WorldWideScience

Sample records for early holocene warming

  1. 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

  2. Recent evolution and divergence among populations of a rare Mexican endemic, Chihuahua spruce, following holocene climatic warming

    Science.gov (United States)

    F. Thomas Ledig; Virginia Jacob-Cervantes; Paul D. Hodgskiss

    1997-01-01

    Fragmentation and reduction in population size are expected to reduce genetic diversity. However, examples from natural populations of forest trees are scarce. The range of Chihuahua spruce retreated northward and fragmented coincident with the warming climate that marked the early Holocene. The isolated populations vary from 15 to 2441 trees, which provided an...

  3. Anticyclonic atmospheric circulation as an analogue for the warm and dry mid-Holocene summer climate in central Scandinavia

    Directory of Open Access Journals (Sweden)

    K. Antonsson

    2008-10-01

    Full Text Available Climate reconstructions from central Scandinavia suggest that annual and summer temperatures were rising during the early Holocene and reached their maximum after 8000 cal yr BP. The period with highest temperatures was characterized by increasingly low lake-levels and dry climate, with driest and warmest conditions at about 7000 to 5000 cal yr BP. We compare the reconstructed climate pattern with simulations of a climate model for the last 9000 years and show that the model, which is predominantly driven by solar insolation patterns, suggests less prominent mid-Holocene dry and warm period in Scandinavia than the reconstructions. As an additional explanation for the reconstructed climate, we argue that the trend from the moist early Holocene towards dry and warm mid-Holocene was caused by a changing atmospheric circulation pattern with a mid-Holocene dominance of summer-time anticyclonic circulation. An extreme case of the anticyclonic conditions is the persistent blocking high, an atmospheric pressure pattern that at present often causes long spells of particularly dry and warm summer weather, or "Indian summers". The argument is tested with daily instrumental temperature and precipitation records in central Sweden and an objective circulation classification based on surface air pressure over the period 1900–2002. We conclude that the differences between the precipitation and temperature climates under anticyclonic and non-anticyclonic conditions are significant. Further, warm and dry combination, as indicated by mid-Holocene reconstructions, is a typical pattern under anticyclonic conditions. These results indicate that the presented hypothesis for the mid-Holocene climate is likely valid.

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

    Science.gov (United States)

    Cui, Jianxin; Zhou, Shangzhe; Chang, Hong

    2009-02-01

    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.

  5. Comparing and contrasting Holocene and Eemian warm periods with greenhouse-gas-induced warming

    International Nuclear Information System (INIS)

    MacCracken, M.C.; Kutzbach, J.

    1990-01-01

    Periods of the past that are estimated to have been warmer than present are of great potential interest for comparison with simulations of future climates associated with greenhouse-gas-induced warming. Certain features of the climates of the mid-Holocene and Eemian periods, both interglacial maxima, are described. The simulated climatic responses to both types of forcing, in terms of land/ocean and latitudinal averages, are also compared. The zonal average and annual (or seasonal) average radiation fluxes associated with the different-from-present orbital conditions that existed for those interglacials are compared to the radiation flux associated with CO 2 -induced warming. There are some similarities but also significant differences in the two types of radiation flux perturbations, and there are both similarities and differences in the simulated climatic responses

  6. Insolation driven biomagnetic response to Holocene Warm Period in semi-arid East Asia

    NARCIS (Netherlands)

    Liu, S.; Deng, Chenglong; Xiao, Jule; Li, Jinhua; Paterson, Greig; Chang, Liao; Yi, Liang; Qin, Huafeng; Pan, Yongxin; Zhu, Rixiang

    2015-01-01

    The Holocene Warm Period (HWP) provides valuable insights into the climate system and biotic responses to environmental variability and thus serves as an excellent analogue for future global climate changes. Here we document, for the first time, that warm and wet HWP conditions were highly

  7. 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

  8. Insolation driven biomagnetic response to the Holocene Warm Period in semi-arid East Asia

    OpenAIRE

    Liu, Suzhen; Deng, Chenglong; Xiao, Jule; Li, Jinhua; Paterson, Greig A.; Chang, Liao; Yi, Liang; Qin, Huafeng; Pan, Yongxin; Zhu, Rixiang

    2015-01-01

    The Holocene Warm Period (HWP) provides valuable insights into the climate system and biotic responses to environmental variability and thus serves as an excellent analogue for future global climate changes. Here we document, for the first time, that warm and wet HWP conditions were highly favourable for magnetofossil proliferation in the semi-arid Asian interior. The pronounced increase of magnetofossil concentrations at ~9.8?ka and decrease at ~5.9?ka in Dali Lake coincided respectively wit...

  9. Insolation driven biomagnetic response to Holocene Warm Period in semi-arid East Asia

    OpenAIRE

    Liu, S.; Deng, Chenglong; Xiao, Jule; Li, Jinhua; Paterson, Greig; Chang, Liao; Yi, Liang; Qin, Huafeng; Pan, Yongxin; Zhu, Rixiang

    2015-01-01

    The Holocene Warm Period (HWP) provides valuable insights into the climate system and biotic responses to environmental variability and thus serves as an excellent analogue for future global climate changes. Here we document, for the first time, that warm and wet HWP conditions were highly favourable for magnetofossil proliferation in the semi-arid Asian interior. The pronounced increase of magnetofossil concentrations at ~9.8 ka and decrease at ~5.9 ka in Dali Lake coincided respectively wit...

  10. 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

    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....... 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...

  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

    , et al., 2013). Reconstruction of the Early Holocene average July air temperatures based on chironomid analysis showed that in the middle of the Peninsula air T July were around + 10.3oC which is below the modern values. A sharp warming took place then during the Mid Holocene optimum (Ilyashuk, 2000; Ilyashuk, 2013). The reconstructed Early Holocene T July of the southern part of the Peninsula are similar to the modern T July + 12oC. For a detailed reconstruction of paleogeographic environments of the south-western part of the Kola Peninsula in Holocene we studied the valley of Kolvica river and the southern shore of lake Kolvitsa (67.01-67.11 N; 33.17-33.48 E). Analysis of lithological sequences and radiocarbon dating of sediments of small lakes present a clear outline of the development of the studied region from 9.3 14C ka (10.5 cal. ka BP) to the present day. Based on micro-paleontological analyzes we performed a qualitative reconstruction of climatic conditions during the Holocene, which shows a clear change of cooling and warming in the studied area, as well as the dynamics of the White Sea coastal zone and the development of the studied lake basins. This project was financed by RFBR 15-35-50479 mol_nr.

  12. The NAO Influence on the Early to Mid-Holocene North Atlantic Coastal Upwelling

    Science.gov (United States)

    Hernandez, A.; Cachão, M.; Sousa, P.; Trigo, R. M.; Freitas, M. C.

    2017-12-01

    Coastal upwelling regions yield some of the oceanic most productive ecosystems, being crucial for the worldwide social and economic development. Most upwelling systems, emerging cold nutrient-rich deep waters, are located in the eastern boundaries of the Atlantic and Pacific basins, and are driven by meridional wind fields parallel to the coastal shore. These winds are associated with the subsiding branch of the large-scale Anticyclonic high pressure systems that dominate the subtropical ocean basins, and therefore can be displaced or intensified within the context of past and future climate changes. However, the role of the current global warming influencing the coastal upwelling is, as yet, unclear. Therefore it is essential to derive a long-term perspective, beyond the era of instrumental measurements, to detect similar warm periods in the past that have triggered changes in the upwelling patterns. In this work, the upwelling dynamics in the Iberian North Atlantic margin during the early and mid-Holocene is reconstructed, using calcareous nannofossils from a decadally resolved estuarine sediment core located in southwestern Portugal. Results suggest that the coastal dynamics reflects changes in winds direction likely related to shifts in the NAO-like conditions. Furthermore, the reconstructed centennial-scale variations in the upwelling are synchronous with changes in solar irradiance, a major external forcing factor of the climate system that is known to exert influence in atmospheric circulation patterns. In addition, these proxy-based data interpretations are in agreement with wind field and solar irradiance simulation modelling for the mid-Holocene. Therefore, the conclusion that the solar activity via the NAO modulation controlled the North Atlantic upwelling of western Iberia during the early and mid-Holocene at decadal to centennial timescales can be derived. The financial support for attending this meeting was possible through FCT project UID/GEO/50019

  13. Insolation driven biomagnetic response to the Holocene Warm Period in semi-arid East Asia

    Science.gov (United States)

    Liu, Suzhen; Deng, Chenglong; Xiao, Jule; Li, Jinhua; Paterson, Greig A.; Chang, Liao; Yi, Liang; Qin, Huafeng; Pan, Yongxin; Zhu, Rixiang

    2015-01-01

    The Holocene Warm Period (HWP) provides valuable insights into the climate system and biotic responses to environmental variability and thus serves as an excellent analogue for future global climate changes. Here we document, for the first time, that warm and wet HWP conditions were highly favourable for magnetofossil proliferation in the semi-arid Asian interior. The pronounced increase of magnetofossil concentrations at ~9.8 ka and decrease at ~5.9 ka in Dali Lake coincided respectively with the onset and termination of the HWP, and are respectively linked to increased nutrient supply due to postglacial warming and poor nutrition due to drying at ~6 ka in the Asian interior. The two-stage transition at ~7.7 ka correlates well with increased organic carbon in middle HWP and suggests that improved climate conditions, leading to high quality nutrient influx, fostered magnetofossil proliferation. Our findings represent an excellent lake record in which magnetofossil abundance is, through nutrient availability, controlled by insolation driven climate changes.

  14. Oleistocene mammals in the late-early Holocene in Santa Lucia river basin (Uruguay southern)

    International Nuclear Information System (INIS)

    Ubilla, M.; Perea, D.; Corona, A.; Rinderknecht, A.; Sanchez, A.

    2012-01-01

    This work is about the fossileferous outcrops belongs to the late Pleistocene - early Holocene in Santa Lucia River. It enable to analyse the last records of megafauna vertebrate extinctions (olistecene mammals) with the climate conditions / environment

  15. 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

    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......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...

  16. Early-Holocene decoupled summer temperature and monsoon precipitation in southwest China

    Science.gov (United States)

    Wu, D.; Chen, F.; Chen, X.; Lv, F.; Zhou, A.; Chen, J.; Abbott, M. B.; Yu, J.

    2017-12-01

    Proxy based reconstructions of Holocene temperature have shown that both the timing and magnitude of the thermal maximum vary substantially between different regions; the simulations results from climate models also show that summers were substantially cooler over regions directly influenced by the presence of the Laurentide ice sheet during the early Holocene, whereas other regions of the Northern Hemisphere were dominated by orbital forcing. However, for lack of summer temperature reconstruction in the low latitude regions like southwestern China dominated by the Indian summer monsoon, the Holocene summer temperature variations and it underlying forcing mechanism are ambiguous. Here we present a well-dated record of pollen-based quantitative summer temperature (mean July; MJT) over the last 14000 years from Xingyun Lake, Yunnan Province, southwest China. It was found that MJT decreased during the YD event, then increased slowly until 7400 yr BP, and decreased thereafter. The MJT shows a pattern with middle Holocene maximum of MJT, indicating a different changing pattern with the carbonate oxygen isotope record (d18O) from the same core during the early Holocene (11500-7400 yr BP), which has the similar variation with speleothem d18O record from Dongge cave, both indicate the variation of monsoon precipitation with the highest precipitation occurred during the early Holocene. Therefore, we propose that the variation of summer temperature and precipitation in southwest China was decoupled during the early Holocene. However, both MJT and monsoon precipitation decreased after the middle Holocene following the boreal summer insolation. We suggest that the high precipitation with strong summer monsoon and hence higher cloud cover may depress the temperature increasing forced by increasing summer insolation during the early Holocene; while melting ice-sheet in the high latitude regions had strongly influenced the summer temperature increase during the deglacial period

  17. Subfossil markers of climate change during the Roman Warm Period of the late Holocene

    Science.gov (United States)

    Jach, Renata; Knutelski, Stanisław; Uchman, Alfred; Hercman, Helena; Dohnalik, Marek

    2018-02-01

    Abundant bog oak trunks occur in alluvial deposits of the Raba River in the village of Targowisko (southern Poland). Several of them contain galleries of the great capricorn beetle ( Cerambyx cerdo L.). A well-preserved subfossil larva and pupa, as well as adults of this species, are concealed in some of the galleries. These galleries co-occur with boring galleries of other insects such as ship-timber beetles (Lymexylidae) and metallic wood borers (Buprestidae). A dry larva of a stag beetle (Lucanidae) and a mite (Acari) have been found in the C. cerdo galleries. Selected samples of the trunks and a sample of the C. cerdo larva were dated, using radiocarbon and dendrochronological methods, to the period from 45 bc to ad 554; one sample was dated to the period from 799 to 700 bc. Accumulation of the channel alluvia containing the bog oak trunks is synchronous with the Roman Warm Period (late antiquity/Early Mediaeval times). The most recent part of this period correlates with massive accumulations of fallen oak trunks noted from various river valleys in the Carpathian region and dated to ad 450-570. The results indicate that C. cerdo was more abundant within the study area during the Roman Warm Period than it is today.

  18. A humid early Holocene in Yemen interpreted from palaeoecology and taxonomy of freshwater ostracods

    Science.gov (United States)

    Mohammed, Munef; Frenzel, Peter; Keyser, Dietmar; Hussain, Fadhl; Abood, Abdulkareem; Sha'af, Abdulmajed; Alzara'e, Sadham; Alammari, Sakher

    2018-01-01

    Lake or marsh sediments in the Qa'a Jahran-Dhamār area indicate a period of higher moisture availability in the early Holocene of the highlands of Yemen. Forty-two marl-peat sediment samples from eight stratigraphic sections of that area have been collected and are examined for the first time for their ostracod associations. Eight species belonging to seven genera and four families are reported. Their ecological tolerances and preferences are used to investigate the climatic and environmental changes in the early to mid-Holocene. Our data are compared and correlated with previous archaeological results, particularly from the region of Qa'a Jahran (Dhamār) in the vicinity of the village of Beyt Nahmi. We conclude that the wettest period of the Holocene was from about 7900 to 7400 cal yr BP, when northwards incursion of the Indian Ocean Monsoon caused intensified monsoon precipitation over southern Arabia.

  19. 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.

  20. 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.

  1. 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.

  2. Testing the Millennial-Scale Holocene Solar-Climate Connection in the Indo-Pacific Warm Pool

    Science.gov (United States)

    Khider, D.; Emile-Geay, J.; McKay, N.; Jackson, C. S.; Routson, C.

    2016-12-01

    The existence of 1000 and 2500-year periodicities found in reconstructions of total solar irradiance (TSI) and a number of Holocene climate records has led to the hypothesis of a causal relationship. However, attributing Holocene millennial-scale variability to solar forcing requires a mechanism by which small changes in total irradiance can influence a global climate response. One possible amplifier within the climate system is the ocean. If this is the case, then we need to know more about where and how this may be occurring. On the other hand, the similarity in spectral peaks could be merely coincidental, and this should be made apparent by a lack of coherence in how that power and phasing are distributed in time and space. The plausibility of the solar forcing hypothesis is assessed through a Bayesian model of the age uncertainties affecting marine sedimentary records that is propagated through spectral analysis of the climate and forcing signals at key frequencies. Preliminary work on Mg/Ca and alkenone records from the Indo-Pacific Warm Pool suggests that despite large uncertainties in the location of the spectral peaks within each individual record arising from age model uncertainty, sea surface variability on timescales of 1025±36 years and 2427±133 years (±standard error of the mean of the median periodicity in each record) are present in at least 95% and 70% of the ensemble spectra, respectively. However, we find a long phase delay between the peak in forcing and the maximum response in at least one of the records, challenging the solar forcing hypothesis and requiring further investigation between low- and high-latitude signals. Remarkably, all records suggest a periodicity near 1470±85 years, reminiscent of the cycles characteristic of Marine Isotope Stage 3; these cycles are absent from existing records of TSI, further questioning the millennial solar-climate connection.

  3. 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...

  4. Early Holocene hydroclimate of Baffin Bay: Understanding the interplay between abrupt climate change events and ice sheet fluctuations

    Science.gov (United States)

    Corcoran, M. C.; Thomas, E. K.; Castañeda, I. S.; Briner, J. P.

    2017-12-01

    Understanding the causes of ice sheet fluctuations resulting in sea level rise is essential in today's warming climate. In high-latitude ice-sheet-proximal environments such as Baffin Bay, studying both the cause and the rate of ice sheet variability during past abrupt climate change events aids in predictions. Past climate reconstructions are used to understand ice sheet responses to changes in temperature and precipitation. The 9,300 and 8,200 yr BP events are examples of abrupt climate change events in the Baffin Bay region during which there were multiple re-advances of the Greenland and Laurentide ice sheets. High-resolution (decadal-scale) hydroclimate variability near the ice sheet margins during these abrupt climate change events is still unknown. We will generate a decadal-scale record of early Holocene temperature and precipitation using leaf wax hydrogen isotopes, δ2Hwax, from a lake sediment archive on Baffin Island, western Baffin Bay, to better understand abrupt climate change in this region. Shifts in temperature and moisture source result in changes in environmental water δ2H, which in turn is reflected in δ2Hwax, allowing for past hydroclimate to be determined from these compound-specific isotopes. The combination of terrestrial and aquatic δ2Hwax is used to determine soil evaporation and is ultimately used to reconstruct moisture variability. We will compare our results with a previous analysis of δ2Hwax and branched glycerol dialkyl glycerol tetraethers, a temperature and pH proxy, in lake sediment from western Greenland, eastern Baffin Bay, which indicates that cool and dry climate occurred in response to freshwater forcing events in the Labrador Sea. Reconstructing and comparing records on both the western and eastern sides of Baffin Bay during the early Holocene will allow for a spatial understanding of temperature and moisture balance changes during abrupt climate events, aiding in ice sheet modeling and predictions of future sea level

  5. Human response to Holocene warming on the Cantabrian Coast (northern Spain): an unexpected outcome

    Science.gov (United States)

    Marín-Arroyo, Ana B.

    2013-12-01

    Subsistence was characterized during the Pleistocene to Holocene transition on the Cantabrian Coast (northern Spain) by a progressive diet widening, with a greater exploitation of marine environments and a more intense consumption of low-ranked species. This trend was also accompanied by a general and noticeable decrease in the amount of ungulates that were recovered from a set of archaeological sites clearly dominated by shells. The causes behind this change in the economic practice of the last hunter-gatherer groups are still being debated. There are currently two opposing views on the matter, with some scholars defending the role of demographic pressure as the main driving force, while other researchers invoke the importance of the environment in the food procurement preferences that were adopted. Due to their overwhelming abundance, the debate has been mainly focused on marine resources, whereas the comparatively less-represented macromammal assemblages have been poorly interpreted. However, it is precisely this scarcity that makes them so remarkable. Here, a new interpretation of the available data is presented, with a special focus on the identification of overhunting evidence and on the comparative productivity of each type of resource. Altogether, the demographic hypothesis seems to be more coherent with the existing facts.

  6. Scaled biotic disruption during early Eocene global warming events

    NARCIS (Netherlands)

    Gibbs, S.J.; Bown, P.R.; Murphy, B.H.; Sluijs, A.; Edgar, K.M.; Pälike, H.; Bolton, C.T.; Zachos, J.C.

    2012-01-01

    Late Paleocene and early Eocene hyperthermals are transient warming events associated with massive perturbations of the global carbon cycle, and are considered partial analogues for current anthropogenic climate change. Because the magnitude of carbon release varied between the events, they are

  7. Carbon dioxide warming of the early Earth

    Science.gov (United States)

    Arrhenius, G.

    1997-01-01

    Svante Arrhenius' research in atmospheric physics extended beyond the recent past and the near future states of the Earth, which today are at the center of sociopolitical attention. His plan encompassed all of the physical phenomena known at the time to relate to the formation and evolution of stars and planets. His two-volume textbook on cosmic physics is a comprehensive synopsis of the field. The inquiry into the possible cause of the ice ages and the theory of selective wavelength filter control led Arrhenius to consider the surface states of the other terrestrial planets, and of the ancient Earth before it had been modified by the emergence of life. The rapid escape of hydrogen and the equilibration with igneous rocks required that carbon in the early atmosphere prevailed mainly in oxidized form as carbon dioxide, together with other photoactive gases exerting a greenhouse effect orders of magnitude larger than in our present atmosphere. This effect, together with the ensuing chemical processes, would have set the conditions for life to evolve on our planet, seeded from spores spreading through an infinite Universe, and propelled, as Arrhenius thought, by stellar radiation pressure.

  8. 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.

  9. 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.

  10. Early Holocene humidity patterns in the Iberian Peninsula reconstructed from lake, pollen and speleothem records

    Science.gov (United States)

    Morellón, Mario; Aranbarri, Josu; Moreno, Ana; González-Sampériz, Penélope; Valero-Garcés, Blas L.

    2018-02-01

    Comparison of selected, well-dated, lacustrine, speleothem and terrestrial pollen records spanning the Holocene onset and the Early Holocene (ca. 11.7-8 cal kyrs BP) in the Iberian Peninsula shows large hydrological fluctuations and landscape changes with a complex regional pattern in timing and intensity. Marine pollen records from Alboran, the Mediterranean and off shore Atlantic sites show a step-wise increase in moisture and forest during this transition. However, available continental records point to two main patterns of spatial and temporal hydrological variability: i) Atlantic-influenced sites located at the northwestern areas (Enol, Sanabria, Lucenza, PRD-4), characterized by a gradual increase in humidity from the end of the Younger Dryas to the Mid Holocene, similarly to most North Atlantic records; and ii) continental and Mediterranean-influenced sites (Laguna Grande, Villarquemado, Fuentillejo, Padul, Estanya, Banyoles, Salines), with prolonged arid conditions of variable temporal extension after the Younger Dryas, followed by an abrupt increase in moisture at 10-9 cal kyrs BP. Different local climate conditions influenced by topography or the variable sensitivity (gradual versus threshold values) of the proxies analyzed in each case are evaluated. Vegetation composition (conifers versus mesothermophilous taxa) and resilience would explain a subdued response of vegetation in central continental areas while in Mediterranean sites, insufficient summer moisture availability could not maintain high lake levels and promote mesophyte forest, in contrast to Atlantic-influenced areas. Comparison with available climate models, Greenland ice cores, North Atlantic marine sequences and continental records from Central and Northern Europe and the whole Mediterranean region underlines the distinctive character of the hydrological changes occurred in inner Iberia throughout the Early Holocene. The persistent arid conditions might be explained by the intensification

  11. Climate extremes and predicted warming threaten Mediterranean Holocene firs forests refugia.

    Science.gov (United States)

    Sánchez-Salguero, Raúl; Camarero, J Julio; Carrer, Marco; Gutiérrez, Emilia; Alla, Arben Q; Andreu-Hayles, Laia; Hevia, Andrea; Koutavas, Athanasios; Martínez-Sancho, Elisabet; Nola, Paola; Papadopoulos, Andreas; Pasho, Edmond; Toromani, Ervin; Carreira, José A; Linares, Juan C

    2017-11-21

    Warmer and drier climatic conditions are projected for the 21st century; however, the role played by extreme climatic events on forest vulnerability is still little understood. For example, more severe droughts and heat waves could threaten quaternary relict tree refugia such as Circum-Mediterranean fir forests (CMFF). Using tree-ring data and a process-based model, we characterized the major climate constraints of recent (1950-2010) CMFF growth to project their vulnerability to 21st-century climate. Simulations predict a 30% growth reduction in some fir species with the 2050s business-as-usual emission scenario, whereas growth would increase in moist refugia due to a longer and warmer growing season. Fir populations currently subjected to warm and dry conditions will be the most vulnerable in the late 21st century when climatic conditions will be analogous to the most severe dry/heat spells causing dieback in the late 20th century. Quantification of growth trends based on climate scenarios could allow defining vulnerability thresholds in tree populations. The presented predictions call for conservation strategies to safeguard relict tree populations and anticipate how many refugia could be threatened by 21st-century dry spells.

  12. Brief communication: DNA from early Holocene American dog.

    Science.gov (United States)

    Tito, Raul Y; Belknap, Samuel L; Sobolik, Kristin D; Ingraham, Robert C; Cleeland, Lauren M; Lewis, Cecil M

    2011-08-01

    We present the oldest genetically identified dog in the Americas, directly dated to 9,260 ± 170 Cal. B.P. The DNA was extracted from an occipital condyle imbedded in a human paleofecal sample from Hinds Cave in southwest Texas. A 368 base pair fragment of the mitochondrial genome control region was sequenced. These data were analyzed with comparable data, which included other ancient dogs and extant dogs, wolves and coyotes from around the world. Compiled with published data, our results characterize ancient American dogs within clades rooted by Eurasian wolves. In the Americas, these data provide no evidence of local interbreeding with wolves. This is a departure from the genetic pattern in other areas of the world where interbreeding with local wolf populations is apparent. Our discovery of domestic dog bone in a human paleofecal sample provides the earliest direct evidence for human consumption of dogs in the New World. These data support the hypothesis that dogs were a food source for early Paleoamericans. Copyright © 2011 Wiley-Liss, Inc.

  13. Coastal Marsh Longevity, Ecological Succession, and Organic Carbon Dynamics During Early Holocene Sea-Level Rise

    Science.gov (United States)

    Vetter, L.; Schreiner, K. M.; Rosenheim, B. E.; Tornqvist, T. E.

    2016-02-01

    Coastal marsh environments perform essential ecosystem services, including nutrient filtering, soil organic matter storage, and storm surge abatement, yet much is still unknown about their formation and fate under periods of sea-level change. During the early Holocene (7-10 ka), rapid sea-level rise in coastal Louisiana was one of the primary controls over marsh development and longevity. Here, we investigate plant community composition and succession and soil organic matter storage in early Holocene coastal marshes in Louisiana using bulk elemental ratios, lignin phenol biomarkers and stable isotopes from peat layers. Sediment cores were collected in southeastern Louisiana and contain a record of an early Holocene transgressive sea-level sequence 16-25 m below present sea-level. The sedimentary record consists of an immature paleosol overlain by basal peat that accumulated in an estuarine marsh, overlain by marine lagoonal muds. A re-established marsh peat is present 1-4 m above the initial transition to marine conditions, indicating a sequence of marsh development, sea-level rise and onset of marine conditions, and then further marsh development as the rate of relative sea-level rise decelerated. Plant community composition in coastal marshes was determined through cupric oxide oxidation and lignin-phenol and non-lignin-phenol biomarker abundances. The degradation state of soil organic matter and the specific source of stabilized organic matter within the sedimentary peats were determined through lignin-phenol biomarker ratios. Organic matter sources ranged from terrestrial to marine over the course of sea-level rise, and different sites showed different amounts of marine organic matter influence and different levels of terrestrial organic matter degradation. These results have important implications for reconstructing the response of coastal marshes and their plant communities to accelerated rates of sea-level rise projected through 2100.

  14. Case for a wet, warm climate on early Mars

    International Nuclear Information System (INIS)

    Pollack, J.B.; Kasting, J.F.; Richardson, S.M.; Poliakoff, K.

    1987-01-01

    Arguments are presented in support of the idea that Mars possessed a dense CO 2 atmosphere and a wet, warm climate early in its history. The plausibility of a CO 2 greenhouse is tested by formulating a simple model of the CO 2 geochemical cycle on early Mars. By scaling the rate of silicate weathering on Earth, researchers estimated a weathering time constant of the order of several times 10 to the 7th power years for early Mars. Thus, a dense atmosphere could have existed for a geologically significant time period (approx. 10 to the 9th power years) only if atmospheric CO 2 was being continuously resupplied. The most likely mechanism by which this could have been accomplished is the thermal decomposition of carbonate rocks induced directly or indirectly by intense, global scale volcanism

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

    NARCIS (Netherlands)

    Blaschek, M.; Renssen, H.

    2013-01-01

    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

  16. Changes in Ocean Circulation with an Ice-Free Arctic: Reconstructing Early Holocene Arctic Ocean Circulation Using Geochemical Signals from Individual Neogloboquadrina pachyderma (sinistral) Shells

    Science.gov (United States)

    Livsey, C.; Spero, H. J.; Kozdon, R.

    2016-12-01

    The impacts of sea ice decrease and consequent hydrologic changes in the Arctic Ocean will be experienced globally as ocean and atmospheric temperatures continue to rise, though it is not evident to what extent. Understanding the structure of the Arctic water column during the early/mid Holocene sea ice minimum ( 6-10 kya), a post-glacial analogue of a seasonally ice-free Arctic, will help us to predict what the changes we can expect as the Earth warms over the next century. Neogloboquadrina pachyderma (sinistral; Nps) is a species of planktonic foraminifera that dominates assemblages in the polar oceans. This species grows its chambers (ontogenetic calcite) in the surface waters and subsequently descends through the water column to below the mixed layer where it quickly adds a thick crust of calcite (Kohfeld et al., 1996). Therefore, geochemical signals from both the surface waters and sub-mixed layer depths are captured within single Nps shells. We were able to target ion mass spectrometry (SIMS), therefore capturing signals from both the ontogenetic and crust calcite in single Nps shells. This data was combined with laser ablation- inductively coupled mass spectrometry (LA-ICPMS) Mg/Ca profiles of trace metals through the two layers of calcite of the same shells, to determine the thermal structure of the water column. Combining δ18O, temperature, and salinity gradients from locations across the Arctic basin allow us to reconstruct the hydrography of the early Holocene Arctic sea ice minimum. These results will be compared with modern Arctic water column characteristics in order to develop a conceptual model of Arctic Ocean oceanographic change due to global warming. Kohfeld, K.E., Fairbanks, R.G., Smith, S.L., Walsh, I.D., 1996. Neogloboquadrina pachyderma(sinistral coiling) as paleoceanographic tracers in polar oceans: Evidence from northeast water polynya plankton tows, sediment traps, and surface sediments. Paleoceanography 11, 679-699.

  17. Late Glacial to Early Holocene socio-ecological responses to climatic instability within the Mediterranean basin

    Science.gov (United States)

    Fernández-López de Pablo, Javier; Jones, Samantha E.; Burjachs, Francesc

    2018-03-01

    The period spanning the Late Glacial and the Early Holocene (≈19-8.2 ka) witnessed a dramatic sequence of climate and palaeoenvironmental changes (Rasmussen et al., 2014). Interestingly, some of the most significant transformations ever documented in human Prehistory took place during this period such as the intensification of hunter-gatherer economic systems, the domestication process of wild plants and animals, and the spread of farming across Eurasia. Understanding the role of climate and environmental dynamics on long-term cultural and economic trajectories, as well as specific human responses to episodes of rapid climate change, still remains as one of the main challenges of archaeological research (Kintigh et al., 2014).

  18. Attractiveness of the landscape: Reconstruction of Early to Middle Holocene landscape and occupation history of Flevoland (central Netherlands)

    Science.gov (United States)

    Van den Biggelaar, Don; Kluiving, Sjoerd; Van Balen, Ronald; Kasse, Kees; Kolen, Jan

    2013-04-01

    The onset of the Holocene (11 500 BP) is marked by climate warming. Climate warming induced the growth of vegetation, which in combination with precipitation and a long period of non-deposition resulted in the formation of soils at the top of the Pleistocene deposits. As these soils have been present at the surface in Flevoland (central Netherlands) during most of the Mesolithic and Neolithic period, the top Pleistocene is an important archaeological level. Prior to the 1990s, prehistoric occupation in wetland areas, such as the Flevoland region, was seen as a challenging living environment due to its marginal nature. However, since the early 1990s a different approach was raised concerning the suitability of wetland occupation by Mesolithic and Neolithic people. Instead of adapting to the natural conditions, prehistoric people selected an area suitable to their way of life. The question remains why it took so long (Mesolithic-Neolithic transition period: 5300-4600 cal BC) for the inhabitants of the Lower Rhine Basin to adapt to the Neolithic lifestyle, in contrast to the adaptation in the loess zone and later in Britain. This difference in adaptation of the Neolithic lifestyle during this transition period cannot be solely explained by a difference in attitude or other cultural arguments. As postglacial sea-level rise caused large parts of Flevoland (central Netherlands) to inundate during the Late Mesolithic and Early Neolithic, the availability of natural resources also changed. It is hypothesized that the availability of a wide range of natural resources, and not exclusively the soil type, predominantly determined the suitability and attractiveness of a region for hunter/gatherers and therefore delayed the transition to a Neolithic lifestyle. To test this hypothesis we have compared two selected areas on the basis of the following parameters: elevation, slope gradient relative to sea-level rise, soil type, past vegetation and the number of archaeological

  19. Liquefaction along Late Pleistocene to early Holocene Faults as Revealed by Lidar in Northwest Tasmania, Australia

    Science.gov (United States)

    Webb, J.; Gardner, T.

    2016-12-01

    In northwest Tasmania well-preserved mid-Holocene beach ridges with maximum radiocarbon ages of 5.25 ka occur along the coast; inland are a parallel set of lower relief beach ridges of probable MIS 5e age. The latter are cut by northeast-striking faults clearly visible on LIDAR images, with a maximum vertical displacement (evident as difference in topographic elevation) of 3 m. Also distinct on the LIDAR images are large sand boils along the fault lines; they are up to 5 m in diameter and 2-3 m high and mostly occur on the hanging wall close to the fault traces. Without LIDAR it would have been almost impossible to distinguish either the fault scarps or the sand boils. Excavations through the sand boils show that they are massive, with no internal structure, suggesting that they formed in a single event. They are composed of well-sorted, very fine white sand, identical to the sand in the underlying beach ridges. The sand boils overlie a peaty paleosol; this formed in the tea-tree swamp that formerly covered the area, and has been offset along the faults. Radiocarbon dating of the buried organic-rich paleosol gave ages of 14.8-7.2 ka, suggesting that the faulting is latest Pleistocene to early Holocene in age; it occurred prior to deposition of the mid-Holocene beach ridges, which are not offset. The beach ridge sediments are up to 7 m thick and contain an iron-cemented hard pan 1-3 m below the surface. The water table is very shallow and close to the ground surface, so the sands of the beach ridges are mostly saturated. During faulting these sands experienced extensive liquefaction. The resulting sand boils rose to a substantial height of 2-3 m, probably possibly reflecting the elevation of the potentiometric surface within the confined part of the beach ridge sediments below the iron-cemented hard pan. Motion on the faults was predominantly dip slip (shown by an absence of horizontal offset) and probably reverse, which is consistent with the present-day northwest

  20. 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.

  1. Scaled biotic disruption during early Eocene global warming events

    Directory of Open Access Journals (Sweden)

    S. J. Gibbs

    2012-11-01

    Full Text Available Late Paleocene and early Eocene hyperthermals are transient warming events associated with massive perturbations of the global carbon cycle, and are considered partial analogues for current anthropogenic climate change. Because the magnitude of carbon release varied between the events, they are natural experiments ideal for exploring the relationship between carbon cycle perturbations, climate change and biotic response. Here we quantify marine biotic variability through three million years of the early Eocene that include five hyperthermals, utilizing a method that allows us to integrate the records of different plankton groups through scenarios ranging from background to major extinction events. Our long time-series calcareous nannoplankton record indicates a scaling of biotic disruption to climate change associated with the amount of carbon released during the various hyperthermals. Critically, only the three largest hyperthermals, the Paleocene–Eocene Thermal Maximum (PETM, Eocene Thermal Maximum 2 (ETM2 and the I1 event, show above-background variance, suggesting that the magnitude of carbon input and associated climate change needs to surpass a threshold value to cause significant biotic disruption.

  2. Preliminary Study of Late Pleistocene to Early Holocene Plant Food Strategies in China

    Science.gov (United States)

    Hayashi Tang, M.; Liu, X.; Fritz, G.; Zhao, Z.

    2017-12-01

    In recent decades, studies on the domestication and early cultivation of seed crops have contributed significantly to how we understand human-plant interactions, and their impact on human social organisation and the environment. It is becoming clear, however, that plants have been critical to the human diet for much longer and in more diverse ways than previously assumed. This paper is a preliminary attempt at identifying and addressing early prehistoric plant food strategies in China. In particular, very little is known about the use of vegetatively propagated plants, despite their significant representation in modern crops. Many ingredients of Chinese medicine are also roots and tubers (or vegetative storage organs, VSOs). Unlike seed crops, however, we lack a systematic criterion for examining diagnostic characters of different VSO taxa in the archaeological record. To address this issue, we characterized commonly consumed and historically significant VSOs in China, by studying experimentally charred modern samples under the optical microscope and scanning electron microscope. We then compared the characteristics of these modern VSO samples against plant remains from Late Pleistocene to early Holocene archaeological sites in China, such as Zengpiyan (Guangxi), Zhaoguodong (Guizhou), and Jiahu (Henan) sites. We found that different taxa of VSOs can be differentiated by using multiple lines of evidence, including: shape and size of various cells, texture and arrangement of cell walls, as well as anatomical arrangements of organs, especially the vascular bundles. Though identification can be difficult when fragile cell structures have collapsed or deteriorated, more robust features are often preserved for diagnosis. Our results suggest that the potential for studying the role of vegetatively propagated plants in early human-environmental interactions is overlooked, and can be expanded significantly with further investment in their systematic identification.

  3. 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

    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......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...... 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...

  4. Sea Surface Temperatures in the Indo-Pacific Warm Pool During the Early Pliocene Warm Period

    Science.gov (United States)

    Dekens, P. S.; Ravelo, A. C.; Griffith, E. M.

    2010-12-01

    The Indo-Pacific warm pool (IPWP) plays an important role in both regional and global climate, but the response of this region to anthropogenic climate change is not well understood. While the early Pliocene is not a perfect analogue for anthropogenic climate change, it is the most recent time in Earth history when global temperatures were warmer than they are today for a sustained period of time. SST in the eastern equatorial Pacific was 2-4○C warmer in the early Pliocene compared to today. A Mg/Ca SST at ODP site 806 in the western equatorial Pacific indicates that SST were stable through the last 5Ma (Wara et al., 2005). We generated a G. sacculifer Mg/Ca record in the Indian Ocean (ODP sit 758) for the last 5 Ma, which also shows that IPWP SST has remained relatively stable through the last 5 Ma and was not warmer in the early Pliocene compared today. A recent paper suggests that the Mg/Ca of seawater may have varied through the last 5 Ma and significantly affected Mg/Ca SST estimates (Medina-Elizalde et al., 2008). However, there is considerable uncertainty in the estimates of seawater Mg/Ca variations through time. We will present a detailed examination of these uncertainties to examine the possible range of seawater Mg/Ca through the last 5 Ma. Due to the lack of culturing work of foraminifera at different Mg/Ca ratios in the growth water there is also uncertainty in how changes in seawater Mg/Ca will affect the temperatures signal in the proxy. We will explore how uncertainties in the record of seawater Mg/Ca variations through time and its effect on the Mg/Ca SST proxy potentially influence the interpretation of the Mg/Ca SST records at ODP sites 806 and 758 in the IPWP, and ODP site 847 in the eastern equatorial Pacific. We will also explore how adjustment of the Mg/Ca SST estimates (due to reconstructed Mg/Ca seawater variations) affects the δ18O of water when adjusted Mg/Ca SST estimates are paired with δ18O measurements of the same samples.

  5. Early-Holocene greening of the Afro-Asian dust belt changed sources of mineral dust in West Asia

    Science.gov (United States)

    Sharifi, Arash; Murphy, Lisa N.; Pourmand, Ali; Clement, Amy C.; Canuel, Elizabeth A.; Naderi Beni, Abdolmajid; Lahijani, Hamid A. K.; Delanghe, Doriane; Ahmady-Birgani, Hesam

    2018-01-01

    Production, transport and deposition of mineral dust have significant impacts on different components of the Earth systems through time and space. In modern times, dust plumes are associated with their source region(s) using satellite and land-based measurements and trajectory analysis of air masses through time. Reconstruction of past changes in the sources of mineral dust as related to changes in climate, however, must rely on the knowledge of the geochemical and mineralogical composition of modern and paleo-dust, and that of their potential source origins. In this contribution, we present a 13,000-yr record of variations in radiogenic Sr-Nd-Hf isotopes and Rare Earth Element (REE) anomalies as well as dust grain size from an ombrotrophic (rain fed) peat core in NW Iran as proxies of past changes in the sources of dust over the interior of West Asia. Our data shows that although the grain size of dust varies in a narrow range through the entire record, the geochemical fingerprint of dust particles deposited during the low-flux, early Holocene period (11,700-6,000 yr BP) is distinctly different from aerosols deposited during high dust flux periods of the Younger Dryas and the mid-late Holocene (6,000-present). Our findings indicate that the composition of mineral dust deposited at the study site changed as a function of prevailing atmospheric circulation regimes and land exposure throughout the last deglacial period and the Holocene. Simulations of atmospheric circulation over the region show the Northern Hemisphere Summer Westerly Jet was displaced poleward across the study area during the early Holocene when Northern Hemisphere insolation was higher due to the Earth's orbital configuration. This shift, coupled with lower dust emissions simulated based on greening of the Afro-Asian Dust Belt during the early Holocene likely led to potential sources in Central Asia dominating dust export to West Asia during this period. In contrast, the dominant western and

  6. Estuarine development and early Holocene transgression across an aeolianite substrate, Caesarea, central Israel

    Science.gov (United States)

    Goff, John A.; Austin, James A.; Goodman-Tchernov, Beverly N.

    2018-04-01

    Estuaries are important features on the coastal landscape due to their potential for rich, diverse, and abundant resources. The modern coast of the southeast Mediterranean is largely devoid of estuaries except in rare circumstances where ample sands are delivered to the shore, such as east of the Nile Delta. Whether or not today's condition is reflective of that present during lower sea-levels is greatly speculative in part due to a dearth of high-resolution sub-surface mapping in the shallower (sediments in water depths 45-10 mbsl, both within paleo-channels of the Crocodile and Hadera rivers, and more broadly across the shelf. These water depths correspond to early Holocene dates ( 10.5-7.5 ka) which, based on global sea-level curves, was a period of rapid ( 1-1.7 cm/yr) sea-level rise. Now-submerged aeolianite ridges (locally referred to as 'kurkar'), cemented aeolian deposits formed during pre-Last-Glacial-Maximum (LGM) seaward advance (regression) of the coastline, likely provided some offshore barrier for estuarine development. These were insufficient, however, to account for all the estuarine deposition interpreted, leading us to hypothesize that sand-constructed barrier islands were also present as sea-level rose during the Holocene. This supply of sand, clearly greater than what is evident today, could have originated from sea-level rise phase eroding Nile Delta sediments transported northward by littoral currents, or from increased output from local rivers during wetter climatic conditions. We also observe a transition from linear, shore-parallel aeolianite ridge morphology features on land and in shallow water, to nested, arcuate features below 30 mbsl. Whereas the linear ridges are thought to be coastal foredune remnants abandoned by the retreating shoreline, the arcuate forms resemble fossil parabolic (blowout) dunes. Based on the recent initiation of parabolic dunes on Cape Cod following anthropogenic denudation of forests there, we suggest that

  7. Early onset of significant local warming in low latitude countries

    International Nuclear Information System (INIS)

    Mahlstein, I; Knutti, R; Solomon, S; Portmann, R W

    2011-01-01

    The Earth is warming on average, and most of the global warming of the past half-century can very likely be attributed to human influence. But the climate in particular locations is much more variable, raising the question of where and when local changes could become perceptible enough to be obvious to people in the form of local warming that exceeds interannual variability; indeed only a few studies have addressed the significance of local signals relative to variability. It is well known that the largest total warming is expected to occur in high latitudes, but high latitudes are also subject to the largest variability, delaying the emergence of significant changes there. Here we show that due to the small temperature variability from one year to another, the earliest emergence of significant warming occurs in the summer season in low latitude countries (∼25 deg. S-25 deg. N). We also show that a local warming signal that exceeds past variability is emerging at present, or will likely emerge in the next two decades, in many tropical countries. Further, for most countries worldwide, a mean global warming of 1 deg. C is sufficient for a significant temperature change, which is less than the total warming projected for any economically plausible emission scenario. The most strongly affected countries emit small amounts of CO 2 per capita and have therefore contributed little to the changes in climate that they are beginning to experience.

  8. Lithostratigraphy and microfacies analyses of the Lateglacial and early Holocene sediment record from Lake Haemelsee (Germany)

    Science.gov (United States)

    Haliuc, Aritina; Brauer, Achim; Dulski, Peter; Engels, Stefan; Lane, Christine

    2015-04-01

    Annually laminated sediments are unique continental archives holding essential paleoenvironmental and paleoclimatic information providing the opportunity (i) to evaluate the climate variability at inter-annual to decadal scale and (ii) to construct independent and reliable chronologies. Lake Haemelsee in northern Germany (19.5 m a.s.l) is a key site for tracing high-resolution climatic and environmental evolution in W Europe because of its partly varved sediments. Here, we apply lithostratigraphical, geochemical and micro-facies analyses for the bottom sediments (~1700 to 1300 cm sediment depth) in order to investigate the driving mechanisms, timing and amplitude of Lateglacial abrupt climate changes to the onset of the Holocene warming. Detailed investigation includes micro-facies analyses on petrographic thin sections combined with high-resolution µ-XRF element scanning on both fresh sediment core halves (200 µm resolution) and impregnated sediment blocks (50µm resolution). Based on these analyses, the sediment composite profile (378 cm) has been divided in ten lithozones, each exhibiting different sedimentation modes in response to regional and local climatic and environmental changes. Micro-facies analyses revealed that sediments consist of organic matter, siderite, calcite, clay/silt and sand. The basal sediments consist of glacio-fluvial material. Fine laminations are best preserved in lithozone 5 (1522-1573 cm), where minima in element proxies for detrital sediments (Ti, K, Si) and maxima in Fe and Mn indicate the prevalence of anoxic meromictic conditions. Three different varve facies types were distinguished: i) the clastic-organic varves are specific for the intervals 1571-1573 cm and 1536-1541 cm; ii) calcite/siderite-organic varves appear between 1568-1571 and 1541-1545 cm; iii) the siderite-organic varves are characteristic for the middle of the lithozone 5 spanning from 1545-1568 cm. These changes in varve facies reflect the complex answer of

  9. Astrochronology of extreme global warming events during the early Eocene greenhouse climate

    NARCIS (Netherlands)

    Lauretano, V.

    2016-01-01

    The early Eocene represents an ideal case study to analyse the impact of enhanced global warming on the ocean-atmosphere system and the relationship between carbon cycling and climate. During this time interval, the Earth’s surface experienced a long-term warming trend that culminated in a period of

  10. 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.

  11. Permafrost distribution in peatlands of west-central Canada during the Holocene warm period 6000 years BP

    Energy Technology Data Exchange (ETDEWEB)

    Zoltai, S.C. [Canadian Forest Service, Edmonton, AB (Canada)

    1995-12-31

    The extent and timing of permafrost development in peatlands of west-central Canada are examined. The floristic composition of the permafrost peatlands was determined from macrofossil samples of cores drilled at 161 locations. Radiocarbon dating of substantial changes in the peat sequences and of basal peat deposition was used to provide chronological control. The reconstructed paleoenvironments show the presence or absence of permafrost at the time of peat formation. Permafrost distribution in peatlands is estimated during the warm period 6000 years BP. It is estimated that the mean annual temperature was approximately 5{degree}C warmer than at present. 42 refs., 3 figs., 4 tabs.

  12. Powerful warm infrared sources in early-type galaxies

    International Nuclear Information System (INIS)

    Dressel, L.L.

    1988-01-01

    IRAS far-infrared sources have been identified with 129 S0, Sa, Sb, and Sc galaxies in a statistically complete sample of 738 galaxies brighter than 14.5 mag and smaller than 4.0 arcmin. In most cases, the far-IR colors and the ratios of far-IR flux to radio flux density are those of normal galactic disks and/or starbursts. The most powerful far-IR sources in S0 and Sa galaxies are just as powerful as the strongest far-IR sources in Sb and Sc galaxies. Bright-IR sources in S0 and Sa galaxies are warm; those in Sc galaxies are cool. Sb galaxies have both warm and cool IR sources. Bright warm IR sources occur much more frequently in barred galaxies than in galaxies without bars for types S0, Sa, and Sb. Bright, cool IR sources are found with increasing frequency along the Hubble sequence, regardless of the presence or absence of a bar. At least some S0 galaxies with warm, bright IR sources have peculiar morphologies and ambiguous classifications. 22 references

  13. 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

  14. Multidecadal variations in the early Holocene outflow of Red Sea Water into the Arabian Sea

    NARCIS (Netherlands)

    Jung, S.J.A.; Ganssen, G.M.; Davies, G.R.

    2001-01-01

    We present Holocene stable oxygen isotope data from the deep Arabian Sea off Somalia at a decadal time resolution as a proxy for the history of intermediate/upper deep water. These data show an overall δ18O reduction by 0.5‰ between 10 and ~6.5 kyr B.P. superimposed upon short-term δ18O variations

  15. Mediterranean moisture source for an Early-Holocene humid period in the Northern Red Sea

    NARCIS (Netherlands)

    Arz, H.W.; Lamy, F.; Paetzold, J.; Mueller, P.J.; Prins, M.A.

    2003-01-01

    Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about

  16. The power of paradigms : examining the evidential basis for Early to Mid-Holocene pigs and pottery in Melanesia

    International Nuclear Information System (INIS)

    O'Connor, S.; Barham, A.; Aplin, K.; Dobney, K.; Fairbairn, A.; Richards, M.

    2011-01-01

    The origin and timing of the introduction of pigs and pottery into New Guinea are continuous topics. Arguments have centred on whether domestic pigs and pottery technology entered New Guinea following the 'Austronesian expansion' from southeast Asia into Island Melanesia, c 3300 calBP, or in the Early to Mid-Holocene. We review the history of the debate and present new dates on pig bone and pottery contexts from archaeological sites, including Taora and Lachitu, on the north coast of mainland Papua New Guinea (PNG), where earlier data supported claims for early pig and pottery. We argue that theoretical positions about 'Neolithic' origins in PNG influenced the relative willingness to accept early dates prima facie and conclude that current evidence shows neither pig nor pottery arrived before 3000 calBP in mainland PNG. (author). 96 refs., 11 figs., 6 tabs.

  17. Early onset of industrial-era warming across the oceans and continents.

    Science.gov (United States)

    Abram, Nerilie J; McGregor, Helen V; Tierney, Jessica E; Evans, Michael N; McKay, Nicholas P; Kaufman, Darrell S

    2016-08-25

    The evolution of industrial-era warming across the continents and oceans provides a context for future climate change and is important for determining climate sensitivity and the processes that control regional warming. Here we use post-ad 1500 palaeoclimate records to show that sustained industrial-era warming of the tropical oceans first developed during the mid-nineteenth century and was nearly synchronous with Northern Hemisphere continental warming. The early onset of sustained, significant warming in palaeoclimate records and model simulations suggests that greenhouse forcing of industrial-era warming commenced as early as the mid-nineteenth century and included an enhanced equatorial ocean response mechanism. The development of Southern Hemisphere warming is delayed in reconstructions, but this apparent delay is not reproduced in climate simulations. Our findings imply that instrumental records are too short to comprehensively assess anthropogenic climate change and that, in some regions, about 180 years of industrial-era warming has already caused surface temperatures to emerge above pre-industrial values, even when taking natural variability into account.

  18. People, lakes and seashores: Studies from the Baltic Sea basin and adjacent areas in the early and Mid-Holocene

    Science.gov (United States)

    Groß, Daniel; Zander, Annabell; Boethius, Adam; Dreibrodt, Stefan; Grøn, Ole; Hansson, Anton; Jessen, Catherine; Koivisto, Satu; Larsson, Lars; Lübke, Harald; Nilsson, Björn

    2018-04-01

    During the Early and Mid-Holocene significant changes in the ecology and socio-cultural spheres occurred around the Baltic Sea. Because of the underlying climatic changes and thus environmental alterations, the area was the scene for various cultural developments during the period under investigation. In the course of the melting of the glaciers at the end of the last Ice Age, isostatic and eustatic movements caused continual changes to the Baltic Sea basin. Changes in water level, however, affected not only the Early and Mid-Holocene coastlines, but also the whole Baltic Sea drainage system, including large lakes, rivers and watersheds in the hinterland were also dramatically impacted by these ecological changes. Prehistoric people were thus affected by changes in resource availability and reduction or enlargement of their territories, respectively. In order to evaluate the impact of changes in the water and land networks on the environment, resource availability, and human behaviour, and to reconstruct human responses to these changes, we pursue an interdisciplinary approach connecting environmental and archaeological research highlighted through different case studies.

  19. 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.

  20. Multidecadal variations in the early Holocene outflow of Red Sea Water into the Arabian Sea

    OpenAIRE

    Jung, S.J.A.; Ganssen, G.M.; Davies, G.R.

    2001-01-01

    We present Holocene stable oxygen isotope data from the deep Arabian Sea off Somalia at a decadal time resolution as a proxy for the history of intermediate/upper deep water. These data show an overall δ18O reduction by 0.5‰ between 10 and ~6.5 kyr B.P. superimposed upon short-term δ18O variations at a decadal-centennial timescale. The amplitude of the decadal variations is 0.3‰ prior, and up to 0.6‰ subsequent, to ~8.1 kyr B.P. We conclude from modeling experiments that the short-term δ18O v...

  1. 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

  2. Early warm-rewarding parenting moderates the genetic contributions to callous-unemotional traits in childhood.

    Science.gov (United States)

    Henry, Jeffrey; Dionne, Ginette; Viding, Essi; Vitaro, Frank; Brendgen, Mara; Tremblay, Richard E; Boivin, Michel

    2018-04-23

    Previous gene-environment interaction studies of CU traits have relied on the candidate gene approach, which does not account for the entire genetic load of complex phenotypes. Moreover, these studies have not examined the role of positive environmental factors such as warm/rewarding parenting. The aim of the present study was to determine whether early warm/rewarding parenting moderates the genetic contributions (i.e., heritability) to callous-unemotional (CU) traits at school age. Data were collected in a population sample of 662 twin pairs (Quebec Newborn Twin Study - QNTS). Mothers reported on their warm/rewarding parenting. Teachers assessed children's CU traits. These reports were subjected to twin modeling. Callous-unemotional traits were highly heritable, with the remaining variance accounted for by nonshared environmental factors. Warm/rewarding parenting significantly moderated the role of genes in CU traits; heritability was lower when children received high warm/rewarding parenting than when they were exposed to low warm/rewarding parenting. High warm/rewarding parenting may partly impede the genetic expression of CU traits. Developmental models of CU traits need to account for such gene-environment processes. © 2018 Association for Child and Adolescent Mental Health.

  3. 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.

  4. Tracking Lateglacial and early Holocene environmental change: a palaeolimnological study of sediment at Preluca Tiganului, NW Romania

    Directory of Open Access Journals (Sweden)

    Angelica Feurdean

    2005-04-01

    Full Text Available Palaeoecological, palaeohydrological, and paleoenvironmental reconstruction of the Late Glacial and the early Holocene have been performed from sediment accumulated in a small former crater lake, in the GutâI Mountains, NW Romania. Pollen, lithology, mineral magnetic, and loss-on-ignition analyses in conjunction to radiocarbon dating have been use for this purpose. The data indicates that during the Late Glacial period, vegetation dynamics were likely driven by climatic fluctuations. The climate events during the Late Glacial are well mirrored in local vegetation assemblage development, and past lake level fluctuations. These climatic events recorded in south-eastern Europe, are well correlated with the climate events from the North Western Europe and Greenland ice core stratigraphy.

  5. Sea-level change and demography during the last glacial termination and early Holocene across the Australian continent

    Science.gov (United States)

    Williams, Alan N.; Ulm, Sean; Sapienza, Tom; Lewis, Stephen; Turney, Chris S. M.

    2018-02-01

    Future changes in sea-level are projected to have significant environmental and social impacts, but we have limited understanding of comparable rates of change in the past. Using comprehensive palaeoenvironmental and archaeological datasets, we report the first quantitative model of the timing, spatial extent and pace of sea-level change in the Sahul region between 35-8 ka, and explore its effects on hunter-gatherer populations. Results show that the continental landmass (excluding New Guinea) increased to 9.80 million km2 during the Last Glacial Maximum (LGM), before a reduction of 2.12 million km2 (or ∼21.6%) to the early Holocene (8 ka). Almost 90% of this inundation occurs during and immediately following Meltwater Pulse (MWP) 1a between 14.6 and 8 ka. The location of coastlines changed on average by 139 km between the LGM and early Holocene, with some areas >300 km, and at a rate of up to 23.7 m per year (∼0.6 km land lost every 25-year generation). Spatially, inundation was highly variable, with greatest impacts across the northern half of Australia, while large parts of the east, south and west coastal margins were relatively unaffected. Hunter-gatherer populations remained low throughout (hypothesis that late Pleistocene coastal populations were low, with use of coastal resources embedded in broad-ranging foraging strategies, and which would have been severely disrupted in some regions and at some time periods by sea-level change outpacing tolerances of mangals and other near-shore ecological communities.

  6. 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.

  7. Early Mars: A Warm Wet Niche for Life

    Science.gov (United States)

    Gibson, Everett K.; McKay, David S.; Thomas-Keprta, Kathie L.; Clemett, Simon J.

    2010-01-01

    Exploration of Mars has begun to unveil the history of the planet. Combinations of remote sensing, in situ compositional measurements and photographic observations have shown Mars had a dynamic and active geologic evolution. Mars geologic evolution had conditions that were suitable for supporting life. A habitable planet must have water, carbon and energy sources along with a dynamic geologic past. Mars meets all of these requirements. The first 600 Ma of Martian history were ripe for life to develop because of the abundance of: (i) Water-as shown by carved canyons and oceans or lakes with the early presence of near surface water shown by precipitated carbonates in ALH84001, well-dated at approx.3.9 Ga, (ii) Energy from the original accretional processes, a molten core which generated a strong magnetic field leaving a permanent record in the early crust, active volcanism continuing throughout Martian history, and continuing impact processes, (iii) Carbon, water and a likely thicker atmosphere from extensive volcanic outgassing (i.e. H2O, CO2, CH4, CO, O2, N2, H2S, SO2, etc.) and (iv) crustal tectonics as revealed by faulting and possible plate movement reflected by the magnetic patterns in the crust [1]. The question arises: "Why would life not develop from these favorable conditions on Mars in its first 600 Ma?" During this period, environmental near-surface conditions on Mars were more favorable to life than at any later time. Standing bodies of water, precipitation and flowing surface water, and possibly abundant hydrothermal energy would favor the formation of early life. (Even if life developed elsewhere on Earth, Venus, or on other bodies-it was transported to Mars where surface conditions were suitable for life to evolve)

  8. An approach to palaeoseismicity in the Olkiluoto (sea) area during the early holocene

    International Nuclear Information System (INIS)

    Hutri, K.L.

    2007-06-01

    Olkiluoto Island is situated in the northern Baltic Sea, near the southwestern coast of Finland, and is the proposed location of a spent nuclear fuel repository. This study examined Holocene palaeoseismicity in the Olkiluoto area and in the surrounding sea areas by computer simulations together with acoustic-seismic, sedimentological and dating methods. The most abundant rock type on the island is migmatic mica gneiss, intruded by tonalites, granodiorites and granites. The surrounding Baltic Sea seabed consists of Palaeoproterozoic crystalline bedrock, which is to a great extent covered by younger Mesoproterozoic sedimentary rocks. The area contains several ancient deep-seated fracture zones that divide it into bedrock blocks. The response of bedrock at the Olkiluoto site was modelled considering four future ice-age scenarios. Each scenario produced shear displacements of fractures with different times of occurrence and varying recovery rates. Generally, the larger the maximum ice load, the larger were the permanent shear displacements. For a basic case, the maximum shear displacements were a few centimetres at the proposed nuclear waste repository level, at proximately 500 m b.s.l. high-resolution, low-frequency echo-sounding was used to examine the Holocene submarine sedimentary structures and possible direct and indirect indicators of palaeoseismic activity in the northern Baltic Sea. Echo-sounding profiles of Holocene submarine sediments revealed slides and slumps, normal faults, debris flows and turbidite-type structures. The profiles also showed pockmarks and other structures related to gas or groundwater seepages, which might be related to fracture zone activation. Evidence of postglacial reactivation in the study area was derived from the spatial occurrence of some of the structures, especial the faults and the seepages, in the vicinity of some old bedrock fracture zones. Palaeoseismic event(s) (a single or several events) in the Olkiluoto area were dated

  9. Multidecadal variations in the early Holocene outflow of Red Sea Water into the Arabian Sea

    Science.gov (United States)

    Jung, S. J. A.; Ganssen, G. M.; Davies, G. R.

    2001-12-01

    We present Holocene stable oxygen isotope data from the deep Arabian Sea off Somalia at a decadal time resolution as a proxy for the history of intermediate/upper deep water. These data show an overall δ18O reduction by 0.5‰ between 10 and ˜6.5 kyr B.P. superimposed upon short-term δ18O variations at a decadal-centennial timescale. The amplitude of the decadal variations is 0.3‰ prior, and up to 0.6‰ subsequent, to ˜8.1 kyr B.P. We conclude from modeling experiments that the short-term δ18O variations between 10 and ˜6.5 kyr B.P. most likely document changes in the evaporation-precipitation balance in the central Red Sea. Changes in water temperature and salinity cause the outflowing Red Sea Water to settle roughly 800 m deeper than today.

  10. Palaeoceanographic and biotic response during early Eocene extreme global warming events. Geologica Ultraiectina (328)

    NARCIS (Netherlands)

    Stap, H.L.

    2010-01-01

    Studying past intervals of abrupt global warming and massive carbon release can improve our knowledge in ways relevant to understanding future climate change. Possible paleo-analogues for future climate change are the early Paleogene hyperthermal events, such as the Paleocene-Eocene Thermal Maximum

  11. 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

  12. Precise Surface Exposure Dating of Early Holocene and Little Ice Age Moraines in the Cordillera Vilcabamba of Southern Peru

    Science.gov (United States)

    Licciardi, J. M.; Schaefer, J. M.; Lund, D. C.; Taggart, J. R.

    2008-12-01

    We have established precise ages of two glacial events in the tropical Andean highlands of southern Peru. The field site is located on the flanks of Nevado Salcantay (6271 m asl; 13°20'S latitude), the highest peak in the Cordillera Vilcabamba. A two-fold sequence of nested lateral and end moraines was mapped in a glacial trough emanating from the south face of Salcantay. Well-defined outer and inner moraines were deposited by valley glaciers that terminated 5 km and 3 km, respectively, from their head on the Salcantay massif. Cosmogenic 10Be surface exposure dating of boulders on the outer (n = 7) and inner (n = 7) moraine crests expands upon initial age control for these deposits and improves substantially on the precision of earlier 10Be measurements. The new results yield mean ages of 9.0 ± 0.3 ka for the outer moraine and 195 ± 24 years for the inner moraine, corresponding to glacial events during the early and latest Holocene. These ages are derived using the CRONUS-Earth 10Be exposure age calculator with Lal-Stone production rate scaling and the default height-pressure relationship. The inner moraine age correlates with the timing of the Little Ice Age as defined from northern mid- and high latitude records, and indicates considerable expansion of glaciers heading on Nevado Salcantay during this climatic minimum. Recent geomorphic mapping has identified similar sequences of moraines in adjacent drainages on and near Salcantay, suggesting a broader regional signal of two prominent Holocene glacial events in this segment of the southern Peruvian Andes; 10Be dating of these additional moraines is underway. Our new glacier chronologies complement ice core and lacustrine paleoclimate records in the vicinity, thereby increasing spatial and temporal coverage for identifying patterns of climate change in the tropical Andes during the Holocene. Apart from their paleoclimatic significance, the results also demonstrate a newly- developed capability of 10Be exposure

  13. Variability of East Asian summer monsoon precipitation during the Holocene and possible forcing mechanisms

    Science.gov (United States)

    Lu, Fuzhi; Ma, Chunmei; Zhu, Cheng; Lu, Huayu; Zhang, Xiaojian; Huang, Kangyou; Guo, Tianhong; Li, Kaifeng; Li, Lan; Li, Bing; Zhang, Wenqing

    2018-03-01

    Projecting how the East Asian summer monsoon (EASM) rainfall will change with global warming is essential for human sustainability. Reconstructing Holocene climate can provide critical insight into its forcing and future variability. However, quantitative reconstructions of Holocene summer precipitation are lacking for tropical and subtropical China, which is the core region of the EASM influence. Here we present high-resolution annual and summer rainfall reconstructions covering the whole Holocene based on the pollen record at Xinjie site from the lower Yangtze region. Summer rainfall was less seasonal and 30% higher than modern values at 10-6 cal kyr BP and gradually declined thereafter, which broadly followed the Northern Hemisphere summer insolation. Over the last two millennia, however, the summer rainfall has deviated from the downward trend of summer insolation. We argue that greenhouse gas forcing might have offset summer insolation forcing and contributed to the late Holocene rainfall anomaly, which is supported by the TraCE-21 ka transient simulation. Besides, tropical sea-surface temperatures could modulate summer rainfall by affecting evaporation of seawater. The rainfall pattern concurs with stalagmite and other proxy records from southern China but differs from mid-Holocene rainfall maximum recorded in arid/semiarid northern China. Summer rainfall in northern China was strongly suppressed by high-northern-latitude ice volume forcing during the early Holocene in spite of high summer insolation. In addition, the El Niño/Southern Oscillation might be responsible for droughts of northern China and floods of southern China during the late Holocene. Furthermore, quantitative rainfall reconstructions indicate that the Paleoclimate Modeling Intercomparison Project (PMIP) simulations underestimate the magnitude of Holocene precipitation changes. Our results highlight the spatial and temporal variability of the Holocene EASM precipitation and potential forcing

  14. Warming Early Mars by Impact Degassing of Reduced Greenhouse Gases

    Science.gov (United States)

    Haberle, R. M.; Zahnle, K.; Barlow, N. G.

    2018-01-01

    Reducing greenhouse gases are once again the latest trend in finding solutions to the early Mars climate dilemma. In its current form collision induced absorptions (CIA) involving H2 and/or CH4 provide enough extra greenhouse power in a predominately CO2 atmosphere to raise global mean surface temperatures to the melting point of water provided the atmosphere is thick enough and the reduced gases are abundant enough. Surface pressures must be at least 500 mb and H2 and/or CH4 concentrations must be at or above the several percent level for CIA to be effective. Atmospheres with 1-2 bars of CO2 and 2- 10% H2 can sustain surface environments favorable for liquid water. Smaller concentrations of H2 are sufficient if CH4 is also present. If thick CO2 atmospheres with percent level concentrations of reduced gases are the solution to the faint young Sun paradox for Mars, then plausible mechanisms must be found to generate and sustain the gases. Possible sources of reducing gases include volcanic outgassing, serpentinization, and impact delivery; sinks include photolyis, oxidation, and escape to space. The viability of the reduced greenhouse hypothesis depends, therefore, on the strength of these sources and sinks. In this paper we focus on impact delivered reduced gases.

  15. Simple technologies and diverse food strategies of the Late Pleistocene and Early Holocene at Huaca Prieta, Coastal Peru.

    Science.gov (United States)

    Dillehay, Tom D; Goodbred, Steve; Pino, Mario; Vásquez Sánchez, Víctor F; Tham, Teresa Rosales; Adovasio, James; Collins, Michael B; Netherly, Patricia J; Hastorf, Christine A; Chiou, Katherine L; Piperno, Dolores; Rey, Isabel; Velchoff, Nancy

    2017-05-01

    Simple pebble tools, ephemeral cultural features, and the remains of maritime and terrestrial foods are present in undisturbed Late Pleistocene and Early Holocene deposits underneath a large human-made mound at Huaca Prieta and nearby sites on the Pacific coast of northern Peru. Radiocarbon ages indicate an intermittent human presence dated between ~15,000 and 8000 calendar years ago before the mound was built. The absence of fishhooks, harpoons, and bifacial stone tools suggests that technologies of gathering, trapping, clubbing, and exchange were used primarily to procure food resources along the shoreline and in estuarine wetlands and distant mountains. The stone artifacts are minimally worked unifacial stone tools characteristic of several areas of South America. Remains of avocado, bean, and possibly cultivated squash and chile pepper are also present, suggesting human transport and consumption. Our new findings emphasize an early coastal lifeway of diverse food procurement strategies that suggest detailed observation of resource availability in multiple environments and a knowledgeable economic organization, although technologies were simple and campsites were seemingly ephemeral and discontinuous. These findings raise questions about the pace of early human movement along some areas of the Pacific coast and the level of knowledge and technology required to exploit maritime and inland resources.

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

    Directory of Open Access Journals (Sweden)

    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.

  17. PALEOENVIRONMENTAL RECONSTRUCTION FROM BENTHIC FORAMINIFERAL ASSEMBLAGES OF EARLY HOLOCENE, SHALLOW MARINE DEPOSITS IN GOMBONG, CENTRAL JAVA

    Directory of Open Access Journals (Sweden)

    Luli Gustiani

    2017-07-01

    Full Text Available A 30m-long sediment core covering the Holocene period was taken from the area of Gombong in the southern part of Central Java. The sediments were deposited in a shallow marine to lagoonal environment that was confirmed by the dominance of Ammonia beccarii along the core intervals. In addition, the species Quinqueloculina poeyana, Miliolinella lakemacquariensis, and Miliolinella subrotunda were also found in the sediments that are typical of normal shallow marine conditions. The decrease and increase in the abundance of these species throughout the core is an expression of sea level change in the area, which results the environmental changes. Low sea level is expressed by the dominance of Ammonia beccarii, and the low abundances or absence of the other three species. In contrast, high sea level stands are reflected by the presence of all four species. The high sea level would imply favorable conditions for benthic foraminifera because it would result in normal shallow marine conditions in the area. Finally, from this benthic assemblages study, it can be assumed that the environmental transformation from the originally shallow marine environment into land was occurred at level 5.5m depths of the sediment core, when all benthic foraminifera were terminated, including Ammonia beccarii. These new results from the shallow marine deposits in the Gombong area are a new contribution to the understanding of paleoenvironmental change in the region, which in turn is important for understanding sea level change as well as climate change in the region.

  18. Developmental and physiological challenges of octopus (Octopus vulgaris) early life stages under ocean warming.

    Science.gov (United States)

    Repolho, Tiago; Baptista, Miguel; Pimentel, Marta S; Dionísio, Gisela; Trübenbach, Katja; Lopes, Vanessa M; Lopes, Ana Rita; Calado, Ricardo; Diniz, Mário; Rosa, Rui

    2014-01-01

    The ability to understand and predict the effects of ocean warming (under realistic scenarios) on marine biota is of paramount importance, especially at the most vulnerable early life stages. Here we investigated the impact of predicted environmental warming (+3 °C) on the development, metabolism, heat shock response and antioxidant defense mechanisms of the early stages of the common octopus, Octopus vulgaris. As expected, warming shortened embryonic developmental time by 13 days, from 38 days at 18 °C to 25 days at 21 °C. Concomitantly, survival decreased significantly (~29.9 %). Size at hatching varied inversely with temperature, and the percentage of smaller premature paralarvae increased drastically, from 0 % at 18 °C to 17.8 % at 21 °C. The metabolic costs of the transition from an encapsulated embryo to a free planktonic form increased significantly with warming, and HSP70 concentrations and glutathione S-transferase activity levels were significantly magnified from late embryonic to paralarval stages. Yet, despite the presence of effective antioxidant defense mechanisms, ocean warming led to an augmentation of malondialdehyde levels (an indicative of enhanced ROS action), a process considered to be one of the most frequent cellular injury mechanisms. Thus, the present study provides clues about how the magnitude and rate of ocean warming will challenge the buffering capacities of octopus embryos and hatchlings' physiology. The prediction and understanding of the biochemical and physiological responses to warmer temperatures (under realistic scenarios) is crucial for the management of highly commercial and ecologically important species, such as O. vulgaris.

  19. High Arctic Holocene temperature record from the Agassiz ice cap and Greenland ice sheet evolution.

    Science.gov (United States)

    Lecavalier, Benoit S; Fisher, David A; Milne, Glenn A; Vinther, Bo M; Tarasov, Lev; Huybrechts, Philippe; Lacelle, Denis; Main, Brittany; Zheng, James; Bourgeois, Jocelyne; Dyke, Arthur S

    2017-06-06

    We present a revised and extended high Arctic air temperature reconstruction from a single proxy that spans the past ∼12,000 y (up to 2009 CE). Our reconstruction from the Agassiz ice cap (Ellesmere Island, Canada) indicates an earlier and warmer Holocene thermal maximum with early Holocene temperatures that are 4-5 °C warmer compared with a previous reconstruction, and regularly exceed contemporary values for a period of ∼3,000 y. Our results show that air temperatures in this region are now at their warmest in the past 6,800-7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene. The warmer early Holocene inferred from the Agassiz ice core leads to an estimated ∼1 km of ice thinning in northwest Greenland during the early Holocene using the Camp Century ice core. Ice modeling results show that this large thinning is consistent with our air temperature reconstruction. The modeling results also demonstrate the broader significance of the enhanced warming, with a retreat of the northern ice margin behind its present position in the mid Holocene and a ∼25% increase in total Greenland ice sheet mass loss (∼1.4 m sea-level equivalent) during the last deglaciation, both of which have implications for interpreting geodetic measurements of land uplift and gravity changes in northern Greenland.

  20. 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.

  1. 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

  2. Early-to-middle Holocene sea-level fluctuations, coastal progradation and the Neolithic occupations in Yaojiang valley of southern Hangzhou bay, eastern China

    Science.gov (United States)

    Liu, Y.; Sun, Q.; Fan, D.; Chen, Z.

    2017-12-01

    The formation of Holocene coast in eastern China provided material base for the development of Neolithic civilizations. The coastal Yaojiang valley of south Hangzhou bay was one of the examples where the well-known Neolithic Hemudu Culture (HC) of Eastern China initiated. Here, we studied the early-to-middle Holocene environment changes in relation to sea-level fluctuations on the basis of a serial of sediment cores based on a set of new Accelerator Mass Spectrometry radiocarbon (AMS 14C) chronology. The result indicated that relative sea-level rose rapidly in the Yaojiang valley at the early Holocene, reaching its maximum at ca. 8000-7800 cal yr BP and then decelerated at ca. 7800-7500 cal yr BP. The alluvial plain in Yaojiang valley began to form at the foothills first and then grew towards the valley center accompanying with the sea-level stabilization after ca. 7500 cal yr BP. This progressive progradation of alluvial plain would attract the early arrivals of foragers to dwell at the foothills to engaging in rice farming after ca.7000 cal yr BP and starting the epic Hemudu Culture. The HC people then move down to the valley center as more land became available thanks to sediment aggregation and progradation. The rise and development of HC were closely associated with the sea-level induced landscape changes in Yaojiang valley at the early-middle Holocene, and the unstable hydraulic condition in the valley after 5000 cal yr BP could be accountable for the cultural termination.

  3. Climate, catchment runoff and limnological drivers of carbon and oxygen isotope composition of diatom frustules from the central andean altiplano during the Lateglacial and Early Holocene

    OpenAIRE

    Hernández, Armand; Bao, Roberto; Giralt, Santiago; Sáez, Alberto; Leng, Melanie J.; Barker, Philips A.; Kendrick, C.P.; Sloane, Hilary J.

    2013-01-01

    Diatom-based carbon and oxygen isotope analyses (δ13Cdiatom and δ18Odiatom) were performed on diatomrich laminated sediments of Lake Chungará (Andean Altiplano, northern Chile) deposited during the Lateglacial and Early Holocene (12,400e8300 cal years BP) to reconstruct climate change and environmental response across this major climate transition. The δ13Cdiatom data show both centennial-tomillennial scale changes related to fluctuations in lake productivity and CO2 concentration in the lake...

  4. 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

    2017-12-01

    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.

  5. Palaeoclimate significance of speleothems in crystalline rocks: a test case from the Late Glacial and early Holocene (Vinschgau, northern Italy)

    Science.gov (United States)

    Koltai, Gabriella; Cheng, Hai; Spötl, Christoph

    2018-03-01

    Partly coeval flowstones formed in fractured gneiss and schist were studied to test the palaeoclimate significance of this new type of speleothem archive on a decadal-to-millennial timescale. The samples encompass a few hundred to a few thousand years of the Late Glacial and the early Holocene. The speleothem fabric is primarily comprised of columnar fascicular optic calcite and acicular aragonite, both indicative of elevated Mg / Ca ratios in the groundwater. Stable isotopes suggest that aragonite is more prone to disequilibrium isotope fractionation driven by evaporation and prior calcite/aragonite precipitation than calcite. Changes in mineralogy are therefore attributed to these two internal fracture processes rather than to palaeoclimate. Flowstones formed in the same fracture show similar δ18O changes on centennial scales, which broadly correspond to regional lacustrine δ18O records, suggesting that such speleothems may provide an opportunity to investigate past climate conditions in non-karstic areas. The shortness of overlapping periods in flowstone growth and the complexity of in-aquifer processes, however, render the establishment of a robust stacked δ18O record challenging.

  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. Pedogenic calcite as evidence for an early Holocene dry period in the San Francisco Bay area, California

    Science.gov (United States)

    Borchardt, G.; Lienkaemper, J.J.

    1999-01-01

    Rainfall at the site of Union City, California, during early Holocene time appears to have been about half that of today, 470 mm/yr. We base this conclusion on detailed descriptions and particle-size analyses of 12 soil profiles and 1:20 scale logs of the fluvial stratigraphy in two 100-m-long, 5-m-deep excavations dug perpendicular to the axis of an alluvial fan along the Hayward fault. Subsidence and right-lateral movement along the fault allowed an offset stream to produce a nearly continuous alluvial record documented by 35 14C ages on detrital charcoal. Bk (calcitic) horizons in paleosols developed in the fan suggest that a relatively dry climatic period occurred from 10 to 7 ka (calendar-corrected ages). The pedogenic calcite exists primarily as vertically oriented filaments and fine, cavernous nodules formed at ped intersections. Soils and paleosols formed before 10 ka or since 7 ka did not have Bk horizons. Bk horizons that were buried suddenly at 7 ka were overlain by leached zones averaging 41 ?? 3 cm thick - about half the current depth of leaching.

  8. 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.

  9. Olea europaea L. in the North Mediterranean Basin during the Pleniglacial and the Early-Middle Holocene

    Science.gov (United States)

    Carrión, Yolanda; Ntinou, Maria; Badal, Ernestina

    2010-04-01

    The paper aims to define the natural distribution of Olea europaea L. var. sylvestris (Miller) Lehr. in the North Mediterranean basin during the Pleniglacial and the Early-Middle Holocene by means of the identification of its wood-charcoal and/or wood at prehistoric sites. For this purpose we have reviewed the previously available information and we have combined it with new wood-charcoal analyses data. We have taken under consideration the presence and frequency of O. europaea L. in the available wood-charcoal sequences, the characteristics of the accompanying flora, the associated chrono-cultural contexts, the broader biogeographical context and the AMS dates provided by Olea wood-charcoal or endocarps. According to the available evidence, during the Middle and Late Pleniglacial (ca 59-11.5 ka cal. BP), Olea would have persisted in thermophilous refugia located in the southern areas of the North Mediterranean basin, the southern Levant and the north of Africa. The Last Glacial Maximum (ca 22-18 ka cal. BP) probably reduced the distribution area of Olea. During the Preboreal and the Boreal (ca 11 500-8800 cal. BP) the species started to expand in the thermomediterranean bioclimatic level. In the western Mediterranean, during the Atlantic period (ca 8800-5600 cal. BP), the species became very abundant or dominant in the thermophilous plant formations and expanded to favorable enclaves outside the limits of the thermomediterranean level.

  10. Cosmogenic 10Be Dating of Early and Latest Holocene Moraines on Nevado Salcantay in the Southern Peruvian Andes

    Science.gov (United States)

    Licciardi, J. M.; Schaefer, J. M.; Lund, D. C.

    2007-12-01

    A two-fold sequence of nested lateral and end moraines was mapped in a glacial trough emanating from the southwest flank of Nevado Salcantay (6271 m; ~13°S latitude), the highest peak in the Cordillera Vilcabamba of southern Peru. The field area is situated 25 km due south of the archaeological site of Machu Picchu. Outer and inner moraines in the sequence were deposited by valley glaciers that terminated ~5 km and ~3 km, respectively, from their headwall on the Salcantay summit massif. Cosmogenic 10Be surface exposure dating of granitic boulders sampled on the Salcantay moraines is underway and has provided the first numerical ages for these deposits. Initial results indicate ages of 8.1 ± 0.1 10Be ka for the outer moraine and 200 ± 20 10Be years for the sharp-crested inner moraine. These ages are derived using the CRONUS-Earth 10Be exposure age calculator (version 2.0) and expressed with respect to the Lal- Stone production rate scaling scheme using the standard atmosphere. The outer and inner moraine ages correspond to glacial events during the early and latest Holocene, respectively. Further 10Be dating of the mapped moraines and similar deposits observed in adjacent drainages on Nevado Salcantay is anticipated to yield a high-resolution chronology of valley glaciation in this segment of the southern Peruvian Andes. The new results bridge an important gap between existing Andean glacier records to the north and south, and complement available ice core and lacustrine paleoclimate records in the vicinity, thereby expanding spatial and temporal coverage for identifying patterns of Holocene climate change in the tropical Andes. Notably, the inner moraine age correlates with the timing of the Little Ice Age as defined in northern mid- and high latitude glacier records, and suggests considerable expansion of valley glaciers in the southern Peruvian Andes during this climatic minimum. Apart from their paleoclimatic significance, the initial results also demonstrate

  11. 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

  12. 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

  13. Alkenone-based reconstructions reveal four-phase Holocene temperature evolution for High Arctic Svalbard

    Science.gov (United States)

    van der Bilt, Willem G. M.; D'Andrea, William J.; Bakke, Jostein; Balascio, Nicholas L.; Werner, Johannes P.; Gjerde, Marthe; Bradley, Raymond S.

    2018-03-01

    Situated at the crossroads of major oceanic and atmospheric circulation patterns, the Arctic is a key component of Earth's climate system. Compounded by sea-ice feedbacks, even modest shifts in the region's heat budget drive large climate responses. This is highlighted by the observed amplified response of the Arctic to global warming. Assessing the imprint and signature of underlying forcing mechanisms require paleoclimate records, allowing us to expand our knowledge beyond the short instrumental period and contextualize ongoing warming. However, such datasets are scarce and sparse in the Arctic, limiting our ability to address these issues. Here, we present two quantitative Holocene-length paleotemperature records from the High Arctic Svalbard archipelago, situated in the climatically sensitive Arctic North Atlantic. Temperature estimates are based on U37K unsaturation ratios from sediment cores of two lakes. Our data reveal a dynamic Holocene temperature evolution, with reconstructed summer lake water temperatures spanning a range of ∼6-8 °C, and characterized by four phases. The Early Holocene was marked by an early onset (∼10.5 ka cal. BP) of insolation-driven Hypsithermal conditions, likely compounded by strengthening oceanic heat transport. This warm interval was interrupted by cooling between ∼10.5-8.3 ka cal. BP that we attribute to cooling effects from the melting Northern Hemisphere ice sheets. Temperatures declined throughout the Middle Holocene, following a gradual trend that was accentuated by two cooling steps between ∼7.8-7 ka cal. BP and around ∼4.4-4.3 ka cal. BP. These transitions coincide with a strengthening influence of Arctic water and sea-ice in the adjacent Fram Strait. During the Late Holocene (past 4 ka), temperature change decoupled from the still-declining insolation, and fluctuated around comparatively cold mean conditions. By showing that Holocene Svalbard temperatures were governed by an alternation of forcings, this study

  14. Insights Into Deglacial Through Holocene Climate Variability At The Peru-Chile Margin From Very High Sedimentation Rate Marine Cores

    Science.gov (United States)

    Chazen, C.; Dejong, H.; Altabet, M.; Herbert, T.

    2007-12-01

    The Peru-Chile upwelling system is situated at the epicenter of the modern ENSO System. The high settling flux of organic materials and poor ventilation of subsurface waters makes the Peru upwelling system one of the world's three major oxygen minimum/denitrification zones (Codispoti and Christensen, 1985). Extremely high sedimentation rates and permanent hypoxic/anoxic subsurface waters create excellent conditions for the preservation of organic matter. Despite the significance of this region in regards to paleoceanography and paleoclimatology, relatively little work has been done to characterize past Peruvian climate because carbonate dissolution hinders the use of conventional paleoclimate methods and hiatuses frequently interrupt the record. However, using nitrogen isotopes and alkenone paleothermometry on multiple sediment cores from the Margin we have managed to overcome many of these challenges to create a nearly continuous SST (Uk`37), productivity (C37total), biogenic opal and denitrification (δN15) record from the LGM through the late Holocene. Remarkably, recent work has revealed an annually laminated core, which spans from 1.4-8.0ka uninterrupted, providing a unique window into Holocene climate variability. Modern-day upwelling induced climate at the Peru-Chile margin is characterized by cold temperatures (21.5°C) high productivity and strong denitrification, which has persisted since the mid Holocene (4ka). The mid Holocene also marks the beginning of a dramatic increase in seasonality and ENSO variability consistent with other tropical climate indicators. Climate variability in the Mid-early Holocene shows a distinctively different pattern from that of the late Holocene; unproductive warm temperatures persist through the early Holocene in what can be described as a permanent El Niño-like state. Early tropical warming occurred near 17ka along with an unprecedented increase in denitrification, which is decoupled from local productivity. Early onset

  15. S-Adenosylmethionine attenuates bile duct early warm ischemia reperfusion injury after rat liver transplantation.

    Science.gov (United States)

    Tang, Yong; Chu, Hongpeng; Cao, Guojun; Du, Xiaolong; Min, Xiaobo; Wan, Chidan

    2018-03-01

    Warm ischemia reperfusion injury (IRI) plays a key role in biliary complication, which is a substantial vulnerability of liver transplantation. The early pathophysiological changes of IRI are characterized by an excessive inflammatory response. S-Adenosylmethionine (SAM) is an important metabolic intermediate that modulates inflammatory reactions; however, its role in bile duct warm IRI is not known. In this study, male rats were treated with or without SAM (170 μmol/kg body weight) after orthotopic autologous liver transplantation. The histopathological observations showed that bile duct injury in the IRI group was more serious than in the SAM group. The alanine aminotransferase (ALT), alkaline phosphatase (ALP) and direct bilirubin (DBIL) levels in the serum of the IRI group were significantly increased compared to the SAM group (P liver and bile duct tissues, down-regulated TNF-α levels and up-regulated IL-10 expression in bile duct tissues compared to the IRI group (P livers were much higher compared to those in SAM-treated rats at 24 h after liver transplantation (P bile ducts against warm IRI by suppressing oxidative stress, inflammatory reactions and apoptosis of biliary epithelial cells after liver transplantation.α. Copyright © 2018 Elsevier Ltd. All rights reserved.

  16. Contributions of a Strengthened Early Holocene Monsoon and Sediment Loading to Present-Day Subsidence of the Ganges-Brahmaputra Delta

    Science.gov (United States)

    Karpytchev, M.; Ballu, V.; Krien, Y.; Becker, M.; Goodbred, S.; Spada, G.; Calmant, S.; Shum, C. K.; Khan, Z.

    2018-02-01

    The contribution of subsidence to relative sea level rise in the Ganges-Brahmaputra delta (GBD) is largely unknown and may considerably enhance exposure of the Bengal Basin populations to sea level rise and storm surges. This paper focuses on estimating the present-day subsidence induced by Holocene sediment in the Bengal Basin and by oceanic loading due to eustatic sea level rise over the past 18 kyr. Using a viscoelastic Earth model and sediment deposition history based on in situ measurements, results suggest that massive sediment influx initiated in the early Holocene under a strengthened South Asian monsoon may have contributed significantly to the present-day subsidence of the GBD. We estimate that the Holocene loading generates up to 1.6 mm/yr of the present-day subsidence along the GBD coast, depending on the rheological model of the Earth. This rate is close to the twentieth century global mean sea level rise (1.1-1.7 mm/yr). Thus, past climate change, by way of enhanced sedimentation, is impacting vulnerability of the GBD populations.

  17. Early to Middle Holocene landscape exploitation in a drying environment: Two case studies compared from the central Sahara (SW Fezzan, Libya)

    Science.gov (United States)

    Cremaschi, Mauro; Zerboni, Andrea

    2009-08-01

    The erg Uan Kasa and the wadi Tanezzuft (Libyan Sahara) reacted in different ways to Holocene climatic changes. Consequently, the human groups settled there responded with different ways of adaptation to the drying environment. In the erg Uan Kasa, shallow lakes were formed from the Early to the Mid-Holocene, and their shores were densely inhabited from the Epipalaeolithic to the Pastoral-Neolithic periods. The erg dried out at c. 5000 years BP, but the area was not completely abandoned, as indicated by minor Late Pastoral-Neolithic sites composed of scattered fireplaces. During the wet Holocene, the wadi Tanezzuft was a large meandering river, and its banks were densely settled. At c. 5000 years BP, the stream was not completely dried out, but it changed its pattern, originating an alluvial plain. A large oasis was formed between c. 4000 and 2000 years BP, exploited by Late Pastoral-Neolithic pastoral communities, and later by Garamantians, which introduced soil management and agricultural practices. The Tanezzuft oasis suffered a drastic reduction in size during the first centuries AD, at the time of the abandonment of the Garamantian settlements.

  18. Fungal decomposition of terrestrial organic matter accelerated Early Jurassic climate warming

    Science.gov (United States)

    Pieńkowski, Grzegorz; Hodbod, Marta; Ullmann, Clemens V.

    2016-08-01

    Soils - constituting the largest terrestrial carbon pool - are vulnerable to climatic warming. Currently existing uncertainties regarding carbon fluxes within terrestrial systems can be addressed by studies of past carbon cycle dynamics and related climate change recorded in sedimentary successions. Here we show an example from the Early Jurassic (early Toarcian, c. 183 mya) marginal-marine strata from Poland, tracking the hinterland response to climatic changes through a super-greenhouse event. In contrast to anoxia-related enhanced carbon storage in coeval open marine environments, Total Organic Carbon (TOC) concentrations in the Polish successions are substantially reduced during this event. Increasing temperature favoured fungal-mediated decomposition of plant litter - specifically of normally resistant woody tissues. The associated injection of oxidized organic matter into the atmosphere corresponds to abrupt changes in standing vegetation and may have contributed significantly to the amplified greenhouse climate on Earth. The characteristic Toarcian signature of multiple warm pulses coinciding with rapidly decreasing carbon isotope ratios may in part be the result of a radical reduction of the terrestrial carbon pool as a response to climate change.

  19. Prebiotic chemistry and atmospheric warming of early Earth by an active young Sun

    Science.gov (United States)

    Airapetian, V. S.; Glocer, A.; Gronoff, G.; Hébrard, E.; Danchi, W.

    2016-06-01

    Nitrogen is a critical ingredient of complex biological molecules. Molecular nitrogen, however, which was outgassed into the Earth’s early atmosphere, is relatively chemically inert and nitrogen fixation into more chemically reactive compounds requires high temperatures. Possible mechanisms of nitrogen fixation include lightning, atmospheric shock heating by meteorites, and solar ultraviolet radiation. Here we show that nitrogen fixation in the early terrestrial atmosphere can be explained by frequent and powerful coronal mass ejection events from the young Sun--so-called superflares. Using magnetohydrodynamic simulations constrained by Kepler Space Telescope observations, we find that successive superflare ejections produce shocks that accelerate energetic particles, which would have compressed the early Earth’s magnetosphere. The resulting extended polar cap openings provide pathways for energetic particles to penetrate into the atmosphere and, according to our atmospheric chemistry simulations, initiate reactions converting molecular nitrogen, carbon dioxide and methane to the potent greenhouse gas nitrous oxide as well as hydrogen cyanide, an essential compound for life. Furthermore, the destruction of N2, CO2 and CH4 suggests that these greenhouse gases cannot explain the stability of liquid water on the early Earth. Instead, we propose that the efficient formation of nitrous oxide could explain a warm early Earth.

  20. Prebiotic Chemistry and Atmospheric Warming of Early Earth by an Active Young Sun

    Science.gov (United States)

    Airapetian, V. S.; Glocer, A.; Gronoff, G.; Hebrard, E.; Danchi, W.

    2016-01-01

    Nitrogen is a critical ingredient of complex biological molecules. Molecular nitrogen, however, which was outgassed Into the Earth's early atmosphere, is relatively chemically inert and nitrogen fixation into more chemically reactive compounds requires high temperatures. Possible mechanisms of nitrogen fixation include lightning, atmospheric shock heating by meteorites, and solar ultraviolet radiation. Here we show that nitrogen fixation in the early terrestrial atmosphere can be explained by frequent and powerful coronal mass ejection events from the young Sun -- so-called superflares. Using magnetohydrodynamic simulations constrained by Kepler Space Telescope observations, we find that successive superflare ejections produce shocks that accelerate energetic particles, which would have compressed the early Earth's magnetosphere. The resulting extended polar cap openings provide pathways for energetic particles to penetrate into the atmosphere and, according to our atmospheric chemistry simulations, initiate reactions converting molecular nitrogen, carbon dioxide and methane to the potent greenhouse gas nitrous oxide as well as hydrogen cyanide, an essential compound for life. Furthermore, the destruction of N2, C02 and CH, suggests that these greenhouse gases cannot explain the stability of liquid water on the early Earth. Instead, we propose that the efficient formation of nitrous oxide could explain a warm early Earth.

  1. Seabird transfer of nutrients and trace elements from the north water polynya to land during the mid-holocene warm period, carey islands, northwest Greenland

    DEFF Research Database (Denmark)

    Outridge, Peter M.; Goodsite, Michael Evan; Bennike, Ole

    2016-01-01

    Seabird guano from large nesting colonies is known to increase trace metal levels in adjacent terrestrial environments today, when global oceans are contaminated with Hg, Cd, and other metals. But the effect of seabird guano in the pre-industrial period has rarely been studied. We used stable C...... and N isotopic and trace element analyses of a peat core that represents ca. 2000 years of organic matter accumulation to examine the effect on trace elements and nutrients of a seabird colony that existed in northern Baffin Bay during the Holocene Thermal Maximum (ca. 8000-5000 yr BP). Although C and N......, in which guano markedly increased environmental Hg concentrations. It could be a consequence of Hg concentrations in Arctic marine food webs in the pre-industrial period that were an order of magnitude lower than those of today....

  2. Unexpected early extinction of the European pond turtle (Emys orbicularis) in Sweden and climatic impact on its Holocene range.

    Science.gov (United States)

    Sommer, Robert S; Lindqvist, Charlotte; Persson, Arne; Bringsøe, Henrik; Rhodin, Anders G J; Schneeweiss, Norbert; Siroký, Pavel; Bachmann, Lutz; Fritz, Uwe

    2009-03-01

    Using ancient DNA sequences of subfossil European pond turtles (Emys orbicularis) from Britain, Central and North Europe and accelerator mass spectrometry radiocarbon dating for turtle remains from most Swedish sites, we provide evidence for a Holocene range expansion of the pond turtle from the southeastern Balkans into Britain, Central Europe and Scandinavia, according to the 'grasshopper pattern' of Hewitt. Northeastern Europe and adjacent Asia were colonized from another refuge located further east. With increasing annual mean temperatures, pond turtles reached southern Sweden approximately 9800 years ago. Until approximately 5500 years ago, rising temperatures facilitated a further range expansion up to Ostergötland, Sweden (approximately 58 degrees 30'N). However, around 5500 years ago pond turtle records suddenly terminate in Sweden, some 1500 years before the Holocene thermal maximum ended in Scandinavia and distinctly earlier than previously thought. This extinction coincides with a temporary cooling oscillation during the Holocene thermal maximum and is likely related to lower summer temperatures deteriorating reproductive success. Although climatic conditions improved later again, recolonization of Sweden from southern source populations was prevented by the Holocene submergence of the previous land connection via the Danish Straits that occurred approximately 8500 years ago.

  3. Early to Middle Holocene sea level fluctuation, coastal progradation and the Neolithic occupation in the Yaojiang Valley of southern Hangzhou Bay, Eastern China

    Science.gov (United States)

    Liu, Yan; Sun, Qianli; Fan, Daidu; Dai, Bin; Ma, Fuwei; Xu, Lichen; Chen, Jing; Chen, Zhongyuan

    2018-06-01

    The Yaojiang Valley (YJV) of southern Hangzhou Bay was the birthplace of the well-known Hemudu Culture (HC), one of the representatives of Neolithic civilization in eastern China. To explore the magnitude of natural environmental effects on the HC trajectory, the palaeo-embayment setting of the YJV was studied in detail for the first time in terms of 3D Holocene strata supported by a series of new radiocarbon-dated cores. The results indicated that the local relative sea level rose rapidly during the Early Holocene in the YJV, reached its maximum flooding surface ca. 7900 cal yr BP, and then remained stable ca. 7900-7600 cal yr BP. Thereupon, an estuary stretching inland was first formed by marine transgression, and then, it was transformed to an alluvial-coastal plain by regressive progradation. The alluvial plain was initiated in the foothills and then spread towards the valley centre after sea level stabilization ca. 7600 cal yr BP. Accompanying these natural environmental changes, the earliest arrivals of foragers in the valley occurred no later than ca. 7000 cal yr BP. They engaged in rice farming and fostered the HC for approximately two millennia from ca. 7000-5000 cal yr BP as more lands developed from coastal progradation. The rise and development of the HC are closely associated with the sea level-induced landscape changes in the YJV in the Early-Middle Holocene, but the enigmatic exodus of the HC people after ca. 5000 cal yr BP is still contentious and possibly linked with the rapid waterlogging and deterioration of this setting in such a low-lying coastal plain as well as with associated social reasons.

  4. 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

    .5 ka and after14.5–13 ka. The Last Glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of Holocene condition. Additionally, centennial scale fluctuations between 16.5 ka and 12.7 ka in the magnetic and geochemical data are seen. A close...... instability in higher northern latitudes. However, centennial scale abrupt changes are attributed to the result of albedo changes on the Himalaya and Tibetan plateau....

  5. Sensitivity of sediment magnetic records to climate change during Holocene for the northern South China Sea

    Science.gov (United States)

    Ouyang, Tingping; Li, Mingkun; Zhao, Xiang; Zhu, Zhaoyu; Tian, Chengjing; Qiu, Yan; Peng, Xuechao; Hu, Qiao

    2016-05-01

    Magnetic property has been proved to be a sensitive proxy to climate change for both terrestrial and marine sediments. Based on the schedule frame established by AMS 14C dating of foraminifera, detail magnetic analyses were performed for core PC24 sediments at sampling intervals of 2 cm to discuss magnetic sensitivity of marine sediment to climate during Holocene for the northern South China Sea. The results indicated that: 1) Concentration dependent magnetic parameters are positive corresponding to variation of temperature. The frequency dependent susceptibility coefficient basically reflected the variation in humidity; 2) XARM/SIRM was more sensitive to detrital magnetite particles and SIRM/X was more effective to biogenic magnetite particles. Variations of XARM/SIRM and SIRM/X are corresponding to precipitation and temperature, respectively; 3) the Holocene Megathermal in the study area was identified as 7.5-3.4 cal. ka BP. The warmest stage of Holocene for the study area should be during 6.1 to 3.9 cal. ka BP; 4) The 8 ka cold event was characterized as cold and dry during 8.55 to 8.25 cal. ka BP; 5) During early and middle Holocene, the climate combinations were warm dry and cold wet. It turned to warm and wet after 2.7 cal. ka BP.

  6. Sensitivity of sediment magnetic records to climate change during Holocene for the northern South China Sea

    Directory of Open Access Journals (Sweden)

    Tingping eOuyang

    2016-05-01

    Full Text Available Magnetic property has been proved to be a sensitive proxy to climate change for both terrestrial and marine sediments. Based on the schedule frame established by AMS 14C dating of foraminifera, detail magnetic analyses were performed for core PC24 sediments at sampling intervals of 2 cm to discuss magnetic sensitivity of marine sediment to climate during Holocene for the northern South China Sea. The results indicated that: 1 Concentration dependent magnetic parameters are positive corresponding to variation of temperature. The frequency dependent susceptibility coefficient basically reflected the variation in humidity; 2 XARM/SIRM was more sensitive to detrital magnetite particles and SIRM/X was more effective to biogenic magnetite particles. Variations of XARM/SIRM and SIRM/X are corresponding to precipitation and temperature, respectively; 3 the Holocene Megathermal in the study area was identified as 7.5-3.4 cal. ka BP. The warmest stage of Holocene for the study area should be during 6.1 to 3.9 cal. ka BP; 4 The 8 ka cold event was characterized as cold and dry during 8.55 to 8.25 cal. ka BP; 5 During early and middle Holocene, the climate combinations were warm dry and cold wet. It turned to warm and wet after 2.7 cal. ka BP.

  7. Quantifying Regional Vegetation Changes in China During Three Contrasting Warming Intervals since the Last Glacial Maximum

    Science.gov (United States)

    Li, Q.; Wu, H.; Yu, Y.; Sun, A.; Luo, Y.

    2017-12-01

    Reconstructing patterns of past vegetation change on a large-scale facilitates a better understanding of the interactions and feedbacks between climate change and the terrestrial biosphere. In addition, reducing the uncertainty in predictions of vegetation change under global warming highlights the importance of reconstructing vegetation patterns during past warming intervals. Here, we present a quantitative regional vegetation reconstruction for China during three intervals: Last Glacial Maximum (LGM, 18±2 14C kyr B.P.), early Holocene (8.5±0.5 14C kyr B.P.), and mid-Holocene (6±0.5 14C kyr B.P.). The biomization method, based on 249 pollen records, was used for the reconstructions. The results demonstrate that during the LGM, steppe and desert expanded eastwards and southwards, reaching the present-day temperate deciduous forest (TEDE) zone, and dominated northern China. In contrast, the forest in Eastern China underwent a substantial southwards retreat and the percentage of forest-type sites was at a minimum. In addition, the warm mixed forest (WAMF) and TEDE shifted southwards of 10° N relative to the present-day, and tropical seasonal rain forest (TSFO) was almost absent. At the same time, the forest-steppe boundary shifted southwards to near the middle and lower reaches of Yangtze River. For the early Holocene and mid-Holocene, the TSFO, WAMF, and TEDE shifted northwards by 2-5° relative to today, and the percentage of forest sites increased and reached a maximum in the mid-Holocene. The slight expansion of forest from the early Holocene to the mid-Holocene caused the forest-steppe boundary to shift northwestwards to near the present-day 300 mm isohyet by the mid-Holocene. Our results also indicate that climatic warming since the LGM, which strengthened the East Asian summer monsoon, favored the development of forest in China. This is potentially an important finding for evaluating the possible response of forest in China to future global warming.

  8. Holocene and latest Pleistocene climate and glacier fluctuations in Iceland

    Science.gov (United States)

    Geirsdóttir, Áslaug; Miller, Gifford H.; Axford, Yarrow; Ólafsdóttir, Sædís

    2009-10-01

    Multiproxy climate records from Iceland document complex changes in terrestrial climate and glacier fluctuations through the Holocene, revealing some coherent patterns of change as well as significant spatial variability. Most studies on the Last Glacial Maximum and subsequent deglaciation reveal a dynamic Iceland Ice Sheet (IIS) that responded abruptly to changes in ocean currents and sea level. The IIS broke up catastrophically around 15 ka as the Polar Front migrated northward and sea level rose. Indications of regional advance or halt of the glaciers are seen in late Alleröd/early Younger Dryas time and again in PreBoreal time. Due to the apparent rise of relative sea level in Iceland during this time, most sites contain evidence for fluctuating, tidewater glacier termini occupying paleo fjords and bays. The time between the end of the Younger Dryas and the Preboreal was characterized by repeated jökulhlaups that eroded glacial deposits. By 10.3 ka, the main ice sheet was in rapid retreat across the highlands of Iceland. The Holocene thermal maximum (HTM) was reached after 8 ka with land temperatures estimated to be 3 °C higher than the 1961-1990 reference, and net precipitation similar to modern. Such temperatures imply largely ice-free conditions across Iceland in the early to mid-Holocene. Several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8.5 and 8 ka, but no moraines have been detected from that time. Termination of the HTM and onset of Neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4.5 and 4.0 ka, intensifying between 3.0 and 2.5 ka. Although a distinct warming during the Medieval Warm Period is not dramatically apparent in Icelandic records, the interval from ca AD 0 to 1200 is commonly characterized by relative stability with slow rates of change. The literature most commonly describes Little Ice Age moraines (ca AD 1250-1900) as representing the

  9. Heavy sediment influx during early Holocene: Inference from clay mineral studies in a core from the western Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Reddy, N.P.C.; Rao, K.M.

    is attributed to heavy sediment influx du r- ing Mid Termination (MT) (12,500 ? 10,000 years BP), due to i n creased precipitation and run - off resulting from high inte n sity monsoonal regime. C LAY minerals are a powerful source for the interpret a... to address to the prov e nance of the sediments in a sediment core from the western Bengal Fan. In this paper, we report clay mi n eralogy and provide an explanation for the heavy sed i ment deposition du r ing the Holocene. A sediment core of 650...

  10. Atmospheric pCO2 reconstructed across five early Eocene global warming events

    Science.gov (United States)

    Cui, Ying; Schubert, Brian A.

    2017-11-01

    Multiple short-lived global warming events, known as hyperthermals, occurred during the early Eocene (56-52 Ma). Five of these events - the Paleocene-Eocene Thermal Maximum (PETM or ETM1), H1 (or ETM2), H2, I1, and I2 - are marked by a carbon isotope excursion (CIE) within both marine and terrestrial sediments. The magnitude of CIE, which is a function of the amount and isotopic composition of carbon added to the ocean-atmosphere system, varies significantly between marine versus terrestrial substrates. Here we use the increase in carbon isotope fractionation by C3 land plants in response to increased pCO2 to reconcile this difference and reconstruct a range of background pCO2 and peak pCO2 for each CIE, provided two potential carbon sources: methane hydrate destabilization and permafrost-thawing/organic matter oxidation. Although the uncertainty on each pCO2 estimate using this approach is low (e.g., median uncertainty = + 23% / - 18%), this work highlights the potential for significant systematic bias in the pCO2 estimate resulting from sampling resolution, substrate type, diagenesis, and environmental change. Careful consideration of each of these factors is required especially when applying this approach to a single marine-terrestrial CIE pair. Given these limitations, we provide an upper estimate for background early Eocene pCO2 of 463 +248/-131 ppmv (methane hydrate scenario) to 806 +127/-104 ppmv (permafrost-thawing/organic matter oxidation scenario). These results, which represent the first pCO2 proxy estimates directly tied to the Eocene hyperthermals, demonstrate that early Eocene warmth was supported by background pCO2 less than ∼3.5× preindustrial levels and that pCO2 > 1000 ppmv may have occurred only briefly, during hyperthermal events.

  11. Quantitative Holocene climatic reconstructions for the lower Yangtze region of China

    Science.gov (United States)

    Li, Jianyong; Dodson, John; Yan, Hong; Wang, Weiming; Innes, James B.; Zong, Yongqiang; Zhang, Xiaojian; Xu, Qinghai; Ni, Jian; Lu, Fengyan

    2018-02-01

    Quantitative proxy-based and high-resolution palaeoclimatic datasets are scarce for the lower reaches of the Yangtze River (LYR) basin. This region is in a transitional vegetation zone which is climatologically sensitive; and as a birthplace for prehistorical civilization in China, it is important to understand how palaeoclimatic dynamics played a role in affecting cultural development in the region. We present a pollen-based and regionally-averaged Holocene climatic twin-dataset for mean total annual precipitation (PANN) and mean annual temperature (TANN) covering the last 10,000 years for the LYR region. This is based on the technique of weighted averaging-partial least squares regression to establish robust calibration models for obtaining reliable climatic inferences. The pollen-based reconstructions generally show an early Holocene climatic optimum with both abundant monsoonal rainfall and warm thermal conditions, and a declining pattern of both PANN and TANN values in the middle to late Holocene. The main driving forces behind the Holocene climatic changes in the LYR area are likely summer solar insolation associated with tropical or subtropical macro-scale climatic circulations such as the Intertropical Convergence Zone (ITCZ), Western Pacific Subtropical High (WPSH), and El Niño/Southern Oscillation (ENSO). Regional multi-proxy comparisons indicate that the Holocene variations in precipitation and temperature for the LYR region display an in-phase relationship with other related proxy records from southern monsoonal China and the Indian monsoon-influenced regions, but are inconsistent with the Holocene moisture or temperature records from northern monsoonal China and the westerly-dominated region in northwestern China. Overall, our comprehensive palaeoclimatic dataset and models may be significant tools for understanding the Holocene Asian monsoonal evolution and for anticipating its future dynamics in eastern Asia.

  12. Early Holocene forest fires, drift sands, and Usselo-type paleosols in the Laarder Wasmeren area near Hilversum, the Netherlands: Implications for the history of sand landscapes and the potential role of Mesolithic land use

    NARCIS (Netherlands)

    Sevink, J.; van Geel, B.; Jansen, B.; Wallinga, J.

    In the Laarder Wasmeren area in the western Netherlands, Late Pleistocene cover sands and overlying early Holocene drift sands show various paleosols, which can be characterized as more or less incipient podzols. We dated those soils and sands by radiocarbon analysis and OSL, and we used

  13. Ocean Warming Enhances Malformations, Premature Hatching, Metabolic Suppression and Oxidative Stress in the Early Life Stages of a Keystone Squid

    Science.gov (United States)

    Rosa, Rui; Pimentel, Marta S.; Boavida-Portugal, Joana; Teixeira, Tatiana; Trübenbach, Katja; Diniz, Mário

    2012-01-01

    Background The knowledge about the capacity of organisms’ early life stages to adapt to elevated temperatures is very limited but crucial to understand how marine biota will respond to global warming. Here we provide a comprehensive and integrated view of biological responses to future warming during the early ontogeny of a keystone invertebrate, the squid Loligo vulgaris. Methodology/Principal Findings Recently-spawned egg masses were collected and reared until hatching at present day and projected near future (+2°C) temperatures, to investigate the ability of early stages to undergo thermal acclimation, namely phenotypic altering of morphological, behavioural, biochemical and physiological features. Our findings showed that under the projected near-future warming, the abiotic conditions inside the eggs promoted metabolic suppression, which was followed by premature hatching. Concomitantly, the less developed newborns showed greater incidence of malformations. After hatching, the metabolic burst associated with the transition from an encapsulated embryo to a planktonic stage increased linearly with temperature. However, the greater exposure to environmental stress by the hatchlings seemed to be compensated by physiological mechanisms that reduce the negative effects on fitness. Heat shock proteins (HSP70/HSC70) and antioxidant enzymes activities constituted an integrated stress response to ocean warming in hatchlings (but not in embryos). Conclusions/Significance The stressful abiotic conditions inside eggs are expected to be aggravated under the projected near-future ocean warming, with deleterious effects on embryo survival and growth. Greater feeding challenges and the lower thermal tolerance limits of the hatchlings are strictly connected to high metabolic demands associated with the planktonic life strategy. Yet, we found some evidence that, in the future, the early stages might support higher energy demands by adjusting some cellular functional properties

  14. Exceptional Arctic warmth of early winter 2016 and attribution to global warming

    Science.gov (United States)

    van Oldenborgh, Geert Jan; Macias-Fauria, Marc; King, Andrew; Uhe, Peter; Philip, Sjoukje; Kew, Sarah; Karoly, David; Otto, Friederike; Allen, Myles; Cullen, Heidi

    2017-04-01

    have risen on the North Pole, modulated by decadal North Atlantic variability. For all phases of this variability, a warm event like the one of this winter would have been extremely unlikely in the climate of a century ago. Both sets of models also give very comparable results and show that the bulk of the arctic temperature increase is due to anthropogenic emissions. This also holds for the warm extremes caused by the type of circulation present in the early winter of 2016.

  15. Palynological evidence for vegetation patterns in the Transvaal (South Africa during the late Pleistocene and Holocene

    Directory of Open Access Journals (Sweden)

    L. Scott

    1983-11-01

    Full Text Available Palynological evidence relating to the nature of Late Quaternary vegetation types and plant migrations in the Transvaal is briefly summarized. It is suggested that, after an early temperate, relatively moist phase and a subsequent relatively dry phase lasting until about 25 000 yr B.P., a vegetation-type with ericaceous elements developed. It resembled belts presently occurring above the treeline and was possibly widespread over the plains of the Transvaal during the last glacial maximum period. In the central parts of the province, warm semi-arid savanna subsequently expanded during the early Holocene and was followed by a more broad-leafed type of woodland in the late Holocene. This change probably resulted from slightly wetter and, at times, also slightly warmer and cooler conditions.

  16. Holocene climate changes in eastern Beringia (NW North America) – A systematic review of multi-proxy evidence

    Science.gov (United States)

    Kaufman, Darrell S.; Axford, Yarrow L.; Henderson, Andrew C.G.; McKay, Nicolas P.; Oswald, W. Wyatt; Saenger, Casey; Anderson, R. Scott; Bailey, Hannah L.; Clegg, Benjamin; Gajewski, Konrad; Hu, Feng Sheng; Jones, Miriam C.; Massa, Charly; Routson, Cody C.; Werner, Al; Wooller, Matthew J.; Yu, Zicheng

    2016-01-01

    Reconstructing climates of the past relies on a variety of evidence from a large number of sites to capture the varied features of climate and the spatial heterogeneity of climate change. This review summarizes available information from diverse Holocene paleoenvironmental records across eastern Beringia (Alaska, westernmost Canada and adjacent seas), and it quantifies the primary trends of temperature- and moisture-sensitive records based in part on midges, pollen, and biogeochemical indicators (compiled in the recently published Arctic Holocene database, and updated here to v2.1). The composite time series from these proxy records are compared with new summaries of mountain-glacier and lake-level fluctuations, terrestrial water-isotope records, sea-ice and sea-surface-temperature analyses, and peatland and thaw-lake initiation frequencies to clarify multi-centennial- to millennial-scale trends in Holocene climate change. To focus the synthesis, the paleo data are used to frame specific questions that can be addressed with simulations by Earth system models to investigate the causes and dynamics of past and future climate change. This systematic review shows that, during the early Holocene (11.7–8.2 ka; 1 ka = 1000 cal yr BP), rather than a prominent thermal maximum as suggested previously, temperatures were highly variable, at times both higher and lower than present (approximate mid-20th-century average), with no clear spatial pattern. Composited pollen, midge and other proxy records average out the variability and show the overall lowest summer and mean-annual temperatures across the study region during the earliest Holocene, followed by warming over the early Holocene. The sparse data available on early Holocene glaciation show that glaciers in southern Alaska were as extensive then as they were during the late Holocene. Early Holocene lake levels were low in interior Alaska, but moisture indicators show pronounced differences across the region. The highest

  17. Prospects for a prolonged slowdown in global warming in the early 21st century

    Science.gov (United States)

    Knutson, Thomas R.; Zhang, Rong; Horowitz, Larry W.

    2016-11-01

    Global mean temperature over 1998 to 2015 increased at a slower rate (0.1 K decade-1) compared with the ensemble mean (forced) warming rate projected by Coupled Model Intercomparison Project 5 (CMIP5) models (0.2 K decade-1). Here we investigate the prospects for this slower rate to persist for a decade or more. The slower rate could persist if the transient climate response is overestimated by CMIP5 models by a factor of two, as suggested by recent low-end estimates. Alternatively, using CMIP5 models' warming rate, the slower rate could still persist due to strong multidecadal internal variability cooling. Combining the CMIP5 ensemble warming rate with internal variability episodes from a single climate model--having the strongest multidecadal variability among CMIP5 models--we estimate that the warming slowdown (2025 or 2030 with probabilities 16%, 11% and 6%, respectively.

  18. Holocene climate in the western Great Lakes national parks and lakeshores: Implications for future climate change

    Science.gov (United States)

    Davis, Margaret; Douglas, Christine; Cole, K.L.; Winkler, Marge; Flaknes, Robyn

    2000-01-01

    We reconstruct Holocene climate history (last 10,000 years) for each of the U.S. National Park Service units in the western Great Lakes region in order to evaluate their sensitivity to global warming. Annual precipitation, annual temperature, and July and January temperatures were reconstructed by comparing fossil pollen in lake sediment with pollen in surface samples, assuming that ancient climates were similar to modern climate near analogous surface samples. In the early Holocene, most of the parks experienced colder winters, warmer summers, and lower precipitation than today. An exception is Voyageurs National Park in northern Minnesota where, by 8000 years ago, January temperatures were higher than today. The combination of high mean annual temperature and lower precipitation at Voyageurs resulted in a dry period between 8000 and 5000 years ago, similar to the Prairie Period in regions to the south and west. A mid-Holocene warm-dry period also occurred at other northern and central parks but was much less strongly developed. In southern parks there was no clear evidence of a mid-Holocene warm-dry period. These differences suggest that global model predictions of a warm, dry climate in the northern Great Plains under doubled atmospheric CO2 may be more applicable to Voyageurs than to the other parks. The contrast in reconstructed temperatures at Voyageurs and Isle Royale indicates that the ameliorating effect of the Great Lakes on temperatures has been in effect throughout the Holocene and presumably will continue in the future, thus reducing the potential for species loss caused by future temperature extremes. Increased numbers of mesic trees at all of the parks in the late Holocene reflect increasing annual precipitation. This trend toward more mesic conditions began 6000 years ago in the south and 4000 years ago in the north and increased sharply in recent millennia at parks located today in lake-effect snow belts. This suggests that lake-effect snowfall is

  19. Anchoring the landscape: human utilization of the Cerro Gavilán 2 rockshelter, Middle Orinoco, from the Early Holocene to the present

    Directory of Open Access Journals (Sweden)

    Kay Scaramelli

    Full Text Available Abstract Initial archaeological investigations at Cerro Gavilán 2, a rockshelter located in the Bolívar State of Venezuela, reveal evidence for human activity that spans the Early Holocene to the present. This report summarizes the information obtained through surface collection, limited excavation, and documentation of the surface features and rock art in the cave. Accelerator mass spectrometry (AMS 14C analysis established dates from excavated strata that range between 9250 ± 60 BP to 3440 ± 40 BP, and are associated with a unifacial flake technology and charred faunal and floral remains, whereas surface remains span the known ceramic sequence for the area. Rock art corresponds to distinctive superimposed styles that indicate continual repainting of the cave through time, serving to anchor the site to the landscape for multiple societies inhabiting the region. It is suggested that the shelter may have fulfilled different functions over time and a sequence of seasonal residential, ritual, and funerary activities is proposed. The rich cultural context found in Cerro Gavilán 2 contributes to advances in Amazonian archaeology that are redefining our knowledge of early developments and the complexity of human/environmental interactions in tropical America.

  20. Chrysophyte cysts from lake sediments reveal the submillennial winter/spring climate variability in the northwestern Mediterranean region throughout the Holocene

    Energy Technology Data Exchange (ETDEWEB)

    Pla, Sergi [Queen' s University, PEARL, Department of Biology, Kingston, ON (Canada); Catalan, Jordi [CSIC, CSIC-UB Limnology Group, Centre for Advanced Studies of Blanes (CEAB), Blanes (Spain)

    2005-02-01

    In the last decade, much effort was dedicated to the reconstruction of past climate at high temporal resolution. Here, we show the suitability of chrysophyte cysts from lake sediments for revealing continental climate variability when used in sensitive sites, such as those in high mountains. We demonstrate that altitude is a main factor influencing the present distribution of chrysophytes and develop a transfer function to evaluate the local ''altitude anomaly'' on a lake site throughout time. Based on our knowledge of chrysophyte ecology, the altitude anomalies are interpreted as winter/spring climate signatures. The method was applied to a Holocene record from a lake in the Pyrenees showing submillennial climatic variability in this northwestern Mediterranean zone. A warming trend was present from the early Holocene to 4 kyear BP. Comparison with pollen-based reconstructions of summer temperatures denoted a contrasting decrease in continentality between the two parts of the Holocene. Oscillations of 1 cycle per ca. 2,000 years appeared throughout the record. The warmest Holocene winters were recorded during the Medieval Warm Period at ca. AD900 and 450 and the Roman Warm Period (2.7-2.4 kyear BP). Winters in the period AD1,050-1,175 were inferred to be as cold as in the Little Ice Age. The period between 3 and 7 kyear BPshowed lower intensity in the fluctuations than in early and late Holocene. The cold event, 8,200 years ago, appeared embedded in a warm fluctuation. Another cold fluctuation was recorded around 9 kyear BP, which is in agreement with Irish and Greenland records. (orig.)

  1. Determining Late Pleistocene to Early Holocene deglaciation of the Baltic Ice Lake through sedimentological core sample analysis of IODP Site M0064

    Science.gov (United States)

    Kelly, A. L.; Passchier, S.

    2016-12-01

    This study investigates the deglaciation history of the Scandinavian Ice Sheet (SIS) within the Baltic Sea's Hanö Bay from the Late Pleistocene to the Holocene using samples from International Ocean Discovery Program (IODP) Site M0064. The research aims to understand how the speed of deglaciation influences Baltic Ice Lake (BIL) drainage patterns and relative sea level changes on a high-resolution timescale. Glacial history of the SIS has been studied through glacial till analysis, surface exposure dating, and modeling, encompassing its most recent deglaciation 20-14ka BP, and suggests ice retreated from the project site 16.7ka BP. Between 17 and 14ka BP global sea level rose 4 meters per century, accompanied by a dramatic increase in atmospheric carbon. This period of rapid sea level rise and global warming is a valuable analog for understanding the Earth's current and projected climate. This project uses particle size analysis to better understand the late-glacial depositional environment in Hanö Bay, and ICP-OES geochemical analysis for evidence pertaining to changing sediment provenance and bottom water oxygenation in the BIL. Diamicton is present between 47 and 9 mbsf in Hole M0064D. At 8 mbsf, the sediment exhibits a prominent upward transition from well-laminated cm-scale grey to more thinly laminated reddish brown rhythmites. With calculated Al/Ti ratios, we find that there is not much provenance change in the sequence, however we see fluctuations in Mn/Al ratios, implying shifts in sediment color may be chemical, possibly indicating redox changes in the water column during sediment deposition. Although we find that particle size in the varve sequence does not change, this factor may be driving chemical fluctuations in the diamicton. These results increase the understanding of ice retreat, paleocirculation and relative sea level changes in the Baltic Sea at the onset of the last deglaciation.

  2. Reconciling divergent trends and millennial variations in Holocene temperatures

    Science.gov (United States)

    Marsicek, Jeremiah; Shuman, Bryan N.; Bartlein, Patrick J.; Shafer, Sarah L.; Brewer, Simon

    2018-02-01

    Cooling during most of the past two millennia has been widely recognized and has been inferred to be the dominant global temperature trend of the past 11,700 years (the Holocene epoch). However, long-term cooling has been difficult to reconcile with global forcing, and climate models consistently simulate long-term warming. The divergence between simulations and reconstructions emerges primarily for northern mid-latitudes, for which pronounced cooling has been inferred from marine and coastal records using multiple approaches. Here we show that temperatures reconstructed from sub-fossil pollen from 642 sites across North America and Europe closely match simulations, and that long-term warming, not cooling, defined the Holocene until around 2,000 years ago. The reconstructions indicate that evidence of long-term cooling was limited to North Atlantic records. Early Holocene temperatures on the continents were more than two degrees Celsius below those of the past two millennia, consistent with the simulated effects of remnant ice sheets in the climate model Community Climate System Model 3 (CCSM3). CCSM3 simulates increases in ‘growing degree days’—a measure of the accumulated warmth above five degrees Celsius per year—of more than 300 kelvin days over the Holocene, consistent with inferences from the pollen data. It also simulates a decrease in mean summer temperatures of more than two degrees Celsius, which correlates with reconstructed marine trends and highlights the potential importance of the different subseasonal sensitivities of the records. Despite the differing trends, pollen- and marine-based reconstructions are correlated at millennial-to-centennial scales, probably in response to ice-sheet and meltwater dynamics, and to stochastic dynamics similar to the temperature variations produced by CCSM3. Although our results depend on a single source of palaeoclimatic data (pollen) and a single climate-model simulation, they reinforce the notion that

  3. 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

  4. Influences of spawning timing, water temperature, and climatic warming on early life history phenology in western Alaska sockeye salmon

    Science.gov (United States)

    Sparks, Morgan M.; Falke, Jeffrey A.; Quinn, Thomas P.; Adkison, Milo D.; Schindler, Daniel E.; Bartz, Krista K.; Young, Daniel B.; Westley, Peter A. H.

    2018-01-01

    We applied an empirical model to predict hatching and emergence timing for 25 western Alaska sockeye salmon (Oncorhynchus nerka) populations in four lake-nursery systems to explore current patterns and potential responses of early life history phenology to warming water temperatures. Given experienced temperature regimes during development, we predicted hatching to occur in as few as 58 d to as many as 260 d depending on spawning timing and temperature. For a focal lake spawning population, our climate-lake temperature model predicted a water temperature increase of 0.7 to 1.4 °C from 2015 to 2099 during the incubation period, which translated to a 16 d to 30 d earlier hatching timing. The most extreme scenarios of warming advanced development by approximately a week earlier than historical minima and thus climatic warming may lead to only modest shifts in phenology during the early life history stage of this population. The marked variation in the predicted timing of hatching and emergence among populations in close proximity on the landscape may serve to buffer this metapopulation from climate change.

  5. Early pest development and loss of biological control are associated with urban warming.

    Science.gov (United States)

    Meineke, Emily K; Dunn, Robert R; Frank, Steven D

    2014-11-01

    Climate warming is predicted to cause many changes in ectotherm communities, one of which is phenological mismatch, wherein one species' development advances relative to an associated species or community. Phenological mismatches already lead to loss of pollination services, and we predict that they also cause loss of biological control. Here, we provide evidence that a pest develops earlier due to urban warming but that phenology of its parasitoid community does not similarly advance. This mismatch is associated with greater egg production that likely leads to more pests on trees. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  6. Large floods and climatic change during the Holocene on the Ara River, Central Japan

    Science.gov (United States)

    Grossman, Michael J.

    2001-07-01

    A reconstruction of part of the Holocene large flood record for the Ara River in central Japan is presented. Maximum intermediate gravel-size dimensions of terrace and modern floodplain gravels were measured along an 18-km reach of the river and were used in tractive force equations to estimate minimum competent flood depths. Results suggest that the magnitudes of large floods on the Ara River have varied in a non-random fashion since the end of the last glacial period. Large floods with greater magnitudes occurred during the warming period of the post-glacial and the warmer early to middle Holocene (to ˜5500 years BP). A shift in the magnitudes of large floods occurred ˜5500-5000 years BP. From this time, during the cooler middle to late Holocene, large floods generally had lower magnitudes. In the modern period, large flood magnitudes are the largest in the data set. As typhoons are the main cause of large floods on the Ara River in the modern record, the variation in large flood magnitudes suggests that the incidence of typhoon visits to the central Japan changed as the climate changed during the Holocene. Further, significant dates in the large flood record on the Ara River correspond to significant dates in Europe and the USA.

  7. Early Holocene environmental change and the impact of Mesolithic man in the Tungelroysche Beek Valley, N-Limburg

    NARCIS (Netherlands)

    Woelders, L.; Kort, J.W. de; Hoek, W.Z.

    2012-01-01

    An archaeological excavation in the Tungelroysche Beek Valley revealed an Early Mesolithic site with the unique discovery of the remains of two red deer specimens (Cervus elaphus), likely the victims of Early Mesolithic hunter-gatherers. A core taken by the Rijksdienst voor het Cultureel Erfgoed

  8. Prospects for a prolonged slowdown in global warming in the early 21st century

    Science.gov (United States)

    Knutson, Thomas R.; Zhang, Rong; Horowitz, Larry W.

    2016-01-01

    Global mean temperature over 1998 to 2015 increased at a slower rate (0.1 K decade−1) compared with the ensemble mean (forced) warming rate projected by Coupled Model Intercomparison Project 5 (CMIP5) models (0.2 K decade−1). Here we investigate the prospects for this slower rate to persist for a decade or more. The slower rate could persist if the transient climate response is overestimated by CMIP5 models by a factor of two, as suggested by recent low-end estimates. Alternatively, using CMIP5 models' warming rate, the slower rate could still persist due to strong multidecadal internal variability cooling. Combining the CMIP5 ensemble warming rate with internal variability episodes from a single climate model—having the strongest multidecadal variability among CMIP5 models—we estimate that the warming slowdown (<0.1 K decade−1 trend beginning in 1998) could persist, due to internal variability cooling, through 2020, 2025 or 2030 with probabilities 16%, 11% and 6%, respectively. PMID:27901045

  9. Latest Pleistocene and Holocene Glacier Fluctuations in southernmost Patagonia

    Science.gov (United States)

    Menounos, B.; Maurer, M.; Clague, J. J.; osborn, G.; Ponce, F.; Davis, P. T.; Rabassa, J.; Coronato, A.; Marr, R.

    2011-12-01

    Summer insolation has been proposed to explain long-term glacier fluctuations during the Holocene. If correct, the record of glacier fluctuations at high latitudes in the Southern Hemisphere should differ from that in the Northern Hemisphere. Testing this insolation hypothesis has been hampered by dating uncertainties of many Holocene glacier chronologies from Patagonia. We report on our ongoing research aimed at developing a regional glacier chronology at the southern end of the Andes north and west of Ushuaia, Argentina. We have found evidence for an advance of cirque glaciers at the end of the Pleistocene; one or locally two closely spaced moraines extend up to 2 km beyond Little Ice Age moraines. Radiocarbon dating of terrestrial macrofossils recovered from basal sediments behind two of these moraines yielded ages of 10,320 ± 25 and 10,330 ± 30 14C yr BP. These moraines may record glacier advances coeval with the Antarctic Cold Reversal; surface exposure dating of these moraines is currently in progress to test this hypothesis. We find no evidence of Holocene moraines older than 6800 14C yr BP, based on the distribution of Hudson tephra of that age. At some sites, there is evidence for an early Neoglacial advance of glaciers slightly beyond (Peru. We have documented multiple wood mats with stumps in growth position separated by till units in a 100 m section of the northeast lateral moraine at Stoppani Glacier (54.78 S, 68.98 W), 50 km west of Ushuaia. Ten radiocarbon ages on these wood mats range in age from 3510 ± 15 to 135 ± 15 14C yr BP. The mats decrease in age up-section; many overlap with published age ranges for Neoglacial advances in western Canada. Taken together, these data: a) do not support the summer insolation hypothesis for Holocene glacier fluctuations in southernmost Patagonia; b) confirm paleobotanical evidence for a warm, dry early Holocene; and c) suggest that many Neoglacial advances in southernmost Patagonia and western North America

  10. Peatland Carbon Dynamics in Alaska During Past Warm Climates

    Science.gov (United States)

    Yu, Z.; Cleary, K.; Massa, C.; Hunt, S. J.; Klein, E. S.; Loisel, J.

    2013-12-01

    Peatlands represent a large belowground carbon (C) pool in the biosphere. However, how peatland C sequestration capacity varies with changes in climate and climate-induced disturbance is still poorly understood and debated. Here we summarize results from Alaskan peatlands to document how peat C accumulation has responded to past warm climate intervals. We find that the greatest C accumulation rates at sites from the Kenai Peninsula to the North Slope occurred during the Holocene thermal maximum (HTM) in the early Holocene. This time period also corresponds with explosive formation and expansion of new peatlands on the landscape across Alaska. In addition, we note that many peatlands that existed during the earlier Holocene on the North Slope have disappeared and are presently covered by mineral soils under tundra or sandy deposits. During the Medieval Climate Anomaly (MCA) around 1000-500 years ago, several peatlands in Alaska show high rates of C accumulation when compared to the period before the MCA during the Neoglacial or the following Little Ice Age period. Altogether, our results indicate that the Alaskan landscape was very different during the last 10,000 years and that peatlands can rapidly accumulate C under warm climatic conditions. We speculate that warmth-stimulated increase in plant production surpasses increase in peat decomposition during the early Holocene, and potentially also during the MCA. Other factors that might have contributed to rapid peat accumulation during the early Holocene include increased summer sunlight, lowered sea levels, and decreased sea-ice cover/duration. Summer insolation was ca. 8% higher than today during the early Holocene due to orbital variations, which likely promoted plant productivity by increasing growing seasons sunlight. Furthermore, lower sea levels and exposed shallow continental shelves in the Beaufort Sea (Arctic Ocean) would have made the present-day Arctic Coastal Plain more continental, with warmer summers

  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. Early to mid-Holocene spatiotemporal vegetation changes and tsunami impact in a paradigmatic coastal transitional system (Doñana National Park, southwestern Europe)

    Science.gov (United States)

    Manzano, Saúl; Carrión, José S.; López-Merino, Lourdes; Ochando, Juan; Munuera, Manuel; Fernández, Santiago; González-Sampériz, Penélope

    2018-02-01

    The southern European Doñana wetlands host a highly biodiverse landscape mosaic of complex transitional ecosystems. It is one of the largest protected natural sites in Europe, nowadays endangered by intensive agricultural practices, and more recently tourism and human-induced fires. Its present-day spatial heterogeneity has been deeply investigated for the last three decades. However, a long-term perspective has not been applied systematically to this unique landscape. In this new study, a palaeoecological approach was selected in order to unravel patterns of landscape dynamism comparing dry upland and aquatic ecosystems. A 709 cm-long sediment core was retrieved and a multi-proxy approach applied (palynological, microcharcoal, grain size, magnetic susceptibility, loss-on-ignition and multivariate statistical analyses). Pollen signatures show how sensitive aquatic wetland vegetation was to environmental changes while terrestrial vegetation was stable at millennial scale. The impact of several high energy events punctuates the Early and Middle Holocene sequence, two of which relate to the local tsunami record ( 6.6 and 9.1 cal. kyr BP). Contrasting impacts of these two events in the aquatic and upland ecosystems show the importance of landscape configuration and the contingent history as key elements for coastal protection.

  13. Human used upper montane ecosystem in the Horton Plains, central Sri Lanka - a link to Lateglacial and early Holocene climate and environmental changes

    Science.gov (United States)

    Premathilake, Rathnasiri

    2012-09-01

    This study utilizes radiocarbon-dated pollen, spores, Sphagnum spp. macrofossils and total organic carbon proxies to examine variability of past climate, environment and human activity in montane rainforest, grassland and wetland of the Horton Plains (HP), central Sri Lanka since the Last Glacial Maximum (LGM). The LGM is largely characterized by grasslands and xerophytic herbs dominated open habitats. Arid-LGM punctuated climatic ameliorations, which took place in short episodes. Humans appear to have reached the HP ecosystem after 18,000 cal yrs BP occasionally. The first Intertropical Convergence Zone (ITCZ) induced changes in South West Monsoon (SWM) rains occurred at low latitudes between 16,200 and 15,900 cal yrs BP suggesting an onset of monsoon rains. After this event, monsoon rains weakened for several millennia except the period 13,700-13,000 cal yrs BP, but human activity seems to have continued with biomass burning and clearances by slash and burn. Very large size grass pollen grains, which are morphologically similar to pollen from closer forms of Oryza nivara, were found after 13,800 cal yrs BP. Early Holocene extreme and abrupt climate changes seem to have promoted the forms of O. nivara populations in association with humans. New data from the HP would therefore be most interesting to investigate the dispersal and use of domesticated rice in South Asia.

  14. Millennial-scale climate variations in western Mediterranean during late Pleistocene-early Holocene: multi-proxy analyses from Padul peatbog (southern Iberian Peninsula)

    Science.gov (United States)

    Camuera, Jon; Jiménez-Moreno, Gonzalo; José Ramos-Román, María; García-Alix, Antonio; Jiménez-Espejo, Francisco; Toney, Jaime L.; Anderson, R. Scott; Kaufman, Darrell; Bright, Jordon; Sachse, Dirk

    2017-04-01

    Padul peatbog, located in southern Iberian Peninsula (western Mediterranean region) is a unique area for palaeoenvironmental studies due to its location, between arid and temperate climates. Previous studies showed that the Padul peatbog contains a continuous record of the last ca. 0.8-1 Ma, so it is an extraordinary site to identify glacial-interglacial phases as well as Heinrich and D-O events, linked to orbital- and suborbital-scale variations. In 2015, a new 42 m long core was taken from this area, providing an excellent sediment record probably for the last ca. 300,000 years. This study is focused on the paleoenvironmental and climatic reconstruction of the late Pleistocene and the early Holocene (ca. from 50,000 to 9,500 cal. yrs BP), using AMS 14C and AAR dating, high-resolution pollen analysis, lithology, continuous XRF-scanning, X-ray diffraction, magnetic susceptibility and organic geochemistry. These different proxies provide information not only about the regional environment change but also about local changes in the conditions of the Padul lake/peatbog due to variations in water temperature, pH or nutrients.

  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 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. 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.

  17. Paleoparasitological finding of eggs of nematodes in rodent coprolites dated at the early Holocene from the archaeological site Cerro Casa de Piedra 7, Santa Cruz, Argentina.

    Science.gov (United States)

    Sardella, N H; Fugassa, M H

    2011-12-01

    The aim of the present study was to examine the parasite remains present in rodent coprolites collected from the archaeological site Cerro Casa de Piedra 7 (CCP7), located in the Perito Moreno National Park (47°57'S, 72°05'W), Santa Cruz Province, Argentina. Eight coprolites obtained from the layer 17, dated at 10,620 ± 40 to 9,390 ± 40 yr B.P., were examined for parasites. Feces were processed whole, rehydrated, homogenized, subjected to spontaneous sedimentation, and examined via light microscopy. Eggs of parasites were measured and photographed. Seven of 8 coprolites possessed 199 eggs of 2, probably new, species of nematodes, including 43 eggs of Heteroxynema sp. Hall, 1916 (Cavioxyura sp. Quentin, 1975) (Oxyurida, Heteroxynematidae), and 156 eggs of Trichuris sp. Roederer, 1761 (Trichinellida, Trichuridae). Heteroxynema sp. is cited for the first time from ancient material worldwide. The finding of Trichuris spp. in both rodents and other host samples from the area under study is indicative of the stability of the biological and environmental conditions for this nematode genus to establish in the Patagonian Early Holocene. The rodent host was assigned to an unknown species of Caviomorpha (Hystricognathi) that lived during the Pleistocenic transition in Patagonia.

  18. Early warming of tropical South America at the last glacial-interglacial transition.

    Science.gov (United States)

    Seltzer, G O; Rodbell, D T; Baker, P A; Fritz, S C; Tapia, P M; Rowe, H D; Dunbar, R B

    2002-05-31

    Glaciation in the humid tropical Andes is a sensitive indicator of mean annual temperature. Here, we present sedimentological data from lakes beyond the glacial limit in the tropical Andes indicating that deglaciation from the Last Glacial Maximum led substantial warming at high northern latitudes. Deglaciation from glacial maximum positions at Lake Titicaca, Peru/Bolivia (16 degrees S), and Lake Junin, Peru (11 degrees S), occurred 22,000 to 19,500 calendar years before the present, several thousand years before the Bølling-Allerød warming of the Northern Hemisphere and deglaciation of the Sierra Nevada, United States (36.5 degrees to 38 degrees N). The tropical Andes deglaciated while climatic conditions remained regionally wet, which reflects the dominant control of mean annual temperature on tropical glaciation.

  19. Decline of coral reefs during late Paleocene to early Eocene global warming

    OpenAIRE

    Scheibner , C.; Speijer , R. P.

    2007-01-01

    International audience; Since the 1980s the frequency of warming events has intensified and simultaneously widespread coral bleaching, and enhanced coral mortality have been observed. Yet, it remains unpredictable how tropical coral reef communities will react to prolonged adverse conditions. Possibly, coral reef systems are sufficiently robust to withstand continued environmental pressures. But if coral mortality increases, what will platform communities of the future look like? The co-evolu...

  20. Climate warming and humans played different roles in triggering Late Quaternary extinctions in east and west Eurasia.

    Science.gov (United States)

    Wan, Xinru; Zhang, Zhibin

    2017-03-29

    Climate change and humans are proposed as the two key drivers of total extinction of many large mammals in the Late Pleistocene and Early Holocene, but disentangling their relative roles remains challenging owing to a lack of quantitative evaluation of human impact and climate-driven distribution changes on the extinctions of these large mammals in a continuous temporal-spatial dimension. Here, our analyses showed that temperature change had significant effects on mammoth (genus Mammuthus ), rhinoceros (Rhinocerotidae), horse (Equidae) and deer (Cervidae). Rapid global warming was the predominant factor driving the total extinction of mammoths and rhinos in frigid zones from the Late Pleistocene and Early Holocene. Humans showed significant, negative effects on extirpations of the four mammalian taxa, and were the predominant factor causing the extinction or major extirpations of rhinos and horses. Deer survived both rapid climate warming and extensive human impacts. Our study indicates that both the current rates of warming and range shifts of species are much faster than those from the Late Pleistocene to Holocene. Our results provide new insight into the extinction of Late Quaternary megafauna by demonstrating taxon-, period- and region-specific differences in extinction drivers of climate change and human disturbances, and some implications about the extinction risk of animals by recent and ongoing climate warming. © 2017 The Author(s).

  1. Human-environment interaction during the Mesolithic- Neolithic transition in the NE Iberian Peninsula. Vegetation history, climate change and human impact during the Early-Middle Holocene in the Eastern Pre-Pyrenees

    Science.gov (United States)

    Revelles, J.; Burjachs, F.; Palomo, A.; Piqué, R.; Iriarte, E.; Pérez-Obiol, R.; Terradas, X.

    2018-03-01

    The synthetic analysis of several pollen records from sub-Mediterranean lowland Pre-Pyrenean regions evidences expansion of forests during the Early Holocene in Northeastern Iberia and the establishment of dense deciduous broadleaf forests during the Holocene Climate Optimum. Pollen records show the broadleaf deciduous forests resilience against cooling phases during the Mid-Holocene period, with slight regressions of oak woodlands and expansion of conifers or xerophytic taxa contemporary to some cooling episodes (i.e. 8.2 and 7.2 kyr cal. BP). Major vegetation changes influenced by climate change occurred in the transition to the Late Holocene, in terms of the start of a succession from broadleaf deciduous forests to evergreen sclerophyllous woodlands. The lack of evidence of previous occupation seems to support the Neolithisation of the NE Iberian Peninsula as a result of a process of migration of farming populations to uninhabited or sparsely inhabited territories. In that context, remarkable changes in vegetation were recorded from 7.3 kyr cal. BP onwards in the Lake Banyoles area, where the establishment of permanent farming settlements caused the deforestation of oak woodlands. In La Garrotxa region, short deforestation episodes affecting broadleaf deciduous forests, together with expansion of grasslands and presence of Cerealia-t were documented in the period 7.4-6.0 kyr cal. BP. Finally, in the coastal area, where less evidence of Early Neolithic occupations is recorded, evidence of Neolithic impact is reflected in the presence of Cerealia-t in 6.5-6.2 kyr cal. BP, but no strong human transformation of landscape was carried out until more recent chronologies.

  2. Impact of recombinant globular adiponectin on early warm ischemia-reperfusion injury in rat bile duct after liver transplantation.

    Science.gov (United States)

    Xia, Yang; Gong, Jian-Ping

    2014-09-19

    Adiponectin (APN) is an adipocyte protein with anti-diabetic properties, which has been recently revealed to have anti-inflammatory activity in organ ischemia- reperfusion injury (IRI). However, little is known about its function in bile duct IRI after liver transplantation. Therefore, we investigated whether APN affects early warm IRI in rat bile duct using a liver autologous transplantation model. In our study, rats were randomly divided into three experimental groups: a sham group, a IRI group, and a APN group. The serum enzyme levels and BDISS scores of bile duct histology associated with bile duct injury, decreased after administration of APN. Subsequently, the expression of proinflammatory cytokines, such as tumor necrosis factor(TNF-α),.interleukin-6(IL-6) and myeloperoxidase (MPO) decreased. Furthermore, pretreatment with APN suppressed the activation of nuclear factor-kappa B (NF-κB) (p65), a transcription factor involved in inflammatory reactions, compared to other two groups. Administration of APN also downregulated the expression of Fas protein and attenuated caspase-3 activity to decrease bile duct apoptosis. Our results illustrate that APN protects the rat bile duct against early warm IRI by suppressing the inflammatory response and hepatocyte apoptosis, and NF-κB (p65) plays an important role in this process.

  3. 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.

  4. Holocene fire dynamics in Fennoscandia

    Science.gov (United States)

    Clear, Jennifer; Seppa, Heikki; Kuosmanen, Niina; Molinari, Chiara; Lehsten, Veiko; Allen, Katherine; Bradshaw, Richard

    2015-04-01

    Prescribed burning is advocated in Fennoscandia to promote regeneration and to encourage biodiversity. This method of forest management is based on the perception that fire was much more frequent in the recent past and over a century of active fire suppression has created a boreal forest ecosystem almost free of natural fire. The absence of fire is thought to have contributed to the widespread dominance of Picea abies (Norway spruce) with the successive spruce dominated forest further reducing fire ignition potential. However, humans have altered the natural fire dynamics of Fennoscandia since the early- to mid-Holocene and disentangling the anthropogenic driven fire dynamics from the natural fire dynamics is challenging. Through palaeoecology and sedimentary charcoal deposits we are able to explore the Holocene spatial and temporal variability and changing drivers of fire and vegetation dynamics in Fennoscandia. At the local-scale, two forest hollow environments (history are compared to identify unique and mutual changes in disturbance history. Pollen derived quantitative reconstruction of vegetation at both the local- and regional-scale identifies local-scale disturbance dynamics and large-scale ecosystem response. Spatio-temporal heterogeneity and variability in biomass burning is explored throughout Fennoscandia and Denmark to identify the changing drives of fire dynamics throughout the Holocene. Palaeo-vegetation reconstructions are compared to process-based, climate driven dynamic vegetation model output to test the significance of fire frequency as a driver of vegetation composition and dynamics. Early-Holocene fire regimes in Fennoscandia are driven by natural climate variations and fuel availability. The establishment and spread of Norway spruce is driven by an increase in continentality of climate, but local natural and anthropogenic ecosystem disturbance may have aided this spread. The expansion of spruce led to a step-wise reduction in regional biomass

  5. Palynological Investigation of the Holocene Thermal Optimum in New Zealand

    Science.gov (United States)

    Newnham, R. M.; McGlone, M. S.; Wilmshurst, J. M.

    2005-12-01

    quantify MAT for a selected range of pollen profiles spanning the last glacial-Holocene interval from across the NZ region. We use the resulting MAT profiles to test the "early HTO hypothesis" (that is, a warming at the beginning of, or even just prior to, the Holocene). As well, we examine the amplitude and spatial uniformity of the HTO and its possible cause. References Hendy CH, Wilson AT. 1968. Nature 219, 48-51. Norton DA, McGlone MS, Wigley TML. 1986. NZJBot 24,331-342. Williams PW et al 2005. EPSL 230, 301-317.

  6. Diatom Stratigraphy of FA-1 Core, Qarun Lake, Records of Holocene Environmental and Climatic Change in Faiyum Oasis, Egypt

    Directory of Open Access Journals (Sweden)

    Zalat Abdelfattah A.

    2017-06-01

    Full Text Available This study evaluates changes in the environmental and climatic conditions in the Faiyum Oasis during the Holocene based on diatom analyses of the sediment FA-1 core from the southern seashore of the Qarun Lake. The studied FA-1 core was 26 m long and covered the time span ca. 9.000 cal. yrs BP. Diatom taxa were abundant and moderately to well-preserved throughout the core sediments. Planktonic taxa were most abundant than the benthic and epiphytic forms, which were very rare and sparsely distributed. The most dominant planktonic genera were Aulacoseira and Stephanodiscus followed by frequently distribution of Cyclostephanos and Cyclotella species. The stratigraphic distribution patterns of the recorded diatoms through the Holocene sediments explained five ecological diatom groups. These groups represent distinctive environmental conditions, which were mainly related to climatic changes through the early and middle Holocene, in addition to anthropogenic activity during the late Holocene. Comparison of diatom assemblages in the studied sediment core suggests that considerable changes occurred in water level as well as salinity. There were several high stands of the freshwater lake level during humid, warmer-wet climatic phases marked by dominance of planktonic, oligohalobous and alkaliphilous diatoms alternated with lowering of the lake level and slight increases in salinity and alkalinity during warm arid conditions evident by prevalence of brackish water diatoms.

  7. Marine methane cycle simulations for the period of early global warming

    Energy Technology Data Exchange (ETDEWEB)

    Elliott, S.; Maltrud, M.; Reagan, M.T.; Moridis, G.J.; Cameron-Smith, P.J.

    2011-01-02

    Geochemical environments, fates, and effects are modeled for methane released into seawater by the decomposition of climate-sensitive clathrates. A contemporary global background cycle is first constructed, within the framework of the Parallel Ocean Program. Input from organics in the upper thermocline is related to oxygen levels, and microbial consumption is parameterized from available rate measurements. Seepage into bottom layers is then superimposed, representing typical seabed fluid flow. The resulting CH{sub 4} distribution is validated against surface saturation ratios, vertical sections, and slope plume studies. Injections of clathrate-derived methane are explored by distributing a small number of point sources around the Arctic continental shelf, where stocks are extensive and susceptible to instability during the first few decades of global warming. Isolated bottom cells are assigned dissolved gas fluxes from porous-media simulation. Given the present bulk removal pattern, methane does not penetrate far from emission sites. Accumulated effects, however, spread to the regional scale following the modeled current system. Both hypoxification and acidification are documented. Sensitivity studies illustrate a potential for material restrictions to broaden the perturbations, since methanotrophic consumers require nutrients and trace metals. When such factors are considered, methane buildup within the Arctic basin is enhanced. However, freshened polar surface waters act as a barrier to atmospheric transfer, diverting products into the deep return flow. Uncertainties in the logic and calculations are enumerated including those inherent in high-latitude clathrate abundance, buoyant effluent rise through the column, representation of the general circulation, and bacterial growth kinetics.

  8. Marine methane cycle simulations for the period of early global warming

    Science.gov (United States)

    Elliott, Scott; Maltrud, Mathew; Reagan, Matthew; Moridis, George; Cameron-Smith, Philip

    2011-03-01

    Geochemical environments, fates, and effects are modeled for methane released into seawater by the decomposition of climate-sensitive clathrates. A contemporary global background cycle is first constructed, within the framework of the Parallel Ocean Program. Input from organics in the upper thermocline is related to oxygen levels, and microbial consumption is parameterized from available rate measurements. Seepage into bottom layers is then superimposed, representing typical seabed fluid flow. The resulting CH4 distribution is validated against surface saturation ratios, vertical sections, and slope plume studies. Injections of clathrate-derived methane are explored by distributing a small number of point sources around the Arctic continental shelf, where stocks are extensive and susceptible to instability during the first few decades of global warming. Isolated bottom cells are assigned dissolved gas fluxes from porous-media simulation. Given the present bulk removal pattern, methane does not penetrate far from emission sites. Accumulated effects, however, spread to the regional scale following the modeled current system. Both hypoxification and acidification are documented. Sensitivity studies illustrate a potential for material restrictions to broaden the perturbations, since methanotrophic consumers require nutrients and trace metals. When such factors are considered, methane buildup within the Arctic basin is enhanced. However, freshened polar surface waters act as a barrier to atmospheric transfer, diverting products into the deep return flow. Uncertainties in the logic and calculations are enumerated including those inherent in high-latitude clathrate abundance, buoyant effluent rise through the column, representation of the general circulation, and bacterial growth kinetics.

  9. Contrasting Responses of the Humboldt Current Ecosystem between the Holocene and MIS5e Interglacials Revealed from Multiple Sediment Records

    Science.gov (United States)

    Salvatteci, R.; Schneider, R. R.; Blanz, T.; Martinez, P.; Crosta, X.

    2016-12-01

    The Humboldt Current Ecosystem (HCE) off Peru yields about 10% of the global fish catch, producing more fish per unit area than any other region in the world. The high productivity is maintained by the upwelling of cold, nutrient-rich water from the oxygen minimum zone (OMZ), driven by strong trade winds. However, the potential impacts of climate change on upwelling dynamics and oceanographic conditions in the near future are uncertain, threatening local and global economies. Here, we unravel the response of the HCE to contrasting climatic conditions during the last two interglacials (i.e. Holocene and MIS5e) providing an independent insight about the relation between climatic factors and upwelling and productivity dynamics. For this purpose, we used multiple cores to reconstruct past changes in OMZ and upwelling intensity, productivity and fish biomass variability. Chronologies for the Holocene were obtained by multiple 14C ages and laminae correlations among cores, while for the MIS5e they were mainly done by correlation of prominent features in several proxies with other published records. We used a multiproxy approach including alkenones to reconstruct sea surface temperatures, δ15N as a proxy for water column denitrification, redox sensitive metals as proxies for sediment redox conditions, and diatom and fish debris assemblages to reconstruct ecological changes. The results show a very different response of the HCE to climate conditions during the last 2 interglacials, likely driven by changes in Tropical Pacific dynamics. During the Holocene we find that 1) the Late Holocene exhibits higher multi-centennial scale variability compared to the Early Holocene, 2) increased upwelling and a weak OMZ during the mid-Holocene, and 3) long term increase in productivity (diatoms and fishes) from the Early to the Late Holocene. During the MIS5e we find an 1) intense OMZ, 2) strong water column stratification, 3) high siliceous biomass, and 4) low fish biomass compared

  10. Early Mars serpentinization-derived CH4 reservoirs, H2 induced warming and paleopressure evolution

    Science.gov (United States)

    Lasue, J.; Chassefiere, E.; Langlais, B.; Quesnel, Y.

    2016-12-01

    CH4 has been observed on Mars both by remote sensing and in situ during the past 15 years. Early Mars serpentinization is one possible abiotic mechanism that could not only produce methane, but also explain the observed Martian remanent magnetic field. Assuming a cold early Mars, a cryosphere could trap such CH4 as clathrates in stable form at depth. We recently estimated the maximum storage capacity of such clathrate layer to be about 2x1019 to 2x1020 moles of methane. Such reservoirs may be stable or unstable, depending on many factors that are poorly constrained: major and sudden geological events such as the Tharsis bulge formation, the Hellas impact or the martian polar wander, could have destabilized the clathrates early in the history of the planet and released large quantities of gas in the atmosphere. Here we estimate the associated amounts of serpentinization-derived CH4 stored in the cryosphere that have been released to the atmosphere at the end of the Noachian and the beginning of the Hesperian. Due to rapid clathrate dissociation and photochemical conversion of CH4 to H2, these episodes of massive CH4 release may have resulted in transient H2-rich atmospheres, at typical levels of 10-20% in a background 1-2 bar CO2 atmosphere. We propose that the early Mars cryosphere had a sufficient CH4 storage capacity to have maintained H2-rich transient atmospheres during a total time period up to several Myr or tens of Myr, having potentially contributed - by collision-induced heating effect of atmospheric H2 - to the formation of valley networks during the late Noachian and early Hesperian.

  11. Holocene record of glacier variability from lake sediments reveals tripartite climate history for Svalbard

    Science.gov (United States)

    van der Bilt, Willem; Bakke, Jostein; Vasskog, Kristian; D`Andrea, William; Bradley, Raymond; Olafsdottir, Sædis

    2016-04-01

    The Arctic is responding sensitively to ongoing global climate change, warming and moistening faster than any other region on the planet. Holocene proxy paleoclimate time series are increasingly used to put this amplified response in perspective by understanding Arctic climate processes beyond the instrumental period. Glaciers rapidly respond to climate shifts as demonstrated by their current demise around the world. This response has a composite climate signature, marked by shifts in hydroclimate (winter precipitation) as well as (summer) temperature. Attendant changes in glacier size are recorded by variations in glacigenic rock flour that may be deposited in downstream lakes. Here, we present a Holocene reconstruction of glacier activity, based on sediments from Hajeren, a glacier-fed lake on northwest Spitsbergen in the High Arctic Svalbard archipelago. Owing to undisturbed sediments and robust age control, we could resolve variability on a sub-centennial scale. To ensure the accurate detection of glacier activity, we applied a toolbox of physical, magnetic and geochemical proxies in conjunction with multivariate statistics. Our findings indicate a three-stage Holocene climate history for Svalbard, driving by melt water pulses, episodic Atlantic cooling and a decline in orbitally driven summer insolation. Correspondence between inferred advances, including a Holocene glacier maximum around 9.5 ka BP, suggests forcing by the melting LIS during the Early Holocene. Following a late Holocene Thermal Maximum around 7.4 ka BP, glaciers disappeared from the catchment. Glaciers reformed around 4.2 ka BP during the regional onset of the Neoglacial, supporting previous findings. This transition did, however, not mark the onset of persistent glacier activity in the catchment, but a series of centennial-scale cycles of growth and decay, including events around 3.3 and 1.1 ka BP. As orbitally driven insolation declined towards the present, the glaciation threshold

  12. Neoglacial Antarctic sea-ice expansion driven by mid-Holocene retreat of the Ross Ice Shelf.

    Science.gov (United States)

    Bendle, J. A.; Newton, K.; Mckay, R. M.; Crosta, X.; Etourneau, J.; Anya, A. B.; Seki, O.; Golledge, N. R.; Bertler, N. A. N.; Willmott, V.; Schouten, S.; Riesselman, C. R.; Masse, G.; Dunbar, R. B.

    2017-12-01

    Recent decades have seen expanding Antarctic sea-ice coverage, coeval with thinning West Antarctic Ice Sheet (WAIS) ice shelves and the rapid freshening of surface and bottom waters along the Antarctic margin. The mid-Holocene Neoglacial transition represents the last comparable baseline shift in sea-ice behaviour. The drivers and feedbacks involved in both the recent and Holocene events are poorly understood and characterised by large proxy-model mismatches. We present new records of compound specific fatty acid isotope analyses (δ2H-FA), highly-branched isoprenoid alkenes (HBIs) TEX86L temperatures, grain-size, mass accumulations rates (MARs) and image analyses from a 171m Holocene sediment sequence from Site U1357 (IODP leg 318). In combination with published records we reconstruct Holocene changes in glacial meltwater, sedimentary inputs and sea-ice. The early Holocene (11 to 10 ka) is characterised by large fluctuations in inputs of deglacial meltwater and sediments and seismic evidence of downlapping material from the south, suggesting a dominating influence from glacial retreat of the local outlet glaciers. From 10 to 8 ka there is decreasing meltwater inputs, an onlapping drift and advection of material from the east. After ca. 8 ka positively correlated δ2H-FA and MARs infer that pulses of glacial melt correlate to stronger easterly currents, driving erosion of material from upstream banks and that the Ross Ice Shelf (RIS) becomes a major influence. A large mid-Holocene meltwater pulse (preceded by warming TEX86L temperatures) is evident between ca. 6 to 4.5 ka, culminating in a rapid and permanent increase in sea-ice from 4.5 ka. This is coeval with cosmogenic nuclide evidence for a rapid thinning of the Antarctic ice sheet during the mid-Holocene (Hein et al., 2016). We suggest this represents a final major pulse of deglaciation from the Ross Ice Shelf, which initiates the Neoglacial, driving cool surface waters along the coast and greater sea

  13. Individual to Community-Level Faunal Responses to Environmental Change from a Marine Fossil Record of Early Miocene Global Warming

    Science.gov (United States)

    Belanger, Christina L.

    2012-01-01

    Modern climate change has a strong potential to shift earth systems and biological communities into novel states that have no present-day analog, leaving ecologists with no observational basis to predict the likely biotic effects. Fossil records contain long time-series of past environmental changes outside the range of modern observation, which are vital for predicting future ecological responses, and are capable of (a) providing detailed information on rates of ecological change, (b) illuminating the environmental drivers of those changes, and (c) recording the effects of environmental change on individual physiological rates. Outcrops of Early Miocene Newport Member of the Astoria Formation (Oregon) provide one such time series. This record of benthic foraminiferal and molluscan community change from continental shelf depths spans a past interval environmental change (∼20.3-16.7 mya) during which the region warmed 2.1–4.5°C, surface productivity and benthic organic carbon flux increased, and benthic oxygenation decreased, perhaps driven by intensified upwelling as on the modern Oregon coast. The Newport Member record shows that (a) ecological responses to natural environmental change can be abrupt, (b) productivity can be the primary driver of faunal change during global warming, (c) molluscs had a threshold response to productivity change while foraminifera changed gradually, and (d) changes in bivalve body size and growth rates parallel changes in taxonomic composition at the community level, indicating that, either directly or indirectly through some other biological parameter, the physiological tolerances of species do influence community change. Ecological studies in modern and fossil records that consider multiple ecological levels, environmental parameters, and taxonomic groups can provide critical information for predicting future ecological change and evaluating species vulnerability. PMID:22558424

  14. Early and late hot extremes, and elongation of the warm period over Greece

    Science.gov (United States)

    Founda, Dimitra; Giannakopoulos, Christos; Pierros, Fragiskos

    2017-04-01

    The eastern Mediterranean has been assigned as one of the most responsive areas in climate change, mainly with respect to the occurrence of warmer and drier conditions. In Greece in particular, observations suggest prominent increases in the summer air temperature which in some areas amount to approximately 1 0C/decade since the mid 1970s, while Regional Climate Models simulate further increases in the near and distant future. These changes are coupled with simultaneous increase in the occurrence of hot extremes. In addition to changes in the frequency and intensity of hot extrems, timing of occurrence is also of special interest. Early heat waves in particular, have been found to increase thermal risk in humans. The study explores variations and trends in timing, namely the date of first and last occurrence of hot extremes within the year, and subsequently the hot extremes period (season), defined as the time interval (number of days) between first and last hot extremes occurrence, over Greece. A case study for the area of Athens covering a longer than 100-years period (1897-2015) was conducted first, which will be extended to other Greek areas. Several heat related climatic indices were used, based either on predefined temperature thresholds such as 'tropical days' (daily maximum air temperature, Tmax >30 0C), 'tropical nights' (daily minimum air temperature, Tmin >20 0C), 'hot days' (Tmax >35 0C), or on local climate statistics such as days with Tmax (or Tmin) > 95th percentile. The analysis revealed significant changes in the period of hot extremes and specifically elongation of the period, attributed to early rather than late hot extremes occurrence. An earlier shift of the first tropical day and the first tropical night occurrence by approximately 2 days/decade was found over the study period. An overall elongation of the 'hot days' season by 2.6 days/decade was also observed, which is more prominent since the early 1980s. Over the last three decades, earlier

  15. The Impact of Global Warming and Anoxia on Marine Benthic Community Dynamics: an Example from the Toarcian (Early Jurassic)

    Science.gov (United States)

    Danise, Silvia; Twitchett, Richard J.; Little, Crispin T. S.; Clémence, Marie-Emilie

    2013-01-01

    The Pliensbachian-Toarcian (Early Jurassic) fossil record is an archive of natural data of benthic community response to global warming and marine long-term hypoxia and anoxia. In the early Toarcian mean temperatures increased by the same order of magnitude as that predicted for the near future; laminated, organic-rich, black shales were deposited in many shallow water epicontinental basins; and a biotic crisis occurred in the marine realm, with the extinction of approximately 5% of families and 26% of genera. High-resolution quantitative abundance data of benthic invertebrates were collected from the Cleveland Basin (North Yorkshire, UK), and analysed with multivariate statistical methods to detect how the fauna responded to environmental changes during the early Toarcian. Twelve biofacies were identified. Their changes through time closely resemble the pattern of faunal degradation and recovery observed in modern habitats affected by anoxia. All four successional stages of community structure recorded in modern studies are recognised in the fossil data (i.e. Stage III: climax; II: transitional; I: pioneer; 0: highly disturbed). Two main faunal turnover events occurred: (i) at the onset of anoxia, with the extinction of most benthic species and the survival of a few adapted to thrive in low-oxygen conditions (Stages I to 0) and (ii) in the recovery, when newly evolved species colonized the re-oxygenated soft sediments and the path of recovery did not retrace of pattern of ecological degradation (Stages I to II). The ordination of samples coupled with sedimentological and palaeotemperature proxy data indicate that the onset of anoxia and the extinction horizon coincide with both a rise in temperature and sea level. Our study of how faunal associations co-vary with long and short term sea level and temperature changes has implications for predicting the long-term effects of “dead zones” in modern oceans. PMID:23457537

  16. Amino and fatty acid dynamics of octopus (Octopus vulgaris) early life stages under ocean warming.

    Science.gov (United States)

    Lopes, Vanessa M; Faleiro, Filipa; Baptista, Miguel; Pimentel, Marta S; Paula, José R; Couto, Ana; Bandarra, Narcisa; Anacleto, Patrícia; Marques, António; Rosa, Rui

    2016-01-01

    The oceans are becoming warmer, and the higher temperatures are expected to have a major impact on marine life at different levels of biological organization, especially at the most vulnerable early life stages. Thus, we hypothesize that the future warmer scenarios (here +3 °C) will affect the biochemical composition (amino acid - AA, and fatty acid-FA) of octopod (Octopus vulgaris) embryos and recently-hatched pelagic paralarvae. The main essential amino acids found in octopus embryos were arginine, leucine and lysine; while aspartic and glutamic acids, and taurine were the main non-essential amino acids. Palmitic, eicosapentaenoic and docosahexaenoic acids were the main FAs found in octopus tissues. Relevant ontogenetic changes were observed, namely a steep decrease in the content of many AAs, and a selective retention of FAs, thus evidencing the protein-based metabolism of these cephalopods. Temperature per si did not elicit significant changes in the overall FA composition, but was responsible for a significant decrease in the content of several AAs, indicating increased embryonic consumption. Copyright © 2015 Elsevier Ltd. All rights reserved.

  17. Holocene climatic fluctuations from Lower Brahmaputra flood plain ...

    Indian Academy of Sciences (India)

    BP which is well-matched with the peak period of the Holocene climatic optimum. However, during ... Warm Period and Little Ice Age (LIA) in this ... The maximum temperature is 30.4 ..... V 2007 Climatic changes during the last 1800 yrs from.

  18. Influence of Holocene environmental change and anthropogenic impact on the diversity and distribution of roe deer.

    Science.gov (United States)

    Baker, K H; Hoelzel, A R

    2014-06-01

    Extant patterns of population structure and levels of diversity are a consequence of factors that vary in both space and time. Our objective in this study is to investigate a species that has responded to both natural and anthropogenic changes in ways that have shaped modern populations and provide insight into the key processes. The roe deer (Capreolus capreolus) is one of the two species of deer native to Britain. During the last glacial maximum (LGM), the British habitat was largely under ice and there was a land bridge to mainland Europe. As the Earth warmed during the early Holocene, the land bridge was lost. Subsequent hunting on the British mainland left the southern region extirpated of roe deer, whereas a refugial population remained in the north. Later reintroductions from Europe led to population expansion, especially in southern United Kingdom. Here, we combine data from ancient and modern DNA to track population dynamics and patterns of connectivity, and test hypotheses about the influence of natural and anthropogenic environmental change. We find that past expansion and divergence events coincided with a warming environment and the subsequent closure of the land bridge between Europe and the United Kingdom. We also find turnover in British roe deer haplotypes between the late-Holocene and modern day that have likely resulted from recent human disturbance activities such as habitat perturbation, overhunting and restocking.

  19. Sources and characteristics of terrestrial carbon in Holocene-scale sediments of the East Siberian Sea

    Science.gov (United States)

    Keskitalo, Kirsi; Tesi, Tommaso; Bröder, Lisa; Andersson, August; Pearce, Christof; Sköld, Martin; Semiletov, Igor P.; Dudarev, Oleg V.; Gustafsson, Örjan

    2017-09-01

    Thawing of permafrost carbon (PF-C) due to climate warming can remobilise considerable amounts of terrestrial carbon from its long-term storage to the marine environment. PF-C can be then be buried in sediments or remineralised to CO2 with implications for the carbon-climate feedback. Studying historical sediment records during past natural climate changes can help us to understand the response of permafrost to current climate warming. In this study, two sediment cores collected from the East Siberian Sea were used to study terrestrial organic carbon sources, composition and degradation during the past ˜ 9500 cal yrs BP. CuO-derived lignin and cutin products (i.e., compounds solely biosynthesised in terrestrial plants) combined with δ13C suggest that there was a higher input of terrestrial organic carbon to the East Siberian Sea between ˜ 9500 and 8200 cal yrs BP than in all later periods. This high input was likely caused by marine transgression and permafrost destabilisation in the early Holocene climatic optimum. Based on source apportionment modelling using dual-carbon isotope (Δ14C, δ13C) data, coastal erosion releasing old Pleistocene permafrost carbon was identified as a significant source of organic matter translocated to the East Siberian Sea during the Holocene.

  20. Slipstream: an early Holocene slump and turbidite record from the frontal ridge of the Cascadia accretionary wedge off western Canada and paleoseismic implications

    Science.gov (United States)

    Hamilton, T.S.; Enkin, Randolph J.; Riedel, Michael; Rogers, Gary C.; Pohlman, John W.; Benway, Heather M.

    2015-01-01

    800 years (marine reservoir correction ΔR= 400 years). Rather, the top of the core appears to be 400 years in the future. A younger marine reservoir age of 400 years (ΔR = 0 years) brings the top to the present and produces better correlations with the nearby Effingham Inlet paleo-earthquake chronology based only on terrestrial carbon requiring no reservoir correction. The high-resolution dating and facies analysis of Slipstream Slump in this isolated slope basin setting demonstrates that this is also a useful type of sedimentary target for sampling the paleoseismic record in addition to the more studied turbidites from submarine canyon and channel systems. The first 10 turbidites at Slipstream Slump were deposited between 10.8 and 6.6 ka BP, after which the system became sediment starved and only two more turbidites were deposited. The recurrence interval for the inferred frequent early Holocene megathrust earthquakes is 460 ± 140 years, compatible with other estimates of paleoseismic megathrust earthquake occurrence rates along the subduction zone.

  1. Geomorphological and cryostratigraphical analyses of the Zackenberg Valley, NE Greenland and significance of Holocene alluvial fans

    Science.gov (United States)

    Cable, Stefanie; Christiansen, Hanne H.; Westergaard-Nielsen, Andreas; Kroon, Aart; Elberling, Bo

    2018-02-01

    In High Arctic northern Greenland, future responses to climatic changes are poorly understood on a landscape scale. Here, we present a study of the geomorphology and cryostratigraphy in the Zackenberg Valley in NE Greenland (74°N) containing a geomorphological map and a simplified geocryological map, combined with analyses of 13 permafrost cores and two exposures. Cores from a solifluction sheet, alluvial fans, and an emerged delta were studied with regards to cryostructures, ice and total carbon contents, grain size distribution, and pore water electrical conductivity; and the samples were AMS 14C dated. The near-surface permafrost on slopes and alluvial fans is ice rich, as opposed to the ice-poor epigenetic permafrost in the emerged delta. Ground ice and carbon distribution are closely linked to sediment transport processes, which largely depend on lithology and topography. Holocene alluvial fans on the lowermost hillslopes, covering 12% of the study area, represent paleoenvironmental archives. During the contrasting climates of the Holocene, the alluvial fans continued to aggrade - through the warmer early Holocene Optimum, the colder late Holocene, and the following climate warming - and by 0.45 mm a- 1, on average. This is caused by three factors: sedimentation, ground ice aggradation, and vegetation growth and is reflected by AMS 14C dating and continuously alternating cryostructures. Highly variable sedimentation rates in space and time at the alluvial fans have been detected. This is also reflected by alternating lenticular and microlenticular cryostructures indicating syngenetic permafrost aggradation during sedimentation with suspended and organic-matrix cryostructures indicating quasi-syngenetic permafrost aggradation in response to vegetation growth in periods with reduced or no sedimentation. Over time, this causes organic matter to become buried, indicating that alluvial fans represent effective carbon sinks that have previously been overlooked.

  2. Long-term deforestation in NW Spain: linking the Holocene fire history to vegetation change and human activities

    Science.gov (United States)

    Kaal, Joeri; Carrión Marco, Yolanda; Asouti, Eleni; Martín Seijo, Maria; Martínez Cortizas, Antonio; Costa Casáis, Manuela; Criado Boado, Felipe

    2011-01-01

    The Holocene fire regime is thought to have had a key role in deforestation and shrubland expansion in Galicia (NW Spain) but the contribution of past societies to vegetation burning remains poorly understood. This may be, in part, due to the fact that detailed fire records from areas in close proximity to archaeological sites are scarce. To fill this gap, we performed charcoal analysis in five colluvial soils from an archaeological area (Campo Lameiro) and compared the results to earlier studies from this area and palaeo-ecological literature from NW Spain. This analysis allowed for the reconstruction of the vegetation and fire dynamics in the area during the last ca 11 000 yrs. In the Early Holocene, Fabaceae and Betula sp. were dominant in the charcoal record. Quercus sp. started to replace these species around 10 000 cal BP, forming a deciduous forest that prevailed during the Holocene Thermal Maximum until ˜5500 cal BP. Following that, several cycles of potentially fire-induced forest regression with subsequent incomplete recovery eventually led to the formation of an open landscape dominated by shrubs (Erica sp. and Fabaceae). Major episodes of forest regression were (1) ˜5500-5000 cal BP, which marks the mid-Holocene cooling after the Holocene Thermal Maximum, but also the period during which agropastoral activities in NW Spain became widespread, and (2) ˜2000-1500 cal BP, which corresponds roughly to the end of the Roman Warm Period and the transition from the Roman to the Germanic period. The low degree of chronological precision, which is inherent in fire history reconstructions from colluvial soils, made it impossible to distinguish climatic from human-induced fires. Nonetheless, the abundance of synanthropic pollen indicators (e.g. Plantago lanceolata and Urtica dioica) since at least ˜6000 cal BP strongly suggests that humans used fire to generate and maintain pasture.

  3. Reconstruction of glacier variability from lake sediments reveals dynamic Holocene climate in Svalbard

    Science.gov (United States)

    van der Bilt, Willem G. M.; Bakke, Jostein; Vasskog, Kristian; D'Andrea, William J.; Bradley, Raymond S.; Ólafsdóttir, Sædis

    2015-10-01

    The Arctic is warming faster than anywhere else on Earth. Holocene proxy time-series are increasingly used to put this amplified response in perspective by understanding Arctic climate processes beyond the instrumental period. However, available datasets are scarce, unevenly distributed and often of coarse resolution. Glaciers are sensitive recorders of climate shifts and variations in rock-flour production transfer this signal to the lacustrine sediment archives of downstream lakes. Here, we present the first full Holocene record of continuous glacier variability on Svalbard from glacier-fed Lake Hajeren. This reconstruction is based on an undisturbed lake sediment core that covers the entire Holocene and resolves variability on centennial scales owing to 26 dating points. A toolbox of physical, geochemical (XRF) and magnetic proxies in combination with multivariate statistics has allowed us to fingerprint glacier activity in addition to other processes affecting the sediment record. Evidence from variations in sediment density, validated by changes in Ti concentrations, reveal glaciers remained present in the catchment following deglaciation prior to 11,300 cal BP, culminating in a Holocene maximum between 9.6 and 9.5 ka cal BP. Correspondence with freshwater pulses from Hudson Strait suggests that Early Holocene glacier advances were driven by the melting Laurentide Ice Sheet (LIS). We find that glaciers disappeared from the catchment between 7.4 and 6.7 ka cal BP, following a late Hypsithermal. Glacier reformation around 4250 cal BP marks the onset of the Neoglacial, supporting previous findings. Between 3380 and 3230 cal BP, we find evidence for a previously unreported centennial-scale glacier advance. Both events are concurrent with well-documented episodes of North Atlantic cooling. We argue that this brief forcing created suitable conditions for glaciers to reform in the catchment against a background of gradual orbital cooling. These findings highlight the

  4. Holocene temperature variability revealed by brGDGTs in subtropical southwestern China

    Science.gov (United States)

    Feng, X.; Zhao, C.

    2017-12-01

    Subtropical areas are important source region of moisture and heat in global climate system. Paleoclimate reconstructions from these regions, especially quantitative records, would not only help to better understand the nature of climate system through time, but also provide important constraining dataset for long-term ecosystem variations in these ecological important areas. To date, quantitative climate records with reliable chronological controls are still limited from terrestrial archives in subtropical areas. Here we present a 50-year-resolution quantitative temperature record throughout the Holocene based on branched GDGTs at a small alpine lake, Tiancai Lake (26°38'E, 99°43'N, 3898 m.a.s.l) in southwestern China. The record is based on a temporal calibration between instrumental mean annual air temperature (MAAT) and brGDGT compounds (GDGT-IIIa, GDGT-IIa', GDGT-IIb, GDGT-Ia and GDGT-Ic). The MAAT was relatively low -0.6 ° between 11 and 7.5 ka, then abruptly increased 1 ° to 4 °until 7 ka. The MAAT was relatively warm 2° between 7 and 1 ka, then decreased to 1° over the last 1 ka. The Middle to Late Holocene was 3 ° warmer than the Early Holocene. The MAAT variation at Lake Tiancai is supported by changes in evergreen oaks and Tsuga from the same sediment core, suggesting that the growth of cold-tolerant forest in place of subtropical evergreen broadleaved forest has been driven by the decrease in MAAT. The early Holocene cold interval revealed by our record and pollen data is different with the chironomid-based summer temperature reconstruction from the same lake, the latter has been driven by summer insolation. This difference suggests that a pronounced winter contribution to the mean annual temperature during the early Holocene, which was probably caused by a low winter insolation, and strengthened by a sparse vegetation cover and influences of winter ice/snow cover in tropical high latitude regions.

  5. Planktonic foraminiferal oxygen isotope analysis by ion microprobe technique suggests warm tropical sea surface temperatures during the Early Paleogene

    Science.gov (United States)

    Kozdon, Reinhard; Kelly, D. Clay; Kita, Noriko T.; Fournelle, John H.; Valley, John W.

    2011-09-01

    Cool tropical sea surface temperatures (SSTs) are reported for warm Paleogene greenhouse climates based on the δ18O of planktonic foraminiferal tests. These results are difficult to reconcile with models of greenhouse gas-forced climate. It has been suggested that this "cool tropics paradox" arises from postdepositional alteration of foraminiferal calcite, yielding erroneously high δ18O values. Recrystallization of foraminiferal tests is cryptic and difficult to quantify, and the compilation of robust δ18O records from moderately altered material remains challenging. Scanning electron microscopy of planktonic foraminiferal chamber-wall cross sections reveals that the basal area of muricae, pustular outgrowths on the chamber walls of species belonging to the genus Morozovella, contain no mural pores and may be less susceptible to postdepositional alteration. We analyzed the δ18O in muricae bases of morozovellids from the central Pacific (Ocean Drilling Program Site 865) by ion microprobe using 10 μm pits with an analytical reproducibility of ±0.34‰ (2 standard deviations). In situ measurements of δ18O in these domains yield consistently lower values than those published for conventional multispecimen analyses. Assuming that the original δ18O is largely preserved in the basal areas of muricae, this new δ18O record indicates Early Paleogene (˜49-56 Ma) tropical SSTs in the central Pacific were 4°-8°C higher than inferred from the previously published δ18O record and that SSTs reached at least ˜33°C during the Paleocene-Eocene thermal maximum. This study demonstrates the utility of ion microprobe analysis for generating more reliable paleoclimate records from moderately altered foraminiferal tests preserved in deep-sea sediments.

  6. Warm springs, early lay dates, and double brooding in a North American migratory songbird, the black-throated blue warbler.

    Directory of Open Access Journals (Sweden)

    Andrea K Townsend

    Full Text Available Numerous studies have correlated the advancement of lay date in birds with warming climate trends, yet the fitness effects associated with this phenological response have been examined in only a small number of species. Most of these species--primarily insectivorous cavity nesters in Europe--exhibit fitness declines associated with increasing asynchrony with prey. Here, we use 25 years of demographic data, collected from 1986 to 2010, to examine the effects of spring temperature on breeding initiation date, double brooding, and annual fecundity in a Nearctic-Neotropical migratory songbird, the black-throated blue warbler (Setophaga caerulescens. Data were collected from birds breeding at the Hubbard Brook Experimental Forest, New Hampshire, USA, where long-term trends toward warmer springs have been recorded. We found that black-throated blue warblers initiated breeding earlier in warmer springs, that early breeders were more likely to attempt a second brood than those starting later in the season, and that double brooding and lay date were linked to higher annual fecundity. Accordingly, we found selection favored earlier breeding in most years. However, in contrast to studies of several other long-distance migratory species in Europe, this selection pressure was not stronger in warmer springs, indicating that these warblers were able to adjust mean lay date appropriately to substantial inter-annual variation in spring temperature. Our results suggest that this North American migratory songbird might not experience the same fecundity declines as songbirds that are unable to adjust their timing of breeding in pace with spring temperatures.

  7. Deep water ventilation in the northwestern North Pacific during the last deglaciation and the early Holocene (15-5 cal. kyr B.P.) based on AMS 14C dating

    International Nuclear Information System (INIS)

    Minoshima, Kayo; Kawahata, Hodaka; Irino, Tomohisa; Ikehara, Ken; Aoki, Kaori; Uchida, Masao; Yoneda, Minoru; Shibata, Yasuyuki

    2007-01-01

    The difference between benthic and planktonic foraminifera radiocarbon (B-P 14 C) age differences in core PC6 (40 o 23.89' N, 143 o 29.87' E) retrieved from the northwestern North Pacific provide a clue to the reconstruction of deep water circulation during the last deglaciation and the early Holocene (15-5 cal. kyr B.P.). The observed B-P 14 C age differences ranged from 1030 to 1630 years, which are comparable to the present-day apparent ventilation age. It suggested that the ventilation generally remained similar during 15-5 cal. kyr B.P. However, B-P 14 C age difference slightly reduced at 14.6 cal. kyr B.P., indicating that the higher ventilation temporality could have occurred in the northwestern North Pacific (∼2200 m water depth)

  8. Earlier flowering did not alter pollen limitation in an early flowering shrub under short-term experimental warming

    OpenAIRE

    Pan, Cheng-Chen; Feng, Qi; Zhao, Ha-Lin; Liu, Lin-De; Li, Yu-Lin; Li, Yu-Qiang; Zhang, Tong-Hui; Yu, Xiao-Ya

    2017-01-01

    In animal pollinated plants, phenological shifts caused by climate change may have important ecological consequences. However, no empirical evidence exists at present on the consequences that flowering phenology shifts have on the strength of pollen limitation under experimental warming. Here, we investigated the effects of experimental warming on flowering phenology, flower density, reproductive success, and pollen limitation intensity in Caragana microphylla and evaluated whether earlier fl...

  9. 1300 km long late Pleistocene-Holocene shelf edge barrier reef system along the western continental shelf of India: Occurrence and significance

    Digital Repository Service at National Institute of Oceanography (India)

    Vora, K.H.; Wagle, B.G.; Veerayya, M.; Almeida, F.; Karisiddaiah, S.M.

    . It is surmised that coral/algal reef growth commenced with the advent of the Holocene trangression and favorable antecedent topography, and continued until early Holocene. Subsequently, rapid sea level rise drowned the reefs. The shelf edge reefs, therefore...

  10. Holocene vegetation change in the northern Peten and its implications for Maya prehistory

    Science.gov (United States)

    Wahl, David; Byrne, Roger; Schreiner, Thomas; Hansen, Richard

    2006-05-01

    An ˜8400 cal yr record of vegetation change from the northern Peten, Guatemala, provides new insights into the environmental history of the archaeological area known as the Mirador Basin. Pollen, loss on ignition, and magnetic susceptibility analyses indicate warm and humid conditions in the early to mid-Holocene. Evidence for a decrease in forest cover around 4600 cal yr B.P. coincides with the first appearance of Zea mays pollen, suggesting that human activity was responsible. The period between 3450 cal yr B.P. and 1000 cal yr B.P. is characterized by a further decline in forest pollen types, includes an abrupt increase in weedy taxa, and exhibits the highest magnetic susceptibility values since the early Holocene, all of which suggest further agricultural disturbance in the watershed. A brief drop in disturbance indicators around 1800 cal yr B.P. may represent the Preclassic abandonment of the area. Changing pollen frequencies around 1000 cal yr B.P. indicate a cessation of human disturbance, which represents the Late Classic collapse of the southern Maya lowlands.

  11. Global change effects on early holocene sedimentation of the Brazilian continental shelf determined from TM-LANDSAT 5 data of the seafloor

    International Nuclear Information System (INIS)

    Cabral, A.P.; Vianna, M.L.; Gherardi, D.F.M.

    1992-01-01

    A study of the shaping of the seafloor morphology on the Brazilian northeast continental shelf caused by climatic changes in the beginning of the Holocene is being made with the support of TM-Landsat 5 data. Special emphasis is given on analysis of data from ancient shorelines between 20-45m depth, to be correlated with abrupt global climate change between 10,000-8,000 BP. The transport of a quartz sand deposit by the ocean currents through time, effected by active sandwave fields at the 20 m isobath is also described. Two images were used corresponding to two dates: 1984 and 1989. Geometric correction, filter application and contrast enhancement were performed. A comparison between 84' and 89' images was carried out, to detect changing patterns of the sand waves, along a 5 year period, caused by the seasonal wintertime wind-forced ocean currents. Based on this registration, estimates of displacement rates for the sand deposit could be made

  12. Biotic turnover rates during the Pleistocene-Holocene transition

    Science.gov (United States)

    Stivrins, Normunds; Soininen, Janne; Amon, Leeli; Fontana, Sonia L.; Gryguc, Gražyna; Heikkilä, Maija; Heiri, Oliver; Kisielienė, Dalia; Reitalu, Triin; Stančikaitė, Miglė; Veski, Siim; Seppä, Heikki

    2016-11-01

    The Northern Hemisphere is currently warming at the rate which is unprecedented during the Holocene. Quantitative palaeoclimatic records show that the most recent time in the geological history with comparable warming rates was during the Pleistocene-Holocene transition (PHT) about 14,000 to 11,000 years ago. To better understand the biotic response to rapid temperature change, we explore the community turnover rates during the PHT by focusing on the Baltic region in the southeastern sector of the Scandinavian Ice Sheet, where an exceptionally dense network on microfossil and macrofossil data that reflect the biotic community history are available. We further use a composite chironomid-based summer temperature reconstruction compiled specifically for our study region to calculate the rate of temperature change during the PHT. The fastest biotic turnover in the terrestrial and aquatic communities occurred during the Younger Dryas-Holocene shift at 11,700 years ago. This general shift in species composition was accompanied by regional extinctions, including disappearance of mammoth (Mammuthus primigenius) and reindeer (Rangifer tarandus) and many arctic-alpine plant taxa, such as Dryas octopetala, Salix polaris and Saxifraga aizoides, from the region. This rapid biotic turnover rate occurred when the rate of warming was 0.17 °C/decade, thus slightly lower than the current Northern Hemisphere warming of 0.2 °C/decade. We therefore conclude that the Younger Dryas-Holocene shift with its rapid turnover rates and associated regional extinctions represents an important palaeoanalogue to the current high latitude warming and gives insights about the probable future turnover rates and patterns of the terrestrial and aquatic ecosystem change.

  13. Holocene climate dynamics in the central part of the East European plain (Russia)

    Science.gov (United States)

    Novenko, Elena

    2013-04-01

    The Holocene climate and vegetation dynamics in the broad-leaved forest zone of the central part of the East European plain have been reconstructed on the base of pollen, plant macrofossil, testate amoebae and radiocarbon data from the mire Klukva (N 53.834812, E 36.252488), located in the kast depression in the Upper Oka River basin (Tula region, European Russia). The reconstruction of main parameters of past climate (the mean annual temperature precipitation) was carried out by the "Best Modern Analog" approach. Reconstructions of vegetation show that in the early Holocene the territory was occupied mainly by birch and pine-birch forests. Significant changes in the plant cover of the Upper Oka River basin are attributed to the 7.5 cal kyr BP). The climatic conditions were favorable for development of the broad-leaved forests those persisted in this area up to industrial period. In the 17th century, when the population density greatly increased and watersheds were ploughed, natural vegetation communities were gradually destroyed and transformed into agricultural landscapes. According to obtained climatic reconstructions the period 10-8.5 cal kyr BP was relatively cold and wet, when the mean annual temperature was in 3°C lower and precipitation was in 50-100 mm higher then nowadays. The significant climate warming occurred in about 7.0-5.0 cal kyr BP (The Holocene thermal maximum): the mean annual temperature in 2°C exceeded the modern value and precipitation was close to that. The environment conditions were drier due to decrease of effective moisture. In the second part of the Holocene the sequence of second-, and even third-order climatic oscillations expressed against the background of the overall slight trend towards cooling have been determined. The most pronounced cool and wet intervals were reconstructed in 2.5-2.0 cal kyr BP and 1.5-1.3 cal kyr BP. The mean annual temperature decreased in 1.5-2 °C and precipitation rose in 200 mm in compare to modern

  14. Human responses to Middle Holocene climate change on California's Channel Islands

    Science.gov (United States)

    Kennett, Douglas J.; Kennett, James P.; Erlandson, Jon M.; Cannariato, Kevin G.

    2007-02-01

    High-resolution archaeological and paleoenvironmental records from California's Channel Islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses. Available climate records in western North America (7-3.8 ka) indicate a severe dry interval between 6.3 and 4.8 ka embedded within a generally warm and dry Middle Holocene. Very dry conditions in western North America between 6.3 and 4.8 ka correlate with cold to moderate sea-surface temperatures (SST) along the southern California Coast evident in Ocean Drilling Program (ODP) Core 893A/B (Santa Barbara Basin). An episode of inferred high marine productivity between 6.3 and 5.8 ka corresponds with the coldest estimated SSTs of the Middle Holocene, otherwise marked by warm/low productivity marine conditions (7.5-3.8 ka). The impact of this severe aridity on humans was different between the northern and southern Channel Islands, apparently related to degree of island isolation, size and productivity of islands relative to population, fresh water availability, and on-going social relationships between island and continental populations. Northern Channel Islanders seem to have been largely unaffected by this severe arid phase. In contrast, cultural changes on the southern Channel Islands were likely influenced by the climatically induced environmental changes. We suggest that productive marine conditions coupled with a dry terrestrial climate between 6.3 and 5.8 ka stimulated early village development and intensified fishing on the more remote southern islands. Contact with people on the adjacent southern California Coast increased during this time with increased participation in a down-the-line trade network extending into the western Great Basin and central Oregon. Genetic similarities between Middle Holocene burial populations on the southern Channel Islands and modern California Uto-Aztecan populations suggest

  15. Holocene Temperature Reconstructions from Arctic Lakes based on Alkenone Paleothermometry and Non-Destructive Scanning Techniques

    Science.gov (United States)

    D'Andrea, W. J.; Balascio, N. L.; Bradley, R. S.; Bakke, J.; Gjerde, M.; Kaufman, D. S.; Briner, J. P.; von Gunten, L.

    2014-12-01

    Generating continuous, accurate and quantitative Holocene temperature estimates from the Arctic is an ongoing challenge. In many Arctic regions, tree ring-based approaches cannot be used and lake sediments provide the most valuable repositories for extracting paleotemperature information. Advances in lacustrine alkenone paleothermometry now allow for quantitative reconstruction of lake-water temperature based on the UK37 values of sedimentary alkenones. In addition, a recent study demonstrated the efficacy of non-destructive scanning reflectance spectroscopy in the visible range (VIS-RS) for high-resolution quantitative temperature reconstruction from arctic lake sediments1. In this presentation, I will report a new UK37-based temperature reconstruction and a scanning VIS-RS record (using the RABD660;670 index as a measure of sedimentary chlorin content) from Kulusuk Lake in southeastern Greenland (65.6°N, 37.1°W). The UK37 record reveals a ~3°C increase in summer lake water temperatures between ~10ka and ~7ka followed by sustained warmth until ~4ka and a gradual (~3°C) cooling until ~400 yr BP. The strong correlation between UK37 and RABD660;670 measured in the same sediment core provides further evidence that in arctic lakes where temperature regulates primary productivity, and thereby sedimentary chlorin content, these proxies can be combined to develop high-resolution quantitative temperature records. The Holocene temperature history of Kulusuk Lake determined using this approach corresponds to changes in the size of the glaciers adjacent to the lake, as inferred from sediment minerogenic properties measured with scanning XRF. Glaciers retreated during early Holocene warming, likely disappeared during the period of mid-Holocene warmth, and advanced after 4ka. I will also discuss new UK37 and RABD660;670 reconstructions from northwestern Svalbard and the central Brooks Range of Alaska within the framework of published regional temperature reconstructions and

  16. Molluscs as evidence for a late Pleistocene and early Holocene humid period in the southern coastal desert of Peru (14.5°S)

    Science.gov (United States)

    Mächtle, Bertil; Unkel, Ingmar; Eitel, Bernhard; Kromer, Bernd; Schiegl, Solveig

    2010-01-01

    The southern Peruvian coastal desert around Palpa, southern Peru (14.5°S) is currently characterized by hyper-arid conditions. However, the presence of two species of molluscs ( Scutalus, Pupoides) and desert-loess deposits indicates the past development of semi-desert and grassland ecosystems caused by a displacement of the eastern desert margin due to hydrological changes. Radiocarbon dating shows that the transition to a semi-arid climate in the southern Peruvian coastal desert took place during the Greenland interstadial 1, ˜ 13.5 cal ka BP. At the beginning of the Holocene, the mollusc fauna vanished due to increasing humidity and the development of grasslands. Dust particles were fixed by the grasses, as indicated by abundant Poaceae phytoliths, and desert loess was formed. The humid period we observe here is out of phase with the palaeoenvironmental records from the Titicaca region, which indicates dry conditions at that time. This paper offers a new idea for this contradiction: an orbitally driven meridional shift of the Bolivian high might have altered the moisture supply across the Andes.

  17. The greening of the McGill Paleoclimate Model. Part II: Simulation of Holocene millennial-scale natural climate changes

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yi; Mysak, Lawrence A.; Wang, Zhaomin [McGill University, Department of Atmospheric and Oceanic Sciences and Global Environmental and Climate Change Centre (GEC3), Montreal, Quebec (Canada); Brovkin, Victor [Potsdam Institute for Climate Impact Research (PIK), 601203, Potsdam (Germany)

    2005-04-01

    Various proxy data reveal that in many regions of the Northern Hemisphere (NH), the middle Holocene (6 kyr BP) was warmer than the early Holocene (8 kyr BP) as well as the later Holocene, up to the end of the pre-industrial period (1800 AD). This pattern of warming and then cooling in the NH represents the response of the climate system to changes in orbital forcing, vegetation cover and the Laurentide Ice Sheet (LIS) during the Holocene. In an attempt to better understand these changes in the climate system, the McGill Paleoclimate Model (MPM) has been coupled to the dynamic global vegetation model known as VECODE (see Part I of this two-part paper), and a number of sensitivity experiments have been performed with the ''green'' MPM. The model results illustrate the following: (1) the orbital forcing together with the vegetation - albedo feedback result in the gradual cooling of global SAT from about 6 kyr BP to the end of the pre-industrial period; (2) the disappearance of the LIS over the period 8-6 kyr BP, associated with vegetation - albedo feedback, allows the global SAT to increase and reach its maximum at around 6 kyr BP; (3) the northern limit of the boreal forest moves northward during the period 8-6.4 kyr BP due to the LIS retreat; (4) during the period 6.4-0 kyr BP, the northern limit of the boreal forest moves southward about 120 km in response to the decreasing summer insolation in the NH; and (5) the desertification of northern Africa during the period 8-2.6 kyr BP is mainly explained by the decreasing summer monsoon precipitation. (orig.)

  18. Holocene lowering of the Laurentide ice sheet affects North Atlantic gyre circulation and climate

    Science.gov (United States)

    Gregoire, Lauren J.; Ivanovic, Ruza F.; Maycock, Amanda C.; Valdes, Paul J.; Stevenson, Samantha

    2018-02-01

    The Laurentide ice sheet, which covered Canada during glacial periods, had a major influence on atmospheric circulation and surface climate, but its role in climate during the early Holocene (9-7 ka), when it was thinner and confined around Hudson Bay, is unclear. It has been suggested that the demise of the ice sheet played a role in the 8.2 ka event (an abrupt 1-3 °C Northern Hemisphere cooling lasting 160 years) through the influence of changing topography on atmospheric circulation. To test this hypothesis, and to investigate the broader implications of changing ice sheet topography for climate, we analyse a set of equilibrium climate simulations with ice sheet topographies taken at 500 year intervals from 9.5 to 8.0 ka. Between 9.5 and 8.0 ka, our simulations show a 2 °C cooling south of Iceland and a 1 °C warming between 40° and 50°N in the North Atlantic. These surface temperature changes are associated with a weakening of the subtropical and subpolar gyres caused by a decreasing wind stress curl over the mid-North Atlantic as the ice sheet lowers. The climate response is strongest during the period of peak ice volume change (9.5-8.5 ka), but becomes negligible after 8.5 ka. The climatic effects of the Laurentide ice sheet lowering during the Holocene are restricted to the North Atlantic sector. Thus, topographic forcing is unlikely to have played a major role in the 8.2 ka event and had only a small effect on Holocene climate change compared to the effects of changes in greenhouse gases, insolation and ice sheet meltwater.

  19. Holocene fire activity and vegetation response in South-Eastern Iberia

    Science.gov (United States)

    Gil-Romera, Graciela; Carrión, José S.; Pausas, Juli G.; Sevilla-Callejo, Miguel; Lamb, Henry F.; Fernández, Santiago; Burjachs, Francesc

    2010-05-01

    Since fire has been recognized as an essential disturbance in Mediterranean landscapes, the study of long-term fire ecology has developed rapidly. We have reconstructed a sequence of vegetation dynamics and fire changes across south-eastern Iberia by coupling records of climate, fire, vegetation and human activities. We calculated fire activity anomalies (FAAs) in relation to 3 ka cal BP for 10-8 ka cal BP, 6 ka cal BP, 4 ka cal BP and the present. For most of the Early to the Mid-Holocene uneven, but low fire events were the main vegetation driver at high altitudes where broadleaved and coniferous trees presented a highly dynamic post-fire response. At mid-altitudes in the mainland Segura Mountains, fire activity remained relatively stable, at similar levels to recent times. We hypothesize that coastal areas, both mountains and lowlands, were more fire-prone landscapes as biomass was more likely to have accumulated than in the inland regions, triggering regular fire events. The wet and warm phase towards the Mid-Holocene (between ca 8 and 6 ka cal BP) affected the whole region and promoted the spread of mesophytic forest co-existing with Pinus, as FAAs appear strongly negative at 6 ka cal BP, with a less important role of fire. Mid and Late Holocene landscapes were shaped by an increasing aridity trend and the rise of human occupation, especially in the coastal mountains where forest disappeared from ca 2 ka cal BP. Mediterranean-type vegetation (evergreen oaks and Pinus pinaster- halepensis types) showed the fastest post-fire vegetation dynamics over time.

  20. Deglacial and Holocene sea-ice variability north of Iceland and response to ocean circulation changes

    Science.gov (United States)

    Xiao, Xiaotong; Zhao, Meixun; Knudsen, Karen Luise; Sha, Longbin; Eiríksson, Jón; Gudmundsdóttir, Esther; Jiang, Hui; Guo, Zhigang

    2017-08-01

    Sea-ice conditions on the North Icelandic shelf constitute a key component for the study of the climatic gradients between the Arctic and the North Atlantic Oceans at the Polar Front between the cold East Icelandic Current delivering Polar surface water and the relatively warm Irminger Current derived from the North Atlantic Current. The variability of sea ice contributes to heat reduction (albedo) and gas exchange between the ocean and the atmosphere, and further affects the deep-water formation. However, lack of long-term and high-resolution sea-ice records in the region hinders the understanding of palaeoceanographic change mechanisms during the last glacial-interglacial cycle. Here, we present a sea-ice record back to 15 ka (cal. ka BP) based on the sea-ice biomarker IP25, phytoplankton biomarker brassicasterol and terrestrial biomarker long-chain n-alkanols in piston core MD99-2272 from the North Icelandic shelf. During the Bølling/Allerød (14.7-12.9 ka), the North Icelandic shelf was characterized by extensive spring sea-ice cover linked to reduced flow of warm Atlantic Water and dominant Polar water influence, as well as strong meltwater input in the area. This pattern showed an anti-phase relationship with the ice-free/less ice conditions in marginal areas of the eastern Nordic Seas, where the Atlantic Water inflow was strong, and contributed to an enhanced deep-water formation. Prolonged sea-ice cover with occasional occurrence of seasonal sea ice prevailed during the Younger Dryas (12.9-11.7 ka) interrupted by a brief interval of enhanced Irminger Current and deposition of the Vedde Ash, as opposed to abruptly increased sea-ice conditions in the eastern Nordic Seas. The seasonal sea ice decreased gradually from the Younger Dryas to the onset of the Holocene corresponding to increasing insolation. Ice-free conditions and sea surface warming were observed for the Early Holocene, followed by expansion of sea ice during the Mid-Holocene.

  1. Evidence for an early land use in the Rhône delta (Mediterranean France) as recorded by late Holocene fluvial paleoenvironments (1640-100 BC)

    Science.gov (United States)

    Arnaud-Fassetta, Gilles; De Beaulieu, Jacques-Louis; Suc, Jean-Pierre; Provansal, Mireille; Williamson, David; Leveau, Philippe; Aloïsi, Jean-Claude; Gadel, François; Giresse, Pierre; Oberlin, Christine; Duzer, Danièle

    The overall objective of this paper is to describe the late Holocene (1640-100 BC) sedimentary and biological evolution of the Rhône-delta-plain, to interpret the sedimentary facies and palynofacies as the result of the effects of fluvial dynamic fluctuations and relative sea level change and to evaluate the paleohydrological constraints in the development of the land use and settlements of the Camargue. Focus is made on the upper part of V III core drilled on NE of the Vaccarès lagoon. By combining sedimentology, palynology, magnetic susceptibility and archeological data, this study allowed to identify the superposition of three types of paleo-environments (marsh, fluvial floodplain, levee/crevasse splay). This sequence indicates a gradual extension of fluvial environments between the end of the second millennium BC and the 1st century BC. The variability of fluvial dynamic is evident during this period with important flood events which contrast with periods of low flow. Pollen record can be a good marker of the fluvial dynamic variability. The expression of the riparian tree pollen grains in the coarser floodplain deposits could correspond to increased fluvial influence and probably to erosion of riverbank during flood events. The local plants are associated to the low energy sedimentary environments. Focuses are made on the relations between the evolution of the environment and land use. The development of the cereal culture in the floodplain of the Rhône delta has been demonstrated between 1640-1410 and 100 BC. The last alluviation of the Rhône perturbs the research of the archaeological sites in the central part of the delta but the existence of the rural villages from the first part of the first millennium BC is highly possible.

  2. Non-uniform and diachronous Holocene floodplain evolution: a case study from the Dijle catchment, Belgium

    NARCIS (Netherlands)

    Broothaerts, N.; Notebaert, B.; Verstraeten, G.; Kasse, C.; Bohncke, S.J.P.; Vandenberghe, J.

    2014-01-01

    Fluvial architecture changed under the influence of increasing human impact throughout the Holocene in many north-west European catchments. Typically, peat formation - in a marshy environment during the Early and Middle Holocene - is replaced by clastic overbank deposition. In this study we show the

  3. Holocene aeolian activity in the Dinggye area (Southern Tibet, China)

    Science.gov (United States)

    Pan, Meihui; Wu, Yongqiu; Zheng, Yinghua; Tan, Lihua

    2014-03-01

    The Dinggye area (Southern Tibet) contains numerous aeolian sediments, including modern and ancient aeolian sand deposition. In this study, we determined the chronological sequences of several profiles of Holocene paleo-aeolian deposits using Optically Stimulate Luminescence (OSL) and radiocarbon (Accelerator Mass Spectrometry (AMS) 14C and conventional 14C) dating. Using the grain size, magnetic susceptibility, organic content and chrome characteristics of the deposits, we reconstructed the Holocene aeolian processes in the Dinggye area. The results from the paleo-aeolian depositional record indicate multiple changes in the intensity of aeolian activity and soil fixing with alternations between cool-dry and warm-humid climate conditions in the Dinggye area during the Holocene. From 12.8 ka B.P. to the present, the climate has fluctuated frequently. From 12.8 to 11.6 ka B.P. and from 9.3 to 4.9 ka B.P., the climate was warm and humid with weak aeolian activity, and a sandy paleosol developed. The peak Holocene megathermal period and the main period of pedogenesis in the study area was from 6.6 to 4.9 ka B.P. Between 11.6 and 9.3 ka B.P. and since 2.0 ka B.P., the sandlot expanded due to a cool, dry and windy climate; aeolian activity was strong and caused the development of moving dunes. The period between 4.9 and 2.0 ka B.P. was relatively cool and dry with slightly strengthened aeolian activity that developed stationary and semi-stationary dunes. In general, the Holocene events recorded by the paleo-aeolian deposits correspond well with those interpreted by other methods, such as records from ice-cores, lacustrine deposits and tree rings, but there are minor discrepancies between the methods.

  4. Holocene fluctuations of Quelccaya Ice Cap, Peru based on lacustrine and surficial geologic archives

    Science.gov (United States)

    Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C. A.

    2013-12-01

    ., 2009). Clastic sedimentation may reflect the glacier thermal regime. Relic plants now being uncovered by the receding QIC (Thompson et al., 2006, 2013) suggest advance of cold-based ice that did not produce significant meltwater or rock flour. Striations, also present on the landscape, indicate warm-based ice conditions, which would produce meltwater and rock flour. We suggest that these striations were likely produced during ice cap retreat. A small QIC during early and middle Holocene time and large QIC during late Holocene time is similar to the Holocene extents of many Northern Hemisphere glaciers and apparently follows the pattern of Northern Hemisphere summer insolation.

  5. Clinal variation of some mammals during the Holocene in Missouri

    Science.gov (United States)

    Purdue, James R.

    1980-03-01

    Eastern cottontail ( Sylvilagus floridanus), fox squirrel ( Sciurus niger), and gray squirrel ( Sciurus carolinensis) were examined for clinal variation during the Holocene. Modern samples of all three species displayed strong east-west patterns along the western edge of the eastern deciduous forest: S. floridanus and S. niger decrease and S. carolinensis increases in size. Archeological samples of S. carolinensis from Rodgers Shelter (23BE125), Benton County, Missouri, and Graham Cave (23MT2), Montgomery County, Missouri, indicated an increase in size from early to middle Holocene. Sylvilagus floridanus from Rodgers Shelter decreased in size from early to middle Holocene and then increased during the late Holocene to modern proportions. A literature survey reveals that clinal variation is a common phenomenon among modern homeotherms. In introduced species, clinal variation has developed after relatively few generations, indicating rapid adaptations to environmental conditions; often winter climatic variables are implicated. Morphological variation in the study species during the Holocene is interpreted as a response to changing climates. Studies of morphological clines may lead to another valuable data source for reconstructing past ecologies.

  6. 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.

  7. Global warming

    International Nuclear Information System (INIS)

    Anon.

    1992-01-01

    Canada's Green Plan strategy for dealing with global warming is being implemented as a multidepartmental partnership involving all Canadians and the international community. Many of the elements of this strategy are built on an existing base of activities predating the Green Plan. Elements of the strategy include programs to limit emissions of greenhouse gases, such as initiatives to encourage more energy-efficient practices and development of alternate fuel sources; studies and policy developments to help Canadians prepare and adapt to climate change; research on the global warming phenomenon; and stimulation of international action on global warming, including obligations arising out of the Framework Convention on Climate Change. All the program elements have been approved, funded, and announced. Major achievements to date are summarized, including improvements in the Energy Efficiency Act, studies on the socioeconomic impacts of global warming, and participation in monitoring networks. Milestones associated with the remaining global warming initiatives are listed

  8. Warm measurements of CBA superconducting magnets

    International Nuclear Information System (INIS)

    Engelmann, R.; Herrera, J.; Kahn, S.; Kirk, H.; Willen, E.; Yamin, P.

    1983-01-01

    We present results on magnetic field measurements of CBA dipole magnets in the warm (normal conductor) and cryogenic (superconducting) states. We apply two methods for the warm measurements, a dc and ac method. We find a good correlation between warm and cryogenic measurements which lends itself to a reliable diagnosis of magnet field errors using warm measurements early in the magnet assembly process. We further find good agreement between the two warm measurement methods, both done at low currents

  9. Accretion history and stratigraphy of mid-Holocene coral reefs from Southeast Florida, USA

    Science.gov (United States)

    Stathakopoulos, A.; Riegl, B. M.; Swart, P. K.

    2013-05-01

    suggest the mid-Holocene (~8-5 ka) was punctuated by a transition to a more moist and warm climate and/or a potentially rapid sea-level rise. The color and texture of cements support increased freshwater input as a likely agent of reef demise. We also observed that the once-dominant Caribbean reef builder Acropora palmata was mostly present throughout the early and mid-Holocene but absent thereafter. Reef geomorphology was strongly determined by the length of presence of this species, as the thickness, size, and shape of the three linear reefs clearly reflect its declining importance during the Holocene in Florida.

  10. 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.

  11. 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.

  12. Effects of Ocean Acidification and Warming on Sperm Activity and Early Life Stages of the Mediterranean Mussel (Mytilus galloprovincialis

    Directory of Open Access Journals (Sweden)

    Mikko Vihtakari

    2013-11-01

    Full Text Available Larval stages are among those most vulnerable to ocean acidification (OA. Projected atmospheric CO2 levels for the end of this century may lead to negative impacts on communities dominated by calcifying taxa with planktonic life stages. We exposed Mediterranean mussel (Mytilus galloprovincialis sperm and early life stages to pHT levels of 8.0 (current pH and 7.6 (2100 level by manipulating pCO2 level (380 and 1000 ppm. Sperm activity was examined at ambient temperatures (16–17 °C using individual males as replicates. We also assessed the effects of temperature (ambient and ≈20 °C and pH on larval size, survival, respiration and calcification of late trochophore/early D-veliger stages using a cross-factorial design. Increased pCO2 had a negative effect on the percentage of motile sperm (mean response ratio R= 71% and sperm swimming speed (R= 74%, possibly indicating reduced fertilization capacity of sperm in low concentrations. Increased temperature had a more prominent effect on larval stages than pCO2, reducing performance (RSize = 90% and RSurvival = 70% and increasing energy demand (RRespiration = 429%. We observed no significant interactions between pCO2 and temperature. Our results suggest that increasing temperature might have a larger impact on very early larval stages of M. galloprovincialis than OA at levels predicted for the end of the century.

  13. Holocene climatic fluctuations and periodic changes in the Asian southwest monsoon region

    Science.gov (United States)

    Zhang, Wenxiang; Niu, Jie; Ming, Qingzhong; Shi, Zhengtao; Lei, Guoliang; Huang, Linpei; Long, Xian'e.; Chang, Fengqin

    2018-05-01

    Climatic changes in the Asian southwest monsoon (ASWM) during the Holocene have become a topic of recent studies. It is important to understand the patterns and causes of Holocene climatic changes and their relationship with global changes. Based on the climate proxies and wavelet analysis of Lugu Lake in the ASWM region, the climatic fluctuations and periodic changes in the ASWM region during the Holocene have been reconstructed with a high-precision chronology. The results indicate the intensification of ASWM began to increase with Northern Hemisphere low-latitude solar insolation (LSI) and solar activity during the early Holocene, and gradually decreased during the late Holocene, exhibiting an apparent synchrony with numerous records of ASWM region. Meanwhile, an apparent 1000-a quasi-periodic signal is present in the environment proxies, and it demonstrates that the environmental change in the ASWM region has been driven mainly by LSI and solar activity.

  14. Holocene Evolution of Qing'ao Embayment, Southern China

    Science.gov (United States)

    Switzer, A. D.; Yu, F.; Chen, B.; Zheng, Z.; Wang, D.

    2012-12-01

    The Holocene evolution of the Qing'ao embayment, Nan'ao Island, southern China, is primarily the result of the interaction of tectonic activity, climate variation and changes in relative sea level. Characterizing the evolutionary history of the relatively small Qing'ao embayment during the Holocene will help improve our understanding of the driving mechanisms of coastal evolution in the area. To reconstruct the Holocene evolution history we analyzed the grain size, loss on ignition (LOI) and carbonate content of modern and core samples. Modern environmental analogs were examined in surface samples ranging from the coastal sand dunes through to offshore. The results of these modern samples suggest that dune sand (mean size of ~2.33Phi) are slightly finer than beach sand (mean size of 2.13Phi), and nearshore sediment is much coarser than offshore sediment (mean size of 5.90Phi). This modern analogs were then applied to 8 percussion cores from the Qing'ao embayment. A chronological framework obtained from 11 radiocarbon samples suggests that the embayment started to accept deposition since early Holocene, ~8500 cal. yr. BP. Three main phases of Holocene evolution were identified. A basin wide shell-rich sand sheet forms the basal Holocene facies and overlies clay rich presumably Pleistocene sediments or bedrock. This facies records an initial sedimentation phase associated with the early Holocene transgression into the embayment (~8500-6000 cal. yr. BP). The basal facies grades upward to a mixed sandy-mud facies which includes lagoonal clayey-silts, flood tide delta sands and records an estuarine phase lasting from ~6000-1000 cal. yr. BP that appears coincident with falling regional sea levels. Coincident with the estuarine phase is a period of coastal dune building recorded as yet undated massive sands that are found in the upper fill. Toward the end of the estuarine phase it is apparent that dune migration has restricted the lagoon entrance and that this was

  15. Holocene paleoclimate inferred from salinity histories of adjacent lakes in southwestern Sicily (Italy)

    Science.gov (United States)

    Curry, B Brandon; Henne, Paul; Mezquita-Joanes, Francesc; Marrone, Federico; Pieri, Valentina; La Mantia, Tommaso; Calo, Camilla; Tinner, Willy

    2016-01-01

    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 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 likely, with relatively more late Holocene precipitation falling during the spring, summer, and fall, than winter compared to the early Holocene. Our ostracode-inferred paleosalinity data indicate that moisture availability did not decline during the late Holocene in the central Mediterranean region. Instead, moisture availability was lowest during the early Holocene, and most abundant during the late Holocene.

  16. Long-term paradoxical aftermath of the Early Permian climatic warming in the Northern Hemisphere: biotic and abiotic aspects

    Science.gov (United States)

    Kossovaya, Olga

    2014-05-01

    Far distant influence of the climatic changes is rather variable and sometimes paradoxical. One of the examples is the flourish of the Photozoan association in the Northern Hemisphere during time of Southern Hemisphere glaciation (P2) and it following collapse in the interglacial phase. Modelling of the possible extrinsic factors using isotope data from the Urals has demonstrated the complex succession of abiotic changes including circulation changes and penetration of cold water from Northern Panthalassa. The invasion of cold water into the Uralian Basin led to disarray of the coastal circulation and rising of cold water via upwelling. It was resulted by change of biota and wide distribution of the heterozoan biota. The replacement took place both in carbonate ramp and reef facies. The depletion of δ18O during the early Artinskian was demonstrated by analyses of the biogenic carbonates from Belaya Gora (Most) section. This coincides with the previously known trend for d18O shown for low latitudes from the Sakmarian to early Artinskian with a minimum during the middle Artinskian and is in accordance with recent data from the South Urals. The heterochrony of the impact in the far-distant and discrete photozoan assemblages depends on their bathymetric and paleo-latitudinal position.

  17. Quantitative Temperature Reconstructions from Holocene and Late Glacial Lake Sediments in the Tropical Andes using Chironomidae (non-biting midges)

    Science.gov (United States)

    Matthews-Bird, F.; Gosling, W. D.; Brooks, S. J.; Montoya, E.; Coe, A. L.

    2014-12-01

    Chironomidae (non-biting midges) is a family of two-winged aquatic insects of the order Diptera. They are globally distributed and one of the most diverse families within aquatic ecosystems. The insects are stenotopic, and the rapid turnover of species and their ability to colonise quickly favourable habitats means chironomids are extremely sensitive to environmental change, notably temperature. Through the development of quantitative temperature inference models chironomids have become important palaeoecological tools. Proxies capable of generating independent estimates of past climate are crucial to disentangling climate signals and ecosystem response in the palaeoecological record. This project has developed the first modern environmental calibration data set in order to use chironomids from the Tropical Andes as quantitative climate proxies. Using surface sediments from c. 60 lakes from Bolivia, Peru and Ecuador we have developed an inference model capable of reconstructing temperatures, with a prediction error of 1-2°C, from fossil assemblages. Here we present the first Lateglacial and Holocene chironomid-inferred temperature reconstructions from two sites in the tropical Andes. The first record, from a high elevation (4153 m asl) lake in the Bolivian Andes, shows persistently cool temperatures for the past 15 kyr, punctuated by warm episodes in the early Holocene (9-10 kyr BP). The chironomid-inferred Holocene temperature trends from a lake sediment record on the eastern Andean flank of Ecuador (1248 m asl) spanning the last 5 millennia are synchronous with temperature changes in the NGRIP ice core record. The temperature estimates suggest along the eastern flank of the Andes, at lower latitudes (~1°S), climate closely resemble the well-established fluctuations of the Northern Hemisphere for this time period. Late-glacial climate fluctuations across South America are still disputed with some palaeoecological records suggesting evidence for Younger Dryas

  18. Interacting effects of warming and drought on regeneration and early growth of Acer pseudoplatanus and A. platanoides.

    Science.gov (United States)

    Carón, M M; De Frenne, P; Brunet, J; Chabrerie, O; Cousins, S A O; De Backer, L; Decocq, G; Diekmann, M; Heinken, T; Kolb, A; Naaf, T; Plue, J; Selvi, F; Strimbeck, G R; Wulf, M; Verheyen, K

    2015-01-01

    Climate change is acting on several aspects of plant life cycles, including the sexual reproductive stage, which is considered amongst the most sensitive life-cycle phases. In temperate forests, it is expected that climate change will lead to a compositional change in community structure due to changes in the dominance of currently more abundant forest tree species. Increasing our understanding of the effects of climate change on currently secondary tree species recruitment is therefore important to better understand and forecast population and community dynamics in forests. Here, we analyse the interactive effects of rising temperatures and soil moisture reduction on germination, seedling survival and early growth of two important secondary European tree species, Acer pseudoplatanus and A. platanoides. Additionally, we analyse the effect of the temperature experienced by the mother tree during seed production by collecting seeds of both species along a 2200-km long latitudinal gradient. For most of the responses, A. platanoides showed higher sensitivity to the treatments applied, and especially to its joint manipulation, which for some variables resulted in additive effects while for others only partial compensation. In both species, germination and survival decreased with rising temperatures and/or soil moisture reduction while early growth decreased with declining soil moisture content. We conclude that although A. platanoides germination and survival were more affected after the applied treatments, its initial higher germination and larger seedlings might allow this species to be relatively more successful than A. pseudoplatanus in the face of climate change. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.

  19. Influence of high-latitude warming and land-use changes in the early 20th century northern Eurasian CO2 sink

    Science.gov (United States)

    Bastos, Ana; Peregon, Anna; Gani, Érico A.; Khudyaev, Sergey; Yue, Chao; Li, Wei; Gouveia, Célia M.; Ciais, Philippe

    2018-06-01

    While the global carbon budget (GCB) is relatively well constrained over the last decades of the 20th century [1], observations and reconstructions of atmospheric CO2 growth rate present large discrepancies during the earlier periods [2]. The large uncertainty in GCB has been attributed to the land biosphere, although it is not clear whether the gaps between observations and reconstructions are mainly because land-surface models (LSMs) underestimate inter-annual to decadal variability in natural ecosystems, or due to inaccuracies in land-use change reconstructions. As Eurasia encompasses about 15% of the terrestrial surface, 20% of the global soil organic carbon pool and constitutes a large CO2 sink, we evaluate the potential contribution of natural and human-driven processes to induce large anomalies in the biospheric CO2 fluxes in the early 20th century. We use an LSM specifically developed for high-latitudes, that correctly simulates Eurasian C-stocks and fluxes from observational records [3], in order to evaluate the sensitivity of the Eurasian sink to the strong high-latitude warming occurring between 1930 and 1950. We show that the LSM with improved high-latitude phenology, hydrology and soil processes, contrary to the group of LSMs in [2], is able to represent enhanced vegetation growth linked to boreal spring warming, consistent with tree-ring time-series [4]. By compiling a dataset of annual agricultural area in the Former Soviet Union that better reflects changes in cropland area linked with socio-economic fluctuations during the early 20th century, we show that land-abadonment during periods of crisis and war may result in reduced CO2 emissions from land-use change (44%–78% lower) detectable at decadal time-scales. Our study points to key processes that may need to be improved in LSMs and LUC datasets in order to better represent decadal variability in the land CO2 sink, and to better constrain the GCB during the pre-observational record.

  20. Holocene vegetation and fire history of the mountains of northern Sicily (Italy)

    Science.gov (United States)

    Tinner, Willy; Vescovi, Elisa; Van Leeuwen, Jacqueline; Colombaroli, Daniele; Henne, Paul; Kaltenrieder, Petra; Morales-Molino, Cesar; Beffa, Giorgia; Gnaegi, Bettina; Van der Knaap, Pim W O; La Mantia, Tommaso; Pasta, Salvatore

    2016-01-01

    Knowledge about vegetation and fire history of the mountains of Northern Sicily is scanty. We analysed five sites to fill this gap and used terrestrial plant macrofossils to establish robust radiocarbon chronologies. Palynological records from Gorgo Tondo, Gorgo Lungo, Marcato Cixé, Urgo Pietra Giordano and Gorgo Pollicino show that under natural or near natural conditions, deciduous forests (Quercus pubescens, Q. cerris, Fraxinus ornus, Ulmus), that included a substantial portion of evergreen broadleaved species (Q. suber, Q. ilex, Hedera helix), prevailed in the upper meso-mediterranean belt. Mesophilous deciduous and evergreen broadleaved trees (Fagus sylvatica, Ilex aquifolium) dominated in the natural or quasi-natural forests of the oro-mediterranean belt. Forests were repeatedly opened for agricultural purposes. Fire activity was closely associated with farming, providing evidence that burning was a primary land use tool since Neolithic times. Land use and fire activity intensified during the Early Neolithic at 5000 bc, at the onset of the Bronze Age at 2500 bc and at the onset of the Iron Age at 800 bc. Our data and previous studies suggest that the large majority of open land communities in Sicily, from the coastal lowlands to the mountain areas below the thorny-cushion Astragalus belt (ca. 1,800 m a.s.l.), would rapidly develop into forests if land use ceased. Mesophilous Fagus-Ilex forests developed under warm mid Holocene conditions and were resilient to the combined impacts of humans and climate. The past ecology suggests a resilience of these summer-drought adapted communities to climate warming of about 2 °C. Hence, they may be particularly suited to provide heat and drought-adaptedFagus sylvatica ecotypes for maintaining drought-sensitive Central European beech forests under global warming conditions.

  1. Holocene lowering of the Laurentide ice sheet affects North Atlantic gyre circulation and climate

    Science.gov (United States)

    Ivanovic, R. F.; Gregoire, L. J.; Maycock, A.; Valdes, P. J.

    2017-12-01

    The Laurentide ice sheet, which covered Canada during glacial periods, had a major influence on atmospheric circulation and surface climate, but its role in climate during the early Holocene (9-7 ka), when it was thinner and confined around Hudson Bay, is unclear. It has been suggested that the demise of the ice sheet played a role in the 8.2 ka event (an abrupt 1-3 °C Northern Hemisphere cooling lasting 160 years) through the influence of changing topography on atmospheric circulation. To test this hypothesis, and to investigate the broader implications of changing ice sheet topography for climate, we analyse a set of equilibrium climate simulations with ice sheet topographies taken at 500 year intervals from 9.5 ka to 8.0 ka. Between 9.5 and 8.0 ka, our simulations show a 2 °C cooling south of Iceland and a 1 °C warming between 40-50° N in the North Atlantic. These surface temperature changes are associated with a weakening of the subtropical and subpolar gyres caused by a decreasing wind stress curl over the mid-North Atlantic as the ice sheet lowers. The climate response is strongest during the period of peak ice volume change (9.5 ka - 8.5 ka), but becomes negligible after 8.5 ka. The climatic effects of the Laurentide ice sheet lowering are restricted to the North Atlantic sector. Thus, topographic forcing did not play a significant role in the 8.2 ka event and had only a small effect on Holocene climate change compared to the effects of changes in greenhouse gases, insolation and ice sheet meltwater.

  2. 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.

  3. Aridity of Central Asia through the Holocene

    Science.gov (United States)

    Aizen, E. M.; Aizen, V. B.; Mayewski, P. A.; Zhou, H.; Rodda, C.; Joswiak, D.; Takeuchi, N.; Fujita, K.; Kurbatov, A.; Grigholm, B. O.

    2017-12-01

    The dynamics of aridity in Central Asia for over the past 12,000 years has been analyzed using deep ice core records recovered from the Siberian Altai, Tien Shan and Pamir glaciers. An analysis of aridity in the 20-21 centuries based on the long-term meteorological observations complements the paleo- climate reconstruction. The goal of our research is to examine an aridity (at low and high temperatures) in Central Asia as a complex of characteristics including air temperature-precipitation relationship (Koppen, 1918, Geiger, 1961, Mezencev, 1973), intensity of dust loading and biomass burning. The stable isotope ratio, soluble ionic and insoluble particulate geochemical components and oxalate preserved in ice were considered in relation to climatic and environmental changes; and to determine the main aerosol sources using ground- and upper-level meteorological data. Multivariate statistical methods were employed for examination of the main geo-chemical components responsible for the preserved aridity variability. Insoluble particle concentrations preserved in the ice core were affected mainly by precipitation regimes and wind speed. Concentration of all size particles was found to be negatively correlated with monthly temperatures indicating low temperatures during the dry particle deposition. Two abrupt depletions in stable isotope records, i.e., Younger Dryas and Centurial Sever Drought (CSD), occurred during cold, dry, windy periods of intensified dust storms in large desert areas. When climate became colder and drier, the Central Asian deserts extended, wind speeds increased loading mineral dust to atmosphere, which formed inversion while the convection processes and precipitation occurrence were limited. Warmer and wetter conditions are associated with less dust loading that occurred during the Holocene climate optimum, medieval warm and modern warm periods. The sudden climate transitions are accompanied by the most intensifying mineral dust loading. From the

  4. Holocene Climate Variability on the Centennial and Millennial Time Scale

    Directory of Open Access Journals (Sweden)

    Eun Hee Lee

    2014-12-01

    Full Text Available There have been many suggestions and much debate about climate variability during the Holocene. However, their complex forcing factors and mechanisms have not yet been clearly identified. In this paper, we have examined the Holocene climate cycles and features based on the wavelet analyses of 14C, 10Be, and 18O records. The wavelet results of the 14C and 10Be data show that the cycles of ~2180-2310, ~970, ~500-520, ~350-360, and ~210-220 years are dominant, and the ~1720 and ~1500 year cycles are relatively weak and subdominant. In particular, the ~2180-2310 year periodicity corresponding to the Hallstatt cycle is constantly significant throughout the Holocene, while the ~970 year cycle corresponding to the Eddy cycle is mainly prominent in the early half of the Holocene. In addition, distinctive signals of the ~210-220 year period corresponding to the de Vries cycle appear recurrently in the wavelet distribution of 14C and 10Be, which coincide with the grand solar minima periods. These de Vries cycle events occurred every ~2270 years on average, implying a connection with the Hallstatt cycle. In contrast, the wavelet results of 18O data show that the cycles of ~1900-2000, ~900-1000, and ~550-560 years are dominant, while the ~2750 and ~2500 year cycles are subdominant. The periods of ~2750, ~2500, and ~1900 years being derived from the 18O records of NGRIP, GRIP and GISP2 ice cores, respectively, are rather longer or shorter than the Hallstatt cycle derived from the 14C and 10Be records. The records of these three sites all show the ~900-1000 year periodicity corresponding to the Eddy cycle in the early half of the Holocene.

  5. Global warming

    International Nuclear Information System (INIS)

    Houghton, John

    2005-01-01

    'Global warming' is a phrase that refers to the effect on the climate of human activities, in particular the burning of fossil fuels (coal, oil and gas) and large-scale deforestation, which cause emissions to the atmosphere of large amounts of 'greenhouse gases', of which the most important is carbon dioxide. Such gases absorb infrared radiation emitted by the Earth's surface and act as blankets over the surface keeping it warmer than it would otherwise be. Associated with this warming are changes of climate. The basic science of the 'greenhouse effect' that leads to the warming is well understood. More detailed understanding relies on numerical models of the climate that integrate the basic dynamical and physical equations describing the complete climate system. Many of the likely characteristics of the resulting changes in climate (such as more frequent heat waves, increases in rainfall, increase in frequency and intensity of many extreme climate events) can be identified. Substantial uncertainties remain in knowledge of some of the feedbacks within the climate system (that affect the overall magnitude of change) and in much of the detail of likely regional change. Because of its negative impacts on human communities (including for instance substantial sea-level rise) and on ecosystems, global warming is the most important environmental problem the world faces. Adaptation to the inevitable impacts and mitigation to reduce their magnitude are both necessary. International action is being taken by the world's scientific and political communities. Because of the need for urgent action, the greatest challenge is to move rapidly to much increased energy efficiency and to non-fossil-fuel energy sources

  6. Extreme Mississippi River Floods in the Late Holocene: Reconstructions and Simulations

    Science.gov (United States)

    Munoz, S. E.; Giosan, L.; Donnelly, J. P.; Dee, S.

    2016-12-01

    Extreme flooding of the Mississippi River is costly in both economic and social terms. Despite ambitious engineering projects conceived in the early 20th century to mitigate damage from extreme floods, economic losses due to flooding have increased over recent years. Forecasting extreme flood occurrence over seasonal or longer time-scales remains a major challenge - especially in light of shifts in hydroclimatic conditions expected in response to continued greenhouse forcing. Here, we present findings from a series of paleoflood records that span the late Holocene derived from laminated sediments deposited in abandoned channels of the Mississippi River. These sedimentary archives record individual overbank floods as unique events beds with upward fining that we identify using grain-size analysis, bulk geochemistry, and radiography. We use sedimentological characteristics to reconstruct flood magnitude by calibrating our records against instrumental streamflow data from nearby gauging stations. We also use the Last Millennium Experiments of the Community Earth System Model (CESM-LME) and historical reanalysis data to examine the state of climate system around river discharge extremes. Our paleo-flood records exhibit strong non-stationarities in flood frequency and magnitude that are associated with fluctuations in the frequency of the El Niño-Southern Oscillation (ENSO), because the warm ENSO phase is associated with increased surface water storage of the lower Mississippi basin that leads to enhanced runoff delivery to the main channel. We also show that the early 20th century was a period of anomalously high flood frequency and magnitude due to the combined effects of river engineering and natural climate variability. Our findings imply that flood risk along the lower Mississippi River is tightly coupled to the frequency of ENSO, highlighting the need for robust projections of ENSO variability under greenhouse warming.

  7. Strength of forest-albedo feedback in mid-Holocene climate simulations

    Directory of Open Access Journals (Sweden)

    J. Otto

    2011-09-01

    Full Text Available Reconstructions of the mid-Holocene climate, 6000 years before present, suggest that spring temperatures were higher at high northern latitudes compared to the pre-industrial period. A positive feedback between expansion of forest and climate presumably contributed to this warming. In the presence of snow, forests have a lower albedo than grass land. Therefore, the expansion of forest likely favoured a warming in spring, counteracting the lower insolation at the mid-Holocene.

    We investigate the sensitivity of the vegetation-atmosphere interaction under mid-Holocene orbital forcing with respect to the strength of the forest-albedo feedback by using a comprehensive coupled atmosphere-vegetation model (ECHAM5/JSBACH. We perform two sets of model simulations: a first set of simulations with a relatively weak reduction of albedo of snow by forest; and a second set of simulations with a relatively strong reduction of the albedo of snow by forest.

    We show that the parameterisation of the albedo of snow leads to uncertainties in the temperature signal. Compared to the set with weak snow masking, the simulations with strong snow masking reveal a spring warming that is three times higher, by 0.34 °C north of 60° N. This warming is related to a forest expansion of only 13%.

  8. Holocene emerged coral reef in Takarajima and Kodakarajima, Ryukyu islands, Southwest Japan

    International Nuclear Information System (INIS)

    Nakata, Takashi; Omoto, Kunio; Koba, Motoharu

    1978-01-01

    Due to the recent development of radiometric dating, coral reefs emerged in Holocene epoch are studied intensively worldwidely in relation to sea level change and coral reef formation. Attempt was made to determine the age, pattern and growth rate of coral reefs in the marginal area of coral sea in the Northwest Pacific. Field observation was made in the emerged coral reefs in Takarajima and Kodakarajima islands and the samples for radiocarbon dating were taken from geological sections across the emerged reefs. These islands are located at about 29 deg 10 min N, 129 deg 15 min E, where warm Kuroshio current pushes the margin of coral sea northward, and furnished with flourishing development of coral reefs emerged in both pleistocence and Holocene epochs. Though without earthquake records, it is assumed that Holocene reefs have been terraced due to sudden uplift associated with major earthquakes. (Mori, K.)

  9. Holocene emerged coral reef in Takarajima and Kodakarajima, Ryukyu islands, Southwest Japan

    Energy Technology Data Exchange (ETDEWEB)

    Nakata, T; Omoto, K; Koba, M [Tohoku Univ., Sendai (Japan). Faculty of Science

    1978-06-01

    Due to the recent development of radiometric dating, coral reefs emerged in Holocene epoch are studied intensively worldwidely in relation to sea level change and coral reef formation. Attempt was made to determine the age, pattern and growth rate of coral reefs in the marginal area of coral sea in the Northwest Pacific. Field observation was made in the emerged coral reefs in Takarajima and Kodakarajima islands and the samples for radiocarbon dating were taken from geological sections across the emerged reefs. These islands are located at about 29 deg 10 min N, 129 deg 15 min E, where warm Kuroshio current pushes the margin of coral sea northward, and furnished with flourishing development of coral reefs emerged in both pleistocence and Holocene epochs. Though without earthquake records, it is assumed that Holocene reefs have been terraced due to sudden uplift associated with major earthquakes.

  10. Slow Warming of the Northern South China Sea during the Last Deglaciation

    Directory of Open Access Journals (Sweden)

    Tomoya Shintani

    2008-01-01

    Full Text Available We have generated a record of alkenone sea surface temperatures (SSTs during the last 28000 years from Core MD97-2146 for the northern South China Sea (SCS. The SST record showed a typical pattern for change in the northern SCS SST. The SST during the LGM was ~25 C, this decreased to ~24 C to 17 ka, increased to ~25.5 C to 14.5 ka, decreased again to ~24.5 C to 11.8 ka, increased gradually to ~27 C to 6 ka, and then increased more gradually to reach ~27.5 C at present. The SST difference ( SSTNSCS = SSTMD97-2146 - SSTMD97-2141 between Cores MD97-2146 (the northern SCS; this study and MD97-2141 (the Sulu Sea; Rosenthal et al. 2003 was used to characterize the SST changes in the northern SCS relative to changes in the adjacent WTPregion. The SSTNSCS decreased from 21 to 11.8 ka and increased after 11.8 ka, indicating slower warming of the northern SCS during the last deglaciation than that of the adjacent western tropical Pacific region.We infer that the slow warming of the northern SCS was principally a result of stronger winter monsoon during the last deglaciation and early Holocene. In addition, the cool water inflow through the Taiwan Strait after 13 ka and the warm water inflow through the Sunda Shelf after 11 ka could influence the SST in the northern SCS.

  11. Heat export from the tropics drives mid to late Holocene palaeoceanographic changes offshore southern Australia

    Science.gov (United States)

    Perner, Kerstin; Moros, Matthias; De Deckker, Patrick; Blanz, Thomas; Wacker, Lukas; Telford, Richard; Siegel, Herbert; Schneider, Ralph; Jansen, Eystein

    2018-01-01

    The Leeuwin Current (LC), an eastern boundary current, transports tropical waters from the Indo-Pacific Warm Pool (IPWP) towards southern latitudes and modulates oceanic conditions offshore southern Australia. New, high-resolution planktic foraminifer assemblage data and alkenone-derived sea surface temperatures (SST) provide an in-depth view on LC variability and mechanisms driving the current's properties during the mid to late Holocene (last c. 7.4 ka BP). Our marine reconstructions highlight a longer-term mid to late Holocene reduction of tropical heat export from the IPWP area into the LC. Mid Holocene (c. 7.4 to 3.5 ka BP) occurrence of high SSTs (>19.5 °C), tropical planktic foraminifera and a well-stratified water column document an enhanced heat export from the tropics. From c. 3.5 ka BP onwards, a weaker LC and a notably reduced tropical heat export cause oceanic cooling offshore southern Australia. The observed mid to late Holocene trends likely result from large-scale changes in the IPWP's heat storage linked to the El Niño-Southern Oscillation (ENSO) phenomenon. We propose that a strong and warm LC occurs in response to a La Niña-like state of ENSO during the mid Holocene. The late Holocene LC cooling, however, results from a shift towards an El Niño-like state and a more variable ENSO system that causes cooling of the IPWP. Superimposed on these longer-term trends we find evidence of distinct late Holocene millennial-scale phases of enhanced El Niño/La Niña development, which appear synchronous with northern hemispheric climatic variability. Phases of dominant El Niño-like states occur parallel to North Atlantic cold phases: the '2800 years BP cooling event', the 'Dark Ages' and the 'Little Ice Age', whereas the 'Roman Warm Period' and the 'Medieval Climate Anomaly' parallel periods of a predominant La Niña-like state. Our findings provide further evidence of coherent interhemispheric climatic and oceanic conditions during the mid to late

  12. Presencia de Antifer ultra Ameghino (=Antifer niemeyeri Casamiquela (Artiodactyla, Cervidae en el Pleistoceno tardío-Holoceno temprano de Chile central (30-35°S Presence of Antifer ultra Ameghino (=Antifer niemeyeri Casamiquela in the late Pleistocene-early Holocene of Central Chile (30-35°S

    Directory of Open Access Journals (Sweden)

    Rafael Labarca E

    2011-01-01

    Full Text Available El presente trabajo discute el estatus taxonómico de la especie Antifer niemeyeri Casamiquela, 1984, definida a partir de astas completas procedentes de la laguna Taguatagua y la quebrada de Quereo (Pleistoceno tardío-Holoceno temprano, en Chile central (30-35°S. Se concluye, a partir de un estudio morfológico y morfométrico detallado, que Antifer niemeyeri debe ser considerado sinónimo de Antifer ultra Ameghino, 1889 dados los caracteres anatómicos compartidos con esta especie. Los resultados amplían la distribución geográfica del taxón, que previamente se registraba en Argentina, Uruguay y sur de Brasil, y confirman su biocrón para el Pleistoceno tardío-Holoceno temprano (edad Lu-janense, aun cuando las fechas radiocarbónicas de Chile central (ca. 9.900 años 14C AP corresponden a las más tardías para la especie. A la luz de la evidencia paleoclimática disponible, se vincula A ultra durante el Pleistoceno de Chile central a ambientes cálidos y abiertos. Considerando estos requerimientos, se discute su posible vía de ingreso al actual territorio chileno a través de corredores ubicados hacia el sur del macizo andino, y su coexistencia con Hippocamelus bisulcus Molina, 1782. De acuerdo a la información estratigráfica y paleoambiental, se postula que ambas especies habrían sido alopátridas, por lo menos en el área de estudio.This paper discusses the taxonomic status of Antifer niemeyeri Casamiquela, 1984, defined from complete antlers from Taguatagua lake and Quereo canyon, both located in central Chile (30-35°S. From a detailed morphological and moiphometrical study, it is concluded that Antifer niemeyeri should be considered synonymous with Antifer ultra Ameghino, 1889, due to the anatomical characters shared between both forms. These results expand the geographical distribution of this taxa previously recorded in Argentina, Uruguay and southern Brazil, confirming their late Pleistocene-early Holocene biochron, in spite

  13. A Holocene record of ocean productivity and upwelling from the northern California continental slope

    Science.gov (United States)

    Addison, Jason A.; Barron, John A.; Finney, Bruce P.; Kusler, Jennifer E.; Bukry, David; Heusser, Linda E.; Alexander, Clark R.

    2018-01-01

    The Holocene upwelling history of the northern California continental slope is examined using the high-resolution record of TN062-O550 (40.9°N, 124.6°W, 550 m water depth). This 7-m-long marine sediment core spans the last ∼7500 years, and we use it to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with Holocene millennial-scale warm intervals. A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ13C and bulk sedimentary δ15N), and key microfossil indicators of upwelling were used to test this hypothesis. The record of biogenic accumulation in TN062-O550 shows considerable Holocene variability despite being located within 50 km of the mouth of the Eel River, which is one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at ∼2900 calibrated years before present (cal yr BP) indicates the onset of modern upwelling in the CCS, and this period also corresponds to the most intense period of upwelling in the last 7500 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification at TN062-O550 corresponds closely to that seen at nearby ODP Site 1019, as well as in the Santa Barbara Basin of southern California. Other CCS records with less refined age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we suggest that CCS warming may be conducive to upwelling intensification, though future changes are unclear as the mechanisms forcing SST variability may differ.

  14. 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 <8 ka, although there is an unusual temporal distribution with the greatest amount of the data (~28%) occurring between 6-8 ka. We reassess and screen radiocarbon and U/Th ages of 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 (< 2 mm/yr), which is related to the reduction of ice equivalent meltwater input and collapse of the proglacial forebulge during the 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.

  15. Global warming

    CERN Document Server

    Hulme, M

    1998-01-01

    Global warming-like deforestation, the ozone hole and the loss of species- has become one of the late 20the century icons of global environmental damage. The threat, is not the reality, of such a global climate change has motivated governments. businesses and environmental organisations, to take serious action ot try and achieve serious control of the future climate. This culminated last December in Kyoto in the agreement for legally-binding climate protocol. In this series of three lectures I will provide a perspective on the phenomenon of global warming that accepts the scientific basis for our concern, but one that also recognises the dynamic interaction between climate and society that has always exited The future will be no different. The challenge of global warning is not to pretend it is not happening (as with some pressure groups), nor to pretend it threatens global civilisation (as with other pressure groups), and it is not even a challenge to try and stop it from happening-we are too far down the ro...

  16. Molecules in the mud: Combining ancient DNA and lipid biomarkers to reconstruct vegetation response to climate variability during the Last Interglacial and the Holocene on Baffin Island, Arctic Canada

    Science.gov (United States)

    Crump, S. E.; Sepúlveda, J.; Bunce, M.; Miller, G. H.

    2017-12-01

    Modern ecological studies are revealing that the "greening" of the Arctic, resulting from a poleward shift in woody vegetation ranges, is already underway. The increasing abundance of shrubs in tundra ecosystems plays an important role in the global climate system through multiple positive feedbacks, yet uncertainty in future predictions of terrestrial vegetation means that climate models are likely not capturing these feedbacks accurately. Recently developed molecular techniques for reconstructing past vegetation and climate allow for a closer look at the paleo-record in order to improve our understanding of tundra community responses to climate variability; our current research focus is to apply these tools to both Last Interglacial and Holocene warm times. Here we present initial results from a small lake on southern Baffin Island spanning the last 7.2 ka. We reconstruct climate with both bulk geochemical and biomarker proxies, primarily using biogenic silica and branched glycerol dialkyl glycerol tetraethers (brGDGTs) as temperature indicators. We assess shifts in plant community using multivariate analysis of sedimentary ancient DNA (sedaDNA) metabarcoding data. This combination of approaches reveals that the vegetation community has responded sensitively to early Holocene warmth, Neoglacial cooling, and possibly modern anthropogenic warming. To our knowledge, this represents the first combination of a quantitative, biomarker-based climate reconstruction with a sedaDNA-based paleoecological reconstruction, and offers a glimpse at the potential of these molecular techniques used in tandem.

  17. Holocene Millennial-scale Surface and Bottom Water Variability, Feni Drift, NE Atlantic Ocean: Foraminiferal Assemblages

    Science.gov (United States)

    Lassen, S. J.; Richter, T. O.; de Stigter, H. C.; van Weering, T. C. E.; de Haas, H.

    A high-resolution sediment core from Feni Drift (ENAM9606, 56N 14W, 2543 m wa- ter depth) was investigated for planktonic and benthic foraminiferal assemblages dur- ing the last 12,000 years. During the Preboreal, peak abundances of T.quinqueloba indicate the passage of the Arctic front over the core site. Holocene planktonic foraminiferal assemblages indicate a gradual warming trend of surface water masses punctuated by a major cooling (8,200ky event s.l.), and possibly a slight cooling dur- ing the last 3,000 years. The interval from 10 to 5kyrs shows higher and fluctuating abundances of T.quinqueloba and G.bulloides, which suggest proximity of the subarc- tic front and enhanced spring blooms compared to the upper Holocene. Abundance peaks of N.pachyderma(s) and/or T.quinqueloba indicate a series of millennial-scale cooling events during the entire Holocene, which can be correlated to similar episodes previously described from other locations in the North Atlantic and Norwegian- Greenland Sea. Benthic foraminiferal assemblages indicate a gradual transition from seasonal, spring-bloom related food supply in the Lower Holocene (dominance of the phytodetritus species E.exigua) to possibly lower, but more sustained food supply in the Upper Holocene (dominance of C.obtusa and C.laevigata).

  18. 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.

  19. 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

  20. Toward explaining the Holocene carbon dioxide and carbon isotope records: Results from transient ocean carbon cycle-climate simulations

    Science.gov (United States)

    Menviel, L.; Joos, F.

    2012-03-01

    The Bern3D model was applied to quantify the mechanisms of carbon cycle changes during the Holocene (last 11,000 years). We rely on scenarios from the literature to prescribe the evolution of shallow water carbonate deposition and of land carbon inventory changes over the glacial termination (18,000 to 11,000 years ago) and the Holocene and modify these scenarios within uncertainties. Model results are consistent with Holocene records of atmospheric CO2 and δ13C as well as the spatiotemporal evolution of δ13C and carbonate ion concentration in the deep sea. Deposition of shallow water carbonate, carbonate compensation of land uptake during the glacial termination, land carbon uptake and release during the Holocene, and the response of the ocean-sediment system to marine changes during the termination contribute roughly equally to the reconstructed late Holocene pCO2 rise of 20 ppmv. The 5 ppmv early Holocene pCO2 decrease reflects terrestrial uptake largely compensated by carbonate deposition and ocean sediment responses. Additional small contributions arise from Holocene changes in sea surface temperature, ocean circulation, and export productivity. The Holocene pCO2 variations result from the subtle balance of forcings and processes acting on different timescales and partly in opposite direction as well as from memory effects associated with changes occurring during the termination. Different interglacial periods with different forcing histories are thus expected to yield different pCO2 evolutions as documented by ice cores.

  1. Patagonian and southern South Atlantic view of Holocene climate

    Science.gov (United States)

    Kaplan, M. R.; Schaefer, J. M.; Strelin, J. A.; Denton, G. H.; Anderson, R. F.; Vandergoes, M. J.; Finkel, R. C.; Schwartz, R.; Travis, S. G.; Garcia, J. L.; Martini, M. A.; Nielsen, S. H. H.

    2016-06-01

    We present a comprehensive 10Be chronology for Holocene moraines in the Lago Argentino basin, on the east side of the South Patagonian Icefield. We focus on three different areas, where prior studies show ample glacier moraine records exist because they were formed by outlet glaciers sensitive to climate change. The 10Be dated records are from the Lago Pearson, Herminita Península-Brazo Upsala, and Lago Frías areas, which span a distance of almost 100 km adjacent to the modern Icefield. New 10Be ages show that expanded glaciers and moraine building events occurred at least at 6120 ± 390 (n = 13), 4450 ± 220 (n = 7), 1450 or 1410 ± 110 (n = 18), 360 ± 30 (n = 5), and 240 ± 20 (n = 8) years ago. Furthermore, other less well-dated glacier expansions of the Upsala Glacier occurred between 1400 and ∼1000 and ∼2300 and ∼2000 years ago. The most extensive glaciers occurred over the interval from ∼6100 to ∼4500 years ago, and their margins over the last ∼600 years were well within and lower than those in the middle Holocene. The 10Be ages agree with 14C-limiting data for the glacier histories in this area. We then link southern South American, adjacent South Atlantic, and other Southern Hemisphere records to elucidate broader regional patterns of climate and their possible causes. In the early Holocene, a far southward position of the westerly winds fostered warmth, small Patagonian glaciers, and reduced sea ice coverage over the South Atlantic. Although we infer a pronounced southward displacement of the westerlies during the early Holocene, these conditions did not occur throughout the southern mid-high latitudes, an important exception being over the southwest Pacific sector. Subsequently, a northward locus and/or expansion of the winds over the Patagonia-South Atlantic sector promoted the largest glaciers between ∼6100 and ∼4500 years ago and greatest sea ice coverage. Over the last few millennia, the South Patagonian Icefield has experienced

  2. LATE GLACIAL AND HOLOCENE ENVIRONMENTAL CHANGE INFERRED FROM THE PÁRAMO OF CAJANUMA IN THE PODOCARPUS NATIONAL PARK, SOUTHERN ECUADOR

    Directory of Open Access Journals (Sweden)

    ANDREA VILLOTA

    2014-12-01

    Full Text Available To reconstruct the environmental history including vegetation, fire and climate dynamics, from the Cajanuma valley area ( 3285 m elevation in the Podocarpus National Park, southern Ecuador , we address the following major research question: (1 How did the mountain vegetation developed during the late Glacial and Holocene? (2 Did fire played an important control on the vegetation change and was it natural or of anthropogenic origin?. Palaeoenvironmental changes were investigated using multiple proxies such as pollen, spores, charcoal analyses and radiocarbon dating. Pollen data indicated that during the late Glacial and transition to the early Holocene (ca. 16 000-10 500 cal yr BP herb páramo was the main vegetation type around the study area, while subpáramo and mountain rainforest were scarcely represented. The early and mid-Holocene (ca. 10 500 to 5600 cal yr BP is marked by high abundance of páramo during the early Holocene followed by a slight expansion of mountain forest during the mid-Holocene. During the mid- to late Holocene (ca. 5600-1200 cal yr BP there is a significant presence of páramo and subpáramo while Lower Mountain Forest decreased substantially, although, Upper Mountain Forest remained relatively stable during this period. The late Holocene, from ca. 1200 cal yr BP to present, was characterized by páramo; however, mountain forest and subpáramo presented significantly abundance compared to the previous periods. Fires became frequent since the late Holocene. The marked increased local and regional fire intensity during the wetter late Holocene strongly suggests that were of anthropogenic origin. During the late Glacial and early Holocene, the upper forest line was located at low elevations; but shifted slightly upslope to higher elevations during the mid-Holocene.

  3. Authropogenic Warming in North Alaska?.

    Science.gov (United States)

    Michaels, Patrick J.; Sappington, David E.; Stooksbury, David E.

    1988-09-01

    Using permafrost boreholes, Lachenbruch and Marshall recently reported evidence for a 2°-4°C warming in North Alaska occurring at some undetermined time during the last century. Popular accounts suggest their findings are evidence for anthropogenic warming caused by trace gases. Analyses of North Alaskan 1000-500 mb thickness onwards back to 1948 indicate that the warming was prior to that date. Relatively sparse thermometric data for the early twentieth century from Jones et al. are too noisy to support any trend since the data record begins in 1910, or to apply to any subperiod of climatic significance. Any warming detected from the permafrost record therefore occurred before the major emissions of thermally active trace gases.

  4. Holocene paleoclimatic variation in the Schirmacher Oasis, East Antarctica: A mineral magnetic approach

    Science.gov (United States)

    Phartiyal, Binita

    2014-12-01

    An analysis of remanent magnetism and radiocarbon ages in the dry lacustrine/sediment fills of the Schirmacher Oasis (SO) in East Antarctica was conducted to reconstruct past climatic condition. The statistically run mineral magnetic data on paleontological statistics software package (multivariate cluster analysis) placed on accelerator mass spectrometer radiocarbon chronology of the three sediment sections, trace 6 phases of climatic fluctuation between 13 and 3 ka, (Phases 1, 3 and 5 represent cold periods while Phases 2, 4, and 6 represent warm periods). One short warm period (Phase 2, ca. 12.5 ka) occurred in the late Pleistocene, and two marked warm periods (Phase 4, 11-8.7 ka; Phase 6, 4.4-3 ka) occurred in the Holocene. High magnetic susceptibility (χ), saturation isothermal remanent magnetism (SIRM), and soft isothermal remanent magnetism (soft IRM) values correspond to colder periods and low values reflect comparatively warmer lacustrine phases. Holocene Optima (Phase 4) and Mid Holocene Hypsithermal (Phase 6) are distinguished by decreased values of concentrations dependent parameters. Remanence is preserved in the low-coercive minerals. Heavy metals in the sediments include, Fe, Rb, Zn, Mo, Co, Pb, Mn, Cu, and As in order of decreasing abundance.

  5. Bacterial GDGTs in Holocene sediments and catchment soils of a high Alpine lake: application of the MBT/CBT-paleothermometer

    Directory of Open Access Journals (Sweden)

    H. Niemann

    2012-05-01

    Full Text Available A novel proxy for continental mean annual air temperature (MAAT and soil pH, the MBT/CBT-paleothermometer, is based on the temperature (T and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a high Alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the past 11 000 yr. The distribution of bacterial GDGTs in the catchment soils is very similar to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record seems undisturbed, probably without any significant alteration of their distribution through in situ production in the lake itself or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C. Moreover, downcore MBT/CBT-derived MAAT estimates match in timing and magnitude other proxy-based T reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century and the Medieval Warm Period (MWP, ~9th to 14th century. Together, our observations indicate the quantitative applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. In addition to the MWP, our lacustrine paleo T record indicates Holocene warm phases at about 3, 5, 7 and 11 kyr before present, which agrees in timing with other records from both the Alps and the sub-polar North-East Atlantic Ocean. The good temporal match of the warm periods determined

  6. Holocene environmental changes recorded in Dicksonfjorden and Woodfjorden, Svalbard: impacts of global climate changes in a glacial-marine system

    Science.gov (United States)

    Joo, Y. J.; Nam, S. I.; Son, Y. J.; Forwick, M.

    2017-12-01

    Fjords in the Svalbard archipelago are characterized by an extreme environmental gradient between 1) the glacial system affected by tidewater glaciers and seasonal sea ice inside the fjords and 2) the warm Atlantic Water intrusion by the West Spitsbergen Current from open ocean. As sediment is largely supplied from the terrestrial source area exposed along the steep slopes of the fjords, the changes in the surface processes affected by glaciers are likely preserved in the sediments in the inner fjords. On the other hand, variations in the influence of the warm Atlantic Water in the marine realm (e.g. marine productivity) can be archived in the sediment deposited in the vicinity of the entrance to the fjords. Since the last deglaciation of the Svalbard-Barents ice sheet ( 13000 yrs BP), the Svalbard fjords have faced dramatic climate changes including the early Holocene Climate Optimum (HCO) and subsequent cooling that eventually led to the current cold and dry climate. We investigate the Holocene environmental changes in both terrestrial and marine realms based on stable isotopic and inorganic geochemical analyses of sediments deposited in Dicksonfjorden and Woodfjorden in the western and northern Spitsbergen, respectively. The two fjords are expected to provide intriguing information regarding how terrestrial and marine realms of the Arctic fjords system responded to regional and global climate changes. Being a branch of the larger Isfjorden, Dicksonfjorden penetrates deeply to the land, whereas Woodfjorden is rather directly connected to the open ocean. Accordingly, the results suggest that the Dicksonfjorden sediment records mainly terrestrial signals with marked fluctuations in sediment composition that coincide with major climate changes (e.g. HCO). On the contrary, the two Woodfjorden cores collected from different parts of the fjord exhibit contrasting results, likely illustrating differing response of terrestrial and marine realms to the climate changes in

  7. Lakeside cemeteries in the Sahara: 5000 years of holocene population and environmental change.

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    Paul C Sereno

    Full Text Available BACKGROUND: Approximately two hundred human burials were discovered on the edge of a paleolake in Niger that provide a uniquely preserved record of human occupation in the Sahara during the Holocene ( approximately 8000 B.C.E. to the present. Called Gobero, this suite of closely spaced sites chronicles the rapid pace of biosocial change in the southern Sahara in response to severe climatic fluctuation. METHODOLOGY/PRINCIPAL FINDINGS: Two main occupational phases are identified that correspond with humid intervals in the early and mid-Holocene, based on 78 direct AMS radiocarbon dates on human remains, fauna and artifacts, as well as 9 OSL dates on paleodune sand. The older occupants have craniofacial dimensions that demonstrate similarities with mid-Holocene occupants of the southern Sahara and Late Pleistocene to early Holocene inhabitants of the Maghreb. Their hyperflexed burials compose the earliest cemetery in the Sahara dating to approximately 7500 B.C.E. These early occupants abandon the area under arid conditions and, when humid conditions return approximately 4600 B.C.E., are replaced by a more gracile people with elaborated grave goods including animal bone and ivory ornaments. CONCLUSIONS/SIGNIFICANCE: The principal significance of Gobero lies in its extraordinary human, faunal, and archaeological record, from which we conclude the following: The early Holocene occupants at Gobero (7700-6200 B.C.E. were largely sedentary hunter-fisher-gatherers with lakeside funerary sites that include the earliest recorded cemetery in the Sahara.Principal components analysis of craniometric variables closely allies the early Holocene occupants at Gobero with a skeletally robust, trans-Saharan assemblage of Late Pleistocene to mid-Holocene human populations from the Maghreb and southern Sahara.Gobero was abandoned during a period of severe aridification possibly as long as one millennium (6200-5200 B.C.E.More gracile humans arrived in the mid-Holocene

  8. 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...

  9. Sequence stratigraphy and environmental background of the late Pleistocene and Holocene occupation in the Southeast Primor'ye (the Russian Far East)

    Science.gov (United States)

    Chlachula, Jiri; Krupyanko, Alexander A.

    2016-06-01

    The paper presents the results of Quaternary palaeoecology and geoarchaeology studies in the Zerkal'naya Basin, with new insights about sequenced natural shifts during the prehistoric occupation of this marginally explored NE Asian maritime territory. The Basin is part of the continental drainage system and the main physiographic and biotic corridor for peopling of the transitive coastal interior SE Primor'ye Region. The Final Pleistocene and Holocene environmental (biotic and abiotic) proxy records from the Upper/Final Palaeolithic to early historical sites document a dynamic climate change with vegetation cover transformations within riverine and mountain valley ecosystems of the Russian Far East. Most of the archaeological sites located on the low terraces and bedrock promontories along the main river channel and its tributary streams suggest traditional hunter gathered lifestyles based on seasonal salmon-fishing supplemented by pastoral economy. Tundra-forests with larch trees, dwarf birch thickets and polypod ferns from the basal stratigraphic units of the late Last Glacial occupation sites associated with the Upper Palaeolithic micro-blade and bifacial stone tool traditions (14C-dated to 19,000-12,000 cal yrs BP) indicate rather pronounced conditions and much lower MAT comparing today. Following a final Pleistocene cooling event, a major climate warming marked the onset of Holocene accompanied by a regional humidity increase promoting the formation of a mixed broadleaved-coniferous oak-dominant taiga, and culminating in the mid-Holocene Climatic Optimum. The appearance of mosaic parklands ca. 5,000-4,000 cal yrs BP. may be partly attributed to the expansion of the Far Eastern Neolithic cultures practicing forest clearance for pastures and dwellings. A progressing landscape opening indicated by the spread of light-demanding thickets and birch-dominated riverine biotopes with Artemisia suggests a further vegetation cover transformation during the late Neolithic

  10. Holocene variations of wildfire occurrence as a guide for sustainable management of the northeastern Canadian boreal forest

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    Ahmed El-Guellab

    2015-05-01

    Full Text Available Background Cumulative impacts of wildfires and forest harvesting can cause shifts from closed-crown forest to open woodland in boreal ecosystems. To lower the probability of occurrence of such catastrophic regime shifts, forest logging must decrease when fire frequency increases, so that the combined disturbance rate does not exceed the Holocene maximum. Knowing how climate warming will affect fire regimes is thus crucial to sustainably manage the forest. This study aimed to provide a guide to determine sustainable forest harvesting levels, by reconstructing the Holocene fire history at the northern limit of commercial forestry in Quebec using charcoal particles preserved in lake sediments. Methods Sediment cores were sampled from four lakes located close to the northern limit of commercial forestry in Quebec. The cores were sliced into consecutive 0.5 cm thick subsamples from which 1 cm3 was extracted to count and measure charcoal particles larger than 150 microns. Age-depth models were obtained for each core based on accelerator mass spectroscopy (AMS radiocarbon dates. Holocene fire histories were reconstructed by combining charcoal counts and age-depth models to obtain charcoal accumulation rates and, after statistical treatment, long-term trends in fire occurrence (expressed as number of fires per 1000 years. Results Fire occurrence varied between the four studied sites, but fires generally occurred more often during warm and dry periods of the Holocene, especially during the Holocene Thermal Maximum (7000–3500 cal. BP, when fire occurrence was twice as high as at present. Conclusions The current fire regime in the study area is still within the natural range of variability observed over the Holocene. However, climatic conditions comparable to the Holocene Thermal Maximum could be reached within the next few decades, thus substantially reducing the amount of wood available to the forest industry.

  11. Appalachian Piedmont landscapes from the Permian to the Holocene

    Science.gov (United States)

    Cleaves, E.T.

    1989-01-01

    Between the Potomac and Susquehanna Rivers and from the Blue Ridge to the Fall Zone, landscapes of the Piedmont are illustrated for times in the Holocene, Late Wisconsin, Early Miocene, Early Cretaceous, Late Triassic, and Permian. Landscape evolution took place in tectonic settings marked by major plate collisions (Permian), arching and rifting (Late Triassic) and development of the Atlantic passive margin by sea floor spreading (Early Cretaceous). Erosion proceeded concurrently with tectonic uplift and continued after cessation of major tectonic activity. Atlantic Outer Continental Shelf sediments record three major erosional periods: (1) Late Triassic-Early Jurassic; (2) Late Jurassic-Early Cretaceous; and (3) Middle Miocene-Holocene. The Middle Miocene-Holocene pulse is related to neotectonic activity and major climatic fluctuations. In the Piedmont upland the Holocene landscape is interpreted as an upland surface of low relief undergoing dissection. Major rivers and streams are incised into a landscape on which the landforms show a delicate adjustment to rock lithologies. The Fall Zone has apparently evolved from a combination of warping, faulting, and differential erosion since Late Miocene. The periglacial environment of the Late Wisconsin (and earlier glacial epochs) resulted in increased physical erosion and reduced chemical weathering. Even with lowered saprolitization rates, geochemical modeling suggests that 80 m or more of saprolite may have formed since Late Miocene. This volume of saprolite suggests major erosion of upland surfaces and seemingly contradicts available field evidence. Greatly subdued relief characterized the Early Miocene time, near the end of a prolonged interval of tropical morphogenesis. The ancestral Susquehanna and Potomac Rivers occupied approximately their present locations. In Early Cretaceous time local relief may have been as much as 900 m, and a major axial river draining both the Piedmont and Appalachians flowed southeast

  12. Holocene sea-level changes in the Falkland Islands

    Science.gov (United States)

    Newton, Tom; Gehrels, Roland; Daley, Tim; Long, Antony; Bentley, Mike

    2014-05-01

    present sea level. RSL then fell slowly during the middle and late Holocene, eroding the elevated tidal flat deposits in places, and allowing development of thin salt marsh deposits and encroachment of freshwater marsh. Our new sea-level index points are roughly in agreement with GIA model predictions but place tight constraints on the timing of early Holocene RSL rise and the height and timing of the maximum Holocene RSL position.

  13. A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch

    Science.gov (United States)

    Walter Anthony, K. M.; Zimov, S. A.; Grosse, G.; Jones, Miriam C.; Anthony, P.; Chapin, F. S.; Finlay, J. C.; Mack, M. C.; Davydov, S.; Frenzel, P.F.; Frolking, S.

    2014-01-01

    Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch1,2,3,4. However, the same thermokarst lakes can also sequester carbon5, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene carbon accumulation in 20 lake sediments (47±10 grams of carbon per square metre per year; mean±standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160petagrams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears7

  14. Global Warming: Understanding and Teaching the Forecast.

    Science.gov (United States)

    Andrews, Bill

    1994-01-01

    A resource for the teaching of the history and causes of climate change. Discusses evidence of climate change from the Viking era, early ice ages, the most recent ice age, natural causes of climate change, human-made causes of climate change, projections of global warming, and unequal warming. (LZ)

  15. 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.

  16. Sediment biomarkers elucidate the Holocene ontogeny of a shallow lake.

    Directory of Open Access Journals (Sweden)

    T E Arnold

    Full Text Available We carried out geochemical analyses on a sediment core from Lake Harris, Florida (USA to identify sources of organic matter to the sediment throughout the Holocene, and relate changes in those sources to shifts in past climate and environmental conditions. We hypothesized that the sources of organic matter changed in response to regional hydrologic shifts following de-glaciation, and to human population expansion in the state during the 20th century. Hydroclimate shifts in Florida were related to: 1 a steady rise in relative sea level and the fresh water table that began in the early Holocene, 2 wetland formation and expansion ca. 5,000 cal yrs BP, and 3 the onset of the modern El Niño (ENSO cycle ~3,000 cal yrs BP. Stratigraphic changes in sediment variables from Lake Harris reflect each of these hydroclimate periods. Early in the Holocene, Lake Harris was a marsh-like system in a relatively dry, open-prairie environment. Organic sediments deposited at that time were derived largely from terrestrial sources, as inferred from high TOC/TN ratios, a dominance of longer-chain of n-alkanes (n-C29-31, relatively negative organic carbon isotope values (δ13CTOC, and low biogenic silica concentrations. In the middle Holocene, a positive shift in δ13CTOC coincided with the onset of wetter conditions in Florida. Submerged macrophyte biomarkers (n-C21-23 dominated, and during that period bulk organic carbon isotope values were most similar to δ13C values of mid-chain-length n-alkanes. In the late Holocene, δ13CTOC values declined, CaCO3 levels decreased to trace amounts, organic carbon concentrations increased and diatom biogenic silica concentrations increased from 10 to 120 mg g-1. Around 2,900 cal yrs BP, the effects of ENSO intensified and many Florida lakes deepened to their current limnetic state. Concentrations of algal and cyanobacterial biomarkers in the Lake Harris core increased by orders of magnitude after about AD 1940, in response to

  17. Holocene Enviromental Changes in AN Amazonian Floodplain Lake

    Science.gov (United States)

    Moreira, L.; Moreira-Turcq, P. F.; Turcq, B.; Cordeiro, R. C.

    2011-12-01

    not change, suggesting the permanence of a flooded vegetation. The carbon flux increases significantly, reaching peaks of 17 g C/m2/year. The Aulacoseira sp became dominant reaching a peak in this phase. These characteristics show conditions progressively wetter during the Late Holocene. The shift from a shorter annual water levels during the Early-Mid Holocene (phase III) to a long annual high water levels since 3200 years cal BP can suggest a climate change from a drier Early-mid Holocene to a wetter Late Holocene.

  18. ENSO related decadal scale climate variability from the Indo-Pacific Warm Pool

    NARCIS (Netherlands)

    Brijker, J.M.; Jung, S.J.A.; Ganssen, G.M.; Bickert, T.; Kroon, D.

    2006-01-01

    The El Niño-Southern Oscillation (ENSO) is a climatic phenomenon that affects socio-economical welfare in vast areas in the world. A continuous record of Holocene ENSO related climate variability of the Indo-Pacific Warm pool (IPWP) is constructed on the basis of stable oxygen isotopes in shells of

  19. A 13,500 Year Record of Holocene Climate, Fire and Vegetation from Swan Lake, Idaho, USA

    Science.gov (United States)

    Wahl, D.; Anderson, L.; Miller, D. M.; Rosario, J. J.; Starratt, S.; McGeehin, J. P.; Bright, J. E.

    2015-12-01

    Modern climate dynamics in the western US are largely determined by a combination of two factors: 1) the strength and position of midlatitude pressure systems, which, in turn, are responsible for the generation and trajectory of winter storms, and 2) the strength of the North America Monsoon (NAM) which brings summer precipitation northward in response to northern hemisphere warming. Paleoclimate records from the Great Basin of the western US suggest some coherence in the timing of major climatic shifts during the Holocene. However, knowledge of the timing and magnitude of these changes at local scales, which can help explain the relative contribution of midlatitude winter storms vs. NAM, is lacking in many places. Here we present new data that constrain the timing and magnitude of late glacial and Holocene climate variability in the northeastern Great Basin, provide insight into past spatial variability of precipitation patterns in the western US, and improve our understanding of regional scale influences on Great Basin climate. In 2011, a 7.65 m sediment core was raised from Swan Lake, a small wetland located in southeastern Idaho that was formed in the spillway channel created by the catastrophic flooding of Lake Bonneville ~18 ka BP. Pollen, charcoal, clumped isotope, diatom, ostracod, and sedimentological data are used to reconstruct vegetation, fire history, and lake level/groundwater flux over the last 13,500 years. Age control is provided by 19 AMS radiocarbon determinations, which are reported as thousands of calibrated years before present (ka BP). This effort builds on earlier work by Bright (1966) who reported on pollen, macrofossils, and sediment type from Swan Lake. Our data suggest cool and wet conditions prevailed until around 12.3 ka BP, after which a drying trend begins. The early Holocene was marked by a warmer, drier climate, which persisted until around 6.2 ka BP. Moister conditions after 6.2 ka BP likely resulted from a combination of enhanced

  20. Glaciation in the Andes during the Lateglacial and Holocene

    Science.gov (United States)

    Rodbell, Donald T.; Smith, Jacqueline A.; Mark, Bryan G.

    2009-10-01

    This review updates the chronology of Andean glaciation during the Lateglacial and the Holocene from the numerous articles and reviews published over the past three decades. The Andes, which include some of the world's wettest and driest mountainous regions, offer an unparalleled opportunity to elucidate spatial and temporal patterns of glaciation along a continuous 68-degree meridional transect. The geographic and altitudinal extent of modern glaciers and the sensitivity of both modern and former glaciers to respond to changes in specific climatic variables reflect broad-scale atmospheric circulation and consequent regional moisture patterns. Glaciers in the tropical Andes and in the mid-latitude Andes are likely to have been far more sensitive to changes in temperature than glaciers in the dry subtropical Andes. Broad-scale temporal and spatial patterns of glaciation during the Lateglacial are apparent. In the southernmost Andes, the Lateglacial chronology appears to have a strong Antarctic signature with the best-dated moraines correlating closely with the Antarctic Cold Reversal. The southernmost Andes do not appear to have experienced a significant ice advance coeval with the Younger Dryas (YD) climatic reversal. At the other end of the Andes, from ˜0 to 9°N, a stronger YD connection may exist, but critical stratigraphic and geochronologic work is required before a YD ice advance can be fully demonstrated. In the central Andes of Peru, well-dated moraines record a significant ice readvance at the onset of the YD, but ice was retreating during much of the remaining YD interval. The spatial-temporal pattern of Holocene glaciation exhibits tantalizing but incomplete evidence for an Early to Mid-Holocene ice advance(s) in many regions, but not in the arid subtropical Andes, where moraines deposited during or slightly prior to the Little Ice Age (LIA) record the most extensive advance of the Holocene. In many regions, there is strong evidence for Neoglacial

  1. Holocene evolution of Apalachicola Bay, Florida

    Science.gov (United States)

    Osterman, L.E.; Twichell, D.C.; Poore, R.Z.

    2009-01-01

    A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS 14C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting that those areas were forested at 8,000 14C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ???6,400 and ???2,500 14C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of the bay. An eastern deltaic lobe was active for a shorter time, between ???5,800 and 5,100 14C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 14C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time. It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream divide. Estuarine conditions were established very early in the post-glacial flooding of the bay. ?? 2009 US Government.

  2. Relationships between holocene vegetation and the spreading out of civilizations and languages in Southwestern-Asia

    International Nuclear Information System (INIS)

    David, F.

    1991-01-01

    A pluridisciplinary approach is proposed, which deals with the reconstitution of holocene environments and estimation of the human impact. This effects varies in time and space, as in the case of South Eastern Mediterranean countries (Turkey, Syria, Iraq, Iran), where advanced civilization appeared very early. Special attention is paid to palynology, archaeology and linguistic

  3. 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

  4. Effects of ocean warming and acidification on survival, growth and skeletal development in the early benthic juvenile sea urchin (Heliocidaris erythrogramma).

    Science.gov (United States)

    Wolfe, Kennedy; Dworjanyn, Symon A; Byrne, Maria

    2013-09-01

    Co-occurring ocean warming, acidification and reduced carbonate mineral saturation have significant impacts on marine biota, especially calcifying organisms. The effects of these stressors on development and calcification in newly metamorphosed juveniles (ca. 0.5 mm test diameter) of the intertidal sea urchin Heliocidaris erythrogramma, an ecologically important species in temperate Australia, were investigated in context with present and projected future conditions. Habitat temperature and pH/pCO2 were documented to place experiments in a biologically and ecologically relevant context. These parameters fluctuated diurnally up to 10 °C and 0.45 pH units. The juveniles were exposed to three temperature (21, 23 and 25 °C) and four pH (8.1, 7.8, 7.6 and 7.4) treatments in all combinations, representing ambient sea surface conditions (21 °C, pH 8.1; pCO2 397; ΩCa 4.7; ΩAr 3.1), near-future projected change (+2-4 °C, -0.3-0.5 pH units; pCO2 400-1820; ΩCa 5.0-1.6; ΩAr 3.3-1.1), and extreme conditions experienced at low tide (+4 °C, -0.3-0.7 pH units; pCO2 2850-2967; ΩCa 1.1-1.0; ΩAr 0.7-0.6). The lowest pH treatment (pH 7.4) was used to assess tolerance levels. Juvenile survival and test growth were resilient to current and near-future warming and acidification. Spine development, however, was negatively affected by near-future increased temperature (+2-4 °C) and extreme acidification (pH 7.4), with a complex interaction between stressors. Near-future warming was the more significant stressor. Spine tips were dissolved in the pH 7.4 treatments. Adaptation to fluctuating temperature-pH conditions in the intertidal may convey resilience to juvenile H. erythrogramma to changing ocean conditions, however, ocean warming and acidification may shift baseline intertidal temperature and pH/pCO2 to levels that exceed tolerance limits. © 2013 John Wiley & Sons Ltd.

  5. New data for natural situation of Prebaikal region in holocene

    International Nuclear Information System (INIS)

    Kuz'min, S.B.; Dan'ko, L.V.; Snytko, V.A.; Bezrukova, E.V.; Orlova, L.A.

    2007-01-01

    On the basis of the radiocarbon dating data one performed a comprehensive study of the paragenetic series of loose deposits of the layers located in the Baikal Lake western coast central part. The main changes of the natural situations of the Baikal Lake region in the holocene were revealed to take place in the early Subatlantic period (2290+-90 14 C years ago), in the latter half of the Medieval optimum (1410 - 1040+-60 14 C years ago) and in the Cryogenic period (885+-30 - 365+-30 14 C years ago) [ru

  6. Middle-Late Holocene environmental history of Kulunda (Southwestern Siberia): vegetation, climate, humans

    Science.gov (United States)

    Rudaya, N.; Nazarova, L.; Papin, D.; Nourgaliev, D.

    2012-04-01

    Environmental reconstruction of Mid-Late Holocene vegetation and climate was inferred from pollen records of Lake Big Yarovoe (Kulunda steppe, Southwestern Siberia). Reconstruction suggests generally prevalence of steppe during last 4.45 ka. Relatively warm and dry climate, open semi-desert and dry steppes with patchy birch forest spread between 4.45 and 3.80 ka BP. The largest development of conifers forest started in Kulunda after 3.80 ka BP. Constant presence of dark-coniferous trees Abies and especially Picea between 3.80 and 2.7 ka BP indicates the most humid period in the region during studied time. Onset of the Late Holocene is characterised by dominance of steppe with birch and pine forests in lowlands and river valleys. After AD 1860, open steppe and semi-desert vegetation with fragmentary birch forest have been dominated parallel to sharp reduction of conifers in Kulunda. These results are in agreement with general scheme of Holocene environmental history of surrounding areas including Baraba forest-steppe, Kazakh Upland and Altai Mountains. Territory of Kulunda consists many archaeological sites of Bronze, Iron and Middle Ages. Second half of Bronze Age (4.45-3.80 ka BP) was represented by local human cultures or migrants from the North Kazakhstan. The main archaeological culture of Kulunda alike in the whole Ob`-Irtysh interfluve in this period was Elunino culture. The economical activities of Elunino community were connected with animal breeding especially with sheep and goats. The most humid period (~1795-710 BC; 3.8-2.7 ka BP) in Kulunda corresponded to the end of early Bronze Age and to the onset of the Iron Age. In 18 century BC Andronovo culture, associated with the Indo-Iranians and migrants from Central Kazakhstan, spread in the region. Cattle breeding economy was distinctive features of Andronovo people, however, increase of sheep, goats and horses with transition to nomadic life style was characteristic of the late Bronze Age. This trend is in

  7. 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).

  8. Lacustrine Records of Holocene Mountain Glacier Fluctuations from Western Greenland

    Science.gov (United States)

    Schweinsberg, A.; Briner, J. P.; Bennike, O.

    2014-12-01

    Recent studies have focused on documenting fluctuations of the Greenland Ice Sheet margin throughout the Holocene but few data exist that constrain past changes of local glaciers independent of the ice sheet. Our research combines proglacial lake sediment analysis with cosmogenic 10Be dating of Holocene moraines and radiocarbon dating of ice-cap-killed vegetation with an overall objective to use this multi-proxy approach to generate a detailed record of the coupled climate-glacier system through the Holocene. Here, we present lacustrine records of mountain glacier variability from continuous pro-glacial lake sediment sequences recovered from two glaciated catchments in northeastern Nuussuaq, western Greenland. We use radiocarbon-dated sediments from Sikuiui and Pauiaivik lakes to reconstruct the timing of advance and retreat of local glaciers. Sediments were characterized with magnetic susceptibility (MS), gamma density, Itrax XRF and visible reflectance spectroscopy at 0.2 cm intervals and sediment organic matter at 0.5 cm intervals. Basal radiocarbon ages provide minimum-age constraints on deglaciation from Sikuiui and Pauiaivik lakes of ~9.6 and 8.7 ka, respectively. Organic-rich gyttja from deglaciation until ~5.0 ka in Pauiaivik Lake suggests minimal glacial extent there while slightly elevated MS values from ~9.0 - 7.0 ka in Sikuiui Lake may reflect early Holocene glacial advances. Minerogenic sediment input gradually increases starting at ~5.0 ka in Pauiaivik Lake, which we interpret as the onset of Neoglaciation in the catchment. Furthermore, a distinct episode of enhanced glacial activity from ~4.0 - 2.2 ka in Sikuiui Lake may be correlative to a period of persistent snowline lowering evidenced by radiocarbon dates of ice-killed vegetation from nearby ice cap margins. Results from these lacustrine records and our ice-killed vegetation dataset suggest a middle Holocene onset of Neoglaciation ~5.0 - 4.0 ka in this region. We are supplementing these records

  9. A Stalagmite record of Holocene Indonesian-Australian summer monsoon variability from the Australian tropics

    Science.gov (United States)

    Denniston, Rhawn F.; Wyrwoll, Karl-Heinz; Polyak, Victor J.; Brown, Josephine R.; Asmerom, Yemane; Wanamaker, Alan D.; LaPointe, Zachary; Ellerbroek, Rebecca; Barthelmes, Michael; Cleary, Daniel; Cugley, John; Woods, David; Humphreys, William F.

    2013-10-01

    Oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave KNI-51, located in the eastern Kimberley region of tropical Western Australia, represent the first absolute-dated, high-resolution speleothem record of the Holocene Indonesian-Australian summer monsoon (IASM) from the Australian tropics. Stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic Holocene IASM which strengthened in the early Holocene, decreased in strength by 4 ka, with a further decrease from ˜2 to 1 ka, before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka. The relationships between the KNI-51 IASM reconstruction and those from published speleothem time series from Flores and Borneo, in combination with other data sets, appear largely inconsistent with changes in the position and/or organization of the Intertropical Convergence Zone (ITCZ). Instead, we argue that the El Niño/Southern Oscillation (ENSO) may have played a dominant role in driving IASM variability since at least the middle Holocene. Given the muted modern monsoon rainfall responses to most El Niño events in the Kimberley, an impact of ENSO on regional monsoon precipitation over northwestern Australia would suggest non-stationarity in the long-term relationship between ENSO forcing and IASM rainfall, possibly due to changes in the mean state of the tropical Pacific over the Holocene.

  10. 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.

  11. Methane turnover and environmental change from Holocene biomarker records in a thermokarst lake in Arctic Alaska

    Science.gov (United States)

    Elvert, Marcus; Pohlman, John; Becker, Kevin W.; Gaglioti, Benjamin V.; Hinrichs, Kai-Uwe; Wooller, Matthew J.

    2016-01-01

    Arctic lakes and wetlands contribute a substantial amount of methane to the contemporary atmosphere, yet profound knowledge gaps remain regarding the intensity and climatic control of past methane emissions from this source. In this study, we reconstruct methane turnover and environmental conditions, including estimates of mean annual and summer temperature, from a thermokarst lake (Lake Qalluuraq) on the Arctic Coastal Plain of northern Alaska for the Holocene by using source-specific lipid biomarkers preserved in a radiocarbon-dated sediment core. Our results document a more prominent role for methane in the carbon cycle when the lake basin was an emergent fen habitat between ~12,300 and ~10,000 cal yr BP, a time period closely coinciding with the Holocene Thermal Maximum (HTM) in North Alaska. Enhanced methane turnover was stimulated by relatively warm temperatures, increased moisture, nutrient supply, and primary productivity. After ~10,000 cal yr BP, a thermokarst lake with abundant submerged mosses evolved, and through the mid-Holocene temperatures were approximately 3°C cooler. Under these conditions, organic matter decomposition was attenuated, which facilitated the accumulation of submerged mosses within a shallower Lake Qalluuraq. Reduced methane assimilation into biomass during the mid-Holocene suggests that thermokarst lakes are carbon sinks during cold periods. In the late-Holocene from ~2700 cal yr BP to the most recent time, however, temperatures and carbon deposition rose and methane oxidation intensified, indicating that more rapid organic matter decomposition and enhanced methane production could amplify climate feedback via potential methane emissions in the future.

  12. Holocene geologic and climatic history around the Gulf of Alaska

    Science.gov (United States)

    Mann, D.H.; Crowell, A.L.; Hamilton, T.D.; Finney, B.P.

    1998-01-01

    Though not as dramatic as during the last Ice Age, pronounced climatic changes occurred in the northeastern Pacific over the last 10,000 years. Summers warmer and drier than today's accompanied a Hypsithermal interval between 9 and 6 ka. Subsequent Neoglaciation was marked by glacier expansion after 5-6 ka and the assembly of modern-type plant communities by 3-4 ka. The Neoglacial interval contained alternating cold and warm intervals, each lasting several hundred years to one millennium, and including both the Medieval Warm Period (ca. AD 900-1350) and the Little Ice Age (ca. AD 1350-1900). Salmon abundance fluctuated during the Little Ice Age in response to local glaciation and probably also to changes in the intensity of the Aleutian Low. Although poorly understood at present, climate fluctuations at all time scales were intimately connected with oceanographic changes in the North Pacific Ocean. The Gulf of Alaska region is tectonically highly active, resulting in a history of frequent geological catastrophes during the Holocene. Twelve to 14 major volcanic eruptions occurred since 12 ka. At intervals of 20-100 years, large earthquakes have raised and lowered sea level instantaneously by meters and generated destructive tsunamis. Sea level has often varied markedly between sites only 50-100 km apart due to tectonism and the isostatic effects of glacier fluctuations.

  13. Sudden Stratospheric Warming Compendium

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Sudden Stratospheric Warming Compendium (SSWC) data set documents the stratospheric, tropospheric, and surface climate impacts of sudden stratospheric warmings. This...

  14. Millennial Scale Variability of the AMOC and its Link to Climate During the Holocene

    Science.gov (United States)

    Thornalley, D. J.; Oppo, D.; Keigwin, L. D.; Hall, I. R.; Moffa Sanchez, P.

    2014-12-01

    Several proxy and modelling studies suggest that there may have been considerable change in the operation the Atlantic Meridional Overturning Circulation (AMOC) during the Holocene. Yet despite its importance for regional and global climate, the Holocene history of the AMOC is poorly constrained. Improving our knowledge of past AMOC variability will contribute to our general understanding of the dynamics of ocean circulation and the role it may play in causing or amplifying climate variability on millennial timescales. We present Holocene grain-size records in depth transects from Blake Outer Ridge and Cape Hatteras, sampling the full-depth range of the Deep Western Boundary Current (DWBC), the lower limb of the AMOC. These records will complement a depth-transect of grain-size records sampling the Iceland-Scotland (I-S) overflow, showing Holocene variations that reflect deglacial meltwater forcing in the early Holocene and insolation-forced trends from the middle-to-late Holocene (Thornalley et al., 2013, Climate of the Past). We will also present detailed grain-size records for the last 2,000 years, both in a depth transect of cores off Cape Hatteras, and from cores in the Iceland Basin, sampling the I-S overflow. Our extensive datasets enable us to provide a coherent synthesis of changes in the flow strength of key components of the AMOC on centennial-millennial and orbital timescales, which we can use to develop our understanding of past millennial-scale climate variability. Specific questions to be addressed include: How well coupled are Holocene trends in Iceland-Scotland overflow and the DWBC? How did I-S overflow and the AMOC vary during the last millennia, including the last ~150 years since the end of the Little Ice Age? Initial results suggest a long-term anti-phasing of the Nordic overflows, wherein mid-late Holocene weakening of the I-S overflow has been compensated for by a strengthening of Denmark Strait overflow. We will also report on pronounced

  15. Reconstruction of Holocene environmental changes in Southern Kurils (North-Western Pacific) based on palaeolake sediment proxies from Shikotan Island

    Science.gov (United States)

    Nazarova, Larisa; Grebennikova, Tatiana A.; Razjigaeva, Nadezhda G.; Ganzey, Larisa A.; Belyanina, Nina I.; Arslanov, Khikmat A.; Kaistrenko, Victor M.; Gorbunov, Aleksey O.; Kharlamov, Andrey A.; Rudaya, Natalia; Palagushkina, Olga; Biskaborn, Boris K.; Diekmann, Bernhard

    2017-12-01

    We investigated a well-dated sediment section of a palaeolake situated in the coastal zone of Shikotan Island (Lesser Kurils) for organic sediment-geochemistry and biotic components (diatoms, chironomids, pollen) in order to provide a reconstruction of the palaeoenvironmental changes and palaeo-events (tsunamis, sea-level fluctuations and landslides) in Holocene. During the ca 8000 years of sedimentation the changes in organic sediment-geochemistry and in composition of the diatoms and chironomids as well as the shifts in composition of terrestrial vegetation suggest that the period until ca 5800 cal yr BP was characterized by a warm and humid climate (corresponds to middle Holocene optimum) with climate cooling thereafter. A warm period reconstructed from ca 900 to at least ca 580 cal yr BP corresponds to a transition to a Nara-Heian-Kamakura warm stage and can be correlated to a Medieval Warm Period. After 580 cal yr PB, the lake gradually dried out and climatic signals could not be obtained from the declining lacustrine biological communities, but the increasing role of spruce and disappearance of the oak from the vegetation give evidences of the climate cooling that can be correlated with the LIA. The marine regression stages at the investigated site are identified for ca 6200-5900 (at the end of the middle Holocene transgression), ca 5500-5100 (Middle Jomon regression or Kemigawa regression), and ca 1070-360 cal yr BP (at the end of Heian transgression). The lithological structure of sediments and the diatom compositions give evidences for the multiple tsunami events of different strengths in the Island. Most remarkable of them can be dated at around ca 7000, 6460, 5750, 4800, 950 cal yr BP. The new results help to understand the Holocene environmental history of the Southern Kurils as a part of the Kuril-Kamchatka and Aleutian Marginal Sea-Island Arc Systems in the North-Western Pacific region.

  16. Ontong Java volcanism initiated long-term climate warming that caused substantial changes in terrestrial vegetation several tens of thousand years before the onset of OAE1a (Early Aptian, Cretaceous)

    Science.gov (United States)

    Keller, Christina E.; Hochuli, Peter A.; Giorgioni, Martino; Garcia, Therese I.; Bernasconi, Stefano M.; Weissert, Helmut

    2010-05-01

    During Cretaceous times, several intense volcanic episodes are proposed as trigger for episodic climate warming, for changes in marine circulation patterns and for elevated marine productivity, which resulted in the widespread black shale deposits of the Oceanic Anoxic Events (OAE). In the sediments underlying the early Aptian OAE1a black shales, a prominent negative carbon isotope excursion is recorded. Its origin had long been controversial (e.g. Arthur, 2000; Jahren et al., 2001) before recent studies attributed it to the Ontong Java volcanism (Méhay et al., 2009; Tejada et al., 2009). Volcanic outgassing results in an increased pCO2 and should lead to a rise in global temperatures. We therefore investigated if the volcanically-induced increase in pCO2 at the onset of OAE1a in the early Aptian led to a temperature rise that was sufficient to affect terrestrial vegetation assemblages. In order to analyse changes in terrestrial palynomorph assemblages, we examined 15 samples from 12 black shale horizons throughout the early Aptian negative C-isotope spike interval of the Pusiano section (Maiolica Formation; N-Italy). These sediments were deposited at the southern continental margin of the alpine Tethys Ocean and have been bio- and magnetostratigraphically dated by Channell et al. (1995). In order to obtain a continuous palynological record of the negative C-isotope spike interval and the base of OAE1a, we combined this pre-OAE1a interval of Pusiano with the OAE1a interval of the nearby Cismon section (Hochuli et al., 1999). The sporomorph assemblages at the base of this composite succession feature abundant bisaccate pollen, which reflects a warm-temperate climate. Rather arid conditions are inferred from low trilete spore percentages. Several tens of thousand years before the onset of OAE1a, C-isotope values started to decrease. Some thousand years later, bisaccate pollen began to decrease, whereas an increase of Classopollis spp. and Araucariacites spp

  17. Geologic records of Pleistocene, Holocene and Anthropocene beach profiles?

    Science.gov (United States)

    Dougherty, Amy; Choi, Jeong-Heon; Dosseto, Anthony

    2017-04-01

    The Anthropocene Working Group recently concluded that we have entered a new Epoch; starting during the last century when carbon dioxide, temperatures, and sea level all exceeding previous Holocene measurements. Climate change models predict a 1m rise in sea-level by 2100 coupled with increased storm intensity. Determining how vulnerable coasts will respond to global warming in the future, requires past records of sea-level and storm impacts to be deciphered. Paying specific attention to any changes prior to, and since, the onset of the Industrial Revolution. Coastal change over centennial time-scales has long fallen within a knowledge gap that exists between our understanding of shoreline behaviour measured over decades and that inferred from the landscape over millennia. Insight on shoreline behaviour across spatial and temporal scales is gained using computers to integrate models of short-term morphodynamics along beaches with longer-term coastal landscape evolution models. However, limitations exist as process-based engineering models depend on wave climate and beach profile data that is restricted to regional/historical records, while large-scale coastal behaviour models are based on general chronostratographic data from topographic profiles, interpolated cores, and isochrons extrapolated from deep radiocarbon ages. Here we demonstrate a unique methodology combining state-of-the-art geophysics, luminescence, and remote sensing techniques on prograded barriers to extract comprehensive chronostratigraphic records. Ground Penetrating Radar (GPR) data document beach and dune stratigraphy at decimetre resolution. Optically Stimulated Luminescence (OSL) directly date the formation of paleo-beachfaces and dunes. Light Detection and Ranging (LiDAR) image the lateral extent of strandplain ridge morphology. The resulting record of paleo-beach profiles spanning from the present-day beach through Holocene and Pleistocene barriers, enables our in-depth understanding of

  18. The Mt Logan Holocene-late Wisconsinan isotope record

    DEFF Research Database (Denmark)

    Dahl-Jensen, Dorthe; Fisher, David; Osterberg, Erich

    2008-01-01

    Mt Logan • stable isotopes • Holocene • ENSO • peat • N Pacific • sudden change Udgivelsesdato: August......Mt Logan • stable isotopes • Holocene • ENSO • peat • N Pacific • sudden change Udgivelsesdato: August...

  19. Onset and Multiple Fluctuations of Holocene Glaciation in the Sierra Nevada, California

    Science.gov (United States)

    Bowerman, N. D.; Clark, D. H.

    2004-12-01

    Multiple sediment cores from two paternoster tarns (First and Second lakes) in North Fork Big Pine Creek, Sierra Nevada, preserve the most detailed and complete record of Holocene glaciation yet recovered in the range; they indicate that the glacier was absent during the early Holocene, reformed in the late Holocene, and experienced several expansions and contractions, culminating with the Matthes maximum during the last ˜200 years. The lakes are fed by outwash from the Palisade Glacier, the largest ( ˜1.3 km2) and presumably longest-lived glacier in the Sierra Nevada, and capture essentially all of the rock flour produced by the glacier. Distinct late-Holocene (Matthes) and late-Pleistocene (Recess Peak) moraines lie between the modern glacier and the lakes. Thus, the lakes have received continuous sedimentation since the retreat of the Tioga glacier ( ˜15,000 yr B.P.), and therefore capture rock flour related to all subsequent advances. First and Second lakes occupy relatively deep bedrock basins at 3036 m and 3066 m asl., respectively. Third Lake, a shallow (rock flour (outwash) from the upstream Palisade Glacier, most likely related to formation and expansions of the glacier in the late Holocene. The maximum peak at the top of the cores confirms the moraine record, which indicates that the maximum Holocene advance of Sierran glaciers occurred during the late Little Ice Age (last ˜200 yr) At least one tephra layer, possibly related to the Mono/Inyo dome complexes, occurs in the middle depths of the First Lake cores. Other narrow peaks in MS may also be associated with tephra deposits. Ongoing detailed analyses of the sediments, including AMS radiocarbon dating, visual and x-ray imaging, particle size analysis, organic content, tephrochronology, diatom assemblages, and palynology will constrain the timing and character of the environmental fluctuations related to the rock-flour flux. We will present results of these analyses at the meeting.

  20. Aeolian processes during the Holocene in Gannan Region, Eastern Tibetan Plateau

    Science.gov (United States)

    Yang, S.; Cheng, T.; Li, S.; Liang, M.

    2016-12-01

    Aeolian desertification occurring in the Tibetan Plateau has received attention recently for it has become a severe environmental problem by accelerating the grassland degradation and eco-environment damage. The Gannan Region is located in the northeastern Tibetan Plateau with a mean altitude of 3500m. It is highly sensitive to global environmental change and human disturbance. Serious soil erosion and desertification and extensive land degradation have caused heavy eco-environmental impacts. To investigate the evolution of the desertification in Holocene in the Plateau is of great importance for understanding the desertification trend under the global changes in the Tibetan Plateau. Loess and aeolian sands is a key geological archive related to desertification processes and the past environment changes. In this study a typical 8.5m-thick loess-sands profile named MQQ, was selected at the Maqu city. It is situated on the first terrace (T1) of the Yellow River. Detailed accelerator mass spectrometry (AMS) 14C dating of bulk organic matter content has shown the Aeolian sediments of the MQQ section occurring since the early Holocene. the mass-specific frequency-dependent magnetic susceptibility (χfd) and grainsize records show a clear upward increase in the contents of superparamagnetic grains and fine fractions in grain size, which indicates a gradual wetting trend during the Holocene.The sediment rates change from very high in the early Holocene to low values after 8.2 ka. The wetting process can be divided into three steps: 10.0-8.2 ka, 8.2-3.0 ka and 3.0-present. It indicates that the climate in the eastern Tibetan Plateau was dry during the early Holocene. After that the climate was getting wet gradually. The variations of the westerlies and the Asian monsoon may cause the environmental change in this region.

  1. Discharge, water temperature, and water quality of Warm Mineral Springs, Sarasota County, Florida: A retrospective analysis

    Science.gov (United States)

    Metz, Patricia A.

    2016-09-27

    Warm Mineral Springs, located in southern Sarasota County, Florida, is a warm, highly mineralized, inland spring. Since 1946, a bathing spa has been in operation at the spring, attracting vacationers and health enthusiasts. During the winter months, the warm water attracts manatees to the adjoining spring run and provides vital habitat for these mammals. Well-preserved late Pleistocene to early Holocene-age human and animal bones, artifacts, and plant remains have been found in and around the spring, and indicate the surrounding sinkhole formed more than 12,000 years ago. The spring is a multiuse resource of hydrologic importance, ecological and archeological significance, and economic value to the community.The pool of Warm Mineral Springs has a circular shape that reflects its origin as a sinkhole. The pool measures about 240 feet in diameter at the surface and has a maximum depth of about 205 feet. The sinkhole developed in the sand, clay, and dolostone of the Arcadia Formation of the Miocene-age to Oligocene-age Hawthorn Group. Underlying the Hawthorn Group are Oligocene-age to Eocene-age limestones and dolostones, including the Suwannee Limestone, Ocala Limestone, and Avon Park Formation. Mineralized groundwater, under artesian pressure in the underlying aquifers, fills the remnant sink, and the overflow discharges into Warm Mineral Springs Creek, to Salt Creek, and subsequently into the Myakka River. Aquifers described in the vicinity of Warm Mineral Springs include the surficial aquifer system, the intermediate aquifer system within the Hawthorn Group, and the Upper Floridan aquifer in the Suwannee Limestone, Ocala Limestone, and Avon Park Formation. The Hawthorn Group acts as an upper confining unit of the Upper Floridan aquifer.Groundwater flow paths are inferred from the configuration of the potentiometric surface of the Upper Floridan aquifer for September 2010. Groundwater flow models indicate the downward flow of water into the Upper Floridan aquifer

  2. Paleohydrology reconstruction and Holocene climate variability in the South Adriatic Sea

    Directory of Open Access Journals (Sweden)

    G. Siani

    2013-02-01

    Full Text Available Holocene paleohydrology reconstruction is derived combining planktonic and benthic stable oxygen and carbon isotopes, sea surface temperatures (SSTs and oxygen isotope composition of seawater (δ18Ow from a high sedimentation core collected in the South Adriatic Sea (SAS. Core chronology is based on 10 AMS 14C measures on planktonic foraminifera and tephra layers. Results reveal two contrasted paleohydrological periods that reflect (i a marked lowering of δ18Ow/salinity during the early to mid-Holocene (11.5 ka to 6.3 ka, including the two-step sapropel S1 deposition, followed during the mid- to upper Holocene by (ii a prevailing period of increased salinity and enhanced arid conditions in the South Adriatic Basin. Superimposed on these trends, short-term centennial-scale hydrological events punctuated the Holocene period in the SAS. During the early to mid-Holocene, two main SST coolings together with prominent δ18Ow/salinity lowering delineate the sapropel S1 interruption and the post-sapropel phase between 7.3 to 6.3 ka. After 6 ka, centennial-scale δ18Ow and G. bulloides δ13C lowering, mostly centered between 3 to 0.6 ka, reflect short-term hydrological changes related to more intensive runoff of the Po and/or Apennine rivers. These short-term events, even of lesser amplitude compared to the early to mid-Holocene period, may have induced a lowering of sea surface density and consequently reduced and/or inhibited the formation of deep bottom waters in the SAS. Comparison of the emerging centennial- to millennial-scale hydrological record with previous climatic records from the central Mediterranean area and north of the Alps reveal possible synchronicities (within the radiocarbon-dating uncertainty between phases of lower salinity in the SAS and periods of wetter climatic conditions around the north-central Adriatic Sea. Finally, wavelet analyses provide new clues about the potential origin of climate variability in the SAS, confirming

  3. The evolution of Saharan dust input in Lanzarote (Canary Islands): Lower Holocene triggering by human activity in the northwest Sahara?

    Science.gov (United States)

    von Suchodoletz, H.; Oberhänsli, H.; Faust, D.; Zöller, L.; Hambach, U.; Fuchs, M.

    2009-04-01

    A Holocene increase of Saharan dust input to the area of the Canary islands is accompanied by a strong coarsening of this material during the Early Holocene as recorded in loess-like sediments deposited on Lanzarote. Whereas natural causes can be ruled out for the coarsening that is exceptional during the period of the last 180 ka, it is assumed that anthropogenic activity strongly mobilized dust in an area on the pathway of dust prior to its arrival in Lanzarote comprising parts of Western Sahara and northern Mauritania. Although scarce archaeological data from the coastal area of that region do not point to strong anthropogenic activity during the Early Holocene yet, a high density of unexplored archaeological remains reported from the coastal hinterlands does not exclude this hypothesis. Thus, the results of this study highlight the need of further archaeological investigations in that Saharan region.

  4. Pleistocene and Holocene Iberian flora: a complete picture and review

    Science.gov (United States)

    González Sampériz, Penélope

    2010-05-01

    A detailed analysis of the location and composition of Iberian vegetation types during the whole Pleistocene and Holocene periods shows a complex patched landscape with persistence of different types of ecosystems, even during glacial times. In addition, recent, high-resolution palaeoecological records are changing the traditional picture of post-glacial vegetation succession in the Iberian Peninsula. The main available charcoal and pollen sequences include, coniferous and deciduous forest, steppes, shrublands, savannahs and glacial refugia during the Pleistocene for Meso-thermophytes (phytodiversity reservoirs), in different proportions. This panorama suggests an environmental complexity that relates biotic responses to climate changes forced by Milankovitch cycles, suborbital forcings and by the latitudinal and physiographic particularities of the Iberian Peninsula. Thus, many factors are critical in the course of vegetational developments and strong regional differences are observed since the Early Pleistocene. Currently, the flora of Iberia is located in two biogeographical/climatic regions: the Eurosiberian and the Mediterranean. The first one includes northern and northwestern areas of the peninsula, where post-glacial responses of vegetation are very similar to Central Europe, although with some particularities due to its proximity to both the Atlantic Ocean and the Mediterranean region. The second one comprises the main territory of Iberia and shows more complex patterns and singularities, now and in the past. Steppe landscapes dominated extensive areas over all the territory during the cold spells of the Quaternary, especially during the Late Pleistocene up to the Last Glacial Maximum, but differences in composition of the dominant taxa (Compositae versus Artemisia) are observed since the Early Pleistocene, probably related to moisture regional gradients. Coastal shelves and intramountainous valleys, even in continental areas, are spots of floristic

  5. Late Pleistocene and Holocene mammal extinctions on continental Africa

    Science.gov (United States)

    Faith, J. Tyler

    2014-01-01

    Understanding the cause of late Quaternary mammal extinctions is the subject of intense debate spanning the fields of archeology and paleontology. In the global context, the losses on continental Africa have received little attention and are poorly understood. This study aims to inspire new discussion of African extinctions through a review of the extinct species and the chronology and possible causes of those extinctions. There are at least 24 large mammal (> 5 kg) species known to have disappeared from continental Africa during the late Pleistocene or Holocene, indicating a much greater taxonomic breadth than previously recognized. Among the better sampled taxa, these losses are restricted to the terminal Pleistocene and early Holocene, between 13,000 and 6000 yrs ago. The African extinctions preferentially affected species that are grazers or prefer grasslands. Where good terrestrial paleoenvironmental records are present, extinctions are associated with changes in the availability, productivity, or structure of grassland habitats, suggesting that environmental changes played a decisive role in the losses. In the broader evolutionary context, these extinctions represent recent examples of selective taxonomic winnowing characterized by the loss of grassland specialists and the establishment of large mammal communities composed of more ecologically flexible taxa over the last million years. There is little reason to believe that humans played an important role in African extinctions.

  6. Mid- to Late Holocene environmental dynamics on the Yukon Coastal Plain and Herschel Island (Canada) – evidence from polygonal peatlands and lake sediment

    OpenAIRE

    Wolter, Juliane

    2017-01-01

    The North American Arctic witnessed high-amplitude climatic change during the Early Holocene that resulted in regional-scale environmental change. These changes are well documented in the literature. The environmental impacts of moderate climatic oscillations during the Mid- to Late Holocene are less well understood, especially on the Yukon Coastal Plain, which is geographically and topographically isolated from the rest of the western Canadian Arctic. The region is currently experiencing inc...

  7. A Late Glacial to Holocene record of environmental change from Lake Dojran (Macedonia, Greece

    Directory of Open Access Journals (Sweden)

    A. Francke

    2013-02-01

    Full Text Available A Late Glacial to Holocene sediment sequence (Co1260, 717 cm from Lake Dojran, located at the boarder of the F.Y.R. of Macedonia and Greece, has been investigated to provide information on climate variability in the Balkan region. A robust age-model was established from 13 radiocarbon ages, and indicates that the base of the sequence was deposited at ca. 12 500 cal yr BP, when the lake-level was low. Variations in sedimentological (H2O, TOC, CaCO3, TS, TOC/TN, TOC/TS, grain-size, XRF, δ18Ocarb, δ13Ccarb, δ13Corg data were linked to hydro-acoustic data and indicate that warmer and more humid climate conditions characterised the remaining period of the Younger Dryas until the beginning of the Holocene. The Holocene exhibits significant environmental variations, including the 8.2 and 4.2 ka cooling events, the Medieval Warm Period and the Little Ice Age. Human induced erosion processes in the catchment of Lake Dojran intensified after 2800 cal yr BP.

  8. Holocene precipitation changes in the deep tropics recorded by Speleothems (Invited)

    Science.gov (United States)

    Wang, X.; Auler, A. S.; Edwards, R.; Kong, X.; Cheng, H.; Cruz, F. W.; Wang, Y.; Broecker, W. S.

    2010-12-01

    We have obtained a high-resolution oxygen isotope (δ18O) record of cave calcite from Paraiso Cave, eastern Amazon, which covers most of the Holocene. Its chronology was determined by U-Th ages from three column-shaped stalagmites. Their δ18O profiles replicate among their contemporaneous growth periods. Therefore, the samples were likely precipitated under equilibrium conditions and their oxygen isotopic variations are primarily caused by climate change. We find that the δ18O decreases steadily from ~11.0 to 5.0 thousand years ago, with a growth gap between ~8.4 to 6.3 thousand years ago, and then gradually increases until the present. The large amplitude of the δ18O change (up to 4 per mil) suggests that the variation in δ18O value is dominated by meteoric precipitation change at this equatorial site. In order to investigate the interactions between the Intertropical Convergence Zone (ITCZ), monsoons and El Niño-Southern Oscillation (ENSO) activity during the Holocene, we compare the Paraiso record to speleothem records from other locations in the deep tropics, namely, cave sites from Flores, Borneo and Peru. We find that all these speleothem records are consistent, with a progressive δ18O decrease (rainfall increase) during the early Holocene, probably in response to the southward retreat of the ITCZ from its northernmost location in the early Holocene. This is evident from the strong anti-correlation between the speleothem monsoonal records from China and southern Brazil. However, our record is distinct from the others during the last 4 thousand years, when it switches to a continuous δ18O increase (rainfall decrease) trend, while the others flatten out. We propose that, during the late Holocene, the strengthened South American Summer Monsoon may override the ENSO influence and cause the discrepancy in precipitation between eastern Amazon and other deep tropical cave sites.

  9. Organic carbon accumulation and reactivity in central Swedish lakes during the Holocene

    Science.gov (United States)

    Chmiel, H.; Kokic, J.; Niggemann, J.; Dittmar, T.; Sobek, S.

    2012-04-01

    Sedimentation and burial of particulate organic carbon (POC), received from terrestrial sources and from lake internal primary production, are responsible for the progressive accumulation and long-term storage of organic matter in lake basins. For lakes in the boreal zone of central Sweden it can be presumed, that the onset of POC accumulation occurred during the early Holocene (˜8000 BP.) after the retreat of the Scandinavian ice sheet. In this study we investigated carbon mass accumulation rates (CMARs), as well as sources and reactivity of deposited organic material, for seven lakes in central Sweden (60°N, 15°E), in order to obtain a detailed temporal resolution of carbon burial and preservation in boreal lakes. Sediment long-cores were sampled in March 2011 from the ice, and CMARs were calculated from water contents, dry bulk densities, carbon contents and radiocarbon (14C) ages of the depth profiles. To indicate the sources of the organic material and characterize its diagenetic state, we determined carbon-nitrogen ratios (C/N) as well as amounts and compositions of lignin phenols. The transitions from organic rich sediment layers to glacial till deposits were found to be in sediment depths of ˜3 m in each lake. POC contents were on average highest (25-34 wt. % C), in small lakes (≤ 0.07 km2) and lowest (10-18 wt. % C) in the larger lakes (≥ 165 km2). The CMARs over the Holocene showed significant variations and were on average lower in the early Holocene, compared to recent accumulation rates. C/N values and the composition of lignin phenols further provided indications of important changes in organic matter source and reactivity over the Holocene. In summary, our data suggest that boreal lake sediments were a significantly stronger sink for organic carbon during the last ~150 years than during earlier periods of the Holocene.

  10. Alpine treeline and timberline dynamics during the Holocene in the Northern Romanian Carpathians

    Directory of Open Access Journals (Sweden)

    Anca GEANTĂ

    2014-11-01

    Full Text Available High altitude environments (treeline and alpine communities are particularly sensitive to climate changes, disturbances and land-use changes due to their limited tolerance and adaptability range, habitat fragmentation and habitat restriction. The current and future climate warming is anticipated to shift the tree- and timberlines upwards thus affecting alpine plant communities and causing land-cover change and fragmentation of alpine habitats. An upslope movement of some trees, shrubs and cold adapted alpine herbs as a response to the current climate warming has already been noted in many montane and subalpine regions.Four Holocene peat and lacustrine sediment sequences located between 1670 and 1918 m a.s.l. (Fig.1, in the Rodna Mountains (Northern Romania, Eastern Carpathians are used with the aim to determine: i the sensitivity of high mountain habitats to climate, fire and land use changes; ii tree- and timberline shifts: and iii the influence of landscape topography on trees and shrubs.

  11. A stable-isotope tree-ring timescale of the Late Glacial/Holocene boundary

    International Nuclear Information System (INIS)

    Becker, Bernd; Kromer, Bernd; Trimborn, Peter

    1991-01-01

    Late Glacial and Holocene tree-ring chronologies, like deep-sea sediments or polar ice cores, contain information about past environments. Changes in tree-ring growth rates can be related to past climate anomalies and changes in the isotope composition of tree-ring cellulose reflect changes in the composition of the atmosphere and the hydrosphere. We have established a 9,928-year absolutely dated dendrochronological record of Holocene oak (Quercus robur, Quercus petraea)-and a 1,604-year floating Late Glacial and Early Holocene chronology of pine (Pinus sylvestris) from subfossil tree remnants deposited in alluvial terraces of south central European rivers. The pine sequence provides records of dendro-dated 14 C, 13 C and 2 H patterns for the late Younger Dryas and the entire Preboreal (10,100-9,000 yr BP). Through the use of dendrochronology, radiocarbon age calibration and stable isotope analysis, we suggest that the Late Glacial/Holocene transition may be identified and dated by 13 C and 2 H tree-ring chronologies. (author)

  12. 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 ...

  13. Glacial-interglacial changes and Holocene variations in Arabian Sea denitrification

    Science.gov (United States)

    Gaye, Birgit; Böll, Anna; Segschneider, Joachim; Burdanowitz, Nicole; Emeis, Kay-Christian; Ramaswamy, Venkitasubramani; Lahajnar, Niko; Lückge, Andreas; Rixen, Tim

    2018-01-01

    At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific. We calculated composite sea surface temperature (SST) and δ15N ratios in time slices of 1000 years of the last 25 kyr to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. Low δ15N values of 4-7 ‰ during the last glacial maximum (LGM) and stadials (Younger Dryas and Heinrich events) suggest that denitrification was inactive or weak during Pleistocene cold phases, while warm interstadials (ISs) had elevated δ15N. Fast changes in upwelling intensities and OMZ ventilation from the Antarctic were responsible for these strong millennial-scale variations during the glacial. During the entire Holocene δ15N values > 6 ‰ indicate a relatively stable OMZ with enhanced denitrification. The OMZ develops parallel to the strengthening of the SW monsoon and monsoonal upwelling after the LGM. Despite the relatively stable climatic conditions of the Holocene, the δ15N records show regionally different trends in the Arabian Sea. In the upwelling areas in the western part of the basin, δ15N values are lower during the mid-Holocene (4.2-8.2 ka BP) compared to the late Holocene ( ventilation of the OMZ during the period of the most intense southwest monsoonal upwelling. In contrast, δ15N values in the northern and eastern Arabian Sea rose during the last 8 kyr. The displacement of the core of the OMZ from the region of maximum productivity in the western Arabian Sea to its present position in the northeast was established during the middle and late Holocene. This was

  14. Microbial Community Dynamics from Permafrost Across the Pleistocene-Holocene Boundary and Response to Abrupt Climate Change

    Science.gov (United States)

    Hammad, A.; Mahony, M.; Froese, D. G.; Lanoil, B. D.

    2014-12-01

    Earth is currently undergoing rapid warming similar to that observed about 10,000 years ago at the end of the Pleistocene. We know a considerable amount about the adaptations and extinctions of mammals and plants at the Pleistocene/Holocene (P/H) boundary, but relatively little about changes at the microbial level. Due to permafrost soils' freezing anoxic conditions, they act as microbial diversity archives allowing us to determine how microbial communities adapted to the abrupt warming at the end of P. Since microbial community composition only helps differentiate viable and extant microorganisms in frozen permafrost, microbial activity in thawing permafrost must be investigated to provide a clear understanding of microbial response to climate change. Current increased temperatures will result in warming and potential thaw of permafrost and release of stored organic carbon, freeing it for microbial utilization; turning permafrost into a carbon source. Studying permafrost viable microbial communities' diversity and activity will provide a better understanding of how these microorganisms respond to soil edaphic variability due to climate change across the P/H boundary, providing insight into the changes that the soil community is currently undergoing in this modern era of rapid climate change. Modern soil, H and P permafrost cores were collected from Lucky Lady II site outside Dawson City, Yukon. 16S rRNA high throughput sequencing of permafrost DNA showed the same trends for total and viable community richness and diversity with both decreasing with permafrost depth and only the richness increasing in mid and early P. The modern, H and P soils had 50.9, 33.9, and 27.3% unique viable species and only 14% of the total number of viable species were shared by all soils. Gas flux measurements of thawed permafrost showed metabolic activity in modern and permafrost soils, aerobic CH­­4 consumption in modern, some H and P soils, and anaerobic CH­­4 production in one H

  15. A marine to freshwater sediment succession from Kowhai Beach wetland, Northland : implications for Holocene sea level

    International Nuclear Information System (INIS)

    Hicks, H.; Nichol, S.L.

    2007-01-01

    An infilled wetland located behind coastal dunes in north-east Northland is used to reconstruct a local history of environmental change spanning early Holocene (c. 7000 yr BP) to modern time. Proxy indicators (sediment texture, diatoms and pollen) provide evidence for a transition from marginal marine- to brackish- to freshwater-conditions in the wetland. Radiocarbon ages constrain the chronology of this succession to 7880-7430 cal. yr BP for the early period of marine conditions, 3570-3210 cal. yr BP for the latter brackish phase and 1060-800 cal. yr BP for the change to freshwater conditions. Within this succession, the diatom record preserves a strong brackish signal at core depths above the limit of the modern tidal range. This is presented as preliminary evidence for a mid-Holocene sea level highstand for northern New Zealand of approximately 1.2 m above present mean sea level. (author). 40 refs., 7 figs., 1 tab

  16. Holocene climate variability in the winter rainfall zone of South Africa

    Directory of Open Access Journals (Sweden)

    S. Weldeab

    2013-10-01

    Full Text Available We established a multi-proxy time series comprising analyses of major elements in bulk sediments, Sr and Nd isotopes, grain size of terrigenous fraction, and δ18O and δ13C in tests of Neogloboquadrina pachyderma (sinistral from a marine sediment sequence recovered off the Orange River. The records reveal coherent patterns of variability that reflect changes in wind strength, precipitation over the river catchments, and upwelling of cold and nutrient-rich coastal waters off western South Africa. The wettest episode of the Holocene in the winter rainfall zone (WRZ of South Africa occurred during the "Little Ice Age" (700–100 cal years BP most likely in response to a northward shift of the austral westerlies. Wet phases and strengthened coastal water upwellings are companied by a decrease of Agulhas water leakage into the South Atlantic and a reduced dust incursion over Antarctica, as indicated in previous studies. A continuous aridification trend in the WRZ and a weakening of the southern Benguela Upwelling System (BUS between 9000 and 5500 cal years BP parallel with increase of dust deposition over Antarctica and an enhanced leakage of warm Agulhas water into the eastern South Atlantic. The temporal relationship between precipitation changes in the WRZ, the thermal state of the coastal surface water, and leakage of warm water in the South Atlantic, and variation of dust incursion over Antarctica suggests a causal link that most likely was related to latitudinal shifts of the Southern Hemisphere westerlies. Our results of the mid-Holocene time interval may serve as an analogue to a possible long-term consequence of the current and future southward shift of the westerlies. Furthermore, warming of the coastal surface water as a result of warm Agulhas water incursion into the southern BUS may affect coastal fog formation.

  17. Multi-proxy Organic Geochemical Reconstruction of Holocene Hydroclimate Near the Western Greenland Ice Sheet Margin

    Science.gov (United States)

    Cluett, A.; Thomas, E. K.

    2017-12-01

    Anthropogenic warming is projected to drive profound change to the Arctic hydrological cycle within the century, most notably in the intensification of rainfall, with potential feedbacks to the climate system and cryosphere. However, the relationship between hydroclimate and cryosphere variability is poorly constrained in the long-term due to a scarcity of high-resolution hydroclimate records from the Arctic. We analyze the stable hydrogen isotopes (dD) of leaf wax biomarkers from lacustrine sediments spanning the Holocene to 9000 cal. year B.P. from Lake Gus (67.032ºN, 52.427ºW, 300 m a.s.l.; informal name), a small lake approximately 90 km from the modern western margin of the Greenland Ice Sheet. We interpret the signal of aquatic leaf wax isotopes in the context of a survey of 100 modern lake water samples from western Greenland across an aridity gradient to better understand the combined climatological and hydrological controls on lake water dD in the study area. We compare variability of aquatic and terrestrial leaf wax isotopes to infer changes in relative moisture throughout the Holocene, and complement our leaf wax record with analysis of glycerol dialkyl glycerol tetraethers (GDGTs) and alkenones, to produce records of summer temperature. Pairing temperature and leaf wax isotope records provides a means to constrain the changing dD-temperature relationship throughout the Holocene and infer moisture source variability. In combination, these proxies produce a comprehensive hydroclimate record at approximately centennial scale to evaluate shifts in relative moisture, temperature, and moisture source, and to investigate the interaction between hydroclimate and Greenland Ice Sheet margin fluctuations through the Holocene.

  18. Novel sedimentological fingerprints link shifting depositional processes to Holocene climate transitions in East Greenland

    Science.gov (United States)

    van der Bilt, Willem G. M.; Rea, Brice; Spagnolo, Matteo; Roerdink, Desiree L.; Jørgensen, Steffen L.; Bakke, Jostein

    2018-05-01

    The Arctic warms faster than any other region of our planet. Besides melting glaciers, thawing permafrost and decreasing sea-ice, this amplified response affects earth surface processes. This geomorphological expression of climate change may alter landscapes and increase the frequency and magnitude of geohazards like floods or mass-movements. Beyond the short span of sparse monitoring time series, geological archives provide a valuable long-term context for future risk assessment. Lake sediment sequences are particularly promising in this respect as continuous recorders of surface process change. Over the past decade, the emergence of new techniques that characterize depositional signatures in more detail has enhanced this potential. Here, we present a well-dated Holocene-length lake sediment sequence from Ammassalik Island on southeast Greenland. This area is particularly sensitive to regional shifts in the Arctic climate system due to its location near the sea-ice limit, the Greenland Ice Sheet and the convergence of polar and Atlantic waters. The expression of Holocene change is fingerprinted using physical (grain size, organic content, density), visual (3-D Computed Tomography) and geochemical (X-Ray Fluorescence, X-Ray Diffraction) evidence. We show that three sharp transitions characterize the Holocene evolution of Ymer Lake. Between 10 and 9.5 cal. ka BP, rapid local glacier loss from the lake catchment culminated in an outburst flood. Following a quiescent Holocene climatic optimum, Neoglacial cooling, lengthening lake ice cover and shifting wind patterns prompted in-lake avalanching of sediments from 4.2 cal. ka BP onwards. Finally, glaciers reformed in the catchment around 1.2 cal. ka BP. The timing of these shifts is consistent with the regional expression of deglaciation, Neoglacial cooling and Little Ice Age-type glacier growth, respectively. The novel multi-proxy approach applied in this study rigorously links depositional sediment signatures to

  19. Warm Mix Asphalt

    Science.gov (United States)

    2009-04-17

    State of Alaska State of Alaska - Warm Mix Project Warm Mix Project: Location - Petersburg, Alaska which is Petersburg, Alaska which is located in the heart of Southeast Alaska located in the heart of Southeast Alaska's Inside Passage at the tip of M...

  20. Precision radiocarbon dating of a Late Holocene vegetation history

    International Nuclear Information System (INIS)

    Prior, C.A.; Chester, P.I.

    2001-01-01

    The purpose of this research is to precisely date vegetation changes associated with early human presence in the Hawkes Bay region. A sequence of AMS radiocarbon ages was obtained using a new technique developed at Rafter Radiocarbon Laboratory. A density separation method was used to concentrate pollen and spores extracted from unconsolidated lake sediments from a small-enclosed lake in coastal foothills of southern Hawkes Bay. Radiocarbon measurements were made on fractions of concentrated pollen, separated from associated organic debris. These ages directly date vegetation communities used to reconstruct the vegetation history of the region. This technique results in more accurate dating of Late Holocene vegetation changes interpreted from palynological analyses than techniques formerly used. Precision dating of palynological studies of New Zealand prehistory and history is necessary for correlation of vegetation changes to cultural changes because of the short time span of human occupation of New Zealand. (author). 35 refs., 3 figs., 1 tab

  1. Holocene Lake and Shallow Water Sediments at Mograt Island, Sudan

    Directory of Open Access Journals (Sweden)

    Dittrich Annett

    2017-06-01

    Full Text Available This paper presents the results of stratigraphic excavation and soil studies carried out at Mograt Island, the largest of the Nilotic islands in Sudan. Due to its restricted insular environments, Holocene alluvial deposits were observed to be interlocked with archaeological remains of different periods, allowing for a combined chronostratigraphic approach to study both cultural and climatic events. To better understand the environmental context through soil components and pedological features at a microscopic scale, soil block samples were accordingly collected and studied by the application of soil micromorphology. This approach provides insights into the history of Nile terrace aggradation through the suspension of Nile sediment loads under stillwater conditions as well as of the periodical establishment of shallow water pools at the islands′ plateaus by the surface run-off from local rains. Since these patterns vary significantly from the present situation, they offer a key to the scenario in which specific early agricultural and animal herding practices evolved.

  2. Early interglacial carbonate-dilution events in the South China Sea: Implications for strengthened typhoon activities over subtropical East Asia

    Science.gov (United States)

    Huang, Enqing; Tian, Jun; Qiao, Peijun; Wan, Sui; Xie, Xin; Yang, Wenguang

    2015-10-01

    A compilation of many late Quaternary marine sediment records from the northern South China Sea (SCS) continental slope confirms 15-50% reductions in sedimentary calcium carbonate concentrations between 11.0 and 8.5 ka BP in the early Holocene. This low carbonate% event occurred at a time when the regional sea level rose from -50 m to -10 m, which drowned large areas of continental shelves especially those near and within the Taiwan Strait. This event is associated with a significant increase in bulk sedimentation rates on the upper continental slope and the relative abundance of fine-grained detritus. Sediment provenance analyses suggest a dominant terrigenous input from Taiwan and a minor contribution from Luzon during the low carbonate% event, similar to the background terrigenous deposition in other periods of the Holocene. Two comparable low carbonate% events, respectively from the beginning of marine isotope stages 5.5 and 7.3, have also been recognized, pointing to similar causal factors. While carbonate dissolution and carbonate accumulation rate should not have been responsible, increased terrigenous input and dilution is considered as the main cause for the recurrent low carbonate% events in early interglacials. We further hypothesize that, during early interglacials, fluvial sediment discharge from Taiwan and Luzon intensified due to stronger typhoon activities, and massive fine-grained sediments from these two end members may have been transported to the northern SCS continental slope via surface and deep ocean currents. The conjecture of strengthened typhoon activities over East Asia during the early Holocene is supported by high ocean heat contents in the West Pacific Warm Pool area with the prevailing La Niña-like conditions.

  3. Climate variability during the deglaciation and Holocene in a high-altitude alpine lake deduced from the sedimentary record from Laguna Seca, Sierra Nevada, southern Iberian Peninsula

    Science.gov (United States)

    Camuera, Jon; Jiménez-Moreno, Gonzalo; José Ramos-Román, María; García-Alix, Antonio; Jiménez-Espejo, Francisco; Anderson, R. Scott

    2017-04-01

    High-resolution X-ray fluorescence (XRF), magnetic susceptibility (MS), color and lithological analyses have been carried out on a 3.6 m-long sediment core from Laguna Seca, a high-elevation dry lake from Sierra Nevada mountain range, southern Spain. This is the longest sedimentary record retrieved from an alpine lake in southern Iberian Peninsula. Besides, alpine lakes are very sensitive environments to climate changes and previous studies showed that Laguna Seca could provide an excellent record to identify millennial-scale climate variations during deglaciation and the whole Holocene. XRF analyses, in particular high calcium and low K/Ca ratios, show aridity phases, very well represented during Last Glacial Maximum (LGM) and the Younger Dryas (YD). Arid events are also shown at ca. 8.1 ka BP, ca. 4.4 ka BP and the latest Holocene. On the other hand, negative values in calcium and positive values in K/Ca appear in the Bølling-Allerød (BA) and during the early Holocene until ca. 6 ka BP, indicating more humidity and higher run-off. A progressive aridification trend is also observed in the Holocene, changing from more humid conditions during the early Holocene to more aridity during the late Holocene.

  4. Nutrient regime and upwelling in the northern Benguela since the middle Holocene in a global context – a multi-proxy approach

    Directory of Open Access Journals (Sweden)

    S. Meisel

    2011-08-01

    Full Text Available The last 5500 years of climate change and environmental response in the northern Benguela Coastal Upwelling are reconstructed by means of three sediment cores from the inner shelf off central Namibia. The study is based on nutrient (δ15N, δ13C and productivity proxies (accumulation rates of total organic carbon; ARTOC. Reconstructed sea surface temperatures (alkenone-derived SST and temperatures at subsurface depths (Tδ18O; based on tests of planktonic foraminifers reflect the physical boundary conditions. The selection of proxy indicators proved a valuable basis for robust palaeo-climatic reconstructions, with the resolution ranging from multi-decadal (NAM1 over centennial (core 178 to millennial scale (core 226620. The northern Benguela experienced pronounced and rapid perturbation during the middle and late Holocene, and apparently, not all are purely local in character. In fact, numerous correlations with records from the adjacent South African subcontinent and the northern hemisphere testify to global climatic teleconnections. The Holocene Hypsithermal, for instance, is just as evident as the Little Ice Age (LIA and the Roman Warm Period. The marked SST-rise associated with the latter is substantiated by other marine and terrestrial data from the South African realm. The LIA (at least its early stages manifests itself in intensified winds and upwelling, which accords with increased rainfall receipts above the continental interior. It appears that climate signals are transferred both via the atmosphere and ocean. The combined analysis of SST and Tδ18O proved a useful tool in order to differentiate between both pathways. SSTs are primarily controlled by the intensity of atmospheric circulation features, reflecting changes of upwelling-favourable winds. Tδ18O records the temperature of the source water and often correlates with global ocean conveyor speed due to varying inputs of warm Agulhas Water. It seems as though conveyor slowdown or

  5. Geochemical record of Holocene to Recent sedimentation on the Western Indus continental shelf, Arabian Sea

    Science.gov (United States)

    Limmer, David R.; BöNing, Philipp; Giosan, Liviu; Ponton, Camilo; KöHler, Cornelia M.; Cooper, Matthew J.; Tabrez, Ali R.; Clift, Peter D.

    2012-01-01

    We present a multiproxy geochemical analysis of two cores recovered from the Indus Shelf spanning the Early Holocene to Recent (<14 ka). Indus-23 is located close to the modern Indus River, while Indus-10 is positioned ˜100 km further west. The Holocene transgression at Indus-10 was over a surface that was strongly weathered during the last glacial sea level lowstand. Lower Holocene sediments at Indus-10 have higherɛNdvalues compared to those at the river mouth indicating some sediment supply from the Makran coast, either during the deposition or via reworking of older sediments outcropping on the shelf. Sediment transport from Makran occurred during transgressive intervals when sea level crossed the mid shelf. The sediment flux from non-Indus sources to Indus-10 peaked between 11 ka and 8 ka. A hiatus at Indus-23 from 8 ka until 1.3 ka indicates non-deposition or erosion of existing Indus Shelf sequences. HigherɛNdvalues seen on the shelf compared to the delta imply reworking of older delta sediments in building Holocene clinoforms. Chemical Index of Alteration (CIA), Mg/Al and Sr isotopes are all affected by erosion of detrital carbonate, which reduced through the Holocene. K/Al data suggest that silicate weathering peaked ca. 4-6 ka and was higher at Indus-10 compared to Indus-23. Fine-grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain. The Indus Shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings.

  6. Sedimentologic and paleontologic study of the southeast coast of Buenos Aires province, Argentina: A late Pleistocene Holocene paleoenvironmental reconstruction

    Science.gov (United States)

    Aramayo, S. A.; Téllez, B. Gutiérrez; Schillizzi, R. A.

    2005-10-01

    A paleoenvironmental reconstruction of the southeast coast of Buenos Aires province, Argentina, is made mainly on the basis of paleontological and paleoichnological studies, supported by sedimentological analyses and radiocarbon dating. Continental late Pleistocene and continental, transitional, and marine Holocene stratigraphic units are identified. The former comprises fossil mammals and ichnites of 16000-12,000 BP. The continental early Holocene time, ca. 8100 BP, is represented by an interdune paleoenvironment in which shallow brackish ponds were colonized by diatoms, fish, rodents, and birds. A transitional paleoenvironment in the middle Holocene—6930-6570 BP—is recorded by deposits formed by estuarine crabs. During the late Holocene, between 5000 and 4800 BP, a marine transgression was recorded by a rich mollusc fauna.

  7. Geomorphic and sedimentary responses of the Bull Creek Valley (Southern High Plains, USA) to Pleistocene and Holocene environmental change

    Science.gov (United States)

    Arauza, Hanna M.; Simms, Alexander R.; Bement, Leland C.; Carter, Brian J.; Conley, Travis; Woldergauy, Ammanuel; Johnson, William C.; Jaiswal, Priyank

    2016-01-01

    Fluvial geomorphology and stratigraphy often reflect past environmental and climate conditions. This study examines the response of Bull Creek, a small ephemeral creek in the Oklahoma panhandle, to environmental conditions through the late Pleistocene and Holocene. Fluvial terraces were mapped and their stratigraphy and sedimentology documented throughout the course of the main valley. Based on their elevations, terraces were broadly grouped into a late-Pleistocene fill terrace (T3) and two Holocene fill-cut terrace sets (T2 and T1). Terrace systems are marked by similar stratigraphies recording the general environmental conditions of the time. Sedimentary sequences preserved in terrace fills record the transition from a perennial fluvial system during the late glacial period and the Younger Dryas to a semiarid environment dominated by loess accumulation and punctuated by flood events during the middle to late Holocene. The highest rates of aeolian accumulation within the valley occurred during the early to middle Holocene. Our data provide significant new information regarding the late-Pleistocene and Holocene environmental history for this region, located between the well-studied Southern and Central High Plains of North America.

  8. Rapid climate variability during warm and cold periods in polar regions and Europe

    DEFF Research Database (Denmark)

    Masson-Delmotte, V.; Landais, A.; Combourieu-Nebout, N.

    2005-01-01

    Typical rapid climate events punctuating the last glacial period in Greenland, Europe and Antarctica are compared to two rapid events occurring under warmer conditions: (i) Dansgaard-Oeschger event 25, the first abrupt warming occurring during last glacial inception; (ii) 8.2 ka BP event, the only...... rapid cooling recorded during the Holocene in Greenland ice cores and in Ammersee, Germany. The rate of warming during previous warmer interglacial periods is estimated from polar ice cores to 1.5 °C per millennium, without abrupt changes. Climate change expected for the 21st century should however...

  9. Reconstruction of Redox Conditions and Productivity in Coastal Waters of the Bothnian Sea during the Holocene

    Science.gov (United States)

    Dijkstra, N.; Quintana Krupinski, N. B.; Slomp, C. P.

    2014-12-01

    Hypoxia is a growing problem in coastal waters worldwide, and is a well-known cause of benthic mortality. The semi-enclosed Baltic Sea is currently the world's largest human-induced dead zone. During the early Holocene, it experienced several periods of natural hypoxia following the intrusion of seawater into the previous freshwater lake. Recent studies suggest that at that time, the hypoxia expanded north to include the deep basin of the Bothnian Sea. In this study, we assess whether the coastal zone of the Bothnian Sea was also hypoxic during the early Holocene. We analysed a unique sediment record (0 - 30 mbsf) from the Ångermanälven estuary, which was retrieved during the International Ocean Discovery Programme (IODP) Baltic Sea Paleoenvironment Expedition 347 in 2013. Using geochemical proxies and foraminifera abundances, we reconstruct the changes in redox conditions, salinity and productivity in the estuary. Our preliminary results suggest that bottom waters in this coastal basin became anoxic upon the intrusion of brackish seawater in the early Holocene and that the productivity was elevated. The presence of benthic foraminifera in this estuary during the mid-Holocene suggests more saline conditions in the Bothnian Sea than today. Due to isostatic uplift, the estuary likely gradually became more isolated from the Bothnian Sea, which itself became more isolated from the Baltic Sea. Both factors likely explain the subsequent re-oxygenation of bottom waters and gradual refreshening of the estuary as recorded in the sediments. Interestingly, the upper meters of sediment are enriched in minerals that contain iron, phosphorus and manganese. We postulate that the refreshening of the estuary triggered the formation of these minerals, thereby increasing the phosphorus retention in these sediments and further reducing primary productivity. This enhanced retention linked to refreshening may contribute to the current oligotrophic conditions in the Bothnian Sea.

  10. Warm-up and performance in competitive swimming.

    Science.gov (United States)

    Neiva, Henrique P; Marques, Mário C; Barbosa, Tiago M; Izquierdo, Mikel; Marinho, Daniel A

    2014-03-01

    Warm-up before physical activity is commonly accepted to be fundamental, and any priming practices are usually thought to optimize performance. However, specifically in swimming, studies on the effects of warm-up are scarce, which may be due to the swimming pool environment, which has a high temperature and humidity, and to the complexity of warm-up procedures. The purpose of this study is to review and summarize the different studies on how warming up affects swimming performance, and to develop recommendations for improving the efficiency of warm-up before competition. Most of the main proposed effects of warm-up, such as elevated core and muscular temperatures, increased blood flow and oxygen delivery to muscle cells and higher efficiency of muscle contractions, support the hypothesis that warm-up enhances performance. However, while many researchers have reported improvements in performance after warm-up, others have found no benefits to warm-up. This lack of consensus emphasizes the need to evaluate the real effects of warm-up and optimize its design. Little is known about the effectiveness of warm-up in competitive swimming, and the variety of warm-up methods and swimming events studied makes it difficult to compare the published conclusions about the role of warm-up in swimming. Recent findings have shown that warm-up has a positive effect on the swimmer's performance, especially for distances greater than 200 m. We recommend that swimmers warm-up for a relatively moderate distance (between 1,000 and 1,500 m) with a proper intensity (a brief approach to race pace velocity) and recovery time sufficient to prevent the early onset of fatigue and to allow the restoration of energy reserves (8-20 min).

  11. Role of neotectonics and climate in development of the Holocene geomorphology and soils of the Gangetic Plains between the Ramganga and Rapti rivers

    Science.gov (United States)

    Srivastava, Pankaj; Parkash, B.; Sehgal, J. L.; Kumar, Sudhir

    1994-12-01

    Fifteen soil-geomorphic units have been delineated from the Gangetic Plains between the Ramganga and Rapti rivers. They were identified by remote sensing and field checks. On the basis of degree of profile development, their soils are grouped into five members (QGH1 to QGH5, QGH5 being the oldest) of a soil chrono-association. Tentative ages assigned to QGH1 to QGH5 are 500, > 2500, 8000 and 13,5000 yr B.P., respectively. From the early Holocene to about 6500 yr. B.P. a cold, arid to semi-arid climate prevailed and pedogenic calcrete developed over large areas in the Gangetic Plains. Later, a warm and humid climate and improved drainage resulted in complete removal of calcrete from soil profiles in some areas or its dissolution and re-precipitation in lower horizons in other areas. Neotectonics seems to have played a significant role in the evolution of the geomorphology and soils of the area. It determined areas of active sedimentation, pedogenesis and erosion (in upland regions). It led to tilting and sagging of large blocks resulting in shifting and increase in sinuosity of the rivers. Tectonic slopes/faults determined the courses of large rivers.

  12. Global Warming: A Myth?

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 6; Issue 7. Global Warming: A Myth? - Credibility of Climate Scenarios Predicted by Systems Simulations. Deepanjan Majumdar. General Article Volume 6 Issue 7 July 2001 pp 13-21 ...

  13. Warm and Cool Dinosaurs.

    Science.gov (United States)

    Mannlein, Sally

    2001-01-01

    Presents an art activity in which first grade students draw dinosaurs in order to learn about the concept of warm and cool colors. Explains how the activity also helped the students learn about the concept of distance when drawing. (CMK)

  14. Global warming yearbook: 1998

    Energy Technology Data Exchange (ETDEWEB)

    Arris, L. [ed.

    1999-02-01

    The report brings together a year`s worth of global warming stories - over 280 in all - in one convenient volume. It provides a one-stop report on the scientific, political and industrial implications of global warming. The report includes: detailed coverage of negotiations on the Kyoto Protocol; scientific findings on carbon sources and sinks, coral bleaching, Antarctic ice shelves, plankton, wildlife and tree growth; new developments on fuel economy, wind power, fuel cells, cogeneration, energy labelling and emissions trading.

  15. Media Pembelajaran Global Warming

    OpenAIRE

    Tham, Fikri Jufri; Liliana, Liliana; Purba, Kristo Radion

    2016-01-01

    Computer based learning media is one of the media has an important role in learning. Learning media will be attractive when packaged through interactive media , such as interactive media created in paper manufacture " instructional media global warming" . The advantage gained is that it can increase knowledge, generally educate people to be more concerned about the environment , and also can be a means of entertainment. This application is focused to learn about global warming and packaged in...

  16. Non-linearities in Holocene floodplain sediment storage

    Science.gov (United States)

    Notebaert, Bastiaan; Nils, Broothaerts; Jean-François, Berger; Gert, Verstraeten

    2013-04-01

    Floodplain sediment storage is an important part of the sediment cascade model, buffering sediment delivery between hillslopes and oceans, which is hitherto not fully quantified in contrast to other global sediment budget components. Quantification and dating of floodplain sediment storage is data and financially demanding, limiting contemporary estimates for larger spatial units to simple linear extrapolations from a number of smaller catchments. In this paper we will present non-linearities in both space and time for floodplain sediment budgets in three different catchments. Holocene floodplain sediments of the Dijle catchment in the Belgian loess region, show a clear distinction between morphological stages: early Holocene peat accumulation, followed by mineral floodplain aggradation from the start of the agricultural period on. Contrary to previous assumptions, detailed dating of this morphological change at different shows an important non-linearity in geomorphologic changes of the floodplain, both between and within cross sections. A second example comes from the Pre-Alpine French Valdaine region, where non-linearities and complex system behavior exists between (temporal) patterns of soil erosion and floodplain sediment deposition. In this region Holocene floodplain deposition is characterized by different cut-and-fill phases. The quantification of these different phases shows a complicated image of increasing and decreasing floodplain sediment storage, which hampers the image of increasing sediment accumulation over time. Although fill stages may correspond with large quantities of deposited sediment and traditionally calculated sedimentation rates for such stages are high, they do not necessary correspond with a long-term net increase in floodplain deposition. A third example is based on the floodplain sediment storage in the Amblève catchment, located in the Belgian Ardennes uplands. Detailed floodplain sediment quantification for this catchments shows

  17. Refrigeration and global warming

    International Nuclear Information System (INIS)

    Anon.

    1997-01-01

    Some aspects of global warming in general, and the implications for refrigerants and refrigerator efficiency in particular, are briefly considered in a question and answer format. The concepts of Global Warming Potential (GWP) and Total Equivalent Warming Impact (TEWI) are explained. GWP is an index which allows a simple comparison to be make between the warming effects of different gases on a kg to kg basis relative to carbon. The GWP depends both on the lifetime of a substance in the atmosphere and its infra-red absorption capacity. The overall warming effect of operating a refrigeration system for its entire life is measured by its TEWI. Chloroflourocarbons (CFCs) which have been widely used as refrigerants are powerful greenhouse gases with high GWPs. Because of the bank of CFCs in refrigerating systems, their levels in the atmosphere are still increasing and it will be some time before refrigerant changes will be effective in reducing the warming effects of refrigerant releases. Hydrocarbons, hydroflourocarbons and ammonia all have a part to play as substitute refrigerants. Refrigerator efficiency is very important in terms of reducing CO 2 emissions. (UK)

  18. Sediment Buffering and Transport in the Holocene Indus River System

    Science.gov (United States)

    Clift, P. D.; Giosan, L.; Henstock, T.; Tabrez, A. R.; Vanlaningham, S.; Alizai, A. H.; Limmer, D. R.; Danish, M.

    2009-12-01

    Submarine fans are the largest sediment bodies on Earth and potentially hold records of erosion that could be used to assess the response of continents to changing climate in terms of both physical erosion and chemical weathering. However, buffering between the mountain sources and the abyssal plain may make detailed correlation of climate and erosion records difficult. We investigated the nature of sediment transport in the Indus drainage in SW Asia. Through trenching in the flood plain, drilling in the delta and new seismic and coring data from the shelf and canyon we can now constrain sediment transport from source to sink since the Last Glacial Maximum (LGM). The Indus was affected by intensification of the summer monsoon during the Early Holocene and subsequent weakening since ca. 8 ka. Sediment delivery to the delta was very rapid at 12-8 ka, but slowed along with the weakening monsoon. At the LGM erosion in the Karakoram dominated the supply of sandy material, while the proportion of Lesser Himalayan flux increased with strengthening summer rainfall after 12 ka. Total load also increased at that time. Since 5 ka incision of rivers into the upper parts of the flood plain has reworked Lower Holocene sediments, although the total flux slowed. Coring in the Indus canyon shows that sediment has not reached the lower canyon since ca. 7 ka, but that sedimentation has recently been very rapid in the head of the canyon. We conclude that variations in sealevel and terrestrial climate have introduced a lag of at least 7 k.y. into the deep sea fan record and that monsoon strength is a primary control on whether sediment is stored or released in the flood plain.

  19. Holocene Dynamics of Temperate Rainforests in West-Central Patagonia

    Directory of Open Access Journals (Sweden)

    Virginia Iglesias

    2018-01-01

    Full Text Available Analyses of long-term ecosystem dynamics offer insights into the conditions that have led to stability vs. rapid change in the past and the importance of disturbance in regulating community composition. In this study, we (1 used lithology, pollen, and charcoal data from Mallín Casanova (47°S to reconstruct the wetland, vegetation, and fire history of west-central Patagonia; and (2 compared the records with independent paleoenvironmental and archeological information to assess the effects of past climate and human activity on ecosystem dynamics. Pollen data indicate that Nothofagus-Pilgerodendron forests were established by 9,000 cal yr BP. Although the biodiversity of the understory increased between 8,480 and 5,630 cal yr BP, forests remained relatively unchanged from 9,000 to 2,000 cal yr BP. The charcoal record registers high fire-episode frequency in the early Holocene followed by low biomass burning between 6,500 and 2,000 cal yr BP. Covarying trends in charcoal, bog development, and Neoglacial advances suggest that climate was the primary driver of these changes. After 2,000 cal yr BP, the proxy data indicate (a increased fire-episode frequency; (b centennial-scale shifts in bog and forest composition; (c the emergence of vegetation-fire linkages not recorded in previous times; and (d paludification in the last 500 years possibly associated with forest loss. Our results therefore suggest that Nothofagus-Pilgerodendron dominance was maintained through much of the Holocene despite long-term changes in climate and fire. Unparalleled fluctuations in local ecosystems during the last two millennia were governed by disturbance-vegetation-hydrology feedbacks likely triggered by greater climate variability and deforestation.

  20. Holocene Planktonic Foraminiferal Assemblage Shifts on the California Margin; Environmental Forcing of Medieval Chumash Society?

    Science.gov (United States)

    Fisler, J. A.; Hendy, I.

    2005-12-01

    The contribution of D. Kennett and J.P. Kennett to recent literature on native Chumash cultural evolution has linked societal changes between 500 and 1300 A.D. with a rapidly-changing environment. As large-amplitude fluctuations in surface water and climate conditions at the California Margin would have had severe implications for local flora and fauna, high resolution paleooceanographic records from ODP Site 893 should record these environmental changes. The planktonic foraminifera of Santa Barbara Basin are known to be sensitive to climate change over glacial/interglacial and stadial/interstadial time scales. Here we present a Holocene record of planktonic foraminiferal assemblage change that demonstrates this sensitivity continued through what is generally considered to be a warm stable climatic interval. Absolute numbers of planktonic foraminifera specimens decreased through the Holocene, from a peak of over 30,000 specimens/cm3 at 9 kyr BP to several thousand in the last millennia. Eurythermal, high nutrient species G. bulloides and G. quinqueloba show opposite abundance trends throughout deglaciation, with significant decreases in G. bulloides abundance during the Late Holocene while G. quinqueloba increases in abundance. Significant assemblage shifts occurring at 2 kyr BP are particularly pronounced in N. pachyderma dextral/sinistral ratios. Large fluctuations in the dextral/sinistral ratio occur during this interval, varying between 50 and 95%. The most recent decrease in the ratio occurs 800 yrs BP before returning to modern values at 500 yr BP. Assemblage data suggest more dramatic environmental change than indicated by planktonic oxygen isotope records. While N. pachyderma dextral/sinistral ratios generally follow oxygen isotopes throughout the Holocene, the records decouple at 2 kyr BP when the first substantial decrease in the ratio occurs. Salinity may, in part, explain this observation. ODP Site 893 is located at the confluence of the cool

  1. A Record of Holocene Paleoclimate Evolution from Robertson Bay, Victoria Land, Antarctica

    Science.gov (United States)

    Riesselman, C. R.; Truax, O.; Wilson, G. S.; Parker, R. L.; Yoo, K. C.; Lee, J. I.; Levy, R. H.; Mckay, R. M.

    2017-12-01

    Regionally representative records of how Antarctica responded to the transition from the Last Glacial Maximum into the Holocene are an essential component of understanding the processes by which the Antarctic cryosphere responds to a changing climate. Here, we present a high-resolution record of Holocene Antarctic paleoclimate evolution from a previously unstudied section of the Victoria Land margin. In 2015 the Korea Polar Research Institute collected a 571 cm sediment core, GC57, from Robertson Bay, a protected embayment west of Cape Adare and adjacent to the outlet glaciers of the Transantarctic Mountains. Using diatom assemblages, bulk sediment geochemistry, and the magnetic properties of GC57, we aim to reconstruct the response of the East Antarctic Ice Sheet to warming associated with deglaciation and the Holocene climatic optima at the interface between the Ross Sea and the Southern Ocean. Our multiproxy approach allows us to study sea ice extent, seasonality, ocean stratification and circulation, and primary productivity from the mid-Holocene (7,400 14C year BP) to the present. A sea-ice associated diatom assemblage indicative of summer sea surface temperatures below 0˚C dominates the basal section of GC57. Although diatoms are well preserved, the unit is characterized by low wt% biogenic silica (average 9%) and a high concentration of magnetic minerals, indicating that biogenic production persisted despite substantial terrigenous input into the bay. A rapid transition at 4708 14C yr BP is identified by a steep increase in wt% BSi (average 13%), a decrease in magnetic minerals, and a subtle assemblage change towards sea-ice associated diatoms with slightly warmer temperature tolerances. The novel ramped pyrolosis 14C dating methodology allows us to date the carbon fixed concurrent with deposition and generate a robust age model for GC57 with an accuracy previously difficult to achieve given the uncertainties associated with dating bulk acid insoluble

  2. Investigation of warm-mix asphalt using Iowa aggregates.

    Science.gov (United States)

    2011-04-01

    The implementation of warm-mix asphalt (WMA) is becoming more widespread with a growing number of contractors utilizing various WMA technologies. Early research suggests WMA may be more susceptible to moisture damage than traditional hot-mix asphalt ...

  3. Global warming on trial

    International Nuclear Information System (INIS)

    Broeker, W.S.

    1992-01-01

    Jim Hansen, a climatologist at NASA's Goddard Space Institute, is convinced that the earth's temperature is rising and places the blame on the buildup of greenhouse gases in the atmosphere. Unconvinced, John Sununu, former White House chief of staff, doubts that the warming will be great enough to produce serious threat and fears that measures to reduce the emissions would throw a wrench into the gears that drive the Unites States' troubled economy. During his three years at the White House, Sununu's view prevailed, and although his role in the debate has diminished, others continue to cast doubt on the reality of global warming. A new lobbying group called the Climate Council has been created to do just this. Burning fossil fuels is not the only problem; a fifth of emissions of carbon dioxide now come from clearing and burning forests. Scientists are also tracking a host of other greenhouse gases that emanate from a variety of human activities; the warming effect of methane, chlorofluorocarbons and nitrous oxide combined equals that of carbon dioxide. Although the current warming from these gases may be difficult to detect against the background noise of natural climate variation, most climatologists are certain that as the gases continue to accumulate, increases in the earth's temperature will become evident even to skeptics. If the reality of global warming were put on trial, each side would have trouble making its case. Jim Hansen's side could not prove beyond a reasonable doubt that carbon dioxide and other greenhouse gases have warmed the planet. But neither could John Sununu's side prove beyond a reasonable doubt that the warming expected from greenhouse gases has not occurred. To see why each side would have difficulty proving its case, this article reviews the arguments that might be presented in such a hearing

  4. Long range global warming

    International Nuclear Information System (INIS)

    Rolle, K.C.; Pulkrabek, W.W.; Fiedler, R.A.

    1995-01-01

    This paper explores one of the causes of global warming that is often overlooked, the direct heating of the environment by engineering systems. Most research and studies of global warming concentrate on the modification that is occurring to atmospheric air as a result of pollution gases being added by various systems; i.e., refrigerants, nitrogen oxides, ozone, hydrocarbons, halon, and others. This modification affects the thermal radiation balance between earth, sun and space, resulting in a decrease of radiation outflow and a slow rise in the earth's steady state temperature. For this reason the solution to the problem is perceived as one of cleaning up the processes and effluents that are discharged into the environment. In this paper arguments are presented that suggest, that there is a far more serious cause for global warming that will manifest itself in the next two or three centuries; direct heating from the exponential growth of energy usage by humankind. Because this is a minor contributor to the global warming problem at present, it is overlooked or ignored. Energy use from the combustion of fuels and from the output of nuclear reactions eventually is manifest as warming of the surroundings. Thus, as energy is used at an ever increasing rate the consequent global warming also increases at an ever increasing rate. Eventually this rate will become equal to a few percent of solar radiation. When this happens the earth's temperature will have risen by several degrees with catastrophic results. The trends in world energy use are reviewed and some mathematical models are presented to suggest future scenarios. These models can be used to predict when the global warming problem will become undeniably apparent, when it will become critical, and when it will become catastrophic

  5. North Pacific deglacial hypoxic events linked to abrupt ocean warming

    Science.gov (United States)

    Praetorius, Summer K; Mix, Alan C.; Davies, Maureen H.; Wolhowe, Matthew D; Addison, Jason A.; Prahl, Frederick G

    2015-01-01

    Marine sediments from the North Pacific document two episodes of expansion and strengthening of the subsurface oxygen minimum zone (OMZ) accompanied by seafloor hypoxia during the last deglacial transition1, 2, 3, 4. The mechanisms driving this hypoxia remain under debate1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. We present a new high-resolution alkenone palaeotemperature reconstruction from the Gulf of Alaska that reveals two abrupt warming events of 4–5 degrees Celsius at the onset of the Bølling and Holocene intervals that coincide with sudden shifts to hypoxia at intermediate depths. The presence of diatomaceous laminations and hypoxia-tolerant benthic foraminiferal species, peaks in redox-sensitive trace metals12, 13, and enhanced 15N/14N ratio of organic matter13, collectively suggest association with high export production. A decrease in 18O/16O values of benthic foraminifera accompanying the most severe deoxygenation event indicates subsurface warming of up to about 2 degrees Celsius. We infer that abrupt warming triggered expansion of the North Pacific OMZ through reduced oxygen solubility and increased marine productivity via physiological effects; following initiation of hypoxia, remobilization of iron from hypoxic sediments could have provided a positive feedback on ocean deoxygenation through increased nutrient utilization and carbon export. Such a biogeochemical amplification process implies high sensitivity of OMZ expansion to warming.

  6. A Geochemical and Sedimentary Record of High Southern Latitude Holocene Climate Evolution from Lago Fagnano, Tierra del Fuego

    Energy Technology Data Exchange (ETDEWEB)

    Moy, C M; Dunbar, R B; Guilderson, T P; Waldmann, N; Mucciarone, D A; Recasens, C; Austin, J A; Anselmetti, F S

    2010-11-19

    temperature from the mid-latitude Chilean continental shelf and Antarctic air temperatures from the Taylor Dome ice core record in East Antarctica. Mid-Holocene warming occurred simultaneously across the Antarctic Frontal Zone, and in particular, in locations currently influenced by the Antarctic Circumpolar Current.

  7. Three distinct Holocene intervals of stalagmite deposition and nondeposition revealed in NW Madagascar, and their paleoclimate implications

    Science.gov (United States)

    Riavo Gilbertinie Voarintsoa, Ny; Railsback, Loren Bruce; Brook, George Albert; Wang, Lixin; Kathayat, Gayatri; Cheng, Hai; Li, Xianglei; Edwards, Richard Lawrence; Rakotondrazafy, Amos Fety Michel; Olga Madison Razanatseheno, Marie

    2017-12-01

    Petrographic features, mineralogy, and stable isotopes from two stalagmites, ANJB-2 and MAJ-5, respectively from Anjohibe and Anjokipoty caves, allow distinction of three intervals of the Holocene in NW Madagascar. The Malagasy early Holocene (between ca. 9.8 and 7.8 ka) and late Holocene (after ca. 1.6 ka) intervals (MEHI and MLHI, respectively) record evidence of stalagmite deposition. The Malagasy middle Holocene interval (MMHI, between ca. 7.8 and 1.6 ka) is marked by a depositional hiatus of ca. 6500 years. Deposition of these stalagmites indicates that the two caves were sufficiently supplied with water to allow stalagmite formation. This suggests that the MEHI and MLHI intervals may have been comparatively wet in NW Madagascar. In contrast, the long-term depositional hiatus during the MMHI implies it was relatively drier than the MEHI and the MLHI. The alternating wet-dry-wet conditions during the Holocene may have been linked to the long-term migrations of the Intertropical Convergence Zone (ITCZ). When the ITCZ's mean position is farther south, NW Madagascar experiences wetter conditions, such as during the MEHI and MLHI, and when it moves north, NW Madagascar climate becomes drier, such as during the MMHI. A similar wet-dry-wet succession during the Holocene has been reported in neighboring locations, such as southeastern Africa. Beyond these three subdivisions, the records also suggest wet conditions around the cold 8.2 ka event, suggesting a causal relationship. However, additional Southern Hemisphere high-resolution data will be needed to confirm this.

  8. G-warm inflation

    Energy Technology Data Exchange (ETDEWEB)

    Herrera, Ramón, E-mail: ramon.herrera@pucv.cl [Instituto de Física, Pontificia Universidad Católica de Valparaíso, Avenida Brasil 2950, Casilla 4059, Valparaíso (Chile)

    2017-05-01

    A warm inflationary universe in the context of Galileon model or G-model is studied. Under a general formalism we study the inflationary dynamics and the cosmological perturbations considering a coupling of the form G (φ, X )= g (φ) X . As a concrete example, we consider an exponential potential together with the cases in which the dissipation and Galilean coefficients are constants. Also, we study the weak regime given by the condition R <1+3 gH φ-dot , and the strong regime in which 1< R +3 gH φ-dot . Additionally, we obtain constraints on the parameters during the evolution of G-warm inflation, assuming the condition for warm inflation in which the temperature T > H , the conditions or the weak and strong regimes, together with the consistency relation r = r ( n {sub s} ) from Planck data.

  9. G-warm inflation

    Science.gov (United States)

    Herrera, Ramón

    2017-05-01

    A warm inflationary universe in the context of Galileon model or G-model is studied. Under a general formalism we study the inflationary dynamics and the cosmological perturbations considering a coupling of the form G(phi,X)=g(phi) X. As a concrete example, we consider an exponential potential together with the cases in which the dissipation and Galilean coefficients are constants. Also, we study the weak regime given by the condition RR+3gHdot phi. Additionally, we obtain constraints on the parameters during the evolution of G-warm inflation, assuming the condition for warm inflation in which the temperature T>H, the conditions or the weak and strong regimes, together with the consistency relation r=r(ns) from Planck data.

  10. The global warming problem

    International Nuclear Information System (INIS)

    Anon.

    1990-01-01

    In this chapter, a discussion is presented of the global warming problem and activities contributing to the formation of acid rain, urban smog and to the depletion of the ozone layer. Globally, about two-thirds of anthropogenic carbon dioxide emissions arise from fossil-fuel burning; the rest arise primarily from deforestation. Chlorofluorocarbons are the second largest contributor to global warming, accounting for about 20% of the total. The third largest contributor is methane, followed by ozone and nitrous oxide. A study of current activities in the US that contribute to global warming shows the following: electric power plants account for about 33% of carbon dioxide emissions; motor vehicles, planes and ships (31%); industrial plants (24%); commercial and residential buildings (11%)

  11. Greenhouse Warming Research

    DEFF Research Database (Denmark)

    Sørensen, Bent Erik

    2016-01-01

    The changing greenhouse effect caused by natural and anthropogenic causes is explained and efforts to model the behavior of the near-surface constituents of the Earth's land, ocean and atmosphere are discussed. Emissions of various substances and other aspects of human activity influence...... the greenhouse warming, and the impacts of the warming may again impact the wellbeing of human societies. Thus physical modeling of the near-surface ocean-soil-atmosphere system cannot be carried out without an idea of the development of human activities, which is done by scenario analysis. The interactive...

  12. A model for the Holocene extinction of the mammal megafauna in Ecuador

    Science.gov (United States)

    Ficcarelli, G.; Coltorti, M.; Moreno-Espinosa, M.; Pieruccini, P. L.; Rook, L.; Torre, D.

    2003-03-01

    This paper presents the results of multidisciplinary research in the Ecuadorian coastal regions, with particular emphasis on the Santa Elena Peninsula. The new evidence, together with previous data gathered on the Ecuadorian cordillera during the last 12 years, allows us to formulate a model that accounts for most of the mammal megafauna extinction at the Pleistocene/Holocene transition. After the illustration of geomorphological and paleontological evidences of the area of the Santa Elena Peninsula (and other sites), and of a summary of the paleoclimatic data, the main results and conclusions of this work are: (1) Late Pleistocene mammal assemblages survived in the Ecuadorian coast until the Early Holocene sea level rise; (2) Prior to the extinction of most of the megafauna elements (mastodons, ground sloths, equids, sabre-tooth felids), the mammal communities at Santa Elena Peninsula comprise elements with differing habitat requirements, attesting conditions of high biological pressure; (3) At the El Cautivo site (Santa Elena Peninsula), we have discovered Holocene sediments containing the first known occurrences in Ecuador of lithic artifacts that are associated with mammal megafauna remains; (4) During the last 10,000 years, the coastal region of Ecuador underwent significant changes in vegetation cover. At the Pleistocene/Holocene transition the climate changed from very arid conditions to humid conditions. Our data indicates that the megafauna definitively abandoned the Cordillera areas around 12,000 yr BP due to t he increasing aridity, and subsequently migrated to coastal areas where ecological conditions still were suitable, Santa Elena Peninsula and mainly Amazonian areas being typical. We conclude that the unusual high faunal concentrations and the change to dense vegetation cover (due to a rapid increase in precipitation in the lower Holocene) at 8000-6000 yr BP, caused the final collapse and extinction of most elements of the mammal megafauna

  13. Warm summer nights and the growth decline of shore pine in Southeast Alaska

    Science.gov (United States)

    Sullivan, Patrick F.; Mulvey, Robin L.; Brownlee, Annalis H.; Barrett, Tara M.; Pattison, Robert R.

    2015-12-01

    Shore pine, which is a subspecies of lodgepole pine, was a widespread and dominant tree species in Southeast Alaska during the early Holocene. At present, the distribution of shore pine in Alaska is restricted to coastal bogs and fens, likely by competition with Sitka spruce and Western hemlock. Monitoring of permanent plots as part of the United States Forest Service Forest Inventory and Analysis program identified a recent loss of shore pine biomass in Southeast Alaska. The apparent loss of shore pine is concerning, because its presence adds a vertical dimension to coastal wetlands, which are the richest plant communities of the coastal temperate rainforest in Alaska. In this study, we examined the shore pine tree-ring record from a newly established plot network throughout Southeast Alaska and explored climate-growth relationships. We found a steep decline in shore pine growth from the early 1960s to the present. Random Forest regression revealed a strong correlation between the decline in shore pine growth and the rise in growing season diurnal minimum air temperature. Warm summer nights, cool daytime temperatures and a reduced diurnal temperature range are associated with greater cloud cover in Southeast Alaska. This suite of conditions could lead to unfavorable tree carbon budgets (reduced daytime photosynthesis and greater nighttime respiration) and/or favor infection by foliar pathogens, such as Dothistroma needle blight, which has recently caused widespread tree mortality on lodgepole pine plantations in British Columbia. Further field study that includes experimental manipulation (e.g., fungicide application) will be necessary to identify the proximal cause(s) of the growth decline. In the meantime, we anticipate continuation of the shore pine growth decline in Southeast Alaska.

  14. Early to middle Holocene valley glaciations on northernmost Greenland

    DEFF Research Database (Denmark)

    Möller, Per; Larsen, Nicolaj K.; Kjær, Kurt H.

    2010-01-01

    This paper presents the glacial stratigraphy and palaeoenvironmental evolution around Constable Bugt, Johannes V. Jensen Land, located on the north coast of Greenland. This is a land of extreme climate: polar desert conditions and a coast bound by a permanent sea ice cover. Our data covers....... This observation can be explained by the altitudinal and temporal distribution of beach-ridge complexes that must have formed by wave action and thus requiring at least partial open-water conditions. With a moisture source at hand, we propose that this lead to enhanced precipitation in the near-coastal areas which...

  15. Isotope heterogeneity of Pre-Holocene groundwater in Iceland

    DEFF Research Database (Denmark)

    Sveinbjörnsdóttir, Á.E.; Arnorsson, S.; Heinemeier, Jan

    2007-01-01

    In recent years, it has been shown that groundwater with a Pre-Holocene component is more common in the Icelandic bedrock than previously thought. Some of the Pre-Holocene water samples are more depleted in delta H-2 and delta O-18 than any mean annual precipitation in Iceland today due to the cold...... climate at that time. However, most often Pre-Holocene water components cannot be detected based on the water isotopes alone due to mixing with younger and isotopically heavier water. The Cl concentration in relation to the water isotopes in specific areas has proved to be a good indicator of a Pre......-Holocene component in the groundwater. The deuterium excess value may also help to identify water from a different climate regime, if no oxygen shift has occurred. The relative abundance of a Pre-Holocene water component of the Icelandic groundwater has led to the understanding that combined interpretation of water...

  16. The Caribbean conundrum of Holocene sea level.

    Science.gov (United States)

    Jackson, Luke; Mound, Jon

    2014-05-01

    In the tropics, pre-historic sea-level curve reconstruction is often problematic because it relies upon sea-level indicators whose vertical relationship to the sea surface is poorly constrained. In the Caribbean, fossil corals, mangrove peats and shell material dominate the pre-historic indicator record. The common approach to reconstruction involves the use of modern analogues to these indicators to establish a fixed vertical habitable range. The aim of these reconstructions is to find spatial variability in the Holocene sea level in an area gradually subsiding (different depths. We use the first catalogue to calibrate 14C ages to give a probabilistic age range for each indicator. We use the second catalogue to define a depth probability distribution function (pdf) for mangroves and each coral species. The Holocene indicators are grouped into 12 sub-regions around the Caribbean. For each sub-region we apply our sea-level reconstruction, which involves stepping a fixed-length time window through time and calculating the position (and rate) of sea-level (change) using a thousand realisations of the time/depth pdfs to define an envelope of probable solutions. We find that the sub-regional relative sea-level curves display spatio-temporal variability including a south-east to north-west 1500 year lag in the arrival of Holocene sea level to that of the present day. We demonstrate that these variations are primarily due to glacial-isostatic-adjustment induced sea-level change and that sub-regional variations (where sufficient data exists) are due to local uplift variability.

  17. Global warming from an energy perspective

    International Nuclear Information System (INIS)

    Edwards, A.G.

    1991-01-01

    Global climate change and energy are integrally related. The majority of greenhouse gas emissions are the result of energy production and use; at the same time, warming will affect energy patterns in California through physical increases in energy demand, physical changes in energy supply, and changes in both energy end-use patterns and supplies resulting from climate-change policies. There seems to be a growing political consensus that the world (as well as the state) needs to act soon to minimize further commitment to future warming. While California is not likely to experience the physical changes resulting from a warmer climate for years or perhaps decades, policy responses to the warming issue may cause more immediate impacts. This chapter will discuss how policy response to potential warming may be the most significant early impact of the issue on California's energy system. Makers of energy policy face the dilemma of deciding how to respond to the climate warming issue in the face of scientific uncertainties about its timing and seriousness. The chapter will conclude by presenting a conceptual framework for dealing with this dilemma, along with general recommendations for action

  18. Warm pre-stressing

    International Nuclear Information System (INIS)

    Hedner, G.

    1983-01-01

    Literature survey and critical evaluation of the phenomenon of warm pre-stressing (WPS) is presented. It is found that the cause of it is not clear and a calculated control is missing. The effect of irradiation is unknown, and the influence of WPS on the behaviour of reactor vessels is discussed. (G.B.)

  19. Being Warm-Hearted

    Institute of Scientific and Technical Information of China (English)

    李函; 任汉鼎

    2017-01-01

    Good morning,ladies and gentlemen.It’s my honor to address[向……致辞] you.My English name is Isabella.I’m a high school student of 17.I have some good personality traits[特点],including being warm-hearted.So here comes my topic:Being

  20. Warm and Cool Cityscapes

    Science.gov (United States)

    Jubelirer, Shelly

    2012-01-01

    Painting cityscapes is a great way to teach first-grade students about warm and cool colors. Before the painting begins, the author and her class have an in-depth discussion about big cities and what types of buildings or structures that might be seen in them. They talk about large apartment and condo buildings, skyscrapers, art museums,…

  1. The global warming scare

    International Nuclear Information System (INIS)

    Sunavala, P.D.

    1992-01-01

    It is argued that the present propaganda about the global warming with its disastrous consequences is a scare spread by some First World countries, especially the United States, to prevent the rapid industrialization of developing third world countries. (author). 6 refs., 1 tab

  2. Paralyzed warming world

    Czech Academy of Sciences Publication Activity Database

    Ač, Alexander

    2010-01-01

    Roč. 2, č. 2 (2010), s. 81-86 ISSN 1876-8156 Institutional research plan: CEZ:AV0Z60870520 Keywords : global warming * climate Subject RIV: EH - Ecology, Behaviour http://ojs.ubvu.vu.nl/alf/article/view/134/250

  3. The roles of fire in Holocene ecosystem changes of West Africa

    Science.gov (United States)

    Dupont, L. M.; Schefuß, E.

    2018-01-01

    The climate changes associated with the Holocene wet phase in the Sahara, the African Humid Period, are subject to ongoing debate discussing interactions between climate and vegetation and possible feedbacks between vegetation, albedo, desertification, and dust. However, very little attention has been given to the role of fire in shaping the land cover, although it is known that fires are important in the formation and consolidation of the African savanna. To fill this gap, we investigated the interaction between precipitation changes, vegetation shifts, and fire occurrence in West Africa by combining stable isotope measurements on plant waxes with pollen and micro-charcoal counts of marine sediments retrieved offshore of Cape Blanc. Our study focuses on the roles of fire at the dry limit of savanna during the Holocene evolution of precipitation changes indicating that the impact of fire during a relative wet climate differs from that during aridification. During the humid early Holocene, increased savanna extension and diversification ran parallel to increased fire occurrence. In contrast, after aridification of northern Africa started at the end of the African Humid Period, a maximum in fire occurrence correlated with a deterioration of the vegetation promoting desertification.

  4. Holocene sea-level changes along the Strait of Magellan and Beagle Channel, southernmost South America

    Science.gov (United States)

    Porter, Stephen C.; Stuiver, Minze; Heusser, Calvin J.

    1984-07-01

    Radiocarbon-dated marine sediments from five coastal sites along the Strait of Magellan and Beagle Channel in southernmost Chile permit construction of a curve of relative sea-level fluctuations during the Holocene. Morphologic and stratigraphic data point to coastal submergence during the early Holocene as the sea rose to a maximum level at least 3.5 m higher than present about 5000 yr ago. Progressive emergence then followed during the late Holocene. Data from widely separated localities define a smooth curve, the form of which is explainable in terms of isostatic and hydroisostatic deformation of the crust resulting from changing ice and water loads. Apparently anomalous data from one site located more than 100 km behind the outer limit of the last glaciation may reflect isostatic response to deglaciation. The sea-level curve resembles one derived by Clark and Bloom (1979, In "Proceedings of the 1978 International Symposium on Coastal Evolution in the Quaternary, Sao Paulo, Brasil," pp. 41-60. Sao Paulo) using a spherical Earth model, both in amplitude and in the timing of the maximum submergence.

  5. Holocene vegetation, fire and climate interactions on the westernmost fringe of the Mediterranean Basin

    Science.gov (United States)

    Morales-Molino, César; García-Antón, Mercedes; Postigo-Mijarra, José M.; Morla, Carlos

    2013-01-01

    A new palaeoecological sequence from the western Iberian Central Range significantly contributes to the knowledge on the Holocene vegetation dynamics in central Iberia. This sequence supports the existence of time-transgressive changes in the vegetation cover during the beginning of the Holocene over these central Iberian mountains, specifically the replacement of boreal birch-pine forests with Mediterranean communities. Anthracological analyses also indicate the replacement of boreal pines (Pinus sylvestris) with Mediterranean ones (Pinus pinaster) during the early Holocene. The observed vegetation changes were generally synchronous with climatic phases previously reconstructed for the western Mediterranean region, and they suggest that the climatic trends were most similar to those recorded in the northern Mediterranean region and central Europe. Several cycles of secondary succession after fire ending with the recovery of mature forest have been identified, which demonstrates that the vegetation of western Iberia was highly resilient to fire disturbance. However, when the recurrence of fire crossed a certain threshold, the original forests were not able to completely recover and shrublands and grasslands became dominant; this occurred approximately 5800-5400 cal yr BP. Afterwards, heathlands established as the dominant vegetation, which were maintained by frequent and severe wildfires most likely associated with human activities in a climatic framework that was less suitable for temperate trees. Finally, our palaeoecological record provides guidelines on how to manage protected areas in Mediterranean mountains of southwestern Europe, especially regarding the conservation and restoration of temperate communities that are threatened there such as birch stands.

  6. Holocene elemental, lead isotope and charcoal record from peat in southern Poland

    Directory of Open Access Journals (Sweden)

    K. Tudyka

    2017-03-01

    Full Text Available This article presents a mid-resolution elemental, isotopic and charcoal record from 10700 BC to AD 500 in a peat core located in Żyglin (southern Poland. The objective is to give insight into the proxies with emphasis on lead (Pb sources in this minerogenic peat deposit. During the Early Holocene (10700–7550 BC the average 206Pb/207Pb quotient was around 1.196. This isotopic signature is consistent with natural dust derived from long-distance soil and rock weathering. The Mid-Holocene period (7550–3200 BC shows a significant change in the peat accumulation conditions. The growth rate is approximately 0.04 mm yr-1 and the 206Pb/207Pb quotients are shifted toward values that are found in local galena ores. This is simultaneous with a significantly increased lead flux which further confirms local sources of material in this peat deposit. In the Late Holocene period (3200 BC–AD 500 a large quantity of charcoal particles with diameters ranging from 2 mm up to 3 cm is found; also, Pb, Zn and Cu fluxes reach their highest values. This period corresponds to the Eneolithic, Bronze and Iron Ages, and human impact is recorded as charcoal.

  7. Takaka Fossil Cave : a stratified Late Glacial to Late Holocene deposit from Takaka Hill, New Zealand

    International Nuclear Information System (INIS)

    Worthy, T.H.; Roscoe, D.

    2003-01-01

    A rich terrestrial vertebrate fauna from the pitfall trap deposit of Takaka Fossil Cave on Takaka Hill, South Island, New Zealand, is described. Radiocarbon ages on moa bones bracket the onset of sedimentation in the site to between 12361 and 11354 14 C yrs BP. Euryapteryx geranoides was in the Late Glacial moa fauna that predates the onset of sedi-mentation in the site, but was absent in younger faunas. The moa Anomalopteryx didiformis was present in the Late Glacial fauna as well throughout the Holocene. A total of 1633 bones from 25 species of birds and a further 895 bones of 154 individuals of vertebrates other than birds (two species of frog, one tuatara, three lizards, two bats, and a rat) were identified in the total recovered fauna. A well-preserved partial skeleton of Haast's eagle (Harpagornis moorei) of Late Glacial age had severe arthritis. Unusually small specimens of Euryapteryx were morphologically diagnosed as E. geranoides, and confirmed as such by mitochondrial DNA analysis. The molluscan fauna contained two aquatic, troglobitic hydrobiids and 29 taxa of land snails. While there is little change in species diversity between lower and upper layers, there are marked changes in relative abundance of some taxa that suggest the environment was drier in the Early and Middle Holocene than it was in the Late Holocene. (author). 26 refs., 3 figs., 4 tabs

  8. Identification of Holocene millennial-scale forcing in the North Atlantic area: Ocean/atmosphere contribution

    Science.gov (United States)

    Debret, M.; Masson-Delmotte, V.; Christophe, C.; de Vernal, A.; Massei, N.; Eynaud, F.; Nicolle, M.; Frank, N.; Mary, Y.; Magny, M.

    2017-12-01

    Millennial (1500-year) cycles were evidenced decades ago from the advance and retreat of glaciers but many subsequent studies failed to demonstrate the unequivocal character of such oscillation from paleoclimate time series. Hence, the identification of a persistent 1500 year periodicity remains controversial both for the last glacial episode and the Holocene. Applying wavelet analysis to Holocene climate records, we have identified synchronous millennial-scale oscillations which permit to establish a North Atlantic millennial variability index (NAV-Index), maximum at 5330 ± 245, 3560 ± 190, 1810 ± 160 cal years BP and minimum at 4430 ± 250, 2640 ± 225 and 970 ± 200 years before present. This NAV-index was compared with the millennial variability of cosmogenic 10Be isotope, a proxy of solar activity. Differences between the two sets of records suggest that an internal mechanism (Ocean/atmosphere) must be at the origin of the North Atlantic millennial scale variability. Our data document an increased coherence and magnitude of the North Atlantic millennial variability since 6000 cal. years BP, with a frequency of 1780 ± 240 years. During the early Holocene, deglacial meltwater fluxes had strong regional impact and the coupling between subpolar gyre migration and Atlantic meridional oceanic circulation observed since afterward seems to be related to the end of the Laurentide and Inuitian ice sheet meltwater discharge. Hence, we may conclude that the evolution of this millennial oscillation in the future will depend upon the Greenland stability or melting.

  9. Preliminary Report on Unique Laminated Holocene Sediments from the Qarun Lake in Egypt

    Directory of Open Access Journals (Sweden)

    Marks Leszek

    2016-06-01

    Full Text Available The Lake Qarun (Faiyum Oasis, northern Egypt is a relic of the much larger Holocene lake. Past lake levels and extensions were reconstructed, based on setting of archaeological sites scattered along northern paleoshores of the ancient lake. However, geoarcheological works did not yield enough data to establish continuous environmental history of the lake. A deep drilling FA-1 on the southeastern shore of the lake, performed in 2014, supplied with a core, 26 m long that is the one of the longest lake sediment cores in northeastern Africa. The basal section of the core consisted of thin-laminated diatom marly deposits, underlain at the Late Pleistocene/Holocene boundary by coarse-grained sands. The sediment lamine were quite well developed, especially in the lower part of the core. Preliminary results indicated annually deposited sediment sequence with seasonality signals provided by microlamine of diatoms, calcite, organic matter and clastic material. Early Holocene varved sediments from the Faiyum Oasis supplied with exceptional paleoenvironmental data for northeastern Africa, which enriched a record from previous logs drilled at the southwestern margin of the Qarun Lake.

  10. History of formation of forests in the plain part of Ukraine in the Holocene

    International Nuclear Information System (INIS)

    Bezusko, L.G.; Mosyakin, S.L.; Tsymbalyuk, Z.M.; Bezusko, A.G.

    2005-01-01

    Full text: The authors analyzed and generalized the results of palynological and radiocarbon-dating studies of Holocene deposits of the forest, forest-steppe and steppe zones of Ukraine. Based on the obtained data, we reconstructed the pattern of main changes of vegetation and climate starting from 10,300 years BP. We consider changes in forest vegetation of the studied area in the Early (PB-1, PB-2, BO-1, BO-2, BO-3), Middle (AT-1, AT-2, AT-3, SB-1, SB-2, SB-3) and Late Holocene. For most important forest-forming trees (species of Pinus, Betula, Alnus, Quercus, Tilia, Carpinus, Fagus etc.), the main periods of their maximum participation in Ukrainian forest vegetation were identified. Broadleaf forests and mixed forests with participation of broadleaf trees were most widespread in Ukraine 4,500-6,200 years BP. During the second phase of the Atlantic time of the Holocene the northern border of the steppe zone in Ukraine was stable. Expansion of forest communities in the steppe zone progressed through gradual increase of forest areas that originally occurred in flood plains and ravines. (author)

  11. Mid-Holocene onset of high-amplitude decadal to centennial scale variability along the Peru Chile Margin

    Science.gov (United States)

    Chazen, C. R.; Altabet, M.; Herbert, T. D.

    2008-12-01

    Understanding the natural climate variations in the eastern tropical Pacific is crucial for predicting the evolution of the El Niño-Southern Oscillation (ENSO) system and for anticipating the ways in which increases in atmospheric CO2 will affect climate. Here we present the first continuous, high-resolution (11-12 yr) climate record across the mid-Holocene transition (10ka-1.4ka) from the Peru-Chile Margin near the epicenter of the modern ENSO system. Although the high productivity of the Peru margin should promote high deposition rates, and the anaerobic bottom water conditions should inhibit sediment mixing by benthic organisms, nearly all sediment cores recovered from this region suffer from major gaps in Holocene sedimentation. Our data comes from a ~5 meter piston core collected from the mid-Peruvian shelf (15° 15"S, 75° 58"W, ~250mwd) in the heart of the oxygen minimum/denitrification zone that provides the first uninterrupted archive of conditions along the Peru-Chile margin. A suite of geochemical proxies allow us to reconstruct sea surface temperature (SST- Uk'37), phytoplankton productivity (C37total and %BSi), and thermocline ventilation (δ15N), variables that are tightly correlated to ENSO events today. Despite the observation that the mean late Holocene state of all three variables did not change over the last 10,000 years, our data reveal a dramatic increase in climate variability after the mid Holocene (~5ka); represented by prolonged periods (50-200yrs) of climate extremes, which are absent in the early Holocene. To further investigate these climate extremes we examine benthic foraminiferal assemblages and oxygen isotopes in combination with our other proxy records in selected late Holocene sections. The roughly centennial-scale oscillations do not show typical El Niño-La Niña correlations between proxies. We therefore posit that a significant fraction of super-ENSO variance during the course of the Holocene may originate outside the tropics

  12. Detrital events and hydroclimate variability in the Romanian Carpathians during the mid-to-late Holocene

    Science.gov (United States)

    Longman, Jack; Ersek, Vasile; Veres, Daniel; Salzmann, Ulrich

    2017-07-01

    The Romanian Carpathians are located at the confluence of three major atmospheric pressure fields: the North Atlantic, the Mediterranean and the Siberian. Despite its importance for understanding past human impact and climate change, high-resolution palaeoenvironmental reconstructions of Holocene hydroclimate variability, and in particular records of extreme precipitation events in the area, are rare. Here we present a 7500-year-long high-resolution record of past climatic change and human impact recorded in a peatbog from the Southern Carpathians, integrating palynological, geochemical and sedimentological proxies. Natural climate fluctuations appear to be dominant until 4500 years before present (yr BP), followed by increasing importance of human impact. Sedimentological and geochemical analyses document regular minerogenic deposition within the bog, linked to periods of high precipitation. Such minerogenic depositional events began 4000 yr BP, with increased depositional rates during the Medieval Warm Period (MWP), the Little Ice Age (LIA) and during periods of societal upheaval (e.g. the Roman conquest of Dacia). The timing of minerogenic events appears to indicate a teleconnection between major shifts in North Atlantic Oscillation (NAO) and hydroclimate variability in southeastern Europe, with increased minerogenic deposition correlating to low NAO index values. By linking the minerogenic deposition to precipitation variability, we state that this link persists throughout the mid-to-late Holocene.

  13. Late mid-Holocene sea-level oscillation: A possible cause

    Science.gov (United States)

    Scott, D. B.; Collins, E. S.

    Sea level oscillated between 5500 and 3500 years ago at Murrells Inlet, South Carolina, Chezzetcook and Baie Verte, Nova Scotia and Montmagny, Quebec. The oscillation is well constrained by foraminiferal marsh zonations in three locations and by diatoms in the fourth one. The implications are: (1) there was a eustatic sea-level oscillation of about 2-10 m in the late mid-Holocene on the southeast coast of North America (South Carolina to Quebec) that is not predicted by present geophysical models of relative sea-level change; (2) this oscillation coincides with oceanographic cooling on the east coast of Canada that we associate with melting ice; and (3) this sea- level oscillation/climatic event coincides exactly with the end of pyramid building in Egypt which is suggested to have resulted from a climate change (i.e. drought, cooling). This sea-level/climatic change is a prime example of feedback where climatic warming in the mid-Holocene promoted ice melt in the Arctic which subsequently caused climatic cooling by opening up Arctic channels releasing cold water into the Inner Labrador Current that continued to intensify until 4000 years ago. This sea-level event may also be the best way of measuring when the final ice melted since most estimates of the ages of the last melting are based on end moraine dates in the Arctic which may not coincide with when the last ice actually melted out, since there is no way of dating the final ice positions.

  14. Origin and dynamics of the northern South American coastal savanna belt during the Holocene - the role of climate, sea-level, fire and humans

    Science.gov (United States)

    Alizadeh, Kamaleddin; Cohen, Marcelo; Behling, Hermann

    2015-08-01

    Presence of a coastal savanna belt expanding from British Guiana to northeastern Brazil cannot be explained by present-day climate. Using pollen and charcoal analyses on an 11.6 k old sediment core from a coastal depression in the savanna belt near the mouth of the Amazon River we investigated the paleoenvironmental history to shed light on this question. Results indicate that small areas of savanna accompanied by a forest type composed primarily by the genus Micropholis (Sapotaceae) that has no modern analog existed at the beginning of the Holocene. After 11,200 cal yr BP, savanna accompanied by few trees replaced the forest. In depressions swamp forest developed and by ca 10,000 cal yr BP replaced by Mauritia swamps. Between 8500 and 5600 cal yr BP gallery forest (composed mainly of Euphorbiaceae) and swamp forest succeeded the treeless savanna. The modern vegetation with alternating gallery forest and savanna developed after 5600 cal yr BP. We suggest that the early Holocene no-analog forest is a relict of previously more extensive forest under cooler and moister Lateglacial conditions. The early Holocene savanna expansion indicates a drier phase probably related to the shift of the Intertropical Convergence Zone (ITCZ) towards its northernmost position. The mid-Holocene forest expansion is probably a result of the combined influence of equatorwards shift of ITCZ joining the South Atlantic Convergence Zone (SACZ). The ecosystem variability during the last 5600 cal yr BP, formed perhaps under influence of intensified ENSO condition. High charcoal concentrations, especially during the early Holocene, indicate that natural and/or anthropogenic fires may have maintained the savanna. However, our results propose that climate change is the main driving factor for the formation of the coastal savanna in this region. Our results also show that the early Holocene sea level rise established mangroves near the study site until 7500 cal yr BP and promoted swamp formation in

  15. Southern westerly winds: a pacemaker of Holocene glacial fluctuations in Patagonia?

    Science.gov (United States)

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

    2017-12-01

    A well-resolved glacial chronology is crucial to compare sequences of glacial/climate events within and between regions, and thus, to unravel mechanisms underlying past climate changes. Important efforts have been made towards understanding the Holocene climate evolution of the Southern Andes; however, the timing, patterns and causes of glacial fluctuations during this period still remain elusive. Recent advances in terrestrial cosmogenic nuclide surface exposure dating, together with the establishment of a Patagonian 10Be production rate, have opened new possibilities for establishing high-resolution glacial chronologies at centennial/decadal scale. Here we present a 10Be surface exposure chronology of fluctuations of a small, climate-sensitive mountain glacier at Mt. Fitz Roy area (49.3°S), spanning from the last glacial termination to the present. Thirty new 10Be ages show glacial advances and moraine building events at 17.1±0.9 ka, 13.5±0.5 ka, 10.2±0.7 ka or 9.9±0.5 ka, 6.9±0.2 ka, 6.1±0.3 ka, 4.5±0.2 ka and 0.5±0.1 ka. Similar to the pattern observed in New Zealand, this sequence features progressively less extensive glacial advances during the late-glacial and early Holocene, followed by advances of roughly similar extent during the mid- to late-Holocene. We suggest that while the magnitude of Holocene glacial fluctuations in Patagonia is modulated by SH summer insolation ("modulator"), the specific timing of these glacial events is influenced by centennial-scale shifts of the Southern Westerly Winds ("pacemaker").

  16. Characterising Late-Holocene glacier variability in the southern tropical Andes

    Science.gov (United States)

    Bromley, G.; Winckler, G.; Hall, B. L.; Schaefer, J. M.

    2011-12-01

    Accurate resolution of both the timing and magnitude of Late-Holocene climate events, such as the Little Ice Age, is vital in order to test different hypotheses for the causes and propagation of such climate variability. However, in contrast to higher latitudes, well-dated records from the tropics are relatively rare and the overall climatic structure of the last millennium remains unresolved. Much of this uncertainty stems from difficulties associated with radiocarbon dating in these dry, often high-altitude environments, a situation that now is being addressed through the application and refinement of cosmogenic surface-exposure methods. We present detailed Late-Holocene moraine records, resolved with radiocarbon and surface-exposure dating, from sites across the Andes of southern Peru. Specifically, we describe glacial records from both the arid Western Cordillera, where glaciation is limited by moisture availability, and the humid Eastern Cordillera, where ablation is controlled primarily by air temperature. In both locations, the most recent advance is marked by two to three unweathered terminal moraines located several hundred metres beyond the modern ice margins. Our chronology indicates that, while the advance occurred broadly in step with the classic 'Little Ice Age', the maximum glacial extent in southern Peru was achieved relatively early on and that the 18th and 19th centuries were dominated by glacier retreat. In a broader temporal context, our data also confirm that, in contrast to northern temperate latitudes, the event in southern Peru was the most recent significant interruption in a progressive Holocene retreat. The consistency in glacier response between the different climate zones suggests (i) that this pattern of Late-Holocene climate variability was of at least regional extent and (ii) that temperature fluctuations were the primary driving mechanism.

  17. Discontinuous Late Pleistocene-Holocene pollen records from Auckland Domain, northern New Zealand

    International Nuclear Information System (INIS)

    Horrocks, M.; O'Loan, A.; Wallace, R.

    2009-01-01

    Two sediment sequences from Pukekawa crater, Auckland Domain, contain silty clay underlain by fibrous peat. The peat contains a pollen flora and wood indicating the presence of a warm-temperate, conifer-hardwood forest with Metrosideros, Agathis, Prumnopitystaxifolia, P. ferruginea, and especially Dacrydium. Radiocarbon dates indicate that the peat was deposited before the Last Glacial Maximum (LGM). Absence of tephras and small amounts of Fuscospora pollen indicate probable non-preservation of the LGM. The pollen flora of most of the clay contains Metrosideros, Ascarina, and ferns, indicating post-LGM warmer, wetter conditions. The two uppermost samples contain exotic pollen, indicating that they are post-European in origin. Excavation and levelling to form sports fields and parkland appears to have curtailed and mixed the Holocene record. (author). 24 refs., 4 figs., 1 tab.

  18. An ikaite record of late Holocene climate at the Antarctic Peninsula

    Science.gov (United States)

    Lu, Zunli; Rickaby, Rosalind E. M.; Kennedy, Hilary; Kennedy, Paul; Pancost, Richard D.; Shaw, Samuel; Lennie, Alistair; Wellner, Julia; Anderson, John B.

    2012-04-01

    Calcium carbonate can crystallize in a hydrated form as ikaite at low temperatures. The hydration water in ikaite grown in laboratory experiments records the δ18O of ambient water, a feature potentially useful for reconstructing δ18O of local seawater. We report the first downcore δ18O record of natural ikaite hydration waters and crystals collected from the Antarctic Peninsula (AP), a region sensitive to climate fluctuations. We are able to establish the zone of ikaite formation within shallow sediments, based on porewater chemical and isotopic data. Having constrained the depth of ikaite formation and δ18O of ikaite crystals and hydration waters, we are able to infer local changes in fjord δ18O versus time during the late Holocene. This ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula.

  19. Floodplain construction of the Rio Grande at El Paso, Texas, USA: response to Holocene climate change

    Science.gov (United States)

    Hall, Stephen A.; Peterson, John A.

    2013-04-01

    The Rio Grande is one of the larger rivers in North America, and the development of its floodplain is related to Holocene climate and climate change. The late Pleistocene through early Holocene channel is characterized by a meander or braided system with lateral cutting and backfilling, resulting in the valley-wide deposition of massive to cross-bedded, fine-to-medium textured sand. The late Pleistocene-early Holocene floodplain is also the sand source for the adjacent Bolson sand sheet. The sand sheet stopped accumulating new sand 5000 yrs ago, an event directly related to the shutting off of the sand supply caused by the deposition of overbank muds that covered and sealed the floodplain surface. During the middle Holocene, the river may have dried intermittently with the floodplain becoming deflated and local sand dunes forming on the floodplain. After 5000 yrs the climate was less arid and the river shifted to a regime of increased flooding and overbank deposition of silt and clay. By 2500 yrs, a late Holocene period of wet climate resulted in further overbank deposition and the formation of a cumulic Mollisol across the floodplain, the Socorro paleosol. The period of wet climate corresponds to the Audubon Neoglacial and active rock glaciers in the southern Rocky Mountains, speleothem growth in nearby caves, and other evidence for wet-cool conditions in the region. After 1000 yrs, the climate became drier, and the deposition and accumulation of overbank muds by the flooding Rio Grande came to a halt. Even though the river has flooded often in historic times, and presumably during late prehistoric times as well, there is little evidence for deposition of overbank sediments on the floodplain since A.D. 1000. Accordingly, the present-day surface of the Lower Valley is ten centuries old. Three channels occur on the US side of the Lower Valley floodplain, and during the past 2500 yrs stream flow has shifted from one to the other by the avulsion process of channel

  20. Soil micromorphogenesis and Early Holocene paleoclimate at the desert margin of Southern Arabia Micromorfoedafogénesis y paleoclima del Holoceno Inferior en el márgen desértico del sur de Arabia Micromorfogénese do solo e paleoclima inicial do Holoceno na margem deserta do Sul da Arábia

    Directory of Open Access Journals (Sweden)

    Peter Kühn

    2013-07-01

    Full Text Available The Ramlat as-Sab'atayn desert margin near Ma'rib, Yemen, displays well-preserved Early Holocene paleosols that are documented by micromorphological and pedological data. The buried soils, which are represented by Ahb horizons, indicate soil formation mostly before 8.3 cal ka BP. In contrast, sandy cover sediments without signs of pedogenesis appeared between 8.3 and 6.6 cal ka BP due to increasing aridity. Characteristic micromorphological features of the cover sediments are a single grain microstructure, crystallitic b-fabric, predominant occurrence of fresh sideromelane, and remnants of microlayers. Micromorphological pedogenic features in the buried Ah horizons include a subangular blocky microstructure, undifferentiated b-fabric as a result of enrichment of organic matter and decalcification, and the predominant occurrence of completely altered sideromelane. Most of these horizons appeared to be nearly completely decalcified so that in parts a stipple speckled b-fabric and neoformed clay coatings could be detected as a result of stronger weathering and soil formation. Pedogenic data provide important information about Holocene climate fluctuations, including the amount of precipitation, which was calculated on the basis of geochemical data from buried A, AB and B horizons. The buried paleosols represent moist climate conditions with precipitation ranging from 400 to 600 mm a-1.En los márgenes del desierto Ramlat as-Sab'atayn, cerca de Ma'rib (Yemen, se encuentran paleosuelos del Holoceno Inferior bien conservados que se documentan con datos micromorfológicos y edáficos. Los suelos enterrados, representados por horizontes Ahb, indican que se formaron mayoritariamente antes de hace 8,3 ka. Por el contrario, los sedimentos arenosos que los cubren sin rasgos de edafogénesis se depositaron posteriormente debido a una aridez creciente hasta hace 6,6 ka. Los rasgos micromorfológicos de los sedimentos arenosos están caracterizados por una

  1. South America Monsoon variability on millennial to multi-centennial time scale during the Holocene in central eastern Brazil

    Science.gov (United States)

    Strikis, N. M.; Cruz, F. W.; Cheng, H.; Karmann, I.; Vuille, M.; Edwards, R.; Wang, X.; Paula, M. S.; Novello, V. F.; Auler, A.

    2011-12-01

    A paleoprecipitation reconstruction based on high resolution and well-dated speleothem oxygen isotope records shows that the monsoon precipitation over central eastern Brazil underwent to strong variations on millennial to multi-centennial time-scales during the Holocene. This new record indicates that abrupt events of increase in monsoon precipitation are correlated to Bond events 6, 5 and 4 and also with 8.2 ky event during the early and mid-Holocene, with a mean amplitude of 1.5 % (PDB). The pacing and structure of such events are general consistent with variations in solar activity suggested by atmospheric Δ14 C records. In the late-Holocene, abrupt events of increase in monsoon precipitation peaking at 3.2, 2.7 and 2.3 ky B.P. are approximately synchronous with periods of low solar minima. In this regard, the most prominent event occurred during the late Holocene occurred at ~2.7 ky B.P. In addition, these positive anomalies of the precipitation recorded in central eastern Brazil are also in good agreement with variations in Titicaca lake level. The good correspondence between the speleothem and marine records imply that the variations in the north Atlantic sea surface temperature is the main forcing for abrupt millennial to multi-centennial precipitations variation within the region under influence of South American Monsoon.

  2. Patch-reef morphology as a proxy for Holocene sea-level variability, Northern Florida Keys, USA

    Science.gov (United States)

    Brock, J.C.; Palaseanu-Lovejoy, M.; Wright, C.W.; Nayegandhi, A.

    2008-01-01

    A portion of the northern Florida Keys reef tract was mapped with the NASA Experimental Advanced Airborne Research Lidar (EAARL) and the morphology of patch reefs was related to variations in Holocene sea level. Following creation of a lidar digital elevation model (DEM), geospatial analyses delineated morphologic attributes of 1,034 patch reefs (reef depth, basal area, height, volume, and topographic complexity). Morphometric analysis revealed two morphologically different populations of patch reefs associated with two distinct depth intervals above and below a water depth of 7.7 m. Compared to shallow reefs, the deep reefs were smaller in area and volume and showed no trend in topographic complexity relative to water depth. Shallow reefs were more variable in area and volume and became flatter and less topographically complex with decreasing water depth. The knoll-like morphology of deep reefs was interpreted as consistent with steady and relatively rapidly rising early Holocene sea level that restricted the lateral growth of reefs. The morphology of shallow 'pancake-shaped' reefs at the highest platform elevations was interpreted as consistent with fluctuating sea level during the late Holocene. Although the ultimate cause for the morphometric depth trends remains open to interpretation, these interpretations are compatible with a recent eustatic sea-level curve that hindcasts fluctuating late Holocene sea level. Thus it is suggested that the morphologic differences represent two stages of reef accretion that occurred during different sea-level conditions. ?? 2008 Springer-Verlag.

  3. 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.

  4. Land-Sea Correlation of Holocene Records in NW Iberian Peninsula

    Science.gov (United States)

    Gonzalez-Alvare, R.; Costas, S.; Bernardez, P.; Frances, G.; Alejo, I.

    2005-12-01

    Holocene climate fluctuations in the temperate region of the Northeast Atlantic have been established by comparing marine and terrestrial proxies. This work is based on suction-cores collected in the Cies Islands lagoon (NW Spain) and vibro-cores from the adjacent continental shelf. The lower Holocene marine record (9400-7000 yr BP) consists on sandy transgressive facies overlying fluvial Pleistocene deposits. During this time the continental shelf was dominated by high energy processes linked to the progressive and fast sea level rise. The rate of sea level rise sharply decelerated at 7000 yr BP and a high productive marine environment was fully established, as revealed by planktonic foraminifera assemblages and biogeochemical markers. In the terrestrial areas, peat deposits were formed beginning around 6000 yr BP in the deeper parts of the paleo-relief that was developed above the granitic basement. The peat was deposited in a fresh-water shallow coastal lake under warm and humid conditions that are brought about by prevailing SW winds. From 4800 yr BP, a progressive rainfall decrease provoked the lowering of the lake level and a weaker fluvial influence on the adjacent shelf. The prevailing eastern winds caused significantly drier conditions between 4000 and 3200 yr BP. During this period the coastal lake dried and the peat layer was covered by aeolian deposits. At the continental shelf a strong stratification of the water column induced a fall in the productivity. The end of this period is marked by the increase of storm regimes caused by a shift to prevailing SW winds. The last 3000 years are characterized by humid and warm conditions, and the enhancement of upwelling regime and terrestrial sediment supply. In Cies Islands, a sand barrier-lagoon complex was developed as a consequence of both the sea level rise and the inundation of the lower areas in the island.

  5. Aquatic ecosystem responses to Holocene climate change and biome development in boreal, central Asia

    Science.gov (United States)

    Mackay, Anson W.; Bezrukova, Elena V.; Leng, Melanie J.; Meaney, Miriam; Nunes, Ana; Piotrowska, Natalia; Self, Angela; Shchetnikov, Alexander; Shilland, Ewan; Tarasov, Pavel; Wang, Luo; White, Dustin

    2012-05-01

    Boreal ecosystems are highly vulnerable to climate change, and severe ecological impacts in the near future are virtually certain to occur. We undertook a multiproxy study on an alpine lake (ESM-1) at the modern tree-line in boreal, southern Siberia. Steppe and tundra biomes were extensive in eastern Sayan landscapes during the early Holocene. Boreal forest quickly expanded by 9.1 ka BP, and dominated the landscape until c 0.7 ka BP, when the greatest period of compositional turnover occurred. At this time, alpine meadow landscape expanded and Picea obovata colonised new habitats along river valleys and lake shorelines, because of prevailing cool, moist conditions. During the early Holocene, chironomid assemblages were dominated by cold stenotherms. Diatoms for much of the Holocene were dominated by alkaliphilous, fragilarioid taxa, up until 0.2 ka BP, when epiphytic species expanded, indicative of increased habitat availability. C/N mass ratios ranged between 9.5 and 13.5 (11.1-15.8 C/N atomic ratios), indicative of algal communities dominating organic matter contributions to bottom sediments with small, persistent contributions from vascular plants. However, δ13C values increased steadily from -34.9‰ during the early Holocene (9.3 ka BP) to -24.8‰ by 0.6 ka BP. This large shift in magnitude may be due to a number of factors, including increasing within-lake productivity, increasing disequilibrium between the isotopic balance of the lake with the atmosphere as the lake became isotopically ‘mature’, and declining soil respiration linked to small, but distinct retreat in forest biomes. The influence of climatic variables on landscape vegetation was assessed using redundancy analysis (RDA), a linear, direct ordination technique. Changes in July insolation at 60 °N significantly explained over one-fifth of the variation in species composition, while changes in estimates of northern hemisphere temperature and ice-rafted debris events in the North Atlantic

  6. Reconstructing warm inflation

    Science.gov (United States)

    Herrera, Ramón

    2018-03-01

    The reconstruction of a warm inflationary universe model from the scalar spectral index n_S(N) and the tensor to scalar ratio r( N) as a function of the number of e-folds N is studied. Under a general formalism we find the effective potential and the dissipative coefficient in terms of the cosmological parameters n_S and r considering the weak and strong dissipative stages under the slow roll approximation. As a specific example, we study the attractors for the index n_S given by nS-1∝ N^{-1} and for the ratio r∝ N^{-2}, in order to reconstruct the model of warm inflation. Here, expressions for the effective potential V(φ ) and the dissipation coefficient Γ (φ ) are obtained.

  7. Thinking About Global Warming

    International Nuclear Information System (INIS)

    Baron, J.

    2006-01-01

    Attitudes toward global warming are influenced by various heuristics, which may distort policy away from what is optimal for the well-being of people. These possible distortions, or biases, include: a focus on harms that we cause, as opposed to those that we can remedy more easily; a feeling that those who cause a problem should fix it; a desire to undo a problem rather than compensate for its presence; parochial concern with one's own group (nation); and neglect of risks that are not available. Although most of these biases tend to make us attend relatively too much to global warming, other biases, such as wishful thinking, cause us to attend too little. I discuss these possible effects and illustrate some of them with an experiment conducted on the World Wide Web

  8. Climate change - global warming

    International Nuclear Information System (INIS)

    Ciconkov, Risto

    2001-01-01

    An explanation about climate, weather, climate changes. What is a greenhouse effect, i.e. global warming and reasons which contribute to this effect. Greenhouse gases (GHG) and GWP (Global Warming Potential) as a factor for estimating their influence on the greenhouse effect. Indicators of the climate changes in the previous period by known international institutions, higher concentrations of global average temperature. Projecting of likely scenarios for the future climate changes and consequences of them on the environment and human activities: industry, energy, agriculture, water resources. The main points of the Kyoto Protocol and problems in its realization. The need of preparing a country strategy concerning the acts of the Kyoto Protocol, suggestions which could contribute in the preparation of the strategy. A special attention is pointed to the energy, its resources, the structure of energy consumption and the energy efficiency. (Author)

  9. Warm natural inflation

    International Nuclear Information System (INIS)

    Mishra, Hiranmaya; Mohanty, Subhendra; Nautiyal, Akhilesh

    2012-01-01

    In warm inflation models there is the requirement of generating large dissipative couplings of the inflaton with radiation, while at the same time, not de-stabilising the flatness of the inflaton potential due to radiative corrections. One way to achieve this without fine tuning unrelated couplings is by supersymmetry. In this Letter we show that if the inflaton and other light fields are pseudo-Nambu-Goldstone bosons then the radiative corrections to the potential are suppressed and the thermal corrections are small as long as the temperature is below the symmetry breaking scale. In such models it is possible to fulfil the contrary requirements of an inflaton potential which is stable under radiative corrections and the generation of a large dissipative coupling of the inflaton field with other light fields. We construct a warm inflation model which gives the observed CMB-anisotropy amplitude and spectral index where the symmetry breaking is at the GUT scale.

  10. Slowing global warming

    International Nuclear Information System (INIS)

    Flavin, C.

    1990-01-01

    According to the authors, global warming promises to be one of the central environmental issues of the nineties. After a decade of scientific concern but popular neglect, the eighties ended with a growing political as well as scientific consensus that the world can no longer afford to procrastinate about this issue. This paper reports on coping with global warming which, according to the author, will force societies to move rapidly into uncharted terrain, reversing powerful trends that have dominated the industrial age. This challenge cannot be met without a strong commitment on the part of both individual consumers and governments. In terms of the earth's carbon balance, the unprecedented policy changes that have now become urgent include a new commitment to greater energy efficiency and renewable energy sources, a carbon tax on fossil fuels, a reversal of deforestation in tropical countries, and the rapid elimination of CFCs

  11. Military Implications of Global Warming.

    Science.gov (United States)

    1999-05-20

    U.S. environmental issues also have important global implications. This paper analyzes current U.S. Policy as it pertains to global warming and climate...for military involvement to reduce global warming . Global warming and other environmental issues are important to the U.S. military. As the United

  12. EFFECTS OF GLOBAL WARMING

    OpenAIRE

    Dr. Basanti Jain

    2017-01-01

    The abnormal increase in the concentration of the greenhouse gases is resulting in higher temperatures. We call this effect is global warming. The average temperature around the world has increased about 1'c over 140 years, 75% of this has risen just over the past 30 years. The solar radiation, as it reaches the earth, produces "greenhouse effect" in the atmosphere. The thick atmospheric layers over the earth behaves as a glass surface, as it permits short wave radiations from coming in, but ...

  13. Holocene millennial to centennial scale carbonate cycles (leeward margin, Great Bahama Bank)

    Science.gov (United States)

    Roth, S.; Reijmer, J. J. G.

    2003-04-01

    The main research topic of this project is the evaluation of Holocene to Recent climatic variability and the impact on shallow-water sediment production of carbonate platforms. A 38m long sediment core (MD992201) was analyzed, obtained from 290m water depth on the leeward margin of Great Bahama Bank. Fourteen Accelerator Mass Spectrometry (AMS) dates determined a core bottom age of 7,230 years BP and permitted the construction of a precise time frame. With a sampling interval of 5cm, a decadal time resolution could be achieved. Sedimentation rates varied between 3 to 14m/kyr. Carbonate content ranges from 96 to almost 100wt%, most of which is aragonite (83-92wt%). High Magnesium Calcite (HMC) makes up the second major fraction with 2-9wt%, while Low Magnesium Calcite occurs with minor percentages (0.5-4wt%). Singular Spectrum Analysis (SSA) of the aragonitic carbonate phase showed two different trends and two primary oscillatory signals. Aragonite production on Great Bahama Bank started at 7,230yr BP when the Holocene sea-level rise flooded the shallow platform top. The first eigenvector captures this long-term trend extending over the entire Mid to Late Holocene succession displaying the Holocene sea-level fluctuations. The second trend indicates millennial scale variations, which can be attributed to a combination of geomagnetic shielding and solar parameters. The two quasi-periodic signals show wavelengths of 400-600 years and approx. 210 years. These oscillations are interpreted in terms of instabilities of the thermohaline circulation and solar parameters, respectively. The oscillatory aragonite signals and oxygen isotope derived temperatures (planktonic foraminifers) agree with northern hemisphere temperature changes (e.g. Medieval Warm Period and Little Ice Age) and the delta-14C record of tree rings (e.g. Oort to Dalton solar minima). This study shows that carbonate platform systems not only respond to sea-level variations but also are precise recorders of

  14. Southwest Greenland's Alpine Glacier History: Recent Glacier Change in the Context of the Holocene Geologic Record

    Science.gov (United States)

    Larocca, L. J.; Axford, Y.; Lasher, G. E.; Lee, C. W.

    2017-12-01

    Due to anthropogenic climate change, the Arctic region is currently undergoing major transformation, and is expected to continue warming much faster than the global average. To put recent and future changes into context, a longer-term understanding of this region's past response to natural climate variability is needed. Given their sensitivity to modest climate change, small alpine glaciers and ice caps on Greenland's coastal margin (beyond the Greenland Ice Sheet) represent ideal features to record climate variability through the Holocene. Here we investigate the Holocene history of a small ( 160 square km) ice cap and adjacent alpine glaciers, located in southwest Greenland approximately 50 km south of Nuuk. We employ measurements on sediment cores from a glacier-fed lake in combination with geospatial analysis of satellite images spanning the past several decades. Sedimentary indicators of sediment source and thus glacial activity, including organic matter abundance, inferred chlorophyll-a content, sediment major element abundances, grain size, and magnetic susceptibility are presented from cores collected from a distal glacier-fed lake (informally referred to here as Per's Lake) in the summer of 2015. These parameters reflect changes in the amount and character of inorganic detrital input into the lake, which may be linked to the size of the upstream glaciers and ice cap and allow us to reconstruct their status through the Holocene. Additionally, we present a complementary record of recent changes in Equilibrium Line Altitude (ELA) for the upstream alpine glaciers. Modern ELAs are inferred using the accumulation area ratio (AAR) method in ArcGIS via Landsat and Worldview-2 satellite imagery, along with elevation data obtained from digital elevation models (DEMs). Paleo-ELAs are inferred from the positions of moraines and trim lines marking the glaciers' most recent expanded state, which we attribute to the Little Ice Age (LIA). This approach will allow us to

  15. Warm natural inflation

    International Nuclear Information System (INIS)

    Mishra, Hiranmaya; Mohanty, Subhendra; Nautiyal, Akhilesh

    2013-01-01

    In warm inflation models there is the requirement of generating large dissipative couplings of the inflation with radiation, while at the same Âătime, not de-stabilising the flatness of the inflation potential due to radiative corrections. One way to achieve this without fine tuning unrelated couplings is by supersymmetry. In this talk we will discuss warm inflation with Pseudo-Nambu-Goldstone Bosons (PNGB). In this case inflation and other light fields are PNGB. So, the radiative corrections to the potential are suppressed and the thermal Âăcorrections are small as long as the temperature is below the symmetry breaking scale. In such models it is possible to fulfill the contrary requirements of an inflation potential which is stable under radiative corrections and the generation of a large dissipative coupling of the inflation field with other light fields. This warm inflation model with PNGB gives the observed CMB-anisotropy amplitude and spectral index having the symmetry breaking scale at the GUT scale. (author)

  16. Palaeovegetation dynamics of an ecotone forest-savanna in southern Brazilian Amazon during the late Pleistocene and Holocene based on carbon isotopes of soil organic matter

    International Nuclear Information System (INIS)

    Pessenda, L.C.R.; Gouveia, S.E.M.; Freitas, H.A. de; Bendassoli, J.A.; Gomes, B.M.; Aravena, R.; Ribeiro, A.S.; Boulet, R.

    2002-01-01

    to warm and dry conditions during the early to middle Holocene. (author)

  17. Glacial to Holocene fluctuations in hydrography and productivity along the southwestern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Rao, V.P.; Schneider, R.R.; Grootes, P.M.

    was highly reduced (S.W.A. Naqvi, personal communication). during 13–6 ka BP, when the intensity of summer Secondly, the dynamics of the upwelling system monsoon is expected to be high. We suggest that along the southwest coast of India oVers an past changes...: S0031-0182(00)00156-5 114 M. Thamban et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 165 (2001) 113–127 during the early to mid-Holocene period, following and Malmgren, 1996; Naqvi and Fairbanks, 1996; Overpeck et al., 1996; Zonneveld et...

  18. Colonizing Dynamic Alluvial and Coastal Landscapes in the Holocene

    Science.gov (United States)

    Kidder, T.; Liu, X.; Ervin, K.

    2017-12-01

    Throughout the Holocene humans have had to adapt to dynamic, rapidly changing alluvial and coastal landscapes. Understanding when people inhabit a given environment is an important starting point for exploring human adaptations, but increasingly we need to consider how, and especially why certain environments are used—or not used— so we can understand the consequences of these human actions. Using four case studies—one from the Yellow River Valley, China, one from coastal Jiangsu, China, one from the Mississippi River Valley (Mississippi, USA) and one from the Mississippi River delta (Louisiana , USA)—we develop a model of how humans at various stages of cultural development colonize new environments. Using archaeological data and ecological modeling we investigate the relationship between the timing of landscape colonization and the ecological richness and predictability of any given environment. As new landscapes emerge and mature humans adopt different strategies for exploiting these novel environments that begins with episodic use and increasingly shifts to stable, long-term habitation. The early phase of landscape colonization appears to be the most significant period because it shapes human environmental practices and sets each culture on a trajectory of socio-cultural development. Thus, human-environment interaction is a critical part of the emergence of cultural patterns that shapes the past, present, and even the future.

  19. Lake Baikal isotope records of Holocene Central Asian precipitation

    Science.gov (United States)

    Swann, George E. A.; Mackay, Anson W.; Vologina, Elena; Jones, Matthew D.; Panizzo, Virginia N.; Leng, Melanie J.; Sloane, Hilary J.; Snelling, Andrea M.; Sturm, Michael

    2018-06-01

    Climate models currently provide conflicting predictions of future climate change across Central Asia. With concern over the potential for a change in water availability to impact communities and ecosystems across the region, an understanding of historical trends in precipitation is required to aid model development and assess the vulnerability of the region to future changes in the hydroclimate. Here we present a record from Lake Baikal, located in the southern Siberian region of central Asia close to the Mongolian border, which demonstrates a relationship between the oxygen isotope composition of diatom silica (δ18Odiatom) and precipitation to the region over the 20th and 21st Century. From this, we suggest that annual rates of precipitation in recent times are at their lowest for the past 10,000 years and identify significant long-term variations in precipitation throughout the early to late Holocene interval. Based on comparisons to other regional records, these trends are suggested to reflect conditions across the wider Central Asian region around Lake Baikal and highlight the potential for further changes in precipitation with future climate change.

  20. On the Holocene evolution of the Ayeyawady megadelta

    Directory of Open Access Journals (Sweden)

    L. Giosan

    2018-06-01

    Full Text Available The Ayeyawady delta is the last Asian megadelta whose evolution has remained essentially unexplored so far. Unlike most other deltas across the world, the Ayeyawady has not yet been affected by dam construction, providing a unique view on largely natural deltaic processes benefiting from abundant sediment loads affected by tectonics and monsoon hydroclimate. To alleviate the information gap and provide a baseline for future work, here we provide a first model for the Holocene development of this megadelta based on drill core sediments collected in 2016 and 2017, dated with radiocarbon and optically stimulated luminescence, together with a reevaluation of published maps, charts and scientific literature. Altogether, these data indicate that Ayeyawady is a mud-dominated delta with tidal and wave influences. The sediment-rich Ayeyawady River built meander belt alluvial ridges with avulsive characters. A more advanced coast in the western half of the delta (i.e., the Pathein lobe was probably favored by the more western location of the early course of the river. Radiogenic isotopic fingerprinting of the sediment suggests that the Pathein lobe coast does not receive significant sediment from neighboring rivers. However, the eastern region of the delta (i.e., Yangon lobe is offset inland and extends east into the mudflats of the Sittaung estuary. Wave-built beach ridge construction during the late Holocene, similar to several other deltas across the Indian monsoon domain, suggests a common climatic control on monsoonal delta morphodynamics through variability in discharge, changes in wave climate or both. Correlation of the delta morphological and stratigraphic architecture information on land with the shelf bathymetry, as well as its tectonic, sedimentary and hydrodynamic characteristics, provides insight on the peculiar growth style of the Ayeyawady delta. The offset between the western Pathein lobe and the eastern deltaic coast appears to be driven

  1. Holocene landscape response to seasonality of storms in the Mojave Desert

    Science.gov (United States)

    Miller, D.M.; Schmidt, K.M.; Mahan, S.A.; McGeehin, J.P.; Owen, L.A.; Barron, J.A.; Lehmkuhl, F.; Lohrer, R.

    2010-01-01

    New optically stimulated and radiocarbon ages for alluvial fan and lake deposits in the Mojave Desert are presented, which greatly improves the temporal resolution of surface processes. The new Mojave Desert climate-landscape record is particularly detailed for the late Holocene. Evidence from ephemeral lake deposits and landforms indicates times of sustained stream flow during a wet interval of the latter part of the Medieval Warm Period at ca. AD 1290 and during the Little Ice Age at ca. AD 1650. The former lakes postdate megadroughts of the Medieval Warm Period, whereas the latter match the Maunder Minimum of the Little Ice Age. Periods of alluvial fan aggradation across the Mojave Desert are 14-9 cal ka and 6-3 cal ka. This timing largely correlates to times of increased sea-surface temperatures in the Gulf of California and enhanced warm-season monsoons. This correlation suggests that sustained alluvial fan aggradation may be driven by intense summer-season storms. These data suggest that the close proximity of the Mojave Desert to the Pacific Ocean and the Gulf of California promotes a partitioning of landscape-process responses to climate forcings that vary with seasonality of the dominant storms. Cool-season Pacific frontal storms cause river flow, ephemeral lakes, and fan incision, whereas periods of intense warm-season storms cause hillslope erosion and alluvial fan aggradation. The proposed landscape-process partitioning has important implications for hazard mitigation given that climate change may increase sea-surface temperatures in the Gulf of California, which indirectly could increase future alluvial fan aggradation.

  2. Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

    Directory of Open Access Journals (Sweden)

    B. Gaye

    2018-01-01

    Full Text Available At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific. We calculated composite sea surface temperature (SST and δ15N ratios in time slices of 1000 years of the last 25 kyr to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. Low δ15N values of 4–7 ‰ during the last glacial maximum (LGM and stadials (Younger Dryas and Heinrich events suggest that denitrification was inactive or weak during Pleistocene cold phases, while warm interstadials (ISs had elevated δ15N. Fast changes in upwelling intensities and OMZ ventilation from the Antarctic were responsible for these strong millennial-scale variations during the glacial. During the entire Holocene δ15N values  >  6 ‰ indicate a relatively stable OMZ with enhanced denitrification. The OMZ develops parallel to the strengthening of the SW monsoon and monsoonal upwelling after the LGM. Despite the relatively stable climatic conditions of the Holocene, the δ15N records show regionally different trends in the Arabian Sea. In the upwelling areas in the western part of the basin, δ15N values are lower during the mid-Holocene (4.2–8.2 ka BP compared to the late Holocene ( <  4.2 ka BP due to stronger ventilation of the OMZ during the period of the most intense southwest monsoonal upwelling. In contrast, δ15N values in the northern and eastern Arabian Sea rose during the last 8 kyr. The displacement of the core of the OMZ from the region of maximum productivity in the western Arabian Sea to its present position

  3. Timing and paleoclimatic significance of Holocene glacier fluctuations in the Cordillera Vilcabamba of southern Peru

    Science.gov (United States)

    Licciardi, J. M.; Taggart, J. R.; Schaefer, J. M.; Lund, D. C.

    2009-12-01

    Past fluctuations in climatically sensitive tropical glaciers provide important insight into regional paleoclimatic trends and forcings, but well-dated chronologies are scarce, particularly during the Holocene. We have established precise cosmogenic 10Be surface exposure ages of moraine sequences in the Cordillera Vilcabamba (13°20’S latitude), located in the outer tropics of southern Peru. Results indicate the dominance of two major glacial culminations and associated climatic shifts in the Vilcabamba, including an early Holocene glacial interval and a somewhat less extensive glaciation late in the ‘Little Ice Age’ (LIA) period. Lichenometric measurements on the youngest moraines support the 10Be ages, but uncertainties in the lichen ages arise from the lack of a local lichen growth curve. The Peruvian glacier chronologies differ from a recently-developed New Zealand record but are broadly correlative with well-dated glacial records in Europe, suggesting climate linkages between the tropics and the North Atlantic region. For the latest Holocene, our leading hypothesis is that climate forcings involving southward migration of the Atlantic Intertropical Convergence Zone can explain concurrent glaciations in tropical South America and northern high latitudes, but the influence of other climate drivers such as the El Niño/Southern Oscillation may have also played a role. Estimated differences between equilibrium-line altitudes (ELAs) on modern glaciers and those inferred for expanded latest Holocene glaciers reveal an ELA rise of 165-200 m since the LIA, suggesting that temperatures 1.1-1.3°C cooler than present could have sustained glaciers at their LIA maximum positions if temperature was the only control, and thus providing an upper bound on temperature depression during the LIA. However, further work is required to constrain the likely role of precipitation changes. These new Peruvian glacier chronologies and ELA reconstructions complement ice core and

  4. Holocene sea levels of Visakhapatnam shelf, east coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, K.M.; Rao, T.C.S.

    The Holocene sea level changes in the shelf areas off Visakhapatnam was studied from sediment distribution pattern and shallow seismic profiling. Morphological features on the shelf indicate a Late Pleistocene regression down to about -130 m below...

  5. Holocene sea-level change and the emergence of Neolithic seafaring in the Fuzhou Basin (Fujian, China)

    Science.gov (United States)

    Rolett, Barry V.; Zheng, Zhuo; Yue, Yuanfu

    2011-04-01

    Neolithic seafaring across the Taiwan Strait began approximately 5000 years ago and involved open-sea voyages over distances of at least 130 km. Rapid sea-level rise preceded the emergence of open-sea voyaging, but the possible role of environmental change as a stimulus for the development of seafaring is poorly understood. We investigate this problem by presenting a record of Holocene sea-level change and coastal transformation based on sediment cores obtained from the Fuzhou Basin on the coast of Fujian, China. The cores are located in direct proximity to archaeological sites of the Tanshishan Neolithic culture (5000-4300 cal BP), which is significant for its similarity to the earliest Neolithic cultures of Taiwan. Multiple lines of evidence record the early Holocene inundation of the Fuzhou Basin around 9000 cal BP, the mid-Holocene sea-level highstand, and the final Holocene marine transgression. This final transition is precisely documented, with AMS dates showing the change occurred close to 1900 cal BP. Our paleogeographic reconstruction shows that a large estuary filled the Fuzhou Basin during the mid-Holocene. Tanshishan and Zhuangbianshan, two of the major Fuzhou Basin Neolithic sites, are located today on hills nearly 80 km from the modern coastline. However, when the sites were settled around 5500-5000 cal BP, the marine transgression had transformed these hills into islands in the upper estuary. We suggest that the Neolithic era estuary setting, together with the lack of land suitable for rice paddy agriculture, inhibited intensive food production but favored a maritime orientation and the development of seafaring.

  6. Global warning, global warming

    International Nuclear Information System (INIS)

    Benarde, M.A.

    1992-01-01

    This book provides insights into the formidable array of issues which, in a warmer world, could impinge upon every facet of readers lives. It examines climatic change and long-term implications of global warming for the ecosystem. Topics include the ozone layer and how it works; the greenhouse effect; the dangers of imbalance and its effects on human and animal life; disruptions to the basic ecology of the planet; and the real scientific evidence for and against aberrant climatic shifts. The author also examines workable social and political programs and changes that must be instituted to avoid ecological disaster

  7. 500-year climate cycles stacking of recent centennial warming documented in an East Asian pollen record

    Science.gov (United States)

    Xu, Deke; Lu, Houyuan; Chu, Guoqiang; Wu, Naiqin; Shen, Caiming; Wang, Can; Mao, Limi

    2014-01-01

    Here we presented a high-resolution 5350-year pollen record from a maar annually laminated lake in East Asia (EA). Pollen record reflected the dynamics of vertical vegetation zones and temperature change. Spectral analysis on pollen percentages/concentrations of Pinus and Quercus, and a temperature proxy, revealed ~500-year quasi-periodic cold-warm fluctuations during the past 5350 years. This ~500-year cyclic climate change occurred in EA during the mid-late Holocene and even the last 150 years dominated by anthropogenic forcing. It was almost in phase with a ~500-year periodic change in solar activity and Greenland temperature change, suggesting that ~500-year small variations in solar output played a prominent role in the mid-late Holocene climate dynamics in EA, linked to high latitude climate system. Its last warm phase might terminate in the next several decades to enter another ~250-year cool phase, and thus this future centennial cyclic temperature minimum could partially slow down man-made global warming. PMID:24402348

  8. Holocene Tree Line and Climate Change on the Queen Charlotte Islands, Canada

    Science.gov (United States)

    Pellatt, Marlow G.; Mathewes, Rolf W.

    1997-07-01

    Palynological study of two subalpine ponds on the Queen Charlotte Islands reveals changes in tree line and climate during the Holocene. The findings agree with previous reconstructions, from nearby Louise Pond on the Queen Charlotte Islands, that suggest a warmer-than-present climate and higher-than-present tree lines in the early Holocene (ca. 9600-6600 14C yr B.P.). Basal ages at SC1 Pond and Shangri-La Bog indicate that the basins did not hold permanent water before 7200 14C yr B.P., consistent with a warmer and drier early Holocene previously inferred from Louise Pond. Pollen and plant macrofossils indicate the initial establishment of subalpine conditions by 6090 ± 90 14C yr B.P., similar to the 5790 ± 130 14C yr B.P. age for cooling inferred from Louise Pond. Conditions similar to present were established at SC1 Pond by 3460 ± 100 14C yr B.P., confirming the previous estimate of 3400 14C yr B.P. at Louise Pond. This 3400 14C yr B.P. vegetation shift on the Queen Charlotte Islands corresponds with the beginning of the Tiedemann glacial advance in the south-coastal mountains of British Columbia (ca. 3300 14C yr B.P.), the Peyto and Robson glacial advances between 3300 and 2800 14C yr B.P. in the Rocky Mountains, and climatic cooling inferred from palynological studies throughout southern British Columbia, northern Washington, and southeast Alaska. These findings confirm that changes in regional climate influenced changes in vegetation in coastal British Columbia.

  9. Holocene vegetation history from fossil rodent middens near Arequipa, Peru

    Science.gov (United States)

    Holmgren, C.A.; Betancourt, J.L.; Rylander, K.A.; Roque, J.; Tovar, O.; Zeballos, H.; Linares, E.; Quade, Jay

    2001-01-01

    Rodent (Abrocoma, Lagidium, Phyllotis) middens collected from 2350 to 2750 m elevation near Arequipa, Peru (16??S), provide an ???9600-yr vegetation history of the northern Atacama Desert, based on identification of >50 species of plant macrofossils. These midden floras show considerable stability throughout the Holocene, with slightly more mesophytic plant assemblages in the middle Holocene. Unlike the southwestern United States, rodent middens of mid-Holocene age are common. In the Arequipa area, the midden record does not reflect any effects of a mid-Holocene mega drought proposed from the extreme lowstand (100 m below modern levels, >6000 to 3500 yr B.P.) of Lake Titicaca, only 200 km east of Arequipa. This is perhaps not surprising, given other evidence for wetter summers on the Pacific slope of the Andes during the middle Holocene as well as the poor correlation of summer rainfall among modern weather stations in the central AndesAtacama Desert. The apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the Holocene to changes in El Nin??o Southern Oscillation modes. ?? 2001 University of Washington.

  10. Last Glacial Maximum to Holocene climate evolution controlled by sea-level change, Leeuwin Current, and Australian Monsoon in the Northwestern Australia

    Science.gov (United States)

    Ishiwa, T.; Yokoyama, Y.; McHugh, C.; Reuning, L.; Gallagher, S. J.

    2017-12-01

    The transition from cold to warm conditions during the last deglaciation influenced climate variability in the Indian Ocean and Pacific as a result of submerge of continental shelf and variations in the Indonesian Throughflow and Australian Monsoon. The shallow continental shelf (Program Expedition 356 Indonesian Throughflow drilled in the northwestern Australian shallow continental shelf and recovered an interval from the Last Glacial Maximum to Holocene in Site U1461. Radiocarbon dating on macrofossils, foraminifera, and bulk organic matter provided a precise age-depth model, leading to high-resolved paleoclimate reconstruction. X-ray elemental analysis results are interpreted as an indicator of sedimentary environmental changes. The upper 20-m part of Site U1461 apparently records the climate transition from the LGM to Holocene in the northwestern Australia, which could be associated with sea-level change, Leeuwin Current activity, and the Australian Monsoon.

  11. Global Warming: A Reduced Threat?.

    Science.gov (United States)

    Michaels, Patrick J.; Stooksbury, David E.

    1992-10-01

    One popular and apocalyptic vision of the world influenced by increasing concentrations of infrared-absorbing trace gases is that of ecological disaster brought about by rapidly rising temperatures, sea level, and evaporation rates. This vision developed from a suite of climate models that have since considerably changed in both their dynamics and their estimates of prospective warming. Observed temperatures indicate that much more warming should already have taken place than predicted by earlier models in the Northern Hemisphere, and that night, rather than day, readings in that hemisphere show a relative warming. A high-latitude polar-night warming or a general night warming could be either benign or beneficial. A large number of plant species show both increased growth and greater water-use efficiency under enhanced carbon dioxide.An extensive body of evidence now indicates that anthropo-generated sulfate emissions are mitigating some of the warming, and that increased cloudiness as a result of these emissions will further enhance night, rather than day, warming. The sulfate emissions, though, are not sufficient to explain all of the night warming. However, the sensitivity of climate to anthropogenerated aerosols, and the general lack of previously predicted warming, could drastically alter the debate on global warming in favor of less expensive policies.

  12. Climatic and environmental conditions favoring the crossing of the Carpathians by early Neolithic populations

    Science.gov (United States)

    Perşoiu, Ioana; Perşoiu, Aurel

    2015-04-01

    The study of the origin and spread of Neolithic has been the subject of heated debate since the early studies of Childe (1942). To what extent the dispersal process was influenced by environmental factors is still debated, one of the issues being whether climatic conditions influencing agricultural practices, could have influenced the dispersal route, "blocking" some of the Neolithic societies in front of ecological barriers. Data from Neolithic sites in SE Europe shows that a continuous stream of people and cultures flowed through the Danube's Iron Gates towards Central Europe, while in the eastern part of Europe this process was delayed, people and cultures "moving" around the Carpathians and crossing them with a delay of ca. 1000 years. One of the possible avenues for this crossing is the floodplain of Someşu Mic River (Transylvanian depression), home to the oldest (~8500 cal. BP) Neolithic settlement in Romania. In this paper, we review the climatic and environmental changes that affected the region at the time of Neolithic dispersal. Pollen and stable isotopes in cave ice indicate an early Holocene rapid warming during summer months, peaking around 7 ka cal. BP; and a delayed warming for autumn and winter months, peaking at 5 ka cal. BP, both followed by a continuous cooling trend towards the present. Someşu Mic River developed and maintained a narrow sinuous channel during the Holocene, with local development of meanders and anabranches, in response to both climatic and geologic controlling factors. Archaeological finds in the floodplain and the lower terraces suggest that human societies in the region responded in sensitive manner to these climatic and environmental changes. During warm and dry periods, with low fluvial activity, the number of settlements increased in the floodplain's perimeter, while during the short cold and humid periods, the number of settlements rapidly increased on the lower terraces and on the valley slopes, disappearing from the

  13. Holocene moisture variations over the arid central Asia revealed by a comprehensive sand-dune record from the central Tian Shan, NW China

    Science.gov (United States)

    Long, Hao; Shen, Ji; Chen, Jianhui; Tsukamoto, Sumiko; Yang, Linhai; Cheng, Hongyi; Frechen, Manfred

    2017-10-01

    Arid central Asia (ACA) is one of the largest arid (desert) areas in the world, and its climate is dominated by the westerlies. In this study, we examined sand dune evolution from the Bayanbulak Basin in the Tian Shan (Xinjiang, NW China), aiming to infer the Holocene moisture history of the ACA. Combined with stratigraphic observation and environmental proxies analysis (grain size, magnetic susceptibility and total organic content), large numbers of luminescence ages from multiple sites (eight sections, 79 samples) were applied to reconstruct the evolution of the sand dune accumulation in the study basin. The overall results imply very dry conditions characterized by sand dune accumulation at ∼12-6.5 ka, a wet interval between ∼6.5 and 0.8 ka when soil formation occurred, and decreased moisture during the last 0.8 ka. This moisture variation pattern is generally consistent with that inferred from many lacustrine records in the core zone of ACA, suggesting a widespread dry period in the early-to-middle Holocene and relatively wet middle-to-late Holocene. Thus, the moisture history derived from the current sand dune system contrasts with that in Asian monsoon areas, which are characterized by a strong monsoon (high precipitation) in the early and mid-Holocene and a weak monsoon (low precipitation and dry climate) during the late Holocene. Our results strongly suggest that the winter solar insolation and the external boundary conditions such as atmospheric CO2 concentration, ice sheets, and meltwater fluxes, have been major influential factors triggering the Holocene moisture evolution in the core zone of ACA.

  14. Antarctica: Cooling or Warming?

    Science.gov (United States)

    Bunde, Armin; Ludescher, Josef; Franzke, Christian

    2013-04-01

    We consider the 14 longest instrumental monthly mean temperature records from the Antarctica and analyse their correlation properties by wavelet and detrended fluctuation analysis. We show that the stations in the western and the eastern part of the Antarctica show significant long-term memory governed by Hurst exponents close to 0.8 and 0.65, respectively. In contrast, the temperature records at the inner part of the continent (South Pole and Vostok), resemble white noise. We use linear regression to estimate the respective temperature differences in the records per decade (i) for the annual data, (ii) for the summer and (iii) for the winter season. Using a recent approach by Lennartz and Bunde [1] we estimate the respective probabilities that these temperature differences can be exceeded naturally without inferring an external (anthropogenic) trend. We find that the warming in the western part of the continent and the cooling at the South Pole is due to a gradually changes in the cold extremes. For the winter months, both cooling and warming are well outside the 95 percent confidence interval, pointing to an anthropogenic origin. In the eastern Antarctica, the temperature increases and decreases are modest and well within the 95 percent confidence interval. [1] S. Lennartz and A. Bunde, Phys. Rev. E 84, 021129 (2011)

  15. Carbon sequestration in Southeast Asian tropical peatlands over the Holocene period: large-scale hydrological controls

    Science.gov (United States)

    Dommain, R.; Couwenberg, J.; Cobb, A.; Gandois, L.; Kai, F.; Su'ut, N.; Abu Salim, K.; Harvey, C. F.; Glaser, P. H.; Joosten, H.

    2012-12-01

    Tropical peatlands are recognized as a significant sink of carbon dioxide and an important source of methane. Low latitude peatlands contain an estimated pool of 90 Pg C, of which ca. 70 Pg C is stored in Southeast Asian peatlands. However, the Holocene development of this carbon reservoir is poorly established. Here we provide a synthesis of carbon uptake rates by tropical peatlands in Southeast Asia across millennial timescales for the past 11,000 years. Our reconstruction of the carbon accumulation history for Borneo, Sumatra and Peninsular Malaysia is based on a synthesis of radiocarbon dated peat profiles, modeling of peatland extent, and a new carbon accumulation record from Brunei (NW-Borneo). During the early Holocene the first peatlands formed in southern Borneo under the influence of a strong monsoon and rapid rise in sea-level. The carbon accumulation rate (CAR) in these peatlands was on average 60 g C m-2 yr-1 at this time. Peatlands started to spread across the coastal lowlands of Borneo, Sumatra and Peninsular Malaysia after 8000 cal BP only when the rate of rising sea-level decreased. The major phase of coastal peatland initiation lasted from 7000 to 4000 cal BP. This period was marked by a Holocene precipitation maximum, suppressed El Niño activity, and the Holocene maximum in sea-level on the Sunda Shelf. The mean CAR of coastal peatlands at this time was 80 g C m-2 yr-1, with a Holocene peak of ~100 g C m-2 yr-1 from 4900 to 4500 cal BP. Significantly, atmospheric CO2 concentrations measured in the Taylor Dome Antarctic ice core indicate a plateau during this period of otherwise rising CO2 concentrations. During the Late Holocene CAR declined both in coastal peatlands (ca. 70 g C m-2 yr-1) and in southern Borneo (ca. 20 g C m-2 yr-1) in response to falling sea-levels and increased El Niño frequency and intensity. In fact, several peatlands in southern Borneo have stopped accumulating peat-carbon under higher El Niño activity. These results

  16. Magnetic fusion development for global warming suppression

    International Nuclear Information System (INIS)

    Li Jiangang; Zhang Jie; Duan Xuru

    2010-01-01

    Energy shortage and environmental pollution are two critical issues for human beings in the 21st century. There is an urgent need for new sustainable energy to meet the fast growing demand for clean energy. Fusion is one of the few options which may be able to satisfy the requirement for large scale sustainable energy generation and global warming suppression and therefore must be developed as quickly as possible. Fusion research has been carried out for the past 50 years. It is too long to wait for another 50 years to generate electricity by fusion. A much more aggressive approach should be taken with international collaboration towards the early use of fusion energy to meet the urgent needs for energy and global warming suppression.

  17. The sensitivity of the Arctic sea ice to orbitally induced insolation changes: a study of the mid-Holocene Paleoclimate Modelling Intercomparison Project 2 and 3 simulations

    Directory of Open Access Journals (Sweden)

    M. Berger

    2013-04-01

    for surface waves. This is in broad agreement with recent analyses of sea-ice proxies, indicating that beach-ridges formed on the north-eastern coast of Greenland during the early- to mid-Holocene.

  18. Multiproxy records of Holocene climate and glacier variability from sediment cores in the Cordillera Vilcabamba of southern Peru

    Science.gov (United States)

    Schweinsberg, A. D.; Licciardi, J. M.; Rodbell, D. T.; Stansell, N.; Tapia, P. M.

    2012-12-01

    Sediments contained in glacier-fed lakes and bogs provide continuous high-resolution records of glacial activity, and preserve multiproxy evidence of Holocene climate change. Tropical glacier fluctuations offer critical insight on regional paleoclimatic trends and controls, however, continuous sediment records of past tropical climates are limited. Recent cosmogenic 10Be surface exposure ages of moraine sequences in the Cordillera Vilcabamba of southern Peru (13°20'S latitude) reveal a glacial culmination during the early Holocene and a less extensive glaciation coincident with the Little Ice Age of the Northern Hemisphere. Here we supplement the existing 10Be moraine chronology with the first continuous records of multiproxy climate data in this mountain range from sediment cores recovered from bogs in direct stratigraphic contact with 10Be-dated moraines. Radiocarbon-dated sedimentological changes in a 2-meter long bog core reveal that the Holocene is characterized by alternating inorganic and organic-rich laminae, suggesting high-frequency climatic variability. Carbon measurements, bulk density, and bulk sedimentation rates are used to derive a record of clastic sediment flux that serves as a proxy indicator of former glacier activity. Preliminary analyses of the bog core reveal approximately 70 diatom taxa that indicate both rheophilic and lentic environments. Initial results show a general decrease in magnetic susceptibility and clastic flux throughout the early to mid-Holocene, which suggests an interval of deglaciation. An episode of high clastic flux from 3.8 to 2.0 ka may reflect a late Holocene glacial readvance. Volcanic glass fragments and an anomalous peak in magnetic susceptibility may correspond to the historical 1600 AD eruption of Huaynaputina. Ten new bog and lake sediment cores were collected during the 2012 field expedition and analytical measurements are underway. Ongoing efforts are focused on analyzing diatom assemblage data, developing

  19. Regional, holocene records of the human dimension of global change: sea-level and land-use change in prehistoric Mexico

    Science.gov (United States)

    Sluyter, Andrew

    1997-02-01

    Regional, Holocene records hold particular relevance for understanding the reciprocal nature of global environmental change and one of its major human dimensions: "sustainable agriculture", i.e., food production strategies which entail fewer causes of and are less susceptible to environmental change. In an epoch of accelerating anthropogenic transformation, those records reveal the protracted regional causes and consequences of change (often agricultural) in the global system as well as informing models of prehistoric, intensive agriculture which, because of long tenures and high productivities, suggest strategies for sustainable agricultural in the present. This study employs physiographic analysis and the palynological, geochemical record from cores of basin fill to understand the reciprocal relation between environmental and land-use change in the Gulf of Mexico tropical lowland, focusing on a coastal basin sensitive to sea-level change and containing vestiges of prehistoric settlement and wetland agriculture. Fossil pollen reveals that the debut of maize cultivation in the Laguna Catarina watershed dates to ca. 4100 BC, predating the earliest evidence for that cultivar anywhere else in the lowlands of Middle America. Such an early date for a cultivar so central to Neotropical agroecology and environmental change, suggests the urgency of further research in the study region. Moreover, the longest period of continuous agriculture in the basin lasted nearly three millennia (ca. 2400 BC-AD 550) despite eustatic sea-level rise. Geochemical fluxes reveal the reciprocity between land-use and environmental change: slope destabilization, basin aggradation, and eutrophication. The consequent theoretical implications pertain to both applied and basic research. Redeploying ancient agroecologies in dynamic environments necessitates reconstructing the changing operational contexts of putative high productivity and sustainability. Adjusting land use in the face of global

  20. Holocene history and environmental reconstruction of a Hercynian mire and surrounding mountain landscape based on multiple proxies

    Science.gov (United States)

    Dudová, Lydie; Hájková, Petra; Opravilová, Věra; Hájek, Michal

    2014-07-01

    We discovered the first peat section covering the entire Holocene in the Hrubý Jeseník Mountains, representing an island of unique alpine vegetation whose history may display transitional features between the Hercynian and Carpathian regions. We analysed pollen, plant macrofossils (more abundant in bottom layers), testate amoebae (more abundant in upper layers), peat stratigraphy and chemistry. We found that the landscape development indeed differed from other Hercynian mountains located westward. This is represented by Pinus cembra and Larix during the Pleistocene/Holocene transition, the early expansion of spruce around 10,450 cal yr BP, and survival of Larix during the climatic optimum. The early Holocene climatic fluctuations are traced in our profile by species compositions of both the mire and surrounding forests. The mire started to develop as a calcium-rich percolation fen with some species recently considered to be postglacial relicts (Meesia triquetra, Betula nana), shifted into ombrotrophy around 7450 cal yr BP by autogenic succession and changed into a pauperised, nutrient-enriched spruce woodland due to modern forestry activities. We therefore concluded that its recent vegetation is not a product of natural processes. From a methodological viewpoint we demonstrated how using multiple biotic proxies and extensive training sets in transfer functions may overcome taphonomic problems.

  1. Stalagmite-derived Last Glacial Maximum - Mid Holocene Indian Monsoon Record from Krem Mawmluh, Meghalaya, NE India

    Science.gov (United States)

    Lone, M. A.; Routh, J.; Kumar, V.; Mangini, A.; Rangarajan, R.; Ghosh, P.; Munnuru Singamshetty, K.; Shen, C. C.; Ahmad, S. M.; Mii, H. S.

    2016-12-01

    Seasonal reversals in monsoon winds strongly influence rainfall patterns on the Indian sub-continent regulating the socio-economy of south Asian region. High-resolution centennial-millennial scale records of climate change from the core zone of the monsoon impacted region are nonetheless very few. Here, we report Indian summer monsoon (ISM) variability record from an 87-cm long stalagmite (KM-1) from Krem Mawmluh in the Khasi Hills, Meghalaya. The absolute dated stalagmite record ranges from 22.7 (LGM) to 6.7 ka (Mid Holocene), revealing last glacial-interglacial paleoclimatic changes over the Indian sub-continent. A sharp change in δ18O ( 5‰) and growth rate post Younger Dryas (YD) is marked by continued rapid speleogenesis in KM-1 and coincides with monsoon intensification during the early Holocene. Prominent multi-centennial to millennial scale dry phases in ISM activity are observed from LGM to YD. During early to mid-Holocene, the record shows significant multi-decadal to centennial scale changes. The high frequency δ18O variations referring to abrupt changes in ISM activity are believed to be driven by changes in temperature and shifting of Inter-Tropical Convergence Zone.

  2. Daytime warming has stronger negative effects on soil nematodes than night-time warming

    OpenAIRE

    Yan, Xiumin; Wang, Kehong; Song, Lihong; Wang, Xuefeng; Wu, Donghui

    2017-01-01

    Warming of the climate system is unequivocal, that is, stronger warming during night-time than during daytime. Here we focus on how soil nematodes respond to the current asymmetric warming. A field infrared heating experiment was performed in the western of the Songnen Plain, Northeast China. Three warming modes, i.e. daytime warming, night-time warming and diurnal warming, were taken to perform the asymmetric warming condition. Our results showed that the daytime and diurnal warming treatmen...

  3. Discontinuity surfaces and event stratigraphy of Okha Shell Limestone Member: Implications for Holocene sea level changes, western India

    Science.gov (United States)

    Bhonde, Uday; Desai, Bhawanisingh G.

    2011-08-01

    The Okha Shell Limestone Member of Chaya Formation is the coarse grained, shell rich deposit commonly recognized as the beach rocks. It has been age bracketed between Late Pleistocene and Holocene. Late Quaternary sea level changes have been studied with beach rocks along the Saurashtra coastal region. The present study has been carried out in the Okhamandal area of the Saurashtra peninsula especially on the Okha Shell Limestone Member as exposed at various locations along the coast from north to south. Temporal and spatial correlations of the observations have revealed three events in the Okha Shell Limestone Member of Chaya Formation that are correlated laterally. The events show depositional breaks represented by discontinuity surfaces, the taphofacies varieties and ichnological variations. The present study in the context of available geochrnological data of the region suggests a prominent depositional break representing low sea level stand (regression) during an Early Holocene during the deposition of Okha Shell Limestone Member.

  4. Quantifying the effects of land use and climate on Holocene vegetation in Europe

    Science.gov (United States)

    Marquer, Laurent; Gaillard, Marie-José; Sugita, Shinya; Poska, Anneli; Trondman, Anna-Kari; Mazier, Florence; Nielsen, Anne Birgitte; Fyfe, Ralph M.; Jönsson, Anna Maria; Smith, Benjamin; Kaplan, Jed O.; Alenius, Teija; Birks, H. John B.; Bjune, Anne E.; Christiansen, Jörg; Dodson, John; Edwards, Kevin J.; Giesecke, Thomas; Herzschuh, Ulrike; Kangur, Mihkel; Koff, Tiiu; Latałowa, Małgorzata; Lechterbeck, Jutta; Olofsson, Jörgen; Seppä, Heikki

    2017-09-01

    Early agriculture can be detected in palaeovegetation records, but quantification of the relative importance of climate and land use in influencing regional vegetation composition since the onset of agriculture is a topic that is rarely addressed. We present a novel approach that combines pollen-based REVEALS estimates of plant cover with climate, anthropogenic land-cover and dynamic vegetation modelling results. This is used to quantify the relative impacts of land use and climate on Holocene vegetation at a sub-continental scale, i.e. northern and western Europe north of the Alps. We use redundancy analysis and variation partitioning to quantify the percentage of variation in vegetation composition explained by the climate and land-use variables, and Monte Carlo permutation tests to assess the statistical significance of each variable. We further use a similarity index to combine pollen-based REVEALS estimates with climate-driven dynamic vegetation modelling results. The overall results indicate that climate is the major driver of vegetation when the Holocene is considered as a whole and at the sub-continental scale, although land use is important regionally. Four critical phases of land-use effects on vegetation are identified. The first phase (from 7000 to 6500 BP) corresponds to the early impacts on vegetation of farming and Neolithic forest clearance and to the dominance of climate as a driver of vegetation change. During the second phase (from 4500 to 4000 BP), land use becomes a major control of vegetation. Climate is still the principal driver, although its influence decreases gradually. The third phase (from 2000 to 1500 BP) is characterised by the continued role of climate on vegetation as a consequence of late-Holocene climate shifts and specific climate events that influence vegetation as well as land use. The last phase (from 500 to 350 BP) shows an acceleration of vegetation changes, in particular during the last century, caused by new farming

  5. Global Warming on Triton

    Science.gov (United States)

    Elliot, J. L.; Hammel, H. B.; Wasserman, L. H.; Franz, O. G.; McDonald, S. W.; Person, M. J.; Olkin, C. B.; Dunham, E. J.; Spencer, J. R.; Stansberry, J. A.; hide

    1998-01-01

    Triton, Neptune's largest moon, has been predicted to undergo significant seasonal changes that would reveal themselves as changes in its mean frost temperature. But whether this temperature should at the present time be increasing, decreasing or constant depends on a number of parameters (such as the thermal properties of the surface, and frost migration patterns) that are unknown. Here we report observations of a recent stellar occultation by Triton which, when combined with earlier results, show that Triton has undergone a period of global warming since 1989. Our most conservative estimates of the rate of temperature and surface-pressure increase during this period imply that the atmosphere is doubling in bulk every 10 years, significantly faster than predicted by any published frost model for Triton. Our result suggests that permanent polar caps on Triton play a c dominant role in regulating seasonal atmospheric changes. Similar processes should also be active on Pluto.

  6. Structure of Warm Nuclei

    International Nuclear Information System (INIS)

    Aaberg, S.; Uhrenholt, H.

    2009-01-01

    We study the structure of nuclei in the energy region between the ground state and the neutron separation energy, here called warm nuclei. The onset of chaos in the nucleus as excitation energy is increased is briefly reviewed. Chaos implies fluctuations of energies and wave functions qualitatively the same for all chaotic nuclei. On the other hand, large structure effects are seen, e.g. in the level-density function at same excitation energies. A microscopic model for the level density is reviewed and we discuss effects on structure of the total level-density function, parity enhancement, and the spin distribution function. Comparisons to data are performed at the neutron separation energy for all observed nuclei, and structure of the level-density function for a few measured cases. The role of structure effects in the level-density function for fission dynamics is exemplified.

  7. Interacting warm dark matter

    International Nuclear Information System (INIS)

    Cruz, Norman; Palma, Guillermo; Zambrano, David; Avelino, Arturo

    2013-01-01

    We explore a cosmological model composed by a dark matter fluid interacting with a dark energy fluid. The interaction term has the non-linear λρ m α ρ e β form, where ρ m and ρ e are the energy densities of the dark matter and dark energy, respectively. The parameters α and β are in principle not constrained to take any particular values, and were estimated from observations. We perform an analytical study of the evolution equations, finding the fixed points and their stability properties in order to characterize suitable physical regions in the phase space of the dark matter and dark energy densities. The constants (λ,α,β) as well as w m and w e of the EoS of dark matter and dark energy respectively, were estimated using the cosmological observations of the type Ia supernovae and the Hubble expansion rate H(z) data sets. We find that the best estimated values for the free parameters of the model correspond to a warm dark matter interacting with a phantom dark energy component, with a well goodness-of-fit to data. However, using the Bayesian Information Criterion (BIC) we find that this model is overcame by a warm dark matter – phantom dark energy model without interaction, as well as by the ΛCDM model. We find also a large dispersion on the best estimated values of the (λ,α,β) parameters, so even if we are not able to set strong constraints on their values, given the goodness-of-fit to data of the model, we find that a large variety of theirs values are well compatible with the observational data used

  8. Decadal evolution of the surface energy budget during the fast warming and global warming hiatus periods in the ERA-interim

    Science.gov (United States)

    Hu, Xiaoming; Sejas, Sergio A.; Cai, Ming; Taylor, Patrick C.; Deng, Yi; Yang, Song

    2018-05-01

    The global-mean surface temperature has experienced a rapid warming from the 1980s to early-2000s but a muted warming since, referred to as the global warming hiatus in the literature. Decadal changes in deep ocean heat uptake are thought to primarily account for the rapid warming and subsequent slowdown. Here, we examine the role of ocean heat uptake in establishing the fast warming and warming hiatus periods in the ERA-Interim through a decomposition of the global-mean surface energy budget. We find the increase of carbon dioxide alone yields a nearly steady increase of the downward longwave radiation at the surface from the 1980s to the present, but neither accounts for the fast warming nor warming hiatus periods. During the global warming hiatus period, the transfer of latent heat energy from the ocean to atmosphere increases and the total downward radiative energy flux to the surface decreases due to a reduction of solar absorption caused primarily by an increase of clouds. The reduction of radiative energy into the ocean and the surface latent heat flux increase cause the ocean heat uptake to decrease and thus contribute to the slowdown of the global-mean surface warming. Our analysis also finds that in addition to a reduction of deep ocean heat uptake, the fast warming period is also driven by enhanced solar absorption due predominantly to a decrease of clouds and by enhanced longwave absorption mainly attributed to the air temperature feedback.

  9. Local warming: daily temperature change influences belief in global warming.

    Science.gov (United States)

    Li, Ye; Johnson, Eric J; Zaval, Lisa

    2011-04-01

    Although people are quite aware of global warming, their beliefs about it may be malleable; specifically, their beliefs may be constructed in response to questions about global warming. Beliefs may reflect irrelevant but salient information, such as the current day's temperature. This replacement of a more complex, less easily accessed judgment with a simple, more accessible one is known as attribute substitution. In three studies, we asked residents of the United States and Australia to report their opinions about global warming and whether the temperature on the day of the study was warmer or cooler than usual. Respondents who thought that day was warmer than usual believed more in and had greater concern about global warming than did respondents who thought that day was colder than usual. They also donated more money to a global-warming charity if they thought that day seemed warmer than usual. We used instrumental variable regression to rule out some alternative explanations.

  10. Role of ISM circulations in Western Kachchh, India during Mid-Late Holocene in disarticulation of Human Settlements

    Science.gov (United States)

    Dabhi, M.

    2017-12-01

    -relatable with the global Medieval Warm Period (MWP). Based on detail study it can be interpreted that the area has been highly affected by Indian Summer Monsoon variability since last 5ka and early historic human occupation that has been affected by the climatic transformations.

  11. Holocene molluscan assemblages in the Magellan region

    Directory of Open Access Journals (Sweden)

    Sandra Gordillo

    1999-12-01

    Full Text Available In the Magellan region, much of the shoreline of the Beagle Channel coast (54°53´S; 67° - 68°W is bordered by Holocene raised beaches, which contain a large number of molluscs and other shelled taxa. The purpose of this work is to document the presence of various molluscan assemblages deposited with little or no postmortem transportation. An epifaunal Chlamys patagonica palaeocommunity (ca. 8,000 - 7,000 BP and three infaunal (Tawera gayi, Ameghinomya antiqua - Hiatella solida and Ameghinomya antiqua - Ensis macha palaeocommunities (ca. 4,400 - 4,000 BP were recognized. All the assemblages studied represent shallow, subtidal, cold-temperate environments. Based on comparisons with modern benthic communities in this region, these associations show that no remarkable ecologic and climatic changes occurred during the period ca. 8,000 - 4,000 BP. Thus, an apparent stability of modern marine communities over a period of several thousand years is suggested.

  12. Evaluating CO2 and CH4 dynamics of Alaskan ecosystems during the Holocene Thermal Maximum

    Science.gov (United States)

    He, Yujie; Jones, Miriam C.; Zhuang, Qianlai; Bochicchio, Christopher; Felzer, B. S.; Mason, Erik; Yu, Zicheng

    2014-01-01

    The Arctic has experienced much greater warming than the global average in recent decades due to polar amplification. Warming has induced ecological changes that have impacted climate carbon-cycle feedbacks, making it important to understand the climate and vegetation controls on carbon (C) dynamics. Here we used the Holocene Thermal Maximum (HTM, 11–9 ka BP, 1 ka BP = 1000 cal yr before present) in Alaska as a case study to examine how ecosystem Cdynamics responded to the past warming climate using an integrated approach of combining paleoecological reconstructions and ecosystem modeling. Our paleoecological synthesis showed expansion of deciduous broadleaf forest (dominated by Populus) into tundra and the establishment of boreal evergreen needleleaf and mixed forest during the second half of the HTM under a warmer- and wetter-than-before climate, coincident with the occurrence of the highest net primary productivity, cumulative net ecosystem productivity, soil C accumulation and CH4 emissions. These series of ecological and biogeochemical shifts mirrored the solar insolation and subsequent temperature and precipitation patterns during HTM, indicating the importance of climate controls on C dynamics. Our simulated regional estimate of CH4 emission rates from Alaska during the HTM ranged from 3.5 to 6.4 Tg CH4 yr−1 and highest annual NPP of 470 Tg C yr−1, significantly higher than previously reported modern estimates. Our results show that the differences in static vegetation distribution maps used in simulations of different time slices have greater influence on modeled C dynamics than climatic fields within each time slice, highlighting the importance of incorporating vegetation community dynamics and their responses to climatic conditions in long-term biogeochemical modeling.

  13. Inside the "African cattle complex": animal burials in the holocene central Sahara.

    Directory of Open Access Journals (Sweden)

    Savino di Lernia

    Full Text Available Cattle pastoralism is an important trait of African cultures. Ethnographic studies describe the central role played by domestic cattle within many societies, highlighting its social and ideological value well beyond its mere function as 'walking larder'. Historical depth of this African legacy has been repeatedly assessed in an archaeological perspective, mostly emphasizing a continental vision. Nevertheless, in-depth site-specific studies, with a few exceptions, are lacking. Despite the long tradition of a multi-disciplinary approach to the analysis of pastoral systems in Africa, rarely do early and middle Holocene archaeological contexts feature in the same area the combination of settlement, ceremonial and rock art features so as to be multi-dimensionally explored: the Messak plateau in the Libyan central Sahara represents an outstanding exception. Known for its rich Pleistocene occupation and abundant Holocene rock art, the region, through our research, has also shown to preserve the material evidence of a complex ritual dated to the Middle Pastoral (6080-5120 BP or 5200-3800 BC. This was centred on the frequent deposition in stone monuments of disarticulated animal remains, mostly cattle. Animal burials are known also from other African contexts, but regional extent of the phenomenon, state of preservation of monuments, and associated rock art make the Messak case unique. GIS analysis, excavation data, radiocarbon dating, zooarchaeological and isotopic (Sr, C, O analyses of animal remains, and botanical information are used to explore this highly formalized ritual and the lifeways of a pastoral community in the Holocene Sahara.

  14. Holocene Demographic Changes and the Emergence of Complex Societies in Prehistoric Australia.

    Directory of Open Access Journals (Sweden)

    Alan N Williams

    Full Text Available A continental-scale model of Holocene Australian hunter-gatherer demography and mobility is generated using radiocarbon data and geospatial techniques. Results show a delayed expansion and settlement of much of Australia following the termination of the late Pleistocene until after 9,000 years ago (or 9ka. The onset of the Holocene climatic optimum (9-6ka coincides with rapid expansion, growth and establishment of regional populations across ~75% of Australia, including much of the arid zone. This diffusion from isolated Pleistocene refugia provides a mechanism for the synchronous spread of pan-continental archaeological and linguistic attributes at this time (e.g. Pama-Nyungan language, Panaramitee art style, backed artefacts. We argue longer patch residence times were possible at the end of the optimum, resulting in a shift to more sedentary lifestyles and establishment of low-level food production in some parts of the continent. The onset of El Niño - Southern Oscillation (ENSO; 4.5-2ka restricted low-level food production, and resulted in population fragmentation, abandonment of marginal areas, and reduction in ranging territory of ~26%. Importantly, climate amelioration brought about by more pervasive La Niña conditions (post-2ka, resulted in an intensification of the mobility strategies and technological innovations that were developed in the early- to mid-Holocene. These changes resulted in population expansion and utilization of the entire continent. We propose that it was under these demographically packed conditions that the complex social and religious societies observed at colonial contact were formed.

  15. Holocene Demographic Changes and the Emergence of Complex Societies in Prehistoric Australia

    Science.gov (United States)

    Williams, Alan N.; Ulm, Sean; Turney, Chris S. M.; Rohde, David; White, Gentry

    2015-01-01

    A continental-scale model of Holocene Australian hunter-gatherer demography and mobility is generated using radiocarbon data and geospatial techniques. Results show a delayed expansion and settlement of much of Australia following the termination of the late Pleistocene until after 9,000 years ago (or 9ka). The onset of the Holocene climatic optimum (9-6ka) coincides with rapid expansion, growth and establishment of regional populations across ~75% of Australia, including much of the arid zone. This diffusion from isolated Pleistocene refugia provides a mechanism for the synchronous spread of pan-continental archaeological and linguistic attributes at this time (e.g. Pama-Nyungan language, Panaramitee art style, backed artefacts). We argue longer patch residence times were possible at the end of the optimum, resulting in a shift to more sedentary lifestyles and establishment of low-level food production in some parts of the continent. The onset of El Niño - Southern Oscillation (ENSO; 4.5-2ka) restricted low-level food production, and resulted in population fragmentation, abandonment of marginal areas, and reduction in ranging territory of ~26%. Importantly, climate amelioration brought about by more pervasive La Niña conditions (post-2ka), resulted in an intensification of the mobility strategies and technological innovations that were developed in the early- to mid-Holocene. These changes resulted in population expansion and utilization of the entire continent. We propose that it was under these demographically packed conditions that the complex social and religious societies observed at colonial contact were formed. PMID:26083101

  16. Rapid Holocene thinning of outlet glaciers followed by readvance in the western Ross Embayment, Antarctica

    Science.gov (United States)

    Jones, R. S.; Whitmore, R.; Mackintosh, A.; Norton, K. P.; Eaves, S.; Stutz, J.

    2017-12-01

    Investigating Antarctic deglaciation following the LGM provides an opportunity to better understand patterns, mechanisms and drivers of ice sheet retreat. In the Ross Sea sector, geomorphic features preserved on the seafloor indicate that streaming East Antarctic outlet glaciers once extended >100 km offshore of South Victoria Land prior to back-stepping towards their modern configurations. In order to adequately interpret the style and causes of this retreat, the timing and magnitude of corresponding ice thickness change is required. We present new constraints on ice surface lowering from Mawson Glacier, an outlet of the East Antarctic Ice Sheet that flows into the western Ross Sea. Surface-exposure (10Be) ages from samples collected in elevation transects above the modern ice surface reveal that rapid thinning occurred at 5-8 ka, broadly coeval with new ages of grounding-line retreat at 6 ka and rapid thinning recorded at nearby Mackay Glacier at 7 ka. Our data also show that a moraine formed near to the modern ice margin of Mawson Glacier at 0.8 ka, which, together with historical observations, indicates that glaciers in this region readvanced during the last thousand years. We argue that 1) the accelerated thinning of outlet glaciers was driven by local grounding-line retreat through overdeepened basins during the early-mid Holocene, and 2) the glaciers subsequently readvanced, possibly linked to late Holocene sea-ice expansion, before retreating to their current positions. Our work demonstrates that these outlet glaciers were closely coupled to environmental and topography-induced perturbations near their termini throughout the Holocene.

  17. Latest Pleistocene and Holocene surficial deposits and landforms of Yosemite Valley, California

    Science.gov (United States)

    Haddon, E. K.; Stock, G. M.; Booth, D. B.

    2016-12-01

    Field studies on the surficial geology and geomorphology of Yosemite Valley since the 1870's formed an early basis for our understanding of Quaternary landscape evolution in the central Sierra Nevada. These landmark studies described the erosional origin of Yosemite's iconic scenery, but left details of the latest Pleistocene and Holocene sedimentary record for later investigation. We combined mapping of deposits and landforms with geochronology to reconstruct the geomorphic evolution of Yosemite Valley since the 15 ka retreat of the Last Glacial Maximum (LGM) valley glacier. We document a sustained period of relative landscape stability, characterized by valley-bottom aggradation of glacial till, fluvial sediments, and lacustrine silts, as well as valley-margin accumulation of talus and fan alluvium. Recessional moraines, episodically emplaced rock avalanches, and alluvial fans impeded surface flow and controlled the local base level. This predominantly aggradational regime then shifted to incision in the earliest Holocene, likely due to a diminishing supply of glacial sediment, and created a flight of fluvial terraces inset by up to 9 m. The volume of fringing talus and fan alluvium in comparison with fluvial terrace sequences emphasizes the importance of valley-wall erosion as a sediment source. Cosmogenic 10Be exposure ages from rock avalanche boulders and 14C charcoal ages from deltaic sequences and inset fluvial gravels suggest variable rates of Holocene river incision. Although some incision events likely record local base level changes at the El Capitan LGM recessional moraine, the presence of perched, well-developed outwash terraces downstream indicates a more regional climatic forcing. These findings, including the depositional record of land-use disturbances over the past two centuries, help illuminate the geologic evolution of this celebrated landscape and inform ongoing river-restoration work.

  18. The challenge of global warming

    International Nuclear Information System (INIS)

    Bryner, G.C.

    1992-01-01

    The chapter outlines the science of global warming, the likely consequences of global warming and some of the major challenges in dealing with global climate change. Some of the major international organisations concerned with environmental issues are listed. International agreements might be used to limit emissions of greenhouse gases. 32 refs., 2 tabs

  19. Global warming and prairie wetlands

    International Nuclear Information System (INIS)

    Poiani, K.A.; Johnson, W.C.

    1991-01-01

    In this article, the authors discuss current understanding and projections of global warming; review wetland vegetation dynamics to establish the strong relationship among climate, wetland hydrology, vegetation patterns and waterfowl habitat; discuss the potential effects of a greenhouse warming on these relationships; and illustrate the potential effects of climate change on wetland habitat by using a simulation model

  20. Warm Bodies: A Student Perspective.

    Science.gov (United States)

    Schario, Tracy A.

    A participant in forensic tournament competition presents her perspective as well as overall student reaction to the function of "warm bodies," competitors who are entered in a tournament by the coach or tournament director only to meet qualifying requirements. Overall, participants in an informal survey believed that the warm body…

  1. Holocene glacier and climate variations in Vestfirðir, Iceland, from the modeling of Drangajökull ice cap

    Science.gov (United States)

    Anderson, Leif S.; Flowers, Gwenn E.; Jarosch, Alexander H.; Aðalgeirsdóttir, Guðfinna Th; Geirsdóttir, Áslaug; Miller, Gifford H.; Harning, David J.; Thorsteinsson, Thorsteinn; Magnússon, Eyjólfur; Pálsson, Finnur

    2018-06-01

    Drangajökull is a maritime ice cap located in northwest (Vestfirðir) Iceland. Drangajökull's evolution is therefore closely linked to atmospheric and ocean variability. In order to better constrain the Holocene climate and glacier history of Vestfirðir we model the past evolution of Drangajökull ice cap. Simulations from 10 ka to present are forced by general circulation model output, ice-core-based temperature reconstructions, and sea-surface temperature reconstructions. Based on these 10-thousand year simulations, Drangajökull did not persist through the Holocene. We estimate that air temperatures were 2.5-3.0 °C higher during the Holocene Thermal Maximum than the local 1960-1990 average. Simulations support Drangajökull's late Holocene inception between 2 and 1 ka, though intermittent ice likely occupied cirques as early as 2.6 ka. Drangajökull is primarily a Little Ice Age ice cap: it expanded between 1300 and 1750 CE, with the most rapid growth occurring between 1600 and 1750 CE. The maximum Holocene extent of Drangajökull occurred between 1700 and 1925 CE, despite the lowest late Holocene temperatures, occurring between 1650 and 1720 CE. Between 1700 and 1925 CE temperatures were likely 0.6-0.8 °C lower than the 1950-2015 reference temperature. The modern equilibrium line altitude (ELA) is bracketed by topographic thresholds: a 1 °C temperature increase from the modern ELA would eliminate the ice cap's accumulation area, while a reduction of 0.5 °C would lead to the rapid expansion of the ice cap across Vestfirðir. The proximity of Drangajökull to topographic thresholds may explain its late inception and rapid expansion during the Little Ice Age.

  2. Vegetation Response and Landscape Dynamics of Indian Summer Monsoon Variations during Holocene: An Eco-Geomorphological Appraisal of Tropical Evergreen Forest Subfossil Logs

    Science.gov (United States)

    Kumaran, Navnith K. P.; Padmalal, Damodaran; Nair, Madhavan K.; Limaye, Ruta B.; Guleria, Jaswant S.; Srivastava, Rashmi; Shukla, Anumeha

    2014-01-01

    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. PMID:24727672

  3. The Deglacial to Holocene Paleoceanography of Bering Strait: Results From the SWERUS-C3 Program

    Science.gov (United States)

    Jakobsson, M.; Anderson, L. G.; Backman, J.; Barrientos, N.; Björk, G. M.; Coxall, H.; Cronin, T. M.; De Boer, A. M.; Gemery, L.; Jerram, K.; Johansson, C.; Kirchner, N.; Mayer, L. A.; Mörth, C. M.; Nilsson, J.; Noormets, R. R. N. N.; O'Regan, M.; Pearce, C.; Semiletov, I. P.; Stranne, C.

    2017-12-01

    The climate-carbon-cryosphere (C3) interactions in the East Siberian Arctic Ocean and related ocean, river and land areas of the Arctic have been the focus for the SWERUS-C3 Program (Swedish - Russian - US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions). This multi-investigator, multi-disciplinary program was carried out on a two-leg 90-day long expedition in 2014 with Swedish icebreaker Oden. One component of the expedition consisted of geophysical mapping and coring of Herald Canyon, located on the Chukchi Sea shelf north of the Bering Strait in the western Arctic Ocean. Herald Canyon is strategically placed to capture the history of the Pacific-Arctic Ocean connection and related changes in Arctic Ocean paleoceanography. Here we present a summary of key results from analyses of the marine geophysical mapping data and cores collected from Herald Canyon on the shelf and slope that proved to be particularly well suited for paleoceanographic reconstruction. For example, we provide a new age constraint of 11 cal ka BP on sediments from the uppermost slope for the initial flooding of the Bering Land Bridge and reestablishment of the Pacific-Arctic Ocean connection following the last glaciation. This age corresponds to meltwater pulse 1b (MWP1b) known as a post-Younger Dryas warming in many sea level and paleoclimate records. In addition, high late Holocene sedimentation rates that range between about 100 and 300 cm kyr-1, in Herald Canyon permitted paleoceanographic reconstructions of ocean circulation and sea ice cover at centennial scales throughout the late Holocene. Evidence suggests varying influence from inflowing Pacific water into the western Arctic Ocean including some evidence for quasi-cyclic variability in several paleoceanographic parameters, e.g. micropaleontological assemblages, isotope geochemistry and sediment physical properties.

  4. Megalake Chad impact on climate and vegetation during the late Pliocene and the mid-Holocene

    Directory of Open Access Journals (Sweden)

    C. Contoux

    2013-07-01

    Full Text Available Given the growing evidence for megalakes in the geological record, assessing their impact on climate and vegetation is important for the validation of palaeoclimate simulations and therefore the accuracy of model–data comparison in lacustrine environments. Megalake Chad (MLC occurrences are documented not only for the mid-Holocene but also for the Mio-Pliocene (Schuster et al., 2009. At this time, the surface covered by water would have reached up to ~350 000 km2 (Ghienne et al., 2002; Schuster et al., 2005; Leblanc et al., 2006, making it an important evaporation source, possibly modifying climate and vegetation in the Chad Basin. We investigated the impact of such a giant continental water area in two different climatic backgrounds within the Paleoclimate Model Intercomparison Project phase 3 (PMIP3: the late Pliocene (3.3 to 3 Ma, i.e. the mid-Piacenzian warm period and the mid-Holocene (6 kyr BP. In all simulations including MLC, precipitation is drastically reduced above the lake surface because deep convection is inhibited by overlying colder air. Meanwhile, convective activity is enhanced around MLC because of the wind increase generated by the flat surface of the megalake, transporting colder and moister air towards the eastern shore of the lake. The effect of MLC on precipitation and temperature is not sufficient to widely impact vegetation patterns. Nevertheless, tropical savanna is present in the Chad Basin in all climatic configurations, even without MLC presence, showing that the climate itself is the driver of favourable environments for sustainable hominid habitats.

  5. Provenance of Holocene calcareous beach-dune sediments, Western Eyre Peninsula, Great Australian Bight, Australia

    Science.gov (United States)

    James, Noel P.; Bone, Yvonne

    2017-07-01

    Much of western Eyre Peninsula adjacent to the Great Australian Bight is veneered with siliceous and calcareous Quaternary aeolian dunes. The lengthy coastline adjacent to this cool-water carbonate factory is a series of Precambrian crystalline bedrock-Pleistocene aeolianite headlands that separate many long, sweeping, Holocene carbonate sand beaches and their backbeach dunes. Incessant SW waves, rolling swells, and onshore winds have resulted in > 350 km of semi-continuous calcareous strandline aeolian sands. The sediment is composed of quartz grains, Cenozoic limestone clasts, and relict particles (extraclasts) but the deposits are overwhelmingly dominated by contemporaneous biofragments from offshore. These skeletal grains are, in order of relative abundance, molluscs > benthic foraminifers > coralline algae > bryozoans, and echinoids. Benthic foraminifers are mostly small (especially rotaliids and miliolids) but the large relict symbiont-bearing protistMarginopora vertebralis, which grew in the latter stages of MIS 2, is present locally. There are no significant onshore-offshore trends within individual beach-dune complexes. There is, however, a prominent spatial partitioning, with extraclast-rich sediments in the north and biofragment-rich deposits in the south. This areal trend is interpreted to result from more active seafloor carbonate production in the south, an area of conspicuous seasonal nutrient upwelling and profound nektic and benthic biological productivity. The overall system is strikingly similar to Holocene and Pleistocene aeolianites along the inboard margin of the Lacepede Shelf and Bonney Coast some 500 km to the southeast, implying a potential universality to the nature of cool-water carbonate aeolianite deposition. The composition of these cool-water aeolianites is more multifaceted than those formed on warm-water, shallow flat-topped platforms, largely because of the comparatively deep, temperate shelf, the high-energy wave and swell

  6. How Hot was Africa during the Mid-Holocene? Reexamining Africa's Thermal History via integrated Climate and Proxy System Modeling

    Science.gov (United States)

    Dee, S.; Russell, J. M.; Morrill, C.

    2017-12-01

    Climate models predict Africa will warm by up to 5°C in the coming century. Reconstructions of African temperature since the Last Glacial Maximum (LGM) have made fundamental contributions to our understanding of past, present, and future climate and can help constrain predictions from general circulation models (GCMs). However, many of these reconstructions are based on proxies of lake temperature, so the confounding influences of lacustrine processes may complicate our interpretations of past changes in tropical climate. These proxy-specific uncertainties require robust methodology for data-model comparison. We develop a new proxy system model (PSM) for paleolimnology to facilitate data-model comparison and to fully characterize uncertainties in climate reconstructions. Output from GCMs are used to force the PSM to simulate lake temperature, hydrology, and associated proxy uncertainties. We compare reconstructed East African lake and air temperatures in individual records and in a stack of 9 lake records to those predicted by our PSM forced with Paleoclimate Model Intercomparison Project (PMIP3) simulations, focusing on the mid-Holocene (6 kyr BP). We additionally employ single-forcing transient climate simulations from TraCE (10 kyr to 4 kyr B.P. and historical), as well as 200-yr time slice simulations from CESM1.0 to run the lake PSM. We test the sensitivity of African climate change during the mid-Holocene to orbital, greenhouse gas, and ice-sheet forcing in single-forcing simulations, and investigate dynamical hypotheses for these changes. Reconstructions of tropical African temperature indicate 1-2ºC warming during the mid-Holocene relative to the present, similar to changes predicted in the coming decades. However, most climate models underestimate the warming observed in these paleoclimate data (Fig. 1, 6kyr B.P.). We investigate this discrepancy using the new lake PSM and climate model simulations, with attention to the (potentially non

  7. Holocene Millennial Time Scale Hydrological Changes In Central-east Africa

    Science.gov (United States)

    Jolly, D.; Bonnefille, R.; Beaufort, L.

    The Holocene hydrological changes of a tropical swamp is reconstructed using a high resolution pollen record (ca 50 yrs) from the Kuruyange valley (Burundi, Africa, 3°35'S, 29°41'E), at 2000 m elevation. The sequence was dated by 10 radiocarbon dates, allowing reconstruction between ca 12 500 and 1000 cal yr B.P. In the Kuruyange swamp, peat accumulated rapidly at a sedimentation rate varying from 0.73 (prior to 6200 cal yr B.P.) to 1.51 mm/yr (during the late Holocene). A pollen index of water table, based on a ratio of aquatic versus non-aquatic plants has been used in order to test the hypothesis of hydrological constraints on the swampy ecosystem. Eight arid phases are evidenced by the index minima at 12 200, 11 200, 9900, 8600, 6500, 5000, 3400, 1600 cal yr B.P. The good agreement existing between this index and independent data such as (i) low-resolution East-African lake level reconstruct ions (Gillespie et al., 1983) and (ii) ?18O analyses from Arabian Sea (Sirocko et al., 1993) suggests the water table level responds to the monsoon dynamic. The Index varies periodically with a combination of 1/1515, 1/880 and 1/431 years-1 frequencies, revealed by time series analyses (Blackman-Tukey and Maximum Entropy). The extrapolation of the composite curve based on these 3 periodicities show that two major climatic events defined in the high latitudes between 1000 and 660 cal yr B.P. (Medieval Warm Period) and between 500 and 100 cal yr B.P. (Little Ice Age) are recorded in our data and show respectively high and low stands of the water table. Our results support some previous pollen-derived climate estimates in Ethiopia done by Bonnefille and Umer (1994). Moreover, the "1500 year" cycle registered in our data from the tropics, already evidenced in higher latitudes (Wijmstra et al., 1984; Bondet al., 1997; Schulz et al., 1999; Bond et al., 2001) support the hypothesis of strong teleconnections between tropical/subtropical and polar climates during the deglaciation

  8. Is global warming mostly at night?

    International Nuclear Information System (INIS)

    Kukla, G.; Quayle, R.G.; Karl, T.

    1994-01-01

    The release of greenhouse gases is expected to lead to substantial future warming. The global mean temperature has indeed risen in recent decades. The causes of the observed warming, and its relation to the greenhouse gas buildup are, however, still debated. One important aspect of the observed temperature change relates to its asymmetry during the day and night. The day-night temperature difference over land in North America, most of Eurasia, Oceania, and portions of Africa and Australia shows a decrease since about 1950. The changes of the daily mean temperature in these areas are principally due to the rising night or early morning temperature, and are accompanied by increasing cloudiness. Their results support the notion that the increase of cloud cover, possibly due to industrial sulfur emissions, mitigates the greenhouse warming. The causes of the changing diurnal temperature range and of the increasing cloudiness will have to be clarified and the future SO 2 emissions reliably projected before any trustworthy prediction of future climates can be made. 37 refs., 7 figs., 2 tabs

  9. 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....

  10. Forests and global warming

    International Nuclear Information System (INIS)

    Curren, T.

    1991-04-01

    The importance of forests to Canada, both in economic and environmental terms, is indisputable. A warmer global climate may well have profound effects on the Canadian boreal forest, and at least some of the effects will not be beneficial. With the state of the current knowledge of climate processes and climate change it is not possible to predict the extent or rate of projected changes of anthropogenic origin. Given these uncertainties, the appropriate course of action for the Canadian forest sector is to develop policies and strategies which will make good sense under the current climatic regime, and which will also be appropriate for actions in a warmer climate scenario. The business as usual approach is not acceptable in the context of pollution control as it has become clear that anthropogenic emissions of greenhouse gases and other pollutants must be substantially reduced, both to prevent (or at least slow the rate of) possible global warming, and to reduce impacts on the biophysical environment and human health. Effective mitigative actions must be introduced on both a national and global scale. Forest management policies more effectively geared to the sustainability of forests are needed. The programs that are developed out of such policies must be cognizant of the real possibility that climate in the present boreal forest regions may change in the near future. 13 refs

  11. Holocene coastal paleoenvironmental record, Bay of Brest

    Science.gov (United States)

    Fernane, Assia; Gandouin, Emmanuel; Goslin, Jérôme; Penaud, Aurélie; Van Vliet lanoë, Brigitte

    2013-04-01

    Coastal areas are sensitive environments regarding the risk of submersion and the impact on biodiversity induced by salinity changes. These areas thus provide good palaeocecological archives to monitor palaeo sea level changes and the associated adaptation of different biological communities. The north-western coast of France has poorly been investigated regarding its Holocene palaeoecological signatures (Morzadec-Kerfourn, 1974; Naughton et al., 2007). Chironomids have been recognized to be an efficient tool for palaeoclimate and palaeosalinity reconstructions in lakes (Brooks, 2006), and more recently in river floodplains (Gandouin et al, 2006). In this study, environmental changes related to both climate processes and human disturbances, were reconstructed over the last 5000 years, based on pollen and chironomid assemblages from two coastal cores retrieved at Pors Milin (Brittany, NW France). The sedimentary sequences consist of terrestrial peaty layers interdigited with marine clastic deposits. The study area is composed by a sandy beach, truncating the peat, limited by a high sandy bar, and a back marsh developed at + 4 m NGF. Pollen and chironomid results reveal that anthropogenic factors would mainly control environmental changes that occurred in this sector. The disappearance of many chironomid taxa (inhabitants of main river channel) and the dramatic fall in diversity may have been induced by the development of the Merovingian forest clearance at Pors Milin. Indeed, we suggest that the development of agriculture, the river embankment and the draining of wetlands may explain the chironomid habitat loss and the subsequent fall of biodiversity. This change in faunal assemblages occurred synchronously with a decrease in the "arborean / non arborean" pollen ratio reflecting the land opening of the watershed. Several nitrophilous and anthropogenic pollen taxa reinforce our hypothesis concerning the development of agricultural and livestock farming activities at

  12. Holocene surface-rupturing earthquakes along the Yadong Cross Structure (Himalaya)

    Science.gov (United States)

    Ferry, M. A.; Roth, T.; Jean-Francois, R.; Cattin, R.

    2017-12-01

    The Himalayan Arc accommodates 2 cm/yr of shortening from the India-Eurasia collision, mostly along the Main Himalayan Thust. Perpendicularly to the main structures, regional cross structures formed by en échelon grabens and half-grabens mark Quaternary extension from central Tibet to the Himalayas. The Yadong-Gulu Rift system is the most striking one with a total length of 500 km. Its southernmost segment -the 100-km-long Yadong half-graben- entrenches through the Himalayas and forms a 500-to-1500-m-deep asymmetric basin. The average basin surface elevation of 4500 m contrasts with high reliefs of the Jomolhari range that reach 7326 m. They are separated by the N15 Yadong normal fault (also called Jomolhari Fault System, JFS) that forms spectacular triangular facets and affects glacial landforms. Though observed as early as the 1980s, offset moraines were never studied in detail in terms of measured displacement or age determination. Recent efforts from paleoclimate studies yielded a high-resolution framework to identify the various stages of Holocene glacial advances and associated moraine formation. These landforms display specific geomorphometric features recognized regionally (ELA, rugosity, crest freshness) that allow correlating across the various glacial valleys within the Yadong Rift and across similar settings in western Bhutan and eastern Nepal. This serves as a robust basis to place our moraine sequence within the Holocene paleoclimatic record and propose formation ages. By combining satellite images from Sentinel-2 (10 m, visible and NIR), Pléiades (0.5 m, visible) and a Pléiades-derived tri-stereo photogrammetric DEM (1 m), we map the fault trace and affected landforms in details and extract topographic profiles to measure vertical offsets. Paleoclimatic age constraints yield age-vs-displacement measurements along the whole 100-km-long JFS and define a chronology of Holocene deformation events. Within the limits of our observations, we conclude

  13. Holocene and Late Glacial sedimentation near steep slopes in southern Lake Baikal

    Directory of Open Access Journals (Sweden)

    Michael Sturm

    2015-07-01

    Full Text Available We here present new data on sedimentation at and near the steep north-slopes of southern Lake Baikal. Short sediment cores were taken at 550 m and at 1366 m water depth, within 3600 m offshore Cape Ivanovskii at the station of the Baikal Deep Underwater NEUTRINO Telescope. The sediments within 3600 m off the northern coast of Southern Lake Baikal are dominated by pelagic deposition. Our data reveal surprisingly little influence from terrigenous material from adjacent coastal areas, tributaries and their catchment. At the shallow-water site (at 550 m water depth, 700 m off shore just 27 cm thick homogenous sediments have accumulated during the Holocene on top of Pleistocene deposits resulting in Holocene sedimentation rates of 0.003 cm a-1. The very low rates are caused by long-term persistent winnowing of fine particles caused by week contour currents along the slope. The uppermost sediments are oxidized down to 22 cm. Very low concentrations of Corg, Sibio and Ntot in Pleistocene sediments increase dramatically within the Holocene. The heavy mineral fraction of the shallow-water sediments contains up to 33.6 % olivine and up to 2.4 % spinel. These rare minerals originate from white marbles of the nearby coastal outcrop Belaya Vyemka of the Early Precambrian Sharyzalgaiskaya Series. At the deep-water site (at 1366 m water depth, 3600 m off shore Holocene sedimentation rates are 10-times higher (0.036 cm a-1. Sediment oxidation occurs just within the uppermost 2 cm. Of the two rare type minerals of the Sharyzalgaiskaya Series spinel does not occur at all and olivine is represented by very diminished concentrations. This indicates insignificant influx of terrestrial material from the nearby shore to the deep-water site . Distal turbidites of far-off sources are intercalated to pelagic sediments at the deep-water site. Breakdown events of deltas at the SE- and S-coast of the basin are suggested to be responsible for the formation of the turbidites

  14. Recent warming of lake Kivu.

    Science.gov (United States)

    Katsev, Sergei; Aaberg, Arthur A; Crowe, Sean A; Hecky, Robert E

    2014-01-01

    Lake Kivu in East Africa has gained notoriety for its prodigious amounts of dissolved methane and dangers of limnic eruption. Being meromictic, it is also expected to accumulate heat due to rising regional air temperatures. To investigate the warming trend and distinguish between atmospheric and geothermal heating sources, we compiled historical temperature data, performed measurements with logging instruments, and simulated heat propagation. We also performed isotopic analyses of water from the lake's main basin and isolated Kabuno Bay. The results reveal that the lake surface is warming at the rate of 0.12°C per decade, which matches the warming rates in other East African lakes. Temperatures increase throughout the entire water column. Though warming is strongest near the surface, warming rates in the deep waters cannot be accounted for solely by propagation of atmospheric heat at presently assumed rates of vertical mixing. Unless the transport rates are significantly higher than presently believed, this indicates significant contributions from subterranean heat sources. Temperature time series in the deep monimolimnion suggest evidence of convection. The progressive deepening of the depth of temperature minimum in the water column is expected to accelerate the warming in deeper waters. The warming trend, however, is unlikely to strongly affect the physical stability of the lake, which depends primarily on salinity gradient.

  15. Recent warming of lake Kivu.

    Directory of Open Access Journals (Sweden)

    Sergei Katsev

    Full Text Available Lake Kivu in East Africa has gained notoriety for its prodigious amounts of dissolved methane and dangers of limnic eruption. Being meromictic, it is also expected to accumulate heat due to rising regional air temperatures. To investigate the warming trend and distinguish between atmospheric and geothermal heating sources, we compiled historical temperature data, performed measurements with logging instruments, and simulated heat propagation. We also performed isotopic analyses of water from the lake's main basin and isolated Kabuno Bay. The results reveal that the lake surface is warming at the rate of 0.12°C per decade, which matches the warming rates in other East African lakes. Temperatures increase throughout the entire water column. Though warming is strongest near the surface, warming rates in the deep waters cannot be accounted for solely by propagation of atmospheric heat at presently assumed rates of vertical mixing. Unless the transport rates are significantly higher than presently believed, this indicates significant contributions from subterranean heat sources. Temperature time series in the deep monimolimnion suggest evidence of convection. The progressive deepening of the depth of temperature minimum in the water column is expected to accelerate the warming in deeper waters. The warming trend, however, is unlikely to strongly affect the physical stability of the lake, which depends primarily on salinity gradient.

  16. Migrating Seals on Shifting Sands: Testing Alternate Hypotheses for Holocene Ecological and Cultural Change on the California Coast

    Science.gov (United States)

    Koch, P. L.; Newsome, S. D.; Gifford-Gonzalez, D.

    2001-12-01

    The coast of California presented Holocene humans with a diverse set of ecosystems and geomorphic features, from large islands off a semi-desert mainland in the south, to a mix of sandy and rocky beaches abutting grassland and oak forest in central California, to a rocky coast hugged by dense coniferous forest in the north. Theories explaining trends in human resource use, settlement patterns, and demography are equally diverse, but can be categorized as 1) driven by diffusion of technological innovations from outside the region, 2) driven by population growth leading to more intensive extraction of resources, or 3) driven by climatic factors that affect the resource base. With respect to climatic shifts, attention has focused on a possible regime shift ca. 5500 BP, following peak Holocene warming, and on evidence for massive droughts and a drop in marine productivity ca. 1000 BP. While evidence for a coincidence between climatic, cultural, and ecological change is present, albeit complex, in southern California, similar data are largely lacking from central and northern California. We are using isotopic and archaeofaunal analysis to test ideas for ecological and cultural change in central California. Three features of the archaeological record are relevant. First, overall use of marine resources by coastal communities declined after 1000 BP. Second, northern fur seals, which are common in earlier sites, drop in abundance relative to remaining marine animals. We have previously established that Holocene humans in central California were hunting gregariously-breeding northern fur seals from mainland rookeries. These seals breed exclusively on offshore islands today, typically at high latitudes. Their restriction to these isolated sites today may be a response to human overexploitation of their mainland rookeries prehistorically. Finally, collection of oxygen and carbon isotope data from mussels at the archaeological sites, while still in a preliminary phase, has

  17. Reconstruction of the vegetation distribution of different topographic units of the Chinese Loess Plateau during the Holocene

    Science.gov (United States)

    Sun, Aizhi; Guo, Zhengtang; Wu, Haibin; Li, Qin; Yu, Yanyan; Luo, Yunli; Jiang, Wenying; Li, Xiaoqiang

    2017-10-01

    Soil erosion and related ecological restoration present a tremendous challenge to the socioeconomic development of the Chinese Loess Plateau (CLP). Although the Chinese government has addressed the problem of soil erosion via an afforestation programme, there have been several negative outcomes. One of the reasons for this is our incomplete understanding of the past natural vegetation distribution in the various topographic units of the CLP under different climate scenarios. Consequently, we used fossil pollen data from 41 sites from different topographic units, together with the biomization method, to reconstruct the Holocene vegetation distribution of the CLP. The results demonstrate significant differences in vegetation types between different topographic units: forest was distributed in mountainous areas, steppe was dominant in Yuan areas, and desert vegetation was distributed in the transition zone between loess and desert. The vegetation in the gully areas exhibited significant spatial differences during the mid-Holocene. In addition, the vegetation on the various topographic units was well-developed during the interval from 9 to 4 ka B.P., when regional moisture levels reached a maximum. This suggests that the East Asian Summer Monsoon was one of the main factors controlling the evolution of vegetation patterns during the Holocene. In addition, our results confirm that both topography and human activity were fundamental factors determining the vegetation distribution of the region. Against a background of ongoing global warming, we advocate a program of vegetation restoration including planting trees and shrubs in the mountainous areas, and promoting the growth of grasses in the Yuan areas and in the transitional zone between loess and desert. In the gully areas, the planting of trees and shrubs is appropriate for reducing soil erosion caused by human activities.

  18. Zoonotic parasites associated with felines from the Patagonian Holocene

    Directory of Open Access Journals (Sweden)

    Martín Horacio Fugassa

    2009-12-01

    Full Text Available Feline coprolites were examined for parasites with the aim of studying ancient infections that occurred in the Patagonian region during the Holocene period. Eggs compatible to Trichuris sp., Calodium sp., Eucoleus sp., Nematodirus sp., Oesophagostomum sp. (Nematoda, Monoecocestus sp. (Cestoda and Eimeria macusaniensis (Coccidia were recovered from faecal samples. The results obtained from the analysis provide evidence of consumption by felids of the viscera of both rodents and camelids. This knowledge allows for improved explanations as to the distribution of parasitism and its significance to the health of humans and animals inhabiting the area under study during the Middle Holocene.

  19. Holocene lake-level fluctuations of Lake Aricota, Southern Peru

    Science.gov (United States)

    Placzek, C.; Quade, Jay; Betancourt, J.L.

    2001-01-01

    Lacustrine deposits exposed around Lake Aricota, Peru (17?? 22???S), a 7.5-km2 lake dammed by debris flows, provide a middle to late Holocene record of lake-level fluctuations. Chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14C reservoir effects (Titicaca (16?? S), which is only 130 km to the northeast and shares a similar climatology. Comparisons with other marine and terrestrial records highlight emerging contradictions over the nature of mid-Holocene climate in the central Andes. ?? 2001 University of Washington.

  20. Variable uplift rate through time: Holocene coral reef and neotectonics of Lutao, eastern Taiwan

    Science.gov (United States)

    Shen, Chuan-Chou; Wu, Chung-Che; Dai, Chang-Feng; Gong, Shou-Yeh

    2018-05-01

    Significant discrepancies have existed regarding rate and timing of the uplift of Lutao (Green Island), located at the border of the ongoing collision between the Eurasia continental plate and the Philippine Sea Plate. To document its neotectonic history, two cores were drilled into Holocene coral reefs exposed at the southeastern coast of Lutao. Twelve pristine fossil corals, nine taken from cores and three on the surface, were 230Th dated. The results show that the coral reefs started to develop at 8,736 ± 56 yr BP (before 1950 CE) with uplift rate varying from 3.6 mm/yr during 8.7-6.0 kyr BP to 1.2 mm/yr in the past six thousand years. Our study strongly suggests that the uplift rate can vary significantly on millennial time scale. Caution should be used when extrapolating uplift rate estimates based on Mid-late Holocene corals to early times for tectonic active locations, such as Lutao.

  1. Holocene vegetation and climate change on the Haanja heights, South-East Estonia

    International Nuclear Information System (INIS)

    Saarse, Leili; Rajamaee, Raivo

    1997-01-01

    The development of forests on the Haanja Heights has been controlled by external factors, including climate, soils, hydrology, and human impact. The sediment sequence from Lake Kirikumaee, which covers about 12 000 years, records the vegetation history throughout the Late Glacial and Holocene. In the Alleroed, woodland tundra with sparse birch and willow was established. Grass-shrub tundra in the Younger Dryas was replaced by birch forest in the Pre-Boreal. During the Holocene two major shifts in vegetation dynamics occurred: the first about 8500 BP with a sharp decline in Betula-Pinus forest and development of broad-leaved forest, and the second about 3500 BP, with a decline in broad-leaved forest and regeneration of Pinus-Betula forest with a high share of Picea. The climate modelling, based on pollen record and lake-level changes, suggest cold, severe climate with low precipitation values in the early Pre-Boreal. Between 9500-8500 BP the climate was rather stable. The lake level first rose, then stabilized, and finally dropped. The sharp climate amelioration in the late Boreal together with the humidity increase resulted in a lake-level rise. The decreased precipitation and rather high summer temperatures, increased evapotranspiration, and reduced water balance are characteristic of the Sub-Boreal. Since 3500 BP, the climate deteriorated and mixed coniferous forest started to dominate. Several small climatic fluctuations, including the Little Ice Age cooling, have been traced by modelling. (author)

  2. Millennial-scale faunal record reveals differential resilience of European large mammals to human impacts across the Holocene.

    Science.gov (United States)

    Crees, Jennifer J; Carbone, Chris; Sommer, Robert S; Benecke, Norbert; Turvey, Samuel T

    2016-03-30

    The use of short-term indicators for understanding patterns and processes of biodiversity loss can mask longer-term faunal responses to human pressures. We use an extensive database of approximately 18,700 mammalian zooarchaeological records for the last 11,700 years across Europe to reconstruct spatio-temporal dynamics of Holocene range change for 15 large-bodied mammal species. European mammals experienced protracted, non-congruent range losses, with significant declines starting in some species approximately 3000 years ago and continuing to the present, and with the timing, duration and magnitude of declines varying individually between species. Some European mammals became globally extinct during the Holocene, whereas others experienced limited or no significant range change. These findings demonstrate the relatively early onset of prehistoric human impacts on postglacial biodiversity, and mirror species-specific patterns of mammalian extinction during the Late Pleistocene. Herbivores experienced significantly greater declines than carnivores, revealing an important historical extinction filter that informs our understanding of relative resilience and vulnerability to human pressures for different taxa. We highlight the importance of large-scale, long-term datasets for understanding complex protracted extinction processes, although the dynamic pattern of progressive faunal depletion of European mammal assemblages across the Holocene challenges easy identification of 'static' past baselines to inform current-day environmental management and restoration. © 2016 The Author(s).

  3. Holocene record of precipitation seasonality from lake calcite δ18O in the central Rocky Mountains, United States

    Science.gov (United States)

    Anderson, Lesleigh

    2011-01-01

    A context for recent hydroclimatic extremes and variability is provided by a ~10 k.y. sediment carbonate oxygen isotope (??18O) record at 5-100 yr resolution from Bison Lake, 3255 m above sea level, in northwestern Colorado (United States). Winter precipitation is the primary water source for the alpine headwater lake in the Upper Colorado River Basin and lake water ??18O measurements reflect seasonal variations in precipitation ??18O. Holocene lake water ??18O variations are inferred from endogenic sedimentary calcite ??18O based on comparisons with historic watershed discharge records and tree-ring reconstructions. Drought periods (i.e., drier winters and/or a more rain-dominated seasonal precipitation balance) generally correspond with higher calcite ??18O values, and vice-versa. Early to middle Holocene ??18O values are higher, implying a rain-dominated seasonal precipitation balance. Lower, more variable ??18O values after ca. 3500 yr ago indicate a snow-dominated but more seasonally variable precipitation balance. The middle to late Holocene ??18O record corresponds with records of El Ni??o Southern Oscillation intensification that supports a teleconnection between Rocky Mountain climate and North Pacific sea-surface temperatures at decade to century time scales. ?? 2011 Geological Society of America.

  4. Global warming: the complete briefing

    Energy Technology Data Exchange (ETDEWEB)

    Houghton, J

    1994-01-01

    The science of global warming, its impacts, and what action might be taken, are described in this book, in a way which the intelligent non-scientist can understand. It also examines ethical and moral issues of concern about global warming, considering mankind as stewards of the earth. Chapter headings of the book are: global warming and climate change; the greenhouse effect; the greenhouse gases; climates of the past; modelling the climate; climate change and business-as-usual; the impacts of climate change; why should we be concerned ; weighing the uncertainty; action to slow and stabilize climate change; energy and transport for the future; and the global village.

  5. Amplified Arctic warming by phytoplankton under greenhouse warming.

    Science.gov (United States)

    Park, Jong-Yeon; Kug, Jong-Seong; Bader, Jürgen; Rolph, Rebecca; Kwon, Minho

    2015-05-12

    Phytoplankton have attracted increasing attention in climate science due to their impacts on climate systems. A new generation of climate models can now provide estimates of future climate change, considering the biological feedbacks through the development of the coupled physical-ecosystem model. Here we present the geophysical impact of phytoplankton, which is often overlooked in future climate projections. A suite of future warming experiments using a fully coupled ocean-atmosphere model that interacts with a marine ecosystem model reveals that the future phytoplankton change influenced by greenhouse warming can amplify Arctic surface warming considerably. The warming-induced sea ice melting and the corresponding increase in shortwave radiation penetrating into the ocean both result in a longer phytoplankton growing season in the Arctic. In turn, the increase in Arctic phytoplankton warms the ocean surface layer through direct biological heating, triggering additional positive feedbacks in the Arctic, and consequently intensifying the Arctic warming further. Our results establish the presence of marine phytoplankton as an important potential driver of the future Arctic climate changes.

  6. Global warming 2007. An update to global warming: the balance of evidence and its policy implications.

    Science.gov (United States)

    Keller, Charles F

    2007-03-09

    -induced warming that needs to be considered carefully. A final topic touched on briefly here is the new understanding of the phenomenon called "global dimming." Several sets of observations of the sun's total radiation at the surface have shown that there has been a reduction in sunlight reaching it. This has been related to the scattering of sunlight by aerosols and has led to a better quantification of the possibility that cleaning up our atmospheric pollution will lead to greater global warming. Adding all these advances together, there is a growing consensus that the 21st century will indeed see some 2 degrees C (3.5 degrees F) or more in additional warming. This is corroborated in the new IPCC Assessment, an early release of which is touched on very briefly here.

  7. Hydroclimate variability of High Arctic Svalbard during the Holocene inferred from hydrogen isotopes of leaf waxes

    Science.gov (United States)

    Balascio, Nicholas L.; D'Andrea, William J.; Gjerde, Marthe; Bakke, Jostein

    2018-03-01

    The response of the Arctic hydrologic cycle to global warming includes changes in precipitation patterns and moisture availability associated with variable sea ice extent and modes of atmospheric circulation. Reconstructions of past hydroclimate changes help constrain the natural range of these systems, identify the manners in which they respond to different forcing mechanisms, and reveal their connections to other components of the climate system, all of which lead to a better understanding of present and future changes. Here we examine hydroclimate changes during the Holocene in the High Arctic archipelago of Svalbard by reconstructing the isotopic composition of precipitation. We measured the hydrogen isotopic composition (δD values) of leaf wax compounds (n-alkanes; C25-C31) in a sediment core from Lake Hakluytvatnet on the island of Amsterdamøya, northwest Spitsbergen. We interpret δD values of mid-chain (C25) and long-chain (C29, C31) length n-alkanes to represent changes in the isotopic composition of lake water and precipitation over the last 12.9 ka. After deglaciation of the catchment, water supply became restricted and the lake experienced significant evaporative isotopic enrichment indicating warmer conditions from 12.8 to 7.5 ka. The isotope values suggest an increase in the delivery of moisture from warmer sub-polar air masses between 12.8 and 9.5 ka, followed by generally warm, but unstable conditions between 9.5 and 7.5 ka, possibly indicating a response to meltwater forcing. Sedimentary evidence indicates a hiatus in deposition c. 7.5-5.0 ka, likely as a result of desiccation of the lake. At c. 5.0 ka lacustrine sedimentation resumed and over the last 5 ka there was a progressive increase in the influence of polar air masses and colder conditions, which culminated in an abrupt shift to colder conditions at c. 1.8 ka. This late Holocene cooling ended c. 0.18 ka, when isotopic data indicate warmer conditions and greater influence of moisture

  8. Equatorial ionospheric electrodynamic perturbations during Southern Hemisphere stratospheric warming events

    DEFF Research Database (Denmark)

    Olson, M. E.; Fejer, B. G.; Stolle, Claudia

    2013-01-01

    quasi 2 day fluctuations during the 2002 early autumnal equinoctial warming. They also show a moderately large multi-day perturbation pattern, resembling those during arctic SSW events, during 2002 late equinox, as the major SSW was weakening. We also compare these data with extensive recent results...

  9. Paleoecological Evidence for Late Holocene Range Shifting of Acropora palmata and Orbicella annularis on the Nearshore Southeast Florida Reef Tract

    Science.gov (United States)

    Modys, A. B.; Zuccarelli, C. L.; Oleinik, A. E.

    2016-02-01

    Climate fluctuations on the southeast Florida reef tract have been linked to long-term geographic distribution shifts in framework-building coral species Acropora palmata and Orbicella annularis. Previous data suggest that the boundary for active reef accretion driven by these corals contracted southward to its current position at Biscayne Bay throughout the early to middle Holocene ( 8500-5500 cal BP). However, recent observations have shown that while A. palmata and O. annularis are still functionally absent north of this boundary, they are well represented within late Holocene sub-fossil death assemblages found at 3-4 m depths on the nearshore ridge complex (NRC). To assess this disparity, we performed a systematic comparison of taxonomic composition and diversity of living and dead coral assemblages at two locations on the northern NRC. We also determined an estimated age range for the death assemblages from 2 samples of A. palmata and 1 sample of O. annularis using high-resolution AMS radiocarbon dating. Our results show a clear transition from a late Holocene reef assemblage dominated by A. palmata and O. annularis to a modern reef assemblage dominated by less sensitive Porites astreoides. Sub-fossil A. palmata samples dated to 2950-3140 cal BP and 1820-1960 cal BP (2σ), and the sub-fossil O. annularis sample dated to 2290-2420 cal BP (2σ), indicating a total growth period of at least 1000 years. Our findings provide new evidence for a distinct late Holocene range shift in A. palmata and O. annularis on the northern shallow-water ridge complex of the southeast Florida reef tract system.

  10. Warm and wet conditions in the Arctic region during Eocene Thermal Maximum 2

    NARCIS (Netherlands)

    Sluijs, A.; Schouten, S.; Donders, T.H.; Schoon, P.L.; Röhl, U.; Reichart, G.-J.; Sangiorgi, F.; Kim, J.-H.; Sinninghe Damsté, J.S.; Brinkhuis, H.

    2009-01-01

    Several episodes of abrupt and transient warming, each lasting between 50,000 and 200,000 years, punctuated the long-term warming during the Late Palaeocene and Early Eocene (58 to 51 Myr ago) epochs1,2. These hyperthermal events, such as the Eocene Thermal Maximum 2 (EMT2) that took place about

  11. Preliminary Evidence for the Amplification of Global Warming in Shallow, Intertidal Estuarine Waters

    Science.gov (United States)

    Over the past 50 years, mean annual water temperature in northeastern U.S. estuaries has increased by approximately 1.2°C, with most of the warming recorded in the winter and early spring. We hypothesize that this warming may be amplified in the shallow (<2m), nearshore portions ...

  12. Fewer bacteria in warm water

    International Nuclear Information System (INIS)

    Bagh, Lene

    1999-01-01

    There has been many suggestions to how the ideal warm water system should be. Particularly whether warm water containers or heat exchangers in larger houses are the best solutions in order to maintain a water quality with low levels of bacteria. In an investigation made by Statens Byggeforskningsinstitutt (Denmark) regarding ''Bacterial growth in warm water installations with heat exchangers'' there were used several heat exchangers made by Gjelsted and Lund of three of which had HWAT heating cables. The bacterial content was low from these exchangers compared to exchangers with circulation. The article presents promising results from a study where the method was investigated over a longer period in two new larger warm water systems. Some energy conservation aspects are discussed

  13. Warm mix asphalt : final report.

    Science.gov (United States)

    2014-11-01

    The performance of pavements constructed using warm mix asphalt (WMA) technology were : compared to the performance of conventional hot mix asphalt (HMA) pavements placed on the : same project. Measurements of friction resistance, rutting/wear, ride ...

  14. Global warming and nuclear power

    International Nuclear Information System (INIS)

    Hodgson, P.E.

    1999-01-01

    The problems of pollution, global warming and renewable energy sources are not going to go away. Governments need to act with urgency if they are to produce a long-term energy policy. This paper looks at the current energy situation, and how this would project into the future without the instigation of radical changes. It concludes that nuclear is the best option available for averting a growing energy, pollution and global warming crisis. (author)

  15. Global warming: A vicious circle

    International Nuclear Information System (INIS)

    Sinclair, J.

    1991-01-01

    As a result of increasing atmospheric concentrations of greenhouse gases the planet is already committed to regional droughts, storms, disruption of fisheries and the extinction of many plant and animal species. But current predictions of global warming do not take into account the reactions and interactions of the planet's land, ocean and ice masses to the rise in temperatures. It seems likely that the greenhouse effect will give rise to positive feedback reactions, leading to greater global warming than predicted

  16. Anthropogenic and geomorphic controls on peatland dynamics in contrasting floodplain environments during the Holocene and its impact on carbon storage

    Science.gov (United States)

    Verstraeten, Gert; Broothaerts, Nils; Notebaert, Bastiaan

    2016-04-01

    Peatlands are an important store of carbon in terrestrial environments, and scientific interest in peatlands has increased strongly in the light of the recent global climatic changes. Much attention has been paid to peatland dynamics in extensive arctic and boreal wetlands or to blanket peat in temperate regions. Nevertheless, long-term dynamics of peat in alluvial wetlands in temperate regions remains largely underresearched. In this study, data from three contrasting environments were used to provide more insights in the anthropogenic and geomorphic controls on peatland dynamics. The results show a high variability in alluvial peatland dynamics between the different study sites. In the central Belgian Loess Belt, alluvial peatlands developed during the early Holocene but gradually disappeared from the Mid-Holocene onwards due to the gradual intensification of agricultural activities in the catchment and consequent higher sedimentation rates in the floodplain system. The end of peat growth is shown to be diachronous at catchment scale, ranging between 6500 and 500 cal a BP. The disappearance of the alluvial peatlands has important implications since it potentially reduces the storage of locally produced C. Nevertheless, it was shown that this reduced production of local C but was outbalanced by the burial of hillslope derived C. Also within the sandy catchments of the Belgian Campine region alluvial peatlands initiated in the early Holocene but, here, they abruptly disappeared in the Mid-Holocene before the onset of intense agricultural activities in the catchment. This suggests that for the sandy regions, anthropogenic impact on peatland dynamics is less important compared to natural factors. For these regions, the disappearance of alluvial peatland formation resulted in a sharp decline in alluvial carbon storage as there is no compensation through hillslope derived C input. For the upper Dee catchment in NE Scotland, Holocene carbon floodplain storage varies

  17. Miscanti-1: Human occupation during the arid Mid-Holocene event in the high-altitude lakes of the Atacama Desert, South America

    Science.gov (United States)

    Núñez, Lautaro; Loyola, Rodrigo; Cartajena, Isabel; López, Patricio; Santander, Boris; Maldonado, Antonio; de Souza, Patricio; Carrasco, Carlos

    2018-02-01

    This paper presents an interdisciplinary study of the Miscanti-1 archaeological site, located in the Holocene terrace deposits accumulated on the eastern margin of Miscanti Lake (4120 m.a.s.l.), northern Chile (23.7° S, 67.7° W). The human response to environmental and climatic variability in the Mid-Holocene (9500-4500 cal yr BP) is discussed through the zooarchaeological, lithic and paleoenvironmental records. We propose that, due to the increased aridity of the period, Miscanti Lake became a brackish paleowetland that attracted discrete groups of hunter-gatherers from lower elevation Andean areas. In contrast with the high frequency of human occupations known for the humid Late Pleistocene and Early Holocene (12600-9500 yr cal BP), the Miscanti-1 site is one of the few occupations recorded in the Atacama Highlands during the Mid-Holocene period. Data analysis suggests logistic and short-term campsite use for hunting the wild camelids that were attracted by the wetlands and fresh water (8100-8300 yr cal BP). In contrast to previous proposals for this period, we propose that access to high altitude environments did not cease, but was made possible by a shift to highly scheduled mobility and a specialized bifacial technology. Finally, the temporal and spatial links of Miscanti-1 are discussed in a regional context.

  18. 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.

  19. Diagenesis of Holocene reef and associated beachrock of certain ...

    Indian Academy of Sciences (India)

    ally exposed corals of Holocene and Last Inter- glacial age, which may be subjected to diagenesis, primarily in the ... During the period of low tide, spring reef flat is covered by ..... Kallankurichchi formation, Ariyalur group, South India and its ...

  20. NW Pacific mid-depth ventilation changes during the Holocene

    Science.gov (United States)

    Rella, S.; Uchida, M.

    2010-12-01

    During the last 50 years the oxygen content of North Pacific Intermediate Water primarily originating in the Okhotsk Sea has declined suggesting decreased mid-depth water circulation, likely leading to changes in biological productivity in the NW Pacific realm and a decrease in CO2 drawdown. It is therefore of high interest to elucidate the climate-oceanic interconnections of the present interglacial period (Holocene) in the NW Pacific, in order to predict possible future climate and surface productivity changes associated with a decrease in mid-depth ventilation in this ecologically sensitive region. However, such efforts have been hampered so far by the lack of appropriate sediment cores with fast sedimentation rates during the Holocene. Core CK05-04 that was recovered in 2005 from off Shimokita peninsula, Japan, at ~1000 m depth shows sedimentation rates of ~80 cm/kyr during the Holocene and therefore presents an ideal opportunity to reconstruct for the first time the Holocene ventilation history of the NW Pacific Ocean. We employ Accelerator Mass Spectroscopy (NIES-TERRA, Tsukuba) radiocarbon analysis of co-existing benthic and planktonic foraminifera to conclude on the ventilation age of the mid-depth water using benthic-planktonic radiocarbon age differences. At the conference we would like to present the results.

  1. Holocene Lake-Level Fluctuations of Lake Aricota, Southern Peru

    Science.gov (United States)

    Placzek, Christa; Quade, Jay; Betancourt, Julio L.

    2001-09-01

    Lacustrine deposits exposed around Lake Aricota, Peru (17° 22‧S), a 7.5-km2 lake dammed by debris flows, provide a middle to late Holocene record of lake-level fluctuations. Chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14C reservoir effects (<350 yr). Diatomites associated with highstands several meters above the modern lake level indicate wet episodes. Maximum Holocene lake level was attained before 6100 14C yr B.P. and ended ∼2700 14C yr B.P. Moderately high lake levels occurred at 1700 and 1300 14C yr B.P. The highstand at Lake Aricota during the middle Holocene is coeval with a major lowstand at Lake Titicaca (16°S), which is only 130 km to the northeast and shares a similar climatology. Comparisons with other marine and terrestrial records highlight emerging contradictions over the nature of mid-Holocene climate in the central Andes.

  2. Holocene eolian activity in the Minot dune field, North Dakota

    Science.gov (United States)

    Muhs, D.R.; Stafford, Thomas W.; Been, J.; Mahan, S.A.; Burdett, J.; Skipp, G.; Rowland, Z.M.

    1997-01-01

    Stabilized eolian sand is common over much of the Great Plains region of the United States and Canada, including a subhumid area of ??? 1500 km2 near Minot, North Dakota. Eolian landforms consist of sand sheets and northwest-trending parabolic dunes. Dunes and sand sheets in the Minot field are presently stabilized by a cover of prairie grasses or oak woodland. Stratigraphic studies and accelerator mass spectrometry radiocarbon dating of paleosols indicate at least two periods of eolian sand movement in the late Holocene. Pedologic data suggest that all of the dune field has experienced late Holocene dune activity, though not all parts of the dune field may have been active simultaneously. Similar immobile element (Ti, Zr, La, Ce) concentrations support the interpretation that eolian sands are derived from local glaciofluvial and glaciolacustrine sediments. However, glaciolacustrine and glaciofluvial source sediments have high Ca concentrations from carbonate minerals, whereas dune sands are depleted in Ca. Because noneolian-derived soils in the area are calcareous, these data indicate that the Minot dune field may have had extended periods of activity in the Holocene, such that eolian abrasion removed soft carbonate minerals. The southwest-facing parts of some presently stabilized dunes were active during the 1930s drought, but were revegetated during the wetter years of the 1940s. These observations indicate that severe droughts accompanied by high temperatures are the most likely cause of Holocene eolian activity.

  3. North Atlantic-Fennoscandian Holocene climate trends and mechanisms

    NARCIS (Netherlands)

    Sejrup, H.P.; Seppä, H.; McKay, N.; Kaufman, D.S.; Geirsdottir, A.; de Vernal, A.; Renssen, H.; Husum, K.; Jennings, A.; Andrews, J.T.

    2016-01-01

    To investigate the mechanisms behind Holocene regional climate trends from north of 58°N in the North Atlantic-Fennoscandian region Principal Component Analysis (PCA) was performed and a temperature anomaly stack produced from 81 proxy derived summer temperature time series from 74 sites. The PC

  4. The Holocene in the coastal zone of Uruguay

    International Nuclear Information System (INIS)

    Garcia Rodriguez, F.

    2011-07-01

    This book represents a compilation of several scientific Holocene paleoenvironmental aspects of the coastal zone in Uruguay. It includes information about geological, geomorphological, evolutionary genetics, paleontological, paleobotanic, paleoclimatological, paleolimnological, paleoceanographic and archeologic aspects. The chapters presented were arbitrated by national and foreign recognized scientists

  5. Peat compaction in deltas : implications for Holocene delta evolution

    NARCIS (Netherlands)

    van Asselen, S.

    2010-01-01

    Many deltas contain substantial amounts of peat, which is the most compressible soil type. Therefore, peat compaction potentially leads to high amounts of subsidence in deltas. The main objective of this research was to quantify subsidence due to peat compaction in Holocene fluvial-deltaic settings

  6. Holocene sea level, a semi-empirical contemplation

    Science.gov (United States)

    Bittermann, K.; Kemp, A.; Vermeer, M.; Rahmstorf, S.

    2017-12-01

    Holocene eustatic sea level from approximately -10,000-1800 CE was characterized by an increase of about 60m, with the rate progressively slowing down until sea level almost stabilizes between 500-1800 CE. Global and northern-hemisphere temperatures rose from the last glacial termination until the `Holocene Optimum'. From ­­there, up to the start of the recent anthropogenic rise, they almost steadily decline. How are the sea-level and temperature evolutions linked? We investigate this with semi-empirical sea-level models. We found that, due to the nature of Milankovitch forcing, northern-hemisphere temperature (we used the Greenland temperature by Vinther et al., 2009) is a better model driver than global mean temperature because the evolving mass of northern-hemisphere land ice was the dominant cause of Holocene global sea-level trends. The adjustment timescale for this contribution is 1200 years (900-1500 years; 90% confidence interval). To fit the observed sea-level history, the model requires a small additional constant rate (Bittermann 2016). This rate turns out to be of the same order of magnitude as reconstructions of Antarctic sea-level contributions (Briggs et al. 2014, Golledge et al. 2014). In reality this contribution is unlikely to be constant but rather has a dominant timescale that is large compared to the time considered. We thus propose that Holocene sea level can be described by a linear combination of a temperature driven rate, which becomes negative in the late Holocene (as Northern Hemisphere ice masses are diminished), and a positive, approximately constant term (possibly from Antarctica), which starts to dominate from the middle of the Holocene until the start of industrialization. Bibliography: Bittermann, K. 2016. Semi-empirical sea-level modelling. PhD Thesis University of Potsdam. Briggs, R.D., et al. 2014. A data-constrained large ensemble analysis of Antarctic evolution since the Eemian. Quaternary science reviews, 103, 91

  7. Unexpected Impacts of Global warming on Extreme Warm Spells

    Science.gov (United States)

    Sardeshmukh, P. D.; Compo, G. P.; McColl, C.; Penland, C.

    2017-12-01

    It is generally presumed that the likelihood of extreme warm spells around the globe has increased, and will continue to increase, due to global warming. However, we find that this is generally not true in three very different types of global observational datasets and uncoupled atmospheric model simulations of the 1959 to 2012 period with prescribed observed global SSTs, sea ice, and radiative forcing changes. While extreme warm spells indeed became more common in many regions, in many other regions their likelihood remained almost the same or even decreased from the first half to the second half of this period. Such regions of unexpected changes covered nearly 40 percent of the globe in both winter and summer. The basic reason for this was a decrease of temperature variability in such regions that offset or even negated the effect of the mean temperature shift on extreme warm spell probabilities. The possibility of such an impact on extreme value probabilities was highlighted in a recent paper by Sardeshmukh, Compo, and Penland (Journal of Climate 2015). The consistency of the changes in extreme warm spell probabilities among the different observational datasets and model simulations examined suggests that they are robust regional aspects of global warming associated with atmospheric circulation changes. This highlights the need for climate models to represent not just the mean regional temperature signals but also the changes in subseasonal temperature variability associated with global warming. However, current climate models (both CMIP3 and CMIP5) generally underestimate the magnitude of the changes in the atmospheric circulation and associated temperature variability. A likely major cause of this is their continuing underestimation of the magnitude of the spatial variation of tropical SST trends. By generating an overly spatially bland tropical SST warming in response to changes in radiative forcing, the models spuriously mute tropically

  8. ANÁLISIS FUNCIONALES EN ARTEFACTOS LÍTICOS DE GRUPOS CAZADORES-RECOLECTORES EN REGIONES TROPICALES DURANTE LA TRANSICIÓN PLEISTOCENO FINAL-HOLOCENO TEMPRANO: EL ABRIGO SANTA MARTA, CHIAPAS, MÉXICO (Functional Analysis of Lithic Artifacts of Hunter-Gatherer Groups in Tropical Regions During the Late Pleistocene-Early Holocene Transition: Santa Marta's Shelter, Chiapas, Mexico

    Directory of Open Access Journals (Sweden)

    Patricia Pérez Martínez

    2018-03-01

    Full Text Available Los análisis funcionales vieron la luz en la década de los sesenta con la publicación de la Tecnología Prehistórica de Semenov (1964, desde entonces se ha realizado un gran número de investigaciones para dilucidar actividades de subsistencia a partir de la funcionalidad de los artefactos. Desafortunadamente, en México pocos han sido los trabajos enfocados a este tipo de análisis (Elizalde y Mandujano 2000; Lewenstein 1990; Mirambell 1964. En el presente estudio se analizaron microscópicamente 36 artefactos líticos con el objetivo de caracterizar los micropulidos e inferir la funcionalidad de estos conjuntos asociados a grupos cazadores-recolectores procedentes de contextos de la transición Pleistoceno-Holoceno (13130-12671 cal. AP. ENGLISH: Use-wear studies began in the 1960s with Semenov’s publication entitled Prehistoric Technology (1964. Since then, a great number of investigations have been carried out to elucidate subsistence activities based on the functionality of the artifacts. Unfortunately, in Mexico few studies have focused on this type of analysis (Elizalde & Mandujano 2000; Lewenstein 1990; Mirambell 1964. In the present study, 36 lithic artifacts associated with hunter-gatherer groups from Pleistocene-Holocene transition contexts (13130–12671 cal. AP were analyzed microscopically with the aim of characterizing micropolishes and inferring functionality.

  9. The Great Warming Brian Fagan

    Science.gov (United States)

    Fagan, B. M.

    2010-12-01

    The Great Warming is a journey back to the world of a thousand years ago, to the Medieval Warm Period. Five centuries of irregular warming from 800 to 1250 had beneficial effects in Europe and the North Atlantic, but brought prolonged droughts to much of the Americas and lands affected by the South Asian monsoon. The book describes these impacts of warming on medieval European societies, as well as the Norse and the Inuit of the far north, then analyzes the impact of harsh, lengthy droughts on hunting societies in western North America and the Ancestral Pueblo farmers of Chaco Canyon, New Mexico. These peoples reacted to drought by relocating entire communities. The Maya civilization was much more vulnerable that small-scale hunter-gatherer societies and subsistence farmers in North America. Maya rulers created huge water storage facilities, but their civilization partially collapsed under the stress of repeated multiyear droughts, while the Chimu lords of coastal Peru adapted with sophisticated irrigation works. The climatic villain was prolonged, cool La Niñalike conditions in the Pacific, which caused droughts from Venezuela to East Asia, and as far west as East Africa. The Great Warming argues that the warm centuries brought savage drought to much of humanity, from China to Peru. It also argues that drought is one of the most dangerous elements in today’s humanly created global warming, often ignored by preoccupied commentators, but with the potential to cause over a billion people to starve. Finally, I use the book to discuss the issues and problems of communicating multidisciplinary science to the general public.

  10. 20th century climate warming and tree-limit rise in the southern Scandes of Sweden.

    Science.gov (United States)

    Kullman, L

    2001-03-01

    Climate warming by ca. 0.8 degree C between the late-19th and late-20th century, although with some fluctuations, has forced multispecies elevational tree-limit advance by > 100 m for the principal tree species in the Swedish part of the Scandinavian mountain range. Predominantly, these processes imply growth in height of old-established individuals and less frequently upslope migration of new individuals. After a slight retardation during some cooler decades after 1940, a new active phase of tree-limit advance has occurred with a series of exceptionally mild winters and some warm summers during the 1990s. The magnitude of total 20th century tree-limit rise varies with topoclimate and is mainly confined to wind-sheltered and snow-rich segments of the landscape. Thickening of birch tree stands in the "advance belt" has profoundly altered the general character of the subalpine/low alpine landscape and provides a positive feedback loop for further progressive change and resilience to short-term cooling episodes. All upslope tree-limit shifts and associated landscape transformations during the 20th century have occurred without appreciable time lags, which constitutes knowledge fundamental to the generation of realistic models concerning vegetation responses to potential future warming. The new and elevated pine tree-limit may be the highest during the past 4000 14C years. Thus, it is tentatively inferred that the 20th century climate is unusually warm in a late-Holocene perspective.

  11. Active Movement Warm-Up Routines

    Science.gov (United States)

    Walter, Teri; Quint, Ashleigh; Fischer, Kim; Kiger, Joy

    2011-01-01

    This article presents warm-ups that are designed to physiologically and psychologically prepare students for vigorous physical activity. An active movement warm-up routine is made up of three parts: (1) active warm-up movement exercises, (2) general preparation, and (3) the energy system. These warm-up routines can be used with all grade levels…

  12. Holocene Glacier Fluctuations in the Peruvian Andes Indicate Northern Climate Linkages

    Science.gov (United States)

    Licciardi, Joseph M.; Schaefer, Joerg M.; Taggart, Jean R.; Lund, David C.

    2009-09-01

    The role of the tropics in triggering, transmitting, and amplifying interhemispheric climate signals remains a key debate in paleoclimatology. Tropical glacier fluctuations provide important insight on regional paleoclimatic trends and forcings, but robust chronologies are scarce. Here, we report precise moraine ages from the Cordillera Vilcabamba (13°20‧S) of southern Peru that indicate prominent glacial events and associated climatic shifts in the outer tropics during the early Holocene and late in the “Little Ice Age” period. Our glacier chronologies differ from the New Zealand record but are broadly correlative with well-dated glacial records in Europe, suggesting climate linkages between the tropics and the North Atlantic region.

  13. Mid-Holocene Climate and Culture Change in the Atacama Desert, Northern Chile

    Science.gov (United States)

    Grosjean, Martin; Núñez, Lautaro; Cartajena, Isabel; Messerli, Bruno

    1997-09-01

    Twenty archaeological campsites intercalated between more than 30 debris flows caused by heavy rainfall events between 6200 and 3100 14C yr B.P. have recently been discovered at Quebrada Puripica in the Atacama Desert of northern Chile. This record provides detailed information about extreme, short-lived climatic events during the hyperarid mid-Holocene period. For the first time, we found evidence of continuous human occupation in this area, filling the regional hiatus in the Atacama basin ("Silencio Arqueologico") between 8000 and 4800 14C yr B.P. The transformation of Early Archaic hunters into the complex Late Archaic cultural tradition was an adaptive process. During this time, the site was a local ecological refuge with abundant resources in a generally hostile environment.

  14. How warm days increase belief in global warming

    Science.gov (United States)

    Zaval, Lisa; Keenan, Elizabeth A.; Johnson, Eric J.; Weber, Elke U.

    2014-02-01

    Climate change judgements can depend on whether today seems warmer or colder than usual, termed the local warming effect. Although previous research has demonstrated that this effect occurs, studies have yet to explain why or how temperature abnormalities influence global warming attitudes. A better understanding of the underlying psychology of this effect can help explain the public's reaction to climate change and inform approaches used to communicate the phenomenon. Across five studies, we find evidence of attribute substitution, whereby individuals use less relevant but available information (for example, today's temperature) in place of more diagnostic but less accessible information (for example, global climate change patterns) when making judgements. Moreover, we rule out alternative hypotheses involving climate change labelling and lay mental models. Ultimately, we show that present temperature abnormalities are given undue weight and lead to an overestimation of the frequency of similar past events, thereby increasing belief in and concern for global warming.

  15. Substrate potential of last interglacial to Holocene permafrost organic matter for future microbial greenhouse gas production

    Science.gov (United States)

    Stapel, Janina G.; Schwamborn, Georg; Schirrmeister, Lutz; Horsfield, Brian; Mangelsdorf, Kai

    2018-04-01

    In this study the organic matter (OM) in several permafrost cores from Bol'shoy Lyakhovsky Island in NE Siberia was investigated. In the context of the observed global warming the aim was to evaluate the potential of freeze-locked OM from different depositional ages to act as a substrate provider for microbial production of greenhouse gases from thawing permafrost. To assess this potential, the concentrations of free and bound acetate, which form an appropriate substrate for methanogenesis, were determined. The largest free-acetate (in pore water) and bound-acetate (organic-matrix-linked) substrate pools were present in interstadial marine isotope stage (MIS) 3 and stadial MIS 4 Yedoma permafrost deposits. In contrast, deposits from the last interglacial MIS 5e (Eemian) contained only a small pool of substrates. The Holocene (MIS 1) deposits revealed a significant bound-acetate pool, representing a future substrate potential upon release during OM degradation. Additionally, pyrolysis experiments on the OM allocated an increased aliphatic character to the MIS 3 and 4 Late Pleistocene deposits, which might indicate less decomposed and presumably more easily degradable OM. Biomarkers for past microbial communities, including those for methanogenic archaea, also showed the highest abundance during MIS 3 and 4, which indicated OM-stimulated microbial degradation and presumably greenhouse gas production during time of deposition. On a broader perspective, Arctic warming will increase and deepen permafrost thaw and favor substrate availability from older freeze-locked permafrost deposits. Thus, the Yedoma deposits especially showed a high potential for providing substrates relevant for microbial greenhouse gas production.

  16. 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

  17. Feedback process responsible for the suppression of ENSO activity during the mid-Holocene

    Science.gov (United States)

    An, Soon-Il; Bong, Hayoung

    2018-05-01

    Using the output of 12 models from the Paleoclimate Modeling Intercomparison Project Phase 3, we investigate the feedback process responsible for changes in El Niño-Southern Oscillation activity during the mid-Holocene based on a linear stability index (Bjerknes stability index; BJ index) analysis. The multi-model ensemble mean (MME) variance of the Niño-3.4 index (sea surface temperature anomalies averaged over 5°S-5°N, 170°-120°W) simulated for 6000 years ago (6 kya) was 13% lower than that for the pre-industrial era (0 kya), while changes in the MME BJ index were negligible. This is due to a balance between enhanced damping by anomalous thermal advection by mean currents (MA) and enhanced positive thermocline feedback (TH). Seven of the models show that MME variance of the Niño-3.4 and BJ indexes for the 6 kya run is 21 and 70% lower, respectively, than the 0 kya run. However, two models show the opposite change. Interestingly, MA in both model groups increases, especially due to the mean meridional current associated with enhanced trade winds, indicating a robust mechanism. The opposite tendency between the two groups is mainly due to large TH in the second group 6 kya, as a result of enhanced air-sea coupling and strongly reduced ocean stratification due to subsurface warming, which led to increased sensitivity of the zonal thermocline contrast to surface zonal wind stress.

  18. Middle Holocene marine flooding and human response in the south Yangtze coastal plain, East China

    Science.gov (United States)

    Wang, Zhanghua; Ryves, David B.; Lei, Shao; Nian, Xiaomei; Lv, Ye; Tang, Liang; Wang, Long; Wang, Jiehua; Chen, Jie

    2018-05-01

    Coastal flooding catastrophes have affected human societies on coastal plains around the world on several occasions in the past, and are threatening 21st century societies under global warming and sea-level rise. However, the role of coastal flooding in the interruption of the Neolithic Liangzhu culture in the lower Yangtze valley, East China coast has been long contested. In this study, we used a well-dated Neolithic site (the Yushan site) close to the present coastline to demonstrate a marine drowning event at the terminal stage of the Liangzhu culture and discuss its linkage to relative sea-level rise. We analysed sedimentology, chronology, organic elemental composition, diatoms and dinoflagellate cysts for several typical profiles at the Yushan site. The field and sedimentary data provided clear evidence of a palaeo-typhoon event that overwhelmed the Yushan site at ∼2560 BCE, which heralded a period of marine inundation and ecological deterioration at the site. We also infer an acceleration in sea-level rise at 2560-2440 BCE from the sedimentary records at Yushan, which explains the widespread signatures of coastal flooding across the south Yangtze coastal plain at that time. The timing of this mid-Holocene coastal flooding coincided with the sudden disappearance of the advanced and widespread Liangzhu culture along the lower Yangtze valley. We infer that extreme events and flooding accompanying accelerated sea-level rise were major causes of vulnerability for prehistoric coastal societies.

  19. Peranan Environmental Accounting Terhadap Global Warming

    OpenAIRE

    Martusa, Riki

    2009-01-01

    This article explores about is global warming. The distortion of nature causes global warming. Industrial sector is one of global warming incurred. Some nations create a group to cope this matter. They try to reduce carbon emission as one of global warming causes by controlling industrial carbon emission through financial reporting. This article explores normatively roles of environmental accounting in cope with global warming.  

  20. Holocene palaeoclimatol trends from palaeoflood analysis

    Science.gov (United States)

    Smith, A. M.

    1992-03-01

    Global correlations of time periods characterised by large floods are noted from northern and southern hemisphere rivers. A late 19th century flood period is recognised from the Mississippi (and some of the southwestern Rivers of the USA), the River Dee (Scotland) and the Orange River (South Africa). The period of the Little Ice Age can be clearly recognised from the flood record of several rivers and some indicate a double pulse (AD 900-1200; AD 1300-1600) which straddles the Medieval Warm Epoch. Although data becomes less reliable and telescoped with time the global flood record appears to show further flood periods between 3000-1800 yr B.P., 4000-5000 yr B.P., possibly 7000-9000 yr B.P. and it is likely that the Younger Dryas was also a flood period. The flood periods appear to coincide with cold and wet palaeoclimates. This work recommends that this research be continued and that a palaeoflood research data base be set up.

  1. Postglacial development of the eastern Gulf of Finland: from Pleistocene glacial lake basins to Holocene lagoon systems

    Science.gov (United States)

    Ryabchuk, Daria; Sergeev, Alexander; Kotilainen, Aarno; Hyttinen, Outi; Grigoriev, Andrey; Gerasimov, Dmitry; Anisimov, Mikhail; Gusentsova, Tatiana; Zhamoida, Vladimir; Amantov, Aleksey; Budanov, Leonid

    2016-04-01

    of the reported project. Results of archeological studies helped to reconstruct paleoenvironment of the Holocene coastal zone and to date the "barren" geological formations, e.g. coastal accretion bodies. On the other hand, based on predictive geological and geomorphological models of the coastal systems formation, during archeological expeditions several new sites of Neolithic - Early Metal Epoch were found (Sosnovaya Gora-1, Kuzemkino 2-6). Research was supported by RFBR projects 13-06-00548, 14-05-91763, 15-05-08169, and 15-06-05548, and Academy of Finland CISU project.

  2. Late Glacial-Holocene Pollen-Based Vegetation History from Pass Lake, Prince of Wales Island, Southeastern Alaska

    Science.gov (United States)

    Ager, Thomas A.; Rosenbaum, Joseph G.

    2009-01-01

    A radiocarbon-dated history of vegetation development since late Wisconsin deglaciation has been reconstructed from pollen evidence preserved in a sediment core from Pass Lake on Prince of Wales Island, southeastern Alaska. The shallow lake is in the south-central part of the island and occupies a low pass that was filled by glacial ice of local origin during the late Wisconsin glaciation. The oldest pollen assemblages indicate that pine woodland (Pinus contorta) had developed in the area by ~13,715 cal yr B.P. An abrupt decline in the pine population, coinciding with expansion of alder (Alnus) and ferns (mostly Polypodiaceae) began ~12,875 yr B.P., and may have been a response to colder, drier climates during the Younger Dryas climatic interval. Mountain hemlock (Tsuga mertensiana) began to colonize central Prince of Wales Island by ~11,920 yr B.P. and was soon followed by Sitka spruce (Picea sitchensis). Pollen of western hemlock (Tsuga heterophylla) began to appear in Pass Lake sediments soon after 11,200 yr B.P. The abundance of western hemlock pollen in the Pass Lake core during most of the Holocene appears to be the result of wind transport from trees growing at lower altitudes on the island. The late Holocene pollen record from Pass Lake is incomplete because of one or more unconformities, but the available record suggests that a vegetation change occurred during the late Holocene. Increases in pollen percentages of pine, cedar (probably yellow cedar, Chamaecyparis nootkatensis), and heaths (Ericales) suggest an expansion of muskeg vegetation occurred in the area during the late Holocene. This vegetation change may be related to the onset of cooler, wetter climates that began as early as ~3,774 yr B.P. in the region. This vegetation history provides the first radiocarbon-dated Late Glacial-Holocene terrestrial paleoecological framework for Prince of Wales Island. An analysis of magnetic properties of core sediments from Pass Lake suggests that unconformities

  3. Pollen-based reconstruction of Holocene vegetation and climate in southern Italy: the case of Lago Trifoglietti

    Directory of Open Access Journals (Sweden)

    S. Joannin

    2012-12-01

    Full Text Available A high-resolution pollen record from Lago Trifoglietti in Calabria (southern Italy provides new insights into the paleoenvironmental and palaeoclimatic changes which characterise the Holocene period in the southern Italy. The chronology is based on 11 AMS radiocarbon dates from terrestrial organic material. The Holocene history of the vegetation cover shows the persistence of an important and relatively stable Fagus forest present over that entire period, offering a rare example of a beech woodstand able to withstand climate changes for more than 11 000 yr. Probably in relation with early Holocene dry climate conditions which affected southern Italy, the Trifoglietti pollen record supports a southward delay in thermophyllous forest expansion dated to ca. 13 500 cal BP at Monticchio, ca. 11 000 cal BP at Trifoglietti, and finally ca. 9800 cal BP in Sicily. Regarding the human impact history, the Trifoglietti pollen record shows only poor imprints of agricultural activities and anthopogenic indicators, apart from those indicating pastoralism activities beneath forest cover. The selective exploitation of Abies appears to have been the strongest human impact on the Trifoglietti surroundings. On the basis of (1 a specific ratio between hygrophilous and terrestrial taxa, and (2 the Modern Analogue Technique, the pollen data collected at Lago Trifoglietti led to the establishment of two palaeoclimatic records tracing changes in (1 lake depth and (2 annual precipitation. On a millennial scale, these records give evidence of increasing moisture from ca. 11 000 to ca. 9400 cal BP and maximum humidity from ca. 9400 to ca. 6200 cal BP, prior to a general trend towards the drier climate conditions that have prevailed up to the present. In addition, several successive centennial-scale oscillations appear to have punctuated the entire Holocene. The identification of a cold dry event around 11 300 cal BP, responsible for a marked decline in

  4. The politics of global warming

    International Nuclear Information System (INIS)

    Moss, N.

    1991-01-01

    The probable warming of the world over the next few decades due to human activity presents a unique threat. The threat of global warming has been brought about by the activities of the entire human race, and only action by a large part of the human race can slow down the process or halt it. Other unwanted effects of industrial activity are trans-national, and require international agreements to regulate them, most obviously radioactivity from nuclear power accidents, acid rain and river pollution; but climatic change, unlike these, is global. International negotiations are going on now to deal with the problem of global warming, mostly by reducing the emission of gases that contribute to it. These are preliminary, yet already different perceptions and conflicting interests are emerging. The aim of the present negotiations is a convention for the UN Conference on Environment and Development (UNCED) to be held in June 1992, the so-called ''Earth Summit''. (author)

  5. Holocene volcanic geology, volcanic hazard, and risk on Taveuni, Fiji

    International Nuclear Information System (INIS)

    Cronin, S.J.; Neall, V.E.

    2001-01-01

    The Holocene volcanic geology of Taveuni has been mapped in order to produce a volcanic hazard and risk assessment for the island. Taveuni is the third-largest island of the Fiji group and home to 14,500 people. At least cubic km 2.7 of olivine-alkali-basalt magma was erupted from over 100 events throughout the Holocene. Vents are concentrated along a northeast-striking rift zone that is parallel to other regional structural trends. There is an overall trend of younging southward along the rift. Holocene lavas and tephras are grouped within six newly defined eruptive periods, established on a basis of radiocarbon dating. Within these periods, 14 tephra layers, useful as local marker horizons, are recognised. At least 58% of Holocene eruptions produced lava flows, while almost all produced some tephra. Individual eruption event volumes ranged between 0.001 and cubic km 0.20 (dense rock equivalent). Many eruptions involved at least some phases of phreatic and/or phreato-magmatic activity, although dominant hydrovolcanic activity was limited to only a few events. A volcanic hazard map is presented, based on the Holocene geology map and statistical analyses of eruption recurrence. The highest levels of ground-based and near-vent hazards are concentrated along the southern portion of the island's rift axis, with the paths of initial lava flows predicted from present topography. Tephra fall hazards are based on eruption parameters interpreted from mapped Holocene tephra layers. Hawaiian explosive-style eruptions appear to be a dominant eruptive process, with prevailing low-level (<3 km) southeasterly winds dispersing most tephra to the northwestern quadrant. Vulnerable elements (population centres, infrastructure, and economy) on Taveuni have been considered in deriving a volcanic risk assessment for the island. A number of infrastructural and subdivision developments are either under way or planned for the island, driven by its highly fertile soils and availability of

  6. Efficiency, sustainability and global warming

    International Nuclear Information System (INIS)

    Woodward, Richard T.; Bishop, Richard C.

    1995-01-01

    Economic analyses of global warming have typically been grounded in the theory of economic efficiency. Such analyses may be inappropriate because many of the underlying concerns about climate change are rooted not in efficiency, but in the intergenerational allocation of economic endowments. A simple economic model is developed which demonstrates that an efficient economy is not necessarily a sustainable economy. This result leads directly to questions about the policy relevance of several economic studies of the issue. We then consider policy alternatives to address global warming in the context of economies with the dual objectives of efficiency and sustainability, with particular attention to carbon-based taxes

  7. Global Warming: Physics and Facts

    International Nuclear Information System (INIS)

    Levi, B.G.; Hafemeister, D.; Scribner, R.

    1992-01-01

    This report contains papers on: A tutorial on global atmospheric energetics and the greenhouse effect; global climate models: what and how; co