Mixing in the Arctic Ocean: using the advection-diffusion equation to estimate the role of diapycnal mixing in Arctic Ocean dynamics

Abstract

An advection – diffusion balance was used to calculate the diapycnal vertical mixing between water masses required to maintain the density stratification in the Arctic Ocean. A box model bounded by a velocity field created from hydrographic measurements at the gateways of the Arctic (Bering, Davis and Fram Strait and the Barents Sea Opening) was used, and the properties in the interior of the Arctic estimated from a climatology dataset (PHC). The density gradient, volume flux, vertical velocity, diapycnal diffusivity, and dissipation rate were calculated. A weak vertical velocity of 10-7 ms-1 and a weak diapycnal mixing of ~2 x 10-6 m2 s-1 were found in the upper layers of the Arctic up to 200 m depth, likely due to weak turbulent mixing resulting from double diffusion, and consistent with microstructure measurements. An apparent negative diffusivity was found in the bottom layers. This is likely due to the effects of the warm, salty Atlantic Water inflow, of which 3.37 Sv enters the Arctic and is diapycnally transported into its adjacent layers, causing buoyancy loss from down-slope convection and densification of water.

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