Does freshwater content of the East Greenland Current show imprints of increasing meltwater runoff?

Accelerated melting of the Greenland Ice Sheet has been identified as a tipping element in the freshwater balance of the subpolar North Atlantic (SPNA), where the East Greenland Current is a primary pathway for transporting Arctic-sourced freshwater and Greenland glacial meltwater. Understanding the freshwater variability of the East Greenland Current (EGC) and Coastal Current (EGCC) and their interaction is of high importance, as these gather the imprint of ice melt once the meltwater leaves the fjords and enters the open ocean. Using a high-resolution model (VIKING20X, 1/20°) and gridded, observational assimilated reanalysis (GLORYS12, 1/12°), we find the freshest water remains close to the shelf with interannual extremes in freshwater content attributable to the imprint of Greenland melt only in years 2010 and 2012. This signal is only found in the VIKING20X simulation, which in contrast to GLORYS12 uses realistic, interannually varying runoff forcing including estimates of the Greenland Ice Sheet mass balance. We further discuss the role of wind forcing, sea ice melt, and Greenland runoff, which all contribute to variability in freshwater content along the boundary current.

Our results show that slackened alongshore winds reduce onshore Ekman transport allowing for freshwater to spread laterally in the EGC, while stronger alongshore winds constrain freshwater closer to the shelf with saline intrusions from the interior basin into the outer EGC. South of ~65°N sea ice melts year round and retreats northward with melting occurring only in summer. Associated salinity and thus freshwater content anomalies are of similar magnitude as those associated with meltwater runoff and overlap in both seasonal timing and advective time scales. This could explain the challenges to identify freshening events originating from extreme melt events on the Greenland Ice Sheet at currently observed magnitudes. Their detection is critically dependent on synoptic and interannually varying processes. Our findings also suggest that ocean models or model-based reanalysis products aiming to illustrate the processes of meltwater redistribution should feature grid resolutions preferably exceeding 1/12° in order to represent coastal dynamics and fjord-shelf-open ocean exchange. With more observations on the Greenland shelf hopefully becoming available in the future, we anticipate the GLORYS12 assimilation product to show similar variability as higher resolution models.