Refining the temperature dependence of the oxygen and clumped isotopic compositions of structurally bound carbonate in apatite

Clumped isotope data from carbonated apatite from in vivo and in vitro samples are presented to refine the relationship between mineral growth temperature and carbonate clumped isotopic composition (Delta(47)). Delta(47), delta O-18 and delta C-13 data were obtained from phosphoric acid digestion (T = 110 degrees C) of chemically untreated teeth from an African elephant, Greenland sharks, sand tiger sharks and synthetic apatites. These data cover a temperature range between 1 degrees C and 80 degrees C and enlarge the calibration dataset presented in Wacker et al. (2016) by a factor of five. Taxon-specific analyses of tooth enamel(oid) and dentine reveal that both tissues show identical Delta(47) values even though the content of organic matter differs by an order of magnitude. The following Delta(47) temperature calibration for (bio)apatite is derived (R-2 = 0.9924, p-value < 0.0001, n = 122; 8 samples): Delta(47 CDES 110) = 0.0325(+/- 0.0012) x 10(6)/T-2 + 0.2137(+/- 0.0124) (with T in K and Delta(47) in parts per thousand) This calibration becomes indistinguishable from a reprocessed empirical calibration of calcite made in the same laboratory if a difference of the acid fractionation factors (AFF) of 0.110 parts per thousand between 25 degrees C and 110 degrees C is considered. The measured AFF for bioapatite matches the one that is extrapolated from experimental data on calcite and aragonite. The oxygen isotope fractionation between structural carbonate in the synthesized carbonated hydroxylapatites (CHAP) and water between 7 degrees C and 80 degrees C closely follows the temperature dependence for the calcite-water system. It is described by the following (CHAP-water) equation (R-2 = 0.997, p-value < 0.04, n = 17; 3 samples): 1000ln(alpha(CNAP-water)) = 17.23(+/- 0.59) x 10(3) x T-1 - 27.28(+/- 1.73) (with T in K) Both calibrations are applied to shark teeth from a modern Greenland shark and a fossil megatooth shark (Carcharodon megalodon) specimen to reconstruct the apparent Delta(47)-based habitat temperature of C. megalodon (19 +/- 4 degrees C) and the oxygen isotopic compositions of seawater. (C) 2019 Elsevier Ltd. All rights reserved.