Hydrothermal fluxes at mid-ocean ridges and on ridge flanks

Hydrothermal fluxes of heat and mass at mid-ocean ridges and on ridge flanks estimated using different approaches are reviewed. Heat and fluid fluxes in high temperature axial systems are best determined by geophysical methods, and are then combined with vent fluid compositions to derive chemical fluxes. Axial chemical fluxes calculated by mass balance using data from hydrothermally altered rocks sampled by deep ocean drilling are generally small, probably because of loss of material during drilling. Most of the hydrothermal heat anomaly in ocean crust occurs at low temperatures in off-axis flank systems, and a significant fraction of this must occur at very low temperatures (<25 °C). Flank processes enhance the axial fluxes of some elements, but offset and cancel the axial fluxes of others. Processes in hydrothermal plumes are also important in determining the net chemical fluxes in MOR systems.