Ocean Temperature Off Northeast Coast Rising

By ecoRI News staff

Rising levels of carbon dioxide in the atmosphere have affected one of the global ocean’s major circulation systems, slowing the redistribution of heat in the North Atlantic Ocean.

The resulting changes have been felt along the Northeast coast and in the Gulf of Maine, which has warmed 99 percent faster than the global ocean during the past 10 years, impacting distributions of fish and other species and their prey.

National Oceanic and Atmospheric Administration (NOAA) Fisheries researcher Vince Saba and European colleagues have compared computer model simulations with direct observations and found the system has slowed down by about 15 percent since the 1950s. Their results were recently published in the journal Nature.

The Atlantic Meridional Overturning Circulation (AMOC) is a large-scale system of ocean currents that circulates warm, salty water from the South Atlantic and tropics via the Gulf Stream to the colder North Atlantic. There, warm salty waters cool, release heat, and eventually sink to the deep ocean and move south. The AMOC plays a key role in the Earth’s climate and is a major component of the Global Conveyor Belt.

“We found a characteristic sea surface temperature fingerprint for an AMOC slowdown or weakening in both a high-resolution global climate model and in temperature trends observed since 1870,” said Saba, a research fishery biologist at NOAA’s Northeast Fisheries Science Center and a co-author of the study.

Saba works with high-resolution global climate models at NOAA’s Geophysical Fluid Dynamics Laboratory at Princeton University. His studies have focused on the impact of changing ocean conditions on fisheries, sea turtles and other marine life.

The rapid ocean warming observed along the Northeast Shelf may be associated with the Gulf Stream shifting northwards and closer to shore, a consequence of the AMOC slowdown. In NOAA’s high-resolution climate model, enhanced warming of ocean bottom temperatures in the Northeast Shelf and in the Gulf of Maine is a result of both a poleward retreat of the Labrador Current and a northward shift of the Gulf Stream.

Continued warming is likely to further weaken the AMOC in the long term, through changes to the hydrological cycle, sea-ice loss, and accelerated melting of the Greenland Ice Sheet, all of which are causing the North Atlantic to become fresher and less dense, according to the recent report.

“If the AMOC continues to weaken,” Saba said, “ocean temperature along the Northeast U.S. Shelf is expected to continue its trend of warming faster than the global ocean, which will further impact fisheries and living marine resources in the region.”