The Ovide program Ovide contributes to the monitoring and the understanding of ocean variability in the northern North Atlantic ocean (transports, water mass properties) An hydrographic section with direct velocity measurements is repeated every 2 years in summer, between Greenland and Portugal FOUREX (A25) section in 1997 2002, 2004 2006: focus of this talk 2008 planned and 2010: last occurrence...although 2014-2015?

Circulation in the North Atlantic subpolar gyre, area studied by OVIDE CTO2, LADCP, nutrients, pH, Alk., CFCs (28 depths) Key water masses, relevant for Geotraces

Ovide 2006 transports NAC EGC 11.8 -7.8 -15.3 17.6 MW LSW -7.4 -3.3 1.2 DWBC ISOW DSOW Iceland basin Irminger sea AABW 0.3 West European basin Greenland Portugal

Transient Tracers : CFCs Apparent Ages of different LSW veins in the North Atlantic during OVIDE 2002 (Data from LCM, Roscoff).

Suggestion: coupling a GEOTRACES section to the reoccupation of OVIDE (2014 or 2015) Strategy: 2 ships working in parallel (one dedicated to CLIVAR, the other to GEOTRACES) Strong hydrological framework (many physical oceanographers + modelers) Key water masses will be documented for tracers (THC, climate related) IMAGES cores and deep sea corals collected in the same area are currently analyzed: windows for paleo! Funders will like the « coupling » and this could weight in favor of getting funded.

Transient Tracers : CFCs Vertical section of CCl4. This tracer is used with other CFCs to determine the apparent ages of the different water masses present along the OVIDE section (Data from LCM, Roscoff).

Comparison with 2002 and 2004 Irminger Sea Iceland Basin West European Basin Iberain Plain EGC EBC NAC Cyclonic circulation in the Irminger Sea weaker in summer 2006 Westward shift of the subarctic front

MOC (Sv) Transp Chaleur (PW) DWBC (Sv) 4X 1997 12.5 ± 1 0.66 ± 0.04 -11.3 OVIDE 2002 8.7 ± 1 0.43 ± 0.06 -9.2 OVIDE 2004 9.7 ± 1 0.58 ± 0.05 -11.4 Interannual variability in the MOC and DWBC transports between 1997 and 2004. (Data from LPO, Brest)

Mass and heat transport summary East Greenland Current Deep Western Boundary Current Top Layer Bottom Layer ? North Atlantic Current 2 couche séparées par Sigma2=36.94 ( s0=27.8). MOC = équilibre entre NAC et DWBC+EGC hors recirculation en Irminger. En densité, le 0 de la MOCs est sur s1 = 32.1 (ici, le NAC est quantifié jusqu’à 32.35 pour comparaison avec la biblio). Barre d’erreur faible sur les transports de masse et de chaleur grâce à la méthode et l’estimation uniquement saisonnière. La MOC 2002 est nettement ralentie par rapport à 1997, conformément aux modèles. 2004 présente une situation intermédiaire, avec cependant un DWBC similaire à 1997, mais une EGC exporté et un NAC + faibles. NACnet (±1.8 Sv) Summer 1997 26.6 Summer 2002 19.6 Summer 2004 22.5 Summer 2006 17.6 EGC (±1 Sv) 27.7 Sv 22.4 Sv 27.6 Sv 15.3 Sv DWBC (±1 Sv) 11.3 Sv 9.2 Sv 11.4 Sv 7.4 Sv MOCs intensity Heat transport 19.1 ± 1.2 Sv 0.66 ± 0.05 PW 16.6 ± 2.3 Sv 0.43 ± 0.04 PW 18.1 ± 2.0 Sv 0.58 ± 0.04 PW 11.8 ± 2.7 Sv 0.33 ± 0.07 PW

Conclusions Main transports and MOC vary jointly in 1997-2002-2004 and 2006 In May-June 2006, all mass transports collapsed, along with the MOC and the heat transport. Model results are needed to interpret these synoptic estimates. (Treguier et al. (2006) for variability between Fourex 1997 and Ovide 2002)