Ice core study evidence casts more doubt on chances of weakening of the Atlantic meridional overturning circulation 

Barents Sea phytoplankton bloom [credit: NASA]

” data-image-caption=”" data-medium-file=”https://tallbloke.wordpress.com/wp-content/uploads/2021/02/barents-sea-phytoplankton-bloom-on-july-26-2020-modis-nasa.jpg?w=300″ data-large-file=”https://tallbloke.wordpress.com/wp-content/uploads/2021/02/barents-sea-phytoplankton-bloom-on-july-26-2020-modis-nasa.jpg?w=500″ tabindex=”0″ role=”button” src=”https://tallbloke.wordpress.com/wp-content/uploads/2021/02/barents-sea-phytoplankton-bloom-on-july-26-2020-modis-nasa.jpg” alt=”" width=”500″ height=”487″ class=”aligncenter size-full wp-image-52224″ />
The study abstract opens by questioning a popular ocean alarm idea: ‘An industrial-era decline in Greenland ice-core methanesulfonic acid [MSA] is thought to herald a collapse in North Atlantic marine phytoplankton stocks related to a weakening of the Atlantic meridional overturning circulation [AMOC]. By contrast, stable levels of total marine biogenic sulfur contradict this interpretation and point to changes in atmospheric oxidation as a potential cause of the methanesulfonic acid decline.’ So it turns out that distant industrial pollution was the prime reason for unexpected declines in a naturally-produced acid normally found in the Arctic atmosphere, rather than a problem with ocean dynamics leading to a decline in phytoplankton stocks. Another setback for climate alarmist theorisers, following the recent discovery by researchers of an AMOC-related 40% observation error (see Talkshop post here). Since 1990 tighter regulation has led to lower levels of Arctic pollution and an ongoing recovery of the MSA levels.
– – –
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, says Phys.org.

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.

The impact of pollution on the Arctic began as soon as widespread fossil fuel usage took hold during the industrial era, according to a report in Nature Geoscience.

The researchers detected this footprint in an unexpected place—they 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.

Phytoplankton are key species in ocean food webs and carbon cycles are considered a bellwether of the ocean’s 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.

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—dimethyl sulfide—to turn into sulfate instead of MSA, leading to a deceptive drop in MSA levels.

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.
. . .
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, “until the mid-20th century when it falls off a table,” Osterberg says.

Researchers in Osterberg’s ICE Lab, initially led by study co-author and Dartmouth alumnus David Polashenski ’17, started investigating what the precipitous drop in MSA levels indicated about the North Pacific. Osterberg and study co-author 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, “but nothing added up,” Osterberg says. “It was a mystery.”

Chalif picked up the project around the time when study co-author and Dartmouth alumna Ursula Jongebloed ’18, now a graduate student at the University of Washington, was re-evaluating a 2019 study 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.

But Jongebloed’s work led to a study published last year reporting that declines in MSA found in the Greenland ice cores are not the result of the marine ecosystem crashing. Instead, they could be caused by pollution preventing the creation of MSA in the first place.
. . .
“Pretty much to the year, when MSA declines at Denali, nitrate skyrockets. A very similar thing happened in Greenland,” Chalif says. “At Denali, MSA is relatively flat for 500 years, no notable trend. Then in 1962, it plummets. Nitrate was similar, but in the opposite direction—it’s basically flat for centuries then it spikes upward. When I saw that, I had a eureka moment.”

Their results showed that air pollution from the burning of fossil fuels disperses across the Atlantic and Pacific Oceans and inhibits the production of MSA in the Arctic. In addition to ruling out widespread marine ecosystem collapse, the findings open a new door to using MSA levels to measure pollution in the atmosphere, especially in regions with no obvious emissions sources, the researchers report.

“Marine ecosystem collapse just wasn’t working as an explanation for these MSA declines, and these young scientists figured out what was really going on,” Osterberg says.

Full article here.
– – –
Image: Barents Sea phytoplankton bloom [credit: NASA]

Study abstract: Pollution drives multidecadal decline in subarctic methanesulfonic acid

Source: https://tallbloke.wordpress.com/2024/09/26/ice-core-study-evidence-casts-more-doubt-on-chances-of-weakening-of-the-atlantic-meridional-overturning-circulation/