Remote sensing observations of winter phytoplankton blooms southwest of the Luzon Strait in the South China Sea

The Luzon Strait is a channel between the Philippine Sea and the South Chin a Sea. This area is traditionally classified as an oligotrophic zone with l ow primary productivity. Even so, high concentrations of pigment were detec ted 100 km southwest of the Strait through analysis of historical Coastal Z one Color Scanner (CZCS) data that the Nimbus-7 satellite collected during the winters of 1979 to 1986. These blooms were observed in December 1979, F ebruary 1983, February 1985, and January 1986, when sea surface temperature s measured with the National Oceanic and Atmospheric Administration's (NOAA s) Advanced Very High Resolution Radiometer (AVHRR) were 23 to 25 degrees C , the lowest in the year. High pigment concentrations (1 to 3 mg m(-3)) per sisted for at least 1 to 3 wk and extended over areas of about 100 x 200 km (2). Results of oceanographic survey published in 1995 also showed that a h igh chlorophyll a concentration (similar to 2.0 mg m(-3)) occurred in the w inter of 1980 in this region. The winter phytoplankton blooms in this area appeared to be related to upwelling, which brings nutrients to the surface waters and lowers the water temperature.