Overwinter Transport of Subsurface Warm Water around the Arctic Chukchi Borderland

Ocean heat transport is a possible important factor for recent sea ice decline, especially in the western Arctic Ocean. It has been indicated that vertical hydrographic profiles in the Canada Basin were characterized by three temperature maxima. The near-surface temperature maximum was the shallowest one arising from summer solar heat absorption and subsequent autumn Ekman downwelling. The subsurface temperature maximum reflected intrusion of Pacific summer water. The deepest maximum was located in the Atlantic layer. Substantial parts of upper ocean heat would eventually affect sea ice freezing/melting. However, spatial and temporal variabilities of these warm layers still remain uncertainties. JAMSTEC field campaign deployed the bottom-tethered year-long mooring with a sediment trap in the Chukchi Abyssal Plain (Station CAP: 75.21°N, 172.55°W, 447 m) of the Chukchi Borderland. The temperature time series at 95 m of Station CAP showed a rapid warming event (from -1.6 to -0.8°C) for December 2012 to March 2013. During this period, high sea level pressure (i.e., anti-cyclones) covering the Canadian Basin induced strong easterly wind near the mooring station, where the sinking flux of lithogenic materials remarkably increased at the sediment trap depth (270 m). These situations suggest that lateral advection of shelf-origin warm water is a key factor for the subsurface warming in the CAP region. To address overwinter transport of subsurface warm water, a pan-Arctic sea ice-ocean modeling was also performed. The horizontal grid size was approximately 5 km to resolve mesoscale eddies and narrow jets. In the interannual experiments, the strong easterly wind produced a westward shelf-break jet along the northern edge of Chukchi shelf in winter of 2012–2013. Warm eddies generated north of the Barrow Canyon were still located east of the Northwind Ridge. Therefore, the subsurface warming event observed at Station CAP would have been attributed to shelf-break jet streams rather than eddy-induced transports. Comparison with other years will also be reported.