Increased ocean heat transport to the central Arctic despite a well working Barents Sea Cooling Machine

Abstract

The Barents Sea is a primary gateway for Atlantic Water entering the central Arctic Ocean and ubiquitous water-mass transformation on the Barents shelf is key for mitigating increases in heat transport to the central Arctic through the St. Anna Trough. Using a mesoscale-permitting reanalysis spanning 40 years, we derive the first long-term estimate of heat transport through the St. Anna trough, finding that it has increased by 0.11 TWyr-1 since 1980. However, this is only half of the 0.23 TWyr-1 trend in the heat transport into the Barents Sea through the Barents Sea Opening. Decomposing the heat transports reveals that these trends are entirely due to warming temperatures at the sections with no discernible trend in the volume transports. We find that a northward migration of the largest heat fluxes from the ocean to the atmosphere have partially mitigated the increased temperature of Atlantic Water entering through the Barents Sea Opening, resulting in the less dramatic temperature trend in the waters exiting through the St. Anna Trough. Finally, we present evidence for a revised version of the “ocean feedback” hypothesis, which modulates volume transport into and out of the Barents Sea on sub-decadal timescales. The revised “ocean feedback” hypothesis relies on denser waters in the northeastern Barents Sea associated with increases in salinity and sufficient cooling from inflowing Atlantic Water. We find that these denser, more saline waters create lower sea surface height relative to the permanently elevated Kara Sea. The resulting gradient enhances downslope flow into the St. Anna Trough, driving increased inflow of saline Atlantic Water through the Barents Sea Opening and sustaining the feedback loop.