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2021 Water Temperatures Break Records in Gulf of Maine, Gulf of St. Lawrence

Temperature records were set in two bodies of water last year, one in Canada and one in the United States. The Gulf of Maine experienced its warmest fall temperatures since records for sea surface temperatures began in 1982. Summer temperatures were the second warmest on record. In Canada, the Gulf of St. Lawrence saw its highest sea surface temperatures since records began 40 years ago during October and November. Temperatures at depth were the highest since data collection began in 1915.

“The Gulf of Maine was really warm throughout the year,” said Kathy Mills, director of the Integrated Systems Ecology Lab at the Gulf of Maine Research Institute (GMRI) in Portland. “A marine heat wave is when the water temperature is above the 90th percentile. Most of 2021 was like that. There were only a few days below.”

Oceanographers point to 2010 as the year in which the Gulf of Maine experienced a “regime shift,” moving from one state to another. Others look at 2012, a year in which the Gulf experienced record-breaking warmth early in the spring, as the key year. Most agree that during the past ten years the Gulf has undergone a rapid increase in average temperature, both at the surface and at depth, as well as changes in its circulation and food chain. “Indicators show a series of inter-related changes in the Gulf, changes in temperature, circulation, stratification of the water column. These lead to changes in composition of zooplankton and phytoplankton,” Mills said.

Lobstermen have come to recognize the name Calanus finmarchicus in recent years. C. finmarchicus is a tiny rice-shaped copepod that is the preferred food of the North Atlantic right whale, which eat the copepods in great mouthfuls. C. finmarchicus is a cold-water creature and exists at the southern extent of its natural range in the Gulf of Maine. As the Gulf has warmed, the right whales have found it hard to find the dense blooms of C. finmarchicus they desire and have journeyed further north, into the Gulf of St. Lawrence, in search of them.

The Gulf of Maine (left) and the Gulf of St. Lawrence (right) are both experiencing unprecedented warm temperatures. What impact will that have on key marine species? Images courtesy of NOAA, DFO, respectively.

But other creatures eat the fat-packed C. finmarchicus as well, including herring and, as recent studies have shown, larval lobsters. “The Gulf of Maine ecosystem has been driven by the energy from Calanus finmarchicus and that is really changing now,” Mills said.

Warmer temperatures have had a beneficial effect on Gulf of Maine lobsters but how long that benefit will remain is subject to question. While warmer water increases the rate of growth among lobsters, Mills points out that it comes at a cost to an individual lobster. “Warmer temperatures increase metabolism. The lobster burns more energy and needs more energy. It needs to find more food to supply that demand,” she explained.

In addition, when water temperatures grow too high, the lobster suffers stress. Research shows that lobsters prefer water temperatures at 16oC. or less; 18o C. is their upper limit. “The Gulf of Maine were hitting and exceeding 16oC. in 2021,” Mill said. “Now and moving forward there will be thermally stressed periods for longer each year. The long-range projections through mid-century are for declining productivity in the Gulf of Maine lobster population. We need to be prepared for changes in the ecosystem and act to buffer those effects.”

The Gulf will continue to warm even as the world’s nations attempt to reign in production of greenhouse gases. “It’s like a moving train, it can’t stop on a dime,” Mills said. “It’s important to adopt a management system that can detect change when it happens so that we don’t need sudden course corrections. We can’t assume the same productivity as in the past.”

The Gulf of St. Lawrence set records in 2021 as well, according to data released by the Canadian Department of Fisheries and Oceans (DFO) in February.

“Everything about the Gulf of St. Lawrence was warmer in 2021,” said federal research scientist Peter Galbraith, in an interview the CBC. Average sea surface temperatures in October and November were the highest since remote sensing started 40 years ago. Temperatures at depth followed the same pattern. Galbraith and fellow DFO researchers recorded temperatures of 4.1o C. (39o F.) at 150 meters, 6o C. (43o F.) at 200 meters, 6.7o C. (44 oF.) at 250 meters and 6.9o C. (44.5o F.) at 300 meters. Those were the highest readings since data collection began in 1915.

An intermediate water layer from 50 to 150 meters, which usually remains cold in summer, was also the warmest in the 40-year record. Most significant, according to Galbraith, was the warming trend in deeper water, between 150 and 300 meters.

Gulf of Maine sea surface temperature graph over time. GMRI image.

“2015, 2016 was the first year where it was higher than any year prior and every year since we’ve beaten that last year’s record. So we’re at really 100-plus year record highs,” Galbraith said. Warming in the deeper water in the gulf has outpaced projections based on climate change.

“Our surface warming that we’ve observed falls in line with global warming of about one degree per 100 years,” he said. “But in the deep layers, it’s been one-and-a-half degrees in 12 years.” The last year with below-normal temperatures at 300 meters depth was in 2009. Since then, they have risen steadily.

Such dramatic changes in temperature will have a future effect on the marine species that live in the Gulf of St. Lawrence, just as they have in the Gulf of Maine.

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