Vertical particle flux in the northeast Atlantic Ocean (POMME experiment)

In the framework of the Programme Ocean Multidisciplinaire Meso Echelle (POMME) experiment, a 1.5 year record (February 2001-June 2002) of downward particle flux at 400 m and 1000 m was measured by sediment traps at four moorings located in the northeast Atlantic between 39 degrees-43 degrees N and 17 degrees-19 degrees W. Thorium-230 was used to estimate sediment trap efficiency, revealing values ranging from 18.5 to 55%. The lowest trapping efficiency was observed for the trap having experienced the highest currents. Significant interannual variability between 2001 and 2002 was clearly linked to the differences observed in the mixed layer depth. At some sites, particulate organic carbon (POC) export was higher (up to a factor of 1.6) during summer than during the spring event. This could be related to the occurrence of short wind events that deepened the thermocline along with the presence of anticyclonic eddies, yielding an input of new nutrients. The average percentage of POC exported compared to the primary production of organic carbon in the surface waters ranged between 1.3 and 5.0%, with higher export efficiency during the spring. Finally, although the area was shown to present a relatively high mesoscale activity that might impact the geochemistry, POC export was rather homogeneous over the POMME area: 4.9 +/- 1.6 gC m(-2) yr(-1) were exported below 1000 m between February 2001 and February 2002. Therefore a large fraction of the new production may be exported through convection and mode water circulation rather than by particle settling.