Evaluation of the GECCO2 ocean synthesis: transports of volume, heat and freshwater in the Atlantic

We present results from a new synthesis (GECCO2) which covers the years 1948 to 2011 employing a similar configuration of the Massachusetts Institute of Technology general circulation model as the previous 50-year (1952 to 2001) GECCO synthesis. In GECCO2, the resolution was increased; it now includes the Arctic Ocean and a dynamic/thermodynamic sea ice model. The synthesis uses the adjoint method to bring the model into consistency with available hydrographic and satellite data as well as prior estimates of surface fluxes. In comparison to GECCO, GECCO2 provides a better agreement with the assimilated data, however the estimated flux adjustments remain similar to GECCO. Global heat content changes are in agreement with recent observational estimates and the estimate of the global heat flux is close to a radiative forcing estimate. Both show a clear effect of the radiative forcing from volcanic eruptions and a weak relation to ENSO events. In contrast to GECCO, the importance of the Denmark Strait overflow for the variability of the Atlantic Meridional Overturning Circulation (AMOC) is replaced in GECCO2 by water mass transformation in the subpolar gyre, which is shown to be part of the thermohaline circulation if the overturning is defined as a function of density. Heat and freshwater transport estimates in the Atlantic are more consistent with previous estimates than the unconstrained run. Decomposing heat and freshwater transports into overturning and gyre components by averaging on density coordinates demonstrates that in these coordinates the contribution from the gyre circulation largely disappears for heat transport and is reduced for the freshwater transport.

[1]  Arne Körtzinger,et al.  Optimization of a Membrane-Based NDIR Sensor for Dissolved Carbon Dioxide , 2010 .

[2]  John Marshall,et al.  Open‐ocean convection: Observations, theory, and models , 1999 .

[3]  Pierre Bahurel,et al.  Mercator Ocean Global to Regional Ocean Monitoring and Forecasting , 2006 .

[4]  Carl Wunsch,et al.  Estimating air‐sea fluxes of heat, freshwater, and momentum through global ocean data assimilation , 2004 .

[5]  D. Rothrock,et al.  Modeling Arctic sea ice with an efficient plastic solution , 2000 .

[6]  S. Levitus,et al.  Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems , 2007 .

[7]  Stephen G. Yeager,et al.  Diurnal to decadal global forcing for ocean and sea-ice models: The data sets and flux climatologies , 2004 .

[8]  K. Speer,et al.  Global Ocean Meridional Overturning , 2007 .

[9]  A. Jäggi,et al.  Combined satellite gravity field model GOCO01S derived from GOCE and GRACE , 2010 .

[10]  Tong Lee,et al.  Ocean State Estimation for Climate Research , 2010 .

[11]  Stephen Cusack,et al.  Improved Surface Temperature Prediction for the Coming Decade from a Global Climate Model , 2007, Science.

[12]  L. Talley.  Freshwater transport estimates and the global overturning circulation: Shallow, deep and throughflow components , 2008 .

[13]  John A. Church,et al.  Changing Expendable Bathythermograph Fall Rates and Their Impact on Estimates of Thermosteric Sea Level Rise , 2008 .

[14]  Peter J. Gleckler,et al.  Improved estimates of upper-ocean warming and multi-decadal sea-level rise , 2008, Nature.

[15]  M. England,et al.  Ekman Transport Dominates Local Air–Sea Fluxes in Driving Variability of Subantarctic Mode Water , 2002 .

[16]  Carl Wunsch,et al.  Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data , 2000, Nature.

[17]  A. Gordon,et al.  Cyclonic gyre in the tropical South Atlantic , 1991 .

[18]  D. Stammer,et al.  Impact of assimilating bottom pressure anomalies from GRACE on ocean circulation estimates , 2012 .

[19]  L. Perelman,et al.  Hydrostatic, quasi‐hydrostatic, and nonhydrostatic ocean modeling , 1997 .

[20]  D. Roemmich,et al.  The global ocean imprint of ENSO , 2011 .

[21]  D. Stammer,et al.  Sea surface freshwater flux estimates from GECCO, HOAPS and NCEP , 2010 .

[22]  C. Ropelewski,et al.  Current approaches to seasonal to interannual climate predictions , 2001 .

[23]  W. Schmitz,et al.  On the North Atlantic Circulation , 1993 .

[24]  M. Huddleston,et al.  Quality control of ocean temperature and salinity profiles — Historical and real-time data , 2007 .

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

[26]  Pablo Sangrà,et al.  Temporal variability of mass transport in the Canary Current , 2002 .

[27]  Carsten Eden,et al.  Mechanism of Interannual to Decadal Variability of the North Atlantic Circulation , 2001 .

[28]  S. Levitus,et al.  Linear trends in salinity for the World Ocean, 1955–1998 , 2005 .

[29]  J. Carton,et al.  Global Decadal Upper-Ocean Heat Content as Viewed in Nine Analyses , 2008 .

[30]  Carl Wunsch,et al.  Two transatlantic sections: meridional circulation and heat flux in the subtropical North Atlantic Ocean , 1985 .

[31]  T. Lee,et al.  Observational Requirements for Global-Scale Ocean Climate Analysis: Lessons from Ocean State Estimation , 2010 .

[32]  S. Levitus,et al.  Linear trends of zonally averaged thermosteric, halosteric, and total steric sea level for individual ocean basins and the world ocean, (1955–1959)–(1994–1998) , 2005 .

[33]  A. Koehl.  Detecting Processes Contributing to Interannual Halosteric and Thermosteric Sea Level Variability , 2014 .

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

[35]  David R. Doelling,et al.  Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty , 2012 .

[36]  Syukuro Manabe,et al.  Interdecadal Variations of the Thermohaline Circulation in a Coupled Ocean-Atmosphere Model , 1993 .

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

[38]  L. Kornblueh,et al.  Advancing decadal-scale climate prediction in the North Atlantic sector , 2008, Nature.

[39]  M. Kimoto,et al.  Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections , 2009 .

[40]  S. Levitus,et al.  Warming of the World Ocean , 2000 .

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

[42]  J. Marotzke,et al.  Monitoring the Atlantic meridional overturning circulation , 2011 .

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

[44]  Lynne D. Talley,et al.  Some aspects of ocean heat transport by the shallow, intermediate and deep overturning Circulations , 2013 .

[45]  Rüdiger Gerdes,et al.  Recent radical shifts of atmospheric circulations and rapid changes in Arctic climate system , 2008 .

[46]  S. Rahmstorf.  On the freshwater forcing and transport of the Atlantic thermohaline circulation , 1996 .

[47]  Yan Xue,et al.  Ocean State Estimation for Global Ocean Monitoring: ENSO and Beyond ENSO , 2010 .

[48]  D. Stammer,et al.  Decadal Sea Level Changes in the 50-Year GECCO Ocean Synthesis , 2008 .

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

[50]  Martin Visbeck,et al.  Interannual to decadal variability of outflow from the Labrador Sea , 2010 .

[51]  E. Trenberth,et al.  New estimates of continental discharge and oceanic freshwater transport [poster] , 2003 .

[52]  F. Schott,et al.  The mean flow field of the tropical Atlantic Ocean , 1999 .

[53]  Tong Lee,et al.  Consistency and fidelity of Indonesian-throughflow total volume transport estimated by 14 ocean data assimilation products , 2010 .

[54]  K. Koltermann,et al.  How much is the ocean really warming? , 2007 .

[55]  Detlef Stammer,et al.  Initializing Decadal Climate Predictions with the GECCO Oceanic Synthesis: Effects on the North Atlantic , 2009 .

[56]  H. Roquet,et al.  Evaluation of operational ECMWF surface freshwater fluxes over oceans during 1991–1997 , 1999 .

[57]  A. Biastoch,et al.  Decadal variability of subpolar gyre transport and its reverberation in the North Atlantic overturning , 2006 .

[58]  Patrick Heimbach,et al.  Ocean information provided through ensemble ocean syntheses , 2010 .

[59]  L. Stramma.  Geostrophic transport in the Warm Water Sphere of the eastern subtropical North Atlantic , 1984 .

[60]  W. Johns,et al.  Transport variability of the Deep Western Boundary Current and the Antilles Current off Abaco Island, Bahamas , 2004 .

[61]  P. Eriksson,et al.  Constraints on Estimating Mass, Heat and Freshwater Transports in the Arctic Ocean: An Exercise , 2008 .

[62]  J. S. Godfrey,et al.  Regional Oceanography: An Introduction , 1994 .

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

[64]  Detlef Stammer,et al.  Variability of the Meridional Overturning in the North Atlantic from the 50-Year GECCO State Estimation , 2006 .

[65]  Variability in North Atlantic heat content and heat transport in a coupled ocean–atmosphere GCM , 2002 .

[67]  M. Balmaseda,et al.  Evaluation of the ECMWF ocean reanalysis system ORAS4 , 2013 .

[68]  W. Large,et al.  Open Ocean Momentum Flux Measurements in Moderate to Strong Winds , 1981 .

[69]  S. Levitus,et al.  World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010 , 2012 .

[70]  Stephen Dye,et al.  Rapid freshening of the deep North Atlantic Ocean over the past four decades , 2002, Nature.

[71]  S. Weber,et al.  The Atlantic freshwater budget as a diagnostic for the existence of a stable shut down of the meridional overturning circulation , 2005 .

[72]  B. Dong,et al.  Mechanism of interdecadal thermohaline circulation variability in a coupled ocean : Atmosphere GCM , 2005 .

[73]  T. H. Haar,et al.  New Estimate of Annual Poleward Energy Transport by Northern Hemisphere Oceans , 1973 .

[74]  V. Mohrholz,et al.  Hydrographic and current measurements in the area of the Angola-Benguela Front , 2000 .

[75]  Kevin E. Trenberth,et al.  Distinctive climate signals in reanalysis of global ocean heat content , 2013 .

[76]  R. Davis,et al.  Revisiting the South Pacific subtropical circulation: A synthesis of World Ocean Circulation Experiment observations along 32°S , 2001 .

[77]  C. Wunsch.  Meridional heat flux of the North Atlantic Ocean. , 1980, Proceedings of the National Academy of Sciences of the United States of America.

[78]  Toru Miyama,et al.  Development of a four‐dimensional variational coupled data assimilation system for enhanced analysis and prediction of seasonal to interannual climate variations , 2008 .

[79]  S. Solomon,et al.  An observationally based energy balance for the Earth since 1950 , 2009 .

[80]  L. Talley.  Shallow, Intermediate, and Deep Overturning Components of the Global Heat Budget , 2003 .

[81]  W. Large,et al.  Sensible and Latent Heat Flux Measurements over the Ocean , 1982 .

[82]  K. Trenberth,et al.  Estimates of Meridional Atmosphere and Ocean Heat Transports , 2001 .