Observed Changes in the Arctic Freshwater Outflow in Fram Strait

Abstract

We have updated time series of liquid fresh water transport (FWT) in the East Greenland Current (EGC) in the western Fram Strait with mooring observations since 2015. Novel data have been used to correct earlier estimates when instrument coverage was lower. The updated FWT (reference salinity 34.9) shows that the increased export between 2010 and 2015 has not continued, but FWT has decreased to pre-2009 levels. Salt transport independent of a reference salinity is shown not to be sensitive to salinity changes. Between 2015 and 2019, the FWT in the Polar Water (PW) decreased to an average of 59.9 (±4.5) mSV, 15% less than the 2003–2019 long-term mean, however, high FWT events occurred in 2017. The overall decrease is related to a slowdown of the EGC, partly attributed to a decrease of the zonal density gradient, due to stronger salinification of the halocline waters (26.5 < σθ < 27.7 kg/m3) over the shelf. This salinification counterbalances the freshening of the surface layer (σθ < 26.5 kg/m3) and the fresh water content decreases. Our results show changes in the PW between 2003 and 2019: Salinity stratification increased as the salinity difference between 155 and 55 m increased by 0.63 psu, the PW layer became thinner by 40–50 m and the Polar-Atlantic front moved ∼10 km west in June 2015. All processes point to an “Atlantification” of the western Fram Strait and a reduced Polar outflow. Including the novel data sets reduced the uncertainty of the FWT to an average of 8% after 2015, as opposed to 17% in earlier estimates.