Satellite-Measured Phytoplankton and Environmental Factors in North Patagonian Gulfs

Abstract

Abstract An extensive series of high-resolution satellite images from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS, 2000?2006) was used in thecharacterization of the phytoplankton biomass seasonal cycle of the north Patagoniangulfs (NPG). The NPG system is formed by the San Matías, San José, and Nuevogulfs (between 40°47′and 43°00′S and 63°00′ and 65°1.2′W) and is an area ofecological importance and of great significance for marine conservation in thePatagonian Argentinean Shelf. The spatio temporal variability of phytoplanktonbiomass in each of these environments was characterized by chlorophyll a datafrom satellite images (Chla-sat). The observed seasonal variability was explainedby factors influencing the growth of phytoplankton: photosynthetically availableradiation (PAR from the SeaWiFS sensor) and sea surface temperature (SST fromthe Advanced Very High-Resolution Radiometer, AVHRR). In situ temperature,nutrient, and chlorophyll a concentration data from oceanographic cruises carriedout in Nuevo (four cruises: 1982?1983), San José (four cruises: 1984?1985), andSan Matías (four cruises: 1986?1994) gulfs were also used to explain the observedpatterns. Cycles of phytoplankton and SST over the NPG are typical of temperatewaters. However, Chla-sat cycles were different among gulfs. At the same time,Chla-sat cycles over the gulfs were different from that over the adjacent middlecontinental shelf. SMG was characterized by a bimodal cycle, although in wintermean values were higher than the mean concentration for the whole area. SJG wascharacterized by a unimodal cycle with relatively high values of chlorophyll aconcentration in spring-summer. NG showed a bimodal cycle with maximum valuesin autumn and spring and minimum values in winter and summer. Particularities ofeach gulf are discussed in relation to the seasonal hydrographic characteristics ofthe water column (temperature and nutrients) and in the context of the Patagonianshelf ecosystem.