Radiolarian biogeography in surface sediments of the western Indian Ocean

Abstract

Recurrent group analysis of Radiolaria in 46 core top samples from a north-south transect in the western Indian Ocean has allowed the discrimination of eight distinctive radiolarian assemblages. Most of the designated assemblages have distribution patterns which closely reflect the major oceanographic fronts and first-order patterns of surface water circulation including the South Equatorial Divergence, Subtropical Gyre, Subtropical Convergence, and Antarctic Convergence. An exotic assemblage consisting of four taxa was found off the Arabian coast. These same taxa were previously reported only in the eastern equatorial Pacific, and may be representative of upwelling with relatively restrictive salinities. Radiolarian abundance drops abruptly near 48°S at the Antarctic Convergence, south of which the sediment is a radiolarian-poor diatomaceous ooze.