East Antarctic Ice Sheet Variability In The Central Transantarctic Mountains Since The Mid Miocene

Abstract. The response of the East Antarctic Ice Sheet to warmer-than-present climate conditions has direct implications for projections of future sea level, ocean circulation, and global radiative forcing. Nonetheless, it remains uncertain whether the ice sheet is likely to undergo net loss due to amplified melting coupled with dynamic instabilities, or whether such losses will be balanced, or even offset, by enhanced accumulation under a higher precipitation regime. The glacial-depositional record from the central Transantarctic Mountains (TAM) provides a robust geologic means to reconstruct the past behaviour of the East Antarctic Ice Sheet, including during periods thought to have been warmer than today, such as the Mid Pliocene Warm Period (~3.3–3.0 Ma). This study describes a new surface-exposure-dated moraine record from Otway Massif in the central TAM spanning the last ~9 Myr, and synthesises these data in the context of previously published moraine chronologies constrained with cosmogenic nuclides. The resulting record, although fragmentary, represents the majority of direct and unambiguous terrestrial evidence for the existence and size of the East Antarctic Ice Sheet during the last 14 Myr, and thus provides new insight into the long-term relationship between the ice sheet and global climate. At face value, the existing TAM moraine record does not exhibit a clear signature of the Mid Pliocene Warm Period, thus precluding a definitive verdict on the East Antarctic Ice Sheet’s response to this event. In contrast, an apparent hiatus in moraine deposition both at Otway Massif and neighbouring Roberts Massif suggests that the ice sheet surface in the central TAM potentially was lower than present during the Late Miocene and earliest Pliocene.