What is it about?

Marine phytoplankton are the base of ocean ecosystems. Decreasing methanesulfonic acid (MSA) concentrations across Greenland ice cores have suggested declining North Atlantic phytoplankton abundance, with implications for ocean ecosystems and climate. MSA is used to infer phytoplankton abundance because phytoplankton emits dimethyl sulfide (DMS), which is oxidized to MSA and sulfate. However, atmospheric chemistry controls how much DMS is converted to MSA vs. sulfate. Here, we measure DMS-derived sulfate compared to MSA in a Greenland ice core over the industrial era. We show that total biogenic sulfur, the sum of MSA and DMS-derived sulfate, is relatively steady over the industrial era, but MSA declines because anthropogenic pollution affects the ratio of MSA vs. DMS-derived sulfate. Therefore, interpreting MSA as a proxy for DMS emissions must consider atmospheric chemistry.

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Why is it important?

Phytoplankton are the base of the ocean food web. If phytoplankton abundance decreases, animals that eat phytoplankton (and animals that eat animals that eat phytoplankton) will have less food to eat. This could affect many creatures living in the ocean and human populations that rely on fishing for sustenance. Finally, phytoplankton consume carbon dioxide through photosynthesis, similarly to trees on land. If primary productivity decreases, this could have implications for our “carbon budget.” A previous study suggested phytoplankton populations in the North Atlantic were declining. Our study shows that the data used to conclude phytoplankton were declining was affected by atmospheric chemistry. When we measured total sulfur from phytoplankton in an ice core, we found that there is no decline over the industrial era.


I have enjoyed people reacting to this article as a piece of "good news." I was surprised by the results and I am hopeful that marine phytoplankton in the North Atlantic may not be declining. More research on atmospheric chemistry can help us understand why the ratio of MSA to DMS-derived sulfate changed over the industrial era.

Ursula Jongebloed
University of Washington

Read the Original

This page is a summary of: Industrial-era decline in Arctic methanesulfonic acid is offset by increased biogenic sulfate aerosol, Proceedings of the National Academy of Sciences, November 2023, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2307587120.
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