Oxygen- and carbon-isotope analyses of the articulate brachiopodLaqueus californianus: a recorder of environmental changes in the subeuphotic zone |
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Authors: | N. Buening H. J. Spero |
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Affiliation: | (1) Department of Geology, University of California, 95616 Davis, California, USA |
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Abstract: | This study is the first systematic attempt to use oxygen and carbon isotopes in modern brachiopods to investigate seasonality and growth rates. A comparison of oxygen-isotope analyses of shells of living specimens ofLaqueus californianus dredged from 80 and 130 m off Santa Catalina Island, California, to available hydrographie data indicates that this articulate brachiopod secretes its shell in or close to oxygen isotopic equilibrium with ambient seawater. Periodic oxygen-isotope depletions appear to result from El Nino events. Unexpectedly low 13C values associated with the 1983 El Nino may be explained by increased bacterial activity or organic loading into the Southern California Bight associated with these warm-water pulses. Growth rates determined from annual cycles in 18O records are variable, but generally average between 2 and 3 mm yr–1 for mature individuals. Because of the longevity ofL. californianus,18O profiles provide high-resolution seasonal temperature records spanning one to two decades. Our data suggest that oxygen isotopes in brachiopod shells can be utilized as monitors of environmental change in the subeuphotic zone. |
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