PNNL

Abstract

The evolving roles of the atmosphere and ocean in Arctic sea ice volume loss from CO2-quadrupling are isolated using a novel decomposition of the ocean heat contributing to sea ice growth and melt (ocean-ice heat fluxes) into components driven by anomalous surface heat fluxes and ocean circulation changes. A sea ice volume budget analysis is used to isolate the roles of the ocean-ice heat fluxes and atmosphere-ice heat fluxes in the evolving Arctic sea ice volume. The role of atmosphere-ocean coupling in this process also isolated by comparing the sea ice volume budget and ocean-ice heat flux components in partially- and fully-coupled experiments. Atmospheric process changes appear to drive most Arctic sea ice loss in the first decade following CO2 increase by increasing melt at the sea ice top, while ocean circulation changes drive Arctic sea ice loss over the longer term by increasing heat transport into the Arctic in winter and driving a decrease in winter sea ice growth. Atmosphere-ocean coupling further supports a negative feedback, causing further weakening of the Atlantic meridional overturning circulation, and significant cooling of the sub-polar Atlantic. As a result, the anomalous heat transport into the Arctic in winter decreases over longer timescales and stabilizes Arctic sea ice decline. Without this coupled response, Arctic sea ice completely disappears in the partially-coupled experiment.