Tag Archives: Meltwater

The Greenland Ice Sheet is leaking mercury — likely natural, but still dangerous

As climate change keeps making our planet hotter and our glaciers melty, scientists report on an unforeseen issue: glacial meltwater from the Greenland Ice Sheet contains high levels of mercury, a toxic heavy metal. According to the report, these levels are comparable to those in rivers where factories dump their waste, creating a major threat to the seafood industry and people who enjoy its products.

Image via Pixabay.

It’s never a dull day with environmental woes. A study that began as an effort to analyze the quality of meltwater from the Greenland ice sheet, and how nutrients therein might support coastal wildlife, ended up uncovering very high levels of mercury in the runoff. The finding raises new questions about how global warming will impact wildlife in the region, one of the foremost exporters of seafood worldwide.

Mermaids, mercury

“There are surprisingly high levels of mercury in the glacier meltwaters we sampled in southwest Greenland,” said Jon Hawkings, a postdoctoral researcher at Florida State University and the German Research Centre for Geosciences. “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.”

Together with glaciologist Jemma Wadham, a professor at the University of Bristol’s Cabot Institute for the Environment, Hawkings initially set out to sample water from three different rivers and two fjords next to the Greenland Ice Sheet. Their aim was to understand how nutrients from glacial meltwater can help to support coastal ecosystems.

Although they also measured for mercury, they didn’t expect to find any meaningful concentrations. Which made the levels of this metal they found in the water all the more surprising.

The baseline for mercury content in rivers is considered to be about 1 to 10 ng / L-1. That’s roughly equivalent to a sand grain of mercury in an Olympic pool of water — so, very low. However, the duo found that mercury levels in the water they sampled were in excess of 150 ng / L-1. Mercury levels in the sediment (called “glacial flour” when it’s produced by glaciers) were over 2000 ng / L-1, which is simply immense.

So far, it remains unclear whether mercury levels drop farther away from this ice sheet, as meltwater gets progressively more diluted. It’s also not yet clear whether the metal is making its way into the marine food web, which would likely make it concentrate further (as animals eat plants and each other).

Although the findings are local, the issue could have global ramifications, as they echo findings in other arctic environments. Greenland is an important producer of seafood, with the export of cold-water shrimp, halibut, and cod being its primary industry. If mercury here does end up in the local food web, it could unknowingly be exported to and consumed by people all over the world.

“We didn’t expect there would be anywhere near that amount of mercury in the glacial water there,” said Associate Professor of Earth, Ocean, and Atmospheric Science Rob Spencer, co-author of the paper. “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.”

“For decades, scientists perceived glaciers as frozen blocks of water that had limited relevance to the Earth’s geochemical and biological processes. 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.”

Roughly 10% of our planet’s dry land is covered in ice, and the results here raise the worrying possibility that they may be seeping mercury into the waters around them. The issue is compounded by the fact that global warming is making these glaciers melt faster, while we still have an imperfect understanding of how the melting process influences the local geochemistry around them.

So far, the team explains that this mercury is most likely coming from a natural source, not from something like fossil fuel use or industrial activity. While this is very relevant for policy-makers, the fact remains that natural mercury is just as toxic as man-made mercury. If it is sourced from natural processes, however, managing its levels in the wild will be much more difficult to do .

“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 said. “But mercury coming from climatically sensitive environments like glaciers could be a source that is much more difficult to manage.”

The paper “Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet” has been published in the journal Nature Geoscience.

One Icelandic glacier-volcano duo is emitting 20 times more methane than all other volcanoes in Europe

Turns out humanity doesn’t have a monopoly on self-destructive behaviors.

Sólheimajökull glacier.

Sólheimajökull glacier, Iceland.
Image credits Chris / Flickr.

One glacier in Iceland is putting out large quantities of methane, a powerful greenhouse gas, a new study reports. The  Sólheimajökull glacier — which flows from the active, ice-covered volcano Katla — generates and releases about 41 tonnes of methane (through meltwater) each day during the summer months. That’s roughly equivalent to the methane produced by 136,000 cows, the team adds.

Melthane

“This is a huge amount of methane lost from the glacial meltwater stream into the atmosphere,” said Dr. Peter Wynn, a glacial biogeochemist from the Lancaster Environment Centre and corresponding author of the study.

“It greatly exceeds average methane loss from non-glacial rivers to the atmosphere reported in the scientific literature. It rivals some of the world’s most methane-producing wetlands; and represents more than twenty times the known methane emissions of all Europe’s other volcanoes put together.”

Methane is a much more powerful greenhouse gas than carbon dioxide (CO2) — 28 times more powerful, to be exact. Knowing exactly how much of it makes its way into the atmosphere thus becomes very important, both from an environmentalist and a legal point of view (for cap-and-trade or similar systems).

Whether or not glaciers release methane has been a matter of some debate. On the one hand, they’re almost perfectly suited for the task: they bring together organic matter, water, and microbes in low-oxygen conditions (all very conducive to methane), capping them all off with a thick layer of ice to trap the gas. On the other hand, nobody had ever checked to make sure. So the team decided to take the matter into their own labs.

They visited the Sólheimajökull glacier in Iceland to retrieve samples from the meltwater lake it forms. The team then measured methane concentrations in the samples and compared them to methane levels in nearby sediments and other rivers, to make sure they weren’t picking up on environmental methane emissions from the surrounding area.

“The highest concentrations were found at the point where the river emerges from underneath the glacier and enters the lake. This demonstrates the methane must be sourced from beneath the glacier,” Dr. Wynn explains.

Subsequent spectrometry analyses revealed that the methane was generated by microbial activity underneath the glacier. However, the volcano also has a part to play here. It doesn’t generate methane directly, but it “is providing the conditions that allow the microbes to thrive and release methane into the surrounding meltwaters,” explains Dr. Wynn.

The thing is that methane really likes oxygen. It likes it so much, in fact, that whenever the two meet they hook up into CO2. What generally happens with glaciers is that oxygen-rich meltwaters seep to the bottom and convert any methane trapped there into CO2. At Sólheimajökull, however, most of the oxygen in this meltwater is neutralized by gases produced by the Katla volcano. The methane remains unaltered, dissolves into the water, and escapes from under the glacier unscathed.

“Understanding the seasonal evolution of Sólheimajökull’s subglacial drainage system and how it interacts with the Katla geothermal area formed part of this work”, said Professor Fiona Tweed, an expert in glacier hydrology at Staffordshire University and co-author of the study.

Heat from Katla also keeps the environment cozy for the microbes living under the glacier and may “greatly accelerate the generation of microbial methane, so in fact you could see Katla as a giant microbial incubator,” adds Dr. Hugh Tuffen, a volcanologist at Lancaster University and co-author on the study.

Such active, ice-bound volcanoes and geothermal systems are abundant in both Iceland and Antarctica. The present paper suggests that these systems can have a meaningful impact on our climate projections. Katla “emits vast amounts of CO2 — it’s in the top five globally in terms of CO2 emissions from volcanoes,” Dr. Tuffen explains.

“If methane produced under these ice caps has a means of escaping as the ice thins, there is the chance we may see short term increases in the release of methane from ice masses into the future,” says lead author Dr. Rebecca Burns.

However, the team says it’s still unclear such processes will play out in the context of climate change. There could be a short-term spike of methane released while glaciers melt and thin out, but the process may be self-limiting in the long-term: without ice, the conditions for methane production are removed.

The paper “Direct isotopic evidence of biogenic methane production and efflux from beneath a temperate glacier” has been published in the journal Scientific Reports.