Ecology of deep-sea benthic foraminifera in the North Atlantic during the last glaciation: Food or temperature control

Abstract

In this study, we explore the paleoecology of nineteen species and two species-groups of deep-sea benthic foraminifera in relation to bottom water temperature and food supply in the central North Atlantic during the last glaciation, ~60,000–28,000years BP. The study is based on core SO82-02GGC, taken from 1730m water depth on the western flank of Reykjanes Ridge. The climate of the investigated period was extremely unstable, interrupted by thirteen warmings and coolings, the so-called Dansgaard-Oeschger events. At SO82-02GGC, surface and bottom water temperatures varied with up to 5°C between the warm interstadials and the cold stadials. Surface productivity, as indicated by the flux of planktic foraminifera, varied with a factor of up to ten. The Dansgaard-Oeschger events had a significant impact on the benthic foraminiferal faunas, which experienced up to 70% replacement between the interstadials and stadials. Multivariate analysis reveals that the investigated species can be separated into two groups. Group 1, including Bulimina costata, Brizalina subspinescens, Epistominella decorata and Trifarina angulosa, was attracted to higher temperatures and high food supply. Group 2, including Pullenia bulloides, Valvulineria laevigata, and Melonis barleeanus, was attracted to colder water and low food supply. Three species belonging to the cold group, Cibicidoides wuellerstorfi, Oridorsalis umbonatus and Eponides tumidulus are almost exclusively confined to sediments rich in ice rafted detritus. A few species including Nonionella iridea and Epistominella vitrea show opportunistic behaviour. Most species are epifaunal to shallow-infaunal and live today in oligotrophic to mesotrophic habitats. Our investigations indicate that temperature was the primary factor responsible for the relative abundance and main grouping of species. However, four species show little influence by temperature and several, perhaps most, were clearly also affected by food supply.