Low winds, high freshwater content and high stratification are contributing factors to high sea surface temperature anomalies in Newfoundland and Labrador’s waters and are among the findings in a new scientific report published in the State of the Planet Journal on Sept. 30, 2025.
Dr. Frédéric Cyr, a research scientist with the Marine Institute’s Centre for Fisheries Ecosystem Research, is one of six co-authors of the scientific paper examining marine heat waves (MHW) on the Newfoundland and Labrador shelf during a four-month period in 2023. Dr. Nancy Soontiens, a scientist with Fisheries and Oceans Canada, is the lead author.
Their study found that marine heat wave occurrence coincided with periods of increased stratification. These higher levels of stratification can be attributed to climate change, which caused an abundance of freshwater from ice melt and runoff.
“With continued anthropogenic climate change, it is likely these marine heat waves will continue to be prevalent in regions of the North Atlantic Ocean, including the Newfoundland and Labrador shelf,” said Dr. Cyr in a media release.
The paper’s findings encourage consideration of marine heat waves when exploring ecosystem impacts.
“As marine heat waves sit on the surface of the ocean, they will have the greatest impact on ecosystem elements that are more reliant on stable surface conditions,” added Dr. Cyr.
“Increased understanding and monitoring of marine heat waves will be important for future studies to see the effects they have on ecosystems in different geographic regions and depths.”
Defined as a prolonged period of above-average sea surface temperatures, marine heat waves form when heat is trapped in a thin layer at the surface, unable to spread out over a thicker layer.
Data was collected from the entire shelf as well as from four specific regions within the shelf: the Labrador shelf, the northeast Newfoundland shelf, the Grand Bank and the Flemish Cap.
Analyzing sea surface temperatures from July to October, the researchers found that a series of marine heat waves occurred in each region throughout the timeframe.
“From July through October, MHWs were detected over most of the Northwest Atlantic. Over the N.L. shelf, MHW categories mainly ranged from moderate to severe, with spatial variability in the intensity and duration. No MHWs were present continuously throughout the entire July to October period, but, rather, a series of MHWs transpired in each region. Each MHW period was associated with higher-than-typical stratification, in many cases exceeding the 90th percentile,” reads the scientific paper.
The study was conducted as part of a larger, annual initiative called the Ocean State Report, which provides changes in the ocean over time, with a particular focus on extreme events from 2023 and 2024. Now in its ninth edition, the report is a collaboration between experts from around the world and is published by Copernicus Marine Service.
“Globally, MHWs are occurring more frequently and with greater duration. As such, it is critical to develop a more complete understanding of their drivers which will lead to improved real-time monitoring efforts and forecasting capabilities… the impact of MHWs on the N.L. shelf ecosystem is an important area for future work,” reads the report.
