Melting glaciers strongly impact productivity in Greenland fjords
25 August 2017
Meltwater runoff from the Greenland Ice Sheet has doubled in the last two decades as a result of climate warming. New data suggest indicate this drastically alters the productivity in the coastal zone around Greenland.
As the Greenland ice sheet and glaciers are melting at an ever accelerating rate, more and more meltwater flows towards the fjords and coastal seas. Lorenz Meire (Climate Research Centre, Greenland Institute of Natural Resources), together with researchers from Greenland, Denmark and Belgium, investigated the impact of the increasing melting on the marine ecosystem.
Patrick Meire (Global Change Ecology Centre, Research group Ecosystem Management): “During the summer months, the ice sheet discharges around 1000 km3 of fresh water into the coastal ocean. This large freshwater runoff strongly affects the physical and chemical properties of the fjords and continental shelves by influencing the circulation patterns and the stratification.”
The research shows that the impact of this freshwater discharge is fundamentally different between fjords with marine terminating glaciers (glaciers flowing all the way to the sea with calving icebergs) and fjords with land-terminating glaciers. At marine-terminating glaciers, meltwater not only flows at the surface but also percolates at the glacier bed, entering the fjord at submarine levels. Once in the fjord, it rises to the surface as a buoyant plume and entrains large volumes of ambient saline fjord water on its way up.
Patrick Meire: “This upwelling of deep nutrient rich water close to the marine-terminating glaciers result in continuous supply of nutrients during the summer months, a supply that is essential to sustain a high productivity in the fjord throughout summer. In contrast, fjords with land-terminating glaciers lack this upwelling mechanism. As a result, the plankton is limited in nutrients after the spring bloom resulting in lower productivity during the summer months.”
This difference in productivity between land and marine terminating glaciers has an important impact on fisheries. Data on commercial halibut landings along the West coast of Greenland confirms that coastal regions under the influence of large marine-terminating glaciers are hotspots of marine productivity, in contrast to the regions with land-terminating glaciers. Patrick Meire: “This productivity will likely be seriously reduced when upwelling of nutrient rich water stops, as some glaciers retreat on land and change from marine to land-terminating glaciers. This is a likely scenario. In recent years, marine-terminating glaciers in Greenland have - on average - retreated by 110 meter per year.”
A lower productivity will negatively impact on fisheries that make up 88 % of Greenland’s export. The results were published in Global Change Biology.
Uummannaq fjord in North-west Greenland, characterized by large halibut fishing and large marine-terminating glaciers (photo: Lorenz Meire)
Marine-terminating glaciers sustain a high productivity in Greenland fjords by creating an upwelling of high amounts of nutrients (photo: Lorenz Meire)