Sedimentary proxies for Pacific water inflow through the Herald Canyon, western Arctic Ocean

Pacific water inflow to the Arctic Ocean occurs through the shallow Bering Strait. With a present sill depth of only 53 m, this gateway has been frequently closed during glacial sea-level low stands of the Pleistocene. Here, we investigate the sedimentological and mineralogical response to sea-level rise and the opening of the Bering Strait during the last deglaciation in a 6.1 m-long marine sediment core (SWERUS-L2-4-PC1) from the Herald Canyon. Grain size data indicate an abrupt erosional contact at 412 cm down core that likely formed when Pacific waters first started to flow into the Arctic Ocean around 11 cal ka BP, and was topographically steered into the Herald Canyon. A transitional unit between 412 and 390 cm appears to be a condensed interval with minimal local sedimentation. The underlying sediments, deposited in a shallow, river-proximal setting, exhibit a rather uniform bulk and clay mineral composition similar to mineral assemblages from surface sediment samples of the Chukchi Sea. Enhanced contributions from Pacific waters above 390 cm (< 8.5 cal ka BP) are reflected by elevated chlorite/illite and (chlorite + kaolinite)/illite ratios, and are anti-correlated with intervals of higher illite/smectite ratios, interpreted as periods of enhanced advection of shelf transformed waters originating from the East Siberian Sea. Clay mineral changes in the Holocene drift sediments are best explained by the interplay between two origins for bottom waters in the Herald Canyon and are consistent with modern oceanographic observations.