How does imposing a spatially-varying map of background vertical diffusivity with rates and spatial structure informed by observations impact the modelled Arctic Ocean state?

Mixing in the Arctic Ocean drives water mass transformations critical to the heat and freshwater budgets of the Arctic Ocean, impacting sea ice extent and volume, stratification, circulation, and heat and freshwater release to the subpolar N. Atlantic. Observations indicate that mixing rates in the Arctic Ocean are highly variable, however this variability is typically not well-represented in models.This study uses a regional Arctic Ocean model to addresses the question “How does imposing a spatially-varying map of background vertical diffusivity with rates and spatial structure informed by observations impact the modelled Arctic Ocean state?” It seeks to understand impacts based on model experiments that systematically vary the diffusivity uniformly in space.It is shown that prescribing the observationally-informed mixing map results in increased heat loss, a redistribution of freshwater storage, and increased heat and freshwater export to the N. Atlantic relative to a control case with an equal-on-average-but-spatially-uniform distribution of mixing. These effects can be understood as the result of enhancing (reducing) mixing on the shelves (basins) relative to the control case. They highlight sensitivities of the Arctic Ocean heat and freshwater budgets to shelf and basin mixing respectively.These findings are relevant to the impacts of the changing Arctic Ocean mixing environment on Arctic Ocean functioning and subpolar ocean variability. They further suggest ways in which the prescription of Arctic Ocean mixing may be important to improving model representations of Arctic Ocean dynamics.