The North Atlantic Ocean Is in a State of Reduced Overturning

The Atlantic Meridional Overturning Circulation (AMOC) is responsible for a variable and climatically important northward transport of heat. Using data from an array of instruments that span the Atlantic at 26°N, we show that the AMOC has been in a state of reduced overturning since 2008 as compared to 2004-2008. This change of AMOC state is concurrent with other changes in the North Atlantic such as a northward shift and broadening of the Gulf Stream, and altered patterns of heat content and sea-surface temperature. These changes resemble the response to a declining AMOC predicted by coupled climate models. Concurrent changes in air-sea fluxes close to the western boundary reveal that the changes in ocean heat transport and SST have altered the pattern of ocean-atmosphere heat exchange over the North Atlantic. These results provide strong observational evidence that the AMOC is a major factor in decadal scale variability of North Atlantic climate.

[1]  S. Rahmstorf,et al.  Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation , 2015 .

[2]  J. Houghton,et al.  Climate Change 2013 - The Physical Science Basis: Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change , 2014 .

[3]  Jie Chen,et al.  Change-point analysis as a tool to detect abrupt climate variations , 2012, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[4]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[5]  Nick Rayner,et al.  EN4: Quality controlled ocean temperature and salinity profiles and monthly objective analyses with uncertainty estimates , 2013 .

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

[7]  L. Beal,et al.  Propagation pathways of classical Labrador Sea water from its source region to 26°N , 2011 .

[8]  G. Vecchi,et al.  The North Atlantic Oscillation as a driver of rapid climate change in the Northern Hemisphere , 2016 .

[9]  M. Lozier,et al.  Assessing variability in the size and strength of the North Atlantic subpolar gyre , 2017 .

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

[11]  M. Balmaseda,et al.  The Importance of Wind and Buoyancy Forcing for the Boundary Density Variations and the Geostrophic Component of the AMOC at 26°N , 2014 .

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

[13]  B. Stevens,et al.  The Atlantic Multidecadal Oscillation without a role for ocean circulation , 2015, Science.

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

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

[16]  D. Stevens,et al.  Upper ocean manifestations of a reducing meridional overturning circulation , 2012 .

[17]  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 .

[18]  Blair R. Tormey,et al.  Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous , 2016, 1602.01393.

[19]  Bengamin I. Moat,et al.  Atlantic meridional overturning circulation observed by the RAPID-MOCHA-WBTS (RAPID-Meridional Overturning Circulation and Heatflux Array-Western Boundary Time Series) array at 26N from 2004 to 2015 , 2016 .

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

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

[22]  J. Marshall,et al.  Exploring Mechanisms of Variability and Predictability of Atlantic Meridional Overturning Circulation in Two Coupled Climate Models , 2012 .

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

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

[25]  E. Hawkins,et al.  Atlantic overturning in decline , 2014 .

[26]  Elizabeth C. Kent,et al.  Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century , 2003 .

[27]  M. Latif,et al.  North Atlantic Ocean control on surface heat flux on multidecadal timescales , 2013, Nature.

[28]  C. D. Roberts,et al.  A Multimodel Study of Sea Surface Temperature and Subsurface Density Fingerprints of the Atlantic Meridional Overturning Circulation , 2013 .

[29]  S. Xie,et al.  Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate , 2017, Science Advances.

[30]  W. Johns,et al.  Wind-Driven Seasonal Cycle of the Atlantic Meridional Overturning Circulation , 2014 .

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

[32]  I. Yashayaev,et al.  Recurrent replenishment of Labrador Sea Water and associated decadal‐scale variability , 2016 .

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