Initiation of the West Antarctic Ice Sheet and estimates of total Antarctic ice volume in the earliest Oligocene

Abstract

Reconstructions of Antarctic paleotopography for the late Eocene suggest that glacial erosion and thermal subsidence have lowered West Antarctic elevations considerably since then, with Antarctic land area having decreased ~20%. A new climate‐ice sheet model based on these reconstructions shows that the West Antarctic Ice Sheet first formed at the Eocene‐Oligocene transition (33.8–33.5 Ma, E‐O) in concert with the continental‐scale expansion of the East Antarctica Ice Sheet and that the total volume of East and West Antarctic ice (33.4–35.9 × 106 km3) was >1.4 times greater than previously assumed. This larger modeled ice volume is consistent with a modest cooling of 1–2°C in the deep ocean during the E‐O transition, lower than other estimates of ~3°C cooling, and suggests the possibility of substantial ice in the Antarctic interior before the Eocene‐Oligocene boundary.

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

“…Alternatively, calculation of benthic δ 18 O can be incorporated in coupled ice sheet-climate models by using parameterisations of the contribution of deep sea temperature (Duplessy et al, 2002) and the isotopic content of ice sheets (Cuffey, 2000). Hitherto, studies using this approach have mostly focused on relatively short time intervals surrounding important climatic events, such as the EoceneOligocene transition (33.9 Myr ago; Tigchelaar et al, 2011;Ladant et al, 2014;Wilson et al, 2013), the mid-Miocene climatic optimum (13.9 Myr ago; Langebroek et al, 2010;Gasson et al, 2016), and the Pliocene-Pleistocene transition (2.6 Myr ago; Willeit et al, 2015) using models of varying complexity. These studies have provided valuable information because they have simulated these key events in great detail.…”

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“…As with all objectives, data integration with modeling studies will be undertaken (cf. Figure F4) Gasson et al, 2016;Golledge et al, 2012;Wilson et al, 2013).…”

“…The transition from a terrestrial (or shallow marine)-based West Antarctica with a seaward-dipping shallow continental shelf to that of the modern overdeepened (i.e., landward-dipping) continental shelf would have a first order control on Antarctic ice sheet volume and mass balance Wilson et al, 2013). First, the cooling threshold for the development of a terrestrial-based ice sheet is lower than that of a marine-based ice sheet, which is highly sensitive to changes in oceanic heat flux ( Figure F4) (Golledge et al, 2012;Pollard and DeConto, 2009).…”

“…A terrestrial (or shallow marine) West Antarctica may have supported a larger ice sheet in warmerthan-present climates, whereas overdeepening of the continental shelves may have resulted in a smaller ice sheet with less frequent ice sheet advances, as hypothesized for the Antarctic Peninsula (e.g., Bart and Iwai, 2012). Ice sheet models indicate that a largely terrestrial West Antarctica could accommodate an extra ~13 million km 2 of grounded ice in the warmer-than-present climates of the Eocene (~30 m SLE; Figure F4) (Wilson et al, 2013). Therefore, constraining the timing of overdeepening in the Ross Sea is critical to reconcile far-field records of eustatic sea level variance into the late Neogene (see Objective 1).…”

“…Expedition 374 sites are located in the most sensitive sector of the Antarctic for assessing ice sheet responses to (A) sea level and (B) ocean heat flux. C-F. A more terrestrial West Antarctica in the Oligocene could support a larger ice sheet than present, despite a warmer climate (Wilson et al, 2013). Thus, the timing of Ross Sea overdeepening has important implications for sea level budgets and for understanding mass balance controls.…”