PLIO-PLEISTOCENE ANTARCTIC CLIMATE FROM ANDRILL'S MCMURDO ICE SHELF SITE AND IMPLICATIONS FOR BI-POLAR CLIMATE LINKAGE

A single 1284.87m-long drill core (AND-1B) was recovered using the McMurdo Ice Shelf, Antarctica as a drilling platform. The Neogene (~0-10 Ma) core includes glacimarine, terrigenous, volcanic and biogenic sediment that provides new knowledge on the Late Neogene behavior and variability of the Ross Ice Shelf (RIS) and the West Antarctic Ice Sheet (WAIS), and their influence on global climate, sea-level and ocean circulation. Repetitive vertical successions of facies imply at least 60 fluctuations, of probable Milankovitch-duration, between subglacial, ice proximal and ice distal open marine environments. These have been grouped into 4 types of facies cycles that correspond to glacial-interglacial variability during climatically distinct periods of the Late Neogene: (1) Cold polar climate and ice (Late Miocene, ~13-10Ma & Pleistocene, ~1-0Ma). (2) Relatively warmer climate, polythermal ice and interglacials dominated by pelagic diatomites (Pliocene, ~5-2Ma). (3) Warmer climate, polythermal ice with interglacials dominated by hemipelagites (early-Late Miocene, ~9-6Ma). A ~80m-thick Early Pliocene interval of diatomite shows no apparent glacial cyclicity and represents an extended period of ice-free conditions indicative of a reduced WAIS. Spectacular Late Pliocene (~2.6-2.2 Ma) glacial-interglacial cycles characterized by abrupt alternations between subglacial/ice-proximal facies and open marine diatomites imply significant WAIS dynamism, and contribution to global ice volume changes coeval with the initiation of Northern Hemisphere glaciations. A ~4m-thick interval of diatomaceous mudstone in the Middle Pleistocene also represents a warm-interglacial ice-free conditions. Intriguingly, glacial deposits interrupted by periodic, small-scale retreats of the grounding line dominate the last 1Ma. We propose that inter-hemispheric ice sheet coupling was controlled by Northern Hemispheric insolation and consequent glacial eustasy that accounts for much of the orbital-scale variability of the WAIS since 2.5 Ma. A further expansion of the WAIS and the establishment of the present WAIS mode occurred across the Mid-Pleistocene Climate Transition.