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Title: Oxygen-isotope fractionation between marine biogenic silica and seawater

Journal Article · · Geochimica et Cosmochimica Acta; (USA)

A stepwise fluorination technique has been used to selectively react away the water component of hydrous silica in order to better investigate the oxygen-isotope fractionation between biogenic opal and seawater, and to determine whether all taxa produce opal which is suitable for oxygen isotope paleothermometry. {delta}{sup 18}O of the tetrahedrally coordinated silicate oxygen of siliceous sponge spicules grown at a wide variety of temperatures varies independently of temperature. {delta}{sup 18}O from an Eocene radiolarian ooze sample is much more enriched than would be expected from any reasonable isotopic temperature curve, given the probable growing temperature of the sample. {delta}{sup 18}O of diatom samples seems to vary systematically with temperature and to conform approximately to the isotopic temperature curve for diatom frustules obtained by Labeyrie and coworkers using an entirely different analytical technique. Sponges appear to precipitate silica in isotopic disequilibrium with seawater oxygen, and old radiolarian silica may exchange readily with could oceanic bottom water. Neither will apparently be useful for paleoclimate reconstructions. Diatoms maybe useful in deducing ancient surface-water temperatures, but the systematic variation of {alpha} with temperature for diatoms may not be related to the quartz-H{sub 2}O equilibrium isotope fractionation.

OSTI ID:
6702685
Journal Information:
Geochimica et Cosmochimica Acta; (USA), Vol. 53:12; ISSN 0016-7037
Country of Publication:
United States
Language:
English