Mémery, Laurent, and Gilles Reverdin

Laboratoire d’Océanographie Dynamique et de Climatologie (LODYC), Université Pierre et Marie Curie, Case 100, 4 Place Jussieu, 75252 Paris Cedex 5, France, E-mail: memery@lodyc.jussieu.fr

The POMME programme: meso scale impact on biological activity in the NE Atlantic

The Programme Océan Multidisciplinaire Méso Echelle (POMME) seeks to understand the impact of meso-scale dynamics on mode water formation and subduction, and on the seasonal evolution of the water mass characteristics and biological activity in the NE Atlantic Ocean (15-20W, 38-45N). The one-year field work, achieved in the autumn 2001, was based on three 6-week cruises with two vessels, nine moorings equipped with current-meters and other instruments, including four with sediment traps, and over 100 drifters and subsurface floats. Real time data assimilation was used to optimize the meso-scale surveys. A significant meso-scale signal was observed in this low-energy region, including a few coherent structures. Their biological impact are strong mostly along the fronts located near the rims of the eddies. On the other hand, we did not observe systematic differences between cyclones and anticyclones. The biological production had already started in the south in February, and has presented a steady, although strong, increase until May in the north. In September, the region is strongly oligotrophic. The heterogeneity driven by the fronts between eddies is large during all seasons at small scales, and overlays a strong seasonal cycle. This area of the North Atlantic is associated with a mean annual CO₂ sink, that is strong mostly during winter and spring, whereas it is a CO₂ source in late summer and early fall.