Diatom-based correlation of early to mid-Pliocene drillcores from the southwestern Ross Sea, Antarctica

Abstract

The ANDRILL AND-1B drillcore in southern Victoria Land Basin, Antarctica recovered an upper Miocene to early Pleistocene continental shelf stratigraphic section, including a spectacular Pliocene and Pleistocene sequence of alternating diamictite and diatom-rich sediments. This punctuated sequence reflects variation between glacial sediments deposited by ice advance over the site and open-marine diatom productivity and sedimentation. An early Pliocene age for the base of diatom-rich sediment is constrained through integrated diatom biostratigraphy and magnetostratigraphy. The presence of marine diatom Shionodiscus tetraoestrupii from the top of the core to 583.64mbsf indicates the lowest diatom-bearing sediments are younger than 5Ma. This drillcore provides important new chronostratigraphic control for paleoenvironmental changes also recorded in three drillcores from the western coast of the McMurdo Sound area, DVDP-10 and -11 in Taylor Valley and CIROS-2 from the seaward edge of Ferrar Fjord. The refined continental shelf biostratigraphy developed from AND-1B provides a framework for regional correlation to understand better the timing and character of large paleoenvironmental changes in the western Ross Sea that involve the history of the West Antarctic Ice Sheet (WAIS). Multivariate analysis, along with traditional biostratigraphic approaches, enables the correlation and comparison of coeval intervals in these drillcores. A composite stratigraphic sequence from these four cores suggests the early and mid-Pliocene Ross Sea experienced extended intervals of open-marine conditions with minimal sea-ice cover and high diatom production and sedimentation. This new information provides important constraints on Antarctic paleoclimate and ice sheet history during an important interval when global climate was warmer than today. The history preserved in these four drillcores will be an important tool to guide and test future ice sheet and climate models.