Deep water temperatures hit 'scary' highs in Gulf of St. Lawrence

A decade-long warming trend in the Gulf of St. Lawrence continued in 2020 with deep waters reaching record highs, according to ocean climate data released Tuesday by the Department of Fisheries and Oceans.

Water temperatures at depths of 200, 250 and 300 metres were higher than any measured in the Gulf since records started in 1915, hitting highs of 5.7 C, 6.6 C and 6.8 C.

All were well above the normal variations.

"It is scary to me because we're completely outside of the known envelope," Peter Galbraith, a longtime federal research scientist, said in an interview.

"When you are one degree, a half a degree outside anything that's been known before those 100 years, then that's like uncharted territory for fisheries management."

No record of this before

The report on physical oceanographic conditions also said temperatures last year were notably warmer in deep water at the entrance to the Gulf in the Laurentian Channel and the Cabot Strait between Nova Scotia and Newfoundland.

Gauging the effects on marine life is a key task, but there's nothing to compare it to in the record, said Galbraith.

"A whole lot of species will be affected. The scary part is that we can't rely on past observations that would be similar to guess at what the ecosystem is responding because it was never similar," Galbraith said from DFO's Maurice Lamontagne Institute in Mont-Joli, Que.

"The bottom temperature of the Gulf has increased by about a degree and a half, which might not seem a whole lot. But for biological species that are used to really, really stable temperatures, increasing from 5.2 to 6.7 is a big deal."

Wild surface-temperature swing 

The inland portion of the Gulf in Quebec, known as the Estuary, recorded the highest surface temperatures in July since those records started in 1982.

By September, surface temperatures hit record lows after strong winds whipped up ocean waters.

"We lost 3.7 degrees in one week basically," said Galbraith. "The warmest week in nearly 40 years of observations to the coldest September in 40 years."

He said January 2021 has already seen its own anomaly — no sea ice in the Gulf.

A recent cold snap was not enough to produce ice because most of the water is above 1 degree.

"Outside of coastal ice, there's really nothing, anything offshore," said Galbraith.

Gulf could stay warm for years

He said the warmer deep water, which is slowly sucked into the Gulf from the Atlantic, will likely keep the Gulf warm for years.

An unusually cold year could provide a reprieve, but it has not materialized in the past decade.

Two currents supply the deep water that flows into the Gulf: the cold Labrador Current from the north and the Gulf Stream from the south.

Scientists are trying to understand what is happening with those currents and what warmer water means in the near term.

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