Exploring the Potential Impact of Greenland Meltwater on Stratification, Photosynthetically Active Radiation, and Primary Production in the Labrador Sea

Abstract

In July 2012, the surface of the Greenland Ice Sheet (GrIS) melted to an extent unprecedented over the last 100 years; we questioned the potential for such an extreme melt event to impact marine phytoplankton offshore. We hypothesized that stratification from meltwater could reduce light limitation for phytoplankton, and used a suite of numerical models to quantify the impact for 2003–2012. Because much of the 2012 meltwater discharged from southern Greenland, our study focused on the southwestern and southeastern coasts of Greenland, and the Labrador Sea. A 1‐D phytoplankton model used output from a Regional Ocean Modeling System (ROMS) coupled with a Regional Climate Model and a hydrological model of meltwater from runoff sources on the ice sheet, peripheral glaciers, and tundra. ROMS was run with and without meltwater to test the sensitivity of phytoplankton photosynthetic rates to the meltwater input. With meltwater, the pycnocline was shallower during late summer and early fall and thus light limitation on photosynthesis was reduced. Averaged over all years, added meltwater had the potential to increase gross primary production by 3–12% in the summer (July–August), and 13–60% in the fall (September–October). This meltwater effect was amplified when light was more limiting, and thus was greatest in the fall, under cloudier conditions, with higher self‐shading, and with more light‐sensitive phytoplankton groups. As the GrIS melt is projected to increase, late summer primary production in this region has the potential to increase as well, which could constitute an important biosphere response to high‐latitude climate change.

Review article: How does glacier discharge affect marine biogeochemistry and primary production in the Arctic?

“…The chemical composition of glacial discharge is now relatively well constrained, especially around Greenland (Yde et al, 2014;Meire et al, 2016a;Stevenson et al, 2017), Alaska (Hood and Berner, 2009;Schroth et al, 2011) and Svalbard (Hodson et al, 2004(Hodson et al, , 2016. Whilst high particle loads (Chu et al, 2012;Overeem et al, 2017) and Si are often associated with glacially modified waters ( Fig. 3a) around the Arctic (Brown et al, 2010;Meire et al, 2016a), the concentrations of all macronutrients in glacial discharge (Meire et al, 2016a) are relatively low and similar to those of coastal seawater (Fig.…”

“…Quantifying the magnitude of environmental perturbations from glacial discharge is complicated by the multiple concurrent, and occasionally counteracting, effects that glacial discharge has in the marine environment. For example, ice-rock abrasion means that glacially fed rivers can carry higher sediment loads than temperate rivers (Chu et al, 2009;Overeem et al, 2017). Extensive sediment plumes where glacier discharge first enters the ocean limit light penetration into the water column (Murray et al, 2015;Halbach et al, 2019), and ingestion of glacial flour particles can be hazardous, or even fatal, to zooplankton, krill and benthic fauna (White and Dagg, 1989;Włodarska-Kowalczuk and Pearson, 2004;Arendt et al, 2011;Fuentes et al, 2016).…”

The Case for a Sustained Greenland Ice Sheet-Ocean Observing System (GrIOOS)

“…In addition to the carbon sink arising from high productivity in some fjords, the mixing of glacial melt with ambient ocean waters results in fjord waters that are significantly undersaturated in CO 2 , suggesting that glacially influenced coastal waters constitute important CO 2 sinks along the Greenland margins (Rysgaard et al, 2012;Fransson et al, 2015;Meire et al, 2015). The correlation between the distribution of meltwater and timing of phytoplankton blooms on parts of the Greenland continental shelf further suggests that meltwater arrival may also be a factor in summertime bloom initiation beyond the confines of glacierfjord systems (Arrigo et al, 2017;Oliver et al, 2018). However, large-scale impacts of freshwater export from the GrIS as a result of the potential export of glacially derived iron to iron-limited regions of the North Atlantic, remain poorly constrained owing to a limited understanding of the fate of glacially modified waters and their nutrients beyond the confines of Greenland's fjords.…”

The biogeochemical impact of glacial meltwater from Southwest Greenland

“…These regions could be a significant trap of dissolved inorganic phases (Meire, Mortensen, Meire, Juul-Pedersen, Sejr et al, 2017), and have the potential to prevent the nutrient-rich glacial waters reaching the coastal seas. Despite this possibility, distal summer phytoplankton blooms have been detected off Southwest Greenland in association with glacial melt (Arrigo, van Dijken, Castelao, Luo, Rennermalm et al, 2017) and ecosystem models indicate sensitivity to meltwater input (Oliver, Luo, Castelao, van Dijken, Mattingly et al, 2018). An understanding of how natural resourcesincluding fisheries, bird, and mammal stocks that are essential for food and encouraging tourism -will respond in the future to increasing anthropogenic stress on a regional and global scale relies on an understanding of foundational processes of these ecosystem services, including marine biogeochemistry and the sources and sinks of essential nutrients (Berthelsen, 2014;Meire et al, 2017;Weatherdon, Magnan, Rogers, Sumaila & Cheung, 2016).…”