Abstract
Late Pleistocene permafrost of the Yedoma type constitutes a valuable paleo-environmental archive due to the presence of numerous and well-preserved floral and faunal fossils. The study of the fossil Yedoma inventory allows for qualitative and quantitative reconstructions of past ecosystem and climate conditions and variations over time. Here, we present the results of combined paleo-proxy studies including pollen, chironomid, diatom and mammal fossil analyses from a prominent Yedoma cliff on Sobo-Sise Island in the eastern Lena Delta, NE Siberia to complement previous and ongoing paleo-ecological research in western Beringia. The Yedoma Ice Complex (IC) cliff on Sobo-Sise Island (up to 28 m high, 1.7 km long) was continuously sampled at 0.5 m resolution. The entire sequence covers the last about 52 cal kyr BP, but is not continuous as it shows substantial hiatuses at 36–29 cal kyr BP, at 20–17 cal kyr BP and at 15–7 cal kyr BP. The Marine Isotope Stage (MIS) 3 Yedoma IC (52–28 cal kyr BP) pollen spectra show typical features of tundra–steppe vegetation. Green algae remains indicate freshwater conditions. The chironomid assemblages vary considerably in abundance and diversity. Chironomid-based TJuly reconstructions during MIS 3 reveal warmer-than-today TJuly at about 51 cal kyr BP, 46-44 and 41 cal kyr BP. The MIS 2 Yedoma IC (28–15 cal kyr BP) pollen spectra represent tundra-steppe vegetation as during MIS 3, but higher abundance of Artemisia and lower abundances of algae remains indicate drier summer conditions. The chironomid records are poor. The MIS 1 (7–0 cal kyr BP) pollen spectra indicate shrub-tundra vegetation. The chironomid fauna is sparse and not diverse. The chironomid-based TJuly reconstruction supports similar-as-today temperatures at 6.4–4.4 cal kyr BP. Diatoms were recorded only after about 6.4 cal kyr BP. The Sobo-Sise Yedoma record preserves traces of the West Beringian tundra-steppe that maintained the Mammoth fauna including rare evidence for woolly rhinoceros’ presence. Chironomid-based TJuly reconstructions complement previous plant-macrofossil based TJuly of regional MIS 3 records. Our study from the eastern Lena Delta fits into and extends previous paleo-ecological Yedoma studies to characterize Beringian paleo-environments in the Laptev Sea coastal region.
Highlights
Late Pleistocene permafrost of the Yedoma type is a prominent and widespread permafrost feature that formed during sea-level lowstands on vast areas of the unglaciated Beringian lowlands and on the nowadays flooded East Siberian shelf between the Laurentide to the east and the Scandinavian ice sheets to the west during marine isotope stages (MIS) 4 to 2 (Hopkins, 1959)
The cluster analysis of the Sobo-Sise Yedoma pollen record results in three units, which correspond to the cryolithological units A-C that were previously defined by Wetterich et al (2020) of MIS 3, MIS 2 and MIS 1 age, respectively (Figure 3)
While the percentages of Pinus sylvestris in Unit A are similar to its respective concentrations, suggesting its real low abundance in the vegetation, the concentrations of Larix are more representative than the Larix pollen percentages because Larix pollen tends to accumulate directly on the site
Summary
Late Pleistocene permafrost of the Yedoma type is a prominent and widespread permafrost feature that formed during sea-level lowstands on vast areas of the unglaciated Beringian lowlands and on the nowadays flooded East Siberian shelf between the Laurentide to the east and the Scandinavian ice sheets to the west during marine isotope stages (MIS) 4 to 2 (Hopkins, 1959). In West Beringia, the main area of potential Yedoma IC distribution includes the submerged East Siberian shelf and Arctic coastal lowlands from Taymyr Peninsula to Chukotka (Grosse et al, 2013), it is described from interior regions of Central Yakutia (Soloviev, 1959) and the Yana Upland (Kunitsky et al, 2013; Opel et al, 2019). The combination of several fossil proxy records from a certain permafrost sequence largely enhances its significance for paleo-ecological interpretations (e.g., Kienast et al, 2011; Wetterich et al, 2018). In this context, the present study combines a pollen-based paleo-vegetation reconstruction with lacustrine chironomid and diatom analyses. If specimen counts per sample are sufficiently high, numerical reconstructions of certain ecological parameters are deducible such as mean air temperature of the warmest month (TJuly), water depth, ion content and pH (Nazarova et al, 2013; Nazarova et al, 2017a; Pestryakova et al, 2018)
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