Revised magnetostratigraphic chronologies for New Harbour drill cores, southern Victoria Land, Antarctica

Abstract

The Taylor Valley (DVDP-10, -11) and Ferrar Fiord (CIROS-2) drill cores offer a window into the evolution of southern Victoria Land glaciers and the Antarctic climate system during the late-Neogene. Here we present new magnetostratigraphic chronologies, which we use to correlate the drill core successions with onshore dry-valleys geomorphic records and offshore deep-ocean records. Magnetostratigraphies were constructed using stepwise AF and/or thermal demagnetisation of discrete specimens from the drill cores. Correlation of magnetostratigraphies with the magnetic polarity timescale was guided by biostratigraphic and radiometric constraints. We recognise five styles of sedimentation in the Taylor/Ferrar fiords, which we correlate with discrete climate phases. During the latest Miocene–early Pliocene, wet based glaciers filled the Taylor and Ferrar fiords with active sedimentation in the Taylor Fiord and erosion of basement rocks in the Ferrar Fiord. Glaciers retreated during the Pliocene warm period leaving open marine conditions and deep fiords (>300m) at a time when the Ross Sea was free of ice and sea surface temperatures around Antarctica were at least 5°C warmer than today. We recognise the first significant cooling in DVDP-11 post 2.6Ma by a shift to current winnowed sediments sourced from the Ross Sea rather than from East Antarctic glaciers. Post 1.7Ma, lacustrine sediments were deposited behind ice-dammed lakes, which formed when West Antarctic ice expanded and grounded across the Ross Embayment and abutted the Transantarctic Mountains.