Particle flux in the Subtropical Atlantic near the Azores: influence of mesozooplankton

The amount and composition of sinking material were studiedat two depths (200 m and base of the photic layer) in the SubtropicalAtlantic Ocean near the Azores during the AZORES I (August 1998)and II (April–May 1999) cruises. Particulate carbon andnitrogen fluxes collected in sediment traps decreased with depth,and presented maximum values near the Azores Front. However,this frontal system represents an increase of only 4.5% in theoverall regional exportation during summer. Sedimentation ratesoutside the front were higher during spring. Particulate organiccarbon exported at 200 m always represented <1.5% of watercolumn (photic zone) standing stock. Mesozooplankton faecalpellets contributed significantly to carbon flux. On average,carbon in the form of faeces represented 31% (spring) and 65%(summer) of total carbon collected at 200 m. Composition ofthe copepod community seems to be related to the pattern offaecal pellet sedimentation, with omnivorous copepods (Oithonaand Oncaea) being more abundant at stations where faecal fluxdecreased with depth. Phytoplankton sedimented at 200 m weredominated by diatoms and dinoflagellates. Phytoplankton exportedat 200 m represented <0.5% of water column (photic zone)standing stock.