Clumped isotope thermometry of carbonate-bearing apatite: Revised sample pre-treatment, acid digestion, and temperature calibration

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• 作者：Ulrike Wacker^a ; ^{ulrike_wacker@eva.mpg.de" class="auth_mail" title="E-mail the corresponding author} ; Tanja Rutz^a ; Niklas Lö ; ffler^a ; Anika C. Conrad^b ; ¹ ; Thomas Tü ; tken^c ; Michael E. Bö ; ttcher^b ; Jens Fiebig^a ; ^d
• 关键词：Carbonate-bearing apatite ; Clumped and bulk C and O isotope composition ; Digestion technique ; Sample pre-treatment ; Calibration
• 刊名：Chemical Geology
• 出版年：2016
• 出版时间：2 December 2016
• 年：2016
• 卷：443
• 期：Complete
• 页码：97-110
• 全文大小：906 K

文摘

It has recently been shown that the clumped isotopic composition (Δ₄₇) of carbonate-bearing hydroxyapatite (CHAP) from teeth and bones reveals important information about the body temperature of vertebrates (Eagle et al., 2010, 2011). In this study we reinvestigate the temperature dependence of Δ₄₇ in CHAP, extending the temperature range from 2 to 59 °C. In addition, the effects of chemical pre-treatment of CHAP on its bulk and clumped isotopic composition are studied.

CHAP is best reacted with phosphoric acid at 90 to 110 °C minimizing the potential of evolved CO₂ or reaction intermediates to re-equilibrate with traces of water in the acid environment. Reaction at 110 °C ensures that digestions of CHAP samples are complete within 60 min. We determined a Δ₄₇ ^⁎ _90–110 value of 0.032 ± 0.008‰ that is - within errors - indistinguishable from a Δ₄₇ ^⁎ _90–110 value of 0.019 ± 0.007‰ received for aragonite.

For tooth enamel pre-treated with H₂O₂ lower Δ₄₇ values, and higher δ¹⁸O and δ¹³C values were measured than for pre-treated tooth dentine. In addition, similar trends were observed for pre-treated dentine and bone material: higher Δ₄₇ values, and lower δ¹⁸O and δ¹³C values were determined compared to untreated samples.

A new tentative clumped isotope temperature calibration based on a synthetic apatite, untreated tooth enamel of an African elephant and enameloid from teeth of a Greenland shark is presented using a reaction temperature of 110 °C. It follows the equation:

Δ₄₇ = 0.0320 (± 0.0022) × 10⁶/T² + 0.1977 (± 0.0259) (Δ₄₇ in ‰ and T in K).

The slope of this regression line is identical to those previously obtained from 90 °C digestions of calcite and/or aragonite in several laboratories (e.g., Henkes et al., 2013; Wacker et al., 2014; Defliese and Lohmann, 2015). The Δ₄₇ data of untreated enamel(oid) samples reacted at 90 °C closely match a Δ₄₇-1/T² relationship for calcite that was made at the same digestion temperature (Wacker et al., 2014). These preliminary results suggest that calcite calibrations made at a reaction temperature of 90 °C might be directly applicable to CHAP samples to determine their formation temperatures.