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

摘要

A quantitative analysis of coccoliths is presented in 18 core-top samples ranging between 26° N and 21° N and coveringtwo major deep brine pools in the northern part of the Red Sea. Non-brine sites are characterized by rich coccoliths thatmay reach up to 3.31×10~9 coccoliths/g made by 22 species, whereas brine sites of Shaban and Kebrit Deeps with additionaltwo non-brine sites are characterized by a decline in coccoliths/g (3.25 × 10~8 coccoliths/g), Shannon diversity, CaCO_3 (%),and high TOC (%). Carbonate dissolution, inferred by qualitative observation and quantitative indices, was only observedat one brine site GeoB7828 in Kebrit Deep. This suggests that the decline in coccolith assemblages may not entirely beattributed to carbonate dissolution. The major decline, however, is probably related to the suspension of fecal pellets andmarine aggregates containing delicate coccolith shields within a nepheloid layer and subsequently grazed by zooplankters inwhich reduced the numbers of coccolith that reached the bottom of the brine sites, or alternatively a deep-sea flow current thatcarried and remobilized some suspended particles outside the brine pool. Latitudinal fluctuations of eutrophic/oligotrophiccoccoliths suggest profound trophic changes in the photic zone in the northern part of the Red Sea. C. braarudii, a valuablenutrient-indicator species is here reported for the first time, along with G. oceanica, H. carteri as well as biogenic opaldominating the assemblage between 26° N and 24° N, suggesting elevated nutrient conditions and supporting recent highchl-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.