Greenland Subglacial Discharge as a Driver of Hotspots of Increasing Coastal Chlorophyll Since the Early 2000s

Subglacial discharge emerging from the base of Greenland's marine‐terminating glaciers drives upwelling of nutrient‐rich bottom waters to the euphotic zone, which can fuel nitrate‐limited phytoplankton growth. Here, we use buoyant plume theory to quantify this subglacial discharge‐driven nutrient supply on a pan‐Greenland scale. The modeled nitrate fluxes were concentrated in a few critical systems, with half of the total modeled nitrate flux anomaly occurring at just 14% of marine‐terminating glaciers. Increasing subglacial discharge fluxes results in elevated nitrate fluxes, with the largest flux occurring at Jakobshavn Isbræ in Disko Bay, where subglacial discharge is largest. Subglacial discharge and nitrate flux anomaly also account for significant temporal variability in summer satellite chlorophyll a (Chl) within 50 km of Greenland's coast, particularly in some regions in central west and northwest Greenland. Plain Language Summary Greenland ice‐sheet runoff is often discharged into fjords at the base of marine‐terminating glaciers as subglacial discharge, which can drive buoyant upwelling of nutrient‐rich bottom waters and fuel phytoplankton growth in the upper ocean. We combine a buoyant plume model with updated estimates of glacier depth, runoff rates, and profiles of temperature, salinity, and nitrate to estimate nutrient upwelling on a pan‐Greenland scale. The modeled nutrient upwelling is concentrated in a few major glacier systems with the largest subglacial discharge fluxes, and increasing runoff drives substantially increased modeled nutrient fluxes. We find that modeled nutrient upwelling can explain temporal variability in coastal surface chlorophyll a in some areas, particularly in west Greenland, which hosts the island's most exported fish catches by volume and value. Key Points We use buoyant plume theory to model subglacial discharge‐driven nitrate fluxes across Greenland's largest marine‐terminating glaciers The largest positive nitrate flux anomalies are concentrated in a few major systems with the largest subglacial discharge fluxes Runoff and modeled nitrate upwelling can explain temporal variability in surface cholorophyll in some coastal areas in west Greenland