Deep-sea benthic foraminifera respond to rapid environmental changes in the central Red Sea during the last glacial period

Abstract

This study investigates the response of deep-sea benthic foraminifera to changes in food fluxes and dissolved bottom water oxygen in the central Red Sea during the last glacial period (Marine Isotope Stages (MIS) 3 and 4). To assess variations in nutrient intrusion from the Arabian Sea and regional organic matter fluxes, we developed the Red Sea Productivity Index (RSPI) based on changes in sea level and African-Arabian monsoon intensity. We found four distinct species groups, each reflecting different ecological niches and opportunistic behavior. Overall, the fauna of MIS 3 is dominated by the generalist species Bolivina subreticulata, which co-occurs or alternates with other preferentially infaunal taxa of varying opportunistic responses. Changes in the dominance of the different species are primarily controlled by seasonal productivity and associated quantity and quality of available organic matter at the sea floor. This is reflected by a close correspondence of the RSPI and a succession of infaunal species, including Uvigerina juncea s.l., and Bolivina variabilis as the most opportunistic taxa, adapted to strong seasonal food pulses. The succession of the species groups are influenced by millennial-scale changes of the African-Arabian monsoon system and Red Sea deep-water ventilation. This suggests a close link to both low- and high-latitude Northern Hemisphere climate variability. Changes in glacial deep-water oxygenation seem to play an important role during MIS 4, when the dominance of Bolivina persiensis indicates a vertical expansion of the oxygen minimum zone. The high glacial deep-water salinities during sea-level lowstands also fostered the occurrence of miliolid taxa.