Faunal changes in Cenozoic deep-sea ostracod assemblages from the South Atlantic and the Southern Ocean and their palaeoceanographical implications

Abstract

The Cenozoic palaeoceanographical history of the South Atlantic and the Southern Ocean is summarised on the basis of changes in the ostracod faunas of DSDP/ODP Sites 329, 513, 689, 699, 1087 and 1088. The results are mainly compared with the global palaeoceanographical history of Benson. The present study failed to find strong evidence for a sudden psychrospheric event (Sites 689 and 699) in the late Eocene, but there is, however, a decrease in abundance and diversity of ostracods from the mid-/late Eocene to the Oligocene at Sites 689 and 699. This suggests a more gradual palaeoceanographical change over a relatively long time interval. Mid-Miocene faunal changes occur at Site 1087 and coincide with the 16–14 Ma event of Benson. However, the faunal changes are, in contrast to Benson, here marked by a decline in abundance, diversity and faunal turnover. The local differences in faunal changes in mid-Miocene deep-sea ostracod faunas may be related to the initiation of NADW and/or a major expansion of the Antarctic ice sheet. We found little or no evidence for the 6.3–4.9 Ma event, which Benson recorded and related to the effects of a series of events such as the Messinian Salinity Crisis and increased glaciation on Antarctica. Similar to Benson's global data, we have also found a major faunal turnover at Sites 1087 and 1088 at 3.5 Ma. This is possibly related to the effects of a closure of the Straits of Panama, increased production of NADW, AAIW and AABW, and/or a major deglaciation of the Antarctica in the mid-Pliocene.