ALBERT

Description: To reconstruct palaeoclimate and palaeonvironmental conditions in the Northeast Siberian Arctic, we studied late Quaternary permafrost deposits at the Oyogos Yar coast (Dmitry Laptev Strait). New infrared stimulated luminescence ages for distinctive floodplain deposits of the Kuchchugui Suite (112.5 ± 9.6 kyr) and thermokarst lake deposits of the Krest Yuryakh Suite (102.4 ± 9.7 kyr), respectively, provide new substantial geochronological data and shed light on the landscape history of the Dmitry Laptev Strait region during the Marine Isotope Stage (MIS) 5. Ground ice stable-isotope data are presented together with cryolithological information for eight cryostratigraphic units and are complemented by data from nearby Bol'shoy Lyakhovsky Island. Our combined record of ice-wedge stable isotopes as proxy for past winter climate conditions covers the last about 200 thousand years and is supplemented by texture-ice stable isotopes which contain annual climate conditions overprinted by freezing processes. Our ice wedge stable-water isotope data indicate substantial variations in Northeast Siberian Arctic winter climate conditions during the late Quaternary, in particular between Glacial and Interglacial but also over the last millennia to decades. Stable isotope values of Ice Complex ice wedges indicate cold to very cold winter temperatures about 200 kyr ago (MIS7), very cold winter conditions about 100 kyr ago (MIS5), very cold to moderate winter conditions between about 60 and 30 kyr ago, and extremely cold winter temperatures during the Last Glacial Maximum (MIS2). Much warmer winter conditions are reflected by extensive thermokarst development during the MIS5c and by Holocene ice-wedge stable-isotopes. Modern ice-wedge stable isotopes are most enriched and testify the recent winter warming in the Arctic. Hence, ice-wedge based reconstructions of changes in winter climate conditions add substantial information to those derived from paleoecological proxies stored in permafrost and allow for distinguishing between seasonal trends of past climate dynamics. Future progress in ice-wedge dating and an improved temporal resolution of ice-wedge derived climate information may help to fully explore the palaeoclimatic potential of ice wedges.

Description: Relative to the past 2,000 years, 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 long-term cooling trend throughout the mid- to late Holocene, whereas climate model simulations show only minor changes or even warming. 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. However, most of these existing proxy records are biased towards summer temperatures. We argue that the opposing trends are related to the seasonally different 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 differing estimates of Arctic and northern high-latitude temperature evolution during the Holocene. © 2015 Macmillan Publishers Limited. All rights reserved

Description: The Arctic climate has experienced a major warming over the past decades, which is unprecedented in the past 2 kyrs. There are, however, still major uncertainties about the temperature evolution during the Holocene. Most Northern Hemisphere proxy reconstructions suggest a cooling in mid-and late Holocene (e.g. Wanner et al., 2008), whereas climate model simulations show only weak changes or even a moderate warming (e.g. Lohmann et al., 2013). In this study, we used ice wedges as most promising climate archive in permafrost that were studied by stable water isotope methods. Ice wedges may be identified by vertically oriented foliations and they form by the repeated filling of winter thermal contraction cracks by snow melt water in spring. Therefore, the isotopic composition (δ18O, δD, d excess) of wedge ice may be attributed to the cold period climate conditions (winter and spring). 42 samples of organic material enclosed in ice wedges has been directly dated by Radiocarbon methods. Here, we present the first stable-isotope winter proxy record in up to centennial-scale resolution from permafrost ice wedges (Lena River Delta; Siberian Arctic) for the Holocene. The Lena ice-wedge record shows that the recent isotopic temperatures were unprecedented in the past 8000 years. While confirming the Arctic temperature reconstructions of the last two millennia (Kaufman et al., 2009), it suggests a winter warming throughout the mid and late Holocene, thus contradicting most existing other proxy records (Wanner et al., 2008). This apparent contradiction can be explained by (1) the seasonality of the ice-wedge genesis and season-specific orbital forcing, (2) greenhouse gas forcing as well as by (3) regional peculiarities (i.e. the marine transgression). We believe that the present model-data mismatch might be an artefact of the summer bias of the existing proxy records and thus, our record provides important new information for the understanding of the seasonality aspect in the northern hemisphere Holocene temperature evolution especially for the Arctic.

Description: Ice wedges are the most abundant type of ground ice in the ice-rich permafrost deposits of the Northeast Siberian Arctic. They are formed by the periodic repetition of frost cracking and subsequent crack filling and refreezing in spring, mostly by melt water of winter snow. Ice wedges can be studied by means of stable-water isotopes. Their isotopic composition is directly linked to atmospheric precipitation (i.e. winter snow) and, therefore, indicative of past climate conditions during the cold season even though also genetic aspects, i.e. sublimation, melting and refreezing in the snowpack and the frost crack, have to be taken into account. In this contribution we present stable-water isotope data of ice wedges from the Oyogos Yar coast of the Dmitry Laptev Strait (72.7°N, 143.5°E). Ice wedges and surrounding sediments were studied and sampled in 2002 and 2007. Ice-wedge stable-water isotopes were analyzed in the stable-isotope lab of the Alfred Wegener Institute in Potsdam, Germany. Sediments and ice wedges were dated using (a) OSL dating, (b) 36Cl/Cl dating (Blinov et al., 2009), (c) radiocarbon dating as well as (d) stratigraphic correlation based on ice-wedge stable isotopes. Based on our chronology the studied ice wedges correspond to different stratigraphic units of the Late Quaternary. These are (1) an Ice Complex of MIS5 age (Wetterich et al., in press), (2) Early Weichselian (MIS4 to MIS3) flood plain deposits, (3) the Middle Weichselian Yedoma Ice Complex of MIS3 age and (d) Holocene themokarst deposits (Opel et al., 2011). Ice wedge stable-water isotope data indicate substantial variations in Northeast Siberian Arctic winter climate conditions (δ18O) as well as shifts in the moisture generation and transport patterns (d excess) during the Late Quaternary, in particular between Glacial and Interglacial but also over the last centuries. An ice wedge of the MIS5 Ice Complex exhibits mean δ18O and d excess values of -33‰ and 7‰, respectively, representing very cold winter temperatures. Small multi-stage ice wedges corresponding to the MIS4 to MIS3 flood plain deposits showed two clusters of isotope values: (1) in their lower parts, i.e. composite sand-ice wedges or “polosatics”, δ18O values of -31 to -28‰ (d excess of 0-5‰) and (2) in their upper parts (classical ice wedge) δ18O values of -34‰ (d excess of 5‰), reflecting rather different formation conditions than climate differences under very cold climate conditions. The huge syngenetic ice wedges of the Weichselian Yedoma Ice Complex (MIS3) are characterized by mean δ18O values of -33‰ to -29‰ and mean d-excess values between 4 and 8‰ corresponding to different altitude levels and reflecting cold to very cold winter temperatures. On top of the Ice Complex as well as in a thermokarst depression of Late Glacial origin, Holocene ice wedges could be found. They have been grown predominantly in the Middle to Late Holocene and exhibit mean δ18O values of about -25‰ and mean d-excess values of 8‰, mirroring distinctly warmer winter temperatures in the Holocene. Recently grown (modern) ice wedges of the last decades are characterized by mean δ18O values of about -21‰ and mean d excess values of 8‰, testifying the recent winter warming in the Arctic. Blinov A, Alfimov V, Beer J, Gilichinsky D, Schirrmeister L, Kholodov A, Nikolskiy P, Opel T, Tikhomirov D, Wetterich S. 2009. Ratio of 36Cl/Cl in ground ice of east Siberia and its application for chronometry. Geochemistry Geophysics Geosystems 10, Q0AA03. Opel T, Dereviagin AY, Meyer H, Schirrmeister L, Wetterich S, 2011. Palaeoclimatic Information from Stable Water Isotopes of Holocene Ice Wedges on the Dmitrii Laptev Strait, Northeast Siberia, Russia. Permafrost and Periglacial Processes 22, 84-100. Wetterich S, Tumskoy V, Rudaya N, Kuznetsov V, Maksimov F, Opel T, Meyer H, Andreev AA, Schirrmeister L, in press. Ice Complex permafrost of MIS5 age in the Dmitry Laptev Strait coastal region (East Siberian Arctic). Quaternary Science Reviews.

Description: To reconstruct palaeoclimate and palaeoenvironmental conditions in the northeast Siberian Arctic, we studied late Quaternary permafrost at the Oyogos Yar coast (Dmitry Laptev Strait). New infrared-stimulated uminescence ages for distinctive floodplain deposits of the Kuchchugui Suite (112.5�9.6 kyr) and thermokarst-lake deposits of the Krest Yuryakh Suite (102.4�9.7 kyr), respectively,provide new substantial geochronological data and shed light on the landscape history of the Dmitry Laptev Strait region during Marine Isotope Stage (MIS) 5. Ground ice stable-isotope data are presented together with cryolithological information for eight cryostratigraphic units and are complemented by data from nearby Bol’shoy Lyakhovsky Island. Our combined record of ice-wedge stable isotopes as a proxy for past winter climate conditions covers about 200 000 years and is supplemented by stable isotopes of pore and segregated ice which reflect annual climate conditions overprinted by freezing processes. Our ice-wedge stable-isotope data indicate substantial variations in northeast Siberian Arctic winter climate conditions during the late Quaternary, in particular between glacial and interglacial times but also over the last millennia to centuries. Stable isotope values of ice complex ice wedges indicate cold to very cold winter temperatures about 200 kyr ago (MIS7), very cold winter conditions about 100 kyr ago (MIS5), very cold to moderate winter conditions between about 60 and 30 kyr ago, and extremely cold winter temperatures during the Last Glacial Maximum (MIS2). Much warmer winter conditions are reflected by extensive thermokarst development during MIS5c and by Holocene ice-wedge stable isotopes. Modern ice-wedge stable isotopes are most enriched and testify to the recent winter warming in the Arctic. Hence, ice-wedgebased reconstructions of changes in winter climate conditions add substantial information to those derived from paleoecological proxies stored in permafrost and allow a distinction between seasonal trends of past climate dynamics. Future progress in ice-wedge dating and an improved temporal resolution of ice-wedge-derived climate information may help to fully explore the palaeoclimatic potential of ice wedges.

Description: Arctic climate has experienced major changes over the past millennia that are not fully understood in terms of their controls and seasonality. Stable isotope data from ice wedges in permafrost provide unique information on past winter climate. Recently, an ice-wedge record from the Lena River Delta suggested for the first time that Siberian winter temperatures increased throughout the Holocene, contradicting most other Arctic palaeoclimate reconstructions which are likely biased towards the summer. However, the representativeness of this single record and the spatial extent of its reconstructed winter warming signal is unclear. Here, we present a new winter temperature record based on paired stable oxygen (δ18O) and radiocarbon age data spanning the last two millennia from the Oyogos Yar coast in northeast Siberia. The record confirms the long-term winter warming signal as well as the unprecedented temperature rise in recent decades. This confirmation demonstrates that winter warming over the last millennia is a coherent feature in the northeastern Siberian Arctic, supporting the hypothesis of an insolation-driven seasonal Holocene temperature evolution followed by a strong warming likely related to anthropogenic forcing.

Description: Relative to the past 2,000 years1,2, 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 Holocene3–5, whereas climate model simulations show only minor changes or even warming6–8. 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 records3,5,9. However, most of these existing proxy records are biased towards summer temperatures. We argue that the opposing trends are related to the seasonally different 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 differing estimates of Arctic and northern high-latitude temperature evolution during the Holocene.