Why The Gulf of St. Lawrence is Losing Oxygen

A new study links rapid deoxygenation in the Gulf of St. Lawrence to two powerful currents: the Gulf Stream and the Labrador Current.

The broad, biologically rich waterway in Eastern Canada which drains North America’s Great Lakes and is popular with fishing boats, whales, and tourists has lost oxygen faster than almost anywhere else in the global oceans.

The paper, which appears 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,” says first author Mariona Claret, a research associate at the University of Washington’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.”

NEAR HYPOXIA

Canada’s fisheries agency has tracked rising salinity and temperature in the St. Lawrence region since 1920. They’ve only monitored oxygen since 1960, and the declining trend is causing concern.

“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,” Claret says.

Oxygen declines have been seen to affect Atlantic wolffish, Claret says, and also threaten Atlantic cod, snow crabs, and Greenland halibut that all live in the depths.

“The oxygen decline in this region was already reported, but what was not explored before was the underlying cause,” says Claret, who did the work while at McGill University.

The findings confirm a recent study showing that, as carbon dioxide levels rose over the past century due to human emissions, the Gulf Stream has shifted northward and the Labrador Current has weakened. The new paper finds that this causes more of the Gulf Stream’s warm, salty, and oxygen-poor water to enter the St. Lawrence Seaway.

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