Turbulence, heat fluxes and the thermohaline structure along the eastern Arctic continental slopes in 2018

Kirstin Schulz, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Physical Oceanography, Bremerhaven, Germany and Markus A Janout, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany
The continental slopes north of the Siberian shelf seas are dynamic regions characterized by fronts, sea ice formation and melt, and the progression of the Arctic Boundary Current (ABC). Increasing evidence points to a greater influence of Atlantic water in the eastern Nansen Basin with a hypothesized shift from a mainly year-round ice covered, quiescent, double diffusion-dominated and stratified system to an ocean that now features long open water seasons, enhanced turbulence and deeper mixed layers. In 2018, we revisited the region to carry out numerous hydrographic and microstructure shelf-to-basin transects along the eastern Kara, Laptev, and East Siberian Seas. The hydrography in summer 2018 was dominated by the Atlantic-derived waters in the ABC and a front separating the warm waters from the cold shelf waters. The temperature in the ABC progressively decreased eastwards between the Kara Sea and the East Siberian Sea, with indications for strong interleaving and mixing north of Severnaya Zemlya. Microstructure turbulence measurements highlight enhanced dissipation rates within the front above the continental slope, with maximum vertical heat fluxes of 10 W/m2 from the Atlantic water into the cold overlying water – an order of magnitude higher than typical heat fluxes associated with double diffusive processes. These heat fluxes will be contrasted with lateral heat loss to emphasize the contribution of both vertical and lateral exchange processes in controlling Atlantic water heat in the Arctic Ocean. With this contribution, we aim to present new observations from an Arctic key region that, like few others, suffers from atmospheric and oceanic warming trends and sea ice retreat. We will further contrast our findings with earlier observations and discuss our results in the context of “Atlantification”.