Eemian and Late Glacial/Holocene palaeoenvironmental records from permafrost sequences at the Dmitry Laptev Strait (NE Siberia, Russia)

摘要

Terrestrial permafrost sections from the southern and northern coasts of Dmitry Laptev Strait have preserved records of landscape transition from glacial to interglacial periods. They allow geomorphologic and environmental changes to be traced from pre-Eemian time to the Eemian, and from the Late Glacial to the Holocene. The transition from one period to another induced extensive thawing of permafrost (thermokarst). Evolving thermokarst depressions transformed formerly frozen ground into taberal (unfrozen) deposits with accumulating overlying lacustrine deposits. Lacustrine horizons rich in palaeontological remains retain evidence of changes in environmental conditions. The pollen records reflect changes from grass-sedge dominated vegetation during the Early Eemian to shrub dominated spectra during the Middle Eemian thermal optimum followed by Late Eemian grass-sedge dominated tundra vegetation. Abundant Larix pollen have been found in Middle Eemian deposits from the south coast of the Dmitry Laptev Strait (Oyogos Yar), but are absent in similar deposits from the north coast (Bol'shoy Lyakhovsky Island), likely indicating that the northern tree line was located near the Oyogos Yar region during the Eemian thermal optimum. Grass-sedge dominated tundra vegetation occurred during the Late Glacial/Holocene transition which was replaced by shrub tundra during the early Holocene. Rich fossil ostracod records from Eemian and Late Glacial/Holocene lacustrine deposits could be correlated with the Eemian thermal optimum and the Late Glacial Allerod warm period. For both periods, the stable oxygen isotope data from the fossil ostracods suggest an approximate mean summer water temperature range between about 10 and 19 degrees C in the palaeo-lakes.