Uneven distribution of rainfall and freshwater scarcity in populated areas in the Island of Maui, Hawaii, renders water resources management a challenge in this complex and ill‐defined hydrological system. A previous study in the Galapagos Islands suggests that noble gas temperatures (NGTs) record seasonality in that fractured, rapid infiltration groundwater system rather than the commonly observed mean annual air temperature (MAAT) in sedimentary systems where infiltration is slower thus, providing information on recharge sources and potential flow paths. Here we report noble gas results from the basal aquifer, springs, and rainwater in Maui to explore the potential for noble gases in characterizing this type of complex fractured hydrologic systems. Most samples display a mass‐dependent depletion pattern with respect to surface conditions consistent with previous observations both in the Galapagos Islands and Michigan rainwater. Basal aquifer and rainwater noble gas patterns are similar and suggest direct, fast recharge from precipitation to the basal aquifer. In contrast, multiple springs, representative of perched aquifers, display highly variable noble gas concentrations suggesting recharge from a variety of sources. The distinct noble gas patterns for the basal aquifer and springs suggest that basal and perched aquifers are separate entities. Maui rainwater displays high apparent NGTs, incompatible with surface conditions, pointing either to an origin at high altitudes with the presence of ice or an ice‐like source of undetermined origin. Overall, noble gas signatures in Maui reflect the source of recharge rather than the expected altitude/temperature relationship commonly observed in sedimentary systems.
This study represents the first comprehensive noble gas study in glacial meltwater from the Greenland Ice Sheet. It shows that most samples are in disequilibrium with surface collection conditions. A preliminary Ne and Xe analysis suggests that about half of the samples equilibrated at a temperature of ~0°C and altitudes between 1000 m and 2000 m, with a few samples pointing to lower equilibration altitudes and temperatures between 2°C and 5°C. Two samples suggest an origin as melted ice and complete lack of equilibration with surface conditions. A helium component analysis suggests that this glacial meltwater was isolated from the atmosphere prior to the 1950s, with most samples yielding residence times ≤ 420 years. Most samples represent a mixture between a dominant atmospheric component originating as precipitation and basal meltwater or groundwater, which has accumulated crustal 4He over time.
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