Activities of ²²³ Ra and ²²⁶ Ra in Fluids From the Lost City Hydrothermal Field Require Short Fluid Residence Times

The residence time of fluids circulating through deep-sea hydrothermal systems influences the extent water-rock reactions and flux major minor elements to ocean. While fluid times in numerous basaltic gabbroic have been determined, those less studied ultramafic are currently unknown. Fluids that interact with mantle rocks fundamentally different chemistries therefore unique on seawater chemistry. In this first investigation radium isotopes a serpentinite-hosted system, vent were discovered contain 10–100 greater activities 223Ra (half-life = 11.4 days) than observed high-temperature basalt-hosted systems. 10–109 dpm L?1 produce 223Ra/226Ra activity ratios ranging from 9 109. These extremely high activities, which accompanied by low 226Ra, place significant constraints adsorption coefficient between rock. Our data constrain nondimensional retardation factor (R) very values 1 4, reflecting Ra is transported more slowly due other processes. results suggest contact serpentinite 2 y perhaps as 0.5 y. They surprisingly similar Thus, share hydrogeological characteristics despite differences rock types, underlying porosity, heat sources, enabling larger-scale models biogeochemistry be developed across