Sediment waves on the Conrad Rise, Southern Indian Ocean: Implications for the migration history of the Antarctic Circumpolar Current

The Antarctic Circumpolar Current (ACC) is the worlds longest and largest current system; therefore, it plays a prominent role in the global distribution of heat, nutrients and greenhouse gasses. While past changes in the ACC have been reconstructed by a number of studies using sedimentary records in the Southern Ocean, a detailed understanding of the relationship between its temporal and spatial variability and the changes in the Earths climatic system remains unclear. In this study, we conducted multibeam bathymetry, multi-channel seismic reflection, and sediment coring surveys on the Conrad Rise, located in the southern Indian Ocean sector of the ACC. These data reveal large scale sediment wave structures with continuous and parallel reflectors that have low to moderate reflection amplitudes in the upper part of the seismic section (Unit A). These phenomena are most likely formed by bottom current interactions with the sea-floor and sediment transport under the ACC. The basal age of Unit A is estimated to be younger than Pliocene/Pleistocene boundary based on the extrapolation of sedimentation rates from a shallow sedimentary core. The lower part of the section (Unit B) is characterized by moderate to high amplitude sub-horizontal to horizontal reflectors that are interpreted as pelagic sedimentation with stronger current influence to the upper part of the unit. Based on the correlation with ODP sites in the Southern Ocean, we estimate that the upper part of Unit B mainly comprises calcareous ooze. Though the age of the change in the sedimentary environment from seismic Units B to A is not specified, it is thought to be caused by a northward shift of the ACC.