First published in Landings, September 2023
The headlines were designed to shock: “Marine Heat Records Shattered” “Unprecedented Temperatures at Sea” or, as NASA put it, “The Ocean has a Fever.” Sea surface temperatures throughout the globe hit high marks this summer, particularly in the Northwest Atlantic.
The Gulf of Maine, however, has had a relatively cool summer, which is odd given that the Gulf has been warming at a rate 3.5 times faster than the global average. In an interview with Boston’s WBUR radio station, Dave Reidmiller, director of the climate center at the Gulf of Maine Research Institute (GMRI), succinctly explained the reason. “It was unusually rainy, gray and overcast for much of June and July. This is highly unusual in New England this time of year. And this broader meteorological pattern has basically kept cooler, wetter conditions here,” he said.
From "Enhanced warming of the Northwest Atlantic Ocean under climate change," Vincent Saba.
The damp, cool, overcast and foggy weather that Mainers complained about for most of the summer had the net effect of keeping the Gulf of Maine cooler than it would have been given the overall temperature hike in the Atlantic Ocean this year.
But what effect will the record-breaking heat in the Northwest Atlantic have on the Gulf ecosystem in the future? That depends on how often such heat waves occur, according to GMRI scientist Kathy Mills.
“The Gulf of Maine has been warming for years now . There are short-term marine heat waves that cause short-term effects,” she said. Mills pointed out that in 2012, when Gulf temperatures shot up to record highs during the spring and early summer, longfin squid quickly moved into the Gulf. Researchers think that they may have preyed on the remaining Northern shrimp in the region; other researchers found that squid made up the majority of prey found in the bellies of tuna that season.
The long-term consequences of continued warming in the Gulf of Maine have already been seen in shifts among marine species found here. Northern shrimp have sought cooler waters. Cod populations have shifted to the Gulf’s cooler easterly waters. New species, such as black sea bass and blue crabs, are now found in areas previously too cold for them to survive.
Something similar could take place in the greater Atlantic Ocean. “If there are repeat patterns of short-term heat events in the Northwest Atlantic, then we will see how the impacts play out among species,” Mills said.
The Labrador Current, which travels south from the Arctic Ocean, and the Gulf Stream, which brings warmth north, influence the temperature in the Gulf of Maine. As the Arctic Ocean continues to warm and melt, the Labrador current has become both warmer and weaker. The Gulf Stream, once a sharply contained river of warm water, now has become a broader, more diffuse current. Its warm water spreads into the Gulf of Maine much more than in years past, adding to the Gulf’s temperature change. “These drivers are not going to reverse any time soon,” Mills said.
While the Gulf of Maine has remained relatively cooler this summer than the neighboring Northwest Atlantic due to poor weather, July was still the fourth warmest July on record, according to GMRI data. In addition, the impacts of the developing El Niño weather pattern were not fully in place this summer, noted Mills. “We’re just beginning to see El Niño now, not in the early summer. If it persists through next summer, it could be a major shock.”
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