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A Dartmouth-led study on ice cores from Alaska and Greenland found that air pollution from the burning of fossil fuels reaches the remote Arctic in amounts large enough to alter its fundamental atmospheric chemistry. The findings illustrate the long reach of fossil fuel emissions and provide support for the importance of clean-air rules, which the team found can reverse the effect.<\/p>\n\n\n\n
The impact of pollution on the Arctic began as soon as widespread fossil fuel usage took hold during the industrial era, the researchers report in Nature Geoscience<\/a>. The researchers detected this footprint in an unexpected place\u2014they measured declines in an airborne byproduct of marine phytoplankton activity known as methanesulfonic acid, or MSA, captured in the ice cores when air pollution began to rise.<\/p>\n\n\n\n Phytoplankton are key species in ocean food webs and carbon cycles considered a bellwether of the ocean\u2019s response to climate change. MSA has been used by scientists as an indicator of reduced phytoplankton productivity and, thus, of an ocean ecosystem in distress. <\/p>\n\n\n\n But the Dartmouth-led team reports that MSA also plummets in environments high in emissions generated by burning fossil fuels, even if phytoplankton numbers are stable. Their models showed that these emissions cause the initial molecule that phytoplankton produce\u2014dimethyl sulfide\u2014to turn into sulfate instead of MSA, leading to a deceptive drop in MSA levels.<\/p>\n\n\n\n The researchers found precipitous drops in MSA that coincided with the start of industrialization. When Europe and North America began burning large amounts of fossil fuels in the mid-1800s, MSA began to plummet in Greenland ice cores. Then, nearly a century later, the same biomarker plummeted in ice cores from Alaska around the time when East Asia underwent large-scale industrialization.<\/p>\n\n\n\n \u201cOur study is a stark example of how air pollution can substantially alter atmospheric chemistry thousands of miles away. The pollution emitted in Asia or Europe was not contained there,\u201d says Jacob Chalif \u201921, first author of the study and a Guarini School of Graduate and Advanced Studies<\/a> student in the lab of senior author Erich Osterberg<\/a>, an associate professor of earth sciences<\/a>.<\/p>\n\n\n\n \u201cBy releasing all this pollution into the world, we\u2019re fundamentally altering atmospheric processes,\u201d Chalif says. \u201cThe fact that these remote areas of the Arctic see these undeniable human imprints shows that there\u2019s literally no corner of this planet we haven\u2019t touched.\u201d<\/p>\n\n\n Professor Erich Osterberg, left, and Guarini student Jacob Chalif \u201921.<\/em>\u00a0<\/p>\n\n\n\n The new study solves a yearslong marine mystery surrounding the significance of MSA, says Osterberg, who led the extraction of a 700-foot ice core from Denali National Park and Preserve that the researchers used in their analysis. Osterberg collected the core in 2013<\/a> with study co-authors and professors Cameron Wake, at the University of New England, and Karl Kreutz and Dominic Winski \u201909, Guarini \u201918, at the University of Maine.<\/p>\n\n\n\n The Denali core contains a millennium of climate data in the form of gas bubbles, particulates, and compounds trapped in the ice, including MSA, which is a common target in ice-core analysis. For centuries, MSA in the Denali core underwent minor fluctuations, \u201cuntil the mid-20th century when it falls off a table,\u201d Osterberg says.<\/p>\n\n\n\n Researchers in Osterberg\u2019s ICE Lab<\/a>, initially led by study coauthor David Polashenski \u201917, started investigating what the precipitous drop in MSA levels indicated about the North Pacific. Osterberg and study coauthor Bess Koffman, a professor at Colby College who was a postdoctoral fellow at Dartmouth, later tested numerous theories to explain why Denali MSA declined. Like the Greenland study, they first considered whether the MSA drop was evidence for a crash in marine productivity, \u201cbut nothing added up,\u201d Osterberg says. \u201cIt was a mystery.\u201d<\/p>\n\n\n\n Chalif picked up the project around the time when study coauthor Ursula Jongebloed \u201918, now a graduate student at the University of Washington, was re-evaluating a 2019 study<\/a> on ice cores in Greenland reporting that MSA there underwent a steady drop beginning in the 1800s. That study tied the decline to a crash in phytoplankton populations in the subarctic Atlantic due to a slowdown in ocean currents.<\/p>\n\n\n\n![\"Erich](\"https:\/\/home.dartmouth.edu\/sites\/home\/files\/styles\/max_width_720px\/public\/2024-09\/jacob-osterberg-diptych.jpg?itok=nISqouBx\")
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