Vertical heat transfer in the Arctic Ocean: The role of double‐diffusive mixing

Abstract

Microstructure profiles collected in the central Amundsen Basin are analyzed in order to quantify the role of double‐diffusive mixing for vertical heat transfer from the Atlantic layer. In the profiles, a persistent, but laterally incoherent thermohaline staircase structure is identified in the 200–260 m depth range. The staircase contains homogeneous layers with average height of 1.3 m and thin, high‐gradient interfaces with average temperature and salinity jumps of about 0.065°C and 0.015, respectively. When inferred from a commonly used diffusive convection parameterization, the average vertical heat flux within the staircase is 0.6 W m−2. This is one order of magnitude larger than the molecular diffusion alone and of the same order as the overall heat loss from the Atlantic layer in the deep basins of the Arctic Ocean. The parameterization is evaluated using observed turbulent heat fluxes and is found to overestimate diffusive convective fluxes with up to an order of magnitude, especially for weak thermal forcing (small temperature jumps in staircase). Staircases coexist with thermohaline intrusions in the vertical temperature and salinity profiles. Lomonosov Ridge is identified as a potential region for formation of intrusions. It is found that salt fingering is the dominant process during intrusion growth whereas diffusive convection is the dominant process in maintaining the intrusions at steady state in the deep basins.