Controls on the Chemistry and Temporal Variability of Seafloor Hydrothermal Fluids

Hydrothermal activity at mid-ocean ridge spreading centers has an influence on all aspects of oceanography. The heat input from these systems affects the mid-depth circulation of the oceans, although the magnitude of this effect has not been rigorously quantified [Stommel, 1982]. The rising hydrothermal plumes also entrain deeper, and often saltier water, carrying it up in the water column thereby also affecting the thermohaline circulation of the oceans [Lupton et al., 1985]. The topography of the ridges may also influence deep circulation patterns. It is the inputs of heat and reduced chemical species from the hydrothermal systems that provide the energy for communities of chemosynthetic organisms, unknown prior to the discovery of venting. Hydrothermal activity also affects the chemistry of seawater by the direct addition and removal of various chemical species, and the more indirect scavenging of mid depth chemical constituents onto the Fe- and Mn-particles fanned in hydrothermal plumes. The composition of the oceanic crust is also changed by the addition and removal of chemical constituents as a result of hydrothermal alteration. Recycling of the oceanic crust into the Earth’s mantle and the eventual transfer of some gases input by hydrothermal activity from the ocean to the atmosphere, extend the Influence of hydrothermal activity to beyond the oceans themselves. While the magnitude and importance of these linkages are still poorly quantified, we were unaware these linkages even existed prior to the discovery of seafloor hydrothermal systems.