Plio‐Pleistocene palaeoceanography of the tropical Indian Ocean (ODP Hole 709C): Radiolarian and CaCO₃ evidence

Abstract

Sediments spanning the Olduvai subchron (1.79-1.95 Ma) of ODP Hole 709C in the tropical Indian Ocean were sampled at 5-cm intervals. High-resolution quantitative radiolarian and CaC03% data have been used as proxies in interpreting palaeoceanographical conditions, and a comparison made with previously obtained oxygen isotope data. Radiolarian data were subjected to principal components analysis, resulting in four varimax factors. Factor 1 accounted for the greatest variation and comprised well-known warm-water and cold-water taxa, with high +ve and -ve scores respectively, which were used in the construction of a temperature index. Results indicate a tripartite temporal division of Olduvai palaeoceanography. In the early Olduvai, prior to 1.895 Ma, and the late Olduvai, approximating the Plio-Pleistocene boundary at 1.81 Ma, divergence-driven equatorial upwelling and high-productivity coincide with isotope-defined 'interglacials', and with generally low CaC03%. However, during the mid-Olduvai, upwelling, productivity and sedimentation rates were all reduced. These changes in palaeoceanography are thought to be linked directly to eccentricity modulated variations in the precession of the Earth's orbit. The early and late Olduvai coincide with periods of minimum eccentricity, when precessional reinforcement of the southwest monsoon is weakest, coastal upwelling along the Oman margin is reduced, and zonal wind-driven equatorial divergence upwelling is increased. The mid-Olduvai, however, corresponds with an eccentricity maximum, during which monsoonal activity is stronger and equatorial divergence upwelling weak. bourM~ of Q~~~~~~~~~

Late Neogene Climates in Australia: Fossil Pollen- and Spore-based Estimates in Retrospect and Prospect

“…These provide comprehensive information on changes in the temperature of surface and deep water in the oceans surrounding Australia such as the Southern Ocean (Hodell and Warnke 1991;Burkle et al 1996), Coral Sea (Feary et al 1991), south-western Pacific and Indian Ocean (Haslett et al 1994). For example, marine data from north-western Australia imply that the Early Pliocene was warmer than either the Late Miocene or Late Pliocene (Quilty 1994).…”

Pliocene–Pleistocene radiolarian and diatom biostratigraphy of ODP Hole 709C (equatorial Indian Ocean)

“…Most shipboard and post-cruise micropalaeontological work was carried out on calcareous microfossils: calcareous nannofossils (Fornaciari et al, 1990;Matsuoka & Okada, 1990;Okada, 1990;Rio et al, 1990), and foraminifera (Boersma, 1990;Premoli-Silva & Spezzaferri, 1990;Haslett & Kersley, 1995). Siliceous microfossils were also investigated: radiolaria (Johnson, 1990;Haslett, 1992;Haslett et al, 1994) and diatoms (Mikkelsen, 1990;Fenner & Mikkelsen, 1990;Kennington, 1992). From the three holes drilled at Site 709, Johnson (1990) concentrated on 709A to provide the Pliocene-Pleistocene radiolarian biostratigraphy, whilst using 709C to provide biostratigraphical data for Eocene-Oligocene sediments.…”