Patterns of primary production in the Red Sea

Abstract

This paper presents data on various parameters of primary production (chlorophyll concentration, carbon uptake, nitrogen uptake, phytoplankton groups) measured in 4 cruises in the Saudi Arabian waters of the Red Sea between 2012 and 2015. The results showed that while there was a tendency for an increase from north to south, the meridional distributions were distinguished by alternating high and low concentrations of chlorophyll, carbon uptake rates and cell densities of various phytoplankton groups, with the higher levels being associated with zonal currents and the lower values lying in between. These patterns of distributions lead us to conclude that the biological production in the Red Sea is influenced more by anticyclonic eddy, and less by meridional, circulations at any time of the year. Synthesizing the present results with earlier ones on the patterns of distributions of nutrients and the flow of Gulf of Aden Intermediate Water (GAIW), we also conclude that entrainment of GAIW in successive eddies is the cause for higher nutrients and biological production in the regions of eddy boundary currents. Data on size-fractionated carbon uptake and nitrogen uptake showed that the eddies in Red Sea favour the proliferation of producers across a range of size classes rather than one class. The amount of nutrients injected into the euphotic zone in the eddy boundary currents is probably not high enough to induce a definite shift in phytoplankton size classes, and the primary production still remains to a significant extent regenerated nutrient-driven.