Late Quaternary permafrost deposits on Big Lyakhovsky Island (New Siberian Islands, Russian Arctic) were studied with the aim of reconstructing the palaeoclimatic and palaeoenvironmental conditions of northern Siberia. Hydrogen and oxygen stable isotope analyses are presented for six different generations of ice wedges as well as for recent ice wedges and precipitation. An age of about 200 ka BP was determined for an autochtonous peat layer in ice‐rich deposits by U/Th method, containing the oldest ice wedges ever analysed for hydrogen and oxygen isotopes. The palaeoclimatic reconstruction revealed a period of severe winter temperatures at that time. After a gap in the sedimentation history of several tens of thousands of years, ice‐wedge growth was re‐initiated around 50 ka BP by a short period of extremely cold winters and rapid sedimentation leading to ice‐wedge burial and characteristic ice‐soil wedges (‘polosatics’). This corresponds to the initial stage for the Late Weichselian Ice Complex, a peculiar cryolithogenic periglacial formation typical of the lowlands of northern Siberia. The Ice Complex ice wedges reflect cold winters and similar climatic conditions as around 200 ka BP. With a sharp rise in δ18O of 6‰ and δD of 40‰, the warming trend between Pleistocene and Holocene ice wedges is documented. Stable isotope data of recent ice wedges show that Big Lyakhovsky Island has never been as warm in winter as today. Copyright © 2002 John Wiley & Sons, Ltd.

Relative to the past 2,000 years 1,2 , the Arctic region has warmed significantly over the past few decades. However, the evolution of Arctic temperatures during the rest of the Holocene is less clear. Proxy reconstructions, suggest a longterm cooling trend throughout the mid-to late Holocene 3-5 , whereas climate model simulations show only minor changes or even warming [6][7][8] . Here we present a record of the oxygen isotope composition of permafrost ice wedges from the Lena River Delta in the Siberian Arctic. The isotope values, which reflect winter season temperatures, became progressively more enriched over the past 7,000 years, reaching unprecedented levels in the past five decades. This warming trend during the mid-to late Holocene is in opposition to the cooling seen in other proxy records 3,5,9. However, most of these existing proxy records are biased towards summer temperatures. We argue that the opposing trends are related to the seasonally di erent orbital forcing over this interval. Furthermore, our reconstructed trend as well as the recent maximum are consistent with the greenhouse gas forcing and climate model simulations, thus reconciling di ering estimates of Arctic and northern high-latitude temperature evolution during the Holocene.

Ice wedges are a characteristic feature of northern permafrost landscapes and grow mainly by snowmelt that refreezes in thermal contraction cracks that open in winter. In high latitudes the stable‐isotope composition of precipitation (δ18O and δD) is sensitive to air temperature. Hence, the integrated climate information of winter precipitation is transferred to individual ice veins and can be preserved over millennia, allowing ice wedges to be used to reconstruct past winter climate. Recent studies indicate a promising potential of ice‐wedge‐based paleoclimate reconstructions for more comprehensive reconstructions of Arctic past climate evolution. We briefly highlight the potential and review the current state of ice‐wedge paleoclimatology. Existing knowledge gaps and challenges are outlined and priorities for future ice‐wedge research are suggested. The major research topics are (1) frost cracking and infilling dynamics, (2) formation and preservation of the stable‐isotope information, (3) ice‐wedge dating, (4) age‐model development and (5) interpretation of stable‐isotope time series. Progress in each of these topics will help to exploit the paleoclimatic potential of ice wedges, particularly in view of their unique cold‐season information, which is not adequately covered by other terrestrial climate archives.

The stable isotopic composition (d 18 O, dD, d) of three Holocene-age ice wedges at the Dmitrii Laptev Strait, Russia (Oyogos Yar coast, 72.78N, 143.58E) was studied at high resolution (100 to 200 samples each) in order to develop palaeoclimatic records. AMS 14 C ages of organic matter in the ice prove the Late Holocene age of the studied horizontal ice-wedge profiles and indicate syngenetic growth associated with sediment accumulation. Co-isotopic relationships of wedge ice close to the Global Meteoric Water Line point to a good suitability for palaeoclimate studies and all three profiles show similar isotopic features. A general Late Holocene winter warming trend is inferred from d 18O data changing from about À26% to values of À23% to À21%, with periods of marked variability superimposed on the trend. This trend is accompanied by a shift in the d excess from 8%-11% to 5%-8%, probably caused by varying proportions of differing moisture sources for precipitation. The highest winter temperatures and an increased influence of regional moisture in recent decades may reflect ongoing Arctic climate change.

Non‐glaciated Arctic lowlands in north‐east Siberia were subjected to extensive landscape and environmental changes during the Late Quaternary. Coastal cliffs along the Arctic shelf seas expose terrestrial archives containing numerous palaeoenvironmental indicators (e.g., pollen, plant macro‐fossils and mammal fossils) preserved in the permafrost. The presented sedimentological (grain size, magnetic susceptibility and biogeochemical parameters), cryolithological, geochronological (radiocarbon, accelerator mass spectrometry and infrared‐stimulated luminescence), heavy mineral and palaeoecological records from Cape Mamontov Klyk record the environmental dynamics of an Arctic shelf lowland east of the Taymyr Peninsula, and thus, near the eastern edge of the Eurasian ice sheet, over the last 60 Ky. This region is also considered to be the westernmost part of Beringia, the non‐glaciated landmass that lay between the Eurasian and the Laurentian ice caps during the Late Pleistocene. Several units and subunits of sand deposits, peat–sand alternations, ice‐rich palaeocryosol sequences (Ice Complex) and peaty fillings of thermokarst depressions and valleys were presented. The recorded proxy data sets reflect cold stadial climate conditions between 60 and 50 Kya, moderate inderstadial conditions between 50 and 25 Kya and cold stadial conditions from 25 to 15 Kya. The Late Pleistocene to Holocene transition, including the Allerød warm period, the early to middle Holocene thermal optimum and the late Holocene cooling, are also recorded. Three phases of landscape dynamic (fluvial/alluvial, irregular slope run‐off and thermokarst) were presented in a schematic model, and were subsequently correlated with the supraregional environmental history between the Early Weichselian and the Holocene.