Modeling the sensitivity of coastal ocean Primary Production to Extreme Melting of the Greenland Ice Sheet

Responding to the July 2012 extreme melting of the Greenland Ice Sheet, this study investigates how marine primary productivity of the region may be affected by changes resulting from increasing meltwater discharge. The freshwater melt from the ice sheet flows primarily to the sea, where wind and ocean currents then distribute and mix it with ocean water. Depending on its delivery, meltwater may increase stratification in the coastal ocean, which is often beneficial to the light-limited phytoplankton typically found in polar regions. While plumes of buoyant meltwater can reduce light limitation by creating a shallower mixed layer, they may also increase nutrient limitation by isolating the phytoplankton from deep nitrogen supplies. Turbidity in the plume would also dampen any meltwater-driven relief from light limitation. To characterize and quantify these responses to melt in the coastal ocean west of Greenland, we created a bottom-up (nutrient-and-light-influenced) marine ecosystem model using model output generated as a part of a larger interdisciplinary Ice Sheet Impact Study. The collaborative project includes an examination of the changes of Greenland’s surface mass balance, a hydrological runoff model of glacial meltwater, and a Regional Ocean Modeling System (ROMS). Meltwater distributions and mixed layer depths from the ROMS model were used to analyze the potential effects on marine phytoplankton. The ROMS produced ocean output for two cases over a ten-year period: with and without meltwater runoff. Using these two cases, we determined the perturbation in mixed layer depth, light availability, and the expected phytoplankton biomass, due to meltwater over different regions and melting conditions. Results are compared to remote sensing data analyzed by other members of the Ice Sheet Impact Study. The sensitivity results indicate an increase in variability of mixed layer depths with increasing meltwater input, and that the increased light availability caused by greater melting allows for increased primary production in late summer.