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The Gulf of St. Lawrence continues to warm. New temperature records were set in 2022. Not only are the surface waters the warmest ever measured, but the upward trend is even faster in the depths of the Gulf.
According to recently compiled data, the water temperature at 300 meters depth, averaged over the entire Gulf of St. Lawrence and for the whole of 2022, was 7.1°C. This is the highest value since records began in 1915.
“Since 2015, the deep waters have been warmer than any year in the previous century. And since 2015, each year has been warmer than the previous one,” explains Peter Galbraith, oceanographer at the Maurice-Lamontagne Institute (Fisheries and Oceans Canada), who presented an annual report on the state of the Gulf to his peers last week. last.
The deep waters of the gulf come from the sea. They travel for a few years in the hollow of the St. Lawrence, rise closer to the surface in the estuary, then flow downstream. Their temperature is closely dependent on the mixing of ocean water masses entering the mouth of the gulf.
However, in recent years, the warm waters of the Gulf Stream, coming from the south, occupy an increasingly large fraction of this mixture, to the detriment of the cold waters of the Labrador Current, coming from the north. And there is no turning back.
“We know that the Gulf will continue to warm because, in the sector of the mouth of the Laurentian Channel, whose waters will flow into the Gulf, we still see warm waters,” explains Mr. Galbraith. No “pocket of cold water” is in sight, he adds.
Between 2009 and 2022, the deep waters of the Gulf have warmed by 1.8°C. “It’s huge,” says the researcher. This warming trend is faster than that observed on the surface, where temperatures vary much more from year to year and depend more directly on the atmosphere.
The fact remains that surface waters also experienced a record year in 2022. For the “non-winter” period, from May to November, these are the warmest recorded since the start of the data series, in 1981. They are 1.6°C warmer than normal. A record was also broken for the month of August.
The storm of the year
The extratropical storm Fiona, which hit the Gulf on September 24, also left its mark on the St. Lawrence. This storm of exceptional intensity — with gusts of up to 125 km/h and waves of 16 meters — vigorously churned up the water in the Gulf.
Result: the surface layer, hot in September, has mixed with the “cold intermediate layer”, which is just below. The upper waters therefore suffered a “big cold snap”, while those below warmed up abnormally, explains Mr. Galbraith. The snow crab, which lives on the seabed, has nowhere to run when such an event occurs.
Storms strong enough to affect oceanographic conditions in the Gulf — such as Fionain 2022, or Dorian, in 2019 — seem to become more frequent, underlines the scientist. “It’s an issue now. We didn’t see that before, it wasn’t on our radar,” he said.
The Gulf of St. Lawrence is therefore warmer than ever. For animal species, this transformation is not trivial. Right whales are increasingly frequenting the Gulf in search of food, while northern shrimp, snow crab and Greenland halibut, among others, do not do well in warmer waters.