title: Evolution of the early Antarctic ice ages.
abstract: Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ∼85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ∼110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago) and across the Oligocene-Miocene Transition (∼23.0 My ago). However, the high-amplitude glacial-interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical-indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2levels on astronomical time scales that is not yet captured in existing proxy reconstructions.
authors.affiliation: National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, United Kingdom; diederik.liebrand@noc.soton.ac.uk.
authors.forename: Diederik
authors.identifier: 0000-0002-6925-7889
authors.initials: D
authors.lastname: Liebrand
authors.affiliation: Department of Physical Geography, Faculty of Geosciences, Utrecht University, 3508 TC Utrecht, The Netherlands.|Littoral Environnement et Sociétés, Université de La Rochelle, 17042 La Rochelle, France.
authors.forename: Anouk T M
authors.initials: AT
authors.lastname: de Bakker
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands.
authors.forename: Helen M
authors.initials: HM
authors.lastname: Beddow
authors.affiliation: National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, United Kingdom.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Wilson
authors.affiliation: National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, United Kingdom.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Bohaty
authors.affiliation: Department of Physical Geography, Faculty of Geosciences, Utrecht University, 3508 TC Utrecht, The Netherlands.
authors.forename: Gerben
authors.identifier: 0000-0001-9526-6087
authors.initials: G
authors.lastname: Ruessink
authors.affiliation: Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany.
authors.forename: Heiko
authors.initials: H
authors.lastname: Pälike
authors.affiliation: Institute of Geosciences, Goethe-University Frankfurt am Main, 60438 Frankfurt, Germany.|Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, United Kingdom.
authors.forename: Sietske J
authors.initials: SJ
authors.lastname: Batenburg
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands.
authors.forename: Frederik J
authors.initials: FJ
authors.lastname: Hilgen
authors.affiliation: Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom.
authors.forename: David A
authors.initials: DA
authors.lastname: Hodell
authors.affiliation: National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, United Kingdom.
authors.forename: Claire E
authors.initials: CE
authors.lastname: Huck
authors.affiliation: School of GeoSciences, Grant Institute, University of Edinburgh, Edinburgh EH9 3FE, United Kingdom.
authors.forename: Dick
authors.initials: D
authors.lastname: Kroon
authors.affiliation: Dipartimento di Ingegneria e Geologia, Università degli Studi "G. d'Annunzio" di Chieti-Pescara, 66013 Chieti Scalo, Italy.
authors.forename: Isabella
authors.initials: I
authors.lastname: Raffi
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands.
authors.forename: Mischa J M
authors.initials: MJ
authors.lastname: Saes
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands.
authors.forename: Arnold E
authors.initials: AE
authors.lastname: van Dijk
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD Utrecht, The Netherlands.
authors.forename: Lucas J
authors.initials: LJ
authors.lastname: Lourens
keywords: Oligocene−Miocene; bispectral analysis; early Antarctic ice sheet; glacial−interglacial cycle geometries; unipolar icehouse