Climate change is causing the ice cap in Greenland to melt rapidly, carrying huge amounts of meltwater into the fjords and the ocean. As this input has an impact on coastal ecosystems, researchers investigated the water quality of meltwater rivers in southwestern Greenland in a recent study. Among other things, they analyzed the meltwater for mercury and found extremely high concentrations of the toxic heavy metal.
Mercury occurs naturally as a mineral (cinnabar, HgS) in areas of former volcanic activity, in hard coal and lignite, and in large quantities in the frozen biomass of permafrost soils in the northern hemisphere, where about twice as much mercury is stored as in all other soils, the atmosphere and the oceans combined. The anthropogenic input of mercury into the environment, for example through gold mining and the operation of coal-fired power plants or cement works, accounts for about 30 percent of total emissions. Mercury can bioaccumulate in organisms and biomagnifies in the food web, mostly in the form of the neurotoxin methyl mercury. Large mercury exposures can have serious consequences for the environment and human health.
The high mercury concentrations in the rivers and fjords into which glaciers from the Greenland ice cap flow surprised Jon Hawkings, postdoctoral researcher at Florida State University and the German Research Center for Geosciences and lead author of the study, and glaciologist Jemma Wadham, professor at the University of Bristol’s Cabot Institute for the Environment. The levels are comparable to concentrations in rivers in industrial China. For Greenlandic communities, whose food supply depends directly on marine resources, this is far from good news. Fishing is also the most important industry – Greenland exports cold water shrimp, halibut and cod.
“There are surprisingly high levels of mercury in the glacier meltwaters we sampled in southwest Greenland,” Hawkings said. “And that’s leading us to look now at a whole host of other questions such as how that mercury could potentially get into the food chain.”
Typically, the concentration of dissolved mercury in rivers lies between 1 and 10 nanograms per litre of water, which corresponds to a grain-of-salt-sized amount of mercury in an Olympic swimming pool. The scientists measured a much higher concentration in the glacial meltwater rivers studied in West Greenland. There, the dissolved mercury content was more than 150 nanograms per liter. The concentration of particulate mercury in the so-called glacial flour – the sediment that makes glacial rivers look milky – was even higher, at more than 2000 nanograms per litre of river water.
It is not yet known whether the glacier-derived mercury is being carried on and finding its way into the aquatic food web.
“We didn’t expect there would be anywhere near that amount of mercury in the glacial water there. Naturally, we have hypotheses as to what is leading to these high mercury concentrations, but these findings have raised a whole host of questions that we don’t have the answers to yet.”Rob Spencer, professor of Earth, Ocean and Atmospheric sciences and co-author of the study
As Jemma Wadham notes, their discovery that glaciers can also carry potential toxins reveals a worrisome dimension to how glaciers affect water quality and downstream communities, especially in light of rapidly advancing climate change in Greenland and around the world.
The reality of the world’s rapidly melting glaciers and ice caps – ten percent of the Earth’s land surface – involves not only ice loss and freshwater input, but is far more complicated and complex as the study results impressively show. Scientists around the world are therefore trying to understand how the rise in temperature affects geochemical processes.
“For decades, scientists perceived glaciers as frozen blocks of water that had limited relevance to the Earth’s geochemical and biological processes,” said Rob Spencer. “But we’ve shown over the past several years that line of thinking isn’t true. This study continues to highlight that these ice sheets are rich with elements of relevance to life.”
In their study, which was published in the journal Nature Geoscience, the international research team with scientists from the USA, Great Britain, the Czech Republic, Norway, Greenland and the Netherlands assumes that the mercury probably originates from the Earth itself, as opposed to anthropogenic input, for example through the burning of fossil resources.
“All the efforts to manage mercury thus far have come from the idea that the increasing concentrations we have been seeing across the Earth system come primarily from direct anthropogenic activity, like industry,” Hawkings says. “But mercury coming from climatically sensitive environments like glaciers could be a source that is much more difficult to manage.”
Julia Hager, PolarJournal
Link to the study: Hawkings, J.R., Linhoff, B.S., Wadham, J.L. et al. Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet. Nat. Geosci. (2021). https://doi.org/10.1038/s41561-021-00753-w
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