Mid-Atlantic Ridge hydrothermal events recorded by deep-sea corals

Trace-element and stable-isotope analyses were performed on azooxanthellate corals from the North Atlantic, at two different tectonic settings. One set was from Orphan Knoll, near Newfoundland (1700 m depth, 50°25.57'N, 46°22.05'W), the other from the Mid-Atlantic Ridge (1200 m depth, 45°14.12'N, 28°34.12'W). The Mid-Atlantic Ridge corals contain significantly greater quantities of Fe, Mn, Cu, Ni, and Zn within their skeletons than the Orphan Knoll corals. The metal concentrations are not homogeneous within the Mid-Atlantic Ridge coral skeletons, but occur as episodic pulses during a decade or two of each coral's lifetime. We believe these metals originated in a hydrothermal discharge zone associated with the Mid-Atlantic spreading centre. If so, it is evidence that the duration of an individual hydrothermal event is from a decade up to 30 years or so. With more specimens of known ages, it may be possible to reconstruct the history of a particular segment of an oceanic spreading centre.