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 the runoff from some melting glaciers contains as much mercury as heavily polluted rivers in densely populated parts of the world.
These are the results of a new study in which the meltwater from the southeast corner of the ice sheet was analyzed. The research raises concerns about the amount of mercury entering nearby rivers and fjords, important sources of fish for Greenland’s coastal communities.
“There are definitely higher levels of mercury in the fjords than we expected before we got into this study,” said lead author Jon Hawkings, a postdoctoral fellow at Florida State University.
The researchers collected meltwater samples on expeditions to the ice sheet in 2012, 2015, and 2018. They also took water samples from several nearby fjords fed by the melting glaciers.
Chemical analyzes showed surprisingly high levels of mercury in the water.
The concentration of mercury in meltwater rivers was at least an order of magnitude higher than concentrations in ordinary rivers in the Arctic. These concentrations were diluted slightly as they flowed into the fjords – but still higher than expected, the researchers say. Even after mixing with the salt water, levels in the fjords remained an order of magnitude higher than the levels of mercury in most open sea waters.
Unlike polluted rivers in other parts of the world that have been contaminated by industrial activities, researchers believe that Greenland’s mercury comes from natural sources. If it comes from human pollution, the snow on the ice sheet should also be full of mercury – but previous studies have shown it to be comparatively clean. Instead, the scientists believe that the meltwater mercury will likely leak from the bedrock under the ice.
Sediments under glaciers can contain large concentrations of naturally occurring mercury. As the ice slides and scrapes over the bedrock, it can release mercury in streams of meltwater that flow out of the ice sheet.
High levels of mercury in Greenland’s coastal waters are a cause for concern, the researchers say. These waters support a rich marine ecosystem. Fishing is the lynchpin of the Greenland economy and a major source of food for the island’s indigenous communities.
It is currently unclear how much mercury is actually entering the food supply. Some of it can fall directly to the sea floor, where it becomes permanently trapped in marine sediments. However, there is evidence from other parts of the Arctic that mercury pollution can build up in fish, which eventually exposes the human communities that eat them.
“A big question is whether the mercury [in Greenland] makes it across that biological limit in organisms in the aquatic food web, ”said Hawkings. In the new study, only the raw concentrations in the water were measured. However, future research could examine the marine ecosystem itself.
It’s also unclear how climate change could affect these mercury levels in the future. The Greenland ice sheet is melting faster and faster over time. More meltwater from coastal glaciers could lead to increased 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 under the glaciers, Hawkings said.
With the uncertainties still so great, more research into the ice sheet is needed.
“More surveillance is needed,” said Hawkings. “Multi-year monitoring of a number of rivers in Greenland is needed to really determine whether or not this is climate sensitive.”
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides important news for energy and environmental professionals.