By Hannah Hickey, UW News

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

A new study led by the University of Washington looks at the causes of this rapid deoxygenation and links it to two of the ocean’s most powerful currents: the Gulf Stream and the Labrador Current. 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 first 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.”

Canada’s fisheries agency has tracked rising salinity and temperature in the St. Lawrence region since 1920. Oxygen has only been monitored 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 said.

Oxygen declines have been seen to affect Atlantic wolffish, Claret said, and 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,” said Claret, who did the work while at Canada’s McGill University.

The research confirms 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.

The new study uses output from NOAA’s Geophysical Fluid Dynamics Laboratory model, a high-resolution computer model that simulates the world’s oceans with a data point every 8 kilometers (5 miles). This simulation took nine months to run using 10,000 computational nodes — huge, even by the standards of global climate models.