A recent study conducted by the European Union’s marine monitoring service has revealed a gradual increase in temperatures in the waters off Nova Scotia. This warming trend is attributed to longer and more intense marine heat waves and a decrease in cold spells, particularly impacting the waters near the ocean floor and the species inhabiting that environment.
Li Zhai, a scientist from the Department of Fisheries and Oceans and a key contributor to the 2025 Ocean State Report by the Copernicus Marine Service, shared findings showing a consistent warming pattern over the past three decades. Surface waters on the Scotian Shelf have seen an increase of approximately 1.5 degrees Celsius, while bottom waters have warmed twice as much, registering around three degrees Celsius.
Zhai emphasized the challenge of monitoring below-surface temperatures due to limited observations, contrasting with the abundance of satellite data available for surface measurements. The report indicated a rise in the number of marine heat wave days at the bottom of the Scotian Shelf, increasing by an average of four days annually. This translates to an extra 120 days of heat waves over three decades, primarily attributed to climate change.
By analyzing data collected from 1993 to 2023 by the Bedford Institute of Oceanography and utilizing ocean model simulations from Copernicus, Zhai’s team gained insights into the occurrence of marine heat waves at different depths, offering a comprehensive perspective on these extreme events in the ocean.
While surface temperatures are influenced by seasonal variations in air temperature and weather conditions, deeper layers are more impacted by external water flows, particularly warm intrusions from the Scotian Slope and Gulf Stream. This warm water, once reaching lower depths, tends to persist longer compared to surface levels.
Conversely, cold intrusions and spells in deeper layers of the Scotian Shelf have become less frequent from 2012 to 2023. The lack of temperature resets between heat waves results in a continuous warming trend in the waters.
Adam Cook, a research scientist at DFO specializing in lobster stock assessment, noted the effects of warming bottom waters on species like lobsters, which respond to increasing water temperatures by becoming more active and requiring more food. While this may lead to short-term benefits such as faster growth and increased catches, Cook cautioned about potential long-term risks for the industry, citing examples from southern New England where similar temperature shifts led to declines in lobster populations.
The report also highlighted the potential threat posed by warmer waters favoring the proliferation of invasive species. Instances in the Mediterranean involving invasive Atlantic blue crabs and fireworms disrupting ecosystems and fisheries serve as a warning for Atlantic Canada if temperatures continue to rise.
Although a 2023 survey indicated a slight cooling of the Scotian Shelf waters, Zhai suggested this was likely a temporary fluctuation rather than a reversal of the warming trend, emphasizing the gradual nature of temperature changes over time. She underscored the importance of considering annual fluctuations in temperature trends.
In conclusion, the study underscores the significant impact of climate change on the marine environment off Nova Scotia, with implications for biodiversity, ecosystem dynamics, and fisheries management.
