Paleotemperatures from deep-sea corals: Overcoming 'vital effects'

Thirty-five azooxanthellate (non-photosynthetic) corals belonging to 18 species were collected at sites ranging from the Norwegian Sea to the Antarctic and of depths ranging from 10 to 5220 m. All specimens showed distinct, well-defined linear correlations between carbonate oxygen and carbon isotopic composition, with slopes ranging from 0.23 to 0.67 (mean 0.45 +/- 0.9) and linear correlation r(2) values that averaged 0.89. These pronounced isotopic disequilibria have, to date, rendered azooxanthellate corals unsuitable for use in paleothermometry. Most, but. not all, of the heaviest skeletal delta(18)O values reached or approached equilibrium. If the isotopically-heavy ends of the delta(18)O us delta(13)C regression lines reliably approximated isotopic equilibrium with seawater these values could be used to estimate the temperature of the water in which the coral grew. The delta(13)C values of the heavy ends of each line, however, were always depleted compared to carbon isotopic equilibrium with ambient bicarbonate by varying amounts. Despite the disequilibria, a reliable method for obtaining paleotemperature data teas obtained. It was found that, ifa delta(18)O vs delta(13)C regression Line from an, individual coral could be generated, the delta(18)Oarag value corresponding to delta(13)C(arag) delta(13)C(water) and corrected for delta(18)O(water) was a linear function of temperature: delta(18)O = -0.25 T(degrees C) + 4.97.