Over the last 20 years, the Gulf Stream has warmed faster than the global oceans and shifted closer to the shore, increasing the likelihood that the tropical ocean current could suddenly impact U.S. coastal fisheries, according to a new study published this month.

Physical oceanographers Robert Todd and Alice Ren from the Woods Hole Oceanographic Institution found the Gulf Stream has warmed 2 degrees Fahrenheit and moved 6 miles closer to the eastern continental shelf since 2001, according to findings published in Nature Climate Change.

The Gulf of Maine is most influenced by the Labrador Current, which brings colder water from the north. The oscillating Gulf Stream generally passes 100 miles south of the Gulf of Maine’s southern border, but warm-water breakaways from it can still increase Gulf of Maine temperatures for months at a time.

Scientists say it is too early to know for sure, but increasingly warm core rings that break away closer to shore could have a significant impact on environmental conditions, and marine wildlife, within the Gulf of Maine, according to Todd, the study’s lead author.

“These rings have a very sharp temperature contrast,” Todd said. “They come in and very suddenly you have very warm water in the spot where you had cold water before. It’s temporary, for the life of the ring, but it’s a long enough period of time that the fish, the shellfish, they care.”

This study focused on the general Gulf Stream that hugs the U.S. coast from Florida up to Cape Cod, before it flows east toward Europe, but Todd notes that other researchers have found the number of warm core rings formed by the Gulf Stream has roughly doubled since 2000.

The balance between Maine’s two dominant ocean currents is shifting, according to Dave Reidmiller, climate center director at the Gulf of Maine Research Institute. The Arctic-infused Labrador Current isn’t as cold as it used to be, he said, and the Gulf Stream is warmer and wider than ever.

Reidmiller said the study’s findings are consistent with the region’s long-term ocean warming trends. The Gulf Stream is not about to enter the Gulf of Maine, he noted – the Labrador Current remains the region’s dominant influence – but its warming and widening will definitely impact the Gulf of Maine.

“It’s another signal that significant changes are underway to this major oceanic current that is very likely to have long-term consequences for the Gulf of Maine and the communities that rely on it for their well-being and livelihoods,” Reidmiller said.

Even small changes in temperature can have a significant impact on some marine wildlife, including cold-water species like herring, which is in decline, and warm-water species like squid and butterfish, which are both increasing. It’s not just fish, either – puffins are changing what they feed to their chicks.

The Gulf of Maine, whose 36,000 sprawling square miles stretch northeast from Cape Cod to Nova Scotia, is warming at a rate of about 1 degree a decade. That’s about four times the rate of the global oceans, which are warming by a quarter of a degree per decade.

This summer was the Gulf of Maine’s eighth-hottest since satellite data has been collected, according to GMRI. It has been a year of headline temperatures for the larger North Atlantic region, which also contributed to sweltering temperatures on land.

With an average temperature of 63.6 degrees Fahrenheit, it was the Gulf’s warmest July on record.

Researchers believe this trend is the result of a distinct regime shift: a combination of the widening of the Gulf Stream, changes in the Labrador Current, and the weakening of a larger system of currents that keeps the northwest Atlantic Ocean’s heat and energy well mixed.

The Woods Hole study, which relies on over 25,000 temperature and salinity observations collected over 20 years from underwater gliders and floats, provided physical confirmation of the Gulf Stream changes that climate models had predicted, Todd said.

The floats from the Argo Program, which Woods Hole helped found in 1999, drift with the ocean currents and collect data as they move up and down between the sea surface down as far as 6,500 feet to the ocean floor.

The gliders move up and down like the Argo floats, but they can also crisscross the Gulf Stream as it carries warm water from the tropics north to higher latitudes as part of the Atlantic Meridional Overturning Circulation.

The gliders and floats take subsurface ocean measurements that satellites cannot, Todd said.

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