Modification of freshwater export by fjord circulation at Sarqardleq Fjord, West Greenland

Surface meltwater runoff from the Greenland Ice Sheet is released from beneath marine-terminating glaciers forming buoyant plumes that mix with ambient water, induce submarine melt and drive fjord circulation. The resulting subglacial discharge, submarine melt and ambient water mixture - glacially modified water (GMW) - is exported onto the continental shelf where it can impact ocean circulation, biogeochemistry and marine ecosystems. To best represent the effects of freshwater export from Greenland in global ocean models, we need to understand how the transport of GMW evolves on its journey from glacier to open ocean. To date, this has largely been addressed through models because of the difficulty of obtaining measurements both at the fjord scale and near the ice-ocean boundary. Here we present in situ observations from Sarqardleq Fjord, a midsize glacial fjord in West Greenland, collected from the edge of the subglacial discharge plume to just beyond the fjord sill. We describe velocity, temperature and salinity sections that show the evolution of GMW as it is transported first in the plume, then in a subsurface jet, and finally exported from the fjord. We calculate volume, salt, and heat fluxes out of the fjord and compare with estimates of subglacial discharge input. We find that while most water transformation occurs adjacent to the glacier in the plume, the overall transport is modified by a larger fjord-scale circulation. The resulting GMW transport is therefore substantially greater than the original runoff input and contains strongly diluted subglacial discharge.