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Evidence for orbitally controlled size variations of the East Antarctic Ice Sheet during the late Miocene

¹ Geosciences Department, Bremen University, P.O. Box 330440, 28334 Bremen, Germany
² Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Borgo Grotta Gigante 42/C, 34010 Sgonico, Italy
³ Department of Geological and Environmental Sciences, 450 Serra Mall, Stanford University, Stanford, California 94305, USA
⁴ Norwegian Geotechnical Institute, P.O. Box 3930, N-0806 Oslo, Norway
⁵ Department of Geological and Environmental Sciences, 450 Serra Mall, Stanford University, Stanford, California 94305, USA
⁶ Geosciences Department, Bremen University, P.O. Box 330440, 28334 Bremen, Germany

Ocean Drilling Program Site 1165 penetrated drift sediments on the East Antarctic continental rise and recovered sediments from a low-energy depositional environment. The sediments are characterized by prominent alternations between a green to greenish-gray diatom-bearing hemipelagic facies and gray to dark gray hemiturbiditic facies. Our investigation of an upper Miocene section, using high-resolution color spectra, multisensor core logs, and X-ray fluorescence scans, reveals that sedimentation changes occur at Milankovitch orbital frequencies of obliquity and precession. We use this finding to derive an astronomical calibrated time scale and to calculate iron mass-accumulation rates, as a proxy for sediment-accumulation rates. Terrigenous iron fluxes change by as much as 100% during each obliquity cycle. This change and an episodic pattern of enhanced ice-rafted debris deposition during times of deglaciation provide evidence for a dynamic and likely wet-based late Miocene East Antarctic Ice Sheet (EAIS) that underwent large size variations at orbital time scales. The dynamic behavior of the EAIS implies that a significant proportion of the variability seen in oxygen isotope records of the late Miocene reflects Antarctic ice-volume changes.

Key Words: paleoclimatology • Ocean Drilling Program • Antarctic Ice Sheet • Prydz Bay • Milankovitch theory • Miocene

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