Seasonal variations of the particle flux in the Peru-Chile current at 30°S under 'normal' and El Nino conditions

Time-series sediment traps were deployed 180 km off the Chilean coast at 30 °S in the Peru-Chile Current during the El Nino period 1991/1992 (6 months) and during the 'normal' period 1993/1994 (12 months). Under normal conditions in 1993/1994 the particle fluxes display a pronounced seasonal cycle marked by a settling phytoplankton bloom in September, intermediate fluxes until January, and low fluxes between January and July. This seasonal pattern is also reflected in stable isotope data, measured on the planktic foraminifera species Neogloboquadrina pachyderma (dex.) and Globigerina bulloides, which indicate persistent upwelling conditions between August and February followed by a stratified water column between March and July. The total flux under normal conditions amounts to 65.1 g m-2 a-1, with the main flux constituents contributing 47.6% (carbonate), 26.4% (lithogenic matter), 17.4% (biogenic opal), and 8.6% (organic matter), respectively. Based on these particle flux data the export production has been estimated to be 42 gC m-2 a-1. Although the main flux event in September was not sampled in the El Nino period 1991/1992, the available record from November 1991 to April 1992 allows an interesting comparison with the fluxes of the normal year. The total amount of fluxes and the timing of minor flux events are very similar under normal and under El Nino conditions. However, increased proportions of organic carbon and lithogenic matter under El Nino conditions are interpreted to reflect faster sedimentation and preferred scavenging of organic matter by elevated lithogenic fluxes rather than increased productivity. The higher lithogenic fluxes under El Nino conditions are probably due to increased precipitation and terrestial runoff in the arid to semiarid northern part of Chile. (C) 2000 Elsevier Science Ltd.