East–west asymmetry in surface mixed layer and ocean heat content in the Pacific sector of the Arctic Ocean derived from AMSR-E sea surface temperature

Deep (greater than 25m) and anomalously warm surface mixed layer (SML) has been evident in the Pacific sector of the Arctic Ocean since 2007. This warm SML contributes to the formation of maximum near surface temperature, which act as the sea-ice formation “inhibitor”, after freeze-up season. In this study, we attempt to estimate the ocean heat content (OHC) in the SML of the Pacific sector of the Arctic Ocean. The surface mixed layer depth (SMLD) and OHC from 2007 to 2010 were estimated from SST measured by the microwave radiometer AMSR-E and NCEP-derived net heat budget, based on the assumption that changes of heat content within SML can be explained by the air–sea heat exchange only. Estimated SMLD and OHC were well comparable with the in-situ CTD measurements, especially, in the western Canada Basin. SMLD greater than 25m (up to 40m) and OHC greater than 300MJ were estimated at southern Northwind Ridge area (73–75°N, 168–150°W), where the catastrophic reduction of sea ice has been reported, while less OHC was estimated at the eastern side of the Canada Basin. Although anomalous high SST has uniformly been captured over the northern Chukchi Sea and the Northwind Ridge area since 2007, our results indicate the nonuniformity of surface OHC distribution in the Canada Basin with relatively large amount in the Northwind Ridge area. Conversely, we can assume that the Northwind Ridge area is the plausible candidate for the Near Surface Temperature Maximum formation area. Recent thin ice condition is probably responsible for deepening SMLD, efficient ocean heat uptake, and delayed onset of sea ice formation in the Pacific sector of the Arctic Ocean. Our results also indicate oceanic horizontal or vertical heat flux along the sea ice edge, which will promote the suppression of sea ice growth during freeze-up season.