Changes in Freshwater Distribution and Pathways in the Arctic Ocean Since 2007 in the Mercator Ocean Global Operational System

Abstract

Low-salinity waters in the upper Arctic Ocean, referred to as “freshwaters”, are cold and play a major role in isolating the sea ice cover from the heat stored in the salty Atlantic Waters (AWs) underneath. We examined changes in Arctic freshwater distribution and circulation since 2007 using the 1/12° global Mercator Ocean operational model. We first evaluated model simulations over the upper water column in the Arctic Ocean, using nearly 20,000 independent in situ temperature-salinity profiles over the 2007？2020 period. Simulated hydrographic properties and water mass distributions were in good agreement with observations. Comparison with long-term mooring data in the Bering Strait and Beaufort Gyre highlighted the model's capabilities for reproducing the interannual evolution of Pacific Water properties. Taking advantage of the good performance of the model, we examined the interannual evolution of the freshwater distribution and circulation over 2007？2020. The Beaufort Gyre is the major freshwater reservoir across the full Arctic Ocean. After 2012 the gyre extended northward and increased the freshwater content (FC) in the Makarov Basin, near the North Pole. Coincidentally, the FC decreased along the East Siberian slope, along with the AW shoaling, and the Transpolar Drift moved from the Lomonosov Ridge to align with the Mendeleev Ridge. We found that these changes in freshwater distribution were followed in 2015 by a marked change in the export of freshwater from the Arctic Ocean with a reduction in Fram Strait (？30%) and an increase in the western Canadian Archipelago (+16%).