New research just published in the journal Nature shows that the Atlantic Meridional Overturning Circulation (AMOC) has slowed down (weakened) since the mid-20th century and that it may have reached a new record low. Ocean observations go back to 1870.

What is the AMOC?

The 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. (via NOAA).)

Image courtesy Wikipedia.

The international research team that conducted this study used computer model simulations to reconstruct changes in the AMOC over time. By comparing these simulations with recent direct ocean measurements, they were able to conclude that the AMOC slowed down by about 15 percent since the 1950s.

Why has it slowed down?

The research team noted that rising levels of atmospheric CO2 may be responsible for this change.

Impacts of this change

The waters along the NE U.S. shelf and Gulf of Maine have warmed 99 percent faster then the global oceans as a whole over the past 10 years.

The slowing of the AMOC is also having an impact on the distributions of fish and their prey, according to the NOAA Fisheries Service report.

The research team was able to find a characteristic sea surface temperature fingerprint for an AMOC slowdown, according to Vincent Saba, a research fishery biologist at NOAA's NE Fisheries Science Center and co-author of the study.

Key excerpts from the report.........

“That fingerprint consists of a pattern of cooling in the North Atlantic Ocean’s subpolar gyre and a warming in the Gulf Stream region due to reduced northward heat transport and an associated northward shift in the Gulf Stream,” Saba said. “In other words, there is warming along the Northeast U.S. Shelf and Gulf Stream region, and at the same time a cooling in the North Atlantic subpolar gyre.”

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. “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.”

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