FY 1989

Variable ³He/heat ratios in submarine hydrothermal systems: Evidence from two plumes over the Juan de Fuca ridge

Lupton, J.E., E.T. Baker, and G.J. Massoth

Nature, 337(6203), 161–169, doi: 10.1038/337161a0 (1989)

The first vent fluid samples recovered from submarine hydrothermal systems on the Galapagos Rift and at 21°N on the East Pacific Rise (EPR) had a nearly identical ratio of ³He/heat of ~0.5 × 10^–12 cm³ STP cal^–1, even though the two hydrothermal systems were separated geographically and had widely differing fluid exit temperatures (~20 and ~350°C, respectively). Jenkins et al. combined this ratio with independent estimates of the flux of mantle ³He through the oceans, to calculate a global oceanic hydrothermal heat flux of 4.9 × 10¹⁹ cal yr^–1, which is in excellent agreement with geophysical estimates for this flux. Other investigators then combined this ³He flux with measured ratios of various chemicals in vent fluids to ³He (such as Mn/³He and Si/³He) to estimate global hydrothermal fluxes for these species. Here we show that ³He/heat ratios vary by over an order of magnitude between submarine hydrothermal systems, suggesting that early measurements of the ³He/heat relation are not representative of all hydrothermal systems, and that flux calculations based on the oceanic ³He flux must be undertaken with caution.