Story at a glance

  • The Atlantic Meridional Overturning Circulation is a weather pattern that transmits different water temperatures up and down the Atlantic Ocean and helps regulate climate.
  • Researchers use substantial proxy data to see if recent weakening trends are part of a larger pattern.

One of the most critical ocean circulation patterns that helps the Earth regulate its temperature has recently reached its weakest state in a millennium, making it more difficult to effectively distribute heat on the planet. 

The Atlantic Meridional Overturning Circulation (AMOC), a series of currents that flow across the Atlantic Ocean, as well as the Nordic and Labrador Seas, helps transport heat from the South Atlantic and North Atlantic to more polar Atlantic waters.

Published in the journal Nature Geoscience, a new study examines evidence pointing to the AMOC’s slowdown due to anthropogenic climate change, or climate change caused by humans. 

Using long-term proxy data to substitute for a lack of information about the AMOC’s patterns before 2004, researchers look at surface temperature patterns that reflect changes in how the AMOC could be transporting heat across oceans. 

Some of the proxies included temperatures, marine productivity and ocean heat content. Select data to measure the heat of subsurface ocean temperatures were derived from coral samples, and marine productivity was recorded by looking at the marine sediment and methanesulfonic acid concentration in Greenland ice cores.

The results indicate that prior to the 19th century, AMOC weather patterns were “relatively stable.”

Declines in movements of the current are visible after the 19th century, with “a phase of particularly rapid decline” measured via proxy data beginning in the 1960s.

Scientists further saw a small recovery in the 1990s, but then saw the same decline occur in the first decade of the 2000s. 

The authors of the report concede that some proxy data could be skewed by complicating variables that aren’t related to the AMOC at all. When testing the strength of results from substitute data, however, 9 out of 11 proxy variables showcase steady declines that run parallel to the AMOC’s reduced capacity to distribute heat effectively. 

“These data consistently show that the modern AMOC slowdown is unprecedented in over a thousand years,” the report concludes.

The authors advocate improved understanding of the AMOC is vital to understanding the potential environmental effects of a changed pattern of ocean currents. It’s possible further weakening could result in more extreme weather events in Europe and rising sea levels on the U.S. East Coast, they note.

Published on Feb 25, 2021