A sensitivity analysis to determine conditions necessary for meltwater-enhanced nutrient export from Greenland’s glacial fjords

The Greenland Ice Sheet is undergoing accelerating mass loss, and these large meltwater fluxes to the ocean can potentially impact coastal marine ecosystems. At Greenland tidewater glaciers, meltwater (from surface runoff and basal melt) is delivered at depth. The delivery of meltwater at depth drives buoyant upwelling of nutrient-rich deep water, where it may support primary productivity. Whether this meltwater-driven nutrient upwelling can enhance nutrient delivery to the shelf is still an open question. This modeling study tests the influence of fjord geometry, hydrology, wind, and the uptake of nutrients by phytoplankton within the fjord on meltwater-driven nutrient export out of fjords. We use a Regional Ocean Modeling System (ROMS) coupled to a buoyant plume model (ICEPLUME) to simulate physical and biogeochemical processes within an idealized marine-terminating glacial fjord. We run the model while independently varying the model grid, initial conditions, and forcing, to test how nutrient export from the fjord mouth changes between configurations. Model results suggest that meltwater-driven nutrient fluxes can be exported to the shelf, and that the flux is sensitive to the subglacial discharge rate, the grounding line depth, and the depth of the interface between nutrient-rich Atlantic Water and nutrient-poor Polar Water. Multivariate impacts are also investigated. We test the sensitivity of nutrient fluxes to covarying the climate-sensitive discharge rate and grounding depth, as well as to covarying the fjord geometry when including shelf-forced baroclinic flows.