Abstract

In evaluating carbon flux in coastal and oceanic waters off central Chile (?36°S), the grazing pressure by copepod size-assemblages and the gravitational flux from the surface layer were estimated during two contrasting seasons: spring upwelling (October 1998) and winter (July 1999) periods. Grazing pressure upon phytoplankton biomass was small (<5%) during both periods at all stations. It was, however, an important proportion of primary production at the coast during the spring (17-43%) but minimal in winter (<5%) while, at the oceanic station, it was significant during both seasons (13-46%). Similarly, the downward flux of particulate organic carbon was a significant percentage of primary production at the coast during the spring (31%) and less so in winter (15%); at the oceanic station, it was a higher fraction during both seasons (46-47%). Copepod pellets were only a minor component of the faecal flux, suggesting that they were rapidly recycled in the water column. The seasonal differences in these carbon fluxes in the coastal upwelling zone were related directly to the larger quantities of organic matter in the water column during the spring upwelling period, including higher chlorophyll a concentrations and primary production rates. During the winter, the particulate organic carbon appears to be mainly recycled in the water column. In the oceanic zone, in contrast to what is expected, a large percentage of the primary production appears to be exported during both periods, though consumption by copepod assemblages was also important, suggesting significant horizontal carbon export from the coast to the open ocean.