Estimated decadal changes in the North Atlantic meridional overturning circulation and heat flux 1993-2004

Abstract Results from a global 1° model constrained by least squares to a multiplicity of datasets over the interval 1992–2004 are used to describe apparent changes in the North Atlantic Ocean meridional overturning circulation and associated heat fluxes at 26°N. The least squares fit is both stable and adequately close to the data to make the analysis worthwhile. Changes over the 12 yr are spatially and temporally complex. A weak statistically significant trend is found in net North Atlantic volume flux above about 1200 m, which drops slightly (−0.19 ± 0.05 Sv yr−1; 1 Sv ≡ 106 m3 s−1) but with a corresponding strengthening of the outflow of North Atlantic Deep Water and inflow of abyssal waters. The slight associated trend in meridional heat flux is very small and not statistically significant. The month-to-month variability implies that single-section determinations of heat and volume flux are subject to serious aliasing errors.

[1]  Carl Wunsch,et al.  Practical global oceanic state estimation , 2007 .

[2]  Vertical partition of ocean heat transport in isothermal coordinates , 2006 .

[3]  Carl Wunsch,et al.  Volume, heat, and freshwater transports of the global ocean circulation 1993-2000, estimated from a general circulation model constrained by World Ocean Circulation Experiment (WOCE) data , 2003 .

[4]  G. Parrilla,et al.  Mechanisms of heat, freshwater, oxygen and nutrient transports and budgets at 24.5°N in the subtropical North Atlantic , 2003 .

[5]  M. Srokosz.  Rapid climate change: scientific challenges and the new NERC programme , 2003, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[6]  K. Koltermann,et al.  WOCE Global Hydrographic Climatology , 2004 .

[7]  W. Owens,et al.  Climatic Warming of Atlantic Intermediate Waters , 2001 .

[8]  G. Parrilla,et al.  Temperature and salinity increase in the eastern North Atlantic along the 24.5°N in the last ten years , 2004 .

[9]  W. Broecker.  Does the Trigger for Abrupt Climate Change Reside in the Ocean or in the Atmosphere? , 2003, Science.

[10]  L. Perelman,et al.  A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers , 1997 .

[11]  Carl Wunsch,et al.  Spatial Mapping of Time-Variable Errors in Jason-1 and TOPEX/Poseidon Sea Surface Height Measurements , 2007 .

[12]  Carl Wunsch,et al.  The Interpretation of Short Climate Records, with Comments on the North Atlantic and Southern Oscillations , 1999 .

[13]  P. Imkeller,et al.  Stochastic climate models , 2001 .

[14]  B. Dickson,et al.  A change in the freshwater balance of the Atlantic Ocean over the past four decades , 2003, Nature.

[15]  D. Quadfasel.  Oceanography: The Atlantic heat conveyor slows , 2005, Nature.

[16]  K. Hasselmann.  Stochastic climate models Part I. Theory , 1976 .

[17]  B. Cornuelle,et al.  Interannual to Decadal Changes in the ECCO Global Synthesis , 2007 .

[18]  J. Marotzke,et al.  Monitoring the meridional overturning circulation in the North Atlantic: a model-based array design study , 2004 .

[19]  Carl Wunsch,et al.  Global ocean circulation during 1992-1997, estimated from ocean observations and a general circulation model , 2002 .

[20]  G. Parrilla,et al.  Rising temperatures in the subtropical North Atlantic Ocean over the past 35 years , 1994, Nature.

[21]  C. Wunsch.  The Ocean Circulation Inverse Problem , 1996 .

[22]  C. Wunsch.  Abrupt climate change: An alternative view , 2006, Quaternary Research.

[23]  R. Ferrari,et al.  The vertical structure of ocean heat transport , 2005 .

[24]  C. Wunsch,et al.  Estimated Global Hydrographic Variability , 2007 .

[25]  J. Church,et al.  Ocean Circulation and Climate: Observing and Modelling the Global Ocean , 2001 .

[26]  R. Molinari,et al.  Atlantic Ocean baroclinic heat flux at 24 to 26° N , 1999 .

[27]  A. Ganachaud.  Error Budget of Inverse Box Models: The North Atlantic , 2003 .

[28]  Sarah T. Gille,et al.  Ocean Circulation and Climate—Observing and Modelling the Global Ocean , 2001 .

[29]  C. Wunsch,et al.  Large-Scale Ocean Heat and Freshwater Transports during the World Ocean Circulation Experiment , 2003 .

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

[31]  H. Bryden,et al.  Thermohaline circulation at three key sections in the North Atlantic over 1985–2002 , 2005 .