Three Forcing Mechanisms of Freshwater Transport in Fram Strait

Abstract

Fram Strait is one of the main gateways for fresh water leaving the Arctic Ocean toward the deep-water formation regions of the North Atlantic. Monitoring transport through Fram Strait is important to quantify the impact of Arctic amplification on the hydrography in lower latitudes. We update existing time series from the moorings in the western Fram Strait and investigate the monthly and interannual variability of the liquid freshwater transport (FWT, reference salinity 34.9), volume transport and freshwater content between 2003 and 2020. We examine composites and correlations of sea-level pressure (SLP) reanalysis, and remote-sensing dynamic-ocean topography (DOT) in the Arctic Ocean. We identify two remote forcing mechanisms of FWT: (a) North Pole convergence freshens the region north of Fram Strait 13–24 months before high FWT events. (b) Beaufort Gyre weakening allows spreading of fresh water to the margins of the Arctic Basin zero to 9 months before high FWT events. In addition a third mechanism occurs locally, (b) Fram Strait northerly winds confine freshwater to the Greenland shelf and drive stronger southward FWT. Additionally, we find a decreasing trend in the total volume transport, concurrent with weakening northerly winds and reducing north-south DOT gradient across the strait. We also examined correlations between the Fram Strait time series and the Arctic Oscillation and Arctic Ocean Oscillation. Both are found to correlate positively with the total volume transport, while the Arctic Oscillation correlates negatively with FWT with 1-year lag.