9633627 Tivey Quantification of Upper Crustal Alteration and Ridge Flank Hydrothermal Fluxes Circulation of seawater through the ocean crust has a major effect on the chemistry of the oceans. The composition of the water that exists from hot springs (hydrothermal vents) can tell us what processes occur in the ocean crust to form the water. Key features of the vent water, including the pH, the abundance of hydrogen and hydrogen sulfide, and temperature, can tell what types of minerals form in the ocean crust, and whether biologic activity is activity is occurring there. Presently, however, pH, H2 and H2S can not be measured because we have no sensors capable of making the measurements at the high temperatures and pressures of the sea floor. These investigators have a prototype instrument and plan to develop, test, and deploy it to make these important measurements.