ALBERT

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: Polygon tundra with tundra-steppe vegetation cover and growing syngenetic ice-wedge nets evolved during stadial and interstadial periods of the late Quaternary in non-glaciated Beringia. The depositional relict of such environments is called Ice Complex (IC; ледовый комплекс [ledovyi kompleks] in Russian) permafrost. The IC archives preserve information of past periglacial and climate landscape conditions of mid- and late Pleistocene Beringian environments. In certain locations of the East Siberian Arctic, IC remnants of different age and extent are known. While using IC deposits as archives of palaeo-landscape and palaeo-environmental dynamics, summer and winter conditions over large time-scales are detectable. Commonly applied summer proxy include palaeontological proxy such as pollen, plant macrofossils, insect fossils and, most prominent, mammal fossils of the Mammoth fauna, while geochemical and stable isotope properties of ground ice allow for insights into freezing and winter conditions. IC chronologies are challenging because the deposition and post-sedimentary preservation of ice-rich permafrost are triggered by palaeo-relief settings and related processes as well as by the intensity of thermokarst. This complicates geochronological interpretations, as representatives of consecutive late Quaternary periods may be found at laterally different positions and altitudes in coastal and riverine exposures. Shifts between permafrost aggradation and degradation over time frequently cause gaps in sequences. Furthermore, numerical dating of IC mainly includes different approaches such as radiocarbon (14C) dating of organic material, infrared and optically-stimulated luminescence (IRSL, OSL) dating on feldspar and quartz grains, radioisotope disequilibria of thorium-230 to uranium-234 (230Th/U) dating of peat, and chlorine-36 to chloride ratios (36Cl/Cl) of ground ice. The application of various geochronologic methods to cover the age intervals of certain IC deposits implies that different permafrost components (organic, mineralic, ice) as well as different geochemical and physical properties have to be employed. At the southern coast of Bol'shoy Lyakhovsky Island at least four distinct IC strata were previously described and dated, which cover among the longest time interval of late Quaternary terrestrial permafrost deposition in East Siberia; starting about 200 kyr ago. With this contribution we seek to present and discuss our current understanding of IC chronologies preserved on the New Siberian Archipelago including MIS2 Yedoma (Sartan) IC, MIS3 Yedoma (Molotkov) IC, MIS5 Buchchagy IC, and MIS7a Yukagir IC. Geocryological and palaeo-environmental proxy data highlight past periglacial landscape and deposition processes to deduce past climate conditions and Beringian palaeo-ecological settings and dynamics.