Nearly a millennium of cooling in the Gulf of Maine has been reversed over the past century.
That’s the finding of a new study, published in the journal Communications Earth and Environment, led by Massachusetts-based Woods Hole Oceanographic Institution, co-written by the University of Maine and funded by the National Science Foundation.
Scientists have long warned that the Gulf of Maine is warming faster than most of the world’s oceans — 2021 was yet another year of record warmth — but the lack of long-term records has made it difficult to compare the 20th and 21st centuries to warming or cooling trends for past periods.
The oldest records available come from a station in Boothbay Harbor, where surface water temperatures have been tracked since 1905.
To overcome this absence of historical records, researchers used shells from the ocean quahog clam from the western end of the gulf. The quahog is well-suited as a proxy, because they have a long lifespan and grow their shells in increments year after year, storing isotopes along the way.
For instance, oxygen isotopes from the shells can be used as proxies to measure long-term changes in water temperatures and ocean salinity, while nitrogen isotopes can be used as a proxy for water mass source.
“Combining precisely dated geochemical data from the clam shells with state-of-the-art climate models provides a powerful method for understanding climate change in the Gulf of Maine. We can see how local conditions are influenced by large-scale patterns through time,” said Karl Kreutz, co-author of the study, director of the School of Earth and Climate Sciences and professor in the Climate Change Institute at the University of Maine.
With 300 years worth of data from the clam shells, researchers ran it through a 1,000-year climate model simulation, developed by the National Center for Atmospheric Research. That showed the Gulf of Maine was undergoing a long-term cooling trend over the millennium, mainly as a result of volcanic activity.
But that underwent a “significant reversal” since the late 1800s, and the past 100 years alone warmed faster than any other 100-year period over the millennium.
“The climate changes that ecosystems and coastal communities are now being forced to adapt to are different from what has occurred in the recent past. That’s important to know when developing policies and decision support tools,” Kreutz said.
It underscores the gravity of change happening in the Gulf of Maine, which could have significant consequences for iconic fisheries like the lobster.
A 2018 study from the Gulf of Maine Research Institute projected that the gulf’s lobster population could decline between 40 percent and 62 percent by 2050. Other studies have found declines in the number of baby lobsters, compared with mature lobsters. The zooplankton population in the gulf has fallen as waters warm, and larval-stage lobster rely on zooplankton to fuel their growing and changing bodies.
The warming waters have made the gulf more attractive to invasive species such as the green and blue crabs, which may wreak havoc on local ecosystems and native shellfish, including the lobster.
Any decline in the lobster population could have serious consequences for Maine’s coastal economy. The 2021 catch was valued at a record $730 million, a more than $300 million increase over the year before. It’s the state’s most significant fishery, accounting for 82 percent of the $890 million in catches brought to the dock last year.