An area of the Atlantic Ocean between Scotland and Greenland is playing a major role in global climate, an international team of scientists has discovered.
Published in the journal Science, the team’s study shows how a deep-ocean process in the North East Atlantic Ocean are playing a much larger role in regulating the Atlantic meridional overturning circulation (AMOC) than previously thought.
The AMOC transfers heat from equatorial regions to the Arctic Ocean, driven by current and westerly winds and warming the atmosphere above. As a consequence, Scotland’s climate is five to 10 degrees Celsius warmer than other maritime countries on a similar latitude. As these waters cool and sink – a process known as overturning – they absorb excess heat from the atmosphere, slowing the rate of global warming.
In a departure from the prevailing scientific view, the study shows that the vast majority of the overturning in the Atlantic is occurring not in the Labrador Sea off Canada, as past modelling studies have suggested, but in regions between Greenland and Scotland. There, warm, salty, shallow waters carried northward from the tropics convert into colder, fresher, deep waters moving southward through the Irminger and Iceland basins.
These new findings will help scientists better predict how the changing AMOC will affect our climate.
“To aid predictions of climate in the years and decades ahead, we need to know where this deep turning is currently taking place and what is causing it to vary,” said Prof Susan Lozier, of Earth and Ocean Sciences at Duke University’s Nicholas School of the Environment, who led the international observational study that produced the new data.
Scientists from 16 research institutions from seven countries collaborated on the new study, part of the five-year OSNAP (Overturning in the Subpolar North Atlantic Program) research project, in which scientists have deployed moored instruments and sub-surface floats across the North Atlantic to measure the ocean’s overturning circulation.
Prof Stuart Cunningham of the Scottish Association for Marine Science (SAMS), an author on the report who has studied the Atlantic for more than 20 years, said the discovery highlighted further the importance of AMOC, a process that may be slowing because of climate change. He added: “These results are a fundamental step change in our ability to continuously observe the ocean circulation that is so important for European climate and ultimately help inform societal decisions on how we deal with the effects of climate change.
“The UK is leading multinational programmes to continually measure the strength and structure of the AMOC in the subtropical and subpolar Atlantic. We use purposefully designed transatlantic arrays of moorings and marine robotics to collect long-term data which are giving us a clearer picture of how the process works.”
The new paper, A Sea Change in Our View of Overturning – First Results from the Overturning in the Subpolar North Atlantic Program contains data collected over a 21-month period from August 2014 to April 2016.
Primary funding came from the U.S. National Science Foundation’s Physical Oceanography Program and the UK’s Natural Environment Research Council. Additional funding came from the European Union 7th Framework Programme and Horizon 2020.
You can view an animation by Dr Sam Jones of SAMS showing how robotic gliders helped to collect data that was important to this new discovery.
Citation: “A Sea Change in Our View of Overturning – First Results from the Overturning in the Subpolar North Atlantic Program,” M.S. Lozier, F. Li, S. Bacon, F. Bahr, A.S. Bower, S.A. Cunningham, M.F. de Jong, L. de Steur, B. DeYoung, J. Fischer, S.F. Gary, N.J.W. Greenan, N.P. Holliday, A. Houk, L. Houpert, M.E. Inall, W.E. Johns, H.L. Johnson, C. Johnson, J. Karstensen, G. Koman, I.A. LeBras, X. Lin, N. Mackay, D.P. Marshall, H. Mercier, M. Oltmanns, R.S. Pickart, A.L. Ramsey, D. Rayner, F. Straneo, V. Thierry, D.J. Torres, R.G. Williams, C. Wilson, J. Yang, I. Yashayaev and J. Zhao. Science, Feb. 1, 2019. DOI: 10.1126/science.aau6592