A recent study conducted by the European Union’s marine monitoring service reveals that the waters surrounding Nova Scotia are experiencing a gradual increase in temperature. This 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 marine species inhabiting that environment.
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, reported a warming trend over the past three decades. Surface waters on the Scotian Shelf have risen by approximately 1.5 degrees, while bottom waters have warmed twice as much, around three degrees.
Zhai explained the challenges in measuring below-surface temperatures due to limited observations, contrasting with the abundant satellite data available for surface temperatures. The study defines a marine heat wave as when the sea surface temperature exceeds the historical average for at least five consecutive days. The report indicates that at the bottom of the Scotian Shelf, the number of heat wave days has been increasing by about four days per year.
The research, utilizing data from the Bedford Institute of Oceanography between 1993 and 2023, alongside Copernicus ocean model simulations, offered a comprehensive view of marine heat waves across various depths. This allowed the team to gain insights into these extreme events in the ocean over time.
While surface temperatures are susceptible to seasonal variations in air temperature and weather patterns, deeper layers are significantly influenced by incoming warm water flows, especially from the Scotian Slope and Gulf Stream. The prolonged presence of warm water at depth contributes to the sustained warming of bottom waters.
Conversely, from 2012 to 2023, there has been a decline in cold intrusions and cold spells in the deeper layers of the Scotian Shelf. This lack of temperature reset between heat waves results in a continuous warming trend in the waters.
Adam Cook, a research scientist at the DFO focusing on lobster stock assessment, highlighted the impact of warming bottom waters on marine species like lobsters. The rising water temperature leads to increased lobster activity and food consumption, potentially leading to faster growth rates and larger catches. However, Cook cautioned that prolonged warming could pose risks for the industry, referencing the decline of lobster stocks in southern New England due to exceeding temperature thresholds.
The report also warns about the advantage warmer waters provide to invasive species, citing examples from the Mediterranean where Atlantic blue crabs and fireworms disrupted ecosystems and fisheries. Cook emphasized the possibility of similar introductions in Atlantic Canada if water temperatures continue to rise.
Although a DFO survey in 2023 suggested a slight cooling off the Scotian Shelf, Zhai dismissed it as a short-term fluctuation, stating that the overall warming trend has been gradual and consistent.
As temperatures continue to fluctuate, researchers stress the importance of monitoring and understanding these changes to assess their long-term impact on marine ecosystems and fisheries.