Hydrogeological behavior of freshwater lake systems in an Antarctic volcanic setting, Deception Island, South Shetlands archipelago

The aquifer system of Deception Island, located in the South Shetlands archipelago, exhibits high transmissivity given the hydraulic conductivity of the pyroclastic sediments that form the aquifer, promoting both high infiltration of meteoric water and rapid groundwater flow. Recharge to the aquifer is primarily driven by snowmelt and precipitation, with a mean annual recharge estimated at 164 mm/yr, representing 41% of the island’s average annual precipitation ( P = 400 mm/yr). The remaining water is lost through evaporation (142 mm/yr and 35% P ) and wind-driven snow transport (95 mm/yr and 24% P ). The aquifer system is characterized by a shallow, seasonally active unconfined aquifer within the permafrost’s active layer, and a highly transmissive permanent aquifer mainly beneath the permafrost. Both aquifers are generally unconfined, but the lower one may become locally confined near the coast due to permafrost. Groundwater discharge maintains the studied lake at levels above sea level (by less than 1 m), preventing salinization and ensuring that they remain fresh despite being located in a morphologically closed volcanic basin. Hydrochemical and isotopic analyses reveal that lake water composition is influenced by marine aerosol deposition, convergence of groundwater flow lines, and proximity to the sea. These findings highlight the dynamic interplay between volcanic geology, permafrost, and hydrogeological processes in sustaining freshwater lake systems in an Antarctic volcanic environment. • Deception Island aquifer is highly transmissive, supporting rapid groundwater flows. • Lake water levels remain less than one meter higher than the mean sea level. • Lake water balance maintains their levels and prevents salinization. • Lake water chemical composition associated with marine environments. • The isotopic content of precipitation shows a vertical lapse rate of –3.3‰/km.