 2010; Kolka, et al., 2013). Palaeoclimatic studies based on micro-paleontological analyzes indicate uneven development of the Kola Peninsula landscapes in the Late Glacial and Early Holocene. The northern coast of the Peninsula became free of ice first. In this area tundra-steppe vegetation was established for a short time and was later replaced by tundra (Snyder et al, 2000). Southern part of the Kola Peninsula was dependent on the conditions of deglaciation of the White Sea basin and cleared of ice much later (Evzerov et al., 2010; Kolka

  12. Early Holocene turnover, followed by stability, in a Caribbean lizard assemblage

    Science.gov (United States)

    Kemp, Melissa E.; Hadly, Elizabeth A.

    2016-03-01

    Understanding how communities are impacted by environmental perturbations is integral for addressing the ongoing biodiversity crisis that impacts ecosystems worldwide. The fossil record serves as a window into ancient interactions and the responses of communities to past perturbations. Here, we re-examine paleontological data from Katouche Bay, Anguilla, a Holocene site in the Lesser Antilles. We reveal that the site was more diverse than previously indicated, with long-term, continuous records of three genera of extant lizards (Anolis, Ameiva, and Thecadactylus), and the early Holocene presence of Leiocephalus, a large ground-dwelling lizard that has since been completely extirpated from the Lesser Antilles. The disappearance of Leiocephalus from Katouche Bay resulted in high turnover, decreased evenness, and decreased species richness-a trend that continues to the present day. Our body size reconstructions for the most abundant genus, Anolis, are consistent with the presence of only one species, Anolis cf. gingivinus, at Katouche Bay throughout the Holocene, contrary to previously published studies. Additionally, we find no evidence of dwarfism in A. cf. gingivinus, which contrasts with a global study of contemporary insular lizards. Our data reveal that the impacts of diversity loss on lizard communities are long lasting and irreversible over millennia.

  13. Climate Change in Lowland Central America During the Late Deglacial and Early Holocene

    Energy Technology Data Exchange (ETDEWEB)

    Hillesheim, M B; Hodell, D A; Leyden, B W; Brenner, M; Curtis, J H; Anselmetti, F S; Ariztegui, D; Buck, D G; Guilderson, T P; Rosenmeier, M F; Schnurrenberger, D W

    2005-02-08

    The transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition ({approx}11,250 to 7,500 cal yr BP) inferred from sediment cores retrieved in Lake Peten Itza, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by {approx}11,250 cal yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11,250 to 10,350 cal yr BP, during the Preboreal period, lithologic changes in sediments from deep-water cores (>50 m below modern water level) indicate several wet-dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1-4) occurred at 11,200, 10,900, 10,700, and 10,400 cal yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10,350 cal yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Peten Itza with other records from the circum-Caribbean demonstrates a coherent climate response during the entire span of our record. Furthermore, lowland Neotropical climate during the late deglacial and early Holocene period appears to be tightly linked to climate change in the high-latitude North Atlantic. We speculate that the observed changes in lowland Neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the Intertropical Convergence Zone and Azores-Bermuda high-pressure system. This mechanism operated on millennial-to-submillennial timescales and may have responded to changes in solar radiation, glacial meltwater, North Atlantic sea ice, and the Atlantic meridional overturning circulation (MOC).

  14. Orbital pacing and ocean circulation-induced collapses of the Mesoamerican monsoon over the past 22,000 y.

    Science.gov (United States)

    Lachniet, Matthew S; Asmerom, Yemane; Bernal, Juan Pablo; Polyak, Victor J; Vazquez-Selem, Lorenzo

    2013-06-04

    The dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles, ocean circulation through its influence on atmospheric circulation, and sea-surface temperatures. However, few records from the summer North American Monsoon system are available to test for a synchronous response with other global monsoons to shared forcings. In particular, the monsoon response to widespread atmospheric reorganizations associated with disruptions of the Atlantic Meridional Overturning Circulation (AMOC) during the deglacial period remains unconstrained. Here, we present a high-resolution and radiometrically dated monsoon rainfall reconstruction over the past 22,000 y from speleothems of tropical southwestern Mexico. The data document an active Last Glacial Maximum (18-24 cal ka B.P.) monsoon with similar δ(18)O values to the modern, and that the monsoon collapsed during periods of weakened AMOC during Heinrich stadial 1 (ca. 17 ka) and the Younger Dryas (12.9-11.5 ka). The Holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation. We conclude that the Mesoamerican monsoon responded in concert with other global monsoon regions, and that monsoon strength was driven by variations in the strength and latitudinal position of the Intertropical Convergence Zone, which was forced by AMOC variations in the North Atlantic Ocean. The surprising observation of an active Last Glacial Maximum monsoon is attributed to an active but shallow AMOC and proximity to the Intertropical Convergence Zone. The emergence of agriculture in southwestern Mexico was likely only possible after monsoon strengthening in the Early Holocene at ca. 11 ka.

  15. Effects of melting ice sheets and orbital forcing on the early Holocene warming in extratropical Northern Hemisphere

    Science.gov (United States)

    zhang, yurui; Renssen, Hans; Seppä, Heikki

    2016-04-01

    The early Holocene is an important climatological period, as it marked the final transition from the last deglaciation to the relatively warm and stable Holocene. Previous studies have analyzed the influence of the demise of the ice sheets and other forcings on the climate system during the Holocene. However, the climate response to the forcings together with the internal feedbacks before 9 ka remains not fully comprehended. In this study, we therefore disentangle how these forcings contributed to climate change during the earliest part of Holocene (11.5-7 ka) by employing the LOVECLIM climate model for both equilibrium and transient experiments. The results of our equilibrium experiments for 11.5 ka reveal that the annual mean temperature at the onset of the Holocene was lower than in the preindustrial era over most of the extratropical Northern Hemisphere. The magnitude of this cooler climate varies regionally and this spatial pattern is suggested by the biologically based proxies as well. In eastern N America and NW Europe the temperatures were 2-5 °C lower than in the preindustrial era as the climate was strongly influenced by the cooling effects of the ice sheets at here. This cooling of the ice-sheet surface was caused both by the enhanced surface albedo and by the orography of the ice sheets. In contrast, in Alaska, temperatures in all seasons were 0.5-3 °C higher than in the control run primarily due to the orbitally induced positive insolation anomaly and the enhanced southerly winds which advected warm air from the South as a response to the high air pressure over the Laurentide Ice Sheet (LIS). Our transient experiments indicate that the Holocene temperature evolution and the early Holocene warming were also geographically heterogeneous. In Alaska, the climate is constantly cooling over the whole Holocene. In contrast, in N Canada, there was an overall warming during the early Holocene up to 1.88 °C ka-1 in summer as a consequence of the progressive

  16. Long-term forest dynamics at Gribskov, eastern Denmark with early-Holocene evidence for thermophilous broadleaved tree species

    DEFF Research Database (Denmark)

    Overballe-Petersen, Mette V; Nielsen, Anne Birgitte; Hannon, Gina E.

    2012-01-01

    thermophilous broadleaved trees, including Quercus sp., Tilia sp. and Ulmus sp. The macrofossils contribute to the vegetation reconstruction with evidence for local presence of species with low pollen productivity or easily degraded pollen types such as Populus. The charcoal record shows frequent burning during...... two periods of the early Holocene and from c. 3000 cal. BP to present. The early-Holocene part of the record indicates a highly disturbed forest ecosystem with frequent fires and abundant macrofossils of particularly Betula sp. and Populus sp. The sediment stratigraphy and age–depth relationships give...

  17. The Y. D. and climate abrupt events in the early and middle Holocene: Stalagmite oxygen isotope record from Maolan, Guizhou, China

    Institute of Scientific and Technical Information of China (English)

    QIN Jiaming; YUAN Daoxian; CHENG Hai; LIN Yushi; ZHANG Meiliang; WANG Fuxing; R. L. Edwards; WANG Hua; RAN Jingcheng

    2005-01-01

    The isotope records which range from 3.9 kaBP to 15.7 kaBP with an average resolution of 90 a have been obtained from 45 cm to 193.6 cm of the upper part of D4 stalagmite from Dongguo Cave in Libo, Guizhou, by using system TIMS U-series dating and carbon and oxygen stable isotope analyses.The study indicates that the last cold event, the YD (Younger Dryas) event, of the last glacial period was apparently shown in D4 record, which started from 12.80 kaBP and ended in 11.58 kaBP, with a great range of drop in temperature. The end of the last glacial period was consistent with the termination I in oceanic isotope records and was with time limit of 11.3 kaBP. The three most distinct cold events in the early and middle Holocene occurred respectively in 10.91 kaBP, 8.27 kaBP and 4.75 kaBP, with a range of drop in temperature reaching 2-5℃. The climate abrupt events in thousand and hundred years scale recorded in stalagmite δ18O can be compared to those in GISP2 ice cores from Greenland in their happening time and the range of their lasting time. The cold events in 8.27 kaBP and 4.75 kaBP can also be compared to CC3 stalagmite records in Ireland, which indicate that climate changes of short range in China monsoon areas, western Europe and polar regions, have the same driving factor. This has a global significance. In addition, the trend of record curves in some time- stages is apparently different, which reflects probably the difference between environment in monsoon climate areas and in polar regions.

  18. Quantitative Evaluation of a Rapid and Severe Early Holocene Drought in NW-Montana

    Science.gov (United States)

    Sperazza, M.; Hofmann, M. H.; Moore, J. N.; Hendrix, M. S.

    2005-12-01

    Extreme abrupt climate changes are common throughout the Holocene and have been recognized from several regions around the world. Here we present a preliminary quantitative evaluation of a severe early Holocene drought as recorded in sediments of Flathead Lake, Montana. Flathead Lake is a large (496km2) open lake system that drains >18,000km2 of high valley plains and mountain terrain. In order to study the records of Pleistocene deglaciation and Holocene climate change, we recovered 19 piston cores from the lake bottom at locations that were tied to a set of 3.5 kHz seismic reflection data. Seismic data and cores obtained within Big Arm Bay, a shallow embayment in the western part of the lake, indicate the presence of an erosional unconformity that we interpret as indicating a significant lowering of lake level at about 7600 cal yr. BP. Sub-unconformity reflectors are clearly truncated and the unconformity itself is onlapped by overlying reflectors. The uppermost onlapped reflector coincides with a ~12cm accumulation of Mt. Mazama tephra (7,630±80 cal yr. BP), providing a temporal constraint on the lowstand. Morphometric analysis of the lake indicates that during this lowstand the surface of the lake dropped about 15m below the modern lake's natural bedrock spillway and Flathead Lake lost about 25% of its present volume. Interestingly none of our core data suggest an increase in CaCO3 at this unconformity. Sedimentologic evidence for a lake lowstand comes from changes in early and middle Holocene grain size observed in several cores. For example, grain size data from core FL-00-9P indicates a significant increase in clay fraction just prior to the Mt Mazama tephra. We interpret the increase in clay as resulting from reduced inflow into Flathead Lake. An increase in grain size, right after the deposition of the Mt Mazama tephra in turn coincides with the actual lake level lowstand and the refilling of the lake. Based on these observations we created a hydrologic

  19. Early and Middle Holocene evidence for plant use and cultivation in the Middle Cauca River Basin, Cordillera Central (Colombia)

    Science.gov (United States)

    Aceituno, Francisco J.; Loaiza, Nicolás

    2014-02-01

    This paper presents the latest results of research done in the Colombian Andean region known as Middle Cauca River Basin, an important location for the study of the origins of plant use and the dispersal of domesticates throughout the Americas due to its geographical position in northwest South America. We discuss human-environment interactions during Pleistocene/Holocene transition to middle Holocene (ca 10,000-4000 BP), specifically human-plant interaction and environmental factors that led to the adoption of horticultural practices. Three lines of evidence are analyzed: archaeological stratigraphy, lithic technology, and microbotanical remains. Our results suggest that early Holocene environmental stability allowed Middle Cauca settlers to use the diverse local resources for several millennia, altering the local vegetation, and leading to the development of horticultural practices that included the use of both local and foreign plants. These results inform the ongoing debate about the antiquity and nature of plant domestication and dispersals in the Americas.

  20. Paleoclimatic Implications of Holocene Plant Remains from the Sierra Bacha, Sonora, Mexico

    Science.gov (United States)

    Van Devender, Thomas R.; Burgess, Tony L.; Piper, Jessie C.; Turner, Raymond M.

    1994-01-01

    A total of 93 plant taxa were identified from 11 packrat ( Neotoma sp.) midden samples from the Sierra Bacha on the coast of the Gulf of California near Puerto Libertad, Sonora, Mexico. Nine indurated samples have radiocarbon dates ranging from 9970 to 320 yr B.P. Sonoran desertscrub was present on rocky slopes throughout the Holocene. Early Holocene assemblages dominated by Fouquieria columnaris (boojum tree) reflect vegetation and climate more like modern Baja California with greater winter rainfall and cooler summers. Middle Holocene vegetation was essentially modern with modest indications of greater monsoonal rainfall even though cold-water upwelling locally inhibits summer precipitation. The results are similar to all previous midden reconstructions of early and middle Holocene climates in the Sonoran Desert, but contradict general atmospheric circulation model simulations.

  1. A ˜25 ka Indian Ocean monsoon variability record from the Andaman Sea

    Science.gov (United States)

    Rashid, H.; Flower, B. P.; Poore, R. Z.; Quinn, T. M.

    2007-10-01

    Recent paleoclimatic work on terrestrial and marine deposits from Asia and the Indian Ocean has indicated abrupt changes in the strength of the Asian monsoon during the last deglaciation. Comparison of marine paleoclimate records that track salinity changes from Asian rivers can help evaluate the coherence of the Indian Ocean monsoon (IOM) with the larger Asian monsoon. Here we present paired Mg/Ca and δ 18O data on the planktic foraminifer Globigerinoides ruber (white) from Andaman Sea core RC12-344 that provide records of sea-surface temperature (SST) and δ 18O of seawater (δ 18O sw) over the past 25,000 years (ka) before present (BP). Age control is based on nine accelerator mass spectrometry (AMS) dates on mixed planktic foraminifera. Mg/Ca-SST data indicate that SST was ˜3 °C cooler during the last glacial maximum (LGM) than the late Holocene. Andaman Sea δ 18O sw exhibited higher than present values during the Lateglacial interval ca 19-15 ka BP and briefly during the Younger Dryas ca 12 ka BP. Lower than present δ 18O sw values during the BØlling/AllerØd ca 14.5-12.6 ka BP and during the early Holocene ca 10.8-5.5 ka BP are interpreted to indicate lower salinity, reflect some combination of decreased evaporation-precipitation (E-P) over the Andaman Sea and increased Irrawaddy River outflow. Our results are consistent with the suggestion that IOM intensity was stronger than present during the BØlling/AllerØd and early Holocene, and weaker during the late glaciation, Younger Dryas, and the late Holocene. These findings support the hypothesis that rapid climate change during the last deglaciation and Holocene included substantial hydrologic changes in the IOM system that were coherent with the larger Asian monsoon.

  2. Early and mid-Holocene climate in the tropical Pacific: seasonal cycle and interannual variability induced by insolation changes

    Directory of Open Access Journals (Sweden)

    Y. Luan

    2012-06-01

    Full Text Available Using a coupled atmosphere-ocean model we analyze the responses of the mean climate and interannual variations in the tropical Pacific to the changes in insolation during the early and mid-Holocene, with experiments in which only the variations of Earth's orbital configuration are considered. We first discuss common features of the Early and mid-Holocene climates compared to the pre-industrial conditions. In particular, an equatorial annual mean cooling that has a "U" shape across the tropical Pacific is simulated, whereas the ocean heat content is enhanced in the western tropical Pacific and decreased in the east. Similarly, the seasonality is enhanced in the west and reduced in the east. We show that the seasonality of the insolation forcing, the cloud radiative forcing and ocean dynamics all contribute to increasing these east–west contrasts. ENSO variability is reduced in the early Holocene and increases towards present-day conditions. Obliquity alone does not affect ENSO characteristics in the model. The reduction of ENSO magnitude results from the relationship between changes in seasonality, which involves wave propagation along the thermocline, and the timing of the development of ENSO anomalies. All these effects are larger in the Early Holocene compared to the mid-Holocene. Despite a one-month difference in the insolation forcing and corresponding response of SST, winds and thermocline depth between these two periods, the timing and changes in the east–west temperature and heat content gradients are similar. We suggest that it explains why the timing of development of ENSO is quite similar between these two climates and does not reflect the differences in the seasonal timing.

  3. Late Pleistocene to early Holocene environmental changes on Store Koldewey, coastal north-east Greenland

    Directory of Open Access Journals (Sweden)

    Martin Klug

    2016-12-01

    Full Text Available A lake sediment sequence from southern Store Koldewey, north-east Greenland, has been investigated using a multidisciplinary approach, including geophysical, geochemical, biogeochemical, biological and sedimentological methods. Chronological constraints are provided by accelerator mass spectrometry (AMS 14C dating of bulk sediment and complemented with published water moss ages. The record consists of three major sediment units. Their individual structural, textural, geophysical and geochemical characteristics indicate variable input of sediment and meltwater due to variable proximity of the ice margin and therefore reflect the growth and decay of a local glacier during the late Weichselian. Radiocarbon dating of bulk sediment samples from the lowermost unit gave ages of 42 to 34 calibrated thousand years (cal Ky B.P. and indicates that this material is redeposited in the lake basin during or after the ice advance at the end of the Pleistocene. Increased meltwater and sediment input from a retreating ice margin following the Younger Dryas is indicated by the occurrence of a sandy to gravely section. Fine-grained and laminated sediments were deposited during the Pleistocene–Holocene transition and indicate calm sedimentation conditions with an ice margin outside of the lake catchment. The reoccurrence of coarse sediments during the early Holocene may indicate increased meltwater input in response to the cold spell at about 9.3 Kya with increased snow accumulation rather than fluctuations of local glaciers. The dating results furthermore show that AMS 14C dating of bulk sediment samples deposited during glacier decay in High Arctic environments can give problematic ages.

  4. Subsistence strategies in Argentina during the late Pleistocene and early Holocene

    Science.gov (United States)

    Martínez, Gustavo; Gutiérrez, María A.; Messineo, Pablo G.; Kaufmann, Cristian A.; Rafuse, Daniel J.

    2016-07-01

    This paper highlights regional and temporal variation in the presence and exploitation of faunal resources from different regions of Argentina during the late Pleistocene and early Holocene. Specifically, the faunal analysis considered here includes the zooarchaeological remains from all sites older than 7500 14C years BP. We include quantitative information for each reported species (genus, family, or order) and we use the number of identified specimens (NISP per taxon and the NISPtotal by sites) as the quantitative measure of taxonomic abundance. The taxonomic richness (Ntaxatotal and Ntaxaexploited) and the taxonomic heterogeneity or Shannon-Wiener index are estimated in order to consider dietary generalization or specialization, and ternary diagrams are used to categorize subsistence patterns of particular sites and regions. The archaeological database is composed of 78 sites which are represented by 110 stratigraphic contexts. Our results demonstrate that although some quantitative differences between regions are observed, artiodactyls (camelids and deer) were the most frequently consumed animal resource in Argentina. Early hunter-gatherers did not follow a specialized predation strategy in megamammals. A variety in subsistence systems, operating in parallel with a strong regional emphasis is shown, according to specific environmental conditions and cultural trajectories.

  5. Early Holocene estuary development of the Hesselø Bay area, southern Kattegat, Denmark and its implication for Ancylus Lake drainage

    DEFF Research Database (Denmark)

    Bendixen, Carina; Boldreel, Lars Ole; Jensen, Jørn Bo

    2017-01-01

    High-resolution shallow seismic data, sediment core information, radiocarbon dating and sequence stratigraphy have been used to interpret the late glacial to early Holocene geological evolution of Hesselø Bay in the southern Kattegat, Denmark. A reconstruction of the early Holocene coastal...... environment and a description of coastal processes associated with a river outlet into the bay are presented. Weichselian glacial deposits form the lowermost interpreted unit, covered by late glacial (LG) and postglacial (PG, Holocene) sediments. A funnel-shaped estuary existed at the mouth of channels...... in the period 10.3–9.2 cal. ka BP; the channels drained water from south to north. The early PG is characterised by estuarine and coastal deposits. The early Holocene bars that developed in the estuary are preserved as morphological features on the present-day seabed, possibly as a result of rapid relative sea...

  6. High-resolution study of Late Glacial and Early Holocene vegetation and tree line changes in the Southern Carpathian Mountains

    Science.gov (United States)

    Magyari, E.; Jakab, G.; Braun, M.; Buczkó, K.; Bálint, M.

    2009-04-01

    The Retezat Massif of the S Carpathian Mountains abounds in glacial lakes, mainly above 1900 m a.s.l., just above the present day tree limit formed by Picea abies and Pinus cembra in the northern slopes. For the reconstruction of Late Glacial and Early Holocene vegetation and tree line changes in this mountain, two lakes were selected: Taul dintre Brazi (1740 m a.s.l.) and Lake Gales (1990 m a.s.l.). Sediments obtained from these lakes extend back to the Late Glacial, and so provide us an exceptional opportunity to study 1) when trees were first established locally around the lower lake following glacial retreat and 2) what tree and shrub species were present and replaced each other in the Late Glacial and early postglacial forests in response to the high-amplitude climatic fluctuation, and in case of the Early Holocene, the high-amplitude climatic amelioration. Pollen, conifer stomata and plant macrofossils were studied from both lake sediments at approximately 100 years resolution. Sediment chronologies were based on multiple AMS radiocarbon dates. Preliminary results from this study show that Pinus mugo, Pinus cembra, Picea abies and Betula nana appeared very early during the lateglacial interstadial, ca. 14,500 cal yr BP followed by Larix decidua around 14,200 cal yr BP. Pinus cembra gained dominance in the Latglacial interstadial forest and survived locally during the Younger Dryas reversal unlike Picea abies. Another important result was the reconstruction of the Early Holocene forest composition around the lower lake that proved much more species rich than the present-day forest; Picea abies grew together with Larix decidua, Pinus mugo, Pinus cembra, Alnus viridis, Juniperus, Betula nana and Betula pubescens during the Early Holocene, furthermore the stomatal record suggested that conifer species were evenly distributed around the lake. In light of our data, the position of the Early Holocene tree line reached 1990 m a.s.l. by ca. 10,700 cal yr BP (i

  7. Effects of melting ice sheets and orbital forcing on the early Holocene warming in extratropical Northern Hemisphere

    Science.gov (United States)

    Zhang, Y.; Renssen, H.; Seppä, H.

    2015-11-01

    The early Holocene is a critical period for climate change, as it marked the final transition from the last deglaciation to the relatively warm and stable Holocene. It is characterized by a warming trend that has been registered in numerous proxy records. This climatic warming was accompanied by major adjustments in different climate components, including the decaying of ice sheets in cryosphere, the perturbation of circulation in the ocean, the expansion of vegetation (over the high latitude) in biosphere. Previous studies have analyzed the influence of the demise of the ice sheets and other forcings on climate system. However, the climate response to the forcings together with the internal feedbacks before 9 ka remains not fully comprehended. In this study, we therefore disentangle how these forcings contributed to climate change during the earliest part of Holocene (11.5-7 ka) by employing the LOVECLIM climate model for both equilibrium and transient experiments. The results of our equilibrium experiments for 11.5 ka reveal that the annual mean temperature at the onset of the Holocene was lower than in the preindustrial era in the Northern extratropics, except in Alaska. The magnitude of this cool anomaly varies regionally as a response to varying climate forcings and diverse mechanisms. In eastern N America and NW Europe the temperatures throughout the whole year were 2-5 °C lower than in the preindustrial control, reaching the maximum cooling as here the climate was strongly influenced by the cooling effects of the ice sheets. This cooling of the ice-sheet surface was caused both by the enhanced surface albedo and by the orography of the ice sheets. For Siberia, a small deviation (-0.5-1.5 °C) in summer temperature and 0.5-1.5 °C cooler annual climate compared to the preindustrial run were caused by the counteraction of the high albedo associated with the tundra vegetation which was more southward extended at 11.5 ka than in the preindustrial period and the

  8. Interactions between climate change and human activities during the early to mid-Holocene in the eastern Mediterranean basins

    Science.gov (United States)

    Berger, Jean-Francois; Lespez, Laurent; Kuzucuoğlu, Catherine; Glais, Arthur; Hourani, Fuad; Barra, Adrien; Guilaine, Jean

    2016-09-01

    This paper focuses on early Holocene rapid climate change (RCC) records in the Mediterranean zone, which are under-represented in continental archives (9.2 to 8.2 ka events) and on their impact on prehistoric societies. This lack of data handicaps the general interpretation of climate impacts on human societies, which flourished in recent years. Key questions remain about the impact of early Holocene cooling events on the Mediterranean climate, ecosystems and human societies. In this paper, we discuss some examples from river and lake systems from the eastern to central Mediterranean area (central Anatolia, Cyprus, northeastern and northwestern Greece) that illustrate some palaeohydrological and erosion variations that modified the sustainability of the first Neolithic populations in this region. Results allow us to present direct land-sea correlations and to reconstruct regional long-term trends as well as millennial- to centennial-scale climatic changes. In this context, we question the socio-economic and geographical adaptation capacities of these societies (mobility, technology, economic practices, social organisation) during the "early Holocene" interval (11.7 to 8.2 ka), which corresponds partly to the Sapropel 1 deposition in the eastern Mediterranean sea.

  9. A regional record of expanded Holocene wetlands and prehistoric human occupation from paleowetland deposits of the western Yarlung Tsangpo valley, southern Tibetan Plateau

    Science.gov (United States)

    Hudson, Adam M.; Olsen, John W.; Quade, Jay; Lei, Guoliang; Huth, Tyler E.; Zhang, Hucai

    2016-07-01

    The Asian Monsoon, which brings ∼80% of annual precipitation to much of the Tibetan Plateau, provides runoff to major rivers across the Asian continent. Paleoclimate records indicate summer insolation and North Atlantic paleotemperature changes forced variations in monsoon rainfall through the Holocene, resulting in hydrologic and ecologic changes in plateau watersheds. We present a record of Holocene hydrologic variability in the Yarlung Tsangpo (YT) valley of the southern Tibetan Plateau, based on sedimentology and 14C dating of organic-rich 'black mats' in paleowetlands deposits, that shows changes in wetlands extent in response to changing monsoon intensity. Four sedimentary units indicate decreasing monsoon intensity since 10.4 ka BP. Wet conditions occurred at ∼10.4 ka BP, ∼9.6 ka BP and ∼7.9-4.8 ka BP, with similar-to-modern conditions from ∼4.6-2.0 ka BP, and drier-than-modern conditions from ∼2.0 ka BP to present. Wetland changes correlate with monsoon intensity changes identified in nearby records, with weak monsoon intervals corresponding to desiccation and erosion of wetlands. Dating of in situ ceramic and microlithic artifacts within the wetlands indicates Epipaleolithic human occupation of the YT valley after 6.6 ka BP, supporting evidence for widespread colonization of the Tibetan Plateau in the early and mid-Holocene during warm, wet post-glacial conditions.

  10. Evidence for cold events in the early Holocene from the Guliya ice core, Tibetan Plateau, China

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Evidence for the "8.2 ka cold event" has been provided mostly from the circum-North Atlantic area. However, whether this cold event occurred in other places is a key to understanding its cause. Here, we provide the evidence for the "8.2 ka cold event" from the Guliya ice core in the northwest Tibetan Plateau, and it was found that the peak cooling (~8.3-8.2 ka) in this ice core was about 7.8-10℃, which was larger than the cooling in the North Atlantic region. The primary causes for this episode were diminished solar activity and weakened thermohaline circulation. Moreover, another weak cold event, centered about 9.4 ka, was also recorded in the Guliya ice core record. These two cold events were concurrent with the ice-rafting episodes in the North Atlantic during the early Holocene, which implies that the millennial-scale climatic cyclicity might exist in the Tibetan Plateau as well as in the North Atlantic.

  11. Early Holocene dune activity linked with final destruction of Glacial Lake Minong, eastern Upper Michigan, USA

    Science.gov (United States)

    Loope, Henry M.; Loope, Walter L.; Goble, Ronald J.; Fisher, Timothy G.; Jol, Harry M.; Seong, J. C.

    2010-07-01

    The early Holocene final drainage of glacial Lake Minong is documented by 21 OSL ages on quartz sand from parabolic dunes and littoral terraces and one radiocarbon age from a lake sediment core adjacent to mapped paleoshorelines in interior eastern Upper Michigan. We employ a simple model wherein lake-level decline exposes unvegetated littoral sediment to deflation, resulting in dune building. Dunes formed subsequent to lake-level decline prior to stabilization by vegetation and provide minimum ages for lake-level decline. Optical ages range from 10.3 to 7.7 ka; 15 ages on dunes adjacent to the lowest Lake Minong shoreline suggest final water-level decline ˜ 9.1 ka. The clustering of optical ages from vertically separated dunes on both sides of the Nadoway-Gros Cap Barrier around 8.8 ka and a basal radiocarbon date behind the barrier (8120 ± 40 14C yr BP [9.1 cal ka BP]) support the hypothesis that the barrier was breached and the final lake-level drop to the Houghton Low occurred coincident with (1) high meltwater flux into the Superior basin and (2) an abrupt, negative shift in oxygen isotope values in Lake Huron.

  12. Holocene climatic change in Hunshandake Desert

    Institute of Scientific and Technical Information of China (English)

    JIN Heling; SU Zhizhu; SUN Liangying; SUN Zhong; ZHANG Hong; JIN Liya

    2004-01-01

    Research on the geological data of Hunshandake Desert in China monsoon region revealed that Holocene summer monsoon had experienced six prevailing periods and seven weakening periods. The climatic humidity and the vegetation had also undergone the similar periodical variation influenced by the monsoon periodicity. The period when summer monsoon prevailed or winter monsoon weakened and climatic humidity and vegetation coverage relatively increased, corresponded to the global warming events;whereas the period when summer monsoon weakened or winter monsoon prevailed and climatic humidity and vegetation coverage relatively decreased, corresponded to the arid events in middle to low latitudes and the cold events in North Atlantic. As for the changing regularity of summer monsoon intensity there were two distinct periodicities of 1456 years and 494 years, also these two periodicities had global significance.

  13. The sensitivity of Arctic sea ice production to shelf flooding during the early Holocene: a modelling study

    Science.gov (United States)

    Blaschek, M.; Renssen, H.

    2012-04-01

    During the last deglaciation, the global sea-level started rising, changing the coastlines from an early Holocene stand (40 m lower than today at approximately 10 kyr BP, Siddall et al., 2003) to modern day coastlines. Proxy evidence shows that this transgression occurred non-uniformly over the globe. For instance, Bauch et al. (2001) report for the Laptev Sea (Arctic Ocean), that the modern coastline was only established at 5 kyr BP after a fast transgression from the early Holocene, leading to a flooding of the extensive shelf area. This shelf area is presently regarded to be an important production zone of Arctic sea ice, playing an important role in the dynamics of sea ice in the Arctic, as well as its export to the Nordic Seas along the East Greenland Current (EGC). Through this sea ice export, changes in the Laptev Sea shelf area during the Holocene could potentially have had a substantial impact on the sea surface conditions of the EGC, and the Denmark Strait, which is known to be sensitive to sea ice. This is consistent with a rapid increase in sea ice export through the EGC around 5 kyr BP as reported by Jennings et al. (2002). In this study we investigate the impact of this Arctic shelf flooding on sea ice production in the Holocene, and on the climate of the Nordic Seas in the LOVECLIM1.2 global ocean-atmosphere-vegetation model. We present results of several experiments in which we study the sensitivity of Arctic sea ice production to various Arctic shelf areas under early Holocene conditions (9 kyr BP). We approach this by changing the land-sea mask to represent different lower-than-present sea-level coastlines. For example, we perform experiments with the Last Glacial Maximum (LGM) land-sea mask, representing a lowering of the sea-level by 120 m, while keeping other forcings at 9 kyr BP. A further step is to modify selected areas in the Arctic, such as the Laptev Sea area, to examine the importance of different areas. Our results help to explain long

  14. Rapid vegetation response to Lateglacial and early Holocene climatic fluctuation in the South Carpathian Mountains (Romania)

    Science.gov (United States)

    Magyari, E. K.; Jakab, G.; Bálint, M.; Kern, Z.; Buczkó, K.; Braun, M.

    2012-03-01

    High-resolution pollen, conifer stomata and plant macrofossil analyses of two glacial lake sediments (1740 and 1990 m a.s.l.) are used to reconstruct Lateglacial (LG) and early Holocene (EH) vegetation and tree line changes in the Retezat Mountains. Our results show that during the LG, tree line was between 1750 and 1800 m a.s.l. formed by Larix decidua, Pinus mugo and Picea abies. Early LG spread to high altitudes suggests refugia of these tree species in the mountain. The Younger Dryas cooling resulted in regional steppe-tundra expansion, but tree line position and composition showed little change. The abundance of trees and shrubs decreased at 1740 m a.s.l., but species richness increased with the arrival of Pinus cembra. Our data support climate-model hindcasts for only modest decrease in accumulated growing season heat at mid-high altitudes. Regionally the pollen records suggest enhanced aridity and seasonality. In the EH, tree line reached 2000 m a.s.l. (higher than today) by ˜11,100 cal yr BP. P. mugo, P. cembra, P. abies established around the upper lake suggesting rapid increase in summer temperatures. The EH maximum of L. decidua between 11,200-10,600 cal yr BP was connected to high summer insolation. High altitude expansion of Abies alba between 10,600-10,300 cal yr BP suggested summer mean temperatures ˜2.8 °C higher then today. In comparison with other mountain sites in Europe, LG interstadial tree line was at similar altitude in the S Alps and ˜350 m higher in the Pirin Mountains. LG tree line fluctuation had similar low amplitude in the SE Alps, Retezat and Pirin Mts suggesting relatively weak influence of the North Atlantic thermohaline circulation changes on growing season temperatures.

  15. Environmental, depositional and cultural changes in the upper Pleistocene and early Holocene; the Cinglera del Capello Sequence (Capellades, Spain)

    Science.gov (United States)

    Vaquero, Manuel; Allue, Ethel; Bischoff, James L.; Burjachs, Francesc; Vallverdu, Josep

    2013-01-01

    The correlation between environmental and cultural changes is one of the primary archeological and paleoanthropological research topics. Analysis of ice and marine cores has yielded a high-resolution record of millennial-scale changes during the Late Pleistocene and Holocene eras. However, cultural changes are documented in low-resolution continental deposits; thus, their correlation with the millennial-scale climatic sequence is often difficult. In this paper, we present a rare occurrence in which a thick archeological sequence is associated with a high-resolution environmental record. The Cinglera del Capello is a tufa-draped cliff located in the northeastern Iberian Peninsula, 50 km west of Barcelona. This cliff harbors several rock-shelters with Late Pleistocene and Early Holocene deposits. Together, the deposits of four rock-shelters span from 7000 to 70,000 years ago and provide a high-resolution record of the environmental and human dynamics during this timespan. This record allows the correlation of the cultural and environmental changes. The multiproxy approach to the Cinglera evidence indicates that the main cultural stages of the Late Pleistocene and Early Holocene (Middle Paleolithic, Upper Paleolithic and Mesolithic) are associated with significant changes in the environmental and depositional contexts.

  16. Provenance of Greenland Ice Sheet icebergs constrained by Ar-Ar radioisotope data from late glacial-early Holocene records

    Science.gov (United States)

    Knutz, P. C.; Storey, M.; Kuijpers, A.

    2009-12-01

    Radiogenic Ar-Ar dating of hornblende has been used to constrain the sources of ice-rafted detritus on the southwest Greenland margin and central Davis Strait. Single hornblende grains (total of 248) were picked from sand-size fractions of two marine cores, DA04-31P and TTR462G, covering the early Holocene to late glacial interval including Heinrich events (HE) 1-3. Paleoceanographic analyses of DA04-31P have indicated that the last deglaciation of the southern Greenland Ice Sheet occurred in multiple steps during the early deglacial/HE1, Allerød and early Holocene intervals (Knutz et al., in review). Each of these collapse stages were preceded by upper ocean warming related to enhanced Irminger Current activity. Pre-HE1, Allerød and Holocene hornblende samples show a bimodal signature of late Archean (2.5-3.0 Ga) and early Proterozoic (1.6-2.2 Ga) ages consistent with southern Greenland bedrock sources. In contrast hornblende grains from detrital carbonate HE layers and within the Younger Dryas interval show a dominant early Proterozoic spectrum that is similar to results obtained from the central North Atlantic IRD belt. The early Proterozoic age of Younger Dryas samples from the Davis Strait site and the high amounts of basalt in this core, presumably derived from the Disko-Nussuaq province, suggests that icebergs carrying Archean material from southern Greenland did not enter the Baffin Bay or at least not for this specific time interval. The conclusion of our study is that the Greenland Ice Sheet appears to have been a much larger contributor to non-Heinrich IRD in the North Atlantic than thought previously. P. C. Knutz, H. Ebbesen, S. Christiansen, M.-A. Sicre and A. Kuijpers. Multiple deglaciation steps of the southern Greenland Ice Sheet driven by vigorous Irminger Current: Significance for the Younger Dryas cooling. Submitted to Quaternary Science Reviews.

  17. 10Be dating reveals early-middle Holocene age of the Drygalski Moraines in central West Greenland

    Science.gov (United States)

    Cronauer, Sandra L.; Briner, Jason P.; Kelley, Samuel E.; Zimmerman, Susan R. H.; Morlighem, Mathieu

    2016-09-01

    We reconstruct the history of the Greenland Ice Sheet margin on the Nuussuaq Peninsula in central West Greenland through the Holocene using lake sediment analysis and cosmogenic 10Be exposure dating of the prominent Drygalski Moraines. Erratics perched on bedrock outboard of the Drygalski Moraines constrain local deglaciation to ∼9.9 ± 0.6 ka (n = 2). Three Drygalski Moraine crests yield mean 10Be ages of 8.6 ± 0.4 ka (n = 2), 8.5 ± 0.2 ka (n = 3), and 7.6 ± 0.1 ka (n = 2) from outer to inner. Perched erratics between the inner two moraines average 7.8 ± 0.1 ka (n = 2) and are consistent with the moraine ages. Sediments from a proglacial lake with a catchment area extending an estimated 2 km beneath (inland of) the present ice sheet terminus constrain an ice sheet minimum extent from 5.4 ka to 0.6 ka. The moraine chronology paired with the lake sediment stratigraphy reveals that the ice margin likely remained within ∼2 km of its present position from ∼9.9 to 5.4 ka. This unexpected early Holocene stability, preceded by rapid ice retreat and followed by minimum ice extent between ∼5.4 and 0.6 ka, contrasts with many records of early Holocene warmth and the Northern Hemisphere summer insolation maximum. We suggest ice margin stability may instead be tied to adjacent ocean temperatures, which reached an optimum in the middle Holocene.

  18. Holocene vegetation variation in the Daihai Lake region of north-central China: a direct indication of the Asian monsoon climatic history

    Science.gov (United States)

    Xiao, Jule; Xu, Qinghai; Nakamura, Toshio; Yang, Xiaolan; Liang, Wendong; Inouchi, Yoshio

    2004-07-01

    DH99a sediment core recovered at the center of Daihai Lake in north-central China was analyzed at 4-cm intervals for pollen assemblage and concentration. The pollen record spanning the last ca 10,000 yr revealed a detailed history of vegetation and climate changes over the Daihai Lake region during the Holocene. From ca 10,250 to 7900 cal yr BP, arid herbs and shrubs dominated the lake basin in company with patches of mixed pine and broadleaved forests, indicating a mild and dry climatic condition. Over this period, the woody plants displayed an increasing trend, which may suggest a gradual increase in warmth and humidity. The period between ca 7900 and 4450 cal yr BP exhibits large-scale covers of mixed coniferous and broadleaved forests, marking a warm and humid climate. Changes in the composition of the forests indicate that both temperature and precipitation displayed obvious fluctuations during this period, i.e., cool and humid ca 7900- 7250 cal yr BP, warm and slightly humid ca 7250- 6050 cal yr BP, warm and humid between ca 6050 and 5100 cal yr BP, mild and slightly humid ca 5100- 4800 cal yr BP, and mild and humid ca 4800- 4450 cal yr BP. The period can be viewed as the Holocene optimum (characterized by a warm and moist climate) of north-central China, with the maximum (dominated both by warmest temperatures and by richest precipitations) occurring from ca 6050 to 5100 cal yr BP. During the period of ca 4450- 2900 cal yr BP, the woody plants declined, and the climate generally became cooler and drier than the preceding period. This period is characterized by a cold, dry episode from ca 4450 to 3950 cal yr BP, a warm, slightly humid interval between ca 3950 and 3500 cal yr BP and a mild, slightly dry episode from ca 3500 to 2900 cal yr BP, and appears to be a transition from warm and humid to cold and dry climatic conditions. Since ca 2900 cal yr ago, the forests disappeared and the vegetation density decreased, reflecting a cool and dry climate. However, a

  19. Wetting and greening Tibetan Plateau in early summer since the late 1970s due to advanced Asian summer monsoon onset

    Science.gov (United States)

    Zhang, Wenxia; Zhou, Tianjun; Zhang, Lixia

    2016-04-01

    Known as the "the world water tower", the Tibetan Plateau (TP) is the origin of the ten largest rivers in Asia, breeding more than 1.4 billion people, and exerts substantial influences on water resources, agriculture, and ecosystems in downstream countries. This region is one of the most susceptible areas around the world to changing climate due to the high elevation. Observed evidence have shown significant climate changes over the TP, including surface air warming and moistening, glaciers shrinking, winds stilling, solar dimming, and atmospheric heat source weakening. However, as an essential part of the hydrological cycle, precipitation changes on the TP remain an ambiguous picture. Changes in precipitation vary largely with different seasons, time periods and climate zones considered. This study shows a robust increase in precipitation amount over the TP in May, when the rainy season starts, over the period 1979-2014 (31% relative to the climatology). The wetting trend is spatially consistent over the south-eastern TP, to which both precipitation frequency and intensity contribute. Circulation trends show that the wetting TP in May is resulted from the advanced onset of Asian summer monsoon, which onsets 1~2 pentads earlier since 1979. It intensified water vapor transport from the Bay of Bengal (BOB) to south of the TP in May and local anomalous convection. This relationship is further validated by the significant correlation coefficient (0.47) between the onset dates of Asian summer monsoon (particularly the BOB summer monsoon, 0.68) and precipitation over the south-eastern TP in May. The wetting TP in May has further exerted profound impacts on the hydrological cycle and ecosystem, such as moistening the soil and animating vegetation activities throughout early summer. Both decadal variations of soil moisture (from May to June) and Normalized Difference Vegetation Index (NDVI) (from May to July) coincide well with that of precipitation over the south

  20. Charcoal reflectance reveals early holocene boreal deciduous forests burned at high intensities.

    Science.gov (United States)

    Hudspith, Victoria A; Belcher, Claire M; Kelly, Ryan; Hu, Feng Sheng

    2015-01-01

    Wildfire size, frequency, and severity are increasing in the Alaskan boreal forest in response to climate warming. One of the potential impacts of this changing fire regime is the alteration of successional trajectories, from black spruce to mixed stands dominated by aspen, a vegetation composition not experienced since the early Holocene. Such changes in vegetation composition may consequently alter the intensity of fires, influencing fire feedbacks to the ecosystem. Paleorecords document past wildfire-vegetation dynamics and as such, are imperative for our understanding of how these ecosystems will respond to future climate warming. For the first time, we have used reflectance measurements of macroscopic charcoal particles (>180μm) from an Alaskan lake-sediment record to estimate ancient charring temperatures (termed pyrolysis intensity). We demonstrate that pyrolysis intensity increased markedly from an interval of birch tundra 11 ky ago (mean 1.52%Ro; 485°C), to the expansion of trees on the landscape ~10.5 ky ago, remaining high to the present (mean 3.54%Ro; 640°C) irrespective of stand composition. Despite differing flammabilities and adaptations to fire, the highest pyrolysis intensities derive from two intervals with distinct vegetation compositions. 1) the expansion of mixed aspen and spruce woodland at 10 cal. kyr BP, and 2) the establishment of black spruce, and the modern boreal forest at 4 cal. kyr BP. Based on our analysis, we infer that predicted expansion of deciduous trees into the boreal forest in the future could lead to high intensity, but low severity fires, potentially moderating future climate-fire feedbacks.

  1. The Brazilian megamastofauna of the Pleistocene/Holocene transition and its relationship with the early human settlement of the continent

    Science.gov (United States)

    Hubbe, Alex; Hubbe, Mark; Neves, Walter A.

    2013-03-01

    One of the most intriguing questions regarding the Brazilian Late Quaternary extinct megafauna and Homo sapiens is to what extent they coexisted and how humans could have contributed to the former's extinction. The aim of this article is to review the chronological and archaeological evidences of their coexistence in Brazil and to evaluate the degree of direct interaction between them. Critical assessment of the Brazilian megafauna chronological data shows that several of the late Pleistoscene/early Holocene dates available so far cannot be considered reliable, but the few that do suggest that at least two species (Catonyx cuvieri, ground sloth; Smilodon populator, saber-toothed cat) survived until the beginning of the Holocene in Southeast Brazil. Archaeological data indicates that the first human groups arrived in Brazil and were inhabiting this region during the last millennia of the Pleistocene and, consequently, they coexisted with the extinct fauna in some parts of Brazil for at least one thousand years. There is no robust evidence favoring any kind of direct interaction between humans and megafauna prior to their extinction. To date, it is not possible to properly judge the indirect influence of humans (landscape transformation, introduction of predators, among others) in this extinction event. Intense and to some extent unique climate changes between the Last Glacial Maximum and the Holocene favors the interpretation that they had a major contribution to the megafauna extinction, although the scarcity of data impedes the proper testing of this hypothesis.

  2. 河南马沟洞石笋记录的早中全新世气候和环境变化%Early to mid-Holocene paleoclimatic changes recorded by the stalagmites from the Magou Cave, Henan Province

    Institute of Scientific and Technical Information of China (English)

    毛瑞雪; 蔡演军; 马乐; 成星

    2016-01-01

    基于河南省禹州市马沟洞2支石笋(MG-1与MG-40)24个230Th年龄和1988个氧同位素数据,建立了研究区13.1—4.9 ka BP分辨率为2—14 a的石笋氧同位素时间序列。马沟洞石笋δ18O的时间序列揭示季风降水在11.2—9.1 ka BP时段在波动中逐渐增加,9.1—4.9 ka BP季风降水显著波动但无明显长期趋势变化。YD事件、9.3 ka事件、8.2 ka事件记录与其他石笋δ18O记录的一致性揭示末次冰消期—早全新世百年—千年尺度气候突变事件的大范围存在和共同的驱动因子。马沟洞全新世大暖期的δ18O记录中检测出的13个数十年尺度的弱季风事件进一步证实全新世大暖期气候的不稳定性。与大气Δ14C记录、NGRIP冰芯δ18O记录的对比及周期分析揭示,太阳活动引起的太阳辐射变化和北半球高纬气候状况共同影响着亚洲季风的变化, ENSO活动及气候系统内部的相互作用也对东亚夏季风降水产生重要的影响。%Background, aim, and scope Henan Province, located in central China, is dominated by monsoonal climate, and has been regarded as the core region of Chinese ancient civilization. Stalagmite has advantages of absolute and high-precision chronology and abundant proxy indexes, and has been widely used to decipher the changes of Asian summer in the past. However, there are few stalagmite records obtained from this region till now and all of them are located in the hilly area of west Henan Province. Here, we present a high-resolution and precisely dated stalagmiteδ18O records attained from two stalagmites (MG-1 and MG-40) from Magou Cave, northern Henan Province, Central China. We reconstruct the history of monsoon precipitation during early to mid Holocene, characterize the climate instability of the Holocene Megathermal and investigate the possible driving forces and dynamics of the Asian Summer Monsoon (ASM) in the study region. We also examine the possible links existed

  3. Spatial and temporal variations and controlling factors of sediment accumulation in the Yangtze River estuary and its adjacent sea area in the Holocene, especially in the Early Holocene

    Science.gov (United States)

    Feng, Zhibing; Liu, Baohua; Zhao, Yuexia; Li, Xishuang; Jiang, Li; Si, Shaokun

    2016-08-01

    The sub-bottom and collected borehole data provide insight into the transport and accumulation processes of the Yangtze-derived sediment in the study area since ~11 kyr BP. Five seismic units were identified according to six major acoustic surfaces. The sedimentary strata consist of fluvial, estuarine and deltaic systems from the bottom up, characterized by two different trends in sediment accumulation rates, i.e., low-high-low, and high-low-high. On the inner shelf of the East China Sea, the terrain with trough and ridge was formed by the Early Holocene transgression strata (formed in ~10 to 12 kyr BP) scoured by the later rectilinear tidal current due to postglacial sea-level transgression, and the sharply protruding seismic units are interpreted to be bedrocks outcropping on the seafloor. An analysis of the sedimentary characteristics in the boreholes and such factors as difference in accumulation rates, and tectonic subsidence led us to conclude that the paleo-coastline was located not far away from and to the east of Core ZK09 at ~9 kyr BP, and the southern bank of the Yangtze River estuary was located to the south of Core ZK09. At ~9 kyr BP, the Yangtze-derived sediments were transported eastwards along the southern bank of the Yangtze River and the barrier due to the influence of the paleo-coastal current from the north, the direction of the Yangtze-derived sediment transport was split on the northeast of the Zhoushan archipelago, and the sediments covered the terrain with trough and ridge. During the high sea level period (7 kyr BP-present), the eastward migration of paleo-coastline had resulted in the increase in accumulation rate. We also conclude that the sharp increase in accumulation rate near the Yangtze River estuary after ~2 kyr BP was not primarily caused by human activities. The position shifts of the estuary caused by the paleo-coastline migration and sea level oscillations since the Holocene is the main cause controlling the Yangtze

  4. Valley evolution of the Lower Rhine in LGM, Lateglacial and Early Holocene.

    NARCIS (Netherlands)

    Cohen, K.M.; Hoek, W.Z.; Stouthamer, E.; Geurts, A.H.; Janssens, M.; Kasse, C.; Busschers, F.S.; Hijma, M.P.; Erkens, G.

    2013-01-01

    The impact of transient climate change, for example at glacial-interglacial transitions, on the alluvial valley of the lower reaches of larger river systems has become a classic topic of fluvial geomorphology and quaternary geological study. The process of contraction of Holocene river activity into

  5. The cultural and chronological context of early Holocene maize and squash domestication in the Central Balsas River Valley, Mexico.

    Science.gov (United States)

    Ranere, Anthony J; Piperno, Dolores R; Holst, Irene; Dickau, Ruth; Iriarte, José

    2009-03-31

    Molecular evidence indicates that the wild ancestor of maize is presently native to the seasonally dry tropical forest of the Central Balsas watershed in southwestern Mexico. We report here on archaeological investigations in a region of the Central Balsas located near the Iguala Valley in Guerrero state that show for the first time a long sequence of human occupation and plant exploitation reaching back to the early Holocene. One of the sites excavated, the Xihuatoxtla Shelter, contains well-stratified deposits and a stone tool assemblage of bifacially flaked points, simple flake tools, and numerous handstones and milling stone bases radiocarbon dated to at least 8700 calendrical years B.P. As reported in a companion paper (Piperno DR, et al., in this issue of PNAS), starch grain and phytolith residues from the ground and chipped stone tools, plus phytoliths from directly associated sediments, provide evidence for maize (Zea mays L.) and domesticated squash (Cucurbita spp.) in contexts contemporaneous with and stratigraphically below the 8700 calendrical years B.P. date. The radiocarbon determinations, stratigraphic integrity of Xihuatoxtla's deposits, and characteristics of the stone tool assemblages associated with the maize and squash remains all indicate that these plants were early Holocene domesticates. Early agriculture in this region of Mexico appears to have involved small groups of cultivators who were shifting their settlements seasonally and engaging in a variety of subsistence pursuits.

  6. A persistent Holocene wetting trend in arid central Asia, with wettest conditions in the late Holocene, revealed by multi-proxy analyses of loess-paleosol sequences in Xinjiang, China

    Science.gov (United States)

    Chen, Fahu; Jia, Jia; Chen, Jianhui; Li, Guoqiang; Zhang, Xiaojian; Xie, Haichao; Xia, Dunsheng; Huang, Wei; An, Chengbang

    2016-08-01

    There are significant differences in the interpretation of the moisture (precipitation) history of arid central Asia (ACA) during the Holocene, as inferred on one hand from speleothem oxygen isotope records, and on the other from lake sediments. Here we present the results of measurements of climatically-sensitive magnetic properties and soil color from four well-dated loess-paleosol sequences from the northern slopes of the Tienshan Mountains and the Yili River valley, Xinjiang, China, in the core area of ACA. Our results demonstrate that the characteristic Holocene paleosol, indicating relatively moist conditions, generally formed after ∼6 ka (1 ka = 1000 cal yr BP) in the study region, and that the accumulation of unweathered loess prevailed during the early Holocene, indicating a dry climate at that time. The magnetic proxies further reveal a trend of generally increasing moisture since the Last Glacial Maximum, with the wettest climate occurring during the late Holocene. This trend of increasing moisture during the Holocene is representative of the Xinjiang region and possibly of the whole of the core area of ACA, and is in marked contrast both to the mid-Holocene moisture maximum observed in the East Asian summer monsoon region and to the general decrease in the strength of the Indian summer monsoon since the early Holocene. Our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the Holocene in the core area of ACA, caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the Arctic Oscillation (AO) or North Atlantic Oscillation (NAO).

  7. Petrology and geochemistry of three early Holocene eruptions from Makushin volcano, Alaska

    Science.gov (United States)

    Larsen, J. F.; Schaefer, J. R.

    2016-12-01

    Makushin volcano is an 1800-meter-high stratovolcano with an ice-filled, 2x3 km summit crater, 25 km west of Dutch Harbor and Unalaska, Alaska on Unalaska Island. This study examines the petrology and geochemistry of the three largest, early Holocene eruptions from Makushin: "CFE", (ca. 9000 BP), "Nateekin" (ca. 8700 BP), and "Driftwood" (ca. 8200 BP). The CFE eruption produced thick scoria fall deposits to the northeast and pyroclastic-flow deposits in upper Makushin and "Waterfall" valleys extending >12 km to the east and north. The Nateekin eruption produced fine ash to fine lapilli deposits that are up to 20 cm thick in the Unalaska town area. The Driftwood eruption produced tan pumice and dense, black scoriaceous fall deposits, up to 2 m thick, primarily in the Driftwood valley area to the northeast. Whole rock major (XRF) and trace element (LA-ICPMS) compositions were collected from the CFE and Driftwood samples. Samples from the Nateekin unit were too fine-grained for whole-rock analyses. Analyses of glass, phenocryst, and microlite phases from all three units were collected at UAF using the JEOL JXA-8530F electron microcprobe. The CFE and Driftwood eruptions produced medium K2O, tholeiitic andesites: CFE = 56 to 60 wt. % SiO2; Driftwood = 60 to 63 wt. % SiO2. The three units have andesite to rhyodacite glass compositions: CFE= 57 to 64 wt. % SiO2; Nateekin = 59 to 61 wt. % SiO2; Driftwood = 67 to 70 wt. % SiO2. The CFE and Driftwood samples have plagioclase, clinopyroxene and orthopyroxene phenocrysts, with minor olivine in the CFE fall deposit scoria. The pyroxenes are uniform in composition: Opx = Wo4.6En58.7Fs36.7 (n=58) and Cpx = Wo39.7En41.9Fs18.4 (n=132). Plagioclase phenocrysts from Driftwood pumice have An52-54 cores and An48-49 rims. CFE plagioclase phenocrysts are bimodal, with a lower An50-54 group and a higher An70-89 group. Nateekin glass compositions are similar to CFE scoria analyses from the middle to top of the unit, indicating little

  8. Ocean forcing of Ice Sheet retreat in central west Greenland from LGM to the early Holocene

    Science.gov (United States)

    Jennings, Anne E.; Andrews, John T.; Ó Cofaigh, Colm; Onge, Guillaume St.; Sheldon, Christina; Belt, Simon T.; Cabedo-Sanz, Patricia; Hillaire-Marcel, Claude

    2017-08-01

    Three radiocarbon dated sediment cores from trough mouth fans on the central west Greenland continental slope were studied to determine the timing and processes of Greenland Ice Sheet (GIS) retreat from the shelf edge during the last deglaciation and to test the role of ocean forcing (i.e. warm ocean water) thereon. Analyses of lithofacies, quantitative x-ray diffraction mineralogy, benthic foraminiferal assemblages, the sea-ice biomarker IP25, and δ18 O of the planktonic foraminifera Neogloboquadrina pachyderma sinistral from sediments in the interval from 17.5-10.8 cal ka BP provide consistent evidence for ocean and ice sheet interactions during central west Greenland (CWG) deglaciation. The Disko and Uummannaq ice streams both retreated from the shelf edge after the last glacial maximum (LGM) under the influence of subsurface, warm Atlantic Water. The warm subsurface water was limited to depths below the ice stream grounding lines during the LGM, when the GIS terminated as a floating ice shelf in a sea-ice covered Baffin Bay. The deeper Uummannaq ice stream retreated first (ca. 17.1 cal ka BP), while the shallower Disko ice stream retreated at ca. 16.2 cal ka BP. The grounding lines were protected from accelerating mass loss (calving) by a buttressing ice shelf and by landward shallowing bathymetry on the outer shelf. Calving retreat was delayed until ca. 15.3 cal ka BP in the Uummannaq Trough and until 15.1 cal ka BP in the Disko Trough, during another interval of ocean warming. Instabilities in the Laurentide, Innuitian and Greenland ice sheets with outlets draining into northern Baffin Bay periodically released cold, fresh water that enhanced sea ice formation and slowed GIS melt. During the Younger Dryas, the CWG records document strong cooling, lack of GIS meltwater, and an increase in iceberg rafted material from northern Baffin Bay. The ice sheet remained in the cross-shelf troughs until the early Holocene, when it retreated rapidly by calving and strong

  9. Small-mammal data on early and middle Holocene climates and biotic communities in the Bonneville Basin, USA

    Science.gov (United States)

    Schmitt, D.N.; Madsen, D.B.; Lupo, K.D.

    2002-01-01

    Archaeological investigations in Camels Back Cave, western Utah, recovered a series of small-mammal bone assemblages from stratified deposits dating between ca. 12,000 and 500 14C yr B.P. The cave's early Holocene fauna includes a number of species adapted to montane or mesic habitats containing grasses and/or sagebrush (e.g., Lepus townsendii, Marmota flaviventris, Reithrodontomys megalotis, and Brachylagus idahoensis) which suggest that the region was relatively cool and moist until after 8800 14C yr B.P. Between ca. 8600 and 8100 14C yr B.P. these mammals became locally extinct, taxonomic diversity declined, and there was an increase in species well-adapted to xeric, low-elevation habitats, including ground squirrels, Lepus californicus and Neotoma lepida. The early small-mammal record from Camels Back Cave is similar to the 11,300-6000 14C yr B.P. mammalian sequence from Homestead Cave, northwestern Utah, and provides corroborative data on Bonneville Basin paleoenvironments and mammalian responses to middle Holocene desertification. ?? 2002 University of Washington.

  10. Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes

    Science.gov (United States)

    Bartlein, P. J.; Edwards, M. E.; Hostetler, S. W.; Shafer, S. L.; Anderson, P. M.; Brubaker, L. B.; Lozhkin, A. V.

    2015-09-01

    Arctic land-cover changes induced by recent global climate change (e.g., expansion of woody vegetation into tundra and effects of permafrost degradation) are expected to generate further feedbacks to the climate system. Past changes can be used to assess our understanding of feedback mechanisms through a combination of process modeling and paleo-observations. The subcontinental region of Beringia (northeastern Siberia, Alaska, and northwestern Canada) was largely ice-free at the peak of deglacial warming and experienced both major vegetation change and loss of permafrost when many arctic regions were still ice covered. The evolution of Beringian climate at this time was largely driven by global features, such as the amplified seasonal cycle of Northern Hemisphere insolation and changes in global ice volume and atmospheric composition, but changes in regional land-surface controls, such as the widespread development of thaw lakes, the replacement of tundra by deciduous forest or woodland, and the flooding of the Bering-Chukchi land bridge, were probably also important. We examined the sensitivity of Beringia's early Holocene climate to these regional-scale controls using a regional climate model (RegCM). Lateral and oceanic boundary conditions were provided by global climate simulations conducted using the GENESIS V2.01 atmospheric general circulation model (AGCM) with a mixed-layer ocean. We carried out two present-day simulations of regional climate - one with modern and one with 11 ka geography - plus another simulation for 6 ka. In addition, we performed five ~ 11 ka climate simulations, each driven by the same global AGCM boundary conditions: (i) 11 ka Control, which represents conditions just prior to the major transitions (exposed land bridge, no thaw lakes or wetlands, widespread tundra vegetation), (ii) sea-level rise, which employed present-day continental outlines, (iii) vegetation change, with deciduous needleleaf and deciduous broadleaf boreal

  11. Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes

    Science.gov (United States)

    Bartlein, P.J.; Edwards, M.E.; Hostetler, Steven W.; Shafer, Sarah; Anderson, P.M.; Brubaker, L. B; Lozhkin, A. V

    2015-01-01

    Arctic land-cover changes induced by recent global climate change (e.g., expansion of woody vegetation into tundra and effects of permafrost degradation) are expected to generate further feedbacks to the climate system. Past changes can be used to assess our understanding of feedback mechanisms through a combination of process modeling and paleo-observations. The subcontinental region of Beringia (northeastern Siberia, Alaska, and northwestern Canada) was largely ice-free at the peak of deglacial warming and experienced both major vegetation change and loss of permafrost when many arctic regions were still ice covered. The evolution of Beringian climate at this time was largely driven by global features, such as the amplified seasonal cycle of Northern Hemisphere insolation and changes in global ice volume and atmospheric composition, but changes in regional land-surface controls, such as the widespread development of thaw lakes, the replacement of tundra by deciduous forest or woodland, and the flooding of the Bering–Chukchi land bridge, were probably also important. We examined the sensitivity of Beringia's early Holocene climate to these regional-scale controls using a regional climate model (RegCM). Lateral and oceanic boundary conditions were provided by global climate simulations conducted using the GENESIS V2.01 atmospheric general circulation model (AGCM) with a mixed-layer ocean. We carried out two present-day simulations of regional climate – one with modern and one with 11 ka geography – plus another simulation for 6 ka. In addition, we performed five ~ 11 ka climate simulations, each driven by the same global AGCM boundary conditions: (i) 11 ka Control, which represents conditions just prior to the major transitions (exposed land bridge, no thaw lakes or wetlands, widespread tundra vegetation), (ii) sea-level rise, which employed present-day continental outlines, (iii) vegetation change, with deciduous needleleaf and deciduous broadleaf boreal

  12. Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes

    Directory of Open Access Journals (Sweden)

    P. J. Bartlein

    2015-03-01

    Full Text Available Arctic land-cover changes (e.g., expansion of woody vegetation into tundra and effects of permafrost degradation that have been induced by recent global climate change are expected to generate further feedbacks to the climate system. Past changes can be used to assess our understanding of feedback mechanisms through a combination of process modelling and paleo-observations. The sub-continental region of Beringia (Northeast Siberia, Alaska, and northwestern Canada was largely ice-free at the peak of deglacial warming and experienced both major vegetation change and loss of permafrost when many arctic regions were still ice covered. The evolution of Beringian climate at this time was largely driven by global features, such as the amplified seasonal cycle of Northern Hemisphere insolation and changes in global ice volume and atmospheric composition, but changes in regional land-surface controls, such as the widespread development of thaw lakes, the replacement of tundra by deciduous forest or woodland, and the flooding of the Bering–Chukchi land bridge, were probably also important. We examined the sensitivity of Beringia's early Holocene climate to these regional-scale controls using a regional climate model (RegCM. Lateral and oceanic boundary conditions were provided by global climate simulations conducted using the GENESIS V2.01 atmospheric general circulation model (AGCM with a mixed-layer ocean. We carried out two present day simulations of regional climate, one with modern and one with 11 ka geography, plus another simulation for 6 ka. In addition, we performed five ∼11 ka climate simulations, each driven by the same global AGCM boundary conditions: (i 11 ka "Control", which represents conditions just prior to the major transitions (exposed land bridge, no thaw lakes or wetlands, widespread tundra vegetation, (ii sea-level rise, which employed present day continental outlines, (iii vegetation change, with deciduous needleleaf and

  13. Holocene aridification of India

    Science.gov (United States)

    Ponton, C.; Giosan, L.; Eglinton, T.I.; Fuller, D.Q.; Johnson, J.E.; Kumar, P.; Collett, T.S.

    2012-01-01

    Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long-term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity-adapted vegetation from ???4,000 until 1,700 years ago followed by the persistence of aridity-adapted plants after that. The oxygen isotopic composition of planktonic foraminifer Globigerinoides ruber detects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub-millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ???4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water-conservation technology in south India. Copyright 2012 by the American Geophysical Union.

  14. Holocene aridification of India

    Science.gov (United States)

    Ponton, Camilo; Giosan, Liviu; Eglinton, Tim I.; Fuller, Dorian Q.; Johnson, Joel E.; Kumar, Pushpendra; Collett, Tim S.

    2012-02-01

    Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long-term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity-adapted vegetation from ˜4,000 until 1,700 years ago followed by the persistence of aridity-adapted plants after that. The oxygen isotopic composition of planktonic foraminifer Globigerinoides ruber detects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub-millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ˜4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water-conservation technology in south India.

  15. Late Pleistocene and Early Holocene Rock Art from the Mongolian Altai: The Material and its Cultural Implications

    Directory of Open Access Journals (Sweden)

    Esther Jacobson-Tepfer

    2013-09-01

    Full Text Available Rock-pecked images from the northern Mongolian Altai attest to the presence of human communities within the high valleys of that region during the Late Pleistocene and Early Holocene. The material provides evidence that is hitherto largely missing from the archaeological record of that region. This paper reviews the rock art, its find sites and larger physical contexts and uses evidence from paleoenvironmental studies to propose dating and cultural significance. The material is compared with other sites said to have Paleolithic imagery from Mongolia and the adjoining Russian Altai. The body of presented material offers a major resource for the study of early hunter-gatherer communities at the interface of Central and North Asia.

  16. A review on Holocene climate changes in Indian subcontinent

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    .5 ka in the Indian subcontinent might be responsible for weak summer monsoon rainfall. Drastic reduction in rainfall could have led to the collapse of Indus Valley Civilization and desiccation of River Holocene Chronology with special reference...

  17. Pollen-based reconstructions of Holocene vegetation and climatic change of Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    唐领余; 李春海; 于革; 沈才明

    2003-01-01

    A synthesis of Holocene pollen records from the Tibetan Plateau shows the history of vegetation and climatic changes during the Holocene. Palynological evidences from 24 cores/sections have been compiled and show that the vegetation shifted from subalpine/alpine conifer forest to subalpine/alpine evergreen sclerophyllous forest in the southeastern part of the plateau; from alpine steppe to alpine desert in the central, western and northern part; and from alpine meadow to alpine steppe in the eastern and southern plateau regions during the Holocene. These records show that increases in precipitation began about 9 ka from the southeast, and a wide ranging level of increased humidity developed over the entire of the plateau around 8-7 ka, followed by aridity from 6 ka and a continuous drying over the plateau after 4-3 ka. The changes in Holocene climates of the plateau can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Indian Monsoon which expanded northwards during the early Holocene and retreated from the plateau since the midHolocene. Also, there is teleconnection between the Tibetan Plateau and North Atlantic.

  18. Detecting human impacts on the flora, fauna, and summer monsoon of Pleistocene Australia

    Directory of Open Access Journals (Sweden)

    G. H. Miller

    2007-08-01

    Full Text Available The moisture balance across northern and central Australia is dominated by changes in the strength of the Australian Summer Monsoon. Lake-level records that record changes in monsoon strength on orbital timescales are most consistent with a Northern Hemisphere insolation control on monsoon strength, a result consistent with recent modeling studies. A weak Holocene monsoon relative to monsoon strength 65–60 ka, despite stronger forcing, suggests a changed monsoon regime after 60 ka. Shortly after 60 ka humans colonized Australia and all of Australia's largest mammals became extinct. Between 60 and 40 ka Australian climate was similar to present and not changing rapidly. Consequently, attention has turned toward plausible human mechanisms for the extinction, with proponents for over-hunting, ecosystem change, and introduced disease. To differentiate between these options we utilize isotopic tracers of diet preserved in eggshells of two large, flightless birds to track the status of ecosystems before and after human colonization. More than 800 dated eggshells of the Australian emu (Dromaius novaehollandiae, an opportunistic, dominantly herbivorous feeder, provide a 140-kyr dietary reconstruction that reveals unprecedented reduction in the bird's food resources about 50 ka, coeval in three distant regions. These data suggest a tree/shrub savannah with occasionally rich grasslands was converted abruptly to the modern desert scrub. The diet of the heavier, extinct Genyornis newtoni, derived from >550 dated eggshells, was more restricted than in co-existing Dromaius, implying a more specialized feeding strategy. We suggest that generalist feeders, such as Dromaius, were able to adapt to a changed vegetation regime, whereas more specialized feeders, such as Genyornis, became extinct. We speculate that ecosystem collapse across arid and semi-arid zones was a consequence of systematic burning by early humans

  19. Detecting human impacts on the flora, fauna, and summer monsoon of Pleistocene Australia

    Science.gov (United States)

    Miller, G. H.; Magee, J. W.; Fogel, M. L.; Gagan, M. K.

    2007-08-01

    The moisture balance across northern and central Australia is dominated by changes in the strength of the Australian Summer Monsoon. Lake-level records that record changes in monsoon strength on orbital timescales are most consistent with a Northern Hemisphere insolation control on monsoon strength, a result consistent with recent modeling studies. A weak Holocene monsoon relative to monsoon strength 65-60 ka, despite stronger forcing, suggests a changed monsoon regime after 60 ka. Shortly after 60 ka humans colonized Australia and all of Australia's largest mammals became extinct. Between 60 and 40 ka Australian climate was similar to present and not changing rapidly. Consequently, attention has turned toward plausible human mechanisms for the extinction, with proponents for over-hunting, ecosystem change, and introduced disease. To differentiate between these options we utilize isotopic tracers of diet preserved in eggshells of two large, flightless birds to track the status of ecosystems before and after human colonization. More than 800 dated eggshells of the Australian emu (Dromaius novaehollandiae), an opportunistic, dominantly herbivorous feeder, provide a 140-kyr dietary reconstruction that reveals unprecedented reduction in the bird's food resources about 50 ka, coeval in three distant regions. These data suggest a tree/shrub savannah with occasionally rich grasslands was converted abruptly to the modern desert scrub. The diet of the heavier, extinct Genyornis newtoni, derived from >550 dated eggshells, was more restricted than in co-existing Dromaius, implying a more specialized feeding strategy. We suggest that generalist feeders, such as Dromaius, were able to adapt to a changed vegetation regime, whereas more specialized feeders, such as Genyornis, became extinct. We speculate that ecosystem collapse across arid and semi-arid zones was a consequence of systematic burning by early humans. We also suggest that altered climate feedbacks linked to changes

  20. Major Δ14C excursions during the late glacial and early Holocene : changes in ocean ventilation or solar forcing of climate change?

    NARCIS (Netherlands)

    van Geel, B.; van der Plicht, Johannes; Renssen, H

    2003-01-01

    The atmospheric 14C record during the Late Glacial and the early Holocene shows sharp increases simultaneous with cold climatic phases. These increases in the atmospheric 14C content are usually explained as the effect of reduced oceanic CO2 ventilation after episodic outbursts of large meltwater re

  1. A high-resolution Early Holocene-late MIS 3 environmental rock- and palaeomagnetic record from Lake Sf. Ana, Carpathian Mts, Romania

    Directory of Open Access Journals (Sweden)

    Daniel VERES

    2014-11-01

    Full Text Available Lacustrine sediments are excellent sources of palaeoenvironmental and palaeoclimatic information because they usually provide continuous and high-resolution records. In centraleastern Europe however lacustrine records that extend beyond the Holocene are rather sparse.Palaeomagnetic records from this region are also insufficiently explored, and usually associated with terrestrial deposits such as loess. In this context, the lacustrine record of Lake Sf. Ana, a volcanic crater lake in the East Carpathians, Romania, provides an important archive for reconstructing past paleomagnetic secular variation in the region from early Holocene to late Marine Isotope Stage (MIS 3.

  2. Early Holocene High Magnitude Debris Flow Events and Environmental Change as Illustrated by the Moxi Platform, Hengduan Mountains, SW China

    Institute of Scientific and Technical Information of China (English)

    ZHANG Junyan; CHENG Genwei; LI Yongfei

    2006-01-01

    Thick debris flow deposits in the Hengduan Mountains of southwestern China record landscape instability at the close of the last glaciation and in the early Holocene. The deposits, ranging in thickness from 100 to 200 m, are common and in high magnitude in the valleys of this region. They are products of large debris flows induced by glacier and enabled by the presence of large amount of glacial debris on the landscape. The carbon 14 dating from Moxi Platform indicates that a period of catastrophic debris flows occurred at c. 7 kyr B.P., and was concurrent with other glacial-fluvial fans and terraces which tied to regional climatic oscillations elsewhere in the Himalaya. The comparable events suggest a strong climatic control on earth surface processes for the dynamics, magnitude, and frequency in this region.

  3. Changes in the Early Holocene lacustrine environment inferred from the subfossil ostracod record in the Varangu section, northern Estonia

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    Tõnu Meidla

    2010-09-01

    Full Text Available The Varangu section is located on the southern slope of the Pandivere Upland in northern Estonia. A silty clay bed formed in the study area at 11 ;200–9300 ;cal ;yr ;BP, according to ostracod subfossils (e.g. Tonnacypris estonica, Leucocythere mirabilis, Limnocytherina sanctipatricii in an oxygen-rich cool and oligotrophic profundal lacustrine environment, with an inflow of surface waters through springs. The record of specific ostracods (e.g. Cyclocypris ovum, Cypridopsis vidua, Metacypris cordata reflects littoral environments, ongoing eutrophication, temperature increase and a progressive shallowing of the lake in the early Holocene (9300–7400 ;cal ;yr ;BP when the tufa bed accumulated. A slight cooling and productivity decrease at 9100–8600 ;cal ;yr ;BP preceded further temperature rise and water level lowering, leading to the development of a eutrophic lake and cease of ; ;tufa precipitation (8600–7400 ;cal ;yr ;BP.

  4. Early Holocene variability in the Arctic Gateway - High-resolution records reflecting Atlantic Water advection and ice coverage

    Science.gov (United States)

    Spielhagen, Robert F.; Bauch, Henning A.; Maudrich, Martin; Not, Christelle; Telesinski, Maciej M.; Werner, Kirstin

    2015-04-01

    The Arctic Gateway between Greenland and Svalbard is the main passage for the advection of Atlantic Water to the Arctic Ocean. Water temperature and intensity of this advection largely determine the degree of ice coverage which is fed by sea ice export from the north. Supported by a maximum in insolation, the Early Holocene was a period of extraordinarily strong advection and relatively high near-surface water temperatures in the eastern Nordic Seas (cf. Risebrobakken et al., 2011, Paleoceanography v. 26). Here we present a synthesis of radiocarbon-dated records from the northern and western part of this area, reaching from the SW Greenland Sea (73°N) to the Yermak Plateau (81°N) and revealing temporal and spatial differences in the development of the so-called Holocene Thermal Maximum (HTM). In the northern part of this region, the HTM started ca. 11-10.5 ka as indicated by rapidly increasing amounts of subpolar planktic foraminifers in the sediments. In the eastern Fram Strait and on the Yermak Plateau, our records of (sub)millennial scale resolution show that the maximum influx terminated already 2,000 years later (9-8 ka). Most likely, this development went along with a N-S relocation of the sea ice margin. According to the current stratigraphic model for a core with submillennial-scale resolution from Vesterisbanken seamount (73°N) in the Greenland Sea, the timing was different there. Increasing total amounts of planktic foraminifers in the sediment indicate an early (11-10 ka) reduction in sea ice coverage also in this region. However, evidence from subpolar planktic foraminifers for maximum Atlantic Water advection is younger (9-6 ka) than in the north. Apparently, the site in the SW Greenland Sea was affected by Atlantic Water in the Greenland Gyre that decoupled from the northward flowing Norwegian Atlantic Current/Westspitsbergen Current south of the Fram Strait. Thus, in a suite of events, strong Atlantic Water advection first affected the

  5. Early- to Mid-Holocene environmental and climate changes in the southern Baltic lowland using XRF scanning data

    Science.gov (United States)

    Tjallingii, Rik; Ott, Florian; Dräger, Nadine; Kramkowski, Mateusz; Slowinski, Michal; Brauer, Achim

    2016-04-01

    The ICLEA project includes several annually laminated (varved) lake records from the southern Baltic lowlands for detailed climatic and environmental reconstructions. Continuous geochemical records have been obtained by XRF scanning and reveal the dominant depositional processes of the German lake Tiefer See and the Polish lakes Głęboczek, Czechowskie and Jelonek. Each lake record has been independently dated by means of varve counting, AMS 14C dating and tephrochronology. The unprecedented age control allows accurate age correlation of individual lake records even over large distances. The detailed stratigraphy is used in combination with micro-XRF core scanning records to link depositional variability with past environmental and climatic changes. However, in each lake the major sedimentological transitions are reflected by different geochemical elements due to the different depositional conditions. Here we present a statistical concept for XRF core scanning data to evaluate the timing and frequency of the most prominent sedimentological transitions of the Early to Mid Holocene. Preliminary results reveal that depositional conditions prevail over relatively long periods (102-103 yrs) between the Younger Dryas and ~6000 yrs. The sedimentological transitions during this period are associated to regional climatic changes in the southern Baltic lowlands during this period. After ~6000 yrs BP, depositional conditions vary at a much higher frequency (10-102 yrs), which are associated with a stronger local and lake internal environmental variability. Ongoing research focuses on a multi-proxy approach to further constrain possible links between depositional changes recorded in these varved lacustrine sediments with Early- to Mid-Holocene climatic and environmental variations. This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution Analysis - ICLEA - of the Helmholtz Association.

  6. European bison as a refugee species? Evidence from isotopic data on Early Holocene bison and other large herbivores in northern Europe.

    Directory of Open Access Journals (Sweden)

    Hervé Bocherens

    Full Text Available According to the refugee species concept, increasing replacement of open steppe by forest cover after the last glacial period and human pressure had together forced European bison (Bison bonasus--the largest extant terrestrial mammal of Europe--into forests as a refuge habitat. The consequent decreased fitness and population density led to the gradual extinction of the species. Understanding the pre-refugee ecology of the species may help its conservation management and ensure its long time survival. In view of this, we investigated the abundance of stable isotopes (δ13C and δ15N in radiocarbon dated skeletal remains of European bison and other large herbivores--aurochs (Bos primigenius, moose (Alces alces, and reindeer (Rangifer tarandus--from the Early Holocene of northern Europe to reconstruct their dietary habits and pattern of habitat use in conditions of low human influence. Carbon and nitrogen isotopic compositions in collagen of the ungulate species in northern central Europe during the Early Holocene showed significant differences in the habitat use and the diet of these herbivores. The values of the δ13C and δ15N isotopes reflected the use of open habitats by bison, with their diet intermediate between that of aurochs (grazer and of moose (browser. Our results show that, despite the partial overlap in carbon and nitrogen isotopic values of some species, Early Holocene large ungulates avoided competition by selection of different habitats or different food sources within similar environments. Although Early Holocene bison and Late Pleistocene steppe bison utilized open habitats, their diets were significantly different, as reflected by their δ15N values. Additional isotopic analyses show that modern populations of European bison utilize much more forested habitats than Early Holocene bison, which supports the refugee status of the species.

  7. Effect of the early and late onset of summer monsoon over the Bay of Bengal on Asian precipitation in May

    Science.gov (United States)

    Xing, Nan; Li, Jianping; Wang, Lanning

    2016-09-01

    The impact of early and late Bay of Bengal (BoB) summer monsoon (BoBSM) onset on Asian precipitation in May is investigated. When the BoBSM occurs earlier (later), May rainfall tends to be enhanced (suppressed) in the southern Indian peninsula (SIP), the Indochinese peninsula (ICP), southwest China (SWC) and the South China Sea (SCS), while south China (SC) rainfall tends to be suppressed (enhanced). When the BoBSM occurs earlier than the climatological mean (late April), strong convective activity emerges earlier over the BoB, which causes local strong convective heating earlier. Then, earlier spread of heating in the BoB towards both sides leads to earlier retreat of the subtropical highs in the western Pacific (WPSH) and Indian Ocean outwards the BoB. Thus, compared to the climatological mean, the two subtropical highs present larger retreat outwards the BoB and smaller meridional extent over the SCS and Arabian Sea in May, which contributes to positive heating anomalies over the SCS and Arabian Sea. Therefore, anomalous cyclonic circulations occur over the BoB, SCS and Arabian Sea in May. Anomalous cyclonic circulation is favorable for low-level convergence over the SIP, and thus resulting in local heavy rainfall. Associated with cyclonic circulation anomalies over the BoB and SCS, anomalous low-level convergent winds and ascending flows favor positive precipitation anomalies in the ICP, SWC, and SCS, while anomalous northeasterlies and descending flows affected by the southward retreat of the WPSH lessen SC rainfall. In late onset years the opposite occurs.

  8. Evidence of Suess solar-cycle bursts in Holocene speleothem d18O records

    DEFF Research Database (Denmark)

    Knudsen, Mads Faurschou; Jacobsen, B. H.; Riisager, Peter

    2012-01-01

    Several studies indicate that changes in solar activity may have driven Holocene subtropical monsoon variability on decadal and centennial timescales, but the strength and nature of this link remains debated. In this study, we combine a recent mapping of the Holocene solar-cycle activity with four...... in driving centennial-scale changes in the hydrological cycle in the subtropics during the Holocene....

  9. Holocene coastal sea surface temperature changes in the northern South China Sea

    Science.gov (United States)

    Zhu, K.; Kong, D.; Wei, G.; Liu, Z.

    2016-12-01

    Holocene sea surface temperature (SST) changes in the northern South China Sea (SCS) coastal region are affected by complex factors. Previous studies have identified a long-term cooling trend, attributed to coastal mixing and intensified East Asian Winter Monsoon (EAWM), yet spatial patterns of coastal cooling along the southern China are still not well established. Here we reconstructed a Holocene Sea Surface Temperature (SST) record, derived from long-chain alkenone unsaturation index - UK'37, in the northern SCS. Our result reveals that a gentle cooling trend dominates the mid-late Holocene. The gradual warming trend occurring during the early Holocene might have resulted from the rising sea level or the rebound of "8.2 ka cold event". Besides, the C37-content also shows an extremely-low level before 8 ka. Later, both alkenone-derived SST and C37-content reach their highest levels during approximately 7-4.5 ka, corresponding to the Holocene Climate Optimum (HCO). Consistent with previous studies, the long-term cooling trend identified in coastal regions, but not offshore ones, presumably indicates intensified EAWM toward present. Further, during the late Holocene, coastal SST changes in the northern SCS show heterogeneous responses to global climatic conditions. In the Mirs Bay, SST was warmer during the Little Ice Age (LIA) than the Medieval Warm Period (WMP) and the current warm period, interpreted as reflecting intensified coastal mixing, due to strengthened East Asian Summer Monsoon (EASM) during warmer periods. However, SST records at other coastal sites, as well as offshore regions, show fluctuations consistent with global/northern hemisphere temperature changes, suggesting that these regions are less influenced by the EASM-induced coastal mixing, probably with the aid of Pearl River freshwater input.

  10. New cosmogenic exposure dates from Sermilik Fjord, southeast Greenland document rapid early Holocene retreat of Helheim Glacier

    Science.gov (United States)

    Hughes, A. L.; Rainsley, E.; Murray, T.; Fogwill, C. J.

    2010-12-01

    Marine-terminating glaciers are currently the dominant route for mass loss from the Greenland Ice Sheet (GrIS). Over the last decade Helheim Glacier, in concert with the majority of marine-terminating glaciers of the southeast sector of the GrIS, has exhibited dramatic changes in speed, thinning and retreat rates. The Holocene retreat history of the outlet glaciers of southeast Greenland is, however, largely unconstrained. Without detailed records of retreat over longer-time scales recent changes cannot be placed in context, nor is there sufficient evidence to constrain ice sheet models for improved estimates of future sea level rise. We present the first direct chronological constraint on the retreat of ice from Sermilik Fjord in southeast Greenland, the former drainage route of Helheim Glacier. Samples spanning the full length of the 80 km fjord were collected from erratics and streamlined bedrock in July 2009-10 and analysed for terrestrial cosmogenic nuclide (10Be) dating. Overlapping exposure ages indicate rapid evacuation of ice from much of the fjord at around 10.5 ka BP. Such substantial early Holocene retreat coincides with establishment of the local marine limit at c. 11 ka BP (Long et al. 2008). The new dates extend and confirm results from a tributary valley close to the fjord mouth that placed retreat from the present day coastline at c. 11.5 ka (Roberts et al. 2008). References: Roberts, D.H., Long, A.J., Schnabel, C., Freeman, S. and Simpson, M.J.R. 2008. The deglacial history of southeast sector of the Greenland Ice Sheet during the Last Glacial Maximum. Quaternary Science Reviews, 27, 1505-1516. Long, A.J., Roberts, R.H., Simpson, M.J.R., Dawson, S., Milne, G.A. and Huybrechts, P. 2008. Late Weichselian relative sea-level changes and ice sheet history in southeast Greenland. Earth and Planetary Science Letters, 272, 8-18.

  11. Mitochondrial haplogroup H1 in north Africa: an early holocene arrival from Iberia.

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    Claudio Ottoni

    Full Text Available The Tuareg of the Fezzan region (Libya are characterized by an extremely high frequency (61% of haplogroup H1, a mitochondrial DNA (mtDNA haplogroup that is common in all Western European populations. To define how and when H1 spread from Europe to North Africa up to the Central Sahara, in Fezzan, we investigated the complete mitochondrial genomes of eleven Libyan Tuareg belonging to H1. Coalescence time estimates suggest an arrival of the European H1 mtDNAs at about 8,000-9,000 years ago, while phylogenetic analyses reveal three novel H1 branches, termed H1v, H1w and H1x, which appear to be specific for North African populations, but whose frequencies can be extremely different even in relatively close Tuareg villages. Overall, these findings support the scenario of an arrival of haplogroup H1 in North Africa from Iberia at the beginning of the Holocene, as a consequence of the improvement in climate conditions after the Younger Dryas cold snap, followed by in situ formation of local H1 sub-haplogroups. This process of autochthonous differentiation continues in the Libyan Tuareg who, probably due to isolation and recent founder events, are characterized by village-specific maternal mtDNA lineages.

  12. Late Wisconsin and early holocene glacial history, inner Ross Embayment, Antarctica

    Science.gov (United States)

    Denton, George H.; Bockheim, James G.; Wilson, Scott C.; Stuiver, Minze

    1991-01-01

    Lateral drift sheets of outlet glaciers that pass through the Transantarctic Mountains constrain past changes of the huge Ross ice drainage system of the Antarctic Ice Sheet. Drift stratigraphy suggests correlation of Reedy III (Reedy Glacier), Beardmore, Britannia (Hatherton/Darwin Glaciers), Ross Sea (McMurdo Sound), and younger (Terra Nova Bay) drifts; radiocarbon dates place the outer limits of Ross Sea drift in late Wisconsin time at 24,000 to 13,000 yr B.P. Outlet glacier profiles from these drifts constrain late Wisconsin ice sheet surface elevations. Within these constraint, two extreme late Wisconsin reconstructions are given of the Ross ice drainage system. Both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner Ross Embayment. However, in the central Ross Embayment, one reconstruction shows floating shelf ice, where as the other shows a grounded ice sheet. Massive late Wisconsin/Holocene recession of grounded ice from the western Ross Embayment, which was underway at 13,040 yr B.P. and completed by 6600 to 6020 yr B.P., was accompanied by little change in plateau ice levels inland of the Transantarctic Mountains.

  13. Climate impact on the Trzechowskie paleolake ecosystem during the Late Glacial and early Holocene in the light of multiproxy analysis

    Science.gov (United States)

    Słowiński, M.; Zawiska, I.; Noryśkiewicz, A. M.; Apolinarska, K.; Lutyńska, M.; Skubała, P.; Ott, F.; Wulf, S.; Brauer, A.

    2012-04-01

    The aim of the research was to reconstruct climate fluctuations during LG and early Holocene and their influence on the development of Trzechowskie paleolake. The paleolake is located in the eastern part of the Pomeranian Lakeland northern Poland (Tuchola Pinewoods). Its genesis is associated with the melting of a buried ice block. Trzechowskie paleolake is about 1.5 km long and the average width is 450 m (area ~ 28 ha). In our research we focused on the bottom sediments and multiproxy high resolution analysis were carryied out. We were able to reconstract local environment changes (plant and animal macrofossils, Cladocera, Diatom, Oribatidae mite, δ13C stable isotope, LOI, carbonate content - CaCO3), and the regional changes (pollen analysis and δ18O stable isotope). The chronology was based on palynological analysis, but also on the age-depth model, developed from five radiocarbon dates AMS14C. It clearly shows that the biogenic accumulation in the Trzechowskie paleolake started during Bølling-Allerød warmer period. The preliminary results of all analysis indicate that climate was the main factor responsible for Trzechowskie paleolake development during LG and early Holocane period. The environmental changes influenced sediment formation process and are marked in the lithology and chemistry but also had a strong effect on water plants, fito and zooplankton.

  14. Rapid and punctuated Late Holocene recession of Siling Co, central Tibet

    Science.gov (United States)

    Shi, Xuhua; Kirby, Eric; Furlong, Kevin P.; Meng, Kai; Robinson, Ruth; Lu, Haijian; Wang, Erchie

    2017-09-01

    Variations in the strength of the Asian monsoon during Holocene time are thought to have been associated with widespread changes in precipitation across much of Tibet. Local records of monsoon strength from cave deposits, ice cores, and lake sediments typically rely on proxy data that relate isotopic variations to changes in precipitation. Lake expansion and contraction in response to changing water balance are likewise inferred from sedimentologic, isotopic and paleobiologic proxies, but relatively few direct records of changes in lake volume from preserved shorelines exist. Here we utilize relict shoreline deposits and associated alluvial fan features around Siling Co, the largest lake in central Tibet, to reconstruct centennial-to-millennial-scale variations in lake area and volume over the Holocene. Mapping and surveying of lacustrine shorelines coupled with optically stimulated luminescence dating of associated deposits indicate protracted occupation of a highstand elevation from >8 ka to 4 ka, followed by rapid recession that was likely punctuated by several stillstands of centennial-scale duration. Calculation of the changes in lake surface area and past hydrologic indices of the Siling Co basin suggests the effective moisture during the early Holocene highstand was approximately three times greater than today. In contrast to other lakes in central and western Tibet, our results suggest that Siling Co did not begin to recede synchronously with decreasing solar insolation at ca. 9-8 ka. Rather, initial recession of Siling Co appears to correspond to a time period of enhanced aridity and weakened monsoon in both Africa and Asia at ca. 4.2 ka. Our results add to a growing body of literature that suggest a period of relatively severe aridity on the Tibetan Plateau at this time. We suggest that subsequent punctuated recession of Siling Co was punctuated by similar periods of abrupt climate change during the Late Holocene.

  15. Pottery use by early Holocene hunter-gatherers of the Korean peninsula closely linked with the exploitation of marine resources

    Science.gov (United States)

    Shoda, Shinya; Lucquin, Alexandre; Ahn, Jae-ho; Hwang, Chul-joo; Craig, Oliver E.

    2017-08-01

    The earliest pottery on the Korean peninsula dates to the early Holocene, notably later than other regions of East Asia, such as Japan, the Russian Far East and Southern China. To shed light on the function of such early Korean pottery and to understand the motivations for its adoption, organic residue analysis was conducted on pottery sherds and adhered surface deposit on the wall of pottery vessels (foodcrusts) excavated from the Sejuk shell midden (7.7-6.8ka calBP) on the southeastern coast and the Jukbyeon-ri site (7.9-6.9ka calBP) on the eastern coast of the Korean peninsula, that represents the earliest pottery assemblages with reliable radiocarbon dates. Through chemical and isotopic residue analysis, we conclude that the use of pottery at these sites was oriented towards marine resources, supported by lipid biomarkers typical of aquatic organisms and stable carbon isotope values that matched authentic marine reference fats. The findings contrast with other archaeological evidence, which shows that a wider range of available food resources were exploited. Therefore, we conclude pottery was used selectively for processing aquatic organisms perhaps including the rendering of aquatic oils for storage. Early pottery use in Korea is broadly similar to other prehistoric temperate hunter-gatherers, such as in Japan, northern Europe and northern America. However, it is also notable that elaborately decorated red burnished pottery excavated from isolated location at the Jukbyeon-ri site had a different usage pattern, which indicates that division of pottery use by vessel form was established even at this early stage.

  16. The impact of early Holocene Arctic Shelf flooding on climate in an atmosphere–ocean–sea–ice model

    Directory of Open Access Journals (Sweden)

    M. Blaschek

    2013-07-01

    Full Text Available Glacial terminations are characterized by a strong rise in sea level related to melting ice sheets. This rise in sea level is not uniform all over the world, because regional effects (uplift and subsidence of coastal zones are superimposed on global trends. During the early Holocene the Siberian Shelf became flooded before 7.5 ka BP and the coastline reached modern-day high stands at 5 ka BP. This area is currently known as a sea–ice production area and contributes significantly to the sea–ice exported from the Arctic through the Fram Strait. This leads to the following hypothesis: during times of rising sea levels, shelves become flooded, increasing sea–ice production on these shelves, increasing sea–ice volume and export through Fram Strait and causing the sea–ice extent to advance in the Nordic Seas, yielding cooler and fresher sea surface conditions. We have tested this hypothesis in an ocean–sea–ice–atmosphere coupled model of intermediate complexity (LOVECLIM. Our results of an early Holocene Siberian Shelf flooding show that in our model the Northern Hemisphere sea–ice production is increased (15% and that the Northern Hemisphere sea–ice extent increases (14% contrary to our hypothesis with lower sea–ice export through Fram Strait (−15%. The reason of this unexpected behaviour has its origin in a weakened polar vortex, induced by the land-ocean changes due to the shelf flooding, and a resulting decrease of zonality in the Nordic Seas pressure regime. Hence the winter Greenland high and the Icelandic low strengthen, yielding stronger winds on both sides of the Nordic Seas. Increased winds along the East Greenland Current support local sea–ice production and transport towards the south, resulting in a wider sea–ice cover and a southward shift of convection areas. The overall strength of the Atlantic Meridional Overturning Circulation is reduced by 4% and the heat transport in the Atlantic basin by 7%, resulting

  17. The impact of early Holocene Arctic shelf flooding on climate in an atmosphere-ocean-sea-ice model

    Science.gov (United States)

    Blaschek, M.; Renssen, H.

    2013-11-01

    Glacial terminations are characterized by a strong rise in sea level related to melting ice sheets. This rise in sea level is not uniform all over the world, because regional effects (uplift and subsidence of coastal zones) are superimposed on global trends. During the early Holocene the Siberian Shelf became flooded before 7.5 ka BP and the coastline reached modern-day high stands at 5 ka BP. This area is currently known as a sea-ice production area and contributes significantly to the sea-ice exported from the Arctic through the Fram Strait. This leads to the following hypothesis: during times of rising sea levels, shelves become flooded, increasing sea-ice production on these shelves, increasing sea-ice volume and export through the Fram Strait and causing the sea-ice extent to advance in the Nordic Seas, yielding cooler and fresher sea surface conditions. We have tested this hypothesis in an atmosphere-ocean-sea-ice coupled model of intermediate complexity (LOVECLIM). Our experiment on early Holocene Siberian Shelf flooding shows that in our model sea-ice production in the Northern Hemisphere increases (15%) and that sea-ice extent in the Northern Hemisphere increases (14%) but sea-ice export decreases (-15%) contrary to our hypothesis. The reason of this unexpected behaviour has its origin in a weakened polar vortex, induced by the land-ocean changes due to the shelf flooding, and a resulting decrease of zonality in the Nordic Seas pressure regime. Hence the winter Greenland high and the Icelandic low strengthen, yielding stronger winds on both sides of the Nordic Seas. Increased winds along the East Greenland Current support local sea-ice production and transport towards the South, resulting in a wider sea-ice cover and a southward shift of convection areas. The overall strength of the Atlantic meridional overturning circulation is reduced by 4% and the heat transport in the Atlantic basin by 7%, resulting in an annual cooling pattern over the Nordic Seas by

  18. Climate and vegetation changes during the Lateglacial and Early-Mid Holocene at Lake Ledro (southern Alps, Italy

    Directory of Open Access Journals (Sweden)

    S. Joannin

    2012-11-01

    Full Text Available Adding to the on-going debate regarding vegetation recolonisation in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081 from Lake Ledro (652 m a.s.l., southern Alps, Italy. Environmental changes that where reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake-levels, magnetic susceptibility and X-ray fluorescence (XRF measurements recorded climate and land-use changes during the Lateglacial and Early-Mid Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of distribution tree species. An altitude-dependent progressive time-delay of the first continuous occurrence of Abies (fir and of the Larix (larch development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills in northern Italy. Preboreal oscillations (ca. 11 000 cal. BP, Boreal oscillations (ca. 10 200, 9300 cal. BP and n.e. 8.2 kyr cold event suggest a centennial-scale short-lasting climate forcing in the studied area. Picea (spruce expansion occurred preferentially around 10 200 cal. BP and 8200 cal. BP in the south-eastern Alps and, therefore, reflects the long-lasting cumulative effects of successive boreal and 8.2 kyr cold events. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200–7300 cal. BP evidenced in high lake-levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal. BP, low signal of pollen-based anthropogenic activities suggest a weak human impact. The period between ca. 5700 and ca. 4100 cal. BP is considered as a transition period to colder and wetter conditions

  19. New insights into broad spectrum communities of the Early Holocene Near East: The birds of Hallan Çemi

    Science.gov (United States)

    Zeder, Melinda A.; Spitzer, Megan D.

    2016-11-01

    The Early Holocene in Near East was a pivotal transitional period that witnessed dramatic changes in climate and environment, human settlement, major changes in subsistence strategies focusing on a broad range of different plant and animal resources, and a radical restructuring of social relations. The remarkable corpus of avifauna from the Early Holocene site of Hallan Çemi in southeastern Turkey sheds new light on key issues about this dynamic period that has been termed the ;Broad Spectrum Revolution;. The avifauna from this important site demonstrate how Hallan Çemi occupants took advantage of the site's strategic location at the junction of multiple environmental zones by extracting a diverse range of seasonally available resources from both near-by and more distant eco-zones to cobble together a stable subsistence economy capable of supporting this small community throughout the year. They give testimony to the impacts of resource utilization over time, especially on species unable to rebound from sustained human hunting. At the same time, they show how Hallan Çemi residents mitigated these impacts by replacing depleted resources with alternative, more resilient ones that could be more sustainably harvested. They open a window onto the growing investment in feasting and ritual activity that helped bind this community together. In so doing they provide a means of empirically evaluating the efficacy of contrasting explanatory frameworks for the Broad Spectrum Revolution that gave rise to the subsequent domestication of plant and animals in the Near East. Contrary to frameworks that cast these developments as responses to resource depression, lessons learned from the Hallan Çemi avifauna lend support to frameworks that emphasize the human capacity to strategically target, capitalize, and improve upon circumscribed resource rich environments in a way that permits more permanent occupation of these niches. And they underscore the degree to which social and

  20. Climate and vegetation changes during the Lateglacial and early-middle Holocene at Lake Ledro (southern Alps, Italy)

    Science.gov (United States)

    Joannin, S.; Vannière, B.; Galop, D.; Peyron, O.; Haas, J. N.; Gilli, A.; Chapron, E.; Wirth, S. B.; Anselmetti, F.; Desmet, M.; Magny, M.

    2013-04-01

    Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652 m a.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early-middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitude-dependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200-7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that

  1. Climate and vegetation changes during the Lateglacial and Early-Mid Holocene at Lake Ledro (southern Alps, Italy)

    Science.gov (United States)

    Joannin, S.; Vannière, B.; Galop, D.; Peyron, O.; Haas, J.-N.; Gilli, A.; Chapron, E.; Wirth, S. B.; Anselmetti, F.; Desmet, M.; Magny, M.

    2012-11-01

    Adding to the on-going debate regarding vegetation recolonisation in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652 m a.s.l., southern Alps, Italy). Environmental changes that where reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake-levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and Early-Mid Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of distribution tree species. An altitude-dependent progressive time-delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal. BP), Boreal oscillations (ca. 10 200, 9300 cal. BP) and n.e. 8.2 kyr cold event suggest a centennial-scale short-lasting climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 cal. BP and 8200 cal. BP in the south-eastern Alps and, therefore, reflects the long-lasting cumulative effects of successive boreal and 8.2 kyr cold events. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200-7300 cal. BP evidenced in high lake-levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal. BP, low signal of pollen-based anthropogenic activities suggest a weak human impact. The period between ca. 5700 and ca. 4100 cal. BP is considered as a transition period to colder and wetter conditions (particularly during summers) that

  2. Early Holocene estuary development of the Hesselø Bay area, southern Kattegat, Denmark and its implication for Ancylus Lake drainage

    Science.gov (United States)

    Bendixen, Carina; Boldreel, Lars Ole; Jensen, Jørn Bo; Bennike, Ole; Hübscher, Christian; Clausen, Ole Rønø

    2017-06-01

    High-resolution shallow seismic data, sediment core information, radiocarbon dating and sequence stratigraphy have been used to interpret the late glacial to early Holocene geological evolution of Hesselø Bay in the southern Kattegat, Denmark. A reconstruction of the early Holocene coastal environment and a description of coastal processes associated with a river outlet into the bay are presented. Weichselian glacial deposits form the lowermost interpreted unit, covered by late glacial (LG) and postglacial (PG, Holocene) sediments. A funnel-shaped estuary existed at the mouth of channels in the period 10.3-9.2 cal. ka BP; the channels drained water from south to north. The early PG is characterised by estuarine and coastal deposits. The early Holocene bars that developed in the estuary are preserved as morphological features on the present-day seabed, possibly as a result of rapid relative sea-level rise. The estuary existed simultaneously with the occurrence and drainage of the Ancylus Lake. The drainage of this lake occurred through the Dana River (palaeo-Great Belt channel) into the southern Kattegat and then into the study area. The level of the Ancylus Lake in the Baltic Sea region dropped significantly at about 10.2 cal. ka BP at the same time as the estuary developed in the Kattegat region. One outcome of the present study is an enhanced understanding of the Ancylus Lake drainage path. No evidence of major erosion is seen, which indicates non-catastrophic continuous water flow from the south without major drainage events of the Ancylus Lake to the southern Kattegat. During the Littorina transgression, coastal estuarine conditions characterized the Hesselø Bay area where elongated ridges formed a bar system. As the Littorina transgression continued, back-stepping of the bar system and coastline occurred. When the transgression breached the Great Belt threshold, flooding caused major erosion throughout the study area.

  3. Holocene moisture changes in western China, Central Asia, inferred from stalagmites

    Science.gov (United States)

    Cai, Yanjun; Chiang, John C. H.; Breitenbach, Sebastian F. M.; Tan, Liangcheng; Cheng, Hai; Edwards, R. Lawrence; An, Zhisheng

    2017-02-01

    Central Asia lies at the convergence between the Mediterranean and Asian monsoon climates, and there is a complex interaction between the westerlies with the monsoon to form the climate of that region and its variability. The region is highly vulnerable to changes in rainfall, highlighting the need to understand the underlying controls. We present a stalagmite-based δ18O record from Kesang Cave in western China, using MC-ICP-MS U-series dating and stable isotope analysis. Stalagmite calcite δ18O largely documents changes in the δ18O of precipitation. δ18O in stalagmites was low during the early and middle Holocene (10.0-3.0 ka BP), and shifted to higher values between 3.0 and 2.0 ka BP. After 2.0 ka BP, δ18O fluctuates with distinct centennial-scale variations. Drawing from results of state-of-the-art atmospheric general circulation model simulations for the preindustrial period and 9 ka BP, we propose that changes in moisture source regions and the wetter climate both contributed to the isotopic depletion of precipitation during the early and middle Holocene. Multiple records from surrounding regions indicate a generally wetter climate during the early and mid- Holocene, supporting our interpretation on the speleothem δ18O. Changes in precipitation seasonality do not appear to be a viable explanation for the observed changes, nor increased penetration of monsoonal moisture to the study site. We speculate that the climatic regime shifted around 3.0-2.0 ka BP towards a drier climate, resulting in temperature having dominant control on precipitation δ18O. The demise of three settlements around 500AD at the margin of Tarim Basin coincided with a period of decreased precipitation and increased temperature that likely affected local water resources, underscoring the potential impact of climate on human habitation in this region.

  4. Impact of the quasi-biweekly oscillation over the western North Pacific on East Asian subtropical monsoon during early summer

    Science.gov (United States)

    Jia, Xiaolong; Yang, Song

    2013-05-01

    The impact of quasi-biweekly oscillation (QBWO) over the western North Pacific on East Asian summer monsoon (EASM) is investigated. The life cycle of QBWO is divided into eight phases defined by the two leading principal components (PC1 and PC2) of an empirical orthogonal function analysis. Subtropical rainfall shows significant changes, with a northwestward propagation of convection from equatorial regions to the South China Sea (SCS). The most significant variations occur in QBWO phases 3 and 4 (enhanced convection over SCS) and phases 7 and 8 (reduced convection over SCS). The East Asia Mei-yu significantly decreases in QBWO phases 3 and 4 but increases in phases 7 and 8. The QBWO influences EASM through modulating the subtropical monsoon flow and extratropical circulation. The response of lower tropospheric atmosphere to QBWO shows a northwestward propagation and a downstream wave train that extends northward into the western North Pacific, modulating the SCS monsoon trough and the EASM flow associated with moisture transportation. The mid-tropospheric extratropical circulation and the western Pacific subtropical high also show obvious changes accompanying QBWO evolution, resulting in circulation patterns associated with cold air activity. Moreover, changes with QBWO are found in the upper tropospheric East Asian westerly jet stream and the South Asian high, and these changes contribute to upper level divergence over subtropical East Asia.

  5. North Atlantic and orbital controls on North American Monsoon rainfall for the past 25,000 years

    Science.gov (United States)

    Lachniet, M. S.; Bernal-Uruchurtu, J. P.; Asmerom, Y.; Polyak, V.; Vazquez-Selem, L.

    2011-12-01

    The paleoclimate controls on Mexican rainfall remain poorly understood, making it difficult to test hypotheses of late Quaternary climate changes in the North American Monsoon region. A high-resolution and chronologically robust integrative paleoclimate history for central and southwestern Mexico is required to evaluate the climate context associated with the late glacial peopling of Mesoamerica, the Holocene domestication of maize, and climate's influence on several advanced pre-Colombian civilizations. Herein, we combine new and previously published precipitation- and temperature-sensitive proxy records to delineate the paleoclimatic history of the "Mesoamerican Monsoon" region since ca. 25,000 yr BP, from stalagmite, glacial, and lacustrine paleoclimatic data. Our results demonstrate a wet last glacial maximum (23 to 18 ka) in southwestern Mexico at 17.4 degrees N, a region that today is outside the influence of nortes or the westerlies. Wet conditions may be attributed to a moderately strong summer monsoon due to near-modern summer insolation values and a cooler eastern tropical Pacific Ocean akin to a modern La Niña-like state. We also document Heinrich stadial 1 and Younger Dryas monsoon weakening coincident with reduced North Atlantic thermohaline circulation, which implicates reduced onshore moisture flux due to a weaker and more southerly position of the Intertropical Convergence Zone. Mesoamerican rainfall was greatest during the early Holocene, and decreased non-linearly to the present in concert with decreasing local summer insolation. Following a relative mid-Holocene wet period, the last 4.5 ka are characterized by increasingly dry conditions, likely related to decreasing summer insolation and a greater El Niño frequency.

  6. Sulfur Geochemistry of a Lacustrine Record from Taiwan Reveals Enhanced Marine Aerosol Input during the Early Holocene.

    Science.gov (United States)

    Ding, Xiaodong; Li, Dawei; Zheng, Liwei; Bao, Hongyan; Chen, Huei-Fen; Kao, Shuh-Ji

    2016-12-12

    Lacustrine record of marine aerosol input has rarely been documented. Here, we present the sulfur geochemistry during the last deglaciation and early Holocene of a sediment core retrieved from the Dongyuan Lake in southern Taiwan. An unusually high sulfur peak accompanying pyrite presence is observed at 10.5 ka BP. Such high sulfur content in lacustrine record is unusual. The δ(34)S of sulfur varied from +9.5 to + 17.1‰ with two significant positive shifts at 10.5 and 9.4 ka BP. The sources of sulfur and potential processes involving the sulfur isotope variation including bacterial sulfate reduction, volcanic emissions, in-catchment sulfide oxidation and marine aerosol input are discussed. Enhanced marine aerosol input is the most likely explanation for such sulfur peaks and δ(34)S shifts. The positive δ(34)S shifts appeared concurrently with the maximum landslide events over Taiwan resulted from enhanced typhoon activities. The synchronicity among records suggests that increased typhoon activities promoted sea spray, and consequently enhanced the marine aerosol input with (34)S-enriched sulfate. Our sulfur geochemistry data revealed sea spray history and marine influence onto terrestrial environment at coastal regions. Wider coverage of spatial-temporal lacustrine sulfur geochemistry record is needed to validate the applicability of sulfur proxy in paleoenvironmental research.

  7. Coastal glaciers advanced onto Jameson Land, East Greenland during the late glacial–early Holocene Milne Land Stade

    Directory of Open Access Journals (Sweden)

    Helena Alexanderson

    2014-01-01

    Full Text Available We report on 10Be and optically stimulated luminescence ages from moraines and glaciolacustrine sediments on eastern Jameson Land, East Greenland. Sampled landforms and sediment are associated with advances of outlet glaciers from the local Liverpool Land ice cap situated in the coastal Scoresby Sund region. Previous studies have tentatively correlated these advances with the Milne Land Stade moraines, which are prominent moraine sets deposited by mountain glaciers in the inner Scoresby Sund region. Recent constraints on the formation of the outer and inner of these moraines have suggested two advances of local glaciers, one prior to or during the Younger Dryas and another during the Preboreal. In this paper, we test the correlation of the Liverpool Land glacial advance with the Milne Land Stade. Our results show that outlet glaciers from the Liverpool Land ice cap reached ice-marginal positions marked by moraines in east-facing valleys on Jameson Land sometime during late glacial–early Holocene time (ca. 13–11 Kya. This confirms the correlation of these moraines with the Milne Land Stade moraines described elsewhere in the Scoresby Sund region.

  8. Sulfur Geochemistry of a Lacustrine Record from Taiwan Reveals Enhanced Marine Aerosol Input during the Early Holocene

    Science.gov (United States)

    Ding, Xiaodong; Li, Dawei; Zheng, Liwei; Bao, Hongyan; Chen, Huei-Fen; Kao, Shuh-Ji

    2016-12-01

    Lacustrine record of marine aerosol input has rarely been documented. Here, we present the sulfur geochemistry during the last deglaciation and early Holocene of a sediment core retrieved from the Dongyuan Lake in southern Taiwan. An unusually high sulfur peak accompanying pyrite presence is observed at 10.5 ka BP. Such high sulfur content in lacustrine record is unusual. The δ34S of sulfur varied from +9.5 to + 17.1‰ with two significant positive shifts at 10.5 and 9.4 ka BP. The sources of sulfur and potential processes involving the sulfur isotope variation including bacterial sulfate reduction, volcanic emissions, in-catchment sulfide oxidation and marine aerosol input are discussed. Enhanced marine aerosol input is the most likely explanation for such sulfur peaks and δ34S shifts. The positive δ34S shifts appeared concurrently with the maximum landslide events over Taiwan resulted from enhanced typhoon activities. The synchronicity among records suggests that increased typhoon activities promoted sea spray, and consequently enhanced the marine aerosol input with 34S-enriched sulfate. Our sulfur geochemistry data revealed sea spray history and marine influence onto terrestrial environment at coastal regions. Wider coverage of spatial-temporal lacustrine sulfur geochemistry record is needed to validate the applicability of sulfur proxy in paleoenvironmental research.

  9. The environmental signal of an early Holocene pollen record from the Shiyang River basin lake sediments, NW China

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Pollen analyses of 85 samples from the Sanjiaocheng section well along the margin of a palaeolake at the end of the Shiyang River, NW China, show that Picea and Sabina dominate the pollen assemblage. Together they reach as high as 40%-60%, with the percentage of Picea varying inversely with that of Sabina. Similar results were obtained from another section in the Shiyang River drainage.Using modern ecological habitat relationship analogues, pollen transport characteristics, and the overall pollen assemblage, we propose that both Picea and Sabina pollen were transported by the river from the mountains at the upper reaches of the Shiyang River, and that the assemblage is more indicative of changes in upland vegetation than of local conditions near the section. This interpretation is supported by pollen data derived from surface samples, water samples,and riverbed samples. Using a moisture indicator (the Picea to Sabina ratio) and calculated pollen concentrations, we identify a series of palaeoenvironmental changes during the early Holocene (10 6.3 14C kaBP).

  10. Environmental changes and human settlement in the central Marches (Italy during the early-middle Holocene

    Directory of Open Access Journals (Sweden)

    Gilberto Calderoni

    2007-12-01

    Full Text Available In the Early Holocene, the central Marches (Italy underwent a widespread development of forest cover and soils which drastically reduced slope degradation and related aggradation processes in riverbeds. In such conditions, streams deeply incised the previous alluvial sediments. In the Apennine sectors, linear erosion was locally prevented by the growth of travertine dams in correspondence with river channel knickpoints and waterfalls. Fluvial deposition prevailed in the peri-Adriatic hilly belt, where river valleys still extended from the present coastline to the uprising Adriatic Sea, as testified by a 50-m-deep cored log, drilled near the Potenza River mouth. Several archaeological sites, ranging from the Mesolithic to the Aeneolithic, testify the recurrent presence of small-scale human groups on the alluvial plains of the lower valley sectors. Sandy-clayey sediments, emplaced by flooding episodes, repeatedly buried these settlements which were commonly located on the riversides. Small Aeneolithic communities were also present in the mountain sectors, around travertine-dammed swampy-lacustrine basins. On top of the sequences, Bronze Age sites were locally found. Widespread deforestation started in the early Iron Age (about 3000 yr BP, when alluvial plains and terraces were permanently occupied by large-scale human settlements. Geo-archaeological evidence of systematic deforestation at 2950 ± 50 14C yr BP, consisting of numerous round-shaped 1.5-3 m wide hollows, filled with soil sediments and upturned blocks of alluvial gravels, were found on top of a fluvial terrace in the Esino River basin. From the Iron Age to recent historical times, notwithstanding the progressive increase of debris supply to the drainage systems due to the spreading agricultural-pastoral activities, erosion dominated almost everywhere in the Marches rivers, likely induced by climatic factors.À l’Holocène inférieur, comme ailleurs dans le monde, les Marches

  11. Holocene aeolian sediments on the NE Tibetan Plateau

    Science.gov (United States)

    Stauch, G.; Lehmkuhl, F.; Hilgers, A.; Zhao, H.

    2012-04-01

    The semiarid climate of the northeastern Tibetan Plateau supports the formation of different types of aeolian sediments and landforms during the Holocene. Aeolians silts and sands in the catchment of the Donggi Cona in an elevation above 4000m to 4800 m asl reflect variable climate conditions during that time as well as different sediment sources. Based on 51 OSL datings and catchment wide geomorphological mapping a complex pattern of long and short distance sediment transport has been reconstructed. Only few aeolian archives are preserved from the late Pleistocene in this mountain environment indicating cold and dry climate conditions which prevented a continuous accumulation. During the early Holocene a phase of increased aeolian sedimentation of sand at the slopes of the mountains has been reconstructed. The sand originated from a large alluvial fan which was highly active during the Pleistocene. In addition, a thin loess cover is preserved at a few sites in the neighboring mountains ranges. The sedimentation of the loess started around 2000 years later than the sedimentation of the sand at the foot slope. Both archives are related to an increase in precipitation at the northern margin of the Tibetan Plateau which was related to a strengthening of the Asian Monsoon during that time. The wetter climate conditions favored the development of a vegetation cover which leads to the trapping and fixation of the aeolian sediments. However, with a further strengthening of the Monsoon systems these archives subsequently eroded due to higher run off and accumulated as colluvial and fluvial deposits in the basins. These phase lasted until 6 ka. A second aeolian period started at around 3 ka with the formation new dunes in the basins. This period can be associated with dry and cold climate of the late Holocene supporting the reactivation of the sand in the area. This might be further enhanced by an increased human impact by grazing during the late Holocene and resulting

  12. Late Würm and Early-Middle Holocene Environmental Change and Human Activities in the Northern Apennines, Italy

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    Nicholas P. Branch

    2015-12-01

    Full Text Available An enhanced radiocarbon-dated pollen-stratigraphical record from Rovegno (Liguria, 812m asl, northern Apennines (Italy, has provided a history of vegetation succession from before 17,056-16,621 cal yrs BP to the present day. The record indicates the transition from open Pinus woodland to Artemisia dominated grassland, and fi nally Juniperus shrubland during the late Würm. This is succeeded by Betula and Pinus woodland, and the expansion of thermophilous taxa, namely Abies, Corylus and Quercus during the Late Würm Lateglacial Interstadial. The ‘Younger Dryas’ is possibly represented by an increase in Betula and Artemisia. During the early Holocene, mixed coniferous-deciduous woodland is dominant with Quercus, as well as Abies, Fagus and Corylus. Fagus woodland becomes established sometime before 6488-6318 cal yrs BP, but never becomes a major component of the woodland cover. Throughout the middle Holocene, Abies woodland fl uctuates, with marked declines between 6488-6318 cal yrs BP and 5287-4835 cal yrs BP, although the cause remains uncertain. Finally, the paper evaluates the application of non-pollen palynomorphs, especially coprophilous fungal spores, at Prato Spilla ‘A’ (Emilia Romagna and concludes that greater caution must be used when interpreting middle Holocene human activity based upon pollen data alone. Una migliore risoluzione cronologica basata su date radiocarboniche per una sequenza pollinica da Rovegno (812 m asl, Appennino settentrionale ligure, Italia, ha permesso di ricostruire i cambiamenti vegetazionali per un periodo compreso da prima di 17,056-16,621 anni cal BP ad oggi. La sequenza mostra il passaggio da un bosco a Pinus con struttura aperta ad una prateria dominata da Artemisia, ed infine un arbusteto a Juniperus nel tardo Würm. Successivamente si sviluppa un bosco a Pinus e Betula, e verso la fine dell’ultimo interstadiale würmiano ha luogo l’espansione di taxa termofili quali Abies, Corylus e Quercus

  13. CHANGES IN EAST ASIAN SUMMER MONSOON DURING THE HOLOCENE RECORDED BY STALAGMITE δ18O RECORDS FROM LIAONING PROVINCE%全新世东亚夏季风演化的辽宁暖和洞石笋δ18O记录

    Institute of Scientific and Technical Information of China (English)

    吴江滢; 汪永进; 董进国

    2011-01-01

    were conducted by Finnigan MAT 262-PRQ type meter at the Isotope Laboratory of Geology and Geophysics Department, Minnesota University,USA. The reported error is in ±2σ.The stalagmite δ180 record, ranging from -7. 96%o to -10. 19%o, indicates that the EASM experienced three stages; ( 1 ) an interval of relative strong summer monsoon intensity is observed between 10.5kaB. P. And 5. 5kaB. P. With δ18O values averaging -9. 2%o,among which the EASM intensity reaches its maximum level from 9. OkaB. P. To 5. 5kaB. P. ; (2) a long-term gradual decrease in monsoon intensity starting at 5. 5kaB. P. Is indicated by a slow shift in δ18O from -9. 6%o at 5. 5kaB. P. To about -8. 0%o at 1. OkaB. P. ; and (3) there is a slow increase in monsoon intensity from 1. OkaB. P. To 0. 3kaB. P. .indicated by decreasing δ18O values from -8. L%o to -8. 8%o. Comparison of our record with other stalagmite records from Oman, Guizhou, Hubei at different latitudes reveals that there is no time-transgressive character of Holocene Optimum. The timing of the onset and termination of the Holocene Optimum was similar in Asian monsoon areas; monsoon intensity declined at 5. 5kaB. P. Indicates the end of the Holocene Optimum. It means the Indian and East Asian monsoon sub-systems changed in phase on orbital scale. The stalagmite δ18O record from Nuanhe Cave generally tracks insolation changes at 65°N latitude on orbital timescales, yet exhibits similar variability to Ti concentration record from Cariaco Basin on trend (r = 0. 67 ). This supports that shifts in the mean position of the Intertropical Convergence Zone (ITCZ) may control monsoon intensity throughout the entire low-latitude region of Asia on orbital timescales. A general consistence of the Holocene monsoon changes in Asia and Africa supports the idea that various monsoon systems could be integrated into a global system under the control of solar radiation and earth boundary conditions.%研究区隶属于典型的东亚季风区

  14. Sensitivity of Holocene atmospheric CO2 and the modern carbon budget to early human land use: analyses with a process-based model

    Directory of Open Access Journals (Sweden)

    F. Joos

    2011-01-01

    Full Text Available A Dynamic Global Vegetation model coupled to a simplified Earth system model is used to simulate the impact of anthropogenic land cover changes (ALCC on Holocene atmospheric CO2 and the contemporary carbon cycle. The model results suggest that early agricultural activities cannot explain the mid to late Holocene CO2 rise of 20 ppm measured on ice cores and that proposed upward revisions of Holocene ALCC imply a smaller contemporary terrestrial carbon sink. A set of illustrative scenarios is applied to test the robustness of these conclusions and to address the large discrepancies between published ALCC reconstructions. Simulated changes in atmospheric CO2 due to ALCC are less than 1 ppm before 1000 AD and 30 ppm at 2004 AD when the HYDE 3.1 ALCC reconstruction is prescribed for the past 12 000 years. Cumulative emissions of 69 GtC at 1850 and 233 GtC at 2004 AD are comparable to earlier estimates. CO2 changes due to ALCC exceed the simulated natural interannual variability only after 1000 AD. To consider evidence that land area used per person was higher before than during early industrialisation, agricultural areas from HYDE 3.1 were increased by a factor of two prior to 1700 AD (scenario H2. For the H2 scenario, the contemporary terrestrial carbon sink required to close the atmospheric CO2 budget is reduced by 0.5 GtC yr−1. Simulated CO2 remains small even in scenarios where average land use per person is increased beyond the range of published estimates. Even extreme assumptions for preindustrial land conversion and high per-capita land use do not result in simulated CO2 emissions that are sufficient to explain the magnitude and the timing of the late Holocene CO2 increase.

  15. Monsoon extremes and society over the past millennium on mainland Southeast Asia

    Science.gov (United States)

    Buckley, Brendan M.; Fletcher, Roland; Wang, Shi-Yu Simon; Zottoli, Brian; Pottier, Christophe

    2014-07-01

    The early 21st century has seen vigorous scientific interest in the Asian monsoon and significant development of paleo-proxies of monsoon strength. These include the Monsoon Asian Drought Atlas - a 700-year, gridded reconstruction of hydroclimate derived from 327 tree ring records - and several long speleothem records from China and India. Similar progress has been made on the study of monsoon climate dynamics through re-analysis data products and General Circulation Model diagnostics. The story has emerged of a variable monsoon over the latter Holocene, with extended droughts and anomalously wet episodes that occasionally and profoundly influenced the course of human history. We focus on Southeast Asia where an anomalous period of unstable climate coincided with the demise of the capital of the Khmer Empire at Angkor between the 14th and the 16th centuries, and we suggest that protracted periods of drought and deluge rain events, the latter of which damaged Angkor's extensive water management systems, may have been a significant factor in the subsequent transfer of the political capital away from Angkor. The late 16th and early 17th century experienced climate instability and the collapse of the Ming Dynasty in China under a period of drought, while Tonkin experienced floods and droughts throughout the 17th century. The 18th century was a period of great turmoil across Southeast Asia, when all of the region's polities saw great unrest and rapid realignment during one of the most extended periods of drought of the past millennium. New paleo-proxy records and the incorporation of historical documentation will improve future analyses of the interaction between climate extremes, social behavior and the collapse or disruption of regional societies, a subject of increasing concern given the uncertainties surrounding projections for future climate.

  16. Early Holocenic and Historic mtDNA African Signatures in the Iberian Peninsula: The Andalusian Region as a Paradigm.

    Directory of Open Access Journals (Sweden)

    Candela L Hernández

    Full Text Available Determining the timing, identity and direction of migrations in the Mediterranean Basin, the role of "migratory routes" in and among regions of Africa, Europe and Asia, and the effects of sex-specific behaviors of population movements have important implications for our understanding of the present human genetic diversity. A crucial component of the Mediterranean world is its westernmost region. Clear features of transcontinental ancient contacts between North African and Iberian populations surrounding the maritime region of Gibraltar Strait have been identified from archeological data. The attempt to discern origin and dates of migration between close geographically related regions has been a challenge in the field of uniparental-based population genetics. Mitochondrial DNA (mtDNA studies have been focused on surveying the H1, H3 and V lineages when trying to ascertain north-south migrations, and U6 and L in the opposite direction, assuming that those lineages are good proxies for the ancestry of each side of the Mediterranean. To this end, in the present work we have screened entire mtDNA sequences belonging to U6, M1 and L haplogroups in Andalusians--from Huelva and Granada provinces--and Moroccan Berbers. We present here pioneer data and interpretations on the role of NW Africa and the Iberian Peninsula regarding the time of origin, number of founders and expansion directions of these specific markers. The estimated entrance of the North African U6 lineages into Iberia at 10 ky correlates well with other L African clades, indicating that U6 and some L lineages moved together from Africa to Iberia in the Early Holocene. Still, founder analysis highlights that the high sharing of lineages between North Africa and Iberia results from a complex process continued through time, impairing simplistic interpretations. In particular, our work supports the existence of an ancient, frequently denied, bridge connecting the Maghreb and Andalusia.

  17. Palaeoclimate from glaciers: Examples from the Eastern Alps during the Alpine Lateglacial and early Holocene

    Science.gov (United States)

    Kerschner, Hanns; Ivy-Ochs, Susan

    2008-01-01

    10Be dating of prominent glacier advances (stadials) in the Alps supports the correlation of the Gschnitz stadial (> 15.4 ka) with the Heinrich 1 ice rafting event (Greenland Stadial 2a), the Egesen-maximum advance (˜ 12.3-12.4 ka) with the early Younger Dryas (Greenland Stadial 1), the Kartell advance (˜ 10.8 ka) with the Preboreal Oscillation and the Kromer advance (˜ 8.4 ka) with the Central European cold phase 3. The interpretation of the glacial record with glacier-climate models in terms of summer temperature change (ΔTs) and precipitation change (Δ P) shows that climate during the Gschnitz stadial was ˜ 10 K colder than at present and precipitation was reduced to ˜ 25% of modern annual sums with a possible tendency towards slightly more humid conditions in the southeastern Alps. During the early Younger Dryas, Δ P depends on the estimated ΔTs. For a ΔTs of - 3.5 K, Δ P along the northern fringe of the Eastern Alps was about 0 to + 15%, in the central valleys Δ P was in the order of - 20 to - 30%. A scenario with a ΔTs of - 5 K leads to generally drier conditions (˜ - 15% vs. ˜ - 50% Δ P) but the spatial pattern of precipitation change remains the same. The Kromer advance was possibly characterised by more humid conditions than today along the northern fringe of the Eastern Alps. In the valleys of the Central Alps, precipitation seems to have been similar to modern values. Methodologically, simple empirical relationships between summer temperature and precipitation at the equilibrium line altitude yield similar results as an analytical glacial-meteorological model. However, the analytical model allows a more detailed analysis of the climatic parameters influencing glacier behaviour. In the case of the Egesen-maximum and Kromer advances, the accuracy of Δ P depends on the reliability of ΔTs, which is derived from timberline depression and on the dating control. In the case of the Gschnitz stadial, the accuracy of ΔTs depends mainly on the

  18. What caused G. truncatulinoides to calcify in shallower water during the early Holocene in the western Atlantic / Gulf of Mexico?

    Energy Technology Data Exchange (ETDEWEB)

    Cleroux, Caroline; Lynch-Stieglitz, Jean, E-mail: ccleroux@ldeo.columbia.ed [School of Earth and Environmental Sciences, Georgia Institute of Technology, Atlanta, GA (United States)

    2010-03-15

    In a recent paper we reconstructed the calcification depth of G. truncatulinoides since the last deglaciation in the Florida Straits. We highlighted a significantly different calcification depth between 8-10 ka and the late Holocene. This migration was found in three different cores over the western North Atlantic American continental margin. This paper presents new Mg/Ca ratio data on G. truncatulinoides in the Florida Strait and new stable isotopic measurements on G. crassaformis in the Gulf of Mexico. Preliminary interpretation to understand the cause of G. truncatulinoides migration in the water column at the beginning of the Holocene is given.

  19. Solar forcing of Nile discharge and sapropel S1 formation in the early to middle Holocene eastern Mediterranean

    NARCIS (Netherlands)

    Hennekam, R.|info:eu-repo/dai/nl/357286081; Jilbert, T.|info:eu-repo/dai/nl/304835714; Schnetger, B.; de Lange, G.J.|info:eu-repo/dai/nl/073930962

    2014-01-01

    We present high-resolution records for oxygen isotopes of the planktic foraminifer Globigerinoidesruber (δ18Oruber) and bulk sediment inorganic geochemistry for Holocene-age sediments from the southeastMediterranean. Our δ18Oruberrecord appears to be dominated by Nile discharge rather than basin-sca

  20. Biomarker evidence for increasing aridity in south-central India over the Holocene

    Science.gov (United States)

    Sarkar, S.; Wilkes, H.; Prasad, S.; Brauer, A.; Basavaiah, N.; Strecker, M. R.; Sachse, D.

    2012-12-01

    Summer monsoonal rainfall has played an important role in the development and sustenance of the largely agro-based economy in the Indian subcontinent in the recent past. A better understanding of past variations in monsoonal rainfall can therefore lead to an assessment of its potential impact on early human societies. However, our knowledge of spatiotemporal patterns of past monsoon strength, as inferred from proxy records, is limited due to the lack of high-resolution paleo-hydrological records from continental archives. Here, we reconstruct centennial-scale hydrological variability associated with changes in the intensity of the Indian Summer Monsoon based on a record of lipid biomarker abundances and compound-specific stable isotopic composition of a 10-m-long sediment core from saline-alkaline Lonar Lake, situated in the core 'monsoon zone' of south-central India. We identified three periods of distinct hydrology over the Holocene in south-central India. The period between 10.4 and 6.5 ka BP was characterized by a relatively high abundance of land-plant biomarkers, such as long-chain n-alkanes. The composition of these leaf-wax n-alkanes (weighted average of concentration of different chain-length n-alkanes, expressed as the ACL index) and their negative δ13C (-30‰ to -33 ‰) indicate the dominance of woody C3 vegetation in the catchment, and negative δD (-170‰ to -175‰) values argue for a wet period due to an intensified monsoon. Rapid fluctuations in abundance of both terrestrial and aquatic biomarkers between 6.5 and 4 ka BP indicate an unstable lake ecosystem, culminating in a transition to arid conditions. Higher ACL values and a pronounced shift to more positive δ13C values (up to -22‰) of leaf-wax n-alkanes over this period indicate a change of dominant vegetation to C4 grasses. Along with a 40‰ increase in leaf wax n-alkane δD values, which likely resulted from less rainfall and/or higher plant evapotranspiration, we interpret this period

  1. Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon concept

    Science.gov (United States)

    Beaufort, L.; van der Kaars, S.; Bassinot, F. C.; Moron, V.

    2010-10-01

    Past variations in the dynamics of the Australian monsoon have been estimated from multi-proxy analysis of a core retrieved in the Eastern Banda Sea. Records of coccolith and pollen assemblages, spanning the last 150 000 years, allow reconstruction of past primary production in the Banda Sea, summer moisture availability, and the length of the dry season in northern Australia and southeastern Indonesia. The amount of moisture available during the summer monsoon follows typical glacial/interglacial dynamics with a broad asymmetrical 100-kyr cycle. Primary production and length of the dry season appear to be closely related, given that they follow the precessional cycle with the same phase. This indicates their independence from ice-volume variations. The present inter-annual variability of both parameters is related to El Niño Southern Oscillation (ENSO), which modulates the Australian Winter Monsoon (AWM). The precessional pattern observed in the past dynamics of the AWM is found in ENSO and monsoon records of other regions. A marked shift in the monsoon intensity occurring during the mid Holocene during a period of constant ice volume, suggests that low latitude climatic variation precedes increases in global ice volume. This precessional pattern suggests that a common forcing mechanism underlies low latitude climate dynamics, acting specifically and synchronously on the different monsoon systems.

  2. Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon

    Science.gov (United States)

    Beaufort, L.; van der Kaars, S.; Bassinot, F. C.; Moron, V.

    2010-06-01

    Past variations in the dynamics of the Australian monsoon have been estimated from multi-proxy analysis of a core retrieved in the Eastern Banda Sea. Records of coccolith and pollen assemblages, spanning the last 150,000 years, allow reconstruction of past primary production in the Banda Sea, summer moisture availability, and the length of the dry season in Northern Australia and Southeastern Indonesia. The amount of moisture available during the summer monsoon follows typical glacial/interglacial dynamics with a broad asymmetrical 100-kyr cycle. Primary production and length of the dry season appear to be closely related, given that they follow the precessional cycle with the same phase (August insolation). This indicates their independence from ice-volume variations. The present inter-annual variability of both parameters is related to El Niño Southern Oscillation (ENSO), which modulates the Australian Winter Monsoon (AWM). The precessional pattern observed in the past dynamics of the AWM is found in ENSO and monsoon records of other regions. A marked shift in the monsoon intensity occurring during the mid Holocene during a period of constant ice volume, suggest that low latitude climatic variation precedes global ice volume. This precessional pattern suggests that a common forcing mechanism underlies low latitude climate dynamics, acting specifically and synchronically on the different monsoon systems.

  3. From climate change to diet change - biochemistry investigations on Late Glacial and Early Holocene brown bear remains from caves in the Alpine region

    Science.gov (United States)

    Döppes, Doris; Rosendahl, Wilfried; Pacher, Martina; Bocherens, Hervé

    2010-05-01

    Bones of brown bears from caves in the Alpine region in Germany, Austria, Italy and Switzerland were examined and dated in the last years. The finds originate from the transition from the Bölling/Alleröd to the Early Holocene. In total we analyzed 15 samples from bones and teeth of directly radiocarbon dated brown bears from the alpine region for isotopic analyses. All collagen considered here exhibit carbon and nitrogen content similar to that of collagen extracted from fresh bones, and most of the bones and teeth contained almost the same quantity of collagen than fresh bone (around 25% weight). Atomic C/N ratios range from 3.1 to 3.4, well within the acceptable range (2.9-3.6). The d13C values are rather high during the Late Glacial then a clear decrease is observed at the beginning of the Holocene. This trend coincides with the development of dense forests at low altitudes and the shift of timberline towards higher altitudes. The d15N values are relatively low in Bölling-Alleröd, then quite high during the Younger Dryas, and they decrease again during the Boreal and more recent periods. For the first time a more precise picture of the former habitat of the brown bears during the transition from the Bölling/Alleröd to the Early Holocene in the Alpine region could be reconstructed. The described investigation can also give an outlook of the coexistence of the herbivore cave bears and the omnivore/carnivore brown bears during the late Upper Pleistocene.

  4. Mapping the unseen: geoarchaeological prospection to the Stone Age heritage in the early Holocene delta deposits of the Rotterdam harbor area (the Netherlands)

    Science.gov (United States)

    Vos, Peter

    2013-04-01

    Mapping the unseen: geoarchaeological prospection to the Stone Age heritage in the early Holocene delta deposits of the Rotterdam harbor area (the Netherlands) Peter C. Vos1 & Dimitri Schiltmans2 1) Deltares, PO Box 85467, 3508 AL Utrecht, The Netherlands E-mail: peter.vos@deltares.nl 2) Bureau Oudheidkundig Onderzoek Rotterdam, Ceintuurbaan 213b, 3051 KC Rotterdam, The Netherlands E-mail: dea.schiltmans@Rotterdam.nl The Port of Rotterdam (PoR) is expanding the Rotterdam harbor area into the sea. A new channel, the Yangtze harbor, will be dug out to a depth of 20 m below sea level in order to connect the existing Maasvlakte harbor area with the new harbor area under construction. The upper part of the sediment, which was dredged out in order to create the new channel, consisted mainly of marine offshore sands. In the lower part, at a depth of about 17-22 m below the Dutch Ordnance Datum (NAP), Late Weichselian fluvial and aeolian sands and Early Holocene deltaic deposits of the Rhine - Meuse were present. From earlier dredging activities in the Maasvlakte area it was known that the Late Weichselian / Early Holocene deposits contain Late Paleolithic and Early Mesolithic artefacts. The deepening of the Yangtze harbor would affect the Late-Weichselian / Early Holocene deposits and destroy the archaeologically valuable objects in these layers. The aim of the archaeological Yangtze harbor project was to predict those locations where archaeological heritage from the Stone Age could be found. A geological-geogenetic approach was applied in order to determine the optimal palaeo-environmental locations for man to settle. A 3D palaeolandscape model was constructed of the harbor area; an area which was about 0.5 km wide and 3 km long. Given this palaeolandscape model, the potential archaeological sites were selected. The multidisciplinary prospection research was carried out in several steps. After each research step the strategy of the following research phase was determined

  5. The early Holocene humid period in the Tayma palaeolake, NW Arabian Peninsula -- A high-resolution micro-facies and geochemical approach

    Science.gov (United States)

    Neugebauer, Ina; Plessen, Birgit; Dinies, Michèle; Engel, Max; Tjallingii, Rik; Brauer, Achim

    2016-04-01

    The Tayma palaeolake is a rare archive of the early Holocene humid period in northern Arabia (Dinies et al. 2015; Engel et al. 2012). Here we present a ca. 1 m thick and 500 years spanning annually laminated sediment section that was deposited in the centre of the former lake from ca. 8500 to 8000 calibrated years (cal. yrs) BP, as determined by AMS 14C dating of pollen concentrates (Dinies et al. 2015). High-resolution micro-facies analyses based on thin section microscopy, μXRF element scanning, δ18Ocarb and δ13Ccarb measurements on single carbonate laminae, as well as geochemical measurements on bulk samples for TOC, CaCO3, C/N ratio, δ18Ocarb, δ13Ccarb, δ13Corg and δ15N determination were performed in order to investigate the sedimentological and geochemical changes along the varved sequence in great detail. The finely laminated marl sediments are mainly composed of sub-mm thick laminae of endogenic aragonite, organic matter and diatoms, as well as occasional, often graded silt-clay layers. Following an early lake phase from ca. 8700 to 8500 cal. yrs BP characterized by coarsely laminated, presumably non-annual marl sediments that are rich in ostracods, three main varved phases can be distinguished within the investigated section: (1) aragonitic-organic varves from ca. 8500 to 8300 cal. yrs BP, (2) diatom-organic varves from ca. 8300 to 8100 cal. yrs BP that frequently include aragonite laminae and occasionally gastropod and ostracod shells, and (3) organic varves from ca. 8100 to 8000 cal. yrs BP with decreasing diatom and aragonite laminae and an increasing frequency of gypsum layers. After this period, gypsum becomes abundant and fine lamination appears only sporadically. In addition, we observe increasing trends of TOC, C/N and δ13Ccarb and decreasing δ18Ocarb during phase 1 and excess δ18Ocarb, δ13Ccarb and TOC values during phase 2, pointing towards the maximum lake productivity and increased seasonal precipitation. We interpret this

  6. Lateglacial and Early Holocene vegetation history of the northern Wetterau and the Amöneburger Basin (Hessen), central-west Germany.

    Science.gov (United States)

    Bos, J A.A.

    2001-06-01

    The Lateglacial and Early Holocene vegetation history of the northern Wetterau and Amöneburger Basin, two intra-montane basins in Hessen, central-west Germany, is reconstructed by means of pollen and macrofossil analyses. Regional pollen assemblage zones are defined for the Lateglacial and Early Holocene. After calibration of the radiocarbon dates and establishment of age/depth relationships, the ages of the pollen zone boundaries are calculated. The regional vegetation changes correlate closely with the major fluctuations in the delta18O curve of the Greenland ice cores spanning the same time period. During the early Lateglacial, the open herbaceous vegetation with dwarf shrubs in the northern Wetterau was replaced by woodlands. Initially these woodlands consisted of birch, but after the immigration of pine, mixed forests of pine and birch developed. Soon after its immigration pine became dominant and pine woodlands largely replaced the birch forests. Only on the locally wetter substrates of the river floodplain did Betula stands persist. Gradually the importance of herbaceous communities declined and the pine woodlands lost their open character. During the Lateglacial two regressive phases in the vegetation succession are reflected in the data which are equated with the Older- and Younger Dryas biozones. At the beginning of the Younger Dryas, the forest-limit was lowered and the importance of herbaceous communities increased. Later, pine woodlands thinned and Ericales became part of the vegetation, indicating the development of more acid, nutrient-poor soils. A subdivision of the Younger Dryas biozone into a wetter, colder first part and a drier, warmer second part is suggested. At the beginning of the Early Holocene, pine woodlands became more closed and soils more stabilised. The transition between the Younger Dryas and Preboreal biozones is indicated by a lithological change to organic (-rich) deposits. Betula stands persisted on the locally wetter substrates

  7. Holocene cyclic climatic variations and the role of the Pacific Ocean as recorded in varved sediments from northeastern China

    Science.gov (United States)

    Chu, Guoqiang; Sun, Qing; Xie, Manman; Lin, Yuan; Shang, Wenyu; Zhu, Qingzen; Shan, Yabing; Xu, Deke; Rioual, Patrick; Wang, Luo; Liu, Jiaqi

    2014-10-01

    We present an n-alkane and compound-specific carbon isotope record of the past 9 ka from the annually laminated sedimentary sequence of Lake Xiaolongwan, northeastern China. The n-alkane distribution suggests that Lake Xiaolongwan has undergone a shift from an oligotrophic state with low algal production and little emergent/submerged macrophytes in the early Holocene, to a eutrophic state with high algal production and abundant emergent/submerged macrophytes since the middle Holocene. The pattern of variation observed in the biomarker proxies ACL (the n-alkane average chain length), Paq (aquatic macrophyte versus aquatic macrophyte and terrestrial plant ratio), and LPTP (lake productivity/terrigenous organic production) is throughout the record similar to that of the total organic carbon. The variation of compound-specific carbon isotopic values in the middle- and short-chain alkanes was mainly regulated by lake productivity and the accumulating organic pool through time. In this forested region, where the vegetation is dominated by C3 plants, the long-chain n-alkanes (C27-C31) are predominantly derived from leaf wax lipids. The compound-specific δ13C27-31 value is sensitive to effective precipitation, and therefore represents a useful indicator of regional monsoonal precipitation. Spectral analysis on the δ13C27-31 time series reveals significant periodicities of 87-89, 205-212, 1020-1050 and 1750-2041 years. On the centennial timescale, the quasi-periodicities around 88 and 210 years suggest a strong link between solar activity and monsoon rainfall. The millennial monsoon cycle in northeastern China is associated with sea surface temperature (SST) variations in two active centers of the summer monsoon, the western Pacific Subtropical High (WPSH) and the Okhotsk High. Increasing SST in the subtropical sea may cause a northwards shift of the WPSH, which extends the monsoon rain band (Meiyu) to northeastern China, and thus increasing rainfall in that region

  8. Paleoecological and archaeological implications of a late Pleistocene/Early holocene record of vegetation and climate from the pacific coastal plain of panama

    Science.gov (United States)

    Piperno, Dolores R.; Jones, John G.

    2003-01-01

    A phytolith record from Monte Oscuro, a crater lake located 10 m above sea level on the Pacific coastal plain of Panama, shows that during the Late Pleistocene the lake bed was dry and savanna-like vegetation expanded at the expense of tropical deciduous forest, the modern potential vegetation. A significant reduction of precipitation below current levels was almost certainly required to effect the changes observed. Core sediment characteristics indicate that permanent inundation of the Monte Oscuro basin with water occurred at about 10,500 14C yr B.P. Pollen and phytolith records show that deciduous tropical forest expanded into the lake's watershed during the early Holocene. Significant burning of the vegetation and increases of weedy plants at ca. 7500 to 7000 14C yr B.P. indicate disturbance, which most likely resulted from early human occupation of the seasonal tropical forest near Monte Oscuro and the development of slash-and-burn methods of cultivation.

  9. Aerosol and monsoon climate interactions over Asia

    Science.gov (United States)

    Li, Zhanqing; Lau, W. K.-M.; Ramanathan, V.; Wu, G.; Ding, Y.; Manoj, M. G.; Liu, J.; Qian, Y.; Li, J.; Zhou, T.; Fan, J.; Rosenfeld, D.; Ming, Y.; Wang, Y.; Huang, J.; Wang, B.; Xu, X.; Lee, S.-S.; Cribb, M.; Zhang, F.; Yang, X.; Zhao, C.; Takemura, T.; Wang, K.; Xia, X.; Yin, Y.; Zhang, H.; Guo, J.; Zhai, P. M.; Sugimoto, N.; Babu, S. S.; Brasseur, G. P.

    2016-12-01

    The increasing severity of droughts/floods and worsening air quality from increasing aerosols in Asia monsoon regions are the two gravest threats facing over 60% of the world population living in Asian monsoon regions. These dual threats have fueled a large body of research in the last decade on the roles of aerosols in impacting Asian monsoon weather and climate. This paper provides a comprehensive review of studies on Asian aerosols, monsoons, and their interactions. The Asian monsoon region is a primary source of emissions of diverse species of aerosols from both anthropogenic and natural origins. The distributions of aerosol loading are strongly influenced by distinct weather and climatic regimes, which are, in turn, modulated by aerosol effects. On a continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulations. The atmospheric thermodynamic state, which determines the formation of clouds, convection, and precipitation, may also be altered by aerosols serving as cloud condensation nuclei or ice nuclei. Absorbing aerosols such as black carbon and desert dust in Asian monsoon regions may also induce dynamical feedback processes, leading to a strengthening of the early monsoon and affecting the subsequent evolution of the monsoon. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of different monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from

  10. Improved marine reservoir age estimation and palaeoclimate synchronisation of the early Holocene Levantine/NW-Arabian region based on identification of the S1 tephra in Dead Sea and Tayma palaeolake sediments

    Science.gov (United States)

    Neugebauer, Ina; Wulf, Sabine; Schwab, Markus J.; Serb, Johanna; Plessen, Birgit; Appelt, Oona; Brauer, Achim

    2017-04-01

    Due to a lack of tephras identified in marine and terrestrial palaeoclimate records from the Levantine-Arabian area, this region is still not sufficiently connected to the eastern Mediterranean tephrostratigraphical lattice. Here we report on the first finding of cryptotephra in the Holocene lacustrine sediment records of the Dead Sea and the Tayma palaeolake (NW Arabian Peninsula). The major elemental chemistry of the rhyolitic glass shards proves this tephra identical to the distal 'S1 tephra' identified in the Yammoûneh palaeolake, Lebanon (Develle et al, 2009), in a marine sediment record from the SE Levantine basin (Hamann et al., 2010) and in the Sodmein Cave archaeological site in Egypt (Barton et al., 2015). The 'S1 tephra', most likely corresponding to the early Holocene 'Dikkartın' dome eruption of the Erciyes Daǧ volcano in central Anatolia, Turkey, has been dated in the marine record at 8830 ± 140 cal yr BP. We present new age estimates of the 'S1 tephra' based on radiocarbon dating of terrestrial plant remains (Migowski et al., 2004) and pollen concentrates (Dinies et al., 2015), which reveal modelled ages of 8939 ± 83 cal yr BP in the Dead Sea sediments and 9041 ± 254 cal yr BP in Tayma. This allows the estimation of an early Holocene marine reservoir age of ca. 320 years in the SE Levantine Sea. The timing of the volcanic eruption during the early Holocene humid period, which led to the formation of sapropel S1 in the Mediterranean Sea, and the identification of the 'S1 tephra' more than 1200 km to the south are crucial for the synchronisation of marine and terrestrial palaeoclimate records in the eastern Mediterranean region. References: Barton et al., 2015. The role of cryptotephra in refining the chronology of Late Pleistocene human evolution and cultural change in North Africa. Quaternary Sci. Rev. 118, 151-169. Develle et al., 2009. Early Holocene volcanic ash fallout in the Yammoûneh lacustrine basin (Lebanon): Tephrochronological

  11. Refining the time span between the early Holocene Askja-S and Hässeldalen tephras through differential dating based on varve counting from Lake Czechowskie (N Poland)

    Science.gov (United States)

    Ott, Florian; Wulf, Sabine; Serb, Johanna; Słowiński, Michał; Obremska, Milena; Tjallingii, Rik; Błaszkiewicz, Mirosław; Brauer, Achim

    2016-04-01

    Robust chronological framework is a crucial necessity for palaeoclimate reconstructions and especially for synchronizing records to decipher climatic teleconnections. Volcanic ash deposits (tephra) provide isochronous time marker that can be utilized as tie-lines to synchronize sedimentary archives. Advances in the detection and identification of non-visible (crypto-) tephra, often transported over thousands of kilometers, also allows identifying ash deposits even in distal records. We report the first findings of co-existing early Holocene Hässeldalen and Askja-S cryptotephras in a varved sediment record in Lake Czechowskie (JC, northern Poland). Annual layer counting was used to establish a varve chronology and micro-facies analyses, relative calcium (Ca) and titanium (Ti) concentrations were used to decipher between lake productivity and detrital flux. Here we focus (i) on the determination of the time span between both tephras, (ii) revised age estimates for the Askja-S tephra and (iii) the sedimentological response of the JC record to the Preboreal Oscillation (PBO), a short lived cold episode during the early Holocene. A differential dating approach revealed a time span of 152 +11/-8 varve years counted in the JC sediment record between both tephras. Since the varved interval of the JC sediment record comprising the tephras is floating, we anchored the floating varve chronology to an absolute timescale by using the radiocarbon-dated Hässeldalen Tephra (11,380 ± 216 cal a BP, Wohlfarth et al, 2006). The resulting age for the Askja-S of 11,454-11,002 cal a BP is, even considering the rather large uncertainties, a few decades to several hundred years older than most radiocarbon based age models, but it supports the original age model from Hässseldala port. The sediment response to the PBO cold period is seen only in a slight decrease in titanium, a proxy for detrital matter flux. Varve micro-facies did not change during this interval confirming a weak impact

  12. Lagged response of summer precipitation to insolation forcing on the northeastern Tibetan Plateau during the Holocene

    Science.gov (United States)

    Zhang, Xiaojian; Jin, Liya; Chen, Jie; Lu, Huayu; Chen, Fahu

    2017-07-01

    The precipitation changes on the northeastern Tibetan Plateau during the Holocene remain unclear due to discrepancies among different proxy records. We compared proxy records with the results from a transient simulation performed using the Kiel Climate Model forced by orbital variations, to analyse summer precipitation changes in this area during the Holocene (9.5-0 ka BP). The model results suggested increasing amounts of summer precipitation from 9.5 to 6.2 ka BP and a persistent decline thereafter, which matched well with pollen records but was inconsistent with ostracod δ18O records. The Holocene climatic optimum lagged the Northern Hemisphere summer insolation maximum by 3.5 ka, caused by the interplay between the East Asian summer monsoon (EASM) circulation and the mid-latitude westerlies. The ostracod δ18O values reflected the strength of the EASM circulation. A strong EASM circulation increased the transport of water vapour towards the northeastern Tibetan Plateau from the northwestern Pacific. Weakened mid-latitude westerlies increased the incursion of cold air masses into the northeastern Tibetan Plateau. During the early Holocene, relatively strong mid-latitude westerlies, resulting from an enhanced Arctic Oscillation, reduced summer precipitation on the northeastern Tibetan Plateau, in spite of a strong insolation-driven EASM circulation. The weakening EASM circulation and the strengthening westerlies together induced the decreasing trend of summer precipitation from the middle to late Holocene. In addition, summer precipitation variations were further modulated by sea-surface temperatures in the northwestern Pacific, through weakening the strength of the EASM.

  13. A Holocene speleothem record from Morocco, NW Africa

    Science.gov (United States)

    Wassenburg, Jasper; Fietzke, Jan; Richter, Detlev; Immenhauser, Adrian

    2010-05-01

    A well dated Holocene speleothem (stalagmite) from the Middle Atlas Mountains in Morocco has been investigated for its continental climate record. The aim is to compile an improved understanding of the climatically complex triple point of the North Atlantic, Mediterranean and Saharan / Monsoonal climate realms in NW Africa. At present, only few studies concerning continental climate reconstructions from NW Africa have been published (Lamb et al. 1995, Cheddadi et al. 1998, Genty et al. 2006). Given the significance of this region, this lack of data forms a strong motivation for additional, well dated climate records. The speleothem (GP2) was sampled in the 'Grotte de Piste' (ca 800 m above sea level), mean annual precipitation is about 930 mm (mainly falling in the winter season) and the mean annual temperature is about 13° C. GP2 is 60 cm tall and grew - based on U/Th MC-ICP-MS data - continuously between 11.5 kyr BP (early Holocene) and 2.9 kyr BP (late Holocene). X-Ray Diffraction data indicate a mainly aragonitic mineralogy. 'Hendy tests' suggest that CaCO3 precipitation was close to isotopic equilibrium with respect to oxygen isotopes, however kinetic effects might have influenced carbon isotopes. Carbon and oxygen isotope data have been measured along a transect with increments of approximately 1 mm representing a resolution of about 15 yrs. Highly covariant oscillations in δ13C and δ18O with an average cyclicity of about 410 yrs. are observed. These oscillations coincide with macroscopically visible high density and low density layers, possibly reflecting a higher or lower amount of inclusions and perhaps higher and lower growth rates. Geochemical analysis of speloan aragonite is accompanied by cave monitoring that has started in November 2009. Parameters quantified include: drip water parameters, cave air humidity, pCO2 and cave air temperature. Precipitation experiments using watch glasses will also be performed. References Cheddadi, R., Lamb, H. F

  14. Precise dating of abrupt shifts in the Asian Monsoon during the last deglaciation based on stalagmite data from Yamen Cave, Guizhou Province, China

    Institute of Scientific and Technical Information of China (English)

    EDWARDS; R.; Lawrence

    2010-01-01

    Based on 33 U/Th dates and 1020 oxygen isotopic data from stalagmite Y1 from Yamen Cave, Guizhou Province, China, a record of the Asian Summer Monsoon (ASM) was established. The record covers the last deglaciation and the early Holocene (from 16.2 to 7.3 ka BP) with an average oxygen isotope resolution of 9 years. The main millennial-scale deglacial events first identified in Greenland (Greenland Interstadial Events: GIS 1e through GIS 1a) and later in China are clearly present in the Y1 record. By analogy to earlier work, we refer to these as Chinese Interstadials (CIS): CIS A.1e to CIS A.1a. The onset of these events in Y1 δ18O records are nominally dated at: 14750±50, 14100±60, 13870±80, 13370±80, and 12990±80 a BP. The end of CIS A.1a or the beginning of the Younger Dryas (YD) event is nominally at 12850±50 a BP and the end of the YD dates to 11500±40 a BP. The δ18O values shift by close to 3‰ during the transition into the Bφlling-Allerφd (BA, the onset of CIS A.1e) and at the end of the YD. Comparisons of Y1 to previously published early Holocene records show no significant phase differences. Thus, the East Asia Monsoon and the Indian Monsoon do not appear to have been out of phase during this interval. The Y1 record confirms earlier work that suggested that solar insolation and North Atlantic climate both affect the Asian Monsoon.

  15. Millennial-scale evolution of Hunshandake Desert and climate change during the Holocene in Inner Mongolia,northern China

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The Hunshandake Desert is located at the northern edge of the East Asian monsoon region,and its natural environment is sensitive to monsoonal changes.Geologic records suggest that desert evolution corresponding to climate change had experienced several cycles in the Holocene,and the evolutionary process can be distinguished by four dominant stages according to changing trends of the environment and climate.(1) Holocene Ameliorative Period(11.0-8.7 cal ka B.P.),when the desert area gradually shrank following an approaching warm-wet climate and strengthening summer monsoon.(2) Holocene Optimum(8.7-6.0 cal ka B.P.),when the majority of moving sand dunes were stabilized and vegetation coverage quickly expanded in a suitable warm-wet climate and a strong summer monsoon.(3) Holocene Multivariate Period(6.0-3.5 cal ka B.P.),during a low-amplitude desert transformed between moving and stabilized types under alternating functions of cold-dry with warm-wet climate,and winter monsoon with summer monsoon.(4) Holocene Decay Period(since 3.5 cal ka B.P.),when the desert area tended to expand along with a weakened summer monsoon and a dry climate.

  16. Evolution of habitat and environment of deer during the Late-glacial and early Holocene: the case of red deer in French Jura.

    Science.gov (United States)

    Drucker, Dorothée.; Bridault, Anne; Hujic, Alisa; Bocherens, Hervé

    2010-05-01

    The Late-glacial and early Holocene transition is a key period of environmental changes in a context of to a global warming. In northwestern Europe, extensive studies have documented the vegetation and faunal recomposition with the replacement of the cold steppe-tundra ecosystem by the forested temperate ecosystem we can still observe. Paleoecological interest focused on the extinct large mammals species like the Mammoth. In comparison, little has been done to decipher the ecological adaptation of the surviving species, especially those that are still present in the very same region than in the past. A better knowledge of the impact of changing environmental conditions on the ecology would be useful to define the degree of selective pressure. Thus, we have studied the habitat and environment evolution of red deer (Cervus elaphus) during the Late-glacial and early Holocene using stable isotopes and radiocarbon investigations. The analyzed bone material was selected from archaeological sites in French Jura. Performing direct radiocarbon dating on the bone collagen of the selected remains solved the problem of possible chronological uncertainties of the stratigraphical record of the sites. The same bone collagen samples were used for stable isotope measurements. We investigated the relative abundances in 13C to examine changes in habitat closure (canopy effect), in 15N to decipher changes in pedogenic activities (soil maturation) of the animals dwelling, and in 18O to track changes in altitude and/or local temperatures of the occupied territories. The results demonstrate that the stable isotopic composition of red deer bone collagen can be a valuable and sensitive indicator of habitat use and environmental conditions. The associated direct dating allows us to reconstruct the chronology of ecological changes. The combined chronological and ecological results evidence local differences in red deer adaptation at a small geographical scale.

  17. A Holocene pollen and diatom record from Vanderlin Island, Gulf of Carpentaria, lowland tropical Australia

    Science.gov (United States)

    Prebble, Matiu; Sim, Robin; Finn, Jan; Fink, David

    2005-11-01

    Sedimentary, palynological and diatom data from a dunefield lake deposit in the interior of Vanderlin Island in the Gulf of Carpentaria are presented. Prior to the formation of present perennial lake conditions, the intensified Australian monsoon associated with the early Holocene marine transgression allowed Cyperaceae sedges to colonise the alluvial margins of an expansive salt flat surrounded by an open Eucalyptus woodland. As sea level stabilised between 7500 and 4500 cal yr B.P. coastal dunes ceased to develop allowing dense Melaleuca forest to establish in a Restionaceae swamp. Dune-sand input into the swamp was diminished further as the increasingly dense vegetation prevented fluvial and aeolian transported sand arriving from coastal sources. This same process impounded the drainage basin allowing a perennial lake to form between 5500 and 4000 cal yr B.P. Myriophyllum and other aquatic taxa colonised the lake periphery under the most extensive woodland recorded for the Holocene. The palynological data support an effective precipitation model proposed for northern Australia that suggests more variable conditions in the late Holocene. A more precise measure of effective precipitation change is provided by diatom-based inferences that indicate few changes in lake hydrology. Such interpretations are explained in terms of palynological sensitivity to adjustments in local fire regimes where regional precipitation change may only be recorded indirectly through fire promoting mechanisms, including intensified ENSO periodicity and human impact.

  18. Holocene evolution of summer winds and marine productivity in the tropical Indian Ocean in response to insolation forcing: data-model comparison

    Directory of Open Access Journals (Sweden)

    F. C. Bassinot

    2011-07-01

    Full Text Available The relative abundance of Globigerinoides bulloides was used to infer Holocene paleo-productivity changes on the Oman margin and at the southern tip of India. Today, the primary productivity at both sites reaches its maximum during the summer season, when monsoon winds result in local Eckman pumping, which brings more nutrients to the surface. On a millennium time-scale, however, the % G. bulloides records indicate an opposite evolution of paleo-productivity at these sites through the Holocene. The Oman Margin productivity was maximal at ~9 ka (boreal summer insolation maximum and has decreased since then, suggesting a direct response to insolation forcing. On the contrary, the productivity at the southern tip of India was minimum at ~9 ka, and strengthened towards the present.

    Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model. These reconstructions are fully coherent with the marine core data. They confirm that the evolution of particulate export production and foraminifera assemblages at our two sites were directly linked with the strength of the upwelling. Model simulations at 9 ka and 6 ka BP show that the relative evolution between the two sites since the early Holocene can be explained by the weakening but also the southward shift of monsoon winds over the Arabian Sea during boreal summer.

  19. Air Pollution over North-West Bay of Bengal in the Early Post-Monsoon Season Based on NASA MERRAero Data

    Science.gov (United States)

    Kishcha, Pavel; DaSilva, Arlindo M.; Starobinets, Boris; Alpert, Pinhas

    2013-01-01

    The MERRA Aerosol Reanalysis (MERRAero) has been recently developed at NASA's Global Modeling Assimilation Office (GMAO). This reanalysis is based on a version of the GEOS-5 model radiatively coupled with GOCART aerosols, and it includes assimilation of bias-corrected Aerosol Optical Thickness (AOT) from the MODIS sensor on both Terra and Aqua satellites. Our main finding is that, in October, in the absence of aerosol sources in north-west Bay of Bengal (BoB), MERRAero showed increasing AOT trends over north-west BoB exceeding those over the east of the Ganges basin. The Ganges basin is characterized by significant population growth accompanied by developing industry, agriculture, and increasing transportation: this has resulted in declining air quality. MERRAero data for the period 2002-2009 was used to study AOT trends over north-west Bay of Bengal (BoB) in the early post-monsoon season. This season is characterized by aerosol transport from the Ganges basin to north-west BoB by prevailing winds; and still significant rainfall of over 150 mmmonth. Different aerosol components showed strong increasing AOT trends over north-west BoB. The following factors contributed to the increasing AOT trend over the area in question in October: an increasing number of days when prevailing winds blew from land to sea, resulting in a drier environment and an increase in air pollution over north-west BoB; wind convergence was observed over north-west BoB causing the accumulation of aerosol particles over that region, when prevailing winds blew from land to sea. MERRAero aerosol reanalysis can be used on a global scale.

  20. Northward extent of East Asian monsoon covaries with intensity on orbital and millennial timescales.

    Science.gov (United States)

    Goldsmith, Yonaton; Broecker, Wallace S; Xu, Hai; Polissar, Pratigya J; deMenocal, Peter B; Porat, Naomi; Lan, Jianghu; Cheng, Peng; Zhou, Weijian; An, Zhisheng

    2017-02-21

    The magnitude, rate, and extent of past and future East Asian monsoon (EAM) rainfall fluctuations remain unresolved. Here, late Pleistocene-Holocene EAM rainfall intensity is reconstructed using a well-dated northeastern China closed-basin lake area record located at the modern northwestern fringe of the EAM. The EAM intensity and northern extent alternated rapidly between wet and dry periods on time scales of centuries. Lake levels were 60 m higher than present during the early and middle Holocene, requiring a twofold increase in annual rainfall, which, based on modern rainfall distribution, requires a ∼400 km northward expansion/migration of the EAM. The lake record is highly correlated with both northern and southern Chinese cave deposit isotope records, supporting rainfall "intensity based" interpretations of these deposits as opposed to an alternative "water vapor sourcing" interpretation. These results indicate that EAM intensity and the northward extent covary on orbital and millennial timescales. The termination of wet conditions at 5.5 ka BP (∼35 m lake drop) triggered a large cultural collapse of Early Neolithic cultures in north China, and possibly promoted the emergence of complex societies of the Late Neolithic.

  1. Northward extent of East Asian monsoon covaries with intensity on orbital and millennial timescales

    Science.gov (United States)

    Goldsmith, Yonaton; Broecker, Wallace S.; Xu, Hai; Polissar, Pratigya J.; deMenocal, Peter B.; Porat, Naomi; Lan, Jianghu; Cheng, Peng; Zhou, Weijian; An, Zhisheng

    2017-02-01

    The magnitude, rate, and extent of past and future East Asian monsoon (EAM) rainfall fluctuations remain unresolved. Here, late Pleistocene-Holocene EAM rainfall intensity is reconstructed using a well-dated northeastern China closed-basin lake area record located at the modern northwestern fringe of the EAM. The EAM intensity and northern extent alternated rapidly between wet and dry periods on time scales of centuries. Lake levels were 60 m higher than present during the early and middle Holocene, requiring a twofold increase in annual rainfall, which, based on modern rainfall distribution, requires a ˜400 km northward expansion/migration of the EAM. The lake record is highly correlated with both northern and southern Chinese cave deposit isotope records, supporting rainfall “intensity based” interpretations of these deposits as opposed to an alternative “water vapor sourcing” interpretation. These results indicate that EAM intensity and the northward extent covary on orbital and millennial timescales. The termination of wet conditions at 5.5 ka BP (˜35 m lake drop) triggered a large cultural collapse of Early Neolithic cultures in north China, and possibly promoted the emergence of complex societies of the Late Neolithic.

  2. Monsoons, history of

    Digital Repository Service at National Institute of Oceanography (India)

    Niitsuma, N.; Naidu, P.D.

    The evolution of the Asian monsoon started at around 9.5 Ma, in response to the uplift of the Himalayas. The monsoonal intensity reached its maximum at around 5 Ma, and from that time the associated easterly trade winds caused intense upwelling...

  3. Holocene climate changes in the central Asia mountain region inferred from a peat sequence from the Altai Mountains, Xinjiang, northwestern China

    Science.gov (United States)

    Zhang, Yan; Meyers, Philip A.; Liu, Xingtu; Wang, Guoping; Ma, Xuehui; Li, Xiaoyu; Yuan, Yuxiang; Wen, Bolong

    2016-11-01

    A continuous peat sequence collected in the Altai Mountains, Xinjiang Province, northwestern China, provides a new opportunity to reconstruct the Holocene climate history in the arid central mountain region of Asia. Based on AMS 14C dating, high resolution records of the humification degree and n-alkane distributions reveal that the region experienced a relatively warm and dry early Holocene (10.0-8.0 ka) and a cold and wet early mid-Holocene (8.0-6.3 ka), followed by a warm and dry mid-Holocene (6.3-5.5 ka). A shift to cold and wet conditions occurred between 5.5 and 4.0 ka, and then the climate entered into a warmer period from 4.0 to 2.5 ka. In the late Holocene (2.5-1.0 ka), the region experienced a colder and wetter climate. A gradual shift to warm and dry conditions occurred during the last 1.0 ky in this region. The regional climate patterns have been generally dominated by alternations of warm-dry and cold-wet episodes during the Holocene that were quite different from the warm-wet and cool-dry episodes in the Asian summer monsoon region. Regional comparisons indicate that the climate changes in arid central Asia have been mainly influenced by the North Atlantic Ocean sea surface temperatures (SSTs) via the westerlies. However, owing to the mountainous character of the study areas, glacial meltwater, and other local factors, the climate changes in the Altai Mountains region have not always been concordant with variations of North Atlantic Ocean SSTs. We postulate that the history of moisture balance between regional precipitation, glacier and snow meltwater, and evaporation has been modulated by air temperatures that were mainly influenced by changes in the summer insolation of the Northern Hemisphere.

  4. Late Glacial and Early Holocene Climatic Changes Based on a Multiproxy Lacustrine Sediment Record from Northeast Siberia

    Energy Technology Data Exchange (ETDEWEB)

    Kokorowski, H D; Anderson, P M; Sletten, R S; Lozhkin, A V; Brown, T A

    2008-05-20

    Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000-11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicates no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000-9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain-sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000-9000 cal. yr BP.

  5. Insolation and Abrupt Climate Change Effects on the Western Pacific Maritime Monsoon

    Science.gov (United States)

    Partin, J. W.; Quinn, T. M.; Shen, C.; Cardenas, M.; Siringan, F. P.; Hori, M.; Okumura, Y.; Banner, J. L.; Lin, K.; Jiang, X.; Taylor, F. W.

    2013-12-01

    Many monsoon-sensitive paleoclimate archives capture the response of the Asian-Australian monsoon system to changes in summer insolation, as well as abrupt climate changes such as the Younger Dryas (YD). The response is commonly a direct one in Holocene and YD archives. In the case of insolation, increased summer insolation leads to increased monsoon rainfall over land, as captured in stalagmite δ18O records from Oman and China. We evaluate this direct response using maritime stalagmite records from the island of Palawan, Philippines (10 N, 119 E). The wet season in Palawan occurs over the same months (June-October) as in Oman, India and China. Therefore, we expected the Palawan stalagmite δ18O record, a proxy of rainfall, to have a similar response to changing insolation and hence, a trend of decreasing monsoon rainfall over the Holocene. However, the Holocene trend in two partially replicated stalagmite δ18O records is opposite to that expected: rainfall increases over the Holocene, despite the decrease of summer insolation over the Holocene. We interpret the Holocene trend observed at Palawan to be the result of an increase in the maritime monsoon that balances the reduction in the land monsoon; an interpretation that is consistent with previously published results from coupled ocean-atmosphere general circulation model runs. Seawater δ18O reconstructions from marine sediment cores in the western tropical Pacific contain a freshening trend over the Holocene, also supporting the hypothesis of increase maritime monsoon rainfall. The direct relationship between monsoon rainfall over land as recorded in the YD interval in Chinese stalagmite records is also observed in maritime monsoon rainfall during the YD at Palawan: both records get drier during the YD cold interval. This agreement between YD stalagmite records from China and Palawan contrasts sharply with the inverse relationship between these records over the Holocene. We further investigate the nature of

  6. Gulf of California Sediment and Proxy SST Records Suggest a Post 6 ka Development of the Arizona Monsoon and Solar Forcing of Cycles

    Science.gov (United States)

    Barron, J. A.; Bukry, D.

    2007-12-01

    Summer monsoonal rains in Arizona and adjacent areas are mainly due to pulses of moisture traveling northward up the Gulf of California (GOC). Modern studies reveal that northern GOC SSTs must exceed 26 deg. C before monsoonal rainfall develops in Arizona and western New Mexico, and over 80 percent of the rainfall in this region occurs after northern GOC SSTs exceed 28.5 deg. C. Warming of GOC occurs progressively from south to north in the late spring, as northwest winds, which dominate in the late fall to early spring, decrease in strength, and tropical waters penetrate northward along the western coast of the GOC. Sediment (CaCO3 and opal) and microfossil (diatom and silicoflagellate) proxies spanning the past 15,000 years from cores in the central GOC suggest that waters of the northern GOC were too cold between ca. 11 and 6 ka to allow development of monsoonal rains in Arizona. Evidence for a post 6 ka intensification of monsoonal rains in Arizona and adjacent areas includes: 1) increased frequency of arroyo cutting in Arizona after ca. 5 ka, 2) increased evidence of paleofloods in Arizona and SW Utah after ca. 6 ka, and 3) the renewal of aggradation of alluvial fans in the Mojave Dessert at ca. 6 ka after a lull in their formation between ca. 11 and 6 ka. Supportive pollen evidence includes : 1) the late Holocene appearance of summer flowering annuals and C-{4} grasses in SE Arizona, and 2) the post 6 ka appearance of a warm, mixed biome in the highlands of northwest Mexico. Other pollen evidence and the scarcity of early and middle Holocene packrat middens in the American southwest, however, have been cited as evidence of increased monsoonal rains during the early and middle parts of the Holocene It is likely that the Gulf of Mexico was the main source of monsoonal moisture in the American southwest prior to ca. 6 ka, especially in the regions east of Arizona. A northward displacement of the Intertropical Convergence Zone in the Caribbean prior to ca. 5.4 ka

  7. Holocene changes in eastern equatorial Atlantic salinity as estimated by water isotopologues

    Science.gov (United States)

    Leduc, G.; Sachs, J. P.; Kawka, O.; Schneider, R. R.

    2011-12-01

    The Holocene tropical North African monsoon evolution was controlled at first order by insolation, but the timing and trends of paleo-records sensitive to precipitation substantially differ upon proxies and locations. Salinity reconstructions based on Ba/Ca and δ18Osw from one marine sediment core recovered from the eastern equatorial Atlantic close to the Niger River mouth integrate rainfall changes over the river catchment located in the northern tropics, and indicate that the region was wetter during the mid-Holocene relative to the present (Weldeab et al., 2007). A closer look those salinity reconstructions which are derived from the same sedimentary sequence however indicates divergent salinity trends as estimated by Ba/Ca and δ18Osw for the late Holocene (Weldeab et al., 2007). In order to refine better the past changes in the regional hydrologic cycle, we have reevaluated salinity records by measuring δD of C37:2 alkenones from the same sedimentary sequence. A smooth, long-term increase of ~10% in δD between 10 and 3 kyr BP is followed by an equivalent but more rapid decrease between 3 kyr BP and core top, where the δD values are slightly lighter than during the early Holocene. Both δ18Osw and alkenone δD suggest a late Holocene sea surface salinity decrease based on the modern relationship between salinity and isotopic composition of seawater, and this result differs from the salinity record derived from Ba/Ca. We apply the method for reconstructing salinity using water isotopologues described in Rohling (2007) and in LeGrande and Schmidt (2011). The new salinity record derived from paired δ18Osw and alkenone δD modifies the salinity trends as estimated by oxygen and deuterium isotopic ratios alone and indicates monotonous salinity increases over the last 7 ka. This result is in better agreement with both the Ba/Ca salinity record and a pollen record from the Lake M'Balang (Cameroon) which reveals a progressive dessication in the region over the

  8. Late Glacial and Holocene Record of Hydroclimate in the San Luis Valley, Southern Colorado, USA

    Science.gov (United States)

    Yuan, F.; Koran, M.

    2012-12-01

    Lake sediments from the San Luis Valley, south-central Colorado, archive a detailed record of Late Glacial and Holocene climatic fluctuations in the southern Rocky Mountains. Together with radiometric dating analysis, measurements of grain size, magnetic susceptibility, total inorganic carbon (TIC), oxygen and carbon isotopic composition of the TIC fraction on sediment samples from San Luis Lake (at an average resolution of 60 years per sample) allow us to generate a sediment record of climatic change in the region spanning the last 16ka (1 ka=1000 cal yrs). This record documents the timing and duration of major climate episodes and trends, comparable to the existing paleoclimate records from the American Southwest. The Late Glacial record of San Luis Lake contains a big wet episode in the late part of the Mystery Interval (MI), a relatively dry climate during Bølling-Allerød (B/A) warm interval, and a relatively wet episode during the Younger Dryas (YD) interval, similar to the lake-level record found in the Estancia basin in central New Mexico. The early to middle Holocene record of d18O in the San Luis Lake parallels the calcite d18O record of Bison Lake in northern Colorado, documenting a history of significant change in precipitation seasonality across the northern boundary of the North American monsoon (NAM). The middle Holocene epoch is characterized by greater variations in magnetic susceptibility, d18O and d13C, suggesting the prevalence of wet, variable or transitional climate conditions. In contrast, the late Holocene climate is relatively dry, as indicated by more positive values of d18O in San Luis Lake. The results of this study reveal a complex history of climate evolution due to the interactions of two seasonally distinct precipitation regimes with mountainous landforms in the region.

  9. Measuring the monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.; Nair, R.R.

    of the monsoons, there are also fluctuations arising from human activities. Most scientists believe that large-scale deforestation and burning of fossil fuels will alter global climatic patterns significantly. For the sake of those people whose lives...

  10. Onset, active and break periods of the Australian monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Shaik, Hakeem A [Northern Territory Regional Office, Australian Bureau of Meteorology, PO Box 40050, NT Regional Office, Bureau of Meteorology, Casuarina NT 0811, Darwin (Australia); Cleland, Samuel J, E-mail: h.shaik@bom.gov.a [Bureau of Meteorology, Cape Grim BAPS, Smithton Tasmania TAS 7300 (Australia)

    2010-08-15

    Four operational techniques of monsoon monitoring the Australian monsoon at Darwin have been developed in the Darwin Regional Specialised Meteorological Centre. Two techniques used the rainfall only criteria and look into the onset of wet season rainfall/monsoon rainfall. The other two techniques are based purely on Darwin wind data. The data used for the study ranges from 14 to 21 years. The main purpose of the study is to develop near-real time monitoring tools for the Australian monsoon at Darwin. The average date of onset of the monsoon ranges from 19 December to 30 December. The average date of monsoon onset is 28 December. In eleven out of twenty-one years the onset date remained within three days range between the two rainfall techniques, whereas it is eleven out of fourteen years between the wind techniques. The median number of active monsoon spells in a wet season is 3 for the rainfall techniques and 6 for the wind techniques. The average length of each active monsoon spell is around 4 days for all of the techniques. The date of onset of the monsoon has shown negative correlation with the Southern Oscillation Index (SOI) that is late onset is found to occur in El Nino years while early onset is more likely in La Nina years.

  11. Final Pleistocene and Early Holocene at Sitio do Meio, Piauí, Brazil: Stratigraphy and comparison with Pedra Furada

    Directory of Open Access Journals (Sweden)

    Giulia Aimola

    2014-09-01

    Full Text Available English: Sitio do Meio, in southern Piaui, Brazil, is the second rock shelter presenting fully Pleistocene dates and artefacts after Pedra Furada.  Despite the anthropogenic origin of Pedra Furada artefacts has been questioned, SDM has better chances to be accepted by the scientific community because of the absence of the most relevant stone breaking agents in this kind of site, i.e. waterfalls. This paper presents a critical revision of the history of excavations (1980-2000, stratigraphy, chronology, and the archaeological content of the site (sector 2. At least 98 stone tools have been identified and described, all of them being older than 12,500 BP, i.e. belonging to the Upper Pleistocenic phase of Pedra Furada 3, as defined in the close reference site. The lithic industry of Serra Talhada phase (lower Holocene is also presented and compared with paleoindian sites of North-Eastern and Central Brazil.French:Le Sitio do meio, dans le  Piaui méridional (Brésil est le deuxième abri sous roche de la région ayant livré des dates pléistocènes en dehors du site de la Pedra Furada. L'article présente une révision critique des fouilles (1980-2000, la chronostratigraphie et le contenu archéologique du secteur 2. Une centaine d'outils lithiques sont décrits, ils sont plus anciens de 12,5 ka BP  et correspondent à la phase Pléistocène Pedra Furada 3 définie dans le site éponyme de référence. On présente aussi l' industrie lithique de la phase Serra Talhada (Holocène  ancien en la comparant aux industries paléoindiennes du Nord-Est et du centre du Brésil.

  12. Late Glacial-Holocene climatic transition record at the Argentinian Andean piedmont between 33–34° S

    Directory of Open Access Journals (Sweden)

    A. E. Mehl

    2013-10-01

    Full Text Available The Arroyo La Estacada (~33°28' S, 69°02' W, eastern Andean piedmont of Argentina, cuts through an extensive piedmont aggradational unit composed of a dominant late Pleistocene–early Holocene (LP–EH alluvial sequence including several paleosols. The arroyo sedimentary record exhibits a paleosol developed affecting the topmost part of likely Lateglacial aeolian deposits aggraded into a floodplain environment by the end of the late Pleistocene. The paleosol shows variable grade of development in the outcrops along the arroyo probably in relation to fluvial valley paleotopography. Organic matter humification, carbonate accumulation and redox processes were the dominant processes associated with paleosol formation. By the early Holocene, when the formation of the paleosol ended, alluvial aggradation renewed and a higher frequency of flooding events could have affected the arroyo's floodplain environment. A period of relative landscape stability in the Arroyo La Estacada basin is inferred from the paleosol developed by the LP–EH transition in response to a climatic amelioration in the Andes cordillera piedmont after the Late Glacial arid conditions. The renewal of early Holocene alluvial aggradation was probably influenced by the South American Monsoon and resulted in a change in the sedimentary dynamics of the arroyo. The analyzed Late Glacial-Holocene alluvial record of the Andean piedmont constitutes a suitable record of the LP–EH climatic transition at the extra Andean region of Argentina. It is in agreement with regional paleoclimatic evidence along the southern tip of the South American continent, where other sedimentary sequences record similar late Quaternary paleoenvironmental changes over both fluvial and interfluvial areas.

  13. The origin and disappearance of the late Pleistocene-early Holocene short-lived coastal wetlands along the Carmel coast, Israel

    Science.gov (United States)

    Sivan, Dorit; Greenbaum, Noam; Cohen-Seffer, Ronit; Sisma-Ventura, Guy; Almogi-Labin, Ahuva

    The formation of short-lived backswamps along the Carmel coast of Israel coincides with the rapid global sea-level rise during the late Pleistocene-early Holocene transition. The current study shows that the wetland phenomena originated around 10,000 yr ago and dried up shortly before the local Pre-Pottery Neolithic humans settled on the wetland dark clay sediments 9430 cal yr BP. Palaeontological and stable-isotope data were used in this study to elucidate previously published sedimentological reconstruction obtained from a core drilled into the western trough of the Carmel coastal plain. The water body contained typical brackish calcareous fauna, with variable numerical abundance and low species richness of ostracods and foraminifera. The δ 18O and δ 13C of the ostracod Cyprideis torosa show close similarity to the present Pleistocene coastal aquifer isotopic values. This study therefore concludes that the wetlands were shallow-water bodies fed by groundwater, with no evidence of sea-water mixing. It seems that they developed as the result of high groundwater levels, transportation of sediments landward, and deposition of sand bars at the paleo-river mouths. It is still not fully understood why these wetlands deteriorated abruptly and disappeared within less than 1000 yr.

  14. Estimating the regional climate signal in a late Pleistocene and early Holocene lake-sediment δ18O record from Vermont, USA.

    Science.gov (United States)

    Mandl, Maximilian Benedict; Shuman, Bryan Nolan; Marsicek, Jeremiah; Grigg, Laurie

    2016-07-01

    We present a new oxygen isotope (δ18O) record from carbonate-rich lake sediments from central Vermont. The record from Twin Ponds spans from 13.5 cal ka BP (1950 AD) to present, but contains a 6 ka long hiatus starting shortly after 7.5 cal ka BP. We compare the record for ca. 13.5-7.5 cal ka BP with published δ18O data from the region after using a Bayesian approach to produce many possible chronologies for each site. Principal component analysis then identified chronologically-robust, multi-site oxygen isotope signals, including negative values during the Younger Dryas, but no significant deviations from the early Holocene mean of the regional records. However, differences among sites indicate significant trends that likely relate to interacting changes in the regional gradients of seasonal temperatures and precipitation as well as moisture sources, moisture pathways, and aridity that were controlled by large-scale climatic controls such as insolation, the progressive decline of the Laurentide Ice Sheet, and changes in oceanic circulation. Centennial shifts punctuate these trends at ca. 9.3 and 8.2 cal ka BP, and reveal that the local character of these short-lived features requires a detailed understanding of lake hydrology and regional isotopic gradients to yield reliable information for regional climate reconstructions.

  15. A previously unrecognized path of early Holocene base flow and elevated discharge from Lake Minong to Lake Chippewa across eastern Upper Michigan

    Science.gov (United States)

    Loope, Walter L.; Jol, Harry M.; Fisher, Timothy G.; Blewett, William L.; Loope, Henry M.; Legg, Robert J.

    2014-01-01

    It has long been hypothesized that flux of fresh meltwater from glacial Lake Minong in North America's Superior Basin to the North Atlantic Ocean triggered rapid climatic shifts during the early Holocene. The spatial context of recent support for this idea demands a reevaluation of the exit point of meltwater from the Superior Basin. We used ground penetrating radar (GPR), foundation borings from six highway bridges, a GIS model of surface topography, geologic maps, U.S. Department of Agriculture–Natural Resources Conservation Service soils maps, and well logs to investigate the possible linkage of Lake Minong with Lake Chippewa in the Lake Michigan Basin across eastern Upper Michigan. GPR suggests that a connecting channel lies buried beneath the present interlake divide at Danaher. A single optical age hints that the channel aggraded to 225 m as elevated receipt of Lake Agassiz meltwater in the Superior Basin began to wane floor was quickly breached and interbasin flow to Lake Chippewa was restored. Basal radiocarbon ages on wood from small lakes along the discharge path and a GIS model of Minong's shoreline are consistent with another transgression of Minong after ca. 9.5 ka. At the peak of the latter transgression, the southeastern rim of the Superior Basin (Nadoway Drift Barrier) failed, ending Lake Minong. Upon Minong's final drop, aggradational sediments were deposited at Danaher, infilling the prior breach.

  16. Structure, distribution, and evolution history of the Early Holocene erosional mud ridge system on the inner East China Sea shelf near the Yangtze River estuary

    Science.gov (United States)

    Feng, Zhibing; Liu, Baohua; Zhao, Yuexia; Li, Xishuang; Dada, Olusegun A.; Jiang, Li; Si, Shaokun

    2017-04-01

    erosional areas by the tidal currents, and the relict mud ridges were built. Evidence shows that the LMRs were formed by the early Holocene strata being scoured by a persistent southeasterly flowing current during 8-10 ka BP. The evolution of the LMRs occurred in three stages: (a) formation of the transgressional strata at 10-12 ka BP, (b) strong trough erosion at 8-10 ka BP, and (c) local adjustment (i.e., local erosion slightly and preservation) after 8 ka BP.

  17. Holocene climate change in Arctic Canada and Greenland

    Science.gov (United States)

    Briner, Jason P.; McKay, Nicholas P.; Axford, Yarrow; Bennike, Ole; Bradley, Raymond S.; de Vernal, Anne; Fisher, David; Francus, Pierre; Fréchette, Bianca; Gajewski, Konrad; Jennings, Anne; Kaufman, Darrell S.; Miller, Gifford; Rouston, Cody; Wagner, Bernd

    2016-09-01

    This synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the Holocene in Arctic Canada and Greenland. Our synthesis includes 47 records from a recently published database of highly resolved Holocene paleoclimate time series from the Arctic (Sundqvist et al., 2014). We analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records, mostly from datasets that did not fit the selection criteria for the Arctic Holocene database. Combined, we review evidence from a variety of proxy archives including glaciers (ice cores and glacial geomorphology), lake sediments, peat sequences, and coastal and deep-marine sediments. The temperature-sensitive records indicate more consistent and earlier Holocene warmth in the north and east, and a more diffuse and later Holocene thermal maximum in the south and west. Principal components analysis reveals two dominant Holocene trends, one with early Holocene warmth followed by cooling in the middle Holocene, the other with a broader period of warmth in the middle Holocene followed by cooling in the late Holocene. The temperature decrease from the warmest to the coolest portions of the Holocene is 3.0 ± 1.0 °C on average (n = 11 sites). The Greenland Ice Sheet retracted to its minimum extent between 5 and 3 ka, consistent with many sites from around Greenland depicting a switch from warm to cool conditions around that time. The spatial pattern of temperature change through the Holocene was likely driven by the decrease in northern latitude summer insolation through the Holocene, the varied influence of waning ice sheets in the early Holocene, and the variable influx of Atlantic Water into the study region.

  18. Climate change and human occupation in the Southern Arabian lowlands during the last deglaciation and the Holocene

    Science.gov (United States)

    Lézine, Anne-Marie; Robert, Christian; Cleuziou, Serge; Inizan, Marie-Louise; Braemer, Frank; Saliège, Jean-François; Sylvestre, Florence; Tiercelin, Jean-Jacques; Crassard, Rémy; Méry, Sophie; Charpentier, Vincent; Steimer-Herbet, Tara

    2010-07-01

    Paleohydrological and archaeological evidence from the Southern and South-Eastern Arabian Peninsula reveal strong relations between phases of human settlements and climate change linked to the Indian monsoon system. During the early to mid-Holocene, large fresh-water lakes extended in the lowland deserts of Ramlat as-Sab'atayn (Yemen) and Wahiba Sands (Oman), which were very similar to those occurring in the North, in the Rub' al-Khali (Saudi Arabia), at that time. Many archaeological sites, characterized by scattered stone artefacts, ostrich-eggshells and bones around hearths, are related to this lacustrine phase, which culminated around 10 000-8000 cal yr B.P. in the lowland deserts before the lakes progressively dried up. The last record of fresh-water bodies' extensions date back 7300 cal yr B.P. at Shabwa (Yemen) and 7500 cal yr B.P. at al-Haid (Oman). Then, fresh-water was probably available only from seasonal run-off from adjacent highlands, where paleolakes persisted into the late Holocene. Dry climate conditions in the inland desert of Yemen during the late Holocene coincide with a phase of intensive human inhabitation as testified by development of irrigation in the piedmontane areas, numerous necropolises of built collective burials and houses.

  19. AMS 14 C dating controlled records of monsoon and Indonesian throughflow variability from the eastern Indian Ocean of the past 32,000 years

    Science.gov (United States)

    Li, Z. Y.; Chen, M. T.; Shi, X.; Liu, S.; Wang, H.

    2015-12-01

    Zi-Ye Li a, Min-Te Chen b, Hou-Jie Wang a, Sheng-Fa Liu c, Xue-Fa Shi ca College of Marine Geosciences, Ocean University of China, Qingdao 266100, P.R. Chinab Institute of Applied Geosciences, National Taiwan Ocean University, Keelung, Taiwan 20224, ROCc First Institute of Oceanography, SOA, Qingdao 266100, P.R. China Indonesian throughflow (ITF) is one of the most important currents responsible for transporting heat and moisture from the western Pacific to the Indian Oceans. The ITF is also well-known as effectively in modulating the global climate change with the interactions among ENSO and Asian monsoons. Here we present an AMS 14C dating controlled sea surface temperature (SST) record from core SO184-10043 (07°18.57'S, 105°03.53'E), which was retrieved from 2171m water depth at a north-south depression located at the southeastern offshore area of Sumatera in the eastern Indian Ocean. Based on our high-resolution SST using Mg/Ca analyses based on planktonic foraminifera shells of Globigerinoides ruber and alkenone index, U k'37-SST, oxygen isotope stratigraphy, and AMC 14C age-controls, our records show that, during the past 32,000 years, the SSTs were decreased which imply weaker ITF during Marine Isotope Stage (MIS) 2 and 3. The weaker UTF may respond to strengthened northeast monsoon during the boreal winter. During 21 to 15ka, the southeast monsoon had been stronger and the northeast monsoon was relatively weaker. During 15 to 8ka, rapid sea level rising may allow the opening of the gateways in the Makassar Strait and Lombok Strait that may have further strengthened the ITF. During the early Holocene, the northeast and southeast monsoons seem to be both strengthened. We will discuss the implications of the hydrographic variability and their age uncertainties in this paper during the meeting.

  20. South American Summer Monsoon history recorded in Brazilian speleothems

    Science.gov (United States)

    Wang, X.; Auler, A. S.; Edwards, R. L.; Cheng, H.

    2008-12-01

    We have obtained three high-resolution oxygen isotopic records of cave calcites from Caverna Botuverá, southern Brazil, Gruta do Padre, central Brazil, and Caverna Paraíso, Amazonian Brazil. All three records have chronologies determined by U-Th dates and span the last 90, 20 and 50 thousand years, respectively. Tests for equilibrium conditions show that their oxygen isotopic variations are primarily caused by climate change. The three records thus can provide information about precipitation history and fluctuations of the South American Summer Monsoon along a latitudinal transect from 28° S to 4° S. During the last glacial period, the three oxygen isotopic profiles show abrupt millennial-scale variations, which are anti- correlated with the Chinese speleothem monsoon records and northern high-latitude ice core records. This is likely related to the displacement of the mean position of the intertropical convergence zone and associated asymmetry of Hadley cells, consistent with an oceanic meridional overturning circulation mechanism for driving the abrupt climate events. However, the three records show distinct isotopic patterns in Holocene epoch. The δ18O values in the Botuvera record decrease steadily throughout Holocene, while in the Padre record, the δ18O drops slightly until ~6-7 thousand years ago and then gradually increases until the present. The Paraiso Holocene record is similar to the Padre one, but with a much greater amplitude. Together with Andean ice core and lake records, our observations suggest asynchronous changes in Holocene monsoonal precipitation in South America, possibly related to strengthened zonal tropical air-sea interactions after the melting of the large northern ice sheets.

  1. Early Holocene environmental change and the presence of Mesolithic people in the Tungelroyse Beek valley near Mildert, the Netherlands

    NARCIS (Netherlands)

    Woelders, Lineke; Bos, Johanna A A; de Kort, Jan Willem; Hoek, Wim Z.

    2016-01-01

    An archaeological excavation in the Tungelroyse Beek valley revealed the remains of two red deer specimens (Cervus elaphus) of Early Mesolithic age that possibly were the victims of hunter-gatherers. The find of animal remains of this age is unique in the Netherlands. In this respect, a sediment cor

  2. The Holocene warm-humid phases in the North China Plain as recorded by multi-proxy records

    Institute of Scientific and Technical Information of China (English)

    CUI Jianxin; ZHOU Shangzhe; CHANG Hong

    2009-01-01

    The grain size and palinology of sediment and the frequency of 14C dada provide an integrated reconstruction of the Holocene warm-humid phases of the North China Plain. Two clear intense and long-lasting warm-humid phases were identified by comprehensive research in this region. The first phase was dated back to the early Holocene (9 000-7 000 a BP), and the second was centered at 5 000-3 000 a BP. The warm-humid episode between 9 000 and 7 000 a BP was also recognized at other sites showing global climatic trends rather than local events. Compared with the concern to the warm-humid phase of the early Holocene, the second one was not paid enough attention in the last few decades. The compilation of the Holocene paleoclimate data suggests that perhaps the second warm-humid phase was pervasive in monsoon region of China. In perspective of environmental archaeology, much attention should be devoted to it, because the flourish and adaptation of the Neolithic cultures and the building up of the first state seem to corresponding to the general warm-humid climatic conditions of this period. In addition, a warm-humid interval at 7 200-6 500 a BP was recognized by the grain size data from three sites. However, this warm-humid event was not shown in pollen assemblage and temporal distribution of 14C data. Perhaps, the resolution for climatic reconstruction from pollen and temporal distribution of 14C data cited here is relatively low and small-amplitude and short-period climatic events cannot be well reflected by the data. Due to the difference in locality and elevation of sampling site, as well as in resolution of proxy records, it is difficult to make precise correlation. Further work is needed in the future.

  3. Early Holocene fauna from a new subfossil site: A first assessment from Christmas River, south central Madagascar

    Directory of Open Access Journals (Sweden)

    Patricia C. Wright

    2012-06-01

    Full Text Available We report on faunal remains recovered during recent explo­rations at ‘Christmas River’, the only subfossil locality known from Madagascar’s south central plateau. Recovered remains of several extinct taxa date to approximately 10,000 14C years before present (BP, including crocodiles, tortoises, the elephant bird Aepyornis, the carnivoran Cryptoprocta spelea, the lemurs Archaeolemur majori, Pachylemur insignis, and Megaladapis edwardsi, and abundant remains of the dwarf hippopotamus, Hippopotamus lemerlei. The presence of southern – limited, forest – dependent species at Christmas River supports the hypothesis that forest once extended, perhaps discontinu­ously, across the central highlands towards the west. One theory is that sites in the north central highlands, which are higher in elevation, maintained more mesic conditions during Plio–Quaternary climate shifts than those of the lower elevation sites of the south central highlands. Thus, elevation above sea level may have acted as a filter that limited species dispersal across the island in the past. Such a scenario would explain the distinction between more humid, higher elevation, northern highland subfossil communities versus more arid, lower eleva­tion, southern subfossil communities. Continued exploration at Christmas River thus provides a remarkable opportunity for deciphering ecological changes that have taken place in south central Madagascar during the Holocene. RÉSUMÉMadagascar est reconnue comme l’une des régions les plus sensibles du monde en ce qui concerne les menaces pesant sur sa biodiversité, et cela à cause de niveaux d’endémisme inégalés, d’une diversité variée et d’un impact humain important sur l’environnement. Suite à la colonisation par l’Homme il y a plus de 2000 ans, des extinctions de masse de la faune et un important recul forestier ont eu lieu en laissant des marques sur les écosystèmes modernes qui sont dans un état de

  4. Eccentricity paced monsoon-like system along the northwestern Tethyan margin during the Valanginian (Early Cretaceous): new insights from detrital and nutrient fluxes into the Vocontian Basin (SE France)

    Science.gov (United States)

    Charbonnier, Guillaume; Duchamp-Alphonse, Stéphanie; Adatte, Thierry; Föllmi, Karl; Spangenberg, Jorge; Gardin, Silvia; Galbrun, Bruno; Colin, Christophe

    2016-04-01

    High-resolution studies document significant fluctuations between arid/humid and cool/warm conditions in the Northwestern Tethyan margin at the late early and late Valanginian. Despite numerous investigations carried out on the Valanginian climate, very few works depict high resolution climate conditions and related changes in the weathering pattern for the whole Valanginian beyond the Weissert Episode and no one astronomically calibrates them. In this study, high-resolution changes in terrigenous and nutrient fluxes into the Vocontian Basin were investigated for the Late Berriasian - Late Valanginian time interval, in order to assess the precipitation patterns in the source areas and to evaluate the effect of orbital forcing on the strength of the hydrological cycle. New high-resolution mineralogical (bulk-rock and clay fraction) and geochemical (phosphorus and oxygen isotope) data are used from the astronomically calibrated Orpierre section. For the first time, Kaolinite, Detrital, and Phosphorus Accumulation Rates (KAR, DAR and PAR) are calculated and compared to a set of 547 geochemical, and 260 mineralogical published data from other Vocontian sections. It appears that three regional increases in the KAR document three successive humid episodes during the Valanginian. This is confirmed by contemporaneous increases in DAR and partly also PAR, which highlight higher terrigenous and nutrient fluxes to the Vocontian Basin during these episodes. Concomitant decreases in the δ18Owhole-rock signals may reflect higher sea-surface temperatures during the early Valanginian and the early-late Valanginian transition. The occurrence of the three humid episodes is interpreted to relate to an orbital-paced monsoonal circulation pattern through seasonally reversing movements of air mass heat and precipitation over the northwestern Tethyan margin. In particular, based on the correlation between the 405 kyr eccentricity cycles and the KAR signal obtained at Orpierre, an

  5. The dating and interpretation of Chusang indicates permanent human occupation of the interior of the Tibetan Plateau in the early Holocene

    Science.gov (United States)

    Meyer, Michael; Aldenderfer, Mark; Wang, Zhijun; Hoffmann, Dirk; Dahl, Jenny; Degering, Detlev; Haas, Randy; Schlütz, Frank; Gliganic, Luke; May, Jan-Hendrik

    2017-04-01

    central plateau. We suggest that migration onto the plateau during the early Holocene was enabled by the wetter regional climate at that time. These findings challenge (i) current models of the occupation of the Tibetan Plateau and (ii) the original dating of Chusang that - based on OSL multi-grain dating - suggests and an age for the imprints of ca. 20 ka. 1. Aldenderfer, M. (2011): Peopling the Tibetan plateau: Insights from archaeology. High Alt. Med. Biol. 12, 141-147. 2. Chen, F. H. et al. (2015): Agriculture facilitated permanent human occupation of the Tibetan Plateau after 3600 B.P. Science 347, 248-250. 3. Meyer, M.C. et al. (2017): Permanent human occupation of the central Tibetan Plateau in the early Holocene. Science 355, 64-67. 4. Lu, D. et al. (2016): Ancestral Origins and Genetic History of Tibetan Highlanders. The American Journal of Human Genetics 99, 580-594. 5. Xiang, K. et al. (2013): Identification of a Tibetan-specific mutation in the hypoxic gene EGLN1 and its contribution to high-altitude adaptation. Molecular biology and evolution 30, 1889-1898.

  6. Timing, cause and consequences of mid-Holocene climate transition in the Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Saraswat, R.; Naik, Dinesh K.; Nigam, R.; Gaur, A.S.

    termination of the Indus valley civilization and Holocene south Asian monsoon variability. Geophysical Research Letters 30, 1425, doi:10.1029/2002GL016822. Steinhilber, F., Beer, J., Fröhlich, C., 2009. Total solar irradiance during the Holocene. Geophysical... of Holocene precipitation for Rajasthan, India, based on pollen and lake level data. Quaternary Research 19, 1-17. Thompson, L.G., Yao, T., Davis, M.E., Henderson, K.A., Mosley-Thompson, E., Lin, P.-N., Beer, J., Synal, H.-A., Cole-Dai, J., Bolzan, J...

  7. Global Change in the Holocene

    Science.gov (United States)

    Alverson, Keith

    2004-05-01

    Many people, even perhaps the occasional Eos reader, associate the term ``global change'' with warming caused by mankind's recent addiction to fossil fuels. Some may also be well aware of enormous global changes in the distant past uninfluenced by humans; for example, Pleistocene ice ages. But was there any ``global change'' between the end of the last ice age and the onset of industrialization? The answer to this question is addressed early-in the title, even-in the new book Global Change in the Holocene. I don't suggest anyone stop reading after the title, though; the rest of the book is both highly informative and a real pleasure to read. The opening chapter tells us that the Holocene is certainly not, as sometimes charged, a ``bland, pastoral coda to the contrasted movements of a stirring Pleistocene symphony.'' Rather, it is a ``period of continuous change.'' Melodious language aside, the combination of sustained and high-amplitude climatic variability and a wealth of well-preserved, precisely datable paleoclimate archives make the Holocene unique. Only by studying the Holocene can we hope to unravel the low-frequency workings of the Earth system and the degree to which humans have changed our world. This book sets out to teach the reader how to obtain the relevant data and how to use it to do much more than showing static analogues of possible future climate states. It challenges researchers to discern in their data the effects of the dynamic processes underlying coupled variability in the Earth's climate and ecosystems. These processes continue to act today, and it is through providing an understanding of these system dynamics in the Holocene that paleo-environmental studies can make the greatest contribution to future-oriented concerns.

  8. A singular spectrum analysis on Holocene climatic oscillation from lake sedimentary record in Minqin Basin,China

    Institute of Scientific and Technical Information of China (English)

    JIN Liya; CHEN Fahu; DING Xiaojun; ZHU Yah

    2007-01-01

    The total organic carbon (TOC) content series from the lake sediment of Minqin Basin (100°57'-104°57'E, 37°48'-39°17'N) in northwestern China, which has a 10 000-year-long paleo-climatic proxy record, was used to analyze the Holocene climate changes in the local region. The proxy record was established in the Sanjiaocheng (SJC), Triangle Town in Chinese, Section (103°20'25"E, 39°00'38"N),which is located at the northwestern boundary of the present Asian summer monsoon in China, and is sensitive to global environmental and climate changes. Applying singular spectrum analysis (SSA) to the TOC series, principal climatic oscillations and periodical changes were studied. The results reveal 3 major patterns of climate change regulated by reconstructed components (RCs). The first pattern is natural long-term trend of climatic change in the local area (Minqin Basin), indicating a relatively wetter stage in early Holocene (starting at 9.5 kaBP), and a relatively dryer stage with a strong lake desiccation and a declined vegetation cover in mid-Holocene (during 7-6 kaBP). From 4.0 kaBP to the present, there has been a gradually decreasing trend in the third reconstructed component (RC3) showing that the local climate changed again into a dryer stage. The second pattern shows millennial-centennial scale oscillations containing cycles of 1 600 and 800 years that have been present throughout almost the entire Holocene period of the last 10 000 years. The third pattern is a millennial-centennial scale variation with a relatively smaller amplitude and unclear cycles showing a nonlinear interaction within the earth's climate systems.

  9. New data on changes in the European distribution of the mammoth and the woolly rhinoceros during the second half of the Late Pleistocene and the early Holocene

    NARCIS (Netherlands)

    Markova, A. K.; Puzachenko, A. Yu.; van Kolfschoten, T.; van der Plicht, J.; Ponomarev, D. V.

    2013-01-01

    The PALEOFAUNA database developed by the authors contains information on more than 5500 Eurasian localities that yielded Late Pleistocene and Holocene mammalian fossils. The database is used to analyze the changes in the geographical distribution during the second half of the Late Pleistocene and th

  10. The expansion of hazel (Corylus avellana L.) in the southern Alps: a key for understanding its early Holocene history in Europe?

    NARCIS (Netherlands)

    Finsinger, W.; Tinner, W.; Knaap, W.O. van der; Ammann, B.

    2006-01-01

    In Northwestern and Central Europe the Holocene expansion of Corylus occurred before or at the same time as that of other thermophilous trees (e.g. Quercus). This sequence of expansion has been explained by migrational lag, competition, climatic changes, human assistance, or disturbance by fire. In

  11. New data on changes in the European distribution of the mammoth and the woolly rhinoceros during the second half of the Late Pleistocene and the early Holocene

    NARCIS (Netherlands)

    Markova, A. K.; Puzachenko, A. Yu.; van Kolfschoten, T.; van der Plicht, J.; Ponomarev, D. V.

    2013-01-01

    The PALEOFAUNA database developed by the authors contains information on more than 5500 Eurasian localities that yielded Late Pleistocene and Holocene mammalian fossils. The database is used to analyze the changes in the geographical distribution during the second half of the Late Pleistocene and

  12. The expansion of hazel (Corylus avellana L.) in the southern Alps: a key for understanding its early Holocene history in Europe?

    NARCIS (Netherlands)

    Finsinger, W.; Tinner, W.; Knaap, W.O. van der; Ammann, B.

    2006-01-01

    In Northwestern and Central Europe the Holocene expansion of Corylus occurred before or at the same time as that of other thermophilous trees (e.g. Quercus). This sequence of expansion has been explained by migrational lag, competition, climatic changes, human assistance, or disturbance by fire. In

  13. An unusual early Holocene diatom event north of the Getz Ice Shelf (Amundsen Sea): Implications for West Antarctic Ice Sheet development

    Science.gov (United States)

    Esper, O.; Gersonde, R.; Hillenbrand, C.; Kuhn, G.; Smith, J.

    2011-12-01

    Modern global change affects not only the polar north but also, and to increasing extent, the southern high latitudes, especially the Antarctic regions covered by the West Antarctic Ice Sheet (WAIS). Consequently, knowledge of the mechanisms controlling past WAIS dynamics and WAIS behaviour at the last deglaciation is critical to predict its development in a future warming world. Geological and palaeobiological information from major drainage areas of the WAIS, like the Amundsen Sea Embayment, shed light on the history of the WAIS glaciers. Sediment records obtained from a deep inner shelf basin north of Getz Ice Shelf document a deglacial warming in three phases. Above a glacial diamicton and a sediment package barren of microfossils that document sediment deposition by grounded ice and below an ice shelf or perennial sea ice cover (possibly fast ice), respectively, a sediment section with diatom assemblages dominated by sea ice taxa indicates ice shelf retreat and seasonal ice-free conditions. This conclusion is supported by diatom-based summer temperature reconstructions. The early retreat was followed by a phase, when exceptional diatom ooze was deposited around 12,500 cal. years B.P. [1]. Microscopical inspection of this ooze revealed excellent preservation of diatom frustules of the species Corethron pennatum together with vegetative Chaetoceros, thus an assemblage usually not preserved in the sedimentary record. Sediments succeeding this section contain diatom assemblages indicating rather constant Holocene cold water conditions with seasonal sea ice. The deposition of the diatom ooze can be related to changes in hydrographic conditions including strong advection of nutrients. However, sediment focussing in the partly steep inner shelf basins cannot be excluded as a factor enhancing the thickness of the ooze deposits. It is not only the presence of the diatom ooze but also the exceptional preservation and the species composition of the diatom assemblage

  14. Holoceno marino en la península Potter, Isla 25 de Mayo, Antártida Marine sediments of the early Holocene in the Potter Península, King George Island, Southern Shetland, Antarctica

    Directory of Open Access Journals (Sweden)

    R.A. del Valle

    2007-11-01

    Full Text Available La sucesión sedimentaria del Holoceno temprano expuesta en la terraza marina de 3,77 m s.n.m. en la costa sur de la caleta Potter (Isla 25 de Mayo/King George Island, islas Shetland del Sur, Antártida contiene invertebrados marinos, algas y huesos de foca y pingüino. Dataciones por radiocarbono de huesos de pingüino obtenidos en esta sucesión dieron edades de 7.562 a cal AP (años calibrados antes del Presente y 7.414 a cal AP. Las dataciones indican que los huesos están entre los restos de vertebrados más antiguos del Holoceno hallados en las Islas Shetland del Sur, y pueden ser consideradas como edades mínimas de ocupación por estas aves de las costas de las islas en el Holoceno temprano. Esto indica condiciones interglaciales en esa época, con situación clima/hielo marino similar a la presente y condiciones marinas estacionalmente abiertas.The early Holocene sedimentary succession exposed at the 3.77 m-high marine terrace on the south coast of Potter Cove (King George Island/Isla 25 de Mayo, South Shetland Islands, Antarctica contains marine invertebrates, seaweed and bones of seals and penguins. Radiocarbon dating on penguin bones from this succession yielded 7,562 cal yr BP and 7,414 cal yr BP. These dates suggest that the bones are among the oldest remains of Holocene vertebrates found in South Shetland Islands, and may be considered as minimum ages of penguin occupation of coastal areas on the islands during the early Holocene. This indicates interglacial conditions in this time, with climate/sea ice situation similar to the present and seasonally open marine conditions.

  15. Diagenetic effects on magnetic minerals in a Holocene lacustrine sediment core from Huguangyan maar lake, southeast China

    Science.gov (United States)

    Wu, Xudong; Wang, Yong; Bian, Liu; Shen, Ji

    2016-09-01

    strong Asian summer monsoon intensity during the early Holocene are accountable for intensive diagenesis in the lowermost subsection. Complete erasing of detrital magnetic input signal at certain positions of the lowermost subsection, and considerable formation of authigenic siderite indicate that palaeomagnetic records of the studied core have been significantly compromised. The studied core has relatively higher TOC content, lower detrital matter content, calmer sedimentary environments, and less DO available at its water-sediment interface than the cores retrieved at relatively shallower water depths, which all contribute to its relatively stronger diagenesis. Progressive thickening of the upper two subsections with increasing water depth is owing to progressive increase in sedimentation rate with increasing water depth, which is the key factor in determining the thickness of each diagenetic subsection of cores from HGY. It would be better that lake sediments for palaeomagnetic investigations collected at a water depth shallower than the depth of its thermocline.

  16. Holocene Lake Records on Kamchatka

    Science.gov (United States)

    Diekmann, Bernhard; Biskaborn, Boris; Chapligin, Bernhard; Dirksen, Oleg; Dirksen, Veronika; Hoff, Ulrike; Meyer, Hanno; Nazarova, Larisa

    2014-05-01

    palaeoecologocal responses in different lake systems under same climatic boundary conditions. Our findings give evidence of longterm climate changes that suggest the existence of a warm and humid early Holocene climate optimum between roughly 9.0 and 4.5 ka BP, followed by climate deterioration of the neoglacial epoch in concert with summer cooling, glacial advances, and enhanced continentality. Two strong cooling episodes punctuated late Holocene climate development between 4.5 and 3.5 ka BP and during the last millennium, marking the prelude of neoglacial cooling and the Little Ice Age. This general development of Holocene climate on Kamchatka is in line with environmental changes in the neighbouring Sea of Okhotsk, where the pattern of sea-ice dynamics is consistent with early Holocene warmth and Neoglacial climate cooling. While the marine records from the Sea of Okhotsk mainly reflect winter conditions, our findings show that summer climate on Kamchatka shows a similar trend of temporal change. Holocene climate variability on Kamchatka was mainly driven by external insolation forcing, changes in solar activity, and internal climate forcing. The latter is dictated by by the relative position of the Aleutan Low in response to the prevailing modes of Pacific Decadal Oscillation and the Arctic Oscillation that both control the influence of maritime or continental air masses and the intensity of rain- or snow-bringing cyclones.

  17. Quaternary ecological responses and impacts of the Indian Ocean Summer Monsoon at Nam Co, Southern Tibetan Plateau

    NARCIS (Netherlands)

    Günther, F.; Witt, R.; Schouten, Stefan|info:eu-repo/dai/nl/137124929; Mausbacher, R.; Daut, G.; Zhu, Liping; Xu, B.; Yao, T.; Gleixner, G.

    2015-01-01

    The transition from the Last Glacial to the current Interglacial, the Holocene, represents an important period with climatic and environmental changes impacting ecosystems. In this study, we examined the interplay between the Indian Ocean Summer Monsoon (IOSM) and the Westerlies at lake Nam Co, sout

  18. Quaternary ecological responses and impacts of the Indian Ocean Summer Monsoon at Nam Co, Southern Tibetan Plateau

    NARCIS (Netherlands)

    Günther, F.; Witt, R.; Schouten, S.; Mausbacher, R.; Daut, G.; Zhu, L.; Xu, B.Q.; Yao, T.; Gleixner, G.

    2015-01-01

    The transition from the Last Glacial to the current Interglacial, the Holocene, represents an important period with climatic and environmental changes impacting ecosystems. In this study, we examined the interplay between the Indian Ocean Summer Monsoon (IOSM) and the Westerlies at lake Nam Co,

  19. Quaternary ecological responses and impacts of the Indian Ocean Summer Monsoon at Nam Co, Southern Tibetan Plateau

    NARCIS (Netherlands)

    Günther, F.; Witt, R.; Schouten, Stefan|info:eu-repo/dai/nl/137124929; Mausbacher, R.; Daut, G.; Zhu, Liping; Xu, B.; Yao, T.; Gleixner, G.

    The transition from the Last Glacial to the current Interglacial, the Holocene, represents an important period with climatic and environmental changes impacting ecosystems. In this study, we examined the interplay between the Indian Ocean Summer Monsoon (IOSM) and the Westerlies at lake Nam Co,

  20. Quantitative reconstruction of summer precipitation using a mid-Holocene δ13C common millet record from Guanzhong Basin, northern China

    Science.gov (United States)

    Yang, Qing; Li, Xiaoqiang; Zhou, Xinying; Zhao, Keliang; Sun, Nan

    2016-12-01

    To quantitatively reconstruct Holocene precipitation for particular geographical areas, suitable proxies and faithful dating controls are required. The fossilized seeds of common millet (Panicum miliaceum) are found throughout the sedimentary strata of northern China and are suited to the production of quantitative Holocene precipitation reconstructions: their isotopic carbon composition (δ13C) gives a measure of the precipitation required during the growing season of summer (here the interval from mid-June to September) and allows these seeds to be dated. We therefore used a regression function, as part of a systematic study of the δ13C of common millet, to produce a quantitative reconstruction of mid-Holocene summer precipitation in the Guanzhong Basin (107°40'-107°49' E, 33°39'-34°45' N). Our results showed that mean summer precipitation at 7.7-3.4 ka BP was 353 mm, ˜ 50 mm or 17 % higher than present levels, and the variability increased, especially after 5.2 ka BP. Maximum mean summer precipitation peaked at 414 mm during the period 6.1-5.5 ka BP, ˜ 109 mm (or 36 %) higher than today, indicating that the East Asian summer monsoon (EASM) peaked at this time. This work can provide a new proxy for further research into continuous paleoprecipitation sequences and the variability of summer precipitation, which will promote the further research into the relation between early human activity and environmental change.

  1. Holocene evolution of summer winds and marine productivity in the tropical Indian Ocean in response to insolation forcing: data-model comparison

    Directory of Open Access Journals (Sweden)

    F. C. Bassinot

    2011-02-01

    Full Text Available The relative abundance of Globigerinoides bulloides was used to infer Holocene paleo-productivity changes at ODP Site 723 (19°03' N, 57°37' E; Oman Margin and core MD77-191 (07°30' N, 76°43' E; Southern tip of India. Today, the primary productivity at both sites peaks during the summer season, when monsoon winds result in local Eckman pumping, which brings more nutrients to the surface. On a millennium time-scale, however, the % G.~bulloides records indicate an opposite evolution of paleo-productivity at these sites through the Holocene. The Oman Margin productivity was maximal at ~9 ka (boreal summer insolation maximum and decreased since then, suggesting a direct response to insolation forcing. On the opposite, the productivity at the southern tip of India was minimum at ~9 ka, and strengthened towards the present.

    Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model. These reconstructions are fully coherent with the marine core data. They confirm that the evolution of particulate export production and foraminifera assemblages at our two sites have been directly linked with the strength of the upwelling. Model simulations at 9 ka and 6 ka BP show that the relative evolution between the two sites since the early Holocene can be explained by the weakening but also the southward shift of monsoon winds over the Arabian sea during boreal summer.

  2. Glacial-interglacial water cycle, global monsoon and atmospheric methane changes

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Zhengtang; Wu, Haibin [Chinese Academy of Sciences, Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Beijing (China); Zhou, Xin [Chinese Academy of Sciences, Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Beijing (China); University of Science and Technology of China, School of Earth and Space Sciences and Institute of Polar Environment, Hefei (China)

    2012-09-15

    The causes of atmospheric methane (CH{sub 4}) changes are still a major contention, in particular with regards to the relative contributions of glacial-interglacial cycles, monsoons in both hemispheres and the late Holocene human intervention. Here, we explore the CH{sub 4} signals in the Antarctic EPICA Dome C and Vostok ice records using the methods of timeseries analyses and correlate them with insolation and geological records to address these issues. The results parse out three distinct groups of CH{sub 4} signals attributable to different drivers. The first group ({proportional_to}80% variance), well tracking the marine {delta}{sup 18}O record, is attributable to glacial-interglacial modulation on the global water cycle with the effects shared by wetlands at all latitudes, from monsoonal and non-monsoonal regions in both hemispheres. The second group ({proportional_to}15% variance), centered at the {proportional_to}10-kyr semi-precession frequency, is linkable with insolation-driven tropical monsoon changes in both hemispheres. The third group ({proportional_to}5% variance), marked by millennial frequencies, is seemingly related with the combined effect of ice-volume and bi-hemispheric insolation changes at the precession bands. These results indicate that bi-hemispheric monsoon changes have been a constant driver of atmospheric CH{sub 4}. This mechanism also partially explains the Holocene CH{sub 4} reversal since {proportional_to}5 kyr BP besides the human intervention. In the light of these results, we propose that global monsoon can be regarded as a system consisting of two main integrated components, one primarily driven by the oscillations of Inter-Tropical Convergence Zone (ITCZ) in response to the low-latitude summer insolation changes, anti-phase between the two hemispheres (i.e. the ITCZ monsoon component); and another modulated by the glacial-interglacial cycles, mostly synchronous at the global scale (i.e. the glacial-interglacial monsoon

  3. Holocene glacial fluctuations in southern South America

    Science.gov (United States)

    Reynhout, S.; Sagredo, E. A.; Kaplan, M. R.; Aravena, J. C.; Martini, M. A.; Strelin, J. A.; Schaefer, J. M.

    2016-12-01

    Understanding the timing and magnitude of former glacier fluctuations is critical to decipher long-term climatic trends and to unravel both natural cycles and human impact on the current glacial behavior. Despite more than seven decades of research efforts, a unifying model of Holocene glacial fluctuations in Southern South America remains elusive. Here, we present the state-of-the-art regarding the timing of Holocene glacial fluctuation in southern Patagonia-Tierra del Fuego, with a focus on a new generation of high-resolution radiocarbon and 10Be surface exposure dating chronologies. Recently acquired evidence suggest that after receding from advanced Late Glacial positions, Patagonian glaciers were for the most part close to, or even behind, present ice margins during the Early Holocene. On the other hand, emerging chronologies indicate that in some areas there were extensive expansions (century scale?) that punctuated the warm interval. Subsequently, we have evidence of multiple millennial timescale glacial advances starting in the middle Holocene. Several glacial maxima are defined by moraines and other landforms from 7000 years ago to the 19th century, with a gap sometime between 4,500 and 2,500 years ago. The last set of advances began around 800-600 years ago. Although glacial activity is documented in Patagonia at the same time as the European Little Ice Age, the extent of these glacial events are less prominent than those of the mid-Holocene. The causes that may explain these glacial fluctuations remain elusive. Finally, we discuss ongoing efforts to better define the timing and extent of Holocene glaciations in southern South America, and to establish the basis to test competing hypothesis of regional Holocene climate variability.

  4. Hydrosedimentary records and Holocene environmental dynamics in the Yamé Valley (Mali, Sudano-Sahelian West Africa)

    Science.gov (United States)

    Le Drézen, Yann; Lespez, Laurent; Rasse, Michel; Garnier, Aline; Coutard, Sylvie; Huysecom, Eric; Ballouche, Aziz

    2010-03-01

    Research conducted in the Yamé Valley (Dogon Country, Mali) provides valuable information about the river systems and their Holocene evolution in Sudano-Sahelian West Africa. Past research in the region has relied primarily on marine and lacustrine records. The new results confirm correlation between palaeoclimatic fluctuations recorded in both the river system and in tropical African lakes. They offer a new continental milestone for understanding of the environmental repercussions of Holocene monsoon oscillations. These studies demonstrate the value of river systems as a palaeoenvironmental record and the role of palaeoclimatic and anthropogenic factors in the Holocene dynamics of Sudano-Sahelian hydrosystems.

  5. The Holocene History of Placentia Bay, Newfoundland

    DEFF Research Database (Denmark)

    Sheldon, Christina; Seidenkrantz, Marit-Solveig; Reynisson, Njall

    2013-01-01

    Marine sediments analyzed from cores taken in Placentia Bay, Newfoundland, located in the Labrador Sea, captured oceanographic and climatic changes from the end of the Younger Dryas through the Holocene. Placentia Bay is an ideal site to capture changes in both the south-flowing Labrador Current...... have been analyzed using several climate proxies, including benthic foraminifera, diatoms, IP25, dinoflagellate cysts and XRF. Together, these cores provide high-resolution records of the changes in climatic conditions over the last ca. 13,000 years in the southern Labrador Sea. After the Younger Dryas...... ended, the beginning of the warmer early Holocene was recorded by an increase in productivity-linked foraminiferal and diatom assemblages, as well as a drop in the presence of the sea-ice indicator IP25 in core 14G (Pearce et al., 2012). Variability in atmospheric circulation during the Holocene...

  6. Pollen and charcoal analyses from Lake Etu-Mustajärvi, Southern Finland, with special reference to an early Holocene Urtica pollen maximum

    Directory of Open Access Journals (Sweden)

    Sarmaja-Korjonen, K.

    1995-06-01

    Full Text Available Sediments of a small lake, Etu-Mustajärvi, in southern Finland, were studied with respect to their fossil pollen and charcoal content. Pollen analysis showed a typical development of vegetation from the earliest Holocene onwards, since the isolation of the lake from the Baltic Ice Lake. The emerged land was first colonised by herbs and bushes, and for the first time in Finland an Urtica maximum of 4 % is reported for this period. It is considered possible that Urtica may have been a commoner part of the pollen flora of newly emerged land in south Finland than has been previously thought. Charcoal analysis was undertaken to examine the Holocene history of forest fires in the area. At least in the Lammi area, charcoal seems to have been most abundant about 8000-6000 BP, a result which is in apparent disagreement with the general concept that the period was moist and thus forest fire frequency could not have been high.

  7. Records from Lake Qinghai: Holocene climate history of Northeastern Tibetan Plateau linking to global change

    Science.gov (United States)

    An, Z.; Colman, S.; Zhou, W.; Brown, E.; Li, X.; Jull, T.; Wang, S.; Liu, W.; Sun, Y.; Lu, X.; Song, Y.; Chang, H.; Cai, Y.; Xu, H.; Wang, X.; Liu, X.; Wu, F.; Han, Y.; Cheng, P.; Ai, L.; Wang, Z.; Qiang, X.; Shen, J.; Zhu, Y.; Wu, Z.; Liu, X.

    2008-12-01

    Lake Qinghai (99°36'-100°16'E, 36°32'-37°15'N ) of the north eastern margin of Tibet Plateau is the largest inland lake of China. It sits on the transitional zone of Asian monsoon- arid areas, receives influences of Asian monsoons and Westerlies, thus sensitive to global climate changes. Although previous studies had investigated Holocene climate change of Lake Qinghai area, it is rare to see precise Holocene climatic sequences of Lake Qinghai, nor in-depth discussions on controlling factors of Lake Qinghai climate changes. In Year 2005, with support from ICDP, Chinese Academy of Sciences (CAS), Chinese Ministry of Science and Technology (MOST) and National Science Foundation of China (NSFC), Drilling, Observation and Sampling of the Earths Continental Crust Corporation (DOSECC) and Institute of Earth Environment, Chinese Academy of Sciences (IEECAS) took a series of shallows cores from the southern basin of Lake Qinghai. West sub-basin sediments display Holocene lacustrine feature for the upper 5m, while the 5-18m are interbeded sediments of shallow lake, eolian-lacustrine and eolian loess. Chinese and US scientists with support from NSFC, MOST, CAS and NSF analysed 1F core from west sub-basin depocenter of the south basin with multiple physical, chemical, biological approaches. By comparing with modern process observation records, we obtained proxies that respectfully reflect precipitation, temperature and lake salinity changes, etc., reconstructed high resolution time sequences of magnetic susceptibility, colour scale, grain size, Corg, C/N, δ13Corg, carbonate, δ13C and δ18O of carbonate and ostracodes, elements, char-soot,Uk'37 and %C37:4 as well as pollen of the last 13Ka. They indicate the climatic change history of Lake Qinghai since past 13Ka, and agreeable evidences are found from adjacent tree ring and stalagmite records. Comparison of Lake Qinghai Holocene climate change sequence with those from high altitude ice core, stalagmites and ocean

  8. Technological Analysis of the World’s Earliest Shamanic Costume: A Multi-Scalar, Experimental Study of a Red Deer Headdress from the Early Holocene Site of Star Carr, North Yorkshire, UK

    Science.gov (United States)

    Little, Aimée; Elliott, Benjamin; Conneller, Chantal; Pomstra, Diederik; Evans, Adrian A.; Fitton, Laura C.; Holland, Andrew; Davis, Robert; Kershaw, Rachel; O’Connor, Sonia; O’Connor, Terry; Sparrow, Thomas; Wilson, Andrew S.; Jordan, Peter; Collins, Matthew J.; Colonese, André Carlo; Craig, Oliver E.; Knight, Rebecca; Lucquin, Alexandre J. A.; Taylor, Barry; Milner, Nicky

    2016-01-01

    Shamanic belief systems represent the first form of religious practice visible within the global archaeological record. Here we report on the earliest known evidence of shamanic costume: modified red deer crania headdresses from the Early Holocene site of Star Carr (c. 11 kya). More than 90% of the examples from prehistoric Europe come from this one site, establishing it as a place of outstanding shamanistic/cosmological significance. Our work, involving a programme of experimental replication, analysis of macroscopic traces, organic residue analysis and 3D image acquisition, metrology and visualisation, represents the first attempt to understand the manufacturing processes used to create these artefacts. The results produced were unexpected—rather than being carefully crafted objects, elements of their production can only be described as expedient. PMID:27073850

  9. The Mid-Holocene and Last Interglacial Experiments in PMIP4/CMIP6

    Science.gov (United States)

    Otto-Bliesner, Bette L.; Braconnot, Pascale; Abe-Ouchi, Ayako

    2016-04-01

    Understanding the forcings and feedbacks that produced interglacial warmth and the outcomes from it can help us better project the future climate of our planet. CMIP6 will include two interglacial experiments to explore the responses of the models to the forcing by orbital variations: the Mid-Holocene (MH 6000 years ago [6 ka]) and Last Interglacial (LIG 127,000 years ago [127 ka]). The dominant orbital forcing changes from modern modified the incoming solar insolation at the top of the atmosphere, resulting in large positive anomalies in summer in the Northern Hemisphere. Greenhouse gas concentrations were close to those of the pre-industrial. This pair of simulations will allow an assessment of the scaling and thresholds of the Earth system to the magnitude of the solar insolation changes (larger seasonal anomalies at 127 ka than 6 ka). High latitude feedbacks from sea-ice, water vapor and clouds will be a focus, and the implications for the stability of the Greenland and West Antarctic (WAIS) ice sheets. This output will be used by the ice sheet modeling community, with an intercomparison being coordinated as a joint activity of PMIP4 and ISMIP6 for CMIP6. As well, these experiments will explore the relative changes of the low-latitude hydrological cycle and monsoons. The MH and LIG are the most suitable of the warm interglacials for a CMIP6 assessment because of the wealth of data including: ice cores providing measurements of well-mixed greenhouse gases, aerosols including dust and sea salt, and stable water isotopes as a proxy for temperature, as well as for Greenland, ice sheet elevation and extent; marine records for ocean temperatures and geotracers that can be interpreted in terms of water masses and overturning strength; speleothems that provide indication of monsoon strength; fossil corals and sediments for interannual to multi-decadal variability; and terrestrial records that indicate temperature, vegetation, lake level, and hydroclimate changes. As

  10. A mid-Holocene drought interval as evidenced by lake desiccation in the Alashan Plateau, Inner Mongolia,China

    Institute of Scientific and Technical Information of China (English)

    CHEN Fahu; WU Wei; J. A. Holmes; D. B. Madsen; ZHU Yan; JIN Min; C. G. Oviatt

    2003-01-01

    The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented.These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000-7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associatedwith the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. Theperiod was also probably colder, at least in the high Asian plateaus and mountains.

  11. Aerosol and rainfall variability over the Indian monsoon region. Distributions, trends and coupling

    Energy Technology Data Exchange (ETDEWEB)

    Gautam, R. [Maryland Univ., Baltimore County, MD (United States). Goddard Earth Science and Technology Center; NASA Goddard Space Flight Center, Greenbelt, MD (United States). Lab. for Atmospheres; Hsu, N.C.; Lau, K.M. [NASA Goddard Space Flight Center, Greenbelt, MD (United States). Lab. for Atmospheres; Kafatos, M. [Chapman Univ., Orange, CA (United States). Center of Excellence in Earth Observing

    2009-07-01

    Aerosol solar absorption over the Indian monsoon region has a potential role of modulating the monsoon circulation and rainfall distribution as suggested by recent studies based on model simulations. Prior to the onset of the monsoon, northern India is influenced by significant dust transport that constitutes the bulk of the regional aerosol loading over the Gangetic-Himalayan region. In this paper, a multi-sensor characterization of the increasing pre-monsoon aerosol loading over northern India, in terms of their spatial, temporal and vertical distribution is presented. Aerosol transport from the northwestern arid regions into the Indo-Gangetic Plains and over the foothills of the Himalayas is found to be vertically extended to elevated altitudes (up to 5 km) as observed from the space-borne lidar measurements (CALIPSO). In relation with the enhanced pre-monsoon aerosol loading and the associated solar absorption effects on tropospheric temperature anomalies, this paper investigates the monsoon rainfall variability over India in recent past decades from an observational viewpoint. It is found that the early summer monsoon rainfall over India is on the rise since 1950s, as indicated by historical rainfall data, with over 20% increase for the period 1950-2004. This large sustained increase in the early summer rainfall is led by the observed strengthening of the pre-monsoon tropospheric land-sea thermal gradient over the Indian monsoon region as indicated by microwave satellite measurements (MSU) of tropospheric temperatures from 1979-2007. Combined analysis of changes in tropospheric temperatures and summer monsoon rainfall in the past three decades, suggest a future possibility of an emerging rainfall pattern of a wetter monsoon over South Asia in early summer followed by a drier period. (orig.)

  12. Volcanic influence on centennial to millennial Holocene Greenland temperature change.

    Science.gov (United States)

    Kobashi, Takuro; Menviel, Laurie; Jeltsch-Thömmes, Aurich; Vinther, Bo M; Box, Jason E; Muscheler, Raimund; Nakaegawa, Toshiyuki; Pfister, Patrik L; Döring, Michael; Leuenberger, Markus; Wanner, Heinz; Ohmura, Atsumu

    2017-05-03

    Solar variability has been hypothesized to be a major driver of North Atlantic millennial-scale climate variations through the Holocene along with orbitally induced insolation change. However, another important climate driver, volcanic forcing has generally been underestimated prior to the past 2,500 years partly owing to the lack of proper proxy temperature records. Here, we reconstruct seasonally unbiased and physically constrained Greenland Summit temperatures over the Holocene using argon and nitrogen isotopes within trapped air in a Greenland ice core (GISP2). We show that a series of volcanic eruptions through the Holocene played an important role in driving centennial to millennial-scale temperature changes in Greenland. The reconstructed Greenland temperature exhibits significant millennial correlations with K(+) and Na(+) ions in the GISP2 ice core (proxies for atmospheric circulation patterns), and δ(18)O of Oman and Chinese Dongge cave stalagmites (proxies for monsoon activity), indicating that the reconstructed temperature contains hemispheric signals. Climate model simulations forced with the volcanic forcing further suggest that a series of large volcanic eruptions induced hemispheric-wide centennial to millennial-scale variability through ocean/sea-ice feedbacks. Therefore, we conclude that volcanic activity played a critical role in driving centennial to millennial-scale Holocene temperature variability in Greenland and likely beyond.

  13. A high resolution history of the El Niño - Southern Oscillation and of the solar activity during the Late Glacial - Early Holocene in the subtropical Andean region.

    Science.gov (United States)

    Giralt, S.; Schimmel, M.; Hernández, A.; Bao, R.; Valero-Garcés, B. L.; Sáez, A.; Pueyo, J. J.

    2009-04-01

    High-resolution laminated lacustrine sediments are excellent archives of the past hydrological changes and they provide valuable insights about the climatic processes that trigger these changes. The paleoclimatic records located in the Southern Hemisphere are fundamental for understanding the evolution of the El Niño - Southern Oscillation (ENSO) since this climatic phenomena is the main cause of droughts and floods in many areas of South America and other regions of the world, like Spain and Egypt. Available regional paleoclimate reconstructions show that modern climatic patterns in South America were established during the Late Holocene. The laminated sediments of Lago Chungará (18° 15' S - 69° 10' W, 4520 m a.s.l., Chilean altiplano) have allowed us to characterize the evolution of this climatic phenomena for the transition Late Glacial - Early Holocene (12,300 - 9,500 calendar years BP) as well as its relationship with other climate forcings, namely the solar activity. The studied sediments correspond to the lowermost 2.4 m of 8 m long Kullemberg cores recovered from this lake. These sediments are mainly made up of greenish and whitish laminae and thin layers constituted by diatomaceous oozes with carbonates and organic matter, arranged in rhythms and cycles. X-ray fluorescence (XRF) (Al, Si, S, K, Ca, Ti, Mn, Fe, Rb, Sr, Zn, Sb and Ba) analyses, total organic carbon (TOC), total carbon (TC), x-ray diffraction (XRD), biogenic silica, stable isotopes (delta18O and delta13C) on carbonates and on diatoms (delta18O) and magnetic susceptibility were determined in order to characterize the sediments of Lago Chungará. Previous statistical studies (cluster and Principal Component Analyses (PCA)) were used to disentangle the paleoclimatic signal from the other ones (volcanic and tectonic). The chronological model framework was built using 6 radiocarbon dates, allowing us to establish that laminated couplets were deposited on a pluriannual basis. These couplets are

  14. Predicting onset and withdrawal of Indian Summer Monsoon in 2016: results of Tipping elements approach

    Science.gov (United States)

    Surovyatkina, Elena; Stolbova, Veronika; Kurths, Jurgen

    2017-04-01

    started to decrease, and after two days meteorological stations reported 'No rain' in the EG and also in areas located across the subcontinent in the direction from the North Pakistan to the Bay of Bengal. Hence, the date of monsoon withdrawal - October 10-th, predicted 70 days in advance, lies within our prediction interval. Our results show that our method allows predicting a future monsoon, and not only retrospectively or hindcast. In 2016 we predicted of the onset and withdrawal dates of the Southwest monsoon over the Eastern Ghats region in Central India for 40 and 70 days in advance respectively. Our general framework for predicting spatial-temporal critical transitions is applicable for systems of different nature. It allows predicting future from observational data only, when the model of a transition does not exist yet. [1] Stolbova, V., E. Surovyatkina, B. Bookhagen, and J. Kurths (2016): Tipping elements of the Indian monsoon: Prediction of onset and withdrawal. Geophys. Res. Lett., 43, 1-9. [2]https://www.pik-potsdam.de/news/press-releases/indian-monsoon-novel-approach-allows-early-forecasting?set_language=en [3] https://www.pik-potsdam.de/kontakt/pressebuero/fotos/monsoon-withdrawal/view

  15. Dynamics of the Asian Summer Monsoon Onset and the Tibetan Plateau Impacts

    Science.gov (United States)

    Yimin, Liu; Guoxiong, Wu; Boqi, Liu; Suling, Ren; Yue, Guan

    2015-04-01

    The formation and development of the South Asian High (SAH) in early spring over South China Sea (SCS) provides upper tropospheric pumping over the Southeast Bay of Bengal (BOB) and leads to the BOB monsoon onset. The strong latent heat release of the BOB monsoon results in the northeastward unstable development of the SAH which contributes to the SCS monsoon onset. The zonal asymmetric unstable development of the SAH after the SCS monsoon onset leads to the Indian summer monsoon onset. In spring over South BOB, usually there is vortex development preceding the Asian summer monsoon onset. The rapid development of the BOB monsoon onset vortex is due to the local strong air-sea interaction, which is modulated by the Tibetan Plateau (TP) forcing and the land-sea thermal contrast across South Asia. Strong heating from BOB monsoon generates stationary Rossby-wave in lower troposphere, producing weak cold advection and convection over North SCS. Development of surface BOB cyclone provides Northeastward water vapor transport towards North SCS where convection develops. Before the Indian Summer Monsoon (ISM) onset, the North- South land- sea thermal contrast increases eastward remarkably on the southeast of Arabian Sea. Air traveling eastward along the near- surface tropical westerly jet gets northward accelerated, forcing a lower tropospheric convergence near and to the north of the jet stream. Such a forced convection development occurs intensively over the southeastern Arabian Sea and southwestern India, contributing to the ISM onset.

  16. Glacial to Holocene changes in trans-Atlantic Saharan dust transport and dust-climate feedbacks.

    Science.gov (United States)

    Williams, Ross H; McGee, David; Kinsley, Christopher W; Ridley, David A; Hu, Shineng; Fedorov, Alexey; Tal, Irit; Murray, Richard W; deMenocal, Peter B

    2016-11-01

    Saharan mineral dust exported over the tropical North Atlantic is thought to have significant impacts on regional climate and ecosystems, but limited data exist documenting past changes in long-range dust transport. This data gap limits investigations of the role of Saharan dust in past climate change, in particular during the mid-Holocene, when climate models consistently underestimate the intensification of the West African monsoon documented by paleorecords. We present reconstructions of African dust deposition in sediments from the Bahamas and the tropical North Atlantic spanning the last 23,000 years. Both sites show early and mid-Holocene dust fluxes 40 to 50% lower than recent values and maximum dust fluxes during the deglaciation, demonstrating agreement with records from the northwest African margin. These quantitative estimates of trans-Atlantic dust transport offer important constraints on past changes in dust-related radiative and biogeochemical impacts. Using idealized climate model experiments to investigate the response to reductions in Saharan dust's radiative forcing over the tropical North Atlantic, we find that small (0.15°C) dust-related increases in regional sea surface temperatures are sufficient to cause significant northward shifts in the Atlantic Intertropical Convergence Zone, increased precipitation in the western Sahel and Sahara, and reductions in easterly and northeasterly winds over dust source regions. Our results suggest that the amplifying feedback of dust on sea surface temperatures and regional climate may be significant and that accurate simulation of dust's radiative effects is likely essential to improving model representations of past and future precipitation variations in North Africa.

  17. Holocene climate variability and anthropogenic impacts from Lago Paixban, a perennial wetland in Peten, Guatemala

    Science.gov (United States)

    Wahl, David B.; Hansen, Richard D.; Byrne, Roger; Anderson, Lysanna; Schreiner, T.

    2016-01-01

    Analyses of an ~ 6 m sediment core from Lago Paixban in Peten, Guatemala, document the complex evolution of a perennial wetland over the last 10,300 years. The basal sediment is comprised of alluvial/colluvial fill deposited in the early Holocene. The absence of pollen and gastropods in the basal sediments suggests intermittently dry conditions until ~ 9000 cal yr. BP (henceforth BP) when the basin began to hold water perennially. Lowland tropical forest taxa dominated the local vegetation at this time. A distinct band of carbonate dating to ~ 8200 BP suggests regionally dry conditions, possibly associated with the 8.2 ka event. Wetter conditions during the Holocene Thermal Maximum are indicated by evidence of a raised water level and an open water lake. The timing of this interval coincides with strengthening of the Central American Monsoon. An abrupt change at 5500 BP involved the development of a sawgrass marsh and onset of peat deposition. The lowest recorded water levels date to 5500–4500 BP. Pollen, isotope, geochemical, and sedimentological data indicate that the coring site was near the edge of the marsh during this period. A rise in the water table after 4500 BP persisted until around 3500 BP. Clay marl deposition from 3500 to 210 BP corresponds to the period of Maya settlement. An increase in δ13C, the presence of Zea pollen, and a reduction in the percentage of forest taxa pollen indicate agricultural activity at this time. In contrast to several nearby paleoenvironmental studies, proxy evidence from Lago Paixban indicates human presence through the Classic/Postclassic period transition (~ 1000 BP) and persisting until the arrival of Europeans. Cessation of human activity around 210 BP resulted in local afforestation and the re-establishment of the current sawgrass marsh at Lago Paixban.

  18. Holocene climate variability and anthropogenic impacts from Lago Paixban, a perennial wetland in Peten, Guatemala

    Science.gov (United States)

    Wahl, David; Hansen, Richard D.; Byrne, Roger; Anderson, Lysanna; Schreiner, Thomas

    2016-03-01

    Analyses of an ~ 6 m sediment core from Lago Paixban in Peten, Guatemala, document the complex evolution of a perennial wetland over the last 10,300 years. The basal sediment is comprised of alluvial/colluvial fill deposited in the early Holocene. The absence of pollen and gastropods in the basal sediments suggests intermittently dry conditions until ~ 9000 cal yr. BP (henceforth BP) when the basin began to hold water perennially. Lowland tropical forest taxa dominated the local vegetation at this time. A distinct band of carbonate dating to ~ 8200 BP suggests regionally dry conditions, possibly associated with the 8.2 ka event. Wetter conditions during the Holocene Thermal Maximum are indicated by evidence of a raised water level and an open water lake. The timing of this interval coincides with strengthening of the Central American Monsoon. An abrupt change at 5500 BP involved the development of a sawgrass marsh and onset of peat deposition. The lowest recorded water levels date to 5500-4500 BP. Pollen, isotope, geochemical, and sedimentological data indicate that the coring site was near the edge of the marsh during this period. A rise in the water table after 4500 BP persisted until around 3500 BP. Clay marl deposition from 3500 to 210 BP corresponds to the period of Maya settlement. An increase in δ13C, the presence of Zea pollen, and a reduction in the percentage of forest taxa pollen indicate agricultural activity at this time. In contrast to several nearby paleoenvironmental studies, proxy evidence from Lago Paixban indicates human presence through the Classic/Postclassic period transition (~ 1000 BP) and persisting until the arrival of Europeans. Cessation of human activity around 210 BP resulted in local afforestation and the re-establishment of the current sawgrass marsh at Lago Paixban.

  19. Late Pleistocene-Holocene uplift driven terrace formation and climate-tectonic interplay from a seismically active intraplate setting: An example from Kachchh, Western India

    Science.gov (United States)

    Prizomwala, S. P.; Das, Archana; Chauhan, G.; Solanki, T.; Basavaiah, N.; Bhatt, Nilesh; Thakkar, M. G.; Rastogi, B. K.

    2016-07-01

    Fluvial terrace formation is often regulated by external forcings like climate, tectonic and eustatic changes. These terraces, particularly in a dryland environment, preserves the discrete signatures of these external forcings, thus enabling us to reconstruct the fluvial response to the late Quaternary palaeoenvironmental changes and factors governing them. The present study focuses on reconstructing the aggradation/incision phases in the Lotia River which is located in the eastern segment of the Northern Hill Range (NHR) of the Kachchh Peninsula. The Lotia river drains through Mesozoic rocks before cutting across the Kachchh Mainland Fault (KMF) and finally debouch in the Banni Plains. Reconstruction based on tectonic geomorphology, sedimentology, sediment geochemistry, mineral magnetic, and OSL chronology suggests the fluvial response to monsoon variability archived during the last 15 ka. The time frame was also marked by incision enhanced by uplift along the KMF, which led to strath terrace formation. The accommodation space thus created was filled by an aggradational event between 14.8 ka and 10.6 ka. Sedimentological and geochemical parameters have also suggested that the time period between 12.5 ka and 11.5 ka showed a decline in the monsoon strength, which coincides with 'Younger Dryas'. It has been observed that the sediments spanning between 10.6 ka and 7.8 ka are absent from the archive, which is most likely the manifestation of the early Holocene optimum that led to severe erosional processes. The period between 7.8 ka and 3.3 ka is marked as another aggradational phase with fluctuating climatic conditions. At 3.3 ka, the region has experienced an incision of 4 m, which led to the formation of Holocene terrace T1, most likely due to tectonic uplift. During the last 3.3 ka, another pulsative uplift has occurred, which led to the formation of unpaired Holocene terrace T2, along with tilting of the Lotia basin. Based on the OSL chronology of bedrock strath

  20. 湛江湖光岩玛珥湖全新世粒度变化特征及古气候意义%Grain size variation and its environmental significance from Huguangyan Maar Lake, Zhanjiang since the Holocene

    Institute of Scientific and Technical Information of China (English)

    吴旭东; 刘国旭; 沈吉

    2016-01-01

    Through investigation on grain size parameters, loss on ignition ( 550℃) and Ti contents of Huguangyan Maar Lake sed-iment during the Holocene, frequency curve of grain size suggests that terrestrial input of Huguangyan Maar Lake are predominantly from its small catchment, and grain size variation of the sediment during the Holocene was determined by precipitation instead of lake level fluctuation, with coarser grain size indicating higher precipitation and finer grain size indicating lower precipitation. Asian monsoon at Zhanjiang area was strong in the early Holocene, and weakened substantially since 6085 a B.P.. The substantial weake-ning of Asian monsoon in the mid-Holocene recorded by Huguangyan Maar Lake sediment occurred at the time which was very close to the time of substantially weakened monsoon event recorded by many other archives around the globe, embodying globalization of monsoon evolution during the Holocene of Zhanjiang area. Weakened Asian monsoon and enhanced drought since 6085 a B. P. might be related to the enhanced ENSO activity. The amplitude of grain size parameters, loss on ignition ( 550℃) and Ti content increased remarkably after 2000 a B.P., which may be due to intensified human activity and it is the result of both human activities and climate change.%对湖光岩玛珥湖沉积物全新世粒度参数、550℃烧失量和Ti元素含量的变化特征研究后认为:粒度频率特征曲线指示湖光岩玛珥湖沉积物的外源输入部分主要来自其小流域;沉积物粒径的变化主要受降雨量,而不是湖泊水位波动的控制;较粗的粒径指示降雨量增加,较细的粒径指示降雨量降低.湛江地区全新世早期季风强盛,6085 a B.P.以后,季风显著减弱.湖光岩沉积物记录的全新世中期季风迅速减弱的发生时间与全球很多地质载体记录的全新世中期季风迅速减弱时间都非常接近,体现了湛江地区全新世季风演化的全球性.

  1. Late Holocene vegetation and ocean variability in the Gulf of Oman

    Science.gov (United States)

    Miller, Charlotte S.; Leroy, Suzanne A. G.; Collins, Philip E. F.; Lahijani, Hamid A. K.

    2016-07-01

    Fossil pollen and dinocyst records in marine sequences are frequently combined to reveal the response of vegetation and ocean conditions to changes in both regional and global climate. In this study we analysed pollen and dinocysts within a clearly-laminated sediment core off the Iranian coast in the Gulf of Oman, an extremely data-poor area, to reconstruct climatic change during the Late Holocene (last 1900 years). The vegetation record from southern Iran indicates a replacement of savannah by desert formations at c. 910 CE, shortly after the Islamic invasion and the subsequent collapse of the Sassanid Empire. From c. 910 to 1145 CE, during the Medieval Climate Anomaly (MCA), the vegetation was heavily dominated by desert formations, such as Amaranthaceae, Caryophyllaceae, Asteraceae, Centaurea and Calligonum. In parallel, in the Gulf of Oman, the presence of Impagidinium paradoxum indicates a lack of freshwater discharge into the ocean around this time. The desert taxa of the MCA were subsequently replaced by savannah formations at c. 1145 CE, comprised mainly of Poaceae and Cyperaceae, corresponding to the Little Ice Age (LIA), indicating generally wetter climatic conditions. A sudden increase in Spiniferites ramosus (1-63%), at c. 1440 CE suggests an increase in the strength of the SW summer monsoon, with increased freshwater discharge into the ocean at this time. Our data indicate that over the past two millennia the NW Arabian Sea region has alternated between contrasting climatic conditions, with firstly a humid phase equivalent to the cultural period of the Sassanid Empire, a significantly drier climate during the MCA and a relatively wetter climate during the LIA. The mechanisms resulting in dry conditions during the MCA in the Middle East associated with the northward shift of the ITCZ and the intensification of the Indian summer monsoon may be similar to those causing the dry conditions which dominated the Early Holocene in the Near East. Our

  2. Investigation of summer monsoon rainfall variability in Pakistan

    Science.gov (United States)

    Hussain, Mian Sabir; Lee, Seungho

    2016-08-01

    This study analyzes the inter-annual and intra-seasonal rainfall variability in Pakistan using daily rainfall data during the summer monsoon season (June to September) recorded from 1980 to 2014. The variability in inter-annual monsoon rainfall ranges from 20 % in northeastern regions to 65 % in southwestern regions of Pakistan. The analysis reveals that the transition of the negative and positive anomalies was not uniform in the investigated dataset. In order to acquire broad observations of the intra-seasonal variability, an objective criterion, the pre-active period, active period and post-active periods of the summer monsoon rainfall have demarcated. The analysis also reveals that the rainfall in June has no significant contribution to the increase in intra-seasonal rainfall in Pakistan. The rainfall has, however, been enhanced in the summer monsoon in August. The rainfall of September demonstrates a sharp decrease, resulting in a high variability in the summer monsoon season. A detailed examination of the intra-seasonal rainfall also reveals frequent amplitude from late July to early August. The daily normal rainfall fluctuates significantly with its maximum in the Murree hills and its minimum in the northwestern Baluchistan.

  3. The expansion of hazel ( Corylus avellana L.) in the southern Alps: a key for understanding its early Holocene history in Europe?

    Science.gov (United States)

    Finsinger, Walter; Tinner, Willy; van der Knaap, W. O.; Ammann, Brigitta

    2006-03-01

    In Northwestern and Central Europe the Holocene expansion of Corylus occurred before or at the same time as that of other thermophilous trees (e.g. Quercus). This sequence of expansion has been explained by migrational lag, competition, climatic changes, human assistance, or disturbance by fire. In the southern Alps, however, hazel expanded around 10,500 cal yr BP, more than two millennia after oak had become important. This delayed expansion is in contrast with the rapid expansion often assumed for hazel in central Northern Europe. We use two well-dated pollen and charcoal records from the southern forelands of the Alps: Lago Piccolo di Avigliana and Lago di Origlio. We conclude that distance of refugia, speed of seed dispersal, and competition cannot sufficiently explain the absence of the hazel expansion prior to the establishment of mixed oak forests in the southern Alps. Instead our records indicate that higher moisture availability and low temperatures inhibited hazel and favoured the establishment of pine and mixed oak forests during the Allerød. The expansion of hazel ˜11,000-10,500 cal yr BP was favoured by a combination of high seasonality, summer drought and frequent fires, which helped hazel to out-compete oak in the south as well as north of the Alps.

  4. Periodicity of Holocene climatic variations in the Huguangyan Maar Lake

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    There exist five primary periods of 2 930, 1 140, 490, 250 and 220 a in the Holocene climatic variations in the Huguangyan Maar Lake, according to the energy-spectrum and filter analyses of high-resolution time sequences (10-15 a) of the sediment dry density. The peak values of the three temperature-decreasing periods with the 2 930 a cycle occur at about 7 300, 4 250 and 1 200 Cal. aBP. There are 7-8 temperature-decreasing periods with the 1 140 a cycle, and the climate fluctuation range is largest in the early Holocene, and reduces gradually in the middle and late Holocene. The millennial-scale climatic change in the Holocene may adjust the global water cycle and the thermohaline circulation intensity through the harmonic tones of the earth's precession cycle, which in turn influences the global climate change.

  5. Holocene paleoenvironments of Northeast Iowa

    Science.gov (United States)

    Baker, R.G.; Bettis, E. Arthur; Schwert, D.R.; Horton, D.G.; Chumbley, C.A.; Gonzalez, Luis A.; Reagan, M.K.

    1996-01-01

    This paper presents the biotic. sedimentary, geomorphic, and climatic history of the upper part of the Roberts Creek Basin, northeastern Iowa for the late-glacial and Holocene, and compares these records with a C-O isotopic sequence from Coldwater Cave. 60 km northwest of Roberts Creek. The biotic record (pollen, vascular plant and bryophyle macrofossils. and insects) is preserved in floodplain alluvium that underlies three constructional surfaces separated by low scarps. Each surface is underlain by a lithologically and temporally distinct alluvial fill. The highest surface is underlain by the Gunder Member of the Deforest Formation, dating from 11 000 to 4000 yr BP; beneath the intermediate level is the Roberts Creek Member, dating from 4000 to 400 yr BP; and the lowest level is underlain by the Camp Creek Member, deposited during the last 380 yr. Pollen and plant macrofossils in the alluvial fill show that a typical late-glacial spruce forest was replaced by Quercus and Ulmus in the early Holocene. This early-to-middle Holocene forest became dominated by mesic elements such as Acer saccharum, Tilia americana, Ostrya virginiana, and Carpinus caroliniana as late as 5500 yr BP; in contrast, the closest sites to the west and north were at their warmest and driest and were covered by prairie vegetation between 6500 and 5500 yr BP. After 5500 yr BP, the forest in the Roberts Creek area was replaced by prairie, as indicated by a rich assemblage of plant macrofossils, although only Ambrosia and Poaceae became abundant in the pollen record. The return of Quercus ??? 3000 BP (while nonarboreal pollen percentages remained relatively high) indicates that oak savanna prevailed with little change until settlement time. The bryophyte assemblages strongly support the vascular plant record. Rich fen species characteristic of boreal habitats occur only in the late-glacial. They are replaced by a number of deciduous-forest elements when early-to-middle Holocene forests were

  6. Quaternary stratigraphy, geochronology and evolution of the Magela Creek catchment in the monsoon tropics of northern Australia

    Science.gov (United States)

    Nanson, Gerald C.; East, T. Jon; Roberts, Richard G.

    1993-03-01

    Magela Creek, a major tributary of the East Alligator River in northern Australia, has left a detailed sedimentary record of a fluvial landscape dominated by climatic and eustatic changes associated with Quaternary glacial-interglacial cycles. Uranium-series dates from young pisoliths in floodplain deposits indicate that ferruginisation is probably ongoing under present conditions while ferricretes in degraded terraces that flank the lower valley reveal a fluvial history extending back to early Pleistocene or Tertiary time. Inset within this older alluvium is a valley fill which, from thermoluminescence dates, was initiated about 300 kyr ago. With each glacial climate change and associated fall in sea level, distinct palaeochannels have been eroded into these floodplains, infilling later with alluvium when climate and base-level conditions were conducive to fluvial deposition. Radiocarbon dates show that the most recent palaeochannel beneath the modern Magela Creek last started to fill by downstream progradation and vertical accretion of bedload sand about 8 kyr. The palaeochannel filled at an accelerating rate, probably as a result of declining stream competence associated with drier conditions in the late Holocene augmented by the backwater effects of sea-level rise. Continued aggradation blocked the mouths of tributary valleys along Magela Creek, forming alluvial-dammed tributary lakes and deferred-junction tributary streams. From about 300 kyr, cyclic episodes of channel incision and sediment evacuation in this tropical-monsoon river valley have become less effective, possibly because increasing aridity in the late Quaternary has reduced the erosional effectiveness of Australia's northern rivers. Reduced flow regime and rising sea level in the late Holocene has resulted in the latest phase of alluvial accretion.

  7. Role of low level flow on the summer monsoon rainfall over the Indian subcontinent during two contrasting monsoon years

    Digital Repository Service at National Institute of Oceanography (India)

    Swapna, P.; RameshKumar, M.R.

    The summer monsoon rainfall over the Indian subcontinent shows 1 large inter-annual variability in three important aspects, namely, the onset date, quantum of monsoon rainfall and the monsoon activity within the monsoon (June - September) period...

  8. Holocene environmental changes in northeast Thailand as reconstructed from a tropical wetland

    Science.gov (United States)

    Wohlfarth, Barbara; Klubseang, Wichuratree; Inthongkaew, Suda; Fritz, Sherilyn C.; Blaauw, Maarten; Reimer, Paula J.; Chabangborn, Akkaneewut; Löwemark, Ludvig; Chawchai, Sakonvan

    2012-07-01

    Geochemical variables (TOC, C/N, TS, δ13C) and diatom assemblages were analyzed in a lake sediment sequence from Nong (Lake) Han Kumphawapi in northeast Thailand to reconstruct regional climatic and environmental history during the Holocene. By around c. 10,000-9400 cal yr BP, a large shallow freshwater lake had formed in the Kumphawapi basin. Oxygenated bottom waters and a well-mixed water column were characteristic of this early lake stage, which was probably initiated by higher effective moisture and a stronger summer monsoon. Decreased run-off after c. 6700 cal yr BP favored increased aquatic productivity in the shallow lake. Multiple proxies indicate a marked lowering of the lake level around 5900 cal yr BP, the development of an extensive wetland around 5400 cal yr BP, and the subsequent transition to a peatland. The shift from shallow lake to wetland and later to a peatland is interpreted as a response to lower effective moisture. A hiatus at the transition from wetland to peatland suggests very low accumulation rates, which may result from very dry climatic conditions. A rise in groundwater and lake level around 3200 cal yr BP allowed the re-establishment of a wetland in the Kumphawapi basin. However, the sediments deposited between c. 3200 and 1600 cal yr BP provide evidence for at least two hiatuses at c. 2700-2500 cal yr BP, and at c. 1900-1600 cal yr BP, which would suggest surface dryness and consequently periods of low effective moisture. Around 1600 cal yr BP a new shallow lake became re-established in the basin. Although the underlying causes for this new lake phase remain unclear, we hypothesize that higher effective moisture was the main driving force. This shallow lake phase continued up to the present but was interrupted by higher nutrient fluxes to the lake around 1000-600 cal yr BP. Whether this was caused by intensified human impact in the catchment or, whether this signals a lowering of the lake level due to reduced effective moisture

  9. Discovery of laterally extensive drape of siliciclastic silt in the Northern Calcareous Alps, Austria: Late-glacial to ?early Holocene aeolian deposition.

    Science.gov (United States)

    Gild, Charlotte; Geitner, Clemens; Haas, Jean Nicolas; Sanders, Diethard

    2016-04-01

    Field surveys in the Northern Calcareous Alps (NCA, a nappe stack of Triassic carbonate rocks) revealed a drape, or drapes, typically 20-40 cm in thickness of siliciclastic silt over extensive landscape areas, from valley floors to LGM (Last Glacial Maximum) nunataks. The drape veneers substrates ranging from country rocks to diverse post-LGM deposits - the latter with depositional and/or erosional topographies. The drape mostly is overlain by vegetated organic material and, in turn, tops inactive/abandoned post-LGM successions of fluvial (including kame terrace), alluvial fan, scree slope, LGM basal till, and rock-avalanche origin. The drape extends over kilometers at least (limit of field investigation in specific areas), up to LGM nunatak plateaus. Deposystems (e.g., scree slopes, alluvial fans) on carbonate-rocky terrain that remained active until the Holocene are not topped by the drape; a level of siliciclastic silt, however, was spotted within a few of these successions. The possibility that several levels of silt are intercalated within or top post-glacial deposits cannot be excluded at present; the large lateral extent and the stratigraphic position, however, suggest that at least most locations pertain to a single widespread level (with that reservation, we prefer to speak in singular of the drape). Over the inspected area (~ 90 x 20 km), the drape consists mainly of silt-sized grains of quartz, feldspars, micas, and amphiboles; at a few sites, calci- or dolosilt are admixed. Most of the grains are angular to subrounded, some grains show features of corrosion. Preliminary palynological analyses of this silt - seven locations from LGM nunataks to kame terrace and alluvial fans - suggest vegetation types that, together, may be assigned to palaeoclimates ranging from the late-glacial (Younger Dryas?) to the middle Holocene. A few of the pollen spectra appear to record sparse vegetation cover allowing for enhanced aeolian deposition, but other spectra (e

  10. Examining Impact of Global warming on the summer monsoon system using regional Climate Model (PRECIS)

    Science.gov (United States)

    Patwardhan, S. K.; Kundeti, K.; Krishna Kumar, K.

    2011-12-01

    Every year, southwest monsoon arrives over Indian region with remarkable regularity. It hits the southern state of Kerala first by the end of May or the early June. More than 70% of the annual precipitation is received during the four monsoon months viz. June to September. This monsoon rainfall is vital for the agriculture as well as for the yearly needs of Indian population. The performance of the monsoon depends on the timely onset over southern tip of India and its progress along the entire country. This northward progression of monsoon to cover the entire Indian landmass, many times, is associated with the formation of synoptic scale system in the Bay of Bengal region and their movement along the monsoon trough region. The analysis of the observed cyclonic disturbances show that their frequency has reduced in recent decades. It is, therefore, necessary to assess the effect of global warming on the monsoon climate of India. A state-of-art regional climate modelling system, known as PRECIS (Providing REgional Climates for Impacts Studies) developed by the Hadley Centre for Climate Prediction and Research, U.K. is applied over the South Asian domain to investigate the impact of global warming on the cyclonic disturbances. The PRECIS simulations at 50 km x 50 km horizontal resolution are made for two time slices, present (1961-1990) and the future (2071-2100), for two socio-economic scenarios A2 and B2. The model skills are evaluated using observed precipitation and surface air temperature. The model has shown reasonably good skill in simulating seasonal monsoon rainfall, whereas cold bias is seen in surface air temperature especially in post-monsoon months. The typical monsoon features like monsoon trough, precipitation maxima over west coast and northeast India are well simulated by the model. The model simulations under the scenarios of increasing greenhouse gas concentrations and sulphate aerosols are analysed to study the likely changes in the quasi

  11. The Influence of Indian Ocean Atmospheric Circulation on Warm Pool Hydroclimate During the Holocene Epoch

    Science.gov (United States)

    Tierney, J.E.; Oppo, D. W.; LeGrande, A. N.; Huang, Y.; Rosenthal, Y.; Linsley, B. K.

    2012-01-01

    Existing paleoclimate data suggest a complex evolution of hydroclimate within the Indo-Pacific Warm Pool (IPWP) during the Holocene epoch. Here we introduce a new leaf wax isotope record from Sulawesi, Indonesia and compare proxy water isotope data with ocean-atmosphere general circulation model (OAGCM) simulations to identify mechanisms influencing Holocene IPWP hydroclimate. Modeling simulations suggest that orbital forcing causes heterogenous changes in precipitation across the IPWP on a seasonal basis that may account for the differences in time-evolution of the proxy data at respective sites. Both the proxies and simulations suggest that precipitation variability during the September-November (SON) season is important for hydroclimate in Borneo. The preeminence of the SON season suggests that a seasonally lagged relationship between the Indian monsoon and Indian Ocean Walker circulation influences IPWP hydroclimatic variability during the Holocene.

  12. Peat record reflecting Holocene climatic change in the Zoige Plateau and AMS radiocarbon dating

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Through the use of reliable AMS dating of high resolution (15-30 years) peat and the establishment of monsoon climate proxies sequence, we have been able to recognize several cold, dry events in the Tibetan Plateau during the Holocene. The more obvious ones occurred around 12800, 11300, 10200, 9580, 8900, 6400, 4400, 3700, 2800 and 1500 cal. aBP. These events correlate well with both ice rafting events recorded in high latitude North Atlantic Ocean sediment cores and cooling events in the low latitude SST. Spectral analysis indicates high frequency climate variation on centennial-millennial time scale during the Holocene. This further reflects Holocene climate instability and the existence of centennial-millenium scale rhythm in mid latitude areas as well.

  13. Meteorological results of monsoon-88 Expedition (pre-monsoon period)

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.; Krishnamurthy, L.; Babu, M.T.

    Mean atmospheric circulation, moisture budget and net heat exchange were studied during a pre-monsoon period (18th March to 3rd May, 1988), making use of the data collected on board "Akademik Korolev" in the central equatorial and southern Arabian...

  14. Holocene marine tephrochronology on the Iceland shelf

    DEFF Research Database (Denmark)

    Guomundsdottir, Esther Ruth; Eiriksson, Jón; Larsen, Guorun

    2012-01-01

    Currently the Late-glacial and Holocene marine tephrochronology on the shelf around Iceland comprises 130 tephra layers from 30 sediment cores ranging in age from 15,000 years cal. BP to AD 1947. A vast majority of the cores and tephra layers are from the North Iceland shelf Much fewer tephra...... layers have been found on the South and West Iceland shell The early Holocene Saksunarvatn ash and Vedde Ash are the only tephra layers identified on all investigated shelf areas. For the last 15,000 years correlated tephra layers from the shelf sediments around Iceland to their terrestrial counterparts...... both in Iceland and overseas are 40 of which 26 are terrestrially dated tephra markers. Thirty correlations are within the last 7050 years. The terrestrially dated tephra markers found on the shelf have been used to constrain past environmental variability in the region, as well as marine reservoir age...

  15. Barnacles Tell no Lies - Bioclastic deposits and in-situ balanid colonies delineate shorelines of the Holocene palaeolake at Tayma (NW Saudi Arabia)

    Science.gov (United States)

    Engel, Max; Frenzel, Peter; Pint, Anna; Dinies, Michèle; Gleixner, Gerd; Hoelzmann, Philipp; Neugebauer, Ina; Plessen, Birgit; Brückner, Helmut

    2016-04-01

    radiocarbon data from the thickest bioclastic shoreline deposit (Engel et al. 2012) and corrections for hardwater effects, the formation of the highest shoreline overlaps with the most humid phase of maximum grassland expansion at around 8600-8000 cal BP inferred from the pollen record of sediments inside the sabkha basin (Dinies et al. 2015). During that time, the lake had a perennial regime, brackish to seasonally even hypersaline conditions, a depth of up to 17 m and a minimum area of 22 km², thus testifying to the profound impact the early to mid-Holocene humid phase had on vegetation, hydrography, and sedimentary environs of NW Arabia. Dinies, M., Plessen, B., Neef, R., and Kürschner, H.: When the desert was green: Grassland expansion during the early Holocene in northwestern Arabia. Quatern. Int., 382, 293-302, 2015. Engel, M, Brückner, H., Pint, A., Wellbrock, K., Ginau, A., Voss, P., Grottker, M., Klasen, N., and Frenzel, P.: The early Holocene humid period in NW Saudi Arabia - sediments, microfossils and palaeohydrological modelling. Quatern. Int., 266, 131-141, 2012. Enzel, Y., Kushnir, Y., and Quade, J.: The middle Holocene climatic records from Arabia: Reassessing lacustrine environments, shift of ITCZ in Arabian Sea, and impacts of the southwest Indian and African monsoons. Global Planet. Change, 129, 69-91, 2015.

  16. Biomarker records of Holocene climate variations in Asian interior

    Science.gov (United States)

    Song, M.; Liu, Z.; Liu, W.; Zhao, C.; Li, S.; He, Y.

    2012-12-01

    Understanding Holocene climate fluctuation may provide clues to projection of future climate change. Lake sediments in the arid central Asia (ACA), as an archive of past climate information, keep attracting considerable interest. We have retrieved several sediment cores from Lake Manas, an endorheic lake in Zunggar desert, Xinjiang Province, China. Biomarker proxies including alkenone Uk'37, %C37:4 and C37 concentration (C37 Conc), and physical proxies including density and magnetic susceptibility (MS) have been analyzed. We have found substantial climatic and environmental changes during the late Holocene. Density, MS and Uk'37 values are high during Medieval Warm Period (MWP) and C37 Conc is very low. During the Little Ice Age, density and MS decrease, Uk'37 values drop to near 0.1, C37 Conc is increased by 2 to 3 magnitude. Thus, warm and dry conditions dominated MWP while cold and wet conditions dominated LIA, a typical "Westerly" pattern which is opposite to the hydrological variation in Asian monsoonal regions. Biomarker records' correlation with solar irradiance (SI), the North Atlantic Oscillation (NAO), the 1000year ACA Moisture Index (ACAM), and the North Hemisphere Temperature (NHT) suggests SI as one of the forcing factor on temperature fluctuation and cold and wet LIA possibly resulting from westerly-jet shift, negative NAO oscillation and the lower evaporation induced by the decrease of temperature. Biomarker records for the whole Holocene will be also presented.

  17. Indian summer monsoon forcing on the deglacial polar cold reversals

    Indian Academy of Sciences (India)

    Virupaxa K Banakar; Sweta Baidya; Alexander M Piotrowski; D Shankar

    2017-08-01

    The deglacial transition from the last glacial maximum at $\\sim$20 kiloyears before present (ka) to the Holocene (11.7 ka to Present) was interrupted by millennial-scale cold reversals, viz., Antarctic Cold Reversal ($\\sim$14.5–12.8 ka) and Greenland Younger Dryas ($\\sim$12.8–11.8 ka) which had different timings and extent of cooling in each hemisphere. The cause of this synchronously initiated, but different hemispheric cooling during these cold reversals (Antarctic Cold Reversal $\\sim$3∘C and Younger Dryas $\\sim$10∘C) is elusive because CO2, the fundamental forcing for deglaciation, and Atlantic meridional overturning circulation, the driver of antiphased bipolar climate response, both fail to explain this asymmetry. We use centennial-resolution records of the local surface water $\\delta ^{18}\\hbox {O}$ of the Eastern Arabian Sea, which constitutes a proxy for the precipitation associated with the Indian Summer Monsoon, and other tropical precipitation records to deduce the role of tropical forcing in the polar cold reversals. We hypothesize a mechanism for tropical forcing, via the Indian Summer Monsoons, of the polar cold reversals by migration of the Inter-Tropical Convergence Zone and the associated cross-equatorial heat transport.

  18. Changes in the in-phase relationship between the Indian and subsequent Australian summer monsoons during the past five decades

    Directory of Open Access Journals (Sweden)

    J.-Y. Yu

    2007-10-01

    Full Text Available This study examines the decadal changes in the in-phase relationship between Indian summer monsoon and the subsequent Australian summer monsoon using observational data from 1950–2005. The in-phase relationship is the tendency for a strong Indian summer monsoon to be followed by a strong Australian summer monsoon and vice versa. It is found that the in-phase relationship was weak during the late 1950s and early 1960s, strengthened to a maximum in the early 1970s just before the 1976/77 Pacific climate shift, then declined until the late 1990s. Pacific SST anomalies are noticed to have strong persistence from boreal to austral summer, providing the memory to connect the Indian and subsequent Australian summer monsoon. The simultaneous correlation between the Pacific SST anomalies and the Indian summer monsoon is always strong. It is the weakening and strengthening of the simultaneous correlation between the Australian summer monsoon and the Pacific SST anomalies that contributes to the decadal variations of the in-phase monsoon relation. This study suggests that the interaction between the Australian monsoon and the Pacific Ocean is crucial to tropical climate variability and has experienced significant changes over the past five decades.

  19. A fluvial record of the mid-Holocene rapid climatic changes in the middle Rhone valley (Espeluche-Lalo, France) and of their impact on Late Mesolithic and Early Neolithic societies

    Science.gov (United States)

    Berger, Jean-François; Delhon, Claire; Magnin, Frédéric; Bonté, Sandrine; Peyric, Dominique; Thiébault, Stéphanie; Guilbert, Raphaele; Beeching, Alain

    2016-03-01

    This multi-proxy study of a small floodplain in the Rhone catchment area, at the northern edge of the Mediterranean morphoclimatic system, provides valuable information concerning the impact of mid-Holocene climate variability (8.5-7.0 ka) and the effects of two rapid climatic changes (8.2 and 7.7/7.1 ka) on an alluvial plain, its basin and the first farming societies of the Rhone valley. Around 7.7/7.1 ka, the combined effects of (1) a strong rate of change in insolation and (2) variations in solar activity amplified marine and atmospheric circulation in the north-west Atlantic (Bond event 5b), which imply continental hydrological, soil and vegetation changes in the small catchment area. For this period, strong fluctuations in the plant cover ratio have been identified, related to a regime of sustained and regular fires, as well as abundant erosion of the hill slopes and frequent fluvial metamorphoses which led to braiding of the watercourse in this floodplain. There are few data available to evaluate the impact of natural events on prehistoric communities. This continental archive offers clear multi-proxy data for discussion of these aspects, having 4 cultural layers interbedded in the fluvial sequence (1 Late Mesolithic, 3 Cardial/Epicardial). Earlier data indicate the difficulty in recognizing such cultural features in the low alluvial plains of southern France during the Mesolithic/Early Neolithic transition, which should lead to caution when developing settlement models for this period.

  20. Holocene Abrupt Climate Shifts and Mid-Holocene Drought Intervals Recorded in Barkol Lake of Northern Xinjiang of China

    Institute of Scientific and Technical Information of China (English)

    XUE Jibin; ZHONG Wei; ZHAO Yinjuan; PENG Xiaoying

    2008-01-01

    Study results in this paper have indicated that the Holocene climate in Xinjiang, Northwestern China hasbeen alternating between wet and dry conditions, and was punctuated with a series of abrupt climate shifts. A sedimentcore taken from Barkol Lake in the northern Xinjiang of Northwest China was analyzed at 1 cm interval for grain-sizedistribution. Abrupt climate shifts revealed by the grain-size proxy occurred at ca 1.4, 3.0, 4.3, 5.6, 8.0 cal kyr B.P.,which were well correlated to both the abrupt shifts recorded in the North Atlantic Ocean (NAO) and the Holocene seasurface temperature (SST) cooling events in the Arabian Ocean. The correlation indicated that the climatic changes inthe extreme arid Northwest China were associated with the NAO, probably via the North Atlantic Oscillation-affectedwesterly winds. The strength and position of westerly winds probably modulated the Siberian-Mongolian high-pressure system (winter monsoon), and played an important role in climate change of Northwest China. Moreover, anevident drought interval during the middle Holocene was also revealed by grain-size proxy.

  1. Holocene trends in the foraminifer record from the Norwegian Sea and the North Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    C. Andersson

    2010-03-01

    Full Text Available The early to mid-Holocene thermal optimum is a well-known feature in a wide variety of paleoclimate archives from the Northern Hemisphere. Reconstructed summer temperature anomalies from across northern Europe show a clear maximum around 6000 years before present (6 ka. For the marine realm, Holocene trends in sea-surface temperature reconstructions for the North Atlantic and Norwegian Sea do not exhibit a consistent pattern of early to mid-Holocene warmth. Sea-surface temperature records based on alkenones and diatoms generally show the existence of a warm early to mid-Holocene optimum. In contrast, several foraminifer and radiolarian based temperature records from the North Atlantic and Norwegian Sea show a cool mid-Holocene anomaly and a trend towards warmer temperatures in the late Holocene. In this paper, we revisit the foraminifer record from the Vøring Plateau in the Norwegian Sea. We also compare this record with published foraminifer based temperature reconstructions from the North Atlantic and with modelled (CCSM3 upper ocean temperatures. Model results indicate that while the seasonal summer warming of the sea-surface was stronger during the mid-Holocene, sub-surface depths experienced a cooling. This hydrographic setting can explain the discrepancies between the Holocene trends exhibited by phytoplankton and zooplankton based temperature proxy records.

  2. Synchronicity of the East Asian Summer Monsoon variability and Northern Hemisphere climate change since the last deglaciation

    Directory of Open Access Journals (Sweden)

    T. Shinozaki

    2011-06-01

    Full Text Available Understanding of the mechanism of the East Asian Summer Monsoon (EASM is required for the prediction of climate change in East Asia in a scenario of modern global warming. In this study, we present high-resolution climate records from peat sediments in Northeast Japan to reconstruct the EASM variability based on peat bulk cellulose δ13C since the last deglaciation. We used a 8.8 m long peat sediment core collected from the Tashiro Bog, Northeast Japan. Based on 42 14C measurements, the core bottom reaches ~15.5 ka. δ13C, accumulation rate and accumulation flux time-series correlate well to Greenland ice core δ18O variability, suggesting that the climate record in Northeast Japan is linked to global climate changes. The δ13C record at Tashiro Bog and other paleo-EASM records at Northeast and Southern China consistently demonstrate that hydrological environments were spatially different in mid-high and mid-low latitude regions over the last 15.5 kyr. During global cooling (warming periods, mid-high and mid-low latitude regions were characterized by wet (dry and dry (wet environments, respectively. We suggest that these climatic patterns are related to the migration of the EASM-related rain belt during global climate changes, as a consequence of variations in intensity and location of both the Intertropical Convergence Zone (ITCZ and the Western Pacific Subtropical High (STH. The location of the rain belt largely influences the East Asian hydrological environment. Our δ13C time-series are characterized by a 1230 yr throughout the Holocene and a 680 yr periodicity during the early Holocene. The 1230 yr periodicity is in agreement with North Atlantic ice-rafted debris (IRD events, suggesting a teleconnection between the Northeast Japan and the North Atlantic during the Holocene. In addition, it is the first evidence that the Bond events were recorded in terrestrial sediment in

  3. History and variability of East Asian monsoon climate since the late Miocene

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    @@ The variability and dynamic mechanism of the East Asian monsoon climate is a major scientific puzzle in the exploration of global change.As early as in the late 1990s,a research team led by Prof.AN Zhisheng from the CAS Institute of Earth Environment started their work in this topic,with an objective of improving the hypothesis of monsoon-controlled East Asian environment and advancing the basic studies of past global changes in eastern Asia.

  4. Inverse correlation between ancient winter and summer monsoons in East Asia?

    Institute of Scientific and Technical Information of China (English)

    ZHOU BoTao; ZHAO Ping

    2009-01-01

    There is a scientific debate on the relationship between ancient winter and summer monsoons in East Asia. Some scholars think that East Asian winter and summer monsoons are anti-correlated, and oth-ers think not. For this reason, this study is motivated to assess their linkage from the paleoclimate simulation perspective, through analyzing the Last Glacial Maximum (LGM) and mid-Holocene (MH) climate simulated by CCSM3 model. Compared to the present climate, the Aleutian low is found to be deepened and the East Asian winter monsoon (EAWM) is stronger during the LGM winter. The Pacific high in summer is noticed to be weakened and the East Asian summer monsoon (EASM) is weaker at the LGM. During the MH, the Aleutian low and the Asian high in winter are intensified, and the Asian low and the Pacific high in summer are enhanced, indicating that the EAWM and EASM are both stronger than today. Therefore, the EAWM is not always negatively correlated to the EASM. Their relationship may be different at different geological stages. It can be obtained at least from the numerical simulation results that the EAWM and the EASM is negatively correlated during the cooling period, while positively correlated during the warming period.

  5. Temperature and Precipitation Changes in China During the Holocene

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    We review here proxy records of temperatare and precipitation in China during the Holocene,especially the last two millennia.The quality of proxy data,methodology of reconstruction,and uncertainties in reconstruction were emphasized in comparing different temperatare and precipitation reconstruction and clarilying temporal and spatial patterns of temperature and precipitation during the Holocene.The Holocene climate was generally warm and wet.The warmest period occurred in 9.6-6.2 cal ka BP,whereas a period of maximum monsoon precipitation started at about 11.0 cal ka BP and lasted until about 8.O-5.0 cal ka BP.There were a series of millennial-scale cold or dry events superimposed on the general trend of climate changes.During past two millennia,a warming trend in the 20th century was clearly detected,but the warming magnitude was smaller than the maximum level of the Medieval Warm Period and the Middle Holocene.Cold conditions occurred over the whole of China during the Little Ice Age (AD 1400-AD 1900),but the warming of the Medieval Warm Period(AD 900-AD 1300)was not distinct in China,especially west China.The spatial pattern of precipitation showed significant regional differences in China,especially east China.The modern warm period has lasted 20、years from 1987 to 2006.Bi-decadal oscillation in precipitation variability was apparent over China during the 20th century. Solar activity and volcanic eruptions both were major forcings governing the climate variability during the last millennium.

  6. Relationship Between East Asian Winter Monsoon and Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    YAN Hongming; YANG Hui; YUAN Yuan; LI Chongyin

    2011-01-01

    Using National Centers for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis data and monthly Hadley Center sea surface temperature (SST) data,and selecting a representative East Asian winter monsoon (EAWM) index,this study investigated the relationship between EAWM and East Asian summer monsoon (EASM) using statistical analyses and numerical simulations.Some possible mechanisms regarding this relationship were also explored.Results indicate a close relationship between EAWM and EASM:a strong EAWM led to a strong EASM in the following summer,and a weak EAWM led to a weak EASM in the following summer.Anomalous EAWM has persistent impacts on the variation of SST in the tropical Indian Ocean and the South China Sea,and on the equatorial atmospheric thermal anomalies at both lower and upper levels.Through these impacts,the EAWM influences the land-sea thermal contrast in summer and the low-level atmospheric divergence and convergence over the Indo-Pacific region.It further affects the meridional monsoon circulation and other features of the EASM.Numerical simulations support the results of diagnostic analysis.The study provides useful information for predicting the EASM by analyzing the variations of preceding EAWM and tropical SST.

  7. EVOLUTION OF TROPOSPHERIC TEMPERATURE FIELDS AND CORRESPONDING THERMAL MECHANISMS BEFORE/AFTER ONSET PERIODS OF ASIAN SUMMER MONSOON

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The evolution of the tropospheric temperature fields over Indian and South China Sea monsoon areas and their thermal mechanisms are compared and analyzed during the period from March to June, 1996. The results show that the onsets of the Indian and South China Sea summer monsoons are closely associated with the seasonal warming in the troposphere over the zonal belt of 10° N ~ 30° N in these areas, which leads to the inversion of meridional temperature gradient. During the pre-onset period, the warming over the South China Sea monsoon region is mainly due to the warm horizontal advection and diabatic (latent) heating processes. Meanwhile, the warming is suppressed by the vertical adiabatic process (cooling). In spring over the Indian monsoon region, the significant adiabatic heating due to the subsidence motion, which compensates the cooling due to the strong cold advection and diabatic cooling processes, results in a larger warming rate than over the South China Sea monsoon region. However, the meridional temperature gradient over the Indian monsoon region is so large during the late winter and early spring that it takes longer time to warm the troposphere to have the reversion of meridional temperature gradient than it does over the South China Sea monsoon region. It results in the phenomenon that the South China Sea summer monsoon generally breaks out earlier than the Indian summer monsoon.

  8. Late-Holocene vegetation and climate change in Jeju Island, Korea and its implications for ENSO influences

    Science.gov (United States)

    Park, Jungjae; Shin, Young Ho; Byrne, Roger

    2016-12-01

    Several recent studies suggest the hypothesis that the El Niño-Southern Oscillation (ENSO) is an important factor controlling the Holocene East Asian Monsoon (EAM). However, the mechanism underlying this influence remains unclear due to the lack of high-resolution paleoclimate records from the coast of East Asia. Here, we provide a new record of late Holocene climate change in coastal East Asia based on multi-proxy evidence (pollen, organic content, magnetic susceptibility, grain size) obtained from a sediment core from Jeju Island, South Korea. As Jeju Island is strongly influenced by the Kuroshio flow, our sediment proxy records contain ENSO signals from the tropical Pacific. The study area was affected by dry/cool conditions in the western tropical Pacific (WTP) between 4350 and 1920 cal yr BP when El Niños were frequent, and by rapid warming/wetting and forestation since 1920 cal yr BP when La Niñas were more common. Jeju Island was relatively dry/cool between 2100 and 1600, 1300-1200, 1100-1000, 800-650, and 300-50 cal yr BP, as opposed to the Galápagos Islands, which were relatively wet/warm, reflecting the ENSO-related negative correlation between eastern and western margins of Pacific. Wet conditions may have prevailed during the early Little Ice Age (LIA) (620-280 cal yr BP) despite consistent cooling. This period of high precipitation may have been associated with the increased landfall of typhoons and with warmer Kuroshio currents under La Niña-like conditions. According to our results, EAM on the East Asian coastal margin was predominantly driven by ENSO activity, rather than by the precession effect. Paleoclimatic data from Jeju Island, with its insular position and closeness to warm Kuroshio currents, provide clear evidence of these ENSO influences.

  9. South Asian summer monsoon variability during the last ˜54 kyrs inferred from surface water salinity and river runoff proxies

    Science.gov (United States)

    Gebregiorgis, D.; Hathorne, E. C.; Sijinkumar, A. V.; Nath, B. Nagender; Nürnberg, D.; Frank, M.

    2016-04-01

    The past variability of the South Asian Monsoon is mostly known from records of wind strength over the Arabian Sea while high-resolution paleorecords from regions of strong monsoon precipitation are still lacking. Here, we present records of past monsoon variability obtained from sediment core SK 168/GC-1, which was collected at the Alcock Seamount complex in the Andaman Sea. We utilize the ecological habitats of different planktic foraminiferal species to reconstruct freshwater-induced stratification based on paired Mg/Ca and δ18O analyses and to estimate seawater δ18O (δ18Osw). The difference between surface and thermocline temperatures (ΔT) and δ18Osw (Δδ18Osw) is used to investigate changes in upper ocean stratification. Additionally, Ba/Ca in G. sacculifer tests is used as a direct proxy for riverine runoff and sea surface salinity (SSS) changes related to monsoon precipitation on land. Our Δδ18Osw time series reveals that upper ocean salinity stratification did not change significantly throughout the last glacial suggesting little influence of NH insolation changes. The strongest increase in temperature gradients between the mixed layer and the thermocline is recorded for the mid-Holocene and indicate the presence of a significantly shallower thermocline. In line with previous work, the δ18Osw and Ba/Ca records demonstrate that monsoon climate during the LGM was characterized by a significantly weaker southwest monsoon circulation and strongly reduced runoff. Based on our data the South Asian Summer Monsoon (SAM) over the Irrawaddyy strengthened gradually after the LGM beginning at ∼18 ka. This is some 3 kyrs before an increase of the Ba/Ca record from the Arabian Sea and indicates that South Asian Monsoon climate dynamics are more complex than the simple N-S displacement of the ITCZ as generally described for other regions. Minimum δ18Osw values recorded during the mid-Holocene are in phase with Ba/Ca marking a stronger monsoon precipitation

  10. Holocene environmental change and archaeology, Yangtze River Valley, China: Review and prospects

    Directory of Open Access Journals (Sweden)

    Li Wu

    2012-11-01

    Full Text Available Holocene environmental change and environmental archaeology are important components of an international project studying the human-earth interaction system. This paper reviews the progress of Holocene environmental change and environmental archaeology research in the Yangtze River Valley over the last three decades, that includes the evolution of large freshwater lakes, Holocene transgression and sea-level changes, Holocene climate change and East Asian monsoon variation, relationship between the rise and fall of primitive civilizations and environmental changes, cultural interruptions and palaeoflood events, as well as relationship between the origin of agriculture and climate change. These research components are underpinned by the dating of lacustrine sediments, stalagmites and peat to establish a chronology of regional environmental and cultural evolution. Interdisciplinary and other environment proxy indicators need to be used in comparative studies of archaeological site formation and natural sedimentary environment in the upper, middle and lower reaches of the Yangtze River Valley. Modern technology such as remote sensing, molecular bioarchaeology, and virtual reality, should be integrated with currently used dating, geochemical, sedimentological, and palaeobotanical methods of analysis in environmental archaeology macro- and micro-studies, so as to provide a greater comprehensive insight into Holocene environmental and cultural interaction and change in the Yangtze River Valley area.

  11. INTENSITY INDEX OF SOUTH CHINA SEA MONSOON AND ITS VARIATION CHARACTERISTICS

    Institute of Scientific and Technical Information of China (English)

    吴尚森; 梁建茵

    2002-01-01

    According to the basic characteristics of the activities of summer monsoon in the South China Sea,a standardized index,, has been designed that integrates a dynamic factor (southwesterly component) and a thermodynamic factor (OLR) for the indication of summer monsoon in the South China Sea.With the index determined for individual months of June,July and August and the entire summertime from 1975 to 1999,specific months and years are indicated that are either strong or weak in monsoon intensity.The variation is studied for the patterns and 's relationship is revealed with the onset of summer monsoon and the precipitation in Guangdong province and China.The results show that there are quasi-10 and quasi-3-4 year cycles in the interannual variation of the monsoon over the past 25 years.When it has an early (late) onset,the summer monsoon is usually strong (weak).In the strong (weak) monsoon years,precipitation tends to be more (less) in the first raining season of the year but normal or less (normal) in the second,in the province,but it would be more (less) in northeastern China and most parts of the northern China and south of the lower reaches of the Changjiang River and less (more) in the middle and lower reaches of the river,western part of northern China and western China.

  12. The footprint of Asian monsoon dynamics in the mass and energy balance of a Tibetan glacier

    Directory of Open Access Journals (Sweden)

    T. Mölg

    2012-08-01

    Full Text Available Determinations of glacier-wide mass and energy balance are still scarce for the remote mountains of the Tibetan Plateau, where field measurements are challenging. Here we run and evaluate a physical, distributed mass balance model for Zhadang glacier (central Tibet, 30° N, based on in-situ measurements over 2009–2011 and an uncertainty estimate by Monte Carlo and ensemble strategies. The model application aims to provide the first quantification of how the Indian Summer Monsoon (ISM impacts an entire glacier over the various stages of the monsoon's annual cycle. We find a strong and systematic ISM footprint on the interannual scale. Early (late monsoon onset causes higher (lower accumulation, and reduces (increases the available energy for ablation primarily through changes in absorbed shortwave radiation. By contrast, only a weak footprint exists in the ISM cessation phase. Most striking though is the core monsoon season: local mass and energy balance variability is fully decoupled from the active/break cycle that defines large-scale atmospheric variability during the ISM. Our results demonstrate quantitatively that monsoon onset strongly affects the ablation season of glaciers in Tibet. However, we find no direct ISM impact on the glacier in the main monsoon season, which has not been acknowledged so far. This result also adds cryospheric evidence that regional modification of the large-scale monsoon flow prevails on the Tibetan Plateau in summer.

  13. The footprint of Asian monsoon dynamics in the mass and energy balance of a Tibetan glacier

    Directory of Open Access Journals (Sweden)

    T. Mölg

    2012-12-01

    Full Text Available Determinations of glacier-wide mass and energy balance are still scarce for the remote mountains of the Tibetan Plateau, where field measurements are challenging. Here we run and evaluate a physical, distributed mass balance model for Zhadang Glacier (central Tibet, 30° N based on in-situ measurements over 2009–2011 and an uncertainty estimate by Monte Carlo and ensemble strategies. The model application aims to provide the first quantification of how the Indian Summer Monsoon (ISM impacts an entire glacier over the various stages of the monsoon's annual cycle. We find a strong and systematic ISM footprint on the interannual scale. Early (late monsoon onset causes higher (lower accumulation, and reduces (increases the available energy for ablation primarily through changes in absorbed shortwave radiation. By contrast, only a weak footprint exists in the ISM cessation phase. Most striking though is the core monsoon season: local mass and energy balance variability is fully decoupled from the active/break cycle that defines large-scale atmospheric variability during the ISM. Our results demonstrate quantitatively that monsoon onset strongly affects the ablation season of glaciers in Tibet. However, we find no direct ISM impact on the glacier in the main monsoon season, which has not been acknowledged so far. This result also adds cryospheric evidence that, once the monsoon is in full swing, regional atmospheric variability prevails on the Tibetan Plateau in summer.

  14. The footprint of Asian monsoon dynamics in the mass and energy balance of a Tibetan glacier

    Science.gov (United States)

    Mölg, T.; Maussion, F.; Yang, W.; Scherer, D.

    2012-12-01

    Determinations of glacier-wide mass and energy balance are still scarce for the remote mountains of the Tibetan Plateau, where field measurements are challenging. Here we run and evaluate a physical, distributed mass balance model for Zhadang Glacier (central Tibet, 30° N) based on in-situ measurements over 2009-2011 and an uncertainty estimate by Monte Carlo and ensemble strategies. The model application aims to provide the first quantification of how the Indian Summer Monsoon (ISM) impacts an entire glacier over the various stages of the monsoon's annual cycle. We find a strong and systematic ISM footprint on the interannual scale. Early (late) monsoon onset causes higher (lower) accumulation, and reduces (increases) the available energy for ablation primarily through changes in absorbed shortwave radiation. By contrast, only a weak footprint exists in the ISM cessation phase. Most striking though is the core monsoon season: local mass and energy balance variability is fully decoupled from the active/break cycle that defines large-scale atmospheric variability during the ISM. Our results demonstrate quantitatively that monsoon onset strongly affects the ablation season of glaciers in Tibet. However, we find no direct ISM impact on the glacier in the main monsoon season, which has not been acknowledged so far. This result also adds cryospheric evidence that, once the monsoon is in full swing, regional atmospheric variability prevails on the Tibetan Plateau in summer.

  15. Evidence of reworking and resuspension of carbonates during last glacial maximum and early deglacial period along the southwest coast of India

    Indian Academy of Sciences (India)

    Kamlesh Verma; M Sudhakar

    2006-12-01

    A gravity core collected from the upper slope of southwest of Quilon at a water depth of 776m (Lat: 8° 12′ 263′′N, Long: 76° 28′ 281′′E) was analysed for texture (carbonate free), calcium carbonate and organic carbon. Variation in silicic fraction seems to be controlled by silt, i.e., enrichment from 15 ka BP to 10 ka BP and then constant in Holocene. Below 15 ka BP, the silicic fraction gets depleted compared to the Holocene section with a minimum around 21 ka BP. Clay content remains nearly constant except in the Holocene where it shows an enrichment. Carbonate content of less than 63 micron when computed by subtracting coarse fraction content from the total carbonate suggests that the total carbonates are mainly concentrated in the finer fraction. All these carbonate phases show an inverse relationship with silicic fraction except in Holocene. Below 15 ka BP, CaCO3 dominates in sediments comprising more than 65%, such an increase is also seen in the coarse fraction. Coarse fraction from these sections contains abundant nodular type aggregates encrusting small forams. This period is marked by a high sedimentation rate comparable to Holocene. These parameters suggest that the productivity and precipitation have increased in the Holocene due to the intensification of the southwest monsoon. During the last glacial maximum and early deglacial period the high sedimentation rate indicates redeposition of the carbonates from the existing carbonate lithofacies situated between Quilon and Cape Comorin probably due to the slope instability.

  16. Linking hemispheric radiation budgets, ITCZ shifts, and monsoons

    Science.gov (United States)

    McGee, D.; Donohoe, A.; Marshall, J.; Ferreira, D.

    2014-12-01

    We explore the relationship between the Intertropical Convergence Zone (ITCZ), hemispheric heat budgets, and monsoon strength in past climates. Modern seasonal and interannual variability in the globally-averaged position of the ITCZ (as estimated by the tropical precipitation centroid) reflects the interhemispheric heat balance, with the ITCZ's displacement toward the warmer hemisphere directly proportional to atmospheric heat transport into the cooler hemisphere. Model simulations suggest that ITCZ shifts are likely to have obeyed the same relationship with interhemispheric heat transport in response to past changes in orbital parameters, ice sheets, and ocean circulation. This relationship implies that even small (±1 degree) shifts in the mean (annually and zonally averaged) ITCZ require large changes in hemispheric heat budgets, placing tight bounds on mean ITCZ shifts in past climates. To test this energetic argument, we use the observed relationship between mean ITCZ position and tropical sea surface temperature (SST) gradients in combination with proxy-based estimates of past SST gradients to show that mean ITCZ shifts for the mid-Holocene, Heinrich Stadial 1 and Last Glacial Maximum are not likely to have been more than 1 degree latitude from its present mean position. In exploring these results, we provide brief descriptions of the estimated radiation budgets of past climates that help demonstrate how different climate forcings change the interhemispheric heat balance and thus the ITCZ's global-mean position. We also address the seeming inconsistency between the small ITCZ shifts indicated by energetic constraints and the large changes in monsoon rainfall suggested by proxy data. We compare global-average and regional-scale tropical precipitation in observations and explore their responses to a variety of forcings (orbital changes, ice sheets, hosing) in models. These comparisons make clear that monsoon precipitation can change substantially even in the

  17. Inter-decadal Shift of East Asian Summer Monsoon in the Early 1990s%20世纪90年代初东亚夏季风的年代际转型

    Institute of Scientific and Technical Information of China (English)

    唐佳; 武炳义

    2012-01-01

    Using JRA-25 and NCEP/NCAR reanalysis data from 1979 to 2009, dominant modes of summer season (June-August) 850 hPa wind field variability over East Asia is revealed by means of the complex vector empirical orthogonal function method. The two reanalysis data are consistent with the description of the first East Asian summer monsoon (EASM) mode, whereas the first mode had been studied, showing that the first mode could not reflect the inter-decadal shift of Chinese summer precipitation in the early 1990s. Consequently, the inter-decadal shift feature of the second EASM mode is deeply analyzed, as well as its effect on summer precipitation in China. Moreover, the possible external forcing factors exerting effects on the inter-decadal shift of EASM are discussed. Results show that, EASM which is revealed,by two sets of reanalysis data to have undergone one inter-decadal shift in the early 1990s. The inter-decadal shift time of EASM is consistent with the inter-decadal shift time of summer precipitation in China. EASM is closely related to the mid-high latitude atmospheric circulation anomalies. Corresponding anomalous 500 hPa geopotential height fields show an anomalous quasi-zonal teleconnection pattern in northern Eurasia, whereas the distribution of summer precipitation anomalies show a meridional dipole pattern. Accompanied by the inter-decadal shift of EASM, after the early 1990s, summer precipitation decreases in the majority of northern China, especially in north of the northeast and the area between the Yangtze River and the Yellow River in the vicinity of 105° E. While summer precipitation increases significantly in South China and the Huaihe River Basin. From the perspective of dynamic, the characteristics of inter-decadal shift of summer precipitation in China are described. The difference distribution of summer 500 hPa geopotential height fields between two periods (1993-2009 and 1979-1992) show northern Eurasian quasi-zonal teleconnection pattern, then

  18. Holocene palaeoenvironmental history of the Amazonian mangrove belt

    Science.gov (United States)

    Cohen, Marcelo Cancela Lisboa; Pessenda, Luiz Carlos Ruiz; Behling, Hermann; de Fátima Rossetti, Dilce; França, Marlon Carlos; Guimarães, José Tasso Felix; Friaes, Yuri; Smith, Clarisse Beltrão

    2012-11-01

    Wetland dynamic in the northern Brazilian Amazon region during the Holocene was reviewed using palynological, carbon and nitrogen isotopes records, and C/N ratio previously published. The integration of 72 radiocarbon dates recorded in 34 sediment cores sampled along the marine and fluvial littoral, and mainly influenced by the Amazon River, reveals that marine influence and mangrove vegetation were wider than today on the mouth of Amazon River between >8990-8690 and 2300-2230 cal yr BP, forming a continuous mangrove belt along the northern Brazilian Amazon littoral. The establishment of this mangrove strip is a direct consequence of the marine incursion caused by post-glacial sea-level rise possibly associated with tectonic subsidence during the Early and Middle Holocene. In the Late Holocene, in areas influenced by the Amazon River discharge, the mangroves were replaced by freshwater vegetation, and the coast morphology evolved from an estuarine dominated into a rectilinear coast due to coastal progradation. Nevertheless, the marine-influenced littoral, which is currently dominated by mangroves and salt-marsh vegetation, has persistently had brackish water vegetation over tidal mud flats throughout the entire Holocene. Likely, the fragmentation of this continuous mangrove line during the Late Holocene was caused by the increase of river freshwater discharge associated to the change from dry into wet climates in the Late Holocene. This caused a significant decrease of tidal water salinity in areas near the mouth of Amazon River. These changes in the Amazon discharge are probably associated with dry and wet periods in the northern Amazon region during the Holocene.

  19. Climatology of monsoon precipitation over the Tibetan Plateau from 13-year TRMM observations

    Science.gov (United States)

    Aijuan, Bai; Guoping, Li

    2016-10-01

    Based on the 13-year data from the Tropical Rainfall Measuring Mission (TRMM) satellite during 2001-2013, the influencing geographical location of the Tibetan Plateau (Plateau) monsoon is determined. It is found that the domain of the Plateau monsoon is bounded by the latitude between 27° N and 37° N and the longitude between 60° E and 103° E. According to the annual relative precipitation, the Plateau monsoon can be divided into three sections: the Plateau winter monsoon (PWM) over Iran and Afghanistan, the Plateau summer monsoon (PSM) over the central Plateau, and the transiting zone of the Plateau monsoon (TPM) over the south, west, and east edges of the Plateau. In PWM and PSM, the monsoon climatology has a shorter rainy season with the mean annual rainfall of less than 800 mm. In TPM, it has a longer rainy season with the mean annual rainfall of more than 1800 mm. PWM experiences a single-peak monthly rainfall with the peak during January to March; PSM usually undergoes a multi-peak pattern with peaks in the warm season; TPM presents a double-peak pattern, with a strong peak in late spring to early summer and a secondary peak in autumn. The Plateau monsoon also characterizes an asymmetrical seasonal advance of the rain belt. In the east of the Plateau, the rain belt migrates in a south-north orientation under the impact of the tropical and subtropical systems' oscillation. In the west of the Plateau, the rain belt advances in an east-west direction, which is mainly controlled by the regional Plateau monsoon.

  20. Holocene grassland vegetation, climate and human impact in central eastern Inner Mongolia

    Institute of Scientific and Technical Information of China (English)

    HUANG; Fei; Kealhofer; Lisa; XIONG; Shangfa; HUANG; Fengb

    2005-01-01

    Phytolith and pollen preserved in the Taipusi Banner paleosol profile, central eastern Inner Mongolia, provide evidence of Holocene grassland vegetation, climate and human impact. The combined phytolith and pollen records reveal a major change in vegetation composition about 5000 a BP. Before 5000 a BP, the vegetation was dominated by Aneurolepidium chinese-Stipa grandis grassland of C4 grasses. After 5000 a BP, C4 grasses rapidly retreated,indicating a shift to colder and more arid conditions. The gradual invasion of Stipa krylovii, Agropyron desertorum, Ephedra, Chenopodiaceae and Caragana reveal the onset of grassland degeneration. Between 10000 and 8720 a BP, the Aneurolepidium chinese-Stipa grandis grassland included a small proportion of Artemisia shrub and Echionopos type plants, implying a strong winter monsoon and very weak summer monsoon. From 8720 to 7000 a BP, C4 grasses were common, indicating a strengthening of the summer monsoon. Between 7000 and 5000 a BP,the Holocene thermal maximum was evident, with a significant expansion of C4 grasses and the presence of some trees (such as Pinus and Betula, and so on) in or near the study site. From 4200-3000 a BP, a sandy grassland of Artemisia and Agropyron desertorum together with As ter-type taxa occurred. Precipitation amelioration took place between 3000 and 2170 a BP, with a rapid development of Echinops type plants and a small expansion of C4 grasses. From 2170 a BP to present, human activities accelerated the process of grassland degeneration.

  1. Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Sperber, K R; Yasunari, T

    2005-12-20

    The Earth's monsoon systems are the life-blood of more than two-thirds of the world's population through the rainfall they provide to the mainly agrarian societies they influence. More than 60 experts gathered to assess the current understanding of monsoon variability and to highlight outstanding problems simulating the monsoon.

  2. The Onset of the Monsoon over the Bay of Bengal: The Year-to-Year Variations

    Institute of Scientific and Technical Information of China (English)

    YU Wei-Dong; LI Kui-Ping; SHI Jian-Wei; LIU Lin; WANG Hui-Wu; LIU Yan-Liang

    2012-01-01

    In situ buoy observation data spanning four years (2008-2011) were used to demonstrate the year-to-year variations of the monsoon onset processes in the Bay of Bengal (BOB). A significant early (late) monsoon onset event in 2009 (2010) was analyzed in detail. It is found that the year-to-year variations of monsoon onset can be attributed to either the interannual variability in the BoB SST or the irregular activities of the intra-seasonal oscillation (ISO). This finding raises concern over the potential difficulties in simulating or predicting the monsoon onset in the BoB region. This uncertainty largely comes from the unsatisfactory model behavior at the intra-seasonal time scale.

  3. The timing of Mediterranean sapropel deposition relative to insolation, sea-level and African monsoon changes

    Science.gov (United States)

    Grant, K. M.; Grimm, R.; Mikolajewicz, U.; Marino, G.; Ziegler, M.; Rohling, E. J.

    2016-05-01

    The Mediterranean basin is sensitive to global sea-level changes and African monsoon variability on orbital timescales. Both of these processes are thought to be important to the deposition of organic-rich sediment layers or 'sapropels' throughout the eastern Mediterranean, yet their relative influences remain ambiguous. A related issue is that an assumed 3-kyr lag between boreal insolation maxima and sapropel mid-points remains to be tested. Here we present new geochemical and ice-volume-corrected planktonic foraminiferal stable isotope records for sapropels S1 (Holocene), S3, S4, and S5 (Marine Isotope Stage 5) in core LC21 from the southern Aegean Sea. The records have a radiometrically constrained chronology that has already been synchronised with the Red Sea relative sea-level record, and this allows detailed examination of the timing of sapropel deposition relative to insolation, sea-level, and African monsoon changes. We find that sapropel onset was near-synchronous with monsoon run-off into the eastern Mediterranean, but that insolation-sapropel/monsoon phasings were not systematic through the last glacial cycle. These latter phasings instead appear to relate to sea-level changes. We propose that persistent meltwater discharges into the North Atlantic (e.g., at glacial terminations) modified the timing of sapropel deposition by delaying the timing of peak African monsoon run-off. These observations may reconcile apparent model-data offsets with respect to the orbital pacing of the African monsoon. Our observations also imply that the previous assumption of a systematic 3-kyr lag between insolation maxima and sapropel midpoints may lead to overestimated insolation-sapropel phasings. Finally, we surmise that both sea-level rise and monsoon run-off contributed to surface-water buoyancy changes at times of sapropel deposition, and their relative influences differed per sapropel case, depending on their magnitudes. Sea-level rise was clearly important for

  4. Holocene shifts of the southern westerlies across the South Atlantic

    Science.gov (United States)

    Voigt, Ines; Chiessi, Cristiano M.; Prange, Matthias; Mulitza, Stefan; Groeneveld, Jeroen; Varma, Vidya; Henrich, Ruediger

    2015-02-01

    The southern westerly winds (SWW) exert a crucial influence over the world ocean and climate. Nevertheless, a comprehensive understanding of the Holocene temporal and spatial evolution of the SWW remains a significant challenge due to the sparsity of high-resolution marine archives and appropriate SWW proxies. Here we present a north-south transect of high-resolution planktonic foraminiferal oxygen isotope records from the western South Atlantic. Our proxy records reveal Holocene migrations of the Brazil-Malvinas Confluence (BMC), a highly sensitive feature for changes in the position and strength of the northern portion of the SWW. Through the tight coupling of the BMC position to the large-scale wind field, the records allow a quantitative reconstruction of Holocene latitudinal displacements of the SWW across the South Atlantic. Our data reveal a gradual poleward movement of the SWW by about 1-1.5° from the early to the mid-Holocene. Afterward, variability in the SWW is dominated by millennial scale displacements on the order of 1° in latitude with no recognizable longer-term trend. These findings are confronted with results from a state-of-the-art transient Holocene climate simulation using a comprehensive coupled atmosphere-ocean general circulation model. Proxy-inferred and modeled SWW shifts compare qualitatively, but the model underestimates both orbitally forced multimillennial and internal millennial SWW variability by almost an order of magnitude. The underestimated natural variability implies a substantial uncertainty in model projections of future SWW shifts.

  5. Evaluation of Holocene pollen records from the Romanian Plain.

    Science.gov (United States)

    Tomescu

    2000-05-01

    This study is a critical review of pollen analyses carried out on Holocene sequences from 15 sites in and near the Romanian Plain. Three sites come from natural sediments, 10 sites are from anthropogenic deposits and two are from both anthropogenic and natural settings. The general reconstruction is of a steppe-forest-steppe vegetation through the Holocene. The nature of the deposits, however, casts doubts on this reconstruction. Deposits of archaeological sites generally yield pollen spectra that are influenced by human activities and thus unsuitable for vegetation reconstructions. Loess deposits are also unfavorable for pollen preservation because of high pH and porosity. Consequently, pollen spectra from loess deposits are strongly biased by selective pollen destruction. Research and experiments carried out by several authors suggest that spectra dominated by Asteraceae, Poaceae, Chenopodiaceae or Pinus pollen in soils and loess are a result of selective pollen destruction, especially if low pollen concentrations, progressive pollen deterioration or high frequencies of deteriorated or unidentifiable pollen are evidenced. The fact that pollen records from the Romanian Plain come from loess, alkaline peat or archaeological sites reduces their reliability for reconstructions of vegetation. The vegetation history of similar regions in Hungary, Bulgaria and Turkey suggests that early Holocene steppe vegetation was gradually replaced by forest or forest-steppe vegetation in the late Holocene. Records from lake sediments are required to find out whether the Holocene vegetation history of the Romanian Plain was similar.

  6. The Influence of the East Asian Winter Monsoon on Indonesian Rainfall During the Past 60,000 Years

    Science.gov (United States)

    Konecky, B. L.; Russell, J. M.; Vogel, H.; Bijaksana, S.; Huang, Y.

    2013-12-01

    EAWM and D-depleted precipitation. In contrast, wet conditions in Central Sulawesi during Marine Isotope Stage 3 (MIS3) and during the early Holocene occurred when the EAWM was weakened. These findings support previous inferences based on Australian data that glacial boundary conditions modified the relationship between the EAWM and the Australian-Indonesian Summer Monsoon (AISM). However, previously proposed mechanisms for this modified EAWM/AISM relationship are not sufficient to explain our observations in Indonesia, and must be expanded. We propose revisions to these mechanisms in order to explain observations of Indonesian rainfall and δDprecip. Our findings provide important context for the circulation patterns that drove rainfall variations in Central Sulawesi during the past 60 kyr, and help to reconcile some of the disagreements among late Pleistocene records of surface runoff and δ18O/δDprecip from the IPWP region.

  7. Climate and environmental change at the end of the Holocene Humid Period: A pollen record off Pakistan

    Science.gov (United States)

    Ivory, Sarah J.; Lézine, Anne-Marie

    2009-08-01

    Pollen studies from core SO90-56KA recovered from the Arabian Sea off the Makran Coast (24° 509N, 65° 559E; 695 m depth) show that the end of the Holocene Humid Period, linked to the weakening of Indian monsoon fluxes, took place between 4700 and 4200 BP. Two periods of strong summer monsoon activity are identified between 5400-4200 BP and 2000-1000 BP during which the montane pollen taxa coming from the Himalayas reached the Makran coast due to increased fluvial activity of the Indus River. A contrasting period, dominated by the winter monsoon between 4200 and 2000 BP, is identified based on the presence of pollen taxa from the Baluchistan plateaus. The regional vegetation of the low- and midaltitudes, arid and semiarid, are remarkably stable from 4500 BP to the present.

  8. Holocene temperature evolution in the Northern Hemisphere high latitudes - Model-data comparisons

    Science.gov (United States)

    Zhang, Yurui; Renssen, Hans; Seppä, Heikki; Valdes, Paul J.

    2017-10-01

    Heterogeneous Holocene climate evolutions in the Northern Hemisphere high latitudes are primarily determined by orbital-scale insolation variations and melting ice sheets. Previous inter-model comparisons have revealed that multi-simulation consistencies vary spatially. We, therefore, compared multiple model results with proxy-based reconstructions in Fennoscandia, Greenland, north Canada, Alaska and Siberia. Our model-data comparisons reveal that data and models generally agree in Fennoscandia, Greenland and Canada, with the early-Holocene warming and subsequent gradual decrease to 0 ka BP (hereinafter referred as ka). In Fennoscandia, simulations and pollen data suggest a 2 °C warming by 8 ka, but this is less expressed in chironomid data. In Canada, a strong early-Holocene warming is suggested by both the simulations and pollen results. In Greenland, the magnitude of early-Holocene warming ranges from 6 °C in simulations to 8 °C in δ18O-based temperatures. Simulated and reconstructed temperatures are mismatched in Alaska. Pollen data suggest strong early-Holocene warming, while the simulations indicate constant Holocene cooling, and chironomid data show a stable trend. Meanwhile, a high frequency of Alaskan peatland initiation before 9 ka can reflect a either high temperature, high soil moisture or large seasonality. In high-latitude Siberia, although simulations and proxy data depict high Holocene temperatures, these signals are noisy owing to a large spread in the simulations and between pollen and chironomid results. On the whole, the Holocene climate evolutions in most regions (Fennoscandia, Greenland and Canada) are well established and understood, but important questions regarding the Holocene temperature trend and mechanisms remain for Alaska and Siberia.

  9. Fingerprinting the Impacts of Aerosols on Long-Term Trends of the Indian Summer Monsoon Regional Rainfall

    Science.gov (United States)

    Laul, K. M.; Kim, K. M.

    2010-01-01

    In this paper, we present corroborative observational evidences from satellites, in-situ observations, and re-analysis data showing possible impacts of absorbing aerosols (black carbon and dust) on subseasonal and regional summer monsoon rainfall over India. We find that increased absorbing aerosols in the Indo-Gangetic Plain in recent decades may have lead to long-term warming of the upper troposphere over northern India and the Tibetan Plateau, enhanced rainfall in northern India and the Himalayas foothill regions in the early part (may-June) of the monsoon season, followed by diminished rainfall over central and southern India in the latter part (July-August) of the monsoon season. These signals which are consistent with current theories of atmospheric heating and solar dimming by aerosol and induced cloudiness in modulating the Indian monsoon, would have been masked by conventional method of using al-India rainfall averaged over the entire monsoon season.

  10. 澧阳平原晚更新世晚期至全新世早中期环境演变及其对人类活动的影响%The Environmental Change of Late Pleistocene to Early and Middle Holocene and Its Impact on Human Activities in Liyang Plain, Hunan Province, China

    Institute of Scientific and Technical Information of China (English)

    郭媛媛; 莫多闻; 毛龙江; 郭伟民

    2016-01-01

    通过对澧阳平原野外调查,多剖面地层对比分析及岩板垱(YBD)剖面样品的粒度、地球化学元素分析和年代测定,揭示该区晚更新世晚期至全新世早中期环境演变,并探讨其对人类活动的影响。研究结果表明,30~6 ka B.P.间,澧阳平原由冲沟发育的黄土台地向河湖发育的平原丘岗地貌过渡;气候环境经历了弱暖湿-气候变差-凉湿-波动回暖-暖湿的变化;更新世末至全新世早期稻作农业的出现与该区的环境条件和文化基础密切相关;环境演变也推动了古人类活动范围和聚落特征的变化。%Based on detailed field surveys, comparison of strata of typical profiles and experimental analysis (in-cluding grain size, geochemical analysis and optically stimulated luminescence (OSL) dating) of samples col-lected at the Yanbangdang (YBD) site, we explored the environmental evolution from Late Pleistocene to Mid-dle Holocene and its impact on human activities, especially on the origin and development of rice agriculture in Liyang Plain. The results showed that the climate of the Liyang Pain during 30-6 ka B.P. experienced five stages:relatively warm and humid in the Late Pleistocene, cool and humid during the Last Glacial Maximum (LGM), fluctuated warming in the terminal Pleistocene and Early Holocene, and warm and humid during the Middle Holocene. In the Late Pleistocene, landforms of the Liyang Plain were characterized by tablelands drained by rivers and gullies in the Late Pleistocene, with topographic relief much higher than present. As cli-matic amelioration during the terminal Pleistocene and Early Holocene, continuous filling and siltation oc-curred in Liyang Plain and large areas of wetland was formed. Landscapes of the Liyang Plain at this time were mainly plains and hillocks with dense rivers and lakes and the topographic relief was gradually reduced. During the Middle Holocene, landforms of Liyang Plain were mainly

  11. Tropical stratospheric circulation and monsoon rainfall

    Science.gov (United States)

    Sikder, A. B.; Patwardhan, S. K.; Bhalme, H. N.

    1993-09-01

    Interannual variability of both SW monsoon (June September) and NE monsoon (October December) rainfall over subdivisions of Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu have been examined in relation to monthly zonal wind anomaly for 10 hPa, 30 hPa and 50 hPa at Balboa (9°N, 80°W) for the 29 year period (1958 1986). Correlations of zonal wind anomalies to SW monsoon rainfall ( r=0.57, significant at 1% level) is highest with the longer lead time (August of the previous year) at 10 hPa level suggesting some predictive value for Coastal Andhra Pradesh. The probabilities estimated from the contingency table reveal non-occurrence of flood during easterly wind anomalies and near non-occurrence of drought during westerly anomalies for August of the previous year at 10 hPa which provides information for forecasting of performance of SW monsoon over Coastal Andhra Pradesh. However, NE monsoon has a weak relationship with zonal wind anomalies of 10 hPa, 30 hPa and 50 hPa for Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu. Tracks of the SW monsoon storms and depressions in association with the stratospheric wind were also examined to couple with the fluctuations in SW monsoon rainfall. It is noted that easterly / westerly wind at 10 hPa, in some manner, suppresses / enhances monsoon storms and depressions activity affecting their tracks.

  12. Worldwide delta initiation, the beginning of the 8.2-ka event, and the base of the Middle Holocene

    NARCIS (Netherlands)

    Cohen, K.M.; Hijma, M.P.

    2015-01-01

    Session P09 Holocene rapid climate changes. Abstract T00351 The Early Holocene is globally characterised by steady postglacial climatic warming and the drowning of continental shelves due to sea level rise (SLR). The 8.2-event sits as a superimposed event on both the climatic and the sea-level recor

  13. Mid-Holocene ocean and vegetation feedbacks over East Asia

    Directory of Open Access Journals (Sweden)

    Z. Tian

    2013-09-01

    Full Text Available Mid-Holocene ocean and vegetation feedbacks over East Asia are investigated by a set of numerical experiments performed with the version 4 of the Community Climate System Model (CCSM4. With reference to the pre-industrial period, most of the mid-Holocene annual and seasonal surface-air temperature and precipitation changes are found to result from a direct response of the atmosphere to insolation forcing, while dynamic ocean and vegetation modulate regional climate of East Asia to some extent. Because of its thermal inertia, the dynamic ocean induced an additional warming of 0.2 K for the annual mean, 0.5 K in winter (December–February, 0.0003 K in summer (June–August, and 1.0 K in autumn (September–November, but a cooling of 0.6 K in spring (March–May averaged over China, and it counteracted (amplified the direct effect of insolation forcing for the annual mean and in winter and autumn (spring for that period. The dynamic vegetation had an area-average impact of no more than 0.4 K on the mid-Holocene annual and seasonal temperatures over China, with an average cooling of 0.2 K for the annual mean. On the other hand, ocean feedback induced a small increase of precipitation in winter (0.04 mm day−1 and autumn (0.05 mm day−1, but a reduction for the annual mean (0.14 mm day−1 and in spring (0.29 mm day−1 and summer (0.34 mm day−1 over China, while it also suppressed the East Asian summer monsoon rainfall. The effect of dynamic vegetation on the mid-Holocene annual and seasonal precipitation was comparatively small, ranging from −0.03 mm day−1 to 0.06 mm day−1 averaged over China. In comparison, the CCSM4 simulated annual and winter cooling over China agrees with simulations within the Paleoclimate Modeling Intercomparison Project (PMIP, but the results are contrary to the warming reconstructed from multiple proxy data for the mid-Holocene. Ocean feedback narrows this model–data mismatch, whereas vegetation feedback plays

  14. Global monsoon in a geological perspective

    Institute of Scientific and Technical Information of China (English)

    WANG PinXian

    2009-01-01

    Monsoon is now considered as a global system rather than regional phenomena only. For over 300 years, monsoon has been viewed as a gigantic land-sea breeze, but now satellite and conventional observations support an alternative hypothesis which considers monsoon as a manifestation of sea-sonal migration of the intertropical convergence zone (ITCZ) and, hence, a climate system of the global scale. As a low-latitude climate system, monsoon exists over all continents but Antarctica, and through all the geological history at least since the Phenorozoic. The time is ripe for systematical studies of monsoon variations in space and time.As evidenced by the geological records, the global monsoon is controlled by the Wilson cycle on the tectonic time scale (106-108a). A "Mega-continent" produces "Mega-monsoon", and its breakdown leads to weakening of the monsoon Intensity. On the time scales of 104-105 a, the global monsoon displays the precessional cycles of~20 ka and eccentricity cycles of 100- and 400-ka, i.e. the orbital cycles. On the time scales of 103 a and below, the global monsoon intensity is modulated by solar cy-cles and other factors. The cyclicity of global monsoon represents one of the fundamental factors re-sponsible for variations in the Earth surface system as well as for the environmental changes of the human society. The 400-ka long eccentricity cycles of the global monsoon is likened to "heartbeat" of the Earth system, and the precession cycle of the global monsoon was responsible for the collapse of several Asian and African ancient cultures at~4000 years ago, whereas the Solar cycles led to the de-mise of the Maya civilization about a thousand years ago. Therefore, paleoclimatology should be fo-cused not only on the high-latitude processes centered at ice cap variations, but also on the low-latitude processes such as monsoons, as the latter are much more common in the geological history compared to the glaciations.

  15. Impacts of dust reduction on the northward expansion of the African monsoon during the Green Sahara period

    Science.gov (United States)

    Pausata, Francesco S. R.; Messori, Gabriele; Zhang, Qiong

    2016-01-01

    The West African Monsoon (WAM) is crucial for the socio-economic stability of millions of people living in the Sahel. Severe droughts have ravaged the region in the last three decades of the 20th century, highlighting the need for a better understanding of the WAM dynamics. One of the most dramatic changes in the West African Monsoon (WAM) occurred between 15000-5000 yr BP, when increased summer rainfall led to the so-called "Green Sahara" and to a reduction in dust emissions from the region. However, model experiments are unable to fully reproduce the intensification and geographical expansion of the WAM during this period, even when vegetation over the Sahara is considered. Here, we use a fully coupled simulation for 6000 yr BP (Mid-Holocene) in which prescribed Saharan vegetation and dust concentrations are changed in turn. A closer agreement with proxy records is obtained only when both the Saharan vegetation changes and dust decrease are taken into account. The dust reduction strengthens the vegetation-albedo feedback, extending the monsoon's northern limit approximately 500 km further than the vegetation-change case only. We therefore conclude that accounting for changes in Saharan dust loadings is essential for improving model simulations of the WAM during the Mid-Holocene.

  16. MM5 Simulations of the China Regional Climate During the Mid-Holocene

    Institute of Scientific and Technical Information of China (English)

    LIU Yu; HE Jinhai; LI Weiliang; CHEN Longxun; LI Wei; ZHANG Bo

    2010-01-01

    Using a regional climate model MM5 nested with an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate responses of the mid-Holocene climate to different factors over China. Model simulations of the mid-Holocene climate change, especially the precipitation change, are in good agreement with the geologic records. Model results show that relative to the present day (PD) climate, the temperature over China increased in the mid-Holocene, and the increase in summer is more than that in winter. The summer monsoon strengthened over the eastern China north of 30°N, and the winter monsoon weakened over the whole eastern China; the precipitation increased over the west part of China, North China, and Northeast China, and decreased over the south part of China. The sensitive experiments indicate that changes in the global climate (large-scale circulation background), vegetation, earth orbital parameter, and CO2 concentration led to the mid-Holocene climate change relative to the PD climate, and changes in precipitation, temperature and wind fields were mainly affected by change of the large-scale circulation background, especially with its effect on precipitation exceeding 50%. Changes in vegetation resulted in increasing of temperature in both winter and summer over China, especially over eastern China; furthermore, its effect on precipitation in North China accounts for 25% of the total change. Change in the orbital parameter produced the larger seasonal variation of solar radiation in the mid-Holocene than the PD, which resulted in declining of temperature in winter and increasing in summer; and also had an important effect on precipitation with an effect equivalent to vegetation in Northeast China and North China. During the mid-Holocene, CO2 content was only 280×l0-6, which reduced temperature in a very small magnitude. Therefore, factors affecting the mid-Holocene climate change over China from

  17. Holocene climate variability and oceanographic changes off western South Africa

    Science.gov (United States)

    Zhao, Xueqin; Dupont, Lydie; E Meadows, Michael; Schefuß, Enno; Bouimetarhan, Ilham; Wefer, Gerold

    2017-04-01

    South Africa is located at a critical transition zone between subtropical and warm-temperate climate zones influenced by the Indian and Atlantic oceans. Presently, the seasonal changes of atmospheric and oceanic systems induce a pronounced rainfall seasonality comprised of two different rainfall zones over South Africa. How did this seasonality develop during the Holocene? To obtain a better understanding of how South African climates have evolved during the Holocene, we conduct a comprehensive spatial-temporal approach including pollen and dinoflagellate cyst records from marine sediment samples retrieved from the Namaqualand mudbelt, a Holocene terrigenous mud deposit on the shelf of western South Africa. The representation of different vegetation communities in western South Africa is assessed through pollen analysis of surface sediments. This approach allows for climate reconstructions of the summer rainfall zone (SRZ) using Group 1 (Poaceae, Cyperaceae, Phragmites-type and Typha) and winter rainfall zone (WRZ) using Group 2 (Restionaceae, Ericaceae, Anthospermum, Stoebe/Elytropappus-type, Cliffortia, Passerina, Artemisia-type and Pentzia-type) from a single marine archive. The fossil pollen data from gravity core GeoB8331-4 indicate contrasting climate patterns in the SRZ and WRZ especially during the early and middle Holocene. The rainfall amount in the SRZ is dominated by insolation forcing, while in the WRZ it is mainly attributed to the latitudinal position of the southern westerlies. Dinoflagellate cyst data show significantly different oceanographic conditions associated with climate changes on land. High percentages of autotrophic taxa like Operculodinium centrocarpum and Spiniferites spp. indicate warm and stratified conditions during the early Holocene, suggesting reduced upwelling. In contrast, the middle Holocene is characterized by a strong increase in heterotrophic taxa in particular Lejeunecysta paratenella and Echinidinium spp., indicating cool

  18. Evidence of a humid mid-Holocene in the western part of Chinese Loess Plateau

    Institute of Scientific and Technical Information of China (English)

    AN Chengbang; FENG Zhaodong; TANG Lingyu

    2003-01-01

    Field works show that the wetland/swamp layers were distributed ubiquitously in the western part of the Chinese Loess Plateau. Universality of the wetland/swampy layer and the consistency of the age reveal that the layer was developed under the humid climatic condition. Dated between 9 and 3.8 kaBP, the wetland/swampy layer is full of aquatic mollusks and has the highest tree and shrub pollen, indicating a humid mid-Holocene. Variations of grain size suggest that winter monsoon weakened during 9-3.8 kaBP while climate change to humid and vegetation cover increased from 9 kaBP onward. After 5.9 kaBP, the humidity declined gradually. In 3.8 kaBP, summer monsoon sharply retreated, and the climate changed to dry.

  19. Latest Pleistocene and Holocene glacier fluctuations on Mount Baker, Washington

    Science.gov (United States)

    Osborn, Gerald; Menounos, Brian; Ryane, Chanone; Riedel, Jon; Clague, John J.; Koch, Johannes; Clark, Douglas; Scott, Kevin; Davis, P. Thompson

    2012-08-01

    Glaciers on stratovolcanoes of the Pacific Northwest of North America offer opportunities for dating late Pleistocene and Holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields. We capitalize on this opportunity by examining the Holocene glacial record at Mount Baker, an active stratovolcano in northwest Washington. Earlier workers concluded that glaciers on Mount Baker during the early Holocene were more extensive than during the Little Ice Age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes. We show that the main argument for an early Holocene glacier advance on Mount Baker, namely the absence of ca 10,000-year-old tephra on part of the south flank of the mountain, is incorrect. Moreover, a lake-sediment core indicates that a small cirque moraine previously thought be of early Holocene age is also likely older than the tephra and consequently of late Pleistocene age. Lateral and end moraines and wood mats ca 2 km downvalley of the present snout of Deming Glacier indicate that an advance during the Younger Dryas interval was little more extensive than the climactic Little Ice Age advance. Tephra and wood between tills in the left lateral moraine of Easton Glacier suggest that ice on Mount Baker was restricted in the early Holocene and that Neoglaciation began ca 6 ka. A series of progressively more extensive Neoglacial advances, dated to about 2.2, 1.6, 0.9, and 0.4 ka, are recorded by stacked tills in the right lateral moraine of Deming Glacier. Intervening retreats were long enough to allow establishment of forests on the moraine. Wood mats in moraines of Coleman and Easton glaciers indicate that Little Ice Age expansion began before 0.7 ka and was followed by retreat and a readvance ca 0.5 ka. Tree-ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid-1800s. The similarity between

  20. Holocene Environmental Magnetic Studies in northeastern Taiwan

    Science.gov (United States)

    Lee, T.; Yang, T.

    2010-12-01

    This study will present the environmental magnetic results analyzed from two lacustrine sediment cores raised from Ta-Hu Lake of Ilan County at northeastern Taiwan. The total recovered length of core DH-7A is of about 53.3 meters and that of the core DH-7B is of about 35.5 meters. Based on the C-14 dating, the former core could provide the information for the whole Holocene and the later one could support the data at least for the last 7,600 years. For those magnetic proxies representing the abundant variation of magnetic minerals, such as SIRM, bIRM, ARM, HIRM etc., show very spiky patterns. High abundant signals are usually accompanied by increasing of the fine grain signal (ARM/χ) and decreasing the S-ratio. Based on the difference between the magnetic results of the two cores and the analysis of organic matters of the core, these spikes might represent the flooding events brought the sediments from the outside drainage area into the lake due to severe heavy rainfalls in the area studied. In addition, based on the characteristic variation patterns of the used magnetic proxies several periods could be delimited. Higher sedimentation rate could be found at the two periods, 7600~5800 yrB.P. and 2000~500 yrB.P., which is of about 3-4 times of the others. Also their magnetic signals changed much frequent than the others. The results may related to the strengthen/weaken evolution of the East Asia monsoon.

  1. Middle Holocene Unconformity in Seneca Lake, NY

    Science.gov (United States)

    Curtin, T. M.; Crocker, M.; Loddengaard, K.

    2008-12-01

    The post-glacial history of the Finger Lakes, NY have involved several changes in lake levels throughout the latest Pleistocene and Holocene, resulting from the changing position of the retreating Laurentide ice sheet, river outlet position, glacial rebound, and water balance. Previous studies of high-resolution seismic reflection profiles from three Finger Lakes define a middle Holocene erosional surface at water depths as great as 26 m in the northern end of each of lake. There are two proposed hypotheses to explain the origin of the observed erosional surfaces: 1) subaerial erosion during a lake lowstand and 2) erosion resulting from increased internal seiche activity. To evaluate these hypotheses, we examined a series of 2 to 5 m long piston cores collected along a north-south transect from one of the Finger Lakes, Seneca Lake. Cores were correlated using distinctive changes in the profiles of grain size, loss-on-ignition, and magnetic susceptibility. We recognize a significant erosional unconformity of early to middle Holocene sediment at modern depths 60 m, the unconformity continues as a conformable zone. We attribute the unconformity to wave abrasion and nearshore current winnowing of the shoreface during a lowstand. With an assumption of an effective 20 m wave base, the depth to the low level lake surface responsible for the unconformity is estimated to be 40 m. The age of the unconformity is ~6 ka, based on radiocarbon ages of lithologic boundaries in the sediment cores. Because the unconformity grades into a conformable zone in deepwater cores that display no change in lithology, we hypothesize that the large-scale lake level drop is likely not the result of climate change, but rather a change in accommodation space in the northern portion of the lake basin due to glacial rebound.

  2. INTENSITY INDEX OF SOUTH CHINA SEA MONSOON AND ITS VARIATION CHARACTERISTICS

    Institute of Scientific and Technical Information of China (English)

    吴尚森; 梁建茵

    2002-01-01

    According to the basic characteristics of the activities of summer monsoon in the South China Sea,Standardized index,Is,has been designed that integrates a dynamic factor(southwesterly component) and a thermodynamic factor(OLR) for the indication of summer monsoon in the South China Sea,With the index determined for individual months of June,July and August and the entire summertime from 1975 to 1999,specific months and years are indicated that are either strong or weak in monsoon intensity,The variation is studied for the patterns and Is's relationship is revealed with the onset of summer monsoon and the precipitation in Guang-dong province and China.The results show that there are quasi-10 and quasi-3-4 year cycles in the interannual variation of the monsooon over the past 25 years.When it has an early(late)onset,the summer monsoon is usually strong (weak),In the strong(weak)monsoon,years,precipitation tends to be more(less)in the first raining season of the year but normal or less(normal)in the second,in the province,but it would be more(less) in northeastern China and most parts of the northern china and south of the lower reaches of the Changjiang River and less(more)in the middle and lower reaches of the river,western part of northern China and western China.

  3. Greening of the Sahara suppressed ENSO activity during the mid-Holocene

    Science.gov (United States)

    Pausata, Francesco S. R.; Zhang, Qiong; Muschitiello, Francesco; Lu, Zhengyao; Chafik, Léon; Niedermeyer, Eva M.; Stager, J. Curt; Cobb, Kim M.; Liu, Zhengyu

    2017-07-01

    The evolution of the El Niño-Southern Oscillation (ENSO) during the Holocene remains uncertain. In particular, a host of new paleoclimate records suggest that ENSO internal variability or other external forcings may have dwarfed the fairly modest ENSO response to precessional insolation changes simulated in climate models. Here, using fully coupled ocean-atmosphere model simulations, we show that accounting for a vegetated and less dusty Sahara during the mid-Holocene relative to preindustrial climate can reduce ENSO variability by 25%, more than twice the decrease obtained using orbital forcing alone. We identify changes in tropical Atlantic mean state and variability caused by the momentous strengthening of the West Africa Monsoon (WAM) as critical factors in amplifying ENSO's response to insolation forcing through changes in the Walker circulation. Our results thus suggest that potential changes in the WAM due to anthropogenic warming may influence ENSO variability in the future as well.

  4. Role of west Asian surface pressure in summer monsoon onset over central India

    Science.gov (United States)

    Chakraborty, Arindam; Agrawal, Shubhi

    2017-07-01

    Using rain-gauge measurements and reanalysis data sets for 1948-2015, we propose a mechanism that controls the interannual variation of summer monsoon onset over central India. In May, about a month before the onset, the low level jet over the Arabian Sea is about 40% stronger and about 2.5 degrees northward during years of early onset as compared to years of late onset. A stronger and northward shifted low level jet carries about 50% more moisture in early onset years, which increases low level moist static energy over central India in the pre-monsoon season. The increase in low level moist static energy decreases the stability of the atmosphere and makes it conducive for convection. The strength and position of the low level jet are determined by surface pressure gradient between western Asia and the west-equatorial Indian Ocean. Thus, an anomalous surface pressure low over western Asia in the pre-monsoon season increases this gradient and strengthens the jet. Moreover, a stronger low level jet increases the meridional shear of zonal wind and supports the formation of an onset vortex in a stronger baroclinic atmosphere. These developments are favourable for an early onset of the monsoon over the central Indian region. Our study postulates a new physical mechanism for the interannual variation of onset over central India, the core of the Indian monsoon region and relevant to Indian agriculture, and could be tested for real-time prediction.

  5. Cyclone trends constrain monsoon variability during Late Oligocene sea level highstands (Kachchh Basin, NW India

    Directory of Open Access Journals (Sweden)

    M. Reuter

    2013-01-01

    Full Text Available Important concerns about the consequences of climate change for India are the potential impact on tropical cyclones and the monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin as an indicator of tropical cyclone activity along the NW Indian coast during the Late Oligocene warming period (~27–24 Ma. Direct proxies providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system in the Early Miocene. The vast shell concentrations comprise a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deep to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished each recording a relative storm wave base depth. (1 A shallow storm wave base is shown by nearshore mollusks, corals and Clypeaster echinoids; (2 an intermediate storm wave base depth is indicated by lepidocyclind foraminifers, Eupatagus echinoids and corallinaceans; and (3 a deep storm wave base is represented by an Amussiopecten–Schizaster echinoid assemblage. Vertical changes in these skeletal associations give evidence of gradually increasing tropical cyclone intensity in line with third-order sea level rise. The intensity of cyclones over the Arabian Sea is primarily linked to the strength of the Indian monsoon. Therefore and since the topographic boundary conditions for the Indian monsoon already existed in the Late Oligocene, the longer-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~26 Ma followed by a period of monsoon weakening during the peak of the Late Oligocene

  6. Effect of precession on the Asian summer monsoon evolution: A systematic review

    Institute of Scientific and Technical Information of China (English)

    LIU XiaoDong; SHI ZhengGuo

    2009-01-01

    Geological climatic records and model simulations on the Asian summer monsoon climate change induced by insolation forcing of the Earth's precession are systematically reviewed in this paper. The presentation of the questions on the mechanism of the Asian monsoon evolution at the precession band, currently existing debates and future research directions are discussed. Since the early 1980s, more and more observed evidence and simulated results, especially the absolute-dated stalagmite re-cords and orbital-scale transient model runs in the last few years, have indicated that the quasi-20ka period in the Quaternary monsoon climate change is caused by precession. However, debates still exist on the dynamic mechanism how precession affects the Asian monsoon. The "zero phase" hypothesis says that the Asian monsoon is merely controlled by summer insolation in the Northern Hemisphere (NH) while the "latent heat" hypothesis emphasizes the dominant effect of latent heat transport from the Southern Hemisphere (SH) besides the role of the northern insolation. The two hypotheses have separately been supported by some evidence. Although we are cognizant of the importance of northern solar radiation and the remote effect of southern insolation, it has still a long way to go before com-prehensively understanding the evolutionary mechanism of the Asian monsoon. In view of the prob-lems existing in present researches of monsoon-dominated climate change at the precession scale, we propose that studies on the environmental significance of geological monsoon proxies, feedback processes in the long-term transient simulations and intercomparisons between observations and modeling results should be strengthened in the future.

  7. Holocene landscape dynamics of the Ghaggar-Hakra floodplain, India: implications for the Indus Civilisation

    Science.gov (United States)

    Durcan, Julie; Thomas, David; Pawar, Vikas; Gupta, Sanjeev; Petrie, Cameron; Singh, Ravindra

    2016-04-01

    The area around the ephemeral Ghaggar-Hakra River system in India and Pakistan is associated with a dense concentration of Indus Civilisation archaeological sites. Giosan et al. (2012) have suggested that a decline, and ultimately cessation, of flow in this river system in response to the weakening of the Asian Monsoon was influential in the collapse of the Indus Civilisation around 4,000 years ago and palaeoclimatic studies in the region (e.g. Berkelhammer et al., 2012; Dixit et al., 2014; Leipe et al., 2014) have shown abrupt drying events during the mid-Holocene, which are superimposed onto a longer-term insolation driven decline in Asian Monsoon intensity. Further work is required to understand the dynamics of this river system during the Holocene and to assess the importance of changing landscape dynamics, as well as climatic variability, in the decline of the Indus Civilisation. This paper presents optically stimulated luminescence (OSL) dates from palaeochannel sediments and associated dune deposits in the Ghaggar-Hakra river system in Northwest India, with the aim of understanding late Quaternary geomorphological and palaeoenvironmental change. Reconstructing palaeoenvironmental variability will allow a comparison between the documented archaeological record of the Indus Civilisation and an absolute chronology of regional landscape dynamism. This comparison will also allow an insight into whether the mid-Holocene collapse and/or transformation of the Indus Civilisation can be correlated with geomorphological and/or climatic variability. Berkelhammer, M., Sinha, A., Stott, L., Cheng, H., Pausata, F.S.R., and Yoshimura, K., 2012, An abrupt shift in the Indian monsoon 4000 years ago, in Giosan, L., Fuller, D.Q., Nicoll, K., Flad, R.K. and Clift P.D. (eds.), Climates, landscapes, and civilizations. American Geophysical Union Geophysical Monograph, 198, 75-87. Dixit, Y., Hodell, D.A. and Petrie, C.A., 2012. Abrupt weakening of the summer monsoon in northwest

  8. Contribution of oceanic and vegetation feedbacks to Holocene climate change in Central and Eastern Asia

    Directory of Open Access Journals (Sweden)

    A. Dallmeyer

    2009-10-01

    Full Text Available The impact of vegetation-atmosphere and ocean-atmosphere interactions on the mid- to late Holocene climate change as well as their synergy is studied for different regions in Central and Eastern Asia (60–140° E, 0–55° N, giving consideration to the large climatic and topographical heterogeneity in that area. With main focus on the Asian monsoon, we concentrate on both, temperature and precipitation changes. For our purpose, we analyze a set of coupled numerical experiments, performed with the Earth system model ECHAM5/JSBACH-MPIOM under present-day and mid-Holocene (6 k orbital configurations (Otto et al., 2009. Like expected, the temperature change caused by the insolation forcing reveals an enhanced seasonal cycle, with a pronounced warming in summer (0.7 K and autumn (1 K and a cooling in the other seasons (spring: −0.8 K; winter −0.5 K. Most of this change can be attributed to the direct response of the atmosphere, but the ocean, whose reaction has a lagged seasonal cycle (warming in autumn and winter, cooling in the other seasons, strongly modifies the signal. The simulated contribution of dynamic vegetation is small and most effective in winter, where it slightly warms the near-surface atmosphere (≈0.05 K. Concerning the precipitation, the most remarkable change is the postponement and enhancement of the Asian monsoon (0.27 mm/d in summer, 0.23 mm/d in autumn, mainly related to the direct atmospheric response. On regional average, the ocean (ca. 0.05 mm/d amplifies the direct effect, but tends to weaken the East Asian summer monsoon and strongly increases the Indian summer monsoon rainfall rate (0.68 mm/d. The influence of dynamic vegetation and synergy effects on precipitation is comparatively small.

  9. East Asian Monsoon and paleoclimatic data analysis: a vegetation point of view

    Directory of Open Access Journals (Sweden)

    J. Guiot

    2008-06-01

    Full Text Available First we review several syntheses of paleodata (pollen, lake-levels showing the climate variations in China and Mongolia from the last glacial maximum to Present and in particular the precipitation increase at mid Holocene related to enhanced monsoon. All these results concur to a much enhanced monsoon on most of China during the first half of the Holocene. Second we present, in some details, a temporal study of a core (Lake Bayanchagan, Inner Mongolia located in an arid region at the edge of the present East Asian Monsoon (EAM influence and then sensitive to climatic change. This study involves pollen data together with other macro-remains and stable isotope curve to obtain a robust climate reconstruction. This study shows a long wet period between 11 000 and 5000 years BP divided in two parts, a warmer one from 11 000 and 8000 (marked by large evapotranspiration and a cooler one more favourable to forest expansion. Third, we present a spatial study based on pollen data only and covering all China and Mongolia at 6000 years BP, but using a mechanistic modelling approach, in an inverse mode. It has the advantage to take into account environmental context different from the present one (lower atmospheric CO2, different seasonality. This study shows temperature generally cooler than present one in southern China, but a significant warming was found over Mongolia, and a slightly higher in northeast China. Precipitation was generally higher than today in southern, northeast China, and northern Mongolia, but lower or similar to today in northwest China and north China. Enhanced EAM was then found in the southern half of China and in northeast China.

  10. Holocene linkages between char, soot, biomass burning and climate from Lake Daihai, China

    Science.gov (United States)

    Han, Y. M.; Marlon, J. R.; Cao, J. J.; Jin, Z. D.; An, Z. S.

    2012-12-01

    Black or elemental carbon (EC), including soot and char, are byproducts of anthropogenic fossil-fuel and biomass burning, and also of wildfires. EC, and particularly soot, strongly affects atmospheric chemistry and physics and thus radiative forcing; it can also alter regional climate and precipitation. Pre-industrial variations in EC as well as its source areas and controls however, are poorly known. Here we use a lake-sediment EC record from China to reconstruct Holocene variations in soot (combustion emissions formed via gas-to-particle conversion processes) and char (combustion residues from pyrolysis) measured with a thermal/optical method. Comparisons with sedimentary charcoal records (i.e., particles measured microscopically), climate and population data are used to infer variations in biomass burning and its controls. During the Holocene, positive correlations are observed between EC and an independent index of regional biomass burning. Negative correlations are observed between EC and monsoon intensity, and tree cover inferred from arboreal pollen percentages. Abrupt declines in temperature are also linked with widespread declines in fire. Our results 1) confirm the robustness of a relatively new method for reconstructing variations in EC; 2) document variations in regional biomass burning; 3) support a strong climatic control of biomass burning throughout the Holocene; and 4) indicate that char levels are higher today than at any time during the Holocene.

  11. Use of Satellite SAR for Understanding Long-Term Human Occupation Dynamics in the Monsoonal Semi-Arid Plains of North Gujarat, India

    Directory of Open Access Journals (Sweden)

    Francesc C. Conesa

    2014-11-01

    Full Text Available This work explores the spatial distribution of monsoonal flooded areas using ENVISAT C-band Advanced Synthetic Aperture Radar (ASAR in the semi-arid region of N. Gujarat, India. The amplitude component of SAR Single Look Complex (SLC images has been used to estimate the extent of surface and near-surface water dynamics using the mean amplitude (MA of monsoonal (July to September and post-monsoonal (October to January seasons. The integration of SAR-derived maps (seasonal flooding maps and seasonal MA change with archaeological data has provided new insights to understand present-day landscape dynamics affecting archaeological preservation and visibility. Furthermore, preliminary results suggest a good correlation between Mid-Holocene settlement patterns and the distribution and extension of seasonal floodable areas within river basin areas, opening interesting inroads to study settlement distribution and resource availability in past socio-ecological systems in semi-arid areas.

  12. TIGERZ I: Aerosols, Monsoon and Synergism

    Science.gov (United States)

    Holben, B. N.; Tripathi, S. N.; Schafer, J. S.; Giles, D. M.; Eck, T. F.; Sinyuk, A.; Smirnov, A.; Krishnmoorthy, K.; Sorokin, M. G.; Newcomb, W. W.; Tran, A. K.; Sikka, D. R.; Goloub, P.; O'Neill, N. T.; Abboud, I.; Randles, C.; Niranjan, K.; Dumka, U. C.; Tiwari, S.; Devara, P. C.; Kumar, S.; Remer, L. A.; Kleidman, R.; Martins, J. V.; Kahn, R.

    2008-12-01

    The Indo-Gangetic Plain of northern India encompasses a vast complex of urban and rural landscapes, cultures that serve as anthropogenic sources of fine mode aerosols mixed with coarse mode particles transported from SW Asia. The summer monsoon and fall Himalayan snowmelt provide the agricultural productivity to sustain an extremely high population density whose affluence is increasing. Variations in the annual monsoon precipitation of 10% define drought, normal and a wet season; the net effects on the ecosystems and quality of life can be dramatic. Clearly investigation of anthropogenic and natural aerosol impacts on the monsoon, either through the onset, monsoon breaks or end points are a great concern to understand and ultimately mitigate. Many national and international field campaigns are being planned and conducted to study various aspects of the Asian monsoon and some coordinated under the Asian Monsoon Years (AMY) umbrella. A small program called TIGERZ conducted during the pre-monsoon of 2008 in North Central India can serve as a model for contributing significant resources to existing field programs while meeting immediate project goals. This poster will discuss preliminary results of the TIGERZ effort including ground-based measurements of aerosol properties in the I-G from AERONET and synergism with various Indian programs, satellite observations and aerosol modeling efforts.

  13. The East Asian subtropical summer monsoon: Recent progress

    Science.gov (United States)

    He, Jinhai; Liu, Boqi

    2016-04-01

    The East Asian subtropical summer monsoon (EASSM) is one component of the East Asian summer monsoon system, and its evolution determines the weather and climate over East China. In the present paper, we firstly demonstrate the formation and advancement of the EASSM rainbelt and its associated circulation and precipitation patterns through reviewing recent studies and our own analysis based on JRA-55 (Japanese 55-yr Reanalysis) data and CMAP (CPC Merged Analysis of Precipitation), GPCP (Global Precipitation Climatology Project), and TRMM (Tropical Rainfall Measuring Mission) precipitation data. The results show that the rainy season of the EASSM starts over the region to the south of the Yangtze River in early April, with the establishment of strong southerly wind in situ. The EASSM rainfall, which is composed of dominant convective and minor stratiform precipitation, is always accompanied by a frontal system and separated from the tropical summer monsoon system. It moves northward following the onset of the South China Sea summer monsoon. Moreover, the role of the land-sea thermal contrast in the formation and maintenance of the EASSM is illustrated, including in particular the effect of the seasonal transition of the zonal land-sea thermal contrast and the influences from the Tibetan Plateau and midlatitudes. In addition, we reveal a possible reason for the subtropical climate difference between East Asia and East America. Finally, the multi-scale variability of the EASSM and its influential factors are summarized to uncover possible reasons for the intraseasonal, interannual, and interdecadal variability of the EASSM and their importance in climate prediction.

  14. Holocene Sea-Level Database For The Caribbean Region

    Science.gov (United States)

    Khan, N. S.; Horton, B.; Engelhart, S. E.; Peltier, W. R.; Scatena, F. N.; Vane, C. H.; Liu, S.

    2013-12-01

    located furthest away from the former Laurentide Ice Sheet. Rates of RSL change were highest during the early Holocene and have decreased over time due primarily to the reduction of ice equivalent meltwater input. Sea-level observations are compared to predictions from glacio-isostatic adjustment (GIA) models, and the relative influence of tectonic vertical land movements on the RSL records in each region is assessed. Background rates of late Holocene RSL change are also compared to local tide gauge records to determine excess rates of 20th century RSL rise.

  15. A Late Glacial Environmental Reconstruction performed on Lacustrine Sediments from the Southern Tibetan Plateau identifies regional Monsoon Variations

    Science.gov (United States)

    Henkel, K.; Ahlborn, M.; Haberzettl, T.; Alivernini, M.; Kasper, T.; Thiele, A.; St-Onge, G.; Daut, G.; Frenzel, P.; Gleixner, G.; Wang, J.; Zhu, L.; Maeusbacher, R.

    2014-12-01

    the Early Holocene, a high lake level with a low salinity and low terrestrial input is observed. At 5,000 cal BP, the carbonate phase changes from calcite to aragonite, representing a higher evaporation rate and a falling lake level and a higher influence of terrestrial biomarkers.

  16. Can an Earth System Model simulate better climate change at mid-Holocene than an AOGCM? A comparison study of MIROC-ESM and MIROC3

    Directory of Open Access Journals (Sweden)

    R. Ohgaito

    2013-07-01

    Full Text Available The importance of evaluating models through paleoclimate simulations is becoming more recognized in efforts to improve climate projection. To evaluate an integrated Earth System Model, MIROC-ESM, we performed simulations in time-slice experiments for the mid-Holocene (6000 yr before present, 6 ka and preindustrial (1850 AD, 0 ka periods under the protocol of the Coupled Model Intercomparison Project 5/Paleoclimate Modelling Intercomparison Project 3. We first give an overview of the simulated global climates by comparing with simulations using a previous version of the MIROC model (MIROC3, which is an atmosphere–ocean coupled general circulation model. We then comprehensively discuss various aspects of climate change with 6 ka forcing and how the differences in the models can affect the results. We also discuss the representation of the precipitation enhancement at 6 ka over northern Africa. The precipitation enhancement at 6 ka over northern Africa according to MIROC-ESM does not differ greatly from that obtained with MIROC3, which means that newly developed components such as dynamic vegetation and improvements in the atmospheric processes do not have significant impacts on the representation of the 6 ka monsoon change suggested by proxy records. Although there is no drastic difference between the African monsoon representations of the two models, there are small but significant differences in the precipitation enhancement over the Sahara in early summer, which can be related to the representation of the sea surface temperature rather than the vegetation coupling in MIROC-ESM. Because the oceanic parts of the two models are identical, the difference in the sea surface temperature change is ultimately attributed to the difference in the atmospheric and/or land modules, and possibly the difference in the representation of low-level clouds.

  17. Latest Pleistocene and Holocene glaciation of Baffin Island, Arctic Canada: key patterns and chronologies

    Science.gov (United States)

    Briner, Jason P.; Davis, P. Thompson; Miller, Gifford H.

    2009-10-01

    Melting glaciers and ice caps on Baffin Island contribute roughly half of the sea-level rise from all ice in Arctic Canada, although they comprise only one-fourth of the total ice in the region. The uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change. We review the key patterns and chronologies of latest Pleistocene and Holocene glaciation on Baffin Island. The deglaciation by the Laurentide Ice Sheet occurred generally slowly and steadily throughout the Holocene to its present margin (Barnes Ice Cap) except for two periods of rapid retreat: An early interval ˜12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds, and a later interval ˜7 ka when ice over Foxe Basin collapsed. In coastal settings, alpine glaciers were smaller during the Younger Dryas period than during the Little Ice Age. At least some alpine glaciers apparently survived the early Holocene thermal maximum, which was several degrees warmer than today, although data on glacier extent during the early Holocene is extremely sparse. Following the early Holocene thermal maximum, glaciers advanced during Neoglaciation, beginning in some places as early as ˜6 ka, although most sites do not record near-Little Ice Age positions until ˜3.5 to 2.5 ka. Alpine glaciers reached their largest Holocene extents during the Little Ice Age, when temperatures were ˜1-1.5 °C cooler than during the late 20th century. Synchronous advances across Baffin Island throughout Neoglaciation indicate sub-Milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability. Future work should further elucidate the state of glaciers and ice caps during the early Holocene thermal maximum and glacier response to climate forcing mechanisms.

  18. Moisture Changes in the Mid-Holocene: Do PMIP3 Simulations Reflect the Proxy Record for the Western United States?

    Science.gov (United States)

    Hermann, N. W.; Oster, J. L.; Ibarra, D. E.

    2015-12-01

    Paleoclimate proxy-model comparisons for past warm periods provide insight into the driving mechanisms of persistent drought, especially pertinent information given the ongoing drought in the western US. A network of 110 hydrologically sensitive proxy records from lake sediments, speleothems, and packrat middens shows increased aridity in the western and northwestern U.S. and increased moisture in the southwest monsoon region during the mid-Holocene, a time of higher summer and lower winter insolation than present. We compare this proxy network to output from 12 climate models from the Paleoclimate Modeling Intercomparison Project Phase III (PMIP3) at the 6ka time slice to determine which models best reflect paleo-precipitation patterns, and therefore, the atmospheric drivers of precipitation change. We carry out a quantitative proxy-model comparison for precipitation (P) and effective moisture (EM = P - evapotranspiration) at 6ka relative to preindustrial simulations. Using a weighted Cohen's Kappa test, we evaluate model agreement at different thresholds of change for annual and seasonal anomalies. Overall, simulated P anomalies show better agreement with the proxy network than EM anomalies. The FGOALS-g2 (FG) model shows the best agreement with the proxy network for annual P anomalies, with increased annual P in the monsoonal southwestern US and northern Mexico, and decreased annual P in northern California, the northern Great Basin, and the Pacific Northwest at 6 ka relative to modern. FG simulates decreased winter P across the entire western US, increased autumn P in the monsoon region and decreased autumn P in the non-monsoon region. While other models simulate increased P from July-September in the monsoon region and more arid conditions at non-monsoon sites, they often do not simulate increased aridity in non-monsoon regions during other seasons. These differences may be due to a less defined autumn Aleutian Low in FG compared with most other models.

  19. Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada

    Science.gov (United States)

    Benson, L.; Kashgarian, Michaele; Rye, R.; Lund, S.; Paillet, F.; Smoot, J.; Kester, C.; Mensing, S.; Meko, D.; Lindstrom, S.

    2002-01-01

    Continuous, high-resolution ??18O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (cal yr). The records are not stationary; during the past 2740 yr, drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200 yr from the Sierra Nevada and the El alpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820 cal yr BP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650 cal yr BP may have impacted much of the western United States.During the middle Holocene (informally defined in this paper as extending from 8000 to 3000 cal yr BP), magnetic susceptibility values of sediments deposited in Pyramid Lake's deep basin were much larger than late-Holocene (3000-0 cal yr BP) values, indicating the presence of a shallow lake. In addition, the mean ?? 18O value of CaCO3 precipitated between 6500 and 3430 cal yr BP was 1.6??? less than the mean value of CaCO3 precipitated after 2740 cal yr BP. Numerical calculations indicate that the shift in the ??18O baseline probably resulted from a transition to a wetter (> 30%) and cooler (3-5??C) climate. The existence of a relatively dry and warm middle-Holocene climate in the Truckee River - Pyramid Lake system is generally consistent with archeological, sedimentological, chemical, physical, and biological records from various sites within the Great Basin of the western United States. Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC and ??18O records from Owens Lake indicate that the first interval in the early Holocene

  20. Mid-Holocene regional reorganization of climate variability

    Directory of Open Access Journals (Sweden)

    K. W. Wirtz

    2009-01-01

    Full Text Available We integrate 130 globally distributed proxy time series to refine the understanding of climate variability during the Holocene. Cyclic anomalies and temporal trends in periodicity from the Lower to the Upper Holocene are extracted by combining Lomb-Scargle Fourier-transformed spectra with bootstrapping. Results were cross-checked by counting events in the time series. Main outcomes are: First, the propensity of the climate system to fluctuations is a region specific property. Many records of adjacent sites reveal a similar change in variability although they belong to different proxy types (e.g., δ18O, lithic composition. Secondly, at most sites, irreversible change occured in the Mid-Holocene. We suggest that altered ocean circulation together with slightly modified coupling intensity between regional climate subsystems around the 5.5 kyr BP event (termination of the African Humid Period were responsible for the shift. Fluctuations especially intensified along a pan-American corridor. This may have led to an unequal crisis probability for early human civilizations in the Old and New World. Our study did not produce evidence for millennial scale cyclicity in some solar activity proxies for the Upper Holocene, nor for a privileged role of the prominent 250, 550, 900 and 1450 yr cycles. This lack of global periodicities corroborates the regional character of climate variability.

  1. Pleistocene and Holocene geomorphological development in the Algarve, southern Portugal

    Science.gov (United States)

    Chester, David K.

    2012-06-01

    A detailed chronological framework for Pleistocene and Holocene geomorphology and landscape evolution in the Algarve is proposed. With regards to the Pleistocene, attention has focused on the origin, dating and stratigraphy of the Ludo Formation. Subsuming the classifications of earlier writers, it is now proposed that during the Pliocene a marine transgression occurred across a tectonically controlled basin that was constrained by the mountains of the Algarve interior to the north. Fluvial sands were then deposited in a regressive phase during the late Pliocene/early Pleistocene, while braided streams operating under semi-arid conditions subsequently laid down sands and gravels in the middle and upper Pleistocene. Lying unconformably over the Ludo Formation is an alluvial deposit (Odiáxere gravels and Loulé sands) of late Pleistocene/early Holocene date that is found within the river valleys of the Algarve. In the early-Holocene (ca.10, 000-ca.7000 BP) and early late-Holocene (ca.5000-ca.3000 BP), the situation in the Algarve was one of climatic amelioration (i.e., warmer and wetter conditions), rising sea levels, vegetation colonization, soil development and towards the end of this period trenching of the Odiáxere gravels and Loulé sands. From ca.3000 BP evidence is abundant that humans became important geomorphological agents either acting on their own or in combination with climatic factors. From around 5000 BP, conditions became dryer and, between ca.3000 BP and ca.700 BP, clearance of land by pre-Roman, Roman, and especially Islamic agricultural settlers caused widespread erosion and the deposition of extensive spreads of topsoil dominated sediment within river valleys (i.e., the Holocene terrace) and in coastal estuaries. A period followed up to 1900 CE when agricultural practices were less damaging to the soil, erosion was reduced and the Holocene terrace - together with coastal and estuarine deposits - was incised. In the past century and under

  2. A hemispheric climatology of monsoon depressions

    Science.gov (United States)

    Hurley, J. V.; Boos, W.

    2012-12-01

    Monsoon depressions are large (1000-2000 km diameter) cyclonic low pressure systems having organized deep convection, best known for forming in the Bay of Bengal and migrating northwest over northern India in the monsoon trough. About 3 to 5 of these systems occur during each monsoon season, contributing about half of the Indian summer rainfall. Despite their importance as a precipitation source, their dynamics are poorly constrained. Furthermore, although they do occur elsewhere, such as around Australia and in the southern Indian Ocean, there does not exist a collective inventory of these systems outside of the Bay of Bengal region. Here we present a climatology of monsoon depressions produced from the ERA-Interim Reanalysis. Feature tracks are identified using an automated tracking algorithm (K. Hodges' TRACK code) applied to the 850 hPa relative vorticity field for local summer, 1989 to 2003. Using criteria based on relative vorticity and sea level pressure, cyclonic low pressure systems are separated into different intensity categories, one of which corresponds to the definition for monsoon depressions used by the India Meteorological Department. The resultant distribution of storms obtained for the Bay of Bengal region compares well with a previously compiled climatology of monsoon depressions that was limited to the region surrounding India. Having validated our ability to identify monsoon depressions in their classic genesis region near India, we then extend the methods to include the western Pacific, Australia, and the southern Indian Ocean. Track distributions and composite structures of monsoon depressions for these different regions will be presented.

  3. Evidence of climatic change during Holocene in the nearshore regions of Konkan (central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Gujar, A.R.; Guptha, M.V.S.

    and micropaleontological aspects. The results have shown that during Early Holocene (Younger Dryas), arid climates prevailed which may be correlatable with global aridity. This has been inferred from feldspar/quartz ratio, occurrence of gypsum crystals, iron stained quartz...

  4. Human Activity Influenced by Climate Change: Response of Spatial Distribution of Ancient Rice Cultivation in China to Climate Change during the Early to Mid-Holocene%气候条件限制下的人类活动——全新世早中期中国栽培水稻分布的变化对气候变迁的响应

    Institute of Scientific and Technical Information of China (English)

    张玲; 梅孙华; 王培敏

    2013-01-01

    Rice cultivation is one of the important human activities in the Neolithic period, and the link between its development and climate change is essential for studies on rice domestication and civilization. Data of archaeological sites with excavated rice remains in China during the early to mid-Holocene (12 000 -5 500 aBP) were compiled, and the link between rice cultivation and climate change was analyzed. The results showed that the origination and early development of rice cultivation were mainly distributed on the edge of regions where wild rice distributed. The early development of rice cultivation during the early to mid-Holocene was also mainly influenced by climate change.%水稻栽培是新石器时代重要的人类活动之一,其发展同气候之间的联系是研究稻作起源和文明发展的一个关键问题.该文利用搜集到的全新世早中期(12 000~5 500 aBP)中国的栽培水稻出土遗址点数据,对全新世早中期中国水稻栽培同气候的关系进行了分析.结果表明,栽培水稻的起源与初期发展具有“边缘效应”,即分布于野生稻分布的边缘地带;而其早期的发展和分布也具有类似的特征,即主要受气候因素的影响,因此全新世早中期栽培水稻的分布范围的变化受到气候条件的限制,该时期环境变化受气候“主导”.

  5. Generation of near-inertial oscillations by summer monsoon onset over the South China Sea in 1998 and 1999

    Science.gov (United States)

    Shu, Yeqiang; Pan, Jiayi; Wang, Dongxiao; Chen, Gengxin; Sun, Lu; Yao, Jinglong

    2016-12-01

    The summer monsoon onset over the South China Sea (SCS) is an abrupt event in May or early June every year. After the summer monsoon onset in 1998 and 1999, strong near-inertial oscillations (NIOs) in the central SCS were observed with Acoustic Doppler Current Profilers (ADCP) mooring data. The near-inertial current speed reached 0.25 ms-1, comparable to that induced by tropical storms (TS) in the same area, although the wind speed ( 10 ms-1) of the monsoon onset was much lower than what is typical of TSs. Further analyses suggest that the shallow mixed-layer (speed and direction resulting from the summer monsoon onset were responsible for developing the near-inertial current. The generated NIOs could be enhanced by a warm eddy appearing during the monsoon onset in the central SCS. The strong NIOs appeared in the middle of the SCS in May when the SCS summer monsoon starts to prevail, which implies that the beginning of the SCS summer monsoon may be a vital factor for generation of the strong NIOs in May.

  6. Millennial-centennial Scales Climate Changes of Holocene Indicated by Magnetic Susceptibility of High-resolution Section in Salawusu River Valley China

    Institute of Scientific and Technical Information of China (English)

    LU Yingxia; LI Baosheng; WEN Xiaohao; QIU Shifan; WANG Fengnian; NIU Dongfeng; LI Zhiwen

    2010-01-01

    The upmost segment(Holocene series)of the Milanggouwan stratigraphic section(MGS1)in the Salawusu River valley shows 11 sedimentary cycles of dune sands and fluvio-lacustrine facies,or dune sands and paleosols.The analysis of the magnetic susceptibility of this segment suggests that there are 11 magnetic susceptibility cycles with the value alternating from low to high,in which the layers of the dune sands correspond to the lower value of the magnetic susceptibility and the layers of fluvio-lacustrine facies and paleosols correspond to the higher peaks.The study reveals that the low and high magnetic susceptibility values indicate the climate dominated by cold-arid winter monsoon and warm-humid summer monsoon of East Asia,respectively,and the study area has experienced at least 22 times of mil-lennial-centennial scales climate alternation from the cold-arid to the warm-humid during the Holocene.In terms of the time and the climate nature,the variations basically correspond to those of the North Atlantic and some records of cold-warm changes in China as well.They might be caused by the alternation of winter and summer monsoons in the Mu Us Desert induced by global climate fluctuations in the Holocene.

  7. Late Pleistocene/Holocene wetland events recorded in southeast Tengger Desert lake sediments, NW China

    Institute of Scientific and Technical Information of China (English)

    D. B. Madsen; CHEN Fahu; Ch. G. Oviatt; ZHU Yan; P. J. Brantingham; R. G. Elston; R. L. Bettinger

    2003-01-01

    The area along the eastern and southeastern margins of the Tengger Desert, NW China, which is sensitive to the summer monsoon variations, was selectedfor studying the environmental conditions surrounding the transition between Paleolithic foragers and Neolithic farmer/pastoral- ists. Short cores were obtained from four lake basins in the southwestern Tengger using a hand-driven piston coring device. Proxies from these cores were supplemented by ra- diocarbon ages obtained from lake sediment cores, shoreline features and spring mound deposits. Together these records provide evidence of millennial-scale climate change events from the Pleistocene-Holocene transition to the present. Lake/wetland events, representing periods of more intensive summer monsoon, occur in the records at ~12.7-11.6, ~10.1, ~9.3, ~8.0, ~5.4, ~1.5, and ~0.8 ka BP. They do suggest that century- to millennial-scale climatic cycles are characteristic of the Holocene in the southeastern Tengger Desert although the chronology must be considered extremely tentative.

  8. Holocene vegetation and climate history of the northern Bighorn Basin, southern Montana

    Science.gov (United States)

    Lyford, M.E.; Betancourt, J.L.; Jackson, S.T.

    2002-01-01

    Records of Holocene vegetation and climate change at low elevations (climate change from 55 14C-dated woodrat middens at two low-elevation sites (1275 to 1590 m, currently vegetated by Juniperus osteosperma woodlands, in the northern Bighorn Basin. Macrofossil and pollen analyses show that the early Holocene was cooler than today, with warming and drying in the middle Holocene. During the Holocene, boreal (Juniperus communis, J. horizontalis) and montane species (J. scopulorum) were replaced by a Great Basin species (J. osteosperma). J. osteosperma colonized the east side of the Pryor Mountains 4700 14C yr B.P. Downward movement of lower treeline indicates wetter conditions between 4400 and 2700 14C yr B.P. Increased aridity after 2700 14C yr B.P. initiated expansion of J. osteosperma from the east to west side of the Pryor Mountains. ?? 2002 University of Washington.

  9. Holocene warming in western continental Eurasia driven by glacial retreat and greenhouse forcing

    Science.gov (United States)

    Baker, Jonathan L.; Lachniet, Matthew S.; Chervyatsova, Olga; Asmerom, Yemane; Polyak, Victor J.

    2017-06-01

    The global temperature evolution during the Holocene is poorly known. Whereas proxy data suggest that warm conditions prevailed in the Early to mid-Holocene with subsequent cooling, model reconstructions show long-term warming associated with ice-sheet retreat and rising greenhouse gas concentrations. One reason for this contradiction could be the under-representation of indicators for winter climate in current global proxy reconstructions. Here we present records of carbon and oxygen isotopes from two U-Th-dated stalagmites from Kinderlinskaya Cave in the southern Ural Mountains that document warming during the winter season from 11,700 years ago to the present. Our data are in line with the global Holocene temperature evolution reconstructed from transient model simulations. We interpret Eurasian winter warming during the Holocene as a response to the retreat of Northern Hemisphere ice sheets until about 7,000 years ago, and to rising atmospheric greenhouse gas concentrations and winter insolation thereafter. We attribute negative δ18O anomalies 11,000 and 8,200 years ago to enhanced meltwater forcing of North Atlantic Ocean circulation, and a rapid decline of δ13C during the Early Holocene with stabilization after about 10,000 years ago to afforestation at our study site. We conclude that winter climate dynamics dominated Holocene temperature evolution in the continental interior of Eurasia, in contrast to regions more proximal to the ocean.

  10. Holocene paleoenvironmental change in southeastern Africa (Makwe Rockshelter, Zambia): Implications for the spread of pastoralism

    Science.gov (United States)

    Robinson, Joshua R.; Rowan, John

    2017-01-01

    The paleoenvironmental conditions surrounding the origins of pastoralism and the movement of herders from eastern to southern Africa sometime between ∼4000 and 2000 ybp have been much debated. We lack, however, detailed paleoenvironmental data from sites sampling the hunter-to-herder transition in southeastern Africa, the likely corridor from eastern to southern Africa for early pastoralists. Here we report on new paleoenvironmental data from a site in the under-sampled area of eastern Zambia, Makwe Rockshelter, which has two aggregates of archaeological horizons representing the mid-Holocene (∼5700-5000 ybp) and the late Holocene (∼1600-800 ybp). The mid-Holocene sediments at Makwe document a foraging society, whereas the late Holocene sediments include both wild game and domestic livestock. Using stable carbon isotopes (δ13C) of herbivore enamel (n = 107), we show that the shift from mid-Holocene to late Holocene paleoenvironments was characterized by an increase in C4 vegetation. These data are complemented by paleoenvironmental records from Lake Malawi that show that C4 vegetation peaked after ∼2000 ybp and was coincident with the onset of cooler, more arid climates. This combined paleoenvironmental record has implications for the spread of pastoralism across southeastern Africa between ∼3000 and 2000 ybp and potential 'animal disease barriers' these early herders may have faced.

  11. Holocene peatland shifts in vegetation, carbon, and climate at Imnavait, Alaska

    Science.gov (United States)

    Peteet, D. M.; Nichols, J. E.; Ouni, S.; Pavia, F.; Pearl, Y.

    2012-12-01

    The Imnavait Creek basin (68 40'N, 149 20'W; elevation 875-945 m) in the foothills of the Brooks Range, AK has been well studied in terms of modern vegetational communities, hydrology, and soils. But paleoclimate and paleovegetation reconstructions are limited. We retrieved a 2-m peatland core to examine the macrofossil/biomarker/carbon sequestration history throughout the Holocene and late-glacial. AMS 14C dates of the macrofossil remains will allow us to calculate carbon sequestration rates. The Holocene history (the top meter) records marked shifts in vascular plant as well as bryophyte history. A tri-partite sequence is apparent, with Andromeda/Sphagnum remains abundant in the early Holocene. The absence of bryophytes and the presence of Eriophorum and Carex achenes characterize the mid-Holocene. Andromeda and Betula nana with Sphagnum remains are abundant in the upper 30 cm of the core. Hydrogen isotope ratios of leaf wax alkanes record higher effective moisture in the early and late Holocene, suggesting more evaporative loss in the mid-Holocene which is characterized by Eriophorum. We compare our results with previously observed palynological shifts from lakes in the region and place this Arctic paleorecord in a larger perspective of peatland histories in a N-S transect covering nearly 10 degrees of latitude across Alaska. This tripartite pattern of effective moisture appears to be the same throughout the Alaskan transect, suggesting strong climatic control.

  12. Holocene paleoclimate inferred from salinity histories of adjacent lakes in southwestern Sicily (Italy)

    Science.gov (United States)

    Curry, Brandon; Henne, Paul D.; Mesquita-Joanes, Francesc; Marrone, Federico; Pieri, Valentina; La Mantia, Tommaso; Calò, Camilla; Tinner, Willy

    2016-10-01

    Marked uncertainties persist regarding the climatic evolution of the Mediterranean region during the Holocene. For instance, whether moisture availability gradually decreased, remained relatively constant, or increased during the last 7000 years remains a matter of debate. To assess Holocene limnology, hydrology and moisture dynamics, the coastal lakes Lago Preola and Gorgo Basso, located in southwestern Sicily, were investigated through several stratigraphic analyses of ostracodes, including multivariate analyses of assemblages, transfer functions of salinity, and biochemical analyses of valves (Sr/Ca, δ18O and δ13C). During the early Holocene, the Gorgo Basso and Lago Preola ostracode records are similar. After an initial period of moderate salinity (1690-6100 mg/l from ca. 10,000-8190 cal yr BP), syndepositional or diagenetic dissolution of ostracode valves suggests that salinity declined to lake at about 6250 cal yr BP was related to sea level rise and resulting intrusion of seawater-influenced groundwater. In contrast, Gorgo Basso remained a freshwater lake. The salinity of Gorgo Basso declined somewhat after 6250 cal yr BP, in comparison to the early Holocene, ranging from about 550 to 1680 mg/L. Cypria ophtalmica, a species capable of rapid swimming and flourishing in waters with low dissolved oxygen levels, became dominant at approximately the time when Greek civilization took root in Sicily (2600 cal yr BP), and it completely dominates the record during Roman occupation (roughly 2100 to 1700 cal yr BP). These freshwater conditions at Gorgo Basso suggest high effective moisture when evergreen olive-oak forests collapsed in response to increased Greco-Roman land use and fire. Ostracode valve geochemistry (Sr/Ca, δ18O) suggests significant changes in early vs. late Holocene hydrochemistry, either as changes in salinity or in the seasonality of precipitation. Harmonizing the autecological and geochemical data from Gorgo Basso suggests the latter was more

  13. Characteristics of monsoon low level jet (MLLJ) as an index of monsoon activity

    Indian Academy of Sciences (India)

    N V Sam; K P R Vittal Murty

    2002-12-01

    Temperature and wind data are used to describe variation in the strength of the Monsoon Low Level Jet (MLLJ) from an active phase of the monsoon to a break phase. Also estimated are the characteristics of turbulence above and below MLLJ.

  14. Aerosol and monsoon climate interactions over Asia: AEROSOL AND MONSOON CLIMATE INTERACTIONS

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhanqing [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Lau, W. K. -M. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Ramanathan, V. [Department of Atmospheric and Climate Sciences, University of California, San Diego California USA; Wu, G. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Ding, Y. [National Climate Center, China Meteorological Administration, Beijing China; Manoj, M. G. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Liu, J. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Qian, Y. [Pacific Northwest National Laboratory, Richland Washington USA; Li, J. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Zhou, T. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Fan, J. [Pacific Northwest National Laboratory, Richland Washington USA; Rosenfeld, D. [Institute of Earth Sciences, Hebrew University, Jerusalem Israel; Ming, Y. [Geophysical Fluid Dynamic Laboratory, NOAA, Princeton New Jersey USA; Wang, Y. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena California USA; Huang, J. [College of Atmospheric Sciences, Lanzhou University, Lanzhou China; Wang, B. [Department of Atmospheric Sciences, University of Hawaii, Honolulu Hawaii USA; School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing China; Xu, X. [Chinese Academy of Meteorological Sciences, Beijing China; Lee, S. -S. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Cribb, M. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Zhang, F. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Yang, X. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Zhao, C. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Takemura, T. [Research Institute for Applied Mechanics, Kyushu University, Fukuoka Japan; Wang, K. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Xia, X. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Yin, Y. [School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing China; Zhang, H. [National Climate Center, China Meteorological Administration, Beijing China; Guo, J. [Chinese Academy of Meteorological Sciences, Beijing China; Zhai, P. M. [Chinese Academy of Meteorological Sciences, Beijing China; Sugimoto, N. [National Institute for Environmental Studies, Tsukuba Japan; Babu, S. S. [Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram India; Brasseur, G. P. [Max Planck Institute for Meteorology, Hamburg Germany

    2016-11-15

    Asian monsoons and aerosols have been studied extensively which are intertwined in influencing the climate of Asia. This paper provides a comprehensive review of ample studies on Asian aerosol, monsoon and their interactions. The region is the primary source of aerosol emissions of varies species, influenced by distinct weather and climatic regimes. On continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulation. The atmospheric thermodynamic state may also be altered by the aerosol serving as cloud condensation nuclei or ice nuclei. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of numerous monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from biomass burning, and biogenic aerosols from vegetation are considered integral components of an intrinsic aerosol-monsoon climate system, subject to external forcings of global warming, anthropogenic aerosols, and land use and change. Future research on aerosol-monsoon interactions calls for an integrated approach and international collaborations based on long-term sustained observations, process measurements, and improved models, as well as using observations to constrain model simulations and projections.

  15. Drivers of Holocene sea-level change in the Caribbean

    Science.gov (United States)

    Khan, Nicole S.; Ashe, Erica; Horton, Benjamin P.; Dutton, Andrea; Kopp, Robert E.; Brocard, Gilles; Engelhart, Simon E.; Hill, David F.; Peltier, W. R.; Vane, Christopher H.; Scatena, Fred N.

    2017-01-01

    We present a Holocene relative sea-level (RSL) database for the Caribbean region (5°N to 25°N and 55°W to 90°W) that consists of 499 sea-level index points and 238 limiting dates. The database was compiled from multiple sea-level indicators (mangrove peat, microbial mats, beach rock and acroporid and massive corals). We subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on RSL. We account for the local-scale processes of sediment compaction and tidal range change using the stratigraphic position (overburden thickness) of index points and paleotidal modeling, respectively. We use a spatio-temporal empirical hierarchical model to estimate RSL position and its rates of change in the Caribbean over 1-ka time slices. Because of meltwater input, the rates of RSL change were highest during the early Holocene, with a maximum of 10.9 ± 0.6 m/ka in Suriname and Guyana and minimum of 7.4 ± 0.7 m/ka in south Florida from 12 to 8 ka. Following complete deglaciation of the Laurentide Ice Sheet (LIS) by ∼7 ka, mid-to late-Holocene rates slowed to model constrains the spatial extent of the mid-Holocene highstand. RSL did not exceed the present height during the Holocene, except on the northern coast of South America, where in Suriname and Guyana, RSL attained a height higher than present by 6.6 ka (82% probability). The highstand reached a maximum elevation of +1.0 ± 1.1 m between 5.3 and 5.2 ka. Regions with a highstand were located furthest away from the former LIS, where the effects from ocean syphoning and hydro-isostasy outweigh the influence of subsidence from forebulge collapse.

  16. Timing and magnitude of the Caribbean mid-Holocene highstand

    Science.gov (United States)

    Ashe, E.; Khan, N.; Horton, B.; Brocard, G. Y.; Dutton, A.; Engelhart, S. E.; Kopp, R. E.; Hill, D. F.; Peltier, W. R.; Scatena, F. N.

    2015-12-01

    We present a database of published and new relative sea-level (RSL) data for the past 13 ka, which constrains the Holocene sea-level histories of the Caribbean coast of Central and South America (Florida Keys, USA to Guyana) and the Bahamas and Greater and Lesser Antilles islands. Our evaluation of mangrove peat and Acropora palmata sea-level indicators from geological investigations provides 503 sea-level index points and 242 limiting dates. We subdivide the database into 21 regions based on the availability of data, tectonic setting, and distance from the former Laurentide ice sheet. Most index points (75%) and limiting dates (90%) are mangrove peat and coral data. We use the stratigraphic position (overburden thickness) of index points account for sediment compaction, and use the paleotidal model of Hill et al. (2011) to account for Holocene changes in paleotidal range. A noisy-input Gaussian process regression model calculates that the rates of RSL change were highest during the early Holocene (3-8 mm/yr) and have decreased over time (Holocene. The sea-level reconstructions demonstrate that RSL did not exceed the present height (0 m) during the Holocene in the majority of locations, with the exception of a small highstand (<2 m) on the northern coast of South America along the Orinoco Delta and Suriname/Guyana located furthest away from the former Laurentide Ice Sheet. The different sea-level histories are an ongoing isostatic response to deglaciation of the Laurentide Ice Sheet and suggest subsidence resulting from collapse of the proglacial forebulge reaches further south than previously considered.

  17. The First Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons

    Energy Technology Data Exchange (ETDEWEB)

    Sperber, K R; Yasunari, T

    2005-07-27

    In 2004 the Joint Scientific Committee (JSC) that provides scientific guidance to the World Climate Research Programme (WCRP) requested an assessment of (1) WCRP monsoon related activities and (2) the range of available observations and analyses in monsoon regions. The purpose of the assessment was to (a) define the essential elements of a pan-WCRP monsoon modeling strategy, (b) identify the procedures for producing this strategy, and (c) promote improvements in monsoon observations and analyses with a view toward their adequacy, and addressing any undue redundancy or duplication. As such, the WCRP sponsored the ''1st Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons'' at the University of California, Irvine, CA, USA from 15-17 June 2005. Experts from the two WCRP programs directly relevant to monsoon studies, the Climate Variability and Predictability Programme (CLIVAR) and the Global Energy and Water Cycle Experiment (GEWEX), gathered to assess the current understanding of the fundamental physical processes governing monsoon variability and to highlight outstanding problems in simulating the monsoon that can be tackled through enhanced cooperation between CLIVAR and GEWEX. The agenda with links to the presentations can be found at: http://www.clivar.org/organization/aamon/WCRPmonsoonWS/agenda.htm. Scientific motivation for a joint CLIVAR-GEWEX approach to investigating monsoons includes the potential for improved medium-range to seasonal prediction through better simulation of intraseasonal (30-60 day) oscillations (ISO's). ISO's are important for the onset of monsoons, as well as the development of active and break periods of rainfall during the monsoon season. Foreknowledge of the active and break phases of the monsoon is important for crop selection, the determination of planting times and mitigation of potential flooding and short-term drought. With a few exceptions simulations of ISO are

  18. Applications of monsoon research: Opportunities to inform decisionmaking and reduce regional vulnerability

    Science.gov (United States)

    Ray, A. J.; Garfin, G. M.; Wilder, M.; Lenart, M.; Vásquez-León, M.; Comrie, A. C.

    2007-05-01

    This presentation will describe ongoing efforts to understand interactions between the North American Monsoon and society, in order to develop applications for monsoon research in a highly complex, multicultural and binational region. The North American Monsoon is an annual precipitation regime that begins in early June in Mexico and progresses northward to the southwestern United States. The region includes stakeholders in large urban complexes, productive agricultural areas, and sparsely populated arid and semi-arid ecosystems. The political, cultural, and socioeconomic divisions between the U.S. and Mexico create a broad range of sensitivities to climate variability as well as capacities to use forecasts and other information to cope with climate. We will highlight methodologies to link climate science with society and analyze opportunities for monsoon science to benefit society in four sectors: natural hazards management, agriculture, public health, and water management. We present a synthesized list of stakeholder needs and a calendar of decisions to help scientists link user needs to potential forecasts and products. To ensure usability of forecasts and other research products, we recommend iterative scientist-stakeholder interactions, through integrated assessments. These knowledge- exchange interactions can improve the capacity for stakeholders to use forecasts thoughtfully and inform the development of research, and for the research community to obtain feedback on climate-related products and receive insights to guide research direction. We expect that integrated assessments can capitalize on the opportunities for monsoon science to inform decisionmaking, in the best instances, reduce regional climate vulnerabilities and enhance regional sustainability

  19. Instability of seawater pH in the South China Sea during the mid-late Holocene: Evidence from boron isotopic composition of corals

    Science.gov (United States)

    Liu, Yajing; Liu, W.; Peng, Z.; Xiao, Y.; Wei, G.; Sun, W.; He, J.; Liu, Gaisheng; Chou, C.-L.

    2009-01-01

    We used positive thermal ionization mass spectrometry (PTIMS) to generate high precision ??11B records in Porites corals of the mid-late Holocene from the South China Sea (SCS). The ??11B values of the Holocene corals vary significantly, ranging from 22.2??? to 25.5???. The paleo-pH records of the SCS, reconstructed from the ??11B data, were not stable as previously thought but show a gradual increase from the Holocene thermal optimal and a sharp decrease to modern values. The latter is likely caused by the large amount of anthropogenic CO2 emissions since the Industrial Revolution but variations of atmospheric pCO2 cannot explain the pH change of the SCS before the Industrial Revolution. We suggest that variations of monsoon intensity during the mid-late Holocene may have driven the sea surface pH increase from the mid to late Holocene. Results of this study indicate that the impact of anthropogenic atmospheric CO2 emissions may have reversed the natural pH trend in the SCS since the mid-Holocene. Such ocean pH records in the current interglacial period can help us better understand the physical and biological controls on ocean pH and possibly predict the long-term impact of climate change on future ocean acidification. ?? 2008 Elsevier Ltd. All rights reserved.

  20. The Joint Aerosol-Monsoon Experiment: A New Challenge to Monsoon Climate Research

    Science.gov (United States)

    Lau, William K. M.

    2008-01-01

    Aerosol and monsoon related droughts and floods are two of the most serious environmental hazards confronting more than 60% of the population of the world living in the Asian monsoon countries. In recent years, thanks to improved satellite and in-situ observations, and better models, great strides have been made in aerosol, and monsoon research respectively. There is now a growing body of evidence suggesting that interaction of aerosol forcing with water cycle dynamics in monsoon regions may substantially alter the redistribution of energy at the earth surface and in the atmosphere, and therefore significantly impact monsoon rainfall variability and long term trends. In this talk, I will describe issues related to societal needs, scientific background, and challenges in studies of aerosol-water cycle interaction in Asian monsoon regions. As a first step towards addressing these issues, the authors call for an integrated observation and modeling research approach aimed at the interactions between aerosol chemistry and radiative effects and monsoon dynamics of the coupled ocean-atmosphere-land system. A Joint Aerosol-Monsoon Experiment (JAMEX) is proposed for 2007-2011, with an enhanced observation period during 2008-09, encompassing diverse arrays of observations from surface, aircraft, unmanned aerial vehicles, and satellites of physical and chemical properties of aerosols, long range aerosol transport as well as meteorological and oceanographic parameters in the Indo-Pacific Asian monsoon region. JAMEX will leverage on coordination among many ongoing and planned national programs on aerosols and monsoon research in China, India, Japan, Nepal, Italy, US, as well as international research programs of the World Climate Research Program (WCRP) and the World Meteorological Organization (WMO).

  1. Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

    Digital Repository Service at National Institute of Oceanography (India)

    Miriyala, P.; Sukumaran, N.P.; Nath, B.N.; Ramamurty, P.B.; Sijinkumar, A.V.; Vijayagopal, B.; Ramaswamy, V.; Sebastian, T.

    brown to grey color transition is typical of hemipelagic sediments with an oxidized top. Age model for core SK168 is well constrained45 which is based on five AMS 14C dates performed on planktic foraminiferal tests and fur- ther refined by correlating δ...12 (Merck) flux and borate beads were prepared in a Minifuse2 induction furnace. Major elements were meas- ured on Wavelength-Dispersive X-ray Fluorescence (XRF-WD; Axios, PANanalytical, The Netherlands) at the National Institute of Oceanography...

  2. Variation in the Indian summer monsoon intensity during the Bolling-Allerod and Holocene

    Digital Repository Service at National Institute of Oceanography (India)

    Kessarkar, P.M.; Rao, V.P.; Naqvi, S.W.A.; Karapurkar, S.G.

    to PDB. Repetitive analysis of the NBS 18, 19 and internal laboratory standards revealed that analytical standard deviation was better than ±0.07‰. Total inorganic carbon (TIC) was determined using a coulometer. CaCO3 (%) was calculated... by multiplying TIC with factor of 8.333, the reproducibility was found to be better than 5 %. In order to estimate total organic carbon (Corg), total carbon was measured by CNS elemental analyser (NCS 2500) and Corg was derived from the difference between...

  3. Holocene reef accretion: southwest Molokai, Hawaii, U.S.A.

    Science.gov (United States)

    Engels, Mary S.; Fletcher, Charles H.; Field, Michael E.; Storlazzi, Curt D.; Grossman, Eric E.; Rooney, John J.B.; Conger, Christopher L.; Glenn, Craig

    2004-01-01

    Two reef systems off south Molokai, Hale O Lono and Hikauhi (separated by only 10 km), show strong and fundamental differences in modern ecosystem structure and Holocene accretion history that reflect the influence of wave-induced near-bed shear stresses on reef development in Hawaii. Both sites are exposed to similar impacts from south, Kona, and trade-wind swell. However, the Hale O Lono site is exposed to north swell and the Hikuahi site is not. As a result, the reef at Hale O Lono records no late Holocene net accretion while the reef at Hikauhi records consistent and robust accretion over late Holocene time. Analysis and dating of 24 cores from Hale O Lono and Hikauhi reveal the presence of five major lithofacies that reflect paleo-environmental conditions. In order of decreasing depositional energy they are: (1) coral-algal bindstone; (2) mixed skeletal rudstone; (3) massive coral framestone; (4) unconsolidated floatstone; and (5) branching coral framestone-bafflestone. At Hale O Lono, 10 cores document a backstepping reef ranging from ∼ 8,100 cal yr BP (offshore) to ∼ 4,800 cal yr BP (nearshore). A depauperate community of modern coral diminishes shoreward and seaward of ∼ 15 m depth due to wave energy, disrupted recruitment activities, and physical abrasion. Evidence suggests a change from conditions conducive to accretion during the early Holocene to conditions detrimental to accretion in the late Holocene. Reef structure at Hikauhi, reconstructed from 14 cores, reveals a thick, rapidly accreting and young reef (maximum age ∼ 900 cal yr BP). Living coral cover on this reef increases seaward with distance from the reef crest but terminates at a depth of ∼ 20 m where the reef ends in a large sand field. The primary limitation on vertical reef growth is accommodation space under wave base, not recruitment activities or energy conditions. Interpretations of cored lithofacies suggest that modern reef growth on the southwest corner of Molokai, and by

  4. Stratigraphic architecture, bedload extraction, and mass balance of Holocene fluvial sediments in a tectonically subsiding basin within the Ganges-Brahmaputra River delta, Bangladesh

    Science.gov (United States)

    Sincavage, R.; Goodbred, S. L., Jr.; Pickering, J.; Wilson, C.; Paola, C.; Hossain, S.; Steckler, M. S.; Seeber, L.

    2014-12-01

    The Brahmaputra River occupied the tectonically active Sylhet Basin in eastern Bangladesh three times during the Holocene. With samples from more than 200 closely-spaced (3-5 km) boreholes, we take advantage of these discrete channel occupations and the high trapping efficiency of the subsiding basin to investigate dispersal of fluvial sediments. Experiment and theory suggest that depositional units transition from channels to lobes as transported sediment mass declines below ~30% of the total measured at the basin head. We test these ideas by reconstructing the geometry and grain size distributions of a large (30 m thick x 80 km wide) sand lobe formed during the mid-Holocene occupation (~7000-4000 years BP) of Sylhet Basin. Based on estimates of modern sediment discharge in the system, the volume of this sediment lobe is insufficient to account for the entire sediment budget. The smaller sediment volume is likely a consequence of reduced sediment discharge during a weakened monsoon. Additional sediment is likely to have also been routed out of the basin via an outlet located approximately along the modern Meghna River channel. Facies within Sylhet Basin can be characterized as stacked braidbelt sands in the proximal portion of the system, with isolated sand lenses further downstream, indicating a transition from a highly mobile braidbelt to a less mobile distributary system. The majority of bed load is extracted within a distance of ~150 km from the avulsion node, approximately coincident with the regional backwater reach of the Bengal Basin, suggesting a link between the hydraulic and "morphodynamic" backwater reaches of the system. Downstream fining is more rapid in sediments associated with the long-term occupation of Sylhet Basin, for which sediment is trapped over a relatively short distance within the sand wedge of central Sylhet Basin, than those from the early- and late-Holocene occupations, for which sediment is distributed over a longer path that follows

  5. Paleosecular variations of geomagnetic field from the Last Glacial Maximum to the Holocene in the north of South China Sea

    Science.gov (United States)

    Yang, X.; Huang, W.; Liu, Q.

    2012-12-01

    The high-resolution geomagnetic field records from the Last Glacial Maximum to the Holocene, which possessed of a notable climate change, were scarce in the global area. In this abstract, two gravity piston cores ZSQD2 (114.16oE, 19.58oN, ~190 cm in length, water depth 681m) and ZSQD34 (114.74oE, 19.05oN, ~184 cm in length, water depth 1820 m), situated in the north of South China Sea, were selected to study the secular variations of geomagnetic field in this area. Radiocarbon ages of G.sacculifer suggest that the deposition rate varied with 56.1 cm/kyr and 3.7 cm/kyr during the Last Glacial and the Holocene, respectively. Rock magnetic results indicate that the pseudo-single domain magnetite with low coercivity dominate the properties of sediments. The characteristic remanent magnetization (ChRM) values are evaluated using the 5-8 AF steps when MAD values are generally <5. Constrained by the radiocarbon chronology, the secular variation curves since ~18 cal. kyr can be constructed using the ChRM directions and NRM/ARM ratios (as a proxy of relative intensity). Comparing the Holocene SV with that from terrestrial lakes in Southern China, similar shape corroborates the reliability of records and uniform pattern of non-dipole magnetic field. Two significant features on SV curves present the geomagnetic field characteristics from ~17 cal. kyr to the early Holocene. One is that the direction variations lag behind the relative intensity on the millennium time scale. Such as a major direction shift occurred around 13 cal. kyr while the relative intensity low was about 14 cal. kyr. Another feature is the fast and frequent wiggles both in direction and intensity between ~17 to ~14.5 cal. kyr. During this period, two significant negative inclination anomalies occurred at ~16.4 and ~15.4 cal. kyr associated with low intensity, respectively. Nevertheless, the corresponding declinations did not show the reversed features although they had also some slight fluctuations. The

  6. Glacial to Holocene dynamics of Indonesian precipitation - New insights from plant-wax dD off Northwest Sumatra

    Science.gov (United States)

    Niedermeyer, E. M.; Mohtadi, M.; Sessions, A. L.; Feakins, S. J.

    2012-12-01

    ENSO and IOD variability, we further address the complex controls on Indonesian climate with emphasis of Holocene rainfall variability. References Griffiths, M.L., Drysdale, R.N., Gagan, M.K., Zhao, J.x., Ayliffe, L.K., Hellstrom, J.C., Hantoro, W.S., Frisia, S., Feng, Y.x., Cartwright, I., Pierre, E.S., Fischer, M.J., Suwargadi, B.W., 2009. Increasing Australian-Indonesian monsoon rainfall linked to early Holocene sea-level rise. Nature Geoscience 2, 636-639. Kirono, D.G.C., Tapper, N.J., McBride, J.L., 1999. Documenting Indonesian rainfall in the 1997/1998 El Nino event. Physical Geography 20, 422-435. Koutavas, A., Lynch-Stieglitz, J., 2005. Variability of the marine ITCZ over the eastern Pacific during the past 30,000 years: Regional perspective and global context. In: Bradley, R.S., Diaz, H.F. (Eds.), The Hadley Circulation: Present Past and Future. Springer, pp. 347-369. Partin, J.W., Cobb, K.M., Adkins, J.F., Clark, B., Fernandez, D.P., 2007. Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum. Nature 449, 452-455. Saji, N.H., Goswami, B.N., Vinayachandran, P.N., Yamagata, T., 1999. A dipole mode in the tropical Indian Ocean. Nature 401, 360-363.

  7. Holocene vegetation changes through Lac Ledro sediments (Trentino, Italy).

    Science.gov (United States)

    Joannin, Sebastien; Vannière, Boris; Galop, Didier; Magny, Michel; Gilli, Adrian; Chapron, Emmanuel; Wirth, Stéfanie; Anselmetti, Flavio; Desmet, Marc

    2010-05-01

    Lake Ledro is part of the French program ANR LAMA (coordinators: M. Magny and N. Combourieu Nebout) which aims to link Holocene paleoenvironmental changes along a north-south transect in Italy. Lake Ledro (652 m a.s.l.; Trentino, north-eastern Italy) is the northward component of the transect. It is located on the southern slope of the Alps and its catchment area covers 131 km2 with mountains culminating at 1500-2000 m. A multi-proxy approach based on biotic and abiotic indicators (lake-level, palynology, geochemistry and geophysic) was developed from deep and littoral cores, including sediment sequences in Early and Middle Bronze Age lake-shore archaeological sites. We aim reconstructing paleoenvironmental changes resulting from both climate and anthropic influences trough the entire Holocene. A deep master core was built after extracting twin cores from a non disturbed sediment zone recognised by seismic-reflexion investigations. The age-depth model is based on 13 AMS 14C ages measured on terrestrial plant macrofossils and the mean temporal resolution for analyses is ca 60 years. Palynological study shows the usual vegetation succession for the southern slope of the Alps. During the first part of the Holocene, abrupt changes are observed in pollen assemblages in relation to changes in other proxies (XRF and Magnetic Susceptibility) and correlate with cold events associated to the deglaciation in the North-Atlantic area. Cool episodes corresponding to the PreBoreal Oscillation (ca 11.3 ka cal BP) and 8.2 ka event are respectively characterized by stopping afforestation and a strong development of Abies in the local ecosystem. During the second part of the Holocene, two declines of arboreal pollen abundance are observed in relation with occurrences in both cereal and anthropic pollen indicators. These two phases are confirmed by increase in soil erosion as indicated by abiotic proxies. They give evidence of two successive steps for human settlement (Early

  8. Nong Thale Pron - a key site from southern Thailand for studying monsoon variability during the past 15000 years

    Science.gov (United States)

    Bredberg, Camilla; Chawchai, Sakonvan; Chabangborn, Akkaneewut; Kylander, Malin; Fritz, Sherilyn; Reimer, Paula J.; Wohlfarth, Barbara

    2014-05-01

    Studies of marine sediments, cave speleothemes, annually laminated corals, and tree rings from Asian monsoon regions have added knowledge to our understanding of the factors that control inter-annual to millennial monsoon variability in the past and have provided important constraints for climate modeling scenarios. In contrast, the spatial and temporal pattern of sub-millennial scale monsoon variability and its impact on land cover in SE Asia are still unresolved. This shortcoming stems from the fact that temporally well-resolved paleo-environmental studies are missing from large parts of SE Asia, especially from Thailand. Given that global and regional climate models are increasingly using terrestrial paleo- data to test their performance, past changes in land cover are therefore important variables to better understand feedbacks between different Earth systems. We obtained sediments from Lake Nong Thale Pron, in southern Thailand (8º 10`N, 99 º23`E; 380 m.asl). The aim of our study is to reconstruct lake status changes and to evaluate whether the extent of these changes are linked to known shifts in monsoon intensity and variability. Preliminary results show that lake infilling started more than 15,000 years ago and that the sediments cover the last deglaciation and the Holocene. Current analyses include Itrax XRF core scanning, loss-on-ignition (LOI at 950 and 550ºC), CN elemental and isotopic composition. We expect that our results will be able to give a picture of how the lake's status has changed over time and whether the extent of these changes is linked to known shifts in monsoon intensity and variability.

  9. 淮河上游全新世黄土及沉积成因%Holocene loess and its deposition dynamics in the upper reaches of the Huaihe River

    Institute of Scientific and Technical Information of China (English)

    何忠; 黄春长; 郑洪波; 周杰; 庞奖励; 李新艳; 王利军

    2011-01-01

    The dust source and transporting system are two indispensable aspects in the process of loess-palaeosol accumulation. It has been proved that the dust of the Loess Plateau mainly comes from the northwestem inland gobi and desert, transported by the East Asia monsoon systems and westerlies. However, there are little researches with respect to the dust source and deposition dynamics of the upper reaches of the Huaihe River. In the present study, we investigated and collected the YPC section with high resolution in the upper reaches of the Huaihe River. The chronological frame was reconstructed by optically stimulated luminescence (OSL) dating and correlated with the published loess time series. By comparison of the magnetic susceptibility (MS) and grain size (GS) of loess-soil profile among YPC profile, XJN profile (western Loess Plateau) and the JYC profile (southern Loess Plateau), we find similar climate change and pedogenic process between the upper reaches of the Huaihe River and the Loess Plateau, both experienced an extreme dry and the weakest pedogenesis during the last glacial, followed by a transitional episodes from the cold-dry last glacial to the warm-humid mid-Holocene and increased pedogenesis in the early Holocene, then a most humid-warm and strong pedogenesis in the mid-Holocene, and climate deterioration and decreased pedogenesis occurred during the late Holocene. But the MS of loess-soil profile sequences in the upper reaches of the Huaihe River was much lower than those in the Loess Plateau, and the GS was much coarser than those in the Loess Plateau. Comparison of GS for these three profiles revealed that there were different dust sources, which belonged to different aeolian transporting systems. The loess in the upper reaches of the Huaihe River was a wind blown deposition of near source, while the coarser dust mainly came from loose alluvial deposits of alluvial and proluvial fans of the Yellow River. The yielding and carrying dynamics of the

  10. How a Sphagnum fuscum-dominated bog changed into a calcareous fen : the unique Holocene history of a Slovak spring-fed mire

    NARCIS (Netherlands)

    Hajkova, Petra; Grootjans, A. B.; Lamentowicz, Mariusz; Rybnickova, Eliska; Madaras, Mikulas; Opravilova, Vera; Michaelis, Dierk; Hajek, Michal; Joosten, Hans; Wolejko, Leslaw; Rybníčková, Eliška; Madaras, Mikuláš; Opravilová, Věra; Wołejko, Lesław; Hajkova, T.

    2012-01-01

    In general, mires develop by autogenic succession from more groundwater-fed to more rainwater-fed. This study from a calcareous mire in the West Carpathians (Slovakia) describes a similar development in the Early Holocene, followed by a reverse development in the Middle and Late Holocene. Pollen, ma

  11. The Holocene thermal maximum in the Nordic Seas: the impact of Greenland Ice Sheet melt and other forcings in a coupled atmosphere-sea ice-ocean model

    NARCIS (Netherlands)

    Blaschek, M.; Renssen, H.

    2012-01-01

    The relatively warm early Holocene climate in the Nordic Seas, known as the Holocene Thermal Maximum (HTM), is often associated with an orbitally forced summer insolation maximum at 10 ka BP. The spatial and temporal response recorded in proxy data in the North Atlantic and the Nordic Seas reveal a

  12. Monsoon signatures in recent corals from the Laccadive Islands

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.A.S.

    have reduced water transparency, thereby curtailing the growth rates. Scanning electron microscopy clearly showed the presence of lithogenic and biogenic material in the monsoonal bands and their absence in the non-monsoonal bands. This indicates...

  13. Thrusts and Prospects on Understanding and Predicting Asian Monsoon Climate

    Institute of Scientific and Technical Information of China (English)

    WANG Bin

    2008-01-01

    Development of monsoon climate prediction through integrated research efforts to improve our understanding of monsoon variability and predictability is a primary goal of the Asian Monsoon Years (2007-2011) and International Monsoon Study under the leadership of the World Climate Research Programme.The present paper reviews recent progress in Asian monsoon research focusing on (1) understanding and modeling of the monsoon variability, (2) determining the sources and limits of predictability, and (3) assessing the current status of climate prediction, with emphasis on the weekly to interannual time scales. Particular attention is paid to identify scientific issues and thrust areas, as well as potential directions to move forward in an attempt to stimulate future research to advance our understanding of monsoon climate dynamics and improve our capability to forecast Asian monsoon climate variation.

  14. Response of arid ecosystems to the Holocene climate variability along west and central Mediterranean gradients.

    Science.gov (United States)

    Jaouadi, Sahbi; Combourieu Nebout, Nathalie; Azuara, Julien; Lebreton, Vincent

    2017-04-01

    Decadal to millennial climate variability is a common feature recorded by environmental series. However interconnections between climate forcing (i.e. insolation, thermohaline circulation) and large atmospheric circulation patterns (i.e. North Atlantic Oscillation, Mediterranean Oscillation, Monsoon) still remain poorly understood considering their respective impacts on the global climate mechanisms. In the Mediterranean area, joint climatic influences from high temperate and low subtropical latitudes result in a high sensitivity of ecosystems to climate changes and especially to extreme events. Several vegetation records illustrate millennial changes in Mediterranean. Nevertheless notable discrepancies in the environmental response arise between Mediterranean edges (east vs west, north vs south). The new paleoenvironmental record from Sebkha Boujmel (33°N, southern Tunisia) covers the last 8kyr and exhibits eight humid/arid fluctuations with cyclic expansion of the desert, related to Middle and Late Holocene rapid climate changes (RCC) occurring at a centennial scale. Sebkha Boujmel record is replaced in the wider context of west Mediterranean and northern hemisphere. Asynchronies and disparity of the Mediterranean RCC occurrence documents north-south and west-east climate gradients in the west Mediterranean and pinpoint Sebkha Boujmel as the single vegetation record tracing as many climate events during the last 8kyr. Indeed the high sensitivity of arid environments triggers the prompt reaction of the southern Tunisian vegetation to Holocene RCC however tenuous. Pattern of RCC geographical occurrence in west and central Mediterranean is interpreted in the light of climate forcings involved for the Holocene centennial variability.

  15. Organic geochemical evidence for climate changes over the lateglacial-Holocene in Lake Suigetsu, Japan

    Science.gov (United States)

    Pearson, E. J.; Nakagawa, T.; Tyler, J.; Juggins, S.; Bronk-Ramsey, C.; Bryant, C.; Staff, R.; Brock, F.; Lamb, H.; Brauer, A.; Marshall, M.; Schlolaut, G.; Yokoyama, Y.; Tarasov, P.; Payne, R. L.; Haraguchi, T.; Yonenobu, H.; Tada, R.; Gotanda, K.; Kossler, A.; Demske, D.; Takemura, K.; Ikehara, M.

    2009-12-01

    Lake Suigetsu is a small lake in central Japan under strong influence from both summer and winter monsoonal systems. In 2006 a ~73m continuous sediment record was collected from the lake, spanning the last ~150ka, and with annually laminated (varved) sediments back to ~70ka. The site was recently named a parastratotype of the Holocene onset [1] following pollen-derived evidence of abrupt warming at the start of the Holocene [2]. Here we examine organic geochemical evidence for climate change at the Holocene onset and 8.2ka. Changes in the total organic content (TOC) of the sediment is determined at ~decadal resolution via a site specific TOC calibration using near-infrared spectroscopy (NIR). Lipid biomarker analysis enables the examination of both autochthonous (within-lake) and catchment responses to climate change and compound specific isotope ratios (D/H) are used as a proxy for precipitation/evaporation variations independent of the evidence derived from pollen. We investigate potential lead/lag between proxies which will be of importance when trying to understand the nature of responses of different proxies to climate change as well as the nature and timing of abrupt climate changes. References: [1] Walker, M. et al. 2009. Journal of Quaternary Science, 24, 3-17 [2] Nakagawa, T. et al. 2003. Science, 299, 688-691.

  16. High-resolution methane records covering the Holocene

    Science.gov (United States)

    Bryant, S.; Mitchell, L.; Brook, E.; Sowers, T.

    2012-04-01

    In order to better understand CH4 variations during the Holocene, we have developed an ultra-high resolution (20-30 year) CH4 record from the WAIS Divide core (79.467°S, 112.085°W). Preliminary results confirm previous Antarctic measurements with early Holocene CH4 values of 690ppb, dropping gradually to mid Holocene values of 565ppb and then climbing to early preanthropogenic values of ~700ppb. The most striking feature of this ultra-high resolution record is the 8.2ka event that is well established in our record. At WAIS, CH4 values drop by 70ppb over ~50 yrs at the start of the 8.2 ka event, before climbing gradually over the ensuing 60 years culminating in a rapid increase over the last 30 years of the record back to pre 8.2ka values (635 ppb). Our new record follows a similar record from the GISP II ice core in magnitude suggesting the interpolar CH4 gradient remained relatively constant throughout the event. This in turn suggests that the 8.2ka event was most likely a global CH4 event impacting tropical emissions. Further insight into CH4 systematics during the Holocene was obtained using a revised version of the BOSCAGE 8-box atmospheric CH4 model. The model is broken into six 30o latitude bins and two stratospheric boxes for the N and S hemispheres. Mixing between the boxes, the latitudinal distribution of sources and sinks and the characteristic isotope values were fixed and maintained throughout the simulations based on present day inversion studies.

  17. Anthropogenic Origin of Siliceous Scoria Droplets from Pleistocene and Holocene Archeaological Sites in Northern Syria

    DEFF Research Database (Denmark)

    Thy, Peter; Willcox, George; Barfod, Gry;

    2015-01-01

    Siliceous scoria droplets, measuring from 1 to 10 mm, from one late Pleistocene and four early Holocene archaeological sites in northern Syria are compared to similar droplets previously suggested to be the result of a cosmic impact at the onset of the Younger Dryas global cooling event. The !ndi......Siliceous scoria droplets, measuring from 1 to 10 mm, from one late Pleistocene and four early Holocene archaeological sites in northern Syria are compared to similar droplets previously suggested to be the result of a cosmic impact at the onset of the Younger Dryas global cooling event...

  18. A Holocene temperature reconstruction from northern New Zealand: a test of North Atlantic Holocene climate patterns as a global template

    Science.gov (United States)

    van den Bos, Valerie; Rees, Andrew; Newnham, Rewi; Augustinus, Paul

    2017-04-01

    Holocene climate variability has been well defined in the North Atlantic (Walker et al., 2012), but the global extent of this climate change stratigraphy is debatable. If the North Atlantic serves as a global template for Holocene climate, then New Zealand (NZ) is ideally positioned to test this assertion, as it is distal from the northern drivers. Additionally, it is one of the few landmasses in the Southern Hemisphere that is influenced by both sub-tropical and extra-tropical climatic regimes, which may be more important controls in the southern mid-latitudes. Although much work has been done to characterise the Holocene in NZ using pollen, most of these records lack the resolution or sensitivity to determine whether abrupt or short-lived events occurred. The NZ-INTIMATE climate event stratigraphy lacks a type section for the Holocene (Alloway et al., 2007). Records from northern NZ typically show little change, other than a possible early Holocene warming. Here, we present a combined pollen and chironomid temperature reconstruction from Lake Pupuke (northern NZ), the first of its kind in NZ that covers the entire Holocene. By comparing mean annual temperatures reconstructed from fossil pollen and mean summer temperatures inferred from chironomid remains, we can assess changes in seasonality. Mean summer temperature was reconstructed from the chironomid record using a weighted averaging partial least squares (WA-PLS) model (n comp = 2, r2booth = 0.77, RMSEP = 1.4°C) developed from an expanded version of Dieffenbacher-Krall et al. (2007)'s chironomid training set. Preliminary results show evidence for cool summers during the early Holocene as well as around the period of the Little Ice Age as defined in the North Atlantic region. These and other climate patterns determined from the Pupuke chironomid and pollen records will be compared with other evidence from northern New Zealand and with the North Atlantic record of Holocene climate variability. References

  19. Warm Mediterranean mid-Holocene summers inferred from fossil midge assemblages

    Science.gov (United States)

    Samartin, Stéphanie; Heiri, Oliver; Joos, Fortunat; Renssen, Hans; Franke, Jörg; Brönnimann, Stefan; Tinner, Willy

    2017-02-01

    Understanding past climate trends is key for reliable projections of global warming and associated risks and hazards. Uncomfortably large discrepancies between vegetation-based summer temperature reconstructions (mainly based on pollen) and climate model results have been reported for the current interglacial, the Holocene. For the Mediterranean region these reconstructions indicate cooler-than-present mid-Holocene summers, in contrast with expectations based on climate models and long-term changes in summer insolation. We present new quantitative and replicated Holocene summer temperature reconstructions based on fossil chironomid midges from the northern central Mediterranean region. The Holocene thermal maximum is reconstructed 9,000-5,000 years ago and estimated to have been 1-2 °C warmer in mean July temperature than the recent pre-industrial period, consistent with glacier and marine records, and with transient climate model runs. This combined evidence implies that widely used pollen-based summer temperature reconstructions in the Mediterranean area are significantly biased by precipitation or other forcings such as early land use. Our interpretation can resolve the previous discrepancy between climate models and quantitative palaeotemperature records for millennial-scale Holocene summer temperature trends in the Mediterranean region. It also suggests that pollen-based evidence for cool mid-Holocene summers in other semi-arid to arid regions of the Northern Hemisphere may have to be reconsidered, with potential implications for global-scale reconstructions.

  20. Reappraisal of Asian Summer Monsoon Indices and the Long-Term Variation of Monsoon

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Webster and Yang monsoon index (WYI)-the zonal wind shear between 850 and 200 hPa was calculated and modified on the basis of NCEP/NCAR reanalysis data. After analyzing the circulation and divergence fields of 150-100 and 200 hPa, however, we found that the 200-hPa level could not reflect the real change of the upper-tropospheric circulation of Asian summer monsoon, especially the characteristics and variation of the tropical easterly jet which is the most important feature of the upper-tropospheric circulation. The zonal wind shear U850-U(150+100) is much larger than U850-U200, and thus it can reflect the strength of monsoon more appropriately. In addition, divergence is the largest at 150 hPa rather than 200 hPa, so 150 hPa in the upper-troposphere can reflect the coupling of the monsoon system. Therefore,WYI is redefined as DHI, i.e., IDH=U*850 - U*(150+100), which is able to characterize the variability of not only the intensity of the center of zonal wind shear in Asia, but also the monsoon system in the upper and lower troposphere. DHI is superior to WYI in featuring the long-term variation of Asian summer monsoon as it indicates there is obvious interdecadal variation in the Asian summer monsoon and the climate abrupt change occurred in 1980. The Asian summer monsoon was stronger before 1980 and it weakened after then due to the weakening of the easterly in the layer of 150-100 hPa, while easterly at 200 hPa did not weaken significantly. After the climate jump year in general, easterly in the upper troposphere weakened in Asia, indicating the weakening of summer monsoon; the land-sea pressure difference and thermal difference reduced, resulting in the weakening of monsoon; the corresponding upper divergence as well as the water vapor transport decreased in Indian Peninsula, central Indo-China Peninsula, North China, and Northeast China, indicating the weakening of summer monsoon as well. The difference between NCEP/NCAR and ERA-40 reanalysis data in

  1. Monsoon triggered formation of Quaternary alluvial megafans in the interior of Oman

    Science.gov (United States)

    Blechschmidt, Ingo; Matter, Albert; Preusser, Frank; Rieke-Zapp, Dirk

    2009-09-01

    A vast bajada consisting of coalescing low-gradient (veneer of weakly cemented Quaternary gravels. A combination of remote sensing, lithological analyses and luminescence dating is used to interpret the complex aggradation history of the Quaternary alluvial fans from the interior of Oman in the context of independent regional climate records. From satellite imagery and clast analysis four fans can be discerned in the study area. While two early periods of fan formation are tentatively correlated to the Miocene-Pliocene and the Early Pleistocene, luminescence dating allows the distinction of five phases of fan aggradation during the Middle-Late Pleistocene. These phases are correlated with pluvial periods from Marine Isotope Stage (MIS) 11 through 3, when southern Arabia was affected by monsoonal precipitation. It is concluded that the aggradation of the alluvial fans was triggered by the interplay of increased sediment production during arid periods and high rainfall with enhanced erosion of hillslopes and transport rates during strong monsoon phases. However, the lack of fine-grained sediments, bioturbation and organic material implies that although the Quaternary fans are sourced by monsoonal rains they formed in a semi-arid environment. Thus, it appears that, in contrast to the Oman Mountains, the interior was not directly affected by monsoonal precipitation.

  2. Investigation of the "Elevated Heat Pump" hypothesis of the Asian monsoon using satellite observations

    Directory of Open Access Journals (Sweden)

    M. M. Wonsick

    2013-04-01

    Full Text Available In recent years, the "Elevated Heat Pump" (EHP hypothesis has been a topic of intensive research and controversy. It postulates that aerosol-induced anomalous mid- and upper-tropospheric warming above the Tibetan Plateau leads to an early onset and intensification of Asian monsoon rainfall. The finding is primarily based on results from a NASA Finite-Volume General Circulation Model run with and without radiative forcing from different types of aerosols. In particular, black carbon emissions from sources in Northern India and dust from Western China, Afghanistan, Pakistan, and Southwest Asia affected the modeled anomalous heating. Since the initial discussion of the EHP hypothesis in 2006, the aerosol-monsoon relationship has been addressed using various modeling and observational techniques. The current study takes an observational approach to detect signatures of the "Elevated Heat Pump" effect in the cloud cover and cloud type distributions as derived from Meteosat-5 observations over the Asian Monsoon region, supplemented with temperature data from the NCEP/NCAR Reanalysis and precipitation data from the Global Precipitation Climatology Project (GPCP. Cloud, convection, precipitation, and temperature features for the highest-aerosol years are compared with lower-aerosol content years during the period 2000–2005. Predicted precipitation features in China and Korea are found to be consistent with the hypothesis, but the early onset and intensification of monsoon rainfall over India are not observed. It is proposed that model inaccuracies and/or indirect aerosol effects caused the disagreement between observed and hypothesized behavior.

  3. On breaks of the Indian monsoon

    Indian Academy of Sciences (India)

    Sulochana Gadgil; P V Joseph

    2003-12-01

    For over a century, the term break has been used for spells in which the rainfall over the Indian monsoon zone is interrupted. The phenomenon of `break monsoon' is of great interest because long intense breaks are often associated with poor monsoon seasons. Such breaks have distinct circulation characteristics (heat trough type circulation) and have a large impact on rainfed agriculture.Although interruption of the monsoon rainfall is considered to be the most important feature of the break monsoon, traditionally breaks have been identified on the basis of the surface pressure and wind patterns over the Indian region. We have defined breaks (and active spells) on the basis of rainfall over the monsoon zone. The rainfall criteria are chosen so as to ensure a large overlap with the traditional breaks documented by Ramamurthy (1969) and De et al (1998). We have identified these rainbreaks for 1901-89. We have also identified active spells on the basis of rainfall over the Indian monsoon zone. We have shown that the all-India summer monsoon rainfall is significantly negatively correlated with the number of rainbreak days (correlation coefficient −0.56) and significantly positively correlated with the number of active days (correlation coefficient 0.47).Thus the interannual variation of the all-India summer monsoon rainfall is shown to be related to the number of days of rainbreaks and active spells identified here. There have been several studies of breaks (and also active spells in several cases) identified on the basis of different criteria over regions differing in spatial scales (e.g., Webster et al 1998; Krishnan et al 2000; Goswami and Mohan 2000; and Annamalai and Slingo 2001). We find that there is considerable overlap between the rainbreaks we have identified and breaks based on the traditional definition. There is some overlap with the breaks identified by Krishnan et al (2000) but little overlap with breaks identified by Webster et al (1998). Further

  4. Characteristics of the Onset of the Asian Summer Monsoon and the Importance of Asian-Australian "Land Bridge"

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Based on summarizing previous achievements and using data as long and new as possible, the onset characteristics of Asian summer monsoon and the role of Asian-Australian "land bridge" in the onset of summer monsoon are further discussed. In particular, the earliest onset area of Asian summer monsoon is comparatively analyzed, and the sudden and progressive characteristics of the onset of summer monsoon in different regions are discussed. Furthermore, the relationships among such critical events during the onset of Asian summer monsoon as the splitting of subtropical high belt over the Bay of Bengal (BOB), the initiation of convection over Indo-China Peninsula, the westward advance, reestablishment of South Asian High, and the rapid northward progression of convection originated from Sumatra in early summer are studied. The important impact of the proper collocation of the latent heating over Indo-China Peninsula and the sensible heating over Indian Peninsula on the splitting of the subtropical high belt, the deepening of BOB trough, the activating of Sri Lanka vortex (twin vortexes in the Northern and Southern Hemispheres),and the subsequent onset of South China Sea summer monsoon are emphasized.

  5. Holocene environmental changes in the Atacama altiplano and paleoclimatic implications

    Directory of Open Access Journals (Sweden)

    1995-01-01

    de 200 mm anuales a 24° S. Diversos factores se consideran para explicar esta evolución paleoclimática: teleconexiones con el hemisferio norte, cambios en la circulación oceánica en el Pacífico oriental, cambios ambientales en la cuenca amazónica donde se origina el vapor de agua, o diferencias en albedo y cubierta de nubes en la región de Atacama. Strengthened summer monsoon brought tropical/continental moisture as far south as 25°S during late-glacial and early Holocene times. Precipitation rates in the Altiplano of the western Andes (24°S increased to 500 mm yr-1 compared to <200 mm yr-1 today. There is evidence of dramatically decreasing lake levels between 8 400 and about 3 000 yr B.P., and conditions drier than today were established. This arid period was interrupted by low-frequency but heavy storms. The monsoon precipitation belt advanced once again in several stages to its current position (200 mm yr-1 isohyeta at 24°S around 3 000 yr B.P. The reasons for these changes are not known: the variable circulation in the E-Pacific, teleconnections to the northern hemisphere, environmental changes in the source area of the moisture (i.e. tropical continent, or internal forcing due to changes in the radiation budget of the Altiplano are considered as possible explanations.

  6. Late Pleistocene and Holocene Fire History of the California Islands

    Science.gov (United States)

    Scott, A. C.; Hardiman, M.; Pinter, N.; Anderson, R.

    2013-12-01

    Charcoal has been recovered from a range of late Pleistocene and Holocene sites on Santa Cruz Island and Santa Rosa Island, both islands part of California's Northern Channel Islands, U.S.A. Sediments have been dated using radiocarbon measurements based on wood charcoal, fungal sclerotia, glassy carbon and fecal pellets and are given as calendar years BP. This charcoal has been used to interpret the fire history of the Islands. Charcoal assemblages from samples dating from 24,690 to 12,900 years are dominated by coniferous wood charcoal. Little angiosperm charcoal was recovered in any of the samples. Fungal sclerotia are frequent in a number of samples from a range of ages both on Santa Cruz and Santa Rosa. Fecal pellets are common in most samples and abundant in others. Some of the fecal pellets have hexagonal sides and are likely to represent termite frass. The sediments are fluvial in origin and the distribution of charcoal is irregular making interpretation of fire return intervals and fire frequency difficult. The charcoal indicates a significant record of fire before the earliest documented human arrival on the islands. Charcoal reflectance data shows the occurrence of predominantly low temperature charcoals suggesting common surface fires in the coniferous forest. Soledad Pond sediments from Santa Rosa Island (Anderson et al., 2010) dating from 11,800 cal years BP show a distinctively different vegetation dominated by angiosperms and showing a very different fire history. Pinus stands, coastal sage scrub dominated by Baccharis sp. and grassland replaced the conifer forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150 cal yr BP. By ca. 6900 cal yr BP grasslands recovered. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the Soledad Pond record, but declines during the early Holocene when minimal biomass suggests extended drought. A general

  7. A Holocene pollen record of vegetation and coastal environmental changes in the coastal swamp forest at Batulicin, South Kalimantan, Indonesia

    Science.gov (United States)

    Yulianto, Eko; Rahardjo, A. T.; Noeradi, Dardji; Siregar, D. A.; Hirakawa, K.

    2005-04-01

    Pollen analysis of a coastal peat swamp core representing 9100 BP from Batulicin, South Kalimantan, Indonesia, shows that mangrove forest, with Rhizophora as its main element has been established since the early Holocene. Vegetation development in general, and particularly mangrove forest, was influenced by Holocene environmental changes. The highest value of Rhizophora at ca. 8200 BP indicates an early Holocene sea level drop and implies sea level at ca. -9 m. Subsequently mangrove forest was severely disrupted by rapid sea level rise at ca. 6400 BP prior to the Holocene Maximum. However, it quickly recovered following a lower rate of sea level rise or subsequent sea level drop at ca. 6000 BP and flourished until ca. 1000 BP. From ca. 6000 BP, the environmental setting around the site seems to have gradually become more terrestrial and changed from mangrove forest to peat swamp forest due to higher precipitation and intensive progradation. Human influence is recognized from ca. 1600 BP.

  8. Holocene seasonal variability inferred from multiple proxy records from Crevice Lake, Yellowstone National Park, USA

    Science.gov (United States)

    Whitlock, Cathy; Dean, Walter E.; Fritz, Sherilyn C.; Stevens, Lora R.; Stone, Jeffery R.; Power, Mitchell J.; Rosenbaum, Joseph R.; Pierce, Kenneth L.; Bracht-Flyr, Brandi B.

    2012-01-01

    A 9400-yr-old record from Crevice Lake, a semi-closed alkaline lake in northern Yellowstone National Park, was analyzed for pollen, charcoal, geochemistry, mineralogy, diatoms, and stable isotopes to develop a nuanced understanding of Holocene environmental history in a region of northern Rocky Mountains that receives both summer and winter precipitation. The limited surface area, conical bathymetry, and deep water (> 31 m) of Crevice Lake create oxygen-deficient conditions in the hypolimnion and preserve annually laminated sediment (varves) for much of the record. Pollen data indicate that the watershed supported a closed Pinus-dominated forest and low fire frequency prior to 8200 cal yr BP, followed by open parkland until 2600 cal yr BP, and open mixed-conifer forest thereafter. Fire activity shifted from infrequent stand-replacing fires initially to frequent surface fires in the middle Holocene and stand-replacing events in recent centuries. Low values of δ18O suggest high winter precipitation in the early Holocene, followed by steadily drier conditions after 8500 cal yr BP. Carbonate-rich sediments before 5000 cal yr BP imply warmer summer conditions than after 5000 cal yr BP. High values of molybdenum (Mo), uranium (U), and sulfur (S) indicate anoxic bottom-waters before 8000 cal yr BP, between 4400 and 3900 cal yr BP, and after 2400 cal yr BP. The diatom record indicates extensive water-column mixing in spring and early summer through much of the Holocene, but a period between 2200 and 800 cal yr BP had strong summer stratification, phosphate limitation, and oxygen-deficient bottom waters. Together, the proxy data suggest wet winters, protracted springs, and warm effectively wet summers in the early Holocene and less snowpack, cool springs, warm dry summers in the middle Holocene. In the late Holocene, the region and lake experienced extreme changes in winter, spring, and summer conditions, with particularly short springs and dry summers and winters during

  9. Effect of the summer monsoon on aerosols at two measurement stations in Northern India – Part 2: Physical and optical properties

    Directory of Open Access Journals (Sweden)

    A.-P. Hyvärinen

    2011-01-01

    Full Text Available Aerosol physical and optical properties were measured at two locations in Northern India during 2006–2010. The first measurement station was a background site in Mukteshwar, about 350 km northeast of New Delhi, in the foothills of the Indian Himalayas. The second measurement site was located in Gual Pahari, about 25 km south of New Delhi. At both stations, the average aerosol concentrations during the monsoon were decreased by 40–75% compared to the pre-monsoon average concentrations. The decrease varied with the total local rainfall. Also the mean aerosol size decreased during the monsoon season. The size distribution at Mukteshwar was unimodal, with a mode diameter at about 80 nm. In Gual Pahari, the ratio of Aitken and accumulation particle concentration was >1, due to wet deposition and new particle formation during the monsoon season. Aerosol concentrations during the early monsoon were found to be affected by mineral dust which in Gual Pahari was observed as an increased particle volume at around 3–4 μm. The single scattering albedo varied from 0.73 to 0.93 during the monsoon season, being slightly lower in Gual Pahari than in Mukteshwar. The aerosol columnar properties, which were measured in Gual Pahari, showed a somewhat different seasonal behavior compared to the surface measurements, with the aerosol optical depth increasing to an annual maximum in the early monsoon season.

  10. Millennial-scale Asian summer monsoon variations in South China since the last deglaciation

    Science.gov (United States)

    Wang, Xisheng; Chu, Guoqiang; Sheng, Mei; Zhang, Shuqin; Li, Jinhua; Chen, Yun; Tang, Ling; Su, Youliang; Pei, Junling; Yang, Zhenyu

    2016-10-01

    Characterizing spatiotemporal variability of the Asian summer monsoon (ASM) is critical for full understanding of its behavior, dynamics, and future impacts. The present knowledge about ASM variations since the last glaciation in South China largely relies on several precisely-dated speleothem stable oxygen isotope (δ18 O) records. Although these speleothem δ18 O signals provide useful evidence for regional past environmental changes, their validity for denoting ASM intensity remains a great controversy. The Huguangyan Maar Lake (HML) provides one of the most complete archives of environmental and climatic changes in the tropical-subtropical South and East Asia since the last glaciation. Here we document a continuous centennial- to millennial-scale ASM record over the past 16 ky BP from the high-sedimentation-rate HML sediments. In contrast with the low-amplitude variations of Chinese speleothem-derived δ18 O signals and the Chinese loess-based monsoon precipitation proxy indexes, our multi-proxy records reveal a pattern of high-amplitude regional climatic fluctuations, including fine-scale oscillations during the Bølling-Allerød warming, the 8.2 ka cooling event, and an abrupt climate shift from 6.5-5.9 ka. The existence of Bond-like cold/dry events indicates a distinct influence of the North Atlantic circulation on low-latitude monsoon changes. The broad comparability between the HML paleo-proxies, Chinese speleothem δ18 O records, and the northern hemisphere summer insolation throughout the Holocene, suggests that solar insolation exerts a profound influence on ASM changes. These findings reinforce a model of combined insolation and glacial forcing of the ASM.

  11. Dynamics of Tropical Waves and Monsoons.

    Science.gov (United States)

    1981-04-01

    large-scale rainband in the Baum season. J Vet’,’,r 1o,. large-scale baroclinic forcing. Japon . 52. 448-451. -72 953 MONTHLY % EATHInR REVIEV% V L l 08...monsoon circulation large orographic structures such as the Himalavas. tan importance emanating from the social -economi- and 4) the perturbation of

  12. Warm Indian Ocean, Weak Asian Monsoon

    Science.gov (United States)

    Koll Roxy, Mathew; Ritika, Kapoor; Terray, Pascal; Murtugudde, Raghu; Ashok, Karumuri; Nath Goswami, Buphendra

    2015-04-01

    There are large uncertainties looming over the status and fate of the South Asian monsoon in a changing climate. Observations and climate models have suggested that anthropogenic warming in the past century has increased the moisture availability and the land-sea thermal contrast in the tropics, favoring an increase in monsoon rainfall. In contrast, we notice that South Asian subcontinent experienced a relatively subdued warming during this period. At the same time, the tropical Indian Ocean experienced a nearly monotonic warming, at a rate faster than the other tropical oceans. Using long-term observations and coupled model experiments, we suggest that the enhanced Indian Ocean warming along with the suppressed warming of the subcontinent weaken the land-sea thermal contrast throughout the troposphere, dampen the monsoon Hadley circulation, and reduce the rainfall over South Asia. As a result, the summer monsoon rainfall during 1901-2012 shows a significant weakening trend over South Asia, extending from Pakistan through central India to Bangladesh.

  13. Late Weichselian and Holocene paleoceanography of Storfjordrenna, southern Svalbard

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    M. Łącka

    2014-08-01

    Full Text Available Multiproxy analyses (incl. benthic and planktonic foraminifera, δ18O and δ13C records, grain-size distribution, ice-rafted debris, XRF geochemistry and magnetic susceptibility were performed on a 14C dated marine sediment core from Storfjordrenna, off southern Svalbard. The sediments in the core cover the termination of Bølling–Allerød, the Younger Dryas and the Holocene, and they reflect general changes in the hydrology/climate of the European Arctic after the last glaciation. Grounded ice of the last Svalbard- Barents Sea Ice Sheet retreated from the coring site ca. 13 850 cal yr BP. During the transition from the sub-glacial to glacimarine setting, Arctic Waters dominated the hydrography in Storfjordrenna. However, the waters were not uniformly cold and experienced several warmer spells. A progressive warming and marked change in the nature of hydrology occurred during the early Holocene. Relatively warm and saline Atlantic Water started to dominate the hydrography from approx. 9500 cal yr BP. Even though the climate in eastern Svalbard was milder at that time than at present (smaller glaciers, there were two slight coolings observed in the periods of 9000–8000 cal yr BP and 6000–5500 cal yr BP. A change of the Storfjordrenna hydrology occurred at the beginning of late Holocene synchronously with glacier growth on land and enhanced bottom current velocities. Although cooling was observed in the surface water, Atlantic Water remained present in the deeper part of water column of Storfjordrenna.

  14. Natural and anthropogenic forest fires recorded in the Holocene pollen record from a Jinchuan peat bog, northeastern China

    OpenAIRE

    Jiang, W; Leroy, SAG; Ogle, N; G. Chu; Wang, L.; J Liu

    2008-01-01

    Pollen and charcoal particles from a Jinchuan peat (northeastern China) were examined to investigate the fire origin and interaction between climate, vegetation, fire and human activity during the Holocene. Pollen results show that: (i) a broadleaved deciduous forest was dominant during the early Holocene; (ii) from ~5500 cal. yr B.P. there was a gradual increase in coniferous trees (mainly Pinus), and a decrease in broadleaved deciduous trees (e.g. Quercus, Juglans, and Ulmus–Zelkov...

  15. Long-term variations in Iceland–Scotland overflow strength during the Holocene

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    D. J. R. Thornalley

    2013-09-01

    Full Text Available The overflow of deep water from the Nordic seas into the North Atlantic plays a critical role in global ocean circulation and climate. Approximately half of this overflow occurs via the Iceland–Scotland (I–S overflow, yet the history of its strength throughout the Holocene (~ 0–11 700 yr ago, ka is poorly constrained, with previous studies presenting apparently contradictory evidence regarding its long-term variability. Here, we provide a comprehensive reconstruction of I–S overflow strength throughout the Holocene using sediment grain size data from a depth transect of 13 cores from the Iceland Basin. Our data are consistent with the hypothesis that the main axis of the I–S overflow on the Iceland slope was shallower during the early Holocene, deepening to its present depth by ~ 7 ka. Our results also reveal weaker I–S overflow during the early and late Holocene, with maximum overflow strength occurring at ~ 7 ka, the time of a regional climate thermal maximum. Climate model simulations suggest a shoaling of deep convection in the Nordic seas during the early and late Holocene, consistent with our evidence for weaker I–S overflow during these intervals. Whereas the reduction in I–S overflow strength during the early Holocene likely resulted from melting remnant glacial ice sheets, the decline throughout the last 7000 yr was caused by an orbitally induced increase in the amount of Arctic sea ice entering the Nordic seas. Although the flux of Arctic sea ice to the Nordic seas is expected to decrease throughout the next century, model simulations predict that under high emissions scenarios, competing effects, such as warmer sea surface temperatures in the Nordic seas, will result in reduced deep convection, likely driving a weaker I–S overflow.

  16. Inception of a global atlas of Holocene sea levels

    Science.gov (United States)

    Khan, Nicole; Rovere, Alessio; Engelhart, Simon; Horton, Benjamin

    2017-04-01

    Determining the rates, mechanisms and geographic variability of sea-level change is a priority science question for the next decade of ocean research. To address these research priorities, the HOLocene SEA-level variability (HOLSEA) working group is developing the first standardized global synthesis of Holocene relative sea-level data to: (1) estimate the magnitudes and rates of global mean sea-level change during the Holocene; and (2) identify trends in spatial variability and decipher the processes responsible for geographic differences in relative sea-level change. Here we present the preliminary efforts of the working group to compile the database, which includes sea-level index points and limiting data from a range of different indicators across seven continents from the Last Glacial Maximum to present. We follow a standard protocol that incorporates full consideration of vertical and temporal uncertainty for each sea-level index point, including uncertainties associated with the relationship of each indicator to past sea-level and the methods used to date each indicator. We describe the composition of the global database, identify gaps in data availability, and highlight our effort to create an online platform to access the data. These data will be made available in a special issue of Quaternary Science Reviews and archived on NOAA's National Centers for Environmental Information (NCEI) in early 2018. We also invite researchers who collect or model Holocene sea-level data to participate. Long-term, this effort will enhance predictions of 21st century sea-level rise, and provide a vital contribution to the assessment of natural hazards with respect to sea-level rise and coastal response.

  17. Holocene reef development where wave energy reduces accommodation

    Science.gov (United States)

    Grossman, Eric E.; Fletcher, Charles H.

    2004-01-01

    Analyses of 32 drill cores obtained from the windward reef of Kailua Bay, Oahu, Hawaii, indicate that high wave energy significantly reduced accommodation space for reef development in the Holocene and produced variable architecture because of the combined influence of sea-level history and wave exposure over a complex antecedent topography. A paleostream valley within the late Pleistocene insular limestone shelf provided accommodation space for more than 11 m of vertical accretion since sea level flooded the bay 8000 yr BP. Virtually no net accretion (pile-up of fore-reef-derived rubble (rudstone) and sparse bindstone, and (3) a final stage of catch-up bindstone accretion in depths > 6 m. Coral framestone accreted at rates of 2.5-6.0 mm/yr in water depths > 11 m during the early Holocene; it abruptly terminated at ~4500 yr BP because of wave scour as sea level stabilized. More than 4 m of rudstone derived from the upper fore reef accreted at depths of 6 to 13 m below sea level between 4000 and 1500 yr BP coincident with late Holocene relative sea-level fall. Variations in the thickness, composition, and age of these reef facies across spatial scales of 10-1000 m within Kailua Bay illustrate the importance of antecedent topography and wave-related stress in reducing accommodation space for reef development set by sea level. Although accommodation space of 6 to 17 m has existed through most of the Holocene, the Kailua reef has been unable to catch up to sea level because of persistent high wave stress.

  18. 毛乌素沙漠东南缘全新世剖面光释光年代及古气候意义%OSL DATING OF HOLOCENE SEQUENCE AND PALAEOCLIMATE CHANGE RECORD IN SOUTHEASTEARN MARGIN OF MU US DESERT,NORTH CHINA

    Institute of Scientific and Technical Information of China (English)

    马冀; 岳乐平; 杨利荣; 孙蕗; 徐永

    2011-01-01

    correspond to three considerable dune fixations. In order to establish reliable timing of dune development, this study applied optically stimulated luminescence ( OSL) dating techniques to the aeolian sediments features. 10 luminescence samples obtained from this profile were dated using the quartz single aliquot regeneration ( SAR) protocol. Combining with palaeoclimate proxies ( e. g. , grain sizes and magnetic susceptibilities) ,the records revealed as many as seven periods of significant rapid climate changes during the time intervals the palaeosoil layers deposited. The spatial and temporal extent of the data have allowed for correlations to be made with evidence from global climate changes. The first arid episode occurred before 7. 5ka in the early Holocene, with widespread aeolian sand mobilization and sparse vegetation. During 7. 5 ~ 3. 9ka , climate turned to be warmer and more humid with the occurrence of thick palaeosoil layers in the lowest, at the same time with Holocene Optimum.When it comes to 3. 9 ~ 2. 9ka .the dune rebounded to reactive with strong winter monsoon , and the climate became arid again. The timing of widespread dune reactivation coincided with well-known 4ka event. The climate became warm and humid during 2. 9 ~ 1. 7ka , with lower magnetic susceptibility than the upper palaeosoil layer. Although the summer monsoon is weakened. the winter monsoon failed to become predominant. Climate fluctuated more frequently after 1. 7ka with a warm climate episode during 1. 0 ~ 0. Ska and an arid one around 0. 2ka. It also revealed that the human significance of Holocene climate variability since 1ka ago. More importantly , the Holocene climate changes and evolution records from the Jinjie section could be correlated with the worldwide millennial-scale climate shifts , suggesting that the activity of East Asia monsoon in the Holocene may have directly been controlled or affected by global climate system. Several intervals coincide with major

  19. Effect of the summer monsoon on aerosols at two measurement stations in Northern India – Part 1: PM and BC concentrations

    Directory of Open Access Journals (Sweden)

    A.-P. Hyvärinen

    2011-01-01

    Full Text Available Particulate matter (PM and black carbon (BC concentrations were measured at two locations in Northern India during 2006–2010. The first measurement station is a background site in Mukteshwar, about 350 km northeast of New Delhi, in the foothills of the Indian Himalayas. The second measurement site was located in Gual Pahari, about 25 km south of New Delhi. Here we focused on resolving the effects of the Indian summer monsoon on the particulate matter and black carbon concentrations at the two stations. The average monsoon time concentrations were decreased by 55–70% compared to the pre-monsoon average concentrations at both stations, having a linear relationship with the total local rainfall during the monsoon season. In Mukteshwar during the monsoon, the 24 h PM2.5 concentrations were always below the Indian National Air Quality Standard of 60 μgm−3. In Gual Pahari, 13% of days exceeded this level during the monsoon season. However, the 24 h guideline of 25 μgm−3 given by the World Health Organization was more difficult to meet. In addition to loss processes, aerosol concentrations during the early monsoon were found to be affected by primary emissions, most likely dust event from the Thar Desert. This resulted in elevated fractions of the coarse mode, PM2.5−10 at both stations. In Mukteshwar, additional dust contribution came from the arid regions on the southern slopes of Himalayas. We also determined the characteristic transition times between the pre-monsoon, monsoon and post-monsoon. The onset and withdrawal transitions occurred faster in Mukteshwar than in Gual Pahari, both being typically less than 10 days. Transition periods in Gual Pahari took between 17 and 31 days. The shorter transition times in Mukteshwar were probably related to the more intense rains due to the mountain location.

  20. Westerly jet-Asian Monsoon Coupling During the Last 30 kyr

    Science.gov (United States)

    Nagashima, K.; Tada, R.; Isozaki, Y.; Toyoda, S.; Tani, A.; Sun, Y.

    2008-12-01

    Increasing evidence has revealed that the East Asian Summer Monsoon (EASM) intensity varies in millennial timescale during the last deglaciation and the Holocene as well as the last glacial period (e.g., Hu et al., 2008). However, the cause and nature of these EASM variations are not well understood. At present, the Asian summer monsoon front, the major convection/rainfall band, moves northward with the northward migration of the westerly jet from April to September (Liang and Wang, 1998), transporting moisture to inner Asia. Thus, it is possible that behavior of the westerly jet strongly influences on variability of the EASM. Then, here we reconstructed the variation in the westerly jet during the last 30 kyr, and examine its relation to the EASM changes. The Japan Sea is located on the eastern margin of the Eurasian continent under the influence of Asian winter monsoon wind and the westerly jet that passes over dry areas in the Eurasian continent. Therefore, it receives significant amount of eolian dust emitted from these dry areas. In order to examine the variability of the westerly jet, here we reconstructed latitudinal changes of the eolian dust provenance using the two sediment cores D-GC-6 and KR07-12-PC8 derived from south and central parts of the Japan Sea, respectively. We use two parameters of quartz, Electron Spin Resonance signal intensity and Crystallinity Index, for the estimation of the eolian dust provenance. The Gobi desert in Mongolia (Mongolian Gobi) and the Taklimakan desert are estimated as the dominant source areas of eolian dust at both sites of the Japan Sea. Latitudinal change of the eolian dust provenance varied in harmony with the EASM variations. Namely, larger contributions of eolian dust from the Taklimakan desert at the south site than the central site are found during the Heinrich 1 and 2, Younger Dryas, and some intervals of the Holocene, which correspond to the periods of weak EASM. Since the latitudinal change of the eolian dust

  1. Holocene glacier fluctuations in the American Cordillera

    Science.gov (United States)

    Davis, P. Thompson

    In many areas of the American Rocky Mountains (Colorado, Wyoming, Utah, Idaho, Montana), Cascade Range (Washington, Oregon), and the Sierra Nevada (California), radiocarbon ages suggest that ice receded to near present limits before 10 ka BP. A pre-Altithermal readvance or stillstand left moraines ca. 1-3 km beyond and ca. 50-300 m below present glacier margins. At one locality on Glacier Peak in Washington, these deposits are perhaps dated to the early Holocene, but in general these deposits are probably at least 10 ka old. Glacial advances during the Altithermal (ca. 8 to 5 ka BP) elsewhere are rare; radiocarbon evidence for Altithermal glacial advances in the Colorado Front Range is questionable. The earliest radiocarbon-dated Neoglacial advances occurred about 5 ka BP in the Washington Cascades; moraines and related deposits believed to be of early Neoglacial age (i.e. 5 to 3 ka BP) elsewhere are poorly dated. For example, moraines believed to date to the early Neoglacial in Colorado (Triple Lakes) and Wyoming (Temple Lake) are actually late Pleistocene age, based on radiocarbon ages derived from lake sediments at the type localities. Although relative-age data (i.e. lichens, rock weathering, soils) from many areas suggest a three-fold Neoglacial sequence, little supporting radiocarbon evidence is available. However, tephrochronology distinguishes three Neoglacial advances near Mount Rainier in Washington. In most mountain ranges of the western United States, fresh, unweathered, sharp-crested moraines usually adjacent to present ice margins, or near headwalls in empty cirques, date to the Little Ice Age of the last several centuries. However, detailed photographic or other historical records of glacial fluctuations during the last century are rare, and detailed mass balance studies rarer still. Whether or not pre-Little Ice Age glacial fluctuations in the American Cordillera are synchronous must await better radiometric dating of local moraine sequences.

  2. Biomization and quantitative climate reconstruction techniques in northwestern Mexico—With an application to four Holocene pollen sequences

    Science.gov (United States)

    Ortega-Rosas, C. I.; Guiot, J.; Peñalba, M. C.; Ortiz-Acosta, M. E.

    2008-04-01

    6 ka. Climate Dynamics 12, 185-194), we modified the pollen-PFT and PFT-biomes assignation of Thompson and Anderson (Thompson, R.S., Anderson, K.H., 2000. Biomes of western North America at 18,000; 6000 and 0 14C yr BP reconstructed from pollen and packrat midden data. Journal of Biogeography 27, 555-584) for a better representation of the modern vegetation of NW Mexico. The biome reconstruction method was validated with the modern pollen sites and applied to the fossil sites. Our results show that, during the early Holocene, a cool conifer forest extended at least down to 1700 m, while today this biome is present above 2000 m in the Chihuahua state. The Younger Dryas event was recorded in one site with cold and dry conditions. The reconstructed annual temperature for this period was 3°-6 °C colder than today, and annual precipitation was 250 mm lower than at present (900 mm/yr). The middle Holocene after 9200 cal yr BP was marked by a warming trend, reaching temperatures 2 °C warmer than today at 7000 cal yr BP, and by the installation of a warm mixed forest, the present day biome, at 1700 m elevation, while at higher elevations (1900 m) the cool conifer forest was still present. Summer precipitation was 200 mm/yr above the early Holocene values, suggesting that monsoon-like conditions strengthened since 9200 cal yr BP at this region. During the last 4000 yr, the same warm mixed forest was reconstructed below 1700 m and a conifer forest above 1700 m. A great variability of vegetation and climate patterns was recorded for the last 3000 yr particularly at high elevation sites, where warming and cooling trends would be coeval of the Medieval warm period and Little Ice Age, likely related to ENSO variability.

  3. Atlantic and Pacific Ocean synergistic forcing of the Mesomerican monsoon over the last two millennia

    Science.gov (United States)

    Lachniet, M. S.; Asmerom, Y.; Polyak, V. J.; Bernal, J. P.

    2015-12-01

    We present a new replicated, high resolution (~2 yrs) and precisely-dated (± 4 yr) wet season hydroclimate reconstruction for the Mesoamerican sector of the North American Monsoon over the past 2250 years. Our new reconstruction is based on two aragonite stalagmites from southwestern Mexico which replicate oxygen isotope variations over the 950-1950 CE interval, and are calibrated to instrumental rainfall variations in the Basin of Mexico. Such data complement existing dendroclimatic reconstructions of early wet season and winter drought severity. Comparisons to indices of ocean-atmosphere circulation show a combined forcing by the North Atlantic Oscillation and the El Niño/Southern Oscillation. Monsoon strengthening coincided with synergistic forcing of a La Niña-like mode and a negative North Atlantic Oscillation, and vice versa for droughts. Although drought is commonly invoked as an stressor leading to societal change, the role of intensified monsoon onto cultural development is rarely explored. We observe that prominent transitions from drought to pluvial conditions are associated with population increases in three of the major highland Mexico civilizations of Teotihuacan, Tula Grande, and the Aztecs. These data suggest a role for ocean-atmosphere dynamics arising from the Atlantic and Pacific Oceans on Mesoamerican monsoon strength.

  4. Holocene temperatures and isotopes of precipitation in Northwest Greenland recorded in lacustrine organic materials

    Science.gov (United States)

    Lasher, G. Everett; Axford, Yarrow; McFarlin, Jamie M.; Kelly, Meredith A.; Osterberg, Erich C.; Berkelhammer, Max B.

    2017-08-01

    Reconstructions of Holocene lake water isotopic composition based upon subfossil aquatic organic material offer new insights into Arctic climate. We present quantitative estimates of warmth during the Holocene Thermal Maximum in northwest Greenland, inferred from oxygen isotopes of chironomid head capsules and aquatic moss preserved in lake sediments. δ18O values of chironomids from surface sediments of multiple Greenland lakes indicate that these subfossil remains record the δ18O values of the lake water in which they grow. Our lake water δ18O reconstruction is supported by downcore agreement with δ18O values in aquatic moss and chironomid remains. δ18O of both organic materials from Secret Lake decrease after 4 ka (ka = thousands of years ago) by 3‰ into the Neoglacial. We argue that lake water at Secret Lake primarily reflects precipitation δ18O values, which is strongly correlated with air temperature in NW Greenland, and that this signal is biased towards summer and early autumn conditions. Other factors may have influenced Secret Lake δ18O values through the Holocene, including evaporation of lake water and changing seasonality and source of precipitation. The maximum early Holocene summer and early autumn-biased temperature anomaly at Secret Lake is 2.5-4 °C warmer than present from 7.7 (the beginning of our record) to ∼6 ka. The maximum late Holocene cold anomaly (which includes the Little Ice Age) is 1.5-3 °C colder than present. These ranges of possible temperature anomalies reflect uncertainty in the δ18O - temperature relationship for precipitation at the study site through the Holocene.

  5. Holocene Abrupt Climate Change Over NW Iran: The Hand That Rocked The Cradle Of Civilization?

    Science.gov (United States)

    Sharifi, A.; Pourmand, A.; Canuel, E. A.; Ferer-Tyler, E.; Peterson, L. C.; Aichner, B.; Feakins, S. J.; Daryaee, T.; Djamali, M.; Naderi Beni, A.; Lahijani, H. A. K.; Swart, P. K.

    2014-12-01

    Human civilizations around the globe have been influenced by abrupt climate change throughout the Holocene. The paucity of high-resolution palaeoclimate data from the "Cradle of Civilization" in West Asia, however, has limited our ability to evaluate the potential role of Holocene climate variability on early societies. We present a high-resolution, multi-proxy reconstruction of aeolian input and palaeoenvironmental conditions based on a 13-kyr record of ombrotrophic (rain fed) peat from Neor Lake in Northwest Iran. Variations in relative abundances of major and trace elements, total organic carbon (TOC), stable carbon isotopes of TOC (δ13CTOC) and compound-specific leaf wax hydrogen isotope (δD) compositions suggest dry and dusty conditions prevailed during the Younger Dryas, and a substantial increase in atmospheric dust loading and decrease in moisture availability occurred between the early and late Holocene. In addition, variations in radiogenic Sr-Nd-Hf isotopic composition and REE anomalies in samples from Neor peat core indicate significant shifts occurred in source contributions of eolian material to the study area between the Younger Dryas, early and late Holocene. Time-series analysis of aeolian input to NE Iran reveals periodicities at 540, 1050 and 2940 years that correspond with solar variability and internal climate feedbacks identified in other records of Holocene climate change from the northern hemisphere. Transitions in major Mesopotamian and Persian civilizations, including the collapse of the Akkadian empire at 4,200 yr BP, the fall of the Ur III empire at 3,955 yr BP, the fall of Elam empire at 2,500 yr BP and the demise of the Achaemenids around 2,280 BP overlap with major dust events from this study. Several other episodes of enhanced atmospheric dust, however, are not reflected in historical or archaeological accounts of the late Holocene. This indicates either abrupt climate change was not the sole driver of societal changes in the

  6. Holocene carbon dynamics at the forest-steppe ecotone of southern Siberia.

    Science.gov (United States)

    Mackay, Anson William; Seddon, Alistair W R; Leng, Melanie J; Heumann, Georg; Morley, David W; Piotrowska, Natalia; Rioual, Patrick; Roberts, Sarah; Swann, George E A

    2016-12-09

    The forest-steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to push the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a deeper understanding of long-term forest-steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to understanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m(-2)  yr(-1) ) and isotope composition of organic matter (δ(13) CTOC ). Forest-steppe dynamics were reconstructed using pollen, and diatom records provided measures of primary production from near- and off-shore communities. We used a generalized additive model (GAM) to identify significant change points in temporal series, and by applying generalized linear least-squares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon dynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to abrupt sub-Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR values range between 2.8 and 12.5 g C m(-2)  yr(-1) . Peak burial rates (and greatest variability) occurred during the early Holocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the neoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr bp provide compelling evidence for the sensitivity of the region to sub-Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake Baikal sediments during the Holocene, almost one-quarter of which was buried during the early Holocene alone. Combined, our results highlight the importance of understanding the close linkages between carbon cycling and hydrological processes, not just temperatures, in southern Siberian

  7. Asynchronous Changes in Vegetation, Runoff and Erosion in the Nile River Watershed during the Holocene

    NARCIS (Netherlands)

    Blanchet, C.; Frank, M.; Schouten, S.

    2014-01-01

    The termination of the African Humid Period in northeastern Africa during the early Holocene was marked by the southward migration of the rain belt and the disappearance of the Green Sahara. This interval of drastic environmental changes was also marked by the initiation of food production by North

  8. Early

    Directory of Open Access Journals (Sweden)

    Kamel Abd Elaziz Mohamed

    2014-04-01

    Conclusion: Early PDT is recommended for patients who require prolonged tracheal intubation in the ICU as outcomes like the duration of mechanical ventilation length of ICU stay and hospital stay were significantly shorter in early tracheostomy.

  9. Tropical Peat and Peatland Development in the Floodplains of the Greater Pamba Basin, South-Western India during the Holocene.

    Directory of Open Access Journals (Sweden)

    Navnith K P Kumaran

    Full Text Available Holocene sequences in the humid tropical region of Kerala, South-western (SW India have preserved abundance of organic-rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub-coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon-lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0-3.0 m thickness in coastal lowlands and river basins during the shorter interval in the Middle Holocene. Vast areas of the coastal plains of Kerala have been converted into carbon rich peatland during the Middle Holocene and transforming the entire coastal stretch and associated landforms as one of the relatively youngest peatlands in the extreme southern tip of India. Unlike the uninterrupted formation of peatlands of considerable extent during the Holocene in Southeast Asia, the south Peninsular Indian region has restricted and short intervals of peatlands in the floodplains and coastal lowlands. Such a scenario is attributed to the topographic relief of the terrain and the prevailing hydrological regimes and environmental conditions as a consequence of monsoon variability since Middle Holocene in SW India. Considering the tropical coastal lowlands and associated peatlands are excellent repositories of carbon, they are very important for regional carbon cycling and habitat diversity. The

  10. Tropical Peat and Peatland Development in the Floodplains of the Greater Pamba Basin, South-Western India during the Holocene

    Science.gov (United States)

    Padmalal, Damodaran; Limaye, Ruta B.; S., Vishnu Mohan; Jennerjahn, Tim; Gamre, Pradeep G.

    2016-01-01

    Holocene sequences in the humid tropical region of Kerala, South-western (SW) India have preserved abundance of organic—rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub—coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon—lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0–3.0 m thickness in coastal lowlands and river basins during the shorter interval in the Middle Holocene. Vast areas of the coastal plains of Kerala have been converted into carbon rich peatland during the Middle Holocene and transforming the entire coastal stretch and associated landforms as one of the relatively youngest peatlands in the extreme southern tip of India. Unlike the uninterrupted formation of peatlands of considerable extent during the Holocene in Southeast Asia, the south Peninsular Indian region has restricted and short intervals of peatlands in the floodplains and coastal lowlands. Such a scenario is attributed to the topographic relief of the terrain and the prevailing hydrological regimes and environmental conditions as a consequence of monsoon variability since Middle Holocene in SW India. Considering the tropical coastal lowlands and associated peatlands are excellent repositories of carbon, they are very important for regional carbon cycling and habitat diversity. The alarming rate of

  11. Tropical Peat and Peatland Development in the Floodplains of the Greater Pamba Basin, South-Western India during the Holocene.

    Science.gov (United States)

    Kumaran, Navnith K P; Padmalal, Damodaran; Limaye, Ruta B; S, Vishnu Mohan; Jennerjahn, Tim; Gamre, Pradeep G

    2016-01-01

    Holocene sequences in the humid tropical region of Kerala, South-western (SW) India have preserved abundance of organic-rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub-coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon-lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0-3.0 m thickness in coastal lowlands and river basins during the shorter interval in the Middle Holocene. Vast areas of the coastal plains of Kerala have been converted into carbon rich peatland during the Middle Holocene and transforming the entire coastal stretch and associated landforms as one of the relatively youngest peatlands in the extreme southern tip of India. Unlike the uninterrupted formation of peatlands of considerable extent during the Holocene in Southeast Asia, the south Peninsular Indian region has restricted and short intervals of peatlands in the floodplains and coastal lowlands. Such a scenario is attributed to the topographic relief of the terrain and the prevailing hydrological regimes and environmental conditions as a consequence of monsoon variability since Middle Holocene in SW India. Considering the tropical coastal lowlands and associated peatlands are excellent repositories of carbon, they are very important for regional carbon cycling and habitat diversity. The alarming rate of land