Cooler Deep Water Predicted in the Gulf Again This Year

We might be feeling the summer’s warmth here in Maine this month but out in the Gulf of Maine things are a bit cooler. In fact, in the Gulf’s deep water temperatures are quite cold, about 0.9 to 1.8o F. cooler this spring compared to the seasonal average, according to a forecast from the National Oceanic and Atmospheric Administration (NOAA).

The relative strengths of the Labrador Current and Gulf Stream affect deep water temperatures in the Gulf of Maine. Graphic by Realclimate.org.

The NOAA computer models’ forecast is in synch with buoy data collected by Bigelow Laboratory for Ocean Sciences senior scientist Nick Record that indicate deep-water temperatures are almost 2o F. colder than measurements taken last year. Those temperatures may give a clue concerning the behavior later this year of endangered North Atlantic right whales.

“Bottom water temperatures are comparable this spring to last year and to the years prior to 2010,” Record said. Bottom water refers to the deepest two-thirds of the water column, Record explained. “I look at temperatures in water 600 to 700 feet deep in the Northeast Channel and Jordan Basin. The deep water gives us an early signal of what later in the year will look like,” he continued.

Colder deep water does not mean that the Gulf of Maine has ceased its rapid warming. That warming was first noticed in 2010 and is largely due to the oceanographic impact of the globe’s increasing temperature. But it does suggest that right whales may be seen in the Gulf later this year in search of their preferred food, tiny copepods called Calanus finmarchicus, which thrive in the colder water.

“There is a strong relationship between the spring water temperatures and where the whales are in the summer and fall,” Record said.

Right whales used to return to the Gulf in late summer to feed around Grand Manan Island at the mouth of the Bay of Fundy or on Browns Bank, stocking up on copepods before making their way along the east coast to their winter calving grounds off Florida and in the Caribbean. As the Gulf warmed and their food moved to cooler waters in Canada, the whales followed. In 2021, 187 right whales, around 40% of the identified population, where seen feeding in the Gulf of St. Lawrence during the summer and fall.

But in 2024 and this past winter, right whales appeared in larger numbers in the Gulf of Maine several months after Record had noted the cooler bottom water temperatures. Researchers reported higher numbers of right whales in historic feeding grounds in the Bay of Fundy and Roseway Basin near the coast of Nova Scotia.

“People say they are in the Gulf of St. Lawrence but sure enough, the whales came back because of the cold water and their food,” Record said. Approximately 90 right whales were sighted feeding on the western side of Jeffreys Ledge in January this year.

The Northeast Channel is key to forecasting what may happen in the Gulf in future months. The temperature of water that enters the Channel at depth is determined by which of two major currents is dominant: the cold Labrador Current originating in the Arctic or the warm Gulf Stream pushing up from the south. During the past decade, the Gulf Stream has often been the stronger presence.

“But it’s a tug-of-war that’s been going on for a very long time,” Record said. “In the last several years it’s swung to colder water, driven by changes in the Arctic more extreme than we’ve seen in the past.”

Though the conditions this year appear to be similar to last year’s, Record stresses it’s not a guarantee that right whales will return to those historically important feeding grounds in the Bay of Fundy later this summer or Jeffreys Basin in winter.