Mercury pollution is a problem of global concern due to its toxic effects. High levels have already been measured in arctic organisms – with worrying effects on ecosystems and the food chain. So far, the Greenland ice cap has not been considered as part of the Arctic mercury cycle. Now, researchers led by Jon Hawkings of the German Research Center for Geosciences in Potsdam and Florida State University are showing that meltwater in southwest Greenland carries considerable amounts of mercury into it. Arctic ocean. Due to the large quantities detected, the researchers assume that they are of geological origin. They present their measurements in the current issue of Nature Geoscience.

Mercury: poison for humans and the environment – especially in the Arctic

Mercury is of little biological benefit, but is found to be all the more toxic in the form of various chemical compounds. It accumulates in the food chain and becomes a danger to humans through the consumption of fish and seafood. The socio-economic costs associated with environmental and health impacts are estimated at more than five billion US dollars per year. .

A significant aggravation of this problem is due to fossil fuel production, industry, mining and transport. But there are also natural sources such as emissions from volcanoes, fires, and weathering of rocks containing mercury. The Arctic is proving to be a particular problematic area in both respects: the mercury content of marine organisms has increased by an order of magnitude over the past 150 years. Dust particles and aerosols enter this region via the atmosphere, and climate change and associated warming of the Arctic are causing higher inputs through more and stronger meltwater.

International team focuses on Greenland ice cap

The Greenland ice cap, which covers about a quarter of the Arctic land mass, has so far received little attention in this context. This was changed by a 22-member international research team led by Jon Hawkings, a postdoctoral fellow in the interfacial geochemistry section of GFZ and Florida State University, with 17 participating institutions from Europe and the United States (see below below). During surveys during the arctic summers of 2012, 2015 and 2018, they collected samples from three ice-basin meltwater flows on the southwestern edge of the Greenland ice sheet and downstream fjords. The melt water was filtered in the laboratory tent, the filtered sediment was air dried, cooled and subjected to initial analyzes. The mercury levels were determined in detail in the laboratories of the participating institutions, among others by mass and fluorescence spectrometry.

Surprisingly high mercury concentrations

Originally, Hawkings and her colleague, glaciologist Jemma Wadham, professor at the Cabot Institute for the Environment at the University of Bristol, wanted to study the content and pathways of nutrients in these waters. During the analysis, they were then surprised by extremely high levels of mercury, comparable to those of rivers in industrial China: the typical level of dissolved mercury in rivers is around 1 to 10 nanograms per liter. This is equivalent to an amount of mercury the size of a grain of salt in an Olympic-size pool of water. However, in the glacial meltwater rivers of Greenland, researchers found much higher levels of over 150 nanograms per liter. Undissolved mercury particles were found in even higher concentrations of over 2000 nanograms per liter.

“The export of dissolved mercury from this region must be considered significant globally,” says Jon Hawkings. He says it can reach 42 tonnes per year, which is about 10% of estimated global riverine exports of mercury to the oceans. “This is one of the highest dissolved mercury concentrations ever measured in natural waters. And ecologically high levels persist in downstream fjords, posing a potential risk of accumulation in coastal food webs,” said Hawkings .

Climate change is likely to make the situation even worse

This finding is particularly relevant, especially in the context of the fact that fishing is Greenland’s main industry, the country being a major exporter of cold-water shrimp, halibut and cod.

“We have learned from many years of fieldwork at these sites in West Greenland that glaciers export nutrients to the ocean, but the discovery that they can also carry potential toxins reveals a worrying dimension of how glaciers influence water quality and communities change in a warming world and underscores the need for more research, ”said Jemma Wadham.

The natural source requires rethinking conservation measures

The source of the large amounts of mercury detected is most likely the Earth itself, at the base of the ice cap, Hawkings believes. This is suggested, among other things, by comparative data of the surface of snow and ice, where it accumulates by burning fossil fuels or other industrial source. It could be important for scientists and policy makers to plan for the management of mercury pollution in the future.

“All efforts to manage mercury so far have come from the idea that the increasing concentrations that we have seen across the Earth system are primarily from direct human activity, such as industry,” Hawkings said. “But mercury from climate-sensitive environments like glaciers could be a much more difficult source to manage.”

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Researchers from the following institutions contributed to the study:

United States (USGS, Woods Hole Oceanographic Institute, University of California Santa Cruz, Brigham Young University), United Kingdom (University of Bristol, University of Glasgow), Czech Republic (Charles University), Norway (UiT The Arctic University of Norway , UiO University of Oslo), Greenland (Greenland Climate Research Center), Netherlands (Royal Netherlands Institute of Sea Research).

** Funding: Jon Hawkings is a postdoctoral researcher at the German GFZ Research Center for Geosciences. As part of its Horizon 2020 MSCA Marie Sk? Odowska Curie Actions, he has been working at Florida State University FSU (USA) for two years from 2018, before continuing his research in Potsdam. His project is called “ICICLES – Iron and carbon interactions and the biogeochemical cycle in subglacial ecosystems”.

Original study: Hawkings, JR, Linhoff, BS, Wadham, JL et al. Large subglacial source of mercury from the southwestern margin of the Greenland ice sheet. Nat. Geosci. (2021). DOI: 10.1038 / s41561-021-00753-w

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