| Summary: | Runoff from the Greenland Ice Sheet (GrIS) is thought to enhance marine productivity byadding bioessential iron and silicic acid to coastal waters. However, experimental data suggestnitrate is the main summertime growth-limiting resource in regions affected by meltwateraround Greenland. While meltwater contains low nitrate concentrations, subglacialdischarge plumes from marine-terminating glaciers entrain large quantities of nitrate fromdeep seawater. Here, we characterize the nitrate fluxes that arise from entrainment ofseawater within these plumes using a subglacial discharge plume model. The upwelled fluxfrom 12 marine-terminating glaciers is estimated to be >1000% of the total nitrate flux fromGrIS discharge. This plume upwelling effect is highly sensitive to the glacier grounding linedepth. For a majority of Greenland’s marine-terminating glaciers nitrate fluxes will diminish asthey retreat. This decline occurs even if discharge volume increases, resulting in a negativeimpact on nitrate availability and thus summertime marine productivity.
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