Do Salinity Variations Along the East Greenland Shelf Show Imprints of Increasing Meltwater Runoff?

Accelerated melting of the Greenland Ice Sheet is considered a tipping element in the freshwater balance of the subpolar North Atlantic (SPNA). The East Greenland Current (EGC) and Coastal Current (EGCC) are the major conduits for transporting Arctic-sourced and Greenland glacial freshwater. Understanding freshwater changes in the EGC system and drivers thereof is crucial for connecting tipping elements in the SPNA. Using the eddy-rich model VIKING20X (1/20 degrees) and Copernicus GLORYS12 (1/12 degrees), we find that from 1993 to 2019 freshwater remains close to the shelf with interannual extremes in freshwater content (FWC) attributable to the imprint of Greenland melt only in years 2010 and 2012. Runoff increased significantly from 1995 to 2005 and Arctic freshwater export after 2005. Overall, regional wind patterns, sea ice melt and increasingly glacial ice and snow meltwater runoff along with the Arctic-sourced Polar Water set interannual FWC variations in the EGC system. We emphasize that these freshwater sources have different seasonal timing. South of 65 degrees N sea ice melts year round and retreats to north of 65 degrees N, where melt in summer prevails. Greenland runoff peaks in June-August with only some locations of year round discharge. Alongshore winds intensify in fall and winter where reduced onshore Ekman transport allows for freshwater to spread laterally in the EGC. We show that sea ice melt, runoff and wind can cause interannual variations of comparable magnitude. All of which makes attributing ocean freshening events to Greenland meltwater inflow at current magnitudes a major challenge. The intensity of Greenland ice sheet melt has greatly accelerated over the past decades bringing more freshwater to the surrounding ocean. The additional freshwater has the potential to reach areas where deep waters are formed, which are an important part of the global ocean circulation. A lid of cool and low salinity water would weaken deep water formation and circulation affecting global heat redistribution. In this study we use a high-resolution model to investigate the effect of Greenland melt, sea ice export, and alongshore winds on freshwater content in the East Greenland Current and its coastal twin from Fram Strait to Cape Farewell. Two fresh extremes in 2010 and 2012 are attributable to local Greenland runoff maxima. We find that it takes 4-8 months for freshwater to propagate all along Greenland's east coast, with freshwater anomalies originating from the Arctic Ocean and additional input from sea ice melt along the journey often masking the Greenland runoff signal. Our results emphasize the need for ocean models and observations to resolve and record meltwater runoff, fjord and shelf processes, and boundary current dynamics to detect and attribute local freshening events. During 1993-2019, the East Greenland Coastal Current is freshest in 2010 and 2012 notably matching years of exceptional Greenland runoffFreshwater anomalies from sea-ice melt and Arctic export advected along east Greenland are of similar magnitudes as those linked to runoffSimulation of fresh coastal waters requires improved surface boundary conditions and/or models capable of representing mesoscale dynamics