Scientists have found that the Atlantic meridional overturning circulation (MOC), a deep-ocean process largely responsible for regulating Earth’s climate, is driven by cold waters off the western coast of Europe, mainly between Greenland and Scotland.
In the waters between these areas, warm, salty, shallow waters that have been carried from the tropics northward via currents and wind, sink, cool, and turn into deeper, fresher waters that then move southward through the Irminger and Iceland basins.
Researchers found that overturning variability within this eastern area of the ocean was seven times greater than in the Labrador Sea, which is where previous theories suspected the majority of the overturning was occurring. But within this new area of waters recently explored, researchers found that 88% of the total variance documented across the entire North Atlantic within a 21-month period was accounted for.
Susan Lozier, the Ronie-Rochele Garcia-Johnson Professor of Earth and Ocean Sciences at Duke University’s Nicholas School of the Environment, believes that knowing this can help scientists better predict how MOC will change and how those changes will affect Earth’s climate.
“To aid predictions of climate in the years and decades ahead, we need to know where this deep overturning is currently taking place and what is causing it to vary,” explained Lozier, who led the international observational study responsible for producing the new data, published January 31st in Science.
“Overturning carries vast amounts of anthropogenic carbon deep into the ocean, helping to slow global warming,” said the study’s co-author Penny Holliday, of the National Oceanography Center in Southampton, U.K. “The largest reservoir of this anthropogenic carbon is in the North Atlantic.”
She continued, “Overturning also transports tropical heat northward, meaning any changes to it could have an impact on glaciers and Arctic sea ice. Understanding what is happening, and what may happen in the years to come, is vital.”
This study, which is the initial phase of the five-year OSNAP (Overturning in the Subpolar North Atlantic Program) research project, used moored instruments and sub-surface floats located across the North Atlantic to measure the ocean’s overturning circulation.
“As scientists, it is exciting to learn that there are more pieces to the overturning puzzle than we first thought,” said study co-author Johannes Karstensen, of the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany. “Though the overturning in the Labrador Sea is smaller than we expected, we have learned that this basin plays a large role in transporting freshwater from the Arctic.”
He added, “Continued measurements in that basin will be increasingly important,” as the Arctic unexpectedly changes.
Image Credit: Carolina Nobre, WHOI Media