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, coupled with a decrease in cold spells, particularly impacting the waters near the ocean floor and the marine life dwelling there.
Li Zhai, a scientist from the Department of Fisheries and Oceans and a key contributor to the Copernicus Marine Service’s 2025 Ocean State Report, highlighted a significant rise in temperatures 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 substantial increase of about three degrees. Zhai emphasized the challenges in obtaining accurate temperature data below the surface due to limited observations.
The report defines a marine heat wave as a period when the sea surface temperature exceeds the historical average for at least five consecutive days. According to the study, the number of heat wave days at the bottom of the Scotian Shelf has been escalating by approximately four days annually. Zhai noted that over a span of 30 years, this equates to an extra 120 days of heat waves primarily driven by climate change.
Utilizing data spanning from 1993 to 2023 from the Bedford Institute of Oceanography and ocean model simulations by Copernicus, Zhai’s team analyzed marine heat waves across various depths, providing a comprehensive understanding of these extreme events in the ocean.
While surface temperatures are influenced by seasonal variations in air temperature, winds, and storms, deeper layers are more significantly impacted by incoming water, particularly warm intrusions from the Scotian Slope and Gulf Stream. This warm water, once reaching deeper depths, tends to persist for extended periods compared to surface waters.
Conversely, between 2012 and 2023, cold intrusions and cold spells in the deeper layers of the Scotian Shelf have become less frequent. The absence of temperature resets between heat waves leads to a continuous warming trend in the waters.
Adam Cook, a DFO research scientist specializing in lobster stock assessment, highlighted the implications of warming bottom waters on marine species like lobsters, which are sensitive to changes in water temperature. As water temperatures rise, lobsters exhibit increased activity and appetite, potentially affecting their growth rates and catch sizes. Cook cautioned that prolonged warming could pose risks to the lobster industry, drawing parallels to lobster stock declines in southern New England caused by rising water temperatures.
Moreover, the report underscored the potential threat posed by warmer waters facilitating the proliferation of invasive species. Instances in the Mediterranean, where invasive Atlantic blue crabs and fireworms have disrupted ecosystems and fisheries, serve as a cautionary tale for Atlantic Canada if water temperatures continue to rise.
In a separate study conducted by the DFO, it was noted that the waters off the Scotian Shelf experienced a slight cooling trend in 2023, raising speculation about a potential return to normal temperatures or a temporary deviation. Zhai suggested that this cooling phase was likely a short-term fluctuation, emphasizing the gradual nature of temperature changes.
As researchers continue to monitor and analyze the impact of climate change on marine ecosystems, the findings underscore the importance of understanding and addressing the consequences of warming waters on marine life and ecosystems.