Description: Paleontological proxy data and cryolithological information from East Siberian Arctic permafrost preserve records of late Quaternary climate and environmental conditions in West Beringia and their variability which results from interglacial-glacial and interstadial-stadial dynamics. A key site for late Pleistocene Ice Complex is situated at the southern coast of Bol’shoy Lyakhovsky Island (Dmitry Laptev Strait) where coastal outcrops expose frozen sediments, ground ice, and fossil remains. A 15 m long sequence of Ice Complex permafrost accumulated continuously between 〉49 and 29 kyr BP in an ice-wedge polygon reflecting the palaeoenvironmental history from the end of the MIS4 stadial to the end of the MIS3 interstadial (Oyogos and Molotkov horizons of the Oyogosskaya Suite). The late MIS4 stadial (〉49 kyr BP) record shows a quickly developing polygon tundra while harsh cold and dry summers are reflected by sparse grass-sedge tundra-steppe and high amounts of redeposited conifers. During the early MIS3 interstadial (〉49 to 48 kyr BP) pollen records show higher Artemisia percentages within a grass-sedge tundra-steppe vegetation that supported dry conditions. The MIS3 interstadial optimum between 48 and 38 kyr BP promoted low-centered polygon tundra with shallow water in polygon centers. Moister conditions in the landscape than during the previous late MIS4 stadial are assumed while the general summer climate conditions likely remained dry, but slightly warmer as reflected by higher Salix abundances. Warmer summer air temperatures and moister conditions on landscape scale during the MIS3 optimum are revealed mainly by Salix and green algae findings in the palynological tundra-steppe records. A late MIS3 cooling trend in summer air temperatures between 38 and 29 kyr BP can be deduced from disappearing Salix pollen. The stable water isotope composition of an ice wedge (mean values of -31‰ in δ18O and -243‰ in δD) point to stable cold winter conditions. Changes in the accumulation conditions are indicated at the end of the MIS3 in transition to the MIS2. The Last Glacial Maximum (LGM) period has been rather poorly represented in East Siberian permafrost records. However, present pollen, sediment, and ground-ice stable water isotope data obtained from coastal exposures on Bol’shoy Lyakhovsky Island mirror the coldest conditions during the MIS 2 stadial (Sartan horizon of the Yanskaya Suite) period between about 26 and 22 kyr BP. The pollen record reveals a cold tundra-steppe vegetation with characteristic predominance of grass pollen over sedge pollen while the stable isotope ice-wedge data indicate extremely cold winter temperatures with mean values of -37 ‰ in δ18O and -290 ‰ in δD. By the use of combined cryolithological, sedimentological, geochemical, geochronological, and palaeontological proxy data, stadial-interstadial environmental variability in arctic West Beringia was elucidated at millennial resolution.

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.

Description: To answer the question “Has the recent warming no analogues in the Siberian north?” we analyzed larch tree samples (Larix gmelinii Rupr.) from permafrost zone in the eastern Taimyr (TAY) (72ºN, 102ºE) using tree-ring and stable isotope analyses for the Climatic Optimum Period (COP) 4111-3806 BC and Medieval Warm Period (MWP) 917-1150 AD, in comparison to the recent period (RP) 1791-2008 AD. We developed a description of the climatic and environmental changes in the eastern Taimyr using tree-ring width and stable isotope (d13C, d18O) data based on statistical verification of the relationships to climatic parameters (temperature and precipitation) Additionally, we compared our new tree-ring and stable isotope data sets with earlier published July temperature and precipitation reconstructions inferred from pollen data of the Lama Lake, Taimyr Peninsula, d18O ice core data from Akademii Nauk ice cap on Severnaya Zemlya (SZ) and d18O ice core data from Greenland (GISP2), as well as tree-ring width and stable carbon and oxygen isotope data from northeastern Yakutia (YAK). We found that the COP in TAY was warmer and drier compared to the MWP but rather similar to the RP. Our results indicate that the MWP in TAY started earlier and was wetter than in YAK. July precipitation reconstructions obtained from pollen data of the Lama Lake, oxygen isotope data from SZ and our carbon isotopes in tree cellulose agree well and indicate wetter climate conditions during the MWP. Consistent large-scale patterns were reflected in significant links between oxygen isotope data in tree cellulose from TAY and YAK, and oxygen isotope data from SZ and GISP2 during the MWP and the RP. Finally, we showed that the recent warming is not unprecedented in the Siberian north. Similar climate conditions were recorded by tree-rings, stable isotopes, pollen, and ice core data 6000 years ago.

Description: Ice Complex deposits (locally known as the Buchchagy Ice Complex) are exposed at both coasts of the East Siberian Dmitry Laptev Strait and preserved below the Yedoma Ice Complex that formed during MIS3 and MIS2 (Marine Isotope Stage) and lateglacial-Holocene thermokarst deposits (MIS1). Radioisotope disequilibria (230Th/U) of peaty horizons date the Buchchagy Ice Complex deposition to 126 þ 16/ �13 kyr and 117 þ 19/�14 kyr until 98 ± 5 kyr and 89 ± 5 kyr. The deposit is characterised by poorlysorted medium-to-coarse silts with cryogenic structures of horizontal ice bands, lens-like, and lenslike reticulated segregation ice. Two peaty horizons within the Buchchagy Ice Complex and syngenetic ice wedges (2e4 m wide, up to 10 m high) are striking. The isotopic composition (d18O, dD) of Buchchagy ice-wedge ice indicates winter conditions colder than during the MIS3 interstadial and warmer than during MIS2 stadial, and similar atmospheric winter moisture sources as during the MIS2 stadial. Buchchagy Ice Complex pollen spectra reveal tundra-steppe vegetation and harsher summer conditions than during the MIS3 interstadial and rather similar vegetation as during the MIS2 stadial. Short-term climatic variability during MIS5 is reflected in the record. Even though the regional chronostratigraphic relationship of the Buchchagy Ice Complex to the Last Interglacial remains unclear because numerical dating is widely lacking, the present study indicates permafrost (Ice Complex) formation during MIS5 sensu lato, and its preservation afterwards. Palaeoenvironmental insights into past climate and the periglacial landscape dynamics of arctic lowlands in eastern Siberia are deduced from the record.

Description: A terrestrial sediment sequence exposed in an eroding pingo provides insights into the late-Quaternary environmental history of the northern Seward Peninsula, Alaska.We have obtained the first radiocarbondated evidence for a mid-Wisconsin thermokarst lake, demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods. High values of Picea pollen and the presence of Larix pollen in sediments dated to 50e40 ka BP strongly suggest the presence of forest or woodland early in MIS 3; the trees grew within a vegetation matrix dominated by grass and sedge, and there is indirect evidence of grazing animals. Thus the interstadial ecosystem was different in structure and composition from the Holocene or from the preceding Last Interglacial period. An early Holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa. Multiple extralimital plant taxa suggest mean July temperatures above modern values. The local presence of spruce during the early Holocene warm interval is evident from a radiocarbon-dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line. The first direct evidence of spruce in Northwest Alaska during the early Holocene has implications for the presence of forest refugia in Central Beringia and previously assumed routes and timing of post-glacial forest expansion in Alaska.

Description: southern coast of Bol’shoy Lyakhovsky Island (New Siberian Archipelago, Dmitry Laptev Strait) was studied to reconstruct past landscape and environmental dynamics. The sequence accumulated during the Marine Isotope Stage 3 (MIS3) Interstadial between 〉49 and 29 ka BP in an ice-wedge polygon. The frozen deposits were cryolithologically described and sampled on a vertical bluff between two ice wedges. According to sedimentological and geochronological data, the section is subdivided into three units which correlate with environmental conditions of the early, middle, and late MIS3 period. Palynological data support this stratification. The stable isotope signature of texture ice in the polygon structure reflects fractionation due to local freezeethaw processes, while the signature of an approximately 5 m wide and more than 17 m high ice wedge fits very well into the regional stable-water isotope record. Regional climate dynamics during the MIS3 Interstadial and local landscape conditions of the polygonal patterned ground controlled the Ice Complex formation. The sequence presented here completes previously published MIS3 permafrost records in Northeast Siberia. Late Quaternary stadialinterstadial climate variability in arctic West Beringia is preserved at millennial resolution in the Ice Complex. A MIS3 climate optimum was revealed between 48 and 38 ka BP from the Ice Complex on Bol’shoy Lyakhovsky Island.

Description: Perennially-frozen deposits are considered as excellent paleoenvironmental archives similar to lacustrine, deep marine, and glacier records because of the long-term and good preservation of fossil records under stable permafrost conditions. A permafrost tunnel in the Vault Creek Valley (Chatanika River Valley, near Fairbanks) exposes a sequence of frozen deposits and ground ice that provides a comprehensive set of proxies to reconstruct the late Quaternary environmental history of Interior Alaska. The multi-proxy approach includes different dating techniques (radiocarbon-accelerator mass spectrometry [AMS 14C], optically stimulated luminescence [OSL], thorium/uranium radioisotope disequilibria [230Th/U]), as well as methods of sedimentology, paleoecology, hydrochemistry, and stable isotope geochemistry of ground ice. The studied sequence consists of 36-m-thick late Quaternary deposits above schistose bedrock. Main portions of the sequence accumulated during the early and middle Wisconsin periods. The lowermost unit A consists of about 9-m-thick ice-bonded fluvial gravels with sand and peat lenses. A late Sangamon (MIS 5a) age of unit A is assumed. Spruce forest with birch, larch, and some shrubby alder dominated the vegetation. High presence of Sphagnum spores and Cyperaceae pollen points to mires in the Vault Creek Valley. The overlying unit B consists of 10-m-thick alternating fluvial gravels, loess-like silt, and sand layers, penetrated by small ice wedges. OSL dates support a stadial early Wisconsin (MIS 4) age of unit B. Pollen and plant macrofossil data point to spruce forests with some birch interspersed with wetlands around the site. The following unit C is composed of 15-m-thick ice-rich loess-like and organic-rich silt with fossil bones and large ice wedges. Unit C formed during the interstadial mid-Wisconsin (MIS 3) and stadial late Wisconsin (MIS 2) as indicated by radiocarbon ages. Post-depositional slope processes significantly deformed both, ground ice and sediments of unit C. Pollen data show that spruce forests and wetlands dominated the area. The macrofossil remains of Picea, Larix, and Alnus incana ssp. tenuifolia also prove the existence of boreal coniferous forests during the mid-Wisconsin interstadial, which were replaced by treeless tundra-steppe vegetation during the late Wisconsin stadial. Unit C is discordantly overlain by the 2-m-thick late Holocene deposits of unit D. The pollen record of unit D indicates boreal forest vegetation similar to the modern one. The permafrost record from the Vault Creek tunnel reflects more than 90 ka of periglacial landscape dynamics triggered by fluvial and eolian accumulation, and formation of ice-wedge polygons and post-depositional deformation by slope processes. The record represents a typical Wisconsin valley-bottom facies in Central Alaska.

Description: In East Siberian Arctic permafrost deposits is increasingly employed as an archive that preserves records of regional environmental history. Pollen records play a leading role among bioindicators because of the common presence of fossil pollen in Quaternary terrestrial periglacial and lacustrine sediments. One of the most promising study areas for collecting information that can be used to highlight the environmental history of West Beringia is Bol’shoy Lyakhovsky Island, located between the Laptev and the East Siberian seas. The southern coast of B.Lyakhovsky Island exposes permafrost outcrops that feature frozen sediments, ground ice, and fossil remains dating from the mid-Pleistocene. During the MIS3 Interstadial, continuous Ice Complex development took place on B.Lyakhovsky Island. Pollen records of Kargin Interstadial reflect some amelioration of the harsh environmental conditions predominant during the previous interval. The studied record of a continuous permafrost sequence dated between 〉 55 and 27 kyr BP reflects the palaeoenvironmental history from the end of the MIS4 to the end of the MIS3. The combined data sets allow to differentiate the late Zyryan Stadial (〉55 to 52 kyr BP) with a quickly developing polygon tundra; harsh cold and dry summers are reflected by sparse grass-sedge tundra-steppe and high amounts of redeposited conifers. During the early Kargin Interstadial (52-48.5 kyr BP) pollen record shows higher Artemisia percentages within a grass-sedge tundra-steppe vegetation that support dry conditions. The Kargin Interstadial optimum between 48.5 and 37 kyr BP promoted low-centered polygon tundra with shallow water in polygon centers. Moister conditions in the landscape than during the previous Zyryan Stadial are assumed while the general summer climate conditions likely remained dry, but slightly warmer as reflected by higher Salix abundances. Warmer summer air temperatures and moister condition on landscape scale during the MIS3 optimum are revealed mainly by Salix and green algae findings in the palynological tundra-steppe records. A cooling trend in summer air temperatures between 37 and 27 kyr BP can be deduced from disappearing Salix pollen. Changes in the accumulation conditions are indicated at the end of the MIS3 in transition to the MIS2. The palynological complex (L7-07) dated to the early Sartan stadial reflects the existence of an impoverished variant of tundra steppe or cryophyte steppe vegetation. The dominance of graminoids, together with abundant Artemisia, and low percentages of Ericales (indicator of wet plant communities) in the pollen spectra point to rather dry climatic conditions. Evidence of an extremely cold climate is given by the dominance of Poaceae over Cyperaceae. The large amount of Caryophyllaceae, Brassicaceae, and Papaveraceae, which are arctic pioneer taxa characteristic of northernmost vascular plant communities in polar deserts, confirms this interpretation.The temporal appearance of LGM conditions in East Siberian permafrost as represented by pollen and ground ice data differs somewhat within the region, but delineates a general trend to coldest and driest climate conditions between about 24 and 18 ka BP. Herb- and shrubdominated Lateglacial vegetation is reflected in pollen data from Bol’shoy Lyakhovsky after the Sartan stadial. Betula sect. Nanae, B. sect. Albae, and Duschekia fruticosa pollen mirror warming climate conditions.