Phytoplankton concentration in the eastern Indian Ocean: seasonal and interannual variability

Abstract

The concentration of phytoplankton in waters off the Western Australian coastline contrast with the coastal waters west of southern Africa and South America. The lack of favourable upwelling conditions results in the majority of the eastern Indian Ocean being nutrient poor, which is reflected in low productivity. Several areas either on, or in close proximity to the coastline, are notably more productive. The associated forcing term(s) generating phytoplankton favourable conditions differ between areas, as do the seasons in which they occur. Measurements of chlorophyll concentration, the major photosynthetic pigment contained in phytoplankton, may be directly related to oceanic bioproductivity. Using data collected by the Coastal Zone Color Scanner (CZCS) between 1979-86, this work aims to improve the understanding of the spatial and temporal changes that occurred in phytoplankton/chlorophyll abundance in the eastern Indian Ocean. The highest seasonal mean concentrations occur in austral summer (January-March) and autumn (April-June). The former occurring in waters of the North West Shelf and the latter in close coastal areas of Western Australia south of North West Cape. Concentrations observed in the oceanic regions are mostly poor. Exceptions to this occur in proximity to the adjacent Indonesian islands and directly south of Albany (possibly due to inflow of subantarctic waters). A considerable interannual variation was also noted, with the highest mean chlorophyll concentrations occurring in 1981, 1982 and 1983.