Physical-biological coupling in the California Current during the 1997-99 El Nino-La Nina cycle

The rapid transition from strong El Nino to strong La Nina conditions in th e equatorial Pacific in 1998 was accompanied by considerable environmental variability in the southern California Current System (CCS). The evolution of this transition in the CCS is investigated based on hydrographic and bio logical data collected on 25 cruises over a 45-month period (February 1996 to October 1999). The El Nino period was characterized by high steric heigh ts and a deep nutricline in the coastal regions, which effectively limited biological production. This was followed by a period of increased cross-sho re dynamic height gradients, a significant shoaling of the nutricline, and a dramatic rebound in primary and secondary production. The observed physic al and biological response in the CCS is remarkably similar to that observe d in the tropical Pacific, but with a lag of several months.