Radium isotopes as tracers of hydrothermal inputs and plume dynamics in the deep ocean: results from Atlantic and Pacific US GEOTRACES cruises

Radium isotopes (²²³Ra t_1/2= 11.4 d, ²²⁴Ra t_1/2= 3.66 d, ²²⁶Ra t_1/2= 1600 y, ²²⁸Ra t_1/2= 5.75 y) are produced by the decay of thorium isotopes in sediments and are relatively soluble in seawater, making them valuable tracers of trace element and isotope (TEI) exchange processes at ocean boundaries. Recent US GEOTRACES cruises such as the North Atlantic Zonal Transect (NAZT, 2011) highlighted important boundary sources such as the TAG hydrothermal vent on the Mid-Atlantic Ridge. New data from the recent US GEOTRACES Eastern Pacific Zonal Transect (EPZT, 2013) reveal an aerially extensive hydrothermal signal emanating from the southern East Pacific Rise. The elevated Ra activities within the neutrally buoyant hydrothermal plumes captured on both the NAZT and EPZT cruises expand our understanding of Ra isotope and associated TEI behavior in hydrothermal systems; in particular, activity ratios of the short-lived Ra isotopes allow for the estimation of plume ages in the near field. Over greater length-scales (western half of the EPZT transect), the longer-lived ²²⁸Ra will be used to investigate the spreading rate of the plume.