Abstract

Recently, the Arctic has undergone substantial changes in sea ice cover and the hydrologic cycle, both of which strongly impact the freshwater storage in, and export from, the Arctic Ocean. The fate of Arctic Ocean freshwater (FW) is of global relevance, as it can impact North Atlantic Deep Water formation and potentially the strength of the Meridional Overturning Circulation. Here we analyze Arctic FW storage and export in 7 climate models from the Coupled Model Intercomparison Project phase 6 (CMIP6) and assess their agreement over the historical period (1980-2000) and in two future emissions scenarios, SSP1 -2.6 and SSP5 -8.5. Rather than focusing on a single realization of each experiment, ensembles from each model are used in order to understand model internal variability and to better constrain inter-model differences.

In both future scenarios the models show an increase in liquid (ocean) freshwater storage that is partially due to a reduction in solid (ice) storage through sea ice melt. This reduction in sea ice coverage also leads to a reduction in solid fluxes through the five major Arctic gateways (Bering Strait, Fram Strait, Nares Strait, Barrow Strait, and the Barents Sea Opening) that is typically larger for SSP5 -8.5 than SSP1 -2.6. The liquid fluxes through the gateways exhibit a more complex pattern, with some models showing a change in sign of the freshwater flux through the Barents Sea Opening, for example. To identify the mechanisms responsible for such changes, the ocean fluxes are decomposed into their salinity and volume contributions. Although the models broadly agree on the sign of the storage and flux changes, substantial differences exist between the magnitude of these changes and the models’ underlying mean states.