Recent morphological changes in the Peninsula Potter lakes, 25 de Mayo Island, Southern Shetland Islands, Antarctica

Abstract

Although the Holocene-Recent environmental history of the Antarctic lakes reported in this paper is less spectacular than that of the big proglacial palaeolakes formed on the eastern flank of the Andes of southern Patagonia during the late Pleistocene-early Holocene, palaeoenvironmental evidence suggests that recurrent changes in drainage accompanied by the stepped descent of Antarctic proglacial lakes were also probably triggered by the deglaciation event, which may have shifted southward in high latitudes of the Southern Hemisphere. This paper focuses on the largest lakes from Potter Peninsula (62°15´S, 58°40´W), King George (25 de Mayo) Island (South Shetland Islands, Antarctica), where the lakes were formed between Neoglacial moraines deposited by the receding front of the peninsula ice field, during late Holocene-Recent times. Following their maximum expansion, the major lakes from Potter Peninsula drained into Bransfield Strait (Mar de la Flota), and their level stepped down due to the opening of outflows at successively lower altitudes. The fluvial channels occupied valleys successively vacated by former outlet glaciers from the ice field of the peninsula. Sediment cores from Potter Peninsula lacustrine basins show glacial deposits alternating with clastic varves, suggesting that the sedimentation within the lakes probably reflects rapid fluctuations of glacier fronts, which characterized this region during the youngermost Holocene. The virtual absence of organic remains impeded radiocarbon dating of deposits; only a maximum age (< 5,500 cal yrs BP) of a drainage change from the older lake studied in this paper could be roughly estimated, whereas the drainage change from the younger lake occurred during the 1999-2000 austral summer. This suggests that the deglaciation event and subsequent partial melting of permafrost, as well as the destruction of morainic dams of lakes on Potter Peninsula, are probably still active.