A new study just published in the journal Nature Geoscience is calling for further analysis of recent research declaring a clear deceleration in the Atlantic Ocean’s surface and deep currents, suggesting the earlier findings were based on a limited and poorly justified data set.
“Real and interesting subtleties and discrepancies in the data still exist,” states the new study, and any impression that the historical Atlantic meridional overturning circulation (AMOC) evolution is confidently known “is misleading until the conflicts are resolved,” conclude Halimeda Kilbourne and her colleagues at the University of Maryland Centre for Environmental Science.
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Kilbourne’s analysis is an explicit response to a March 2021 study by scientists from the Potsdam Institute, Ireland’s Maynooth University, and University College London, also published in Nature Geoscience. It sought to buttress earlier research suggesting the AMOC has been undergoing a rapid deceleration, by about 15%, since 1950. The researchers used a statistical analysis of 11 pieces of indirect “proxy” evidence (including a “cold blob” of water that remains stuck off the coast of Greenland, and precipitous warming in the Gulf of Maine) to support their theory of a clear trend towards AMOC deceleration.
At the time, the Washington Post wrote that the findings would have “implications for everything from the climate of Europe to the rates of sea level rise along the U.S. East Coast.”
Kilbourne and her team contend that, although the argument and selected evidence proposed by the collaboration have some merits, their conclusions might be different if “a more complete array of data available in the North Atlantic region is considered.”
Such an array does exist—and did so even at the time of the Potsdam study. Flagging work by Durham University paleoceanographer Paola Moffa-Sánchez of Durham University compiling “a comprehensive set of paleo-climate proxy data from the North Atlantic and Arctic regions using objective criteria to identify high-quality datasets of ocean conditions that span the past two millennia,” Kilbourne argues that, “the time history of the AMOC system becomes less certain” when such a comprehensive dataset is factored in.
Kilbourne said the rigour inherent in the research by Moffa-Sánchez and colleagues was lacking in the work by the Potsdam team, which did not “identify the reasoning or criteria for selecting [the proxies chosen] over many others that are probably related to aspects of AMOC dynamics.”
“Objective and inclusive data selection standards are especially important when addressing AMOC, which is a system composed of many different components that can behave differently at different latitudes, depths, and time scales, and looking at any singular index of AMOC inherently oversimplifies the system,” she adds.