Large-scale patterns of chlorophyll off Peru and Chile during the 1997-98 El Nino

A twenty month time series of SeaWiFS satellite data is used to document the evolution of large-scale surface chlorophyll patterns along the South American west coast during the 1997-98 El Nino. SeaWiFS data first become available in September 1997, when in situ hydrographic data indicate a relaxation period between the two major pulses of El Nino conditions of May 1997 and December 1997. SeaWiFS data document the temporal and spatial evolution of chlorophyll from this relaxation period, through the maximum hydrographic anomalies of winter 1997-98, (December-February) and the subsequent recovery to more normal hydrographic condition by May 1998. Contrasts between SeaWiFS data from two austral summer periods (1997-98 and 1998-99) illustrate the extent to which the seasonal cycle was disrupted by El Nino conditions, and it's latitudinal variability. Austral summer chlorophyll concentrations in 1998 (January - February) are both lower and more closely associated with the coast than those of 1999. This pattern was strongest at lower latitudes, and weaker poleward of approximately 33 S. These patterns are compared to large-scale wind forcing and surface temperature patterns from the same period to document linkages between physical forcing and biological response. Latitudinal and temporal development of chlorophyll patterns in the Peru-Chile Current are first contrasted with those in the California Current to examine similarities and differences in El Nino development and lastly contrasted to those of the Benguela Current System to quantify differences and similarities between seasonal cycles in these two southern hemisphere upwelling systems.