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article imageNew study: Gulf of St. Lawrence shows a dramatic oxygen decline

By Karen Graham     Sep 18, 2018 in Science
The Gulf of St. Lawrence has warmed and lost oxygen faster than almost anywhere else in the global oceans due to large-scale climate change, raising the possibility the Gulf could soon be unable to support marine life, according to a new study.
The Gulf of Saint Lawrence is a broad, biologically rich waterway in Eastern Canada that drains the North American Great Lakes via the Saint Lawrence River into the Atlantic Ocean. The gulf is a semi-enclosed sea, covering an area of about 226,000 square kilometers (87,000 square miles), with an average depth of 152 meters (499 feet).
A study led by University of Washington researchers looked at the causes behind the warming and the rapid deoxygenation of the Gulf - which the scientists say has been happening since at least 1960 - and linked it to two of the ocean's most powerful currents: the Gulf Stream and the Labrador Current, reports CTV News.
The Gulf Stream and Labrador Current both split near the Laurentian Channel  a deep channel within t...
The Gulf Stream and Labrador Current both split near the Laurentian Channel, a deep channel within the Gulf of St. Lawrence fed by both currents. The Gulf Stream in turn is sensitive to changes in the Atlantic Meridional Overturning Circulation.
Mariona Claret/University of Washington
The study, published Sept. 17 in Nature Climate Change, explains how large-scale climate change already is causing oxygen levels to drop in the deeper parts of this waterway.
"The area south of Newfoundland is one of the best-sampled regions in the ocean," said lead author Mariona Claret, a research associate at the UW's Joint Institute for the Study of the Atmosphere and Ocean. "It's also a very interesting area because it's at the crossroads where two big, larger-scale currents interact."
Fisheries and Oceans Canada has tracked rising salinity and temperature in the Gulf since the 1920s and started tracking oxygen levels in the 1960s, said Claret.
“This is very concerning,” she said. “The effects right now are kind of mild, but in the near future, it can get worse. Observations in the very inner Gulf of St. Lawrence show a dramatic oxygen decline, which is reaching hypoxic conditions, meaning it can't fully support marine life."
The computer model is detailed enough to resolve eddies that are important for ocean circulation. Th...
The computer model is detailed enough to resolve eddies that are important for ocean circulation. The triangle-shaped island of Newfoundland, center, is at the eastern edge of the study area, the mouth of the Gulf of St. Lawrence. This graphic shows oxygen at the surface, where red shows more oxygen.
Mariona Claret/University of Washington
The Labrador Current and the Gulf Stream
The Labrador Current is a cold current in the North Atlantic Ocean which flows from the Arctic Ocean south along the coast of Labrador and passes around Newfoundland, continuing south along the east coast of Nova Scotia.
The Gulf Stream, together with its northern extension the North Atlantic Drift, is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and stretches to the tip of Florida and follows the eastern coastlines of the U.S. and Newfoundland before crossing the Atlantic Ocean.
The study found hydrographic evidence that shows a Labrador Current retreat is playing a key role in the deoxygenation on the northwest Atlantic shelf, creating a decline of saturation oxygen concentrations in the region.
Bonaventure Island (officially in French: île Bonaventure) is a Canadian island in the Gulf of St. ...
Bonaventure Island (officially in French: île Bonaventure) is a Canadian island in the Gulf of St. Lawrence located 3.5 kilometres (2.2 mi) off the southern coast of Quebec's Gaspé Peninsula.
Michel Rathwell from Cornwall, Canada
In other words, the Gulf Stream has shifted northward and the Labrador Current has weakened. This shift allows more of the salty and oxygen-poor water from the Gulf Stream to enter the St. Lawrence Seaway. Gulf Stream water is replacing Labrador Sea water in the deeper parts of the St. Lawrence Gulf.
And this shift to less oxygenated and warmer water deep in the Gulf of St. Lawrence will impact Canadian fisheries. According to a study by the Departement d'Oceanographie, Universite du Quebec, and the Science Branch, Gulf Region, Department of Fisheries and Oceans, The Gulf of St. Lawrence provides about 40 percent of Canada's marine fish catch.
The shallower areas of the Gulf are among the world's best grounds for lobsters, Atlantic herring, Atlantic cod, shellfish, and Irish moss. And here is what is so sad about what's happening now. This study was published in 1988, and even then, the authors talked about climatic change on the one hand and human-induced interferences such as physical modification, pollution, and over-harvesting on the other hand as being major sources of stress in the Gulf.
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