For its 20th anniversary, we at Mercator Océan would like to express our pride in being part of the French, European and International operational oceanography community. Mercator Océan has been involved in many projects or working groups over the last 20 years, among which, GODAE OceanView, MERSEA, MyOcean, GSOP, ICE-ARC, CLIVAR, Nemo Consortium, Mercator Vert, Clipper, Drakkar and many others. The work we have done on our own and with our partners has strengthened the operational oceanography community. Mercator Océan is justly proud to be part of this concerted effort. Since its founding in 2001, the Mercator Océan Newsletter has been a regular forum for many scientists from different backgrounds; for instance it is a space in which, as odd as it may seem, people working on research as far removed as theoretical data assimilation techniques or on elephant seals monitoring the Southern Ocean all share the same objective of a better understanding of the Ocean. It means personal engagement of many scientists. I would like to take the opportunity in this special commemorative issue of paying tribute to our late colleague, Nicolas Ferry, who made a great contribution to high resolution global reanalysis at Mercator Océan.
The newsletter format is simple and allows 3 to 4 issues a year with a specific theme per issue, thus publishing the latest scientific results from various scientific teams in the same place. This is convenient in that it provides readers with several scientific theories or results on a given theme, but also in that it strengthens a feeling of belonging to a community among authors who have the same objectives of better observing, modeling and thus monitoring the ocean. Building up the operational oceanography community and sharing scientific ideas are important objectives for Mercator Océan.

Mercator Océan has been entrusted by the European Union to implement the Copernicus Marine Environment and Monitoring Service (CMEMS). This new mandate comes with a set of demanding constraints and challenges. An operational service is one for which products have to be made available promptly in order to meet user requirements. Eric Dombrowsky, with whom I created Mercator Océan before he became its first scientific director, has always been the first to defend this idea that science was a major asset of operational oceanography in building a strong value for users. Far from driving us away from science, we believe this European mandate gives us an opportunity to ensure that scientific progress remains a strong asset of Mercator Océan and CMEMS in the operational phase.

At 20 years old Mercator Océan has now come of age and this special issue of the Newsletter encourages us to pursue our endeavors to develop tomorrow’s operational oceanography systems.

Pierre Bahurel
CEO, Mercator Océan

• SIMULATION OF MESO-SCALE EDDIES IN THE MERCATOR GLOBAL OCEAN HIGH RESOLUTION MODEL By O. Le Galloudec, R. Bourdallé Badie, Y. Drillet, C. Derval and C. Bricaud
• NEMO-SHELF, TOWARDS OPERATIONAL OCEANOGRAPHY WITH SST DATA ASSIMILATION ON THE NORTH WEST EUROPEAN SHELF By J. O’Dea, J. While, R. Furner, P. Hyder, A. Arnold, D. Storkey, J. R. Siddorn, M. Martin, H. Liu and J. T. Holt
• COUPLED PHYSICAL-BIOGEOCHEMICAL OCEAN MODELLING USING NEMO COMPONENTS By M. Gehlen, A. Yool , M. Vichi , R. Barciela, C. Perruche, A. El Moussaoui and C. Ethé
• ARCTIC OCEAN ECOSYSTEM MODELLING IN MYOCEAN By A. Samuelsen and L. Bertino
• SEA ICE CONCENTRATION, ICE DRIFT AND/OR ICE THICKNESS DATA ASSIMILATION: A REVIEW OF THE WORK DONE IN NORWAY, UK, FRANCE, BELGIUM AND CANADA By L. Bertino, K. Lisaeter, J. Stark, A. Hines, G. Garric, J. Pernin, C-E. Testut, E. Greiner, F. Girard-Ardhuin, D. Croize-Fillon, V. Dulière, T. Fichefet, A. Caya, M. Buehner and T. Carrieres
• IAOOS ICE – ATMOSPHERE – ARCTIC OCEAN OBSERVING SYSTEM, 2011-2019 By C. Provost and J. Pelon, Coordinators: N. Sennéchael, M. Calzas, F. Blouzon, A. Desautez, J. Descloitres, Work Package (Co)-Leaders: J.C. Gascard1, N. Villacieros Robineau, V. Mariage, J.P. Pommereau, T. Foujols, C. Drezen, A. Guillot, N. Geyskens, N. Amarouche, A. Sarkissian, N. Pascal, M. Garracio, P.D. Mahé, J. Sayadi, J.J. Correia, P. Genau, N. Wegmüller and J-L. Maria
• REGIONAL OCEAN FORECASTING: DOWNSCALING STRATEGY FOR COASTAL AND SUBMESOSCALE PHENOMENA By P.Marchesiello, Z. Li And A. Sepulveda
• PREVIMER, A FRENCH PRE-OPERATIONAL COASTAL OCEAN FORECASTING CAPABILITY By F. Dumas, L. Pineau-Guillou, F. Lecornu, J.-F. Le Roux And B. Le Squère
• GLORYS2V1 GLOBAL OCEAN REANALYSIS OF THE ALTIMETRIC ERA (1993-2009) AT MESO SCALE By N. Ferry, L. Parent, G. Garric, C. Bricaud, C-E. Testut, O. Le Galloudec, J-M. Lellouche, M. Drévillon, E. Greiner, B. Barnier, J-M. Molines, N. Jourdain, S. Guinehut, C. Cabanes And L. Zawadzki
• CORA3, A COMPREHENSIVE AND QUALIFIED OCEAN IN-SITU DATASET FROM 1990 TO 2010 By C. Cabanes, A. Grouazel, V. Turpin, F. Paris, C. Coatanoan, K. Von Schuckmann, L. Petit De La Villeon, T. Carval And S. Pouliquen
• MAIN ACHIEVEMENTS FOR NEMO EVOLUTION DURING MYOCEAN PERIOD – NEMO System Team: R. Bourdalle-Badie, P-A. Bouttier, C. Bricaud, D. Bruciaferri, J. Chanut, S. A. Ciliberti, E. Clementi, A. Coward, D. Delrosso, C. Ethé, S. Flavoni, T. Graham, J. Harle, D. Iovino, D. Lea, C. Lévy, T. Lovato, G. Madec, N. Martin, S. Masson, P. Mathiot, S. Mocavero, G. Nurser, E. O’Dea, J. Paul, C. Rousset, D. Storkey And A. Storto
• NEMO ORGANISATION By C. Lévy and R. Benshila
•  NUMERICAL WAVE MODELLING IN PREVIMER: MULTI-SCALE AND MULTIPARAMETER DEMONSTRATIONS By F.Ardhuin, M. Accensi, A. Roland, F. Girard, J.-F. Filipot, F. Leckler and J.-F. Le Roux
• OPTIMALLY IMPROVING THE ATMOSPHERIC FORCING OF LONG-TERM GLOBAL OCEAN SIMULATIONS WITH SEA-SURFACE TEMPERATURE OBSERVATIONS By M. Meinvielle, P. Brasseur, J-M. Brankart, B. Barnier, T. Penduff and J-M. Molines
• IS THERE A SIMPLE WAY OF CONTROLLING THE FORCING FUNCTION OF THE OCEAN? By J-M. Brankart, B. Barnier, D. Béal, P. Brasseur, L. Brodeau, G. Broquet, F. Castruccio, E. Cosme, C. Lauvernet, P. Mathiot, M. Meinvielle, J-M. Molines, Y. Ourmières, T. Penduff, S. Skachko, C. Skandrani, C. Ubelmann And J. Verron
• RECENT PROGRESS IN SEA ICE DATA ASSIMILATION AT ENVIRONMENT CANADA By M .Buehner, A. Caya, M. Ross, Y. Luo, T. Carrieres and L. Pogson
• NEMO IN MyOCEAN MONITORING AND FORECASTING CENTERS (MFCS) By E. Dombrowsky, L. Bertino, J. Chanut, Y. Drillet, V. Huess, A. Misyuk, J. Siddorn and M. Tonani
• OCEAN U.S. GODAE: GLOBAL OCEAN PREDICTION WITH THE HYBRID COORDINATE OCEAN MODEL (HYCOM) By E. P. Chassignet and H. E. Hurlburt
• CORIOLIS 2014-2020: AN INTEGRATED IN-SITU OCEAN OBSERVATION INFRASTRUCTURE FOR OPERATIONAL OCEANOGRAPHY AND OCEAN/CLIMATE RESEARCH By P.Y. Le Traon
• THE EURO-ARGO ERIC OFFICIALLY SET UP By S. Pouliquen, P-Y. Le Traon and Euro-Argo Members And Observers
• ELEPHANT SEALS HELP US TO BETTER OBSERVE THE SOUTHERN OCEAN By F.Roquet, S. Blain, C. Guinet and G. Reverdin
• EGO: TOWARDS A GLOBAL GLIDER INFRASTRUCTURE FOR THE BENEFIT OF MARINE RESEARCH AND OPERATIONAL OCEANOGRAPHY By P. Testor and , L. Mortier, J. Karstensen, E. Mauri, K. Heywood, D. Hayes, P. Alenius, A. Alvarez, C. Barrera, L. Beguery, K. Bernardet, L. Bertino, A. Beszczynska-Möller, T. Carval, F. Counillon, E. Dumont, G. Griffiths, P. M. Haugan, J. Kaiser, D. Kasis, G. Krahmann, O. Llinas, L. Merckelbach, B. Mourre, K. Nittis, R. Onken, F. D’ortenzio, S. Pouliquen, A. Proelss, R. Riethmüller, S. Ruiz, T. Sherwin, D. Smeed, L. Stemmann, K. Tikka And J. Tintoré