Detection of Low-Temperature Hydrothermal Fluxes by Seawater Mg and Ca Anomalies

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Science  30 Jul 1999:
Vol. 285, Issue 5428, pp. 721-723
DOI: 10.1126/science.285.5428.721

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Geochemical fluxes into and out of the ocean control its chemical composition. Measurements of the magnesium (Mg) content of seawater, an assumed “conservative” element in the ocean, reveal mid-depth Mg depletions in the vicinity of the East Pacific Rise. The magnitude of the anomalies suggests that fluxes associated with the low-temperature circulation of seawater through axial mid-ocean ridge systems are much larger than the high-temperature axial component. A higher total axial hydrothermal flux provides a mechanism that simultaneously satisfies the mass balance requirement of several major seawater constituents.

  • * Present address: Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa. E-mail: steph{at}

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