Future Arctic Ocean atmosphere-ice-ocean momentum transfer and impacts on ocean circulation

Abstract

Over the last few decades, the Arctic has experienced surface warming at more than twice the global rate and extensive sea ice loss. The reduced sea ice cover affects the mechanical and thermodynamical coupling between the atmosphere and the ocean. A commonly repeated hypothesis is that a thinner and more mobile sea ice cover will increase momentum transfer, resulting in a spin-up of upper Arctic Ocean circulation and enhanced vertical mixing. In general, sea ice protects the ocean from interaction with the atmosphere, and a thinning and shrinking sea ice cover implies a more direct transfer of momentum and heat. For example, several observational studies show a more energetic ocean after strong wind events over open water than wind events over ice-covered water. However, previous modeling studies show that seasonality is very important and that the total momentum transfer can decrease with more open water because the ice surface provides greater drag than the open water surface. We here present numerical simulations of future scenarios with the Norwegian Earth System Model (NorESM) and show how the momentum transfer is projected to change with changing sea ice and wind conditions in various regions of the Arctic Ocean. We then compare our results with output from other CMIP6 models and present how different wind conditions and the diminishing ice cover impacts the upper ocean circulation.