As the Greenland Ice Sheet recedes, Mercury is releasing from the bedrock below

As the Greenland Ice Sheet recedes, Mercury is releasing from the bedrock below

Retreating Greenland Ice Sheet Has become a symbol of the climate crisis. The reason why its retreat poses a threat to the world is well known: as the huge ice sheet melts, sea level rises, and the earth’s albedo declines, the global ocean circulation will be disrupted.This melting can even affect international Gravitational field. Now, May 2021 Learn An article published in the journal Nature warned of a problem that no one had foreseen.

In 2012, Jon Hawkins, the lead author of the paper, attended a conference where he talked with scientists from the United States. Woods Hole Oceanographic Institute About their work on the Greenland Ice Sheet. They said that as part of a series of other tests, they have sampled mercury in the water and they read unusually high levels.

Hawkins is an environmental geochemist who works at Florida State University and the German Geoscience Center in Potsdam. In 2015, when he returned to Greenland for research, he decided to collect more samples and specifically look for mercury.

“Mercury is a trace element, so it is difficult to sample,” Hawkins explained in an interview with GlacierHub. “Even if it exists at toxic levels, its concentration is very low-we are talking about a grain of sand in an Olympic-sized swimming pool.” The results of the new round of sampling are similar to those obtained by his colleagues three years ago. “We cross-referenced our samples with samples collected by Woods Hole scientists earlier, and they are at the same level,” he said. “Very high.”

Views of Nuup Kangerlua (fjord) and icebergs originating from the terminating glacier. Photo by Rupert Perkins.

After the 2015 discovery, Hawkins returned to Greenland in 2018 and sampled two other glaciers. Hawkins said: “Very high levels of mercury have been found in all three glaciers, and the levels of mercury in the downstream fjords are also high.” “This allows us to link the two systems. We are more confident that The mercury content is not an anomaly, nor is it something that only happened on a glacier.”

Mercury is an element that exists naturally on the earth. In its elemental or metallic state, it is liquid at room temperature, so it is often called “mercury”. Historically, it has been used in thermometers and light bulbs. Inorganic mercury is a form of mercury found in non-biological organisms. It has no carbon bonds in its molecular structure and is widely present in nature, usually as part of the mineral cinnabar. Organic mercury mainly exists in living organisms. It contains carbon and hydrogen atoms and mercury. It is also widely present on our planet and is highly toxic.

The natural release of inorganic mercury mainly occurs through rock weathering. However, since industrialization, human activities have begun to dominate the earth’s mercury cycle. Power plants, waste treatment, and manufacturing all release inorganic mercury, which then enters the soil, water, and air.

When inorganic mercury (such as that released by the Greenland ice sheet) circulates in the atmosphere, some of the mercury combines with carbon and hydrogen atoms to form methylmercury, which is a dangerous organic form of neurotoxin. contact Methylmercury can cause cognitive impairment, deterioration of motor skills, and muscle weakness. Exposure to elemental mercury can have more serious consequences, such as organ failure and death.

Birds like this great blue heron can be exposed to methylmercury by ingesting fish that have accumulated methylmercury in their tissues. source: Dklaughman on Flickr

Once methylmercury is introduced into the ecosystem, it will evolve up the marine food chain, from bottom feeders to larger predatory fish, humans, and seabirds.

Researchers need to determine the source of the inorganic mercury they found in their samples. The mercury readings obtained by Hawkins and his team were inconsistent throughout the depth of the ice sheet. The mercury content of surface snow and ice is much lower, which leads scientists to believe that the source of mercury is the bedrock beneath the ice sheet.

Hawkins explained: “All the melt water flows to the subglacial environment where the ice meets the bedrock.” “As it flows along that interface, it interacts with a large amount of sediment and grinds the bedrock.” When the rock is rich in mercury, this weathering of the melt water will release the mercury into the water.

What is the “very high” reading for mercury? “We estimate the flux from southwestern Greenland, and we know that the bedrock geology there is very consistent, about 5-10% of the estimated global fluvial mercury flux,” Hawkins said. “This is indeed a huge number. If you standardize the flux in this area, it is two orders of magnitude higher than other rivers.” The mercury concentration in the measurement area (a catchment area of ​​7,500 square kilometers) is that of other Arctic rivers 130 to 165 times of that.

Meltwater rich in sediment flows over the waterfall from the Levet Glacier in southwest Greenland. Provided by Jon Hawkins.

Even in glaciology, the biogeochemical effects of ice loss are not very clear. This makes it even more critical to contain ice loss as much as possible. Hawkins said: “We will see great changes in the amount of ice and melt water in Greenland, and we can’t do anything about it now.” “We must minimize quality loss.”

Much remains to be seen as to what these findings mean for our future. The mercury deposits at this study site may be higher than the mercury deposits elsewhere in the ice cap bedrock. It is also possible that when the ice melts, the added water will dilute the mercury so that it will not be a long-term problem. Hawkins said: “There are still many questions to answer, but it may be a very high flux, a worryingly high flux, not included in current estimates, and may be sensitive to climate.” “This will Very difficult to manage.”