Deep-sea benthic foraminifera from the central Red Sea

The distribution of living (Rose Bengal-stained), dead and fossil benthic foraminifera was investigated in six short cores (multicores, 30-32 cm total length) recovered from the central Red Sea. The ecological preferences as well as the relationship between the live and dead/fossil assemblages (preserved down-core) were examined. The sites, located along a W-E profile between the depth of 366 1782 m, extend from the center of the oxygen minimum zone (OMZ, ∼200-650 m), through its margin at ∼600 m, down to the well-aerated deep-water environment. Live (Rose-Bengal stained) coexisting dead foraminifera were studied in the upper 5 cm of each of the sites, the fossil record was studied down to ∼32 cm. Q-mode Principal Component Analysis was used four distinct foraminiferal fossil assemblages were determined. These assemblages follow different water mass properties. In the center of the OMZ, where the organic carbon content is highest the oxygen concentration is lowest (≤0.5 ml O₂/1), the Bolivina persiensis-Bulimina marginata-Discorbinella rhodiensis assemblage dominates. The slightly more aerated and lower organic-carbon-content seafloor, at the margin of the OMZ, is characterized by the Neouvigerina porrecta-Gyroidinoides cf. G. soldanii assemblage. The transitional environment, between 900-1200 m, with its well-aerated oligotrophic seafloor, is dominated by the Neouvigerina ampullacea-Cibicides mabahethi assemblage. The deeper water (>1500 m), characterized by the most oxygenated oligotrophic seafloor conditions, is associated with the Astrononion s A-Hanzawaia sp. A assemblage. Throughout the Red Sea extremely high values of temperature salinity are constant below ∼200 m depth, but the flux of organic matter to the sea floor varies considerably with bathymetry appears to be the main controlling factor governing the distribution pattern of the benthic foraminifera. Comparison between live and the dead/fossil assemblages reveals a large difference between the two. Processes that may control this difference include species-specific high turnover rates, preferential predation loss of fragile taxa (either by chemical or microbial processes). Significant variations in the degree of loss of the organic-cemented agglutinants were observed down core. This group is preserved down to 5-10 cm at the shallow OMZ sites and down to greater depths at well-aerated and oligotrophic sites. The lower rate of disintegration of these forms, in the deeper locations of the Red Sea, may be related to low microbial activity. This results in the preservation of increasing numbers of organic-cemented shells down-core.