Greenland Freshwater Input to the North Atlantic

The Greenland Ice Sheet (GrIS) is losing mass at an unprecedented rate. The associated increased freshwater flux directly contributes to sea level rise, but also has dynamical implications for the Atlantic Meridional Overturning Circulation and global climate. The freshwater buoyancy forcing from marine terminating outlet glaciers is distributed throughout the depth of coastal fjords. When coupled with strong fjord stratification, this buoyancy forcing can drive significant water mass transformation (WMT) of subsurface waters in the fjord. The WMT differs substantially from a simple freshwater input to the surface ocean. This often overlooked small-scale overturning has potentially important consequences for the influence of GrIS freshwater on large scale ocean circulation and needs to be accounted for in studies of GrIS impact on the ocean. From ship-based and moored hydrographic measurements in East Greenland (2008 to 2013) we describe the character and temporal variability of meltwater driven WMT. While melting always adds freshwater to the ocean, the corresponding WMT causes a seasonally variable vertical redistribution of heat and salt. Observations show that the seasonal cycle of the WMT lags surface air temperatures by several months. We discuss how the WMT and its timing might impact the boundary current system in East Greenland, and implications for its representation in numerical models and impact on North Atlantic deep convection.