Palaeooceanographic significance of bottom-current fluctuations in the Southern Ocean

Abstract

Hiatuses in the sedimentary record of the Southern Ocean are usually attributed to erosion by high-velocity bottom currents^1–3. To test for palaeoclimatic mechanisms which intensified bottom circulation, however, the timing of increases in bottom-current velocity must be known. As the sedimentary record of the period of initial erosion is lost within the hiatus, the timing of increased velocity must be determined in cores which are adjacent to the axis of highest velocity^4,5. In those cores the accumulation rates are reduced due to the current but a record of the period of initiation of scour is preserved as a zone of particle-size winnowing of the fine-fraction^3–4. The timing of major episodes of bottom-current intensification in the South Australian Basin for the past 4.5 Myr are reported here for the first time and may be used to examine the role of palaeoclimatic fluctuations on bottom-current intensity.