Benthic foraminifera in high latitude contourite drift systems (North Atlantic: Björn, Gardar and Eirik drifts)

Abstract

Benthic foraminifera colonize a wide range of marine environments including contourite drift systems. Contourites form elongated sedimentary bodies deposited under persistent contour-parallel bottom currents, and certain suspension-feeding foraminifera benefit from the entrained nutrient load. Their distribution patterns have been shown to be highly valuable for reconstructing ocean circulation at mid-latitudes. However, comparable faunal studies from the high-latitude North Atlantic, a crucial region for global ocean circulation and the widespread deposition of contourites drifts, are missing. This study examines foraminiferal faunas >250 μm from surface samples of the Björn and Gardar drifts in the Iceland Basin and the Eirik Drift south off Greenland. It serves as baseline for understanding the biogeographic patterns of benthic foraminifera from high latitude contourites.The results show that four types of suspension-feeding species characterize different hydrodynamic environments. Bottom currents <3 cm s−1 at the Björn Drift sustain assemblages rich in the finely branching, erect species Saccorhiza ramosa and Rhizammina algaeformis, which capture food particles with a pseudopodial net. The northern Gardar Drift displays intermediate flow velocities up to 10 cm s−1 and is determined by tubular branching and facultative suspension-feeding species such as Rhabdammina abyssorum. Assemblages with abundant Rhabdammina abyssorum and Hoeglundina elegans colonize the southern detached and finer grained Gardar Drift. The Eirik Drift off Greenland with flow velocities of 12 to 22 cm s−1 displays a fauna different from the contourites of the Iceland Basin. Assemblages with attached Cibicidoides wuellerstorfi and Heterolepa broeckhiana largely determine the benthic community. Also attached species, but composed primarily of Cibicides lobatulus, Cibicides refulgens, and Cibicidoides pachyderma, settle at the Greenland continental margin in high energy areas with velocities up to 40 cm s−1.