A recent investigation into ice cores from Alaska and Greenland has revealed that air pollution from fossil fuel combustion is making its way to the distant Arctic in quantities sufficient to change its basic atmospheric chemistry. Researchers stumbled upon evidence of pollution’s impact through observed declines in a specific airborne byproduct linked to marine phytoplankton, known as methanesulfonic acid (MSA), which dramatically decreased as fossil fuel use expanded during the industrial era. These outcomes highlight the extensive reach of emissions from fossil fuels.
A new study led by Dartmouth involving ice cores from Alaska and Greenland has uncovered that fossil fuel pollution reaches the far-off Arctic in levels significant enough to shift its core atmospheric chemistry. This finding emphasizes the far-reaching effects of fossil fuel emissions and supports the need for clean-air regulations, which have been shown to help reverse these impacts.
According to a report in Nature Geoscience, the influence of pollution in the Arctic began with the extensive use of fossil fuels during the industrial period. Researchers identified this impact through a surprising metric — declines in the airborne byproduct of marine phytoplankton, methanesulfonic acid (MSA), found in the ice cores, which began to decrease as pollution levels increased.
Phytoplankton play a crucial role in oceanic food webs and carbon cycles, making them key indicators of the ocean’s response to climate change. Scientists utilize MSA as a marker for reduced productivity in phytoplankton, implying that the marine ecosystem is facing challenges.
The Dartmouth researchers have found that MSA levels also sharply decrease in high-emission areas due to fossil fuel combustion, even when phytoplankton populations remain steady. Their models suggested that pollution transforms the initial compounds produced by phytoplankton — specifically dimethyl sulfide — into sulfate instead of MSA, leading to misleadingly low MSA readings.
Significant drops in MSA levels were observed to coincide with the onset of industrialization. As Europe and North America ramped up fossil fuel consumption in the mid-1800s, MSA levels began to fall in ice cores from Greenland. Almost a century later, this same biomarker also drastically decreased in Alaskan ice cores, correlating with large-scale industrial growth in East Asia.
“Our research vividly illustrates how air pollution can profoundly modify atmospheric chemistry even thousands of miles away. Pollution released in Asia or Europe is not contained,” stated Jacob Chalif, the study’s lead author and a graduate student collaborating with Erich Osterberg, a Dartmouth earth sciences associate professor.
“By discharging this pollution into the environment, we’re altering atmospheric processes at their core,” Chalif emphasized. “The fact that even the remote Arctic regions show unmistakable signs of human impact indicates that there isn’t a corner of this planet that hasn’t been influenced by us.”
This new research resolves a long-standing mystery regarding the significance of MSA in marine environments, led by Osterberg who gathered a 700-foot ice core from Denali National Park in 2013, used in their analysis along with coauthors from various institutions.
The Denali core holds a millennium’s worth of climate data captured in bubbles, particulates, and compounds embedded in the ice, including MSA. For many centuries, MSA levels fluctuated minimally, “until the mid-20th century when there was a drastic decline,” according to Osterberg.
Researchers in Osterberg’s lab, initially guided by coauthor David Polashenski, began exploring the reasons behind the sharp decline in MSA levels linked to the North Pacific. Osterberg and Bess Koffman, a former Dartmouth postdoctorate and current professor at Colby College, evaluated various hypotheses to explain the reduction of MSA in Denali. They initially considered whether the decline pointed to a drop in marine productivity, but found no correlation, leading to confusion.
Chalif rejoined the project while Jongebloed was reassessing a 2019 study about MSA drops in Greenland ice cores which had linked this trend to decreasing phytoplankton due to slowed ocean currents.
However, Jongebloed’s findings suggested that the changes in MSA levels were not due to an ecosystem collapse, but rather because pollution was preventing the formation of MSA itself.
At a conference in Switzerland, Chalif and Jongebloed exchanged ideas about the MSA data from Greenland and Denali. “We re-evaluated our earlier assumptions,” Chalif shared. “Given the decline in MSA at Denali was not linked to marine productivity, we realized that a shift in atmospheric chemistry must be involved.”
They explored how nitrate pollution, commonly emitted from fossil fuel use, might impact MSA levels. That very evening, Chalif began researching the influence of nitrate on MSA.
“The timing was striking — MSA began to decline at Denali almost exactly as nitrate levels soared. A similar pattern was observed in Greenland,” Chalif noticed. “In Denali, MSA remained stable for 500 years until it sharply dropped in 1962, while nitrate levels rose dramatically after centuries of stability. At that moment, I realized the connection.”
Their findings indicated that fossil fuel emissions spread over the Atlantic and Pacific Oceans, suppressing MSA production in Arctic regions. By eliminating the idea of a major marine ecosystem collapse, the research opens up new potential for using MSA levels as a pollution indicator in the atmosphere, even in places lacking clear emission sources.
“We concluded that the assumed marine collapse didn’t align with the observed MSA lowerings, and these young scientists uncovered the true dynamics,” noted Osterberg.
“This research reshapes our understanding of pollution’s consequences on our atmosphere,” he explained. “On a positive note, it suggests that we aren’t witnessing the marine ecosystem collapse we once feared. On the downside, air pollution is indeed driving this change.”
Data from the Greenland core indicates improvement in the local atmosphere once air pollution from Europe and America was regulated. MSA levels saw an uptick in the 1990s as nitrogen pollution decreased. Nitrogen oxides, which interfere with MSA, dissipate quickly, unlike carbon dioxide that remains in the atmosphere for centuries.
“This data exemplifies the efficacy of regulations to curb air pollution — the effects can be instantaneous once we tighten emissions,” Osterberg stated. “I’m concerned about younger generations feeling defeated by environmental challenges given the pervasive negative narratives. It’s crucial to recognize positive developments. In this case, regulation has shown tangible results.”
