Response of Red Sea deep-water agglutinated foraminifera to water-mass changes during the Late Quaternary

The distribution of deep-water agglutinated foraminifera was determined in core material taken in the central Red Sea by the R/V Meteor, cruise 5, leg 2. The sedimentary record represents the last 380 kyr, which includes four glacial/interglacial cycles. The agglutinate assemblage is of low diversity, and in general is a minor component of the benthic foraminifera. It comprises 14 species belonging to the following genera: Ammobaculites, Lagenammina, Plotnikovina, Pseudogaudryina, Reophax, Sahulia, Siphotextularia, Spiroplectinella, Textularia and a doubtful genus of unknown taxonomic position: 'Psammosphaera'. Three sub-groups were identified in the core according to their occurrence either in interglacial stages or in both glacial and interglacial intervals, reflecting mainly tolerance to salinity variations. Exceptional bottom-water conditions during the last 60 kyr caused a remarkable decrease in the abundance and diversity of this group. The development of dysaerobic bottom water between approx. 60 and 26 kyr, the presence of a deep-water mass of extremely high salinity (ca. 55%) between 26 and 13 kyr, and the occurrence of anoxic bottom sediments between 12.9 and 9.6 kyr seem to have caused the extreme impoverishment. During the last 9.6 kyr the agglutinated foraminifera gradually recolonized the deep water. A diverse assemblage composed of the above mentioned genera is found in Holocene sediments only in the core top sample. In addition. small (63-149 μm), noncanaliculate organic cemented agglutinated foraminifera belonging to the genera Ammodiscus, Cribrostomoides, 'Eggerella', Glomospira, Haplophragmoides, Morulaeplecta, Spiroplectammina, Paratrochammina and Trochammina are preserved preferentially only in the uppermost part of the core (0-28 cm depth), in sediments younger than 3 kyr.