Disentangling the Coupled Atmosphere‐Ocean‐Ice Interactions Driving Arctic Sea Ice Response to CO 2 Increases.

A novel decomposition of the ocean heat energy that contributes to sea ice melt and growth (ocean‐ice and frazil heat) into components that are driven by surface heat flux and ocean circulation changes is used to isolate the evolving roles of the atmosphere and ocean in the Arctic sea ice loss from CO2 increases. A sea ice volume budget analysis is used to separate the impacts of the anomalous frazil/ocean‐ice heat from those of atmosphere‐ice heat on the evolving Arctic sea ice volume. The role of atmosphere‐ocean coupling in augmenting or curtailing the atmosphere‐ and ocean‐driven sea ice losses is further isolated by comparing the ice volume budget and the anomalous frazil/ocean‐ice heat components in partially and fully coupled experiments. Atmosphere‐ice heat fluxes drive most of Arctic sea ice loss in the first decade following CO2 increase by increasing the sea ice top face melt in summer, while ocean circulation changes drive the loss over the longer term through the anomalous increase of heat transport into the Arctic, which drive decreases in frazil ice growth and sea ice extent in winter. Atmosphere‐ocean coupling in the subpolar Atlantic further supports a negative feedback that attenuates the ocean‐driven sea ice losses over time; by accelerating the weakening of the Atlantic meridional overturning circulation, it causes a large cooling of the subpolar Atlantic and attenuation of the anomalous heat transport into the Arctic in winter, allowing for a seasonal Arctic sea ice in the fully coupled experiment, while the Arctic completely becomes ice free in the partially coupled experiment. Plain Language Summary: The interactions between the atmosphere, ocean, and sea ice are disentangled in order to isolate their individual roles in driving Arctic sea ice losses and how these roles change over time. We introduce a new decomposition of the ocean heat that contributes to melting and growing sea ice into parts that are caused by changes in the surface heat input into the ocean and ocean circulation. We analyze the contributions of the ocean heat and atmosphere heat to the overall Arctic sea ice volume changes, both in an experiment where a two‐way interaction between the atmosphere and ocean is allowed and in another where this two‐way interaction is not allowed. Our results suggest that the atmosphere causes most of Arctic sea ice loss (within a decade) by increasing sea ice top face melt, while the ocean causes the long‐term sea ice changes in the Arctic by decreasing winter bottom face growth. The interactions between the atmosphere and ocean further enhance the ocean circulation weakening and surface cooling in the subpolar Atlantic and thereby stop the winter heat transport increase into the Arctic and eventually curtail the ocean‐driven sea ice loss and prevent the total loss of Arctic sea ice. Key Points: A novel decomposition isolates how ocean surface heating, circulation changes, and air‐sea interactions drive sea ice loss from CO2 increasesAtmosphere changes determine Arctic sea ice loss within the first decade; ocean circulation changes drive longer term ice lossesAtmosphere‐ocean coupling feedbacks on ocean circulation change in the subpolar Atlantic stabilizes Arctic sea ice loss in the long term [ABSTRACT FROM AUTHOR]