The melting Greenland ice sheet could be a surprising source of toxic mercury.
The island is one of the most remote places on Earth—yet runoff water from some melting glaciers contains as much mercury as highly polluted rivers in heavily populated parts of the world.
These are the findings of a new study that analyzed meltwater flowing from the southeast corner of the ice sheet. The research raises concerns about the amount of mercury entering nearby rivers and fjords, important sources of fish for coastal Greenland communities.
“There is definitely higher mercury concentrations in the fjords than we would have expected before we came into this study,” said lead author Jon Hawkings, a postdoctoral research fellow at Florida State University.
The researchers collected meltwater samples on expeditions to the ice sheet in 2012, 2015 and 2018. They also sampled water from several nearby fjords fed by the melting glaciers.
Chemical analyses revealed surprisingly high levels of mercury dissolved in the water.
Mercury concentration in the meltwater rivers were at least an order of magnitude higher than the concentrations found in ordinary rivers across the Arctic. These concentrations became slightly diluted by the time they flowed out into the fjords—but were still higher than expected, the researchers say. Even after mingling with the salty water, the levels in the fjords remained about an order of magnitude higher than the mercury levels found in most open ocean waters.
Unlike polluted rivers in other parts of the world, contaminated by industrial activity, the researchers believe the Greenland mercury is coming from natural sources. If it were coming from human pollution, then the snow on top of the ice sheet should also be full of mercury—yet previous studies have shown it’s comparatively clean. Instead, the scientists believe the meltwater mercury is probably leaching out of the bedrock beneath the ice.
Sediments underneath glaciers can contain large concentrations of naturally occurring mercury. As the ice slips and grinds over the bedrock, it can release mercury into streams of meltwater flowing out from the ice sheet.
High mercury concentrations in Greenland’s coastal waters are cause for concern, the researchers say. These waters support a rich marine ecosystem. Fisheries are the linchpin of Greenland’s economy, as well as a primary food source for the island’s Indigenous communities.
For now, it’s unclear how much of the mercury is actually getting into the food supply. Some of it may fall straight to the bottom of the sea, where it gets permanently trapped in marine sediments. But there’s evidence from other parts of the Arctic that mercury pollution can accumulate in fish—eventually exposing the human communities that eat them.
“A big question is whether the mercury [in Greenland] makes it across that biological boundary into organisms in the aquatic food web,” Hawkings said. The new study only measured raw concentrations in the water—but future research could examine the marine ecosystem, itself.
It’s also unclear how climate change might affect these mercury levels in the future. The Greenland ice sheet is melting at faster and faster rates over time. More meltwater from coastal glaciers could translate into more mercury contamination in the water.
On the other hand, much of Greenland’s future melting is expected to come from the surface of the ice sheet—and the surface is relatively mercury-free. An increase in surface runoff could help dilute some of the mercury flowing from underneath the glaciers, Hawkings pointed out.
Because the uncertainties are still so large, more research is needed across the ice sheet.
“More monitoring is needed,” Hawkings said. “Multiyear monitoring of a number of rivers around Greenland is needed to really establish whether this is climatically sensitive or not.”
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential news for energy and environment professionals.