Temporal and compositional diversity in seafloor hydrothermal fluids

Within the last 4 years a number of discoveries have significantly improved our understanding of the processes occurring in seafloor hydrothermal systems, and their net effects on the chemical and physical properties of the fluids. Prior to the 1990's time series samplings of vent fluids suggested that they were characterized by great temporal stability in their chemistry [e.g., Campbell et al , 1988]. In the late 1980's, the discoveries of megaplumes in the water column over the Juan de Fuca Ridge provided evidence for the episodicity of hydrothermal processes [ Baker et al , 1987]. We therefore had a basic contradiction in our observations ‐ astounding temporal stability in the vent systems that had been sampled numerous times (primarily 21°N East Pacific Rise (EPR), Guaymas Basin, South Cleft on the Juan de Fuca Ridge) (Figure 1) versus the water column evidence for temporal variability. The observation of volcanic eruptions at three sites on the world ridge crest system has provided the resolution to this apparent contradiction, and provided new insights into the evolution of seafloor hydrothermal systems. Direct information on the third dimension of a hydrothermal system became available for the first time, with the successful drilling of an active hydrothermal site at Middle Valley by the Ocean Drilling Program (ODP). Evaluating the hydrothermal input to the ocean (i.e., the flux) has become more problematic, but progress in understanding the underlying processes responsible for controlling vent chemistry, and in defining the flux of chemicals from the ocean ridge flanks, are important steps to eventual resolution of the flux question.