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

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 similar to 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 similar to 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. (c) 2025 John Wiley & Sons, Ltd.