Arctic MIZ Sensitivity to Atmospheric Forcing and Feedbacks

Abstract:

Over the past few decades, as the summer Arctic sea ice cover has been shrinking, the marginal ice zone (MIZ) has been widening. Projections indicate that the majority of the sea ice cover will become marginal (here defined as that region with ice area fractions between 0.15 and 0.8) over the next few decades. The impact of the change in atmospheric forcings on the sea ice cover and MIZ between the 1980s and the 2010s is evaluated using a coupled sea ice (CICE)-mixed layer model, that includes a prognostic floe size-thickness distribution (FSD) model. Systematically changing each atmospheric forcing field showed no single forcing to dominate the sea ice response, with surface air temperature, incoming shortwave radiation, incoming longwave radiation, snowfall rate and humidity to all have a significant on the sea ice and MIZ extent. The results show the response to the forcings to be highly nonlinear. As the MIZ accounts for a greater fraction of the sea ice cover, some feedbacks with the atmosphere and ocean are expected to strengthen. The role of sea ice feedbacks with the atmosphere and ocean in response to the change in atmospheric conditions between the 1980s to the 2010s will be evaluated using feedback denial simulations. In particular: i) the albedo feedback; ii) feedbacks associated with changes to mixed layer stratification (including changes in mixed layer properties) and therefore the ocean heat flux to the sea ice; and iii) changes to the lateral melt rate due to decreasing floe sizes.