Primary productivity and chlorophyll a in the central part of the Gulf of California (Autumn 1987)

Abstract

A cruise was carried out in the central part of the Gulf of California from 27 October to 7 November, 1987. Seawater samples were taken from 0, 5, 15, 25 and 50 m depth to determine chlorophyll a and phaeophytin a content at 22 stations. Six experiments of productivity in the euphotic zone and one experiment of photosynthesis-irradiante were generated. The vertical profile of chlorophyll a in Ballenas Channel was more homogeneous at the southern end of the channel due to mixing and the increase in the euphotic zone. In the region of the islands, the distribution of chlorophyll a was more variable due to mixing processes that occur in that area. In the southern part of the study area, chlorophyll a decreased from the coast to the open sea. Similar assimilation numbers and photosynthetic rates were obtained with samples collected at 22 and 60% of surface irradiance in one productivity versus irradiante (P-E) experiment in Ballenas Channel. It is inferred that vertical transport of phytoplankton occurred in the water column. Surface primary productivity values were three to four times higher in the northern part of the study area than in the southern part, whereas integrated productivity values were one to two times higher in the northern part.

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