Southern hemisphere Miocene bottom-water circulation: a palaeobathymetric analysis

Abstract

Abstract Palaeobathymetric reconstructions of the southern hemisphere are used to assess the potential flow paths and extent of proto-Antarctic Bottom Water (proto-AABW) for three time slices during the Miocene: 20 Ma (early), 15 Ma (middle) and 10 Ma (late). The depth ranges of fluctuations in this water mass were derived from its waxing/waning curve, based on an analysis of hiatuses within drill sites from the Indian Ocean. Proto-AABW was likely to be expressed at depths below −4400 m, −5500 m and −4700 m at 20 Ma, 15 Ma and 10 Ma respectively. These depth ranges were extended into the South Atlantic and South Pacific Oceans to allow a first approximation of potential proto-AABW flow paths. An understanding of modem oceanography and the distribution of suspended sediment particle concentrations within the nepheloid layer and sediment drifts were used to constrain flow paths. This interpretation was made on the basis that proto-Antarctic Bottom Water was an analogue of it modern equivalent and was likely to have followed similar flow paths. The palaeobathymetric analysis reveals that at 20 Ma (early Miocene) the deep basins of the southern hemisphere were well connected and proto-AABW flow paths were likely to have been widespread. By 15 Ma (middle Miocene), however, the waning of proto-AABW led to the disconnection of the deep ocean basins and this water mass was probably restricted to the Antarctic Basin. Waxing of proto-AABW during the late Miocene allowed the reconnection of the deep basins but not to the same extent as at 20 Ma (early Miocene).