Reinterpretation of ice-sheet history and geomorphology in the Lambert-Amery system, East Antarctica, from cosmogenic in-situ 14C analysis

Reconstructing the history of the Antarctic Ice Sheet provides valuable insights into ice-sheet response to climate change. The Lambert Glacier-Amery Ice Shelf system is the largest glacial system in East Antarctica, but reconstructing the state of this glacier system is challenging. Common approaches, such as geomorphic interpretation and exposure dating using long-lived cosmogenic nuclides such as 10 Be may give misleading or ambiguous results, making the timing and magnitude of deglaciation unclear. Here, we show that surface-exposure chronologies of past ice-thickness changes derived from in - situ cosmogenic- 14 C dating of erratic cobbles from the Prince Charles Mountains provide critical new constraints on past ice thickness. Our 14 C data from Accidental Valley show 224 m of ice thinning beginning at least ∼12.1 ka and ending ∼4.1 ka, while, at Mt. Lanyon, our 14 C data show 44 m of ice thinning occurring later (∼5.9 ka and ending ∼5.4 ka), followed by thinning of a local ice cap (∼3.4 to ∼2.9 ka). These chronologies redefine the history of the Lambert-Amery system, revealing that (i) Last Glacial Maximum (LGM) ice limits based on 10 Be alone may be unreliable, (ii) there were possibly large spatial differences in thinning since the LGM, and (iii) the bulk of ice thinning occurred within the last 15 kyr. Our results provide new context for geomorphic features and older 10 Be ages, showing that cosmogenic 14 C dating is essential for accurately resolving ice thickness at the LGM and during subsequent deglaciation in Antarctica.