Southwestern Greenland is a hotspot of mercury release
Mercury pollution is an issue of global concern due to the high toxicity of the element. High levels of mercury have previously been found in Arctic organisms. However, whether the Greenland Ice Sheet is a source of mercury and how significantly it affects downstream regions in the Arctic remained unknown. Such information is urgently needed, as the Greenland Ice Sheet is melting at an accelerated rate as the climate warms.
Concentrations 30 times as high
An international team of ocean researchers led by Jon Hawkings from GFZ, the German Research Center for Geosciences in Potsdam, measured mercury concentrations in meltwaters from three glacial catchments on the southwestern margin of the Greenland Ice Sheet during the summer melting season. Oceanographer Lorenz Meire of the NIOZ Royal Netherlands Institute for Sea Research contributed to the study. “To investigate whether mercury was exported by the Ice Sheet, samples were collected both from meltwater rivers and in fjord surface layers where rivers discharge. I was involved in collecting water samples from fjords near the Greenland capital Nuuk, where I have been working over the last ten years.”
The authors found very high concentrations of dissolved mercury in meltwater rivers flowing from the glacial catchments to downstream fjords. Meire: “The amount of mercury released per square kilometer was 100 times higher compared to other Arctic areas, leading to 30 times higher concentrations in the rivers. The trace element most probably ended up in the meltwater due to erosion of rocks by the moving glaciers.”
Potentially toxic to marine life
Export of dissolved mercury from this region is estimated to be globally significant — up to about 42 tons per year — equivalent to around 10% of the estimated global riverine export to the oceans. Concentrations of dissolved mercury in meltwaters were found to be among the highest recorded in natural waters.
High concentrations of mercury also persist in downstream fjords, leading to potential risks of bioaccumulation in coastal food webs. “Such high concentrations of this harmful trace element may accumulate in marine organisms and in the end also be dangerous to humans. This is relevant for the local communities, as they strongly rely on marine organisms such as fish and marine mammals”, says Meire. According to the researchers, further research is needed to understand mercury dynamics in ice sheet runoff across Greenland, given the potentially increasing exposure of humans and ecosystems to this element due to climate change.
Jon R. Hawkings, Lorenz Meire et al. Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet Nature Geoscience DOI: https://www.nature.com/articles/s41561-021-00753-w
This article is based on the press release by Nature Geoscience.