Evidence for the onset of the last Glacial Period at Barton Peninsula (King George Island, Antarctica): Luminescence (pIRIR) dating of glacial till underlying the Holocene patterned ground structures

ABSTRACT Understanding the long‐term Quaternary glacial history of the Antarctic Peninsula and South Shetland Islands is crucial for contextualizing ice sheet responses to climate change. While Holocene deglaciation is relatively well‐studied, direct terrestrial evidence for pre‐Last Glacial Maximum (LGM) events remains scarce. This study investigates the depositional age of glacial sediments underlying Holocene patterned ground on Barton Peninsula, King George Island. A 50.5 cm sediment core (AG‐9) from a homogeneous diamicton at ~25 m above present sea level (a.s.l.) revealed a provenance from local Eocene magmatic bedrocks. Feldspar post‐infrared stimulated luminescence (pIRIR) dating, focusing on a cumulative analysis of all accepted aliquots from the core, yielded a Central Age Model De of 226 ± 12 Gy. Combined with an environmental dose rate of 2.32 ± 0.12 Gy/ka and a g ‐value of 2.07 ± 0.84%/decade, this results in a fading‐corrected luminescence age of 121 ± 9 ka. This age places the till deposition within Marine Isotope Stage 5e (MIS‐5e), the Last Interglacial. Key implications include the following: (1) The MIS‐5e glaciation provides a terminus post quem (a point in time after which an event must have occurred) for the onset of the subsequent glacial cycle in this locality. (2) The in‐situ preservation of the bulk of these MIS‐5e deposits, which subsequently served as the substrate for Holocene periglacial landforms, suggests largely continuous and non‐erosive ice cover from MIS‐5e until Holocene deglaciation. (3) The depositional setting at ~25 m a.s.l. is interpreted as a terrestrial marker of glacial advance to the higher MIS‐5e relative sea level, considering subsequent glacio‐isostatic adjustments. The MIS‐5e age challenges narratives focused solely on LGM/Holocene events, highlights the potential for uncovering older Quaternary terrestrial records, and offers new perspectives on the region's long‐term glacial dynamics and ice‐sheet sensitivity.