Radiokrypton unveils dual moisture sources of a deep desert aquifer

Significance Paleoprecipitation records and subsurface water storage properties are essential data ingredients for accurate hydroclimate and water balance projections. Although both types of data could be extracted from groundwater, their application over long timescales had been limited by the lack of appropriate chronometers. We used a long-lived radiokrypton isotope and identified two distinct moisture source contributions to a deep desert aquifer from low eccentricity periods, one recent and the other 360 ky ago. The groundwater recharge periods show the sensitivity of the moisture transport processes to orbital forcing, whereas the long storage reflects subsurface flow attenuation exerted by faults. Krypton-81 enables groundwater to serve as a direct record of paleoprecipitation over land and of subsurface water storage for the past 1,300 ky.