Sample records for holocene climate derived

  1. Late holocene climate derived from vegetation history and plant cellulose stable isotope records from the Great Basin of western North America

    Wigand, P.E.; Hemphill, M.L.; Patra, S.M.


    Integration of pollen records, and fossil woodrat midden data recovered from multiple strata of fossil woodrat (Neotoma spp.) dens (middens) in both northern and southern Nevada reveal a detailed paleoclimatic proxy record for the Great Basin during the last 45,000 years in growing detail. Clear, late Holocene climate-linked elevational depressions of plant species' distributions have occurred throughout the Great Basin of up to 200 m below today's and by as much as 1000 m below what they were during the middle Holocene. Horizontal plant range extentions during the Holocene reflecting the final northern most adjustments to Holocene climates range up to several hundred kilometers in the Great Basin. Well documented lags evidenced in the late Holocene response of vegetation communities to increased precipitation indicate reduced effectiveness in the ability of plant communities to assimilate excess precipitation. This resulted in significant runoff that was available for recharge. These responses, although indicating both rapid and dramatic fluctuations of climate for the Holocene, fall far short of the scale of such changes during the late Pleistocene. Extension of these results to Pleistocene woodrat den and pollen data evidence spans lasting several hundred to a thousand or more years during which significantly greater amounts of precipitation would have been available for runnoff or recharge

  2. North Atlantic-Fennoscandian Holocene climate trends and mechanisms

    Sejrup, H.P.; Seppä, H.; McKay, N.; Kaufman, D.S.; Geirsdottir, A.; de Vernal, A.; Renssen, H.; Husum, K.; Jennings, A.; Andrews, J.T.


    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

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

    Eun Hee Lee


    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.

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

    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.

  5. Holocene climate variability and oceanographic changes off western South Africa

    Zhao, Xueqin; Dupont, Lydie; E Meadows, Michael; Schefuß, Enno; Bouimetarhan, Ilham; Wefer, Gerold


    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

  6. Biomarker records of Holocene climate variations in Asian interior

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


    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.

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

    G. Siani


    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

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

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


    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. Patagonian and southern South Atlantic view of Holocene climate

    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.


    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

  10. Holocene environmental changes and climate development in Greenland

    Engels, Stefan; Helmens, Karin


    The primary aim of this report is to give an overview of the Holocene environmental and climatic changes in Greenland and to describe the development of the periglacial environment during the Holocene. Special emphasis is given to the influence of the ice sheet on its surroundings, both in terms of time (with respect to the response of the biosphere to deglaciation or ice sheet proximity) and in space (through the influence of the ice sheet on the regional climate, more specifically on temperature and aridity). Published records are reviewed, and regional trends are summarized. A range of different natural archives is available for such studies, including ice-core data, marine records, and continental sources of information, including peat profiles and lacustrine records. Because of the high number of lakes in all ice-free areas of Greenland, the lacustrine records offer the opportunity to get a spatial overview of past changes in environment and climate as well. This report focuses on (palaeo-) ecological studies, as it is intended to assemble basic information for future studies on adaptation of the biosphere to changes in climate. There is a bias towards pollen- and macro-remain-based reconstructions of past changes, as these dominate performed palaeoecological studies in Greenland; unfortunately, only a limited number of studies exist that include more modern proxies such as diatoms or chironomids (climate-indicators), but where available in the literature, these have been included. The report starts with an introduction where the current climatic and biological zonation of Greenland is discussed together with an overview of the geology of Greenland (on the full geological timescale) in order to put the following sections in perspective. Chapter 2 discusses the ice sheet history of Greenland from the Last Glacial Maximum (LGM) onward where special emphasis is given to the spatial variability of deglaciation at the onset of the Holocene. To enhance the

  11. Holocene environmental changes and climate development in Greenland

    Engels, Stefan; Helmens, Karin (Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden))


    The primary aim of this report is to give an overview of the Holocene environmental and climatic changes in Greenland and to describe the development of the periglacial environment during the Holocene. Special emphasis is given to the influence of the ice sheet on its surroundings, both in terms of time (with respect to the response of the biosphere to deglaciation or ice sheet proximity) and in space (through the influence of the ice sheet on the regional climate, more specifically on temperature and aridity). Published records are reviewed, and regional trends are summarized. A range of different natural archives is available for such studies, including ice-core data, marine records, and continental sources of information, including peat profiles and lacustrine records. Because of the high number of lakes in all ice-free areas of Greenland, the lacustrine records offer the opportunity to get a spatial overview of past changes in environment and climate as well. This report focuses on (palaeo-) ecological studies, as it is intended to assemble basic information for future studies on adaptation of the biosphere to changes in climate. There is a bias towards pollen- and macro-remain-based reconstructions of past changes, as these dominate performed palaeoecological studies in Greenland; unfortunately, only a limited number of studies exist that include more modern proxies such as diatoms or chironomids (climate-indicators), but where available in the literature, these have been included. The report starts with an introduction where the current climatic and biological zonation of Greenland is discussed together with an overview of the geology of Greenland (on the full geological timescale) in order to put the following sections in perspective. Chapter 2 discusses the ice sheet history of Greenland from the Last Glacial Maximum (LGM) onward where special emphasis is given to the spatial variability of deglaciation at the onset of the Holocene. To enhance the

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

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


    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.

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

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

    -50,000 years cal BP. Radiocarbon 51, 1111-1150. Roberts, N., Brayshaw, D., Kuzucuoglu, C., Perez, R., Sadori, L., 2011. The mid-Holocene climatic transition in the Mediterranean: Causes and consequences. The Holocene 21, 3-13. Ruddiman, W.F., Ellis, E...

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

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


    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

  15. Pollen-based reconstruction of Holocene climate variability in the Eifel region evaluated with stable isotopes

    Kühl, Norbert; Moschen, Robert; Wagner, Stefanie


    sediments might strongly react to anthropogenic deforestation, as carbon isotope time series from the adjacent Lake Holzmaar suggest. Reconstructions based on pollen with the pdf-method are robust to the human impact during the last 4000 years, but do not reproduce the fine scale climate variability that can be derived from the stable isotope series (Kühl et al., in press). In contrast, reconstructions on the basis of pollen data show relatively pronounced climate variability (here: January temperature) during the Mid-Holocene, which is known from many other European records. The oxygen isotope time series as available now indicate that at least some of the observed variability indeed reflects climate variability. However, stable carbon isotopes show little concordance. At this stage our results point in the direction that 1) the isotopic composition might reflect a shift in influencing factors during the Holocene, 2) climate trends can robustly be reconstructed with the pdf method and 3) fine scale climate variability can potentially be reconstructed using the pdf-method, given that climate sensitive taxa at their distribution limit are present. The latter two conclusions are of particular importance for the reconstruction of climatic trends and variability of interglacials older than the Holocene, when sites are rare and pollen is often the only suitable proxy in terrestrial records. Kühl, N., Moschen, R., Wagner, S., Brewer, S., Peyron, O., in press. A multiproxy record of Late Holocene natural and anthropogenic environmental change from the Sphagnum peat bog Dürres Maar, Germany: implications for quantitative climate reconstructions based on pollen. J. Quat. Sci., DOI: 10.1002/jqs.1342. Available online. Moschen, R., Kühl, N., Rehberger, I., Lücke, A., 2009. Stable carbon and oxygen isotopes in sub-fossil Sphagnum: Assessment of their applicability for palaeoclimatology. Chemical Geology 259, 262-272.

  16. A Holocene temperature reconstruction from northern New Zealand: a test of North Atlantic Holocene climate patterns as a global template

    van den Bos, Valerie; Rees, Andrew; Newnham, Rewi; Augustinus, Paul


    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

  17. Holocene evolution of the Tabasco delta – Mexico : impact of climate, volcanism and humans

    Nooren, C.A.M.


    This research revealed the impact of climate, volcanism and humans on the late Holocene evolution of a tropical delta in southern Mexico. Palynological, tephrochronological, limnological, geomorphological and sedimentological techniques have been applied to reconstruct the evolution of the

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

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


    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.

  19. New evidence for "far-field" Holocene sea level oscillations and links to global climate records

    Leonard, N. D.; Welsh, K. J.; Clark, T. R.; Feng, Y.-x.; Pandolfi, J. M.; Zhao, J.-x.


    Rising sea level in the coming century is of significant concern, yet predicting relative sea level change in response to eustatic sea level variability is complex. Potential analogues are provided by the recent geological past but, until recently, many sea level reconstructions have been limited to millennial scale interpretations due to age uncertainties and paucity in proxy derived records. Here we present a sea level history for the tectonically stable "far-field" Great Barrier Reef, Australia, derived from 94 high precision uranium-thorium dates of sub-fossil coral microatolls. Our results provide evidence for at least two periods of relative sea level instability during the Holocene. These sea level oscillations are broadly synchronous with Indo-Pacific negative sea surface temperature anomalies, rapid global cooling events and glacial advances. We propose that the pace and magnitude of these oscillations are suggestive of eustatic/thermosteric processes operating in conjunction with regional climatic controls.

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

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


    Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean-atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55{sup o}S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8,000 years based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcan Hudson eruption. Combining bulk organic isotopic ({delta}{sup 13}C and {delta}{sup 15}N) and elemental (C and N) parameters with physical sediment properties allow us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8,000 years. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived precipitation. Increased wind strength and precipitation in the late Holocene drives the Nothofagus forest eastward and enhances run-off and terrigenous inputs to the lake. Superimposed on the long-term trend are a series of abrupt 9 negative departures in C/N ratio, which constrain the presence of seismically-driven mass flow events in the record. We identify an increase in bulk {delta}{sup 13}C between 7,000 and 5,000 cal yr BP that we attribute to enhanced aquatic productivity driven by warmer summer temperatures. The Lago Fagnano {delta}{sup 13}C record shows similarities with Holocene records of sea surface

  1. Funding climate adaptation strategies with climate derivatives

    L. Richard Little


    Full Text Available Climate adaptation requires large capital investments that could be provided not only by traditional sources like governments and banks, but also by derivatives markets. Such markets would allow two parties with different tolerances and expectations about climate risks to transact for their mutual benefit and, in so doing, finance climate adaptation. Here we calculate the price of a derivative called a European put option, based on future sea surface temperature (SST in Tasmania, Australia, with an 18 °C strike threshold. This price represents a quantifiable indicator of climate risk, and forms the basis for aquaculture industries exposed to the risk of higher SST to finance adaptation strategies through the sale of derivative contracts. Such contracts provide a real incentive to parties with different climate outlooks, or risk exposure to take a market assessment of climate change.

  2. Multiproxy records of Holocene climate and glacier variability from sediment cores in the Cordillera Vilcabamba of southern Peru

    Schweinsberg, A. D.; Licciardi, J. M.; Rodbell, D. T.; Stansell, N.; Tapia, P. M.


    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

  3. Reconstructing Holocene climate using a climate model: Model strategy and preliminary results

    Haberkorn, K.; Blender, R.; Lunkeit, F.; Fraedrich, K.


    An Earth system model of intermediate complexity (Planet Simulator; PlaSim) is used to reconstruct Holocene climate based on proxy data. The Planet Simulator is a user friendly general circulation model (GCM) suitable for palaeoclimate research. Its easy handling and the modular structure allow for fast and problem dependent simulations. The spectral model is based on the moist primitive equations conserving momentum, mass, energy and moisture. Besides the atmospheric part, a mixed layer-ocean with sea ice and a land surface with biosphere are included. The present-day climate of PlaSim, based on an AMIP II control-run (T21/10L resolution), shows reasonable agreement with ERA-40 reanalysis data. Combining PlaSim with a socio-technological model (GLUES; DFG priority project INTERDYNAMIK) provides improved knowledge on the shift from hunting-gathering to agropastoral subsistence societies. This is achieved by a data assimilation approach, incorporating proxy time series into PlaSim to initialize palaeoclimate simulations during the Holocene. For this, the following strategy is applied: The sensitivities of the terrestrial PlaSim climate are determined with respect to sea surface temperature (SST) anomalies. Here, the focus is the impact of regionally varying SST both in the tropics and the Northern Hemisphere mid-latitudes. The inverse of these sensitivities is used to determine the SST conditions necessary for the nudging of land and coastal proxy climates. Preliminary results indicate the potential, the uncertainty and the limitations of the method.

  4. Late Holocene vegetation changes in relation with climate fluctuations and human activities in Languedoc (Southern France)

    J. Azuara; N. Combourieu-Nebout; V. Lebreton; F. Mazier; S. D. Müller; L. Dezileau


    Holocene climate fluctuations and human activities since the Neolithic have shaped present-day Mediterranean environments. Separating anthropogenic effects from climatic impacts to reconstruct Mediterranean paleoenvironments over the last millennia remains a challenging issue. High resolution pollen analyses were undertaken on two cores from the Palavasian lagoon system (Hérault, southern France). These records allow reconstruction of vegetation dynamics ove...

  5. Holocene glacier variability: three case studies using an intermediate-complexity climate model

    Weber, S.L.; Oerlemans, J.


    Synthetic glacier length records are generated for the Holocene epoch using a process-based glacier model coupled to the intermediate-complexity climate model ECBilt. The glacier model consists of a massbalance component and an ice-flow component. The climate model is forced by the insolation change

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

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


    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.

  7. Holocene fluctuations in human population demonstrate repeated links to food production and climate.

    Bevan, Andrew; Colledge, Sue; Fuller, Dorian; Fyfe, Ralph; Shennan, Stephen; Stevens, Chris


    We consider the long-term relationship between human demography, food production, and Holocene climate via an archaeological radiocarbon date series of unprecedented sampling density and detail. There is striking consistency in the inferred human population dynamics across different regions of Britain and Ireland during the middle and later Holocene. Major cross-regional population downturns in population coincide with episodes of more abrupt change in North Atlantic climate and witness societal responses in food procurement as visible in directly dated plants and animals, often with moves toward hardier cereals, increased pastoralism, and/or gathered resources. For the Neolithic, this evidence questions existing models of wholly endogenous demographic boom-bust. For the wider Holocene, it demonstrates that climate-related disruptions have been quasi-periodic drivers of societal and subsistence change. Copyright © 2017 the Author(s). Published by PNAS.

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

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


    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

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

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


    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...

  10. Holocene climate variability revealed by oxygen isotope analysis of Sphagnum cellulose from Walton Moss, northern England

    Daley, T. J.; Barber, K. E.; Street-Perrott, F. A.; Loader, N. J.; Marshall, J. D.; Crowley, S. F.; Fisher, E. H.


    Stable isotope analyses of Sphagnum alpha-cellulose, precipitation and bog water from three sites across northwestern Europe (Raheenmore, Ireland, Walton Moss, northern England and Dosenmoor, northern Germany) over a total period of 26 months were used to investigate the nature of the climatic signal recorded by Sphagnum moss. The δ18O values of modern alpha-cellulose tracked precipitation more closely than bog water, with a mean isotopic fractionation factor αcellulose-precipitation of 1.0274 ± 0.001 (1 σ) (≈27‰). Sub-samples of isolated Sphagnum alpha-cellulose were subsequently analysed from core WLM22, Walton Moss, northern England yielding a Sphagnum-specific isotope record spanning the last 4300 years. The palaeo-record, calibrated using the modern data, provides evidence for large amplitude variations in the estimated oxygen isotope composition of precipitation during the mid- to late Holocene. Estimates of palaeotemperature change derived from statistical relationships between modern surface air temperatures and δ18O precipitation values for the British Isles give unrealistically large variation in comparison to proxies from other archives. We conclude that use of such relationships to calibrate mid-latitude palaeo-data must be undertaken with caution. The δ18O record from Sphagnum cellulose was highly correlated with a palaeoecologically-derived index of bog surface wetness (BSW), suggesting a common climatic driver.

  11. Mid-Holocene to Present Climate Transition in Tropical South America

    Turcq, B.; Cordeiro, R.; Sifeddine, A.; Braconnot, P.; Dias, P. S.; Costa, R.; Jorgetti, T.


    The classical illustration of Holocene climate changes in tropical South America is the huge rising of Titicaca lake level from 4400 to 4000 cal BP. Because the Amazon basin is the source of Andean rainfalls we have explored Amazonian data of climate changes during the Holocene to better understand the cause of this abrupt transition. Amazonian data confirm the existence of mid-Holocene dryness: (1) lacustrine level studies show a lower precipitation/evaporation budget than present, with the lowest lake levels between 8500 and 6800 cal BP; (2) although the dominant Holocene vegetation has always been the rainforest in the heart of Amazonia, this forest expanded towards the northwestern and southwestern regions from 6800 to 1550 cal BP, moreover, pioneer elements of the rainforest developed during the mid-Holocene and the best example is those of Cecropia, between 9000 and 5000 cal BP. (3) soil d13C indicates a forest expansion over savannas areas in Roraima (north), Mato Grosso and Rondonia (southwest), during the Holocene. (4) the mid-Holocene (8000- 4000 cal BP) is characterized by repeated occurrences of forest fires, marked by the presence of charcoals in soils and lacustrine sediments. However these different records are not characterized by abrupt transitions at the end of the Middle Holocene in Amazonia. In the Andean records there is a clear north-south shift in the timing of the transition. Analysis of coupled Ocean Atmosphere Model simulations suggest that convection in Amazon basin is directly controlled by insolation leading to an almost linear response of local climate to the global forcing. Differently, in the eastern and south-western regions where the rain is brought by the South American Monsoon, the climate transition appears more abrupt. It may be because the involved climate mechanisms are more complex and depend on Ocean/Atmosphere/Vegetation coupled process (ITCZ position, ZCAS formation, etc.). Tectonic movements or threshold links to

  12. Holocene vegetation and climate history of the northern Bighorn Basin, southern Montana

    Lyford, M.E.; Betancourt, J.L.; Jackson, S.T.


    Records of Holocene vegetation and climate change at low elevations (treeline indicates wetter conditions between 4400 and 2700 14C yr B.P. Increased aridity after 2700 14C yr B.P. initiated expansion of J. osteosperma from the east to west side of the Pryor Mountains. ?? 2002 University of Washington.

  13. Simulation of the Holocene climate evolution in Nothern Africa: the termination of the African Humid Period.

    Renssen, H.; Brovkin, V.; Fichefet, T.; Goosse, H.


    The Holocene climate evolution in Northern Africa is studied in a 9000-yr-long transient simulation with a coupled atmosphere-ocean-vegetation model forced by changes in insolation and atmospheric greenhouse gas concentrations. The model simulates in the monsoonal domains a significant decrease in

  14. A multiple-proxy approach to understanding rapid Holocene climate change in Southeast Greenland

    Davin, S. H.; Bradley, R. S.; Balascio, N. L.; de Wet, G.


    The susceptibility of the Arctic to climate change has made it an excellent workshop for paleoclimatological research. Although there have been previous studies concerning climate variability carried out in the Arctic, there remains a critical dearth of knowledge due the limited number of high-resolution Holocene climate-proxy records available from this region. This gap skews our understanding of observed and predicted climate change, and fuels uncertainty both in the realms of science and policy. This study takes a comprehensive approach to tracking Holocene climate variability in the vicinity of Tasiilaq, Southeast Greenland using a ~5.6 m sediment core from Lower Sermilik Lake. An age-depth model for the core has been established using 8 radiocarbon dates, the oldest of which was taken at 4 m down core and has been been dated to approximately 6.2 kyr BP. The bottom meter of the core below the final radiocarbon date contains a transition from cobbles and coarse sand to organic-rich laminations, indicating the termination of direct glacial influence and therefore likely marking the end of the last glacial period in this region. The remainder of the core is similarly organic-rich, with light-to-dark brown laminations ranging from 0.5 -1 cm in thickness and riddled with turbidites. Using this core in tandem with findings from an on-site assessment of the geomorphic history of the locale we attempt to assess and infer the rapid climatic shifts associated with the Holocene on a sub-centennial scale. Such changes include the termination of the last glacial period, the Mid-Holocene Climatic Optimum, the Neoglacial Period, the Medieval Climatic Optimum, and the Little Ice Age. A multiple proxy approach including magnetic susceptibility, bulk organic geochemistry, elemental profiles acquired by XRF scanning, grain-size, and spectral data will be used to characterize the sediment and infer paleoclimate conditions. Additionally, percent biogenic silica by weight has been

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

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


    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

  16. Late Holocene vegetation changes in relation with climate fluctuations and human activity in Languedoc (southern France)

    Azuara , J; Combourieu-Nebout , N; Lebreton , V; Mazier , F; Müller , S D; Dezileau , L ,


    International audience; Holocene climate fluctuations and human activity since the Neolithic have shaped present-day Mediter-ranean environments. Separating anthropogenic effects from climatic impacts to better understand Mediterranean pale-oenvironmental changes over the last millennia remains a challenging issue. High-resolution pollen analyses were un-dertaken on two cores from the Palavasian lagoon system (Hérault, southern France). These records allow reconstruction of vegetation dynamic...

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

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


    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.

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

    Tingping eOuyang


    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.

  19. Palaeoenvironmental transfer functions in a bayesian framework with application to holocene climate variability in the near east

    Schoelzel, C. [Bonn Univ. (Germany). Meteorologisches Inst.


    Ram data requires the derivation of the posterior distribution given the coexistence of the taxa found in the fossil spectrum. For both models, the prior densities are informative, using the recent climate mean and the largest expected Holocene variation as variance. The results are probabilistic reconstructions of the climate of the Holocene Near East in a Bayesian framework. (orig.)

  20. A review on Holocene climate changes in Indian subcontinent

    Naidu, P.D.

    and terrestrial records document that the climate started shifting from humid to dry arid from 5 ka and reached an arid phase at 3.5 ka. In other tropics of the world also onset of arid climate was documented during the same period. The onset of arid climate at 3...

  1. Quantifying the effects of land use and climate on Holocene vegetation in Europe

    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


    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

  2. Millennial- to century-scale variability in Gulf of Mexico Holocene climate records

    Poore, R.Z.; Dowsett, H.J.; Verardo, S.; Quinn, T.M.


    Proxy records from two piston cores in the Gulf of Mexico (GOM) provide a detailed (50-100 year resolution) record of climate variability over the last 14,000 years. Long-term (millennial-scale) trends and changes are related to the transition from glacial to interglacial conditions and movement of the average position of the Intertropical Convergence Zone (ITCZ) related to orbital forcing. The ??18O of the surface-dwelling planktic foraminifer Globigerinoides ruber show negative excursions between 14 and 10.2 ka (radiocarbon years) that reflect influx of meltwater into the western GOM during melting of the Laurentide Ice Sheet. The relative abundance of the planktic foraminifer Globigerinoides sacculifer is related to transport of Caribbean water into the GOM. Maximum transport of Caribbean surface waters and moisture into the GOM associated with a northward migration of the average position of the ITCZ occurs between about 6.5 and 4.5 ka. In addition, abundance variations of G. sacculifer show century-scale variability throughout most of the Holocene. The GOM record is consistent with records from other areas, suggesting that century-scale variability is a pervasive feature of Holocene climate. The frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability, indicating that at least some of the century-scale climate variability during the Holocene is due to external (solar) forcing.

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

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


    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. A Pseudoproxy-Ensemble Study of Late-Holocene Climate Field Reconstructions Using CCA

    Amrhein, D. E.; Smerdon, J. E.


    Recent evaluations of late-Holocene multi-proxy reconstruction methods have used pseudoproxy experiments derived from millennial General Circulation Model (GCM) integrations. These experiments assess the performance of a reconstruction technique by comparing pseudoproxy reconstructions, which use restricted subsets of model data, against complete GCM data fields. Most previous studies have tested methodologies using different pseudoproxy noise levels, but only with single realizations for each noise classification. A more robust evaluation of performance is to create an ensemble of pseudoproxy networks with distinct sets of noise realizations and a corresponding reconstruction ensemble that can be evaluated for consistency and sensitivity to random error. This work investigates canonical correlation analysis (CCA) as a late-Holocene climate field reconstruction (CFR) technique using ensembles of pseudoproxy experiments derived from the NCAR CSM 1.4 millennial integration. Three 200-member reconstruction ensembles are computed using pseudoproxies with signal-to-noise ratios (by standard deviation) of 1, 0.5, and 0.25 and locations that approximate the spatial distribution of real-world multiproxy networks. An important component of these ensemble calculations is the independent optimization of the three CCA truncation parameters for each ensemble member. This task is accomplished using an inexpensive discrete optimization algorithm that minimizes both RMS error in the calibration interval and the number of free parameters in the reconstruction model to avoid artificial skill. Within this framework, CCA is investigated for its sensitivity to the level of noise in the pseudoproxy network and the spatial distribution of the network. Warm biases, variance losses, and validation-interval error increase with noise level and vary spatially within the reconstructed fields. Reconstruction skill, measured as grid-point correlations during the validation interval, is lowest in

  5. Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates

    Lambert, Fabrice; Tagliabue, Alessandro; Shaffer, Gary; Lamy, Frank; Winckler, Gisela; Farias, Laura; Gallardo, Laura; De Pol-Holz, Ricardo


    Mineral dust aerosols play a major role in present and past climates. To date, we rely on climate models for estimates of dust fluxes to calculate the impact of airborne micronutrients on biogeochemical cycles. Here we provide a new global dust flux data set for Holocene and Last Glacial Maximum (LGM) conditions based on observational data. A comparison with dust flux simulations highlights regional differences between observations and models. By forcing a biogeochemical model with our new data set and using this model's results to guide a millennial-scale Earth System Model simulation, we calculate the impact of enhanced glacial oceanic iron deposition on the LGM-Holocene carbon cycle. On centennial timescales, the higher LGM dust deposition results in a weak reduction of pump. This is followed by a further ~10 ppm reduction over millennial timescales due to greater carbon burial and carbonate compensation.

  6. Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models

    Wang, Yi; Notaro, Michael; Liu, Zhengyu; Gallimore, Robert; Levis, Samuel; Kutzbach, John E.


    Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte- Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.

  7. Holocene vegetation and climate change on the Haanja heights, South-East Estonia

    Saarse, Leili; Rajamaee, Raivo


    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)

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

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


    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

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

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


    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.

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

    Mayle, Francis E; Power, Mitchell J


    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.

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

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


    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.

  12. Climate fluctuations during the Holocene in NW Iberia: High and low latitude linkages

    Pena, L. D.; Francés, G.; Diz, P.; Esparza, M.; Grimalt, J. O.; Nombela, M. A.; Alejo, I.


    High resolution benthic foraminiferal stable isotopes (δ 18O, δ 13C) and molecular biomarkers in the sediments are used here to infer rapid climatic changes for the last 8200 years in the Ría de Muros (NW Iberian Margin). Benthic foraminiferal δ 18O and δ 13C potentially register migrations in the position of the hydrographic front formed between two different intermediate water masses: Eastern North Atlantic Central Water of subpolar origin (ENACW sp) and subtropical origin (ENACW st). The molecular biomarkers in the sediment show a strong coupling between continental organic matter inputs and negative δ 13C values in benthic foraminifera. The rapid centennial and millennial events registered in these records have been compared with two well known North Atlantic Holocene records from the subtropical Atlantic sea surface temperatures (SST) anomalies off Cape Blanc, NW Africa and the subpolar Atlantic (Hematite Stained Grains percentage, subpolar North Atlantic). Comparison supports a strong link between high- and low-latitude climatic perturbations at centennial-millennial time scales during the Holocene. Spectral analyses also points to a pole-to-equator propagation of the so-called 1500 yr cycles. Our results demonstrate that during the Holocene, the NW Iberian Margin has undergone a series of rapid events which are likely triggered at high latitudes in the North Atlantic and are rapidly propagated towards lower latitudes. Conceivably, the propagation of these rapid climatic changes involves a shift in atmospheric and oceanic circulatory systems.

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

    Hall, Stephen A.; Peterson, John A.


    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

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

    Grossman, Michael J.


    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.

  15. Cultural responses to climate change during the late Holocene.

    deMenocal, P B


    Modern complex societies exhibit marked resilience to interannual-to- decadal droughts, but cultural responses to multidecadal-to-multicentury droughts can only be addressed by integrating detailed archaeological and paleoclimatic records. Four case studies drawn from New and Old World civilizations document societal responses to prolonged drought, including population dislocations, urban abandonment, and state collapse. Further study of past cultural adaptations to persistent climate change may provide valuable perspective on possible responses of modern societies to future climate change.

  16. Tracking climate variability in the western Mediterranean during the Late Holocene: a multiproxy approach

    V. Nieto-Moreno


    Full Text Available Climate variability in the western Mediterranean is reconstructed for the last 4000 yr using marine sediments recovered in the west Algerian-Balearic Basin, near the Alboran Basin. Fluctuations in chemical and mineralogical sediment composition as well as grain size distribution are linked to fluvial-eolian oscillations, changes in redox conditions and paleocurrent intensity. Multivariate analyses allowed us to characterize three main groups of geochemical and mineralogical proxies determining the sedimentary record of this region. These three statistical groups were applied to reconstruct paleoclimate conditions at high resolution during the Late Holocene. An increase in riverine input (fluvial-derived elements – Rb/Al, Ba/Al, REE/Al, Si/Al, Ti/Al, Mg/Al and K/Al ratios, and a decrease in Saharan eolian input (Zr/Al ratio depict the Roman Humid Period and the Little Ice Age, while drier environmental conditions are recognized during the Late Bronze Age-Iron Age, the Dark Ages and the Medieval Climate Anomaly. Additionally, faster bottom currents and more energetic hydrodynamic conditions for the former periods are evidenced by enhanced sortable silt (10-63 μm and quartz content, and by better oxygenated bottom waters – as reflected by decreasing redox-sensitive elements (V/Al, Cr/Al, Ni/Al and Zn/Al ratios. In contrast, opposite paleoceanographic conditions are distinguished during the latter periods, i.e. the Late Bronze Age-Iron Age, the Dark Ages and the Medieval Climate Anomaly. Although no Ba excess was registered, other paleoproductivity indicators (total organic carbon content, Br/Al ratio, and organometallic ligands such as U and Cu display the highest values during the Roman Humid Period, and together with increasing preservation of organic matter, this period exhibits by far the most intense productivity of the last 4000 yr. Fluctuations in detrital input into the basin as the main process managing deposition, reflected by the

  17. Paleoclimate from ice cores : abrupt climate change and the prolonged Holocene

    White, J.W.C.


    Ice cores provide valuable information about the Earth's past climates and past environments. They can also help in predicting future climates and the nature of climate change. Recent findings in ice cores have shown large and abrupt climate changes in the past. This paper addressed abrupt climate changes and the peculiar nature of the Holocene. An abrupt climate change is a shift of 5 degrees C in mean annual temperature in less than 50 years. This is considered to be the most threatening aspect of potential future climate change since it leaves very little time for adaptation by humans or any other part of the Earth's ecosystem. This paper also discussed the arrival of the next glacial period. In the past 50 years, scientists have recognized the importance of the Earth's orbit around the sun in pacing the occurrence of large ice sheets. The timing of orbital forcing suggests that the Earth is overdue for the next major glaciation. The reason for this anomaly was discussed. Abrupt climate shifts seem to be caused by mode changes in sensitive points in the climate system, such as the North Atlantic Deep Water Formation and its impact on sea ice cover in the North Atlantic. These changes have been observed in ice cores in Greenland but they are not restricted to Greenland. Evidence from Antarctic ice cores suggest that abrupt climate change may also occur in the Southern Hemisphere. The Vostok ice core in Antarctica indicates that the 11,000 year long interglacial period that we are in right now is longer than the previous four interglacial periods. The Holocene epoch is unique because both methane and carbon dioxide rise in the last 6,000 years, an atypical response from these greenhouse gases during an interglacial period. It was suggested that the rise in methane can be attributed to human activities. 13 refs., 2 figs

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

    J. Otto


    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%.

  19. Late Holocene vegetation changes in relation with climate fluctuations and human activities in Languedoc (Southern France)

    Azuara, J.; Combourieu-Nebout, N.; Lebreton, V.; Mazier, F.; Müller, S. D.; Dezileau, L.


    Holocene climate fluctuations and human activities since the Neolithic have shaped present-day Mediterranean environments. Separating anthropogenic effects from climatic impacts to reconstruct Mediterranean paleoenvironments over the last millennia remains a challenging issue. High resolution pollen analyses were undertaken on two cores from the Palavasian lagoon system (Hérault, southern France). These records allow reconstruction of vegetation dynamics over the last 4500 years. Results are compared with climatic, historical and archeological archives. A long-term aridification trend is highlighted during the Late Holocene and three superimposed arid events are recorded at 4600-4300, 2800-2400 and 1300-1100 cal BP. These periods of climatic instability coincide in time with the rapid climatic events depicted in the Atlantic Ocean (Bond et al., 2001). From the Bronze Age (4000 cal BP) to the end of the Iron Age (around 2000 cal BP), the spread of evergreen taxa and loss of forest cover result from anthropogenic impact. The Antiquity is characterized by a major reforestation event related to the concentration of rural activities and populations in coastal plains leading to forest recovery in the mountains. A major regional deforestation occurred at the beginning of the High Middle Ages. Around 1000 cal BP, forest cover is minimal while cover of olive, chestnut and walnut expands in relation to increasing human influence. The present day vegetation dominated by Mediterranean shrubland and pines has been in existence since the beginning of the 20th century.

  20. Late Holocene vegetation changes in relation with climate fluctuations and human activity in Languedoc (southern France)

    Azuara, J.; Combourieu-Nebout, N.; Lebreton, V.; Mazier, F.; Müller, S. D.; Dezileau, L.


    Holocene climate fluctuations and human activity since the Neolithic have shaped present-day Mediterranean environments. Separating anthropogenic effects from climatic impacts to better understand Mediterranean paleoenvironmental changes over the last millennia remains a challenging issue. High-resolution pollen analyses were undertaken on two cores from the Palavasian lagoon system (Hérault, southern France). These records allow reconstruction of vegetation dynamics over the last 4500 years. Results are compared with climatic, historical and archeological archives. A long-term aridification trend is highlighted during the late Holocene, and three superimposed arid events are recorded at 4600-4300, 2800-2400 and 1300-1100 cal BP. These periods of high-frequency climate variability coincide in time with the rapid climatic events observed in the Atlantic Ocean (Bond et al., 2001). From the Bronze Age (4000 cal BP) to the end of the Iron Age (around 2000 cal BP), the spread of sclerophyllous taxa and loss of forest cover result from anthropogenic impact. Classical Antiquity is characterized by a major reforestation event related to the concentration of rural activity and populations in coastal plains leading to forest recovery in the mountains. A major regional deforestation occurred at the beginning of the High Middle Ages. Around 1000 cal BP, forest cover is minimal while the cover of olive, chestnut and walnut expands in relation to increasing human influence. The present-day vegetation dominated by Mediterranean shrubland and pines has been in existence since the beginning of the 20th century.

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

    K. Antonsson


    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.

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

    Novenko, Elena


    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

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

    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


    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

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

    Pellatt, Marlow G.; Mathewes, Rolf W.


    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.

  5. Isotopic chemical weathering behaviour of Pb derived from a high-Alpine Holocene lake-sediment record

    Gutjahr, Marcus; Süfke, Finn; Gilli, Adrian; Anselmetti, Flavio; Glur, Lukas; Eisenhauer, Anton


    Several studies assessing the chemical weathering systematics of Pb isotopes provided evidence for the incongruent release of Pb from source rocks during early stages of chemical weathering, resulting in runoff compositions more radiogenic (higher) than the bulk source-rock composition [e.g. 1]. Deep NW Atlantic seawater Pb isotope records covering the last glacial-interglacial transition further support these findings. Clear excursions towards highly radiogenic Pb isotopic input in the deep NW Atlantic seen during the early Holocene, hence after the large-scale retreat of the Laurentide Ice Sheet in North America, are interpreted to be controlled by preferential release of radiogenic Pb from U- and Th-rich mineral phases during early stages of chemical weathering that are less resistant to chemical dissolution than other rock-forming mineral phases [2-4]. To date, however, no terrestrial Pb isotope record exists that could corroborate the evidence from deep marine sites for efficient late deglacial weathering and washout of radiogenic Pb. We present a high-resolution adsorbed Pb isotope record from a sediment core retrieved from Alpine Lake Grimsel (1908 m.a.s.l.) in Switzerland, consisting of 117 Pb compositions over the past 10 kyr. This high-Alpine study area is ideally located for incipient and prolonged chemical weathering studies. The method used to extract the adsorbed lake Pb isotope signal is identical to previous marine approaches targeting the authigenic Fe-Mn oxyhydroxides fraction within the lake sediments [5, 6]. The Pb isotope compositions are further accompanied by various elemental ratios derived from the same samples that equally trace climatic boundary conditions in the Grimsel Lake area. The Pb isotopic composition recorded in Lake Grimsel is remarkably constant throughout the majority of the Holocene until ˜2.5 ka BP, despite variable sediment composition and -age, and isotopically relatively close to the signature of the granitic source rock


    Joseph H. Hartman


    This literature study investigated methods and areas to deduce climate change and climate patterns, looking for short-term cycle phenomena and the means to interpret them. Many groups are actively engaged in intensive climate-related research. Ongoing research might be (overly) simplified into three categories: (1) historic data on weather that can be used for trend analysis and modeling; (2) detailed geological, biological (subfossil), and analytical (geochemical, radiocarbon, etc.) studies covering the last 10,000 years (about since last glaciation); and (3) geological, paleontological, and analytical (geochemical, radiometric, etc.) studies over millions of years. Of importance is our ultimate ability to join these various lines of inquiry into an effective means of interpretation. At this point, the process of integration is fraught with methodological troubles and misconceptions about what each group can contribute. This project has met its goals to the extent that it provided an opportunity to study resource materials and consider options for future effort toward the goal of understanding the natural climate variation that has shaped our current civilization. A further outcome of this project is a proposed methodology based on ''climate sections'' that provides spatial and temporal correlation within a region. The method would integrate cultural and climate data to establish the climate history of a region with increasing accuracy with progressive study and scientific advancement (e. g., better integration of regional and global models). The goal of this project is to better understand natural climatic variations in the recent past (last 5000 years). The information generated by this work is intended to provide better context within which to examine global climate change. The ongoing project will help to establish a basis upon which to interpret late Holocene short-term climate variability as evidenced in various studies in the northern

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

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


    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.

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

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


    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

  9. Skill and reliability of climate model ensembles at the Last Glacial Maximum and mid-Holocene

    J. C. Hargreaves


    Full Text Available Paleoclimate simulations provide us with an opportunity to critically confront and evaluate the performance of climate models in simulating the response of the climate system to changes in radiative forcing and other boundary conditions. Hargreaves et al. (2011 analysed the reliability of the Paleoclimate Modelling Intercomparison Project, PMIP2 model ensemble with respect to the MARGO sea surface temperature data synthesis (MARGO Project Members, 2009 for the Last Glacial Maximum (LGM, 21 ka BP. Here we extend that work to include a new comprehensive collection of land surface data (Bartlein et al., 2011, and introduce a novel analysis of the predictive skill of the models. We include output from the PMIP3 experiments, from the two models for which suitable data are currently available. We also perform the same analyses for the PMIP2 mid-Holocene (6 ka BP ensembles and available proxy data sets. Our results are predominantly positive for the LGM, suggesting that as well as the global mean change, the models can reproduce the observed pattern of change on the broadest scales, such as the overall land–sea contrast and polar amplification, although the more detailed sub-continental scale patterns of change remains elusive. In contrast, our results for the mid-Holocene are substantially negative, with the models failing to reproduce the observed changes with any degree of skill. One cause of this problem could be that the globally- and annually-averaged forcing anomaly is very weak at the mid-Holocene, and so the results are dominated by the more localised regional patterns in the parts of globe for which data are available. The root cause of the model-data mismatch at these scales is unclear. If the proxy calibration is itself reliable, then representativity error in the data-model comparison, and missing climate feedbacks in the models are other possible sources of error.

  10. Holocene Glacier Fluctuations in the Peruvian Andes Indicate Northern Climate Linkages

    Licciardi, Joseph M.; Schaefer, Joerg M.; Taggart, Jean R.; Lund, David C.


    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.

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

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


    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).

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

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


    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

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

    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


    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

  14. Macrophysical climate models and Holocene hunter-gatherer subsistence shifts in Central Texas, USA

    Mauldin, R. P.; Munoz, C.


    We use stable carbon isotopic values from bone collagen, as well as carbon values from carbonate extracted from bone apatite from 69 prehistoric human skeletal samples to investigate past resource use and climate relationships over the Middle and Late Holocene in Central Texas. Bone samples come from seven archaeological sites and samples date from 6,900 BP to the close of the prehistoric sequence at about 350 BP. Carbon isotopes from these samples suggest four broad dietary trends. From 6,900 through about 3,800 BP, carbon isotopes suggest a gradual increase in the consumption of resources that ultimately use a C3 photosynthetic pathway. A decline in δ13C in both collagen and carbonate values follows, suggesting a decrease in C3 resource use through roughly 2,900 BP. A variable, but once again increasing pattern on C3 resource use by prehistoric hunter-gatherers is indicated in bone isotopes through about 1,000 BP. After that date, a decrease in C3 resource dependence, with hints at greater subsistence diversity, is suggested through the close of the sequence at 350 BP. To assess the impact of climate shifts on this isotopic pattern, we developed a series of macrophysical climate models (MCM) for several locations in Central Texas focusing on fall, winter, and early spring precipitation. This fall-spring rainfall should closely determine C3 production. If subsistence shifts are responding to climate-induced changes in resource availability, then the measured hunter-gatherer carbon isotope trends summarized above should pattern with C3 production as monitored by the modeled fall-spring precipitation values. For the Middle Holocene portion of the sequence, the precipitation models suggest increasing C3 production, consistent with increasing C3 dependence shown in the isotopic data. A decline in C3 production between 3,900 and 3,000 BP in the models is also consistent with the isotopic decline at that point. After 3,000 BP, however, the coupling between fall

  15. Megalake Chad impact on climate and vegetation during the late Pliocene and the mid-Holocene

    C. Contoux


    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.

  16. A multi-proxy reconstruction of Holocene climate change from Blessberg Cave, Germany

    Breitenbach, Sebastian F. M.; Plessen, Birgit; Wenz, Sarah; Leonhardt, Jens; Tjallingii, Rik; Scholz, Denis; Jochum, Klaus Peter; Marwan, Norbert


    Although Holocene climate dynamics were relatively stable compared to glacial conditions, climatic changes had significant impact on ecosystems and human society on various timescales (Mayewski et al. 2004, Donges et al. 2015, Tan et al. 2015). Precious few high-resolution records on Holocene temperature and precipitation conditions in Central Europe are available (e.g., von Grafenstein et al. 1999, Fohlmeister et al. 2012). Here we present a speleothem-based reconstruction of past climate dynamics from Blessberg Cave, Thuringia, central Germany. Three calcitic stalagmites were recovered when the cave was discovered during tunneling operations in 2008. Samples BB-1, -2 and -3 were precisely dated by the 230Th/U-method, with errors between 10 and 160 years (2σ). The combined record covers large parts of the Holocene (10 - 0.4 ka BP). δ13C and δ18O were analysed at 100 μm resolution. To gain additional insights in infiltration conditions, Sr/Ca and S/Ca were measured on BB-1 and BB-3 using an Röntgenanalytik Eagle XXL μXRF scanner. Differences to other central European records (e.g., von Grafenstein et al. 1999, Fohlmeister et al. 2012) suggest complex interaction between multiple factors influencing speleothem δ18O in Blessberg Cave. Furthermore, no clear influence of the North Atlantic Oscillation on our proxies is found. However, a link across the N Atlantic realm is indicated by a centennial-scale correlation between Blessberg δ18O values and minerogenic input into lake SS1220 in Greenland over the last 5 ka (Olsen et al. 2012). In addition, recurrence analysis indicates an imprint of Atlantic Bond events on Blessberg δ18O values (Marwan et al. 2014), corroborating the suggested link with high northern latitudes. Larger runoff into the Greenland lake seems to be associated with lower δ18O, higher δ13C and S/Ca ratios, as well as lower Sr/Ca ratios in Blessberg Cave speleothems. This might be linked to lower local temperature and/or changes in

  17. Holocene vegetation and climate changes in the central Mediterranean inferred from a high-resolution marine pollen record (Adriatic Sea

    N. Combourieu-Nebout


    Full Text Available The high-resolution multiproxy study of the Adriatic marine core MD 90-917 provides new insights to reconstruct vegetation and regional climate changes over the southcentral Mediterranean during the Younger Dryas (YD and Holocene. Pollen records show the rapid forest colonization of the Italian and Balkan borderlands and the gradual installation of the Mediterranean association during the Holocene. Quantitative estimates based on pollen data provide Holocene precipitations and temperatures in the Adriatic Sea using a multi-method approach. Clay mineral ratios from the same core reflect the relative contributions of riverine (illite and smectite and eolian (kaolinite contributions to the site, and thus act as an additional proxy with which to evaluate precipitation changes in the Holocene. Vegetation climate reconstructions show the response to the Preboreal oscillation (PBO, most likely driven by changes in temperature and seasonal precipitation, which is linked to increasing river inputs from Adriatic rivers recorded by increase in clay mineral contribution to marine sediments. Pollen-inferred temperature declines during the early–mid Holocene, then increases during the mid–late Holocene, similar to southwestern Mediterranean climatic patterns during the Holocene. Several short vegetation and climatic events appear in the record, indicating the sensitivity of vegetation in the region to millennial-scale variability. Reconstructed summer precipitation shows a regional maximum (170–200 mm between 8000 and 7000 similar to the general pattern across southern Europe. Two important shifts in vegetation occur at 7700 cal yr BP (calendar years before present and between 7500 and 7000 cal yr BP and are correlated with increased river inputs around the Adriatic Basin respectively from the northern (7700 event and from the central Adriatic borderlands (7500–7000 event. During the mid-Holocene, the wet summers lead to permanent moisture all year

  18. Late Holocene climate variability in the southwestern Mediterranean region: an integrated marine and terrestrial geochemical approach

    C. Martín-Puertas


    Full Text Available A combination of marine (Alboran Sea cores, ODP 976 and TTR 300 G and terrestrial (Zoñar Lake, Andalucia, Spain geochemical proxies provides a high-resolution reconstruction of climate variability and human influence in the southwestern Mediterranean region for the last 4000 years at inter-centennial resolution. Proxies respond to changes in precipitation rather than temperature alone. Our combined terrestrial and marine archive documents a succession of dry and wet periods coherent with the North Atlantic climate signal. A dry period occurred prior to 2.7 cal ka BP – synchronously to the global aridity crisis of the third-millennium BC – and during the Medieval Climate Anomaly (1.4–0.7 cal ka BP. Wetter conditions prevailed from 2.7 to 1.4 cal ka BP. Hydrological signatures during the Little Ice Age are highly variable but consistent with more humidity than the Medieval Climate Anomaly. Additionally, Pb anomalies in sediments at the end of the Bronze Age suggest anthropogenic pollution earlier than the Roman Empire development in the Iberian Peninsula. The Late Holocene climate evolution of the in the study area confirms the see-saw pattern between the eastern and western Mediterranean regions and the higher influence of the North Atlantic dynamics in the western Mediterranean.

  19. Decadal to millennial time scale climate variability in the Central Mediterranean during the Holocene: a reconstruction based on geochemical proxies from high resolution sedimentary records

    Goudeau, M.S.


    To assess potential anthropogenic contributions to future climate change it is necessary to understand natural climate variability. This can be achieved by studying climate variability during the Holocene, when similar basic climate boundary conditions persisted as today. During this period climate

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

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


    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...

  1. Holocene alluvial stratigraphy and response to climate change in the Roaring River valley, Front Range, Colorado, USA

    Madole, Richard F.


    Stratigraphic analyses and radiocarbon geochronology of alluvial deposits exposed along the Roaring River, Colorado, lead to three principal conclusions: (1) the opinion that stream channels in the higher parts of the Front Range are relics of the Pleistocene and nonalluvial under the present climate, as argued in a water-rights trial USA v. Colorado, is untenable, (2) beds of clast-supported gravel alternate in vertical succession with beds of fine-grained sediment (sand, mud, and peat) in response to centennial-scale changes in snowmelt-driven peak discharges, and (3) alluvial strata provide information about Holocene climate history that complements the history provided by cirque moraines, periglacial deposits, and paleontological data. Most alluvial strata are of late Holocene age and record, among other things, that: (1) the largest peak flows since the end of the Pleistocene occurred during the late Holocene; (2) the occurrence of a mid- to late Holocene interval (~ 2450-1630(?) cal yr BP) of warmer climate, which is not clearly identified in palynological records; and (3) the Little Ice Age climate seems to have had little impact on stream channels, except perhaps for minor (~ 1 m) incision.

  2. Holocene changes in climate and vegetation in the Ammassalik area, East Greenland, recorded in lake sediments and soil profiles

    Jakobsen, Bjarne Holm; Fredskild, Bent; Pedersen, Jørn Bjarke Torp


    , appears to have experienced the warmest Holocene summer conditions, ice-free seas and limited snow covers. The climate situation seems to have been to a considerable extent based on internal regional meteorological processes and largely without strong and regular cyclonic impacts from lower latitudes...

  3. Holocene Activity of the Enriquillo-Plantain Garden Fault in Lake Enriquillo Derived from Seismic Stratigraphy

    Rios, J. K.; McHugh, C. M.; Hornbach, M. J.; Mann, P.; Wright, V. D.; Gurung, D.


    BP. Unit 3: acoustically transparent is 5-10 m thick. This unit shows top-lap terminations with the overlying strata and is interpreted as marine. Based on coral reef ages it was deposited during the Holocene 10 to 2 ka BP. Unit 4: laminated strata is ~ 5 m thick and downlaps offshore forming progradational packages. Pending Pb-210 ages from LE sediment cores a correlation between the two basins is proposed. During the latest Pleistocene sea level lowstand LE was separated from the BPP and the global ocean. The BPP was only partly connected to the sea. Sedimentation in both basins was dominated by wet and dry climate. The initial rise to high-stand of sea level into the BPP was at 14 ka BP. LE marine incursion was at 9.7 ka BP. At 2.8 ka BP LE became separated from the BPP possibly due to increased alluvial fan sedimentation. Evaporative conditions dominated the lake from 2.8 ka BP to the present and the lake waters lowered to ~43 m below sea level. We interpret the top laminated strata as deposited during the evaporative stage of the lake. Sediment progradation resulted from increased sedimentation due to lowering of base level. There is no evidence of tectonic activity in the BPP during the Holocene. In contrast, there are breaks in the Holocene strata in LE. So the EPGF is technically active across LE.

  4. Late-Holocene environment and climatic changes in Ameralik Fjord, southwest Greenland: evidence from the sedimentary record

    Møller, Henrik S.; Jensen, Karin G.; Kuijpers, Antoon


      Sedimentological and geochemical (XRF) data together with information from diatom and benthic foraminifera records of a 3.5 m long gravity core from Ameralik fjord, southern West Greenland, is used for reconstructing late Holocene environmental changes in this area. The changes are linked...... to large-scale North Atlantic ocean and climate variability. AMS 14C-dating of benthic foraminifera indicates that the sediment core covers the last 4400 years and may include the termination of the Holocene Thermal Maximum (HTM). The late HTM (4.4-3.2 ka BP) is characterized by high accumulation rates...

  5. Ancient DNA derived from alkenone-biosynthesizing haptophytes and other algae in Holocene sediments from the Black Sea

    Coolen, M.J.L.; Boere, A.; Abbas, M.; Wakeham, S.G.; Sinninghe Damsté, J.S.


    Holocene sea surface temperatures (SST) of the Black Sea have been reconstructed using sedimentary C37 unsaturated alkenones assumed to be derived from the coccolithophorid haptophyte Emiliania huxleyi, whose fossil coccoliths are an important constituent of the unit I sediments. However,

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

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


    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.

  7. Mid-Holocene Climate and Culture Change in the Atacama Desert, Northern Chile

    Grosjean, Martin; Núñez, Lautaro; Cartajena, Isabel; Messerli, Bruno


    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.

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

    Zalat Abdelfattah A.


    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.

  9. Holocene hydrologic variation at Lake Titicaca, Bolivia/Peru, and its relationship to North Atlantic climate variation

    Baker, P. A.; Fritz, S. C.; Garland, J.; Ekdahl, E.


    A growing number of sites in the Northern Hemisphere show centennial- to millennial-scale climate variation that has been correlated with change in solar variability or with change in North Atlantic circulation. However, it is unclear how (or whether) these oscillations in the climate system are manifest in the Southern Hemisphere because of a lack of sites with suitably high sampling resolution. In this paper, we reconstruct the lake-level history of Lake Titicaca, using the carbon isotopic content of sedimentary organic matter, to evaluate centennial- to millennial-scale precipitation variation and its phasing relative to sites in the Northern Hemisphere. The pattern and timing of lake-level change in Lake Titicaca is similar to the ice-rafted debris record of Holocene Bond events, demonstrating a possible coupling between precipitation variation on the Altiplano and North Atlantic sea-surface temperatures (SSTs). The cold periods of the Holocene Bond events correspond with periods of increased precipitation on the Altiplano. Holocene precipitation variability on the Altiplano is anti-phased with respect to precipitation in the Northern Hemisphere monsoon region. More generally, the tropical Andes underwent large changes in precipitation on centennial-to-millennial timescales during the Holocene.

  10. Middle and late Holocene climate change and human impact inferred from diatoms, algae and aquatic macrophyte pollen in sediments from Lake Montcortès (NE Iberian Peninsula)

    Scussolini, P.; Vegas-Vilarrúbia, T.; Rull, V.; Corella, J.P.; Valero-Garcés, B.; Gomà, J.


    During the middle and late Holocene, the Iberian Peninsula underwent large climatic and hydrologic changes, but the temporal resolution and regional distribution of available palaeoenvironmental records is still insufficient for a comprehensive assessment of the regional variability. The high

  11. Late Holocene vegetation, climate, and land-use impacts on carbon dynamics in the Florida Everglades

    Jones, Miriam C.; Bernhardt, Christopher E.; Willard, Debra A.


    Tropical and subtropical peatlands are considered a significant carbon sink. The Florida Everglades includes 6000-km2 of peat-accumulating wetland; however, detailed carbon dynamics from different environments within the Everglades have not been extensively studied or compared. Here we present carbon accumulation rates from 13 cores and 4 different environments, including sawgrass ridges and sloughs, tree islands, and marl prairies, whose hydroperiods and vegetation communities differ. We find that the lowest rates of C accumulation occur in sloughs in the southern Everglades. The highest rates are found where hydroperiods are generally shorter, including near-tails of tree islands and drier ridges. Long-term average rates of 100 to >200 g C m−2 yr−1 are as high, and in some cases, higher than rates recorded from the tropics and 10–20 times higher than boreal averages. C accumulation rates were impacted by both the Medieval Climate Anomaly and the Little Ice Age, but the largest impacts to C accumulation rates over the Holocene record have been the anthropogenic changes associated with expansion of agriculture and construction of canals and levees to control movement of surface water. Water management practices in the 20th century have altered the natural hydroperiods and fire regimes of the Everglades. The Florida Everglades as a whole has acted as a significant carbon sink over the mid- to late-Holocene, but reduction of the spatial extent of the original wetland area, as well as the alteration of natural hydrology in the late 19th and 20th centuries, have significantly reduced the carbon sink capacity of this subtropical wetland.

  12. A multiproxy fjord sediment record of Holocene climate change from the subantarctic Auckland Islands

    Browne, I. M.; Moy, C. M.; Wilson, G. S.; Neil, H.; Riesselman, C. R.


    The Southern Hemisphere Westerly Winds (SHWW) and the associated oceanic fronts have a major influence on atmospheric and oceanic circulation in the Southern Hemisphere. Sediment cores recovered from fjords along the eastern margin of the sub-Antarctic Auckland Islands (51°S, 166°E) are ideally located to sensitively record changes in the strength and position of the SHWW throughout the Holocene. A 5.75m core from Hanfield Inlet preserves both marine and terrestrial environmental components, which we use to develop a multiproxy record of past climatic conditions. This core, composed entirely of brown marine mud and silt, was recovered from a depth of 44m. Based on the entrance sill depth of the fjord (10mbsl) and our knowledge of regional sea level rise, we infer that the base of the core will be early Holocene in age, which will be confirmed using radiocarbon age dating. Benthic foraminiferal assemblages (125-500μm fraction) in surface and downcore samples are dominated by three taxa, Nonionellina flemingi, Cassidulina carinata and Quinqueloculina seminula. These species are either shallow infaunal or infaunal. We will use stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope geochemistry of the benthic foraminifera Nonionellina flemingi, Bolivina cf. earlandi, Trifarina angulosa, Bulimina marginata f. marginata and Cibicides species (all identified from Rose Bengal stained box-core samples) to reconstruct water column fluctuations associated with frontal migration. These results will compliment bulk sediment C and N concentration and isotope reconstructions of terrestrial organic matter delivery to fjord sub-basins over the past 12,000 years.

  13. A proxy late Holocene climatic record deduced from northwest Alaskan beach ridges

    Mason, O.K.; Jordan, J.W.


    A climatically-sensitive, oscillatory pattern of progradation and erosion is revealed in late Holocene accretionary sand ridge and barrier island complexes of Seward Peninsula, northwest Alaska. Archaeological and geological radiocarbon dates constrain the authors chronology for the Cape Espenberg beach ridge plain and the Shishmaref barrier islands, 50 km to the southwest. Cape Espenberg, acts as the depositional sink for the northeastward longshore transport system and contains the oldest sedimentary deposits: based on 3700±90 B.P. (β-23170) old grass from a paleosol capping a low dune facies. The oldest date on the Shishmaref barrier islands is 1550±70 B.P. (β-23183) and implies that the modem barrier is a comparatively recent phenomenon. Late Holocene sedimentation varies between intervals of erosion and rapid progradation. During erosional periods higher dunes are built atop beach ridges: as between 3000-2000 yrs. BP and intermittently from 1000 BP to the present. At other times, rapid progradation predominated, generating wide swales and low beach ridges without dunes. Tentatively, dune formation is correlative with the Neo-glacial and Little Ice Age glacial advances and increased alluviation in north Alaska. Rapid progradation is contemporaneous with warmer intervals of soil and peat formation atop alluvial terraces, dated to ca. 4000-3500 and 2000-1000 yrs. B.P. In the record of the last 1000 years, dune building is correlative with heightened storminess, as reflected in northwest Alaska tree-ring chronologies and weather anomalies such as spring dust storms and winter thunderstorms in East Asian locations

  14. Punctuated Holocene climate of Vestfirðir, Iceland, linked to internal/external variables and oceanographic conditions

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


    Emerging Holocene paleoclimate datasets point to a non-linear response of Icelandic climate against a background of steady orbital cooling. The Vestfirðir peninsula (NW Iceland) is an ideal target for continued climate reconstructions due to the presence of a small ice cap (Drangajökull) and numerous lakes, which provide two independent means to evaluate existing Icelandic climate records and to constrain the forcing mechanisms behind centennial-scale cold anomalies. Here, we present new evidence for Holocene expansions of Drangajökull based on 14C dates from entombed dead vegetation as well as two continuous Holocene lake sediment records. Lake sediments were analyzed for both bulk physical (MS) and biological (%TOC, δ13C, C/N, and BSi) parameters. Composite BSi and C/N records from the two lakes yield a sub-centennial qualitative perspective on algal (diatom) productivity and terrestrial landscape stability, respectively. The Vestfirðir lake proxies suggest initiation of the Holocene Thermal Maximum by ∼8.8 ka with subsequent and pronounced cooling not apparent until ∼3 ka. Synchronous periods of reduced algal productivity and accelerated landscape instability point to cold anomalies centered at ∼8.2, 6.6, 4.2, 3.3, 2.3, 1.8, 1, and 0.25 ka. Triggers for cold anomalies are linked to variable combinations of freshwater pulses, low total solar irradiance, explosive and effusive volcanism, and internal modes of climate variability, with cooling likely sustained by ocean/sea-ice feedbacks. The climate evolution reflected by our glacial and organic proxy records corresponds closely to marine records from the North Iceland Shelf.

  15. Mapping the Holocene forest formations with the use of key climate indicators – heat and moisture

    S. K. Farber


    Full Text Available The article deals with the methodology of mapping the Holocene forest formations on the basis of the DEM and the key indicators of the climate – heat and moisture. The work is carried out by means of GIS. The test site is located within the boundaries of the axial West Sayan district of mountain taiga forests, which ensures homogeneity of natural and climatic conditions. Stages of the method: creation of rasters on groups of absolute heights, exposures and inclinations with their subsequent combination into a single Combine raster; obtaining the regularities of spatial distribution of heat and moisture and their representation in the form of rasters (digital models; and interactive mapping of the Holocene forests with various combinations of heat and moisture. The use of Combine raster makes it possible to refuse to use any other contours as – landscape, geomorphological, forest inventory. To determine parameters of climatic boundaries of forest formations, the types of forests are linked to the heat and moisture indicators. As a result of linking, a graphic image is produced, where forest formations and their productivity are located in a certain order. The mapping technique involves creating a dBASE table with a field containing information about forest formations. The row-wise change in the records of forest formations as they move to other values of heat and moisture is performed interactively. Each next combination of heat and moisture on maps corresponds to a certain distribution of forest formations and site productivity (bonitet classes. (1900 ± 65 years ago the river valleys were treeless, flat meadows occupied meadows, and the slopes were steppes. As the hypsometric level increases, larch stands, spruce-Siberian stone pine with an admixture of larch, Siberian stone pine-larch with an admixture of fir, and the Siberian stone pine formations appear. (2200 ± 100 years ago the tundra prevailed. Larch forests of V–Va classes of

  16. Roles of Sea Level and Climate Change in the Development of Holocene Deltaic Sequences in the Yellow Sea

    Liu, J.; Milliman, J. D.


    Both post-glacial sea-level and climatic changes are preserved in the the shallow, low gradient, sediment-dominated Yellow Sea. As a result of rapid flooding during melt-water pulse (MWP) 1A, 14.3-14.1 ka BP, sea level reached the southern edge of the North Yellow Sea (NYS), and after MWP-1B (11.6-11.4 ka BP) sea level entered the Bohai Sea. The first major Yellow River-derived deltaic deposit formed in the NYS during decelerated transgression following MWP-1B and increased river discharge in response to re-intensification of the summer monsoon about 11 ka cal BP. A second subaqueous delta formed in the South Yellow Sea about 9-7 ka BP during decelerated transgression after MWP-1C flooding and in response to the southern shift of the Yellow River mouth. The modern subaqueous and subaerial deltas in the west Bahai Gulf and (to a lesser extent) along the Jiangus coast have formed during the modern sea-level highstand. These changing Holocene patterns are most clearly illustrated by a short film clip.

  17. Western equatorial African forest-savanna mosaics: a legacy of late Holocene climatic change?

    A. Ngomanda


    Full Text Available Past vegetation and climate changes reconstructed using two pollen records from Lakes Maridor and Nguène, located in the coastal savannas and inland rainforest of Gabon, respectively, provide new insights into the environmental history of western equatorial African rainforests during the last 4500 cal yr BP. These pollen records indicate that the coastal savannas of western equatorial Africa did not exist during the mid-Holocene and instead the region was covered by evergreen rainforests. From ca. 4000 cal yr BP a progressive decline of inland evergreen rainforest, accompanied by the expansion of semi-deciduous rainforest, occurred synchronously with grassland colonisation in the coastal region of Gabon. The contraction of moist evergreen rainforest and the establishment of coastal savannas in Gabon suggest decreasing humidity from ca. 4000 cal yr BP. The marked reduction in evergreen rainforest and subsequent savanna expansion was followed from 2700 cal yr BP by the colonization of secondary forests dominated by the palm, Elaeis guineensis, and the shrub, Alchornea cordifolia (Euphorbiaceae. A return to wetter climatic conditions from about 1400 cal yr BP led to the renewed spread of evergreen rainforest inland, whereas a forest-savanna mosaic still persists in the coastal region. There is no evidence to suggest that the major environmental changes observed were driven by human impact.

  18. Lateglacial and Holocene climate, disturbance and permafrost peatland dynamics on the Seward Peninsula, western Alaska

    Hunt, Stephanie D.; Yu, Zicheng; Jones, Miriam C.


    Northern peatlands have accumulated large carbon (C) stocks, acting as a long-term atmospheric C sink since the last deglaciation. How these C-rich ecosystems will respond to future climate change, however, is still poorly understood. Furthermore, many northern peatlands exist in regions underlain by permafrost, adding to the challenge of projecting C balance under changing climate and permafrost dynamics. In this study, we used a paleoecological approach to examine the effect of past climates and local disturbances on vegetation and C accumulation at a peatland complex on the southern Seward Peninsula, Alaska over the past ∼15 ka (1 ka = 1000 cal yr BP). We analyzed two cores about 30 m apart, NL10-1 (from a permafrost peat plateau) and NL10-2 (from an adjacent thermokarst collapse-scar bog), for peat organic matter (OM), C accumulation rates, macrofossil, pollen and grain size analysis.A wet rich fen occurred during the initial stages of peatland development at the thermokarst site (NL10-2). The presence of tree pollen from Picea spp. and Larix laricinia at 13.5–12.1 ka indicates a warm regional climate, corresponding with the well-documented Bølling–Allerød warm period. A cold and dry climate interval at 12.1–11.1 ka is indicated by the disappearance of tree pollen and increase in Poaceae pollen and an increase in woody material, likely representing a local expression of the Younger Dryas (YD) event. Following the YD, the warm Holocene Thermal Maximum (HTM) is characterized by the presence of Populus pollen, while the presence of Sphagnum spp. and increased C accumulation rates suggest high peatland productivity under a warm climate. Toward the end of the HTM and throughout the mid-Holocene a wet climate-induced several major flooding disturbance events at 10 ka, 8.1 ka, 6 ka, 5.4 ka and 4.7 ka, as evidenced by decreases in OM, and increases in coarse sand abundance and aquatic fossils (algae Chara and water fleas Daphnia). The initial

  19. Late-Holocene environment and climatic changes in Ameralik Fjord, southwest Greenland: evidence from the sedimentary record

    Møller, Henrik S.; Jensen, Karin G.; Kuijpers, Antoon


      Sedimentological and geochemical (XRF) data together with information from diatom and benthic foraminifera records of a 3.5 m long gravity core from Ameralik fjord, southern West Greenland, is used for reconstructing late Holocene environmental changes in this area. The changes are linked...... to large-scale North Atlantic ocean and climate variability. AMS 14C-dating of benthic foraminifera indicates that the sediment core covers the last 4400 years and may include the termination of the Holocene Thermal Maximum (HTM). The late HTM (4.4-3.2 ka BP) is characterized by high accumulation rates...... conditions were further characterised by limited sea ice probably related to a mild and relatively windy winter climate. After 3.2 ka BP lower fine-grained sedimentation rates, but a larger input from sea-ice rafted or aeolian coarse material prevailed. This can be related to colder atmospheric conditions...

  20. Effects of late Holocene climate variability and anthropogenic stressors on the vegetation of the Maya highlands

    Franco-Gaviria, F.; Correa-Metrio, A.; Cordero-Oviedo, C.; López-Pérez, M.; Cárdenes-Sandí, G. M.; Romero, F. M.


    Climate variability and human activities have shaped the vegetation communities of the Maya region of southern Mexico and Central America on centennial to millennial timescales. Most research efforts in the region have focused on the lowlands, with relatively little known about the environmental history of the regional highlands. Here we present data from two sediment sequences collected from lakes in the highlands of Chiapas, Mexico. Our aim was to disentangle the relative contributions of climate and human activities in the development of regional vegetation during the late Holocene. The records reveal a long-term trend towards drier conditions with superimposed centennial-scale droughts. A declining moisture trend from 3400 to 1500 cal yr BP is consistent with previously reported southward displacement of the Intertropical Convergence Zone, whereas periodic droughts were probably a consequence of drivers such as El Niño. These conditions, together with dense human occupation, converted the vegetation from forest to more open systems. According to the paleoecological records, cultural abandonment of the area occurred ca. 1500 cal yr BP, favoring forest recovery that was somewhat limited by low moisture availability. About 600 cal yr BP, wetter conditions promoted the establishment of modern montane cloud forests, which consist of a diverse mixture of temperate and tropical elements. The vegetation types that occupied the study area during the last few millennia have remained within the envelope defined by the modern vegetation mosaic. This finding highlights the importance of microhabitats in the maintenance biodiversity through time, even under scenarios of high climate variability and anthropogenic pressure.

  1. Response of Landscapes of the Sikhote-Alin Western Slopes to the Middle-Late Holocene Climatic Changes

    Razzhigaeva, N. G.; Ganzey, L. A.; Panichev, A. M.; Grebennikova, T. A.; Mokhova, L. M.; Kopoteva, T. A.; Kudryavtseva, E. P.; Arslanov, Kh. A.; Maksimov, F. E.; Starikova, A. A.; Zakusin, S. V.


    The response of landscape biotic components of the western slope of the Sikhote-Alin Mountains (Bikin River middle flow) to the Middle-Late Holocene climate changes is discussed. The paleoreconstruction object was the Krasny Yar mari, which developed under the control of multidirectional short-term climatic changes. The last millennium was marked by particularly rapid and frequent changes in the local landscapes. The closely spaced orographic barrier strongly affected the development of biotic components and changes in the swamp hydrological regime. The moisture dynamics within the river catchment considerably controlled the development and change of the peat-forming plants. Several stages of the mari development were reconstructed; each began from the accumulation of eutrophic peat. It was followed by the transitional eutrophic-mesotrophic stage, with a higher role of atmospheric supply. The larch forests appeared in this part of the valley within the Atlantic-Subboreal cooling period. Korean pine developed in the forest vegetation in the low mountain relief at the beginning of the Subboreal and became one of the leading trees 2.6-2.3 ka BP. The lower role of the Korean pine and birch forest expansion in the first half of the Subatlantic could be related to the fires. The broadleaf-Korean pine forests became widespread in the Medieval Warm Period. Local swamp landscapes changed dramatically in the Little Ice Age, while the slope vegetation was not subject to any major changes. The landscapes were also affected by the fires, which became more frequent. The derivative communities with birch appeared on the mari. Moreover, this part of the valley was occasionally subject to heavy flooding.

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

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


    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. Blue Carbon Sequestration in Florida Coastal Wetlands - Response to Recent Climate Change and Holocene Climate Variability

    Vaughn, D.; Bianchi, T. S.; Osborne, T.; Shields, M. R.; Kenney, W.


    Intertidal forests and salt marshes represent a major component of Florida's coasts and are essential to the health and integrity of coastal Florida's ecological and economic systems. In addition, coastal wetlands have been recognized as highly efficient carbon sinks with their ability to store carbon on time scales from centuries to millennia. Although losses of salt marshes, mangroves, and seagrass beds through both natural and anthropogenic forces are threatening their ability to act as carbon sinks globally, the poleward encroachment of mangroves into higher latitude salt marshes may lead to regional increases in carbon sequestration as mangroves store more carbon than salt marshes. For Florida, this encroachment of mangroves into salt marshes is prominent along the northern coasts where fewer freeze events have coincided with an increase in mangrove extent over the past several decades. Soil cores collected from a northeastern Florida wetland will allow us to determine whether the recent poleward encroachment of mangroves into northern Florida salt marshes has led to an increase in belowground carbon storage. The soil cores, which are approximately two to three meters in length, will also provide the first known record of carbon storage in a northern Florida wetland during the Holocene. Initial results from the top 40 cm, which represents 100 years based on dating of other northern Florida wetland cores, suggest more carbon is currently being stored within the transition between marsh and mangrove than in areas currently covered by salt marsh vegetation or mangroves. The transitional zone also has a much larger loss of carbon within the top 40 cm compared to the mangrove and marsh cores. Lignin-based degradation indices along with other biomarker data and 210Pb/137Cs ages will be presented to demonstrate how much of this loss of carbon may be related to degradation and how much may be related to changes in carbon sources.

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

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


    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

  5. Lateglacial and Holocene climatic changes in south-eastern Patagonia inferred from carbonate isotope records of Laguna Potrok Aike (Argentina)

    Oehlerich, M.; Mayr, C.; Gussone, N.; Hahn, A.; Hölzl, S.; Lücke, A.; Ohlendorf, C.; Rummel, S.; Teichert, B. M. A.; Zolitschka, B.


    First results of strontium, calcium, carbon and oxygen isotope analyses of bulk carbonates from a 106 m long sediment record of Laguna Potrok Aike, located in southern Patagonia are presented. Morphological and isotopic investigations of μm-sized carbonate crystals in the sediment reveal an endogenic origin for the entire Holocene. During this time period the calcium carbonate record of Laguna Potrok Aike turned out to be most likely ikaite-derived. As ikaite precipitation in nature has only been observed in a narrow temperature window between 0 and 7 °C, the respective carbonate oxygen isotope ratios serve as a proxy of hydrological variations rather than of palaeotemperatures. We suggest that oxygen isotope ratios are sensitive to changes of the lake water balance induced by intensity variations of the Southern Hemisphere Westerlies and discuss the role of this wind belt as a driver for climate change in southern South America. In combination with other proxy records the evolution of westerly wind intensities is reconstructed. Our data suggest that weak SHW prevailed during the Lateglacial and the early Holocene, interrupted by an interval with strengthened Westerlies between 13.4 and 11.3 ka cal BP. Wind strength increased at 9.2 ka cal BP and significantly intensified until 7.0 ka cal BP. Subsequently, the wind intensity diminished and stabilised to conditions similar to present day after a period of reduced evaporation during the "Little Ice Age". Strontium isotopes (87Sr/86Sr ratio) were identified as a potential lake-level indicator and point to a lowering from overflow conditions during the Glacial (∼17 ka cal BP) to lowest lake levels around 8 ka cal BP. Thereafter the strontium isotope curve resembles the lake-level curve which is stepwise rising until the "Little Ice Age". The variability of the Ca isotope composition of the sediment reflects changes in the Ca budget of the lake, indicating higher degrees of Ca utilisation during the period with

  6. Pollen-based reconstruction of Holocene vegetation and climate in southern Italy: the case of Lago Trifoglietti

    S. Joannin


    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

  7. Holocene climate variability in the western Mediterranean through a multiproxy analysis from Padul peat bog (Sierra Nevada, Spain)

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


    The Iberian Peninsula, located in the Mediterranean area, is an interesting location for paleoclimate studies due to its geographic situation between arid and humid climates. Sediments from peat bogs and lakes from Sierra Nevada, in southeastern Iberian Peninsula, have been very informative in terms of how vegetation and wetland environments were impacted by Holocene climate change. These studies are essential if we want to understand the past climate change in the area, which is the key to identify the possible environmental response of the Sierra Nevada ecosystems to future climate scenarios. Padul basin, located in the southwest of the Sierra Nevada mountain range, contains a ca. 100 m-thick peat bog sedimentary sequence that was deposited during the past 1 Ma making this area interesting for paleoenvironmental and paleoclimatic reconstructions. A new 43 m-long sedimentary record has recently been retrieved from the Padul peat bog. In this study we have developed a multiproxy analysis of the Holocene part of the Padul-15-05 core including pollen analysis, XRF-core scanner, magnetic susceptibility and organic geochemistry, supported by an age control based on AMS radiocarbon dates, providing with information about vegetation and climate variability during the past 9.9 cal ka BP. This multiproxy reconstruction of the Padul-15-05 evidences the Mediterranean as a sensitive area with respect to global-scale climate system, showing relevant climate episodes such as the ca. 8, 7.5, 6.5 and 5.5 cal ka BP events during the early and middle Holocene. The trend to aridification to the late Holocene is interrupted by more arid and humid periods as the Iberian Roman Humid Period (from ca. 3 to 1.6 cal ka BP), the Dark Ages (from ca. 1.5 to 1.1 cal ka BP), the Medieval Climate Anomaly (from ca. 1.1 to 1.3 cal ka BP) and the Little Ice Age period (from ca. 500 to 100 cal yr BP).

  8. Derivatives Trading, Climate Science and Human Rights

    Haigh, Matthew

    for capital flows associated with climate management. Media communications and decision making theories are used to interpret data drawn from participant observation and interviews with climate scientists, policy makers and institutional investors. Findings - The framework suggests a digital divide between...... the heaviest polluters as contributing to carbon-minimised investment portfolios. Assets owned by privately managed pension funds have remained materially exposed to risks posed by climate change. In public finance, a narrow range of financial instruments centred on derivatives trading has entrenched global...... between human rights, climate change, and the stability of private pensions provision. Originality/value - Provides policy sciences useful assessments of communication media and financial instruments used in climate management. Establishes bases for theoretical and applied communications research...

  9. Rapid response of a marine mammal species to holocene climate and habitat change.

    Mark de Bruyn


    Full Text Available Environmental change drives demographic and evolutionary processes that determine diversity within and among species. Tracking these processes during periods of change reveals mechanisms for the establishment of populations and provides predictive data on response to potential future impacts, including those caused by anthropogenic climate change. Here we show how a highly mobile marine species responded to the gain and loss of new breeding habitat. Southern elephant seal, Mirounga leonina, remains were found along the Victoria Land Coast (VLC in the Ross Sea, Antarctica, 2,500 km from the nearest extant breeding site on Macquarie Island (MQ. This habitat was released after retreat of the grounded ice sheet in the Ross Sea Embayment 7,500-8,000 cal YBP, and is within the range of modern foraging excursions from the MQ colony. Using ancient mtDNA and coalescent models, we tracked the population dynamics of the now extinct VLC colony and the connectivity between this and extant breeding sites. We found a clear expansion signal in the VLC population approximately 8,000 YBP, followed by directional migration away from VLC and the loss of diversity at approximately 1,000 YBP, when sea ice is thought to have expanded. Our data suggest that VLC seals came initially from MQ and that some returned there once the VLC habitat was lost, approximately 7,000 years later. We track the founder-extinction dynamics of a population from inception to extinction in the context of Holocene climate change and present evidence that an unexpectedly diverse, differentiated breeding population was founded from a distant source population soon after habitat became available.

  10. Rapid response of a marine mammal species to holocene climate and habitat change.

    de Bruyn, Mark; Hall, Brenda L; Chauke, Lucas F; Baroni, Carlo; Koch, Paul L; Hoelzel, A Rus


    Environmental change drives demographic and evolutionary processes that determine diversity within and among species. Tracking these processes during periods of change reveals mechanisms for the establishment of populations and provides predictive data on response to potential future impacts, including those caused by anthropogenic climate change. Here we show how a highly mobile marine species responded to the gain and loss of new breeding habitat. Southern elephant seal, Mirounga leonina, remains were found along the Victoria Land Coast (VLC) in the Ross Sea, Antarctica, 2,500 km from the nearest extant breeding site on Macquarie Island (MQ). This habitat was released after retreat of the grounded ice sheet in the Ross Sea Embayment 7,500-8,000 cal YBP, and is within the range of modern foraging excursions from the MQ colony. Using ancient mtDNA and coalescent models, we tracked the population dynamics of the now extinct VLC colony and the connectivity between this and extant breeding sites. We found a clear expansion signal in the VLC population approximately 8,000 YBP, followed by directional migration away from VLC and the loss of diversity at approximately 1,000 YBP, when sea ice is thought to have expanded. Our data suggest that VLC seals came initially from MQ and that some returned there once the VLC habitat was lost, approximately 7,000 years later. We track the founder-extinction dynamics of a population from inception to extinction in the context of Holocene climate change and present evidence that an unexpectedly diverse, differentiated breeding population was founded from a distant source population soon after habitat became available.

  11. Stalagmite-derived Last Glacial Maximum - Mid Holocene Indian Monsoon Record from Krem Mawmluh, Meghalaya, NE India

    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.


    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.

  12. Impact of Earth's orbit and freshwater fluxes on Holocene climate mean seasonal cycle and ENSO characteristics

    Braconnot, P.; Zheng, W. [unite mixte CEA-CNRS-UVSQ, Laboratoire des Sciences du climat et de l' Environnement, Gif-sur-Yvette Cedex (France); Luan, Y. [unite mixte CEA-CNRS-UVSQ, Laboratoire des Sciences du climat et de l' Environnement, Gif-sur-Yvette Cedex (France); Chinese Academy of Sciences (CAS), State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Brewer, Simon [University of Wyoming, Department of Botany, Laramie, WY (United States)


    We use a state-of-the-art 3-dimensional coupled model to investigate the relative impact of long term variations in the Holocene insolation forcing and of a freshwater release in the North Atlantic. We show that insolation has a greater effect on seasonality and La Nina events and is the major driver of sea surface temperature changes. In contrast, the variations in precipitation reflect changes in El Nino events. The impact of ice-sheet melting may have offset the impact of insolation on El Nino Southern Oscillation variability at the beginning of the Holocene. These simulations provide a coherent framework to refine the interpretation of proxy data and show that changes in seasonality may bias the projection of relationships established between proxy indicators and climate variations in the east Pacific from present day records. (orig.)

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

    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)


    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.)

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

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


    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

  15. Holocene climate aridification trend and human impact interrupted by millennial- and centennial-scale climate fluctuations from a new sedimentary record from Padul (Sierra Nevada, southern Iberian Peninsula)

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


    Holocene centennial-scale paleoenvironmental variability has been described in a multiproxy analysis (i.e., lithology, geochemistry, macrofossil, and microfossil analyses) of a paleoecological record from the Padul Basin in Sierra Nevada, southern Iberian Peninsula. This sequence covers a relevant time interval hitherto unreported in the studies of the Padul sedimentary sequence. The ˜ 4700-year record has preserved proxies of climate variability, with vegetation, lake levels, and sedimentological change during the Holocene in one of the most unique and southernmost wetlands in Europe. The progressive middle and late Holocene trend toward arid conditions identified by numerous authors in the western Mediterranean region, mostly related to a decrease in summer insolation, is also documented in this record; here it is also superimposed by centennial-scale variability in humidity. In turn, this record shows centennial-scale climate oscillations in temperature that correlate with well-known climatic events during the late Holocene in the western Mediterranean region, synchronous with variability in solar and atmospheric dynamics. The multiproxy Padul record first shows a transition from a relatively humid middle Holocene in the western Mediterranean region to more aridity from ˜ 4700 to ˜ 2800 cal yr BP. A relatively warm and humid period occurred between ˜ 2600 and ˜ 1600 cal yr BP, coinciding with persistent negative North Atlantic Oscillation (NAO) conditions and the historic Iberian-Roman Humid Period. Enhanced arid conditions, co-occurring with overall positive NAO conditions and increasing solar activity, are observed between ˜ 1550 and ˜ 450 cal yr BP (˜ 400 to ˜ 1400 CE) and colder and warmer conditions occurred during the Dark Ages and Medieval Climate Anomaly (MCA), respectively. Slightly wetter conditions took place during the end of the MCA and the first part of the Little Ice Age, which could be related to a change towards negative NAO conditions

  16. Holocene climate aridification trend and human impact interrupted by millennial- and centennial-scale climate fluctuations from a new sedimentary record from Padul (Sierra Nevada, southern Iberian Peninsula

    M. J. Ramos-Román


    Full Text Available Holocene centennial-scale paleoenvironmental variability has been described in a multiproxy analysis (i.e., lithology, geochemistry, macrofossil, and microfossil analyses of a paleoecological record from the Padul Basin in Sierra Nevada, southern Iberian Peninsula. This sequence covers a relevant time interval hitherto unreported in the studies of the Padul sedimentary sequence. The  ∼  4700-year record has preserved proxies of climate variability, with vegetation, lake levels, and sedimentological change during the Holocene in one of the most unique and southernmost wetlands in Europe. The progressive middle and late Holocene trend toward arid conditions identified by numerous authors in the western Mediterranean region, mostly related to a decrease in summer insolation, is also documented in this record; here it is also superimposed by centennial-scale variability in humidity. In turn, this record shows centennial-scale climate oscillations in temperature that correlate with well-known climatic events during the late Holocene in the western Mediterranean region, synchronous with variability in solar and atmospheric dynamics. The multiproxy Padul record first shows a transition from a relatively humid middle Holocene in the western Mediterranean region to more aridity from  ∼  4700 to  ∼  2800 cal yr BP. A relatively warm and humid period occurred between  ∼  2600 and  ∼  1600 cal yr BP, coinciding with persistent negative North Atlantic Oscillation (NAO conditions and the historic Iberian–Roman Humid Period. Enhanced arid conditions, co-occurring with overall positive NAO conditions and increasing solar activity, are observed between  ∼  1550 and  ∼  450 cal yr BP (∼  400 to  ∼  1400 CE and colder and warmer conditions occurred during the Dark Ages and Medieval Climate Anomaly (MCA, respectively. Slightly wetter conditions took place during the end of

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

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


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

  18. Climatic-eustatic control of Holocene nearshore parasequence development, southeastern Texas coast

    Morton, Robert A.; Kindinger, Jack G.; Flocks, James G.; Stewart, Laura B.


    Sediment cores, seismic profiles, radiocarbon dates, and faunal assemblages were used to interpret the depositional setting and geological evolution of the southeastern Texas coast during the last glacio-eustatic cycle. Discrete lithofacies and biofacies zones in the ebb-dominated Sabine Lake estuary and adjacent chenier plain record alternating periods of rapid marine flooding and gradual shoaling related to linked climatic/eustatic fluctuations. Monospecific zones of the mollusks Rangia cuneata and Crassostrea virginica, respectively, indicate high fresh water outflow followed by invasion of marine water, whereas intervening organic-rich zones record bayhead delta deposition. High-frequency parasequence stacking patterns within the valley fill and across the adjacent interfluve reflect an initial rapid rise in sea level about 9 ka that flooded abandoned alluvial terraces and caused onlap of Holocene marsh in the incised valley. The rapid rise was followed by slowly rising and oscillating sea level that filled the deepest portions of the incised valleys with fluvially dominated estuarine deposits, and then a maximum highstand (+1 m msl) about 5 ka that flooded the former subaerial coastal plain between the incised valleys and constructed the highest beach ridges. Between 3.5 and 1.5 ka, sea level oscillated and gradually fell, causing a forced regression and rapid progradation of both the chenier plain and accretionary barrier islands. The only significant sands in the valley fill are (1) falling-stage and lowstand-fluvial sediments between the basal sequence boundary and transgressive surface unconformity, and (2) highstand beach-ridge sediments of the chenier plain.

  19. Late Glacial and Holocene Climate Change in the subantarctic Auckland Islands

    Gilmer, G.; Moy, C. M.; Vandergoes, M.; Gadd, P.; Riesselman, C. R.; Jacobsen, G. E.; Wilson, G. S.; Visinand, C.


    Situated within the core of the Southern Hemisphere westerly winds, and between the subtropical and subantarctic fronts, the New Zealand subantarctic islands are uniquely positioned to evaluate past ocean and atmospheric change in the middle to high southern latitudes. We collected a series of sediment cores from Auckland Island fjords to produce a high-resolution record of climate change following the Last Glacial Maximum. Physical property and organic geochemical data, Itrax XRF, and visual core descriptions indicate the cores capture several phases of sedimentation. From these studies, we identify four primary sedimentary facies: 1) a deglacial facies exhibiting mm-scale laminae defined by magnetic susceptibility and density contrasts and high counts of elements associated with terrigenous sources; 2) a lacustrine facies defined by very low density, high organic carbon concentrations and low counts of lithophilic elements; 3) a marine transgression facies with moderate density, moderate bioturbation and alternating marine and lacustrine sedimentary components; 4) a marine facies that contains biogenic carbonate. Radiocarbon results indicate deglacial sedimentation was underway in the basin by approximately 19,000 cal yr BP. Lacustrine deposition in ice-free conditions began around 15,600 cal yr BP and continued until marine transgression at approximately 9,500 cal yr BP. During the early Holocene between 11 and 9.5 ka, we observe elevated n-alkane δD values and an overall increase in redox-sensitive elements that signal a combination of warmer atmospheric temperatures and reduced westerly wind strength that drives fjord stratification. Poleward-shifted westerlies south of the Auckland Islands could accommodate these results, but there are few records to corroborate this interpretation. We will discuss these results within the context of developing New Zealand and subantarctic paleoclimate records in order to provide a more comprehensive record of past change.

  20. How Hot was Africa during the Mid-Holocene? Reexamining Africa's Thermal History via integrated Climate and Proxy System Modeling

    Dee, S.; Russell, J. M.; Morrill, C.


    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

  1. On the astronomical origin of the Hallstatt oscillation found in radiocarbon and climate records throughout the Holocene

    Scafetta, Nicola; Milani, Franco; Bianchini, Antonio; Ortolani, Sergio


    An oscillation with a period of about 2100-2500 years, the Hallstatt cycle, is found in cosmogenic radioisotopes (14C and 10Be) and in paleoclimate records throughout the Holocene. This oscillation is typically associated with solar variations, but its primary physical origin remains uncertain. Herein we show strong evidences for an astronomical origin of this cycle. Namely, this oscillation is coherent to a repeating pattern in the periodic revolution of the planets around the Sun: the major stable resonance involving the four Jovian planets - Jupiter, Saturn, Uranus and Neptune - which has a period of about p=2318 yr. Inspired by the Milanković's theory of an astronomical origin of the glacial cycles, we test whether the Hallstatt cycle could derive from the rhythmic variation of the circularity of the solar system disk assuming that this dynamics could eventually modulate the solar wind and, consequently, the incoming cosmic ray flux and/or the interplanetary/cosmic dust concentration around the Earth-Moon system. The orbit of the planetary mass center (PMC) relative to the Sun is used as a proxy. We analyzed how the instantaneous eccentricity vector of this virtual orbit varies from 13,000 B. C. to 17,000 A. D.. We found that it undergoes a kind of pulsations and clearly presents rhythmic contraction and expansion patterns with a 2318 yr period together with a number of already known faster oscillations associated to the planetary orbital stable resonances. There exists a quasi π/2 phase shift between the 2100-2500 yr oscillation found in the 14C record and that of the calculated eccentricity function. Namely, at the Hallstatt-cycle time scale, a larger production of radionucleotide particles occurs while the Sun-PMC orbit evolves from more elliptical shapes (e≈0.598) to more circular ones (e≈0.590), that is while the orbital system is slowly imploding or bursting inward; a smaller production of radionucleotide particles occurs while the Sun-PMC orbit

  2. 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

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


    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.

  3. Holocene climate and fjord glaciations in Northeast Greenland: implications for IRD deposition in the North Atlantic

    Reeh, Niels


    been released by intensive sub-glacial melting during the long stay of the ice-islands in coastal waters. The Holocene glacial geological record from Northeast Greenland is compared to the record of ice rafted debris (IRD) from North Atlantic deep-sea sediment cores. The comparison shows that transport...... by icebergs in the form of basal debris is unlikely to be the dominant transport mechanism of IRD to deposition sites in the North Atlantic during the Holocene. The ice rafted debris is more likely to be carried at the surface of sea- (or glacier) ice. This supports the result of previous studies by other...... workers that changes of atmospheric and ocean-surface circulation and temperature are the likely causes of Holocene cycles in IRD concentration in North Atlantic deep-sea sediments....

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

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


    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

  5. Evidence for a possible modern and mid-Holocene solar influence on climate from Lake Titicaca, South America

    Theissen, K. M.; Dunbar, R. B.


    In tropical regions, there are few paleoclimate archives with the necessary resolution to investigate climate variability at interannual-to-decadal timescales prior to the onset of the instrumental record. Interannual variability associated with the El Niño Southern Oscillation (ENSO) is well documented in the instrumental record and the importance of the precessional forcing of millennial variability has been established in studies of tropical paleoclimate records. In contrast, decade-to-century variability is still poorly understood. Here, we examine interannual to decadal variability in the northern Altiplano of South America using digital image analysis of a floating interval of varved sediments of middle Holocene age (~6160-6310 yr BP) from Lake Titicaca. Multi-taper method (MTM) and wavelet frequency-domain analyses were performed on a time series generated from a gray-scaled digital image of the mm-thick laminations. Our results indicate significant power at a decadal periodicity (10-12 years) associated with the Schwabe cycle of solar activity. Frequency-domain analysis also indicates power at 2-2.5 year periodicities associated with ENSO. Similarly, spectral analysis of a 75 year instrumental record of Titicaca lake level shows significant power at both solar and ENSO periodicities. Although both of the examined records are short, our results imply that during both the mid-Holocene and modern times, solar and ENSO variability may have contributed to high frequency climate fluctuations over the northern Altiplano. We suspect that solar influence on large-scale atmospheric circulation features may account for the decadal variability in the mid-Holocene and present-day water balance of the Altiplano.

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

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


    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.

  7. Beaver Activity, Holocene Climate and Riparian Landscape Change Across Stream Scales in the Greater Yellowstone Ecosystem

    Levine, R.; Meyer, G. A.


    Beaver (Castor canadensis) have been part of the fluvial and riparian landscape across much of North America since the Pleistocene, increasing channel habitat complexity and expanding riparian landscapes. The fur trade, however, decimated beaver populations by the 1840s, and other human activities have limited beaver in many areas, including parts of the Greater Yellowstone Ecosystem (GYE). Understanding fluctuations in beaver occupation through the Holocene will aid in understanding the natural range of variability in beaver activity as well as climatic and anthropogenic impacts to fluvial systems. We are developing a detailed chronology of beaver-assisted sedimentation and overall fluvial activity for Odell and Red Rock Creeks (basin areas 83 and 99 km2) in Centennial Valley (CV), Montana, to augment related studies on the long-term effects of beaver on smaller GYE fluvial systems (basin areas 0.1-50 km2). In developing the CV chronology, we use the presence of concentrations of beaver-chewed sticks as a proxy for beaver occupancy. Beaver-stick deposits are found in paleochannel and fluvial terrace exposures. The relative ages of exposures were determined by elevation data from airborne LiDAR and ground surveys. Numerical ages were obtained from 36 14C ages (~30 more are pending) of beaver-stick wood collected during investigation of the stratigraphy. Most beaver-stick deposits are associated with ~ 1 meter of fine-grained sediment, interpreted as overbank deposits, commonly overlying gravelly sand or pebble gravel channel deposits which is consistent with enhanced overbank sedimentation associated with active beaver dams in CV streams. The CV deposits differ from those on smaller GYE streams where beaver-stick deposits are associated with abandoned dams (berms), infilled ponds and laminated sediments. The lack of pond-related deposition associated with CV beaver-stick deposits is consistent with frequent dam breaching (≤ 5 years) in the modern channel of Odell

  8. Late-Holocene vegetation dynamics in response to a changing climate and anthropogenic influences - Insights from stratigraphic records and subfossil trees from southeast Lithuania

    Edvardsson, Johannes; Stančikaitė, Miglė; Miras, Yannick; Corona, Christophe; Gryguc, Gražyna; Gedminienė, Laura; Mažeika, Jonas; Stoffel, Markus


    To increase our understanding of long-term climate dynamics and its effects on different ecosystems, palaeoclimatic and long-term botanical reconstructions need to be improved, in particular in underutilized geographical regions. In this study, vegetation, (hydro)climate, and land-use changes were documented at two southeast Lithuanian peatland complexes - Čepkeliai and Rieznyčia - for the Late-Holocene period. The documentation was based on a combination of pollen, plant macrofossils, peat stratigraphic records, and subfossil trees. Our results cover the last two millennia and reveal the existence of moist conditions in Southern Lithuania between 300 and 500 CE and from 950 to 1850 CE. Conversely, changes towards warmer and/or dryer conditions have been recorded in 100, 600, and 750 CE, and since the 1850s. Significant differences with other Baltic proxies prevent deriving a complete and precise long-term reconstruction of past hydroclimatic variability at the regional scale. Yet, our results provide an important cornerstone for an improved understanding of regional climate change, i.e. in a region for which only (i) few detailed palaeobotanical studies exist and which has, in addition, been considered as (ii) an ecologically sensitive region at the interface between the temperate and boreal bioclimatic zones.

  9. Late Holocene Vegetation and Climate at the Mid Altitudes of the Western Himalaya

    ROY, I.; Ranhotra, P. S.; Shekhar, M.; Bhattacharyya, A.; Agrawal, S.; Kumar, P.; Patil, S. K.; Pal, A. K.


    The palynological, stable carbon isotope and magnetic susceptibility studies of a 42 cm deep sedimentary core collected from palaeolacustrine deposit at the Nachiketa area ( 2,400 m amsl) near Uttarkashi of Western Himalaya provides the late Holocene vegetation and climatic scenario of the area. Between 3200 to 1650 cal yrs BP, the high susceptibility (χlf) values along with the good frequency of fern spores might indicate the prevailing moist conditions due to high summer monsoon with good influx of the sediments. However, the low pollen concentration between 3200 to 2680 cal years BP might be due to less ground vegetation cover or poor pollen preservation in the sediments. The well represented fern spores along with the other ground vegetation taxa in the period from 1650 cal yrs BP to 600 cal yrs BP also indicates the continuous prevalence of moist conditions that can be related with the globally known medieval warm period (MWP), supported by the δ13C values around -24‰ during this time and the high χLF values. Moreover, the good representation of Cyperaceae pollen suggests the in-filling of the lake followed by the invasion of ground vegetation viz. Cheno/Ams, Apiaceae, Poaceae etc. The good pollen frequency of broadleaved taxa viz. Quercus and Alnus also supports the moist conditions. Since 600 cal years BP the lowered χLF values signifies reduced input from the surrounding suggesting the filling of the lake. The marked increase in the pollen frequency of Cheno/Ams with low values of fern spores suggest less moist conditions with reduced summer monsoon that can be related to Little Ice Age (LIA) episode. Also the low negative δ13C values (around -21‰) indicates the less ground moisture supporting the C4 taxa. The Quercus and Alnus also reduced in their pollen presence. Whereas the Pinus pollen increased gradually since nearly before 410 cal years BP till recent showing the increased invasion of this taxa to near proximity of the area. The

  10. Late Holocene monsoon climate as evidenced by proxy records from a lacustrine sediment sequence in western Guangdong, South China

    Zhong, Wei; Cao, jiayuan; Xue, Jibin; Ouyang, Jun; Tang, Xiaohong; Yin, Huanling; Liao, Congyun; Long, Kun


    The study of a 300-cm-thick exposed lacustrine sediment section in the Hedong village in Zhaoqing area which is located in sub-tropical west Guangdong Province in South China, demonstrates that the lacustrine sedimentary sequence possibly contains evidence for exploring variation of Asian monsoon climate. Multi-proxy records, including the humification intensity, total organic carbon, and grain size fractions, reveal a general trend towards dry and cold conditions in the late Holocene that this is because of a decrease in solar insolation on an orbital scale. Three intensified Asian summer monsoon (ASM) intervals (˜3300-3000 cal yr BP, ˜2600-1600 cal yr BP, and ˜900-600 cal yr BP), and three weakened ASM intervals (˜4000-3300 cal yr BP, ˜3000-2600 cal yr BP, and ˜1600-900 cal yr BP) are identified. Our humification record (HDcal) shows a good correlation on multi-centennial scale with the tree ring Δ14C record, a proxy of solar activity. A spectral analysis of HDcal reveals four significant cycles, i.e., ˜1250 yr, 300 yr, 110 yr, and 70 yr, and most of these cycles are related to the solar activity. Our findings indicate that solar output and oceanic-atmospheric circulation probably have influenced the late Holocene climate variability in the study region.

  11. Lake Ecosystem Responses to Holocene Climate Change at the Subarctic Tree-Line in Northern Sweden

    Reuss, Nina Steenberg; Hammarlund, Dan; Rundgren, Mats


    sedimentary pigments, diatoms, chironomids, pollen, biogenic silica (BSi), carbon (C), nitrogen (N) elemental and stable-isotope records, and total lake-water organic carbon (TOC) concentration inferred from near-infrared spectroscopy (NIRS), suggest that the Holocene development of Lake Seukokjaure...

  12. A Collaborative Proposal: Simulating and Understanding Abrupt Climate-Ecosystem Changes During Holocene with NCAR-CCSM3.

    Zhengyu Liu, Bette Otto-Bliesner


    We have made significant progress in our proposed work in the last 4 years (3 years plus 1 year of no cost extension). In anticipation of the next phase of study, we have spent time on the abrupt changes since the last glacial maximum. First, we have performed further model-data comparison based on our baseline TRACE-21 simulation and made important progress towards the understanding of several major climate transitions. Second, we have made a significant effort in processing the model output of TRACE-21 and have put this output on a website for access by the community. Third, we have completed many additional sensitivity experiments. In addition, we have organized synthesis workshops to facilitate and promote transient model-data comparison for the international community. Finally, we have identified new areas of interest for Holocene climate changes.

  13. Broadleaf deciduous forest counterbalanced the direct effect of climate on Holocene fire regime in hemiboreal/boreal region (NE Europe)

    Feurdean, Angelica; Veski, Siim; Florescu, Gabriela; Vannière, Boris; Pfeiffer, Mirjam; O'Hara, Robert B.; Stivrins, Normunds; Amon, Leeli; Heinsalu, Atko; Vassiljev, Jüri; Hickler, Thomas


    Disturbances by fire are essential for the functioning of boreal/hemiboreal forests, but knowledge of long-term fire regime dynamics is limited. We analysed macrocharcoal morphologies and pollen of a sediment record from Lake Lielais Svētiņu (eastern Latvia), and in conjunction with fire traits analysis present the first record of Holocene variability in fire regime, fuel sources and fire types in boreal forests of the Baltic region. We found a phase of moderate to high fire activity during the cool and moist early (mean fire return interval; mFRI of ∼280 years; 11,700-7500 cal yr BP) and the late (mFRI of ∼190 years; 4500-0 cal yr BP) Holocene and low fire activity (mFRI of ∼630 years) during the Holocene Thermal Optimum (7500-4500 cal yr BP). Charcoal morphotypes and the pollen record show the predominance of frequent surface fires, occasionally transitioning to the crown during Pinus sylvestris-Betula boreal forests and less frequent surface fires during the dominance of temperate deciduous forests. In contrast to the prevailing opinion that fires in boreal forests are mostly low to moderate severity surface fires, we found evidence for common occurrence of stand-replacing crown fires in Picea abies canopy. Our results highlight that charcoal morphotypes analysis allows for distinguishing the fuel types and surface from crown fires, therefore significantly advancing our interpretation of fire regime. Future warmer temperatures and increase in the frequency of dry spells and abundant biomass accumulation can enhance the fire risk on the one hand, but will probably promote the expansion of broadleaf deciduous forests to higher latitudes, on the other hand. By highlighting the capability of broadleaf deciduous forests to act as fire-suppressing landscape elements, our results suggest that fire activity may not increase in the Baltic area under future climate change.

  14. An abrupt centennial-scale drought event and mid-holocene climate change patterns in monsoon marginal zones of East Asia.

    Yu Li

    Full Text Available The mid-latitudes of East Asia are characterized by the interaction between the Asian summer monsoon and the westerly winds. Understanding long-term climate change in the marginal regions of the Asian monsoon is critical for understanding the millennial-scale interactions between the Asian monsoon and the westerly winds. Abrupt climate events are always associated with changes in large-scale circulation patterns; therefore, investigations into abrupt climate changes provide clues for responses of circulation patterns to extreme climate events. In this paper, we examined the time scale and mid-Holocene climatic background of an abrupt dry mid-Holocene event in the Shiyang River drainage basin in the northwest margin of the Asian monsoon. Mid-Holocene lacustrine records were collected from the middle reaches and the terminal lake of the basin. Using radiocarbon and OSL ages, a centennial-scale drought event, which is characterized by a sand layer in lacustrine sediments both from the middle and lower reaches of the basin, was absolutely dated between 8.0-7.0 cal kyr BP. Grain size data suggest an abrupt decline in lake level and a dry environment in the middle reaches of the basin during the dry interval. Previous studies have shown mid-Holocene drought events in other places of monsoon marginal zones; however, their chronologies are not strong enough to study the mechanism. According to the absolutely dated records, we proposed a new hypothesis that the mid-Holocene dry interval can be related to the weakening Asian summer monsoon and the relatively arid environment in arid Central Asia. Furthermore, abrupt dry climatic events are directly linked to the basin-wide effective moisture change in semi-arid and arid regions. Effective moisture is affected by basin-wide precipitation, evapotranspiration, lake surface evaporation and other geographical settings. As a result, the time scales of the dry interval could vary according to locations due to

  15. Late Glacial to Holocene climate change and human impact in the Mediterranean : The last ca. 17ka diatom record of Lake Prespa (Macedonia/Albania/Greece)

    Cvetkoska, Aleksandra; Levkov, Zlatko; Reed, Jane M.; Wagner, Bernd


    Lake Prespa (Macedonia/Albania/Greece) occupies an important location between Mediterranean and central European climate zones. Although previous multi-proxy research on the Late Glacial to Holocene sequence, core Co1215 (320cm; ca. 17cal ka BP to present), has demonstrated its great value as an

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

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


    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

  17. Climate control on late Holocene high-energy sedimentation along coasts of the northeastern Atlantic Ocean

    Poirier , Clément; Tessier , Bernadette; Chaumillon , Eric


    International audience; Abundant sedimentological and geochronological data gathered on European sandy coasts highlight major phases of increased high-energy sedimentation in the North Atlantic Ocean during the late Holocene. Owing to an inconsistent use of the terminology, it is often difficult to determine whether studies have described storm-built or wave-built deposits. Both deposits can be identified by overall similar coarse-grained sedimentary facies, but may provide contradictory pale...

  18. Compilation of information on the climate and evaluation of the hydrochemical and isotopic composition during Late Pleistocene and Holocene

    Andersson, Cecilia


    This report summarises and evaluates some of the existing information on the Late Pleistocene and Holocene climates, i.e. the last 130 000 years. An estimation of the conditions at the Aespoe island (southeast Sweden) has also been made during this time span. The knowledge about Late Pleistocene (Eemian Interglacial and Weichselian glacial) is not yet fully understood. There are still a lot of assumptions concerning this period and more information is needed to be able to establish the climatic conditions. This is not the case for the Weichselian deglaciation and the present interglacial, Holocene, for which the environmental conditions are quite certain. It has been concluded, however, that the Eemian climatic development probably was similar to the Holocene but perhaps somewhat warmer and more humid. The Eemian Baltic Sea level was probably also higher than the present Baltic Sea level and there was a connection between it and the White Sea in the northeast. Aespoe was probably situated below sea level during the greater part of Eemian. Not much is known about the last glacial period, the Weichselian glaciation, until the final deglaciation. The ice sheet during Early Weichselian was probably mostly concentrated to the Scandinavian mountain area and in northern Scandinavia. At least two intervals with higher temperatures have been recorded, the Broerup and Odderade interstadials. The Middle Weichselian substage is characterised by fluctuations, melting and re-advances. Aespoe was probably not glaciated until the middle or latter part of Middle Weichselian. The maximum extension of the Weichselian ice sheet occurred in Late Weichselian, around 20 to 18 ka BP, which was succeeded by the final deglaciation. The retreat of the Weichselian ice sheet is described by for example end moraines and glacial varved clay. The Aespoe area was glaciated until 12 500 BP. Huge quantities of glacial meltwater was released into the Baltic basin as the ice receded. Due to different

  19. Compilation of information on the climate and evaluation of the hydrochemical and isotopic composition during Late Pleistocene and Holocene

    Andersson, Cecilia [Intera KB (Sweden)


    This report summarises and evaluates some of the existing information on the Late Pleistocene and Holocene climates, i.e. the last 130 000 years. An estimation of the conditions at the Aespoe island (southeast Sweden) has also been made during this time span. The knowledge about Late Pleistocene (Eemian Interglacial and Weichselian glacial) is not yet fully understood. There are still a lot of assumptions concerning this period and more information is needed to be able to establish the climatic conditions. This is not the case for the Weichselian deglaciation and the present interglacial, Holocene, for which the environmental conditions are quite certain. It has been concluded, however, that the Eemian climatic development probably was similar to the Holocene but perhaps somewhat warmer and more humid. The Eemian Baltic Sea level was probably also higher than the present Baltic Sea level and there was a connection between it and the White Sea in the northeast. Aespoe was probably situated below sea level during the greater part of Eemian. Not much is known about the last glacial period, the Weichselian glaciation, until the final deglaciation. The ice sheet during Early Weichselian was probably mostly concentrated to the Scandinavian mountain area and in northern Scandinavia. At least two intervals with higher temperatures have been recorded, the Broerup and Odderade interstadials. The Middle Weichselian substage is characterised by fluctuations, melting and re-advances. Aespoe was probably not glaciated until the middle or latter part of Middle Weichselian. The maximum extension of the Weichselian ice sheet occurred in Late Weichselian, around 20 to 18 ka BP, which was succeeded by the final deglaciation. The retreat of the Weichselian ice sheet is described by for example end moraines and glacial varved clay. The Aespoe area was glaciated until 12 500 BP. Huge quantities of glacial meltwater was released into the Baltic basin as the ice receded. Due to different

  20. Climate and lake-level history of the northern Altiplano, Bolivia, as recorded in Holocene sediments of the Rio Desaguadero

    Baucom, P.C.; Rigsby, C.A. [East Carolina Univ., Greenville, NC (United States). Dept. of Geology


    Strata exposed in terraces and modern cutbanks along the Rio Desaguadero contain a variety of lithofacies that were deposited in four distinct facies associations. These facies associations document a history of aggradation and downcutting that is linked to Holocene climate change on the Altiplano. Braided-stream, meandering-stream, deltaic and shoreline, and lacustrine sediments preserved in multi-level terraces in the northern Rio Desaguadero valley record two high-water intervals: one between 4,500 and 3,900 yr BP and another between 2,000 and 2,200 yr BP. These wet periods were interrupted by three periods of fluvial downcutting, centered at approximately 4,000 yr BP, 3,600 yr BP, and after 2,000 yr BP. Braided-river sediments preserved in a single terrace level in the southern Rio Desaguadero valley record a history of nearly continuous fluvial sedimentation from at least 7,000 yr BP until approximately 3,200 yr BP that was followed by a single episode (post-3,210 yr BP) of down-cutting and lateral migration. The deposition and subsequent fluvial downcutting of the northern strata was controlled by changes in effective moisture that can be correlated to Holocene water-level fluctuations of Lake Titicaca. The deposition and dissection of braided-stream sediments to the south are more likely controlled by a combination of base-level change and sediment input from the Rio Mauri.

  1. Holocene evolution of a montane lake catchment inferred from multiproxy sediment analysis : climatic and anthropic impacts in french prealps

    Bajard, Manon; Sabatier, Pierre; Poulenard, Jérôme; David, Fernand; Arnaud, Fabien; Develle, Anne-Lise; Reyss, Jean-Louis; Fanget, Bernard; Malet, Emmanuel; Crouzet, Christian


    Lake La Thuile in the Massif des Bauges (874 m a.s.l. French Alps) provides a 18 meters sedimentary sequence. Due to its mid-altitude position, this lake is one of the first to be formed through the glacial retreat and documents the evolution of its catchment since the Late Glacial Maximum. The first 6 meters of the core cover the last 12 000 years, and allowed to study human/climate/environment interactions in a carbonated environment. This study is the first one to investigate a mid-altitude lake in the French Alps for paleoenvironment reconstruction from lake sediment archive. Its altitudinal position presents the advantage to be very accessible to human activities and allows more developed agriculture than in higher altitude. This study aims to determined how and when is expressed the erosive response of such an environment to human settlement. High resolution multiproxy analysis of the first 6 meters including sedimentological, palynological and geochemical data associated to a well-constrained chronology over the Holocene period allows us to understand the respective impacts of both climate and human on the evolution of Lake La Thuile environment. Five major phases of evolution have been highlighted over this period. From 12 000 to 10 000 yr cal. BP, the vegetation is developing with the onset of hardwood species and the disappearance of Pinus. From 10 000 to 4500 yr cal. BP the warmer climatic conditions of the middle of the Holocene allows the forest to densify and the very low sedimentation rate indicates that the forest stabilizes slopes and prevents from the erosion on the watershed. The climate cooling of the Neoglacial period triggers a first erosive phase with a decreasing of the forest around 3300 cal. BP. Human settlements are suggested at La Thuile from 2500 yr cal. BP by palynological evidence of anthropic taxa. The triggered clearing is accompanied by a second erosive phase related to anthropic activities during the Roman period. Erosion

  2. Climate and vegetation changes during the Lateglacial and early–middle Holocene at Lake Ledro (southern Alps, Italy

    S. Joannin


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

  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

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


    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. Holocene soil-geomorphic surfaces influence the role of salmon-derived nutrients in the coastal temperate rainforest of Southeast Alaska

    David V. D' Amore; Nicholas S. Bonzey; Jacob Berkowitz; Janine Rüegg; Scott. Bridgham


    The influence of salmon-derived nutrients (SDN) is widely accepted as a potential factor in the maintenance of aquatic and terrestrial productivity in North American Coastal rainforests. Holocene alluvial landforms are intimately connected with the return of anadromous salmon, but the influence of the soils that occupy these landforms and support this important...

  5. Latest Holocene Climate Variability revealed by a high-resolution multiple Proxy Record off Lisbon (Portugal)

    Abrantes, F.; Lebreiro, S.; Ferreira, A.; Gil, I.; Jonsdottir, H.; Rodrigues, T.; Kissel, C.; Grimalt, J.


    The North Atlantic Oscillation (NAO) is known to have a major influence on the wintertime climate of the Atlantic basin and surrounding countries, determining precipitation and wind conditions at mid-latitudes. A comparison of Hurrel's NAO index to the mean winter (January-March) discharge of the Iberian Tagus River reveals a good negative correlation to negative NAO, while the years of largest upwelling anomalies, as referred in the literature, appear to be in good agreement with positive NAO. On this basis, a better understanding of the long-term variability of the NAO and Atlantic climate variability can be gained from high-resolution climate records from the Lisbon area. Climate variability of the last 2,000 years is assessed through a multiple proxy study of sedimentary sequences recovered from the Tagus prodelta deposition center, off Lisbon (Western Iberia). Physical properties, XRF and magnetic properties from core logging, grain size, δ18O, TOC, CaCO3, total alkenones, n-alkanes, alkenone SST, diatoms, benthic and planktonic foraminiferal assemblage compositions and fluxes are the proxies employed. The age model for site D13902 is based on AMS C-14 dates from mollusc and planktonic foraminifera shells, the reservoir correction for which was obtained by dating 3 pre-bomb, mollusc shells from the study area. Preliminary results indicate a Little Ice Age (LIA - 1300 - 1600 AD) alkenone derived SSTs around 15 degC followed by a sharp and rapid increase towards 19 degC. In spite the strong variability observed for most records, this low temperature interval is marked by a general increase in organic carbon, total alkenone concentration, diatom and foraminiferal abundances, as well as an increase in the sediment fine fraction and XRF determined Fe content, pointing to important river input and higher productivity. The Medieval Warm Period (1080 - 1300 AD) is characterized by 17-18 degC SSTs, increased mean grain size, but lower magnetic susceptibility and Fe

  6. Holocene fire dynamics in Fennoscandia

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


    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

  7. Late Holocene climate and environmental change from Asiul cave speleothems: interpretations in light of modern cave monitoring.

    Smith, Andrew; Wynn, Peter; Barker, Philip; Leng, Melanie; Noble, Steve; Tych, Wlodek


    Northern Iberia offers an excellent location to study fluctuations in North Atlantic Ocean (NA) conditions and the impact that changes in the NA have on atmospheric systems, which dominate Europe's climate. Two speleothems from Cueva de Asiul (Matienzo, N. Spain) have been used to reconstruct rainfall variability in N. Spain throughout the Holocene (Smith et al., 2016a). The carbonate δ18O records from these speleothems are interpreted in the light of a rigorous modern cave monitoring program undertaken at Cueva de Asiul (Smith et al., 2016b). Drip water δ18O reflects a modern rainfall amount effect whilst δ13C appears influenced by Prior Calcite Precipitation (PCP) in the short term and changes in vegetation at long timescales. The speleothem δ18O shows that long duration ( 1500 year) cycles in wetting and drying are prevalent in N. Spain during the Holocene and that dry climate phases are related to the timing of cold events (Bond et al., 2001) in the NA. Here we look in more detail at one of these speleothems, assessing both δ18O and δ13C during the last two thousand years. We show that Cueva de Asiul speleothems not only preserve long duration climate cycles in δ18O, but that they also appear influenced by shorter duration changes in the North Atlantic Oscillation (NAO), in-sync with other NAO archives (Olsen et al., 2012). However, the Cueva de Asiul record does not appear to preserve a predominately positive NAO signal during the Medieval Climate Anomaly (MCA) as is common within many European archives (Trouet et al., 2009), possibly due to the sites' close proximity to the NA and localised oceanic weather systems (Moreno et al., 2012). Alongside climatic changes, the speleothem δ13C shows a clear transition toward higher isotope values around 360 years BP (BP=1950), signalling a major environmental change in the region possibly due to anthropogenic removal of vast swathes of natural forest to support ship building and industry related to the Spanish

  8. Holocene climate and environmental change in the Palliser Triangle: a geoscientific context for evaluating the impacts of climate change on the southern Canadian prairies

    Lemmen, D. S.; Vance, R. E. [eds.


    The Palliser Triangle is the driest portion of the Canadian Prairies, and one of the most climatically sensitive regions in Canada. As proof of that, it has suffered severe droughts in the 1920s, 1930s and the 1980s. General climatic models predict that future global warming will be most pronounced in northern regions and continental interiors, including the Great Plains of North America. Evidence of warming is already present in the regional climate record, suggesting that the Palliser Triangle is likely to become even more arid, and drought frequency may increase. This volume contains 18 papers related to major objectives of a project involving the use of the unique paleoenvironmental records available in the Palliser Triangle to assess the impacts of future climate change. Two major objectives of the project are of particular focus: the reconstruction of the Holocene (post-glacial) climatic and hydrological changes, and the evaluation of the relationship between climate and landscape processes. Each paper is capable of standing on its own as a contribution to a specific geoscience discipline; by bringing them together in one regionally focused volume, the editors intend to highlight the need for interdisciplinary and multidisciplinary approaches to the study of global climate change issues. The first paper provides a broad summary of the major results, followed by nine papers devoted to records of past climate and hydrological change documented in paleolimnological and hydrogeological studies. The remaining eight papers focus on geomorphic processes in the Palliser Triangle, and on explanations of how these processes respond to climate forcing. Since each contribution can stand its own, each paper has its own abstract in English and French and its own bibliography. There is an author index for the volume as whole.

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

    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)


    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.)

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

    Alizadeh, Kamaleddin; Cohen, Marcelo; Behling, Hermann


    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

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

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


    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.

  12. Mid-late Holocene climate and vegetation in northeastern part of the Altai Mountains recorded in Lake Teletskoye

    Rudaya, Natalia; Nazarova, Larisa; Novenko, Elena; Babich, Valery; Kalugin, Ivan; Daryin, Andrei


    We report the first high-resolution (with intervals ca. 20-50 years) late-Holocene (4200 yr BP) pollen record from Lake Teletskoye, Altai Mountains, obtained from the underwater Ridge of Sofia Lepneva in 2006 (core Tel 2006). The study presents (i) the results of palynological analysis of Tel 2006; (ii) the results of spectral analysis of natural cycles based on the periodical fluctuation of taiga-biome curve; and (iii) quantitative reconstructions of the late-Holocene regional vegetation, woody coverage and climate in northern part of the Altai Mountains in order to define place of Northeast Altai on the map of the late-Holocene Central Asian environmental history. Late Holocene vegetation of the northeastern part of Altai recorded in Tel 2006 core is characterized by spread of dark-coniferous forest with structure similar to modern. Dominant trees, Siberian pine (Pinus sibirica) and Siberian fir (Abies sibirica), are the most ecological sensitive taxa between Siberian conifers (Shumilova, 1962), that as a whole suggests mild and humid climatic conditions during last 4200 years. However, changes of pollen taxa percentages and results of numerical analysis reveal pronounced fluctuation of climate and vegetation. Relatively cool and dry stage occurred prior to ca. 3500 cal yr BP. Open vegetation was widespread in the region with maximum deforestation and minimal July temperatures between 3800-3500 cal yr BP. Steppe-like communities with Artemisia, Chenopodiaceae and Cyperaceae could grow on the open sites around Lake Teletskoye. Reconstructed woody coverage is very low and varies between 29-35%. After ca. 3500 cal yr BP the area of dark-coniferous mountain taiga has significantly enlarged with maximums of woody coverages and taiga biome scores between ca. 2470-1040 cal yr BP. In the period of ~3500-2500 cal yr BP the averages July temperatures increased more than 1 0C. Climate became warmer and wetter. During last millennium (after 1040 cal yr BP) average July

  13. Biomization and quantitative climate reconstruction techniques in northwestern Mexico—With an application to four Holocene pollen sequences

    Ortega-Rosas, C. I.; Guiot, J.; Peñalba, M. C.; Ortiz-Acosta, M. E.


    New paleovegetation and paleoclimatic reconstructions from the Sierra Madre Occidental (SMO) in northwestern Mexico are presented. This work involves climate and biome reconstruction using Plant Functional Types (PFT) assigned to pollen taxa. We used fossil pollen data from four Holocene peat bogs located at different altitudes (1500-2000 m) at the border region of Sonora and Chihuahua at around 28° N latitude (Ortega-Rosas, C.I. 2003. Palinología de la Ciénega de Camilo: datos para la historia de la vegetación y el clima del Holoceno medio y superior en el NW de la Sierra Madre Occidental, Sonora, Mexico. Master Thesis, Universidad Nacional Autónoma de México, México D.F.; Ortega-Rosas, C.I., Peñalba, M.C., Guiot, J. Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico. Submitted for publication of Palaeobotany and Palynology). The closest modern pollen data come from pollen analysis across an altitudinal transect from the Sonoran Desert towards the highlands of the temperate SMO at the same latitude (Ortega-Rosas, C.I. 2003. Palinología de la Ciénega de Camilo: datos para la historia de la vegetación y el clima del Holoceno medio y superior en el NW de la Sierra Madre Occidental, Sonora, Mexico. Master Thesis, Universidad Nacional Autónoma de México, México D.F.). An additional modern pollen dataset of 400 sites across NW Mexico and the SW United States was compiled from different sources (Davis, O.K., 1995. Climate and vegetation pattern in surface samples from arid western U.S.A.: application to Holocene climatic reconstruction. Palynology 19, 95-119, North American Pollen Database, Latin-American Pollen Database, personal data, and different scientific papers). For the biomization method (Prentice, I.C., Guiot, J., Huntley, B., Jolly, D., Cheddadi, R., 1996. Reconstructing biomes from paleoecological data: a general method and its application to European pollen data at 0 and

  14. Climate change between the mid and late Holocene in northern high latitudes – Part 2: Model-data comparisons

    K. Holmgren


    Full Text Available The climate response over northern high latitudes to the mid-Holocene orbital forcing has been investigated in three types of PMIP (Paleoclimate Modelling Intercomparison Project simulations with different complexity of the modelled climate system. By first undertaking model-data comparison, an objective selection method has been applied to evaluate the capability of the climate models to reproduce the spatial response pattern seen in proxy data. The possible feedback mechanisms behind the climate response have been explored based on the selected model simulations. Subsequent model-model comparisons indicate the importance of including the different physical feedbacks in the climate models. The comparisons between the proxy-based reconstructions and the best fit selected simulations show that over the northern high latitudes, summer temperature change follows closely the insolation change and shows a common feature with strong warming over land and relatively weak warming over ocean at 6 ka compared to 0 ka. Furthermore, the sea-ice-albedo positive feedback enhances this response. The reconstructions of temperature show a stronger response to enhanced insolation in the annual mean temperature than winter and summer temperature. This is verified in the model simulations and the behaviour is attributed to the larger contribution from the large response in autumn. Despite a smaller insolation during winter at 6 ka, a pronounced warming centre is found over Barents Sea in winter in the simulations, which is also supported by the nearby northern Eurasian continental and Fennoscandian reconstructions. This indicates that in the Arctic region, the response of the ocean and the sea ice to the enhanced summer insolation is more important for the winter temperature than the synchronous decrease of the insolation.

  15. Holocene megathermal abrupt environmental changes derived from {sup 14}C dating of a coral reef at Leizhou Peninsula, South China Sea

    Shen Chengde; Yi Weixi E-mail:; Yu Kefu; Sun Yanmin; Liu Tungsheng; Beer, J.; Hajdas, I.; Bonani, G


    A depth profile of a Goniopora coral reef at Leizhou Peninsula, South China Sea, was radiocarbon dated using liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS). The time of formation, during 6600-7400 cal BP, can be divided into nine stages, each terminated by abrupt growth cessation of Goniopora and appearance of Ostrea shells. The results show that, during the Holocene megathermal (8.2-3.3 ka BP), large climatic changes have occurred in the South China Sea area.

  16. Salinity-induced stratification and the onset of hypoxia during the Holocene Thermal Maximum and the Medieval Climate Anomaly

    Papadomanolaki, Nina; Dijkstra, Nikki; van Helmond, Niels; Sangiorgi, Francesca; Hagens, Mathilde; Kotthoff, Ulrich; Slomp, Caroline


    During the past ~8000 years the Baltic Sea has experienced three distinct intervals of hypoxia, of which the last one is still ongoing. These intervals are characterized by enhanced sedimentary organic matter burial and enrichment of redox-sensitive metals, such as molybdenum and iron. The first two of these intervals occurred during the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA), two phases with high temperatures and changed precipitation patterns. Studies focussing on the Holocene sedimentary record of the Baltic Sea aim at clarifying the causes of the initiation, evolution and termination of these hypoxic intervals, as well as their consequences. This information could help to potentially aid in finding solutions for the mitigation of present-day hypoxia in the Baltic Sea. The factors contributing to hypoxia development during the HTM and MCA are still debated. Here we present data from a core retrieved during Integrated Ocean Drilling Program (IODP) Expedition 347 in the Landsort Deep basin, the deepest basin of the Baltic Sea at 463m water depth. Sediments were analysed at a high resolution using inorganic geochemical and (mainly marine) palynological proxies. Dinoflagellate cyst (dinocyst) assemblages and total elemental compositions provide clues on the role of salinity in enhancing stratification, ultimately causing hypoxia. During the onset of the HTM changes in salinity, as indicated by the palynology, closely follow changes in sedimentary organic carbon burial and trace metal concentrations. This suggests that stratification was an important cause of hypoxia during the HTM. In contrast, the palynology suggests that reduced stratification did not contribute to re-oxygenation during the termination of the HTM. We did not observe major changes in the palynology throughout the hypoxic interval of the MCA. Our results thus suggest that changes in salinity did not cause the onset and termination of hypoxia during the MCA.

  17. Holocene environmental and parasequence development of the St. Jones Estuary, Delaware (USA): Foraminiferal proxies of natural climatic and anthropogenic change

    Leorri, E.; Martin, R.; McLaughlin, P.


    The benthic foraminiferal record of marshes located along western Delaware Bay (St. Jones Estuary, USA) reflects the response of estuaries to sea-level and paleoclimate change during the Holocene. System tracts are recognized and within them parasequences based on sedimentological and foraminiferal assemblages identification. The parasequences defined by foraminiferal assemblages appear correlative with rapid Holocene climate changes that are of worldwide significance: 6000-5000, 4200-3800, 3500-2500, 1200-1000, and 600??cal years BP. Following postglacial sea-level rise, modern subestuaries and marshes in the region began to develop between 6000 and 4000??years BP, depending on their proximity to the mouth of Delaware Bay and coastal geomorphology. Initial sediments were fluvial in origin, with freshwater marshes established around 4000??years BP. The subsequent sea-level transgression occurred sufficiently slowly that freshwater marshes alternated with salt marshes at the same sites to around 3000??years BP. Locally another two transgressions are identified at 1800 and 1000??years BP respectively. Marine influence increased in the estuaries until 600??years BP (Little Ice Age), when regression occurred. Sea-level began to rise again during the mid-19th Century at the end of the Little Ice Age, when marshes became established. The presence of a sand lens in the upper and middle estuary and the reduction in the number of tests in the top samples in cores from the same area also suggest an anthropogenic influence. The estuary infill resulted in a sharp transgressive sequence, represented by salt marsh foraminiferal assemblages in the upper part of the cores. The increase in marsh foraminifera in both areas suggests an increase in marine influence that might be due to the transgression beginning at the end of the Little Ice Age about 150-180??years ago coupled with anthropogenic straightening of the channel in 1913. ?? 2006 Elsevier B.V. All rights reserved.

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

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


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

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

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


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

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

    S. Weldeab


    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.

  1. Distribution of mountain wetlands and their response to Holocene climate change in the Hachimantai Volcanic Groups, northeastern Japan

    Sasaki, N.; Sugai, T.


    Mountain wetlands, natural peatlands or lakes, with narrow catchment areas need abundant water supply and topography retaining water because of unstable water condition. This study examines wetland distribution with a focus on topography and snow accumulation, and discuss wetland evolution responding to Holocene climate change in the Hachimantai Volcanic Group, northeastern Japan, where the East Asian winter monsoon brings heavier snow and where has many wetlands of varied origin: crater lakes and wetlands in nivation hollows on original volcanic surfaces, and wetlands in depressions formed by landslides. We identified and classified wetlands using aerial photographs and 5-m and 10-m digital elevation models. Wetlands on the original volcanic surfaces tend to be concentrated under the small scarps with much snow or on saddles of the mountain ridge where snowmelt from surrounding slopes maintains a moist environment. More lake type wetlands are formed in the saddle than in the snowdrifts. That may represent that the saddles can correct more recharge water and may be a more suitable topographic condition for wetland formation and endurance. On the contrary, wetlands on landslides lie at the foot of the scarps where spring water can be abundantly supplied, regardless of snow accumulation. We used lithological analysis, 14C dating, tephra age data, and carbon contents of wetland cores to compare the evolution of wetlands, one (the Oyachi wetland) within a huge landslide and three (the Appi Highland wetlands) outside of a landslide area. We suggest that the evolution of the wetland in the landslide is primarily influenced by landslide movements and stream dissection rather than climate change. In the Appi Highland wetlands, peatlands appeared much later and at the almost same time in the Medieval Warm Period. We suggest that the development of mountain wetlands outside of landslide areas is primarily related to climate changes. Responsiveness of mountain wetlands to

  2. Population differentiation in the context of Holocene climate change for a migratory marine species, the southern elephant seal.

    Corrigan, L J; Fabiani, A; Chauke, L F; McMahon, C R; de Bruyn, M; Bester, M N; Bastos, A; Campagna, C; Muelbert, M M C; Hoelzel, A R


    Understanding observed patterns of connectivity requires an understanding of the evolutionary processes that determine genetic structure among populations, with the most common models being associated with isolation by distance, allopatry or vicariance. Pinnipeds are annual breeders with the capacity for extensive range overlap during seasonal migrations, establishing the potential for the evolution of isolation by distance. Here, we assess the pattern of differentiation among six breeding colonies of the southern elephant seal, Mirounga leonina, based on mtDNA and 15 neutral microsatellite DNA markers, and consider measures of their demography and connectivity. We show that all breeding colonies are genetically divergent and that connectivity in this highly mobile pinniped is not strongly associated with geographic distance, but more likely linked to Holocene climate change and demographic processes. Estimates of divergence times between populations were all after the last glacial maximum, and there was evidence for directional migration in a clockwise pattern (with the prevailing current) around the Antarctic. We discuss the mechanisms by which climate change may have contributed to the contemporary genetic structure of southern elephant seal populations and the broader implications. © 2016 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2016 European Society For Evolutionary Biology.

  3. Holocene glacier and climate variations in Vestfirðir, Iceland, from the modeling of Drangajökull ice cap

    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


    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.

  4. Modern pollen–climate relationships in north Xinjiang, northwestern China : Implications for pollen-based reconstruction of Holocene climate

    Li, Furong; Zhao, Yan; Gaillard, Marie José; Li, Huan; Sun, Jinghui; Xu, Qinghai


    Fossil pollen records are widely used to reconstruct past climate. Such reconstructions require that the relationships between pollen assemblages, vegetation, and climate are well understood. These can be studied in present circumstances given we assume that modern vegetation and climate are

  5. Coring of Karakel’ Lake sediments (Teberda River valley and prospects for reconstruction of glaciation and Holocene climate history in the Caucasus

    O. N. Solomina


    Full Text Available Lacustrine sediments represent an important data source for glacial and palaeoclimatic reconstructions. Having a number of certain advantages, they can be successfully used as a means of specification of glacier situation and age of moraine deposits, as well as a basis for detailed climatic models of the Holocene. The article focuses on the coring of sediments of Lake Kakakel (Western Caucasus that has its goal to clarify the Holocene climatic history for the region, providing the sampling methods, lithologic description of the sediment core, obtained radiocarbon dating and the element composition of the sediments. The primary outlook over the results of coring of the sediments of the Lake Karakyol helped to reconsider the conventional opinion on the glacial fluctuations in the valley of Teberda and to assume the future possibility for high-definition palaeoclimatic reconstruction for Western Caucasus.

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

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


    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.

  7. Holocene climate change and the evidence for solar and other forcings

    Beer, J.; van Geel, B.; Battarbee, R.W.; Binney, H.A.


    Future climate change may have considerable effects on the hydrologic cycle and temperature, with significant consequences for sea level, food production, world economy, health, and biodiversity. How and why does the natural climate system vary on decadal to millennial time-scales? Do we

  8. The diatom flora of Lake Kinneret (Israel) - Paleolimnological evidence for Holocene climate change and human impact in the southeastern Mediterranean

    Vossel, Hannah; Reed, Jane M.; Litt, Thomas


    The Mediterranean basin is a region of highly complex topography and climatic variability, such that our understanding of the past environmental variability is still limited. Diatoms (single-celled siliceous algae, Bacillariophyceae) are abundant, diverse and sensitive to a wide range of environmental parameters. They are often well preserved in lake sediment records, and have well-recognised potential to generate high-quality paleolimnological data. Diatoms remain one of the least-exploited proxies in Mediterranean palaeoclimate research. Here, we present results of diatom analysis of an 18 m sediment core from Lake Kinneret (Israel) as part of a multi-proxy study of Holocene climate change and human impact in the Levant ( Results are compared with other proxy data including pollen, and with output data from regional climate modelling, to strengthen interpretation of environmental change in the southeastern Mediterranean. The results show remarkable shifts in the diatom flora over the last ca. 8,000 years. Preliminary investigations show that 98% of the diatom taxa can be classified as oligohalobous-indifferent and as alkaliphilous, as is typical of freshwater, alkaline lakes of open hydrology in limestone, karst-dominated catchments. Changes in the diatom data over time can be interpreted mainly in terms of productivity shifts, with a clear trend from oligotrophic at the base to hypereutrophic in the modern lake. The eutrophication trend accelerates after ca. 3,000 cal. yrs. BP, indicating the influence of increased human activity in the catchment, identified previously by analysis of the vegetational history (Schiebel, 2013). The analysis of the composition of the diatom flora also provides some evidence for lake-level fluctuations, as a proxy for shifts in moisture availability. Low lake-level stands are characterized by low diatom concentration and increased relative abundance of littoral taxa. High lake-level stands are marked

  9. Holocene Substrate Influences on Plant and Fire Response to Climate Change

    Briles, C.; Whitlock, C. L.


    The role of substrates in facilitating plant responses to climate change in the past has received little attention. Ecological studies, documenting the relative role of fertile and infertile substrates in mediating the effects of climate change, lack the temporal information that paleoecological lake studies provide on how plants have responded under equal, larger and more rapid past climate events than today. In this paper, pollen and macroscopic charcoal preserved in the sediments of eight lakes surrounded by infertile ultramafic soils and more fertile soils in the Klamath Mountains of northern California were analyzed. Comparison of late-Quaternary paleoecological sites suggests that infertile and fertile substrates supported distinctly different plant communities. Trees and shrubs on infertile substrates were less responsive to climate change than those on fertile substrates, with the only major compositional change occurring at the glacial/interglacial transition (~11.5ka), when temperature rose 5oC. Trees and shrubs on fertile substrates were more responsive to climate changes, and tracked climate by moving along elevational gradients, including during more recent climate events such as the Little Ice Age and Medieval Climate Anomaly. Fire regimes were similar until 4ka on both substrate types. After 4ka, understory fuels on infertile substrates became sparse and fire activity decreased, while on fertile substrates forests became increasingly denser and fire activity increased. The complacency of plant communities on infertile sites to climate change contrasts with the individualistic and rapid adjustments of species on fertile sites. The findings differ from observations on shorter time scales that show the most change in herb cover and richness in the last 60 years on infertile substrates. Thus, the paleorecord provides unique long-term ecological data necessary to evaluate the response of plants to future climate change under different levels of soil

  10. Late-glacial and Holocene Vegetation and Climate Variability, Including Major Droughts, in the Sky Lakes Region of Southeastern New York State

    Menking, Kirsten M.; Peteet, Dorothy M.; Anderson, Roger Y.


    Sediment cores from Lakes Minnewaska and Mohonk in the Shawangunk Mountains of southeastern New York were analyzed for pollen, plantmacrofossils, macroscopic charcoal, organic carbon content, carbon isotopic composition, carbon/nitrogen ratio, and lithologic changes to determine the vegetation and landscape history of the greater Catskill Mountain region since deglaciation. Pollen stratigraphy generally matches the New England pollen zones identified by Deevey (1939) and Davis (1969), with boreal genera (Picea, Abies) present during the late Pleistocene yielding to a mixed Pinus, Quercus and Tsuga forest in the early Holocene. Lake Minnewaska sediments record the Younger Dryas and possibly the 8.2 cal kyr BP climatic events in pollen and sediment chemistry along with an 1400 cal yr interval of wet conditions (increasing Tsuga and declining Quercus) centered about 6400 cal yr BP. BothMinnewaska andMohonk reveal a protracted drought interval in themiddle Holocene, 5700-4100 cal yr BP, during which Pinus rigida colonized the watershed, lake levels fell, and frequent fires led to enhanced hillslope erosion. Together, the records show at least three wet-dry cycles throughout the Holocene and both similarities and differences to climate records in New England and central New York. Drought intervals raise concerns for water resources in the New York City metropolitan area and may reflect a combination of enhanced La Niña, negative phase NAO, and positive phase PNA climatic patterns and/or northward shifts of storm tracks.

  11. Different regional climatic drivers of Holocene large wildfires in boreal forests of northeastern America

    Remy, Cécile C.; Hély, Christelle; Blarquez, Olivier; Magnan, Gabriel; Bergeron, Yves; Lavoie, Martin; Ali, Adam A.


    Global warming could increase climatic instability and large wildfire activity in circumboreal regions, potentially impairing both ecosystem functioning and human health. However, links between large wildfire events and climatic and/or meteorological conditions are still poorly understood, partly because few studies have covered a wide range of past climate-fire interactions. We compared palaeofire and simulated climatic data over the last 7000 years to assess causes of large wildfire events in three coniferous boreal forest regions in north-eastern Canada. These regions span an east-west cline, from a hilly region influenced by the Atlantic Ocean currently dominated by Picea mariana and Abies balsamea to a flatter continental region dominated by Picea mariana and Pinus banksiana. The largest wildfires occurred across the entire study zone between 3000 and 1000 cal. BP. In western and central continental regions these events were triggered by increases in both the fire-season length and summer/spring temperatures, while in the eastern region close to the ocean they were likely responses to hydrological (precipitation/evapotranspiration) variability. The impact of climatic drivers on fire size varied spatially across the study zone, confirming that regional climate dynamics could modulate effects of global climate change on wildfire regimes.

  12. Holocene climate variability in arid Central Asia as revealed from high-resolution sedimentological and geochemical analyses of laminated sediments from Lake Chatyr Kol (Central Tian Shan, Kyrgyzstan)

    Lauterbach, S.; Plessen, B.; Dulski, P.; Mingram, J.; Prasad, S.


    A pronounced trend from a predominantly wet climate during the early Holocene towards significantly drier conditions since the mid-Holocene, mainly attributed to the weakening of the Asian summer monsoon (ASM), is documented in numerous palaeoclimate records from the monsoon-influenced parts of Asia, e.g. the Tibetan Plateau and north- and southeastern China. In contrast, climate in the adjacent regions of mid-latitude arid Central Asia, located north and northwest of the Tibetan Plateau, is supposed to have been characterized by pronounced dry conditions during the early Holocene, wet conditions during the mid-Holocene and a rather moderate drying during the late Holocene, which is mainly attributed to the complex interplay between the mid-latitude Westerlies and the ASM. However, although mid-latitude Central Asia thus might represent a key region for the understanding of teleconnections between the ASM system and the Westerlies, knowledge about past climate development in this region is still ambiguous due to the limited number of high-resolution palaeoclimate records. Hence, new well-dated and highly resolved palaeoclimate records from this region are expected to provide important information about spatio-temporal changes in the regional interplay between Westerlies and ASM and thus aid the understanding of global climate teleconnections. As a part of the project CADY (Central Asian Climate Dynamics), aiming at reconstructing past climatic and hydrological variability in Central Asia, a sediment core of about 6.25 m length has been recovered from alpine Lake Chatyr Kol (40°36' N, 75°14' E, 3530 m a. s. l., surface area ~170 km2, maximum depth ~20 m), located in the Central Tian Shan of Kyrgyzstan. Sediment microfacies analysis on large-scale petrographic thin sections reveals continuously sub-mm scale laminated sediments throughout the record except for the uppermost ca. 60 cm. Microsedimentological characterization of these laminae, which are most probably

  13. Lake Sediment Records as an Indicator of Holocene Fluctuations of Quelccaya Ice Cap, Peru and Regional Climate

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


    The past fluctuations of Quelccaya Ice Cap, (QIC; 13°S, 70°W, 5200 m asl) located in the southeastern Peruvian Andes, provide a record of tropical climate since the last glacial-interglacial transition. A detailed surficial geomorphic record of past glacial extents developed over the last several decades (e.g. Mercer and Palacios 1977; Buffen et al. 2009; Kelly et al. 2012 accepted) demonstrates that QIC is a dynamic glacial system. These records show that the ice cap was larger than present and retreating by ~11,500 yr BP, and smaller than present between ~7,000 and ~4,600 yr BP. The most recent advance occurred during the late Holocene (Little Ice Age;LIA), dated with 10Be surface exposure ages (510±90 yrs (n = 8)) (Stroup et al. in prep.). This overrode earlier deposits obscuring a complete Holocene record; we aim to address the gaps in glacial chronology using the sedimentary record archived in lakes. We retrieved two sets cores (8 and 5 m-long) from Laguna Challpacocha (13.91°S, 70.86°W, 5040 m asl), a lake that currently receives meltwater from QIC. Four radiocarbon ages from the cores suggest a continuous record dating to at least ~10,500 cal. yr BP. Variations in magnetic susceptibility, percent organic and inorganic carbon, bulk density, grayscale and X-ray fluorescence chemistry indicate changes in the amount of clastic sediment deposition. We interpret clastic sediments to have been deposited from ice cap meltwater, thus indicating more extensive ice. Clastic sediments compose the top of the core from 4 to 30 cm depth, below there is a sharp transition to organic sediments radiocarbon dated to (500±30 and 550±20 cal. yr BP). The radiocarbon ages are similar to the 10Be dated (LIA) glacial position. At least three other clastic units exist in the core; dating to ~2600-4300, ~4800-7300 and older then ~10,500 cal. yr BP based on a linear age model with four radiocarbon dates. We obtained two, ~4 m long, cores from Laguna Yanacocha (13.95°S,70.87

  14. Holocene soil pH changes and East Asian summer monsoon evolution derived from loess brGDGTs in the northeastern Tibetan Plateau

    Duan, Y.; Sun, Q.; Zhao, H.


    GDGTs-based proxies have been used successfully to reconstruct paleo-temperature from loess-paleosol sequences during the past few years. However, the pH variations of loess sediments derived from GDGTs covering the geological history remain poorly constrained. Here we present two pH records spanning the last 12 ka (1ka=1000years) based on the modified cyclization ratio index (CBT') of the branched GDGTs using regional CBT'-pH empirical relationship from two well-dated loess-paleosol sections (YWY14 and SHD09) in the northeastern Tibetan Plateau. The results indicate that a slightly alkaline condition occurred during 12 8.5 ka with pH values ranging from 6.98 to 7.24, then CBT'-derived pH decreased from 8.5 to 6.5 ka with values from 7.19 to 6.49 and gradually increased thereafter. The reconstructed pH values from topmost samples can be well compared with instrumental pH values of the surrounding surface soil. The lowest intervals of CBT'-derived pH values during the mid-Holocene in our records are consistent with the results of highest tree pollen percentage from the adjacent lake sediments and regional weakest aeolian activities, which reveals that the moisture maximum during that period, but conflicted with previous results of the wettest early-Holocene inferred from speleothem or ostracod shell oxygen isotope (δ18O) values. Taking together, we conclude that Holocene humidity evolution (wettest middle Holocene) in response to the East Asian summer monsoon (EASM) changes exerts important control on pH variations of loess deposits in northeastern Tibetan Plateau. CBT'-derived pH variations can be potentially used as an indicator of EASM evolution reconstructions. In addition, we argue that speleothem or ostracod shell δ18O records are essentially a signal of the isotopic composition of precipitations rather than EASM intensity.

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

    Menviel, L.; Joos, F.


    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.

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

    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


    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.

  17. Response of northern hemisphere environmental and atmospheric conditions to climate changes using Greenland aerosol records from the Eemian to the Holocene

    Fischer, H.


    The Northern Hemisphere experienced dramatic climate changes over the last glacial cycle, including vast ice sheet expansion and frequent abrupt climate events. Moreover, high northern latitudes during the last interglacial (Eemian) were warmer than today and may provide guidance for future climate change scenarios. However, little evidence exists regarding the environmental alterations connected to these climate changes. Using aerosol concentration records in decadal resolution from the North Greenland Eemian Ice Drilling (NEEM) over the last 128,000 years we extract quantitative information on environmental changes, including the first comparison of northern hemisphere environmental conditions between the warmer than present Eemian and the early Holocene. Separating source changes from transport effects, we find that changes in the ice concentration greatly overestimate the changes in atmospheric concentrations in the aerosol source region, the latter mirroring changes in aerosol emissions. Glacial times were characterized by a strong reduction in terrestrial biogenic emissions (only 10-20% of the early Holocene value) reflecting the net loss of vegetated area in mid to high latitudes, while rapid climate changes during the glacial had essentially no effect on terrestrial biogenic aerosol emissions. An increase in terrestrial dust emissions of approximately a factor of eight during peak glacial and cold stadial intervals indicates higher aridity and dust storm activity in Asian deserts. Glacial sea salt aerosol emissions increased only moderately (by approximately 50%), likely due to sea ice expansion, while marked stadial/interstadial variations in sea salt concentrations in the ice reflect mainly changes in wet deposition en route. Eemian ice contains lower aerosol concentrations than ice from the early Holocene, due to shortened atmospheric residence time during the warmer Eemian, suggesting that generally 2°C warmer climate in high northern latitudes did not

  18. Holocene fire, vegetation, and climate dynamics inferred from charcoal and pollen record in the eastern Tibetan Plateau

    Zhao, Wenwei; Zhao, Yan; Qin, Feng


    Understanding fire history and its driving mechanisms can provide valuable insights into present fire regime (intensity, severity and frequency), the interplay between vegetation and fire, and trigger of fire activities. Here we reconstruct the Holocene fire history in the Zoige Basin on the eastern Tibetan Plateau, on the basis of sedimentary micro-charcoal record over the last 10.0 ka (1 ka = 1000 cal yr BP) and discuss the influences of vegetation and climate on fire dynamics. Our results show that regional fire was active at 10.0-3.3 ka and a significant decrease in fire activity characterized the period after 3.3 ka. The high regional fire frequency at 10.0-3.3 ka is consistent with the forested landscape suggested by high affinity scores of cool mixed forest biome (mainly consisted of spruce), implying that fire dynamics during this period was generally controlled by the variations of arboreal biomass and summer temperature. During 6.3-4.6 ka the prevailing Asian summer monsoon provided increased moisture to this region and thus suppressed fire activities to an extent, despite the availability of abundant biomass. Declined tree biomass after 3.3 ka probably accounted for the decreased fire activities. In addition, two successive fire events at ca. 3.5-3.3 ka were likely responsible for the subsequent abrupt decline of forest components in the landscape.

  19. A complete Holocene record of trematode-bivalve infection and implications for the response of parasitism to climate change.

    Huntley, John Warren; Fürsich, Franz T; Alberti, Matthias; Hethke, Manja; Liu, Chunlian


    Increasing global temperature and sea-level rise have led to concern about expansions in the distribution and prevalence of complex-lifecycle parasites (CLPs). Indeed, numerous environmental variables can influence the infectivity and reproductive output of many pathogens. Digenean trematodes are CLPs with intermediate invertebrate and definitive vertebrate hosts. Global warming and sea level rise may affect these hosts to varying degrees, and the effect of increasing temperature on parasite prevalence has proven to be nonlinear and difficult to predict. Projecting the response of parasites to anthropogenic climate change is vital for human health, and a longer term perspective (10(4) y) offered by the subfossil record is necessary to complement the experimental and historical approaches of shorter temporal duration (10(-1) to 10(3) y). We demonstrate, using a high-resolution 9,600-y record of trematode parasite traces in bivalve hosts from the Holocene Pearl River Delta, that prevalence was significantly higher during the earliest stages of sea level rise, significantly lower during the maximum transgression, and statistically indistinguishable in the other stages of sea-level rise and delta progradation. This stratigraphic paleobiological pattern represents the only long-term high-resolution record of pathogen response to global change, is consistent with fossil and recent data from other marine basins, and is instructive regarding the future of disease. We predict an increase in trematode prevalence concurrent with anthropogenic warming and marine transgression, with negative implications for estuarine macrobenthos, marine fisheries, and human health.

  20. Impact of millennial-scale Holocene climate variability on eastern North American terrestrial ecosystems: Pollen-based climatic reconstruction

    Willard, D.A.; Bernhardt, C.E.; Korejwo, D.A.; Meyers, S.R.


    We present paleoclimatic evidence for a series of Holocene millennial-scale cool intervals in eastern North America that occurred every ???1400 years and lasted ???300-500 years, based on pollen data from Chesapeake Bay in the mid-Atlantic region of the United States. The cool events are indicated by significant decreases in pine pollen, which we interpret as representing decreases in January temperatures of between 0.2??and 2??C. These temperature decreases include excursions during the Little Ice Age (???1300-1600 AD) and the 8 ka cold event. The timing of the pine minima is correlated with a series of quasi-periodic cold intervals documented by various proxies in Greenland, North Atlantic, and Alaskan cores and with solar minima interpreted from cosmogenic isotope records. These events may represent changes in circumpolar vortex size and configuration in response to intervals of decreased solar activity, which altered jet stream patterns to enhance meridional circulation over eastern North America. ?? 2004 Elsevier B.V. All rights reserved.

  1. Mid- to late Holocene climate-driven regime shifts inferred from diatom, ostracod and stable isotope records from Lake Son Kol (Central Tian Shan, Kyrgyzstan)

    Schwarz, Anja; Turner, Falko; Lauterbach, Stefan; Plessen, Birgit; Krahn, Kim J.; Glodniok, Sven; Mischke, Steffen; Stebich, Martina; Witt, Roman; Mingram, Jens; Schwalb, Antje


    Arid Central Asia represents a key region for understanding climate variability and interactions in the Northern Hemisphere. Patterns and mechanisms of Holocene climate change in arid Central Asia are, however, only partially understood. Multi-proxy data combining diatom, ostracod, sedimentological, geochemical and stable isotope analyses from a ca. 6000-year-old lake sediment core from Son Kol (Central Kyrgyzstan) show distinct and repeated changes in species assemblages. Diatom- and ostracod-inferred conductivity shifts between meso-euhaline and freshwater conditions suggest water balance and regime shifts. Organism-derived data are corroborated by stable isotope, mineralogical and geochemical records, underlining that Son Kol was affected by strong lake level fluctuations of several meters. The δ13Ccarb/δ18Ocarb correlation shows repeated switchovers from a closed to an open lake system. From 6000 to 3800 and 3250 to 1950 cal. yr BP, Son Kol was a closed basin lake with higher conductivities, increased nutrient availability and a water level located below the modern outflow. Son Kol became again a hydrologically open lake at 3800 and 1950 cal. yr BP. Comparisons to other local and regional paleoclimate records indicate that these regime shifts were largely controlled by changing intensity and position of the Westerlies and the Siberian Anticyclone that triggered changes in the amount of winter precipitation. A strong influence of the Westerlies ca. 5000-4400, 3800-3250 and since 1950 cal. yr BP enhanced the amount of precipitation during spring, autumn and winter, whereas cold and dry winters prevailed during phases with a strong Siberian Anticyclone and southward shifted Westerlies at ca. 6000-5000, 4400-3800 and 3250-1950 cal. yr BP. Similarities between variations in winter precipitation at Son Kol and records of the predominant NAO-mode further suggest a teleconnection between wet (dry) winter climate in Central Asia and a positive (negative) NAO

  2. Inferring late-Holocene climate in the Ecuadorian Andes using a chironomid-based temperature inference model

    Matthews-Bird, Frazer; Brooks, Stephen J.; Holden, Philip B.; Montoya, Encarni; Gosling, William D.


    Presented here is the first chironomid calibration data set for tropical South America. Surface sediments were collected from 59 lakes across Bolivia (15 lakes), Peru (32 lakes), and Ecuador (12 lakes) between 2004 and 2013 over an altitudinal gradient from 150 m above sea level (a.s.l) to 4655 m a.s.l, between 0-17° S and 64-78° W. The study sites cover a mean annual temperature (MAT) gradient of 25 °C. In total, 55 chironomid taxa were identified in the 59 calibration data set lakes. When used as a single explanatory variable, MAT explains 12.9 % of the variance (λ1/λ2 = 1.431). Two inference models were developed using weighted averaging (WA) and Bayesian methods. The best-performing model using conventional statistical methods was a WA (inverse) model (R2jack = 0.890; RMSEPjack = 2.404 °C, RMSEP - root mean squared error of prediction; mean biasjack = -0.017 °C; max biasjack = 4.665 °C). The Bayesian method produced a model with R2jack = 0.909, RMSEPjack = 2.373 °C, mean biasjack = 0.598 °C, and max biasjack = 3.158 °C. Both models were used to infer past temperatures from a ca. 3000-year record from the tropical Andes of Ecuador, Laguna Pindo. Inferred temperatures fluctuated around modern-day conditions but showed significant departures at certain intervals (ca. 1600 cal yr BP; ca. 3000-2500 cal yr BP). Both methods (WA and Bayesian) showed similar patterns of temperature variability; however, the magnitude of fluctuations differed. In general the WA method was more variable and often underestimated Holocene temperatures (by ca. -7 ± 2.5 °C relative to the modern period). The Bayesian method provided temperature anomaly estimates for cool periods that lay within the expected range of the Holocene (ca. -3 ± 3.4 °C). The error associated with both reconstructions is consistent with a constant temperature of 20 °C for the past 3000 years. We would caution, however, against an over-interpretation at this stage. The reconstruction can only

  3. Changes in climatic conditions, vegetation cover and erosion during the Holocene in southeast Spain

    Bellin, N.; Vanacker, V.


    The present-day landscape in Southeast Spain is the result of a long occupation history. To have a better understanding of the impact of human societies on soil degradation, we analysed the main shifts in vegetation cover, climate and human occupation for the last 12000 years. Our analyses use recently published information from continental and marine pollen series. The data suggest that climatic factors appear to be important driving factors of vegetation degradation induced by an increased aridity that is already recorded at about 5000 years ago. (Author) 19 refs.

  4. Changes in climatic conditions, vegetation cover and erosion during the Holocene in southeast Spain

    Bellin, N.; Vanacker, V.


    The present-day landscape in Southeast Spain is the result of a long occupation history. To have a better understanding of the impact of human societies on soil degradation, we analysed the main shifts in vegetation cover, climate and human occupation for the last 12000 years. Our analyses use recently published information from continental and marine pollen series. The data suggest that climatic factors appear to be important driving factors of vegetation degradation induced by an increased aridity that is already recorded at about 5000 years ago. (Author) 19 refs.

  5. Moderate climate signature in cranial anatomy of late holocene human populations from Southern South America.

    Paula Menéndez, Lumila


    The aim of this study is to analyze the association between cranial variation and climate in order to discuss their role during the diversification of southern South American populations. Therefore, the specific objectives are: (1) to explore the spatial pattern of cranial variation with regard to the climatic diversity of the region, and (2) to evaluate the differential impact that the climatic factors may have had on the shape and size of the diverse cranial structures studied. The variation in shape and size of 361 crania was studied, registering 62 3D landmarks that capture shape and size variation in the face, cranial vault, and base. Mean, minimum, and maximum annual temperature, as well as mean annual precipitation, but also diet and altitude, were matched for each population sample. A PCA, as well as spatial statistical techniques, including kriging, regression, and multimodel inference were employed. The facial skeleton size presents a latitudinal pattern which is partially associated with temperature diversity. Both diet and altitude are the variables that mainly explain the skull shape variation, although mean annual temperature also plays a role. The association between climate factors and cranial variation is low to moderate, mean annual temperature explains almost 40% of the entire skull, facial skeleton and cranial vault shape variation, while annual precipitation and minimum annual temperature only contribute to the morphological variation when considered together with maximum annual temperature. The cranial base is the structure less associated with climate diversity. These results suggest that climate factors may have had a partial impact on the facial and vault shape, and therefore contributed moderately to the diversification of southern South American populations, while diet and altitude might have had a stronger impact. Therefore, cranial variation at the southern cone has been shaped both by random and nonrandom factors. Particularly, the

  6. Late-Holocene palaeoenvironments of Southern Crimea: Soils, soil-climate relationship and human impact

    Lisetskii, Fedor N.; Stolba, Vladimir; Pichura, Vitalii I.


    Occupying 4% of Crimea’s territory, the sub-Mediterranean landscapes of Southern Crimea stand out for their distinct soil-climatic conditions and record of human activity. This paper presents the results of study of the newly formed and well-dated soils from 21 archaeological sites, making...

  7. Subfossil bog-pine horizons document climate and ecosystem changes during the Mid-Holocene

    Eckstein, J.; Leuschner, H.H.; Bauerochse, A.; Sass-Klaassen, U.


    Extended dendrochronological investigations were performed on subfossil pine entombed in peat layers of former raised bogs in Lower Saxony (NW Germany). The aim was to study of dynamics in bog development in response to local environmental conditions and regional changes in climate throughout the

  8. Tracking climate variability in the western Mediterranean during the Late Holocene: A multiproxy approach

    Nieto-Moreno, V.; Martínez-Ruiz, F.; Giralt, S.; Jimenéz-Espejo, F.; Gallego-Torres, D.; Rodrigo-Gámiz, M.; Garcia-Orellana, J.; Ortega-Huertas, M.; de Lange, G.J.


    Climate variability in the western Mediterranean is reconstructed for the last 4000 yr using marine sediments recovered in the west Algerian-Balearic basin, near the Alboran basin. Fluctuations in chemical and mineralogical sediment composition as well as grain size distribution are linked to

  9. Holocene climate on the Modoc Plateau, northern California, USA: The view from Medicine Lake

    Starratt, Scott W.


    available for colonization by benthic diatoms and Isoetes. These fluctuations are not typical of the small number of low-elevation Holocene lake records in the region, and probably reflect the hydrologic conditions unique to Medicine Lake.

  10. Application of /sup 14/C-dating to sedimentary geology and climatology: Sea-level and climate change during the Holocene

    Nakai, Nobuyuki; Ohishi, Shyoji; Kuriyama, Toyoko; Nakamura, Toshio


    AMS /sup 14/C dating of small sized fossil shells, wood chips and sedimentary humic matter has been applied to the investigation of paleoclimatic and sea-level changes in the Holocene, using three estuarine and brackish lake sediment cores, drilled in Kawasaki city and Lake Hamanako, Japan. Precise and detailed ages at differing depths clarified large transitions of Holocene sedimentation rates, of two orders of magnitude. The vertical variation in delta/sup 13/C and C/N results for sedimentary organic matter, combined with AMS /sup 14/C ages, established continous climatic and sea-level fluctuation patterns through time and indicated the existence of neoglaciation coincident with the marine regression at 7500 to 7000 yr BP.

  11. Late Holocene climate variability from Lake Pupuke maar, Auckland, New Zealand

    Striewski, B.; Shulmeister, J.; Augustinus, P. C.; Soderholm, J.


    Spectral analyses of quasi-annual organo-diatomaceous laminae couplets in an Auckland maar lake indicate brief (sub-decadal scale) episodes with strong spectral power and long periods of weak to no spectral power between c. 1700 to c. 550 cal. yr BP. Laminae couplet thickness appears to be a function of changes in wind flow over the basin, with enhanced wind flow deepening the mixing zone and providing additional nutrients for laminae formation. Aeolian dust from Australia amplifies the wind signal. Spectral signals in the high power episodes are focused in Auckland climate whereby strongly negative (positive) ENSO are associated with enhanced (diminished) SW airflow over Auckland. ENSO events interact in the modern climate and the spectral results indicate that this is the case when spectral power is strong in the laminae. These results highlight strong but intermittent ENSO activity between 600 and 1400 cal. yr BP.

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

    Jin, Liya; Zhang, Xiaojian


    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

  13. Reconstructing Holocene (sub)tropical climate and cyclone variability using geochemical proxies

    van Soelen, E.E.


    Anthropogenic greenhouse gas emissions are responsible for a warming trend that cannot easily be reversed. This warming trend is expected to have a large impact on global weather patterns and local environmental conditions, for example by changing precipitation patterns, sea level rise and increasing tropical cyclone activity. Therefore, (sub)tropical coastal regions are expected to be heavily impacted by future climate change. To improve our understanding of the possible consequences of futu...

  14. Reconstructing Late Holocene Climate Variability in North East China From Varved Maar Lake Sediments

    Panizzo, V. N.; Mackay, A. W.; Rioual, P.; Chu, G.; Leng, M. J.


    Reconstructing climatic variability over the past c. 2 ka years is recognised as a key PAGES timeframe (focus 2). However few high-resolution records exist from the climate sensitive region of N) China which receives the majority of its precipitation from the east Asian summer monsoon (EASM). Interactions between the EASM and the global climate system have great resonance. Such examples include how the EASM responded to changes in climate over the documented e.g. "Medieval Warm Period" (c. AD 900 - 1300), "Little Ice Age" (c. AD 1350-1850) and recent warming. At present, literature remains contradictory to such environmental changes in NE China over this time-frame due to poor chronological control, low resolution of existing studies and even due to the inexact terminology of these climatic periods. Xiaolongwan Lake (XLW) is a small, closed, maar lake located in the Long Gang Volcanic Field, NE China (42°18'N; 126°19'E). It is at an elevation of 655 m a.s.l. with a maximum depth of 15 m. A varve chronology has been created for a 143 cm composite core (2 cores collected in 2006), and here we present diatoms and organic geochemistry (δ13C, TOC, C/N) evidence for environmental change over the past c. 2 ka years. Results show a gradual change in diatom species, moving from a composition where opportunistic species (e.g. Achnanthidium minutissimum) dominate (between c. 100 BC to 500 years AD) at the beginning of the record to one comprised of benthic/epiphytic species (e.g. Staurosira construens var venter, Punctastriata discoidea, Gomphonema parvulum). The introduction after c. 1850 years AD of the planktonic diatom species, Discotella woltereckii, not previously seen in the record, coincides with recent warming. This may be a response to changing limnological conditions, such as decreasing duration of lake ice-cover. Bulk organic δ13C results conducted on a short core collected from XLW in summer 2007, show that over the past c. 350 years there is a distinct

  15. Holocene vegetation and climatic variations in Central India: A study based on multiproxy evidences

    Chauhan, M. S.; Sharma, Anupam; Phartiyal, Binita; Kumar, Kamlesh


    Palynology, texture, mineralogy, geochemistry, and magnetic susceptibility analysis of a 2 m deep sediment core from Padauna Swamp, southeastern Madhya Pradesh infers that between 8600 and 7500 cal yr BP a warm and relatively less-humid climate prevailed with open tree-savannahs dominated by grasses followed by sedges, Artemisia and members of Chenopodiaceae/Amaranthaceae with scanty trees viz., Schrebera, Aegle marmelos and Sterculia urens. This is well supported by lower organic to carbonate carbon ratio, coarser texture having relatively low CIA and magnetic susceptibility values and presence of some primary minerals. Between 7500 and 6250 cal yr BP the tree-savannahs were succeeded by open mixed deciduous forests with the invasion of a few more trees viz., Madhuca indica, Holoptelea, Emblica officinalis, Mitragyna parvifolia and members of Anacardiaceae in response to onset of a warm and humid climate. A considerable rise in organic carbon generated from the degradation of plentiful biomass along with increase in clay content with signs of kaolinite and increase in immobile over mobile elements with slightly higher CIA and magnetic susceptibility values also suggest climatic amelioration. The presence of ruderal plants such as Artemisia, Cannabis sativa and Cheno/Am further infers initiation of human activities in the region. Between 6250 and 2800 cal yr BP, the mixed deciduous forests became more diverse and dense, subduing grasses and other herbaceous elements. Sporadic incursion of Shorea robusta (Sal) in forest floristic was recorded around 5000 cal yr BP. The overall change in the vegetation mosaic reflects that a warm and more-humid climate prevailed in the region, probably on account of invigoration of southwest monsoon. This observation is further corroborated by other proxy data showing a spurt in organic/inorganic carbon ratio, increase in clay content with matured mineralogy, significantly higher CIA and magnetic susceptibility values. Since 2800 cal

  16. 8800 years of high-altitude vegetation and climate history at the Rutor Glacier forefield, Italian Alps. Evidence of middle Holocene timberline rise and glacier contraction

    Badino, Federica; Ravazzi, Cesare; Vallè, Francesca; Pini, Roberta; Aceti, Amelia; Brunetti, Michele; Champvillair, Elena; Maggi, Valter; Maspero, Francesco; Perego, Renata; Orombelli, Giuseppe


    Sedimentary archives at or near the timberline ecotone in Alpine glaciated areas contain records to study Holocene climate change and the interplay between climate, ecosystems, and humans. We focused on records of timberline and glacier oscillations in the Rutor Glacier forefield (Western Italian Alps) in the last 8800 years. Human activity in this area was negligible for most of the Holocene. We adopted an integrative stratigraphic approach including proxies for glacier advance and timberline estimation, sedimentary events, and reconstructed temperatures. Changes in timberline ecotone correlate to climate until the Middle Ages. Pollen-stratigraphic evidence of a primary plant succession highlights a lag beween local deglaciation and the first reliable 14C age. The radiocarbon chronology points to a prolonged phase of glacier contraction between 8.8 and 3.7 ka cal BP. Even later the glacier remained within its LIA limits. Between 8.4 and 4 ka cal BP MAT-inferred TJuly fluctuated near 12.4 °C, ca. 3.1 °C higher than today. During this period, a Pinus cembra forest belt grew at 2600 m asl with an upper limit of tree groves placed 434 ± 310 m above the current open forest limit. This Holocene phase of thermal maximum ended between 3.98 and 3.51 ± 70 ka cal BP and with a substantial rearrangement of forest composition; temperature reconstruction shows a decrease of 1.8 °C. This climate deterioration concluded the Subboreal thermal optimum, mirroring glacial advances widely documented in the Alps. The Rutor Glacier advanced at ca. AD 1093 ± 65, and remained inside the LIA maximum extent. The LIA started since AD 1594, and culminated between AD 1751 and 1864.

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

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


    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

  18. Evidence of climatic change during Holocene in the nearshore regions of Konkan (central west coast of India

    Gujar, A.R.; Guptha, M.V.S.

    grains, variation in the stability index and significantly poor diversity and scarcity of benthic foraminifera. In contrast, during the mid Holocene humid phase, the number of benthic foraminifera was very high. It is also remarked that Ammonia beccarii...

  19. Fluvial response to the last Holocene rapid climate change in the Northwestern Mediterranean coastlands

    Degeai, Jean-Philippe; Devillers, Benoît; Blanchemanche, Philippe; Dezileau, Laurent; Oueslati, Hamza; Tillier, Margaux; Bohbot, Hervé


    The variability of fluvial activity in the Northwestern Mediterranean coastal lowlands and its relationship with modes of climate change were analysed from the late 9th to the 18th centuries CE. Geochemical analyses were undertaken from a lagoonal sequence and surrounding sediments in order to track the fluvial inputs into the lagoon. An index based on the K/S and Rb/S ratios was used to evidence the main periods of fluvial activity. This index reveals that the Medieval Climate Anomaly (MCA) was a drier period characterized by a lower fluvial activity, while the Little Ice Age (LIA) was a wetter period with an increase of the river dynamics. Three periods of higher than average fluvial activity were evidenced at the end of the first millennium CE (ca. 900-950 cal yr CE), in the first half of the second millennium CE (ca. 1150-1550 cal yr CE), and during the 1600s-1700s CE (ca. 1650-1800 cal yr CE). The comparison of these fluvial periods with other records of riverine or lacustrine floods in Spain, Italy, and South of France seems to indicate a general increase in fluvial and flood patterns in the Northwestern Mediterranean in response to the climate change from the MCA to the LIA, although some episodes of flooding are not found in all records. Besides, the phases of higher than average fluvial dynamics are in good agreement with the North Atlantic cold events evidenced from records of ice-rafted debris. The evolution of fluvial activity in the Northwestern Mediterranean coastlands during the last millennium could have been driven by atmospheric and oceanic circulation patterns.

  20. Late Holocene climate and chemical change at high latitudes: case studies from contaminated sites in subarctic and arctic Canada

    Galloway, Jennifer M.; Cooney, Darryl; Crann, Carley; Falck, Hendrik; Howell, Dana; Jamieson, Heather; Macumber, Andrew; Nasser, Nawaf; Palmer, Michael; Patterson, R. Timothy; Parsons, Michael; Roe, Helen M.; Sanei, Hamed; Spence, Christopher; Stavinga, Drew; Swindles, Graeme T.


    preserved in the lake sediment cores are informed by our characterization of sediments from over 50 lakes in the region. In the longer record obtained from the Giant Mine area we show that the concentration of aqua regia leached As increases prior to resource development and that concentrations are variable over millennia. Lowest concentrations of As in the ~3500 cal yr BP record are coincident with regional Neoglacial cooling. As concentrations begin to increase from concentrations near 100 ppm to over 1000 ppm in the lastest Holocene, coincident with a period of regional warming associated with the Medieval Warm period, although at this point we cannot rule out post-depositional remobilization of As from higher in the sediment column. Concentrations in excess of 10,000 ppm at the top of the sediment core are likely associated with anthropogenic release of this contaminant. At the more northern Courageous Lake site, the sediment record extends back about a hundred years, and reveals that concentrations of As in lake sediments prior to development of the area were about 40 ppm. Increases in As are associated with drilling and mine production but continued increases after 1999 may be due to remobilization of As due to on-going climate warming, recent remediation efforts, or vertical movement of this element in the sediment column.

  1. Climate-derived tensions in Arctic security.

    Backus, George A.; Strickland, James Hassler


    Globally, there is no lack of security threats. Many of them demand priority engagement and there can never be adequate resources to address all threats. In this context, climate is just another aspect of global security and the Arctic just another region. In light of physical and budgetary constraints, new security needs must be integrated and prioritized with existing ones. This discussion approaches the security impacts of climate from that perspective, starting with the broad security picture and establishing how climate may affect it. This method provides a different view from one that starts with climate and projects it, in isolation, as the source of a hypothetical security burden. That said, the Arctic does appear to present high-priority security challenges. Uncertainty in the timing of an ice-free Arctic affects how quickly it will become a security priority. Uncertainty in the emergent extreme and variable weather conditions will determine the difficulty (cost) of maintaining adequate security (order) in the area. The resolution of sovereignty boundaries affects the ability to enforce security measures, and the U.S. will most probably need a military presence to back-up negotiated sovereignty agreements. Without additional global warming, technology already allows the Arctic to become a strategic link in the global supply chain, possibly with northern Russia as its main hub. Additionally, the multinational corporations reaping the economic bounty may affect security tensions more than nation-states themselves. Countries will depend ever more heavily on the global supply chains. China has particular needs to protect its trade flows. In matters of security, nation-state and multinational-corporate interests will become heavily intertwined.

  2. Comment on "Donders, T.H. 2014. Middle Holocene humidity increase in Florida: climate or sea-level? Quaternary Science Reviews 103:170-174."

    Glaser, Paul H.; Hansen, Barbara CS; Donovan, Joseph J.; Givnish, Thomas J.; Stricker, Craig A.; Volin, John C.


    Donders (2014) has recently proposed that the climate of Florida became progressively wetter over the past 5000 years in response to a marked strengthening of the El Niño regime. This reconstruction is largely based on a re-analysis of pollen records from regions north of Lake Okeechobee (Fig. 1) using a new set of pollen transfer functions. Donders concluded that a latitudinal gradient in precipitation prevailed across Florida since the mid Holocene, but the overall trend was toward progressively wetter conditions from 5000 cal BP to the present.

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

    L. Jin


    Full Text Available The impacts of various scenarios of a gradual snow and glaciers developing over the Tibetan Plateau on climate change in Afro-Asian monsoon region and other regions during the Holocene (9 kyr BP–0 kyr BP are studied by using the Earth system model of intermediate complexity, CLIMBER-2. The simulations show that the imposed snow and glaciers over the Tibetan Plateau in the mid-Holocene induce global summer temperature decreases over most of Eurasia but in the Southern Asia temperature response is opposite. With the imposed snow and glaciers, summer precipitation decreases strongly in North Africa and South Asia as well as northeastern China, while it increases in Southeast Asia and the Mediterranean. For the whole period of Holocene (9 kyr BP–0 kyr BP, the response of vegetation cover to the imposed snow and glaciers cover over the Tibetan Plateau is not synchronous in South Asia and in North Africa, showing an earlier and a more rapid decrease in vegetation cover in North Africa from 9 kyr BP to 6 kyr BP while it has only minor influence on that in South Asia until 5 kyr BP. The precipitation decreases rapidly in North Africa and South Asia while it decreases slowly or unchanged during 6 kyr BP to 0 kyr BP with imposed snow and glacier cover over the Tibetan Plateau. The different scenarios of snow and glacier developing over the Tibetan Plateau would result in differences in variation of temperature, precipitation and vegetation cover in North Africa, South Asia and Southeast Asia. The model results suggest that the development of snow and ice cover over Tibetan Plateau represents an additional important climate feedback, which amplify orbital forcing and produces a significant synergy with the positive vegetation feedback.

  4. Late holocene ice core records of climate and environment from the Tropical Andes, Peru


    Full Text Available DONNÉES CLIMATIQUES ET ENVIRONNEMENTALES DÉDUITES DES CAROTTES DE GLACE DES ANDES TROPICALES (PÉROU À L’HOLOCÈNE RÉCENT. On compare l’histoire du climat et de l’environnement reconstituée à partir des carottes extraites de la calotte de glace de Quelccaya (13º56’S, 70º50’O, 5 670 m et de la “Garganta” du Huascarán (9°06’S, 77°36’O, 6 048 m s.n.m. Les paramètres analysés sont le rapport isotopique de l’oxygène ( 18O considéré comme un indicateur des températures, les poussières non solubles et (pour le Huascarán seulement la concentration en nitrates (NO3-, qui est un indicateur des fluctuations de la végétation dans la forêt amazonienne. Les profils du  18O et du NO3- au Huascarán pour les derniers 3 000 ans montrent qu’il y a eu une baisse générale des températures accompagnée par une diminution de l’activité biologique dans le bassin amazonien, avec des valeurs minimales atteintes pendant le Petit Age de Glace, de 200 à 500 ans BP. Il y a eu après une augmentation rapide du  18O, qui a atteint les valeurs d’il y a 3 000 ans BP. Ce réchauffement rapide a dominé les deux derniers siècles sur les deux sites. Les niveaux de NO3- au Huascarán ont aussi augmenté pendant cette période, bien que moins rapidement. L’évidence d’un léger enrichissement isotopique (réchauffement existe entre 1 150 y 900 ans BP, qui pourrait être mis en relation avec “l’Optimum Médiéval”. Le niveau des poussières, constant depuis 3 000 ans, a été interrompu par un événement de fortes concentrations de poussières entre 2 000 y 1 800 ans BP (0-200 A.D. centré sur les années 1 900 BP (100 A.D.. Des pics de moindre importance sont observés de 1 400 à 1 600 ans BP (400 a 600 A.D. et entre 1300 et 1030 BP (entre 700 et 960 A.D.. L’analyse des poussières associées à cet épisode révèle un matériau déposé par les vents de même composition que celui qui affleure en Cordill

  5. Investigating the consistency between proxy-based reconstructions and climate models using data assimilation: a mid-Holocene case study

    A. Mairesse; H. Goosse; P. Mathiot; H. Wanner; S. Dubinkina (Svetlana)


    htmlabstractThe mid-Holocene (6 kyr BP; thousand years before present) is a key period to study the consistency between model results and proxy-based reconstruction data as it corresponds to a standard test for models and a reasonable number of proxy-based records is available. Taking advantage of

  6. Modeling the sensitivity of sediment and water runoff dynamics to Holocene climate and land use changes at the catchment scale

    Notebaert, B.; Verstraeten, G.; Ward, P.J.; Renssen, H.; Van Rompaey, A.


    An increasing number of studies have indicated that soil erosion, sediment redistribution and water discharge during the Holocene have varied greatly under influence of environmental changes. In this paper we have used a modeling approach to study the driving forces for soil erosion and sediment

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

    Blaschek, M.; Renssen, H.


    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

  8. On the differences between Last Glacial Maximum and Mid-Holocene climates in southern South America simulated by PMIP3 models

    Berman, Ana Laura; Silvestri, Gabriel E.; Tonello, Marcela S.


    Differences between climate conditions during the Last Glacial Maximum (LGM) and the Mid-Holocene (MH) in southern South America inferred from the state-of-the-art PMIP3 paleoclimatic simulations are described for the first time in this paper. The aim is to expose characteristics of past climate changes occurred without human influence. In this context, numerical simulations are an indispensable tool for inferring changes in near-surface air temperature and precipitation in regions where proxy information is scarce or absent. The analyzed PMIP3 models describe MH temperatures significantly warmer than those of LGM with magnitudes of change depending on the season and the specific geographic region. In addition, models indicate that seasonal mean precipitation during MH increased with respect to LGM values in wide southern continental areas to the east of the Andes Cordillera whereas seasonal precipitation developed in areas to the west of Patagonian Andes reduced from LGM to MH.

  9. Mid- to Late Holocene climate development in Central Asia as revealed from multi-proxy analyses of sediments from Lake Son Kol (Kyrgyzstan)

    Lauterbach, Stefan; Dulski, Peter; Gleixner, Gerd; Hettler-Riedel, Sabine; Mingram, Jens; Plessen, Birgit; Prasad, Sushma; Schwalb, Antje; Schwarz, Anja; Stebich, Martina; Witt, Roman


    A mid-Holocene shift from predominantly wet to significantly drier climate conditions, attributed to the weakening of the Asian summer monsoon (ASM), is documented in numerous palaeoclimate records from the monsoon-influenced parts of Asia, e.g. the Tibetan Plateau and north- and southeastern China. In contrast, Holocene climate development in the arid regions of mid-latitude Central Asia, located north and northwest of the Tibetan Plateau, is less well-constrained but supposed to have been influenced by a complex interaction between the mid-latitude Westerlies and the ASM. Hence, well-dated and highly resolved palaeoclimate records from Central Asia might provide important information about spatio-temporal changes in the regional interplay between Westerlies and ASM and thus aid the understanding of global climate teleconnections. As a part of the project CADY (Central Asian Climate Dynamics), aiming at reconstructing past climatic and hydrological variability in Central Asia, several sediment cores were recovered from alpine Lake Son Kol (41° 48'N, 75° 12'E, 3016 m a. s. l.) in the Central Tian Shan of Kyrgyzstan. A radiocarbon-dated sediment sequence of 154.5 cm length, covering approximately the last 6000 years, was investigated by using a multi-proxy approach, including sedimentological, (bio)geochemical, isotopic and micropalaeontological analyses. Preliminary proxy data indicate hydrologically variable but predominantly wet conditions until ca. 5100 cal. a BP, characterized by the deposition of finely laminated organic-carbonatic sediments. In contrast to monsoonal Asia, where a distinct trend towards drier conditions is observed since the mid-Holocene, the hydrologically variable interval at Lake Son Kol was apparently followed by an only short-term dry episode between ca. 5100 and 4200 cal. a BP. This is characterized by a higher δD of the C29 n-alkanes, probably reflecting increased evapotranspiration. Also pollen, diatom and ostracod data point

  10. Climate reconstructions derived from global glacier length records

    Klok, E.J.; Oerlemans, J.


    As glacier length fluctuations provide useful information about past climate, we derived historic fluctuations in the equilibrium-line altitude (ELA) on the basis of 19 glacier length records from different parts of the world. We used a model that takes into account the geometry of the glacier,

  11. Holocene River Dynamics, Climate Change and Floodwater Farming in the Watersheds of the Pamir and Tien Shan Mountains of Inner Asia

    Macklin, M. G.; Panyushkina, I. P.; Toonen, W. H. J.


    The Ili, Syr Dayra and Amu Dayra rivers of Inner Asia are emerging as critical areas for the development of irrigation-based agriculture in the ancient world. Following research by Russian archaeologists in the 1970s it is evident that these watersheds had flourishing riverine civilizations comparable to those in Mesopotamia and the Indus Valley. But unlike these areas where the relationship between Holocene river dynamics, climate change and floodwater farming is increasingly underpinned by radiometric dating, the alluvial archaeology of Inner Asia is significantly under researched. To address this, a major multi-disciplinary research program was begun in 2011 centred on the Talgar catchment, a south-bank tributary of the Ili river, southeast Kazakhstan. Building on archaeological excavations and surveys conducted over the past 20 years, we have undertaken one of the most detailed investigations of Holocene people-river environment interactions in Inner Asia. River development has been reconstructed over the last 20,000 years and human settlement histories from the Eneolithic to the Medieval period documented. Periods of Holocene river aggradation and high water levels in Lake Balkhash and Aral Sea correspond with cooler and wetter neoglacial episodes while river entrenchment and floodplain soil development are associated with warmer and drier conditions. Floodwater farming in the Talgar river reached its acme in the late Iron Age (400-200 cal. BC) with more than 60 settlement sites and 550 burial mounds. This corresponds to a period of reduced flood flows, river stability and glacier retreat in the Tien Shan headwaters. A new hydroclimatic-based model for the spatial and temporal dynamics of floodwater farming in the Ili, Syr Dayra and Amu Dayra watersheds is proposed, which explains the large scale expansion (down-river) and contraction (up-river) of settlements since the first use of irrigation in the Neolithic through to the late Medieval period.

  12. Past Holocene detritism quantification and modeling from lacustrine archives in order to deconvoluate human-climate interactions on natural ecosystem over long time-scale

    Simonneau, Anaëlle; Chapron, Emmanuel; Di Giovanni, Christian; Galop, Didier; Darboux, Frédéric


    Water budget is one of the main challenges to paleoclimate researchers in relation to present-day global warming and its consequences for human societies. Associated soil degradation and erosion are thereby becoming a major concern in many parts of the world and more particularly in the Alps. Moreover, humans are considered as geomorphologic agents since few thousand years and it is now recognized that such an impact on natural ecosystem profoundly modified soils properties as well as aquatic ecosystems dynamics over long-term periods. The quantification of such inference over long time-scale is therefore essential to establish new policies to reduce mechanic soil erosion, which is one of the dominant processes in Europe, and anticipate the potential consequences of future climate change on hydric erosion. The mechanical erosion of continental surfaces results from climatic forcing, but can be amplified by the anthropogenic one. We therefore suggest that quantifying and modelling soil erosion processes within comparable Holocene lacustrine archives, allows to estimate and date which and when past human activities have had an impact on soil fluxes over the last 10000 years. Based on the present-day geomorphology of the surrounding watershed and the evolution of the vegetation cover during the Holocene, we develop an interdisciplinary approach combining quantitative organic petrography (i.e. optical characterization and quantification of soil particles within lake sediments) with high-resolution seismic profiling, age-depth models on lacustrine sediment cores and soil erosional susceptibility modeling, in order to estimate the annual volume of soil eroded over the last 10000 years, and in fine to quantify the volume of human-induced soil erosion during the Holocene period. This method is applied to close but contrasted mountainous lacustrine environments from the western French Alps: lakes Blanc Huez and Paladru, sensitive to same climatic influences but where past

  13. Pollen record of the mid- to late-Holocene centennial climate change on the East coast of South Korea and its influential factors

    Song, Bing; Yi, Sangheon; Jia, Hongjuan; Nahm, Wook-Hyun; Kim, Jin-Cheul; Lim, Jaesoo; Lee, Jin-Young; Sha, Longbin; Mao, Limi; Yang, Zhongyong; Nakanishi, Toshimichi; Hong, Wan; Li, Zhen


    To understand historical climate change in western Pacific coastal areas, a sediment core (SOJ-2) from the stable sedimentary environment of the Songjiho Lagoon on the east coast of South Korea was obtained for centennial-resolution palynological analysis. The ages of the SOJ-2 core is well controlled by carbon 14 dating with high-resolution accelerator mass spectrometry (AMS), and the results indicated a general warm to cold climate trend from the mid-Holocene to the present, which can be divided into two different stages: a warmer stage between 6842 and 1297 cal yr BP and a colder stage from 1297 cal yr BP to the present, with fluctuations during these stages. The climate was wetter from 6842 to 6227 cal yr BP and 4520 to 1297 cal yr BP and was drier from 6227 to 4520 cal yr BP. The climate changed to cold and dry during the period from 1297-425 cal yr BP. The impact of human activity on the climate began at approximately 1297 cal yr BP and became pronounced starting in 425 cal yr BP. The general cooling trend may represent a response to decreasing solar insolation; however, the relative dryness or wetness of the climate may have been co-determined by westerlies and the East Asian summer monsoon (EASM). The climate had a teleconnection with the North Atlantic region, resulting from changes in solar activity. Nevertheless, EI Niño-Southern Oscillation (ENSO) activity played an important role in impacting the EASM changes in western Pacific coastal areas.

  14. Potential influence of the late Holocene climate on settled farming versus nomadic cattle herding in the Minusinsk Hollow, south-central Siberia

    Blyakharchuk, T A; Tchebakova, N M; Parfenova, E I; Soja, A J


    Prehistoric and early historic human cultures are known to be closely connected to and dependent on their natural environments. We test the hypothesis that climate change influenced the means of subsistence of ancient tribes and favored agricultural or cattle herding economic strategies. Our study area is the Khakass–Minusinsk Hollow, located in the foothills of the Sayan Mountains, south-central Siberia, which was, for a few millennia, a buffer zone for human migrations across the Great Eurasian Steppe. Three different methods (the Montane BioClimatic Model, MontBCliM; the biomization method; and the actualizm method) are employed to reconstruct vegetation taken from the fossil pollen of sediment cores in two mountain lakes at eleven time slices related to successive human cultures back to the mid-Holocene. MontBCliM model is used inversely to convert site paleo-vegetation into site paleo-climates. Climate-based regression models are developed and applied to reconstructed climates to evaluate possible pasture and grain crops for these time slices. Pollen-based reconstructions of the climate fluctuations uncovered several dry periods with steppe and forest-steppe and wetter periods with forests since 6000 BP. Grasslands increased by an order of magnitude during the dry periods and provided extensive open space suitable for pastoralism; however, both grain and pasture yields decreased during these dry periods. During wetter climates, both grain and pasture yields increased twofold and supported more fixed human settlements centered around farming and cattle herding. Thus, the dry periods favored pastoralist rather than farming activities. Conversely, tribes that practiced agriculture had some advantage in the wet periods. (papers)

  15. Response of C3 and C4 plants to middle-Holocene climatic variation near the prairie-forest ecotone of Minnesota, U.S.A.

    Tian, J; Brown, T A; Hu, F S; Stefanova, I; Nelson, D M


    Paleorecords of the middle Holocene (MH) from the North American midcontinent can offer insights into ecological responses to pervasive drought that may accompany future climatic warming. We analyzed MH sediments from West Olaf Lake (WOL) and Steel Lake (SL) in Minnesota to examine the effects of warm/dry climatic conditions on prairie-woodland ecosystems. Mineral composition and carbonate {delta}{sup 18}O were used to determine climatic variations, whereas pollen assemblages, charcoal {delta}{sup 13}C, and charcoal accumulation rates were used to reconstruct vegetation composition, C{sub 3} and C{sub 4} plant abundance, and fire. The ratio of aragonite:calcite at WOL and {delta}{sup 18}O at SL suggest that pronounced droughts occurred during the MH but that drought severity decreased with time. From charcoal {delta}{sup 13}C data we estimated that the MH abundance of C{sub 4} plants averaged 50% at WOL and 43% at SL. At WOL C{sub 4} abundance was negatively correlated with aragonite:calcite, suggesting that severe moisture deficits suppressed C{sub 4} plants in favor of weedy C{sub 3} plants (e.g., Ambrosia). As climate ameliorated C{sub 4} abundance increased (from {approx}33 to 66%) at the expense of weedy species, enhancing fuel availability and fire occurrence. In contrast, farther east at SL climate was cooler and wetter than at WOL, and C{sub 4} abundance showed no correlation with {delta}{sup 18}O-inferred aridity. Woody C{sub 3} plants (e.g., Quercus) were more abundant, biomass flammability lower, and fires less important at SL than at WOL. Our results suggest that C{sub 4} plants are adapted to warm/dry climatic conditions, but not to extreme droughts, and that the fire regime is controlled by biomass-climate interactions.

  16. Synthesizing late Holocene paleoclimate reconstructions: Lessons learned, common challenges, and implications for future research

    Rodysill, J. R.


    Proxy-based reconstructions provide vital information for developing histories of environmental and climate changes. Networks of spatiotemporal paleoclimate information are powerful tools for understanding dynamical processes within the global climate system and improving model-based predictions of the patterns and magnitudes of climate changes at local- to global-scales. Compiling individual paleoclimate records and integrating reconstructed climate information in the context of an ensemble of multi-proxy records, which are fundamental for developing a spatiotemporal climate data network, are hindered by challenges related to data and information accessibility, chronological uncertainty, sampling resolution, climate proxy type, and differences between depositional environments. The U.S. Geological Survey (USGS) North American Holocene Climate Synthesis Working Group has been compiling and integrating multi-proxy paleoclimate data as part of an ongoing effort to synthesize Holocene climate records from North America. The USGS North American Holocene Climate Synthesis Working Group recently completed a late Holocene hydroclimate synthesis for the North American continent using several proxy types from a range of depositional environments, including lakes, wetlands, coastal marine, and cave speleothems. Using new age-depth relationships derived from the Bacon software package, we identified century-scale patterns of wetness and dryness for the past 2000 years with an age uncertainty-based confidence rating for each proxy record. Additionally, for highly-resolved North American lake sediment records, we computed average late Holocene sediment deposition rates and identified temporal trends in age uncertainty that are common to multiple lakes. This presentation addresses strengths and challenges of compiling and integrating data from different paleoclimate archives, with a particular focus on lake sediments, which may inform and guide future paleolimnological studies.

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

    Premathilake, Rathnasiri


    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.

  18. Combining satellite derived phenology with climate data for climate change impact assessment

    Ivits, E.; Cherlet, M.; Tóth, G.; Sommer, S.; Mehl, W.; Vogt, J.; Micale, F.


    The projected influence of climate change on the timing and volume of phytomass production is expected to affect a number of ecosystem services. In order to develop coherent and locally effective adaptation and mitigation strategies, spatially explicit information on the observed changes is needed. Long-term variations of the vegetative growing season in different environmental zones of Europe for 1982-2006 have been derived by analysing time series of GIMMS NDVI data. The associations of phenologically homogenous spatial clusters to time series of temperature and precipitation data were evaluated. North-east Europe showed a trend to an earlier and longer growing season, particularly in the northern Baltic areas. Despite the earlier greening up large areas of Europe exhibited rather stable season length indicating the shift of the entire growing season to an earlier period. The northern Mediterranean displayed a growing season shift towards later dates while some agglomerations of earlier and shorter growing season were also seen. The correlation of phenological time series with climate data shows a cause-and-effect relationship over the semi natural areas consistent with results in literature. Managed ecosystems however appear to have heterogeneous change pattern with less or no correlation to climatic trends. Over these areas climatic trends seemed to overlap in a complex manner with more pronounced effects of local biophysical conditions and/or land management practices. Our results underline the importance of satellite derived phenological observations to explain local nonconformities to climatic trends for climate change impact assessment.

  19. Biomarker-indicated extent of oxidation of plant-derived organic carbon (OC) in relation to geomorphology in an arsenic contaminated Holocene aquifer, Cambodia.

    Magnone, Daniel; Richards, Laura A; Polya, David A; Bryant, Charlotte; Jones, Merren; van Dongen, Bart E


    The poisoning of rural populations in South and Southeast Asia due to high groundwater arsenic concentrations is one of the world's largest ongoing natural disasters. It is important to consider environmental processes related to the release of geogenic arsenic, including geomorphological and organic geochemical processes. Arsenic is released from sediments when iron-oxide minerals, onto which arsenic is adsorbed or incorporated, react with organic carbon (OC) and the OC is oxidised. In this study we build a new geomorphological framework for Kandal Province, a highly studied arsenic affected region of Cambodia, and tie this into wider regional environmental change throughout the Holocene. Analyses shows that the concentration of OC in the sediments is strongly inversely correlated to grainsize. Furthermore, the type of OC is also related to grain size with the clay containing mostly (immature) plant derived OC and sand containing mostly thermally mature derived OC. Finally, analyses indicate that within the plant derived OC relative oxidation is strongly grouped by stratigraphy with the older bound OC more oxidised than younger OC.

  20. Low-frequency and high-frequency changes in temperature and effective humidity during the Holocene in south-central Sweden: implications for atmospheric and oceanic forcings of climate

    Seppae, H. [University of Helsinki, Department of Geology, 64, Helsinki (Finland); Hammarlund, D. [Lund University, GeoBiosphere Science Centre, Quaternary Sciences, Lund (Sweden); Antonsson, K. [Uppsala University, Department of Earth Sciences, Uppsala (Sweden)


    An integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes. Here we report a 10,000 year quantitative record of annual mean temperature (T{sub ann}), based on pollen-climate transfer functions and pollen-stratigraphical data from Lake Flarken, south-central Sweden. The pollen-based temperature reconstruction is compared with a reconstruction of effective humidity, as reflected by a {delta}{sup 18}O record obtained on stratigraphy of lacustrine carbonates from Lake Igelsjoen, c. 10 km from Lake Flarken, which gives evidence of pronounced changes in effective humidity. The relatively low T{sub ann}, and high effective humidity as reflected by a low evaporation/inflow ratio suggest a maritime early Holocene climate (10,000-8,300 cal year BP), seemingly incompatible with the highly seasonal solar insolation configuration. We argue that the maritime climate was due to the stronger-than-present zonal flow, enhanced by the high early Holocene sea-surface temperatures in the North Atlantic. The maritime climate mode was disrupted by the abrupt cold event at 8,200 cal year BP, followed at 8,000 cal year BP by a stable Holocene Thermal Maximum. The latter was characterized by T{sub ann} values about 2.5 C higher than at present and markedly dry conditions, indicative of stable summer-time anti-cyclonic circulation, possibly corresponding with modern blocking anticyclonic conditions. The last 4,300 year period is characterized by an increasingly cold, moist, and unstable climate. The results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability, generality, and interpretability of the palaeoclimatic results. Further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial

  1. Impacts of Evolutionary History on Endangerment in a Changing Climate: Miocene upwelling, Holocene Pluvial Cycles and Endemics at the Mouth of the Colorado River.

    Jacobs, D. K.


    The environmental conditions communities experienced during their diversification and recent geologic history informs us as to which environmental changes are most likely to impact species in those communities. Three examples follow: 1) Recent compilation of molecular and paleontological data document that higher aspects of the trophic chain in the Pacific Northwest, including the salmon genus Onchoyrhynchus, alcid birds (Auks & Puffins) and crabs of the genus Cancer speciated dramatically in response to enhanced upwelling of the mid Miocene (Jacobs et al. 2004). Consistent with this evolutionary origin, population dynamics and endangerment of these taxa are associated with the changing productivity regime of the Pacific as well as more direct human impacts. 2) Pluvials in the Eurasian and African continent respond to the precession cycle, as a result wetland habitats were much more expansive in the early and middle Holocene. Late Holocene wetland habitat contraction combines with increasing anthropogenic manipulation of these cyclically limited hydrologic resources to yield a suite of endangered taxa across these continents as is statistically documented by analysis of Redbook data. 3) Our recent work documents the evolution of endemic fish and Molluscan taxa in association with the Colorado River Delta. These endemic taxa are then vulnerable to the to impacts on the Colorado Delta where anthropogenic use of water resources combine with the threat of climate provide combined threats to this ecosystem. The Environmental/Evolutionary history of lineages clearly has strong implications for how anthropogenic changes impacts and endangers those lineages. Jacobs D.K. et al. Annu. Rev. Earth Planet. Sci. 2004. 32:601 52

  2. A late Holocene metal record of Andean climate and anthropogenic activity in lake sediments near Quelccaya Ice Cap, Peru

    Beal, S. A.; Kelly, M. A.; Jackson, B. P.; Stroup, J. S.; Osterberg, E. C.


    The tropical hypothesis maintains that major changes in global climate are motivated by phenomena based at tropical latitudes. Evidence for this hypothesis lies in: modern-day observations of El Niño Southern Oscillation (ENSO); East African lake sediment records of Intertropical Convergence Zone (ITCZ) position that precede high-latitude changes; and the potential for ITCZ shifts to cause major CO2 degassing from the Southern Ocean. In order to improve the understanding of these phenomena we present an ~1800 year record of atmospheric metal deposition in a lake sediment core near Quelccaya Ice Cap, Peru (13.9 °S). In June, 2010 we collected a 1.45 meter-long core from Yanacocha - a small, closed-basin tarn that has been isolated from glacial input since ~11,200 BP. The chronology for the core is based on 4 of 6 AMS 14C dates on aquatic macrofossils and one sharp Zr/Ti anomaly at 36 cm, likely derived from the 350 BP eruption of Huaynaputina. We completely digested organic-rich core samples at 1 cm resolution using HNO3, HCl, and HF in a closed-vessel microwave system, and then analyzed the digestates for 67 metals by inductively coupled plasma mass spectrometry. Here we show fluxes of lithogenic metals (Fe, Nb, Ti, and Zr) that reflect changes in wind strength and aridity, fluxes of lithogenic metal isotopes (REEs and Pb) that reflect wind direction, and enrichment factors (EFs) of metals (Ag, As, Cd, Cu, Hg, and Pb) that reflect anthropogenic activity. Five episodic peaks in lithogenic metal fluxes, centered around 1800, 1300, 900, 600, and 100 yrs BP, are thought to result from either drier or windier conditions, potentially caused by a northern ITCZ position or a more persistent El Niño state. The provenance of atmospheric deposition, evidenced by REE ratios (light REEs / heavy REEs), suggest that high lithogenic fluxes are associated with a change in wind direction, possibly caused by a change in the ENSO state, which will be explored with forthcoming Pb

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

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


    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.

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

    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


    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.

  5. Relation between the sedimentary organic record and the climatic oscilations in the Holocene attested by palynofacies and organic geochemical analyses from a pond of altitude in southern Brazil



    Full Text Available This paper presents the quantitative and qualitative results obtained from palynofacies and geochemistry analyses carried out on a core covering approximately 8000 years of sedimentation of a pond of altitude located at the mining district of Ametista do Sul, southernmost Brazil. The main objective of this paper is to consider the paleoclimatic and paleoenvironmental significance of these analyses. The hydrological isolation renders this pond climatically sensitive to variations in pluviometric regime and this enabled infer rainfall events during the early Holocene, which was responsible for the beginning of the processes of water accumulation in the gossan and the sedimentation of the pond. Changes in the pattern of moisture over the time become the drier environment, resulting in the intermittent pattern of water depth that currently exists at the site. The fluctuations in water depth are inferred from the frequency of Botryococcus and other algae, which tend to decrease progressively toward the top where the autochthonous elements are replaced by parautochthonous and allochthonous elements. Pseudoschizaea, in turn, appears to act as a biological marker of these transitional intervals. The present results are of great importance for understanding the extent of climate change and its environmental impacts at regional and global levels.

  6. Effect of climate changes in the holocene on the distribution of humic substances in the profile of forest-tundra peat mounds

    Vasilevich, R. S.; Beznosikov, V. A.


    The molecular composition of humic substances in permafrost peatlands of the forest-tundra zone in northeastern European Russia has been characterized for the first time on the basis of systematic studies. Changes in the molar x(H): x(C) ratio along the peat profiles have been revealed, which is due to the activation of cryogenic processes in the upper part of the seasonally thawing layer, the natural selection of condensed humic molecules, and the botanical composition and degree of degradation of peat, which reflect the climatic features of the area in the Holocene. Dry-peat soils of mounds are worse heated during the summer period because of the buffering effect of moss litter, which results in a lower degree of condensation of humic and fulvic acid molecules in the peat horizons down to the permafrost table. Transformation of quantitative and qualitative parameters of specific organic compounds occurs at the permafrost boundary of peatlands, which can serve as an indicator of recent climate changes in high latitudes.

  7. Past Holocene soil erosion modeling as a new way to decipher human-climate-environment interactions on natural geo-ecosystem over long time-scale.

    Simonneau, Anaëlle; Di Giovanni, Christian; Chapron, Emmanuel


    Soil erosion is a global phenomenon dealing with both environmental, societal and economic issues. Soil erosion is also one of the key processes when it is a matter of Human-climate-environment interactions [1, 2] since if mechanical erosion of continental surfaces initially results from climatic forcing, it can be largely amplified by anthropogenic activities. Using multi-scalar datasets to model long-term (Holocene) erosion fluxes in contrasted areas, where human pressure is well documented by geoarchaeology, we address how landscape evolution, geomorphological processes, ecosystem response and human impacts have been connected over time. Beyond that, such interdisciplinary and integrative approach allow (1) to locally date, qualify, and in particular quantify, both climate variability (rainfall) and impacts of human activities on soils, and (2) to discuss of potential feedback mechanisms and the legacy of past socio-cultural systems on actual geo-ecosystems. Lacustrine sediment represents one of the more relevant natural archives in order to reconstruct environmental or climatic variability and human activities over the past thousand years. Over the last 50 years, the edges of lakes Paladru (low altitude site, 640 m a.s.l.) and Blanc Huez (high-altitude site, 2250 m a.s.l.), both located in Western French Alps and therefore sensitive to the same climatic influences, have been deeply studied by archaeologists who documented and dated periods of enhanced human pressures (agriculture, mining [3, 4]). In these two case-studies, we were therefore able to confront the specific calendars of local human activities with past landscape evolution (vegetation cover, 5) and soil erosion fluxes reconstituted from specific organic tracers quantified into the lacustrine sediments [3, 6]. Results demonstrated that, over the Holocene, climatic forcing, and more particularly glacial fluctuations, influenced human accessibility to high-altitude sites (lake Blanc Huez) and therefore

  8. Late-Holocene climate evolution at the WAIS Divide site, West Antarctica: Bubble number-density estimates

    Fegyveresi, John M.; Alley, R.B.; Spencer, M.K.; Fitzpatrick, J.J.; Steig, E.J.; White, J.W.C.; McConnell, J.R.; Taylor, K.C.


    A surface cooling of ???1.7??C occurred over the ???two millennia prior to ???1700 CE at the West Antarctic ice sheet (WAIS) Divide site, based on trends in observed bubble number-density of samples from the WDC06A ice core, and on an independently constructed accumulation-rate history using annual-layer dating corrected for density variations and thinning from ice flow. Density increase and grain growth in polar firn are both controlled by temperature and accumulation rate, and the integrated effects are recorded in the number-density of bubbles as the firn changes to ice. Numberdensity is conserved in bubbly ice following pore close-off, allowing reconstruction of either paleotemperature or paleo-accumulation rate if the other is known. A quantitative late-Holocene paleoclimate reconstruction is presented for West Antarctica using data obtained from the WAIS Divide WDC06A ice core and a steady-state bubble number-density model. The resultant temperature history agrees closely with independent reconstructions based on stable-isotopic ratios of ice. The ???1.7??C cooling trend observed is consistent with a decrease in Antarctic summer duration from changing orbital obliquity, although it remains possible that elevation change at the site contributed part of the signal. Accumulation rate and temperature dropped together, broadly consistent with control by saturation vapor pressure.

  9. Loco or no loco? Holocene climatic fluctuations, human demography and community base management of coastal resources in northern Chile

    Santoro, Calogero M.; Gayo, Eugenia M.; Carter, Chris; Standen, Vivien G.; Castro, Victoria; Valenzuela, Daniela; De Pol-Holz, Ricardo; Marquet, Pablo A.; Latorre, Claudio


    The abundance of the southern Pacific mollusk loco (Concholepas concholepas), among other conspicuous marine supplies, are often cited as critical resources behind the long-term cultural and demographic fluctuations of prehistoric hunter-gatherers at the coastal Atacama Desert. These societies inhabited one of the world’s most productive marine environments flanked by one the world’s driest deserts. Both of these environments have witnessed significant ecological variation since people first colonized them at the end of the Pleistocene (c. 13,000 cal yr BP). Here, we examine the relationship between the relative abundance of shellfish (a staple resource) along a 9,500-year sequence of archaeological shell midden accumulations at Caleta (a small inlet or cove) Vitor, with past demographic trends (established via summed probability distributions of radiocarbon ages) and technological innovations together with paleoceanographic data on past primary productivity. We find that shellfish extraction varied considerably from one cultural period to the next in terms of the number of species and their abundance, with diversity increasing during periods of regionally decreased productivity. Such shifts in consumption patterns are considered community based management decisions, and for the most part they were synchronous with large and unusual regional demographic fluctuations experienced by prehistoric coastal societies in northern Chile. When taken together with their technological innovations, our data illustrates how these human groups tailored their socio-cultural patterns to what were often abrupt and prolonged environmental changes throughout the Holocene.

  10. Loco or no Loco? Holocene Climatic Fluctuations, Human Demography, and Community Based Management of Coastal Resources in Northern Chile

    Calogero M. Santoro


    Full Text Available The abundance of the southern Pacific mollusk loco (Concholepas concholepas, among other conspicuous marine supplies, are often cited as critical resources behind the long-term cultural and demographic fluctuations of prehistoric hunter-gatherers in the coastal Atacama Desert. These societies inhabited one of the world's most productive marine environments flanked by one the world's driest deserts. Both of these environments have witnessed significant ecological variation since people first colonized them at the end of the Pleistocene (c. 13,000 cal yr BP. Here, we examine the relationship between the relative abundance of shellfish (a staple resource along a 9,500-year sequence of archeological shell midden accumulations at Caleta (a small inlet or cove Vitor, with past demographic trends (established via summed probability distributions of radiocarbon ages and technological innovations together with paleoceanographic data on past primary productivity. We find that shellfish extraction varied considerably from one cultural period to the next in terms of the number of species and their abundance, with diversity increasing during periods of regionally decreased productivity. Such shifts in consumption patterns are considered community based management decisions, and for the most part they were synchronous with large and unusual regional demographic fluctuations experienced by prehistoric coastal societies in northern Chile. When taken together with their technological innovations, our data illustrates how these human groups tailored their socio-cultural patterns to what were often abrupt and prolonged environmental changes throughout the Holocene.

  11. Holocene aridification of India

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


    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.

  12. 8000-year monsoonal record from Himalaya revealing reinforcement of tropical and global climate systems since mid-Holocene.

    Srivastava, Pradeep; Agnihotri, Rajesh; Sharma, Deepti; Meena, Narendra; Sundriyal, Y P; Saxena, Anju; Bhushan, Ravi; Sawlani, R; Banerji, Upasana S; Sharma, C; Bisht, P; Rana, N; Jayangondaperumal, R


    We provide the first continuous Indian Summer Monsoon (ISM) climate record for the higher Himalayas (Kedarnath, India) by analyzing a 14 C-dated peat sequence covering the last ~8000 years, with ~50 years temporal resolution. The ISM variability inferred using various proxies reveal striking similarity with the Greenland ice core (GISP2) temperature record and rapid denitrification changes recorded in the sediments off Peru. The Kedarnath record provides compelling evidence for a reorganization of the global climate system taking place at ~5.5 ka BP possibly after sea level stabilization and the advent of inter-annual climate variability governed by the modern ENSO phenomenon. The ISM record also captures warm-wet and cold-dry conditions during the Medieval Climate Anomaly and Little Ice Age, respectively.

  13. 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

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


    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.

  14. Holocene Vegetation Succession and Response to Climate Change on the South Bank of the Heilongjiang-Amur River, Mohe County, Northeast China

    Chao Zhao


    Full Text Available Pollen samples from peat sediments on the south bank of the Heilongjiang River in northern Northeast China (NE China were analyzed to reconstruct the historical response of vegetation to climate change since 7800 cal yr BP. Vegetation was found to have experienced five successions from cold-temperate mixed coniferous and broadleaved forest to forest-steppe, steppe-woodland, steppe, and finally meadow-woodland. From 7800 to 7300 cal yr BP, the study area was warmer than present, and Betula, Larix, and Picea-dominated mixed coniferous and broadleaved forests thrived. Two cooling events at 7300 cal yr BP and 4500 cal yr BP led to a decrease in Betula and other broadleaved forests, whereas herbs of Poaceae expanded, leading to forest-steppe and then steppe-woodland environments. After 2500 cal yr BP, reduced temperatures and a decrease in evaporation rates are likely to have resulted in permafrost expansion and surface ponding, with meadow and isolated coniferous forests developing a resistance to the cold-wet environment. The Holocene warm period in NE China (7800–7300 cal yr BP could have resulted in a strengthening of precipitation in northernmost NE China and encouraged the development of broadleaved forests.

  15. Evaluation of PMIP2 and PMIP3 simulations of mid-Holocene climate in the Indo-Pacific, Australasian and Southern Ocean regions

    D. Ackerley


    Full Text Available This study uses the simplified patterns of temperature and effective precipitation approach from the Australian component of the international palaeoclimate synthesis effort (INTegration of Ice core, MArine and TErrestrial records – OZ-INTIMATE to compare atmosphere–ocean general circulation model (AOGCM simulations and proxy reconstructions. The approach is used in order to identify important properties (e.g. circulation and precipitation of past climatic states from the models and proxies, which is a primary objective of the Southern Hemisphere Assessment of PalaeoEnvironment (SHAPE initiative. The AOGCM data are taken from the Paleoclimate Modelling Intercomparison Project (PMIP mid-Holocene (ca. 6000 years before present, 6 ka and pre-industrial control (ca. 1750 CE, 0 ka experiments. The synthesis presented here shows that the models and proxies agree on the differences in climate state for 6 ka relative to 0 ka, when they are insolation driven. The largest uncertainty between the models and the proxies occurs over the Indo-Pacific Warm Pool (IPWP. The analysis shows that the lower temperatures in the Pacific at around 6 ka in the models may be the result of an enhancement of an existing systematic error. It is therefore difficult to decipher which one of the proxies and/or the models is correct. This study also shows that a reduction in the Equator-to-pole temperature difference in the Southern Hemisphere causes the mid-latitude westerly wind strength to reduce in the models; however, the simulated rainfall actually increases over the southern temperate zone of Australia as a result of higher convective precipitation. Such a mechanism (increased convection may be useful for resolving disparities between different regional proxy records and model simulations. Finally, after assessing the available datasets (model and proxy, opportunities for better model–proxy integrated research are discussed.

  16. Evaluation of PMIP2 and PMIP3 simulations of mid-Holocene climate in the Indo-Pacific, Australasian and Southern Ocean regions

    Ackerley, Duncan; Reeves, Jessica; Barr, Cameron; Bostock, Helen; Fitzsimmons, Kathryn; Fletcher, Michael-Shawn; Gouramanis, Chris; McGregor, Helen; Mooney, Scott; Phipps, Steven J.; Tibby, John; Tyler, Jonathan


    This study uses the simplified patterns of temperature and effective precipitation approach from the Australian component of the international palaeoclimate synthesis effort (INTegration of Ice core, MArine and TErrestrial records - OZ-INTIMATE) to compare atmosphere-ocean general circulation model (AOGCM) simulations and proxy reconstructions. The approach is used in order to identify important properties (e.g. circulation and precipitation) of past climatic states from the models and proxies, which is a primary objective of the Southern Hemisphere Assessment of PalaeoEnvironment (SHAPE) initiative. The AOGCM data are taken from the Paleoclimate Modelling Intercomparison Project (PMIP) mid-Holocene (ca. 6000 years before present, 6 ka) and pre-industrial control (ca. 1750 CE, 0 ka) experiments. The synthesis presented here shows that the models and proxies agree on the differences in climate state for 6 ka relative to 0 ka, when they are insolation driven. The largest uncertainty between the models and the proxies occurs over the Indo-Pacific Warm Pool (IPWP). The analysis shows that the lower temperatures in the Pacific at around 6 ka in the models may be the result of an enhancement of an existing systematic error. It is therefore difficult to decipher which one of the proxies and/or the models is correct. This study also shows that a reduction in the Equator-to-pole temperature difference in the Southern Hemisphere causes the mid-latitude westerly wind strength to reduce in the models; however, the simulated rainfall actually increases over the southern temperate zone of Australia as a result of higher convective precipitation. Such a mechanism (increased convection) may be useful for resolving disparities between different regional proxy records and model simulations. Finally, after assessing the available datasets (model and proxy), opportunities for better model-proxy integrated research are discussed.

  17. A 700 year record of combustion-derived pollution in northern Spain: Tools to identify the Holocene/Anthropocene transition in coastal environments

    Leorri, Eduardo; Mitra, Siddhartha; Irabien, María Jesús; Zimmerman, Andrew R.; Blake, William H.; Cearreta, Alejandro


    There is an uneven geographical distribution of historic records of atmospheric pollutants from SW Europe and those that exist are very limited in temporal extent. Alternative data source is required to understand temporal trends in human impacts on atmospheric pollution. Polycyclic aromatic hydrocarbons (PAHs), heavy metal content and stable Pb isotopic ratios in a sediment core from a salt marsh in northern Spain were used to reconstruct the regional history of contaminant inputs over the last 700 years. Pre-1800s concentrations of Pb and PAHs represented baseline concentrations, i.e. pre-Industrial, conditions. During the initial stages of the Industrial Revolution, 1800s to 1860s, PAH concentrations increased by a factor of about two above baseline levels in the sediment column. By the 1930s, PAH levels reached ca. 10 times pre-Industrial levels and, along with Pb, reached a peak at ca. 1975 CE. Since then, sedimentary PAH and Pb concentrations decreased significantly. A combination of PAH isomer and Pb stable isotope ratios suggests that the contaminant sources are regional, likely derived partially from wood, but mainly coal used by the metallurgic industry in the Basque country since the 1800s and until the 1970s when leaded petrol saw increased use. This chronology of regional atmosphere-derived pollution expands current southwest Europe emission records and shows coastal salt marsh sediments to be useful in reconstructing the Anthropocene. - Highlights: • Historic records of atmospheric pollutant emissions in SW Europe are needed. • PAH and Pb concentrations and ratios from a north Spain salt marsh core were used. • Atmosphere emissions mainly from regional coal burning increased in the early 1800s. • Emissions associated with leaded gasoline peaked in 1975 CE. • The results suggest 1800 CE as the Holocene/Anthropocene transition

  18. A 700 year record of combustion-derived pollution in northern Spain: Tools to identify the Holocene/Anthropocene transition in coastal environments

    Leorri, Eduardo, E-mail: [Department of Geological Sciences, East Carolina University, Graham Building 103B, Greenville, NC 27858 (United States); Mitra, Siddhartha, E-mail: [Department of Geological Sciences, East Carolina University, Graham Building 103B, Greenville, NC 27858 (United States); Irabien, María Jesús, E-mail: [Departamento de Mineralogía y Petrología, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Apartado 644, 48080 Bilbao (Spain); Zimmerman, Andrew R., E-mail: [Department of Geological Sciences, University of Florida, 241 Williamson Hall, P.O. Box 112120, Gainesville, FL 32611 (United States); Blake, William H., E-mail: [Consolidated Radioisotope Facility, University of Plymouth, Plymouth (United Kingdom); Cearreta, Alejandro, E-mail: [Departamento de Estratigrafía y Paleontología, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Apartado 644, 48080 Bilbao (Spain)


    There is an uneven geographical distribution of historic records of atmospheric pollutants from SW Europe and those that exist are very limited in temporal extent. Alternative data source is required to understand temporal trends in human impacts on atmospheric pollution. Polycyclic aromatic hydrocarbons (PAHs), heavy metal content and stable Pb isotopic ratios in a sediment core from a salt marsh in northern Spain were used to reconstruct the regional history of contaminant inputs over the last 700 years. Pre-1800s concentrations of Pb and PAHs represented baseline concentrations, i.e. pre-Industrial, conditions. During the initial stages of the Industrial Revolution, 1800s to 1860s, PAH concentrations increased by a factor of about two above baseline levels in the sediment column. By the 1930s, PAH levels reached ca. 10 times pre-Industrial levels and, along with Pb, reached a peak at ca. 1975 CE. Since then, sedimentary PAH and Pb concentrations decreased significantly. A combination of PAH isomer and Pb stable isotope ratios suggests that the contaminant sources are regional, likely derived partially from wood, but mainly coal used by the metallurgic industry in the Basque country since the 1800s and until the 1970s when leaded petrol saw increased use. This chronology of regional atmosphere-derived pollution expands current southwest Europe emission records and shows coastal salt marsh sediments to be useful in reconstructing the Anthropocene. - Highlights: • Historic records of atmospheric pollutant emissions in SW Europe are needed. • PAH and Pb concentrations and ratios from a north Spain salt marsh core were used. • Atmosphere emissions mainly from regional coal burning increased in the early 1800s. • Emissions associated with leaded gasoline peaked in 1975 CE. • The results suggest 1800 CE as the Holocene/Anthropocene transition.

  19. Simulating the Holocene climate evolution at northern high latitudes using a coupled atmosphere-sea ice-ocean-vegetation model

    Renssen, H.; Goosse, H.; Fichefet, T.; Brovkin, V.; Driesschaert, E.; Wolk, F.


    The response of the climate at high northern latitudes to slowly changing external forcings was studied in a 9,000-year long simulation with the coupled atmosphere-sea ice-ocean-vegetation model ECBilt-CLIO-VECODE. Only long-term changes in insolation and atmospheric CO

  20. 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

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


    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.

  1. Integrating the EMPD with an Alpine altitudinal training set to reconstruct climate variables in Holocene pollen records from high-altitude peat bogs

    Furlanetto, Giulia; Badino, Federica; Brunetti, Michele; Champvillair, Elena; De Amicis, Mattia; Maggi, Valter; Pini, Roberta; Ravazzi, Cesare; Vallé, Francesca


    ., 2014), starting from a dense and quality-controlled observational dataset. In the most advanced step, we designed calibration functions using modern pollen and climate data stored in the EMPD and integrated with the 27 samples from the altitudinal training set. Regression and calibration method (LWWA) and MAT (Modern Analogue Technique) were used to reconstruct temperatures and precipitation. We applied the models to our fossil site to infer temperatures of the coldest (Tjan) and warmest (Tjul) months and the mean annual precipitation (Pann). Finally we compared our results with established climate proxy records (oxygen isotope records from ice cores, records of Alpine Glaciers fluctuations, stalagmites). This research is promoted by the CNR-DTA NextData Project. Brunetti et al., 2014. International Journal of Climatology 34, 1278-1296. Cañellas-Boltà et al., 2009. The Holocene 19(8), 1185-1200. Davis et al., 2013. Vegetation History and Archaeobotany 22, 521-530.

  2. Synchronous mid-Holocene climate deteriorations in circum-Mediterranean and their links with ancient civilizations: first speloethem and archeological evidences from N-Algeria

    Ruan, Jiaoyang; Kherbouche, Farid; Genty, Dominique; Cheng, Hai; Dewilde, Fabien; Blamart, Dominique


    Over the last decades, ancient civilizations during the Holocene were heavily studied at many places around the Mediterranean region such as Libya and Italy, and changes in the past social activities were widely assumed to be linked to regional climate variability. However, in many cases the climatic records were apart from the archaeological sites and the archaeological chronologies were not well constrained, which makes these links uncertain. Here we present a 230Th-dated decadal resolution climate record for 6034-3185yr BP based on the δ18O and δ13C analyses of two overlapping stalagmites from Gueldaman GLD1 Cave (36°26'N, 4°34'E, 507 m asl), N-Algeria. Recent archaeological work in this cave brought first information about the Neolithisation process since ca 7000yr cal BP in the region where little was known before. Together with new charcoal 14C dates from the digging sections we test the link between past climate change and human activities in the cave. GLD1 stalagmite records reveal a dry event at ca 5700-5500yr BP and a drying trend toward extreme aridity, since ca 4700yr BP, peaking at ca 4200yr BP. These climatic deteriorations in N-Algeria, within dating errors, are synchronous with dry phases observed on speleothem records from central (Corchia Cave and Renella Cave, Italy) and eastern (Soreq Cave, Israel) Mediterranean. Specifically, climatic condition was harsher at ca 4200yr BP than at ca 5700-5500yr BP in central and W-Mediterranean; while it was harsher at ca 5700-5500yr BP in E-Mediterranean. The new 14C dates relatively well anchor the age of sediment layers with the richest anthropogenic deposits (i.e. charcoal, bone and Neolithic pottery) to ca 4900-4400yr cal BP, coinciding with the wettest period inferred from the stalagmite records. Shortly following this period, archaeological remains were becoming very rare in the sediments, which might be the consequence of establishing extremely arid phase at ca 4200yr BP. This suggests a possible

  3. Ancestral genetic diversity associated with the rapid spread of stress-tolerant coral symbionts in response to Holocene climate change

    Hume, Benjamin C. C.


    Coral communities in the Persian/Arabian Gulf (PAG) withstand unusually high salinity levels and regular summer temperature maxima of up to ∼35 °C that kill conspecifics elsewhere. Due to the recent formation of the PAG and its subsequent shift to a hot climate, these corals have had only <6, 000 y to adapt to these extreme conditions and can therefore inform on how coral reefs may respond to global warming. One key to coral survival in the world\\'s warmest reefs are symbioses with a newly discovered alga, Symbiodinium thermophilum. Currently, it is unknown whether this symbiont originated elsewhere or emerged from unexpectedly fast evolution catalyzed by the extreme environment. Analyzing genetic diversity of symbiotic algae across >5, 000 km of the PAG, the Gulf of Oman, and the Red Sea coastline, we show that S. thermophilum is a member of a highly diverse, ancient group of symbionts cryptically distributed outside the PAG. We argue that the adjustment to temperature extremes by PAG corals was facilitated by the positive selection of preadapted symbionts. Our findings suggest that maintaining the largest possible pool of potentially stress-tolerant genotypes by protecting existing biodiversity is crucial to promote rapid adaptation to present-day climate change, not only for coral reefs, but for ecosystems in general.

  4. Impact of Late Holocene climate variability and anthropogenic activities on Biscayne Bay (Florida, U.S.A.): evidence from diatoms

    Wachnicka, Anna; Gaiser, Evelyn; Wingard, Lynn; Briceño, Henry; Harlem, Peter


    Shallow marine ecosystems are experiencing significant environmental alterations as a result of changing climate and increasing human activities along coasts. Intensive urbanization of the southeast Florida coast and intensification of climate change over the last few centuries changed the character of coastal ecosystems in the semi-enclosed Biscayne Bay, Florida. In order to develop management policies for the Bay, it is vital to obtain reliable scientific evidence of past ecological conditions. The long-term records of subfossil diatoms obtained from No Name Bank and Featherbed Bank in the Central Biscayne Bay, and from the Card Sound Bank in the neighboring Card Sound, were used to study the magnitude of the environmental change caused by climate variability and water management over the last ~ 600 yr. Analyses of these records revealed that the major shifts in the diatom assemblage structures at No Name Bank occurred in 1956, at Featherbed Bank in 1966, and at Card Sound Bank in 1957. Smaller magnitude shifts were also recorded at Featherbed Bank in 1893, 1942, 1974 and 1983. Most of these changes coincided with severe drought periods that developed during the cold phases of El Niño Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), or when AMO was in warm phase and PDO was in the cold phase. Only the 1983 change coincided with an unusually wet period that developed during the warm phases of ENSO and PDO. Quantitative reconstructions of salinity using the weighted averaging partial least squares (WA-PLS) diatom-based salinity model revealed a gradual increase in salinity at the three coring locations over the last ~ 600 yr, which was primarily caused by continuously rising sea level and in the last several decades also by the reduction of the amount of freshwater inflow from the mainland. Concentration of sediment total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) increased in the

  5. Holocene extreme hydrological events and their climatic implications: evidence from the middle Satluj valley, western Himalaya, India

    Sharma, Shubhra; Shukla, Anil; Marh, Bhupinder; Bartarya, Sukesh; Juyal, Navin


    Extreme hydrological events and associated climatic processes are investigated and inferred through palaeoflood deposits preserved in the middle Satluj valley, India. Satluj River is the largest tributary of the Indus River having third largest catchment area in the Himalaya. Both Indian summer monsoon (ISM) and the mid-latitude westerlies contribute to the hydrological budget of the river. The steep southern orographic front prevents the northward penetration of ISM, while the mid-latitude westerlies bring moisture in form of winter snow to the orogenic interiors. It has been observed that the floods in the Himalaya are intimately associated with the variability in the above climate systems. The optical chronology indicates that floods were clustered around three time domains. The oldest flood phase-1 is dated to ˜14-12 ka which climatically occurred during the initiation of the ISM after the Last Glacial Maximum. The second phase-2 is dated between 8-5 ka and is attributed to the moderate ISM. Whereas, the youngest phase-3 is assigned the Little Ice Age (LIA) and were associated with the variability in the mid-latitude westerlies. Geochemical analyses suggest that floods were generated in higher Himalayan crystalline (HHC) zone, as the extreme precipitation destabilised the precipitous slopes creating Landslide induced Lake Outbursts Floods (LLOFs). Further, the average interval between floods has decreased since 14 ka from 500 years, to 250 years and 100 years during respective flood phases. The southern slopes of Himalaya are influenced by both the monsoon and mid-latitude westerlies and any abrupt changes in the circulation pattern were found to associate with heavy rainfall events in this region. Although an interaction between the westerlies and the monsoon is implicated for extreme floods in the western Himalaya. However, exact mechanism of these interactions is still illusive except for the observational based studies which state that extreme floods

  6. Late Holocene flood probabilities in the Black Hills, South Dakota with emphasis on the Medieval Climate Anomaly

    Harden, Tessa M.; O'Connor, James E.; Driscoll, Daniel G.


    A stratigraphic record of 35 large paleofloods and four large historical floods during the last 2000 years for four basins in the Black Hills of South Dakota reveals three long-term flooding episodes, identified using probability distributions, at A.D.: 120–395, 900–1290, and 1410 to present. During the Medieval Climate Anomaly (~ A.D. 900–1300) the four basins collectively experienced 13 large floods compared to nine large floods in the previous 800 years, including the largest floods of the last 2000 years for two of the four basins. This high concentration of extreme floods is likely caused by one or more of the following: 1) instability of air masses caused by stronger than normal westerlies; 2) larger or more frequent hurricanes in the Gulf of Mexico and Atlantic Ocean; and/or 3) reduced land covering vegetation or increased forest fires caused by persistent regional drought.

  7. Late-Holocene Climate Change and Human Impact; Palaeoecological Evidence From Peat Deposits in Sweden and Germany

    van der Linden, M.; van Geel, B.


    With the aim of investigating the effects of climate change and human impact on vegetation and carbon accumulation, we took peat cores of ca. 1 meter depth from four raised bogs situated on a North-South transect, at intervals of c. 500 km, Umeå in Sweden to Angermünde in northern Germany. A number of analyses were conducted (plant macrofossils, pollen/non-pollen microfossils, colorimetric humification, carbon/nitrogen ratios, bulk densities, loss on ignition), and 14C wiggle-match dating was applied to obtain a fine-resolution chronology. The cores from the northern and southern site encompass ca. 1000 years of vegetation history, showing evidence for the end of the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the twentieth century warming. The middle Swedish and German sites are high resolution records of the last 400 years. The end of the MWP and the cooling at the start of the LIA are reflected by a decline in thermophilous tree species. Changes in the macrofossil composition may also represent changes in climate. Shifts in Sphagnum composition, the dominant peat former, reflect changes in precipitation. Evidence for wet conditions and increased carbon accumulation is found during the Little Ice Age. Human activities affected the peat bog and the surrounding vegetation. Sweden suffered many wars during the 16^{th} and 17^{th} century, which caused a decline in population density. Diseases such as the plague and famines caused by crop failures fastened the population decrease. As a consequence, agricultural land was abandoned, resulting in reforestation by Betula. Later, in the modern part of the records, land-use change and planting of trees comprised the major regional vegetation changes. In the southern site, human activities (drainage to facilitate peat cutting) affected the raised bog itself. A part of the peat archive was lost owing to secondary decomposition which resulted in very low carbon accumulation.

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

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


    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

  9. The Late-Glacial and Holocene Marboré Lake sequence (2612 m a.s.l., Central Pyrenees, Spain): Testing high altitude sites sensitivity to millennial scale vegetation and climate variability

    Leunda, Maria; González-Sampériz, Penélope; Gil-Romera, Graciela; Aranbarri, Josu; Moreno, Ana; Oliva-Urcia, Belén; Sevilla-Callejo, Miguel; Valero-Garcés, Blas


    This paper presents the environmental, climate and vegetation changes reconstructed for the last 14.6 kyr cal BP from the Marboré Lake sedimentary sequence, the highest altitude record (2612 m a.s.l.) in the Pyrenees studied up to date. We investigate the sensitivity of this high altitude site to vegetational and climate dynamics and altitudinal shifts during the Holocene by comparing palynological spectra of the fossil sequence and pollen rain content from current moss pollsters. We hypothesize that the input of sediments in lakes at such altitude is strongly controlled by ice phenology (ice-free summer months) and that during cold periods Pollen Accumulation Rate (PAR) and Pollen Concentration (PC) reflect changes in ice-cover and thus is linked to temperature changes. Low sedimentation rates and low PC and PAR occurred during colder periods as the Younger Dryas (GS-1) and the Holocene onset (12.6-10.2 kyr cal BP), suggesting that the lake-surface remained ice-covered for most of the year during these periods. Warmer conditions are not evident until 10.2 kyr cal BP, when an abrupt increase in sedimentation rate, PC and PAR occur, pointing to a delayed onset of the Holocene temperature increase at high altitude. Well-developed pinewoods and deciduous forest dominated the mid montane belt since 9.3 kyr cal BP until mid-Holocene (5.2 kyr cal BP). A downwards shift in the deciduous forest occurred after 5.2 kyr cal BP, in agreement with the aridity trend observed at a regional and Mediterranean context. The increase of herbaceous taxa during the late-Holocene (3.5 kyr cal BP-present) reflects a general trend to reduced montane forest, as anthropogenic disturbances were not evident until 1.3 kyr cal BP when Olea proportions from lowland areas and other anthropogenic indicators clearly expand. Our study demonstrates the need to perform local experimental approaches to check the effect of ice phenology on high altitude lakes sensitivity to vegetation changes to obtain

  10. Corrigendum to "Upper ocean climate of the Eastern Mediterranean Sea during the Holocene Insolation Maximum – a model study" published in Clim. Past, 7, 1103–1122, 2011

    G. Schmiedl


    Full Text Available Nine thousand years ago (9 ka BP, the Northern Hemisphere experienced enhanced seasonality caused by an orbital configuration close to the minimum of the precession index. To assess the impact of this "Holocene Insolation Maximum" (HIM on the Mediterranean Sea, we use a regional ocean general circulation model forced by atmospheric input derived from global simulations. A stronger seasonal cycle is simulated by the model, which shows a relatively homogeneous winter cooling and a summer warming with well-defined spatial patterns, in particular, a subsurface warming in the Cretan and western Levantine areas. The comparison between the SST simulated for the HIM and a reconstruction from planktonic foraminifera transfer functions shows a poor agreement, especially for summer, when the vertical temperature gradient is strong. As a novel approach, we propose a reinterpretation of the reconstruction, to consider the conditions throughout the upper water column rather than at a single depth. We claim that such a depth-integrated approach is more adequate for surface temperature comparison purposes in a situation where the upper ocean structure in the past was different from the present-day. In this case, the depth-integrated interpretation of the proxy data strongly improves the agreement between modelled and reconstructed temperature signal with the subsurface summer warming being recorded by both model and proxies, with a small shift to the south in the model results. The mechanisms responsible for the peculiar subsurface pattern are found to be a combination of enhanced downwelling and wind mixing due to strengthened Etesian winds, and enhanced thermal forcing due to the stronger summer insolation in the Northern Hemisphere. Together, these processes induce a stronger heat transfer from the surface to the subsurface during late summer in the western Levantine; this leads to an enhanced heat piracy in this region, a process never identified before

  11. Causes of early Holocene desertification in arid central Asia

    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)


    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

  12. New high-resolution record of Holocene climate change in the Weddell Sea from combined biomarker analysis of the Patriot Hills blue ice area

    Fogwill, Christopher; Turney, Chris; Baker, Andy; Ellis, Bethany; Cooper, Alan; Etheridge, David; Rubino, Mauro; Thornton, David; Fernando, Francisco; Bird, Michale; Munksgaard, Niels


    We report preliminary analysis of biomarkers (including dissolved organic matter (DOM) and DNA) from the Patriot Hills blue ice area (BIA), from the Ellsworth Mountains in the Weddell Sea Embayment. Preliminary isotopic and multiple gas analysis (CO2, CH4, N2O and CO) demonstrate that the Holocene comprises more than 50% of the 800m long BIA record, and in combination isotopic and biomarker analysis reveals a remarkable record of centennial variability through the Holocene in this sector of the Weddell Sea. Analysis using a Horiba Aqualog - which measures the fluorescence of DOM by producing a map of the fluorescence through an excitation-emission matrix (EEM) - identifies the presence of two marine protein-like components in both modern snow pit samples and within the Holocene part of Patriot Hills BIA transect. Intriguingly, the modern seasonal trends in DOM, recorded in contemporary snow pits, have relatively low signals compared to those recorded in the mid-Holocene record, suggesting a reduction in DOM signal in contemporary times. Given that the δD excess data suggests the source of precipitation has remained constant through the Holocene, the biomarker signal must relate to multi-year marine productivity signals from the Weddell Sea. The marked variability in DOM between the mid-Holocene and contemporary times can only relate to periods of sustained, enhanced biological productivity in the Weddell Sea associated with shifts in Southern Annular Mode, sea ice variability, changes in ventilation or polynya activity. Here we discuss the possible drivers of these changes and describe how this approach at this BIA could benefit conventional ice core records regionally.

  13. Soil archives of mardel deposits: the impact of Late Holocene vegetation development, climatic oscillations and historical land use on soil erosion in Luxembourg

    van Mourik, Jan; Slotboom, Ruud


    Mardel genesis. Mardels are small scale circular to elongated closed depressions (Ø > 50 m). They occur in Luxembourg on the Lias plateau in the Gutland, but also in other regions with landscapes, developed on Keuper and Lias deposits (as Lorraine). We can distinguish geogenetic and anthropogenic mardels. There are two types of genetic mardels, sink holes (controlled by diaclases in the Luxembourger sandstone and 'true mardels' or subsidence basins (controlled by dissolved gypsic lenses in marls of the Keuper deposits). These mardels developed during the Holocene. The age of the mardel sediments is Subatlantic; the sediments have been deposited on a palaeosol. Anthropogenic mardels are the result of historic clay excavation (Roman Time or younger). The age of these mardels is Subatlantic. The age of the sediments is also Subatlantic; the sediments have been deposited on a truncated soil in excavations. In all the genetic types of mardels, the sediments can consist of peat, peaty loam, or colluvic clayloam and the mardel sediments contain always valuable soil archives for the reconstruction of the impact of vegetation development, climatic oscillations and land use on soil erosion and deposition. Comparison of mardel deposits and valley deposits. - Pre-Holocene mardels have been eroded during the Weichselian. Geogenic mardels have been developed during the Holocene, anthropogenic mardels have been excavated since Roman Time. The age of the clastic (colluvic) deposits in mardels is Subatlantic - In the Late Glacial, valley bottoms were rather broad and covered with a gravelly bed load. Till the Subboreal river incision was active in primary valleys and peat accumulation took place on broad valley bottoms of secondary valleys. Since Celtic/Roman Time deforestation and extension of agriculture. During the Subatlantic colluvic/alluvic sedimentation took place on all the valley bottoms. The Subatlantic is a period of accelerated sedimentation of clastic sediments in

  14. Deriving nearshore wave climate along South African coast

    Rossouw, M


    Full Text Available The present study addressed aspects of the highly interrelated study area of coastal safety and vulnerability, climate change and setback lines for South African coast. A medium resolution numerical wave analysis was undertaken, in the form...

  15. Isotope heterogeneity of Pre-Holocene groundwater in Iceland

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


    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. Holocene glacial fluctuations in southern South America

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


    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.

  17. Changes in solar activity and Holocene climatic shifts derived from C-14 wiggle-match dated peat deposits

    Mauquoy, D; van Geel, B; Speranza, A; van der Plicht, J; Blaauw, Maarten

    Closely spaced sequences of accelerator mass spectrometer (AMS) C-14 dates of peat deposits display century-scale wiggles which can be fitted to the radiocarbon calibration curve. By wiggle-matching such sequences, high-precision calendar age chronologies can be generated which show that changes in

  18. Changes in solar activity and Holocene climatic shifts derived from 14C wiggle-match dated peat deposits

    Mauquoy, Dmitri; Geel, Bas van; Blaauw, Maarten; Speranza, Alessandra; Plicht, Johannes van der


    Closely spaced sequences of accelerator mass spectrometer (AMS) 14C dates of peat deposits display century-scale wiggles which can be fitted to the radiocarbon calibration curve. By wiggle-matching such sequences, high-precision calendar age chronologies can be generated which show that changes in

  19. The Holocene History of Placentia Bay, Newfoundland

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


    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 ...

  20. Empirically derived climate predictability over the extratropical northern hemisphere

    J. B. Elsner


    Full Text Available A novel application of a technique developed from chaos theory is used in describing seasonal to interannual climate predictability over the Northern Hemisphere (NH. The technique is based on an empirical forecast scheme - local approximation in a reconstructed phase space - for time-series data. Data are monthly 500 hPa heights on a latitude-longitude grid covering the NH from 20° N to the equator. Predictability is estimated based on the linear correlation between actual and predicted heights averaged over a forecast range of one- to twelve.month lead. The method is capable of extracting the major climate signals on this time scale including ENSO and the North Atlantic Oscillation.

  1. Deriving user-informed climate information from climate model ensemble results

    Huebener, Heike; Hoffmann, Peter; Keuler, Klaus; Pfeifer, Susanne; Ramthun, Hans; Spekat, Arne; Steger, Christian; Warrach-Sagi, Kirsten


    Communication between providers and users of climate model simulation results still needs to be improved. In the German regional climate modeling project ReKliEs-De a midterm user workshop was conducted to allow the intended users of the project results to assess the preliminary results and to streamline the final project results to their needs. The user feedback highlighted, in particular, the still considerable gap between climate research output and user-tailored input for climate impact research. Two major requests from the user community addressed the selection of sub-ensembles and some condensed, easy to understand information on the strengths and weaknesses of the climate models involved in the project.

  2. Estimating daily climatologies for climate indices derived from climate model data and observations

    Mahlstein, Irina; Spirig, Christoph; Liniger, Mark A; Appenzeller, Christof


    Climate indices help to describe the past, present, and the future climate. They are usually closer related to possible impacts and are therefore more illustrative to users than simple climate means. Indices are often based on daily data series and thresholds. It is shown that the percentile-based thresholds are sensitive to the method of computation, and so are the climatological daily mean and the daily standard deviation, which are used for bias corrections of daily climate model data. Sample size issues of either the observed reference period or the model data lead to uncertainties in these estimations. A large number of past ensemble seasonal forecasts, called hindcasts, is used to explore these sampling uncertainties and to compare two different approaches. Based on a perfect model approach it is shown that a fitting approach can improve substantially the estimates of daily climatologies of percentile-based thresholds over land areas, as well as the mean and the variability. These improvements are relevant for bias removal in long-range forecasts or predictions of climate indices based on percentile thresholds. But also for climate change studies, the method shows potential for use. Key Points More robust estimates of daily climate characteristics Statistical fitting approach Based on a perfect model approach PMID:26042192

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

    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

  4. Continuity of Climate Data Records derived from Microwave Observations

    Mears, C. A.; Wentz, F. J.; Brewer, M.; Meissner, T.; Ricciardulli, L.


    Remote Sensing Systems ( has been producing and distributing microwave climate data products from microwave imagers (SSMI, TMI, AMSR, WindSat, GMI, Aquarius, SMAP) over the global oceans since the launch of the first SSMI in 1987. Interest in these data products has been significant as researchers around the world have downloaded the approximate equivalent of 1 million satellite years of processed data. Users, including NASA, NOAA, US National Laboratories, US Navy, UK Met, ECMWF, JAXA, JMA, CMC, the Australian Bureau of Meteorology, as well as many hundreds of other agencies and universities routinely access these microwave data products. The quality of these data records has increased as more observations have become available and inter-calibration techniques have improved. The impending end of missions for WindSat, AMSR-2, and the remaining SSMIs will have significant impact on the quality and continuity of long term microwave climate data records. In addition to the problem of reduced numbers of observations, there is a real danger of losing overlapping observations. Simultaneous operation of satellites, especially when the observations are at similar local crossing times, provides a significant benefit in the effort to inter-calibrate satellites to yield accurate and stable long-term records. The end of WindSat and AMSR-2 will leave us without microwave SSTs in cold water, as there will be no microwave imagers with C-band channels. Microwave SSTs have a crucial advantage over IR SSTs, which is not able to measure SST in clouds or if aerosols are present. The gap in ocean wind vectors will be somewhat mitigated as the European ASCAT C-band scatterometer mission on MetOp is continuing. Nonetheless, the anticipated cease of several microwave satellite radiometers retrieving ocean winds in the coming years will lead to a significant gap in temporal coverage. Atmospheric water vapor, cloud liquid water, and rain rate are all important climate

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

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


    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.

  6. A Temperature and Monsoon Record Derived from Environmental Tracers in the Groundwater of Northwest India

    Wieser, M.; Aeschbach-Hertig, W.; Schneider, T. [Institute of Environmental Physics, University of Heidelberg, Heidelberg (Germany); Deshpande, R. D.; Gupta, S. K. [Physical Research Laboratory, Ahmedabad (India)


    A quantitative palaeoclimate record was derived from the aquifer system of the cambay Basin, gujarat, India, a region characterised by a semi arid, monsoon dominated climate. Stable isotopes generally increase with flow distance and {sup 14}C age, whereas noble gas temperatures (NGTs) show a decline with age, amounting to a difference of {approx}3.5{sup o}C between Holocene and last glacial samples. The paper focuses on the Holocene covariation of the climate proxies. Stable isotopes and excess air show consistent variations, confirming their interpretation as proxies for palaeohumidity. A group of early to mid Holocene samples depleted in stable isotopes and enriched in excess air indicates a phase of strong monsoon during the Holocene climate optimum. This is followed by a drying trend in the second half of the Holocene, and more humid conditions in the youngest part of the record. A temporary rise of NGT in the dry late Holocene may reflect a change in the soil temperature-air temperature relationship. (author)

  7. Empirically Derived and Simulated Sensitivity of Vegetation to Climate Across Global Gradients of Temperature and Precipitation

    Quetin, G. R.; Swann, A. L. S.


    Successfully predicting the state of vegetation in a novel environment is dependent on our process level understanding of the ecosystem and its interactions with the environment. We derive a global empirical map of the sensitivity of vegetation to climate using the response of satellite-observed greenness and leaf area to interannual variations in temperature and precipitation. Our analysis provides observations of ecosystem functioning; the vegetation interactions with the physical environment, across a wide range of climates and provide a functional constraint for hypotheses engendered in process-based models. We infer mechanisms constraining ecosystem functioning by contrasting how the observed and simulated sensitivity of vegetation to climate varies across climate space. Our analysis yields empirical evidence for multiple physical and biological mediators of the sensitivity of vegetation to climate as a systematic change across climate space. Our comparison of remote sensing-based vegetation sensitivity with modeled estimates provides evidence for which physiological mechanisms - photosynthetic efficiency, respiration, water supply, atmospheric water demand, and sunlight availability - dominate the ecosystem functioning in places with different climates. Earth system models are generally successful in reproducing the broad sign and shape of ecosystem functioning across climate space. However, this general agreement breaks down in hot wet climates where models simulate less leaf area during a warmer year, while observations show a mixed response but overall more leaf area during warmer years. In addition, simulated ecosystem interaction with temperature is generally larger and changes more rapidly across a gradient of temperature than is observed. We hypothesize that the amplified interaction and change are both due to a lack of adaptation and acclimation in simulations. This discrepancy with observations suggests that simulated responses of vegetation to

  8. Using climate derivatives for assessment of meteorological parameter relationships in RCM and observations

    Timuhins, Andrejs; Bethers, Uldis; Bethers, Peteris; Klints, Ilze; Sennikovs, Juris; Frishfelds, Vilnis


    In a changing climate it is essential to estimate its impacts on different economic fields. In our study we tried to create a framework for climate change assessment and climate change impact estimation for the territory of Latvia and to create results which are also understandable for non-scientists (stakeholder, media and public). This approach allowed us to more carefully assess the presentation and interpretation of results and their validation, for public viewing. For the presentation of our work a website was created ( containing two types of documents in a unified framework, meteorological parameter analysis of different easily interpretable derivative values. Both of these include analysis of the current situation as well as illustrate the projection for future time periods. Derivate values are calculated using two data sources: the bias corrected regional climate data and meteorological observation data. Derivative documents contain description of derived value, some interesting facts and conclusions. Additionally, all results may be viewed in temporal and spatial graphs and maps, for different time periods as well as different seasons. Bias correction (Sennikovs and Bethers, 2009) for the control period 1961-1990 is applied to RCM data series. Meteorological observation data of the Latvian Environment, Geology, and Meteorology Agency and ENSEMBLES project daily data of 13 RCM runs for the period 1960-2100 are used. All the documents are prepared in python notebooks, which allow for flexible changes. At the moment following derivative values have been published: forest fire risk index, wind energy, phenology (Degree days), road condition (friction, ice conditions), daily minimal meteorological visibility, headache occurrence rate, firs snow date and meteorological parameter analysis: temperature, precipitation, wind speed, relative humidity, and cloudiness. While creating these products RCM ability to represent the actual climate was

  9. Holocene moisture variations over the arid central Asia revealed by a comprehensive sand-dune record from the central Tian Shan, NW China

    Long, Hao; Shen, Ji; Chen, Jianhui; Tsukamoto, Sumiko; Yang, Linhai; Cheng, Hongyi; Frechen, Manfred


    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.

  10. Paleoclimatic and paleoenvironmental reconstruction for middle and late holocene in Uruguay southeastern New contributions

    Del Puerto, L.; Bracco, R.; Inda, H.; Garcia, F.; Panario, D.; Castineira, C.; Capdepont, I.


    This work is about the study carried out within the framework of the environmental evolution and the prehistoric human occupation on coastal lagoons in the east of Uruguay. The analysis of the sediments in the zone enable the reconstruction of the Holocene climate history as well as the construction of the Paleoclimatic and paleoenvironmental model belong to the middle and late Holocene

  11. Hydrologic-energy balance constraints on the Holocene lake-level history of lake Titicaca, South America

    Rowe, H.D.; Dunbar, R.B. [Stanford University, Geological and Environmental Sciences, Stanford, CA (United States)


    A basin-scale hydrologic-energy balance model that integrates modern climatological, hydrological, and hypsographic observations was developed for the modern Lake Titicaca watershed (northern Altiplano, South America) and operated under variable conditions to understand controls on post-glacial changes in lake level. The model simulates changes in five environmental variables (air temperature, cloud fraction, precipitation, relative humidity, and land surface albedo). Relatively small changes in three meteorological variables (mean annual precipitation, temperature, and/or cloud fraction) explain the large mid-Holocene lake-level decrease ({proportional_to}85 m) inferred from seismic reflection profiling and supported by sediment-based paleoproxies from lake sediments. Climatic controls that shape the present-day Altiplano and the sediment-based record of Holocene lake-level change are combined to interpret model-derived lake-level simulations in terms of changes in the mean state of ENSO and its impact on moisture transport to the Altiplano. (orig.)

  12. Hydrologic-energy balance constraints on the Holocene lake-level history of lake Titicaca, South America

    Rowe, H. D.; Dunbar, R. B.


    A basin-scale hydrologic-energy balance model that integrates modern climatological, hydrological, and hypsographic observations was developed for the modern Lake Titicaca watershed (northern Altiplano, South America) and operated under variable conditions to understand controls on post-glacial changes in lake level. The model simulates changes in five environmental variables (air temperature, cloud fraction, precipitation, relative humidity, and land surface albedo). Relatively small changes in three meteorological variables (mean annual precipitation, temperature, and/or cloud fraction) explain the large mid-Holocene lake-level decrease (˜85 m) inferred from seismic reflection profiling and supported by sediment-based paleoproxies from lake sediments. Climatic controls that shape the present-day Altiplano and the sediment-based record of Holocene lake-level change are combined to interpret model-derived lake-level simulations in terms of changes in the mean state of ENSO and its impact on moisture transport to the Altiplano.

  13. The relationship between early holocene climate change and neolithic settlement in central Anatolia, Turkey: current issues and prospects for future research:

    Asouti, Eleni


    Episodes of global climate change have traditionally been invoked as explanations for settlement re-organisation and socio-economic transformation in the prehistory of the Middle East (e.g., the Neolithic period). By focusing on the 8.2K event, this paper presents a theoretical and methodological argument against the assumption of unilinear, passive responses by prehistoric societies to global climate change, using as a case study datasets recently obtained from the Konya Plain in Central Ana...

  14. Comparison of elevation and remote sensing derived products as auxiliary data for climate surface interpolation

    Alvarez, Otto; Guo, Qinghua; Klinger, Robert C.; Li, Wenkai; Doherty, Paul


    Climate models may be limited in their inferential use if they cannot be locally validated or do not account for spatial uncertainty. Much of the focus has gone into determining which interpolation method is best suited for creating gridded climate surfaces, which often a covariate such as elevation (Digital Elevation Model, DEM) is used to improve the interpolation accuracy. One key area where little research has addressed is in determining which covariate best improves the accuracy in the interpolation. In this study, a comprehensive evaluation was carried out in determining which covariates were most suitable for interpolating climatic variables (e.g. precipitation, mean temperature, minimum temperature, and maximum temperature). We compiled data for each climate variable from 1950 to 1999 from approximately 500 weather stations across the Western United States (32° to 49° latitude and −124.7° to −112.9° longitude). In addition, we examined the uncertainty of the interpolated climate surface. Specifically, Thin Plate Spline (TPS) was used as the interpolation method since it is one of the most popular interpolation techniques to generate climate surfaces. We considered several covariates, including DEM, slope, distance to coast (Euclidean distance), aspect, solar potential, radar, and two Normalized Difference Vegetation Index (NDVI) products derived from Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS). A tenfold cross-validation was applied to determine the uncertainty of the interpolation based on each covariate. In general, the leading covariate for precipitation was radar, while DEM was the leading covariate for maximum, mean, and minimum temperatures. A comparison to other products such as PRISM and WorldClim showed strong agreement across large geographic areas but climate surfaces generated in this study (ClimSurf) had greater variability at high elevation regions, such as in the Sierra

  15. Influence of orbital forcing and solar activity on water isotopes in precipitation during the mid- and late Holocene

    S. Dietrich


    Full Text Available In this study we investigate the impact of mid- and late Holocene orbital forcing and solar activity on variations of the oxygen isotopic composition in precipitation. The investigation is motivated by a recently published speleothem δ18O record from the well-monitored Bunker Cave in Germany. The record reveals some high variability on multi-centennial to millennial scales that does not linearly correspond to orbital forcing. Our model study is based on a set of novel climate simulations performed with the atmosphere general circulation model ECHAM5-wiso enhanced by explicit water isotope diagnostics. From the performed model experiments, we derive the following major results: (1 the response of both orbital and solar forcing lead to changes in surface temperatures and δ18O in precipitation with similar magnitudes during the mid- and late Holocene. (2 Past δ18O anomalies correspond to changing temperatures in the orbital driven simulations. This does not hold true if an additional solar forcing is added. (3 Two orbital driven mid-Holocene experiments, simulating the mean climate state approximately 5000 and 6000 yr ago, yield very similar results. However, if an identical additional solar activity-induced forcing is added, the simulated changes of surface temperatures as well as δ18O between both periods differ. We conclude from our simulation results that non-linear effects and feedbacks of the orbital and solar activity forcing substantially alter the δ18O in precipitation pattern and its relation to temperature change.

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

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


    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

  17. Satellite-derived SIF and CO2 Observations Show Coherent Responses to Interannual Climate Variations

    Butterfield, Z.; Hogikyan, A.; Kulawik, S. S.; Keppel-Aleks, G.


    Gross primary production (GPP) is the single largest carbon flux in the Earth system, but its sensitivity to changes in climate is subject to significant uncertainty. Satellite measurements of solar-induced chlorophyll fluorescence (SIF) offer insight into spatial and temporal patterns in GPP at a global scale and, combined with other satellite-derived datasets, provide unprecedented opportunity to explore interactions between atmospheric CO2, GPP, and climate variability. To explore potential drivers of GPP in the Northern Hemisphere (NH), we compare monthly-averaged SIF data from the Global Ozone Monitoring Experiment 2 (GOME-2) with observed anomalies in temperature (T; CRU-TS), liquid water equivalent (LWE) from the Gravity Recovery and Climate Experiment (GRACE), and photosynthetically active radiation (PAR; CERES SYN1deg). Using observations from 2007 through 2015 for several NH regions, we calculate month-specific sensitivities of SIF to variability in T, LWE, and PAR. These sensitivities provide insight into the seasonal progression of how productivity is affected by climate variability and can be used to effectively model the observed SIF signal. In general, we find that high temperatures are beneficial to productivity in the spring, but detrimental in the summer. The influences of PAR and LWE are more heterogeneous between regions; for example, higher LWE in North American temperate forest leads to decreased springtime productivity, while exhibiting a contrasting effect in water-limited regions. Lastly, we assess the influence of variations in terrestrial productivity on atmospheric carbon using a new lower tropospheric CO2 product derived from the Greenhouse Gases Observing Satellite (GOSAT). Together, these data shed light on the drivers of interannual variability in the annual cycle of NH atmospheric CO2, and may provide improved constraints on projections of long-term carbon cycle responses to climate change.

  18. An automated system for access to derived climate indices in support of ecological impacts assessments and resource management

    Walker, J.; Morisette, J. T.; Talbert, C.; Blodgett, D. L.; Kunicki, T.


    A U.S. Geological Survey team is working with several providers to establish standard data services for the climate projection data they host. To meet the needs of climate adaptation science and landscape management communities, the team is establishing a set of climate index calculation algorithms that will consume data from various providers and provide directly useful data derivatives. Climate projections coming from various scenarios, modeling centers, and downscaling methods are increasing in number and size. Global change impact modeling and assessment, generally, requires inputs in the form of climate indices or values derived from raw climate projections. This requirement puts a large burden on a community not familiar with climate data formats, semantics, and processing techniques and requires storage capacity and computing resources out of the reach of most. In order to fully understand the implications of our best available climate projections, assessments must take into account an ensemble of climate projections and potentially a range of parameters for calculation of climate indices. These requirements around data access and processing are not unique from project to project, or even among projected climate data sets, pointing to the need for a reusable tool to generate climate indices. The U.S. Geological Survey has developed a pilot application and supporting web service framework that automates the generation of climate indices. The web service framework consists of standards-based data servers and a data integration broker. The resulting system allows data producers to publish and maintain ownership of their data and data consumers to access climate derivatives via a simple to use "data product ordering" workflow. Data access and processing is completed on enterprise "cloud" computing resources and only the relatively small, derived climate indices are delivered to the scientist or land manager. These services will assist the scientific and land

  19. Ground Penetrating Radar, Magnetic and Compositional Analysis of Sediment Cores and Surface Samples: The Relationships Between Lacustrine Sediments and Holocene Lake- Level and Climate Change at Deming Lake, Minnesota, USA

    Murray, R.; Lascu, I.; Plank, C.


    Deming Lake is a small (Deming. Cores were sampled continuously at a 1-2 cm resolution and sediment composition (in terms of percent organic matter, carbonate material, and minerogenic residue) was determined via loss on ignition (LOI). Isothermal remanent magnetization (IRM) and anhysteretic remanent magnetization (ARM) were used as proxies of magnetic mineral concentration and grain size. Four lithostratigraphic units were identified and correlated between cores based on these analyses. Changes in GPR facies corroborate the correlation between the two shallow cores. In order to inform our interpretation of down-core variations in magnetic properties and LOI values in terms of variations in lake depth, a suite of over 70 modern sediment samples were collected from the basin and analyzed. LOI compositional variability across the basin was high, with no clear trends related to depth or distance from shore. A sharp decrease in minerogenic content was observed at depths consistent with a predicted wave-base of 0.5 m, but aside from this trend it appears the steep slopes of much of the basin promote gravity driven slumping and mixing of sediments at depth. In the profundal sediments IRM values are routinely 5% higher than in the slope and littoral environments, while ARM/IRM ratios indicate an increase in magnetic grain size with water depth. We infer that an increase in coarse organic material in the shallow-water cores of Deming records a period of aridity (associated with a decrease lake-level less than 2m based on GPR profiles) and/or increased water clarity during the regionally expansive mid-Holocene dry period. We do not see clear evidence of late-Holocene lake level change of a significant magnitude (i.e. >1m). While remanence measurements (especially IRM) often correlate with the LOI residue, interference in the IRM resulting from the dissolution of magnetic minerals casts uncertainty into the reliability of our magnetic measurements as a signal of climate

  20. The relationship between Early Holocene climate change and Neolithic settlement in central Anatolia, Turkey: current issues and prospects for future research

    Eleni Asouti


    Full Text Available Episodes of global climate change have traditionally been invoked as explanations for settlement re-organisation and socio-economic transformation in the prehistory of the Middle East (e.g., the Neolithic period. By focusing on the 8.2K event, this paper presents a theoretical and methodological argument against the assumption of unilinear, passive responses by prehistoric societies to global climate change, using as a case study datasets recently obtained from the Konya Plain in Central Anatolia, Turkey.

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

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


    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

  2. A climate index derived from satellite measured spectral infrared radiation. Ph.D. Thesis

    Abel, M. D.; Fox, S. K.


    The vertical infrared radiative emitting structure (VIRES) climate index, based on radiative transfer theory and derived from the spectral radiances typically used to retrieve temperature profiles, is introduced. It is assumed that clouds and climate are closely related and a change in one will result in a change in the other. The index is a function of the cloud, temperature, and moisture distributions. It is more accurately retrieved from satellite data than is cloudiness per se. The VIRES index is based upon the shape and relative magnitude of the broadband weighting function of the infrared radiative transfer equation. The broadband weighting curves are retrieved from simulated satellite infrared sounder data (spectral radiances). The retrieval procedure is described and the error error sensitivities of the method investigated. Index measuring options and possible applications of the VIRES index are proposed.

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

    Purdue, James R.


    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.

  4. The application of carbon isotope discrimination of charred wheat grains to reconstruct Late Holocene climate change and identify water management strategy in northwest China

    Wang, W.; An, C.; Duan, F.; Zhao, Y.; Cao, Z.


    The AMS 14C dating and corresponding carbon stable isotope datum of charred wheat grains from archaeological sites in northwest China especially Hexi Corridor and Xinjiang have been collected widely to study its potential roles in reconstructing past climate change and identifying water management strategies through comparison with integrated regional humidity index, carbon isotope data of wheat grown under modern irrigation environment from study area and Mediterranean charred wheat carbon isotope data. The results suggest (1) carbon isotope discrimination values of charred wheat both in Hexi corridor and Xinjiang could respond well to regional moisture change, and there are also good positive correlation relationship between them (2) in contrast to consistent relationship between decreased carbon isotope discrimination values of charred wheat and dry climate condition, increased carbon isotope discrimination values does not represent wetter regional climate completely and may also reveal effects of human irrigation activities. The higher carbon isotope discrimination value of charred wheat which occurred in the Hexi Corridor from 4000 to 3850 a BP, 2100 a BP and 550 a BP and in Tianshan area of Xinjiang from 3730 a BP could be likely to be related with human activities (3) the carbon isotope discrimination value of charred wheat may have a certain limit which is generally not beyond 19‰. And this upper limit could influence its availability in reflecting abrupt change of precipitation/humidity especially rapid wetter trend. We conclude that carbon isotope analysis of charred wheat grains could be a good tool for reconstructing past climate change and identifying ancient irrigation practices.

  5. Late Holocene vegetation and climate change on the southeastern Tibetan Plateau: Implications for the Indian Summer Monsoon and links to the Indian Ocean Dipole

    Li, Kai; Liu, Xingqi; Wang, Yongbo; Herzschuh, Ulrike; Ni, Jian; Liao, Mengna; Xiao, Xiayun


    The Indian Summer Monsoon (ISM) is one of the most important climate systems, whose variability and driving mechanisms are of broad interest for academic and societal communities. Here, we present a well-dated high-resolution pollen analysis from a 4.82-m long sediment core taken from Basomtso, in the southeastern Tibetan Plateau (TP), which depicts the regional climate changes of the past millennium. Our results show that subalpine coniferous forest was dominant around Basomtso from ca. 867 to ca. 750 cal. yr BP, indicating a warm and semi-humid climate. The timberline in the study area significantly decreased from ca. 750 to ca. 100 cal. yr BP, and a cold climate, corresponding to the Little Ice Age (LIA) prevailed. Since ca. 100 cal. yr BP, the vegetation type changed to forest-meadow with rising temperatures and moisture. Ordination analysis reveals that the migration of vegetation was dominated by regional temperatures and then by moisture. Further comparisons between the Basomtso pollen record and the regional temperature reconstructions underscore the relevance of the Basomtso record from the southeastern TP for regional and global climatologies. Our pollen based moisture reconstruction demonstrates the strong multicentennial-scale link to ISM variability, providing solid evidence for the increase of monsoonal strengths over the past four centuries. Spectral analysis indicates the potential influence of solar forcing. However, a closer relationship has been observed between multicentennial ISM variations and Indian Ocean sea surface temperature anomalies (SSTs), suggesting that the variations in monsoonal precipitation over the southeastern TP are probably driven by the Indian Ocean Dipole on the multicentennial scale.

  6. Deriving evaluation indicators for knowledge transfer and dialogue processes in the context of climate research

    Treffeisen, Renate; Grosfeld, Klaus; Kuhlmann, Franziska


    Knowledge transfer and dialogue processes in the field of climate science have captured intensive attention in recent years as being an important part of research activities. Therefore, the demand and pressure to develop a set of indicators for the evaluation of different activities in this field have increased, too. Research institutes are being asked more and more to build up structures in order to map these activities and, thus, are obliged to demonstrate the success of these efforts. This paper aims to serve as an input to stimulate further reflection on the field of evaluation of knowledge transfer and dialogue processes in the context of climate sciences. The work performed in this paper is embedded in the efforts of the German Helmholtz Association in the research field of earth and environment and is driven by the need to apply suitable indicators for knowledge transfer and dialogue processes in climate research center evaluations. We carry out a comparative analysis of three long-term activities and derive a set of indicators for measuring their output and outcome by balancing the wide diversity and range of activity contents as well as the different tools to realize them. The case examples are based on activities which are part of the regional Helmholtz Climate Initiative Regional Climate Change (REKLIM) and the Climate Office for Polar Regions and Sea Level Rise at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research. Both institutional units have been working on a wide range of different knowledge transfer and dialogue processes since 2008/2009. We demonstrate that indicators for the evaluation must be based on the unique objectives of the individual activities and the framework they are embedded in (e.g., research foci which provide the background for the performed knowledge transfer and dialogue processes) but can partly be classified in a principle two-dimensional scheme. This scheme might serve as a usable basis for climate

  7. Ecological response to climate change and human activities indicated by n-alkane proxy during the mid- to late Holocene: a case study from an alpine lake

    Zhang, C.; Zhao, C.


    Paleolimonological records provide long-term dynamics information of past climate, environment, human activities and ecological variations and give evolutionary perspectives to understand responses process of ecological shift to internal or external trigger. In this study, a powerful biomarkers, n-alkanes, was used to reconstruct the past 5000 years organic matter sources and ecological evolution history of Beilianchi Lake in the southwestern of Loess Plateau after preliminary investigation of modern samples. Climate-environment change and human activities were also traced by total organic matter (TOC), magnetic susceptibility (MS) and relevant proxies. The results showed that the ecosystem related to organic matter composition in Beilianchi Lake might be mainly controlled by climate change before 1400 cal B.P., whereas after that, it was significantly influenced by soil erosion induced by increasing population and enhanced human activities. Lake ecosystem experienced periodical change from relatively stable stage with combination of allochthonous-autochthonous organic sources prior to 1400 cal B.P. to extremely instability and final return to steady state with allochthonous-dominant organic source since 300 cal B.P.. During the period of instability, organic matter composition during 1400-800 cal B.P. indicated a obvious bimodal distribution based on probability density distribution analysis, which reflected the lake ecosystem might stay at bistable state and switched repeatedly from more-macrophytes state (regime A with low ACL) towards less-macrophytes state (regime B with high ACL) controlled by disturbance of soil erosion. The flickering during this period could serve as the early warning signal of transition towards more-macrophytes state or less-macrophytes state in lake ecosystems.

  8. Climatic changes in Eurasia and Africa at the last glacial maximum and mid-Holocene: reconstruction from pollen data using inverse vegetation modelling

    Wu, Haibin [Chinese Academy of Sciences, SKLLQ, Institute of Earth Environment, Xi' an (China); CEREGE, UMR 6635, CNRS/Universite Paul Cezanne, CEREGE BP 80, Europole Mediterraneen de l' Arbois, Aix-en-Provence Cedex 4 (France); Guiot, Joel; Brewer, Simon [CEREGE, UMR 6635, CNRS/Universite Paul Cezanne, CEREGE BP 80, Europole Mediterraneen de l' Arbois, Aix-en-Provence Cedex 4 (France); Guo, Zhengtang [Chinese Academy of Sciences, SKLLQ, Institute of Earth Environment, Xi' an (China); Chinese Academy of Sciences, Institute of Geology and Geophysics, P.O. Box 9825, Beijing (China)


    In order to improve the reliability of climate reconstruction, especially the climatologies outside the modern observed climate space, an improved inverse vegetation model using a recent version of BIOME4 has been designed to quantitatively reconstruct past climates, based on pollen biome scores from the BIOME6000 project. The method has been validated with surface pollen spectra from Eurasia and Africa, and applied to palaeoclimate reconstruction. At 6 cal ka BP (calendar years), the climate was generally wetter than today in southern Europe and northern Africa, especially in the summer. Winter temperatures were higher (1-5 C) than present in southern Scandinavia, northeastern Europe, and southern Africa, but cooler in southern Eurasia and in tropical Africa, especially in Mediterranean regions. Summer temperatures were generally higher than today in most of Eurasia and Africa, with a significant warming from {proportional_to}3 to 5 C over northwestern and southern Europe, southern Africa, and eastern Africa. In contrast, summers were 1-3 C cooler than present in the Mediterranean lowlands and in a band from the eastern Black Sea to Siberia. At 21 cal ka BP, a marked hydrological change can be seen in the tropical zone, where annual precipitation was {proportional_to}200-1,000 mm/year lower than today in equatorial East Africa compared to the present. A robust inverse relationship is shown between precipitation change and elevation in Africa. This relationship indicates that precipitation likely had an important role in controlling equilibrium-line altitudes (ELA) changes in the tropics during the LGM period. In Eurasia, hydrological decreases follow a longitudinal gradient from Europe to Siberia. Winter temperatures were {proportional_to}10-17 C lower than today in Eurasia with a more significant decrease in northern regions. In Africa, winter temperature was {proportional_to}10-15 C lower than present in the south, while it was only reduced by {proportional_to}0

  9. Stable isotope ratios in swale sequences of Lake Superior as indicators of climate and lake level fluctuations during the Late Holocene

    Sharma, Shruti; Mora, G.; Johnston, J.W.; Thompson, T.A.


    Beach ridges along the coastline of Lake Superior provide a long-term and detailed record of lake level fluctuations for the past 4000 cal BP. Although climate change has been invoked to explain these fluctuations, its role is still in debate. Here, we reconstruct water balance by employing peat samples collected from swale deposits present between beach ridge sequences at two locations along the coastline of Lake Superior. Carbon isotope ratios for Sphagnum remains from these peat deposits are used as a proxy for water balance because the presence or absence of water films on Sphagnum controls the overall isotope discrimination effects. Consequently, increased average water content in Sphagnum produces elevated ??13C values. Two maxima of Sphagnum ??13C values interpreted to reflect wetter conditions prevailed from 3400 to 2400 cal BP and from about 1900 to 1400 cal BP. There are two relatively short drier periods as inferred from low Sphagnum ??13C values: one is centered at about 2300 cal BP, and one begins at 1400 cal BP. A good covariance was found between Sphagnum ??13C values and reconstructed lake-levels for Lake Michigan in which elevated carbon isotope values correlate well with higher lake levels. Based on this covariance, we conclude that climate exerts a strong influence on lake levels in Lake Superior for the past 4000 cal BP. ?? 2005 Elsevier Ltd. All rights reserved.

  10. Multidecadal, centennial, and millennial variability in sardine and anchovy abundances in the western North Pacific and climate-fish linkages during the late Holocene

    Kuwae, Michinobu; Yamamoto, Masanobu; Sagawa, Takuya; Ikehara, Ken; Irino, Tomohisa; Takemura, Keiji; Takeoka, Hidetaka; Sugimoto, Takashige


    Paleorecords of pelagic fish abundance could better define the nature of fishery productivity dynamics and help understand responses of pelagic fish stocks to long-term climate changes. We report a high-resolution record of sardine and anchovy scale deposition rates (SDRs) from Beppu Bay, Southwest Japan, showing multidecadal and centennial variability in the abundance of Japanese sardine and Japanese anchovy during the last 2850 years. Variations in the sardine SDR showed periodicities at ∼50, ∼100, and ∼300 yr, while variations in the anchovy SDR showed periodicities at ∼30 and ∼260 yr. Comparisons between and correlation analyses of the time series of the sardine and anchovy SDRs demonstrate that there is not a consistent out-of-phase relationship during the last 2850 years. This indicates that the multidecadal alternations in the sardine and anchovy populations commonly seen in the 20th century did not necessarily occur during earlier periods. The Japanese sardine SDR record shows a long-term decreasing trend in the amplitudes of the multidecadal to centennial fluctuations. This decreasing trend may have resulted from an increasing trend in the winter sea surface temperature in the western North Pacific. The multicentennial variability in sardine abundance during the last millennium is consistent with the variabilities in the abnormal snow index in East Asia and the American tree ring-based Pacific Decadal Oscillation index, suggesting a basin-wide or regional climate-marine ecosystem linkage.

  11. Holocene lake-level fluctuations of Lake Aricota, Southern Peru

    Placzek, C.; Quade, Jay; Betancourt, J.L.


    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.

  12. Holocene climate change in North Africa and the end of the African humid period - results of new high-resolution transient simulations with the MPI-ESM 1.3

    Dallmeyer, Anne; Claussen, Martin; Lorenz, Stephan


    The Max-Planck-Institute for Meteorology has recently undertaken high-resolution transient Holocene simulations using the fully-coupled Earth System Model MPI-ESM 1.3. The simulations cover the last 8000 years and are forced not only by reconstructed Holocene orbital variations and atmospheric greenhouse gas concentrations, but also by recent compilations of Holocene volcanic aerosol distributions, variations in spectral solar irradiance, stratospheric ozone and land-use change. The simulations reveal the ubiquitous "Holocene conundrum": simulated global mean temperatures increase during the mid-Holocene and stay constant during the late Holocene. Simulated mid-Holocene near-surface temperatures are too cold in large parts of the world. Simulated precipitation, however, agrees much better with reconstruction than temperatures do. Likewise simulated global biome pattern fit reconstructions nicely, except for North Western America. First results of these simulations are presented with the main focus on the North African monsoon region. The amplitude of the mid-Holocene African Humid Period (AHP) is well captured in terms of precipitation and vegetation cover, so is the south-ward transgression of the termination of the AHP seen in reconstructions. The Holocene weakening and southward retreat of the North African monsoon as well as changes in the monsoon dynamic including shifts in the seasonal cycle and their relation to the locally varying termination of the AHP are discussed in detail. Members of the Hamburg Holocene Team: Jürgen Bader (1), Sebastian Bathiany (2), Victor Brovkin (1), Martin Claussen (1,3), Traute Crüger (1), Roberta D'agostino (1), Anne Dallmeyer (1), Sabine Egerer (1), Vivienne Groner (1), Matthias Heinze (1), Tatiana Ilyina (1), Johann Jungclaus (1), Thomas Kleinen (1), Alexander Lemburg (1), Stephan Lorenz (1), Thomas Raddatz (1), Hauke Schmidt (1), Gerhard Schmiedl (3), Bjorn Stevens (1), Claudia Timmreck (1), Matthew Toohey (4) (1) Max

  13. A new CM SAF Solar Surface Radiation Climate Data Set derived from Meteosat Satellite Observations

    Trentmann, J.; Mueller, R. W.; Pfeifroth, U.; Träger-Chatterjee, C.; Cremer, R.


    The incoming surface solar radiation has been defined as an essential climate variable by GCOS. It is mandatory to monitor this part of the earth's energy balance, and thus gain insights on the state and variability of the climate system. In addition, data sets of the surface solar radiation have received increased attention over the recent years as an important source of information for the planning of solar energy applications. The EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) is deriving surface solar radiation from geostationary and polar-orbiting satellite instruments. While CM SAF is focusing on the generation of high-quality long-term climate data records, also operationally data is provided in short time latency within 8 weeks. Here we present SARAH (Solar Surface Radiation Dataset - Heliosat), i.e. the new CM SAF Solar Surface Radiation data set based on Meteosat satellite observations. SARAH provides instantaneous, daily- and monthly-averaged data of the effective cloud albedo (CAL), the direct normalized solar radiation (DNI) and the solar irradiance (SIS) from 1983 to 2013 for the full view of the Meteosat satellite (i.e, Europe, Africa, parts of South America, and the Atlantic ocean). The data sets are generated with a high spatial resolution of 0.05 deg allowing for detailed regional studies, and are available in netcdf-format at no cost without restrictions at We provide an overview of the data sets, including a validation against reference measurements from the BSRN and GEBA surface station networks.

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

    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


    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.

  15. Holocene palaeoenvironmental history of the Amazonian mangrove belt

    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


    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.

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

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


    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.

  17. Past and current sediment dispersion pattern estimates through numerical modeling of wave climate: an example of the Holocene delta of the Doce River, Espírito Santo, Brazil

    Abílio C.S.P. Bittencourt


    Full Text Available This paper presents a numerical modeling estimation of the sediment dispersion patterns caused by waves inciding through four distinct coastline contours of the delta plain of the Doce River during the Late Holocene. For this, a wave climate model based on the construction of wave refraction diagrams, as a function of current boundary conditions, was defined and was assumed to be valid for the four coastlines. The numerical modeling was carried out on basis of the refraction diagrams, taking into account the angle of approximation and the wave height along the coastline. The results are shown to be comparable with existing data regarding the directions of net longshore drift of sediments estimated from the integration of sediment cores, interpretation of aerial photographs and C14 datings. This fact apparently suggests that, on average, current boundary conditions appear to have remained with the same general characteristics since 5600 cal yr BP to the present. The used approach may prove useful to evaluate the sediment dispersion patterns during the Late Holocene in the Brazilian east-northeast coastal region.O presente trabalho apresenta uma estimativa, por modelagem numérica, dos padrões de dispersão de sedimentos causados por ondas ao longo de quatro distintos traçados da linha decosta durante o Holoceno Tardio na planície deltaica do Rio Doce. Para tanto, foi definido um modelo de clima de ondas baseado na construção de diagramas de refração de ondas, em função das condições de contorno atuais, que foi assumido como válido para as quatro linhas de costa. A modelagem numérica foi realizada a partir dos diagramas de refração, levando-se em conta o ângulo de aproximação e a altura da onda ao longo da linha de costa. Os resultados obtidos mostraram-se compatíveis com os dados existentes relativos aos sentidos da deriva litorânea efetiva de sedimentos estimados a partir da integração de testemunhos de vibra

  18. Changing Requirements for Archiving Climate Data Records Derived From Remotely Sensed Data

    Fleig, A. J.; Tilmes, C.


    With the arrival of long term sets of measurements of remotely sensed data it becomes important to improve the standard practices associated with archival of information needed to allow creation of climate data records, CDRs, from individual sets of measurements. Several aspects of the production of CDRs suggest that there should be changes in standard best practices for archival. A fundamental requirement for understanding long- term trends in climate data is that changes with time shown by the data reflect changes in actual geophysical parameters rather than changes in the measurement system. Even well developed and validated data sets from remotely sensed measurements contain artifacts. If the nature of the measurement and the algorithm is consistent over time, these artifacts may have little impact on trends derived from the data. However data sets derived with different algorithms created with different assumptions are likely to introduce non-physical changes in trend data. Yet technology for making measurements and analyzing data improves with time and this must be accounted for. To do this for an ongoing long term data set based on multiple instruments it is important to understand exactly how the preceding data was produced. But we are reaching the point where the scientists and engineers that developed the initial measurements and algorithms are no longer available to explain and assist in adapting today's systems for use with future measurement systems. In an era where tens to hundreds of man years are involved in calibrating an instrument and producing and validating a set of geophysical measurements from the calibrated data we have long passed the time when it was reasonable to say "just give me the basic measurement and a bright graduate student and I can produce anything I need in a year." Examples of problems encountered and alternative solutions will be provided based on developing and reprocessing data sets from long term measurements of

  19. NW Pacific mid-depth ventilation changes during the Holocene

    Rella, S.; Uchida, M.


    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.

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

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


    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

  1. Contrasting evidence of Holocene ice margin retreat, south-western Greenland

    Levy, L. B.; Larsen, N. K.; Davidson, T. A.


    Constraining the Greenland Ice Sheet's (GrIS) response to Holocene climate change provides calibrations for ice sheet models that hindcast past ice margin fluctuations. Ice sheet models predict enhanced ice retreat in south-western Greenland during the middle Holocene; however, few geological...... observations corroborating the extensive retreat are available. We present new data from lake sediment cores from the Isua region, south-western Greenland, which provide constraints on Holocene fluctuations of the GrIS margins. Our data indicate that the main GrIS margin was 30 km west of its present...

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

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


    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

  3. Possibilities of climate reconstruction in the Holocene using δ13C and δ2H values from annual tree rings on the basis of climate chamber experiments and studies on present-day organisms

    Mayr, C.


    This study deals with the climatic information content of 2 H and 13 C levels in annual tree rings and plant material. The influence of variations in air temperature, relative humidity and water availability on stable isotope ratios in three different C 3 plant species (Brassica oleracea, Eucalyptus globulus, Vicia faba) was studied in climate chamber experiments. Furthermore, calibration studies using δ 13 C and δ 2 H time series from Southern German spruce (Picea abies) from two stands (Schussbach, Klosterreichenbach) were performed. Correlations with meteorological data from a nearby meteorological station prove stable isotope ratios to be dependent on weather conditions in the summer months (June through August). Using the δ 13 C ''response surfaces'' obtained from these experiments as well as correlations from long gridbox precipitation series it was shown that for the climate mode under study the δ 13 C values largely reflect water availability to trees, which is greatly influenced by summer precipitation, especially at the more arid of the two sites. The results of the climate chamber experiments also suggest that the spruce δ 2 H values largely reflect the isotope variation in soil water and hence the δ 2 H fluctuations in summer precipitation. The study closes with a discussion of methodological approaches to creating long isotope series from annual tree rings of subfossil oak trees

  4. Late Glacial and Holocene Flow Dynamics of the Denmark Strait Overflow Water

    Williams, M.; Schmidt, D. N.; Andersen, M. B.; Barker, S.; McCave, I. N. N.


    The overflow of dense water from the Nordic Seas to the North Atlantic across the Greenland-Scotland Ridge forms a major component of the deep branch of the Atlantic Meridional Overturning Circulation and influences the climate system in Northwest Europe. Research has focused on deep convection of the Iceland Scotland Overflow Water (ISOW) and its links to climate variability in the North Atlantic. Our understanding of the history of the Denmark Strait Overflow Water (DSOW) is significantly less constrained and yet it accounts for half of the total overflow production today. We focus on the Eirik Drift south of Greenland in the vicinity of the DSOW. Down-core 230Thxs derived sediment focusing factors (Ψ) and measurements of the mean size of sortable silt reveal winnowed sediments during the Last Glacial Maximum and Heinrich 1 suggesting an influx of vigorous southern sourced waters and restricted DSOW production. Reduced overflow may be due to glacial isostatic processes which shoaled the Denmark Strait sill combined with a southward shift of deep convection sites in response to enhanced ice cover in the Nordic Seas. Intensification of the DSOW is evident between 9 and 13ka BP indicating initial deepening of the Denmark Strait sill and northward migration of the locus of deep water production. Ψ values for the Holocene suggest an active DSOW with a shift in the flow regime at 6.8 ka BP indicated by a reduction and subsequent stabilization of mean size sortable silt during the mid-late Holocene. This is corroborated by other studies showing a reorganization of the deep water after 7ka. An establishment of the Labrador Sea Water at intermediate depths altered the density structure of the deep western boundary current and weakened the ISOW. Changes in deep water circulation occur as North Atlantic climate entered Neoglacial cooling determined by Mg/Ca derived sea surface temperatures and abundances of the polar planktic foraminifera species N. pachyderma. They

  5. The climate is going drifting off: how adapt?; Un climat a la derive: comment s'adapter?



    This report is studying the extreme meteorological events, the signs of the climatic changes, the vulnerability to these events and the strategies of adaptation. It is concluded by nine proposals. (A.L.B.)

  6. The climate is going drifting off: how adapt?; Un climat a la derive: comment s'adapter?



    This report is studying the extreme meteorological events, the signs of the climatic changes, the vulnerability to these events and the strategies of adaptation. It is concluded by nine proposals. (A.L.B.)

  7. Fine-spatial scale predictions of understory species using climate- and LiDAR-derived terrain and canopy metrics

    Nijland, Wiebe; Nielsen, Scott E.; Coops, Nicholas C.; Wulder, Michael A.; Stenhouse, Gordon B.


    Food and habitat resources are critical components of wildlife management and conservation efforts. The grizzly bear (Ursus arctos) has diverse diets and habitat requirements particularly for understory plant species, which are impacted by human developments and forest management activities. We use light detection and ranging (LiDAR) data to predict the occurrence of 14 understory plant species relevant to bear forage and compare our predictions with more conventional climate- and land cover-based models. We use boosted regression trees to model each of the 14 understory species across 4435 km2 using occurrence (presence-absence) data from 1941 field plots. Three sets of models were fitted: climate only, climate and basic land and forest covers from Landsat 30-m imagery, and a climate- and LiDAR-derived model describing both the terrain and forest canopy. Resulting model accuracies varied widely among species. Overall, 8 of 14 species models were improved by including the LiDAR-derived variables. For climate-only models, mean annual precipitation and frost-free periods were the most important variables. With inclusion of LiDAR-derived attributes, depth-to-water table, terrain-intercepted annual radiation, and elevation were most often selected. This suggests that fine-scale terrain conditions affect the distribution of the studied species more than canopy conditions.

  8. Pacific southwest United States Holocene summer paleoclimate inferred from sediment calcite oxygen isotopes (Lake Elsinore, CA)

    Kirby, M.; Patterson, W. P.; Lachniet, M. S.; Anderson, M.; Noblet, J. A.


    Records of past climate inform on the natural range and mechanisms of climate change. In the arid Pacific southwest United States (pswUS), there exist a variety of Holocene records that infer past winter conditions (moisture and/or temperature). Holocene records of summer climate, however, are rare excepting short-lived (zone (Kirby et al. 2004) shows similar changes providing confidence in our longer record. Various forcing mechanisms are examined to explain the Elsinore summer record including insolation, Pacific SSTs, and trace gas radiative forcing.

  9. Precise chronologies of Holocene glacial culminations in the Cordillera Vilcabamba of southern Peru

    Licciardi, J. M.; Schaefer, J. M.; Schweinsberg, A. D.


    Records of past fluctuations in climatically sensitive tropical mountain glaciers are among the best indicators of regional paleoclimatic trends and controls. The majority of the world's present-day tropical glaciers are found in the Peruvian Andes, but accurate and precise chronologies of past glacial activity in this region remain relatively scarce, particularly during the Holocene. Here we present ~50 new 10Be exposure ages derived from boulders on well-preserved moraine successions in several glaciated drainages in the Cordillera Vilcabamba of southern Peru (13°20'S latitude). The new results suggest that prominent moraines in these valleys are correlative with previously published moraine ages near Nevado Salcantay in this range (Licciardi et al., 2009), but also expand on the initial surface exposure chronologies to reveal additional periods of glacier stabilization not found in previous work. A provisional composite chronology that merges the new and previously obtained moraine ages indicates at least five discrete glacial culminations from the Lateglacial to the late Holocene. Forthcoming 10Be ages from an additional ~50 samples collected from moraine boulders will increase the precision and completeness of the Vilcabamba moraine chronologies. Basal radiocarbon ages are being developed from bog and lake sediments in stratigraphic contact with the 10Be-dated moraines. These new 14C age data will help constrain the local cosmogenic 10Be production rate, thereby increasing the accuracy of the 10Be chronologies.

  10. Climate change projections for Tamil Nadu, India: deriving high-resolution climate data by a downscaling approach using PRECIS

    Bal, Prasanta Kumar; Ramachandran, A.; Geetha, R.; Bhaskaran, B.; Thirumurugan, P.; Indumathi, J.; Jayanthi, N.


    In this paper, we present regional climate change projections for the Tamil Nadu state of India, simulated by the Met Office Hadley Centre regional climate model. The model is run at 25 km horizontal resolution driven by lateral boundary conditions generated by a perturbed physical ensemble of 17 simulations produced by a version of Hadley Centre coupled climate model, known as HadCM3Q under A1B scenario. The large scale features of these 17 simulations were evaluated for the target region to choose lateral boundary conditions from six members that represent a range of climate variations over the study region. The regional climate, known as PRECIS, was then run 130 years from 1970. The analyses primarily focus on maximum and minimum temperatures and rainfall over the region. For the Tamil Nadu as a whole, the projections of maximum temperature show an increase of 1.0, 2.2 and 3.1 °C for the periods 2020s (2005-2035), 2050s (2035-2065) and 2080s (2065-2095), respectively, with respect to baseline period (1970-2000). Similarly, the projections of minimum temperature show an increase of 1.1, 2.4 and 3.5 °C, respectively. This increasing trend is statistically significant (Mann-Kendall trend test). The annual rainfall projections for the same periods indicate a general decrease in rainfall of about 2-7, 1-4 and 4-9 %, respectively. However, significant exceptions are noticed over some pockets of western hilly areas and high rainfall areas where increases in rainfall are seen. There are also indications of increasing heavy rainfall events during the northeast monsoon season and a slight decrease during the southwest monsoon season. Such an approach of using climate models may maximize the utility of high-resolution climate change information for impact-adaptation-vulnerability assessments.

  11. Lipid biomarkers in Holocene and glacial sediments from ancient Lake Ohrid (Macedonia, Albania

    J. Holtvoeth


    Full Text Available Organic matter preserved in Lake Ohrid sediments originates from aquatic and terrestrial sources. Its variable composition reflects climate-controlled changes in the lake basin's hydrology and related organic matter export, i.e. changes in primary productivity, terrestrial plant matter input and soil erosion. Here, we present first results from lipid biomarker investigations of Lake Ohrid sediments from two near-shore settings: site Lz1120 near the southern shore, with low-lying lands nearby and probably influenced by river discharge, and site Co1202 which is close to the steep eastern slopes. Variable proportions of terrestrial n-alkanoic acids and n-alkanols as well as compositional changes of ω-hydroxy acids document differences in soil organic matter supply between the sites and during different climate stages (glacial, Holocene, 8.2 ka cooling event. Changes in the vegetation cover are suggested by changes in the dominant chain length of terrestrial n-alkanols. Effective microbial degradation of labile organic matter and in situ contribution of organic matter derived from the microbes themselves are both evident in the sediments. We found evidence for anoxic conditions within the photic zone by detecting epicholestanol and tetrahymanol from sulphur-oxidising phototrophic bacteria and bacterivorous ciliates and for the influence of a settled human community from the occurrence of coprostanol, a biomarker for human and animal faeces (pigs, sheep, goats, in an early Holocene sample. This study illustrates the potential of lipid biomarkers for future environmental reconstructions using one of Europe's oldest continental climate archives, Lake Ohrid.

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

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


    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

  13. Anthropogenic and geomorphic controls on peatland dynamics in contrasting floodplain environments during the Holocene and its impact on carbon storage

    Verstraeten, Gert; Broothaerts, Nils; Notebaert, Bastiaan


    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

  14. Past climate changes derived from isotope measurements in polar ice cores

    Beer, J.; Muscheler, R.; Wagner, G.; Kubik, P.K.


    Measurements of stable and radioactive isotopes in polar ice cores provide a wealth of information on the climate conditions of the past. Stable isotopes (δ 18 O, δD) reflect mainly the temperature, whereas δ 18 O of oxygen in air bubbles reveals predominantly the global ice volume and the biospheric activity. Cosmic ray produced radioisotopes (cosmogenic nuclides) such as 10 Be and 36 Cl record information on the solar variability and possibly also on the solar irradiance. If the flux of a cosmogenic nuclide into the ice is known the accumulation rate can be derived from the measured concentration. The comparison of 10 Be from ice with 14 C from tree rings allows deciding whether observed 14 C variations are caused by production or system effects. Finally, isotope measurements are very useful for establishing and improving time scales. The 10 Be/ 36 Cl ratio changes with an apparent half-life of 376,000 years and is therefore well suited to date old ice. Significant abrupt changes in the records of 10 Be, 36 Cl from ice and of δ 18 O from atmospheric oxygen representing global signals can be used to synchronize ice and sediment cores. (author)

  15. The Holocene Sedimentation in Sandstone Rockshelters of Northern Bohemia

    Cílek, Václav


    Roč. 11, - (2000), s. 66-69 ISSN 1210-9606. [International Conference on Past Global Changes Upper Pleistocene and Holocene Climatic Variations. Prague, 06.09.2000-09.09.2000] Grant - others:US(XC) National Geographic Society 6330-98 "The last foragers of the Northern Europe" Institutional research plan: CEZ:AV0Z3013912 Subject RIV: DB - Geology ; Mineralogy

  16. The Acridian plagues, a new Holocene and Pleistocene palaeoclimatic indicator

    Meco, Joaquín; Petit-Maire, Nicole; Ballester, Javier; Betancort, Juan F.; Ramos, Antonio J. G.


    Five palaeosols, intercalated within the Quaternary dune beds of Fuerteventura and Lanzarote (Canary Islands), off the Moroccan coast, mark wetter climatic episodes. In all of them, billions of calcified insect ootheca testify to past occurrences of Acridian plagues, such as those reaching the western Sahara following heavy rainfall events over the Sahel. The most massive infestation is in the Holocene, and should coincide with the climax of Saharo-Sahelian humidity at the peak of the present interglacial.

  17. Holocene eolian activity in the Minot dune field, North Dakota

    Muhs, D.R.; Stafford, Thomas W.; Been, J.; Mahan, S.A.; Burdett, J.; Skipp, G.; Rowland, Z.M.


    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.

  18. Holocene Lake-Level Fluctuations of Lake Aricota, Southern Peru

    Placzek, Christa; Quade, Jay; Betancourt, Julio L.


    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.

  19. Holocene Millennial Time Scale Hydrological Changes In Central-east Africa

    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

  20. Aridity of Central Asia through the Holocene

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


    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

  1. Exploring the Causes of Mid-Holocene Drought in the Rocky Mountains Using Hydrologic Forward Models

    Meador, E.; Morrill, C.


    We present a quantitative model-data comparison for mid-Holocene (6 ka) lake levels in the Rocky Mountains, with the goals of assessing the skill coupled climate models and hydrologic forward models in simulating climate change and improving our understanding of the factors causing past changes in water resources. The mid-Holocene climate in this area may in some ways be similar to expected future climate, thus improved understanding of the factors causing past changes in water resources have the potential to aid in the process of water allocation for large areas that share a relatively small water source. This project focuses on Little Windy Hill Pond in the Medicine Bow Forest in the Rocky Mountains in southern Wyoming. We first calibrated the Variable Infiltration Capacity (VIC) catchment hydrologic model and the one-dimensional Hostetler Bartlein lake energy-balance model to modern observations, using U.S. Geological Survey stream discharge data and Snow Telemetry (SNOTEL) data to ensure appropriate selection of model parameters. Once the models were calibrated to modern conditions, we forced them with output from eight mid-Holocene coupled climate model simulations completed as part of the Coupled Model Intercomparison Project, Phase 5. Forcing from nearly all of the CMIP5 models generates intense, short-lived droughts for the mid-Holocene that are more severe than any we modeled for the past six decades. The severity of the mid-Holocene droughts could be sufficient, depending on sediment processes in the lake, to account for low lake levels recorded by loss-on-ignition in sediment cores. Our preliminary analysis of model output indicates that the combined effects of decreased snowmelt runoff and increased summer lake evaporation cause low mid-Holocene lake levels. These factors are also expected to be important in the future under anthropogenic climate change.

  2. Holocene Sea-Level Database For The Caribbean Region

    Khan, N. S.; Horton, B.; Engelhart, S. E.; Peltier, W. R.; Scatena, F. N.; Vane, C. H.; Liu, S.


    Holocene relative sea-level (RSL) records from far-field locations are important for understanding the driving mechanisms controlling the nature and timing of the mid-late Holocene reduction in global meltwaters and providing background rates of late Holocene RSL change with which to compare the magnitude of 20th century RSL rise. The Caribbean region has traditionally been considered far-field (i.e., with negligible glacio-isostatic adjustment (GIA) influence), although recent investigations indicate otherwise. Here, we consider the spatial variability in glacio-isostatic, tectonic and local contributions on RSL records from the circum-Caribbean region to infer a Holocene eustatic sea-level signal. We have constructed a database of quality-controlled, spatially comprehensive, Holocene RSL observations for the circum-Caribbean region. The database contains over 500 index points, which locate the position of RSL in time and space. The database incorporates sea-level observations from a latitudinal range of 5°N to 25°N and longitudinal range of 55°W to 90°W. We include sea-level observations from 11 ka BP to present, although the majority of the index points in the database are younger than 8 ka BP. The database is sub-divided into 13 regions based on the distance from the former Laurentide Ice Sheet and regional tectonic setting. The index points were primarily derived from mangrove peat deposits, which in the Caribbean form in the upper half of the tidal range, and corals (predominantly Acropora palmata), the growth of which is constrained to the upper 5 m of water depth. The index points are classified on the basis of their susceptibility to compaction (e.g., intercalated, basal). The influence of temporal changes in tidal range on index points is also considered. The sea-level reconstructions demonstrate that RSL did not exceed the present height (0 m) during the Holocene in the majority of locations, except at sites in Suriname/Guayana and possibly Trinidad

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

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


    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.

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

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


    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

  5. Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records

    Walker, Mike; Johnsen, Sigfus Johann; Rasmussen, Sune Olander


    The Greenland ice core from NorthGRIP (NGRIP) contains a proxy climate record across the Pleistocene-Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs...... the Global Stratotype Section and Point (GSSP) for the base of the Holocene Series/Epoch (Quaternary System/Period) has been ratified by the International Union of Geological Sciences. Five auxiliary stratotypes for the Pleistocene-Holocene boundary have also been recognised....

  6. Deriving a sea surface temperature record suitable for climate change research from the along-track scanning radiometers

    Merchant, C. J.; Llewellyn-Jones, D.; Saunders, R. W.; Rayner, N. A.; Kent, E. C.; Old, C. P.; Berry, D.; Birks, A. R.; Blackmore, T.; Corlett, G. K.; Embury, O.; Jay, V. L.; Kennedy, J.; Mutlow, C. T.; Nightingale, T. J.; O'Carroll, A. G.; Pritchard, M. J.; Remedios, J. J.; Tett, S.

    We describe the approach to be adopted for a major new initiative to derive a homogeneous record of sea surface temperature for 1991 2007 from the observations of the series of three along-track scanning radiometers (ATSRs). This initiative is called (A)RC: (Advanced) ATSR Re-analysis for Climate. The main objectives are to reduce regional biases in retrieved sea surface temperature (SST) to less than 0.1 K for all global oceans, while creating a very homogenous record that is stable in time to within 0.05 K decade-1, with maximum independence of the record from existing analyses of SST used in climate change research. If these stringent targets are achieved, this record will enable significantly improved estimates of surface temperature trends and variability of sufficient quality to advance questions of climate change attribution, climate sensitivity and historical reconstruction of surface temperature changes. The approach includes development of new, consistent estimators for SST for each of the ATSRs, and detailed analysis of overlap periods. Novel aspects of the approach include generation of multiple versions of the record using alternative channel sets and cloud detection techniques, to assess for the first time the effect of such choices. There will be extensive effort in quality control, validation and analysis of the impact on climate SST data sets. Evidence for the plausibility of the 0.1 K target for systematic error is reviewed, as is the need for alternative cloud screening methods in this context.

  7. Climate signals derived from cell anatomy of Scots pine in NE Germany.

    Liang, Wei; Heinrich, Ingo; Simard, Sonia; Helle, Gerhard; Liñán, Isabel Dorado; Heinken, Thilo


    Tree-ring chronologies of Pinus sylvestris L. from latitudinal and altitudinal limits of the species distribution have been widely used for climate reconstructions, but there are many sites within the temperate climate zone, as is the case in northeastern Germany, at which there is little evidence of a clear climate signal in the chronologies. In this study, we developed long chronologies of several cell structure variables (e.g., average lumen area and cell wall thickness) from P. sylvestris growing in northeastern Germany and investigated the influence of climate on ring widths and cell structure variables. We found significant correlations between cell structure variables and temperature, and between tree-ring width and relative humidity and vapor pressure, respectively, enabling the development of robust reconstructions from temperate sites that have not yet been realized. Moreover, it has been shown that it may not be necessary to detrend chronologies of cell structure variables and thus low-frequency climate signals may be retrieved from longer cell structure chronologies. The relatively extensive resource of archaeological material of P. sylvestris covering approximately the last millennium may now be useful for climate reconstructions in northeastern Germany and other sites in the temperate climate zone.

  8. Holocene Faunal Trends in West Siberia and Their Causes

    Gashev, S. N.; Aleshina, A. O.; Zuban, I. A.; Lupinos, M. Y.; Mardonova, L. B.; Mitropolskiy, M. G.; Selyukov, A. G.; Sorokina, N. V.; Stolbov, V. A.; Shapovalov, S. I.


    Based on an analysis of the transformation of vertebrate and invertebrate fauna of West Siberia in the Holocene, the classification and periodization of the main faunal trends are presented. Against the background of changing environmental conditions, the key regularities of the faunal dynamics, and the ways some species penetrate into the territory of the region and others disappear from the beginning of the Holocene to the present time have been indicated. Three global and four fluctuating trends are identified. The anthropogenic trend is ascertained separately. A conclusion is made about the prevailing causes of these changes, associated primarily with periodic climatic processes of different levels, determined by planetary geological and cosmic cycles. It is emphasized that, in the historical period, anthropogenic factors play a significant role in the regional faunal dynamics.

  9. The Holocene vegetation history of northern West Jutland

    Odgaard, Bent Vad


    . The Holocene history of each lake basin was investigated by mapping of sediment distribution, analysis of loss-on-ignition, coarse inorganic matter, humus content, mineral magnetics, 6°C. pollen and selected other microfossils. These techniques were supplemented by plant macrofossil analysis at one site....... Holocene terrestrial vegetational development was inferred at each site from analyses of pollen and microscopical charred particles. Chronologies were provided by numerous I4C dates. Stratigraphies of wet ground and terrestrial pollen and spore types were zooned by stratigraphically constrained cluster......, the synchronous timing of relatively rapid inferred change in lake and terrestrial vegetation around AD 600 may reflect changes in climate as well as in land-use. Redundancy analysis was used to develop a model between fire intensity (inferred from microscopical charred particles) and vegetational response...

  10. Multiple glacial culminations from the Lateglacial to the late Holocene in central and southern Peru (Invited)

    Licciardi, J. M.; Schaefer, J. M.; Rodbell, D. T.; Stansell, N.; Schweinsberg, A.; Finkel, R. C.; Zimmerman, S. R.


    Fluctuations in small tropical mountain glaciers serve as sensitive indicators of variations in past and present-day climate. Most of the world's modern tropical glaciers reside in the Peruvian Andes, where a growing number of well-dated glacial records have recently been developed. As additional records are documented, regional patterns of late Pleistocene to Holocene glacial activity have begun to emerge. Here we present a compilation of new and previously obtained 10Be surface exposure ages from boulders on well-preserved moraine successions in two glaciated Andean ranges: the Cordillera Vilcabamba of southern Peru (13°20'S, 72°32'W) and the Huaguruncho massif (10°32'S, 75°56'W), located in central Peru ~450 km northwest of the Vilcabamba. A high-resolution composite chronology that merges >100 10Be measurements on moraine sequences in five glaciated drainages of the Cordillera Vilcabamba reveals the occurrence of at least five discrete glacial culminations from the Lateglacial to the late Holocene. At the Huaguruncho massif, >20 10Be exposure ages obtained from moraine sequences in a south-facing cirque indicate at least three major glacial stages spanning the Lateglacial to the Little Ice Age. The moraine ages at Huaguruncho are broadly correlative with the Vilcabamba moraine chronologies, with some dated moraine belts exhibiting geomorphic expressions that closely resemble those of their coeval counterparts in the Vilcabamba. A recurring finding in both field areas is a mismatch between basal radiocarbon ages from bog and lake sediments and 10Be exposure ages on outboard moraines, which enclose the depositional basins. These age discrepancies suggest that cosmogenic 10Be production rates scaled to high altitudes in the tropics are substantially lower than previous estimates. While we anticipate that future refinements to scaled isotope production rates may significantly affect correlation of 10Be exposure ages in the high Andes with ages derived from

  11. Empirical methods for estimating future climatic conditions



    Applying the empirical approach permits the derivation of estimates of the future climate that are nearly independent of conclusions based on theoretical (model) estimates. This creates an opportunity to compare these results with those derived from the model simulations of the forthcoming changes in climate, thus increasing confidence in areas of agreement and focusing research attention on areas of disagreements. The premise underlying this approach for predicting anthropogenic climate change is based on associating the conditions of the climatic optimums of the Holocene, Eemian, and Pliocene with corresponding stages of the projected increase of mean global surface air temperature. Provided that certain assumptions are fulfilled in matching the value of the increased mean temperature for a certain epoch with the model-projected change in global mean temperature in the future, the empirical approach suggests that relationships leading to the regional variations in air temperature and other meteorological elements could be deduced and interpreted based on use of empirical data describing climatic conditions for past warm epochs. Considerable care must be taken, of course, in making use of these spatial relationships, especially in accounting for possible large-scale differences that might, in some cases, result from different factors contributing to past climate changes than future changes and, in other cases, might result from the possible influences of changes in orography and geography on regional climatic conditions over time

  12. 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

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


    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).

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

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


    It has long been assumed in New Zealand (NZ) that the Holocene Thermal Optimum (HTO) occurred at the beginning of the Holocene. Nearly 40 years ago, Hendy and Wilson pioneered the use of 18O/16O composition of calcite in NZ speleothems to reconstruct past climate and in so doing showed an HTO occurring earlier in NZ than in comparable Northern Hemisphere records (Hendy & Wilson,1968). More recent work on NZ speleothems (Williams et al., 2005) corroborates the concept of an early HTO dated between ca 11.7 and 10.6 ka, but there is no definitive description of the event as a NZ-wide phenomenon, no intensive dating of it, nor temperature quantification. Moreover, there is no firm conclusion as to whether it is registered consistently between different proxies and across NZ regions. Until recently, attempts to quantify past climate change from NZ pollen data have been hindered by failure to demonstrate robust relationships between modern pollen assemblages and climate due, it is thought, to strong anthropogenic modification of natural vegetation patterns and steep climatic gradients (Norton et al., 1986). However, as deforestation commenced only ca 700 years ago, and is unambiguously detected in pollen records from throughout NZ, an almost unique opportunity exists to develop pollen-climate transfer functions using pre-human pollen-vegetation sources. McGlone and Wilmshurst have assembled an extensive (138-site) `modern' pollen database, based on ca 700 yr BP pre-deforestation pollen assemblages from peat and lake cores. This now provides a basis for more secure pollen-climate reconstruction than hitherto has been possible. Statistical modelling of the environmental determinants of patterns in the pre-deforestation pollen database indicates the strongest relationship (r2 > 0.8) is with Mean Annual Temperature (MAT) and suggests that this parameter can be reliably reconstructed, with error estimates, from Late Quaternary NZ pollen profiles. We use this database to

  14. Reconciling divergent trends and millennial variations in Holocene temperatures

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


    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

  15. Climate

    Fellous, J.L.


    This book starts with a series of about 20 preconceived ideas about climate and climatic change and analyses each of them in the light of the present day knowledge. Using this approach, it makes a status of the reality of the climatic change, of its causes and of the measures to be implemented to limit its impacts and reduce its most harmful consequences. (J.S.)

  16. Holocene sea-level fluctuation in the southern hemisphere

    Isla, Federico Ignacio

    If rising sea levels dominate in the northern hemisphere (NH), falling or fluctuating sea levels predominate in the southern hemisphere (SH). Endogenic processes (tectonics, isostasy or geoidal changes) could explain local or regional mean sea level (MSL) fluctuations but not an hemispherical one. Evidence from South America, Africa, Antarctica, Australia and the Pacific and Indian Oceans suggest that the Holocene transgression rose above the present MSL, in higher latitudes before the tropics. By plotting latitude against the age of MSL arrival at present coasts, good correlation is observed. Oceanic salinity mixing has been already proposed to explain this mid-Holocene sea-level fluctuation. Climate could be the only factor responsible for this hemisphere-wide behavior of MSL. It has been suggested previously that the climate of the SH precedes that of the NH by 3000 years. The climatic optimum, or maximum warmth, occurred predominantly about 6000 BP in the NH, but about 10-9000 BP in the SH. Short-term climatic effects on the sea level (monsoons, southern oscillation/El Niño phenomena) should have significant occurrences during the past in the windiest oceanic hemisphere. This latitudinal trend in former MSL should be considered when using shorelines as reference points for measuring vertical crustal movements.

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

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


    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

  18. Vegetation and climate history during the last millennium derived from Anggertu Lake, Tengger Desert

    Duan, F.; An, C.; Zhao, Y.; Wang, W.; Cao, Z.


    Studying the climate changes during the last millennium can help us to understand current relationship between human-social activities and natural environment changes, and improve projections of future climate. Pollen assemblages, loss-on-ignition (LOIorg at 550 °C) and grain size data collected from sediment core (AGE15A) from the center of Anggertu lake (eastern Tengger Desert, Inner Mongolia) are presented to reconstruct regional vegetation and climate history during the last millennium. Results show that: 1) desert or desert steppe dominated by Artemisia and Amaranthaceae expanded around this region during the period of 988 1437 A.D., indicating a generally dry climate condition with two short humid periods (1003 1082 A.D. and 1388 1437 A.D). These two wet periods are characterized by relatively high vegetation cover and bio-productivity, reflected by high pollen concentrations and LOIorg. Increase in the steppe or meadow vegetation communities (Poaceae, Cyperaceae) and vegetation cover during the period of 1437 2015 A.D. suggest a wetting trend, as also indicated by gradually finer grain size. The relatively high LOI indicate a high bio-productivity during this interval. And then unstable lacustrine environment was found with frequent fluctuations in pollen concentration and grain size since 1842 A.D.. 2) This study recorded a relatively dry Medieval Warm Period (MWP; 1082 1388 A.D.) and a wet Little Ice Age (LIA; 1437 1842 A.D.), which is generally consistent with climate characteristics in arid central Asia (ACA). 3) Increased Amaranthaceae and high abundance of Poaceae were related to overgrazing and agricultural activities at that time to some extent. Thus vegetation evolution of the lake region was influenced by human activities and climate changes.

  19. Use of radar QPE for the derivation of Intensity-Duration-Frequency curves in a range of climatic regimes

    Marra, Francesco; Morin, Efrat


    Intensity-Duration-Frequency (IDF) curves are widely used in flood risk management because they provide an easy link between the characteristics of a rainfall event and the probability of its occurrence. Weather radars provide distributed rainfall estimates with high spatial and temporal resolutions and overcome the scarce representativeness of point-based rainfall for regions characterized by large gradients in rainfall climatology. This work explores the use of radar quantitative precipitation estimation (QPE) for the identification of IDF curves over a region with steep climatic transitions (Israel) using a unique radar data record (23 yr) and combined physical and empirical adjustment of the radar data. IDF relationships were derived by fitting a generalized extreme value distribution to the annual maximum series for durations of 20 min, 1 h and 4 h. Arid, semi-arid and Mediterranean climates were explored using 14 study cases. IDF curves derived from the study rain gauges were compared to those derived from radar and from nearby rain gauges characterized by similar climatology, taking into account the uncertainty linked with the fitting technique. Radar annual maxima and IDF curves were generally overestimated but in 70% of the cases (60% for a 100 yr return period), they lay within the rain gauge IDF confidence intervals. Overestimation tended to increase with return period, and this effect was enhanced in arid climates. This was mainly associated with radar estimation uncertainty, even if other effects, such as rain gauge temporal resolution, cannot be neglected. Climatological classification remained meaningful for the analysis of rainfall extremes and radar was able to discern climatology from rainfall frequency analysis.

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

    Wolter, Juliane


    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...

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

    Li Wu


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

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

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


    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

  3. A model-data comparison of the Holocene global sea surface temperature evolution

    Lohmann, G.; Pfeiffer, M.; Laepple, T.; Leduc, G.; Kim, J.-H.


    We compare the ocean temperature evolution of the Holocene as simulated by climate models and reconstructed from marine temperature proxies. We use transient simulations from a coupled atmosphere-ocean general circulation model, as well as an ensemble of time slice simulations from the Paleoclimate

  4. Holocene stratigraphy and vegetation history in the Scoresby Sund area, East Greenland

    Funder, Svend Visby


    The Holocene stratigraphy in Scoresby Sund is based on climatic change as reflected by fluctuations in fjord and valley glaciers, immigration and extinction of marine molluscs, and the vegetation history recorded in pollen diagrams from five lakes. The histories are dated by C-14, and indirectly...

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

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


    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

  6. Holocene glacier activity reconstructed from proglacial lake Gjøavatnet on Amsterdamøya, NW Svalbard

    de Wet, Gregory A.; Balascio, Nicholas L.; D'Andrea, William J.; Bakke, Jostein; Bradley, Raymond S.; Perren, Bianca


    Well-dated and highly resolved paleoclimate records from high latitudes allow for a better understanding of past climate change. Lake sediments are excellent archives of environmental change, and can record processes occurring within the catchment, such as the growth or demise of an upstream glacier. Here we present a Holocene-length, multi-proxy lake sediment record from proglacial lake Gjøavatnet on the island of Amsterdamøya, northwest Svalbard. Today, Gjøavatnet receives meltwater from the Annabreen glacier and contains a record of changes in glacier activity linked to regional climate conditions. We measured changes in organic matter content, dry bulk density, bulk carbon isotopes, elemental concentrations via Itrax core-scanning, and diatom community composition to reconstruct variability in glacier extent back through time. Our reconstruction indicates that glacially derived sedimentation in the lake decreased markedly at ∼11.1 cal kyr BP, although a glacier likely persisted in the catchment until ∼8.4 cal kyr BP. During the mid-Holocene (∼8.4-1.0 cal kyr BP) there was significantly limited glacial influence in the catchment and enhanced deposition of organic-rich sediment in the lake. The deposition of organic rich sediments during this time was interrupted by at least three multi-centennial intervals of reduced organic matter accumulation (∼5.9-5.0, 2.7-2.0, and 1.7-1.5 cal kyr BP). Considering our chronological information and a sedimentological comparison with intervals of enhanced glacier input, we interpret these intervals not as glacial advances, but rather as cold/dry episodes that inhibited organic matter production in the lake and surrounding catchment. At ∼1.0 cal kyr BP, input of glacially derived sediment to Gjøavatnet abruptly increased, representing the rapid expansion of the Annabreen glacier.

  7. Lakes or wetlands? A comment on 'The middle Holocene climatic records from Arabia: Reassessing lacustrine environments, shift of ITCZ in Arabian Sea, and impacts of the southwest Indian and African monsoons' by Enzel et al.

    Engel, Max; Matter, Albert; Parker, Adrian G.; Parton, Ash; Petraglia, Michael D.; Preston, Gareth W.; Preusser, Frank


    Enzel et al. (2015) reassess sedimentary records of Early to Mid-Holocene lake sites in Arabia based on a reinterpretation of published multiproxy data and a qualitative analysis of satellite imagery. The authors conclude that these sites represent palaeo-wetland environments rather than palaeolakes and that the majority of the Arabian Peninsula experienced no or, if at all, only a very minor increase of rainfall at that time mainly due to eastward expansion of the East African Summer Monsoon. We disagree with their reassessment and identify several cases where unequivocal evidence for early Late Pleistocene and Early to Mid-Holocene perennial lake environments in Arabia, lasting for centuries to millennia, was neglected by Enzel et al. (2015). Here we summarize findings which indicate the presence of lakes from the sites of Jubbah, Tayma, Mundafan (all Saudi Arabia), Wahalah, Awafi (both UAE), and the Wahiba Sands (Oman), supported by evidence including occurrence of barnacle colonies in living position, remnant bioclastic shoreline deposits, undisturbed varve formation, shallowing-up lacustrine sequences, various aquatic freshwater, brackish and saline micro- and macrofossils, such as ichnofaunal remains, which are the result of prolonged field-based research. While the precise depth, hydrology and ecology of these water bodies is still not entirely resolved, their perennial nature is indicative of a markedly increased precipitation regime, which, in combination with more abundant groundwater and increased spring outflow in terminal basins fed by charged aquifers, was sufficient to overcome evaporative losses. The palaeolakes' influence on sustaining prehistoric populations is corroborated by the presence of rich archaeological evidence.

  8. Holocene reef development where wave energy reduces accommodation

    Grossman, Eric E.; Fletcher, Charles H.


    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.

  9. Sources of Holocene variability of oxygen isotopes in paleoclimate archives

    A. N. LeGrande


    Full Text Available Variability in water isotopes has been captured in numerous archives and used to infer past climate changes. Here we examine water isotope variability over the course of the Holocene using the water-isotope enabled, coupled atmosphere-ocean general circulation model, GISS ModelE-R. Eight Holocene time slices, ~1000 years apart are simulated and driven by estimated changes in orbital configuration, greenhouse gases, and ice sheet extent. We find that simulated water isotope archives match well with those seen in ice cores, ocean sediment cores, and speleothems. The climate changes associated with the water isotope changes, however, are more complex than simple modern spatial slope interpretations might suggest. In particular, water isotope variability in Asian speleothems is linked to alterations in landward water vapor transport, not local precipitation, and ice sheet changes over North America lead to the masking of temperature signals in Summit, Greenland. Salinity-seawater isotope variability is complicated by inter-ocean basin exchanges of water vapor. Water isotopes do reflect variability in the hydrology, but are better interpreted in terms of regional hydrological cycle changes rather than as indicators of local climate.

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

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


    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...

  11. Explanation of climate and human impacts on sediment discharge change in Darwinian hydrology: Derivation of a differential equation

    Zhang, Jianjun; Gao, Guangyao; Fu, Bojie; Zhang, Lu


    The assessment for impacts of climate variability and human activities on suspended sediment yield (SSY) change has long been a question of great interest. However, the sediment generation processes are sophisticated with high nonlinearity and great uncertainty, which give rise to extreme complexity for SSY change assessment in Newtonian approach. Consequently, few approaches can be simply but widely applied to decompose impacts of climatic variability and human activities on SSY change. Thus, it is an urgent need to develop advanced methods that are simple and robust. Since that the Newtonian approach is hardly achievable due to limitation of either observations or knowledge of mechanisms, there have been repeated calls to capture the hydrologic system in Darwinian approach for hydrological change prediction or explanation. As streamflow is the carrier of suspended sediment, SSY change are thus documented in changes of sediment concentrated flow and suspended sediment concentration - water discharge (C-Q) relationships. By deduced corollaries, a differential equation of sediment discharge change was derived to explicitly decompose impacts of climate variability and human activities in Darwinian hydrology. Besides, a new form of sediment rating curves was proposed and curved as C-Q relationships and probability distribution of sediment concentrated flow. River sediment flux can be revealed by this representation, which simply elucidates mechanism of SSY generation covering a range of time scales from finer than rainfall-event to long term. By the new sediment rating curves, the differential equation was partly solved using a segmentation algorithm proposed and validated in this paper, and then was submitted to water balance framework expressed by Budyko-type equation. Thus, for catchment management, hydrologists can obtain explicit explanation of how climate variation and human activities propagate through landscape and result in sediment discharge change. The

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

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


    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.

  13. Scenario and modelling uncertainty in global mean temperature change derived from emission driven Global Climate Models

    Booth, B. B. B.; Bernie, D.; McNeall, D.; Hawkins, E.; Caesar, J.; Boulton, C.; Friedlingstein, P.; Sexton, D.


    We compare future changes in global mean temperature in response to different future scenarios which, for the first time, arise from emission driven rather than concentration driven perturbed parameter ensemble of a Global Climate Model (GCM). These new GCM simulations sample uncertainties in atmospheric feedbacks, land carbon cycle, ocean physics and aerosol sulphur cycle processes. We find broader ranges of projected temperature responses arising when considering emission rather than concentration driven simulations (with 10-90 percentile ranges of 1.7 K for the aggressive mitigation scenario up to 3.9 K for the high end business as usual scenario). A small minority of simulations resulting from combinations of strong atmospheric feedbacks and carbon cycle responses show temperature increases in excess of 9 degrees (RCP8.5) and even under aggressive mitigation (RCP2.6) temperatures in excess of 4 K. While the simulations point to much larger temperature ranges for emission driven experiments, they do not change existing expectations (based on previous concentration driven experiments) on the timescale that different sources of uncertainty are important. The new simulations sample a range of future atmospheric concentrations for each emission scenario. Both in case of SRES A1B and the Representative Concentration Pathways (RCPs), the concentration pathways used to drive GCM ensembles lies towards the lower end of our simulated distribution. This design decision (a legecy of previous assessments) is likely to lead concentration driven experiments to under-sample strong feedback responses in concentration driven projections. Our ensemble of emission driven simulations span the global temperature response of other multi-model frameworks except at the low end, where combinations of low climate sensitivity and low carbon cycle feedbacks lead to responses outside our ensemble range. The ensemble simulates a number of high end responses which lie above the CMIP5 carbon

  14. Holocene volcanic geology, volcanic hazard, and risk on Taveuni, Fiji

    Cronin, S.J.; Neall, V.E.


    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

  15. Climatic influence in NRM and 10 Be-derived geomagnetic paleointensity data


    One can determine geomagnetic paleointensities from natural remanent magnetizations (NRM) and by inverting production rates of cosmogenic isotopes such as 10 Be and 14 C. Recently, two independently derived 200-kyr stacks [Y. Guyodo, J.-P. Valet, Relative variations in geomagnetic intensity from

  16. Holocene environmental changes in northern Lebanon as inferred from a multiproxy study on lacustrine-palustrine sediment

    Vidal, Laurence; Jenna, Hage-Hassen; Demory, François; Develle, Anne-Lise; van Campo, Elise; Elias, Ata


    The reconstruction of the Levantine post-glacial environmental evolution is essential to understand the interactions between variability of regional water cycle, dynamics of the global climate, and cultural evolution. We present a paleolacustrine record from the karstic Yammouneh basin (34.06N-34.09N; 36.0E-36.03E, 1360 m a.s.l.), located on the eastern flank of Mount Lebanon (northern Levant). Holocene sediments (retrieved from gully and a trenbch) (1.5 to 3.6 m thick) consist of pale lacustrine chalk interrupted by an ash layer and remarkable centimetric beds of ocher to dark brown silty clays used, in addition to 14C ages, as stratigraphical markers. Lacustrine biogenic remains are diversified and abundant (ostracods, gastropods, charophytes, chlorophyceae, plant debris…) all reflecting a freswater, generally shallow waterbody. We analysed the sediment mineralogy and geochemistry, TOM contents, magnetic properties, pollen and calcite oxygen isotope composition derived from ostracod shells. These sequences are compared to former data from 2 trenches and 1 core collected in different points of the basin (Daeron et al., 2007; Develle et al., 2009, 2010). A total of 42 AMS 14C dating (partly carbonized wood) provide a solid chronology from the YD to present. Results reveal the following main features : 1- intervals dominated by authigenic calcite suggest that the major water supply was the karstic springs, which still deliver Ca-rich water and low surface runoff; 2- the lake oxygen isotope composition has been impacted by the source isotope composition throughout the Holocene and by increased inland rainfall during the early Holocene; 3- a decideous oak forest, implying much more soil water availability than today, was developed around the lake from ca. 11.5 to 9.5 kyr (the very bad pollen preservation after 8.3 kyr reflects oxidation or frequent oscillations of the water level); 4- four paleosols evidenced from lithofacies and magnetic properties are identified

  17. Assessing millennial-scale variability during the Holocene: A perspective from the western tropical Pacific

    Khider, D.; Jackson, C. S.; Stott, L. D.


    We investigate the relationship between tropical Pacific and Southern Ocean variability during the Holocene using the stable oxygen isotope and magnesium/calcium records of cooccurring planktonic and benthic foraminifera from a marine sediment core collected in the western equatorial Pacific. The planktonic record exhibits millennial-scale sea surface temperature (SST) oscillations over the Holocene of 0.5°C while the benthic δ18Oc document 0.10‰ millennial-scale changes of Upper Circumpolar Deep Water (UCDW), a water mass which outcrops in the Southern Ocean. Solar forcing as an explanation for millennial-scale SST variability requires (1) a large climate sensitivity and (2) a long 400 year delayed response, suggesting that if solar forcing is the cause of the variability, it would need to be considerably amplified by processes within the climate system at least at the core location. We also explore the possibility that SST variability arose from volcanic forcing using a simple red noise model. Our best estimates of volcanic forcing falls short of reproducing the amplitude of observed SST variations although it produces power at low-frequency similar to that observed in the MD81 record. Although we cannot totally discount the volcanic and solar forcing hypotheses, we are left to consider that the most plausible source for Holocene millennial-scale variability lies within the climate system itself. In particular, UCDW variability coincided with deep North Atlantic changes, indicating a role for the deep ocean in Holocene millennial-scale variability.

  18. Holocene molluscan assemblages in the Magellan region

    Sandra Gordillo


    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.

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

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


    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

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

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


    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.


    E. Brugiapaglia


    Full Text Available The pollen record from Trifoglietti lake (Calabria region provides new information about the paleoenvironmental and palaeoclimatic changes occurred during the LateGlacial and Holocene period. The LateGlacial part of the record, for which only preliminary data is available, is a new and original sequence from southern Italy. The Holocene sequence, with 11 AMS radiocarbon dates shows a stable Fagus forest for the entire period. Apart from sporadic pastoralism activities and the selective exploitation of Abies, only a weak human impact is recognized in the pollen records. Lake level oscillations have been reconstructed and annual precipitations quantified using the Modern Analogue Technique. The reconstruction was effectuated both at millennial and centennial scale: the first shows an increasing of moisture from 11000 to 9400 cal BP and a maximum of humidity from 9400 to 6200 cal BP. Moreover, several climatic oscillations punctuated the Holocene and therefore superimposed the millennial trend.

  2. Radiation Climatology of the Greenland Ice Sheet Derived from Greenland Climate Network Data

    Steffen, Konrad; Box, Jason


    The magnitude of shortwave and longwave dative fluxes are critical to surface energy balance variations over the Greenland ice sheet, affecting many aspects of its climate, including melt rates, the nature of low-level temperature inversions, the katabatic wind regime and buoyant stability of the atmosphere. Nevertheless, reliable measurements of the radiative fluxes over the ice sheet are few in number, and have been of limited duration and areal distribution (e.g. Ambach, 1960; 1963, Konzelmann et al., 1994, Harding et al., 1995, Van den Broeke, 1996). Hourly GC-Net radiation flux measurements spanning 1995-2001 period have been used to produce a monthly dataset of surface radiation balance components. The measurements are distributed widely across Greenland and incorporate multiple sensors

  3. Glaciation in the Andes during the Lateglacial and Holocene

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


    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

  4. The Holocene Geoarchaeology of the Desert Nile in Northern Sudan

    Woodward, Jamie; Macklin, Mark; Spencer, Neal; Welsby, Derek; Dalton, Matthew; Hay, Sophie; Hardy, Andrew


    Invited Paper Forty years ago Colin Renfrew declared that "every archaeological problem starts as a problem in geoarchaeology" (Renfrew, 1976 p. 2). With this assertion in mind, this paper draws upon the findings from field research in two sectors of the Nile Valley of Northern Sudan dedicated to the exploration of human-environment interactions during the middle and late Holocene. This part of the Nile corridor contains a rich cultural record and an exceptionally well preserved Holocene fluvial archive. A distinctive feature of these records is the variety of evidence for interaction between desert and river over a range of spatial and temporal scales. This interaction presented both challenges and opportunities for its ancient inhabitants. This paper will present evidence for large-scale landscape changes driven by shifts in global climate. It will also show how we have integrated the archaeological and geological records in the Northern Dongola Reach and at Amara West - where long-term field projects led by archaeologists from the British Museum have recognised the importance of a sustained commitment to interdisciplinary research to achieve a fully integrated geoarchaeological approach across a range of scales. The former project is a large-scale landscape survey with multiple sites across an 80 km reach of the Nile whilst the latter has a strong focus on a single New Kingdom town site and changes in its environmental setting. By combining multiple archaeological and geological datasets - and pioneering the use of OSL dating and strontium isotope analysis in the Desert Nile - we have developed a new understanding of human responses to Holocene climate and landscape change in this region. Renfrew, C. (1976) Archaeology and the earth sciences. In: D.A. Davidson and M.I. Shackley (eds) Geoarchaeology: Earth Science and the Past, Duckworth, London, 1-5.

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

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


    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

  6. Holocene Enviromental Changes in AN Amazonian Floodplain Lake

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


    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.




    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.

  8. Identifying Typhoon Tracks based on Event Synchronization derived Spatially Embedded Climate Networks

    Ozturk, Ugur; Marwan, Norbert; Kurths, Jürgen


    Complex networks are commonly used for investigating spatiotemporal dynamics of complex systems, e.g. extreme rainfall. Especially directed networks are very effective tools in identifying climatic patterns on spatially embedded networks. They can capture the network flux, so as the principal dynamics of spreading significant phenomena. Network measures, such as network divergence, bare the source-receptor relation of the directed networks. However, it is still a challenge how to catch fast evolving atmospheric events, i.e. typhoons. In this study, we propose a new technique, namely Radial Ranks, to detect the general pattern of typhoons forward direction based on the strength parameter of the event synchronization over Japan. We suggest to subset a circular zone of high correlation around the selected grid based on the strength parameter. Radial sums of the strength parameter along vectors within this zone, radial ranks are measured for potential directions, which allows us to trace the network flux over long distances. We employed also the delay parameter of event synchronization to identify and separate the frontal storms' and typhoons' individual behaviors.

  9. Energy use of US residential refrigerators and freezers. Function derivation based on household and climate characteristics

    Greenblatt, J.; Letschert, V. [Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Hopkins, A. [Vermont Department of Public Service, Burlington, VT (United States); Blasnik, M. [Blasnik Consulting, Boston, MA (United States)


    Field-metered energy use data for 1,467 refrigerators and 185 freezers from seven studies conducted between 1992 and 2010 were used to calculate usage adjustment factors (UAFs), defined as the ratio of measured to tested annual energy use. Multiple regressions of UAFs against several household and climate variables were then performed to obtain separate predictive functions for primary (most-used) refrigerators, secondary (second most-used) refrigerators, and freezers, and residual differences between observed and modeled UAFs were fit to log normal distributions. These UAF functions were used to project energy use in the more than 4,000 households in the 2005 Residential Energy Consumption Survey, a statistical representation of US homes. These energy use projections formed the basis of calculating lifecycle energy savings for more efficient refrigerators and freezers, as well as national energy and cost savings. Results were compared with previous published work by the Department of Energy, demonstrating how UAFs impact energy and cost savings. Such an approach could be further improved with additional data and adapted for other appliances in future analyses.

  10. Use of the Köppen-Trewartha climate classification to evaluate climatic refugia in statistically derived ecoregions for the People’s Republic of China

    B. Baker; Henry Diaz; William Hargrove; Forrest. Hoffman


    Changes in climate as projected by state-of-the-art climate models are likely to result in novel combinations of climate and topo-edaphic factors that will have substantial impacts on the distribution and persistence of natural vegetation and animal species. We have used multivariate techniques to quantify some of these changes; the...

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

    González Sampériz, Penélope


    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

  12. Role of the mid-Holocene environmental transition in the decline of late Neolithic cultures in the deserts of NE China

    Guo, Licheng; Xiong, Shangfa; Ding, Zhongli; Jin, Guiyun; Wu, Jiabin; Ye, Wei


    The mid-Holocene environmental transition was characterised by global cooling and the abrupt weakening of the Northern Hemisphere monsoon systems. It is generally considered the key driver of the collapse of several mid-Holocene agricultural societies, on a global scale. However, only a few previous studies have tried to verify the climatic origin of the collapse of these societies, using the compilation of spatiotemporal data at a large scale. Especially, the nature of mid-Holocene human-environment interactions in the climatically-sensitive margin of the East Asian summer monsoon front remains to be thoroughly understood. However, a systematic compilation of archaeological data at a regional scale can be used to verify the role the mid-Holocene environmental transition played in the collapse of late Neolithic cultures in China. Here, we present a regional compilation of Holocene records from sub-aerial sedimentary deposits, lake sediments, and archaeological sites in the deserts of NE China and the adjacent regions to explore human-environment interactions during the mid-Holocene. Comparison of the records of Holocene climate change with the evolution of archaeological sites reveals that the mid-Holocene environmental transition resulted in ecosystem degradation in the deserts of NE China, rendering these areas much less habitable. Faced with substantially increased environmental pressures, the late Neolithic inhabitants used several subsistence strategies to adapt to the environmental transition, including change in agricultural practices and ultimately migration. Overall, our results support the view that a widespread mid-Holocene drought destroyed the rain-fed agricultural and/or plant-based subsistence economies, ultimately contributing to the collapse of late Neolithic cultures in NE China.

  13. Review of probabilistic pollen-climate transfer methods

    Ohlwein, Christian; Wahl, Eugene R.


    Pollen-climate transfer methods are reviewed from a Bayesian perspective and with a special focus on the formulation of uncertainties. This approach is motivated by recent developments of spatial multi-proxy Bayesian hierarchical models (BHM), which allow synthesizing local reconstructions from different proxies for a spatially complete picture of past climate. In order to enhance the pollen realism in these models we try to bridge the gap between spatial statistics and paleoclimatology and show how far classical pollen-climate transfer concepts such as regression methods, mutual climatic range, modern analogues, plant functional types, and biomes can be understood in novel ways by refining the data models used in BHMs. As a case study, we discuss modeling of uncertainty by introducing a new probabilistic pollen ratio model, which is a simplified variation of the modern analogue technique (MAT) including the concept of response surfaces and designed for later inclusion in a spatial multiproxy BHM. Applications to fossil pollen data from varved sediments in three nearby lakes in west-central Wisconsin, USA and for a Holocene fossil pollen record from southern California, USA provide local climate reconstructions of summer temperature for the past millennium and the Holocene respectively. The performance of the probabilistic model is generally similar in comparison to MAT-derived reconstructions using the same data. Furthermore, the combination of co-location and precise dating for the three fossil sites in Wisconsin allows us to study the issue of site-specific uncertainty and to test the assumption of ergodicity in a real-world example. A multivariate ensemble kernel dressing approach derived from the post-processing of climate simulations reveals that the overall interpretation based on the individual reconstructions remains essentially unchanged, but the single-site reconstructions underestimate the overall uncertainty.

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

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


    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

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

    Virginia Iglesias


    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.

  16. Appalachian Piedmont landscapes from the Permian to the Holocene

    Cleaves, E.T.


    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

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

    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.


    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

  18. Holocene seasonal variability inferred from multiple proxy records from Crevice Lake, Yellowstone National Park, USA

    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.


    the Roman Warm Period (~ 2000 cal yr BP) and Medieval Climate Anomaly (1200–800 cal yr BP). Long springs and mild summers occurred during the Little Ice Age, and these conditions persist to the present. Although the proxy data indicate effectively wet summer conditions in the early Holocene and drier conditions in the middle and late Holocene, none point specifically to changes in summer precipitation as the cause. Instead, summer conditions were governed by multi-seasonal controls on effective moisture that operated over multiple time scales.

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

    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

  20. A model–data comparison of the Holocene global sea surface temperature evolution

    G. Lohmann


    Full Text Available We compare the ocean temperature evolution of the Holocene as simulated by climate models and reconstructed from marine temperature proxies. We use transient simulations from a coupled atmosphere–ocean general circulation model, as well as an ensemble of time slice simulations from the Paleoclimate Modelling Intercomparison Project. The general pattern of sea surface temperature (SST in the models shows a high-latitude cooling and a low-latitude warming. The proxy dataset comprises a global compilation of marine alkenone- and Mg/Ca-derived SST estimates. Independently of the choice of the climate model, we observe significant mismatches between modelled and estimated SST amplitudes in the trends for the last 6000 yr. Alkenone-based SST records show a similar pattern as the simulated annual mean SSTs, but the simulated SST trends underestimate the alkenone-based SST trends by a factor of two to five. For Mg/Ca, no significant relationship between model simulations and proxy reconstructions can be detected. We test if such discrepancies can be caused by too simplistic interpretations of the proxy data. We explore whether consideration of different growing seasons and depth habitats of the planktonic organisms used for temperature reconstruction could lead to a better agreement of model results with proxy data on a regional scale. The extent to which temporal shifts in growing season or vertical shifts in depth habitat can reduce model–data misfits is determined. We find that invoking shifts in the living season and habitat depth can remove some of the model–data discrepancies in SST trends. Regardless whether such adjustments in the environmental parameters during the Holocene are realistic, they indicate that when modelled temperature trends are set up to allow drastic shifts in the ecological behaviour of planktonic organisms, they do not capture the full range of reconstructed SST trends. Results indicate that modelled and reconstructed

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

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


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

  2. Late Holocene higher sea level and its radiocarbon dates in Okierabu-jima, Ryukyus

    Koba, Motoharu; Omoto, Kunio; Takahashi, Tatsuo.


    Okierabu-jima of the Ryukyu Islands, which is a poly-terraced Pleistocene raised coral reef island, doesn't have a Holocene raised coral reef, but coastal erosional features showing higher sea levels in Holocene. The authors obtained some data indicating the period of one of the Holocene higher sea levels. All radiocarbon dates concerning Okierabu-jima's Holocene sea-level changes are plotted on the date-height coordinates. The paleo sea level between 5000 and 2000 y. B. P. lies above the broken line drawn from 6 m below to 2.18 m above the present sea level. The period of the highest sea level in Holocene seems to be about 3000 to 2000 y. B. P. in this island. Its height is presumably 2.4 m a. s. l. derived on an average from heights of stacks and coastal benches in the almost all coasts of the island (Koba, 1974). Beach rocks were already formed at the landward extremity of the reef flat corresponding to the almost present sea level about 1300 y. B. P. (author)

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

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


    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

  4. Regional scale climatic trends derived from Younger Dryas glaciers in the U.K.

    Pearce, D.; Rea, B. R.; Barr, I.; Small, D.; McDougall, D.


    In the U.K., the glacial geomorphological record has been utilised to infer paleo-glacier geometries and ice dynamics, with much of this work focussing on the Scottish Highlands during the Younger Dryas (YD; c. 12.9 - 11.7 ka BP). During the YD the West Highlands Ice-cap covered the majority of the Scottish Highlands (c. 13,000 sq mi), which is thought to have affected accumulation rates beyond the ice-cap margins, resulting in a steep (c. 80%) easterly decline in precipitation and smaller ice-masses. We present multi-proxy data investigating YD glaciation in the Tweedsmuir Hills, Southern Uplands, Scotland (55°46' N, 03°34' W), suggesting conditions were less arid. The area forms the most easterly upland region in the Southern Uplands and south of the West Highlands Ice-cap, reaching an altitude of 840 m and covering c. 200 sq mi. Results of air-photo interpretation and field mapping, which utilised a morphostratigraphic approach, have demonstrated a more extensive glaciation than previously mapped. The reconstruction consists of two separate icefields covering an area c. 40 sq mi. and new 14C dates of basal contact organics place the ice-mass within the context of the YD but new Cosmogenic Nuclide Analysis (CNA) of bedrock and in situ boulders are inconclusive, implying limited erosion and limited resetting during the YD. Equilibrium Line Altitudes are calculated to have ranged from c. 419 - 634 m. Paleo-precipitation values were derived using two precipitation-temperature relationships and suggest slightly lower totals than YD ice-masses located on the west coast of the U.K. but do not support a significant easterly reduction in precipitation. Analysis of present-day (c. 30 year) meteorological data across the U.K. demonstrates a pronounced reduction in precipitation of c. 50% on the east coast. This disparity between present-day and glacier-based YD precipitation patterns is partly attributable to the methodology employed in glacier reconstruction and

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

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


    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.

  6. Latest Pleistocene to Holocene Evolution of the Baie de Port au Prince, Haiti

    Rios, J. K.; McHugh, C. M.; Seeber, L.; Blair, S.; Sorlien, C. C.


    slope. The late Pleistocene sediment is laminated and microfossils assemblages reveal sediment reworking and shallow water depths. Normal marine sedimentation resumed from ~14 ka BP to the present. The climate was characterized by wet or high discharge intervals noted by an influx of wood fragments and sediment most likely derived from land (>Si weight %, Al%, Fe% and Cu ppm). Wet periods were less frequent in the Holocene. The late Holocene trend is to dryer climate consistent with previous studies of the region. Evaporation is manifested by an increase in subhedral gypsum coated in calcite. Limited chirp profiles across the BPP suggest subsidence to the south. Ages from the base of the cores will verify this possibility. Coseismic 2010 uplift was documented in the southwestern part of the Leogane delta, an area that has no evidence of long-term uplift. Chirp profiles and multibeam bathymetry close to this uplift, show a deepening of the sea-floor suggestive of ongoing subsidence. More studies are needed to better understand the long-term patterns of subsidence and uplift in this region.

  7. Middle Holocene rapid environmental changes and human adaptation in Greece

    Lespez, Laurent; Glais, Arthur; Lopez-Saez, José-Antonio; Le Drezen, Yann; Tsirtsoni, Zoï; Davidson, Robert; Biree, Laetitia; Malamidou, Dimitra


    Numerous researchers discuss of the collapse of civilizations in response to abrupt climate change in the Mediterranean region. The period between 6500 and 5000 cal yr BP is one of the least studied episodes of rapid climate change at the end of the Late Neolithic. This period is characterized by a dramatic decline in settlement and a cultural break in the Balkans. High-resolution paleoenvironmental proxy data obtained in the Lower Angitis Valley enables an examination of the societal responses to rapid climatic change in Greece. Development of a lasting fluvio-lacustrine environment followed by enhanced fluvial activity is evident from 6000 cal yr BP. Paleoecological data show a succession of dry events at 5800-5700, 5450 and 5000-4900 cal yr BP. These events correspond to incursion of cold air masses to the eastern Mediterranean, confirming the climatic instability of the middle Holocene climate transition. Two periods with farming and pastural activities (6300-5600 and 5100-4700 cal BP) are evident. The intervening period is marked by environmental changes, but the continuous occurrence of anthropogenic taxa suggests the persistence of human activities despite the absence of archaeological evidence. The environmental factors alone were not sufficient to trigger the observed societal changes.

  8. Multi-Decadal to Millennial Scale Holocene Hydrologic Variation in the Southern Hemisphere Tropics of South America

    Ekdahl, E. J.; Fritz, S. C.; Baker, P. A.; Burns, S. J.; Coley, K.; Rigsby, C. A.


    Numerous sites in the Northern Hemisphere show multi-decadal to millennial scale climate variation during the Holocene, many of which have been correlated with changes in atmospheric radiocarbon production or with changes in North Atlantic oceanic circulation. The manifestation of such climate variability in the hydrology of the Southern Hemisphere tropics of South America is unclear, because of the limited number of records at suitably high resolution. In the Lake Titicaca drainage basin of Bolivia and Peru, high-resolution lacustrine records reveal the overall pattern of Holocene lake-level change, the influence of precessional forcing of the South American Summer Monsoon, and the effects of high-frequency climate variability in records of lake productivity and lake ecology. Precessional forcing of regional precipitation is evident in the Lake Titicaca basin as a massive (ca. 85 m) mid-Holocene decline in lake level beginning about 7800 cal yr BP and a subsequent rise in lake level after 4000 cal yr BP. Here we show that multi-decadal to millennial-scale climate variability, superimposed upon the envelope of change at orbital time scales, is similar in timing and pattern to the ice-rafted debris record of Holocene Bond events in the North Atlantic. A high-resolution carbon isotopic record from Lake Titicaca that spans the entire Holocene suggests that cold intervals of Holocene Bond events are periods of increased precipitation, thus indicating an anti-phasing of precipitation variation on the Altiplano relative to the Northern Hemisphere tropics. A similar pattern of variation is also evident in high-resolution (2-30 yr spacing) diatom and geochemical records that span the last 7000 yr from two smaller lakes, Lagos Umayo and Lagunillas, in the Lake Titicaca drainage basin.

  9. Fire history and climate variability during the Mid-Late Holocene in the Picos de Europa (Cantabrian Mountains, NW Spain), based on sedimentary sequence of Belbín

    Ruiz-Fernández, Jesús; Nieuwendam, Alexandre; Oliva, Marc; Lopes, Vera; Cruces, Anabela; Conceição Freitas, Maria; Janeiro, Ana; López-Sáez, José Antonio; García-Hernández, Cristina


    The environmental changes during the last millennia in the Mediterranian Region (including the Cantabrian Mountains in the NW part of the Iberian Peninsula) are partially related to fire activity, generated by early human societies for grazing purposes. Fire activity has mostly been reconstructed based on the analysis of pollen, spores and other macro- and microscopic organic remains, such as charcoal particles. However, new techniques (as the analysis of micro-scale frost weathering of quartz grains), can provide further information about the magnitude and intensity of fire as a landscape modeler. The purpose of this work was to analyze a sedimentary sequence collected from Belbín depression in the Western Massif of the Picos de Europa (Cantabrian Mountains, NW Spain) by using an innovative multi-proxy approach, in order to reconstruct the fire history in this area. The Picos de Europa Mountains constitute the highest and most extensive massif in the Cantabrian Mountains. This area encloses three different massifs separated by deep gorges carved by four rivers (Dobra, Cares, Duje and Deva). The Western Massif is the largest of the three units (137 km2). The Picos de Europa are essentially composed by Carboniferous limestones. This mountain area was heavily glaciated during the Last Glaciation, though the post-glacial environmental evolution is still poorly understood. Within the Western Massif, the mid-altitude area of Belbín is a karstic depression dammed by a lateral moraine generated by Enol Glacier during the Last Glaciation. Between 23 and 8 ky cal BP this depression was a lake that became progressively infilled with sediments, and nowadays it is occupied by grasslands (Ruiz-Fernández et al., 2016). In order to study the environmental changes during the Mid-Late Holocene in this massif, a 182 cm-long sequence was retrieved in the Belbín area. The core was subsampled every centimeter in the top most superficial 60 cm. The laboratory analyses were: 1

  10. Younger-Dryas cooling and sea-ice feedbacks were prominent features of the Pleistocene-Holocene transition in Arctic Alaska

    Gaglioti, Benjamin V.; Mann, Daniel H.; Wooller, Matthew J.; Jones, Benjamin M.; Wiles, Gregory C.; Groves, Pamela; Kunz, Michael L.; Baughman, Carson A.; Reanier, Richard E.


    Declining sea-ice extent is currently amplifying climate warming in the Arctic. Instrumental records at high latitudes are too short-term to provide sufficient historical context for these trends, so paleoclimate archives are needed to better understand the functioning of the sea ice-albedo feedback. Here we use the oxygen isotope values of wood cellulose in living and sub-fossil willow shrubs (δ18Owc) (Salix spp.) that have been radiocarbon-dated (14C) to produce a multi-millennial record of climatic change on Alaska's North Slope during the Pleistocene-Holocene transition (13,500-7500 calibrated 14C years before present; 13.5-7.5 ka). We first analyzed the spatial and temporal patterns of δ18Owc in living willows growing at upland sites and found that over the last 30 years δ18Owc values in individual growth rings correlate with local summer temperature and inter-annual variations in summer sea-ice extent. Deglacial δ18Owc values from 145 samples of subfossil willows clearly record the Allerød warm period (∼13.2 ka), the Younger Dryas cold period (12.9-11.7 ka), and the Holocene Thermal Maximum (11.7-9.0 ka). The magnitudes of isotopic changes over these rapid climate oscillations were ∼4.5‰, which is about 60% of the differences in δ18Owc between those willows growing during the last glacial period and today. Modeling of isotope-precipitation relationships based on Rayleigh distillation processes suggests that during the Younger Dryas these large shifts in δ18Owc values were caused by interactions between local temperature and changes in evaporative moisture sources, the latter controlled by sea ice extent in the Arctic Ocean and Bering Sea. Based on these results and on the effects that sea-ice have on climate today, we infer that ocean-derived feedbacks amplified temperature changes and enhanced precipitation in coastal regions of Arctic Alaska during warm times in the past. Today, isotope values in willows on the North Slope of Alaska are similar

  11. Younger-Dryas cooling and sea-ice feedbacks were prominent features of the Pleistocene-Holocene transition in Arctic Alaska

    Gaglioti, Benjamin V.; Mann, Daniel H.; Wooller, Matthew J.; Jones, Benjamin M.; Wiles, Gregory C.; Groves, Pamela; Kunz, Michael L.; Baughman, Carson; Reanier, Richard E.


    Declining sea-ice extent is currently amplifying climate warming in the Arctic. Instrumental records at high latitudes are too short-term to provide sufficient historical context for these trends, so paleoclimate archives are needed to better understand the functioning of the sea ice-albedo feedback. Here we use the oxygen isotope values of wood cellulose in living and sub-fossil willow shrubs (δ18Owc) (Salix spp.) that have been radiocarbon-dated (14C) to produce a multi-millennial record of climatic change on Alaska's North Slope during the Pleistocene-Holocene transition (13,500–7500 calibrated 14C years before present; 13.5–7.5 ka). We first analyzed the spatial and temporal patterns of δ18Owc in living willows growing at upland sites and found that over the last 30 years δ18Owc values in individual growth rings correlate with local summer temperature and inter-annual variations in summer sea-ice extent. Deglacial δ18Owcvalues from 145 samples of subfossil willows clearly record the Allerød warm period (∼13.2 ka), the Younger Dryas cold period (12.9–11.7 ka), and the Holocene Thermal Maximum (11.7–9.0 ka). The magnitudes of isotopic changes over these rapid climate oscillations were ∼4.5‰, which is about 60% of the differences in δ18Owc between those willows growing during the last glacial period and today. Modeling of isotope-precipitation relationships based on Rayleigh distillation processes suggests that during the Younger Dryas these large shifts in δ18Owc values were caused by interactions between local temperature and changes in evaporative moisture sources, the latter controlled by seaice extent in the Arctic Ocean and Bering Sea. Based on these results and on the effects that sea-ice have on climate today, we infer that ocean-derived feedbacks amplified temperature changes and enhanced precipitation in coastal regions of Arctic Alaska during warm times in the past. Today, isotope values in willows on the North Slope of Alaska are

  12. Holocene coastal paleoenvironmental record, Bay of Brest

    Fernane, Assia; Gandouin, Emmanuel; Goslin, Jérôme; Penaud, Aurélie; Van Vliet lanoë, Brigitte


    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

  13. A Satellite-Based Surface Radiation Climatology Derived by Combining Climate Data Records and Near-Real-Time Data

    Bodo Ahrens


    Full Text Available This study presents a method for adjusting long-term climate data records (CDRs for the integrated use with near-real-time data using the example of surface incoming solar irradiance (SIS. Recently, a 23-year long (1983–2005 continuous SIS CDR has been generated based on the visible channel (0.45–1 μm of the MVIRI radiometers onboard the geostationary Meteosat First Generation Platform. The CDR is available from the EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF. Here, it is assessed whether a homogeneous extension of the SIS CDR to the present is possible with operationally generated surface radiation data provided by CM SAF using the SEVIRI and GERB instruments onboard the Meteosat Second Generation satellites. Three extended CM SAF SIS CDR versions consisting of MVIRI-derived SIS (1983–2005 and three different SIS products derived from the SEVIRI and GERB instruments onboard the MSG satellites (2006 onwards were tested. A procedure to detect shift inhomogeneities in the extended data record (1983–present was applied that combines the Standard Normal Homogeneity Test (SNHT and a penalized maximal T-test with visual inspection. Shift detection was done by comparing the SIS time series with the ground stations mean, in accordance with statistical significance. Several stations of the Baseline Surface Radiation Network (BSRN and about 50 stations of the Global Energy Balance Archive (GEBA over Europe were used as the ground-based reference. The analysis indicates several breaks in the data record between 1987 and 1994 probably due to artefacts in the raw data and instrument failures. After 2005 the MVIRI radiometer was replaced by the narrow-band SEVIRI and the broadband GERB radiometers and a new retrieval algorithm was applied. This induces significant challenges for the homogenisation across the satellite generations. Homogenisation is performed by applying a mean-shift correction depending on the shift size of

  14. Critical role of climate change in plant selection and millet domestication in North China.

    Yang, Xiaoyan; Wu, Wenxiang; Perry, Linda; Ma, Zhikun; Bar-Yosef, Ofer; Cohen, David J; Zheng, Hongbo; Ge, Quansheng


    While North China is one of the earliest independent centers for cereal domestication in the world, the earliest stages of the long process of agricultural origins remain unclear. While only millets were eventually domesticated in early sedentary societies there, recent archaeobotanical evidence reported here indicates that grasses from the Paniceae (including millets) and Triticeae tribes were exploited together by foraging groups from the Last Glacial Maximum to the mid-Holocene. Here we explore how and why millets were selected for domestication while Triticeae were abandoned. We document the different exploitation and cultivation trajectories of the two tribes employing ancient starch data derived from nine archaeological sites dating from 25,000 to 5500 cal BP (LGM through mid-Holocene) in North China. With this diachronic overview, we can place the trajectories into the context of paleoclimatic reconstructions for this period. Entering the Holocene, climatic changes increased the yield stability, abundance, and availability of the wild progenitors of millets, with growing conditions increasingly favoring millets while becoming more unfavorable for grasses of the Triticeae tribe. We thus hypothesize that climate change played a critical role in the selection of millet species for domestication in North China, with early domestication evidenced by 8700 cal BP.

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

    Ahmed El-Guellab


    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.

  16. Understanding north-western Mediterranean climate variability: a multi-proxy and multi-sequence approach based on wavelet analysis.

    Azuara, Julien; Lebreton, Vincent; Jalali, Bassem; Sicre, Marie-Alexandrine; Sabatier, Pierre; Dezileau, Laurent; Peyron, Odile; Frigola, Jaime; Combourieu-Nebout, Nathalie


    Forcings and physical mechanisms underlying Holocene climate variability still remain poorly understood. Comparison of different paleoclimatic reconstructions using spectral analysis allows to investigate their common periodicities and helps to understand the causes of past climate changes. Wavelet analysis applied on several proxy time series from the Atlantic domain already revealed the first key-issues on the origin of Holocene climate variability. However the differences in duration, resolution and variance between the time-series are important issues for comparing paleoclimatic sequences in the frequency domain. This work compiles 7 paleoclimatic proxy records from 4 time-series from the north-western Mediterranean all ranging from 7000 to 1000 yrs cal BP: -pollen and clay mineral contents from the lagoonal sediment core PB06 recovered in southern France, -Sea Surface Temperatures (SST) derived from alkenones, concentration of terrestrial alkanes and their average chain length (ACL) from core KSGC-31_GolHo-1B recovered in the Gulf of Lion inner-shelf, - δ18O record from speleothems recovered in the Asiul Cave in north-western Spain, -grain size record from the deep basin sediment drift core MD99-2343 north of Minorca island. A comparison of their frequency content is proposed using wavelet analysis and cluster analysis of wavelet power spectra. Common cyclicities are assessed using cross-wavelet analysis. In addition, a new algorithm is used in order to propagate the age model errors within wavelet power spectra. Results are consistents with a non-stationnary Holocene climate variability. The Halstatt cycles (2000-2500 years) depicted in many proxies (ACL, errestrial alkanes and SSTs) demonstrate solar activity influence in the north-western Mediterranean climate. Cluster analysis shows that pollen and ACL proxies, both indicating changes in aridity, are clearly distinct from other proxies and share significant common periodicities around 1000 and 600 years

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

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


    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.

  18. Placing the Common Era in a Holocene context: millennial to centennial patterns and trends in the hydroclimate of North America over the past 2000 years

    Shuman, Bryan N.; Routson, Cody; McKay, Nicholas; Fritz, Sherilyn; Kaufman, Darrell; Kirby, Matthew E.; Nolan, Connor; Pederson, Gregory T.; St-Jacques, Jeannine-Marie


    A synthesis of 93 hydrologic records from across North and Central America, and adjacent tropical and Arctic islands, reveals centennial to millennial trends in the regional hydroclimates of the Common Era (CE; past 2000 years). The hydrological records derive from materials stored in lakes, bogs, caves, and ice from extant glaciers, which have the continuity through time to preserve low-frequency ( > 100 year) climate signals that may extend deeper into the Holocene. The most common pattern, represented in 46 (49 %) of the records, indicates that the centuries before 1000 CE were drier than the centuries since that time. Principal component analysis indicates that millennial-scale trends represent the dominant pattern of variance in the southwestern US, northeastern US, mid-continent, Pacific Northwest, Arctic, and tropics, although not all records within a region show the same direction of change. The Pacific Northwest and the southernmost tier of the tropical sites tended to dry toward present, as many other areas became wetter than before. In 22 records (24 %), the Medieval Climate Anomaly period (800-1300 CE) was drier than the Little Ice Age (1400-1900 CE), but in many cases the difference was part of the longer millennial-scale trend, and, in 25 records (27 %), the Medieval Climate Anomaly period represented a pluvial (wet) phase. Where quantitative records permitted a comparison, we found that centennial-scale fluctuations over the Common Era represented changes of 3-7 % in the modern interannual range of variability in precipitation, but the accumulation of these long-term trends over the entirety of the Holocene caused recent centuries to be significantly wetter, on average, than most of the past 11 000 years.

  19. Placing the Common Era in a Holocene context: Millennial to centennial patterns and trends in the hydroclimate of North America over the past 2000 years

    Shuman, Bryan; Routson, Cody C.; McKay, Nicholas P.; Fritz, Sherilyn; Kaufman, Darrell S.; Kirby, Matthew; Nolan, Connor; Pederson, Gregory T.; St. Jacques, Jeannine-Marie


    A synthesis of 93 hydrologic records from across North and Central America, and adjacent tropical and Arctic islands, reveals centennial to millennial trends in the regional hydroclimates of the Common Era (CE; past 2000 years). The hydrological records derive from materials stored in lakes, bogs, caves, and ice from extant glaciers, which have the continuity through time to preserve low-frequency ( > 100 year) climate signals that may extend deeper into the Holocene. The most common pattern, represented in 46 (49 %) of the records, indicates that the centuries before 1000 CE were drier than the centuries since that time. Principal component analysis indicates that millennial-scale trends represent the dominant pattern of variance in the southwestern US, northeastern US, mid-continent, Pacific Northwest, Arctic, and tropics, although not all records within a region show the same direction of change. The Pacific Northwest and the southernmost tier of the tropical sites tended to dry toward present, as many other areas became wetter than before. In 22 records (24 %), the Medieval Climate Anomaly period (800–1300 CE) was drier than the Little Ice Age (1400–1900 CE), but in many cases the difference was part of the longer millennial-scale trend, and, in 25 records (27 %), the Medieval Climate Anomaly period represented a pluvial (wet) phase. Where quantitative records permitted a comparison, we found that centennial-scale fluctuations over the Common Era represented changes of 3–7 % in the modern interannual range of variability in precipitation, but the accumulation of these long-term trends over the entirety of the Holocene caused recent centuries to be significantly wetter, on average, than most of the past 11 000 years.

  20. Holocene North Atlantic Overturning in an atmosphere-ocean-sea-ice model compared to proxy-based reconstructions

    Blaschek, M.; Renssen, H.; Kissel, C.; Thornalley, D.


    Climate and ocean circulation in the North Atlantic region changed over the course of the Holocene, partly because of disintegrating ice sheets and partly because of an orbital-induced insolation trend. In the Nordic Seas, this impact was accompanied by a rather small, but significant, amount of

  1. Contrasting trends in North Atlantic deep-water formation in the Labrador Sea and Nordic Seas during the Holocene

    Renssen, H.; Goosse, H.; Fichefet, T.


    The Holocene North Atlantic deep-water formation is studied in a 9,000-year long simulation with a coupled climate model of intermediate complexity, forced by changes in orbital forcing and atmospheric trace gas concentrations. During the experiment, deep-water formation in the Nordic Seas is

  2. Application of accelerator mass spectrometry on Environmental studies concerning ages of holocene fires in Central amazon forest

    Santos, G.M.; Gomes, P. R. S.; Anjos, R. M.; Lubian, J.; Cordeiro, R.C.; Turcq, B.; Sifeddine, A.; Di Tada, M.; Cresswell, R. G.; Fifield, L. K.


    The Accelerator Mass Spectrometry (AMS) technique was used to determine the radiocarbon age of Holocene fires in forests of the Amazon Region. Most of the ages were found to be within the 1000-1500 years range. These disturbances were probably caused by climatic anomalies, and they have modified the structure and dynamics of the region vegetation

  3. The Effects of Climate Variability on Phytoplankton Composition in the Equatorial Pacific Ocean using a Model and a Satellite-Derived Approach

    Rousseaux, C. S.; Gregg, W. W.


    Compared the interannual variation in diatoms, cyanobacteria, coccolithophores and chlorophytes from the NASA Ocean Biogeochemical Model with those derived from satellite data (Hirata et al. 2011) between 1998 and 2006 in the Equatorial Pacific. Using NOBM, La Ni a events were characterized by an increase in diatoms (correlation with MEI, r=-0.81, Pphytoplankton community in response to climate variability. However, satellite-derived phytoplankton groups were all negatively correlated with climate variability (r ranged from -0.39 for diatoms to -0.64 for coccolithophores, Pphytoplankton groups except diatoms than NOBM. However, the different responses of phytoplankton to intense interannual events in the Equatorial Pacific raises questions about the representation of phytoplankton dynamics in models and algorithms: is a phytoplankton community shift as in the model or an across-the-board change in abundances of all phytoplankton as in the satellite-derived approach.

  4. Global monsoons in the mid-Holocene and oceanic feedback

    Liu, Z.; Kutzbach, J. [Center for Climatic Research, University of Wisconsin-Madison, 1225 W. Dayton Street, Madison, WI 53706 (United States); Harrison, S.P. [Max Planck Institute for Biogeochemistry, P.O. Box 100164, 07701 Jena (Germany); Otto-Bliesner, B. [National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307 (United States)


    The response of the six major summer monsoon systems (the North American monsoon, the northern Africa monsoon, the Asia monsoon, the northern Australasian monsoon, the South America monsoon and the southern Africa monsoon) to mid-Holocene orbital forcing has been investigated using a coupled ocean-atmosphere general circulation model (FOAM), with the focus on the distinct roles of the direct insolation forcing and oceanic feedback. The simulation result is also found to compare well with the NCAR CSM. The direct effects of the change in insolation produce an enhancement of the Northern Hemisphere monsoons and a reduction of the Southern Hemisphere monsoons. Ocean feedbacks produce a further enhancement of the northern Africa monsoon and the North American monsoon. However, ocean feedbacks appear to weaken the Asia monsoon, although the overall effect (direct insolation forcing plus ocean feedback) remains a strengthened monsoon. The impact of ocean feedbacks on the South American and southern African monsoons is relatively small, and therefore these regions, especially the South America, experienced a reduced monsoon regime compared to present. However, there is a strong ocean feedback on the northern Australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region. A new synthesis is made for mid-Holocene paleoenvironmental records and is compared with the model simulations. Overall, model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations. (orig.)

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

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


    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.

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

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


    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.

  7. 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

    M. Berger


    Full Text Available In the present work the Arctic sea ice in the mid-Holocene and the pre-industrial climates are analysed and compared on the basis of climate-model results from the Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2 and phase 3 (PMIP3. The PMIP3 models generally simulate smaller and thinner sea-ice extents than the PMIP2 models both for the pre-industrial and the mid-Holocene climate. Further, the PMIP2 and PMIP3 models all simulate a smaller and thinner Arctic summer sea-ice cover in the mid-Holocene than in the pre-industrial control climate. The PMIP3 models also simulate thinner winter sea ice than the PMIP2 models. The winter sea-ice extent response, i.e. the difference between the mid-Holocene and the pre-industrial climate, varies among both PMIP2 and PMIP3 models. Approximately one half of the models simulate a decrease in winter sea-ice extent and one half simulates an increase. The model-mean summer sea-ice extent is 11 % (21 % smaller in the mid-Holocene than in the pre-industrial climate simulations in the PMIP2 (PMIP3. In accordance with the simple model of Thorndike (1992, the sea-ice thickness response to the insolation change from the pre-industrial to the mid-Holocene is stronger in models with thicker ice in the pre-industrial climate simulation. Further, the analyses show that climate models for which the Arctic sea-ice responses to increasing atmospheric CO2 concentrations are similar may simulate rather different sea-ice responses to the change in solar forcing between the mid-Holocene and the pre-industrial. For two specific models, which are analysed in detail, this difference is found to be associated with differences in the simulated cloud fractions in the summer Arctic; in the model with a larger cloud fraction the effect of insolation change is muted. A sub-set of the mid-Holocene simulations in the PMIP ensemble exhibit open water off the north-eastern coast of Greenland in summer, which can provide a fetch

  8. Holocene glaciation of the central Sierra Nevada, California

    Bowerman, Nicole D.; Clark, Douglas H.


    Sediment cores from two bedrock-dammed lakes in North Fork Big Pine Creek, Sierra Nevada, California, preserve the most detailed and complete record of Holocene glaciation yet recovered in the region. The lakes are fed by outwash from the Palisade Glacier, the largest (˜1.3 km 2) and presumably longest-lived glacier in the range, and capture essentially all of the rock flour it produces. Distinct late-Holocene (Matthes) and late-Pleistocene (Recess Peak) moraines lie between the modern glacier and the lakes. The lakes have therefore received continuous sedimentation from the basin since the retreat of the Tioga glacier (Last Glacial Maximum) and capture rock flour related to all post-LGM advances. A total of eight long cores (up to 5.5 m sediment depth) and one short surface sediment short core preserve a coherent record of fluctuating rock flour flux to the lakes through the Holocene. Age constraints on rock flour spikes in First and Second lakes based on 31 14C-dated macrofossils indicate Holocene glaciation began ˜3200 cal yr B P, followed by a possible glacier maximum at ˜2800 cal yr B P and four distinct glacier maxima at ˜2200, ˜1600, ˜700 and ˜250-170 cal yr. B.P., the most recent maximum being the largest. Reconstruction of the equilibrium-line altitudes (ELA) associated with each distinct advance recorded in the moraines (Recess Peak, Matthes, and modern) indicates ELA depressions (relative to modern) of ˜250 m and 90 m for Recess Peak and Matthes advances, respectively. These differences represent decreases in summer temperatures of 1.7-2.8 °C (Recess Peak) and 0.2-2° (Matthes), and increases in winter precipitation of 22-34 cm snow water equivalent (s.w.e.) (Recess Peak) and 3-26 cm s.w.e. (Matthes) compared to modern conditions. Although small, these changes are significant and similar to those noted in the Cascade Range to the north, and represent a significant departure from historical climate trends in the region.

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

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


    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").

  10. Holocene environmental change in the Albertine Rift : sediment-based evidence from Virunga volcanoes

    McGlynn, Gayle


    The Albertine Rift is one of the most important conservation areas in tropical Africa, with exceptionally high levels of biodiversity (including rare and endemic montane flora and fauna) and high human population densities. Environmental changes in the Albertine Rift during the Holocene have been influenced both by long-term climate change and by human activity, although establishing clear cause-effect relationships is often problematic - particularly as this area is known to have had a long ...

  11. Mega Scale Constructions and Art on Deep Gulf of Mexico Sonar Images Reveal Extensive Very Ancient Civilizations. Radical Holocene Climate Changes May Relate to Large Shifts in Gulf Surface Areas.

    Allen, R. L.


    Enhanced images from subsea sonar scanning of the Western Gulf of Mexico have revealed quite large temples (4 km. in length), ruins of cities (14 km. by 11 km.), pyramids, amphitheaters, and many other structures. Some human faces have beards implying much earlier migrations of Europeans or North Africans. Several temples have paleo astronomy alignments and similarities to Stone Henge. Southern and Southwestern USA satellite land images display characteristics in common with several subsea designs. Water depths indicate that many structures go back about as far as the late Ice Age and are likely to be over ten thousand years old. Chronologies of civilizations, especially in North America will need to be seriously reconsidered. Greatly rising sea levels and radical climate changes must have helped to destroy relatively advanced cultures. Suprisingly deep water depths of many architectures provide evidence for closures within the Gulf of Mexico to open seas. Closures and openings may have influenced ancient radical climate swings between warmth and cooling as Gulf contributions to water temperatures contracted or expanded. These creations of very old and surprisingly advanced civilizations need protection.

  12. The Mt Logan Holocene-late Wisconsinan isotope record

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


    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...

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

    Dupont, L. M.; Schefuß, E.


    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.

  14. Influence of cloud radiative effects on tropical circulation and hydrological cycle in the Mid-Holocene

    Izumi, Kenji; Kageyama, Masa; Bony, Sandrine; Braconnot, Pascale


    Paleoenvironmental data in particular, vegetation and lake-status at mid-Holocene (6,000 years ago) in Sahara shows that African monsoon extended much further north than today. Much of this change results from the changes in insolation driven by precession of the Earth's orbit, but in the state-of-the-art climate models, this factor alone is insufficient to explain the magnitude of the change. Previous studies showed that ocean and vegetation feedbacks affect the mid-Holocene monsoon and that the incorporation of these feedbacks in models improves the simulation of the hydrological cycle. However, it is not sufficient to reduce the discrepancies between simulated and reconstructed surface climates. In this study, we investigate the extent to which the simulation of cloud-radiative effects matters for the simulation of paleo-climatic changes, and past changes in the position and strength of the tropical rain belts in particular. This is done by running a general circulation model with and without clouds-radiation interactions using the IPSL model. The impact of cloud -radiative effects, which prevents the precipitation band to move north, on the tropical circulation and precipitation changes in mid-Holocene experiments will be discussed. Additionally, we will show the simulated effects of land cover change over Sahara.

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

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


    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.

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

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


    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

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

    Becker, Bernd; Kromer, Bernd; Trimborn, Peter


    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)

  18. Holocene vegetation, environment, and tephra recorded from Lake Pupuke, Auckland, New Zealand

    Horrocks, M.; Augustinus, P.; Deng, Y.; Shane, P.; Andersson, S.


    Lake Pupuke provides a near-complete, high-resolution environmental record of the Holocene from northern New Zealand. Tephra beds constrain the timing of a range of proxy indicators of environmental change, and demonstrate errors in a radiocarbon chronology. Agathis australis forest progressively increases from c. 7000 yr BP and, in conjunction with indicators of reduced biomass productivity, support a model of long-term climate change to drier conditions over the Holocene. However, except for Agathis, conifer-hardwood forest dominated mainly by Dacrydium cupressinum shows little change throughout the pre-human Holocene, suggesting environmental stability. Dramatic vegetation change occurred only within the last millennium as a result of large-scale Polynesian deforestation by fire. This happened a short time before the local eruption of c. 638 cal. yr BP Rangitoto Tephra. The identification of two eruptions of tephra from Rangitoto volcano has implications for future hazard planning in the Auckland region, because the volcanoes were previously considered single event centres. Changes in atmospheric circulation since the Late Glacial, possibly causing lower frequency of distal ashfall in Auckland during the Holocene, complicates the use of long-term records in hazard frequency assessment. (author). 39 refs., 7 figs., 2 tabs

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

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


    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

  20. Holocene RSL variation on southwestern Disko Island (Greenland)

    Emerich Souza, Priscila; Nielsen, Lars; Kroon, Aart

    We investigate RSL variations during the Holocene in Lakse Bugt by assessing topography, internal structure, and luminescence ages of fossil beach ridges and the modern beach. Lakse Bugt (Bay) lies on the southwestern coast of Disko Island in a mesotidal regime and a mild wave climate. Beach ridges...... are widespread over the marine terrace, extending from ~40 above sea level (m asl). The most recent ridges terminate either at the beach or at the coastal sandy cliffs ~8 m asl immediately behind the modern beach. These ridges are covered mainly by rounded boulders; the terrain surfaces of the swales have...... clearly been deformed by freezing and thawing processes, in contrast to those of the ridge crests, which are relatively smooth. High-resolution reflection GPR data and high resolution topographical data were collected along cross-shore transects using a shielded 250 MHz antennae system and a DGPS system...

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

    Dittrich Annett


    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. Prediction of spatial patterns of collapsed pipes in loess-derived soils in a temperate humid climate using logistic regression

    Verachtert, E.; Den Eeckhaut, M. Van; Poesen, J.; Govers, G.; Deckers, J.


    Soil piping (tunnel erosion) has been recognised as an important erosion process in collapsible loess-derived soils of temperate humid climates, which can cause collapse of the topsoil and formation of discontinuous gullies. Information about the spatial patterns of collapsed pipes and regional models describing these patterns is still limited. Therefore, this study aims at better understanding the factors controlling the spatial distribution and predicting pipe collapse. A dataset with parcels suffering from collapsed pipes (n = 560) and parcels without collapsed pipes was obtained through a regional survey in a 236 km² study area in the Flemish Ardennes (Belgium). Logistic regression was applied to find the best model describing the relationship between the presence/absence of a collapsed pipe and a set of independent explanatory variables (i.e. slope gradient, drainage area, distance-to-thalweg, curvature, aspect, soil type and lithology). Special attention was paid to the selection procedure of the grid cells without collapsed pipes. Apart from the first piping susceptibility map created by logistic regression modelling, a second map was made based on topographical thresholds of slope gradient and upslope drainage area. The logistic regression model allowed identification of the most important factors controlling pipe collapse. Pipes are much more likely to occur when a topographical threshold depending on both slope gradient and upslope area is exceeded in zones with a sufficient water supply (due to topographical convergence and/or the presence of a clay-rich lithology). On the other hand, the use of slope-area thresholds only results in reasonable predictions of piping susceptibility, with minimum information.

  3. Precipitation change and its effects on prehistorical human activities in the Gonghe Basin, Northeastern Qinghai-Tibet Plateau during middle and late Holocene

    Hou, Xiaoqing; Hou, Guangliang; Wang, Fangfang; Wang, Qingbo


    Northeastern Qinghai-tibet Plateau is considered as the ideal region for study of the climate change during the Holocene. Based on the meteorological data, the surface & fossil pollen data, this paper reconstructed the precipitation series of the region since middle Holocene with the GIS and MAT techniques, and discussed its relationship with prehistorical human activities. The results indicate that there are four major climatic phases: (I) Middle Holocene Humid Phase (6300-5000 aBP), with the primitive millet-farming first imported into the region; (II) Late Middle Holocene Sub-humid Phase (5000-3900 aBP), with the millet-farming spread rapidly within the region; (III) Late Holocene Fluctuation Phase (3900-2900 aBP), with the mean annual precipitation dropped down to lower than 240 mm, and a production mode-shift to a combination of cropping and husbandry; (IV) Late Holocene Stationary Phase (2900-0 aBP), with a precipitation alike the modern time, and a steady farming-pastoral economic pattern.

  4. Transient coupling relationships of the Holocene Australian monsoon

    McRobie, F. H.; Stemler, T.; Wyrwoll, K.-H.


    The northwest Australian summer monsoon owes a notable degree of its interannual variability to interactions with other regional monsoon systems. Therefore, changes in the nature of these relationships may contribute to variability in monsoon strength over longer time scales. Previous attempts to evaluate how proxy records from the Indonesian-Australian monsoon region correspond to other records from the Indian and East Asian monsoon regions, as well as to El Niño-related proxy records, have been qualitative, relying on 'curve-fitting' methods. Here, we seek a quantitative approach for identifying coupling relationships between paleoclimate proxy records, employing statistical techniques to compute the interdependence of two paleoclimate time series. We verify the use of complex networks to identify coupling relationships between modern climate indices. This method is then extended to a set of paleoclimate proxy records from the Asian, Australasian and South American regions spanning the past 9000 years. The resulting networks demonstrate the existence of coupling relationships between regional monsoon systems on millennial time scales, but also highlight the transient nature of teleconnections during this period. In the context of the northwest Australian summer monsoon, we recognise a shift in coupling relationships from strong interhemispheric links with East Asian and ITCZ-related proxy records in the mid-Holocene to significantly weaker coupling in the later Holocene. Although the identified links cannot explain the underlying physical processes leading to coupling between regional monsoon systems, this method provides a step towards understanding the role that changes in teleconnections play in millennial-to orbital-scale climate variability.

  5. Uniform climate development between the subtropical and subpolar Northeast Atlantic across marine isotope stage 11

    J. P. Helmke


    Full Text Available Proxy records from a core site off Northwest Africa were generated and compared with data from the subpolar Northeast Atlantic to unravel some main climatic features of interglacial marine isotope stage (MIS 11 (423–362 ka. The records point to an almost 25 kyr lasting full interglacial period during stage 11 that was preceded by a considerably long glacial-interglacial transition (Termination V. Off NW Africa, a strong reduction of terrestrially derived iron input is noted after 420 ka suggesting a pronounced increase in continental humidity and vegetation cover over Northwest Africa. In analogy to the Holocene climate of the region, this early wet phase of MIS 11 was likely associated with enhanced influence of the West African monsoon system on the Saharan-Sahel region which led to both a reduction in trade wind intensity off NW Africa and the formation of sapropel S11 in the Mediterranean Sea. A detailed comparison with data from the subpolar North Atlantic indicates a remarkable coherent timing for the main environmental changes in both regions giving evidence for strong interglacial climate connection between the low and high latitude North Atlantic. Although our records of MIS 11 compare well with the Holocene in terms of some major climate characteristics there are distinct differences in the temporal evolution of each peak warm interval. This suggests that care should be taken when using MIS 11 as analogue to forecast future interglacial conditions.

  6. Hydroclimate variability of High Arctic Svalbard during the Holocene inferred from hydrogen isotopes of leaf waxes

    Balascio, Nicholas L.; D'Andrea, William J.; Gjerde, Marthe; Bakke, Jostein


    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

  7. A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya.

    Colin J Courtney Mustaphi

    Full Text Available High-elevation ecosystems, such as those on Mount Kenya are undergoing significant changes, with accelerated glacial ice losses over the twentieth century creating new space for alpine plants to establish. These ecosystems respond rapidly to climatic variability and within decades of glacial retreat, Afroalpine pioneering taxa stabilize barren land and facilitate soil development, promoting complex patches of alpine vegetation. Periglacial lake sediment records can be used to examine centennial and millennial scale variations in alpine and montane vegetation compositions. Here we present a 5300-year composite pollen record from an alpine tarn (4370 m asl in the Hausberg Valley of Mount Kenya. Overall, the record shows little apparent variation in the pollen assemblage through time with abundant montane forest taxa derived and transported from mid elevations, notably high abundances of aerophilous Podocarpus pollen. Afroalpine taxa included Alchemilla, Helichrysum and Dendrosenecio-type, reflecting local vegetation cover. Pollen from the ericaceous zone was present throughout the record and Poaceae percentages were high, similar to other high elevation pollen records from eastern Africa. The Oblong Tarn record pollen assemblage composition and abundances of Podocarpus and Poaceae since the late Holocene (~4000 cal yr BP-present are similar to pollen records from mid-to-high elevation sites of nearby high mountains such as Mount Elgon and Kilimanjaro. These results suggest a significant amount of uphill pollen transport with only minor apparent variation in local taxa. Slight decreasing trends in alpine and ericaceous taxonomic groups show a long-term response to global late Holocene cooling and a step decrease in rate of change estimated from the pollen assemblages at 3100 cal yr BP in response to regional hydroclimatic variability. Changes in the principal component axis scores of the pollen assemblage were coherent with an independent mid

  8. Peat in the 'Niayes' of Senegal: depositional environment and Holocene evolution

    Lezine, A.-M.; Chateauneuf, J.-J. (Laboratoire de Geologie du Quaternaire, Marseille (France). Faculte des Sciences de Luminy)


    The 'Niayes' peat deposits north of Dakar, in Senegal, provide an unusual opportunity to study the continental and littoral detrital environment of the Holocene in West Africa. These organic deposits, that may attain a thickness of 10 m, accumulated in Late Pleistocene interdune basins whose extent and morphology depend closely upon the palaeohydrologic evolution of and the continental model for this zone during the Holocene. The present sub-Canarian climate of this region allows the preservation of an azonal vegetation of Guinean chorological affinity that is evidence of the wider development of now more southerly vegetation during the older Holocene. The nature of the sedimentary facies of these peatfields is closely related to the altitude of the basins of accumulation and the position of the fresh/salt water interface which conditions the recharge of the shallow aquifer. Thus, fresh-water and mangrove-swamp peats exist more or less closely associated according to the site. {sup 14}C age determination gives ages for these deposits between 12000 B.P. and the present, and detailed palynological studies have shown that there were two periods of climatic optimum, one between 9000 and 7000 B.P. and one between 4000 and 2000 B.P. The highly variable rates of sedimentation (0.2-12,5 mm/y for the continental zones and 2 mm/y for the mangrove swamps) are related to the paleotopography of the water-table or to very local fluctuations of sea level. The evolution of the vegetal biomass, evaluated both qualitatively (relative representation of the various vegetation levels) and quantitatively (concentration of pollen per gram of dry sediment) during the course of the Holocene enables reconstruction of the complete climatic and hydrologic history of the region up to dawn of the Present. 38 refs., 5 figs., 1 tab.

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

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


    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.

  10. Effects of global climate change on the US forest sector: response functions derived from a dynamic resource and market simulator.

    Bruce A. McCarl; Darius M. Adams; Ralph J. Alig; Diana Burton; Chi-Chung. Chen


    A multiperiod, regional, mathematical programming economic model is used to evaluate the potential economic impacts of global climatic change on the US forest sector. A wide range of scenarios for the biological response of forests to climate change are developed, ranging from small to large changes in forest growth rates. These scenarios are simulated in the economic...

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

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


    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...

  12. Lake Baikal isotope records of Holocene Central Asian precipitation

    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


    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.

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

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


    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

  14. Estimating carbon flux phenology with satellite-derived land surface phenology and climate drivers for different biomes: a synthesis of AmeriFlux observations.

    Wenquan Zhu

    Full Text Available Carbon Flux Phenology (CFP can affect the interannual variation in Net Ecosystem Exchange (NEE of carbon between terrestrial ecosystems and the atmosphere. In this study, we proposed a methodology to estimate CFP metrics with satellite-derived Land Surface Phenology (LSP metrics and climate drivers for 4 biomes (i.e., deciduous broadleaf forest, evergreen needleleaf forest, grasslands and croplands, using 159 site-years of NEE and climate data from 32 AmeriFlux sites and MODIS vegetation index time-series data. LSP metrics combined with optimal climate drivers can explain the variability in Start of Carbon Uptake (SCU by more than 70% and End of Carbon Uptake (ECU by more than 60%. The Root Mean Square Error (RMSE of the estimations was within 8.5 days for both SCU and ECU. The estimation performance for this methodology was primarily dependent on the optimal combination of the LSP retrieval methods, the explanatory climate drivers, the biome types, and the specific CFP metric. This methodology has a potential for allowing extrapolation of CFP metrics for biomes with a distinct and detectable seasonal cycle over large areas, based on synoptic multi-temporal optical satellite data and climate data.

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

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


    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.

  16. Locally Downscaled and Spatially Customizable Climate Data for Historical and Future Periods for North America.

    Wang, Tongli; Hamann, Andreas; Spittlehouse, Dave; Carroll, Carlos


    Large volumes of gridded climate data have become available in recent years including interpolated historical data from weather stations and future predictions from general circulation models. These datasets, however, are at various spatial resolutions that need to be converted to scales meaningful for applications such as climate change risk and impact assessments or sample-based ecological research. Extracting climate data for specific locations from large datasets is not a trivial task and typically requires advanced GIS and data management skills. In this study, we developed a software package, ClimateNA, that facilitates this task and provides a user-friendly interface suitable for resource managers and decision makers as well as scientists. The software locally downscales historical and future monthly climate data layers into scale-free point estimates of climate values for the entire North American continent. The software also calculates a large number of biologically relevant climate variables that are usually derived from daily weather data. ClimateNA covers 1) 104 years of historical data (1901-2014) in monthly, annual, decadal and 30-year time steps; 2) three paleoclimatic periods (Last Glacial Maximum, Mid Holocene and Last Millennium); 3) three future periods (2020s, 2050s and 2080s); and 4) annual time-series of model projections for 2011-2100. Multiple general circulation models (GCMs) were included for both paleo and future periods, and two representative concentration pathways (RCP4.5 and 8.5) were chosen for future climate data.

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

    J. H. C. Bosmans


    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.

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

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


    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.

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

    A. Francke


    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.

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

    Phartiyal, Binita


    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.

  1. Holocene coastal dune development and environmental changes in Helis area (NW Peloponnese, Greece



    Full Text Available The coastal area of western Peloponnese is characterized by Pleistocene and Holocene marine deposits. The study area shows the effects of different phases of coastal morphology evolution and is located along a wave-dominated and microtidal coast in the northwestern Peloponnese, 40 km southwest of Patras city. Three significant morphogenetic phases occurred during the Holocene. The first was radiometrically aged from 7000 to 3810 years BP, marking the end of the rapid postglacial transgression. The second, between 3810 and 1400 years BP, was characterized by high rates of sedimentation, possibly because of the proximity of the mouth of the Peneus River, and resulted in the accumulation of predominantly fluvial sediments. During the third and younger phase, from 1400 years BP to the present, landward migration of the coast and deposition of aeolian sands occurred. Archaeological and morphological evidences suggest that this last phase should be related to a low sea-level stand followed by a slow sea-level rise, up to the present-day position and by humid-temperate climate. The collected data concerning the Holocene coastal dune belts, suggest that main phases of dune development could be related to the effects of sea-level changes, climatic conditions, and in a subordinate way, to human activity.

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

    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.

  3. Temporal derivative of Total Solar Irradiance and anomalous Indian summer monsoon: An empirical evidence for a Sun–climate connection

    Agnihotri, R.; Dutta, K.; Soon, W.

    and Solar-Terrestrial Physics 73 (2011) 1980–1987 1985 a factor of 5–10 times larger than the top of the atmosphere forcing. Several other researchers have also carefully evaluated and highlighted the complex pathways and processes that may be involved... irradiance and the variance of ENSO variability. Hence, a meaningful study of Sun– climate relation must involve not only careful consideration of the solar forcing factors, but also the proper measures for the local and regional climatic responses...

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

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


    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.

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

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


    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