Transformation of overflow water in the East Greenland Current mediated through lateral processes

Abstract. The East Greenland Current (EGC) transports dense waters equatorward along east Greenland, supplying more than half of the Denmark Strait Overflow Water and thus contributing substantially to the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). Previously, overlying freshwater and sea ice insulated the EGC’s overflow water from the atmosphere. However, recent studies indicate that periods with reduced sea ice and freshwater may intermittently allow surface-forced transformation of the EGC’s overflow water. Here, we examine surface-forced water mass transformation within and near the EGC over the last decades using the ocean reanalysis GLORYS12. We find that while water mass transformation within the EGC's core is relatively sparse and likely not yet responsible for much transformation, it occurs more frequently offshore of the EGC. To test whether offshore transformation may influence the EGC's overflow water, we use an idealized process model and residual overturning theory. We suggest that buoyancy-driven eddy exchange can transfer newly transformed water offshore of the EGC into the current, destratifying and densifying the overflow water without direct contact with the atmosphere. Furthermore, under strong atmospheric forcing, slantwise convection may provide a second destratification mechanism. These lateral water mass transformation processes may play an important role in stabilizing the supply and density of overflow water transported to Denmark Strait, potentially imparting resilience to the Nordic Seas’ contribution to the lower limb of the AMOC.