Sea surface temperatures in the vast Gulf of Maine hit a near-record high of 68.93 degrees Fahrenheit on Aug. 8, part of what scientists called a month-long “marine heat wave” in the normally chilly waters that are home to everything from lobsters to whales.
Using satellite data, scientists at the Gulf of Maine Research Institute said that over the past 30 years, the waters there have warmed at a rate more than three times the global average. Over the past 15 years, it has warmed at seven times that average.
“This event is surprising in the sense that it happened really quickly and we hit these record temperatures,” said Andrew Pershing, chief scientific officer at the Gulf of Maine Research Institute. “But what’s unsurprising is that average conditions have been so warm. We’re getting heat waves or near heat waves almost every year, and in some years almost every day.
“We’ve set 10 daily temperature records this summer, after setting 18 this winter,” Pershing said, adding that the institute “had to add new colors to our temperature illustrations to reflect just how warm the Gulf of Maine has been this year.”
The satellite data, which goes back to 1981, came from the National Oceanic and Atmospheric Administration and NASA. The temperatures reflect average conditions over an area of 80,447 square miles and as far as a meter below the surface. So far this year, surface temperatures rank third-highest, after 2012 and 2016.
Concerns about marine heat waves have been rising in recent years, in the wake of the widespread bleaching and death of corals caused by similar events in the globe’s tropical belt.
In Maine’s case, the unusually warm waters could also affect sea life, though there haven’t been any studies yet. Squid and butterfish that like warm water could migrate north from their usual mid-Atlantic habitats, possibly causing problems for puffins that feed by diving into the water. And the quantity of plankton and small shrimp, which prefer cold water, could drop. That might force right whales, which normally feed in the Bay of Fundy, to remain farther north in the Gulf of St. Lawrence, where their prey would be more plentiful.
Pershing said a warm mass of water was sitting 40 miles offshore, east of Cape Cod and south of Nova Scotia. He said the warm mass — a “dark blob” on satellite maps — had stalled there, blocking colder, less salty water that might have come down from Canada and the Arctic.
The marine heat wave may be the result of a “weakening” of the ocean currents — known as the Atlantic Meridional Overturning Circulation — that carry warm water north along the east coast of the United States, he said.
“In order to get a heat wave, you usually have to have a couple of things that add together,” Pershing said. “The background conditions have been set by the unusual changes in circulation in the North Atlantic. Add on top of that really warm conditions in the northeast in July and early August.”
So far this year, all but 40 days had reached “heat wave” threshold, he said, with temperatures rising above the 90th percentile for the period going back to 1982.
David Townsend, a professor of oceanography at the University of Maine, cautioned against relying too heavily on satellite data. His own study of temperature, salinity and nutrients based on measurements by buoys in the Gulf of Maine shows greater fluctuation than Pershing’s findings. But those fluctuations are also indirectly tied to global warming and changes in ocean currents.
Townsend said his data indicate a probable slowing of the Gulf Stream and a quickening of the melting of Arctic ice — which results in “weird things happening in the Gulf of Maine.”
There has been one earlier period of very warm waters in the Gulf of Maine, stretching across the late 1940s, Pershing said. It is unclear what caused that, he said.
The new study by the Maine group is in line with a study earlier this year by Canadian scientists that found record high temperatures in April in the deep water flowing into the main entrance to the Gulf of Maine. Normally, a current flows into the gulf through a deep passage between Georges and Browns banks. The scientists said the waters exceeded 57 degrees at depths of 150 to 450 feet — nearly 11 degrees higher than normal for that time of year.