Persistent freshening of the Arctic ocean caused by summer-enhanced sea ice decline

Arctic sea ice has been declining over past several decades with the largest ice loss occurring in summer. This implies a strengthening of the sea ice seasonal cycle with more ice melting in summer and refreezing and brine rejection in winter. Here, we examine global ocean salinity response to such intensification of the seasonal cycle in simulations wherein we impose a radiative heat imbalance at the sea ice surface, inducing a sea ice decline comparable to the observed. The imposed perturbation leads to enhanced seasonal melting and a rapid sea ice retreat within the first 5 years. Over the next decades we observe a gradual freshening of the upper Arctic Ocean that continues for about a century, with upper-ocean mean salinity decreasing by ~0.6 psu. The freshening occurs via a distillation-like process in which denser waters with increased salinity at the outer boundary of the region are exported from the Arctic to the subtropical/tropical North Atlantic by meridional overturning circulation, while fresher waters remain in the upper Arctic ocean. Thus, enhanced seasonal sea ice melting in a warmer climate can lead to a persistent Arctic freshening and impact global salinity distribution.