Cyclicity of ice rafted debris in the Bering Sea (Site U1341) during the early Pleistocene

We present the first record of ice rafted debris (IRD) flux (grains/cm^2/kyr) from the Bering Sea (Site U1341) during the early Pleistocene (1.5-1.85 Ma). The presence of IRD reflects the existence of sea ice cover at open ocean Site U1341 and is defined as mineral and lithic grains (> 250 µm). Sea ice is a crucial seasonal component of the modern Bering Sea system that influences productivity and plays a role in climate feedbacks. Past work reveals sea ice may have extended well beyond its modern boundary and perennial sea-ice existed during the last glacial maximum. On land, some studies suggest the presence of an East Siberian ice sheet during Pleistocene glaciations while others suggest extensive mountain glaciers. Despite this work, questions remain about the extent and cyclicity of sea-ice and glaciations, especially in the early Pleistocene. We find that orbital and sub-orbital variability is a prominent characteristic of IRD transport in the Bering Sea. This is evaluated using cross-spectral analysis of IRD flux and clay mineral abundance, which reveals in-phase coherency at 10 kyr and lagged coherency at 38 kyr, where clay content leads IRD flux by 4 kyr. Shape analysis of ice rafted quartz grains and compositional analysis of the IRD fraction provides evidence that sea-ice transport was active at both 10 kyr and 38 kyr periodicities. Preliminary results indicate a shift in provenance at the 38 kyr periodicity, which could be attributed to either active iceberg transport of IRD or sea ice transport of subaqueous moraine debris. This record provides evidence of active sea-ice transport and the presence of ice sheets in the Bering Sea during the early Pleistocene.