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Greenland has become an important symbol of climate change because of its retreating ice sheet. The melting of glaciers in the polar regions is a global threat. As the massive ice sheets melt, sea levels rise, and the Earth’s albedo decreases. Albedo measures how well a surface can reflect back the radiation incident on it. But in May 2021, a study warned of a problem from the retreating Greenland ice sheet that no one expected.
Jon Hawkings, a geochemist at the Florida State University, discovered that an ice sheet in southwestern Greenland is releasing vast amounts of mercury into nearby rivers. Hawkings first detected mercury in a Greenland glacier in 2015. In 2018, he returned to Greenland to sample two more glaciers. He found high levels of mercury in the sample from all three glaciers. He also reported that the fjords downstream contained environmentally high concentrations of mercury. He linked the two systems and concluded that the ice sheet was leaking mercury into the fjords and rivers. He said that the mercury released from Greenland’s ice sheet, with a catchment area of around 7,500 sq. km. is 130 to 165 times higher than that in other Arctic rivers.
Mercury is a trace element. Trace elements are substances present in minuscule amounts in a sample. Therefore, Hawkings said that sampling the mercury was difficult. Even when mercury is present at levels considered toxic, its actual concentration is very low. Imagine a grain of sand in a swimming pool the size of those at the Olympics. That’s the concentration we’re talking about. Hawkings said the levels detected from the Greenland ice sheet are very high.
The Greenland ice sheet releases 800 cubic meters of meltwater every second. Hawkings and his team found that these meltwaters contain mercury concentrations that are ten times higher than in an average river. The fjords had slightly diluted concentrations of mercury but were still higher than expected.
The mercury released from Greenland’s ice sheet is of the same concentration as highly polluted rivers around today’s industrial areas. The only difference is that in the case of the ice sheet, mercury wasn’t introduced directly by humans. But we’ll talk about where the mercury in the ice sheet came from later.
Although humans were not the cause of Greenland’s mercury concentrations, the ice sheet is melting fast due to climate change. The rapidly melting ice sheet means that mercury concentrations in its meltwaters, and therefore in the fjords and oceans, will increase. Greenland’s ice sheet could be releasing up to 42 tonnes of mercury every year. The mercury released from Greenland’s ice sheet is the highest ever recorded in natural waters not contaminated by humans and their activities.
Mercury occurs naturally on Earth. It is a liquid at room temperatures and is often known as ‘quicksilver’. We commonly use it in thermometers and lightbulbs. Inorganic mercury occurs in nature in non-living things, primarily in rocks, as part of the mineral cinnabar. Organic mercury contains carbon and hydrogen bonds and occurs in living organisms. Living organisms convert the inorganic mercury in soils to organic mercury inside their bodies. Mercury, whether organic or inorganic, is toxic.
When rocks undergo natural weathering, they release inorganic mercury. But the industrial revolution forever changes the planet’s natural mercury cycle. Power plants, manufacturing units, and waste disposal facilities release inorganic mercury. This mercury travels through the air, water, and soil and can reach as far as the poles.
However, researchers believe human activity isn’t the cause of the mercury released from Greenland’s ice sheet. If it were, then the top of the ice sheet would have high mercury concentrations too. But recent research shows that the ice sheet is comparatively clean. Mercury has been detected only from the ice sheet’s meltwaters. Scientists believe that the bedrock beneath the ice sheet contains significant concentrations of naturally occurring mercury. As the glacier above moves and grinds the bedrock, it can release that mercury into the meltwater flowing below it.
After its release from the ice sheet, inorganic mercury can bond with carbon and hydrogen to form methylmercury. Methylmercury is an organic form of mercury and a dangerous neurotoxin. Exposure to organic mercury can result in muscle weakness and cognitive impairment. It can even have more drastic consequences, including organ failure and death.
Once mercury enters an ecosystem, it can work its way up and accumulate in food webs. The further up the food chain we go, the higher the concentrations of mercury become. Mercury can travel from bottom-feeders to large predatory fish to humans and seabirds.
Mercury toxicity in Arctic marine environments poses a severe concern for indigenous communities of the region. The Arctic is both a region that contains lots of melting glaciers and indigenous communities. These communities traditionally depend heavily on fish and marine animals as food sources. Now, along with glaciers melting due to climate change, Arctic communities have to battle the threat of toxicity in their food source.
We cannot change the concentration of mercury in the ice sheet. But we can help slow down climate change. Climate change mitigation will ensure that the Arctic glaciers melt much slower, thereby reducing the amount of mercury it releases. This will, in turn, protect the Arctic’s indigenous people, their food sources and livelihoods, and the region’s ecosystems.