The D48 Proxy: Calibration and Beyond
Abstract
The clumped isotope proxy has traditionally been applied to the difference between the measured and the theoretical distribution of mass 47 when measuring CO2 released from carbonate minerals, the Δ47 proxy. Here we present results for the same principal, but applied to mass 48. The measurement of the Δ48 value is considerably more challenging than Δ47 because the concentration of 12C18O18O (the principal species at mass 48) is only ~ 4 ppm of the total concentration, an order of magnitude less than mass 47. As such considerable more care is needed is preventing contamination, fractionation, and exchange with H20 (as well as many other things) when measuring Δ48 compared to Δ47. The first task is to construct a carbon dioxide equilibrated scale (CDES) for Δ48 using CO2 equilibrated at three different temperatures and correlated to theoretical values. Even with a mass spectrometer such as the 253 plus, which has a small negative base line at mass 48 and more sensitive amplifiers than other instruments, correction of the mass 48 peak varies as to where the background is measured and as a consequence has a significant influence on the slope between δ48 and Δ48. Once the CDES scale has been established it is possible to calibrate the Δ48 values to temperature using material precipitated at known temperatures. This calibration will be presented here and has a slightly reduced slope relative to the Δ47 calibration with temperature, consistent with theoretical calculations. Once the temperature calibration has been established one can apply the Δ48 proxy to a multitude of applications including solid state resetting as a result of heating during burial and systems such as coral and speleothems which are known to have non-equilibrium behavior as regards Δ47. In this presentation we present data which illustrate difference in the behavior of this proxy in all these systems. In addition, we present data which shows that the Δ48 is more sensitive to solid-state reordering than Δ47 and illustrate how Δ48 can be used in conjunction with Δ47 values to illuminate burial history. These differences illustrate the importance of adding the Δ48 proxy into the clumped isotope arsenal and how they can significantly improve the interpretation of carbonate precipitation and burial diagenesis relative to the use of the conventional stable isotopes and Δ47. As a consequence measurement of Δ48 is a significant advance in understanding carbonate formation and diagenesis.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP34B..07S
- Keywords:
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- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 1051 Sedimentary geochemistry;
- GEOCHEMISTRY;
- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL;
- 4912 Biogeochemical cycles;
- processes;
- and modeling;
- PALEOCEANOGRAPHY