Holocene relative sea-level change and deglaciation on Alexander Island, Antarctic Peninsula, from elevated lake deltas

Field data constraining the rate and spatial pattern of deglaciation and relative sea-level (RSL) change on the Antarctic Peninsula (AP) are relatively sparse, but are needed to improve regional ice sheet and RSL change models, and contribute to better model predictions of future sea-level rise. We investigated the geomorphology, sedimentology and quartz-fraction single aliquot regeneration optically-stimulated luminescence (SAR-OSL) geochronology of elevated deltas around two epishelf lakes, Ablation Lake (AL) and Moutonnée Lake (ML), Alexander Island, Antarctic Peninsula. AL and ML are dammed by George VI Ice Shelf, and maintain a direct hydraulic connection to the sea; hence, their water levels are controlled by changes in RSL. Our aim was to provide new terrestrial constraints on RSL and deglaciation for the southern AP by comparing the formation processes, age and altitude of the AL and ML deltas with: (1) existing RSL curves for the AP; (2) isostatically-coupled AP ice sheet models, and (3) existing AP deglaciation history and SAR-OSL ages from elevated deltas around the nearby inland Hodgson Lake (HL). Although there was insufficient quartz in the ML samples for SAR-OSL dating, the 4.6 ± 0.4 ka SAR-OSL age of the elevated delta at AL represents the last time active deltas were forming higher than present day lake level, and implies: (1) a fall in RSL of up to 14.4 m since the mid-Holocene in this part of Alexander Island, which is consistent with existing field-based RSL chronologies for the AP; (2) relatively smaller ice masses than suggested by some (but not all) isostatically-coupled ice sheet models since the mid-Holocene, and (3) significant mid-Holocene thinning of the AP ice sheets, which is consistent with regional sediment core data and cosmogenic exposure ages, and the 4.4 ± 0.7 ka SAR-OSL age of the lowermost HL delta.