Upwelling of Macronutrients and Dissolved Inorganic Carbon by a Subglacial Freshwater Driven Plume in Bowdoin Fjord, Northwestern Greenland

Abstract

AbstractIn Greenland, tidewater glaciers discharge turbid subglacial freshwater into fjords, forming a plume near the calving front. To elucidate the effects of this discharge on nutrient and dissolved inorganic carbon transport to the surface in these fjords, we conducted observational studies on Bowdoin Glacier and in its fjord in northwestern Greenland during the summer of 2016. Our results provide evidence of macronutrient and dissolved inorganic carbon transport from deep in the fjord to the surface in front of the glacier. This transport is driven by plume formation resulting from subglacial freshwater discharge and subsequent upwelling along the glacier calving front. The plume water is a mixture of subglacial freshwater and entrained fjord water. The fraction of glacial meltwater in the plume water is ~14% when it reaches the surface. The plume water is highly turbid because it contains substantial amounts of sediment derived from subglacial weathering. After reaching the surface, the plume water submerges and forms a turbid subsurface layer below fresher surface water at densities of 25.0 to 26.5 σθ. Phytoplankton blooms (~6.5 μg/L chlorophyll a) were observed near the boundary between the fresher surface and turbid subsurface layers. The bloom was associated with a strong upward NO3− + NO2− flux, which was caused by the subduction of plume water. Our study demonstrated that the subglacial discharge and plume formation at the front of Bowdoin Glacier play a key role in the availability of nutrients and the subsequent growth of phytoplankton in the glaciated fjord.