Abstract
<p> <p id="x-x-sp0005"> Considerable efforts have been made to calibrate the Δ <sub> 47 </sub> paleothermometer, which derives from the quantity of <sup> 13 </sup> C– <sup> 18 </sup> O bonds in carbon dioxide produced during acid digestion of carbonate minerals versus its expected stochastic abundance, in a range of materials. However the impacts of precipitation rate, ionic strength, and pH on carbonate Δ <sub> 47 </sub> values are still unclear. Here we present a set of 75 measurements of Δ <sub> 47 </sub> values from inorganic calcites grown under well-controlled experimental conditions, where we evaluate the impact on Δ <sub> 47 </sub> values of precipitation rate (log <em> R </em> = 1.8–4.4 μmol/m <sup> 2 </sup> /h), pH (8.3–10.5; NBS pH scale), and ionic strength ( <em> I </em> = 35–832 mM). With the data available and at the current instrumental resolution, our study does not resolve any clear effects of pH, ionic strength, growth rate effects on measured Δ <sub> 47 </sub> when compared in magnitude to the effects on δ <sup> 18 </sup> O over most of the ranges of parameters sampled by our analyses. If these relationships exist, they must be smaller than our current ability to resolve them within our dataset. Under our experimental conditions, a Δ <sub> 47 </sub> -temperature equation, which is apparently insensitive to variation in pH, precipitation rate, and ionic strength over the range of variables sampled, can be written asΔ47=(0.0387±0.0072)×106/T2+(0.2532±0.0829)(r2=0.9998,p=0.009)">Δ47=(0.0387±0.0072)×106/T2+(0.2532±0.0829)(r2=0.9998,p=0.009) where Δ <sub> 47 </sub> values were reported on the absolute Δ <sub> 47 </sub> reference frame after normalizing to conventional 25 °C reaction temperature using an acid fractionation factor of −0.00141‰ °C <sup> −1 </sup> . </p></p>
Original language | American English |
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Journal | Geochimica et Cosmochimica Acta |
Volume | 134 |
DOIs | |
State | Published - Jan 1 2014 |
Externally published | Yes |
Disciplines
- Life Sciences