New scientific research has revealed that summer temperatures in the Gulf of Maine, the second fastest warming part of the world’s oceans, are persisting two months longer than they were as recently as the early 1980s.
The findings, by a Maine-led team of scientists, have ramifications for marine life, fishermen and the strength of hurricanes, which appear in late summer and are fueled by warm water.
“What we found was quite astonishing in that almost all the warming is in the late summer and the winter is not contributing very much at all,” says the project’s lead scientist, University of Maine oceanographer Andrew Thomas. “You can think of impacts all across the food chain, from animals that have actual temperature tolerances to the distribution of species, their prey, and even their predators, not to mention the bacteria and viruses, which we have no idea how they will react.”
The researchers used daily satellite readings collected between 1982 and 2014 to map changes in sea surface temperatures along the Eastern Seaboard from North Carolina to Nova Scotia, breaking out the data by month to reveal seasonal differences in warming rates. They weren’t surprised to find the strongest warming in the Gulf of Maine and adjacent Scotia Shelf – team members had worked with Andrew Pershing of the Gulf of Maine Research Institute in Portland to demonstrate this in a 2015 study – but the profound seasonal differences were unexpected.
The satellite data show warming trends across the Gulf of Maine for every month and very sharp increases during July, August and September, especially off the Maine coast. While the Gulf of Maine warmed by an average of 0.72 degrees Fahrenheit per decade during the 33-year period, the warming rate was twice that in the months of July through September, or 1.44 degrees F per decade.
The only reprieve in the warming trend has been in a small section in the central gulf during the months of February and March, the only time of the year when sea surface temperatures there haven’t increased in recent decades.
LESS OF A STORM STOPPER
In addition, the scientists found summer conditions in the gulf were starting earlier and ending later, increasing the length of the season by an average of two days per year, or more than two months over the 33-year study period.
This means the Gulf of Maine isn’t as effective a “speed bump” for Maine-bound hurricanes, which weaken as they cross cold water.
“It’s warm water that feeds a hurricane, so hurricanes crossing our shelf are not going to lose as much energy as they have in past decades, because our shelf water is warmer in the fall than it used to be,” says Thomas, who collaborated with researchers from Gulf of Maine Research Institute, the Bigelow Laboratory for Ocean Sciences, the National Oceanic and Atmospheric Administration and the State University of New York at Stony Brook, many of whom also collaborated on Pershing’s earlier research.
It also means the Gulf of Maine will become more stratified or layered, making it harder for tides and currents to mix the ever-warmer, less dense surface waters with colder, nutrient-rich waters underneath. This will make it harder for marine algae – the meadows of the sea on which most other marine life ultimately depends – to grow, Thomas says, as they need both sunlight (found near the surface) and nutrients (which, without mixing, tend to fall to the dark depths).
SHAKING UP SEA LIFE
Other ecological effects are already being documented.
Last year, several of the same researchers used federal fish survey data to examine how various commercial fish species on the Atlantic seaboard had responded to the longer summer temperatures in recent decades. They found winners and losers, with weaker cod, sculpin, skate and rock crab populations at the end of summer and stronger lobster, redfish, dogfish, herring and summer flounder ones.
“Warmer temperatures can mean a longer growing season, and a longer summer season can mean more time in favorable or unfavorable temperatures, depending on what species you are looking at,” says that project’s lead researcher, Elizabeth Henderson, a doctoral student in fisheries oceanography at Stony Brook. “Going forward, we may see fewer cod and increases in the biomass of other fish that prefer the warmer waters.”
The latest study on sea surface temperature trends appears in the new issue of the scientific journal Elementa.
In May, a team of federal fisheries scientists released results of a study predicting that current warming trends in the gulf would by century’s end eliminate all thermally appropriate habitat for many of the groundfish species that were the mainstay of the New England fishing industry, including pollock, haddock, hake, flounder and redfish.
Since 2004, the Gulf of Maine – which extends from Massachusetts to the head of the Bay of Fundy and includes all of coastal Maine – has warmed faster than anyplace else on the planet, except for an area northeast of Japan, raising concerns about the long-term stability of its traditional fisheries and ecosystem.