Description: The southward flow of North Atlantic Deep Water makes up the major component of the deepwater limb of the Atlantic Meridional Overturning Circulation (AMOC). In the subtropical North Atlantic, it's flow is concentrated along the continental slope, forming a coherent Deep Western Boundary Current (DWBC). Both, observations and models show a high variability of the flow in this region. Here we use an eddy-rich ocean model to show that this variability is mainly caused by eddies and meanders. Their formation process involves an important contribution from energy transfer by barotropic instability. They occur along the entire DWBC pathway and introduce several recirculation gyres that result in a decorrelation of the DWBC transport at 26.5°N and 16°N, despite the fact that a considerable mean transport of 20 Sv connects the two latitudes. Water in the DWBC at 26.5°N is partly returned northward. Because the amount of water returned depends on the DWBC transport itself, a stronger DWBC does not necessarily lead to an increased amount of water that reaches 16°N. Along the pathway to 16°N, the transport signal is altered by a broad and temporally variable transit time distribution. Thus, advection in the DWBC cannot account for coherent AMOC changes on interannual timescales seen in the model.

Description: Key Points: - During 1993–2019, the East Greenland Coastal Current is freshest in 2010 and 2012 notably matching years of exceptional Greenland runoff - Freshwater anomalies from sea-ice melt and Arctic export advected along east Greenland are of similar magnitudes as those linked to runoff - Simulation of fresh coastal waters requires improved surface boundary conditions and/or models capable of representing mesoscale dynamics 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°) and Copernicus GLORYS12 (1/12°), 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°N sea ice melts year round and retreats to north of 65°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.