Separately, search teams typically make longer trips every 18 months to remove and replace sensors from three or four anchors on the eastern side of the Bahamas. Their UK counterparts perform the same task on the eastern side of the ocean and along the Atlantic.
Other groups have set up arrays of anchors across different parts of the Atlantic in order to better understand how the different components work, how tightly the system is connected, and whether changes in one part are rippling all the time.
Susan Luzier, an oceanographer at Georgia Institute of Technology, is leading an international effort known as OSNAP, which began in 2014. Cables have been installed across the Labrador Sea and from the southeastern edge of Greenland to the coast of Scotland.
The hope for international research efforts has been to go to the sources of deep-water sinking, largely responsible for driving currents in the Atlantic Ocean, “to try to gain a better understanding of the mechanisms driving change in the AMOC,” Luzier says.
So far, what the monitoring programs have largely found is that the circulation of the Atlantic is more variable than previously thought, she said.
Its strength and speed fluctuate greatly from month to month, year to year, and region to region. It appears that most deep-water drowning in the North Atlantic does not occur in the Labrador Sea, as has long been thought, but rather in the basins east of Greenland. The parties flowing north and south operate more independently than previously understood. Local wind patterns appear to be playing a more influential role than expected. Some of the results are puzzling.
It is very likely that the circulation of the Atlantic Ocean has weakened. Studies by Rahmstorf of the Potsdam Institute and others conclude that it is about 15% slower than it was during the mid-20th century and may be at its weakest in more than 1,000 years. Both findings are based, in part, on long-term reconstructions of their behavior using records such as Atlantic temperatures and ocean floor grain size, which can reflect changes in deep-sea currents.
There is also “strong agreement” in the models that currents will continue to weaken this century if greenhouse gas emissions continue.
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