Exploring late Pleistocene bioturbation on Yermak Plateau to assess sea-ice conditions and primary productivity through the Ethological Ichno Quotient.

Central Arctic, interglacial intervals have traditionally been associated with diverse and intense bioturbation, and abundant foraminifera, interpreted as indicating relatively low sea-ice concentrations and productive surface waters, while glacial intervals, typically barren, support the inverse. In this respect, the Yermak Plateau is anomalous. Biomarker studies suggest that glacial intervals were characterized by comparatively open water, while interglacials are marked by severe sea-ice conditions. Here we study downcore Ethological Ichno Quotient (EIQ) variations in trace fossils and bioturbation to test the hypothesis that different ethological classes vary in accordance with late Pleistocene changes in sea-ice extent, with deposit feeders increasing during reduced sea-ice cover and chemosymbiotic traces increasing during periods of thick perennial sea-ice conditions. Our results generally demonstrate that the abundance of traces like Planolites, Scolicia, and burrows produced by deposit feeders increase during episodes of seasonal sea-ice cover. In contrast, intervals with more severe sea-ice conditions are characterized by chemosymbiotic traces such as Chondrites and Trichichnus/Mycellia, suggesting lower food delivery and poorly ventilated bottom water conditions. The study thus confirms previous reconstructions of sea-ice conditions on the Yermak Plateau during interglacials, demonstrating that bioturbation variation provides insights into bentho-pelagic coupling under variable sea ice regimes in the Arctic Ocean.