“Waters in Atlantic Canada have seen varying degrees of warming over the past 10 years,” says Kathryn Hallett, Fisheries and Oceans Canada media relations.
Hallett said there is an important distinction between sea surface temperatures (SSTs) that are highly influenced by air temperature, and temperatures at depth. “The warming trend observed in air temperature since the 1870s of about 1°C per century is expected to have occurred in surface water temperatures across Atlantic Canada,” she said.
In the Gulf of St. Lawrence, “surface temperatures averaged over the ice-free season of May to November have increased from a near normal (relative to 1991–2020 climatology) value of 9.9 Celsius in 2013 to the two warmest years on record in 2021 and 2022, at 11.2 and 11.3 Celsius,” said Hallett. “However interannual variability is strong and at this time we do not know that 2023 will be as warm as the two previous years.”
There is much less variability from year-to-year for deep water temperatures in the Gulf, said Hallett. “The waters are slowly transported in the Gulf by estuarine circulation, taking several years to transit all the way to the Estuary. The average temperature at 300 m has increased from 5.3 Celsius in 2009 to 7.1 Celsius in 2022. It has been at 100+ year record highs since 2016, increasing every year since and now by +0.9 Celsius over the record set in 2016.”
On the Scotian Shelf, SSTs averaged over the whole year increased by approximately 1.25°C from 2010 to 2022, says Hallett. “Bottom temperatures for the western half of the Scotian Shelf from 2010 to 2022 (no data in 2022 for the eastern half) increased on average approximately 2.5°C. From 2010 to 2020, the average increase on the whole Scotian Shelf was about 1.2°C.”
In Newfoundland and Labrador, SSTs were at their warmest ever recorded (for the satellite era since the 1980s) in 2022 and 2021, respectively, followed by 2012 and 2020, said Hallett. “Although exhibiting large natural fluctuations, the fact that the last three years are among the four warmest years on record is a sign that the surface ocean is trending warmer in N.L.”
In 2023, while most of the North Atlantic was record warm in June, surface temperatures in N.L. were near-normal or even cooler than normal; the situation however changed in July, said Hallett. “Driven by the warm weather, SSTs are now much warmer than normal in this part of the Atlantic Ocean.”
Hallett noted surface temperatures are not necessarily representative of what is going on at depth in N.L. “For example, at depths greater than 100 metres, temperatures on the N.L. shelf are usually remnant of the previous winter conditions. As such, a cold winter would lead to cooler deep water temperatures in the summer, and so on. No clear trend has been observed at depth and the temperature is exhibiting large interannual fluctuations.”
Many marine species have been impacted by increasing ocean temperatures, but there is considerable variability in the nature of the effects, said Hallett.
“All species have an optimal temperature range, which in some instances can result in expansions of the available habitat but in many instances, optimal areas have declined in their extent.”
DFO monitors the changing marine environment through several research programs, said Hallett. “Ongoing research and monitoring efforts have found that climate change contributes to changing ocean chemistry and ocean temperatures. These changes to marine conditions can result in changes to zooplankton abundance and species composition, which affects the range, distribution and migration patterns of North Atlantic right whales. This information is factored into much of the work of the Department, such as determining fishery management measures (e.g. timing, range) to protect species such as the North Atlantic right whale, and science advice on fish distribution and productivity. Our ongoing research and monitoring will help us understand the current and potential future impacts of climate change on marine species.”
As recent years have demonstrated, the arrival, departure and distribution of North Atlantic right whales are variable in our waters, said Hallett. “Between 2017 and 2022, the first visual observations of North Atlantic right whales in Canada in the Gulf of St. Lawrence took place between the end of April and mid-May. The last visual observations of them in Atlantic Canada are typically between early and mid-November, in line with the end of most survey effort. However, North Atlantic right whales have been observed as late as mid-December when surveillance was conducted.”
Hallett said a “key driver for North Atlantic right whale migration is the availability of their preferred zooplankton species food source. While these whales were historically present in the Bay of Fundy/Roseway Basin and Gulf of Maine in the spring, summer and fall, climate change has decreased their food source in these areas, causing them to travel to the Gulf of St. Lawrence to feed.”