A recent study conducted by the marine monitoring service of the European Union 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 affecting the waters near the ocean floor and the species inhabiting that environment.
Leading the research team, Li Zhai from the Department of Fisheries and Oceans emphasized the rising trend observed over the past three decades. Surface waters on the Scotian Shelf have warmed by approximately 1.5 degrees, while bottom waters have experienced a more significant increase of around three degrees. Zhai highlighted the challenge of limited observations below the surface, making it harder to monitor temperature changes accurately.
The report defines a marine heat wave as a period when the sea surface temperature remains above the historical average for at least five consecutive days. In the depths of the Scotian Shelf, the number of heat wave days has been increasing by about four days annually. Zhai attributed this change to climate change, resulting in an additional 120 days of heat waves over three decades.
Utilizing data from the Bedford Institute of Oceanography spanning from 1993 to 2023 and ocean model simulations by Copernicus, the research team analyzed marine heat waves across various depths. This comprehensive approach provided a multidimensional perspective on extreme oceanic events.
While surface temperatures are influenced by seasonal variations in air temperature and weather patterns, deeper layers are significantly impacted by warm water intrusions from the Scotian Slope and Gulf Stream. The persistence of warm water at depth contributes to the continuous warming of the waters, with cold intrusions becoming less frequent in recent years.
Adam Cook, a DFO research scientist, highlighted the effects of warming bottom waters on marine species, especially lobsters. As water temperatures increase, lobsters become more active and require more food, potentially leading to faster growth and increased catches. However, Cook warned of potential long-term risks for the industry, citing the decline of lobster stocks in southern New England due to rising temperatures.
Additionally, the report raised concerns about the advantage warmer waters provide to invasive species. In regions like the Mediterranean, invasive species such as Atlantic blue crabs and fireworms have disrupted ecosystems and fisheries. Cook cautioned that similar introductions could occur in Atlantic Canada if water temperatures continue to rise.
While a recent cooling trend was observed in 2023 off the Scotian Shelf, Zhai noted that this was likely a temporary fluctuation rather than a significant shift. She emphasized the gradual nature of temperature changes, highlighting the variability that occurs from year to year.
In conclusion, the study underscores the ongoing impact of climate change on marine ecosystems off Nova Scotia, emphasizing the need for continued monitoring and adaptive management strategies to mitigate potential risks.