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Sample records for holocene climatic record

  1. Biomarker records of Holocene climate variations in Asian interior

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

    2012-12-01

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

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

    DEFF Research Database (Denmark)

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

    2007-01-01

    around 9.3 ka before present, and the Preboreal Oscillation during the first centuries of the Holocene. For each of these sections, we present a d18O anomaly curve and a common accumulation signal that represents regional changes in the accumulation rate over the Greenland ice cap....... and accumulation anomalies that are common to the three cores in the Early Holocene (7.9–11.7 ka before present). Three time periods with significant and synchronous anomalies in the d18O and accumulation signals stand out: the well-known 8.2 ka event, an event of shorter duration but of almost similar amplitude...

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

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

    2003-01-01

    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.

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

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

    2016-04-01

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

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

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

    2012-04-01

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

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

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

    2018-04-01

    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.

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

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    N. Combourieu-Nebout

    2013-09-01

    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

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

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

    2014-12-01

    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.

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

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

    2006-01-01

      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...

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

    International Nuclear Information System (INIS)

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

    1991-01-01

    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

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

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

    2012-12-01

    Sediments contained in glacier-fed lakes and bogs provide continuous high-resolution records of glacial activity, and preserve multiproxy evidence of Holocene climate change. Tropical glacier fluctuations offer critical insight on regional paleoclimatic trends and controls, however, continuous sediment records of past tropical climates are limited. Recent cosmogenic 10Be surface exposure ages of moraine sequences in the Cordillera Vilcabamba of southern Peru (13°20'S latitude) reveal a glacial culmination during the early Holocene and a less extensive glaciation coincident with the Little Ice Age of the Northern Hemisphere. Here we supplement the existing 10Be moraine chronology with the first continuous records of multiproxy climate data in this mountain range from sediment cores recovered from bogs in direct stratigraphic contact with 10Be-dated moraines. Radiocarbon-dated sedimentological changes in a 2-meter long bog core reveal that the Holocene is characterized by alternating inorganic and organic-rich laminae, suggesting high-frequency climatic variability. Carbon measurements, bulk density, and bulk sedimentation rates are used to derive a record of clastic sediment flux that serves as a proxy indicator of former glacier activity. Preliminary analyses of the bog core reveal approximately 70 diatom taxa that indicate both rheophilic and lentic environments. Initial results show a general decrease in magnetic susceptibility and clastic flux throughout the early to mid-Holocene, which suggests an interval of deglaciation. An episode of high clastic flux from 3.8 to 2.0 ka may reflect a late Holocene glacial readvance. Volcanic glass fragments and an anomalous peak in magnetic susceptibility may correspond to the historical 1600 AD eruption of Huaynaputina. Ten new bog and lake sediment cores were collected during the 2012 field expedition and analytical measurements are underway. Ongoing efforts are focused on analyzing diatom assemblage data, developing

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

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

    2016-05-01

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

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

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    Tingping eOuyang

    2016-05-01

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

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

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

    2010-11-19

    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

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

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    Zalat Abdelfattah A.

    2017-06-01

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

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

    DEFF Research Database (Denmark)

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

    2006-01-01

      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...

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

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

    2014-02-01

    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.

  18. 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)

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

    2018-01-01

    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

  19. 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

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    M. J. Ramos-Román

    2018-01-01

    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

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

    International Nuclear Information System (INIS)

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

    1994-01-01

    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

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

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

    2015-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-05-01

    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.

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

    Science.gov (United States)

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

    2017-04-01

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

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

    Science.gov (United States)

    Menviel, L.; Joos, F.

    2012-03-01

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

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

    Science.gov (United States)

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

    2017-12-01

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

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

    Science.gov (United States)

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

    2012-12-01

    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

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

    Science.gov (United States)

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

    2015-04-01

    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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-05-20

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

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

    Science.gov (United States)

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

    2003-04-01

    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

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

    Science.gov (United States)

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

    2014-12-23

    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.

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

    DEFF Research Database (Denmark)

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

    2008-01-01

    , 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...

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

    Science.gov (United States)

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

    2015-04-01

    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

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

    Science.gov (United States)

    Zhao, Wenwei; Zhao, Yan; Qin, Feng

    2017-10-01

    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.

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

    Directory of Open Access Journals (Sweden)

    1995-01-01

    relacionado con el “Optimum Medieval”. El registro de polvo del Huascarán, de nivel constante durante los 3 000 años, fue interrumpido por un evento de alta concentración de polvo entre 2 000 y 1 800 años BP (0-200 A.D. centrado en los años 1 900s BP (100 A.D.. Picos menos marcados se observan de 1 400 a 1 600 años BP (400 a 600 A.D. y de 1300 a 1030 años BP (700 a 960 A.D. El análisis del polvo asociado a este evento indica un material acumulado por los vientos de misma composición que la roca que constituyen la Cordillera Blanca (granodiórita. Los más recientes picos son parcialmente sincrónicos con el mayor evento de 400 a 620 A.D. encontrado en Quelccaya, lo que sugiere que este evento fue muy extenso. El más reciente evento de alta concentración de polvo registrado en Quelccaya y fechado de 830 a 960 A.D. permite observar bajas concentraciones en el Huascarán éste podría ser un argumento más para relacionar el principio de la emisión de polvo en Quelccaya con las actividades agrícolas en la cuenca del Titicaca (Thompson et al., 1988. A 1 500-year history of climatic and environmental variations from the Quelccaya ice cap (13°56’S, 70°50’W, 5 670 m a.s.l. is compared to a similar 3 000-year ice core record from the col of Huascarán (9°06’S, 77°36’W, 6 048 m a.s.l.. The parameters which are presented are oxygen isotopic ratios ( 18O, considered to be indicative of temperature, insoluble dust, and (for Huascarán only nitrate concentrations (NO3- which is indicative of vegetation fluctuations in the Amazon rainforest. The Huascarán  18O and NO3- profiles for the most recent 3 000 years show that there has been a general decrease in temperature along with a decrease in biological activity in the Amazon Basin, with the lowest values occurring during the “Little Ice Age” (LIA, 200 to 500 yrs BP. This was followed by an abrupt change in  18O, which increased to the levels of 3 000 years ago. This abrupt warming has

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

    Science.gov (United States)

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

    2017-04-01

    evolves from more circular shapes (e≈0.590) to a more elliptical ones (e≈0.598), that is while the orbital system is slowly exploding or bursting outward. Since at this timescale the PMC eccentricity variation is relatively small (e=0.594±0.004), the physical origin of the astronomical 2318 yr cycle is better identified and distinguished from faster orbital oscillations by the times it takes the PMC to make pericycles and epicycles around the Sun and the times it takes to move from minimum to maximum distance from the Sun within those arcs. These particular proxies reveal a macroscopic 2318 yr period oscillation, together with other three stable outer planet orbital resonances with periods of 159, 171 and 185 yr. This 2318 yr oscillation is found to be spectrally coherent with the Δ14C Holocene record with a statistical confidence above 95%, as determined by spectral analysis and cross wavelet and wavelet coherence analysis. At the Hallstatt time scale, maxima of the radionucleotide production occurred when, within each pericycle-apocycle orbital arc, the time required by the PMC to move from the minimum to the maximum distance from the Sun varies from about 8 to 16 years while the time required by the same to move from the maximum to the minimum distance from the Sun varies from about 7 to 14 years, and viceversa. Thus, we found that a fast expansion of the Sun-PMC orbit followed by a slow contraction appears to prevent cosmic rays to enter within the system inner region while a slow expansion followed by a fast contraction favors it. Similarly, the same dynamics could modulate the amount of interplanetary/cosmic dust falling on Earth. Indeed, many other stable orbital resonance frequencies (e.g. at periods of 20 yr, 45 yr, 60 yr, 85 yr, 159-171-185 yr, etc.) are found in radionucleotide, solar, aurora and climate records, as determined in the scientific literature. Thus, the result supports a planetary theory of solar and/or climate variation that has recently

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

    Science.gov (United States)

    Fischer, H.

    2017-12-01

    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

  17. 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

    NARCIS (Netherlands)

    Goudeau, M.S.

    2014-01-01

    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

  18. 8000-year monsoonal record from Himalaya revealing reinforcement of tropical and global climate systems since mid-Holocene.

    Science.gov (United States)

    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

    2017-11-06

    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.

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

    Science.gov (United States)

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

    2018-04-01

    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.

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

    NARCIS (Netherlands)

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

    2014-01-01

    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

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

    Science.gov (United States)

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

    2017-04-01

    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.

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

    Science.gov (United States)

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

    2011-12-01

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

    Science.gov (United States)

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

    2017-12-01

    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

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

    Science.gov (United States)

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

    2016-04-01

    ., 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.

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

    Science.gov (United States)

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

    2017-04-01

    South Africa is located at a critical transition zone between subtropical and warm-temperate climate zones influenced by the Indian and Atlantic oceans. Presently, the seasonal changes of atmospheric and oceanic systems induce a pronounced rainfall seasonality comprised of two different rainfall zones over South Africa. How did this seasonality develop during the Holocene? To obtain a better understanding of how South African climates have evolved during the Holocene, we conduct a comprehensive spatial-temporal approach including pollen and dinoflagellate cyst records from marine sediment samples retrieved from the Namaqualand mudbelt, a Holocene terrigenous mud deposit on the shelf of western South Africa. The representation of different vegetation communities in western South Africa is assessed through pollen analysis of surface sediments. This approach allows for climate reconstructions of the summer rainfall zone (SRZ) using Group 1 (Poaceae, Cyperaceae, Phragmites-type and Typha) and winter rainfall zone (WRZ) using Group 2 (Restionaceae, Ericaceae, Anthospermum, Stoebe/Elytropappus-type, Cliffortia, Passerina, Artemisia-type and Pentzia-type) from a single marine archive. The fossil pollen data from gravity core GeoB8331-4 indicate contrasting climate patterns in the SRZ and WRZ especially during the early and middle Holocene. The rainfall amount in the SRZ is dominated by insolation forcing, while in the WRZ it is mainly attributed to the latitudinal position of the southern westerlies. Dinoflagellate cyst data show significantly different oceanographic conditions associated with climate changes on land. High percentages of autotrophic taxa like Operculodinium centrocarpum and Spiniferites spp. indicate warm and stratified conditions during the early Holocene, suggesting reduced upwelling. In contrast, the middle Holocene is characterized by a strong increase in heterotrophic taxa in particular Lejeunecysta paratenella and Echinidinium spp., indicating cool

  6. A pollen-based record of late glacial-Holocene climatic variability in the southern lake district, Chile

    NARCIS (Netherlands)

    Vargas-Ramirez, L.; Roche, E.; Gerrienne, P.; Hooghiemstra, H.

    2008-01-01

    A pollen record from Puyehue area (40°S; 72°W) in the southern Lake District, Chile, indicates that prior to 13,410 14C yr BP (ca. 16,500-15,200 cal yr BP), cold resistant and hygrophilous vegetation, particularly Nothofagus forest and myricaceous vegetation, covered the area. From ca. 15,000 cal yr

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

    Directory of Open Access Journals (Sweden)

    Eun Hee Lee

    2014-12-01

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

  8. Holocene vegetation and climate change recorded in alpine bog sediments from the Borreguiles de la Virgen, Sierra Nevada, southern Spain

    Science.gov (United States)

    Jiménez-Moreno, Gonzalo; Anderson, R. Scott

    2012-01-01

    High-resolution pollen and magnetic susceptibility (MS) analyses have been carried out on a sediment core taken from a high-elevation alpine bog area located in Sierra Nevada, southern Spain. The earliest part of the record, from 8200 to about 7000 cal yr BP, is characterized by the highest abundance of arboreal pollen and Pediastrum, indicating the warmest and wettest conditions in the area at that time. The pollen record shows a progressive aridification since 7000 cal yr BP that occurred in two steps, first shown by a decrease in Pinus, replaced by Poaceae from 7000 to 4600 cal yr BP and then by Cyperaceae, Artemisia and Amaranthaceae from 4600 to 1200 cal yr BP. Pediastrum also decreased progressively and totally disappeared at ca. 3000 yr ago. The progressive aridification is punctuated by periodically enhanced drought at ca. 6500, 5200 and 4000 cal yr BP that coincide in timing and duration with well-known dry events in the Mediterranean and other areas. Since 1200 cal yr BP, several changes are observed in the vegetation that probably indicate the high-impact of humans in the Sierra Nevada, with pasturing leading to nutrient enrichment and eutrophication of the bog, Pinus reforestation and Olea cultivation at lower elevations.

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

    Science.gov (United States)

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

    2018-05-01

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

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

    Science.gov (United States)

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

    2014-12-01

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

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

    Science.gov (United States)

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

    2009-10-01

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

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

    Science.gov (United States)

    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

    2018-01-01

    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.

  13. Patagonian and southern South Atlantic view of Holocene climate

    Science.gov (United States)

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

    2016-06-01

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

  14. 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

    Directory of Open Access Journals (Sweden)

    GABRIELLI T. GADENS-MARCON

    2014-09-01

    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.

  15. Holocene coastal paleoenvironmental record, Bay of Brest

    Science.gov (United States)

    Fernane, Assia; Gandouin, Emmanuel; Goslin, Jérôme; Penaud, Aurélie; Van Vliet lanoë, Brigitte

    2013-04-01

    Coastal areas are sensitive environments regarding the risk of submersion and the impact on biodiversity induced by salinity changes. These areas thus provide good palaeocecological archives to monitor palaeo sea level changes and the associated adaptation of different biological communities. The north-western coast of France has poorly been investigated regarding its Holocene palaeoecological signatures (Morzadec-Kerfourn, 1974; Naughton et al., 2007). Chironomids have been recognized to be an efficient tool for palaeoclimate and palaeosalinity reconstructions in lakes (Brooks, 2006), and more recently in river floodplains (Gandouin et al, 2006). In this study, environmental changes related to both climate processes and human disturbances, were reconstructed over the last 5000 years, based on pollen and chironomid assemblages from two coastal cores retrieved at Pors Milin (Brittany, NW France). The sedimentary sequences consist of terrestrial peaty layers interdigited with marine clastic deposits. The study area is composed by a sandy beach, truncating the peat, limited by a high sandy bar, and a back marsh developed at + 4 m NGF. Pollen and chironomid results reveal that anthropogenic factors would mainly control environmental changes that occurred in this sector. The disappearance of many chironomid taxa (inhabitants of main river channel) and the dramatic fall in diversity may have been induced by the development of the Merovingian forest clearance at Pors Milin. Indeed, we suggest that the development of agriculture, the river embankment and the draining of wetlands may explain the chironomid habitat loss and the subsequent fall of biodiversity. This change in faunal assemblages occurred synchronously with a decrease in the "arborean / non arborean" pollen ratio reflecting the land opening of the watershed. Several nitrophilous and anthropogenic pollen taxa reinforce our hypothesis concerning the development of agricultural and livestock farming activities at

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

    Science.gov (United States)

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

    2017-04-01

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

  17. Holocene environmental changes and climate development in Greenland

    International Nuclear Information System (INIS)

    Engels, Stefan; Helmens, Karin

    2010-12-01

    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

  18. Holocene environmental changes and climate development in Greenland

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-12-15

    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

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

    OpenAIRE

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

    2015-01-01

    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...

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

    NARCIS (Netherlands)

    Weber, S.L.; Oerlemans, J.

    2003-01-01

    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

  1. Lake Baikal isotope records of Holocene Central Asian precipitation

    Science.gov (United States)

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

    2018-06-01

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

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

    Science.gov (United States)

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

    2017-04-01

    Holocene climate variability has been well defined in the North Atlantic (Walker et al., 2012), but the global extent of this climate change stratigraphy is debatable. If the North Atlantic serves as a global template for Holocene climate, then New Zealand (NZ) is ideally positioned to test this assertion, as it is distal from the northern drivers. Additionally, it is one of the few landmasses in the Southern Hemisphere that is influenced by both sub-tropical and extra-tropical climatic regimes, which may be more important controls in the southern mid-latitudes. Although much work has been done to characterise the Holocene in NZ using pollen, most of these records lack the resolution or sensitivity to determine whether abrupt or short-lived events occurred. The NZ-INTIMATE climate event stratigraphy lacks a type section for the Holocene (Alloway et al., 2007). Records from northern NZ typically show little change, other than a possible early Holocene warming. Here, we present a combined pollen and chironomid temperature reconstruction from Lake Pupuke (northern NZ), the first of its kind in NZ that covers the entire Holocene. By comparing mean annual temperatures reconstructed from fossil pollen and mean summer temperatures inferred from chironomid remains, we can assess changes in seasonality. Mean summer temperature was reconstructed from the chironomid record using a weighted averaging partial least squares (WA-PLS) model (n comp = 2, r2booth = 0.77, RMSEP = 1.4°C) developed from an expanded version of Dieffenbacher-Krall et al. (2007)'s chironomid training set. Preliminary results show evidence for cool summers during the early Holocene as well as around the period of the Little Ice Age as defined in the North Atlantic region. These and other climate patterns determined from the Pupuke chironomid and pollen records will be compared with other evidence from northern New Zealand and with the North Atlantic record of Holocene climate variability. References

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

    Science.gov (United States)

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

    2018-02-01

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

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

    Science.gov (United States)

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

    2014-12-01

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

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

    Science.gov (United States)

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

    2002-01-01

    Records of Holocene vegetation and climate change at low elevations (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.

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

    Indian Academy of Sciences (India)

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

  7. Climate Record Books

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Climate Record Books contain daily, monthly, seasonal, and annual averages, extremes, or occurrences. Most data are sequential by period of record 1871-1910,...

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

    OpenAIRE

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

    2015-01-01

    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...

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

    Science.gov (United States)

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

    2008-12-01

    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

  10. Holocene seasonal variability inferred from multiple proxy records from Crevice Lake, Yellowstone National Park, USA

    Science.gov (United States)

    Whitlock, Cathy; Dean, Walter E.; Fritz, Sherilyn C.; Stevens, Lora R.; Stone, Jeffery R.; Power, Mitchell J.; Rosenbaum, Joseph R.; Pierce, Kenneth L.; Bracht-Flyr, Brandi B.

    2012-01-01

    A 9400-yr-old record from Crevice Lake, a semi-closed alkaline lake in northern Yellowstone National Park, was analyzed for pollen, charcoal, geochemistry, mineralogy, diatoms, and stable isotopes to develop a nuanced understanding of Holocene environmental history in a region of northern Rocky Mountains that receives both summer and winter precipitation. The limited surface area, conical bathymetry, and deep water (> 31 m) of Crevice Lake create oxygen-deficient conditions in the hypolimnion and preserve annually laminated sediment (varves) for much of the record. Pollen data indicate that the watershed supported a closed Pinus-dominated forest and low fire frequency prior to 8200 cal yr BP, followed by open parkland until 2600 cal yr BP, and open mixed-conifer forest thereafter. Fire activity shifted from infrequent stand-replacing fires initially to frequent surface fires in the middle Holocene and stand-replacing events in recent centuries. Low values of δ18O suggest high winter precipitation in the early Holocene, followed by steadily drier conditions after 8500 cal yr BP. Carbonate-rich sediments before 5000 cal yr BP imply warmer summer conditions than after 5000 cal yr BP. High values of molybdenum (Mo), uranium (U), and sulfur (S) indicate anoxic bottom-waters before 8000 cal yr BP, between 4400 and 3900 cal yr BP, and after 2400 cal yr BP. The diatom record indicates extensive water-column mixing in spring and early summer through much of the Holocene, but a period between 2200 and 800 cal yr BP had strong summer stratification, phosphate limitation, and oxygen-deficient bottom waters. Together, the proxy data suggest wet winters, protracted springs, and warm effectively wet summers in the early Holocene and less snowpack, cool springs, warm dry summers in the middle Holocene. In the late Holocene, the region and lake experienced extreme changes in winter, spring, and summer conditions, with particularly short springs and dry summers and winters during

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

    Science.gov (United States)

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

    2010-12-01

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

  12. North Atlantic-Fennoscandian Holocene climate trends and mechanisms

    NARCIS (Netherlands)

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

    2016-01-01

    To investigate the mechanisms behind Holocene regional climate trends from north of 58°N in the North Atlantic-Fennoscandian region Principal Component Analysis (PCA) was performed and a temperature anomaly stack produced from 81 proxy derived summer temperature time series from 74 sites. The PC

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

    Science.gov (United States)

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

    2018-02-01

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

  14. Holocene vegetation, environment, and tephra recorded from Lake Pupuke, Auckland, New Zealand

    International Nuclear Information System (INIS)

    Horrocks, M.; Augustinus, P.; Deng, Y.; Shane, P.; Andersson, S.

    2005-01-01

    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

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

    Science.gov (United States)

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

    2012-12-01

    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

  16. 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

    DEFF Research Database (Denmark)

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

    2009-01-01

    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....

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

    Science.gov (United States)

    Cui, Jianxin; Zhou, Shangzhe; Chang, Hong

    2009-02-01

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

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

    Directory of Open Access Journals (Sweden)

    G. Siani

    2013-02-01

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

  19. 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)

    NARCIS (Netherlands)

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

    2011-01-01

    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

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

    Science.gov (United States)

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

    2016-01-01

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

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

    Science.gov (United States)

    Grossman, Michael J.

    2001-07-01

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

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

    Science.gov (United States)

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

    2015-10-01

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

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

    International Nuclear Information System (INIS)

    Saarse, Leili; Rajamaee, Raivo

    1997-01-01

    The development of forests on the Haanja Heights has been controlled by external factors, including climate, soils, hydrology, and human impact. The sediment sequence from Lake Kirikumaee, which covers about 12 000 years, records the vegetation history throughout the Late Glacial and Holocene. In the Alleroed, woodland tundra with sparse birch and willow was established. Grass-shrub tundra in the Younger Dryas was replaced by birch forest in the Pre-Boreal. During the Holocene two major shifts in vegetation dynamics occurred: the first about 8500 BP with a sharp decline in Betula-Pinus forest and development of broad-leaved forest, and the second about 3500 BP, with a decline in broad-leaved forest and regeneration of Pinus-Betula forest with a high share of Picea. The climate modelling, based on pollen record and lake-level changes, suggest cold, severe climate with low precipitation values in the early Pre-Boreal. Between 9500-8500 BP the climate was rather stable. The lake level first rose, then stabilized, and finally dropped. The sharp climate amelioration in the late Boreal together with the humidity increase resulted in a lake-level rise. The decreased precipitation and rather high summer temperatures, increased evapotranspiration, and reduced water balance are characteristic of the Sub-Boreal. Since 3500 BP, the climate deteriorated and mixed coniferous forest started to dominate. Several small climatic fluctuations, including the Little Ice Age cooling, have been traced by modelling. (author)

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

    Directory of Open Access Journals (Sweden)

    K. Antonsson

    2008-10-01

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

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

    Science.gov (United States)

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

    2013-01-01

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

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

    Science.gov (United States)

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

    2010-07-01

    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.

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

    Science.gov (United States)

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

    2007-12-01

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

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

    Science.gov (United States)

    Marquer, Laurent; Gaillard, Marie-José; Sugita, Shinya; Poska, Anneli; Trondman, Anna-Kari; Mazier, Florence; Nielsen, Anne Birgitte; Fyfe, Ralph M.; Jönsson, Anna Maria; Smith, Benjamin; Kaplan, Jed O.; Alenius, Teija; Birks, H. John B.; Bjune, Anne E.; Christiansen, Jörg; Dodson, John; Edwards, Kevin J.; Giesecke, Thomas; Herzschuh, Ulrike; Kangur, Mihkel; Koff, Tiiu; Latałowa, Małgorzata; Lechterbeck, Jutta; Olofsson, Jörgen; Seppä, Heikki

    2017-09-01

    Early agriculture can be detected in palaeovegetation records, but quantification of the relative importance of climate and land use in influencing regional vegetation composition since the onset of agriculture is a topic that is rarely addressed. We present a novel approach that combines pollen-based REVEALS estimates of plant cover with climate, anthropogenic land-cover and dynamic vegetation modelling results. This is used to quantify the relative impacts of land use and climate on Holocene vegetation at a sub-continental scale, i.e. northern and western Europe north of the Alps. We use redundancy analysis and variation partitioning to quantify the percentage of variation in vegetation composition explained by the climate and land-use variables, and Monte Carlo permutation tests to assess the statistical significance of each variable. We further use a similarity index to combine pollen-based REVEALS estimates with climate-driven dynamic vegetation modelling results. The overall results indicate that climate is the major driver of vegetation when the Holocene is considered as a whole and at the sub-continental scale, although land use is important regionally. Four critical phases of land-use effects on vegetation are identified. The first phase (from 7000 to 6500 BP) corresponds to the early impacts on vegetation of farming and Neolithic forest clearance and to the dominance of climate as a driver of vegetation change. During the second phase (from 4500 to 4000 BP), land use becomes a major control of vegetation. Climate is still the principal driver, although its influence decreases gradually. The third phase (from 2000 to 1500 BP) is characterised by the continued role of climate on vegetation as a consequence of late-Holocene climate shifts and specific climate events that influence vegetation as well as land use. The last phase (from 500 to 350 BP) shows an acceleration of vegetation changes, in particular during the last century, caused by new farming

  9. The Mt Logan Holocene-late Wisconsinan isotope record

    DEFF Research Database (Denmark)

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

    2008-01-01

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

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

    Science.gov (United States)

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

    2017-12-01

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

  11. Major hydrologic shifts in northwest Florida during the Holocene from a lacustrine sediment record

    Science.gov (United States)

    Rodysill, J. R.; Donnelly, J. P.

    2011-12-01

    Recent climate extremes have threatened water resource availability and destroyed homes and infrastructure along the heavily populated northern Gulf of Mexico coast. Water resources in Northwest Florida, in particular, suffer from declining aquifer levels and salt water intrusion despite the presence of extensive river and aquifer systems. Intensive water resource management has been necessary to meet water supply demands during recent droughts. Advanced preparedness for abrupt climate events requires the ability to anticipate when hydrologic extremes are likely to occur; however, the long-term history of hydrologic extremes is not well known, and the instrumental record is too short to resolve longer-term hydrologic variability. Reconstructing the pre-instrumental hydrologic history is essential to building our understanding of the timing of and the driving forces behind wet and dry extremes. Here we present a new record of paleohydrology in northwest Florida based upon variations in sediment lithology and geochemistry from Rattlesnake Lake. We see evidence for both brief and long-lived changes in the lake environment during the Holocene. We compare our record to published pollen-based reconstructions of paleohydrology to examine the spatial and temporal patterns of paleohydrologic extremes across the northern Gulf of Mexico region during the Holocene.

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

    Science.gov (United States)

    Mayle, Francis E; Power, Mitchell J

    2008-05-27

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

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

    Science.gov (United States)

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

    2015-09-01

    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.

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

    Science.gov (United States)

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

    2015-12-01

    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.

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

    Science.gov (United States)

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

    2018-05-01

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

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

    Science.gov (United States)

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

    2017-12-01

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

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

    Science.gov (United States)

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

    2009-09-01

    The role of the tropics in triggering, transmitting, and amplifying interhemispheric climate signals remains a key debate in paleoclimatology. Tropical glacier fluctuations provide important insight on regional paleoclimatic trends and forcings, but robust chronologies are scarce. Here, we report precise moraine ages from the Cordillera Vilcabamba (13°20‧S) of southern Peru that indicate prominent glacial events and associated climatic shifts in the outer tropics during the early Holocene and late in the “Little Ice Age” period. Our glacier chronologies differ from the New Zealand record but are broadly correlative with well-dated glacial records in Europe, suggesting climate linkages between the tropics and the North Atlantic region.

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

    Science.gov (United States)

    Madole, Richard F.

    2012-09-01

    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.

  19. A review on Holocene climate changes in Indian subcontinent

    Digital Repository Service at National Institute of Oceanography (India)

    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...

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

    Science.gov (United States)

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

    2016-12-01

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

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

    Science.gov (United States)

    Kühl, Norbert; Moschen, Robert; Wagner, Stefanie

    2010-05-01

    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.

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

    Science.gov (United States)

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

    2018-06-01

    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.

  3. 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.

    Science.gov (United States)

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

    2017-01-01

    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.

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

    Digital Repository Service at National Institute of Oceanography (India)

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

    -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...

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

    Science.gov (United States)

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

    2007-02-01

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

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

    Science.gov (United States)

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

    2000-01-01

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

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

    NARCIS (Netherlands)

    Nooren, C.A.M.

    2017-01-01

    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

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

    Science.gov (United States)

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

    2016-04-01

    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

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

    Science.gov (United States)

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

    1998-01-01

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

  10. Holocene record of precipitation seasonality from lake calcite δ18O in the central Rocky Mountains, United States

    Science.gov (United States)

    Anderson, Lesleigh

    2011-01-01

    A context for recent hydroclimatic extremes and variability is provided by a ~10 k.y. sediment carbonate oxygen isotope (??18O) record at 5-100 yr resolution from Bison Lake, 3255 m above sea level, in northwestern Colorado (United States). Winter precipitation is the primary water source for the alpine headwater lake in the Upper Colorado River Basin and lake water ??18O measurements reflect seasonal variations in precipitation ??18O. Holocene lake water ??18O variations are inferred from endogenic sedimentary calcite ??18O based on comparisons with historic watershed discharge records and tree-ring reconstructions. Drought periods (i.e., drier winters and/or a more rain-dominated seasonal precipitation balance) generally correspond with higher calcite ??18O values, and vice-versa. Early to middle Holocene ??18O values are higher, implying a rain-dominated seasonal precipitation balance. Lower, more variable ??18O values after ca. 3500 yr ago indicate a snow-dominated but more seasonally variable precipitation balance. The middle to late Holocene ??18O record corresponds with records of El Ni??o Southern Oscillation intensification that supports a teleconnection between Rocky Mountain climate and North Pacific sea-surface temperatures at decade to century time scales. ?? 2011 Geological Society of America.

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

    Science.gov (United States)

    Lone, M. A.; Routh, J.; Kumar, V.; Mangini, A.; Rangarajan, R.; Ghosh, P.; Munnuru Singamshetty, K.; Shen, C. C.; Ahmad, S. M.; Mii, H. S.

    2016-12-01

    Seasonal reversals in monsoon winds strongly influence rainfall patterns on the Indian sub-continent regulating the socio-economy of south Asian region. High-resolution centennial-millennial scale records of climate change from the core zone of the monsoon impacted region are nonetheless very few. Here, we report Indian summer monsoon (ISM) variability record from an 87-cm long stalagmite (KM-1) from Krem Mawmluh in the Khasi Hills, Meghalaya. The absolute dated stalagmite record ranges from 22.7 (LGM) to 6.7 ka (Mid Holocene), revealing last glacial-interglacial paleoclimatic changes over the Indian sub-continent. A sharp change in δ18O ( 5‰) and growth rate post Younger Dryas (YD) is marked by continued rapid speleogenesis in KM-1 and coincides with monsoon intensification during the early Holocene. Prominent multi-centennial to millennial scale dry phases in ISM activity are observed from LGM to YD. During early to mid-Holocene, the record shows significant multi-decadal to centennial scale changes. The high frequency δ18O variations referring to abrupt changes in ISM activity are believed to be driven by changes in temperature and shifting of Inter-Tropical Convergence Zone.

  12. Proxy records of Holocene storm events in coastal barrier systems: Storm-wave induced markers

    Science.gov (United States)

    Goslin, Jérôme; Clemmensen, Lars B.

    2017-10-01

    Extreme storm events in the coastal zone are one of the main forcing agents of short-term coastal system behavior. As such, storms represent a major threat to human activities concentrated along the coasts worldwide. In order to better understand the frequency of extreme events like storms, climate science must rely on longer-time records than the century-scale records of instrumental weather data. Proxy records of storm-wave or storm-wind induced activity in coastal barrier systems deposits have been widely used worldwide in recent years to document past storm events during the last millennia. This review provides a detailed state-of-the-art compilation of the proxies available from coastal barrier systems to reconstruct Holocene storm chronologies (paleotempestology). The present paper aims (I) to describe the erosional and depositional processes caused by storm-wave action in barrier and back-barrier systems (i.e. beach ridges, storm scarps and washover deposits), (ii) to understand how storm records can be extracted from barrier and back-barrier sedimentary bodies using stratigraphical, sedimentological, micro-paleontological and geochemical proxies and (iii) to show how to obtain chronological control on past storm events recorded in the sedimentary successions. The challenges that paleotempestology studies still face in the reconstruction of representative and reliable storm-chronologies using these various proxies are discussed, and future research prospects are outlined.

  13. A high-resolution Holocene speleothem record from NE Romania: the nexus of Arctic and North Atlantic atmospheric circulations

    Science.gov (United States)

    Constantin, S.; Pourmand, A.; Moldovan, O.; Sharifi, A.; Mehterian, S.; Swart, P. K.

    2017-12-01

    The Romanian Carpathians act as a geomorphological barrier between different atmospheric circulation systems over Central and Eastern Europe; the NW of Romania lies under the remote influence of the North Atlantic oscillation, while the NE is influenced by the Arctic climate. In NW Romania, previous stable isotope studies of speleothems have not yielded a clear account of abrupt climate oscillations during the Holocene. Here we present results from a stalagmite collected from the Tauşoare Cave, located in NE Carpathians. The chronology of stalagmite T141 is based on 15 high-precision Th/U dates ranging between 32 and 1.1 ka with a continuous growth between 13.3 and 1.1 ka. The portion of the record within the Holocene was analyzed for δ18O and δ13C at a resolution ranging between 15 to 200 years/sample. The resulting δ18O record captures the Younger Dryas (YD) event centered at 12.9 ka, with δ18O values about 4 ‰ more depleted than those corresponding to the Holocene Climatic Optimum. The 8.2 ka event appears to be also captured in the record, although less prominent. The T141 isotope record is significantly different when compared to coeval records measured in speleothems from NW Carpathians, which do not exhibit marked changes during the YD or 8.2 ka events. This is likely due to the contrasting effect of temperature and atmospheric transport on δ18O signal in NW Romania. Within a distance of 200 km to the east, on the eastern flank of the Carpathian range, the δ18O signal of the Arctic circulation appears to be more prominent and clearly exhibits a positive relationship with temperature changes.

  14. A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya.

    Directory of Open Access Journals (Sweden)

    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

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

    Directory of Open Access Journals (Sweden)

    C. Contoux

    2013-07-01

    Full Text Available Given the growing evidence for megalakes in the geological record, assessing their impact on climate and vegetation is important for the validation of palaeoclimate simulations and therefore the accuracy of model–data comparison in lacustrine environments. Megalake Chad (MLC occurrences are documented not only for the mid-Holocene but also for the Mio-Pliocene (Schuster et al., 2009. At this time, the surface covered by water would have reached up to ~350 000 km2 (Ghienne et al., 2002; Schuster et al., 2005; Leblanc et al., 2006, making it an important evaporation source, possibly modifying climate and vegetation in the Chad Basin. We investigated the impact of such a giant continental water area in two different climatic backgrounds within the Paleoclimate Model Intercomparison Project phase 3 (PMIP3: the late Pliocene (3.3 to 3 Ma, i.e. the mid-Piacenzian warm period and the mid-Holocene (6 kyr BP. In all simulations including MLC, precipitation is drastically reduced above the lake surface because deep convection is inhibited by overlying colder air. Meanwhile, convective activity is enhanced around MLC because of the wind increase generated by the flat surface of the megalake, transporting colder and moister air towards the eastern shore of the lake. The effect of MLC on precipitation and temperature is not sufficient to widely impact vegetation patterns. Nevertheless, tropical savanna is present in the Chad Basin in all climatic configurations, even without MLC presence, showing that the climate itself is the driver of favourable environments for sustainable hominid habitats.

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

    Science.gov (United States)

    deMenocal, P B

    2001-04-27

    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.

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

    Science.gov (United States)

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

    2005-10-01

    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.

  18. Inferring climate variability from skewed proxy records

    Science.gov (United States)

    Emile-Geay, J.; Tingley, M.

    2013-12-01

    compared to other proxy records. (2) a multiproxy reconstruction of temperature over the Common Era (Mann et al., 2009), where we find that about one third of the records display significant departures from normality. Accordingly, accounting for skewness in proxy predictors has a notable influence on both reconstructed global mean and spatial patterns of temperature change. Inferring climate variability from skewed proxy records thus requires cares, but can be done with relatively simple tools. References - Mann, M. E., Z. Zhang, S. Rutherford, R. S. Bradley, M. K. Hughes, D. Shindell, C. Ammann, G. Faluvegi, and F. Ni (2009), Global signatures and dynamical origins of the little ice age and medieval climate anomaly, Science, 326(5957), 1256-1260, doi:10.1126/science.1177303. - Moy, C., G. Seltzer, D. Rodbell, and D. Anderson (2002), Variability of El Niño/Southern Oscillation activ- ity at millennial timescales during the Holocene epoch, Nature, 420(6912), 162-165.

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

    Directory of Open Access Journals (Sweden)

    S. Joannin

    2012-12-01

    Full Text Available A high-resolution pollen record from Lago Trifoglietti in Calabria (southern Italy provides new insights into the paleoenvironmental and palaeoclimatic changes which characterise the Holocene period in the southern Italy. The chronology is based on 11 AMS radiocarbon dates from terrestrial organic material. The Holocene history of the vegetation cover shows the persistence of an important and relatively stable Fagus forest present over that entire period, offering a rare example of a beech woodstand able to withstand climate changes for more than 11 000 yr. Probably in relation with early Holocene dry climate conditions which affected southern Italy, the Trifoglietti pollen record supports a southward delay in thermophyllous forest expansion dated to ca. 13 500 cal BP at Monticchio, ca. 11 000 cal BP at Trifoglietti, and finally ca. 9800 cal BP in Sicily. Regarding the human impact history, the Trifoglietti pollen record shows only poor imprints of agricultural activities and anthopogenic indicators, apart from those indicating pastoralism activities beneath forest cover. The selective exploitation of Abies appears to have been the strongest human impact on the Trifoglietti surroundings. On the basis of (1 a specific ratio between hygrophilous and terrestrial taxa, and (2 the Modern Analogue Technique, the pollen data collected at Lago Trifoglietti led to the establishment of two palaeoclimatic records tracing changes in (1 lake depth and (2 annual precipitation. On a millennial scale, these records give evidence of increasing moisture from ca. 11 000 to ca. 9400 cal BP and maximum humidity from ca. 9400 to ca. 6200 cal BP, prior to a general trend towards the drier climate conditions that have prevailed up to the present. In addition, several successive centennial-scale oscillations appear to have punctuated the entire Holocene. The identification of a cold dry event around 11 300 cal BP, responsible for a marked decline in

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

    Science.gov (United States)

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

    2009-04-01

    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.

  1. Late Holocene geomorphic record of fire in ponderosa pine and mixed-conifer forests, Kendrick Mountain, northern Arizona, USA

    Science.gov (United States)

    Jenkins, S.E.; Hull, Sieg C.; Anderson, D.E.; Kaufman, D.S.; Pearthree, P.A.

    2011-01-01

    Long-term fire history reconstructions enhance our understanding of fire behaviour and associated geomorphic hazards in forested ecosystems. We used 14C ages on charcoal from fire-induced debris-flow deposits to date prehistoric fires on Kendrick Mountain, northern Arizona, USA. Fire-related debris-flow sedimentation dominates Holocene fan deposition in the study area. Radiocarbon ages indicate that stand-replacing fire has been an important phenomenon in late Holocene ponderosa pine (Pinus ponderosa) and ponderosa pine-mixed conifer forests on steep slopes. Fires have occurred on centennial scales during this period, although temporal hiatuses between recorded fires vary widely and appear to have decreased during the past 2000 years. Steep slopes and complex terrain may be responsible for localised crown fire behaviour through preheating by vertical fuel arrangement and accumulation of excessive fuels. Holocene wildfire-induced debris flow events occurred without a clear relationship to regional climatic shifts (decadal to millennial), suggesting that interannual moisture variability may determine fire year. Fire-debris flow sequences are recorded when (1) sufficient time has passed (centuries) to accumulate fuels; and (2) stored sediment is available to support debris flows. The frequency of reconstructed debris flows should be considered a minimum for severe events in the study area, as fuel production may outpace sediment storage. ?? IAWF 2011.

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

    Science.gov (United States)

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

    2010-07-01

    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.

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

    Science.gov (United States)

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

    1997-09-01

    Twenty archaeological campsites intercalated between more than 30 debris flows caused by heavy rainfall events between 6200 and 3100 14C yr B.P. have recently been discovered at Quebrada Puripica in the Atacama Desert of northern Chile. This record provides detailed information about extreme, short-lived climatic events during the hyperarid mid-Holocene period. For the first time, we found evidence of continuous human occupation in this area, filling the regional hiatus in the Atacama basin ("Silencio Arqueologico") between 8000 and 4800 14C yr B.P. The transformation of Early Archaic hunters into the complex Late Archaic cultural tradition was an adaptive process. During this time, the site was a local ecological refuge with abundant resources in a generally hostile environment.

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

    Science.gov (United States)

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

    2005-12-01

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

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

    Science.gov (United States)

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

    2016-12-01

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

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

    Science.gov (United States)

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

    2009-03-01

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

  7. Drivers of Change in a 7300-Year Holocene Diatom Record from the Hemi-Boreal Region of Ontario, Canada.

    Directory of Open Access Journals (Sweden)

    Kristen K Beck

    Full Text Available A Holocene lake sediment record spanning the past 7300 years from Wishart Lake in the Turkey Lakes Watershed in the Hemi-Boreal of central Ontario, Canada, was used to evaluate the potential drivers of long-term change in diatom assemblages at this site. An analysis of diatom assemblages found that benthic and epiphytic taxa dominated the mid-Holocene (7300-4000 cal yr BP, indicating shallow, oligotrophic, circum-neutral conditions, with macrophytes present. A significant shift in diatom assemblages towards more planktonic species (mainly Cyclotella sensu lato, but also several species of Aulacoseira, and Tabellaria flocculosa occurred ~4000 cal yr BP. This change likely reflects an increase in lake level, coincident with the onset of a more strongly positive moisture balance following the drier climates of the middle Holocene, established by numerous regional paleoclimate records. Pollen-inferred regional changes in vegetation around 4000 yrs BP, including an increase in Betula and other mesic taxa, may have also promoted changes in diatom assemblages through watershed processes mediated by the chemistry of runoff. A more recent significant change in limnological conditions is marked by further increases in Cyclotella sensu lato beginning in the late 19th century, synchronous with the Ambrosia pollen rise and increases in sediment bulk density, signaling regional and local land clearance at the time of Euro-Canadian settlement (1880 AD. In contrast to the mid-Holocene increase in planktonic diatoms, the modern increase in Cyclotella sensu lato likely indicates a response to land use and vegetation change, and erosion from the watershed, rather than a further increase in water level. The results from Wishart Lake illustrate the close connection between paleoclimate change, regional vegetation, watershed processes, and diatom assemblages and also provides insight into the controls on abundance of Cyclotella sensu lato, a diatom taxonomic group

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

    Science.gov (United States)

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

    2018-01-01

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

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

    Science.gov (United States)

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

    2017-12-05

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

    2012-03-15

    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.)

  11. Two Holocene paleofire records from Peten, Guatemala: Implications for natural fire regime and prehispanic Maya land use

    Science.gov (United States)

    Anderson, Lysanna; Wahl, David

    2016-03-01

    Although fire was arguably the primary tool used by the Maya to alter the landscape and extract resources, little attention has been paid to biomass burning in paleoenvironmental reconstructions from the Maya lowlands. Here we report two new well-dated, high-resolution records of biomass burning based on analysis of macroscopic fossil charcoal recovered from lacustrine sediment cores. The records extend from the early Holocene, through the full arc of Maya prehistory, the Colonial, and post-Colonial periods ( 9000 cal yr BP to the present). (Hereafter BP) The study sites, Lago Paixban and Lago Puerto Arturo, are located in northern Peten, Guatemala. Results provide the first quantitative analysis from the region demonstrating that frequent fires have occurred in the closed canopy forests since at least the early Holocene ( 9000 BP), prior to occupation by sedentary agriculturalists. Following the arrival of agriculture around 4600 BP, the system transitioned from climate controlled to anthropogenic control. During the Maya period, changes in fire regime are muted and do not appear to be driven by changes in climate conditions. Low charcoal influx and fire frequency in the Earliest Preclassic period suggest that land use strategies may have included intensive agriculture much earlier than previously thought. Preliminary results showing concentrations of soot/black-carbon during the middle and late Preclassic periods are lower than modern background values, providing intriguing implications regarding the efficiency of Maya fuel consumption.

  12. Two Holocene paleofire records from Peten, Guatemala: Implications for natural fire regime and prehispanic Maya land use

    Science.gov (United States)

    Anderson, Lysanna; Wahl, David B.

    2016-01-01

    Although fire was arguably the primary tool used by the Maya to alter the landscape and extract resources, little attention has been paid to biomass burning in paleoenvironmental reconstructions from the Maya lowlands. Here we report two new well-dated, high-resolution records of biomass burning based on analysis of macroscopic fossil charcoal recovered from lacustrine sediment cores. The records extend from the early Holocene, through the full arc of Maya prehistory, the Colonial, and post-Colonial periods (~ 9000 cal yr BP to the present). (Hereafter BP) The study sites, Lago Paixban and Lago Puerto Arturo, are located in northern Peten, Guatemala. Results provide the first quantitative analysis from the region demonstrating that frequent fires have occurred in the closed canopy forests since at least the early Holocene (~ 9000 BP), prior to occupation by sedentary agriculturalists. Following the arrival of agriculture around 4600 BP, the system transitioned from climate controlled to anthropogenic control. During the Maya period, changes in fire regime are muted and do not appear to be driven by changes in climate conditions. Low charcoal influx and fire frequency in the Earliest Preclassic period suggest that land use strategies may have included intensive agriculture much earlier than previously thought. Preliminary results showing concentrations of soot/black-carbon during the middle and late Preclassic periods are lower than modern background values, providing intriguing implications regarding the efficiency of Maya fuel consumption.

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

    Directory of Open Access Journals (Sweden)

    A. Ngomanda

    2009-10-01

    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.

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

    Science.gov (United States)

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

    2017-04-01

    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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-02-01

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

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

    Science.gov (United States)

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

    2013-10-01

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

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

    Science.gov (United States)

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

    2014-01-01

    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.

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

    Science.gov (United States)

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

    2005-12-01

    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.

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

    Science.gov (United States)

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

    2017-12-01

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

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

    Science.gov (United States)

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

    2017-04-01

    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).

  1. Holocene Paleohydrology of the tropical andes from lake records

    Energy Technology Data Exchange (ETDEWEB)

    Abbott, M. B., LLNL

    1997-03-03

    Two century-scale time series in northern Bolivia constrain the ages of abrupt changes in the physical, geochemical, and biological characteristics of sediments obtained from lakes that formed during deglaciation from the late Pleistocene glacial maximum. The watersheds of Laguna Viscachani (16{degrees}12`S, 68{degrees}07`W, 3780m) and Lago Taypi Chaka Kkota (16{degrees}13`S, 68{degrees}21`W, 4300m), located on the eastern and western slopes of the Cordillera Real, respectively, contain small cirque glaciers. A high-resolution chronology of the lake sediments is provided by 23 AMS {sup 14}C dates of discrete macro-fossils. Late Pleistocene glaciers retreated rapidly, exposing the lake basins between 10,700 and 9700 {sup 14}C yr B.P. The sedimentary facies suggest that after 8900 {sup 14}C B.P. glaciers were absent from the watersheds and remained so during the middle Holocene. An increase in the precipitation-evaporation balance is indicated above unconformities dated to about 2300 {sup 14}C yr B.P. in both Lago Taypi Chaka Kkota and Laguna Viscachani. An abrupt increase in sediment accumulation rated after 1400 {sup 14}C yr B.P. signals the onset of Neoglaciation. A possible link exists between the observed millennial-scale shifts in the regional precipitation- evaporation balance and seasonal shifts in tropical insolation.

  2. Holocene record of benthic foraminiferal morphogroups from the ...

    Indian Academy of Sciences (India)

    35

    The Arabian Sea is characterized today by a well-developed and perennial oxygen minimum. 15 ... inventory contributing to global climate change. 18 .... Water (ASW) and Persian Gulf Water (PGW) in the eastern Arabian Sea is less evident.

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

    Directory of Open Access Journals (Sweden)

    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

  4. A Holocene Record of Monsoon Intensity From Speleothems in Flores, Indonesia

    Science.gov (United States)

    Griffiths, M. L.; Drysdale, R.; Gagan, M.; Ayliffe, L.; Zhao, J.; St. Pierre, E.; Hantoro, W.; Suwargadi, B.

    2007-12-01

    The Australasian monsoon is among the largest monsoon systems on Earth. The affected region experiences a marked seasonal cycle in winds and precipitation, similar to its Northern Hemisphere counterparts (e.g., Asian monsoons). The Australasian monsoon is the life blood of the millions of people of the Indonesian archipelago. Since the climate is the dominating factor controlling food production, it is of great significance and urgency that we gain a firmer grasp on the parameters that control variations in monsoon intensity. Precise uranium series dating of two actively growing speleothems measuring ~1.25 (LR06-B1) and ~1.61 (LR06-B3) meters in length from Liang Luar cave (Flores, eastern Indonesia), reveal basal ages of ~12,846±103 and 23,605±171 years respectively. In previous studies, stable isotope ratios (δ18O and δ13C) and trace element concentrations in speleothems have revealed past environmental change (e.g., Burns et al., 2001; Wang et al., 2001; Fleitmann et al., 2004; Drysdale et al., 2004).In monsoon-affected regions, the δ18O signal recorded in stalagmites seems to be dominated by the amount of precipitation (so-called `amount effect'), whereby more negative (positive) δ18O values indicate enhanced (diminished) precipitation. Preliminary results from LR06-B1 indicate that δ18O values show a general increase in monsoon intensity from the beginning of the record to ~2000 years BP: this more or less follows insolation changes over the Australian continent.Comparison of our record with D4 from Dongge Cave reveals an anticorrelation during the Holocene, further supporting the hypothesis that tropical monsoon intensity is largely controlled by changes in insolation in both the Northern and Southern Hemisphere. Examination of our δ13C record demonstrates a high-frequency signal superimposed on low- frequency variability which correlates with the reconstructed sunspot cycle: higher (lower) sunspot numbers, and hence increased solar activity

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

    Science.gov (United States)

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

    2016-01-01

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

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

    NARCIS (Netherlands)

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

    2006-01-01

    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

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

    Science.gov (United States)

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

    2016-04-01

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

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

    Science.gov (United States)

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

    2018-06-01

    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.

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

    Science.gov (United States)

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

    2017-10-01

    Arid central Asia (ACA) is one of the largest arid (desert) areas in the world, and its climate is dominated by the westerlies. In this study, we examined sand dune evolution from the Bayanbulak Basin in the Tian Shan (Xinjiang, NW China), aiming to infer the Holocene moisture history of the ACA. Combined with stratigraphic observation and environmental proxies analysis (grain size, magnetic susceptibility and total organic content), large numbers of luminescence ages from multiple sites (eight sections, 79 samples) were applied to reconstruct the evolution of the sand dune accumulation in the study basin. The overall results imply very dry conditions characterized by sand dune accumulation at ∼12-6.5 ka, a wet interval between ∼6.5 and 0.8 ka when soil formation occurred, and decreased moisture during the last 0.8 ka. This moisture variation pattern is generally consistent with that inferred from many lacustrine records in the core zone of ACA, suggesting a widespread dry period in the early-to-middle Holocene and relatively wet middle-to-late Holocene. Thus, the moisture history derived from the current sand dune system contrasts with that in Asian monsoon areas, which are characterized by a strong monsoon (high precipitation) in the early and mid-Holocene and a weak monsoon (low precipitation and dry climate) during the late Holocene. Our results strongly suggest that the winter solar insolation and the external boundary conditions such as atmospheric CO2 concentration, ice sheets, and meltwater fluxes, have been major influential factors triggering the Holocene moisture evolution in the core zone of ACA.

  10. Late Glacial–Holocene record of benthic foraminiferal ...

    Indian Academy of Sciences (India)

    K Verma

    2018-03-06

    Mar 6, 2018 ... influence of oxygen-rich Antarctic Intermediate Water (AAIW). Keywords. Paleontology; benthic ..... nent changes at millennial scale are noticed during certain intervals ...... become environmental change? The proxy record of ...

  11. Sediment records of Yellow River channel migration and Holocene environmental evolution of the Hetao Plain, northern China

    Science.gov (United States)

    Wang, Jingzhong; Wu, Jinglu; Pan, Baotian; Jia, Hongjuan; Li, Xiao; Wei, Hao

    2018-05-01

    The origin and evolution of lakes in the Hetao Plain, northern China, were influenced by climate variation, channel migration, and human activity. We analyzed a suite of sediment cores from the region to investigate Yellow River channel migration and environmental change in this region over the Holocene. Short sediment cores show that environmental indicators changed markedly around CE 1850, a time that corresponds to flood events, when large amounts of river water accumulated in the western part of the Hetao Plain, giving rise to abundant small lakes. Multiple sediment variables (environmental proxies) from two long cores collected in the Tushenze Paleolake area show that sediments deposited between 12.0 and 9.0 cal ka BP were yellow clay, indicative of fluvial deposition and channel migration. From 9.0 to 7.5 cal ka BP, sand was deposited, reflecting a desert environment. From 7.5 to 2.2 cal ka BP, however, the sediments were blue-gray clay that represents lacustrine facies of Lake Tushenze, which owes its origin to an increase in strength of the East Asian monsoon. At about 2.2 cal ka BP, the north branch of the Yellow River was flooded, and the Tushenze Paleolake developed further. Around 2.0 cal ka BP, the paleolake shrank and eolian sedimentation was recorded. The analyzed sediment records are consistent with the written history from the region, which documents channel migration and environmental changes in the Hetao Plain over the Holocene.

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

    Science.gov (United States)

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

    2017-12-01

    Climate models predict Africa will warm by up to 5°C in the coming century. Reconstructions of African temperature since the Last Glacial Maximum (LGM) have made fundamental contributions to our understanding of past, present, and future climate and can help constrain predictions from general circulation models (GCMs). However, many of these reconstructions are based on proxies of lake temperature, so the confounding influences of lacustrine processes may complicate our interpretations of past changes in tropical climate. These proxy-specific uncertainties require robust methodology for data-model comparison. We develop a new proxy system model (PSM) for paleolimnology to facilitate data-model comparison and to fully characterize uncertainties in climate reconstructions. Output from GCMs are used to force the PSM to simulate lake temperature, hydrology, and associated proxy uncertainties. We compare reconstructed East African lake and air temperatures in individual records and in a stack of 9 lake records to those predicted by our PSM forced with Paleoclimate Model Intercomparison Project (PMIP3) simulations, focusing on the mid-Holocene (6 kyr BP). We additionally employ single-forcing transient climate simulations from TraCE (10 kyr to 4 kyr B.P. and historical), as well as 200-yr time slice simulations from CESM1.0 to run the lake PSM. We test the sensitivity of African climate change during the mid-Holocene to orbital, greenhouse gas, and ice-sheet forcing in single-forcing simulations, and investigate dynamical hypotheses for these changes. Reconstructions of tropical African temperature indicate 1-2ºC warming during the mid-Holocene relative to the present, similar to changes predicted in the coming decades. However, most climate models underestimate the warming observed in these paleoclimate data (Fig. 1, 6kyr B.P.). We investigate this discrepancy using the new lake PSM and climate model simulations, with attention to the (potentially non

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

    DEFF Research Database (Denmark)

    Reeh, Niels

    2004-01-01

    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....

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

    Directory of Open Access Journals (Sweden)

    S. K. Farber

    2017-12-01

    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

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

    Directory of Open Access Journals (Sweden)

    A. Francke

    2013-02-01

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

  16. Holocene pollen and sediment record from the tangle lakes area, central Alaska

    Science.gov (United States)

    Ager, Thomas A.; Sims, John D.

    1981-01-01

    trees. In this case, improved moisture conditions may have promoted spruce growth and reproduction in spite of somewhat cooler temperatures.Previous pollen records from Alaska suggest that Artemisia pollen contributed little to the pollen rain of most taiga and tundra sites during Holocene time. The pollen record from Tangle Lakes, however shows rather high percentages (7–13 percent) of Artemisia deposited during the approximate time interval 4700 to 3500 years B.P. Local habitats that have well‐drained soils derived from glacial deposits support patches of Artemisia telesii and other Artemisia species. These local habitats may account for the source of Artemisiapollen deposited in the Tangle Lakes area during Holocene time.

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

    Science.gov (United States)

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

    2012-01-01

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

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

    DEFF Research Database (Denmark)

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

    2010-01-01

    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...

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

    Science.gov (United States)

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

    2017-12-01

    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. New deglacial and Holocene micropaleontological and geochemical records from the southern margin of the Svalbard Archipelago (Arctic Ocean)

    Science.gov (United States)

    Rigual-Hernández, Andrés.

    2010-05-01

    This study is presented in the context of the Spanish research project "The development of an Arctic ice stream-dominated sedimentary system: The southern Svalbard continental margin" (SVAIS), developed within the framework of the International Polar Year (IPY) Activity N. 367 (NICE STREAMS). Its main goal is to understand the evolution of glacial continental margins and their relationship with the changes in ice sheet dynamics induced by natural climatic changes, combining the geophysical data with the sediment record both collected during an oceanographic cruise in the Storfjorden area (SW Svalbard margin) in August 2007. This marine depositional system, dominated by an ice stream during the last glacial period, was selected due to its small size inducing a rapid response to climatic changes, and for the oceanographic relevance of the area for global ocean circulation. The results obtained aim to define the sedimentary architecture and morphology, and to provide more insight into the paleoceanographic and paleoclimatic evolution of the region. We specifically report on new micropaleontological and geochemical data obtained from the sediment cores. A preliminary age model indicates that the sediment sequences cover approximately the Last Deglaciation and the Holocene. Microfossils are generally well preserved, although the abundances of the different groups show marked shifts along the record. Low concentrations of coccolithophores, diatoms, planktic foraminifers and cysts of organic-walled dinoflagellates (dinocysts) are found at the lower half of the sequence (IRD-rich, coarser-grained sediments), and increase towards the Late Holocene (fine-grained bioturbated sediments). The Climatic Optimum is characterized by the warmest sea surface temperatures as estimated from the fossil assemblage, diverse transfer functions and biogeochemical proxies, and by high nutrient contents in the bottom waters shown by light carbon isotope values and high Cd/Ca ratios in benthic

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

    Directory of Open Access Journals (Sweden)

    K. Tudyka

    2017-03-01

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

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

    Science.gov (United States)

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

    2012-04-01

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

  3. Molecular records of climate variability and vegetation response since the Late Pleistocene in the Lake Victoria basin, East Africa

    NARCIS (Netherlands)

    Berke, M.A.; Johnson, T.C.; Werne, J.P.; Grice, K.; Schouten, S.; Sinninghe Damsté, J.S.

    2012-01-01

    New molecular proxies of temperature and hydrology are helping to constrain tropical climate change and elucidate possible forcing mechanisms during the Holocene. Here, we examine a similar to 14,000 year record of climate variability from Lake Victoria, East Africa, the world's second largest

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

    Science.gov (United States)

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

    2017-08-01

    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.

  5. Upper Pleistocene and Holocene palaeoenvironmental records in Cueva Mayor karst (Atapuerca, Spain from different proxies: speleothem crystal fabrics, palynology and archaeology.

    Directory of Open Access Journals (Sweden)

    Virginia Martínez-Pillado

    2014-01-01

    Full Text Available The Cueva Mayor karst system of Atapuerca, in Northern Spain, hosts a highly significant record of human occupation from the Pleistocene. The climatic context of the human activities during the Pleistocene-Holocene for this inland site has not been well constrained, since existing records of the palaeoclimatic evolution of the Northern Iberian Peninsula are from more distal coastal and high-elevation sites. In this study, we interpret the palaeoenvironmental information recorded on the petrography of a stalagmite and the pollen spectra of the Sierra de Atapuerca karst system during the last 20 kyr. The integration of both types of records has allowed us to define four palaeoenvironmental stages. During the Upper Pleistocene and until 12.8 kyr BP, the climate was cold and dry, toward the end of the interval evolving to wetter and warmer conditions. From 12.8 to 7.7 kyr BP, during the Mesolithic-Neolithic, a major erosion event in both records marks the Pleistocene-Holocene transition. Around 5.9 kyr BP, the Late Neolithic, environmental conditions indicate a climatic optimum with a marked seasonality. The environmental conditions became drier from 4.2 kyr BP until the present, with a decrease in the woodlands. This aridity signal might be amplified by the impact of a more intense human agricultural activity after 3.1 kyr BP, during the Bronze Age.

  6. 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)

    Science.gov (United States)

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

    2013-12-01

    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

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

    Science.gov (United States)

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

    2012-01-01

    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.

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

    Science.gov (United States)

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

    2015-07-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-03-31

    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.

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

    Science.gov (United States)

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

    2018-02-01

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

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

    Science.gov (United States)

    Hall, Stephen A.; Peterson, John A.

    2013-04-01

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

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

    Science.gov (United States)

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

    1999-01-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-07-01

    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.

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

    Science.gov (United States)

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

    2017-12-01

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

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

    Directory of Open Access Journals (Sweden)

    V. Nieto-Moreno

    2011-12-01

    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

  16. Observed periodicities and the spectrum of field variations in Holocene magnetic records

    DEFF Research Database (Denmark)

    Panovska, S.; Finlay, Chris; Hirt, A.M.

    2013-01-01

    , globally observed, periods. Rather we find a continuous broadband spectrum, with a slope corresponding to a power law with exponent of -2.3 ± 0.6 for the period range between 300 and 4000 yr. This is consistent with the hypothesis that chaotic convection in the outer core drives the majority of secular......In order to understand mechanisms that maintain and drive the evolution of the Earth's magnetic field, a characterization of its behavior on time scales of centuries to millennia is required. We have conducted a search for periodicities in Holocene sediment magnetic records, by applying three...

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

    Digital Repository Service at National Institute of Oceanography (India)

    Agnihotri, R.; Kurian, S.

    stream_size 72460 stream_content_type text/plain stream_name Earth_Sci_India_1_258.pdf.txt stream_source_info Earth_Sci_India_1_258.pdf.txt Content-Encoding UTF-8 Content-Type text/plain; charset=UTF-8 Agnihotri http://www....earthscienceindia.info/Agnihotri.htm 1 of 14 10/15/2008 9:41 AM Earth Science India Vol.1 (IV), October, 2008, pp. 258-287 http://www.earthscienceindia.info/ Recently studied sedimentary records from the eastern Arabian Sea: Implications to Holocene monsoonal variability Rajesh...

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

    International Nuclear Information System (INIS)

    White, J.W.C.

    2001-01-01

    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

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

    Directory of Open Access Journals (Sweden)

    J. Otto

    2011-09-01

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

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

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

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

    Directory of Open Access Journals (Sweden)

    S. Joannin

    2013-04-01

    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

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

    Science.gov (United States)

    Novenko, Elena

    2013-04-01

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

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

    Science.gov (United States)

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

    2012-05-01

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

  3. Mid to Late Holocene climate variability and anthropogenic impacts

    DEFF Research Database (Denmark)

    Olsen, J.; Noe-Nygaard, Nanna; Wolfe, B. B.

    2010-01-01

    this was interrupted by very wet conditions from 5,300 to 5,150, 4,300 to 4,050 and 3,700 to 3,450 cal year BP. The timing of the latter two moist intervals is consistent with other Scandinavian paleoclimatic records. Dry conditions at Lake Bliden between 3,450 and 2,800 cal year BP is consistent with other...... paleolimnological records from southern Sweden but contrasts with records in central Sweden, possibly suggesting a more northerly trajectory of prevailing westerlies carrying moisture from the North Atlantic at this time. Overall, fluctuating moisture conditions at Lake Bliden appear to be strongly linked...... susceptibility, d13CORG, d13Ccarb and d18Ocarb records suggest that the Medieval Warm Period was dry and the Little Ice Age was wet....

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

    Science.gov (United States)

    Pellatt, Marlow G.; Mathewes, Rolf W.

    1997-07-01

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

  5. Atmospheric carbon dioxide and the climate record

    International Nuclear Information System (INIS)

    Ellsaesser, H.W.

    1989-04-01

    This paper is an attempt to provide a summary review of conclusions from previous studies on this subject. Subject headings include: conceptualization of the greenhouse effect, the climatic effect of doubled CO 2 , interpretation of the climatic record, diagnosis of apparent and possible model deficiencies, and the palaeoclimatic record

  6. Atmospheric carbon dioxide and the climate record

    Energy Technology Data Exchange (ETDEWEB)

    Ellsaesser, H.W.

    1989-04-01

    This paper is an attempt to provide a summary review of conclusions from previous studies on this subject. Subject headings include: conceptualization of the greenhouse effect, the climatic effect of doubled CO/sub 2/, interpretation of the climatic record, diagnosis of apparent and possible model deficiencies, and the palaeoclimatic record.

  7. EVALUATING SHORT-TERM CLIMATE VARIABILITY IN THE LATE HOLOCENE OF THE NORTHERN GREAT PLAINS

    Energy Technology Data Exchange (ETDEWEB)

    Joseph H. Hartman

    1999-09-01

    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

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

    Science.gov (United States)

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

    2017-12-01

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

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

    Science.gov (United States)

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

    2017-12-01

    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.

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

    DEFF Research Database (Denmark)

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

    2012-01-01

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

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

    Directory of Open Access Journals (Sweden)

    J. C. Hargreaves

    2013-03-01

    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.

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

    Science.gov (United States)

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

    2018-03-01

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

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

    International Nuclear Information System (INIS)

    Andersson, Cecilia

    1998-01-01

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, Cecilia [Intera KB (Sweden)

    1998-01-01

    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

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

    Science.gov (United States)

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

    2017-04-01

    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

  16. Revisiting Caveiro Lake sediment record: the Holocene NAO and AMO impact on Pico Island (Azores archipelago)

    Science.gov (United States)

    Hernandez, A.; Giralt, S.; Raposeiro, P. M.; Gonçalves, V. M.; Pueyo, J. J.; Trigo, R. M.; Bao, R.; Sáez, A.

    2017-12-01

    Northern Hemisphere climate is partly conditioned by a number of atmospheric and oceanic patterns which occur in the North Atlantic sector. The favourable location of the Azores Archipelago (37°-40° N, 25°-31° W) results in a privileged place to generate high-resolution Holocene climatic proxy data that can contribute to deep our understanding on the evolution of these atmospheric and oceanic patterns. In the frame of three research projects, namely PALEONAO (CGL2010-15767), RAPIDNAO (CGL2013-40608-R) and PALEOMODES (CGL2016-75281-C2), high-resolution proxy-based reconstructions from Azores Archipelago have recently shown a combined impact of atmospheric and oceanic patterns at multiannual and decadal time-scales (Rubio-Inglés et al. 2016; Hernández et al. 2017). However, the long-term evolution coupling/uncoupling of these patterns is not well-determined yet. Here, we present a new high-resolution climate reconstruction based on the Caveiro Lake sedimentary sequence in order to fill this gap. Previously, Björck et al. (2006) studied a section of this sequence (the uppermost 4.6 m covering last 6 Ka cal BP) concluding that changes in the thermohaline circulation and the SST were the main drivers in the long-term precipitation variability, whereas the NAO impact was the main atmospheric driver of short-term precipitation changes. However, they only distinguished the NAO impact for the last 600 years owing to the low resolution of the study for the lower portion of the core. The new studied sequence (8.40 m long, 8.2 Ka cal BP) has been analysed at decadal-to centennial time-scale resolution for X-ray diffraction (XRD), X-ray fluorescence (XRF) core scanning and elemental and isotope geochemistry on bulk organic matter. The statistical multivariate analysis of the data highlights the main drivers triggering the sedimentary infill of the lake would be the NAO and AMO by controlling the lacustrine productivity via nutrients input. This new high

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

    Science.gov (United States)

    Mauldin, R. P.; Munoz, C.

    2013-12-01

    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

  18. Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

    Science.gov (United States)

    Anderson, Lesleigh; Max Berkelhammer,; Barron, John A.; Steinman, Byron A.; Finney, Bruce P.; Abbott, Mark B.

    2016-01-01

    Lake sediment oxygen isotope records (calcium carbonate-δ18O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean–atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ18O records along with a new compilation of lake water δ18O and δ2H that are used to characterize lake sediment sensitivity to precipitation-δ18O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ18O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north–south precipitation-δ18O patterns that is evidence for a highly non-stationary influence by Pacific ocean–atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ18O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ18O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean–atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north–south precipitation-δ18O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean–atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ18O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the

  19. Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

    Science.gov (United States)

    Anderson, Lesleigh; Berkelhammer, Max; Barron, John A.; Steinman, Byron A.; Finney, Bruce P.; Abbott, Mark B.

    2016-02-01

    Lake sediment oxygen isotope records (calcium carbonate-δ18O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean-atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ18O records along with a new compilation of lake water δ18O and δ2H that are used to characterize lake sediment sensitivity to precipitation-δ18O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ18O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north-south precipitation-δ18O patterns that is evidence for a highly non-stationary influence by Pacific ocean-atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ18O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ18O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean-atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north-south precipitation-δ18O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean-atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ18O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the processes that drive

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

    International Nuclear Information System (INIS)

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

    2009-01-01

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

  1. 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

    Science.gov (United States)

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

    2018-04-01

    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.

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

    Science.gov (United States)

    Jin, Liya; Zhang, Xiaojian

    2017-04-01

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

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

    Science.gov (United States)

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

    2015-01-01

    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.

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

    Directory of Open Access Journals (Sweden)

    C. Martín-Puertas

    2010-12-01

    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.

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

    Science.gov (United States)

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

    2008-04-01

    6 ka. Climate Dynamics 12, 185-194), we modified the pollen-PFT and PFT-biomes assignation of Thompson and Anderson (Thompson, R.S., Anderson, K.H., 2000. Biomes of western North America at 18,000; 6000 and 0 14C yr BP reconstructed from pollen and packrat midden data. Journal of Biogeography 27, 555-584) for a better representation of the modern vegetation of NW Mexico. The biome reconstruction method was validated with the modern pollen sites and applied to the fossil sites. Our results show that, during the early Holocene, a cool conifer forest extended at least down to 1700 m, while today this biome is present above 2000 m in the Chihuahua state. The Younger Dryas event was recorded in one site with cold and dry conditions. The reconstructed annual temperature for this period was 3°-6 °C colder than today, and annual precipitation was 250 mm lower than at present (900 mm/yr). The middle Holocene after 9200 cal yr BP was marked by a warming trend, reaching temperatures 2 °C warmer than today at 7000 cal yr BP, and by the installation of a warm mixed forest, the present day biome, at 1700 m elevation, while at higher elevations (1900 m) the cool conifer forest was still present. Summer precipitation was 200 mm/yr above the early Holocene values, suggesting that monsoon-like conditions strengthened since 9200 cal yr BP at this region. During the last 4000 yr, the same warm mixed forest was reconstructed below 1700 m and a conifer forest above 1700 m. A great variability of vegetation and climate patterns was recorded for the last 3000 yr particularly at high elevation sites, where warming and cooling trends would be coeval of the Medieval warm period and Little Ice Age, likely related to ENSO variability.

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

    Science.gov (United States)

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

    2015-04-01

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

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

    NARCIS (Netherlands)

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

    2017-01-01

    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

  8. Lake sediment records on climate change and human activities in the Xingyun Lake catchment, SW China.

    Science.gov (United States)

    Zhang, Wenxiang; Ming, Qingzhong; Shi, Zhengtao; Chen, Guangjie; Niu, Jie; Lei, Guoliang; Chang, Fengqin; Zhang, Hucai

    2014-01-01

    Sediments from Xinyun Lake in central Yunnan, southwest China, provide a record of environmental history since the Holocene. With the application of multi-proxy indicators (total organic carbon (TOC), total nitrogen (TN), δ13C and δ15N isotopes, C/N ratio, grain size, magnetic susceptibility (MS) and CaCO3 content), as well as accelerator mass spectrometry (AMS) 14C datings, four major climatic stages during the Holocene have been identified in Xingyun's catchment. A marked increase in lacustrine palaeoproductivity occurred from 11.06 to 9.98 cal. ka BP, which likely resulted from an enhanced Asian southwest monsoon and warm-humid climate. Between 9.98 and 5.93 cal. ka BP, a gradually increased lake level might have reached the optimum water depth, causing a marked decline in coverage by aquatic plants and lake productivity of the lake. This was caused by strong Asian southwest monsoon, and coincided with the global Holocene Optimum. During the period of 5.60-1.35 cal. ka BP, it resulted in a warm and dry climate at this stage, which is comparable to the aridification of India during the mid- and late Holocene. The intensifying human activity and land-use in the lake catchment since the early Tang Dynasty (∼1.35 cal. ka BP) were associated with the ancient Dian culture within Xingyun's catchment. The extensive deforestation and development of agriculture in the lake catchment caused heavy soil loss. Our study clearly shows that long-term human activities and land-use change have strongly impacted the evolution of the lake environment and therefore modulated the sediment records of the regional climate in central Yunnan for more than one thousand years.

  9. Lake sediment records on climate change and human activities in the Xingyun Lake catchment, SW China.

    Directory of Open Access Journals (Sweden)

    Wenxiang Zhang

    Full Text Available Sediments from Xinyun Lake in central Yunnan, southwest China, provide a record of environmental history since the Holocene. With the application of multi-proxy indicators (total organic carbon (TOC, total nitrogen (TN, δ13C and δ15N isotopes, C/N ratio, grain size, magnetic susceptibility (MS and CaCO3 content, as well as accelerator mass spectrometry (AMS 14C datings, four major climatic stages during the Holocene have been identified in Xingyun's catchment. A marked increase in lacustrine palaeoproductivity occurred from 11.06 to 9.98 cal. ka BP, which likely resulted from an enhanced Asian southwest monsoon and warm-humid climate. Between 9.98 and 5.93 cal. ka BP, a gradually increased lake level might have reached the optimum water depth, causing a marked decline in coverage by aquatic plants and lake productivity of the lake. This was caused by strong Asian southwest monsoon, and coincided with the global Holocene Optimum. During the period of 5.60-1.35 cal. ka BP, it resulted in a warm and dry climate at this stage, which is comparable to the aridification of India during the mid- and late Holocene. The intensifying human activity and land-use in the lake catchment since the early Tang Dynasty (∼1.35 cal. ka BP were associated with the ancient Dian culture within Xingyun's catchment. The extensive deforestation and development of agriculture in the lake catchment caused heavy soil loss. Our study clearly shows that long-term human activities and land-use change have strongly impacted the evolution of the lake environment and therefore modulated the sediment records of the regional climate in central Yunnan for more than one thousand years.

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

    Science.gov (United States)

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

    1997-01-01

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

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

    Science.gov (United States)

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

    2016-04-01

    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.

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

    Science.gov (United States)

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

    2006-01-01

    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.

  13. A geochemical record of the link between chemical weathering and the East Asian summer monsoon during the late Holocene preserved in lacustrine sediments from Poyang Lake, central China

    Science.gov (United States)

    Huang, Chao; Wei, Gangjian; Li, Wuxian; Liu, Ying

    2018-04-01

    This paper presents relatively high-resolution geochemical records spanning the past 4000 cal yr BP obtained from the lacustrine sediments of Poyang Lake in central China. The variations in the intensity of the East Asian summer monsoon (EASM) are traced using the K/Na, Ti/Na, Al/K, kaolinite/illite and clay/feldspar ratios, together with the chemical index of alteration (CIA), as indicators of chemical weathering. During the last 4000 years, the proxy records of chemical weathering from Poyang Lake exhibit an overall enhanced trend, consistent with regional hydrological changes in previous independent records. Further comparisons and analyses demonstrate that regional moisture variations in central China is inversely correlated with the EASM intensity, with weak EASM generating high precipitation in central China. Our data reveal three intervals of dramatically dry climatic conditions (i.e., ca. 4000-3200 cal yr BP, ca. 2800-2400 cal yr BP, and ca. 500-200 cal yr BP). A period of weak chemical weathering, related to cold and dry climatic conditions, occurred during the Little Ice Age (LIA), whereas more intense chemical weathering, reflecting warm and humid climatic conditions, was recorded during the Medieval Warm Period (MWP). Besides, an intensification of chemical weathering in Poyang Lake during the late Holocene agrees well with strong ENSO activity, suggesting that moisture variations in central China may be predominantly driven by ENSO variability.

  14. A high-resolution record of Holocene millennial-scale oscillations of surface water, foraminiferal paleoecology and sediment redox chemistry in the SE Brazilian margin

    Science.gov (United States)

    Dias, B. B.; Barbosa, C. F.; Albuquerque, A. L.; Piotrowski, A. M.

    2014-12-01

    Holocene millennial-scale oscillations and Bond Events (Bond et al. 1997) are well reported in the North Atlantic as consequence of fresh water input and weaking of the Atlantic Meridional Overturning Circulation (AMOC). It has been hypothesized that the effect of weaking of AMOC would lead to warming in the South Atlantic due to "heat piracy", causing surface waters to warm and a reorganization of surface circulation. There are few reconstructions of AMOC strength in the South Atlantic, and none with a high resolution Holocene record of changes of productivity and the biological pump. We reconstruct past changes in the surface water mass hydrography, productivity, and sediment redox changes in high-resolution in the core KCF10-01B, located 128 mbsl water depth off Cabo Frio, Brazil, a location where upwelling is strongly linked to surface ocean hydrography. We use Benthic Foraminiferal Accumulation Rate (BFAR) to reconstruct productivity, which reveals a 1.3kyr cyclicity during the mid- and late-Holocene. The geochemistry of trace and rare earth elements on foraminiferal Fe-Mn oxide coatings show changes in redox-sensitive elements indicating that during periods of high productivity there were more reducing conditions in sediment porewaters, producing a Ce anomaly and reduction and re-precipitation of Mn oxides. Bond events 1-7 were identified by a productivity increase along with reducing sediment conditions which was likely caused by Brazil Current displacement offshore allowing upwelling of the nutritive bottom water South Atlantic Central Waters (SACW) to the euphotic zone and a stronger local biological pump. In a global context, correlation with other records show that this occurred during weakened AMOC and southward displacement of the ITCZ. We conclude that Bond climatic events and millennial-scale variability of AMOC caused sea surface hydrographic changes off the Brazilian Margin leading to biological and geochemical changes recorded in coastal records

  15. Seychelles coral record of changes in sea surface temperature bimodality in the western Indian Ocean from the Mid-Holocene to the present

    Science.gov (United States)

    Zinke, J.; Pfeiffer, M.; Park, W.; Schneider, B.; Reuning, L.; Dullo, W.-Chr.; Camoin, G. F.; Mangini, A.; Schroeder-Ritzrau, A.; Garbe-Schönberg, D.; Davies, G. R.

    2014-08-01

    We report fossil coral records from the Seychelles comprising individual time slices of 14-20 sclerochronological years between 2 and 6.2 kyr BP to reconstruct changes in the seasonal cycle of western Indian Ocean sea surface temperature (SST) compared to the present (1990-2003). These reconstructions allowed us to link changes in the SST bimodality to orbital changes, which were causing a reorganization of the seasonal insolation pattern. Our results reveal the lowest seasonal SST range in the Mid-Holocene (6.2-5.2 kyr BP) and around 2 kyr BP, while the highest range is observed around 4.6 kyr BP and between 1990 and 2003. The season of maximum temperature shifts from austral spring (September to November) to austral autumn (March to May), following changes in seasonal insolation over the past 6 kyr. However, the changes in SST bimodality do not linearly follow the insolation seasonality. For example, the 5.2 and 6.2 kyr BP corals show only subtle SST differences in austral spring and autumn. We use paleoclimate simulations of a fully coupled atmosphere-ocean general circulation model to compare with proxy data for the Mid-Holocene around 6 kyr BP. The model results show that in the Mid-Holocene the austral winter and spring seasons in the western Indian Ocean were warmer while austral summer was cooler. This is qualitatively consistent with the coral data from 6.2 to 5.2 kyr BP, which shows a similar reduction in the seasonal amplitude compared to the present day. However, the pattern of the seasonal SST cycle in the model appears to follow the changes in insolation more directly than indicated by the corals. Our results highlight the importance of ocean-atmosphere interactions for Indian Ocean SST seasonality throughout the Holocene. In order to understand Holocene climate variability in the countries surrounding the Indian Ocean, we need a much more comprehensive analysis of seasonally resolved archives from the tropical Indian Ocean. Insolation data alone only

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

    Science.gov (United States)

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

    2015-04-01

    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 (http://www.sfb806.uni-koeln.de). 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

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

    NARCIS (Netherlands)

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

    2013-01-01

    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

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

    Science.gov (United States)

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

    2017-06-06

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

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

    Science.gov (United States)

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

    2013-04-01

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

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

    Science.gov (United States)

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

    2013-01-01

    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

  1. 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

    Energy Technology Data Exchange (ETDEWEB)

    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)

    2005-08-01

    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

  2. Time-Transgressive Nature of the Magnetic Susceptibility Record across the Chinese Loess Plateau at the Pleistocene/Holocene Transition

    Science.gov (United States)

    Dong, Yajie; Wu, Naiqin; Li, Fengjiang; Huang, Linpei; Wen, Wenwen

    2015-01-01

    The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS) has previously been assumed to be synchronous with the Marine Isotope Stage (MIS) 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP). However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR) protocol to the 45–63 μm quartz grain-size fraction to derive luminescence ages for the last glacial and Holocene sections of three loess sections on a transect from southeast to northwest across the CLP. Based on the 33 closely spaced optically stimulated luminescence (OSL) samples from the three sections, OSL chronologies were established using a polynomial curve fit at each section. Based on the OSL chronology, the timing of the Pleistocene/Holocene boundary, as defined by rapid changes in MS values, is dated at ~10.5 ka, 8.5 ka and 7.5 ka in the Yaoxian section, Jingchuan and Huanxian sections respectively. These results are clearly inconsistent with the MIS 2/1 boundary age of 12.05 ka, and therefore we conclude that the automatic correlation of the Pleistocene/Holocene transition, as inferred from the MS record, with the MIS 2/1 boundary is incorrect. The results clearly demonstrate that the marked changes in MS along the southeast to northwest transect are time-transgressive among the different sites, with the timing of significant paleosol development as indicated by the MS record being delayed by 3–4 ka in the northwest compared to the southeast. Our results suggest that this asynchronous paleosol development during the last deglacial was caused by the delayed arrival of the summer monsoon in the northwest CLP compared to the southeast. PMID:26186443

  3. Time-Transgressive Nature of the Magnetic Susceptibility Record across the Chinese Loess Plateau at the Pleistocene/Holocene Transition.

    Directory of Open Access Journals (Sweden)

    Yajie Dong

    Full Text Available The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS has previously been assumed to be synchronous with the Marine Isotope Stage (MIS 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP. However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR protocol to the 45-63 μm quartz grain-size fraction to derive luminescence ages for the last glacial and Holocene sections of three loess sections on a transect from southeast to northwest across the CLP. Based on the 33 closely spaced optically stimulated luminescence (OSL samples from the three sections, OSL chronologies were established using a polynomial curve fit at each section. Based on the OSL chronology, the timing of the Pleistocene/Holocene boundary, as defined by rapid changes in MS values, is dated at ~10.5 ka, 8.5 ka and 7.5 ka in the Yaoxian section, Jingchuan and Huanxian sections respectively. These results are clearly inconsistent with the MIS 2/1 boundary age of 12.05 ka, and therefore we conclude that the automatic correlation of the Pleistocene/Holocene transition, as inferred from the MS record, with the MIS 2/1 boundary is incorrect. The results clearly demonstrate that the marked changes in MS along the southeast to northwest transect are time-transgressive among the different sites, with the timing of significant paleosol development as indicated by the MS record being delayed by 3-4 ka in the northwest compared to the southeast. Our results suggest that this asynchronous paleosol development during the last deglacial was caused by the delayed arrival of the summer monsoon in the northwest CLP compared to the southeast.

  4. Causes of early Holocene desertification in arid central Asia

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-04-15

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

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

    Science.gov (United States)

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

    2016-01-01

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

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

    Science.gov (United States)

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

    2016-03-01

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

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

    Directory of Open Access Journals (Sweden)

    S. Weldeab

    2013-10-01

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

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

    Science.gov (United States)

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

    2013-04-01

    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

  9. Modern climate challenges and the geological record

    Science.gov (United States)

    Cronin, Thomas M.

    2010-01-01

    Today's changing climate poses challenges about the influence of human activity, such as greenhouse gas emissions and land use changes, the natural variability of Earth's climate, and complex feedback processes. Ice core and instrumental records show that over the last century, atmospheric carbon dioxide (CO2) concentrations have risen to 390 parts per million volume (ppmv), about 40% above pre-Industrial Age concentrations of 280 ppmv and nearly twice those of the last glacial maximum about 22,000 years ago. Similar historical increases are recorded in atmospheric methane (CH4) and nitrous oxide (N2O). There is general agreement that human activity is largely responsible for these trends. Substantial evidence also suggests that elevated greenhouse gas concentrations are responsible for much of the recent atmospheric and oceanic warming, rising sea level, declining Arctic sea-ice cover, retreating glaciers and small ice caps, decreased mass balance of the Greenland and parts of the Antarctic ice sheets, and decreasing ocean pH (ocean "acidification"). Elevated CO2 concentrations raise concern not only from observations of the climate system, but because feedbacks associated with reduced reflectivity from in land and sea ice, sea level, and land vegetation relatively slowly (centuries or longer) to elevated 2 levels. This means that additional human-induced climate change is expected even if the rate of CO2 emissions is reduced or concentrations immediately stabilized.

  10. Late Glacial to Holocene environments in the present-day coldest region of the Northern Hemisphere inferred from a pollen record of Lake Billyakh, Verkhoyansk Mts, NE Siberia

    Directory of Open Access Journals (Sweden)

    S. Müller

    2009-03-01

    Full Text Available In this study, a radiocarbon-dated pollen record from Lake Billyakh (65°17' N, 126°47' E; 340 m a.s.l. in the Verkhoyansk Mountains was used to reconstruct vegetation and climate change since about 15 kyr BP. The pollen record and pollen-based biome reconstruction suggest that open cool steppe (STEP and grass and sedge tundra (TUND communities with Poaceae, Cyperaceae, Artemisia, Chenopodiaceae, Caryophyllaceae and Selaginella rupestris dominated the area from 15 to 13.5 kyr BP. On the other hand, the constant presence of Larix pollen in quantities comparable to today's values points to the constant presence of boreal deciduous conifer (CLDE trees in the regional vegetation during the Late Glacial. A major spread of shrub tundra communities, including birch (Betula sect. Nanae, alder (Duschekia fruticosa and willow (Salix species, is dated to 13.5–12.7 kyr BP, indicating a noticeable increase in precipitation toward the end of the Last Glaciation, particularly during the Bølling-Allerød Interstadial. Between 12.7 and 11.4 kyr BP pollen percentages of herbaceous taxa rapidly increased, whereas shrub taxa percentages decreased, suggesting strengthening of the steppe communities associated with the relatively cold and dry Younger Dryas Stadial. However, the pollen data in hand indicate that Younger Dryas climate was less severe than the climate during the earlier interval from 15 to 13.5 kyr BP. The onset of the Holocene is marked in the pollen record by the highest values of shrub and lowest values of herbaceous taxa, suggesting a return of warmer and wetter conditions after 11.4 kyr BP. Percentages of tree taxa increase gradually and reach maximum values after 7 kyr BP, reflecting the spread of boreal cold deciduous and taiga forests in the region. An interval between 7 and 2 kyr BP is noticeable for the highest percentages of Scots pine (Pinus subgen.

  11. Millennial-scale faunal record reveals differential resilience of European large mammals to human impacts across the Holocene.

    Science.gov (United States)

    Crees, Jennifer J; Carbone, Chris; Sommer, Robert S; Benecke, Norbert; Turvey, Samuel T

    2016-03-30

    The use of short-term indicators for understanding patterns and processes of biodiversity loss can mask longer-term faunal responses to human pressures. We use an extensive database of approximately 18,700 mammalian zooarchaeological records for the last 11,700 years across Europe to reconstruct spatio-temporal dynamics of Holocene range change for 15 large-bodied mammal species. European mammals experienced protracted, non-congruent range losses, with significant declines starting in some species approximately 3000 years ago and continuing to the present, and with the timing, duration and magnitude of declines varying individually between species. Some European mammals became globally extinct during the Holocene, whereas others experienced limited or no significant range change. These findings demonstrate the relatively early onset of prehistoric human impacts on postglacial biodiversity, and mirror species-specific patterns of mammalian extinction during the Late Pleistocene. Herbivores experienced significantly greater declines than carnivores, revealing an important historical extinction filter that informs our understanding of relative resilience and vulnerability to human pressures for different taxa. We highlight the importance of large-scale, long-term datasets for understanding complex protracted extinction processes, although the dynamic pattern of progressive faunal depletion of European mammal assemblages across the Holocene challenges easy identification of 'static' past baselines to inform current-day environmental management and restoration. © 2016 The Author(s).

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

    Science.gov (United States)

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

    2016-06-01

    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

  13. Holocene environmental changes in southern Kamchatka, Far Eastern Russia, inferred from a pollen and testate amoebae peat succession record

    Science.gov (United States)

    Klimaschewski, A.; Barnekow, L.; Bennett, K. D.; Andreev, A. A.; Andrén, E.; Bobrov, A. A.; Hammarlund, D.

    2015-11-01

    High resolution palaeoenvironmental records in Far-Eastern Russia are rare, and the Kamchatka Peninsula is among the least studied areas of the region. This paper describes a record spanning the last ca. 11,000 yr, obtained from a bog in the southern part of Kamchatka. The radiocarbon dated core was analysed for pollen, testate amoebae, charcoal and loss-on-ignition (LOI). The vegetation during the early Holocene was dominated by grasses (Poaceae), birch (Betula) and heath (Ericaceae p. p.). Around 10,300 cal yr BP there was a substantial change in the vegetation cover to shrub alder (Alnus viridis s.l.) stands with sedges and ferns (Polypodiophyta) as well as herbs such as meadow rue (Thalictrum) in the understory. In the surroundings of Utka peatlands started to form. The variations in the vegetation cover were most probably caused by climatic changes. At the beginning of sediment accumulation, before 10,300 cal yr BP, the composition of the vegetation points to cooler summers and/or decreased annual precipitation. Around 10,300 cal yr BP, changes in vegetation occurred due to rising temperatures and/or changed water regimes. Increased abundancies of dry indicating testate amoebae after 9100 cal yr BP point to intermediate to dry soil conditions. Between 8600 and 7700 cal yr BP tree alder (Alnus incana) was widely spread at the site which probably indicates optimal environmental conditions. The tephra layer at 381-384.5 cm (ca. 8500 cal yr BP) produces a strong impact on the testate amoebae assemblages. At 7700 cal yr BP there was a sudden drop of A. incana in the local vegetation. From this time on, A. incana and also A. viridis decrease continuously whereas Betula gradually increases. The upper part of the sequence (after 6300 cal yr BP) shows higher abundancies of meadowsweet (Filipendula) and sweet gale (Myrica) pollen. After 6300 cal yr BP, changes in testate amoebae demonstrate variable soil moisture conditions at the site. Between 3700 and 1800 cal yr BP

  14. 500-year climate cycles stacking of recent centennial warming documented in an East Asian pollen record

    Science.gov (United States)

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

    2014-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Daniel VERES

    2014-11-01

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

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

    Directory of Open Access Journals (Sweden)

    Mark de Bruyn

    2009-07-01

    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.

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

    Science.gov (United States)

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

    2009-07-01

    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.

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

    Science.gov (United States)

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

    2009-12-01

    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

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

    Science.gov (United States)

    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.

    2015-04-01

    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.

  20. Multiproxy Holocene paleoclimate records from the southern Peruvian Andes - what new can we learn from the stable carbon isotope composition of high altitude organic matter deposits?

    Science.gov (United States)

    Skrzypek, Grzegorz; Engel, Zbyněk

    2015-04-01

    Interpretation of the Central Andean paleoclimate over the last millennia still represents a research challenge demanding deeper studies [1,2]. Several high-resolution paleoclimate proxies for the last 10,000 years have been developed for the northern hemisphere. However, similar proxies are very limited for South America, particularly for high altitudes where, for example, tree-ring chronologies are not available and instrumental records are very limited. Consequently, our knowledge of high altitude climate changes in arid regions of the Peruvian Andes mainly relies on ice-core and lake deposit studies. In our study, we used a new alternative proxy for interpretation of palaeoclimate conditions based on a peat core taken from the Carhuasanta Valley at the foot of Nevado Mismi in the southern Peruvian Andes (15° 30'S, 71° 43'W, 4809m a.s.l.). The stable carbon isotope composition (δ13C) of Distichia peat reflects mainly the relative variation of the mean air temperature during subsequent growing seasons [3], and allows reconstructions of palaeotemperature changes. In contrast, peat organic carbon concentration (C % wt) records mainly wetness in the valley, directly corresponding to the changes in runoff in the upper part of the catchment. The most prominent climate changes recorded in the peat over last 4ka occurred between 3040 and 2750 cal. yrs BP. The initial warming turned to a very rapid cooling to temperatures at least 2° C lower than the mean for the Late Holocene. Initially drier conditions within this event turned to a short wet phase after 2780 cal. yrs BP, when the temperature increased again. This event coincides with significant changes in peat and ice core records in the Central Andes that match the timing of the global climate event around 2.8 cal. ka BP. Climatic conditions in the study area became relatively dry and stable after the event for about 800 years. Highly variable temperatures and humidity prevailed during the last 2000 years, when

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

    DEFF Research Database (Denmark)

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

    2017-01-01

    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...

  2. Lake sediment records of Quaternary climate change

    International Nuclear Information System (INIS)

    Moy, C.

    2012-01-01

    Lake sediment records provide an excellent means to reconstruct past climate and environmental change because they typically provide long, high-resolution and continuous archives of environmental change. Lake sediment records typically exhibit high sedimentation rates (centennial to millennial scale variability is common and annual resolution is possible in some sites), contain sedimentary components well-suited for a multi-proxy approach, multiple dating methods can be applied, tend to exhibit a broad geographic distribution, and are relatively accessible. Furthermore, a number of geochemical techniques can be applied to reconstruct components of the climate system based on the stable isotope geochemistry of carbonate or organic phases preserved and exposed in lacustrine sediment cores. Various stable isotope methods can be applied to lacustrine systems and these are a valuable tool that can be used to monitor physical processes (e.g. evaporation), vegetation dynamics within the watershed (C 3 vs C 4 plant distributions), biologic processes (aquatic productivity), all of which can be driven by a regional climate forcing. (author). 31 refs., 11 figs., 1 tab.

  3. A late Holocene record of arid events from the Cuzco region, Peru

    Science.gov (United States)

    Chepstow-Lusty, Alex; Frogley, Michael R.; Bauer, Brian S.; Bush, Mark. B.; Tupayachi Herrera, Alfredo

    2003-09-01

    The small recently infilled lake basin of Marcacocha (13°13S, 72°12W, 3355 m) in the Cuzco region of Peru has a morphology and location that renders it extremely sensitive to environmental change. A record of vegetation, human impact and climatic change during the past 4200 yr has been obtained from a highly organic core taken from the centre of the basin. Sustained arid episodes that affected the Peruvian Andes may be detectable using the proxy indicator of sedge (Cyperaceae) pollen abundances. As the lake-level was lowered during sustained drier conditions, the local catchment was colonised by Cyperaceae, whereas during lake floods, they retreated or were submerged and pollen production was correspondingly reduced. Drier episodes during prehistoric times occurred around 900 bc, 500 bc, ad 100 and ad 550, with a longer dry episode occurring from ad 900 to 1800. Evidence from the independently derived Quelccaya ice-core record and the archaeological chronology for the Cuzco region appears to support the climatic inferences derived from the sedge data. Many of these aridity episodes appear to correspond with important cultural changes in the Cuzco region and elsewhere in the Central Andes. Copyright

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

    International Nuclear Information System (INIS)

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

    2012-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-04-01

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

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

    Science.gov (United States)

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

    2018-03-01

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

  7. PLEISTOCENE-HOLOCENE PALAEOENVIRONMENTAL RECORDS FROM PERMAFROST SEQUENCES AT THE KARA SEA COAST (NW SIBERIA, RUSSIA

    Directory of Open Access Journals (Sweden)

    Irina Streletskaya

    2013-01-01

    Full Text Available The Kara Sea coasts were studied using comprehensive stratigraphic and geocryological methods. The paper presents the new analytical studies of ground ice and Quaternary deposits of Western Taymyr and presents the results of spore and pollen, foraminifera, grain-size, mineralogical, geochemical, oxygen isotopic, and other analyses. Several stratigraphic-geocryological transects from Yenisey and Gydan Bays enable us to refine the stratigraphy and palaeogeographical reconstruction of the environments and freezing of Late Pleistocene-Holocene sediments. Marine sedimentation conditions during the late Kargino time (MIS3 changed to continental conditions in MIS2 and MIS1. Marine sediments were frozen syn- and epigenetically with cryotexture and ground ice formation. Ice wedges formation corresponds to the end of the Pleistocene (MIS2 and during cooler periods of the Holocene.

  8. High-resolution paleoclimate records of Holocene hydroclimatic variability in the Eastern Colombian Andes from Lago de Tota

    Science.gov (United States)

    Ahmed, M. N.; Bird, B. W.; Escobar, J.; Polissar, P. J.

    2017-12-01

    The Northern Hemisphere (NH) South American Monsoon (SAM) is a significant source of precipitation for the North Andes (north of 0˚) and has major control over regional hydroclimate variability. Holocene-length histories of NH SAM variability are few compared to the Southern Hemisphere (SH), limiting understanding of how these systems are connected on orbital and shorter timescales. Here, we present multi-proxy lake-sediment-based paleoclimate and paleohydrologic reconstructions from Lago de Tota, Colombia, using sedimentological, geochemical and leaf-wax hydrogen isotopic indicators from radiometically dated cores. The results indicate periods of wet and dry climate phases during the past 9000 BP with an average Holocene sedimentation rate 33cm/kyr. An increase in total organic matter (TOM) content and finer grain-size distributions was observed from 8000 to 3200 BP, suggesting a period of high lake level. This was followed by lower TOM and coarser grain sizes, suggesting lower lake levels from 3200 BP to the present. Although Tota's lake level pattern is antiphased with other lake level reconstructions from the NH and SH Andes, it is consistent with hypothesized changes in atmospheric convection over the Andes during the Holocene and the way in which they would be modified by the so-called dry island effect in the Colombian Andes. This suggests that a common forcing mechanism can be invoked to explain differing millennial-scale Andean hydroclimate changes, namely atmospheric convection. Orbital and Pacific atmosphere-forcing are therefore likely to have played a significant role in driving pan-Andean hydroclimate variability based on their inter-hemispheric influence on Andean convection.

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

    Energy Technology Data Exchange (ETDEWEB)

    Bellin, N.; Vanacker, V.

    2009-07-01

    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.

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

    International Nuclear Information System (INIS)

    Bellin, N.; Vanacker, V.

    2009-01-01

    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.

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

    Science.gov (United States)

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

    2005-01-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-07-01

    This thesis presents the development of statistical climatological-botanical transfer functions in order to provide reconstructions of Holocene climate variability in the Near East region. Two classical concepts, the biomisation as well as the indicator taxa approach, are translated into a Bayesian network. Fossil pollen spectra of laminated sediments from the Ein Gedi location at the western shoreline of the Dead Sea and from the crater lake Birkat Ram in the northern Golan serve as proxy data, covering the past 10000 and 6500 years, respectively. The climatological variables are winter temperature, summer temperature, and annual precipitation, obtained from the 0.5 x 0.5 degree climatology CRU TS 1.0. The Bayesian biome model is based on the three main vegetation territories, the Mediterranean, the Irano-Turanian, and the Saharo-Arabian territory, which are digitized on the same grid as the climate data. From their spatial extend, a classification in the phase space is described by estimating the conditional probability for the existence of a certain biome given the climate. These biome specific likelihood functions are modelled by a generalised linear model, including second order monomials of the climate variables. A statistical mixture model is applied to the biome probabilities as estimated by the Ein Gedi data, resulting in a posterior probability density function for the three dimensional climate state vector. The indicator taxa model is based on the distribution of 15 Mediterranean taxa. Their spatial extend allows to estimate the taxon specific likelihood functions. In this case, they are conditional probability density functions for the climate state vector given the existence of a certain taxon. In order to address the general problem of multivariate non-normally distributed populations, multivariate normal Copulas are used, which allow to create distribution functions with gamma as well as normal marginal distributions. Applying the model to the Birkat

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

    Science.gov (United States)

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

    2017-12-01

    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.

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

    Science.gov (United States)

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

    2017-12-01

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

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

    Science.gov (United States)

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

    2008-12-01

    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

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

    Science.gov (United States)

    Starratt, Scott W.

    2009-01-01

    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.

  17. Towards realistic Holocene land cover scenarios: integration of archaeological, palynological and geomorphological records and comparison to global land cover scenarios.

    Science.gov (United States)

    De Brue, Hanne; Verstraeten, Gert; Broothaerts, Nils; Notebaert, Bastiaan

    2016-04-01

    Accurate and spatially explicit landscape reconstructions for distinct time periods in human history are essential for the quantification of the effect of anthropogenic land cover changes on, e.g., global biogeochemical cycles, ecology, and geomorphic processes, and to improve our understanding of interaction between humans and the environment in general. A long-term perspective covering Mid and Late Holocene land use changes is recommended in this context, as it provides a baseline to evaluate human impact in more recent periods. Previous efforts to assess the evolution and intensity of agricultural land cover in past centuries or millennia have predominantly focused on palynological records. An increasing number of quantitative techniques has been developed during the last two decades to transfer palynological data to land cover estimates. However, these techniques have to deal with equifinality issues and, furthermore, do not sufficiently allow to reconstruct spatial patterns of past land cover. On the other hand, several continental and global databases of historical anthropogenic land cover changes based on estimates of global population and the required agricultural land per capita have been developed in the past decennium. However, at such long temporal and spatial scales, reconstruction of past anthropogenic land cover intensities and spatial patterns necessarily involves many uncertainties and assumptions as well. Here, we present a novel approach that combines archaeological, palynological and geomorphological data for the Dijle catchment in the central Belgium Loess Belt in order to arrive at more realistic Holocene land cover histories. Multiple land cover scenarios (> 60.000) are constructed using probabilistic rules and used as input into a sediment delivery model (WaTEM/SEDEM). Model outcomes are confronted with a detailed geomorphic dataset on Holocene sediment fluxes and with REVEALS based estimates of vegetation cover using palynological data from

  18. Holocene vegetational and coastal environmental changes from the Lago Crispim record in northeastern Pará State, eastern Amazonia.

    Science.gov (United States)

    Behling, H; Lima da Costa, M

    2001-04-01

    Vegetational and coastal environmental changes have been interpreted from a 600cm long and 764014C yr B.P. old sediment core from Lago Crispim located in the northeastern Pará State in northern Brazil. The radiocarbon dated sediment core was studied by multi-element geochemistry, pollen and charcoal analysis.Holocene Atlantic sea-level rise caused an elevation of local water table, which allowed the formation of organic deposits in a probably former inter-dune valley. Dense, diverse and tall Amazon rain forest, and some restinga (coastal vegetation) covered the study area at the beginning of the record at 764014C yr B.P. Mangrove vegetation developed along rivers close to the core site at that time. Subsequent decrease in less mangrove vegetation near the study site indicates a sea-level regression, beginning since around 700014C yr B.P. Lower sea-levels probably favoured the formation of a local Mauritia/Mauritiella palm swamp at 662014C yr B.P. Oscillations of higher and lower sea-level stands probably changed the size of the local palm swamp area several times between 6620 and 363014C yr B.P. Sea-level transgression at around 363014C yr B.P., caused marked coastal environmental changes: the development of mangroves near the site, the replacement of the local palm swamp by a Cyperaceae swamp, the substitution of the surrounding former Amazon rain forest and some restinga vegetation mainly by salt marshes. High amount carbonised particles suggest a strong human impact by burning on the coastal ecosystems during this late Holocene period.Highest concentrations of NaCl and also Ca, Mg and K in the upper sediment core indicate that the Atlantic was close during the late Holocene period. The core site, which is today 500m from the coastline and only 1-2m above modern sea-level, was apparently never reached by marine excursions during the Holocene.Less representation of mangrove since ca. 184014C yr B.P., may be related due to a slightly lower sea-level or to human

  19. Foraminiferal record of Holocene paleo-earthquakes on the subsiding south-western Poverty Bay coastline, New Zealand

    International Nuclear Information System (INIS)

    Hayward, B.W.; Sabaa, A.T.; Grenfell, H.R.; Cochran, U.A.; Clark, K.J.; Litchfield, N.J.; Wallace, L.M.; Marden, M.; Palmer, A.S.

    2015-01-01

    Foraminiferal faunas in 29 short cores (maximum depth 7 m) of estuarine and coastal wetland sediment were used to reconstruct the middle-late Holocene (last 7 ka) elevational history on the southern shores of Poverty Bay, North Island, New Zealand. This coast is on the southwest side of a rapidly subsiding area beneath western Poverty Bay. Modern Analogue Technique paleo-elevation estimates based on fossil foraminiferal faunas indicate that the four study areas have gradual late Holocene (<3.5 ka) subsidence rates that increase from the southwest (mean c. 0.5 m ka - - 1 ) to northeast (mean c. 1.0 m ka -1 ). Only two rapid, possibly co-seismic, vertical displacement events are recognised: (1) c. 1.2 m of subsidence at 5.7 ± 0.4 ka (cal yr BP), which may have been generated by a subduction interface earthquake centred offshore and recorded in other published studies in northern Hawkes Bay, c. 35 km to the south; and (2) c. 1 m of uplift (relative sea-level fall) at c. 4.5 ± 0.3 ka, which might have been generated by rupture on an offshore upper plate fault that also uplifted coastal terraces at Pakarae and Mahia, 40 km to the north and south of the study area, or by rupture on the subduction interface penetrating beneath Poverty Bay. No sudden displacement events are recognised during the last 4 ka although subsidence, possibly aseismic, has continued. (author).

  20. Middle Holocene Organic Carbon and Biomarker Records from the South Yellow Sea: Relationship to the East Asian Monsoon

    Science.gov (United States)

    Zou, Liang; Hu, Bangqi; Li, Jun; Dou, Yanguang; Xie, Luhua; Dong, Liang

    2018-03-01

    The East Asian monsoon system influences the sedimentation and transport of organic matter in East Asian marginal seas that is derived from both terrestrial and marine sources. In this study, we determined organic carbon (OC) isotope values, concentrations of marine biomarkers, and levels of OC and total nitrogen (TN) in core YSC-1 from the central South Yellow Sea (SYS). Our objectives were to trace the sources of OC and variations in palaeoproductivity since the middle Holocene, and their relationships with the East Asian monsoon system. The relative contributions of terrestrial versus marine organic matter in core sediments were estimated using a two-end-member mixing model of OC isotopes. Results show that marine organic matter has been the main sediment constituent since the middle Holocene. The variation of terrestrial organic carbon concentration (OCter) is similar to the EASM history. However, the variation of marine organic carbon concentration (OCmar) is opposite to that of the EASM curve, suggesting OCmar is distinctly influenced by terrestrial material input. Inputs of terrestrial nutrients into the SYS occur in the form of fluvial and aeolian dust, while concentrations of nutrients in surface water are derived mainly from bottom water via the Yellow Sea circulation system, which is controlled by the East Asian winter monsoon (EAWM). Variations in palaeoproductivity represented by marine organic matter and biomarker records are, in general, consistent with the recent EAWM intensity studies, thus, compared with EASM, EAWM may play the main role to control the marine productivity variations in the SYS.

  1. A Holocene progradation record from Okains Bay, Banks Peninsula, Canterbury, New Zealand

    International Nuclear Information System (INIS)

    Stephenson, W.; Shulmeister, J.

    1999-01-01

    Fifty-eight distinct ridges are preserved on the Holocene progradation plain in Okains Bay, Banks Peninsula, Canterbury. Of these, 48 represent beach berm and foredune complexes and the remaining 10 are transverse dune ridges. Periods of rapid coastal progradation are marked by multiple beach berm preservation, whereas intervening periods of lower sediment accumulation result in a stable coastline and transverse dune formation. Infilling of the bay began following sea-level stabilisation in the mid Holocene. The fill is dominantly fine sand, which is derived from sediment carried around Banks Peninsula in the Southland Current and washed into Okains Bay by wave action. Variations in the progradation rate are therefore proxy indicators of coastal erosion in the Canterbury Bight. We demonstrate that there is little progradational fill preserved between c. 6500 and 2000 yr BP. This implies significant changes in sediment delivery to the Southland Current within the last 2000 yr, which we attribute to increased coastal erosion in South Canterbury. We speculate that this increasing erosion resulted from increased wave energy regimes, which in turn may relate to increasing Southern Hemisphere seasonality following the precessional cycle. (author). 32 refs., 4 figs., 3 tabs

  2. Seasonal and interannual variability of the Mid-Holocene East Asian monsoon in coral δ18O records from the South China Sea

    Science.gov (United States)

    Sun, Donghuai; Gagan, Michael K.; Cheng, Hai; Scott-Gagan, Heather; Dykoski, Carolyn A.; Edwards, R. Lawrence; Su, Ruixia

    2005-08-01

    Understanding the full range of past monsoon variability, with reference to specific monsoon seasons, is essential to test coupled climate models and improve their predictive capabilities. We present a 54-year long, high-resolution skeletal oxygen isotope (δ18O) record extracted from a well-preserved, massive Porites sp. coral at Hainan Island, South China Sea, to investigate East Asian monsoon variability during summer and winter ∼4400 calendar yr ago. Analysis of modern coral δ18O confirms that Porites from Hainan Island are well positioned to record winter monsoon forcing of sea surface temperature (SST), as well as the influence of summer monsoon rainfall on sea surface salinity (SSS). The coral record for ∼4400 yr ago shows ∼9% amplification of the annual cycle of δ18O, in good agreement with coupled ocean-atmosphere models showing higher summer rainfall (lower coral δ18O) and cooler winter SSTs (higher coral δ18O) in response to greater Northern Hemisphere insolation seasonality during the Middle Holocene. Mean SSTs in the South China Sea during the Mid-Holocene were within 0.5 °C of modern values, yet the mean δ18O for the fossil coral is ∼0.6‰ higher than that for the modern coral, suggesting that the δ18O of surface seawater was higher by at least ∼0.5‰, relative to modern values. The 18O-enrichment is likely to be driven by greater advection of moisture towards the Asian landmass, enhanced monsoon wind-induced evaporation and vertical mixing, and/or invigorated advection of saltier 18O-enriched Pacific water into the relatively fresh South China Sea. The 18O-enrichment of the northern South China Sea ∼4400 yr ago contributes to mounting evidence for recent freshening of the tropical Western Pacific. Today, winter SST and summer SSS variability in the South China Sea reflect the interannual influence of ENSO and the biennial variability inherent to monsoon precipitation. Spectral analysis of winter SSTs ∼4400 yr ago reveals a

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

    Science.gov (United States)

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

    2014-05-01

    human activities were different (mining versus agriculture, respectively). Lakes Blanc Huez and Paladru are defined by good Holocene chronologies and well detailed lithologies (1, 2). Both archaeological evidences and interdisciplinary characterizations of the two systems demonstrated that Lake Blanc Huez sedimentary infill is only sensitive to climate forcing and that soil fluxes are therefore only proportional to snow and/or water rainfalls (1), whereas the sedimentation recorded within Lake Paladru results both from climate and anthropogenic forcing. Results demonstrate that around Lake Paladru, human-induced soil erosion is effective since the Neolithic period and the beginning of agrarian activities (2). Following our quantification and modelling, human activities were able to explain up to 50% of soil fluxes in particular between the Bronze Age and the Middle Age suggesting that the actual geomorphology of the drainage basin is inherited from several millenary and not only from modern activities. (1) Simonneau et al., accepted, Quaternary Science Reviews (2) Simonneau et al., 2013, Journal of Archaeological Science, 40: 1636-1645.

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

    Science.gov (United States)

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

    2017-04-01

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

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

    Science.gov (United States)

    Levine, R.; Meyer, G. A.

    2013-12-01

    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

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

    Science.gov (United States)

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

    2017-12-01

    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

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

    Science.gov (United States)

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

    2017-05-01

    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.

  8. Towards a record of Holocene tsunami and storms for northern Hawke's Bay, New Zealand

    International Nuclear Information System (INIS)

    Cochran, U.A.; Berryman, K.R.; Mildenhall, D.C.; Hayward, B.W.; Southall, K.; Hollis, C.J.

    2005-01-01

    Eleven sand layers occur within Holocene low-energy estuarine and marginal marine sequences of blue-grey silty clay at two sites on the coastal plain between Wairoa and Mahia Peninsula, northern Hawke's Bay, New Zealand. The sedimentology and fossil assemblages of these layers are consistent with deposition by high-energy influxes to the sites. Three influxes are terrestrial in nature and are thought to represent alluvial flood events. All other sand layers are marine derived and are likely to be the result of storm surges or tsunami. Tsunami inundation is favoured for two sand layers that occur in association with evidence for sudden subsidence at c. 6300 and c. 4800 yr BP. The c. 6300 yr inundation also coincides with previously identified evidence for a tsunami at a site 10 km westwards along the coast. Further investigation is required to distinguish between tsunami and storm surge deposition for the remaining six layers. (author). 50 refs., 4 figs., 2 tabs

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhengyu Liu, Bette Otto-Bliesner

    2013-02-01

    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.

  10. Late Pleistocene to Holocene environmental changes as recorded in the sulfur geochemistry of coastal plain sediments, southwestern Taiwan

    Science.gov (United States)

    Chen, Y.-G.; Liu, J.C.-L.; Shieh, Y.-N.; Liu, T.-K.

    2004-01-01

    A core, drilled at San-liao-wan in the southwestern coastal plain of Taiwan, has been analyzed for total sulfur contents, isotopic values, as well as ratios of pyritic sulfur to organic carbon. Our results demonstrate a close relationship between late Pleistocene sea-level change and the proxies generated in this study. The inorganic sulfur contents indicate that at our study site, the Holocene transgression started at ???11 ka and remained under seawater for thousands of years until the late Holocene, corresponding to a depth of 20 m in the study core. The uppermost 20 m of core shows relatively high total organic carbon (TOC) and ??34S of inorganic sulfur, suggesting a transitional environment such as muddy lagoon or marsh, before the site turned into a modern coastal plain. In the lower part of the core, at depths of 110-145 m (corresponding ages of ???12-30 ka), low sulfur contents are recorded, probably indicating fluvial sediments deposited during the oceanic isotope stage (OIS) 2, a sea-level lowstand. The lower part of the core, roughly within OIS 3, records at least two transgressions, although the transgressional signals may be somewhat obscured by subsequent weathering. The reworked origin of organic matter reported in previous studies is confirmed by our organic sulfur data; however, the marine organic source was periodically dominant. The modern high sulfate concentrations in pore water have no correlation to the other sulfur species in the sediments, probably indicating that the sulfate migrated into the site subsequent to early diagenesis. ?? 2003 Elsevier Ltd. All rights reserved.

  11. A Holocene pollen record of vegetation change and human impact from Pantano de Vargas, an intra-Andean basin of Duitama, Colombia

    NARCIS (Netherlands)

    Gomez, A.; Berrio, J.C.; Hooghiemstra, H.; Becerra, M.; Marchant, R.

    2007-01-01

    Holocene environments in the intra-Andean basin of Duitama (Eastern Cordillera of Colombia, 2510 m altitude) are presented based on the 620 cm long Vargas pollen and sediment record. Seven AMS radiocarbon dates show these lake and swamp sediments represent the period from 8800 to 2610 14C yr BP. We

  12. A simple conceptual model to interpret the 100 000 years dynamics of paleo-climate records

    Directory of Open Access Journals (Sweden)

    C. S. Quiroga Lombard

    2010-10-01

    Full Text Available Spectral analyses performed on records of cosmogenic nuclides reveal a group of dominant spectral components during the Holocene period. Only a few of them are related to known solar cycles, i.e., the De Vries/Suess, Gleissberg and Hallstatt cycles. The origin of the others remains uncertain. On the other hand, time series of North Atlantic atmospheric/sea surface temperatures during the last ice age display the existence of repeated large-scale warming events, called Dansgaard-Oeschger (DO events, spaced around multiples of 1470 years. The De Vries/Suess and Gleissberg cycles with periods close to 1470/7 (~210 and 1470/17 (~86.5 years have been proposed to explain these observations. In this work we found that a conceptual bistable model forced with the De Vries/Suess and Gleissberg cycles plus noise displays a group of dominant frequencies similar to those obtained in the Fourier spectra from paleo-climate during the Holocene. Moreover, we show that simply changing the noise amplitude in the model we obtain similar power spectra to those corresponding to GISP2 δ18O (Greenland Ice Sheet Project 2 during the last ice age. These results give a general dynamical framework which allows us to interpret the main characteristic of paleoclimate records from the last 100 000 years.

  13. Holocene aridification of India

    Science.gov (United States)

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

    2012-01-01

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

  14. Preservation of a Late Glacial terrestrial and Holocene estuarine record on the margins of Kaipara Harbour, Northland, New Zealand

    International Nuclear Information System (INIS)

    Nichol, S.; Deng, Y.; Horrocks, M.; Zhou, W.; Hume, T.

    2009-01-01

    Subtidal to intertidal deposits from the margins of Kaipara Harbour in Northland preserve a c. 23,000 year incomplete sedimentary record of the transition from terrestrial to estuarine conditions. Cores are used to reconstruct the depositional setting for this transition, interpreted as a succession from dune and freshwater wetland to shallow estuarine environments. The fossil pollen record provides a proxy of Last Glacial Maximum and Late Glacial vegetation for the area. Stability of the Pleistocene dune landscape during the postglacial marine transgression is interpreted on the basis of strong dominance of tall forest taxa (Dacrydium) in the pollen record and soil development in dune sands, with preservation aided by location along the estuary margin. During the Holocene, reworking of the buried dune and wetland sediments has only reached to a depth of 1.5 m below the modern tidal flat. As such, the site provides a rare example of good preservation of Pleistocene deposits at the coast, where extensive reworking and loss of record are more typical. (author). 41 refs., 6 figs., 1 tab

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

    Science.gov (United States)

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

    2016-12-12

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

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

    OpenAIRE

    Poirier , Clément; Tessier , Bernadette; Chaumillon , Eric

    2017-01-01

    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...

  17. Regional, holocene records of the human dimension of global change: sea-level and land-use change in prehistoric Mexico

    Science.gov (United States)

    Sluyter, Andrew

    1997-02-01

    Regional, Holocene records hold particular relevance for understanding the reciprocal nature of global environmental change and one of its major human dimensions: "sustainable agriculture", i.e., food production strategies which entail fewer causes of and are less susceptible to environmental change. In an epoch of accelerating anthropogenic transformation, those records reveal the protracted regional causes and consequences of change (often agricultural) in the global system as well as informing models of prehistoric, intensive agriculture which, because of long tenures and high productivities, suggest strategies for sustainable agricultural in the present. This study employs physiographic analysis and the palynological, geochemical record from cores of basin fill to understand the reciprocal relation between environmental and land-use change in the Gulf of Mexico tropical lowland, focusing on a coastal basin sensitive to sea-level change and containing vestiges of prehistoric settlement and wetland agriculture. Fossil pollen reveals that the debut of maize cultivation in the Laguna Catarina watershed dates to ca. 4100 BC, predating the earliest evidence for that cultivar anywhere else in the lowlands of Middle America. Such an early date for a cultivar so central to Neotropical agroecology and environmental change, suggests the urgency of further research in the study region. Moreover, the longest period of continuous agriculture in the basin lasted nearly three millennia (ca. 2400 BC-AD 550) despite eustatic sea-level rise. Geochemical fluxes reveal the reciprocity between land-use and environmental change: slope destabilization, basin aggradation, and eutrophication. The consequent theoretical implications pertain to both applied and basic research. Redeploying ancient agroecologies in dynamic environments necessitates reconstructing the changing operational contexts of putative high productivity and sustainability. Adjusting land use in the face of global

  18. An overview of European efforts in generating climate data records

    NARCIS (Netherlands)

    Su, Z.; Timmermans, W.J.; Zeng, Y.; Schulz, J.; John, V.O.; Roebeling, R.A.; Poli, P.; Tan, D.; Kaspar, F.; Kaiser-Weiss, A.; Swinnen, E.; Tote, C.; Gregow, H.; Manninen, T.; Riihela, A.; Calvet, J.C.; Ma, Yaoming; Wen, Jun

    2018-01-01

    The Coordinating Earth Observation Data Validation for Reanalysis for Climate Services project (CORE-CLIMAX) aimed to substantiate how Copernicus observations and products can contribute to climate change analyses. CORE-CLIMAX assessed the European capability to provide climate data records (CDRs)

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

    Science.gov (United States)

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

    2013-11-01

    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

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

    Science.gov (United States)

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

    2015-04-01

    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

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

    OpenAIRE

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

    2013-01-01

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

  2. Recording of the Holocene sediment infilling in a confined tide-dominated estuary: the bay of Brest (Britanny, France)

    Science.gov (United States)

    Gregoire, Gwendoline; Le Roy, Pascal; Ehrhold, Axel; Jouet, Gwenael; Garlan, Thierry

    2016-04-01

    Modern estuaries constitute key areas for the preservation of sedimentary deposits related to the Holocene period. Several previous studies using stratigraphic reconstructions in such environments allowed to characterise the major parameters controlling the Holocene transgressive sequence and to decipher their respective role in the sedimentary infill: (1) the evolution of main hydrologic factors (wave or tide-dominated environment), (2) the sea level fluctuation and (3) the morphologies of the bedrock and the coastline. Nevertheless, the timing of the transgressive deposits and the detailed facies need to be precise in regard to the stratigraphic schemes. The Bay of Brest (Western Brittany, France) offers the opportunity to examine these points and to compare with previous studies. It constitutes an original tide-dominated estuary that communicates to the open sea (Iroise Sea) by a narrow strait. Two main rivers (Aulne and Elorn) are connected to a submerged paleovalleys network that was incised in the Paleozoic basement during lowstands and still preserved in the present morphology. It delineates the central basin surrounded by tidal flat located in sheltered area. The analysis of high and very-high resolution seismic lines recorded through the whole bay combined with sediment cores (up to 4.5 m long) and radiocarbon dating allow to precise the architecture and the timing of the thick Holocene coastal wedge. It is preserved from the valley network to the shore and presents a longitudinal variability (downstream-upstream evolution). The infill is divided into two successive stages (corresponding to the transgressive and highstand system tracts) which laterally evolve from the paleo-valley to the coast. Two units constitute the transgressive system tract. The oldest, dated from 8200 to 7000 cal B.P. is composed of fine-grained, organic-rich tidal flat deposits located in the sheltered area and organised in levees on the terrace bordering the paleo-valley. A tidal

  3. The horse pinworm (Oxyuris equi) in archaeology during the Holocene: Review of past records and new data.

    Science.gov (United States)

    Dufour, Benjamin; Hugot, Jean-Pierre; Lepetz, Sébastien; Le Bailly, Matthieu

    2015-07-01

    This paper focuses on the horse pinworm, Oxyuris equi, in archaeology during the Holocene period, and presents an overview of past published occurrences, early mentions in texts, and new data from our paleoparasitology research. This original compilation shows that the most ancient record of the horse pinworm dates to ca. 2500 years before present (ybp) in Central Asia and to ca. 2020 ybp in Western Europe. It also shows that the parasite is not detected on the American continent until contemporary periods. The role of European migrations from 1492 (Christopher Columbus) is discussed to explain the transfer of the horse pinworm from the Old World to the Americas. The absence of any record of this parasite before ca. 2500 ybp in Eurasia could be explained by parasite ecology, unfavorable sampling and scarcity of horse archeological remains. For the Americas, the absence of horse for long periods can be an additional explanation for the absence of the parasite. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Holocene fire dynamics in Fennoscandia

    Science.gov (United States)

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

    2015-04-01

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

  5. 16,000 Years of Tropical Eastern Ocean Climate Variability Recorded in a Speleothem From Sumatra, Indonesia

    Science.gov (United States)

    Wurtzel, J. B.; Abram, N.; Hantoro, W. S.; Rifai, H.; Hellstrom, J. C.; Heslop, D.; Troitzsch, U.; Eggins, S.

    2015-12-01

    Holocene climate variability in the Indo-Pacific has largely been inferred from sediment cores primarily from the central and eastern Warm Pool region. A limited number of speleothem oxygen-isotope records have provided decadally-resolved time-series of past rainfall variability over the central Indo-Pacific Warm Pool region, however no records currently exist for the Indian Ocean sector of the IPWP. Here we present the first continuous, high-resolution (~15year) speleothem record from the eastern tropical Indian Ocean, collected from central western Sumatra, Indonesia. Petrographic and geochemical analysis reveals that the sample is primarily composed of aragonite but is punctuated by intervals of primary calcite growth. In addition to Raman spectroscopy, trace element analysis by laser ablation ICP-MS reveals strongly antiphased behaviour between magnesium and strontium, attributed to the strong preference of those elements for the calcite and aragonite lattices, respectively. This relationship is utilized to develop a quantitative correction for the stable isotope fractionation offset between the two calcium carbonate polymorphs identified in the speleothem. The corrected oxygen isotope record shows a rapid transition from drier conditions during the Younger Dryas (YD) into a wetter Holocene, similar in timing and pattern to that recorded in Dongge Cave, China. This is strikingly different from other IPWP speleothem records, which show no YD or a wetter YD, suggesting that different mechanisms may be controlling rainfall amount in the eastern tropical Indian Ocean. These disparate responses are further explored through proxy-model comparison.

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

    Science.gov (United States)

    Alizadeh, Kamaleddin; Cohen, Marcelo; Behling, Hermann

    2015-08-01

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

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

    Directory of Open Access Journals (Sweden)

    K. Holmgren

    2010-09-01

    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.

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

    Directory of Open Access Journals (Sweden)

    D. Ackerley

    2017-11-01

    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.

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

    Science.gov (United States)

    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

    2017-11-01

    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.

  10. Lake sediment records of Quaternary climate change

    International Nuclear Information System (INIS)

    Moy, C.

    2013-01-01

    Lake sediments are excellent archives of climate and environmental change. Lakes typically exhibit high sedimentation rates, contain sedimentary components well-suited for a multi-proxy approach, multiple dating methods can be applied, exhibit a broad geographic distribution, and are relatively accessible for study. Furthermore, a number of geochemical techniques can be applied to recontsruct components of the climate system based on the stable isotope geochemistry of carbonate or organic phases preserved and exposed in lacustrine sedimentary cores. Various stable isotope methods can be applied to lacustrine systems and these are a valuable tool that can be used to monitor physical processes (e.g. evaporation), vegetation dynamics within the watershed (C 3 vs C 4 plant distributions), biologic processes (aquatic productivity), all of which can be driven by a regional climate forcing. (author). 31 refs., 11 figs.

  11. Lake sediment records of Quaternary climate change

    International Nuclear Information System (INIS)

    Moy, C.

    2016-01-01

    Lake sediments are excellent archives of climate and environmental change. Lakes typically exhibit high sedimentation rates, contain sedimentary components well-suited for a multi-proxy approach, multiple dating methods can be applied, exhibit a broad geographic distribution, and are relatively accessible for study. Furthermore, a number of geochemical techniques can be applied to recontsruct components of the climate system based on the stable isotope geochemistry of carbonate or organic phases preserved and exposed in lacustrine sedimentary cores. Various stable isotope methods can be applied to lacustrine systems and these are a valuable tool that can be used to monitor physical processes (e.g. evaporation), vegetation dynamics within the watershed (C 3 vs C 4 plant distributions), biologic processes (aquatic productivity), all of which can be driven by a regional climate forcing. (author).

  12. Lake sediment records of Quaternary climate change

    International Nuclear Information System (INIS)

    Moy, C.

    2014-01-01

    Lake sediments are excellent archives of climate and environmental change. Lakes typically exhibit high sedimentation rates, contain sedimentary components well-suited for a multi-proxy approach, multiple dating methods can be applied, exhibit a broad geographic distribution, and are relatively accessible for study. Furthermore, a number of geochemical techniques can be applied to recontsruct components of the climate system based on the stable isotope geochemistry of carbonate or organic phases preserved and exposed in lacustrine sedimentary cores. Various stable isotope methods can be applied to lacustrine systems and these are a valuable tool that can be used to monitor physical processes (e.g. evaporation), vegetation dynamics within the watershed (C 3 vs C 4 plant distributions), biologic processes (aquatic productivity), all of which can be driven by a regional climate forcing. (author)

  13. Lake sediment records of Quaternary climate change

    International Nuclear Information System (INIS)

    Moy, C.

    2015-01-01

    Lake sediments are excellent archives of climate and environmental change. Lakes typically exhibit high sedimentation rates, contain sedimentary components well-suited for a multi-proxy approach, multiple dating methods can be applied, exhibit a broad geographic distribution, and are relatively accessible for study. Furthermore, a number of geochemical techniques can be applied to recontsruct components of the climate system based on the stable isotope geochemistry of carbonate or organic phases preserved and exposed in lacustrine sedimentary cores. Various stable isotope methods can be applied to lacustrine systems and these are a valuable tool that can be used to monitor physical processes (e.g. evaporation), vegetation dynamics within the watershed (C 3 vs C 4 plant distributions), biologic processes (aquatic productivity), all of which can be driven by a regional climate forcing. (author)

  14. High resolution Holocene paleomagnetic secular variation records from Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Usapkar, A.; Dewangan, P.; Badesab, F.K.; Mazumdar, A.; Ramprasad, T.; Krishna, K.S.; Basavaiah, N.

    /8 probably due to local effects. Paleoinclination records of MD161/8, MD161/11 and MD161/13 show a low between ~2.4 and 2.0 cal. kyr BP, an increase between 2.0 and 1.4 cal. kyr BP and a decrease towards the present. To varying degrees these trends can...

  15. Sustained Satellite Missions for Climate Data Records

    Science.gov (United States)

    Halpern, David

    2012-01-01

    Satellite CDRs possess the accuracy, longevity, and stability for sustained moni toring of critical variables to enhance understanding of the global integrated Earth system and predict future conditions. center dot Satellite CDRs are a critical element of a global climate observing system. center dot Satellite CDRs are a difficult challenge and require high - level managerial commitment, extensive intellectual capital, and adequate funding.

  16. Rapid climatic changes recorded in loess successions

    NARCIS (Netherlands)

    Vandenberghe, J.; Nugteren, G.D.

    2001-01-01

    Detailed grain-size analyses, both in China and western Europe, indicate the occurrence of short climatic cycles during loess deposition of the last glacial. Cold episodes coincided with enhanced deposition of relatively coarse loess and alternated with relatively warmer episodes with decreased

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

    Science.gov (United States)

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

    2001-01-01

    Lacustrine deposits exposed around Lake Aricota, Peru (17?? 22???S), a 7.5-km2 lake dammed by debris flows, provide a middle to late Holocene record of lake-level fluctuations. Chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14C reservoir effects (Titicaca (16?? S), which is only 130 km to the northeast and shares a similar climatology. Comparisons with other marine and terrestrial records highlight emerging contradictions over the nature of mid-Holocene climate in the central Andes. ?? 2001 University of Washington.

  18. Terrestrial climate variability and seasonality changes in the Mediterranean region between 15 000 and 4000 years BP deduced from marine pollen records

    Directory of Open Access Journals (Sweden)

    I. Dormoy

    2009-10-01

    Full Text Available Pollen-based climate reconstructions were performed on two high-resolution pollen marines cores from the Alboran and Aegean Seas in order to unravel the climatic variability in the coastal settings of the Mediterranean region between 15 000 and 4000 years BP (the Lateglacial, and early to mid-Holocene. The quantitative climate reconstructions for the Alboran and Aegean Sea records focus mainly on the reconstruction of the seasonality changes (temperatures and precipitation, a crucial parameter in the Mediterranean region. This study is based on a multi-method approach comprising 3 methods: the Modern Analogues Technique (MAT, the recent Non-Metric Multidimensional Scaling/Generalized Additive Model method (NMDS/GAM and Partial Least Squares regression (PLS. The climate signal inferred from this comparative approach confirms that cold and dry conditions prevailed in the Mediterranean region during the Oldest and Younger Dryas periods, while temperate conditions prevailed during the Bølling/Allerød and the Holocene. Our records suggest a West/East gradient of decreasing precipitation across the Mediterranean region during the cooler Late-glacial and early Holocene periods, similar to present-day conditions. Winter precipitation was highest during warm intervals and lowest during cooling phases. Several short-lived cool intervals (i.e. Older Dryas, another oscillation after this one (GI-1c2, Gerzensee/Preboreal Oscillations, 8.2 ka event, Bond events connected to the North Atlantic climate system are documented in the Alboran and Aegean Sea records indicating that the climate oscillations associated with the successive steps of the deglaciation in the North Atlantic area occurred in both the western and eastern Mediterranean regions. This observation confirms the presence of strong climatic linkages between the North Atlantic and Mediterranean regions.

  19. 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

    Science.gov (United States)

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

    2017-10-01

    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

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

    Science.gov (United States)

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

    2015-04-01

    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

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

    Science.gov (United States)

    Sasaki, N.; Sugai, T.

    2017-12-01

    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.

    Science.gov (United States)

    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

    2016-09-01

    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

    Science.gov (United States)

    Anderson, Leif S.; Flowers, Gwenn E.; Jarosch, Alexander H.; Aðalgeirsdóttir, Guðfinna Th; Geirsdóttir, Áslaug; Miller, Gifford H.; Harning, David J.; Thorsteinsson, Thorsteinn; Magnússon, Eyjólfur; Pálsson, Finnur

    2018-06-01

    Drangajökull is a maritime ice cap located in northwest (Vestfirðir) Iceland. Drangajökull's evolution is therefore closely linked to atmospheric and ocean variability. In order to better constrain the Holocene climate and glacier history of Vestfirðir we model the past evolution of Drangajökull ice cap. Simulations from 10 ka to present are forced by general circulation model output, ice-core-based temperature reconstructions, and sea-surface temperature reconstructions. Based on these 10-thousand year simulations, Drangajökull did not persist through the Holocene. We estimate that air temperatures were 2.5-3.0 °C higher during the Holocene Thermal Maximum than the local 1960-1990 average. Simulations support Drangajökull's late Holocene inception between 2 and 1 ka, though intermittent ice likely occupied cirques as early as 2.6 ka. Drangajökull is primarily a Little Ice Age ice cap: it expanded between 1300 and 1750 CE, with the most rapid growth occurring between 1600 and 1750 CE. The maximum Holocene extent of Drangajökull occurred between 1700 and 1925 CE, despite the lowest late Holocene temperatures, occurring between 1650 and 1720 CE. Between 1700 and 1925 CE temperatures were likely 0.6-0.8 °C lower than the 1950-2015 reference temperature. The modern equilibrium line altitude (ELA) is bracketed by topographic thresholds: a 1 °C temperature increase from the modern ELA would eliminate the ice cap's accumulation area, while a reduction of 0.5 °C would lead to the rapid expansion of the ice cap across Vestfirðir. The proximity of Drangajökull to topographic thresholds may explain its late inception and rapid expansion during the Little Ice Age.

  4. Climate variability from isotope records in precipitation

    International Nuclear Information System (INIS)

    Grassl, H.; Latif, M.; Schotterer, U.; Gourcy, L.

    2002-01-01

    Selected time series from the Global Network for Isotopes in Precipitation (GNIP) revealed a close relationship to climate variability phenomena like El Nino - Southern Oscillation (ENSO) or the North Atlantic Oscillation (NAO) although the precipitation anomaly in the case studies of Manaus (Brazil) and Groningen (The Netherlands) is rather weak. For a sound understanding of this relationship especially in the case of Manaus, the data should include major events like the 1997/98 El Nino, however, the time series are interrupted frequently or important stations are even closed. Improvements are only possible if existing key stations and new ones (placed at 'hot spots' derived from model experiments) are supported continuously. A close link of GNIP to important scientific programmes like CLIVAR, the Climate Variability and Predictability Programme seems to be indispensable for a successful continuation. (author)

  5. Diverse plant and animal genetic records from Holocene and Pleistocene sediments

    DEFF Research Database (Denmark)

    Willerslev, E.; Hansen, Anders J.; Binladen, J.

    2003-01-01

    Genetic analyses of permafrost and temperate sediments reveal that plant and animal DNA may be preserved for long periods, even in the absence of obvious macrofossils. In Siberia, five permafrost cores ranging from 400,000 to 10,000 years old contained at least 19 different plant taxa, including...... the oldest authenticated ancient DNA sequences known, and megafaunal sequences including mammoth, bison, and horse. The genetic data record a number of dramatic changes in the taxonomic diversity and composition of Beringian vegetation and fauna. Temperate cave sediments in New Zealand also yielded DNA...

  6. A Holocene pollen and sediment record of Whangape Harbour, far northern New Zealand

    International Nuclear Information System (INIS)

    Horrocks, M.; Nichol, S.L.; Gregory, M.R.; Creese, R.; Augustinus, P.C.

    2001-01-01

    The sediment record of Whangape Harbour shows that there were significant fluctuations in depositional energy in the harbour during the period from c. >8000 cal. yr BP to some time within the last millenium, and that fluvial influences increased as the harbour infilled. The pollen record (highly discontinuous) from Whangape Harbour indicates that conifer-hardwood forest covered the hills surrounding the harbour during this period. The main canopy conifers were Dacrydium and Prumnopitys taxifolia, with some Libocedrus, Dacrycarpus, and Phyllocladus. Agathis was also present. Common canopy hardwoods were Metrosideros and, in the latter part of the period, Elaeocarpus. Ascarina and Cyathea were abundant in the sub-canopy. Leptospermum grew on disturbed areas fringing the estuary. Marsh or swamp environments probably never developed on a large scale in the harbour. Avicennia, extremely under-represented in the pollen flora, has been present on tidal flats in the harbour since at least c. 2500 cal. yr BP. Large-scale anthropogenic deforestation by burning commenced in the Whangape catchment some time during or since 700-430 cal. yr BP. The associated increase in erosion rates in the catchment resulted in a change towards a sandier sediment regime in the harbour which has continued to the present day. Weinmannia and Ackama, previously rare in the catchment, expanded in remaining forest. (author). 39 refs., 3 figs., 1 tab

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

    Directory of Open Access Journals (Sweden)

    O. N. Solomina

    2013-01-01

    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.

  8. Holocene evolution of the River Nile drainage system as revealed from the Lake Dendi sediment record, central Ethiopian highlands

    Science.gov (United States)

    Wagner, B.; Viehberg, F. A.; Wennrich, V.; Junginger, A.; Kolvenbach, A.; Rethemeyer, J.; Schaebitz, F.; Schmiedl, G. H.

    2015-12-01

    A 12 m long sediment sequence from Dendi Crater lakes, located on the central Ethiopian Plateau, was analysed with sedimentological and geochemical methods to reconstruct the regional environmental history. Bulk organic carbon samples from 23 horizons throughout the sequence were used for AMS radiocarbon dating and indicate that the sediment sequence spans the last ca. 12 cal kyr BP. Microscope analyses and sedimentological data reveal three tephra layers, of which the most prominent layer with a thickness of ~2 m was deposited at 10.2 cal kyr BP and probably originates from an eruption of the Wenchi crater 12 km to the west of the Dendi lakes. Sedimentological data of the pelagic deposits indicate shifts in erosion and rainfall throughout the record. A decrease in Ca and Sr at 11.6 cal kyr BP is related to the shift of less humid condition during the Younger Dryas (YD) to the return to full humid conditions of the African Humid Period (AHP). Single thin horizons with high carbonate content or high Ti and K imply that short spells of dry conditions and significantly increased rainfall superimpose the generally more humid conditions during the AHP. The end of the AHP is gradual. Relatively stable and less humid conditions characterised the Dendi Crater lakes until around 3.9 cal kyr BP. A highly variable increase in clastic matter over the last 1500 years indicates higher erosion due to short-term variations in precipitation within the Dendi catchment. Overall, the sediment record suggests moderate change of precipitation during the Holocene, which is probably due to their exposed location in the Ethiopian highlands. The data from the Dendi Crater lakes show, in concert with other records from the Nile catchment and the Eastern Mediterranean Sea (EMS), that the Blue Nile provided the main freshwater source for maintaining EMS stratification and sapropel S1 formation between ca. 10.0 and 8.7 cal kyr BP. Subsequent aridification is recorded from equatorial East Africa

  9. Reconstruction of a high-resolution late holocene arctic paleoclimate record from Colville River delta sediments.

    Energy Technology Data Exchange (ETDEWEB)

    Schreiner, Kathryn Melissa; Lowry, Thomas Stephen

    2013-10-01

    This work was partially supported by the Sandia National Laboratories, Laboratory Directed Research and Development (LDRD) fellowship program in conjunction with Texas A&M University (TAMU). The research described herein is the work of Kathryn M. Schreiner (Katie) and her advisor, Thomas S. Bianchi and represents a concise description of Katies dissertation that was submitted to the TAMU Office of Graduate Studies in May 2013 in partial fulfillment of her doctorate of philosophy degree. High Arctic permafrost soils contain a massive amount of organic carbon, accounting for twice as much carbon as what is currently stored as carbon dioxide in the atmosphere. However, with current warming trends this sink is in danger of thawing and potentially releasing large amounts of carbon as both carbon dioxide and methane into the atmosphere. It is difficult to make predictions about the future of this sink without knowing how it has reacted to past temperature and climate changes. This project investigated long term, fine scale particulate organic carbon (POC) delivery by the high-Arctic Colville River into Simpsons Lagoon in the near-shore Beaufort Sea. Modern POC was determined to be a mixture of three sources (riverine soils, coastal erosion, and marine). Downcore POC measurements were performed in a core close to the Colville River output and a core close to intense coastal erosion. Inputs of the three major sources were found to vary throughout the last two millennia, and in the Colville River core covary significantly with Alaskan temperature reconstructions.

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

    NARCIS (Netherlands)

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

    2008-01-01

    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

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

    Science.gov (United States)

    Briles, C.; Whitlock, C. L.

    2011-12-01

    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

  12. Mid- and late Holocene human impact recorded by the Coltrondo peat bog (NE Italian Alps)

    Science.gov (United States)

    Segnana, Michela; Poto, Luisa; Gabrieli, Jacopo; Martino, Matteo; Oeggl, Klaus; Barbante, Carlo

    2016-04-01

    Peat bogs are ideal archives for the study of environmental changes, whether these are natural or human induced. Indeed, receiving water and nutrients exclusively from dry and wet atmospheric depositions, they are among the most suitable matrices for palaeoenvironmental reconstruction. The present study is focused on the Eastern sector of the Italian Alps, where we sampled the Coltrondo peat bog, in the Comelico area (ca. 1800 m a.s.l.) The knowledge of the human history in this area is rather scarce: the only pieces of archaeological evidence found in this area dates back to the Mesolithic and the absence of later archaeological finds makes it difficult to reconstruct the human settlement in the valley. With the main aim to obtain information about the human settlement in that area we selected a multi-proxy approach, combining the study of biotic and abiotic sedimentary components archived in the 7900 years-peat bog record. Pollen analysis is performed along the core registering human impacts on the area from ca. 2500 cal BP, when land-use changes are well evidenced by the presence of human-related pollen and non-pollen palynomorphs (NPPs), as well as by the increase in micro-charcoal particles. Periods of increased human impact are recorded at the end of the Middle Ages and later, at the end of the 19th century. The analysis of trace elements, such as lead, is performed by means of ICP-MS technique and its enrichment factor (EF) is calculated. A first slight increase of Pb EF during Roman Times is possibly related to mining activities carried out by the Romans. Mining activities carried out in the area are registered during the Middle Ages, while the advent of the industrialization in the 20th century is marked by the highest EF values registered on the top of the core. To help and support the interpretation of geochemical data, lead isotopes ratios are also measured using ICP-MS to discriminate between natural and anthropogenic sources of lead. The 206Pb/207Pb

  13. Holocene facies analysis of the sedimentary record with anthropogenic impacts in the Ria de Vigo (NW Spain)

    Science.gov (United States)

    Rubio, B.; Garcia-Gil, S.; Vilas, F.; Garcia, A.

    2004-05-01

    The Ria de Vigo constitutes the southernmost ria of the Rias Bajas. The reconnaisance studies of this ria indicate a heterogeneous distribution of both terrigenous and carbonate sediments with a major axial deposit of cohesive sediments. These fine sediments are relatively rich in organic matter, particularly in the inner part of the ria. This is the result of a progressive change in hydrodynamic conditions along the ria. The outer parts are affected by severe storms in winter and by upwelling processes in summer, whilst the inner parts have an estuarine character throughout the year. The upwelling produces a marked increase in the biological productivity in the Ria and, consequently, these sediments have typically very high contents of organic matter. In recent years, increasing interest has been shown in the levels of heavy metals in sediments of the Galician Rias. Particularly, some of these studies showed a higher concentration of heavy metals in the muddiest surficial sediments in the Ria de Vigo. However, and despite of the important human and industrial settlement in the Galician rias, knowledge about the evolution of historical contamination along the Holocene sedimentary record is scarce. In order to ascertain this evolution have been selected 8 gravity corer located along the axial part of the ria. This evaluation was focused on the muddy sediments of the axial part of the ria due to the dependence of metal levels on grain size, resulting from the association of metals with the finer particles, as it has been demonstrated by previous studies in the ria. On these sediments, the combination of geochemical, mineralogical and sedimentological data, facies interpretations (obtained from x-ray radiography), and their integration with high resolution seismic data (Uniboom and 3.5 Khz subbottom profiler) have allowed to establish the evolution of certain heavy metals (Zn, Cu and Pb) along the Holocene recent sedimentary record in the Ria de Vigo. Sediments in the

  14. High - Resolution SST Record Based on Mg/Ca Ratios of Late Holocene Planktonic Foraminifers From the Great Bahama Bank

    Science.gov (United States)

    Mueller, A.; Reijmer, J. J.; Roth, S.

    2001-12-01

    We analyzed five different planktic foraminifera species in the high resolution core MD 992201 off the Great Bahama Bank (79° 16.34 W; 25° 53.49 N) in 290 m water depth. This 38.05 m long core comprises a 7,000 year long Holocene record. The selected species were Orbulina universa, Globigerinoides ruber, Globigerinoides sacculifer, Globorotalia menardii and Globigerinella aequilateralis, which live in the upper 200 m of the water column. The Mg/Ca ratios of these different foraminifers show species-specific values, which represent a distinct habitat depth. With this species-specific Mg/Ca ratios we can reconstruct a temperature profile through the water column. The lowest Mg/Ca are shown by G. menardii (2.5 - 4 mmol/mol), followed by G. sacculifer (4.2 - 5.6 mmol/mol), G. ruber (5.1 - 7.2 mmol/mol) and G. aequilateralis (5.5 - 8.7 mmol/mol). Highest are shown by O. universa (6 - 14 mmol/mol). During the Little Ice Age, the Mg/Ca ratios of all species except for the deeper dwelling G. menardii, became more variable and showed lower ratios. The shallow dwelling species like G. ruber and G. sacculifer display an increase in the Mg/Ca ratios during the Medieval Warm Period. Our data show that transferring Mg/Ca ratios into SST based calibration curves known from literature needs re-evaluation. Species-specific calibration seems to be necessary to achieve reliable results.

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

    Science.gov (United States)

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

    2017-03-01

    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.

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

    Science.gov (United States)

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

    2017-11-21

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

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

    Science.gov (United States)

    Liu, J.; Milliman, J. D.

    2002-12-01

    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.

  18. Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska

    Science.gov (United States)

    Nelson, Alan R.; Briggs, Richard; Dura, Tina; Engelhart, Simon E.; Gelfenbaum, Guy; Bradley, Lee-Ann; Forman, S.L.; Vane, Christopher H.; Kelley, K.A.

    2015-01-01

    Despite the role of the Alaska-Aleutian megathrust as the source of some of the largest earthquakes and tsunamis, the history of its pre–twentieth century tsunamis is largely unknown west of the rupture zone of the great (magnitude, M 9.2) 1964 earthquake. Stratigraphy in core transects at two boggy lowland sites on Chirikof Island’s southwest coast preserves tsunami deposits dating from the postglacial to the twentieth century. In a 500-m-long basin 13–15 m above sea level and 400 m from the sea, 4 of 10 sandy to silty beds in a 3–5-m-thick sequence of freshwater peat were probably deposited by tsunamis. The freshwater peat sequence beneath a gently sloping alluvial fan 2 km to the east, 5–15 m above sea level and 550 m from the sea, contains 20 sandy to silty beds deposited since 3.5 ka; at least 13 were probably deposited by tsunamis. Although most of the sandy beds have consistent thicknesses (over distances of 10–265 m), sharp lower contacts, good sorting, and/or upward fining typical of tsunami deposits, the beds contain abundant freshwater diatoms, very few brackish-water diatoms, and no marine diatoms. Apparently, tsunamis traveling inland over low dunes and boggy lowland entrained largely freshwater diatoms. Abundant fragmented diatoms, and lake species in some sandy beds not found in host peat, were probably transported by tsunamis to elevations of >10 m at the eastern site. Single-aliquot regeneration optically stimulated luminescence dating of the third youngest bed is consistent with its having been deposited by the tsunami recorded at Russian hunting outposts in 1788, and with the second youngest bed being deposited by a tsunami during an upper plate earthquake in 1880. We infer from stratigraphy, 14C-dated peat deposition rates, and unpublished analyses of the island’s history that the 1938 tsunami may locally have reached an elevation of >10 m. As this is the first record of Aleutian tsunamis extending throughout the Holocene, we

  19. 18 Ka BP records of climatic changes, Bay of Bengal: Isotopic and sedimentological evidences

    Digital Repository Service at National Institute of Oceanography (India)

    Chauhan, O.S.; Suneethi, J.

    are also identified at 10.3 and 11.5 Ka BP. The later event matches well with that of the ‘Younger Dryas’ event of world climate models. The beginning of the Holocene is marked by lighter d18O values (at around 9.5 Ka BP), which has been interpreted...

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

    Science.gov (United States)

    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.

    2017-12-01

    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.

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

    Science.gov (United States)

    Paula Menéndez, Lumila

    2018-02-01

    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

  2. Holocene Record of Major and Trace Components in the Sediments of an Urban Impoundment on the Mississippi River: Lake Pepin, Minnesota and Wisconsin

    Science.gov (United States)

    Dean, Walter E.

    2009-01-01

    Lake Pepin is a natural impoundment formed by damming of the Mississippi River about 9,180 radiocarbon years ago (19,600 calendar years) by an alluvial fan deposited by the Chippewa River, a tributary of the Mississippi in Wisconsin. Unique among 26 Mississippi River impoundments, Lake Pepin has stratigraphically preserved Holocene materials, including pollutants, that have been transported down the Mississippi. This natural Holocene record can then be compared to changes that have occurred since European settlement (ca. AD 1830), and since enactment of clean air and water legislation. The most immediate response to settlement in the sediments of Lake Pepin was an increase in bulk-sediment accumulation rate. This was accompanied by gradual increases in concentrations of phosphorus (P), and organic carbon (OC), followed by dramatic increases in these elements beginning about 1940. The increase in P was far greater than any of the minor fluctuations in P that occurred throughout the Holocene, but the increase in OC was comparable to an increase in OC that occurred in the mid-Holocene. The concentrations of several metals (for example, cadmium [Cd], and lead [Pb]) also are elevated in recent sediments. Increased Cd concentrations lasted only about two decades during the industrial era between World War II and the enactment of clean water standards in the 1970s. Increased Pb emissions, on the other hand, occurred over more than 100 years, first from burning of coal and smelting of lead ores, and then, beginning in the 1930s, burning of leaded gasoline. Concentrations of Pb in the sediments of Lake Pepin decreased to about two times preindustrial levels within a decade of enactment of unleaded gasoline restrictions.

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

    NARCIS (Netherlands)

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

    2009-01-01

    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

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

    NARCIS (Netherlands)

    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.

    2011-01-01

    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

  5. Climatic Changes on Tibetan Plateau Based on Ice Core Records

    Science.gov (United States)

    Yao, T.

    2008-12-01

    Climatic changes have been reconstructed for the Tibetan Plateau based on ice core records. The Guliya ice core on the Tibetan Plateau presents climatic changes in the past 100,000 years, thus is comparative with that from Vostok ice core in Antarctica and GISP2 record in Arctic. These three records share an important common feature, i.e., our climate is not stable. It is also evident that the major patterns of climatic changes are similar on the earth. Why does climatic change over the earth follow a same pattern? It might be attributed to solar radiation. We found that the cold periods correspond to low insolation periods, and warm periods to high insolation periods. We found abrupt climatic change in the ice core climatic records, which presented dramatic temperature variation of as much as 10 °C in 50 or 60 years. Our major challenge in the study of both climate and environment is that greenhouse gases such as CO2, CH4 are possibly amplifying global warming, though at what degree remains unclear. One of the ways to understand the role of greenhouse gases is to reconstruct the past greenhouse gases recorded in ice. In 1997, we drilled an ice core from 7100 m a.s.l. in the Himalayas to reconstruct methane record. Based on the record, we found seasonal cycles in methane variation. In particular, the methane concentration is high in summer, suggestiing active methane emission from wet land in summer. Based on the seasonal cycle, we can reconstruct the methane fluctuation history in the past 500 years. The most prominent feature of the methane record in the Himalayan ice core is the abrupt increase since 1850 A.D.. This is closely related to the industrial revolution worldwide. We can also observe sudden decrease in methane concentration during the World War I and World War II. It implies that the industrial revolution has dominated the atmospheric greenhouse gas emission for about 100 years. Besides, the average methane concentration in the Himalayan ice core is

  6. Climate and Provenance Evolution Recorded in the Sub-aqueous Indus Delta since the Last Glacial Maximum

    Science.gov (United States)

    Limmer, D. R.; Clift, P. D.; Koehler, C.; Giosan, L.; Ponton, C.; Henstock, T.; Tabrez, A.

    2010-12-01

    Source to sink processes in large fluvial systems are complicated by large transport distances and the potential to store and rework material on route to the submarine fan. We target the Indus river system and assess how climate change since the Last Glacial Maximum (LGM) may have affected the storage and deposition of sediment in the nearshore shelf setting. While sediment reworking within the floodplain appears to have been strong during the Holocene, it is unclear whether this can be observed in the deep sea or in the submarine delta. We present a multi-proxy record of mineralogical and geochemical change from two cores obtained from the Indus Shelf during Winter 2008/9, one located close to the modern river and one located in the north-west shelf. Results show a strong contrast in the geochemistry, reflectance spectroscopy and clay mineralogy between Holocene sediments from the two cores. We propose that these differences are caused by both local variations in sediment source and transport mechanisms. Trends common in both cores could be related to climatic processes, such as low values in the chemical alteration index (CIA) and low 87Sr/86Sr that rise between 11 and 8ka suggests more intense chemical weathering at that time. This period coincides with presumed warmer, wet conditions and a stronger summer monsoon. A small decline in chemical weathering after 8ka could be caused by an apparent weakening of the monsoon since that time. These data suggest that sediment weathered in the floodplains is transported quickly to the submarine delta during the Holocene, but that this material has not yet been re-deposited into the deep water via the Indus Canyon.

  7. Variations of the Geomagnetic Field During the Holocene-Pleistocene: Relative Paleointensity Records From South-Western Argentina

    Science.gov (United States)

    Gogorza, C. S.

    2008-05-01

    I present a review of the research carried out by the Group of Geomagnetism at Universidad Nacional del Centro (Argentina) on paleointensity records from bottom sediments from three lakes: Escondido (Gogorza et al., 2004), Moreno (Gogorza et al., 2006) and El Trébol (Gogorza et al., 2007; Irurzun et al., 2008) (South-Western Argentina, 41° S, 71° 30'W). Based on these studies, we construct a first relative (RPI) stack for South-Western Argentina covering the last 21,000 14C years BP. The degree of down-core homogeneity of magnetic mineral content as well as magnetic mineral concentration and grain sizes vary between all lakes and are quantified by high-resolution rock magnetic measurements. Rock magnetic studies suggest that the main carriers of magnetization are ferrimagnetic minerals, predominantly pseudo-single domain magnetite The remanent magnetization at 20 mT (NRM20mT) was normalized using the anhysteric remanent magnetization at 20mT (ARM20mT), the saturation of the isothermal remanent at 20 mT (SIRM20mT) and the low field magnetic susceptibility {k}. Coherence function analysis indicates that the normalised records are free of environmental influences. Our paleointensity (NRM20mT/ ARM20mT) versus age curve shows a good agreement with published records from other parts of the world suggesting that, in suitable sediments, paleointensity of the geomagnetic field can give a globally coherent, dominantly dipolar signal. References Gogorza, C.S.G., Irurzun, M.A., Chaparro, M.A.E., Lirio, J.M., Nuñez, H., Bercoff, P.G., Sinito, A.M. Relative Paleointensity of the Geomagnetic Field over the last 21,000 years bp from Sediment Cores, Lake El Trébol, (Patagonia, Argentina). Earth, Planets and Space. V58(10), 1323-1332. 2006. Gogorza, C.S.G., Sinito, A.M., Lirio, J.M., Nuñez, H., Chaparro, M.A.E., Bertorello, H.R. Paleointensity Studies on Holocene-Pleistocene Sediments from Lake Escondido, Argentina. Physical of the Earth and Planetary Interiors, Elsevier, ISSN

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1987-11-01

    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.

  9. Spatiotemporal climatic, hydrological, and environmental variations based on records of annually laminated lake sediments from northern Poland

    Science.gov (United States)

    Tylmann, W.; Blanke, L.; Kinder, M.; Loewe, T.; Mayr, C.; Ohlendorf, C.; Zolitschka, B.

    2009-12-01

    In northern Poland there is the unique opportunity to compare varved lake sediment records with distinct climatic trends along a 700 km long W-E transect. Annually laminated Holocene sediment sequences from Lake Lubinskie, Lake Suminko, Lake Lazduny, and Lake Szurpily were cored for high-resolution multiproxy climate and environmental reconstruction in the framework of the Polish-German project “Northern Polish Lake Research” (NORPOLAR). First results from a 139 cm long gravity core of Lake Lazduny (53°51.4’N, 21°57.3’E) document deposition of an organic (mean organic matter: 13.9%; mean biogenic opal: 9.8%) and highly carbonaceous gyttja (mean calcite content: 61.6%). The finely laminated sediment consists of biochemical varves. Pale spring/summer layers composed of autochthonous carbonates alternate with dark fall/winter layers made of organic and minerogenic detritus. The established chronology for the last 1500 calendar-years is based on thin section analysis supported by independent radiometric dating (C-14, Pb-210). Sedimentological, geochemical and stable isotope analyses were carried out with a decadal temporal resolution. Additionally, non-destructive and high-resolution XRF scanning data reveal a rhythmic variation in the Ca content that reflects seasonal calcite deposition. Redox-sensitive elements like Fe, Mn and S are interpreted to be the response to mean winter temperatures: colder winter temperatures → extended lake ice cover → intensification of meromixis → increased Fe/Mn ratio. In turn, these parameters can be linked to NAO (North Atlantic Oscillation) variability, because a negative NAO is related to colder and drier conditions in northeastern Europe. Climate variability is also mirrored by the δ13C record of the endogenic calcite fraction. In mid-latitude lakes calcite precipitation is dominated by productivity-controlled consumption of the dissolved inorganic carbon (DIC) pool. Thus the δ13C record potentially provides a

  10. The ESA climate change initiative: Satellite data records for essential climate variables

    DEFF Research Database (Denmark)

    Hollmann, R.; Merchant, C.J.; Saunders, R.

    2013-01-01

    The European Space Agency (ESA) has launched the Climate Change Initiative (CCI) to provide satellite-based climate data records (CDRs) that meet the challenging requirements of the climate community. The aim is to realize the full potential of the long-term Earth observation (EO) archives...... that both ESA and third parties have established. This includes aspects of producing a CDR, which involve data acquisition, calibration, algorithm development, validation, maintenance, and provision of the data to the climate research community. The CCI is consistent with several international efforts...... targeting the generation of satellite derived climate data records. One focus of the CCI is to provide products for climate modelers who increasingly use satellite data to initialize, constrain, and validate models on a wide range of space and time scales....

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

    Science.gov (United States)

    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.

    2011-01-01

    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.

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

    Science.gov (United States)

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

    2013-10-01

    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.

  13. Tropical Pacific climate variability over the last 6000 years as recorded in Bainbridge Crater Lake, Galápagos

    Science.gov (United States)

    Thompson, Diane M.; Conroy, Jessica L.; Collins, Aaron; Hlohowskyj, Stephan R.; Overpeck, Jonathan T.; Riedinger-Whitmore, Melanie; Cole, Julia E.; Bush, Mark B.; Whitney, H.; Corley, Timothy L.; Kannan, Miriam Steinitz

    2017-08-01

    Finely laminated sediments within Bainbridge Crater Lake, Galápagos, provide a record of El Niño-Southern Oscillation (ENSO) events over the Holocene. Despite the importance of this sediment record, hypotheses for how climate variability is preserved in the lake sediments have not been tested. Here we present results of long-term monitoring of the local climate and limnology and a revised interpretation of the sediment record. Brown-green, organic-rich, siliciclastic laminae reflect warm, wet conditions typical of El Niño events, whereas carbonate and gypsum precipitate during cool, dry La Niña events and persistent dry periods, respectively. Applying this new interpretation, we find that ENSO events of both phases were generally less frequent during the mid-Holocene ( 6100-4000 calendar years B.P.) relative to the last 1500 calendar years. Abundant carbonate laminations between 3500 and 3000 calendar years B.P. imply that conditions in the Galápagos region were cool and dry during this period when the tropical Pacific E-W sea surface temperature (SST) gradient likely strengthened. The frequency of El Niño and La Niña events then intensified dramatically around 1750-2000 calendar years B.P., consistent with a weaker SST gradient and an increased frequency of ENSO events in other regional records. This strong interannual variability persisted until 700 calendar years B.P., when ENSO-related variability at the lake decreased as the SST gradient strengthened. Persistent, dry conditions then dominated between 300 and 50 calendar years B.P. (A.D. 1650-1900, ± 100 years), whereas wetter conditions and frequent El Niño events dominated in the most recent century.

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

    OpenAIRE

    van Soelen, E.E.

    2012-01-01

    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...

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

    Science.gov (United States)

    Rodysill, J. R.

    2017-12-01

    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.

  16. Climatic change during historical times in japan : reconstruction from climatic hazard records

    OpenAIRE

    Maejima, Ikuo; Tagami, Yoshio

    1986-01-01

    A synoptic analysis of climatic hazard records in historical times of Japan is presented. The cool age (7-9c.), the warm age (10-14c.) and the cold age (15-19c.) are indicated. The relationship between summer and winter conditions in the climatic change is also shown. Thus, the knowledge of the climatic change in Japan from the 7th to the 19th century was systematically summarized.

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

    Science.gov (United States)

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

    2014-12-01

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

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

    Digital Repository Service at National Institute of Oceanography (India)

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

    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. Climate reconstructions derived from global glacier length records

    NARCIS (Netherlands)

    Klok, E.J.; Oerlemans, J.

    2004-01-01

    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,

  20. Satellite Climate Data Records: Development, Applications, and Societal Benefits

    Directory of Open Access Journals (Sweden)

    Wenze Yang

    2016-04-01

    Full Text Available This review paper discusses how to develop, produce, sustain, and serve satellite climate data records (CDRs in the context of transitioning research to operation (R2O. Requirements and critical procedures of producing various CDRs, including Fundamental CDRs (FCDRs, Thematic CDRs (TCDRs, Interim CDRs (ICDRs, and climate information records (CIRs are discussed in detail, including radiance/reflectance and the essential climate variables (ECVs of land, ocean, and atmosphere. Major international CDR initiatives, programs, and projects are summarized. Societal benefits of CDRs in various user sectors, including Agriculture, Forestry, Fisheries, Energy, Heath, Water, Transportation, and Tourism are also briefly discussed. The challenges and opportunities for CDR development, production and service are also addressed. It is essential to maintain credible CDR products by allowing free access to products and keeping the production process transparent by making source code and documentation available with the dataset.

  1. Continuing the Total and Spectral Solar Irradiance Climate Data Record

    Science.gov (United States)

    Coddington, O.; Pilewskie, P.; Kopp, G.; Richard, E. C.; Sparn, T.; Woods, T. N.

    2017-12-01

    Radiative energy from the Sun establishes the basic climate of the Earth's surface and atmosphere and defines the terrestrial environment that supports all life on the planet. External solar variability on a wide range of scales ubiquitously affects the Earth system, and combines with internal forcings, including anthropogenic changes in greenhouse gases and aerosols, and natural modes such as ENSO, and volcanic forcing, to define past, present, and future climates. Understanding these effects requires continuous measurements of total and spectrally resolved solar irradiance that meet the stringent requirements of climate-quality accuracy and stability over time. The current uninterrupted 39-year total solar irradiance (TSI) climate data record is the result of several overlapping instruments flown on different missions. Measurement continuity, required to link successive instruments to the existing data record to discern long-term trends makes this important climate data record susceptible to loss in the event of a gap in measurements. While improvements in future instrument accuracy will reduce the risk of a gap, the 2017 launch of TSIS-1 ensures continuity of the solar irradiance record into the next decade. There are scientific and programmatic motivations for addressing the challenges of maintaining the solar irradiance data record beyond TSIS-1. The science rests on well-founded requirements of establishing a trusted climate observing network that can monitor trends in fundamental climate variables. Programmatically, the long-term monitoring of solar irradiance must be balanced within the broader goals of NASA Earth Science. New concepts for a low-risk, cost efficient observing strategy is a priority. New highly capable small spacecraft, low-cost launch vehicles and a multi-decadal plan to provide overlapping TSI and SSI data records are components of a low risk/high reliability plan with lower annual cost than past implementations. This paper provides the

  2. Developing NOAA's Climate Data Records From AVHRR and Other Data

    Science.gov (United States)

    Privette, J. L.; Bates, J. J.; Kearns, E. J.

    2010-12-01

    As part of the provisional NOAA Climate Service, NOAA is providing leadership in the development of authoritative, measurement-based information on climate change and variability. NOAA’s National Climatic Data Center (NCDC) recently initiated a satellite Climate Data Record Program (CDRP) to provide sustained and objective climate information derived from meteorological satellite data that NOAA has collected over the past 30+ years - particularly from its Polar Orbiting Environmental Satellites (POES) program. These are the longest sustained global measurement records in the world and represent billions of dollars of investment. NOAA is now applying advanced analysis methods -- which have improved remarkably over the last decade -- to the POES AVHRR and other instrument data. Data from other satellite programs, including NASA and international research programs and the Defense Meteorological Satellite Program (DMSP), are also being used. This process will unravel the underlying climate trend and variability information and return new value from the records. In parallel, NCDC will extend these records by applying the same methods to present-day and future satellite measurements, including the Joint Polar Satellite System (JPSS) and Jason-3. In this presentation, we will describe the AVHRR-related algorithm development activities that CDRP recently selected and funded through open competitions. We will particularly discuss some of the technical challenges related to adapting and using AVHRR algorithms with the VIIRS data that should become available with the launch of the NPOESS Preparatory Project (NPP) satellite in early 2012. We will also describe IT system development activities that will provide data processing and reprocessing, storage and management. We will also outline the maturing Program framework, including the strategies for coding and development standards, community reviews, independent program oversight, and research-to-operations algorithm

  3. Middle-to-late Holocene palaeoenvironmental reconstruction from the A294 ice-cave record (Central Pyrenees, northern Spain)

    Science.gov (United States)

    Sancho, Carlos; Belmonte, Ánchel; Bartolomé, Miguel; Moreno, Ana; Leunda, María; López-Martínez, Jerónimo

    2018-02-01

    Perennial ice deposits in caves represent unique, but underexplored, terrestrial sequences that potentially contain outstanding palaeoclimatic records. Here, we present a pioneer palaeoenvironmental study of an ice deposit preserved in a small sag-type cave (A294) in the Central Pyrenees (northern Iberian Peninsula). The 9.25-m-thick sequence, which is dated from 6100 ± 107 to 1888 ± 64 cal BP, represents the oldest known firn ice record worldwide. The stratigraphy (detrital layers, unconformities, and cross stratification), plant macrofossils, and isotopic signature (similarity between the ice linear distribution, δ2H = 7.83δ18O + 8.4, and the Global Meteoric Water Line) of the ice point to the diagenesis of snow introduced to the cave by winter snowstorms. Four phases of rapid ice accumulation (6100-5515, 4945-4250, 3810-3155, and 2450-1890 cal BP) are related to wetter and colder winters. Comparison of the isotopic composition (δ18O and deuterium excess) of the ice with other paleoclimate records show that both source effects and the North Atlantic Oscillation (NAO) mechanism exert a dominant influence on the ice cave record. The NAO signal may be a combination of source effects and rainfall amount. Three intervals with low ice accumulation occurred between the phases of rapid accumulation and were related to drier, and possibly warmer, winters. These centennial-scale episodes appear to be in-phase with regional arid events, as established from high altitude lacustrine records and can be correlated to global Rapid Climate Change events. The current warming trend has dramatically decreased the volume of the ice deposit in cave A294.

  4. Inter-annual precipitation variabiity inferred from late Holocene speleothem records from Fiji: implications for SPCZ localisation and ENSO behaviour

    Science.gov (United States)

    Mattey, D.; Stephens, M.; Hoffmann, D.; Brett, M.

    2015-12-01

    The modern tropical Fiji climate is characterised by seasonal rainfall controlled by the position of the South Pacific Convergence Zone (SPCZ). Interannual rainfall is strongly modulated on decadal timescales by ENSO with higher rainfall associated with La Nina events. Voli Voli cave near Sigatoga (Viti Levu) is a stream passage that has been monitored since 2009. A U-Th dated laminated speleothem spans a 1500 year interval across the transition from the Medieval Warm Period into the Little Ice Age marked by a fabric change from finely laminated calcite with thin clay layers, to white well-laminated calcite. The older record is characterised by rising δ13C values followed by a rapid decrease in δ13C around 1200 AD. Evidence from cave monitoring shows that cave air CO2 levels are strongly seasonal as a result of greater ventilation by winter trade winds and high resolution δ13C record shows regularly spaced peaks correlated with paired laminae and cycles in P and S which provide annual markers driven by rainfall and seasonal ventilation. δ18O values remain relatively unchanged throughout the record but micromilling at sub-annual resolution reveals systematic cycles in δ18O that span groups of paired laminae with an inferred periodicity of 3-7 years i.e. a similar frequency to modern ENSO. The presence of these sub-decadal cycles in δ18O may be a result of a combination of factors. The amplitude of 2-3‰ would be equivalent to an amount-effect related change in annual precipitation of around 50% but an additional smoothing process, perhaps a result of aquifer storage, is required to attenuate interannual variance in precipitation. The Voli Voli record provides evidence of an underlying climatic change to more frequent La Niña conditions from 1200 AD and may be associated with increased conflict, shifts in settlements and changes in subsistence strategies on the island. Coeval speleothem isotope records from tropical Pacific Islands provide a provide a

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

    Science.gov (United States)

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

    2014-03-01

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

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

    Digital Repository Service at National Institute of Oceanography (India)

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

    ., 2005). Recently a 11,000 yr reconstruction of sunspots using tree ring ∆ 14 C data revealed exceptional changes in sunspot activity within the Holocene (Solanki et al., 2004). Since sun is the principal source of energy, changes in solar energy output... seem to be stimulated by the sun, suggest- ing the importance of small changes in solar activity lead- ing to perceptible changes in monsoon conditions. Acknowledgements We thank the Directors of National Centre for Ant- arctic and Ocean Research (NCAOR...

  7. Holocene environmental change along the southern Cape coast of South Africa - Insights from the Eilandvlei sediment record spanning the last 8.9 kyr

    Science.gov (United States)

    Wündsch, Michael; Haberzettl, Torsten; Cawthra, Hayley C.; Kirsten, Kelly L.; Quick, Lynne J.; Zabel, Matthias; Frenzel, Peter; Hahn, Annette; Baade, Jussi; Daut, Gerhard; Kasper, Thomas; Meadows, Michael E.; Mäusbacher, Roland

    2018-04-01

    This study investigates Holocene sediments from Eilandvlei, a coastal lake located within the Wilderness embayment at the southern Cape coast of South Africa. The evolution of the present estuarine/coastal lake system is reconstructed based on seismic data as well as a multi-proxy approach on a 30.5 m sediment core spanning the last 8.9 kyr. Geochemical (Ca, TOC/S, Br/TOC) and micropalaeontological data (diatoms, foraminifera) reflect changes in the degree of marine influence at the core site. The embayment likely developed via distinct phases of connectivity to the Indian Ocean caused by sea level changes and dune progradation. Marine conditions prevailed at the core site from 8900 to 4700 cal BP. The rapid sea level rise during the early Holocene caused the inundation of a palaeovalley that most likely had formed at lower sea levels during the Pleistocene. Towards the mid-Holocene the sea level exceeded its present height around 7500 cal BP creating a marine embayment. At 4700 cal BP, the embayment became distinctly more disconnected from the ocean turning into a lagoon system that persisted until 1200 cal BP. Subsequently, the marine influence further decreased and the present estuarine/coastal lake system was established. Grain size and geochemical data (Fe, Si/Al, chemical index of alteration (CIA)) further reflect changes in the deposition of terrigenous sediments at the core site. While the sedimentation of fine-grained (climatic conditions than today from 8900 to 7900 cal BP and 6400 to 3000 cal BP. In contrast, the periods between 7900-6400 cal BP and 3000 cal BP-present were likely characterized by high river discharge and thus, generally more rainfall. The reconstructed palaeoclimatic variations are discussed within the context of e.g., shifts in the position of the Antarctic sea ice extent and the mid-latitude westerly wind belt as well as changes in the El Niño-Southern Oscillation (ENSO).

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

    Science.gov (United States)

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

    2012-12-01

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

  9. Holocene palaeoenvironmental history of the Amazonian mangrove belt

    Science.gov (United States)

    Cohen, Marcelo Cancela Lisboa; Pessenda, Luiz Carlos Ruiz; Behling, Hermann; de Fátima Rossetti, Dilce; França, Marlon Carlos; Guimarães, José Tasso Felix; Friaes, Yuri; Smith, Clarisse Beltrão

    2012-11-01

    Wetland dynamic in the northern Brazilian Amazon region during the Holocene was reviewed using palynological, carbon and nitrogen isotopes records, and C/N ratio previously published. The integration of 72 radiocarbon dates recorded in 34 sediment cores sampled along the marine and fluvial littoral, and mainly influenced by the Amazon River, reveals that marine influence and mangrove vegetation were wider than today on the mouth of Amazon River between >8990-8690 and 2300-2230 cal yr BP, forming a continuous mangrove belt along the northern Brazilian Amazon littoral. The establishment of this mangrove strip is a direct consequence of the marine incursion caused by post-glacial sea-level rise possibly associated with tectonic subsidence during the Early and Middle Holocene. In the Late Holocene, in areas influenced by the Amazon River discharge, the mangroves were replaced by freshwater vegetation, and the coast morphology evolved from an estuarine dominated into a rectilinear coast due to coastal progradation. Nevertheless, the marine-influenced littoral, which is currently dominated by mangroves and salt-marsh vegetation, has persistently had brackish water vegetation over tidal mud flats throughout the entire Holocene. Likely, the fragmentation of this continuous mangrove line during the Late Holocene was caused by the increase of river freshwater discharge associated to the change from dry into wet climates in the Late Holocene. This caused a significant decrease of tidal water salinity in areas near the mouth of Amazon River. These changes in the Amazon discharge are probably associated with dry and wet periods in the northern Amazon region during the Holocene.

  10. A Late Holocene Record of Human Impact in the Tropical Lowlands of the Mexican Gulf Coast: Lago Verde.

    Science.gov (United States)

    Socorro, L.; Sosa, S.; Caballero, M.; Rodriguez, A.; Ortega, B.

    2005-05-01

    Lago Verde is a maar lake (18 36 43 N; 95 20 52 W) located on the Gulf Coast of Mexico in "Los Tuxtlas" region. The area was cover by tropical rain forest and is part of the core area of the earliest Mesoamerican cultures. A 6 m sediment core was obtained in order to document vegetation and lake level history of this area. Lago Verde is a shallow, eutrophic lake (max. 4 m), the natural vegetation has been removed and grasslands with some tropical trees such Bursera grows around the lake. According with the radiocarbon chronology the sequence covers the last 2500 yr BP. At the base of the sequence low abundance of tropical trees is record, with intermediate lake levels. A sudden change in the pollen stratigraphy occurs at ca. 2000 yr BP, with important presence of Poaceae, Ambrosia and Cheno.-Am. along with Zea mays indicating human activity in the area. This is associated with a change in limnological conditions, recording turbid, shallow environments. This pollen signals correlates with dry phases in Yucatan, suggesting that this dry climatic signal probably had effect on an ample area of Mexico. However, at 1200 yr BP, no more Zea mays pollen is recovered suggesting the abandonment of the area. Lake levels recover as well as the tropical forest. The last 150 yr BP is characterized by the reduction in the pollen of tropical forest trees, presence of Zea mays, increased erosion rates, turbidity and eutrophication in the lake, all related to deforestation.

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

    Science.gov (United States)

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

    2018-03-01

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

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

    Science.gov (United States)

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

    2017-08-01

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

  13. Extent, timing, and climatic significance of latest Pleistocene and Holocene glaciation in the Sierra Nevada, California

    Energy Technology Data Exchange (ETDEWEB)

    Clark, Douglas Howe [Univ. of Washington, Seattle, WA (United States)

    1995-01-01

    Despite more than a century of study, scant attention has been paid to the glacial record in the northern end of the Sierra Nevada, and to the smaller moraines deposited after the retreat of the Tioga (last glacial maximum) glaciers. Equilibrium-line altitude (ELA) estimates of the ice fields indicate that the Tioga ELA gradients there are consistent with similar estimates for the southern half of the range, and with an intensification of the modern temperature/precipitation pattern in the region. The Recess Peak advance has traditionally been considered to be mid-Neoglacial age, about 2--3,000 yr B.P., on the basis of relative weathering estimates. Sediment cores of lakes dammed behind moraines correlative with Recess Peak in four widely spaced sites yields a series of high-resolution AMS radiocarbon dates which demonstrate that Recess Peak glaciers retreated before ~13,100 cal yr B.P.. This minimum limiting age indicates that the advance predates the North Atlantic Younger Dryas cooling. It also implies that there have been no advances larger than the Matthes in the roughly 12,000 year interval between it and the Recess Peak advance. This finding casts doubt on several recent studies that claim Younger Dryas glacier advances in western North America. The 13,100 cal yr B.P. date is also a minimum age for deglaciation of the sample sites used to calibrate the in situ production rates of cosmogenic 10Be and 26Al. The discrepancy between this age and the 11,000 cal yr B.P. exposure age assumed in the original calibration introduces a large (> 19%) potential error in late-Pleistocene exposure ages calculated using these production rates.

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

    Directory of Open Access Journals (Sweden)

    L. Jin

    2009-08-01

    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.

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

    Science.gov (United States)

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

    2017-05-03

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

  16. First record of a Late Holocene fauna associated with an ephemeral fluvial sequence in La Pampa Province, Argentina. Taphonomy and paleoenvironment

    Science.gov (United States)

    Montalvo, Claudia I.; Fernández, Fernando J.; Bargo, M. Susana; Tomassini, Rodrigo L.; Mehl, Adriana

    2017-07-01

    The first Late Holocene mammal assemblage (mainly micromammals) of La Pampa Province was found in Quehué paleontological site, associated with an ephemeral fluvial sequence. Taphonomical features of the collected materials were evaluated in order to increase the knowledge of the ancient vertebrate communities of this area and to interpret the origin of the assemblages. Field data and taphonomic analysis of the specimens, suggested the recognition of three assemblages with different taphonomic histories: 1) large to medium sized mammals; 2) micromammals found inside burrows or associated with them; and 3) discrete accumulations of micromammals and other microvertebrates (amphibians, reptiles and birds). Additionally, the paleoenvironmental analysis based mainly on the record of small mammals reflected the predominance of semi-arid conditions associated with a mosaic of open shrub steppe, grasslands and xerophytic forests of Espinal, similar to the present one in the Quehué valley area. However, the presence of Lestodelphys halli in the Quehué site during the Late Holocene (∼1.2 ky BP), suggests a more heterogeneous environment and perhaps relative colder and drier than current times, which are featured by more mesic conditions and anthropic activities, mainly agriculture and livestock during the last centuries.

  17. Paleoenvironmental Reconstruction of the North Atlantic Current Variations from MIS 3 to Holocene Based on Multiproxy Record from the North-East Scotland Continental Margin.

    Science.gov (United States)

    Ovsepyan, Y.; Tikhonova, A.; Novichkova, E.; Gupta, R. M.; Korsun, S.; Matul, A.

    2017-12-01

    In order to reconstruct the history of water mass interaction between the North Atlantic and the Nordic Seas since MIS 3 to the present, the sediment core from the North-East Scotland continental slope was investigated. The site of core AI-3521 (59°30.009 N, 7°20.062 E) from the 1051 m water depth is located beneath the pathway of the North Atlantic current which transports warm and saline Atlantic surface water to the Norwegian Sea. The age model of the sequence is based on stable isotope record of benthic Cassidulina neoteretis and planktic Neogloboquadrina pachyderma sin. and Globigerina bulloides. The Holocene interval of the upper 1.5 m is characterized by high sedimentation rates and the high biodiversity of microfauna. The distribution of ice rafted debris and CaCO3 content; benthic and planktic foraminiferal assemblages; oxygen, carbon and boron isotopes, Mg/Ca ratio were used to reconstruct the regional paleoceanographic conditions (bioproductivity, temperature, salinity) and to compare with the paleoclimatic events in the subpolar North Atlantic in the frame of the global environmental changes during the Late Pleistocene and Holocene. The research was supported by Russian Science Foundation projects 16-47-02009 and 14-50-00095.

  18. Hydro-climatic changes since 13.000 years B.P. in eastern Tibet and north of Xinjiang (China). Approach using the study of some lacustrine records

    International Nuclear Information System (INIS)

    Assaraj, A.

    1997-01-01

    The aim of this study is to build the chronology of the medium and short term climatic changes that took place during the last glacial and Holocene periods using sedimentological and isotopic data obtained on cores from the Aibi lake (north of Xinjiang, China) and from the Madoi and Donxi lakes (eastern part of the Tibetan plateau). At Aibi, after the chemical, isotopic and physico-chemical characterization of the lake waters, and the sedimentological study of the laminae (granulometry and mineralogy) have been done, the measurements of 18 O and 13 C of the authigenous carbonates and of the thickness variations of laminae have evidenced the seasonal character of the laminae. The spectral analyses of the thickness variations indicate periodicities linked with the quasi-biennial oscillations (2 or 3 years) and with the solar cycles (10-11 years). East of the Tibetan plateau, the sedimentological and isotopic study of the cores from the Madoi and Donxi lakes show more humid and hot climate conditions during the lower and middle Holocene. The sedimentary record of lake Madoi show one or several lacustrine or fluvio-lacustrine phases after 13000-12000 years B.P. A high dryness period took place within the Younger Dryas chrono-zone. Since 10000 year B.P. the 3 lakes are filled with isotopically diluted waters. The last glacial-Holocene transition seems to be very sharp and located around 10000 years B.P. both in northern Xinjiang and eastern Tibet and confirm the results previously obtained in Qinghai and northern-Xinjiang. After the optimum hydrologic phase of the lower and middle Holocene, the come back of dryer conditions started at about 6000 or 5000 years B.P. and hydrological conditions became close to the present day ones since 3000 years B.P. (J.S.)

  19. Evidence for Isostatic Emergence and Holocene Environmental Change Recorded in Chironomid Assemblages and Sediment Composition of Coastal Lake T1 in SW Greenland

    Science.gov (United States)

    Berman, K.; Axford, Y.; Lasher, G. E.

    2017-12-01

    Multi-proxy analysis of a coastal lake in southwest Greenland near Nuuk provides evidence for regional environmental changes, including the timing of isostatic rebound and the temperature history of the area. T1 (informal name) is a small lake 50 km south of Nuuk, at 17.5 m elevation and currently isolated from glacial meltwater drainage. The lake's sediment record begins approximately 9500 cal years BP, when the site was submerged beneath sea level due to glacial isostatic depression following the Last Glacial Maximum. The record captures the transition of the environment from a submerged, glacially-influenced marine site to a non-glacially fed (and initially meromictic) freshwater lake 8600 cal years BP. Magnetic susceptibility, a proxy for sediment minerogenic content, decreased rapidly from 9500 to 8600 years BP, before abruptly stabilizing and remaining relatively low and steady for the rest of the record. The transition to a lacustrine environment was characterized by a rapid and relatively simultaneous increase in primary productivity (inferred from biogenic silica concentrations) and shift towards terrestrial versus marine sources of organic matter (inferred from carbon:nitrogen ratios and nitrogen isotopes) between 8700 and 8400 years BP. Together, these proxies and the presence of marine shells below the transition provide robust evidence for the transition from a marine environment to a freshwater lake in response to regional postglacial isostatic rebound. Within the Holocene, measures of bulk sediment composition (e.g., biogenic silica, loss-on-ignition and magnetic susceptibility) are relatively stable. Chironomid (Insecta: Diptera: Chironomidae) assemblages, which in some environments are quantitative proxies for summer temperature changes, show species-level shifts within the Holocene that will be interpreted in this presentation alongside indicators of landscape change including carbon:nitrogen ratios, bulk sediment spectral reflectance and bulk

  20. Reconciliation of the Devils Hole climate record with orbital forcing.

    Science.gov (United States)

    Moseley, Gina E; Edwards, R Lawrence; Wendt, Kathleen A; Cheng, Hai; Dublyansky, Yuri; Lu, Yanbin; Boch, Ronny; Spötl, Christoph

    2016-01-08

    The driving force behind Quaternary glacial-interglacial cycles and much associated climate change is widely considered to be orbital forcing. However, previous versions of the iconic Devils Hole (Nevada) subaqueous calcite record exhibit shifts to interglacial values ~10,000 years before orbitally forced ice age terminations, and interglacial durations ~10,000 years longer than other estimates. Our measurements from Devils Hole 2 replicate virtually all aspects of the past 204,000 years of earlier records, except for the timing during terminations, and they lower the age of the record near Termination II by ~8000 years, removing both ~10,000-year anomalies. The shift to interglacial values now broadly coincides with the rise in boreal summer insolation, the marine termination, and the rise in atmospheric CO2, which is consistent with mechanisms ultimately tied to orbital forcing. Copyright © 2016, American Association for the Advancement of Science.

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

    NARCIS (Netherlands)

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

    2011-01-01

    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

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

    NARCIS (Netherlands)

    Blaschek, M.; Renssen, H.

    2013-01-01

    Glacial terminations are characterized by a strong rise in sea level related to melting ice sheets. This rise in sea level is not uniform all over the world, because regional effects (uplift and subsidence of coastal zones) are superimposed on global trends. During the early Holocene the Siberian

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

    DEFF Research Database (Denmark)

    Funder, Svend Visby

    1978-01-01

    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...

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

    Science.gov (United States)

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

    2018-04-01

    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.

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

    Science.gov (United States)

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

    2016-01-01

    Marked uncertainties persist regarding the climatic evolution of the Mediterranean region during the Holocene. For instance, whether moisture availability gradually decreased, remained relatively constant, or increased during the last 7000 years remains a matter of debate. To assess Holocene limnology, hydrology and moisture dynamics, the coastal lakes Lago Preola and Gorgo Basso, located in southwestern Sicily, were investigated through several stratigraphic analyses of ostracodes, including multivariate analyses of assemblages, transfer functions of salinity, and biochemical analyses of valves (Sr/Ca, δ18O and δ13C). During the early Holocene, the Gorgo Basso and Lago Preola ostracode records are similar. After an initial period of moderate salinity (1690–6100 mg/l from ca. 10,000–8190 cal yr BP), syndepositional or diagenetic dissolution of ostracode valves suggests that salinity declined to Greek civilization took root in Sicily (2600 cal yr BP), and it completely dominates the record during Roman occupation (roughly 2100 to 1700 cal yr BP). These freshwater conditions at Gorgo Basso suggest high effective moisture when evergreen olive-oak forests collapsed in response to increased Greco-Roman land use and fire. Ostracode valve geochemistry (Sr/Ca, δ18O) suggests significant changes in early vs. late Holocene hydrochemistry, either as changes in salinity or in the seasonality of precipitation. Harmonizing the autecological and geochemical data from Gorgo Basso suggests the latter was more likely, with relatively more late Holocene precipitation falling during the spring, summer, and fall, than winter compared to the early Holocene. Our ostracode-inferred paleosalinity data indicate that moisture availability did not decline during the late Holocene in the central Mediterranean region. Instead, moisture availability was lowest during the early Holocene, and most abundant during the late Holocene.

  6. Landslides and megathrust splay faults captured by the late Holocene sediment record of eastern Prince William Sound, Alaska

    Science.gov (United States)

    Finn, S.P.; Liberty, Lee M.; Haeussler, Peter J.; Pratt, Thomas L.

    2015-01-01

    We present new marine seismic‐reflection profiles and bathymetric maps to characterize Holocene depositional patterns, submarine landslides, and active faults beneath eastern and central Prince William Sound (PWS), Alaska, which is the eastern rupture patch of the 1964 Mw 9.2 earthquake. We show evidence that submarine landslides, many of which are likely earthquake triggered, repeatedly released along the southern margin of Orca Bay in eastern PWS. We document motion on reverse faults during the 1964 Great Alaska earthquake and estimate late Holocene slip rates for these growth faults, which splay from the subduction zone megathrust. Regional bathymetric lineations help define the faults that extend 40–70 km in length, some of which show slip rates as great as 3.75  mm/yr. We infer that faults mapped below eastern PWS connect to faults mapped beneath central PWS and possibly onto the Alaska mainland via an en echelon style of faulting. Moderate (Mw>4) upper‐plate earthquakes since 1964 give rise to the possibility that these faults may rupture independently to potentially generate Mw 7–8 earthquakes, and that these earthquakes could damage local infrastructure from ground shaking. Submarine landslides, regardless of the source of initiation, could generate local tsunamis to produce large run‐ups along nearby shorelines. In a more general sense, the PWS area shows that faults that splay from the underlying plate boundary present proximal, perhaps independent seismic sources within the accretionary prism, creating a broad zone of potential surface rupture that can extend inland 150 km or more from subduction zone trenches.

  7. Homogeneity of a Global Multisatellite Soil Moisture Climate Data Record

    Science.gov (United States)

    Su, Chun-Hsu; Ryu, Dongryeol; Dorigo, Wouter; Zwieback, Simon; Gruber, Alexander; Albergel, Clement; Reichle, Rolf H.; Wagner, Wolfgang

    2016-01-01

    Climate Data Records (CDR) that blend multiple satellite products are invaluable for climate studies, trend analysis and risk assessments. Knowledge of any inhomogeneities in the CDR is therefore critical for making correct inferences. This work proposes a methodology to identify the spatiotemporal extent of the inhomogeneities in a 36-year, global multisatellite soil moisture CDR as the result of changing observing systems. Inhomogeneities are detected at up to 24 percent of the tested pixels with spatial extent varying with satellite changeover times. Nevertheless, the contiguous periods without inhomogeneities at changeover times are generally longer than 10 years. Although the inhomogeneities have measurable impact on the derived trends, these trends are similar to those observed in ground data and land surface reanalysis, with an average error less than 0.003 cubic meters per cubic meter per year. These results strengthen the basis of using the product for long-term studies and demonstrate the necessity of homogeneity testing of multisatellite CDRs in general.

  8. Environmental response to the cold climate event 8200 years ago as recorded at Hoejby Soe, Denmark

    Energy Technology Data Exchange (ETDEWEB)

    Rasmussen, Peter (Geological Survey of Denmark and Greenland, Copenhagen (Denmark)); Ulfeldt Hede, M.; Noe-Nygaard, N. (Univ. of Copenhagen, Dept. of Geography and Geology, Copenhagen (Denmark)); Clarke, A.L. (APEM Manchester Lab., Stockport (United Kingdom)); Vinebrooke, R.D. (Univ. of Alberta, Dept. of Biological Science - Freshwater Biodiversity Lab., Edmonton (Canada))

    2008-07-15

    The need for accurate predictions of future environmental change under conditions of global warming has led to a great interest in the most pronounced climate change known from the Holocene: an abrupt cooling event around 8200 years before present (present = A.D. 1950), also known as the '8.2 ka cooling event' (ka = kilo-annum = 1000 years). This event has been recorded as a negative delta18OMICRON excursion in the central Greenland ice cores (lasting 160 years with the lowest temperature at 8150) and in a variety of other palaeoclimatic archives including lake sediments, ocean cores, speleothems, tree rings, and glacier oscillations from most of the Northern Hemisphere. In Greenland the maximum cooling was estimated to be 6 +- 2 deg. C while in southern Fennoscandia and the Baltic countries pollenbased quantitative temperature reconstructions indicate a maximum annual mean temperature decrease of around 1.5 deg. C. Today there is a general consensus that the primary cause of the cooling event was the final collapse of the Laurentide ice sheet near Hudson Bay and the associated sudden drainage of the proglacial Lake Agassiz into the North Atlantic Ocean around 8400 B.P. . This freshwater outflow, estimated to amount to c. 164,000 km3 of water, reduced the strength of the North Atlantic thermohaline circulation and thereby the heat transported to the North Atlantic region, resulting in an atmospheric cooling. The climatic consequences of this meltwater flood are assumed to be a good geological analogue for future climate-change scenarios, as a freshening of the North Atlantic is projected by almost all global-warming models and is also currently being registered in the region. In an ongoing project, the influence of the 8.2 ka cooling event on a Danish terrestrial and lake ecosystem is being investigated using a variety of biological and geochemical proxy data from a sediment core extracted from Hojby So, north-west Sjaelland. Here we present data on

  9. Synchronizing Greenland ice-core records and the Meerfelder maar sediment record via the global cosmogenic radionuclide signature and insights on climate around 11,230 years BP

    Science.gov (United States)

    Mekhaldi, F.; Czymzik, M.; Brauer, A.; Martin-Puertas, C.; Aldahan, A.; Possnert, G.; Muscheler, R.

    2017-12-01

    The causal investigation of multiple paleoclimate records relies on the accuracy of their respective chronostratigraphy. To achieve relative synchronization, cosmogenic radionuclides are an excellent tool because their common signature is global and can be retrieved and measured in different paleoclimate archives. For instance, 10Be can be measured in both ice cores and lake sediments (Berggren et al., 2013; Czymzik et al., 2016) which allows for both archives to be anchored onto radiocarbon timescales by synchronizing 10Be with 14C. We investigate the period 11,500-11,000 years BP when a short cold climate spell is known, from ice-core proxy records, to have occurred in Greenland shortly after the onset of the Holocene - the Preboreal Oscillation (PBO). This period also coincides with one of the largest and longest-lived increase in 14C production rate during the Holocene, which most likely corresponds to a grand solar minimum (around 11,230-11,000 years BP). In consequence, this period ideally illustrates the potential of using a known and clear signal in the production rate of cosmogenic radionuclides as a synchronizing tool, such as caused by large variations in solar activity. Here we measure 10Be in Meerfelder Maar (a well-dated and widely used sediment record from Germany) around 11,230 years BP which allows us to align the 10Be signal in both the Meerfelder Maar (MFM) sediment record and the GRIP ice core to IntCal13. Doing so, we report that i) the structure of the grand solar minimum is well-preserved in the 10Be signal of MFM sediments, ii) the PBO in Greenland occurs during high levels of solar activity and is not clearly observed in MFM, and iii) the PBO in Greenland ends precisely at the onset of the grand solar minimum at 11,230 years BP which also corresponds to a depositional change in MFM sediments (Martin-Puertas et al., 2017). These results thus suggest that changes in solar activity could have been a forcing at play eventually resulting in the

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

    Science.gov (United States)

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

    2014-12-01

    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.

  11. Uncertainty information in climate data records from Earth observation

    Science.gov (United States)

    Merchant, Christopher J.; Paul, Frank; Popp, Thomas; Ablain, Michael; Bontemps, Sophie; Defourny, Pierre; Hollmann, Rainer; Lavergne, Thomas; Laeng, Alexandra; de Leeuw, Gerrit; Mittaz, Jonathan; Poulsen, Caroline; Povey, Adam C.; Reuter, Max; Sathyendranath, Shubha; Sandven, Stein; Sofieva, Viktoria F.; Wagner, Wolfgang

    2017-07-01

    The question of how to derive and present uncertainty information in climate data records (CDRs) has received sustained attention within the European Space Agency Climate Change Initiative (CCI), a programme to generate CDRs addressing a range of essential climate variables (ECVs) from satellite data. Here, we review the nature, mathematics, practicalities, and communication of uncertainty information in CDRs from Earth observations. This review paper argues that CDRs derived from satellite-based Earth observation (EO) should include rigorous uncertainty information to support the application of the data in contexts such as policy, climate modelling, and numerical weather prediction reanalysis. Uncertainty, error, and quality are distinct concepts, and the case is made that CDR products should follow international metrological norms for presenting quantified uncertainty. As a baseline for good practice, total standard uncertainty should be quantified per datum in a CDR, meaning that uncertainty estimates should clearly discriminate more and less certain data. In this case, flags for data quality should not duplicate uncertainty information, but instead describe complementary information (such as the confidence in the uncertainty estimate provided or indicators of conditions violating the retrieval assumptions). The paper discusses the many sources of error in CDRs, noting that different errors may be correlated across a wide range of timescales and space scales. Error effects that contribute negligibly to the total uncertainty in a single-satellite measurement can be the dominant sources of uncertainty in a CDR on the large space scales and long timescales that are highly relevant for some climate applications. For this reason, identifying and characterizing the relevant sources of uncertainty for CDRs is particularly challenging. The characterization of uncertainty caused by a given error effect involves assessing the magnitude of the effect, the shape of the

  12. Reassessing the stable water isotope record in understanding past climate

    International Nuclear Information System (INIS)

    Noone, D.; Simmonds, I.

    1999-01-01

    Full text: The impact of atmospheric circulation on the stable water isotope record has been examined using an atmospheric general circulation model to reassess the validity of using isotopes to reconstruct Earth's climate history. Global temperature changes are classically estimated from the variations in (polar) isotopic values assuming a simple linear relationship. Such a relationship can be justified from first order theoretical considerations given that the isotopic fractionation at the deposition (ice core) site is temperature dependent. However, it is found that the history of a given air mass is more important that local processes because of the net effect of condensation events active along the transport pathway from the source region. Modulations in the hemispheric flow are seen to be crucial to Antarctic precipitation and the isotopic signal. Similarly, both transient and stationary disturbances influence the pathways of the air masses associated with Antarctic precipitation. During different climate regimes, such as that of the Last Glacial Maximum, the properties of these types of disturbances may not be assumed to be the same. As such, we may not assume that the condensation histories are the same as under different climate conditions. Therefore, the veracity of the linear climate reconstructions becomes questionable. Notwithstanding this result, the types of changes to the circulation regime that are expected generally correspond to changes in the global temperature. This fortunate result does not disallow the use of regressional reconstruction, however, the uncertainties associated with these circulation changes are of the same magnitude as the differences suggested by conventional linear regression in climate reconstruction. This indicates that interpretation of ice core data must be accompanied by detailed examination of the atmospheric processes and quantification of the impacts of their changes. Copyright (1999) Geological Society of Australia

  13. Long-term bird study records Arctic climate change

    Science.gov (United States)

    Zielinski, Sarah

    Alaska's summer of 2005 was the second warmest on record there, with a record retreat of arctic pack ice. As Alaskan temperatures gradually increase, artic birds, such as the black guillemots of Cooper Island, near Barrow, Alaska, are experiencing drastic habitat changes. Though these small black and white birds—the subjects of a long-term study of climate change—fared better this year than they have in the recent past (due to local cool conditions), they are nonetheless struggling to adapt as their artic island summer home becomes subarctic.George Divokyan ornithologist at the Institute of Arctic Biology, University of Alaska Fairbanks, discovered the Cooper Island colony of guillemots in the early 1970s and has spent every summer since 1975 there studying these birds. He presented his latest research during a 3 November talk in Washington, D.C.

  14. LATE GLACIAL AND HOLOCENE BIOCLIMATIC RECONSTRUCTION IN SOUTHERN ITALY: THE TRIFOGLIETTI LAKE

    Directory of Open Access Journals (Sweden)

    E. Brugiapaglia

    2013-04-01

    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.

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

    Science.gov (United States)

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

    2013-01-01

    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

  16. The Late Pleistocene-Holocene community development in Central and SE-Europe in direct fossil record: scope of the approach, common patterns and inter-regional differences.

    Science.gov (United States)

    Horacek, Ivan; Lozek, Vojen

    2010-05-01

    The information provided by modern instrumental approaches (molecular phylogeography, ancient DNA analyses, large scale radiocarbon datings etc.) refined the knowledge on Late Quaternary faunal development and range history of particular taxa in essential way. Nevertheless, the direct fossil record remains still an essential substrate in study of that topics, and to reveal all the information, that it may provide, and integrate it with the outputs of the other approaches presents one of the essential aim of the present meeting. Unfortunately, the immediate use of fossil record for the paleoecologic and paleobiogeographic inferences is often limited by its fragmentarity (both in temporal and spatial respects), taphonomic influences and/or locally specific post-sedimentary effects which all may bias it in a considerable degree. Hence, each particular record is to be carefully reexamined in respect to all factor which may bias it - unfortunately, often it is not too easy to respond that task, particularly when the record is retrived from secondary sources. It should also be remembered that the records representing narrow time slices without a robust lithostratigraphic context do not provide any information on the historical and contextual setting of the respective faunal situation. Such information that is essential for reconstructions of paleobiogeography of community development and similar locally-sensitive phenomena can only be retrived from the continuous sedimentary series which establish the sequence of particular faunal events by direct superposition. A sufficiently dense network of such series provides than a possibility of direct inter-regional comparisons and a high resolution information on the paleobiogeography of the Late Pleistocene-Holocene rearrangements of mammalian communities, local variation in history of particular species and its community context. We illustrate productivity of such approach on with aid of the fossil record obtained from

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

    Science.gov (United States)

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

    2015-01-01

    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.

  18. Continuity of Climate Data Records derived from Microwave Observations

    Science.gov (United States)

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

    2017-12-01

    Remote Sensing Systems (www.remss.com) 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

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

    Science.gov (United States)

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

    2006-12-01

    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.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

    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)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2003-12-24

    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.

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

    Science.gov (United States)

    Meador, E.; Morrill, C.

    2017-12-01

    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.

  3. Multi-Decadal to Millennial Scale Holocene Hydrologic Variation in the Southern Hemisphere Tropics of South America

    Science.gov (United States)

    Ekdahl, E. J.; Fritz, S. C.; Baker, P. A.; Burns, S. J.; Coley, K.; Rigsby, C. A.

    2005-12-01

    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.

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

    Science.gov (United States)

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

    2001-09-01

    Lacustrine deposits exposed around Lake Aricota, Peru (17° 22‧S), a 7.5-km2 lake dammed by debris flows, provide a middle to late Holocene record of lake-level fluctuations. Chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14C reservoir effects (<350 yr). Diatomites associated with highstands several meters above the modern lake level indicate wet episodes. Maximum Holocene lake level was attained before 6100 14C yr B.P. and ended ∼2700 14C yr B.P. Moderately high lake levels occurred at 1700 and 1300 14C yr B.P. The highstand at Lake Aricota during the middle Holocene is coeval with a major lowstand at Lake Titicaca (16°S), which is only 130 km to the northeast and shares a similar climatology. Comparisons with other marine and terrestrial records highlight emerging contradictions over the nature of mid-Holocene climate in the central Andes.

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

    Science.gov (United States)

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

    2016-08-01

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

  6. Roosevelt Island Climate Evolution Project (RICE): A 65 Kyr ice core record of black carbon aerosol deposition to the Ross Ice Shelf, West Antarctica.

    Science.gov (United States)

    Edwards, Ross; Bertler, Nancy; Tuohy, Andrea; Neff, Peter; Proemse, Bernedette; Feiteng, Wang; Goodwin, Ian; Hogan, Chad

    2015-04-01

    Emitted by fires, black carbon aerosols (rBC) perturb the atmosphere's physical and chemical properties and are climatically active. Sedimentary charcoal and other paleo-fire records suggest that rBC emissions have varied significantly in the past due to human activity and climate variability. However, few paleo rBC records exist to constrain reconstructions of the past rBC atmospheric distribution and its climate interaction. As part of the international Roosevelt Island Climate Evolution (RICE) project, we have developed an Antarctic rBC ice core record spanning the past ~65 Kyr. The RICE deep ice core was drilled from the Roosevelt Island ice dome in West Antarctica from 2011 to 2013. The high depth resolution (~ 1 cm) record was developed using a single particle intracavity laser-induced incandescence soot photometer (SP2) coupled to an ice core melter system. The rBC record displays sub-annual variability consistent with both austral dry-season and summer biomass burning. The record exhibits significant decadal to millennial-scale variability consistent with known changes in climate. Glacial rBC concentrations were much lower than Holocene concentrations with the exception of several periods of abrupt increases in rBC. The transition from glacial to interglacial rBC concentrations occurred over a much longer time relative to other ice core climate proxies such as water isotopes and suggests . The protracted increase in rBC during the transition may reflected Southern hemisphere ecosystem / fire regime changes in response to hydroclimate and human activity.

  7. Vegetation, climate and fire-dynamics in East Africa inferred from the Maundi crater pollen record from Mt Kilimanjaro during the last glacial-interglacial cycle

    Science.gov (United States)

    Schüler, Lisa; Hemp, Andreas; Zech, Wolfgang; Behling, Hermann

    2012-04-01

    The pollen, charcoal and sedimentological record from the Maundi crater, located at 2780 m elevation on the south-eastern slope of Mt Kilimanjaro, is one of the longest terrestrial records in equatorial East Africa, giving an interesting insight into the vegetation and climate dynamics back to the early last Glacial period. Our sediment record has a reliable chronology until 42 ka BP. An extrapolation of the age-depth model, as well as matching with other palaeo-records from tropical East Africa, suggest a total age of about 90 ka BP at the bottom of the record. During the last Glacial the distribution as well as the composition of the vegetation belts classified as colline savanna, submontane woodland, montane forest, ericaceous belt, and alpine vegetation changed. The early last Glacial is characterized by high amounts of Poaceae and Asteraceae pollen suggesting a climatically dry but stable phase. Based on the absence of pollen grains in samples deposited around 70 ka BP, we assume the occurrence of distinct drought periods. During the pre-LGM (Last Glacial Maximum) a higher taxa diversity of the ericaceous and montane zone is recorded and suggests a spread of forest and shrub vegetation, thus indicating a more humid period. The taxa diversity increases steadily during the recorded time span. The decent of vegetation zones indicate dry and cold conditions during the LGM and seem to have been detrimental for many taxa, especially those of the forest vegetation; however, the early last Glacial seems to have been markedly drier than the LGM. The reappearance of most of the taxa (most importantly Alchemilla, Araliaceae, Dodonea, Hagenia, Ilex, Myrsine, Moraceae, Piperaceae) during the deglacial and Holocene period suggest a shift into humid conditions. An increase in ferns and the decrease in grasses during the Holocene also indicate increasing humidity. Fire played an important role in controlling the development and elevation of the ericaceous zone and the tree

  8. Applying Metrological Techniques to Satellite Fundamental Climate Data Records

    Science.gov (United States)

    Woolliams, Emma R.; Mittaz, Jonathan PD; Merchant, Christopher J.; Hunt, Samuel E.; Harris, Peter M.

    2018-02-01

    Quantifying long-term environmental variability, including climatic trends, requires decadal-scale time series of observations. The reliability of such trend analysis depends on the long-term stability of the data record, and understanding the sources of uncertainty in historic, current and future sensors. We give a brief overview on how metrological techniques can be applied to historical satellite data sets. In particular we discuss the implications of error correlation at different spatial and temporal scales and the forms of such correlation and consider how uncertainty is propagated with partial correlation. We give a form of the Law of Propagation of Uncertainties that considers the propagation of uncertainties associated with common errors to give the covariance associated with Earth observations in different spectral channels.

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

    Science.gov (United States)

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

    2018-03-01

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

  10. Evaluating and Extending the Ocean Wind Climate Data Record

    Science.gov (United States)

    Ricciardulli, Lucrezia; Rodriguez, Ernesto; Stiles, Bryan W.; Bourassa, Mark A.; Long, David G.; Hoffman, Ross N.; Stoffelen, Ad; Verhoef, Anton; O'Neill, Larry W.; Farrar, J. Tomas; Vandemark, Douglas; Fore, Alexander G.; Hristova-Veleva, Svetla M.; Turk, F. Joseph; Gaston, Robert; Tyler, Douglas

    2017-01-01

    Satellite microwave sensors, both active scatterometers and passive radiometers, have been systematically measuring near-surface ocean winds for nearly 40 years, establishing an important legacy in studying and monitoring weather and climate variability. As an aid to such activities, the various wind datasets are being intercalibrated and merged into consistent climate data records (CDRs). The ocean wind CDRs (OW-CDRs) are evaluated by comparisons with ocean buoys and intercomparisons among the different satellite sensors and among the different data providers. Extending the OW-CDR into the future requires exploiting all available datasets, such as OSCAT-2 scheduled to launch in July 2016. Three planned methods of calibrating the OSCAT-2 σo measurements include 1) direct Ku-band σo intercalibration to QuikSCAT and RapidScat; 2) multisensor wind speed intercalibration; and 3) calibration to stable rainforest targets. Unfortunately, RapidScat failed in August 2016 and cannot be used to directly calibrate OSCAT-2. A particular future continuity concern is the absence of scheduled new or continuation radiometer missions capable of measuring wind speed. Specialized model assimilations provide 30-year long high temporal/spatial resolution wind vector grids that composite the satellite wind information from OW-CDRs of multiple satellites viewing the Earth at different local times. PMID:28824741

  11. Late Holocene paleoenvironments of the floodplain of the Solimões River, Central Amazonia, based on the palynological record of Lake Cabaliana

    Directory of Open Access Journals (Sweden)

    Natália de Paula Sá

    Full Text Available ABSTRACT The core PD-67 of 160 cm depth was collected from the delta of Lake Cabaliana situated on the Solimões River. Seventeen samples were removed for palynological and sedimentological analysis and three for radiocarbon analysis. Two dry periods, both in the Late Holocene, were observed (2800-2550 cal yr BP, 1450-550 cal yr BP separated by a wetter phase (2550-1450 cal yr BP. In 2800-2550 cal yr BP, varzea forests of Alchornea, Symmeria, Cecropia, Alternanthera and Asteraceae were predominant. Beginning in 2,550-1450 cal yr BP, the varzea was characterized by pioneer elements, such as Cassia, Laetia, Mabea, Symmeria and Cecropia, and by the expansion of Poaceae, Cyperaceae, Sagittaria, Montrichardia and Asteraceae. In 1450-550 cal yr BP the succession of varzea continued with Pseudobombax, Laetia, Luehea/Lueheopsis and Ryanaea increasing simultaneously with the terra firme vegetation of Rutaceae, Sapotaceae, Styrax, Scleronema, Anthurium, Araceae, pteridophytes and Pariana. The successional dynamics at Lake Cabaliana indicated that the local varzea had become established recently, and is composed of a mosaic of different successional stages of vegetation influenced mainly by flood pulse and variation in rainfall. It is therefore possible to propose that the recent climate history of Central Amazonia reflects changes in rainfall patterns in the basin.

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

    Science.gov (United States)

    Premathilake, Rathnasiri

    2012-09-01

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

  13. Assessing millennial-scale variability during the Holocene: A perspective from the western tropical Pacific

    Science.gov (United States)

    Khider, D.; Jackson, C. S.; Stott, L. D.

    2014-03-01

    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.

  14. Postglacial Records of Southern Hemisphere Climate and Oceanographic Change From the New Zealand Subantarctic Auckland Islands

    Science.gov (United States)

    Moy, C. M.; Gilmer, G.; Nichols, J. E.; Browne, I. M.; Curtin, L.; Vandergoes, M.; Aebig, C.; Wilson, G. S.

    2017-12-01

    The strength and latitudinal position of the Southern Hemisphere westerly winds (SHWW) play a fundamental role in influencing mid-latitude climate and CO2 exchange between the Southern Ocean and the atmosphere along seasonal to glaicial-interglacial timescales. Despite their importance, our understanding of past SHWW change is limited by the small number of paleoclimate records from the modern wind maximum, which are often not in agreement. The New Zealand subantarctic Auckland Islands are located within the core of the modern wind belt (50°S), a key latitude where ocean-atmospheric linkages between the Antarctic and mid-latitudes are strong. In contrast to other subantarctic islands on the Campbell Plateau, the Auckland Islands have multiple protected fjord sub-basins, deep lakes, and peatlands that are advantageous for the development of high-resolution paleoclimate records. We will present ongoing work towards the establishment of multi-proxy and multi-site reconstructions of past SHWW variability from the Auckland Islands. Modern process and paleoclimate studies suggest that in lacustrine and fjord settings, the degree of water column mixing, the stable isotopic composition of n-alkanes and benthic foraminifera, and the influx of terrestrial organic matter are good indicators of wind-induced mixing of the water column or precipitation-driven erosion within catchments. During the Late Glacial and early Holocene (15 to 9 ka), elevated long-chain n-alkane δD values from ombrotrophic peatlands and an increase in the concentration of redox-sensitive elements in fjord sediment cores, signal weakening of the SHWW that appears to be coincident with periods of rapid deglacial warming of West Antarctica. Since 5.5 ka, we interpret declining n-alkane δD values to indicate enhanced westerly flow. These interpretations are in broad agreement with terrestrial paleoclimate records developed from southern South America and argue for a symmetrical response of the SHWW during

  15. The late Wisconsinan and Holocene record of Walrus (Odobenus rosmarus) from North America: A review with new data from Arctic and Atlantic Canada

    Science.gov (United States)

    Dyke, A.S.; Hooper, J.; Harington, C.R.; Savelle, J.M.

    1999-01-01

    The Late Wisconsinan and Holocene record of the Atlantic walrus is known from numerous collections of bones and tusks from Arctic Canada and south to North Carolina, as well as from many archaeological sites in the Arctic and Subarctic. In contrast, the Pacific walrus has no dated Late Wisconsinan or early Holocene record in North America, and it may have been displaced into the northwest Pacific at Last Glacial Maximum (LGM). The Atlantic walrus rapidly exploited newly deglaciated territory, moving northward from its LGM refugium and reaching the Bay of Fundy by 12800 B.P., the Grand Banks by 12500 B.P., southern Labrador by 11500 B.P., and the central Canadian Arctic Archipelago (CAA) by 9700 B.P. Its southern range limit may have retracted to the Bay of Fundy by ca. 7500 B.P. Within the CAA, walrus remains cluster in two main age groups: 9700 to 8500 B.P. and 5000 to 4/3000 B.P. This pattern strongly resembles the distribution of bowhead whale radiocarbon ages from the same area, which suggests a common control by sea-ice conditions. Walrus remains occur in Indian culture archaeological sites as old as 7500 B.P. and, in some cases (Namu, British Columbia, and Mackinac Island, Michigan), they evidently represent long-distance human transport. They are much more common in Paleoeskimo and Neoeskimo culture sites. However, they occur in very low abundances, and generally as debitage, in sites older than Dorset (2500 B.P.). The walrus, therefore, may not have been hunted by early Paleoeskimos. Beginning with Early Dorset, walrus remains occur in definite diet-related contexts. Middle Dorset (2300 to 1500 B.P.) and late Thule (High Arctic, and there may be a similar gap in the middle Pre-Dorset (3400 to 2600 B.P.). Sea-ice conditions at these times may have adversely affected availability of walrus and other marine mammal resources. Walrus is a prominent faunal element in Middle Dorset sites on the Labrador coast; this is consistent with a southward displacement of

  16. Shoreface translation and the Holocene stratigraphic record: Examples from Nova Scotia, the Mississippi Delta and eastern Australia

    Science.gov (United States)

    Boyd, Ron; Penland, S.

    1984-01-01

    Classic descriptive models of barrier sedimentation have been developed with data from the Atlantic and Gulf coasts of the United States. These models are dominated by low to moderate rates of relative sea level (RSL) rise and wave energy. Barriers respond by landward recycling of sediment through the mechanism of shoreface retreat. Sedimentation processes on the central coast of New South Wales (N.S.W.), Australia, consist of rapid RSL rise in early Holocene times followed by a stillstand since 6500 B.P. Wave energy is relatively high year-round and sand sources for barrier formation are only found on the inner shelf. Barrier sedimentation on the central coast of N.S.W. exhibits a thick, composite sequence composed of a basal marine transgressive sand overlain by regressive beach and dune facies. The Louisiana coast surrounding the Mississippi delta is underlain by compacting deltaic muds which generate very rapid rates of RSL rise. The Louisiana coast experiences low wave energy punctuated by high-energy tropical and extra-tropical storm events. Barrier sediments accumulate from the erosion of deltaic headlands and undergo a transformation from subaerial barrier island systems to subaqueous shoals located on the inner shelf. Drumlins experience coastal erosion on the Eastern Shore of Nova Scotia and provide a sediment source for compartmented estuary mouth barriers. An ongoing, moderate rise of RSL results from the passage of a glacial forebulge. Wave energy is intermediate between Louisiana and N.S.W. and displays a seasonal pattern dominated by frequent winter storms. Coastal barrier sedimentation is episodic, consisting of a period of beach ridge progradation followed by barrier destruction and re-establishment further landward. The three contrasting sedimentary sequences found in examples from Louisiana, N.S.W. and Nova Scotia indicate that presently available sedimentation models from locations such as the middle Atlantic or Texas coasts of the United States

  17. 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

    Science.gov (United States)

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

    2007-12-01

    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

  18. Uncertainty information in climate data records from Earth observation

    Science.gov (United States)

    Merchant, C. J.

    2017-12-01

    How to derive and present uncertainty in climate data records (CDRs) has been debated within the European Space Agency Climate Change Initiative, in search of common principles applicable across a range of essential climate variables. Various points of consensus have been reached, including the importance of improving provision of uncertainty information and the benefit of adopting international norms of metrology for language around the distinct concepts of uncertainty and error. Providing an estimate of standard uncertainty per datum (or the means to readily calculate it) emerged as baseline good practice, and should be highly relevant to users of CDRs when the uncertainty in data is variable (the usual case). Given this baseline, the role of quality flags is clarified as being complementary to and not repetitive of uncertainty information. Data with high uncertainty are not poor quality if a valid estimate of the uncertainty is available. For CDRs and their applications, the error correlation properties across spatio-temporal scales present important challenges that are not fully solved. Error effects that are negligible in the uncertainty of a single pixel may dominate uncertainty in the large-scale and long-term. A further principle is that uncertainty estimates should themselves be validated. The concepts of estimating and propagating uncertainty are generally acknowledged in geophysical sciences, but less widely practised in Earth observation and development of CDRs. Uncertainty in a CDR depends in part (and usually significantly) on the error covariance of the radiances and auxiliary data used in the retrieval. Typically, error covariance information is not available in the fundamental CDR (FCDR) (i.e., with the level-1 radiances), since provision of adequate level-1 uncertainty information is not yet standard practice. Those deriving CDRs thus cannot propagate the radiance uncertainty to their geophysical products. The FIDUCEO project (www.fiduceo.eu) is

  19. Limnological controls on stable isotope records of late-holocene palaeoenvironment change in sw greenland: A paired lake study

    DEFF Research Database (Denmark)

    Olsen, Jesper; John Anderson, N.; Leng, M.J.

    2013-01-01

    Stable isotope records are increasingly being used in palaeoenvironmental studies of Arctic lakes. Here we compare stable isotope and elemental records (δ13C, δ15N, C/N) with high resolution XRF-derived geochemical and colour data from low Arctic lakes (SS1220 and SS85) in southwest Greenland. Lake...... SS1220 sediments are laminated gyttja whereas SS85 consist of homogeneous gyttja, both records cover the last c. 5000 years. d13C and carbon content suggest that organic matter in both lakes is predominantly autochthonous. The C/N variability, ranging between 11 and 15, is interpreted...... composition of lake sediments when there is a reasonable understanding of limnological processes, and records may be lake specific....

  20. Role of the mid-Holocene environmental transition in the decline of late Neolithic cultures in the deserts of NE China

    Science.gov (United States)

    Guo, Licheng; Xiong, Shangfa; Ding, Zhongli; Jin, Guiyun; Wu, Jiabin; Ye, Wei

    2018-06-01

    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.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    Leorri, Eduardo, E-mail: leorrie@ecu.edu [Department of Geological Sciences, East Carolina University, Graham Building 103B, Greenville, NC 27858 (United States); Mitra, Siddhartha, E-mail: mitras@ecu.edu [Department of Geological Sciences, East Carolina University, Graham Building 103B, Greenville, NC 27858 (United States); Irabien, María Jesús, E-mail: mariajesus.irabien@ehu.es [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: azimmer@ufl.edu [Department of Geological Sciences, University of Florida, 241 Williamson Hall, P.O. Box 112120, Gainesville, FL 32611 (United States); Blake, William H., E-mail: william.blake@plymouth.ac.uk [Consolidated Radioisotope Facility, University of Plymouth, Plymouth (United Kingdom); Cearreta, Alejandro, E-mail: alejandro.cearreta@ehu.es [Departamento de Estratigrafía y Paleontología, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Apartado 644, 48080 Bilbao (Spain)

    2014-02-01

    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.

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

    Science.gov (United States)

    Jacobs, D. K.

    2006-12-01

    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

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

    Science.gov (United States)

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

    1994-12-01

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

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

    Science.gov (United States)

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

    2017-11-01

    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.

  6. ICE-6G models of postglacial relative sea-level history applied to Holocene coral reef and mangrove records of the western Caribbean

    Science.gov (United States)

    Toscano, M. A.; Peltier, W. R.; Drummond, R.; Gonzalez, J.

    2012-12-01

    Fossil coral reefs and mangrove peat accumulations at western Caribbean sites along a latitudinal gradient from the Florida Keys through Belize and Panama provide dated and interpreted 8,000 year Holocene sea-level records for comparison with RSL predictions of the ICE-6G (VM5A, VM5B; L90) models of glacio-hydro-isostatic adjustment, with and without rotational feedback. These presumably passive continental margin sites provide the means to establish a N-S spatial trend in the varying influences of GIA, eustatic components of Holocene sea level, extent of forebulge collapse and influence of rotational feedback over a 20° latitudinal range. Previous ICE6G (VM5A) model-coral data comparisons for St Croix, USVI, Antigua, Martinique and Barbados (Toscano, Peltier and Drummond, 2011, QSR) along the eastern Caribbean plate and island arc illustrated the close model-data compatibility, the influence of rotational feedback acting as a significant factor in reducing misfits, and the need for high quality in situ data to confirm the extension of the proglacial forebulge into tropical latitudes. The gradient of western Caribbean continental shelf sites comprises a much more varied range of model-data relationships based on extensive combined Acropora palmata (reef crest coral) and Rhizophora mangle (microtidal mangrove) peat datasets in all cases. Starting at the northernmost region with the Florida Keys, there exist negative model misfits to the data, suggesting the possibility of a positive tectonic overprint upon expectations related to the glacial isostatic adjustment process acting alone, even though this region is normally believed to be tectonically stable. The largest multi-proxy database from Belize supports the likelihood of increasing rates of subsidence from north to south in the Belize Lagoon, which may account for numerous positive GIA model-data misfits. The southernmost site at Panama is most similar to Belize in the possible nature of tectonic influences on

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

    Science.gov (United States)

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

    2017-04-01

    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. Impact of climate variability on terrestrial environment in Western Europe between 45 and 9 kyr cal. BP: vegetation dynamics recorded by the Bergsee Lake (Black Forest, Germany).

    Science.gov (United States)

    Duprat-Oualid, Fanny; Begeot, Carole; Rius, Damien; Millet, Laurent; Magny, Michel

    2016-04-01

    Between 9 and 45 kyr cal. BP, two great transitions lead the global climate system to evolve from the Last-Glacial period (115-14.7 kyr cal. BP), to two successive warmer periods, the Late-Glacial Interstadial (14.7-11.7 kyr cal. BP) and the Holocene (11.7-0 kyr cal. BP). δ18O variations recorded in Greenland ice cores (GRIP & NGRIP) revealed high frequency climate variability within the Last Glacial. These reference isotopic records highlighted a succession of centennial-to-millennial warm/cold events, the so-called Greenland Interstadials (GI) and Greenland Stadials (GS). The number continental records about the period 14.7-0 kyr cal. BP is substantial. This allowed to understand the vegetation dynamics in response to climate changes this period at the North-Atlantic scale. However, sequences covering the glacial period (beyond 20 kyr cal.BP) remain rare, because of hiatuses mostly due to local glaciers. Therefore, sedimentary continuous records of vegetation dynamics are still needed to better understand climate changes during the Last Glacial in Western Europe (Heiri et al. 2014). Here we present a new high-resolution pollen record from Lake Bergsee (47°34'20''N, 7°56'11''E, 382 m a.s.l). This lake is located south of Black Forest and north of the Alps, beyond the zone of glaciers maximal extension. Therefore it could have recorded the whole last climatic cycle, i.e. 120-0 kyr cal. BP. In 2013, a 29 m long core was extracted from the Bergsee. According to the depth-age model based on 14C AMS dating and the Laacher See Tephra (LST), the record spans continuously at least the last 45 kyrs. The first series of pollen analysis, focused on the 45-9 kyr cal. BP time window, allows us to reconstruct a precise, faithful and continuous vegetation history at the centennial scale. This high temporal resolution enabled to assess the response of vegetation to secular climate events (e.g. GI-4 = 200 yrs). First, our results show that vegetation responded to climate

  9. VIIRS Climate Raw Data Record (C-RDR) from Suomi NPP, Version 1

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Suomi NPP Climate Raw Data Record (C-RDR) developed at the NOAA NCDC is an intermediate product processing level (NOAA Level 1b) between a Raw Data Record (RDR)...

  10. NOAA Climate Data Record (CDR) of Northern Hemisphere (NH) Snow Cover Extent (SCE), Version 1

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This NOAA Climate Data Record (CDR) is a record for the Northern Hemisphere (NH) Snow Cover Extent (SCE) spanning from October 4, 1966 to present, updated monthly...

  11. Climatic influences on species: Evidence from the fossil record

    Science.gov (United States)

    Cronin, T. M.; Schneider, C.E.

    1990-01-01

    The detailed Neogene and Quaternary paleoclimatic reconstructions now available provide a means to test how species respond to environmental change. Paleontologic studies of marine organisms show that climatic change causes evolution (via cladogenesis and anagenesis), ecophenotypic variation, migration, morphologic stasis and extinction. Evolution during climatic change is a rare event relative to the number of climatic cycles that have occurred, but climate-related environmental barriers, usually temperature, may play an important role in the isolation of populations during allopatric speciation.

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

    Science.gov (United States)

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

    2017-12-01

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

  13. Past climate variability between 97 and 7 ka reconstructed from a multi proxy speleothem record from Western Cuba

    Science.gov (United States)

    Winterhalder, Sophie; Scholz, Denis; Mangini, Augusto; Spötl, Christoph; Jochum, Klaus Peter; Pajón, Jesús M.

    2016-04-01

    . Due to the competing influence of the NA, the Gulf of Mexico and the Pacific Ocean, the proposed severe changes in the tropical hydrological cycle during that time (such as variations of the ITCZ, insolation and the thermohaline circulation (THC)) have potentially lead to significant changes in sources and trajectories of precipitation in Western Cuba. Our record, thus, provides an important contribution towards understanding and differentiating these parameters on Caribbean climate during glacial climate changes. References: Fensterer, C., Scholz, D., Hoffmann, D., Spötl, C., Pajón, J.M., Mangini, A., 2012. Cuban stalagmite suggests relationship between Caribbean precipitation and the Atlantic Multidecadal Oscillation during the past 1.3 ka. The Holocene, 0959683612449759. Fensterer, C., Scholz, D., Hoffmann, D.L., Spötl, C., Schröder-Ritzrau, A., Horn, C., Pajón, J.M., Mangini, A., 2013. Millennial-scale climate variability during the last 12.5 ka recorded in a Caribbean speleothem. Earth and Planetary Science Letters 361, 143-151. Winter, A., Miller, T., Kushnir, Y., Sinha, A., Timmermann, A., Jury, M.R., Gallup, C., Cheng, H., Edwards, R.L., 2011. Evidence for 800years of North Atlantic multi-decadal variability from a Puerto Rican speleothem. Earth and Planetary Science Letters 308, 23-28.

  14. Centennial-scale vegetation dynamics and climate variability in SE Europe during Marine Isotope Stage 11 based on a pollen record from Lake Ohrid

    Science.gov (United States)

    Kousis, Ilias; Koutsodendris, Andreas; Peyron, Odile; Leicher, Niklas; Francke, Alexander; Wagner, Bernd; Giaccio, Biagio; Knipping, Maria; Pross, Jörg

    2018-06-01

    To better understand climate variability during Marine Isotope Stage (MIS) 11, we here present a new, centennial-scale-resolution pollen record from Lake Ohrid (Balkan Peninsula) derived from sediment cores retrieved during an International Continental Scientific Drilling Program (ICDP) campaign. Our palynological data, augmented by quantitative pollen-based climate reconstructions, provide insight into the vegetation dynamics and thus also climate variability in SE Europe during one of the best orbital analogues for the Holocene. Comparison of our palynological results with other proxy data from Lake Ohrid as well as with regional and global climate records shows that the vegetation in SE Europe responded sensitively both to long- and short-term climate change during MIS 11. The chronology of our palynological record is based on orbital tuning, and is further supported by the detection of a new tephra from the Vico volcano, central Italy, dated to 410 ± 2 ka. Our study indicates that MIS 11c (∼424-398 ka) was the warmest interval of MIS 11. The younger part of the interglacial (i.e., MIS 11b-11a; ∼398-367 ka) exhibits a gradual cooling trend passing over into MIS 10. It is characterized by considerable millennial-scale variability as inferred by six abrupt forest-contraction events. Interestingly, the first forest contraction occurred during full interglacial conditions of MIS 11c; this event lasted for ∼1.7 kyrs (406.2-404.5 ka) and was characterized by substantial reductions in winter temperature and annual precipitation. Most notably, it occurred ∼7 ka before the end of MIS 11c and ∼15 ka before the first strong ice-rafted debris event in the North Atlantic. Our findings suggest that millennial-scale climate variability during MIS 11 was established in Southern Europe already during MIS 11c, which is earlier than in the North Atlantic where it is registered only from MIS 11b onwards.

  15. A palaeoenvironmental record of natural and human change from the Auckland Isthmus, New Zealand, during the Late Holocene

    International Nuclear Information System (INIS)

    Horrocks, M.; Deng, Y.; Nichol, S.L.; Shane, P.A.; Ogden, J.

    2002-01-01

    A multi-proxy analysis of a sediment core from Waiatarua, Auckland Isthmus, adds to an environmental history from the local wetland spanning the Late Glacial to modern times. Several distal tephra were recorded in the core: 8.5 ka Rotoma (reworked), 6.1 ka Tuhua (primary and reworked), most likely the 1.8 ka Taupo (the latter is previously unreported for the Auckland Isthmus), and one unidentified, possibly 665 yr BP Kaharoa. Pollen and diatom analyses of the core show that during the period c. 6000-c. 4800 yr BP, the site was a lake fringed with Cyperaceae/Leptospermum swamp. The lake became progressively shallower after c. 4800 yr BP, probably due to hydroseral infilling. Surrounding the lake was forest dominated by Dacrydium, Prumnopitys, Metrosideros, and Nestegis. Transition to the Polynesian era appears unclear because the site probably endured a hiatus due to destruction of peat by burning in European times. (author). 39 refs., 4 figs., 2 tabs

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

    Science.gov (United States)

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

    2017-10-01

    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.

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

    Directory of Open Access Journals (Sweden)

    Calogero M. Santoro

    2017-10-01

    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.

  18. Reconciling divergent trends and millennial variations in Holocene temperatures

    Science.gov (United States)

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

    2018-02-01

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

  19. Revised paleoenvironmental analysis of the Holocene portion of the Barbados sea-level record: Cobbler's Reef revisited

    Science.gov (United States)

    Toscano, Marguerite A.

    2016-06-01

    Sample elevations corrected for tectonic uplift and assessed relative to local modeled sea levels provide a new perspective on paleoenvironmental history at Cobbler's Reef, Barbados. Previously, 14C-dated surface samples of fragmented Acropora palmata plotted above paleo sea level based on their present (uplifted) elevations, suggesting supratidal rubble deposited during a period of extreme storms (4500-3000 cal BP), precipitating reef demise. At several sites, however, A. palmata persisted, existing until ~370 cal BP. Uplift-corrected A. palmata sample elevations lie below the western Atlantic sea-level curve, and ~2 m below ICE-6G-modeled paleo sea level, under slow rates of sea-level rise, negating the possibility that Cobbler's Reef is a supratidal storm ridge. Most sites show limited age ranges from corals likely damaged/killed on the reef crest, not the mixed ages of rubble ridges, strongly suggesting the reef framework died off in stages over 6500 yr. Reef crest death assemblages invoke multiple paleohistoric causes, from ubiquitous hurricanes to anthropogenic impacts. Comparison of death assemblage ages to dated regional paleotempestological sequences, proxy-based paleotemperatures, recorded hurricanes, tsunamis, European settlement, deforestation, and resulting turbidity, reveals many possible factors inimical to the survival of A. palmata along Cobbler's Reef.

  20. The Holocene sedimentary record of cyanobacterial glycolipids in the Baltic Sea: an evaluation of their application as tracers of past nitrogen fixation

    Directory of Open Access Journals (Sweden)

    M. Sollai

    2017-12-01

    Full Text Available Heterocyst glycolipids (HGs are lipids exclusively produced by heterocystous dinitrogen-fixing cyanobacteria. The Baltic Sea is an ideal environment to study the distribution of HGs and test their potential as biomarkers because of its recurring summer phytoplankton blooms, dominated by a few heterocystous cyanobacterial species of the genera Nodularia and Aphanizomenon. A multi-core and a gravity core from the Gotland Basin were analyzed to determine the abundance and distribution of a suite of selected HGs at a high resolution to investigate the changes in past cyanobacterial communities during the Holocene. The HG distribution of the sediments deposited during the Modern Warm Period (MoWP was compared with those of cultivated heterocystous cyanobacteria, including those isolated from Baltic Sea waters, revealing high similarity. However, the abundance of HGs dropped substantially with depth, and this may be caused by either a decrease in the occurrence of the cyanobacterial blooms or diagenesis, resulting in partial destruction of the HGs. The record also shows that the HG distribution has remained stable since the Baltic turned into a brackish semi-enclosed basin ∼ 7200 cal. yr BP. This suggests that the heterocystous cyanobacterial species composition remained relatively stable as well. During the earlier freshwater phase of the Baltic (i.e., the Ancylus Lake and Yoldia Sea phases, the distribution of the HGs varied much more than in the subsequent brackish phase, and the absolute abundance of HGs was much lower than during the brackish phase. This suggests that the cyanobacterial community adjusted to the different environmental conditions in the basin. Our results confirm the potential of HGs as a specific biomarker of heterocystous cyanobacteria in paleo-environmental studies.

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

    Science.gov (United States)

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

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

  2. Bacteriohopanepolyols record stratification, nitrogen fixation and other biogeochemical perturbations in Holocene sediments of the central Baltic Sea

    Directory of Open Access Journals (Sweden)

    M. Blumenberg

    2013-04-01

    Full Text Available The Baltic Sea, one of the world's largest brackish-marine basins, established after deglaciation of Scandinavia about 17 000 to 15 000 yr ago. In the changeable history of the Baltic Sea, the initial freshwater system was connected to the North Sea about 8000 yr ago and the modern brackish-marine setting (Littorina Sea was established. Today, a relatively stable stratification has developed in the water column of the deep basins due to salinity differences. Stratification is only occasionally interrupted by mixing events, and it controls nutrient availability and growth of specifically adapted microorganisms and algae. We studied bacteriohopanepolyols (BHPs, lipids of specific bacterial groups, in a sediment core from the central Baltic Sea (Gotland Deep and found considerable differences between the distinct stages of the Baltic Sea's history. Some individual BHP structures indicate contributions from as yet unknown redoxcline-specific bacteria (bacteriohopanetetrol isomer, methanotrophic bacteria (35-aminobacteriohopanetetrol, cyanobacteria (bacteriohopanetetrol cyclitol ether isomer and from soil bacteria (adenosylhopane through allochthonous input after the Littorina transgression, whereas the origin of other BHPs in the core has still to be identified. Notably high BHP abundances were observed in the deposits of the brackish-marine Littorina phase, particularly in laminated sediment layers. Because these sediments record periods of stable water column stratification, bacteria specifically adapted to these conditions may account for the high portions of BHPs. An additional and/or accompanying source may be nitrogen-fixing (cyanobacteria, which is indicated by a positive correlation of BHP abundances with Corg and δ15N.

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

    Directory of Open Access Journals (Sweden)

    Chao Zhao

    2016-01-01

    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.

  4. Climate, atmosphere, and volatile inventory evolution: polar processes, climate records, volatile inventories

    International Nuclear Information System (INIS)

    Pollack, J.B.

    1988-01-01

    Climate change on Mars was driven by long term changes in the solar luminosity, variations in the partitioning of volatiles between the atmosphere and near-surface reservoirs, and astronomical variations in axial and orbital properties. There are important parallels between these drives for Mars and comparable ones for Earth. In the early history of the solar system, the Sun's luminosity was 25 to 30 percent lower than its current value. It is suggested that an early benign