Late Pleistocene to Holocene fluctuations of the East Antarctic Ice Sheet in Adélie Land using cosmogenic nuclides: combining in situ 10Be/26Al on glacial landforms with meteoric 10Be in marine sediments

East Antarctic Ice Sheet (EAIS) dynamics are source of uncertainty in past and future sea level variations. The assessment of the EAIS stability lies on a lack of data, especially since the Last Glacial Maximum (LGM). Although previous works focused on the LGM ice sheet front at the shelf break or its modern position reached ~8 ka ago, these offshore marine records did not document the post-LGM to Holocene ice sheet fluctuations driven by climatic or oceanic circulation variations. In Adélie Land (136°E-142°E), glacial landforms (i.e., morainic ridges, erratics and glacially polished bedrocks) as well as sedimentary deposits (i.e., along the Adélie bank) suggest multiple post-LGM oscillations of the EAIS front position which have not yet been fully assessed so far. With a new set of cosmogenic nuclides data on well preserved terrestrial and marine archives, we aim to shed new light on the EAIS response to both climatic and oceanic changes with improved spatial and temporal resolution.

We propose new data using terrestrial cosmogenic nuclides - ¹⁰Be and ²⁶Al - from morainic ridges (Lacroix moraine) and glacially-polished bedrocks scattered on the Pointe Géologie archipelago (Dumont d’Urville basecamp). We combine these results with more distal marine data proxies through meteoric ¹⁰Be/⁹Be ratios measured on the authigenic phase of the sediment core MD03-2601 (66°03.07’S; 138°33.43’E, 746m water depth), collected on the continental shelf of Adélie Land and already investigated with environmental proxies over the Holocene.

¹⁰Be/²⁶Al exposure dating of glacially polished bedrocks displays complex exposure histories and diachronous timing for ice sheet retreat along the coastline and within Pointe Géologie archipelago. Here, the onset of ice sheet retreat appears to range from > 60 ka to the LGM period, linked to the Astrolabe ice-stream dynamics. In contrast, the inland Lacroix moraine documents a more recent deglaciation period around 2.5 ka. These terrestrial deposits thus record non-synchronous late-Pleistocene ice sheet dynamics and final withdraw along the Terre Adélie.

Comparatively, in the marine sediment core, we evidence a major meteoric ¹⁰Be input around 6 ka associated to changes in sedimentation rates. Based on the distal core location, we propose this event to be linked with either a modified Circumpolar Deep-Water or easterly currents incursions. ⁹Be data are in agreement with other environmental proxies and record ice-sheet oscillations: (1) a major ice-sheet re-advance and detrital input at 4.2ka; and (2) ice-sheet retreat since around 2.5 ka, synchronous to deglaciation ages on the coast. Our results record at least three main oscillations of the EAIS at different space and time during the late Pleistocene to Holocene period, illustrating its sensitivity to short-term climate forcing.