Orbitally induced oscillations in the East Antarctic ice sheet at the Oligocene/Miocene boundary


Between 34 and 15 million years (Myr) ago, when planetary temperatures were 3–4 °C warmer than at present and atmospheric CO2 concentrations were twice as high as today1, the Antarctic ice sheets may have been unstable2,3,4,5,6,7. Oxygen isotope records from deep-sea sediment cores suggest that during this time fluctuations in global temperatures and high-latitude continental ice volumes were influenced by orbital cycles8,9,10. But it has hitherto not been possible to calibrate the inferred changes in ice volume with direct evidence for oscillations of the Antarctic ice sheets11. Here we present sediment data from shallow marine cores in the western Ross Sea that exhibit well dated cyclic variations, and which link the extent of the East Antarctic ice sheet directly to orbital cycles during the Oligocene/Miocene transition (24.1–23.7 Myr ago). Three rapidly deposited glacimarine sequences are constrained to a period of less than 450 kyr by our age model, suggesting that orbital influences at the frequencies of obliquity (40 kyr) and eccentricity (125 kyr) controlled the oscillations of the ice margin at that time. An erosional hiatus covering 250 kyr provides direct evidence for a major episode of global cooling and ice-sheet expansion about 23.7 Myr ago, which had previously been inferred from oxygen isotope data (Mi1 event5).

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Figure 1: Cross-section through Cenozoic strata beneath the western flank of Roberts ridge, western Ross Sea.
Figure 2: Lithological and environmental changes through sequence 11.
Figure 3: Lithostratigraphy, sequence stratigraphy, variation in sand content and age models for sequences 9, 10 and 11 (130.27–306.65 m) from the CRP-2/2A drill hole.
Figure 4: Correlation of sequences 9,10 and 11 in CRP-2/2A core, western Ross Sea with deep-water benthic foraminiferal δ18O record of ODP site 929, western equatorial Atlantic.


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This Letter is dedicated to the memory of Ken Woolfe, sedimentologist and ISC member of the Cape Roberts Project. The Cape Roberts Project was supported by the Antarctic programmes of Italy, New Zealand, the USA, Germany, Australia, the UK and The Netherlands, with field operations organised by Antarctica New Zealand. We acknowledge the efforts of the Cape Roberts Project International Steering Committee, the Operations/Logistics Management Group, as well as the drilling, logistic support and science teams who provided the material on which this Letter is based. We also acknowledge the support of our home institutions and funding agencies.

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Correspondence to Tim R. Naish.

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Naish, T., Woolfe, K., Barrett, P. et al. Orbitally induced oscillations in the East Antarctic ice sheet at the Oligocene/Miocene boundary. Nature 413, 719–723 (2001). https://doi.org/10.1038/35099534

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