Evolutionary inferences from the sedimentary deposits of Lake LH73, Larsemann Hills, East Antarctica

Abstract

Lakes from the coastal oasis of Larsemann Hills respond to changes in regional climate. They are mainly influenced by the ice-sheet dynamics and regional eustatic variation based on their proximity to either of them or both. The sedimentary sequences of the ice-free regions of Antarctica offer unique climate records (lake sediment deposits). Here, we present the evolution of a lake reconstructed from its sedimentary sequence. A 60 cm long radiocarbon-dated sediment core spanning the last 11.8 kyr from Lake LH73 located in Broknes Peninsula of Larsemann Hills is studied for grain size fractions, magnetic susceptibility, and diatom abundance. Based on the diatom and grain fraction data, it is inferred that the lake persisted as a proglacial lake during the early-Holocene (11.8 to 7.2 ky BP) dammed by ice-sheet towards the south. The lake level was at least 3 m higher than the present level (4 m) as inferred from the diatom transfer function owing to the presence of ice dam. The retreat of the ice-sheet and the collapse of the ice dam between 7.2 and 7 ky BP resulted in the lake transitioning to an isolated lake with the lake level attaining current level (4 m). As a consequence, the catchment area increased and the lake received meltwater from the snowbanks hence largely modulating the sedimentary process. The absence of glacial clay from 5 ky BP suggests that the lake was cut-off from the glacial input. The appearance of diatom at ~ 8.6 ky BP indicates the establishment of optimal condition for productivity in the lake ecosystem. Stauroforma inermis and Plannothidium quadripunctatum (Psammothidium abundans) dominates between 7 ky BP till present (11.8 to 7 ky BP), responding to lake level variation. Ice-sheet retrieval and ablation led to transition of proglacial-to-isolated lake leading to shallowing of the lake as reflected in diatom assemblage changes.