Atlantic Meridional Overturning Circulation: Observed Transport and Variability

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.

Patrick Heimbach | Bengamin I. Moat | Herlé Mercier | Johannes Karstensen | Gustavo Goni | David A. Smeed | Matthias Lankhorst | Johanna Baehr | Harry L. Bryden | Gerard D. McCarthy | Kathleen A. Donohue | Stuart A. Cunningham | Meric A. Srokosz | Gokhan Danabasoglu | Kevin E. Trenberth | Tarron Lamont | Uwe Send | Gael Forget | Denis Volkov | Sheldon Bacon | Christian Mertens | Eleanor Frajka-Williams | Chris Wilson | M. Susan Lozier | Shane Elipot | N. Penny Holliday | K. Trenberth | G. Danabasoglu | C. Mertens | P. Heimbach | J. Karstensen | S. Dong | D. Volkov | S. Bacon | S. Speich | D. Smeed | M. Lozier | M. Rhein | L. Jackson | J. Baehr | H. Bryden | N. P. Holliday | I. Ansorge | M. van den Berg | G. Goñi | C. Meinen | R. Perez | C. Wilson | U. Send | M. Srokosz | S. Elipot | E. Frajka‐Williams | M. Lankhorst | M. P. Chidichimo | R. Hummels | T. Lamont | G. Forget | C. Piecuch | Sabrina Speich | Shenfu Dong | K. Donohue | Isabelle J. Ansorge | Christopher G. Piecuch | Christopher S. Meinen | B. Moat | H. Mercier | Maria Paz Chidichimo | Rebecca Hummels | Laura C. Jackson | Isabela A. Le Bras | Elaine L. McDonagh | Renellys C. Perez | Monika Rhein | Dagmar Kieke | Jannes Koelling | Marcel van den Berg | S. Cunningham | D. Kieke | G. McCarthy | E. McDonagh | J. Koelling | Marcel Berg | I. Bras | I. L. Le Bras | S. Cunningham | Gustavo Goni | Chris Wilson | Renellys C. Perez | Chris Wilson | Chris Wilson | Johanna Baehr | Laura C. Jackson | Sheldon Bacon | Denis L. Volkov | Chris Wilson | Marcel van den Berg | Shenfu Dong | Johanna Baehr | Laura C. Jackson | Marcel van den Berg | D. Volkov | L. C. Jackson | Marcel A. van den Berg | S. A. Cunningham | L. Jackson

[1]  L. Houpert,et al.  A sea change in our view of overturning in the subpolar North Atlantic , 2019, Science.

[2]  K. Trenberth,et al.  Applications of an Updated Atmospheric Energetics Formulation , 2018, Journal of Climate.

[3]  R. Ponte,et al.  River-discharge effects on United States Atlantic and Gulf coast sea-level changes , 2018, Proceedings of the National Academy of Sciences.

[4]  R. Ferrari,et al.  Dynamics of an Abyssal Circulation Driven by Bottom-Intensified Mixing on Slopes , 2018, Journal of Physical Oceanography.

[5]  S. Dong,et al.  Meridional Overturning Circulation Transport Variability at 34.5°S During 2009–2017: Baroclinic and Barotropic Flows and the Dueling Influence of the Boundaries , 2018 .

[6]  U. Send,et al.  Coherent Circulation Changes in the Deep North Atlantic From 16°N and 26°N Transport Arrays , 2018 .

[7]  J. Robson,et al.  How Robust Are the Surface Temperature Fingerprints of the Atlantic Overturning Meridional Circulation on Monthly Time Scales? , 2018 .

[8]  David A. Smeed,et al.  The North Atlantic Ocean Is in a State of Reduced Overturning , 2018 .

[9]  Chris W. Hughes,et al.  A window on the deep ocean: the special value of ocean bottom pressure for monitoring the large-scale, deep-ocean circulation , 2018 .

[10]  S. Rahmstorf,et al.  Observed fingerprint of a weakening Atlantic Ocean overturning circulation , 2017, Nature.

[11]  S. Speich,et al.  Moored observations of mesoscale features in the Cape Basin: characteristics and local impacts on water mass distributions , 2017, Ocean Science.

[12]  G. Evensen,et al.  Data assimilation in the geosciences: An overview of methods, issues, and perspectives , 2017, WIREs Climate Change.

[13]  M. Lozier,et al.  On the Linkage between Labrador Sea Water Volume and Overturning Circulation in the Labrador Sea: A Case Study on Proxies , 2017, Journal of Climate.

[14]  Kenneth J. Connell,et al.  Comparison of ATLAS and T-Flex Mooring Data , 2018 .

[15]  Feili Li.  Data from: Microcat, current meter and ADCP data from the eastern mid-Atlantic ridge mooring array as part of OSNAP (Overturning in the Subpolar North Atlantic Program) , 2018 .

[16]  Lawrence E. Flynn,et al.  How long do satellites need to overlap? Evaluation of climate data stability from overlapping satellite records , 2017 .

[17]  J. Toole,et al.  Moored observations of the Deep Western Boundary Current in the NW Atlantic: 2004-2014 , 2017 .

[18]  M. Lozier,et al.  Calculating the Meridional Volume, Heat, and Freshwater Transports from an Observing System in the Subpolar North Atlantic: Observing System Simulation Experiment , 2017 .

[19]  J. Toole,et al.  Tracking Labrador Sea Water property signals along the Deep Western Boundary Current , 2017 .

[20]  R. Ponte,et al.  On the relationship between the meridional overturning circulation, alongshore wind stress, and United States East Coast sea level in the Community Earth System Model Large Ensemble: AMOC-SEA LEVEL IN CESM-LE , 2017 .

[21]  N. Schneider,et al.  Western Boundary Sea Level: A Theory, Rule of Thumb, and Application to Climate Models , 2017 .

[22]  Patrick Heimbach,et al.  Overturning in the Subpolar North Atlantic Program: A New International Ocean Observing System , 2017 .

[23]  S. Dong,et al.  A reconstructed South Atlantic Meridional Overturning Circulation time series since 1870 , 2017 .

[24]  A. Bower,et al.  Observed and modeled pathways of the Iceland Scotland Overflow Water in the eastern North Atlantic , 2017 .

[25]  Arne Biastoch,et al.  Flow paths and variability of the North Atlantic Current: A comparison of observations and a high‐resolution model , 2017 .

[26]  J. Toole,et al.  Recent Wind-Driven Variability in Atlantic Water Mass Distribution and Meridional Overturning Circulation , 2017 .

[27]  J. Karstensen,et al.  From interannual to decadal: 17 years of boundary current transports at the exit of the Labrador Sea , 2017 .

[28]  S. Olhede,et al.  Observed Basin-Scale Response of the North Atlantic Meridional Overturning Circulation to Wind Stress Forcing , 2017 .

[29]  M. Ostrowski,et al.  The Angola Current: Flow and hydrographic characteristics as observed at 11°S , 2017 .

[30]  Kevin E. Trenberth,et al.  Atlantic meridional heat transports computed from balancing Earth's energy locally , 2017 .

[31]  K. Haines,et al.  Using lagged covariances in data assimilation , 2017 .

[32]  Edmo Campos,et al.  Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014 , 2016 .

[33]  C. Schmid,et al.  An observations and model‐based analysis of meridional transports in the South Atlantic , 2016 .

[34]  L. Thompson,et al.  Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports , 2016 .

[35]  D. Berry,et al.  Drivers of exceptionally cold North Atlantic Ocean temperatures and their link to the 2015 European heat wave , 2016 .

[36]  R. Wood,et al.  Recent slowing of Atlantic overturning circulation as a recovery from earlier strengthening , 2016 .

[37]  G. Danabasoglu,et al.  Comment on “The Atlantic Multidecadal Oscillation without a role for ocean circulation” , 2016, Science.

[38]  D. Smeed,et al.  Major variations in subtropical North Atlantic heat transport at short (5 day) timescales and their causes , 2016 .

[39]  P. Heimbach,et al.  Dynamical Attribution of Recent Variability in Atlantic Overturning , 2016 .

[40]  D. Smeed,et al.  Potential for seasonal prediction of Atlantic sea surface temperatures using the RAPID array at 26$$^{\circ }$$∘N , 2016 .

[41]  J. Toole,et al.  Stirring by deep cyclones and the evolution of Denmark strait overflow water observed at line W , 2016 .

[42]  P. Heimbach,et al.  Ocean Data Assimilation in Support of Climate Applications: Status and Perspectives. , 2016, Annual review of marine science.

[43]  J. Marshall,et al.  Reviews of Geophysics Observations , inferences , andmechanisms of Atlantic Meridional Overturning Circulation variability : A review , 2016 .

[44]  B. Samuels,et al.  North Atlantic simulations in Coordinated Ocean-ice Reference Experiments phase II (CORE-II). Part II: Inter-annual to decadal variability , 2016 .

[45]  G. Danabasoglu,et al.  Comparison of the Atlantic meridional overturning circulation between 1960 and 2007 in six ocean reanalysis products , 2017, Climate Dynamics.

[46]  John Marshall,et al.  Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review , 2016 .

[47]  C. Atkinson,et al.  Continuous Estimate of Atlantic Oceanic Freshwater Flux at 26.5°N , 2015 .

[48]  North Atlantic meridional overturning circulation variations from GRACE ocean bottom pressure anomalies , 2015 .

[49]  C. Wunsch,et al.  ECCO version 4: an integrated framework for non-linear inverse modeling and global ocean state estimation , 2015 .

[50]  Jonathan V. Durgadoo,et al.  Interannual to decadal changes in the western boundary circulation in the Atlantic at 11°S , 2015 .

[51]  S. Dong,et al.  Temporal variability of the South Atlantic Meridional Overturning Circulation between 20°S and 35°S , 2015 .

[52]  R. Ponte,et al.  Inverted barometer contributions to recent sea level changes along the northeast coast of North America , 2015 .

[53]  M. Tamisiea,et al.  Detecting trends in bottom pressure measured using a tall mooring and altimetry , 2015 .

[54]  H. Bryden,et al.  Observing the Atlantic Meridional Overturning Circulation yields a decade of inevitable surprises , 2015, Science.

[55]  C. Mertens,et al.  Long‐term observations of North Atlantic Current transport at the gateway between western and eastern Atlantic , 2015 .

[56]  D. Smeed,et al.  Ocean impact on decadal Atlantic climate variability revealed by sea-level observations , 2015, Nature.

[57]  E. Frajka‐Williams.  Estimating the Atlantic overturning at 26°N using satellite altimetry and cable measurements , 2015 .

[58]  Tong Lee,et al.  The Ocean Reanalyses Intercomparison Project (ORA-IP) , 2015 .

[59]  M. Rhein,et al.  Advection of North Atlantic Deep Water from the Labrador Sea to the southern hemisphere , 2015 .

[60]  F. Gaillard,et al.  Variability of the meridional overturning circulation at the Greenland-Portugal OVIDE section from 1993 to 2010 , 2015 .

[61]  Shaoqing Zhang,et al.  An extreme event of sea-level rise along the Northeast coast of North America in 2009–2010 , 2015, Nature Communications.

[62]  J. Palter.  The role of the Gulf Stream in European climate. , 2015, Annual review of marine science.

[63]  T. Rossby,et al.  A comparison of transport and position between the Gulf Stream east of Cape Hatteras and the Florida Current , 2015 .

[64]  Armin Köhl,et al.  Evaluation of the GECCO2 ocean synthesis: transports of volume, heat and freshwater in the Atlantic , 2015 .

[65]  Bengamin I. Moat,et al.  Measuring the Atlantic Meridional Overturning Circulation at 26°N , 2015 .

[66]  M. Maqueda,et al.  Mean sea-level variability along the northeast American Atlantic coast and the roles of the wind and the overturning circulation , 2015 .

[67]  C. Mertens,et al.  Circulation and transports in the Newfoundland Basin, western subpolar North Atlantic , 2014 .

[68]  Doug M. Smith,et al.  A novel transport assimilation method for the Atlantic meridional overturning circulation at 26°N , 2014 .

[69]  E. Frajka‐Williams,et al.  Vertical structure of eddies and Rossby waves, and their effect on the Atlantic meridional overturning circulation at 26.5°N , 2014 .

[70]  C. Schmid.  Mean vertical and horizontal structure of the subtropical circulation in the South Atlantic from three-dimensional observed velocity fields , 2014 .

[71]  S. Tett,et al.  How Much Has the North Atlantic Ocean Overturning Circulation Changed in the Last 50 Years , 2014 .

[72]  S. Garzoli,et al.  Attribution of Deep Western Boundary Current variability at 26.5°N , 2014 .

[73]  S. Dong,et al.  Seasonal variations in the South Atlantic Meridional Overturning Circulation from observations and numerical models , 2014 .

[74]  W. Johns,et al.  Wind‐forced interannual variability of the Atlantic Meridional Overturning Circulation at 26.5°N , 2014 .

[75]  Josh K. Willis,et al.  The Observed North Atlantic Meridional Overturning Circulation: Its Meridional Coherence and Ocean Bottom Pressure , 2014 .

[76]  J. Lillibridge,et al.  On the long‐term stability of Gulf Stream transport based on 20 years of direct measurements , 2014 .

[77]  Patrick Heimbach,et al.  North Atlantic simulations in Coordinated Ocean-ice Reference Experiments phase II (CORE-II). Part I: Mean states , 2014 .

[78]  S. Dong,et al.  Temporal variability of the meridional overturning circulation at 34.5°S: Results from two pilot boundary arrays in the South Atlantic , 2013 .

[79]  J. Toole,et al.  Interannual sea level variability in the western North Atlantic: Regional forcing and remote response , 2013 .

[80]  D. Lea,et al.  Atmosphere drives recent interannual variability of the Atlantic meridional , 2017 .

[81]  Bengamin I. Moat,et al.  Observed decline of the Atlantic meridional overturning circulation 2004–2012 , 2013 .

[82]  Carl Wunsch,et al.  Two Decades of the Atlantic Meridional Overturning Circulation: Anatomy, Variations, Extremes, Prediction, and Overcoming Its Limitations , 2013 .

[83]  J. Lyman,et al.  The Coherence and Impact of Meridional Heat Transport Anomalies in the Atlantic Ocean Inferred from Observations , 2013 .

[84]  R. Kopp,et al.  Does the mid‐Atlantic United States sea level acceleration hot spot reflect ocean dynamic variability? , 2013 .

[85]  M. A. Morales Maqueda,et al.  Test of a Method for Monitoring the Geostrophic Meridional Overturning Circulation Using Only Boundary Measurements , 2013 .

[86]  Keith W. Dixon,et al.  Have Aerosols Caused the Observed Atlantic Multidecadal Variability , 2013 .

[87]  J. Baehr,et al.  Observed and simulated variability of the AMOC at 26°N and 41°N , 2013 .

[88]  Bill Wilson,et al.  In a relationship , 2013 .

[89]  F. F. Pérèz,et al.  Atlantic Ocean CO2 uptake reduced by weakening of the meridional overturning circulation , 2013 .

[90]  W. Johns,et al.  Variability of the Deep Western Boundary Current at 26.5°N during 2004–2009 , 2013 .

[91]  M. Baringer,et al.  Ocean Heat Transport , 2013 .

[92]  A. Bower,et al.  Simulated pathways of the overflow waters in the North Atlantic: Subpolar to subtropical export , 2013 .

[93]  F. F. Pérèz,et al.  Atlantic Ocean CO 2 uptake reduced by weakening of the meridional overturning circulation , 2013 .

[94]  Peter A. Howd,et al.  Hotspot of accelerated sea-level rise on the Atlantic coast of North America , 2012 .

[95]  William E. Johns,et al.  Observed interannual variability of the Atlantic meridional overturning circulation at 26.5°N , 2012 .

[96]  K. Haines,et al.  Assimilation of RAPID array observations into an ocean model , 2012 .

[97]  K. Haines,et al.  Transports and budgets in a 1/4 ° global ocean reanalysis 1989–2010 , 2012 .

[98]  Nicolas Bellouin,et al.  Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability , 2012, Nature.

[99]  H. Melling,et al.  Observations in the Ocean , 2012 .

[100]  M. Lozier.  Overturning in the North Atlantic. , 2012, Annual review of marine science.

[101]  U. Send,et al.  Observation of decadal change in the Atlantic meridional overturning circulation using 10 years of continuous transport data , 2011 .

[102]  H. Bryden,et al.  Variability of Antarctic Bottom Water at 24.5°N in the Atlantic , 2011 .

[103]  J. Toole,et al.  Recent changes in the Labrador Sea Water within the Deep Western Boundary Current southeast of Cape Cod , 2011 .

[104]  C. Mertens,et al.  Deep water formation, the subpolar gyre, and the meridional overturning circulation in the subpolar North Atlantic , 2011 .

[105]  E. Muñoz,et al.  Varied representation of the Atlantic Meridional Overturning across multidecadal ocean reanalyses , 2011 .

[106]  J. Schröter,et al.  Can sea surface height be used to estimate oceanic transport variability? , 2011 .

[107]  William E. Johns,et al.  Continuous, Array-Based Estimates of Atlantic Ocean Heat Transport at 26.5°N , 2011 .

[108]  Patrick Heimbach,et al.  Optimal Excitation of Interannual Atlantic Meridional Overturning Circulation Variability , 2011 .

[109]  M. Lozier,et al.  Opposing decadal changes for the North Atlantic meridional overturning circulation , 2010 .

[110]  J. Baehr.  Influence of the 26 degrees N RAPID-MOCHA Array and Florida Current Cable Observations on the ECCO-GODAE State Estimate , 2010 .

[111]  J. Willis.  Can in situ floats and satellite altimeters detect long‐term changes in Atlantic Ocean overturning? , 2010 .

[112]  J. Marotzke,et al.  Observed and simulated estimates of the meridional overturning circulation at 26.5° N in the Atlantic , 2009 .

[113]  A. Bower,et al.  Interior pathways of the North Atlantic meridional overturning circulation , 2009, Nature.

[114]  J. Marotzke,et al.  Sub-seasonal to seasonal variability of the Atlantic Meridional Overturning Circulation at 26.5N , 2009 .

[115]  H. Bryden,et al.  Basinwide Integrated Volume Transports in an Eddy-Filled Ocean , 2009 .

[116]  Rory J. Bingham,et al.  Signature of the Atlantic meridional overturning circulation in sea level along the east coast of North America , 2009 .

[117]  Rong‐Hua Zhang.  Coherent surface‐subsurface fingerprint of the Atlantic meridional overturning circulation , 2008 .

[118]  Rory J. Bingham,et al.  Determining North Atlantic meridional transport variability from pressure on the western boundary: A model investigation , 2008 .

[119]  R. Weiss,et al.  The formation rate of North Atlantic Deep Water and Eighteen Degree Water calculated from CFC-11 inventories observed during WOCE , 2008 .

[120]  P. Richardson.  On the history of meridional overturning circulation schematic diagrams , 2008 .

[121]  C. Wunsch.  Mass and volume transport variability in an eddy-filled ocean , 2008 .

[122]  C. S. Wong,et al.  Climatological mean and decadal change in surface ocean pCO2, and net seaair CO2 flux over the global oceans , 2009 .

[123]  Richard G. Williams,et al.  Meridional coherence of the North Atlantic meridional overturning circulation , 2007 .

[124]  M. Balmaseda,et al.  Impact of Argo on analyses of the global ocean , 2007 .

[125]  J. Marotzke,et al.  Temporal Variability of the Atlantic Meridional Overturning Circulation at 26.5°N , 2007, Science.

[126]  Stefan Rahmstorf,et al.  On the driving processes of the Atlantic meridional overturning circulation , 2007 .

[127]  Rong‐Hua Zhang.  Anticorrelated multidecadal variations between surface and subsurface tropical North Atlantic , 2007 .

[128]  H. Dijkstra.  Characterization of the multiple equilibria regime in a global ocean model , 2007 .

[129]  T. Wilbanks,et al.  Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change , 2007 .

[130]  Johanna Baehr,et al.  Detecting potential changes in the meridional overturning circulation at 26˚N in the Atlantic , 2008 .

[131]  S. Speich,et al.  Role of bathymetry in Agulhas Current configuration and behaviour , 2006 .

[132]  Carl Wunsch,et al.  Estimated decadal changes in the North Atlantic meridional overturning circulation and heat flux 1993-2004 , 2006 .

[133]  H. Bryden,et al.  Slowing of the Atlantic meridional overturning circulation at 25° N , 2005, Nature.

[134]  J. Fischer,et al.  The shallow and deep western boundary circulation of the South Atlantic at 5-11°S , 2005 .

[135]  Bernard Barnier,et al.  Variability of the meridional overturning circulation of the North Atlantic: sensitivity to overflows of dense water masses , 2004 .

[136]  F. Schott,et al.  Break-up of the Atlantic deep western boundary current into eddies at 8 degrees S. , 2004, Nature.

[137]  Charlie N. Barron,et al.  The Cape Cauldron: A regime of turbulent inter-ocean exchange , 2003 .

[138]  Wilbert Weijer,et al.  Indian‐Atlantic interocean exchange: Dynamics, estimation and impact , 1999 .

[139]  J. Toggweiler,et al.  On the Ocean’s Large-Scale Circulation near the Limit of No Vertical Mixing , 1998 .

[140]  D. Easterling,et al.  Indices of Climate Change for the United States , 1996 .

[141]  Columbus O’Donnell Iselin,et al.  Preliminary Report on Long-Period Variations in the Transport of the Gulf Stream System , 1940 .

[142]  Measuring the Atlantic Meridional Overturning , 2022 .