Ecosystem dynamics and export production in the central and eastern equatorial Pacific: A modeling study of impact of ENSO

Biogeochemical responses to physical changes associated with the El Niño/Southern Oscillation (ENSO) phenomenon are studied for the period of 1990-2001 using a physical-biogeochemical model. During warm ENSO, the ferricline deepens in the central and eastern equatorial Pacific, resulting in low biomass and low export production. Zooplankton and large phytoplankton are more depressed than small phytoplankton in particular during the 1997-98 El Niño. The recovery from the warm ENSO alleviated iron stress, resulting in an increase of phytoplankton growth. In addition to extra iron input, the mid-1998 blooms are also attributable to extremely low grazing pressure. The rapid turn to a cold ENSO in mid-1998 may enhance export production by a factor of eight in the Niño3 area. Large phytoplankton are largely responsible for the increase of export production in the central and eastern equatorial Pacific.