A look at the ocean in the EC-Earth climate model Andreas Sterl • Richard Bintanja • Laurent Brodeau • Emily Gleeson • Torben Koenigk • Torben Schmith • Tido Semmler • Camiel Severijns • Klaus Wyser • Shuting Yang Received: 29 June 2011 / Accepted: 30 October 2011 / Published online: 13 November 2011 Ó Springer-Verlag 2011 Abstract EC-Earth is a newly developed global climate system model. Its core components are the Integrated Forecast System (IFS) of the European Centre for Medium Range Weather Forecasts (ECMWF) as the atmosphere component and the Nucleus for European Modelling of the Ocean (NEMO) developed by Institute Pierre Simon Laplace (IPSL) as the ocean component. Both components are used with a horizontal resolution of roughly one degree. In this paper we describe the performance of NEMO in the coupled system by comparing model output with ocean observations. We concentrate on the surface ocean and mass transports. It appears that in general the model has a cold and fresh bias, but a much too warm Southern Ocean. While sea ice concentration and extent have realistic val- ues, the ice tends to be too thick along the Siberian coast. Transports through important straits have realistic values, but generally are at the lower end of the range of obser- vational estimates. Exceptions are very narrow straits (Gibraltar, Bering) which are too wide due to the limited resolution. Consequently the modelled transports through them are too high. The strength of the Atlantic meridional overturning circulation is also at the lower end of obser- vational estimates. The interannual variability of key variables and correlations between them are realistic in size and pattern. This is especially true for the variability of surface temperature in the tropical Pacific (El Nin ˜o). Overall the ocean component of EC-Earth performs well and helps making EC-Earth a reliable climate model. Keywords Climate model  NEMO ocean model: general ocean circulation  Surface fluxes  Sea ice  Ocean heat transport 1 Introduction Societies are dependent on, and adapted to, their local climate for a wide range of activities, from farming prac- tices and water availability to health and living conditions. This also means that societies are vulnerable to climate changes, be it caused by natural variability or anthropo- genic activity. Information about future (changes of) cli- mate is therefore important to take timely adaptation measures. Climate arises from a complex interplay between atmosphere, ocean, ice and soil. Besides physical processes (e.g., radiation, energy transport) also chemical (e.g., ozone destruction) and biological (e.g., CO 2 uptake by plants or This paper is a contribution to the special issue on EC-Earth, a global climate and earth system model based on the seasonal forecast system of the European Centre for Medium-Range Weather Forecasts, and developed by the international EC-Earth consortium. This special issue is coordinated by Wilco Hazeleger (chair of the EC-Earth consortium) and Richard Bintanja. A. Sterl (&)  R. Bintanja  C. Severijns Royal Netherlands Meteorological Institute (KNMI), P.O. Box 201, 3730 AE De Bilt, Netherlands e-mail: sterl@knmi.nl L. Brodeau Department of Meteorology, Stockholm University, Stockholm, Sweden E. Gleeson  T. Semmler Met E ´ ireann, Dublin, Ireland T. Koenigk  K. Wyser Swedish Meteorological and Hydrological Institute (SMHI), Norrko ¨ping, Sweden T. Schmith  S. Yang Danish Meteorological Institute (DMI), Copenhagen, Denmark 123 Clim Dyn (2012) 39:2631–2657 DOI 10.1007/s00382-011-1239-2