July 31, 2025 — The Gulf of Maine—home to commercial fisheries for oysters, clams and mussels—has unexpectedly avoided an increase in seawater acidity, helping to preserve the health of its fisheries.
“Contrary to expectation,” a team of scientists wrote in a paper published in the journal Scientific Reports, we … find that pH has increased (+ 0.2 pH units) over the past 40 years, despite concurrent rising atmospheric CO2.” (Determining the decades-long trend required measurements of boron isotopes within annual skeletal bands built by crustose coralline algae. More about that later.)
The Gulf’s acidity levels are unexpected because atmospheric levels of carbon dioxide continue to climb. And because carbon dioxide is absorbed faster and easier into cold water, the frigid waters of the Gulf would be expected to take in more carbon. More carbon in water generally lowers pH and increases acidity.
“One goes down and the other goes up,” said Alan Wanamaker, an Iowa State University professor of earth, atmosphere, and climate and a paper co-author. “That’s what we’ve seen in the open ocean.”