On the Along-Slope Heat Loss of the Boundary Current in the Eastern Arctic Ocean

This study presents recent observations to quantify oceanic heat fluxes along the continental slope of the Eurasian pert of the Arctic Ocean, in order to understand the dominant processes leading to the observed along-track heat loss of the Arctic Boundary Current. We investigate the fate of warm Atlantic Water along the Arctic Ocean continental margin of the Siberian Seas based on 11 cross-slope CTD transects and direct heat flux estimates from microstructure profiles obtained in summer 2018. The Arctic Boundary Current loses on average O(108) J m−2 per 100 km during its propagation along the Siberian shelves, corresponding to an average heat flux of 47 W m−2 out of the Atlantic Water layer. The measured vertical heat flux on the upper Atlantic Water interface of on average 10 W m−2 in the deep basin, and 3.7 W m−2 above the continental slope is larger than previously reported values. Still, these heat fluxes explain less than 20 % of the observed heat loss within the boundary current. Heat fluxes are significantly increased in the turbulent near-bottom layer, where Atlantic Water intersects the continental slope, and at the lee side of a topographic irregularity. This indicates that mixing with ambient colder water along the continental margins is an important contribution to Atlantic Water heat loss. Furthermore, the cold halocline layer receives approximately the same amount of heat due to upward mixing from the Atlantic Water, compared to heat input from the summer-warmed surface layer above. This underlines the importance of both surface warming and increased vertical mixing in a future ice-free Arctic Ocean in summer.