Climate change is causing the deeper waters of Gulf of St. Lawrence and the Scotian Shelf to become warmer and lose oxygen faster than almost anywhere else in the global oceans, according to a new study.
The research, led by the University of Washington’s Mariona Claret, looked at the area south of Newfoundland where the Gulf Stream and Labrador Current interact.
The fact that this is happening is not new, Claret, an oceanographer, said Thursday. But what her study shows is the reason for the decline in oxygen in the depths is because of carbon emissions in the atmosphere.
Extensive data and computer modelling show that as carbon dioxide levels rise, the Gulf Stream current flowing from the southern U.S. moves farther north while the Labrador Current, which tends to churn with oxygenated water due to storms, weakens.
While the Labrador Current can move water from the surface where it picks up oxygen into the depths, the Gulf Stream’s layers have a more stable, stratified nature and do not have that exchange. The top layers closest to the surface are oxygenated but as you look deeper, the oxygen gets used up by biological processes and is not replenished. Warmer water also can’t hold oxygen as well as cooler water.
The Gulf Stream moving north means more of the deep, deoxygenated water is moving into the Gulf of St. Lawrence.
Dalhousie University researcher Katja Fennel — who couldn’t be reached for comment — contributed to the study.
Claret said Fennel’s work on the Scotian Shelf shows the same decline in oxygen.
“We also observed that (waters of the Scotian Shelf) are warming very fast, especially over the last six years,” Claret said.
“(But) we don’t focus on the six years warming. We focus on the 50 years warming in order to say there is a climate trend. <ellipsis> Since 1960, there were oxygen observations both in the Gulf of St. Lawrence and the Scotian Shelf.”
Data contributions came from the Canadian Department of Fisheries and Oceans and the U.S. National Oceanic and Atmospheric Administration’s high-resolution computer model. The model crunched the numbers for nine months, revealing the pattern and projecting it continuing into the future.
“So we used a model to say that this is caused by carbon emissions because the large-scale circulation of the ocean is adjusting to global warming caused by greenhouse gases. So one of the effects of this adjusting of the ocean circulation at the large scale is that the Gulf Stream is moving to the north and this very little change actually is being amplified in the Scotian Shelf waters and the Gulf Stream waters in terms of oxygen because it drives a detectable and large decline in oxygen that we can observe.”
Claret considers deoxygenation in the ocean to be one of the big three threats of climate change.
“That’s why we call this story the canary in the coal mine, meaning that this is an indicator that things can get worse in the near future and right now we (need to take time) to act on these changes.”
The oxygen decline has the potential to affect a variety of species in the Atlantic, including the Atlantic wolffish, cod, snow crab, and Greenland halibut.
The situation has not hit a point of no return, she said. There’s still a chance to maintain current levels by taking actions as nations and individuals to reduce greenhouse gas emissions.
“It’s not like this is the end of the life of the St. Lawrence or the Scotian Shelf, but it is concerning,” Claret said.