Seasonal and interannual variability in the flux of planktic foraminifera in the Humboldt Current System off central Chile (30°S)

Seasonal and interannual changes in the flux of planktic foraminifers were studied in the Humboldt Current System off Coquimbo, Chile (30°S; 73°15′W), using material collected by time series sediment traps located at 2300 m water depth and 100 nautical miles from the coast. The almost continuous record spans 6 years (1993–1998) with a temporal resolution of 6–13 days. The seasonal flux pattern of planktic foraminifers was marked by high fluxes during austral late winter–early summer (August–January) and low fluxes during the fall–early winter period (March–July). Five species contributed ∼90% of the total flux of planktic foraminifers: Globigerina bulloides, Neogloboquadrina incompta, N. pachyderma, N. dutertrei, and Globigerinella calida. Stable oxygen isotope variability in foraminifer shells appears to be driven by seasonal changes in surface seawater temperature; isotope data of G. bulloides and N. incompta (>212 and 150–212 μm size classes) suggest that water-column stratification dominates during the low-flux period and mixing during the high-flux period. The strong 1997–1998 El Niño event had only a limited impact on the planktic foraminifer flux. The most significant El Niño-related signal was a remarkable increase in the flux and abundance of species that, under normal conditions, only accounted for <10% of the total planktic foraminiferal assemblage.