SEA-FLOOR HYDROTHERMAL SYSTEMS

The discovery of seafloor hydrothermal systems approximately two decad es ago has led to a major reassessment of the Earth's thermal and geoc hemical budgets and has revolutionized our understanding of biological processes. This review traces the development of the study of seafloo r hydrothermal systems from the indirect evidence provided by conducti ve heat flow anomalies to the discovery of approximate to 350 degrees C black smoker vents on the East Pacific Rise at 21 degrees N. Althoug h the review focuses on physical characteristics and processes, it out lines some key characteristics of vent fluid chemistry that provide co nstraints on physical models. Ridge crest systems have thermal power o utputs ranging from 10 to 10(4) MW. They are transient systems, driven by magmatic heat sources, but episodic events such as megaplumes, the interplay between focused and diffuse venting, and other aspects rela ted to their thermal, chemical, and biological evolution remain poorly understood. Advances will be made by continuing exploration and disco very to determine the full range of possible phenomena both on and off axis and in different tectonic settings. In order to understand the c omplete, integrated ridge system, however, future studies must include long-term monitoring of an active system, deep drilling into the reac tion zone, and mathematical modeling that incorporates both physical a nd chemical constraints.