Updated calibration of the clumped isotope thermometer in planktonic and benthic foraminifera

Accurate reconstruction of past ocean temperatures is of critical importance to paleoclimatology. Carbonate clumped isotope thermometry (Delta(47)) is a relatively recent technique based on the strong relationship between calcification temperature and the statistical excess of C-13-O-1(8) bonds in carbonates. Its application to foraminifera holds great scientific potential, particularly because Delta(47) paleotemperature reconstructions do not require assumptions regarding the 18 0 composition of seawater. However there are still relatively few published observations investigating the potential influence of parameters such as salinity or foraminiferal size and species. We present a new calibration data set based on 234 replicate analyses of 9 planktonic and 2 benthic species of foraminifera collected from recent core-top sediments, with calcification temperatures ranging from -2 to 25 degrees C. We observe a strong relationship between Delta(47) values and independent, oxygen-18 estimates of calcification temperatures: Delta(47) = 41.63x10(3)/T-2+ 0.2056 The formal precision of this regression (+/- 0.7-1.0 degrees C at 95% confidence level) is much smaller than typical analytical errors. Our observations confirm the absence of significant species-specific biases or salinity effects. We also investigate potential foraminifer size effects between 200 and >560 mu m in 6 species, and conclude that all size fractions from a given core-top location and species display statistically undistinguishable Delta(47) values. These findings provide a robust foundation for future interlaboratories comparisons and paleoceanographic applications. (C) 2018 Elsevier Ltd. All rights reserved.