A 14.5-million-year record of East Antarctic Ice Sheet fluctuations from the central Transantarctic Mountains, constrained with cosmogenic &amp;lt;sup&amp;gt;3&amp;lt;/sup&amp;gt;He, &amp;lt;sup&amp;gt;10&amp;lt;/sup&amp;gt;Be, &amp;lt;sup&amp;gt;21&amp;lt;/sup&amp;gt;Ne, and &amp;lt;sup&amp;gt;26&amp;lt;/sup&amp;gt;Al

Allie Balter-Kennedy,Gordon Bromley,Holly Thomas,Margaret S Jackson,Greg Balco

doi:10.5194/tc-14-2647-2020

Abstract

Abstract. The distribution of moraines in the Transantarctic Mountains affords direct constraint of past ice-marginal positions of the East Antarctic Ice Sheet (EAIS). Here, we describe glacial geologic observations and cosmogenic-nuclide exposure ages from Roberts Massif, an ice-free area in the central Transantarctic Mountains. We measured cosmogenic 3He, 10Be, 21Ne, and 26Al in 168 dolerite and sandstone boulders collected from 24 distinct deposits. Our data show that a cold-based EAIS was present, in a configuration similar to today, for many periods over the last ∼14.5 Myr, including the mid-Miocene, late Pliocene, and early to Middle Pleistocene. Moraine ages at Roberts Massif increase with distance from, and elevation above, the modern ice margin, which is consistent with a persistent EAIS extent during glacial maxima and slow, isostatic uplift of the massif itself in response to trough incision by outlet glaciers. We also employ the exceptionally high cosmogenic-nuclide concentrations in several boulders, along with multi-isotope measurements in sandstone boulders, to infer extremely low erosion rates (≪5 cm Myr−1) over the period covered by our record. Although our data are not a direct measure of ice volume, the Roberts Massif glacial record indicates that the EAIS was present and similar to its current configuration during at least some periods when the global temperature was believed to be warmer and/or atmospheric CO2 concentrations were likely higher than today.

Highlights

We describe glacial deposits preserved in the central Transantarctic Mountains (TAM; Fig. 1) that provide unambiguous evidence for the presence of the East Antarctic Ice Sheet (EAIS), in a configuration similar to today, for periods of the middle Miocene, late Pliocene, and early to Middle Pleistocene
The preservation of numerous, vertically offset ice-marginal deposits is most plausibly explained by the persistence of an EAIS similar in configuration to today during multiple glacial maxima, accompanied by gradual isostatic uplift of Roberts Massif
The Roberts Massif record is not a direct measure of East Antarctic ice volume, our dataset indicates that the EAIS was not any larger during the late Pliocene–early

Summary

Introduction

We describe glacial deposits preserved in the central Transantarctic Mountains (TAM; Fig. 1) that provide unambiguous evidence for the presence of the East Antarctic Ice Sheet (EAIS), in a configuration similar to today, for periods of the middle Miocene, late Pliocene, and early to Middle Pleistocene. Current estimates of pre-Pleistocene EAIS ice volume are based largely on δ18O of benthic foraminifera (e.g., Shevenell et al, 2008), which primarily records global temperature and ice volume, and far-field sea-level indicators (e.g., Miller et al, 2005), such as raised shorelines (e.g., Rovere et al, 2014) These proxy records (e.g., Holbourn et al, 2013), along with stratigraphic evidence from ice-proximal sediment cores (Levy et al, 2016) and modeling studies (Gasson et al, 2016), suggest that during the middle Miocene the EAIS oscillated between states both larger and smaller than present in response to fluctuations in CO2 and temperature.

Methods

Results

Discussion

Conclusion