The Mutual Interaction Between Ice Production and Ocean Heat Transport in a Greenhouse Warming Scenario

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Most global climate models predict an increase in the northward oceanic heat transport north of about 60 N in future climate scenarios as compared to the present day. This increase in heat transport is reminiscent of explanations posed for recent observed warming in the Atlantic layer in the western Eurasian Basin of the Arctic Ocean. An implication is that warmings like those that occurred in the recent past, which have been attributed to wind variations by some, could also occur in the future due to greenhouse gas forcing.This work hypothesizes that the increase in heat transport in the future greenhouse scenario is in response to the transition from perennial to first year ice in the Barents Sea and Arctic Ocean, and the attendant increase in heat loss and brine rejection in fall and winter. Sea ice production rejects brine, driving gravitational convection, which creates dense shelf waters and encourages heat and mass exchange from the Atlantic layer to the surface. If the hypothesis is correct, the ice production-heat transport interaction must outweigh the increase in stability from increased precipitation and runoff in the Arctic in a warmer climate. Such a mechanism would further accelerate the transition from perennial to first year ice and reduce the overall sea ice cover in the future.Simulations with the Community Climate System Model Version 3 (CCSM3), a fully coupled atmosphere-ocean model that explicitly resolves the sea ice thickness distribution, show that northward oceanic heat transport (and the meridional overturning circulation) peak at about the same time that ice production peaks in the Arctic Ocean in a future scenario. This is a two part study: the first objective is to investigate the reason that heat transport increases into the Nordic Seas and Arctic Ocean in future scenarios with global climate models and assess the consequences of this increase for the sea ice cover. The second objective is to understand the sensitivity of the sea ice thickness distribution to increased greenhouse gases, and its relation, if any, to the increase oceanic heat transport into the Arctic in future climate change scenarios. This investigation of a positive feedback between sea ice-ocean system may explain the increase in oceanic heat transport into the Arctic that is seen in greenhouse warming scenarios with climate models. A transformation from perennial sea ice to first year sea ice in the Arctic, and the attendant increase in ice production is the first step of the feedback process. This work will also develop a general method for predicting the change in the ice thickness distribution in response to a climate perturbation.