Mid-ocean ridge hydrothermal fluxes and the chemical composition of the ocean

Geophysical estimates of mid-ocean ridge axial heat fluxes (2-4 x 10(12) W) and of the total hydrothermal flux (9 +/- 2 x 10(12) W) are well established. Problems arise in calculation of water fluxes because of uncertainties in (a) values of off-axis fluxes and (b) the partition of axial heat flow between high-temperature black smoker and lower-temperature diffuse flow. Of the various geochemical methods of estimating fluxes, He-3/heat data are extremely variable, the Mg method is sensitive to flank fluxes, Sr isotopes agree with geophysical estimates only if flank fluxes are important, Li isotopes data are consistent with geophysical values, and Ge/Si ratios give low fluxes, which may reflect low-temperature processes not yet fully quantified. Estimates of hydrothermal heat and water fluxes derived from these approaches are presented as are hydrothermal chemical fluxes at the ridge axis, off axis, and as affected by hydrothermal plumes.