Offshore export of shelf production in the Cape Blanc (Mauritania) Giant Filament as derived from Coastal Zone Color Scanner Imagery

Abstract

Particulate organic carbon flux from the shelf to oceanic waters durir.g upwelling between 19ºN and 25ºN off Mauritania has been ana!yzed using coastal zone color scanner (CZCS) imagery . Biomass ir. the giant tilament has been estimated usir.g surface pigment concentration registered by CZCS during time series in December 1983 , March 1984, and October 1984 . Evidence for active phytoplankton growth ir. offshorc waters is presented . Formation of the giant filamcnt seems to be favored by the combination of a number of ffac tors perhaps unique to the Mauritanian shelf. The large-scale ci rci.:lation pattems promote ofshore advection, and the typically long perio¿ of wind forcing can move the upwelling center to thc shclf break arca, thus causing maximal phytop!ankton growth rate to be achieved in ocean:c waters . The relatively high pigmcnt concentrations registered by CZCS in oceanic waters suggest that nu trients have not been de pleted on thc shelf and that in situ growth is occurring in deep waters. We have u sed a baroc:inic. hydrodynamic model to estímate cr l oss-slope flux of particulate organic carbon ;,.t the 200-m isobath and derive a mean value of abou, 1 x !O g C s - J during each of the CZCS time series.