A recent study conducted by the European Union’s marine monitoring service has revealed a gradual increase in water temperature off the coast of Nova Scotia. This rise in temperature has led to longer and more intense marine heat waves while reducing the occurrence of cold spells, particularly impacting the waters near the ocean floor and the species residing there.
According to Li Zhai, a scientist from the Department of Fisheries and Oceans who played a key role in the Copernicus Marine Service’s 2025 Ocean State Report, the team observed a warming trend spanning the past three decades. Surface waters on the Scotian Shelf have experienced an increase of approximately 1.5 degrees, with bottom waters warming at twice that rate, around three degrees.
Zhai noted the challenge of obtaining below-surface temperature data due to limited observations, unlike the abundance of satellite data for surface temperatures. The report defines a marine heat wave as occurring when the sea surface temperature remains above the historical average for a minimum of five consecutive days. In the case of the Scotian Shelf’s ocean floor, the report indicates a rise of about four heat wave days per year over the years, totaling an extra 120 days of heat waves primarily attributed to climate change.
Utilizing data spanning from 1993 to 2023 from the Bedford Institute of Oceanography, in conjunction with ocean model simulations by Copernicus, Zhai’s team managed to track marine heat waves across various depths, offering a comprehensive view of these extreme events in the ocean.
While the surface is directly impacted by seasonal air temperature variations and weather patterns, the deeper layers are heavily influenced by incoming water movements, particularly warm intrusions from the Scotian Slope and Gulf Stream. The prolonged presence of warm water at depth contrasts with the surface’s more transient exposure.
Conversely, between 2012 and 2023, the occurrence of cold intrusions and spells in the deeper layers of the Scotian Shelf has decreased. As a result, temperatures are not reverting back to normal levels between heat waves, leading to a continuous warming trend in the waters.
In a related development, Adam Cook, a DFO research scientist specializing in lobster stock assessments, pointed out that the warming of bottom waters is already impacting species residing near the ocean floor, such as lobsters. Due to their body temperature rising with the water temperature, lobsters exhibit increased activity and appetite in warmer waters, potentially resulting in accelerated growth and higher catches. However, Cook cautioned that prolonged warming could pose risks to the industry, citing the decline of lobster stocks in southern New England due to surpassing the species’ temperature tolerance threshold.
The report also underscores the threat posed by warmer waters favoring invasive species, akin to the situation in the Mediterranean where Atlantic blue crabs and fireworms have disrupted ecosystems and fisheries. Cook warned of a similar scenario in Atlantic Canada if water temperatures continue to rise.
While a DFO survey in 2023 indicated a slight cooling of the waters off the Scotian Shelf, Zhai attributed this to short-term fluctuations rather than a reversal of the overall warming trend. She emphasized the need to consider yearly temperature variations and the gradual nature of temperature changes.
In summary, the findings of the report shed light on the significant impact of warming waters off Nova Scotia, emphasizing the need for continued monitoring and proactive measures to address the evolving marine environment in the region.
