The origin of the ice-free areas of the Hurd Peninsula (Livingston Island, Antarctica)

Abstract

Spatio-temporal patterns of glacial retreat determine the intensity of geomorphological, hydrological, and ecological processes in the ice-free areas of the Antarctic Peninsula region. The chronology of glacial oscillations in the region following the Last Glacial Maximum (LGM) is still poorly constrained and mostly limited to data from a few sites adjacent to research stations. The Hurd Peninsula, located on Livingston Island (South Shetland Islands), is mainly covered by the Hurd Peninsula Ice Cap (HPIC); there is a ca. 20 km² ice-free area downvalley of the ice cap in the peninsula's southern sector in addition to numerous nunataks that protrude above the HPIC. In this study, we present an approach combining two direct surface exposure dating methods, cosmic-ray exposure (CRE) dating and lichenometry, to reconstruct the spatio-temporal patterns of glacial thinning and ice cap retreat on the Hurd Peninsula. To understand the patterns of deglaciation on the peninsula, 26 samples for CRE dating (in situ cosmogenic ¹⁰Be) were taken from glacially polished surfaces and moraine boulders along a transect from the nunatak summits to the coast. On the most recent moraines, boulder stabilisation (i.e., indicative of glacier withdrawal) was dated through the longest axis of the 10 largest thalli of the lichen species Rhizocarpon geographicum. Ice thinning might have begun before the LGM at ca. 31.6 ka, when the highest areas close to the coast became exposed, and subsequently accelerated during the LGM at 20-18 ka. The upper surfaces were completely deglaciated between 16 and 14 ka. The HPIC was relatively stable until the mid-Holocene, when neoglacial advances of its outlet glaciers built moraines at ca. 4.5 ka. Subsequently, late Holocene polygenic moraines formed before the development of the external ridges of the most recent moraine system left by the HPIC outlets during the Little Ice Age, at 0.3 ka. The internal moraines correspond to glacial advances from the late 19th and early 20th centuries, as indicated by lichenometric dating. This work presents a comprehensive chronology of glacial oscillations on the Hurd Peninsula, enhancing our understanding of deglaciation patterns and offering insights into glacier dynamics due to climate variability and change.