Primary production measurements in the north coastal waters of South America

Measurements of surface light intensity, water transparency and concentration of chlorophyll a were made in the northern coastal waters of South America during October and November 1958. Phytoplankton collections were made simultaneously. The highest gross production rates were encountered in the Gulf of Cariaco (3·75 g C/m²/day), over the Cariaco Trench (2·30 g C/m²/day), in Lake Maracaibo (1·23 g C/m²/day) and the Gulf of Venezuela (1·20 g C/m²/day). Upwelling appears to be the source of nutrients for production in the Gulfs of Cariaco and Venezuela. This relationship is less well established over the Cariaco Trench. High silt concentrations limit light for photosynthetic production in the Gulf of Darien, at the mouth of the Magdalena River and to the east of Margarita Island. Phytoplankton reduces materially the light available for photosynthesis in Lake Maracaibo.