Duvanny Yar is a stratigraphic key site for the Late Quaternary in Beringia, the non-glaciated land-mass between the Taymyr Peninsula and Alaska. Moreover, Duvanny Yar is characteristic for ice-rich permafrost sequences, termed as “Ice Complex” or “Yedoma Suite” in Northeast Siberia and an impor-tant reference site for the Late Pleistocene history of Beringia. The investigated outcrop (68.6319°N, 159.1420°E) is exposed by the Kolyma River and is located in the Kolyma Lowland at the north-eastern edge of the Sakha (Yakutia) Republic.
The aim of this study was to reconstruct the paleoenvironmental dynamics at the Duvanny Yar site for the Late Quaternary using its terrestrial permafrost archive. A multidisciplinary approach of geocryological, geochronological, sedimentological, hydrochemical and isotope geochemical methods was applied to obtain multiproxy records. Sediment samples were analysed for ice contents, grain size parameters, biogeochemistry (total carbon, total organic carbon, total nitrogen and stable carbon iso-topes), mineral density, mass specific magnetic susceptibility and for radiocarbon age. Stable isotopes of water were measured for ground ice (ice wedges, fissure ice, segregated ice and pore ice), modern surface waters and modern precipitation. Six profiles along the riverbank were sampled in August 2008. They contained Eemian lacustrine deposits, long sequences of Late Pleistocene Ice Complex deposits, Holocene lacustrine and boggy deposits in thermokarst depressions. All profiles showed very bad sorted sediment of fine to coarse silt. A remarkable homogeneity in the polymodal grain size dis-tribution for the ice-rich Ice Complex (~30 to 60 wt % ice content) reveals different but proportionate stable processes of origin like alluvial, aeolian and in-situ frost weathering processes. Thus the pure “arctic loess” hypothesis for Ice Complex deposits of Duvanny Yar is disproved. Measurements of bulk density, ice content and total organic carbon content (TOC) enable relative carbon content calcu-lations for Ice Complex and alas deposits of Duvanny Yar. The mean value of organic carbon at the ~43 m thick sampled Ice Complex is 14 ± 9 kg TOC ∙ m-3; for the short Holocene alas sequence it is 29 ± 16 kg TOC ∙ m-3. Geochronological results based on eight new AMS ages reveal that the Ice Com-plex was continuously formed from the Middle Weichselian (~40000 a BP) and at least until the Late Glacial period (~12000 a BP). Stable water isotopes measured in ice wedges, segregated ice and ice lenses were used to estimate paleotemperature changes. Isotopic signals reveal warm temperatures at Eemian times and stable cold and dry conditions for the whole period of Ice Complex formation. At the Pleistocene/Holocene transition the isotopes show a climate warming.
A better understanding of the paleoenvironmental dynamics at Duvanny Yar and further research may provide a basis for more reliable predictions of future reaction on global warming of organic-bearing ice-rich permafrost in Siberia, which is considered as potential greenhouse gas source permafrost.