Impact of ice cover and freshwater discharge on the pelagic food web

Mass loss from the Greenland Ice Sheet (GrIS) quadrupled over the past two decades owing to increased surface melt and the widespread retreat and speedup of marine-terminating glaciers. These physical changes have sparked interest in Greenland’s glacial fjords - the conduits between the large-scale ocean and the ice sheet - for two reasons. First, it is plausible that a sizable portion of the observed glacier acceleration and retreat was triggered by increased submarine melting of the glaciers’ margins. Second, the melt water from Greenland must transit through the fjord before reaching Greenland’s continental shelves - where it can impact the ocean circulation and the downstream marine ecosystems. Using data collected from several Greenland fjord/glacier systems we show that the freshwater discharge in these coastal waters is mediated by a complex interplay of atmospheric forcing, subglacial processes, as well as both shelf and fjord dynamics. In these strongly stratified waters dominated by relatively cold, fresh Polar Waters overlying warm, salty Atlantic Waters, the discharge of surface and submarine melt at depth can result in subsurface intrusions of a third water mass. These glacially modified waters ultimately govern the freshwater export both at the surface and at depth. Ocean circulation within the fjords, which results from the interplay between buoyancy-driven (i.e. driven by glacial inputs) and shelf-driven flows (a consequence of gradients between fjord and continental shelf waters), in turn regulates this export by controlling melt processes as well as the residence time of glacially modified waters in these systems. While freshwater input into surface waters can fundamentally impact the marine ecosystem via changes in water column stratification and the biochemistry of surface waters, a better understanding of variability within these systems is needed to constrain the consequences of GrIS mass loss on the coastal ocean