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Geophysical Monograph Series



  • Deep-sea ecology—Congresses
  • Mid-ocean ridges—Congresses



Geophysical constraints on the subseafloor environment near mid-ocean ridges

William S. D. Wilcock

School of Oceanography, University of Washington, Seattle, Washington

Andrew T. Fisher

Earth Sciences Department and Center for the Study of Imaging and Dynamics of the Earth, University of California, Santa Cruz, California

Studies of the subseafloor biosphere require an understanding of the physical characteristics of oceanic crust and in particular its hydrological state. Marine geophysics provides many tools to infer subsurface structure and processes remotely, but hydrological properties are difficult to infer from other physical parameters and are best constrained by controlled, in situ experiments. Because of the lack of boreholes at unsedimented ridge-crest sites, our knowledge of hydrological processes at mid-ocean ridges is derived indirectly by using geophysical images, geological studies, measurements in vent fields, and comparisons with off-axis sites as constraints for models of hydrothermal circulation. A synthesis of results from three well-studied ridge segments shows that there have been considerable advances in our understanding of the thermal structure of young oceanic crust and the linkages between hydrothermal, magmatic, and tectonic processes. However, there are still many unanswered questions related to processes in the heat uptake zone, the geometry of circulation, the formation and fate of brines, the effect of volcanic and tectonic events on hydrothermal systems, and the critical linkages between the many processes that affect crustal permeability and drive fluid flow. We argue that geophysical investigations will contribute most to studies of the subsurface biosphere near mid-ocean ridges if they first focus on shallow processes in the vicinity of hydrothermal upflow zones. The role of geophysical studies is likely to be enhanced by advances in underwater vehicle capabilities, the move towards establishing long-term seafloor observatories, and the prospects for new techniques to drill bare rock.

Citation: Wilcock, W. S. D., and A. T. Fisher (2004), Geophysical constraints on the subseafloor environment near mid-ocean ridges, in The Subseafloor Biosphere at Mid-Ocean Ridges, Geophys. Monogr. Ser., vol. 144, edited by W. S. Wilcock et al., pp. 51–74, AGU, Washington, D. C., doi:10.1029/144GM05.


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