A recent study conducted by the marine monitoring service of the European Union reveals that the waters off Nova Scotia are experiencing gradual warming. This warming is attributed to prolonged 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.
According to Li Zhai, a scientist from the Department of Fisheries and Oceans involved in the Copernicus Marine Service’s 2025 Ocean State Report, there has been a noticeable warming trend over the past three decades. Surface waters on the Scotian Shelf have increased by approximately 1.5 degrees, while bottom waters have warmed twice as much, around three degrees.
Zhai emphasized the challenge of obtaining accurate data on below-surface temperatures due to limited observations, contrasting with the abundance of satellite data available for surface temperatures. The report defines a marine heat wave as a period where sea surface temperature surpasses the historical average for at least five consecutive days. In the deeper layers of the Scotian Shelf, the duration of heat wave days has been rising by approximately four days annually.
The study, released on Monday, highlights an additional 120 days of heat waves over 30 years, mainly attributed to climate change. By analyzing data from 1993 to 2023 from the Bedford Institute of Oceanography and utilizing ocean model simulations from Copernicus, Zhai’s team gained insights into the occurrence of marine heat waves across various depths, providing a comprehensive view of these extreme events in the ocean.
While surface temperatures are influenced by seasonal variations in air temperature, wind, and storms, deeper layers are predominantly affected by inflowing warm water from areas like the Scotian Slope and Gulf Stream. This warm water tends to persist longer at depth compared to the surface, contributing to continuous warming.
Conversely, between 2012 and 2023, cold intrusions and spells in the deeper layers of the Scotian Shelf have decreased, resulting in a lack of temperature resetting between heat waves, leading to a continuous warming trend.
Adam Cook, a research scientist from the Department of Fisheries and Oceans, noted that the warming of bottom waters is impacting species dwelling on or near the ocean floor, such as lobster. As lobsters’ activity and food consumption increase with rising water temperatures, there could be short-term benefits like faster growth and increased catches. However, Cook cautioned about potential long-term risks for the industry, citing the decline of lobster stocks in southern New England due to excessive warming.
The report also raises concerns about warmer waters providing an advantage to invasive species, as witnessed in the Mediterranean with the disruption of ecosystems by invasive Atlantic blue crabs and fireworms. Cook warned that similar introductions could occur in Atlantic Canada if water temperatures continue to rise.
Although a 2023 survey by the Department of Fisheries and Oceans suggested a slight cooling of the waters off the Scotian Shelf, Zhai believes this to be a temporary fluctuation amidst a gradual warming trend. She emphasized the variability in temperature fluctuations over the years, underscoring the need to consider long-term trends.
The study underscores the intricate relationship between climate change and marine ecosystems, emphasizing the importance of monitoring and understanding these changes for the conservation of marine biodiversity and sustainable fisheries.