Oceanographic implications of recent planktonic foraminifera along the southern Australian margin

Abstract

The distribution of planktonic foraminifera along the southern Australian margin is strongly gradational from warmer assemblages in the west to more temperate assemblages in the east. This pattern follows a decreasing temperature gradient generated by the warm Leeuwin Current which flows southward and then eastward on the southern margin. The abundances of tropical and subtropical species including Globorotalia menardii and Globigerinoides trilobus s.l. decrease rapidly after rounding the south-western corner, while the temperate index species Globorotalia inflata increases and subsequently dominates the fauna towards the east, especially on the Lincoln and Lacepede shelves of South Australia. This W–E gradation is also observed in the relict Pleistocene assemblages, indicating that the Leeuwin Current has been influential since at least the last interglacial time. The interaction between the warm and saline water from the Great Australian Bight and cold water from the south produced an assemblage in deeper parts of the Bight with abundant small species such as Globigerina falconensis, Globotur-borotalita rubescens, Neogloboquadrina pachyderma and Turborotalita quinqueloba.