A study has unraveled an ocean mystery by linking marine biomarkers to pollution levels. A study led by Dartmouth College used ice cores from Alaska and Greenland to reveal that massive amounts of air pollution from burning fossil fuels have reached the Arctic, having a significant impact on the chemistry of its atmosphere. These results highlight the wide-ranging impact of fossil fuel emissions, while also highlighting the effectiveness of clean air regulations.
According to a report in Nature Geoscience, the polluting effects of the widespread use of fossil fuels in the industrial age on the Arctic are beginning to be felt. The researchers found this footprint in an unexpected place – they measured a decrease in methanesulfonic acid, or MSA, an air byproduct of marine phytoplankton activity captured in ice cores, as air pollution began to intensify.
Phytoplankton are key species in the marine food web and carbon cycle and are considered to be a bellwether of the ocean's response to climate change. Scientists have long cited MSA as an indicator of declining phytoplankton productivity and therefore of marine ecosystems.
But a research team led by Dartmouth University reports that in high-emission environments from fossil fuel combustion, MSA declines dramatically even when phytoplankton populations are stable. Their model showed that these emissions caused the initial molecule produced by phytoplankton, dimethyl sulfide, to turn into sulfate, rather than MSA, leading to a deceptive decline in MSA levels.
The researchers found that the sharp decline in MSA coincided with the beginning of industrialization. When Europe and North America began burning fossil fuels in large quantities in the mid-19th century, MSA in Greenland's ice cores began to decline dramatically. Nearly a century later, around the time of mass industrialization in East Asia, the same biomarker in Alaskan ice cores also began to decline dramatically.
Long-term effects of air pollution
"Our study is a stark example of how air pollution can dramatically alter the chemical composition of the atmosphere thousands of miles away." Jacob Chalif, the study's first author and senior author and associate professor of earth sciences at Dartmouth University, a graduate student in the lab of Erich Osterberg's lab, said: "The pollution emitted in Asia or Europe is not being controlled there. "
"By releasing these pollutants into the world, we are fundamentally changing atmospheric processes," Chariff said. In these remote parts of the Arctic, we see these undeniable human imprints, which show that there is no corner of the planet that we have not touched. "
Researchers in the lab of Erich Osterberg, an associate professor of earth sciences at Dartmouth University, have found that methylsulfonic acid (MSA), an airborne byproduct of marine phytoplankton activity, had remained stable for centuries before a sharp decline in the mid-20th century. They first looked at whether this sharp decline was indicative of a collapse in ocean productivity in the North Pacific, and then found that in an environment where fossil fuel combustion produces large amounts of emissions, methanesulfonic acid can decline dramatically even if marine ecosystems remain stable. Source: Seth Campbell
The new study, which unravels a years-long ocean mystery surrounding the importance of MSA, leads efforts to extract a 700-foot ice core from Denali National Park and Reserve, which researchers used in their analysis, Osterberg said. Osterberg was joined by study co-author Cameron Wake, a professor at the University of New England, and Karl Kreutz and Dartmouth Class of '09 alumnus Dominic Winski '09 — who also received his Ph.D. from Dartmouth University in 2018 — collected the ice core at the University of Maine.
Denali ice cores contain millennia of climate data in the form of bubbles, particulates and compounds trapped in the ice, including MSAs, a common target in ice core analysis. The MSA in the Denali ice core has been fluctuating slightly for centuries, "and it wasn't until the mid-20th century that it underwent a major transformation." Osterberg said.
Researchers at Osterberg's ICE lab began studying the effects of the sharp decline in MSA levels on the North Pacific, initially led by David Polashenski, co-author of the study and a Dartmouth Class of '17 alumnus. Osterberg and the study's co-author, Bess Koffman (a professor at Colby College and a former postdoctoral fellow at Dartmouth), later tested multiple theories to explain the decline in Denali Island's MSA. As with the Greenland study, they first considered whether the decline in MSA was evidence of a collapse in ocean productivity, but nothing came to a conclusion.
When Chariffe took over the project, the study's co-author, Dartmouth College alumnus Ursula · Jongebloed '18 (now a graduate student at the University of Washington), was re-evaluating a 2019 study on Greenland's ice cores, which reported that Greenland's MSA had been steadily declining since the 19th century. The study linked this decline to the collapse of subarctic Atlantic phytoplankton populations due to slowing ocean currents.
But Jongeblod's work led to a study published last year that found that the decline in MSA found in Greenland's ice cores was not the result of the collapse of the marine ecosystem. Instead, they may be caused by contamination that prevents the formation of MSA.
Chaliff and Jongeblod exchanged at a meeting in Switzerland in 2022 and discussed MSA records in Greenland and Denali. "We reconsidered all of our previous assumptions," Chariff said. "We know that the decline in MSA at Denali is not due to ocean productivity, so we know it must have something to do with some kind of change in atmospheric chemistry."
They discussed the possible effects of nitrate pollution, which is often emitted through burning fossil fuels. That evening, Chariff began to delve into the effects of nitrates on MSA.
"Almost every year, when the MSA at Denali Peak drops, nitrates spike. Very similar things are happening in Greenland," Charif said. "At Denali Peak, MSA has been relatively flat for 500 years, with no clear trend. Then in 1962, it dropped dramatically. It's a similar story with nitrate, but in the opposite direction – it basically stays flat for centuries and then rises suddenly. When I saw this, I had an epiphany. ”
Their findings suggest that air pollution from burning fossil fuels spreads to the Atlantic and Pacific oceans and inhibits the production of Arctic MSAs. In addition to ruling out the possibility of widespread marine ecosystem collapse, the findings open a new door to the use of MSA levels to measure air pollution, especially in areas where there are no obvious sources of emissions, the researchers report.
"The collapse of the marine ecosystem doesn't explain the decline in MSA, and these young scientists have figured out what's really going on," Osterberg said. "For me, it's a new way to understand how pollution affects the atmosphere, and the good news is that we're not seeing the collapse of marine ecosystems that we thought we we'd be. The bad news is that air pollution is causing this. ”
Greenland Core data shows that when air pollution in Europe and the United States became more regulated, the local atmosphere began to stabilize. MSA rebounded in the 90s of the 20th century as nitrogen pollution levels declined. This is because nitrogen oxides, the pollutants that affect MSA, dissipate within a few days, while carbon dioxide stays in the atmosphere for centuries.
"This data shows that regulations have a powerful effect on reducing air pollution, and as soon as you turn off the taps, you can see an immediate effect," Osterberg said. "I'm worried that young people will turn a blind eye to the environmental crisis because all they hear is bad news. I think it's important to acknowledge good news when we hear it. Here we see that the regulations are in effect. ”
编译自/SciTechDaily