Disko Bay in west Greenland hosts the largest glacier in the northern hemisphere, Sermeq Kujalleq. Whilst meltwater is often a diluting influence on nutrient concentrations in the marine environment, physical mixing processes close to glacier outflows can be a regionally important driver of marine productivity. Where buoyant subglacial discharge emerges at deep glacier grounding lines, the entrainment and vertical transport of nutrients in the upwelling plume can constitute a considerable vertical redistribution of nutrients in the water column —impacting the nutricline structure and productivity. Here we constrain the effects of glacial outflows from Sermeq Kujalleq on Disko Bay during summer 2022.

Across the entrance of the Ilulissat Icefjord that hosts Sermeq Kujalleq, a 250-m sill restricts the inflow of saline, nutrient rich water into the fjord. In August 2022, outflow of glacially-modified freshwater was evident in the upper 100 m of the water column. Large, positive nutrient anomalies for nitrate, phosphate and silica were detected in the upper 0–60 m. Nutrient ratios in the plume reaffirmed re-circulation of seawater that entered the fjord at depth as the largest nutrient source to the plume, yet also suggested that in-fjord processes may affect the ratio of nitrate and silica within the 50-km-long ice-covered fjord. Our results confirm the role of outflow from Sermeq Kujalleq as the major driver of an annually reoccurring summertime phytoplankton bloom in Disko Bay, which sustains Greenland’s largest inshore fishery. Due to its large size compared to any other Arctic glacier system, Sermeq Kujalleq is a rather unusual case study. Nevertheless, the clearly-identifiable outflowing plume is an ideal site to explore the physical and biogeochemical effects of glacier discharge on the marine environment.

 

Glacier,GReenland,Biogeochemistry