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Front. Mar. Sci. | doi: 10.3389/fmars.2019.00260

Atlantic Meridional Overturning Circulation: Observed transports and variability

 Eleanor Frajka-Williams1*, Isabelle J. Ansorge2,  Johanna Baehr3, Harry L. Bryden4,  Maria Paz Chidichimo5,  Stuart A. Cunningham6, Gokhan Danabasoglu7,  Shenfu Dong8,  Kathleen A. Donohue9, Shane Elipot10,  N. Penny Holliday1,  Rebecca Hummels11, Laura C. Jackson12,  Johannes Karstensen11,  Matthias Lankhorst13,  Isabela Le Bras13, M. Susan Lozier14, Elaine L. McDonagh1,  Christopher S. Meinen8,  Herle Mercier15, Bengamin I. Moat1,  Renellys C. Perez8, Christopher G. Piecuch16, Monika Rhein17,  Meric Srokosz1,  Kevin E. Trenberth7, Sheldon Bacon1,  Gael Forget18,  Gustavo J. Goni8,  Patrick Heimbach19, Dagmar Kieke17,  Jannes Koelling13,  Tarron Lamont2, Gerard McCarthy20, Christian Mertens17, Uwe Send13, David A. Smeed1, Marcel van den Berg21,  Denis Volkov8 and  Chris Wilson1, 22
  • 1National Oceanography Centre, University of Southampton, United Kingdom
  • 2Department of Oceanography, Faculty of Science, University of Cape Town, South Africa
  • 3Institut für Meereskunde, Fachbereich Geowissenschaften, Universität Hamburg, Germany
  • 4University of Southampton, United Kingdom
  • 5National Council for Scientific and Technical Research (CONICET), Argentina
  • 6Scottish Association For Marine Science, United Kingdom
  • 7National Center for Atmospheric Research (UCAR), United States
  • 8Atlantic Oceanographic and Meteorological Laboratory (NOAA), United States
  • 9University of Rhode Island, United States
  • 10Rosenstiel School of Marine and Atmospheric Science, University of Miami, United States
  • 11GEOMAR Helmholtz Center for Ocean Research Kiel, Germany
  • 12Met Office Hadley Centre (MOHC), United Kingdom
  • 13Scripps Institution of Oceanography, University of California, San Diego, United States
  • 14Duke University, United States
  • 15UMR6523 Laboratoire d'Oceanographie Physique et Spatiale (LOPS), France
  • 16Woods Hole Oceanographic Institution, United States
  • 17Center for Marine Environmental Sciences, University of Bremen, Germany
  • 18Massachusetts Institute of Technology, United States
  • 19Jackson School of Geosciences, The University of Texas at Austin, United States
  • 20ICARUS Climate Research Centre, Faculty of Social Sciences, Maynooth University, Ireland
  • 21Department of Environmental Affairs, South Africa
  • 22National Oceanography Centre, University of Southampton, United Kingdom

The Atlantic Meridional Overturning Circulation (AMOC) extends from the Southern Ocean to the northern North Atlantic, transporting heat northwards throughout the South and North Atlantic, and sinking carbon and nutrients into the deep ocean. Climate models indicate that changes to the AMOC both herald and drive climate shifts. Intensive trans-basin AMOC observational systems have been put in place to continuously monitor meridional volume transport variability, and in some cases, heat, freshwater and carbon transport. These observational programs have been used to diagnose the magnitude and origins of transport variability, and to investigate impacts of variability on essential climate variables such as sea surface temperature, ocean heat content and coastal sea level. AMOC observing approaches vary between the different systems, ranging from trans-basin arrays (OSNAP, RAPID 26 N, 11 S, SAMBA 34.5 N) to arrays concentrating on western boundaries (e.g., RAPID WAVE, MOVE 16 N). In this paper, we outline the different approaches (aims, strengths and limitations) and summarize the key results to date. We also discuss alternate approaches for capturing AMOC variability including direct estimates (e.g., using sea level, bottom pressure, and hydrography from Lagrangian floats), indirect estimates applying budgetary approaches, state estimates or ocean reanalyses, and proxies. Based on the existing observations and their results, and the potential of new observational and formal synthesis approaches, we make suggestions as to how to evaluate a comprehensive, future-proof observational network of the AMOC to deepen our understanding of the AMOC and its role in global climate.

Keywords: Meridional overturning circulation (MOC), Thermohaline circulation (THC), ocean heat content (OHC), Observing System Simulation Experiment (OSSE), Carbon Storage

Received: 15 Nov 2018; Accepted: 02 May 2019.

Edited by:

Fei Chai, Second Institute of Oceanography, State Oceanic Administration, China

Reviewed by:

Ru Chen, University of California, Los Angeles, United States
Helen E. Phillips, University of Tasmania, Australia
Wen-Zhou Zhang, Xiamen University, China  

Copyright: © 2019 Frajka-Williams, Ansorge, Baehr, Bryden, Chidichimo, Cunningham, Danabasoglu, Dong, Donohue, Elipot, Holliday, Hummels, Jackson, Karstensen, Lankhorst, Le Bras, Lozier, McDonagh, Meinen, Mercier, Moat, Perez, Piecuch, Rhein, Srokosz, Trenberth, Bacon, Forget, Goni, Heimbach, Kieke, Koelling, Lamont, McCarthy, Mertens, Send, Smeed, van den Berg, Volkov and Wilson. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Eleanor Frajka-Williams, National Oceanography Centre, University of Southampton, Southampton, SO14 3ZH, England, United Kingdom, eleanorfrajka@gmail.com