Distribution and Diversity of Coccolithophores in Surface Sediments of the Northern Red Sea: Coccolith Accumulation in Brine Pools and Observation of Productivity

Abstract

A quantitative analysis of coccoliths is presented in 18 core-top samples ranging between 26° N and 21° N and covering two major deep brine pools in the northern part of the Red Sea. Non-brine sites are characterized by rich coccoliths that may reach up to 3.31 × 109 coccoliths/g made by 22 species, whereas brine sites of Shaban and Kebrit Deeps with additional two non-brine sites are characterized by a decline in coccoliths/g (3.25 × 108 coccoliths/g), Shannon diversity, CaCO3 (%), and high TOC (%). Carbonate dissolution, inferred by qualitative observation and quantitative indices, was only observed at one brine site GeoB7828 in Kebrit Deep. This suggests that the decline in coccolith assemblages may not entirely be attributed to carbonate dissolution. The major decline, however, is probably related to the suspension of fecal pellets and marine aggregates containing delicate coccolith shields within a nepheloid layer and subsequently grazed by zooplankters in which reduced the numbers of coccolith that reached the bottom of the brine sites, or alternatively a deep-sea flow current that carried and remobilized some suspended particles outside the brine pool. Latitudinal fluctuations of eutrophic/oligotrophic coccoliths suggest profound trophic changes in the photic zone in the northern part of the Red Sea. C. braarudii, a valuable nutrient-indicator species is here reported for the first time, along with G. oceanica, H. carteri as well as biogenic opal dominating the assemblage between 26° N and 24° N, suggesting elevated nutrient conditions and supporting recent high chl-a records, whereas areas between 21° N and 23° N lie under oligotrophic conditions due to the presence of U. sibogae, U. tenuis, R. clavigera, F. profunda, and S. pulchra.