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Oxygen isotopic analysis of marine carbonate shells (δ18Oc) is a standard paleoceanographic technique used to document the chronology of seawater temperature change. Shell δ18Oc depends not only upon seawater temperature, but also upon the isotopic composition of the seawater (δ18Ow; related to salinity) and any species-specific fractionation that occurs during biomineralization. In the past, the interpretation of shell δ18Oc has been based upon theoretical studies of chemical equilibrium and kinetics, or laboratory experiments involving the inorganic precipitation of CaCO3 from solution. Other methods have employed an empirical calibration done by measuring the δ18Oc of collected shells where only estimates of time-series variability of the key parameters in the isotope paleothermometry equation (water temperature and δ18Ow) could be made. The actual environmental conditions during biomineralization, any species-dependent fractionation, any growth-dependent changes in δ18Oc including growth hiati, and any geographical/latitudinal influences that may be affecting δ18Oc cannot be quantified by these methods. Hence, the ability to quantitatively estimate paleotemperatures and salinities from any particular species of interest and any specific environment is limited.
This project sought to empirically calibrate δ18Oc in a cultured marine mollusc (Mytilus edulis) with controlled and monitored water temperatures, salinities, and δ18Ow. The development of this technique enables better correlation of δ18Ow and δ18Oc by increasing the temperature and salinity ranges to be used in calibration. The method will contribute significantly to the field of isotope paleoceanography, as it can be used to culture a wide range of species under specific environmental parameters. For example, we are particularly interested in fossil molluscan assemblages from ice-proximal environments where reliable temperature and salinity proxies are unknown.
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Kreutz, Karl J.; Borns, Harold; Introne, Douglas; Barber, Bruce; and Funder, Sven, "Aquaculture-Based Calibration of the M.edulis Isotope Paleothermometer" (2005). University of Maine Office of Research Administration: Grant Reports. 62.