Passage
As Arctic permafrost thaws, it unleashes a vicious cycle—the unfrozen soil releases its carbon reserves that intensify climate change, in turn accelerating the thaw. Now researchers have reported another disturbing discovery: The permafrost holds a much greater cache of mercury than thought—and as the ground warms, it could potentially release that toxic metal on the world.
In the new study, published in Geophysical Research Letters, an international team of scientists drilled 13 permafrost soil cores at various locations in Alaska. Back at their lab they analysed the frozen cores to measure factors such as moisture, organic carbon and mercury content. The 50-to 100-centimeter cores spanned a time between 22,000 and 2,400 years ago, meaning the vast majority of mercury they hold came from nonhuman sources. The researchers used their measurements to extrapolate an estimate of how much mercury is stored in the entire Northern Hemisphere’s permafrost.
Their results indicate Arctic permafrost holds about 793 gigagrams of mercury—more than 15 million gallons, or the equivalent of about 23 Olympic swimming pools, says Paul Schuster, a research geologist for the U.S. Geological Survey and one of the study authors. When the researchers calculated the amount of mercury likely stored in both the permafrost and the layer of soil that sits above it (and routinely thaws for part of the year), they estimated there is a total of 1,656 gigagrams. “The active layer and the permafrost together contain nearly twice as much [mercury] as all the other soils, the ocean and the atmosphere combined,” the researchers wrote in their study.
Permafrost is frozen soil, rock or sediment that stays at or below freezing for at least two consecutive years. It covers about a quarter of the Northern Hemisphere’s landmass, which helps explain why it holds so much mercury. But permafrost is also unique in that its frozen state traps the mercury in the soil, rather than allowing it to be mobile in the environment. “In [other locations such as] the Lower 48 [U.S. states], soils are hydrologically connected and mercury cycles through. It’s part of the whole global mercury cycle,” Schuster says. “In the Arctic you’re locking in the mercury—it’s not reacting with the rest of the world.”
The new findings have potentially massive implications for ecosystems and human health. Between 30 and 99 percent of the Arctic’s near-surface permafrost is predicted to thaw by 2100, according to the study. As it does so, at least a portion of the previously locked-away mercury will probably become mobile. “It becomes not just an Arctic problem, but a global problem,” says Elsie Sunderland, an associate professor of environmental science and engineering at Harvard University who was not involved in the study. “It doesn’t just stay in the [same] place.”
The mercury could either be washed into the Arctic Ocean and then circulate through the global marine system or escape into the atmosphere and travel to other parts of the planet. Either in the Arctic soil or in the broader environment, mercury can get converted into a form dangerous to humans and other wildlife, including marine animals. “The other half of the story—the one that most people are concerned with—is how does this affect the health of our environment, our aquatic systems, us?” Schuster says. “This has major ramifications.”
Other experts concur: “It really reinforces the [idea] that climate change can make a lot of other environmental issues worse,” says Noelle Selin, an associate professor of data, systems, and society, and atmospheric chemistry at Massachusetts Institute of Technology. Carl Lamborg, an assistant professor of ocean sciences at the University of California, Santa Cruz, agrees it is definitely a concern that humans have potentially “added a whole bunch of mercury into the global mercury cycle.” But he also notes, “it’s a little hard to know exactly what’s going to happen when this permafrost soil thaws. Just because the soil warms, is all of the mercury going to get released? I don’t think we know, but it’s definitely something to be worried about.”
Schuster says this is exactly what experts want to find out now: “The next question is, if it’s going to be released, where is it going to go?”
Question for 100 RCs for Practice Questions- 50
Try yourself:Which of the following best describes what the writer is attempting to do in this passage?
Explanation
Option 1 is incorrect. The writer explains the discovery of large amounts of mercury in the Northern Hemisphere’s permafrost and says that it may get released owing to natural thawing – he calls it a vicious cycle. The writer does not attribute the potential release to man-made climate change. His position is that “climate change can make a lot of other environmental issues worse.” Option 1 which states ‘sooner than expected” and ascribing a direct cause effect relationship between an environmental issue and human activities is not his purpose. Option 2 is incorrect. The option says“hitherto unknown existence” of mercury on the Northern Hemisphere. This distorts the passage and the purpose. The discovery helped the scientist to understand that ‘the permafrost held a much greater cache of mercury that thought.’ Option 3 is incorrect. Option 3 is too general, though it can apply to the passage. The specific nature of the discovery that has massive implications is not specified in the option. Option 4 is correct. It captures the purpose of the writer in brief. He points out that scientists have only recently realized the extent of mercury in the permafrost in the Northern Hemisphere. And that its potential release owing to natural thawing of the permafrost can become a global problem. And, like many other environmental issues this problem can also be aggravated by human made climate change.
Report a problem
Question for 100 RCs for Practice Questions- 50
Try yourself:In the light of the passage, the enormous amount of mercury locked-in in the Arctic permafrost is “something to be worried about” because:
Explanation
The reason for the worry can be briefly explained this way: A recent research estimated the quantity of mercury held sealed by the permafrost to be massive. As permafrost thaws, this mercury can be potentially released into the environment causing harm to humans and animals. The worry mainly springs from the possibility of the thawing of the arctic permafrost.
Option 1 is incorrect. It is a fact that mercury exists in the Arctic. That it can get converted into harmful forms cannot be worrisome only if it is released into the environment. Option 1 does no indicate nay such possibility. Option 2 is correct. As explained in the passage, the thaw of the Arctic will make the mercury so far sealed within the permafrost mobile. Its release into the environment has major ramifications. These ramifications are worrisome. Option 3 is incorrect. t talks about the human contribution to the store of mercury. It cannot answer the question why mercury in the Arctic permafrost is worrisome. Option 4 is incorrect. The routine and periodical thaw of the ‘active layer’ is not advanced as of any major concern in the passage. It is explained as a periodical occurrence and a part of the mercury cycle, hence not worrisome or elated to the mercury locked in by the arctic permafrost.
Report a problem
Question for 100 RCs for Practice Questions- 50
Try yourself:According to the passage, all these are true EXCEPT
Explanation
Option 1 is actually correct. One-fourth of the Northern Hemisphere is Permafrost and this permafrost and the active layer together contain as much mercury as all other sources put together – in effect 1/4th of the Northern Hemisphere holds this mercury. Options 2 and 4 are true according to the passage. Option 2 is stated in the second paragraph. The researchers found that the vast majority of mercury the permafrost holds came from non-human sources. The cores they examined spanned a time between 22000 and 2400 years ago. So Mercury occurring in the active layer and the permafrost is a naturally occurring phenomenon. Option 3 is factually incorrect. Mercury in the permafrost is locked up in the permafrost and not part of the mercury cycle. Paragraph 4 states “… permafrost is also unique in that its frozen state traps the mercury in the soil, rather than allowing it to be mobile in the environment. … In the Arctic you’re locking in the mercury—it’s not reacting with the rest of the world.” Option 4 is factually correct. The fourth paragraph explains this cycle. It is only in the permafrost keeps the mercury locked in. At places other than the Arctic, for example, in the Lower 48 US states, soils are hydrologically connected and mercury cycles through. The passage then states that it is a part of the global phenomenon.
Report a problem
Question for 100 RCs for Practice Questions- 50
Try yourself:Which one of the following, about permafrost, is NOT asserted in the passage?
Explanation
Options 1, 3 and 4 are explicitly stated in the passage. An explanation of what the permafrost is, can be found in the 4th paragraph. The permafrost is frozen soil, rock or sediment that stays at or below freezing for at least two consecutive years. This makes option 1 correct. Option 3 is stated in the same paragraph that it (permafrost) covers about a quarter of the Northern Hemisphere’s landmass. The beginning of paragraph 3 states that Arctic permafrost holds about 793 gigagrams of mercury. This makes option 4 also correct. Option 2 is not correct. The first paragraph states that “As Arctic permafrost thaws, it unleashes a vicious cycle—the unfrozen soil releases its carbon reserves that intensify climate change, in turn accelerating the thaw.” The fourth paragraph states that the mercury in the permafrost does not react with the rest of the world.
Report a problem
Question for 100 RCs for Practice Questions- 50
Try yourself:It can be inferred from the passage that …
Explanation
Option 1 is correct. At the beginning of the passage it is stated that “As Arctic permafrost thaws, it unleashes a vicious cycle—the unfrozen soil releases its carbon reserves that intensify climate change, in turn accelerating the thaw.” Thus the permafrost directly contributes to climate change naturally. Option 2 is incorrect. The passage states that the permafrost is predicted to thaw from 30 to 99 % by 2100 – that makes the first part of the option correct, however, in the second last paragraph, Carl Lamborg of University of California expresses the opinion that it is difficult to know whether all of the mercury will be released because of the thaw. Option 3 is incorrect. The passage does not support the inference that the effects of the thaw of the permafrost is felt already. The research appears to be new and the discovery of enormous amounts of mercury locked-in in the permafrost is recent. The research merely states that its thaw “could potentially release toxic metal on the world.” Option 4 is incorrect. The mercury held locked-in in the permafrost has no role to play in the mercury cycle. The passage explicitly states in the fourth paragraph that it is not reacting with the rest of the world.
Report a problem
