Examining the role of atmosphere-ocean interactions and ocean circulation changes in the Arctic sea ice response to CO2 forcing

Tuesday, December 11, 2018 - 08:00
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The mechanisms of rapid Arctic sea ice decline is still an active area of research with studies pointing to atmospheric radiative forcing, ocean warming, heat transport, and feedbacks as major drivers of Arctic sea ice decline. We use an unusual and powerful decomposition of ocean ice growth/melt rates into components driven by surface heat fluxes and ocean circulation changes to isolate the role of atmosphere, ocean and the coupling between them in the coupled simulations in Arctic ice evolution under CO2 quadrupling. The feedback from the ocean is removed from the surface-heat-flux-driven interactions in a partially-coupled simulation, in order to isolate atmosphere-driven changes from those driven by ocean circulation changes. We also diagnose impacts of ocean circulation changes and surface fluxes on ocean heat transport. Initially (in the first decade) Arctic sea ice loss is driven by the atmosphere-driven surface heat flux changes into the Arctic and increase in summer ice melt. However, ocean circulation changes play an increasing role in ice loss with time by driving ocean heat transport changes into the Arctic that reduces winter ice growth. The circulation changes initially increase ocean heat transport into Arctic sea ice loss in both partially and fully coupled simulations. Our analysis indicates that as the surface flux feedback to ocean circulation changes, the subpolar Atlantic becomes increasingly cool, eventually reversing the circulation-driven anomalous heat transport into the Arctic, acting to counter some Arctic ice loss in the fully-coupled simulation. Without this negative surface flux feedback, Arctic sea ice completely disappears in the partially-coupled simulation. Further analysis show that the Atlantic subpolar gyre weakening plays a role in the later stabilization of Arctic sea ice loss.

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