Ostracod Paleoecology and Reconstruction of Environmental Changes in the Laptev and Kara Seas during the Postglacial Transgression

Ostracods represent an important group of crustaceans inhabiting a wide range of aquatic environments. They settle in new ecological environments relatively fast and can reflect changes in water parameters on decadal time scale, which makes analysis of ostracod assemblages a very precise instrument for paleoenvironmental reconstructions. Four core sections from the Laptev Sea and one from the eastern Kara Sea shelf were analyzed. Cores from the Laptev Sea shelf are restricted to paleovalleys of the rivers Lena, Yana and Khatanga, and one core originates from the western continental slope. The core from the Kara Sea was recovered from the Yenisei paleo-estuary. Detailed chronology of all cores is based on AMS radiocarbon dates of marine biogenic carbonate (bivalves, ostracods, foraminifers).

In the Laptev and Kara seas modern ostracod assemblages replace each other with depth and increasing distance from the coast (estuarine, inner-shelf, middle-shelf, outer-shelf, upper continental slope). The same happens with fossil assemblages of all studied cores during the Postglacial transgression. Five out of six distinguished fossil assemblages have modern analogs and are easy to trace in time and space. The deglacial assemblage of the upper continental slope stands out as a specific community dominated by arctic, North Atlantic and euryhaline species, indicating inflows of Atlantic-derived waters and downslope sand slides due to the proximity of the paleocoastline. Assemblages are taxonomically stable, but are characterized by minor taxonomic variety due to ostracod sensitivity to environmental changes.

Diversity-abundance correlation shows that near-shore and freshwater environments are less stable than those from the deeper shelf and upper continental slope, since Arctic shelves are shallow and can not be compared to real deep-water dynamic environments. In the Kara and Laptev seas abundance diminishes with depth and distance from the coast, while taxonomic diversity increases.