EU report finds Scotian Shelf bottom ocean floor warming twice as fast as surface, threatening marine life and fisheries over 30 years.
Decades of Warming Beneath Nova Scotia’s Waves
A new European Union marine report reveals that the waters off Nova Scotia are warming at alarming rates, with ocean floor temperatures rising twice as fast as surface waters. Over the last 30 years, surface waters on the Scotian Shelf increased by about 1.5°C, while bottom waters rose roughly 3°C, driven largely by longer and more intense marine heat waves.
Tracking the Heat Below the Surface
Scientists from the Department of Fisheries and Oceans (DFO) contributed to the Copernicus Marine Service’s 2025 Ocean State Report, using a combination of satellite data, Bedford Institute of Oceanography measurements, and ocean model simulations. Lead scientist Li Zhai noted that while surface temperatures are easier to track, subsurface measurements are scarce. “We now have a four-dimensional view of extreme ocean events, from surface to depth,” she said.
Warm Intrusions and Lingering Effects
Unlike the surface, which experiences seasonal swings, deeper waters are influenced by incoming currents from the Scotian Slope and the Gulf Stream. These warm intrusions tend to persist longer at depth, while cold spells have become less frequent since 2012, preventing temperatures from resetting between heat waves. According to the report, the Scotian Shelf’s deep layers have seen about four additional heat wave days per year, totaling roughly 120 extra heat wave days over three decades.
Impacts on Marine Life and Fisheries
Rising bottom temperatures are already affecting species that inhabit the ocean floor. Adam Cook, a DFO research scientist specializing in lobster stocks, said warmer waters increase lobster activity and appetite, potentially boosting growth and short-term catches. However, he warned that prolonged warming could exceed lobsters’ tolerance limits, as seen in southern New England, posing long-term risks to the fishery.
Threat of Invasive Species
The report also highlighted that warming waters could favor invasive species, similar to disruptions observed in the Mediterranean. Atlantic blue crabs and fireworms have previously devastated ecosystems abroad, and Canadian waters may face similar threats if warming continues.
Short-Term Cooling Not a Reversal
A slight cooling trend observed in 2023 raised questions about whether the Scotian Shelf might be returning to historical norms. Zhai emphasized that short-term dips are likely temporary, noting, “Some years you get warmer than the long-term trend. Some years temperature dips down. We have to keep that in mind.”
A Call for Vigilance
The study underscores the need for continued monitoring of Canada’s marine environments as climate change accelerates warming. With deeper waters heating faster than the surface, scientists warn that both ecosystems and fisheries may face unprecedented challenges in the decades ahead.
