Greenland Glacial Fjord Dynamics and Impacts on Nutrient Supply and Phytoplankton Community Structure

Glacial fjords along the coast of Greenland serve as conduits linking the large-scale ocean and the Greenland Ice Sheet (GrIS). They are significant pathways of seasonal glacial meltwater export and important sites of primary and secondary productivity. In recent years, warming of both atmosphere and ocean in the high latitude North Atlantic has led to the retreat of glaciers in southern Greenland, resulting in unprecedented ice loss from the GrIS and increased export of freshwater to the North Atlantic through these coastal fjords. Through changes in physical (e.g. stratification, turbidity) and chemical (e.g. nutrient distributions and concentrations) properties of the water column, glacial meltwater may serve as a primary forcing on phytoplankton dynamics and primary productivity. However, the impact of this increased coastal meltwater input on phytoplankton dynamics both in the fjord and downstream on the continental shelf have been poorly constrained. We took part in an August 2015 cruise to Sermilik Fjord at the edge of Helheim Glacier (a major glacier of the GrIS) in SE Greenland to investigate the impact of ice-ocean interactions and meltwater input on phytoplankton and nutrient dynamics. Glacially modified waters were found throughout the fjord both at the surface and at depth, with maxima in meltwater content found near the glacier termini. These physical patterns were paralleled by gradients in macro-nutrient distributions, with higher surface concentrations near the glacial termini resulting from buoyancy-driven circulation and a vertical flux of deep nutrients to the euphotic zone. Changes in both chl-a biomass and phytoplankton community composition, as assessed using an Imaging FlowCytobot in near-real time, were also associated with differences in meltwater content, indicating a potential link between freshwater inputs and phytoplankton dynamics in these important coastal ecosystems.