Climate Dynamics

, Volume 50, Issue 9–10, pp 3783–3798 | Cite as

Ocean heat content variability in an ensemble of twentieth century ocean reanalyses

  • Eric de BoissésonEmail author
  • Magdalena Alonso Balmaseda
  • Michael Mayer


This paper presents a ten-member ensemble of twentieth century Ocean ReAnalyses called ORA-20C. ORA-20C assimilates temperature and salinity profiles and is forced by the ECMWF twentieth century atmospheric reanalysis (ERA-20C) over the 1900–2010 period. This study attempts to identify robust signals of ocean heat content change in ORA-20C and detect contamination by model errors, initial condition uncertainty, surface fluxes and observing system changes. It is shown that ORA-20C trends and variability in the first part of the century result from the surface fluxes and model drift towards a warmer mean state and weak meridional overturning circulation. The impact of the observing system in correcting the mean state causes the deceleration of the warming trend and alters the long-term climate signal. The ensemble spread reflects the long-lasting memory of the initial conditions and the convergence of the system to a solution compatible with surface fluxes, the ocean model and observational constraints. Observations constrain the ocean heat uptake trend in the last decades of the twentieth century, which is similar to trend estimations from the post-satellite era. An ocean heat budget analysis attributes ORA-20C heat content changes to surface fluxes in the first part of the century. The heat flux variability reflects spurious signals stemming from ERA-20C surface fields, which in return result from changes in the atmospheric observing system. The influence of the temperature assimilation increments on the heat budget is growing with time. Increments control the most recent ocean heat uptake signals, highlighting imbalances in forced reanalysis systems in the ocean as well as in the atmosphere.


Ocean reanalysis Twentieth century record Climate signals Observing system changes 



This work was EU-funded by the FP7 ERA-CLIM2 project. The contribution of M. Mayer was funded by the Austrian Wissenschaftsfonds (FWF project P28818-N29) and COST-EOS.


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Copyright information

© Springer-Verlag GmbH Germany 2017

Authors and Affiliations

  1. 1.European Centre for Medium-Range Weather ForecastsReadingUK
  2. 2.Department of Meteorology and GeophysicsUniversity of ViennaViennaAustria

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