Abstract:
Cenozoic palaeoceanography of the SE Atlantic and Southern Oceans has been investigated using Late Eocene/Early Oligocene to Quaternary ostracod assemblages from 49 samples of ODP Sites 1087 and 1088. The overall abundance of ostracods is relatively low and there is an apparently high level of endemism. Three major changes in the faunal assemblages are identified at Site 1087 (A, B, and C) and two at Site 1088 (B' and C'). The assemblage boundaries, detected on the basis of stepwise changes in the abundance, diversity, dominance, endemism, faunal turnover, and relative abundance of common taxa, coincide broadly with previously identified, ostracod-based paleoceanographical 'events' discussed by Benson and co-workers over the last two decades. The data do not extend sufficiently far back to record the initiation of Assemblage A, but the faunal change between Assemblages A and B, marked by a decline in abundance, species diversity and faunal turnover, occurs within the middle Miocene. It coincides with a previously documented palaeoceanographical "event" at 16-14 Ma which is suggested to possibly be related to the initiation of North Atlantic Deep Water (NADW) production and/or an expansion of the East Antarctic ice sheet. Assemblage B' (super 1) and B' (super 2) sub-assemblage boundary cannot be related to any previously documented faunal change in deep-sea ostracods. Changes associated with the boundaries between Assemblages B and C, and B' and C' include a decrease in diversity and abundance. Two strong turnover peaks occur near the B'/C' boundary at Site 1088. The B/C and B'/C' boundaries coincide with a previously documented mid-Pliocene "event" (3.5 Ma) which may be linked to closure of the Straits of Panama and increased production of NADW. The increase in NADW may have lead to increased production of Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW). On the other hand, fluctuations in size of the Antarctic ice sheet during possible Pliocene warm periods could indirectly be responsible for the observed mid-Pliocene faunal changes. (Mod. auth. abstr.)