OSL and 14C chronologies of a Holocene sedimentary record (Garding‐2 core) from the German North Sea coast

The history of sea‐level change and sediment accumulation since the last deglaciation along the German North Sea coast is still controversial because of a limitation in the quantity and quality of chronological data. In the current study, the chronology of a 16‐ka coastal sedimentary record from the Garding‐2 core, retrieved from the Eiderstedt Peninsula in Schleswig‐Holstein, northern Germany, was established using OSL and AMS ¹⁴C dating techniques. The robust chronology using 14 radiocarbon and 25 OSL dates from the Garding‐2 core is the first long‐term record that covers the Holocene as well as the last deglaciation period in one succession in the German North Sea area. It provides a new insight into understanding the Holocene transgression and coastal accumulation histories. The combined evidence from the sedimentology and chronology investigations indicates that an estuarine environment dominated in Eiderstedt Peninsula from 16 to 13 ka, followed by a depositional hiatus between 13 and 8.3 ka, attributed to erosion caused by the Holocene transgression; the onset of the Holocene transgression at the core site occurred at around 8.3 ka. The sea level continued to rise with a decelerated rate until around 3 ka. Since 3 ka, the shoreline has begun to prograde. Foreshore (tidal flat) sediments have been deposited at the drilling site with a very high sedimentation rate of about 10 m ka^?1. At around 2 ka, a sandy beach deposit accumulated in the sedimentary succession, indicating that the coastline shifted landward, which may represent a small‐scale transgression in the late Holocene. At around 1.5 ka, terrestrial clastic sediment started to accumulate, indicating a retreat of the relative sea level in this area, which may be related to local diking activities undertaken since the 11th century.     

Schmidt‐hammer exposure‐age dating (SHD): application to early Holocene moraines and a reappraisal of the reliability of terrestrial cosmogenic‐nuclide dating (TCND) at Austanbotnbreen,Jotunheimen, Norway

Matthews, J. A. & Winkler, S. 2010: Schmidt‐hammer exposure‐age dating (SHD): application to early Holocene moraines and a reappraisal of the reliability of terrestrial cosmogenic‐nuclide dating (TCND) at Austanbotnbreen, Jotunheimen, Norway. Boreas, 10.1111/j.1502‐3885.2010.00178.x. ISSN 0300‐9483. Schmidt‐hammer exposure‐age dating (SHD) and terrestrial cosmogenic‐nuclide dating (TCND) are complementary techniques that can be used for mutual testing. SHD is low‐cost but requires local control points of known age and may be affected by local geological variation and other environmental factors that influence weathering rates. TCND is vulnerable to the occurrence of anomalous boulders, other geomorphological uncertainties and the effects of snow‐shielding at high altitudes. Both techniques are sensitive to post‐depositional disturbances if other than solid bedrock is sampled. SHD was applied to two moraine ridges beyond the Little Ice Age limit of Austanbotnbreen in the Hurrungane massif, southern Norway. Independent regional and experimental local age‐calibration curves were used to reappraise previous TCND results. Neither the two boulder surfaces nor their proximal bedrock surfaces could be differentiated statistically in terms of SHD exposure ages or their mean R‐values (±95% confidence intervals), which ranged from 40.73±1.72 to 43.34±0.69. The best of the independent regional‐calibration curves produced SHD exposure ages of 9413±723 and 9304±602 years, which are consistent with moraine formation early (c. 10.2 ka) and late (c. 9.7 ka) within the late‐Preboreal Erdalen Event. The current precision of SHD, as reflected in 95% confidence intervals of ±500–900 years, enables rejection of a Finse Event (c. 8.2 ka) age for either moraine. Results are consistent with a retracted Austanbotnbreen between the Erdalen Event and the Little Ice Age, and a modified model of Neoglaciation.     

The 10Be deglaciation chronology of the Göschenertal,central Swiss Alps,and new insights into the Göschenen Cold Phases

The Göschenertal (Göschenen valley) is the type locality of the so‐called Göschenen Cold Phases I (~3–2.3 ka) and II (~1.8–1.1 ka). According to earlier studies, these Late Holocene climatic cooling periods were characterized by changes in vegetation and pronounced glacier advances. As a peculiarity, the Göschenen Cold Phase I was thought to be connected to a local surge‐type advance of the Chelengletscher (Chelen glacier) – an exceptional event of unparalleled dimension in the European Alps. Based on cosmogenic ¹⁰Be exposure ages from moraine boulders, we investigated the local glacier chronology. In contrast to former research, moraines at different positions within the Göschenen valley (central Swiss Alps) have been dated to the Younger Dryas and the Early Holocene. This questions the applicability of palaeo‐Equilibrium Line Altitude (ELA) calculations for stadial attributions without additional numerical age constraints. Furthermore, we have found compelling evidence that the proposed non‐climatic glacier advance attributed to the Göschenen Cold Phase I did not occur. The present results, along with a reappraisal of the original study, question the scientific reliability and the glaciological definition of the Göschenen Cold Phases as glacier advances that clearly exceeded the Little Ice Age positions. While our data do not exclude potential changes in climate and vegetation, we nonetheless show that the Göschenen Cold Phases are not suitable as reference stadials in the system of Alpine Holocene glacier fluctuations.     

Advance,deglacial and sea‐level chronology for Foxe Peninsula,Baffin Island,Nunavut

The impact of the Laurentide Ice Sheet (LIS) deglaciation on Northern Hemisphere early Holocene climate can be evaluated only once a detailed chronology of ice history and sea‐level change is established. Foxe Peninsula is ideally situated on the northern boundary of Hudson Strait, and preserves a chronostratigraphy that provides important glaciological insights regarding changes in ice‐sheet position and relative sea level before and after the 8.2 ka cooling event. We utilized a combination of radiocarbon ages, adjusted with a new locally derived ΔR, and terrestrial in‐situ cosmogenic nuclide (TCN) exposure ages to develop a chronology for early‐Holocene events in the northern Hudson Strait. A marine limit at 192 m a.s.l., dated at 8.1–7.9 cal. ka BP, provides the timing of deglaciation following the 8.2 ka event, confirming that ice persisted at least north of Hudson Bay until then. A moraine complex and esker morphosequence, the Foxe Moraine, relates to glaciomarine outwash deltas and beaches at 160 m a.s.l., and is tightly dated at 7.6 cal. ka BP with a combination of shell dates and exposure ages on boulders. The final rapid collapse of Foxe Peninsula ice occurred by 7.1–6.9 cal. ka BP (radiocarbon dates and TCN depth profile age on an outwash delta), which supports the hypothesis that LIS melting contributed to the contemporaneous global sea‐level rise known as the Catastrophic Rise Event 3 (CRE‐3).     

Mid‐Holocene frozen ground in China from PMIP3 simulations

Extensive degradation of frozen ground in the mid‐Holocene is widely assumed on the basis of sparse proxy data. Here, the simulated soil temperature from the Paleoclimate Modelling Intercomparison Project Phase 3 is used to address this issue over China. By comparing with the results of a preindustrial (0 ka, baseline) simulation, we show that frozen ground in the mid‐Holocene (6 ka) simulation is degraded mainly in northeast China and on the northern Tibetan Plateau. The change follows closely orbitally induced variations in insolation. Quantitatively, permafrost area reduces by 0.02×10⁶ km² in northeast China in response to an orbitally induced increase in boreal summer insolation but increases by 0.08×10⁶ km² on the southern Tibetan Plateau due to local summer cooling. Changing values of active layer thickness vary greatly amongst different locations. On average, they are 3 and 4 cm thicker than the preindustrial values in northeast China and on the Tibetan Plateau, respectively. No degradation in seasonally frozen ground is detected over China as a whole. Regionally, its coverage increases by 0.21×10⁶ km² near the middle and lower reaches of the Yangtze River valley. In addition, the maximum depth of seasonal frost penetration is on average 8.5 cm deeper than preindustrial values due to widespread winter cooling. The changes in frozen ground are consistent amongst models. However, the models disagree with proxy data in terms of not only the changes in frozen ground but also climate. Further modelling improvements and adequate proxy data are both needed to fill in the gaps between models and the data in our knowledge of the mid‐Holocene frozen ground.     

Comparison of sedimentation and occupation histories inside and outside rock shelters,Keep‐River region,northwestern Australia

This paper compares archaeological evidence of Aboriginal occupation inside rock shelters and outside in adjacent sand sheets, focusing on two locations in the Keep‐River region, northwestern Australia. Luminescence and radiocarbon dating reveal that occupation sequences inside rock shelters are generally younger ( < 10,000 yr B.P.) than outside ( < 18,000 yr B.P.). Differences in occupation chronology and artifact assemblages inside and outside rock shelters result from depositional and postdepositional processes and shifts in site function. An increase in regional sedimentation rate from 10 cm/ka ^{− 1} in the Pleistocene to 20 cm/ka ^{− 1} in the Holocene may account for late buildup of sediments within rock shelters, increased artifact accumulation, and reduced postdepositional disturbance in some settings. More intense use of rock shelters in the Late Holocene is indicated from a change in hunting technology and greater production of rock art. The results indicate that some cultural interpretations might be flawed unless archaeological evidence from rock‐shelter and open‐site excavations is integrated. © 2006 Wiley Periodicals, Inc.     

Holocene permafrost history and cryostratigraphy in the High‐Arctic Adventdalen Valley,central Svalbard

This paper presents the history and cryostratigraphy of the upper permafrost in the High‐Arctic Adventdalen Valley, central Svalbard. Nineteen frozen sediment cores, up to 10.7 m long, obtained at five periglacial landforms, were analysed for cryostructures, ice, carbon and solute contents, and grain‐size distribution, and were ¹⁴C‐ and OSL‐dated. Spatial variability in ice and carbon contents is closely related to the sedimentary history and mode of permafrost aggradation. In the valley bottom, saline epigenetic permafrost with pore ice down to depths of 10.7 m depth formed in deltaic sediments since the mid‐Holocene; cryopegs were encountered below 6 m. In the top 1 to 5 m, syngenetic and quasi‐syngenetic permafrost with microlenticular, lenticular, suspended and organic‐matrix cryostructures developed due to loess and alluvial sedimentation since the colder late Holocene, which resulted in the burial of organic material. At the transition between deltaic sediments and loess, massive ice bodies occurred. A pingo developed where the deltaic sediments reached the surface. On hillslopes, suspended cryostructure on solifluction sheets indicates quasi‐syngenetic permafrost aggradation; lobes, in contrast, were ice‐poor. Suspended cryostructure in eluvial deposits reflects epigenetic or quasi‐syngenetic permafrost formation on a weathered bedrock plateau. Landform‐scale spatial variations in ground ice and carbon relate to variations in slope, sedimentation rate, moisture conditions and stratigraphy. Although the study reveals close links between Holocene landscape evolution and permafrost history, our results emphasize a large uncertainty in using terrain surface indicators to infer ground‐ice contents and upscale from core to landform scale in mountainous permafrost landscapes.     

Holocene development and permafrost history in sub‐arctic peatlands in Tavvavuoma,northern Sweden

Under changing climatic conditions permafrost peatlands can play an important role in the global carbon budget through permafrost carbon feedbacks and shifts in carbon assimilation. To better predict future dynamics in these ecosystems an increased understanding of their Holocene carbon and permafrost history is needed. In Tavvavuoma, northern Sweden, we have performed detailed analyses of vegetation succession and geochemical properties at six permafrost peatland sites. Peatland initiation took place around 10 000 to 9600 cal. a BP, soon after retreat of the Fennoscandian Ice Sheet, and the peatlands have remained permafrost‐free fens throughout most of the Holocene. At the four sites that showed a continuous accumulation record during the late Holocene radiocarbon dating of the shift from wet fen to dry bog vegetation, characteristic of the present permafrost peatland surface, suggests that permafrost developed at around 600–100 cal. a BP. At the other two sites peat accumulation was halted during the late Holocene, possibly due to abrasion, making it more difficult to imply the timing of permafrost aggradation. However also at these sites there are no indications of permafrost inception prior to the Little Ice Age. The mean long‐term Holocene carbon accumulation rate at all six sites was 12.3±2.4 gC m⁻² a⁻¹ (±SD), and the mean soil organic carbon storage was 114±27 kg m⁻².     

10Be ages of late Pleistocene deglaciation and Neoglaciation in the north‐central Brooks Range,Arctic Alaska

We present a chronology of late Pleistocene deglaciation and Neoglaciation for two valleys in the north‐central Brooks Range, Alaska, using cosmogenic ¹⁰Be exposure dating. The two valleys show evidence of ice retreat from the northern range front before ～16–15 ka, and into individual cirques by ～14 ka. There is no evidence for a standstill or re‐advance during the Lateglacial period, indicating that a glacier advance during the Younger Dryas, if any, was less extensive than during the Neoglaciation. The maximum glacier expansion during the Neoglacial is delimited by moraines in two cirques separated by about 200 km and dated to 4.6 ± 0.5 and 2.7 ± 0.2 cal ka BP. Both moraine ages agree with previously published lichen‐inferred ages, and confirm that glaciers in the Brooks Range experienced multiple advances of similar magnitude throughout the late Holocene. The similar extent of glaciers during the middle Holocene and the Little Ice Age may imply that the effect of decreasing summer insolation was surpassed by increasing aridity to limit glacier growth as Neoglaciation progressed. Copyright © 2012 John Wiley & Sons, Ltd.     

Late Pleistocene and Holocene glaciation of the Fish Lake valley,northeastern Alaska Range,Alaska

We reconstructed a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley in the north‐eastern Alaska Range using ¹⁰Be surface exposure dating and lichenometry. After it attained its maximum late Wisconsin extent, the Fish Lake valley glacier began to retreat ca. 16.5 ka, and then experienced a readvance or standstill at 11.6 ± 0.3 ka. Evidence of the earliest Holocene glacial activity in the valley is a moraine immediately in front of Little Ice Age (LIA) moraines and is dated to 3.3–3.0 ka. A subsequent advance culminated at ca. AD 610–900 and several LIA moraine crests date to AD 1290, 1640, 1860 and 1910. Our results indicate that ¹⁰Be dating from high‐elevation sites can be used to help constrain late Holocene glacial histories in Alaska, even when other dating techniques are unavailable. Close agreement between ¹⁰Be and lichenometric ages reveal that ¹⁰Be ages on late Holocene moraines may be as accurate as other dating methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Evidence of Abrupt Climate Change during the Mid- to Late- Holocene Recorded in a Tropical Lake, Southern China

Research on abrupt paleoclimatic and paleoenvironmental change provides a scientific basis for evaluating future climate. Because of spatial variability in monsoonal rainfall, our knowledge about climate change during the mid-to lateHolocene in southern China is still limited. We present a multi-proxy record of paleoclimatic change in a crater lake, Lake Shuangchi. Based on the age-depth model from 210 Pb, 137 Cs and AMS14 C data, high-resolution mid-to late-Holocene climatic and environmental records were reconstructed using multiple indices(TOC, TN, C/N, δ13 C and grain size). Shuangchi underwent a marked change from a peat bog to a lake around 1.4 kaBP. The C3 plants likely dominated during 7.0–5.9 ka and 2.5–1.4 kaBP, while C4 plants dominated between 5.9–3.2 and 3.0–2.5 kaBP. Algae were dominant sources of organic matter in the lake sediments after 1.4 kaBP. Several intervals with high concentrations of coarser grain sizes might be due to flood events. These results reveal that several abrupt paleoclimatic events occurred around 6.6 ka, 6.1 ka, 5.9 ka, 3.0 ka, 2.5 ka and 1.4 kaBP. The paleoclimatic change recorded in the lake may be related to the migration of the Intertropical Convergence Zone(ITCZ) and El Ni?o-Southern Oscillation(ENSO) activity.     

Post‐Last Glacial Maximum glacier fluctuations in the southern Écrins massif (westernmost Alps): insights from 10Be cosmic ray exposure dating

Only a few chronological constraints on Lateglacial and Early Holocene glacier variability in the westernmost Alps have hitherto been obtained. In this paper, moraines of two palaeoglaciers in the southern Écrins massif were mapped. The chronology of the stabilization of selected moraines was established through the use of ¹⁰Be cosmic ray exposure (CRE) dating. The equilibrium line altitude (ELA) during moraine deposition was reconstructed assuming an accumulation area ratio (AAR) of 0.67. Ten pre‐Little Ice Age (LIA) ice‐marginal positions of the Rougnoux palaeoglacier were identified and seven of these have been dated. The ¹⁰Be CRE age of a boulder on the lowermost sampled moraine indicates that the landform may have been first formed during a period of stable glaciers at around 16.2±1.7 ka (kiloyears before AD 2017) or that the sampled boulder experienced pre‐exposure to secondary cosmic radiation. The moraine was re‐occupied or, alternatively, shaped somewhat before 12.2±0.6 ka when the ELA was lowered by 230 m relative to the LIA ELA. At least six periods of stable ice margins occurred thereafter when the ELA was 220–160 m lower than during the LIA. The innermost dated moraine stabilized at or before 10.9±0.7 ka. Three ¹⁰Be CRE ages from a moraine of the Prelles palaeoglacier indicate a period of stationary ice margins at or before 10.9±0.6 ka when the ELA was lowered by 160 m with respect to the end of the LIA. The presented ¹⁰Be CRE ages are in good agreement with those of moraines that have been attributed to the Egesen stadial. Assuming unchanged precipitation, summer temperature in the southern Écrins massif at ~12 ka must have been at least 2 °C lower relative to the LIA.     

Evidence of multiple thermokarst lake generations from an 11 800‐year‐old permafrost core on the northern Seward Peninsula,Alaska

Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site‐specific palaeo‐records are needed. Here we present a multi‐proxy study of a 350‐cm‐long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial to Holocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain‐size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, δ¹³C_org) and stable water isotopes (δ¹⁸O, δD, d excess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre‐lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22 800±280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11 800 cal. a BP (Unit B). At about 9000 cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060 cal. a BP, including post‐drainage sediment freezing from the top down to 154 cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core‐based reconstruction of multiple thermokarst lake generations since 11 800 cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice‐rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst‐affected regions of the Arctic.     

Punctuated environmental change along the Holocene (<6 ka) bank margin of south-west Exuma Sound, Bahamas

Characteristics of environmental change along the Holocene (<6 ka BP) bank margin of south‐west Exuma Sound, Bahamas, are defined by comparing mineral, isotope and lithologic stratigraphic patterns in deep‐water (1081 m) slope strata in ODP Hole 631A (Exuma Sound) with proximal (≈6 km) shoal‐water and insular geology of the Lee Stocking Island (LSI) region. After platform submergence, a bank‐top transition from non‐skeletal‐ to skeletal‐dominated deposition occurred in the LSI region by ≈3·8 ka, and is recorded in the adjacent slope sediments by a contemporaneous change in the abundance of transported allochems. The transition at Site 631 is punctuated by an anomalous shift in foraminiferal δ¹³C (–1‰) and δ¹⁸O (–3‰), which may represent a period of climate change that established a brackish coastal zone at least 6 km wide, coincident (≈3·8–4 ka) with bank‐top erosion and pedogenesis. Non‐skeletal allochems reappeared in Hole 631A sediments as the dominant transported allochem type by ≈2·4 ka, then again over the last several hundred years, and are contemporaneous with periods of increased platform‐margin circulation in the LSI region. Such rejuvenation of platform circulation may have resulted from rapid relative rises in sea level, superimposed on the net gradual post‐glacial rise. At Site 631, a prominent (25%) decline in aragonite abundance occurred during the period from 2·4 ka to the last few hundred years, and coincided with an increase in magnesian calcite and skeletal debris, and a positive shift in foraminiferal δ¹⁸O values. These patterns lend support to the hypothesis that, during this period, the LSI margin was barred by skeletal shoals, allowing bank‐top trapping of aragonite and hypersaline water, with increased coastal salinity (resulting from reflux of hypersaline waters through the shoals) and/or cooled coastal waters (caused by reduced exchange of warmed bank‐derived water relative to wind‐generated upwelling). Along the Exuma slope, a diagenetic overprint may further enhance the recent decline in aragonite accumulation. Integration of Holocene deep‐water slope and bank‐top stratigraphies along the bank margin of south‐west Exuma Sound reveals a pattern of punctuated environmental change superimposed on longer term development of interglacial conditions.     

Sub‐arctic Holocene climatic and oceanographic variability in Stjernsund,northern Norway: evidence from benthic foraminifera and stable isotopes

A high‐resolution record, covering 9.3–0.2 ka BP, from the sub‐arctic Stjernsund (70°N) was studied for benthic foraminiferal faunas and stable isotopes, revealing three informally named main phases during the Holocene. The Early‐ to Mid‐Holocene (9.3–5.0 ka BP) was characterized by the strong influence of the North Atlantic Current (NAC), which prevented the reflection of the Holocene Climatic Optimum (HCO) in the bottom‐water temperature. During the Mid‐Holocene Transition (5.0–2.5 ka BP), a turnover of benthic foraminiferal faunas occurred, Atlantic Water species decreased while Arctic‐Polar species increased, and the oxygen isotope record showed larger fluctuations. Those variations correspond to a period of global climate change, to spatially more heterogeneous benthic foraminiferal faunas in the Nordic Seas region, and to regionally diverging terrestrial temperatures. The Cool Late Holocene (2.5–0.2 ka BP) was characterized by increased abundances of Arctic‐Polar species and a steady cooling trend reflected in the oxygen isotopes. In this period, our record differs considerably from those on the SW Barents Sea shelf and locations farther south. Therefore, we argue that regional atmospheric cooling triggered the late Holocene cooling trend. Several cold episodes centred at ～8.3, ～7.8, ～6.5, ～4.9, ～3.9 and ～3.3 ka BP were identified from the benthic foraminiferal faunas and the δ¹⁸O record, which correlated with marine and atmospherically driven proxy records. This suggests that short‐term cold events may result from reduced heat advection via the NAC or from colder air temperatures.     

Oxygen isotope and palaeotemperature records from six Greenland ice‐core stations: Camp Century,Dye‐3, GRIP,GISP2, Renland and NorthGRIP

Oxygen isotope variations spanning the last glacial cycle and the Holocene derived from ice‐core records for six sites in Greenland (Camp Century, Dye‐3, GRIP, GISP2, Renland and NorthGRIP) show strong similarities. This suggests that the dominant influence on oxygen isotope variations reflected in the ice‐sheet records was regional climatic change. Differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios. Palaeotemperature estimates have been obtained from the records using three approaches: (i) inferences based on the measured relationship between mean annual δ¹⁸O of snow and of mean annual surface temperature over Greenland; (ii) modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile, or (iii) by using Monte Carlo simulation techniques. The third of these approaches was adopted to reconstruct Holocene temperature variations for the Dye 3 and GRIP temperature profiles, which yields remarkably compatible results. A new record of Holocene isotope variations obtained from the NorthGRIP ice‐core matches the GRIP short‐term isotope record, and also shows similar long‐term trends to the Dye‐3 and GRIP inverted temperature data. The NorthGRIP isotope record reflects: (i) a generally stronger isotopic signal than is found in the GRIP record; (ii) several short‐lived temperature fluctuations during the first 1500 yr of the Holocene; (iii) a marked cold event at ca. 8.2 ka (the ‘8.2 ka event’); (iv) optimum temperatures for the Holocene between ca. 8.6 and 4.3 ka, a signal that is 0.6‰ stronger than for the GRIP profile; (v) a clear signal for the Little Ice Age; and (vi) a clear signal of climate warming during the last century. These data suggest that the NorthGRIP stable isotope record responded in a sensitive manner to temperature fluctuations during the Holocene. Copyright © 2001 John Wiley & Sons, Ltd.     

Glacial and climate history of the last 24 000 years in the Polar Ural Mountains,Arctic Russia,inferred from partly varved lake sediments

We present a well‐dated, high‐resolution and continuous sediment record spanning the last c. 24 000 years from lake Bolshoye Shchuchye located in the Polar Ural Mountains, Arctic Russia. This is the first continuous sediment succession reaching back into the Last Glacial Maximum (LGM) ever retrieved from this region. We reconstruct the glacial and climate history in the area since the LGM based on sedimentological and geochemical analysis of a 24‐m‐long sediment core. A robust chronology was established using a combination of AMS ¹⁴C‐dating, the position of the Vedde Ash and varve counting. The varved part of the sediment core spans across the LGM from 24 to 18.7 cal. ka BP. We conclude that the lake basin remained ice‐free throughout the LGM, but that mountain glaciers were present in the lake catchment. A decrease in both glacial varve preservation and sedimentation rate suggests that these glaciers started to retreat c. 18.7 cal. ka BP and had disappeared from the catchment by 14.35 cal. ka BP. There are no indications of glacier regrowth during the Younger Dryas. We infer a distinct climatic amelioration following the onset of the Holocene and an Early to Middle Holocene thermal optimum between 10–5 cal. ka BP. Our results provide a long‐awaited continuous and high‐resolution record of past climate that supplements the existing, more fragmentary data from moraines and exposed strata along river banks and coastal cliffs around the Russian Arctic.     

Ostracod palaeoecology and environmental change in the Laptev and Kara seas (Siberian Arctic) during the last 18 000 years

Fossil ostracod assemblages were investigated in five AMS ¹⁴ C‐dated cores from various water depths of the Laptev and Kara seas ranging from the upper continental slope (270 m) to the present‐day shelf depth (40 m). Six fossil assemblages were distinguished. These represent the varying environmental conditions at the North Siberian continental margin since about 18 ka. In the cores from the shelf the ostracod assemblages reflect the gradual transition from an estuarine brackish‐water environment to modern marine conditions since 12.3 ka, as induced by the regional early Holocene transgression. The core from the upper continental slope dates back to c. 17.6 ka and contains assemblages that are absent in the shelf cores. The assemblage older than 10 ka stands out as a specific community dominated by relatively deep‐water Arctic and North Atlantic species that also contains euryhaline species. Such an assemblage provides evidence for past inflows of Atlantic‐derived waters from as early as c. 17.2 ka, probably facilitated by upwelling in coastal polynyas, and a considerable riverine freshwater influence with enhanced surface water stratification owing to the proximity of the palaeocoastline until early Holocene times. In all studied cores, relative increases in euryhaline species dominant in the inner‐shelf regions are recorded in the mid–late Holocene sediments (<7 ka), which otherwise already contain modern‐like ostracod assemblages with relatively deep‐water species. This observation suggests euryhaline species to be largely sea‐ice‐ and/or iceberg‐rafted and therefore may provide evidence for a climate cooling trend.     

GIS‐based reconstruction of Late Weichselian proglacial lakes in northwestern Russia and Belarus

Reconstructing ice‐lake histories is of considerable importance for understanding deglacial meltwater budgets and the role of meltwater reservoirs for sea‐level rise in response to climate warming. We used the latest data on chronology and ice‐sheet extents combined with an isostatically adjusted digital elevation model to reconstruct the development of proglacial lakes in the area of the Karelian ice stream complex of the Late Weichselian Scandinavian Ice Sheet on the East European Plain. We derived the deglacial ice lake development in seven time‐slices from 19 to 13.8 ka, assuming the individual ice‐marginal positions to be isochronous throughout the studied domain. Modelling is based on mapping of critical drainage thresholds and filling the depressions that are potentially able to hold meltwater. Such an approach underestimates the real dimensions of the ice lakes, because the role of erosion at the thresholds is not considered. Our modelling approach is sensitive to the (local) ice‐margin location. Our results prove the southward drainage of meltwater during the glacier extent maxima and at the beginning of deglaciation whereas rerouting to the west had taken place already around 17.5 ka, which is some 1.5 ka earlier than hitherto supposed. The total ice‐lake volume in the study area was lowest (~300 km³) during the maximum glacier extent and highest (~2000 km³) during the highstand of the Privalday Lake at c. 14.6 ka. At 14.6–14.4 ka, the Privalday Lake drained to the early Baltic Ice Lake. The released ~1500 km³ of water approximately corresponds to 20% of the early Baltic Ice Lake water volume and therefore it is unlikely that it was accommodated there. Thus, we argue that the additional meltwater drained through the Öresund threshold area between the early Baltic Ice Lake and the sea, becoming a part of the Scandinavian Ice Sheet's contribution to the Meltwater Pulse 1A event.     

The last Eurasian ice sheets – a chronological database and time‐slice reconstruction,DATED‐1

We present a new time‐slice reconstruction of the Eurasian ice sheets (British–Irish, Svalbard–Barents–Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time‐slice maps of ice‐sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice‐sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice‐margin lines for each time‐slice; a most‐credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice‐sheet area. According to our compilation the westernmost limit along the British–Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c. 27–26 ka) than the eastern limit on the Russian Plain (at c. 20–19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm²) and volume (~24 m Sea Level Equivalent) at c. 21 ka. Our continental‐scale approach highlights instances of conflicting evidence and gaps in the ice‐sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time‐slices (DATED‐1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA ( www.bcdc.no ; http://doi.pangaea.de/10.1594/PANGAEA.848117 ).