Sea surface temperature variation in the galapagos archipelago: A comparison between AVHRR nighttime satellite data and in situ instrumentation (1982-1998)

A multi-year study was undertaken to evaluate the relationship between sea surface temperatures (SSTs) derived from two methodologies: Advanced Very H igh Resolution Radiometer (AVHRR on NOAA satellites) and in situ instrument ation. Comparisons within sites were made at six widely distributed locatio ns in the Galapagos Archipelago: Academy Bay, Santa Cruz, Bartolome, Champi on, Punta Espinosa, Fernandina, and Wolf. Comparisons were made at monthly (1982-1998) and weekly (1997-1998) resolution. Results of within-site compa risons indicated that the differences in monthly SSTS for the two methods, at four primary sites, ranged from a mean difference of -0.62 degreesC to a high of +1.39 degreesC. Weekly comparisons made during the very strong 199 7-1998 ENSO event revealed smaller differences between methodologies (-0.33 to +0.99) due to the widespread warming resulting from ENSO conditions. Wh ile a statistical evaluation of the data revealed few overall differences b etween sites and methods, two sites, Champion and Urvina Bay, showed consis tent differences between the two methodologies. At Urvina Bay in situ data were consistently lower than satellite measurements, and vice versa at Cham pion. These differences could be explained by heating in the shallow nearsh ore waters of Urvina Day, and at Champion by the placement of the in situ i nstrument below the depth of a shallow thermocline. Lastly, a comparison of AVHRR-derived SSTs from 1982-1998 at six widespread sites was used to eval uate patterns of seasonal SST variability within the archipelago. Although several distinct temperature zones were identified, average differences bet ween zones previously suggested by Harris (1969) were found to be lower tha n proposed.