BIOGENIC PARTICLE FLUXES IN THE EQUATORIAL PACIFIC: EVIDENCE FOR BOTH HIGH AND LOW PRODUCTIVITY DURING THE 1982-1983 EL NINO

Sediment traps deployed at two sites in the equatorial Pacific during and following the 1982-1983 El Nino southern oscillation (ENSO) demonstrate the biological effects of this event. Biogenic particle fluxes for a site 1 north of the equator were at least a factor of 2 lower during a 3 month period of intense ENSO influence compared to fluxes recorded at any other time during a 28-month period beginning in December 1982. These low particle fluxes reflect the expected decrease in primary production in response to the ENSO event. Surprisingly, the biogenic particle fluxes measured at the second site, 11N, were anomalously high during this same ENSO-affected period. The apparent increase in productivity north of the equator seems to be a consequence of enhanced flow of the North Equatorial Countercurrent (NECC) and the associated doming of the shallow thermocline. The observed temporal variability in magnitude of the biogenic particle flux was accompanied by compositional changes in the biogenic components. The period of high carbon flux at the 11N site was a time of exceptional opal flux, while the particle flux during the period of low carbon flux observed at 1N during the ENSO was depleted in opal. These patterns appear to reflect the dominance of diatom productivity relative to coccolithophorid productivity during conditions of greater nutrient availability.