Observed Changes in the Arctic Freshwater Outflow in Fram Strait

• Published in: Journal of geophysical research. Oceans Vol. 127; no. 3
• Main Authors: Karpouzoglou, T., Steur, L., Smedsrud, L. H., Sumata, H.
• Format: Journal Article
• Language: English
• Published: 01.03.2022
• Subjects: Arctic Ocean; Atlantification; East Greenland Current; Fram Strait; fresh water transport; Polar Water
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2021JC018122

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. Plain Language Summary The East Greenland Current (EGC) brings fresh and cold Polar Water (PW) southwards from the central Arctic Ocean. In the Fram Strait, between Greenland and Svalbard, the strength and properties of this current have been observed using moored instruments since 1997. We present updated time series for the 2015–2019 period and re‐analyze earlier variability and estimates. Our results indicate that the fresh water transport since 2015 has decreased, however, with an exception in 2017. This general decrease is caused by a reduction in the southward flow speed and the amount of fresh Polar Water. The front between Polar and Atlantic water has moved westward, and the Polar Water layer has become thinner and more stratified. Moreover, the amount of Atlantic Water in the section increased, pointing to an “Atlantification” of the western Fram Strait. We also refine the time series of the EGC back in time based on the new data, calculate the uncertainty, and show how it depends on the amount of instruments. Finally, we evaluate possible drivers of the observed changes and discuss a connection with Arctic freshwater storage. Key Points Mean fresh water transport of the East Greenland Current in Fram Strait decreased after 2015 due to weaker velocity and increased salinity Both the vertical as well as the lateral extent of the Polar Water has decreased relative to 2003–2015 Large fresh water transport from the Arctic in 2017 formed an exception to the Atlantification trend observed in the western Fram Strait