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New knowledge of deep currents can help to predict future climate impacts – ScienceDaily



A new international study found that the Atlantic Meridional Reversed Circulation (MOC), a deep oceanic process that plays a key role in regulating the Earth's climate, is primarily driven by cooling water to the west of Europe.

Deviating from the prevailing scientific view, the study shows that most overturning and variability does not occur in the Labrador Sea outside of Canada, as suggested by previous model studies, but in the regions between Greenland and Scotland. There, the warm, salty, shallow waters transported north of the tropics through the currents and winds, dive and convert to the cooler, fresh, deep waters moving south across Irminger and the Icelandic Basin.

The inverted variability in this eastern part of the ocean was seven times greater than in the Labrador Sea, accounting for 88 percent of total deviations documented throughout the North Atlantic during the 21-month period.

These findings, which may be unexpected, can help scientists better predict what changes could occur in the MOC, and what impact the change will have on climate change, said Susan Lozier, Professor of Earth and Ocean Science Ronie-Rochele Garcia-Johnson Duke University Nicholas School of Environment.

"In order to help weather forecasts in the years and decades to come, we need to know where this deep roll-over is going and what causes it to change," said Lozier, who led an international observation study that produced new data.

"Overturning carries a huge amount of anthropogenic carbon deep into the ocean, which helps slow down global warming," said co-author Penny Holliday of the Southampton National Oceanographic Center in the US. "The largest reservoir of this anthropogenic carbon is in the North Atlantic."

"The overturning also transmits tropical heat to the north," said Holliday, "which means that any changes can affect glaciers and glaciers at sea.

Scientists from 16 research institutions from seven countries collaborated on a new study. In February, they published their reviewed findings Science.

"I can not say enough about the importance of this international collaboration for the success of this project," Lozier said. "Measuring circulation in the subpolar North Atlantic is incredibly demanding, so we definitely needed access" on all decks. ""

This article is the first of the five-year initial phase of the OSNAP research project, in which scientists deployed anchored instruments and subsurface vessels across the North Atlantic to measure oceanic overturning and illumination of the factors causing it. Lozier is the lead investigator of the project, which began in 2014.

"As a scientist, it is exciting to learn that there is more to the overturned puzzle than we thought," said co-author Johannes Karstensen of GEOMAR Helmholtz Center for Ocean Research Kiel in Germany.

"Although the overturning in the Labrador Sea is less than we expected, we found that this tank plays a major role in the transport of fresh Arctic water," said Karstensen. "Continuing measurements in this pan will become more important," as the Arctic changes unexpectedly.

The new article contains data collected over a 21-month period from August 2014 to April 2016.

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