δ17O and Δ47—The Heavens can Wait.

Abstract:

Most terrestrial systems fall on or close to the Global Meteoric Water Line, GMWL, for ¹⁷O and ¹⁸O isotopes. Luz and Barken (2010) recently discussed variations from the GMWL, and typically the differences were in the 50 per meg, or 0.05‰, ¹⁷O excess. Landais et al. also looked at water from a Vostok ice core, covering the past 150,000 years, and see differences from GMWL on the order of 45 per meg ¹⁷O excess. Carbonate samples are analyze for their ¹³C and ¹⁸O to help understand paleo-climate, water sources, and by looking at clumped isotopes, Δ₄₇, the excess of ¹³C-¹⁸O bonds measured by mass spectroscopy on m/z 47. Those samples will also carry thru the ¹⁷O-excess in their waters of formation. We modeled the effect of ¹⁷O excess on Δ₄₇ and basically there is little effect in the 50 per meg ¹⁷O excess range. We also looked at what would happen with ¹⁸O spiked samples, presuming the spike does not add ¹⁷O. In that case, a 100 ‰ shift in ¹⁸O would give rise to -49‰ ¹⁷O excess anomaly. That shows a significant effect, a 1.8 ‰ shift in Δ₄₇ and even a 3.5 ‰ shift in the δ¹³C reading. So spiked samples are not good candidates for clumped isotope analysis, terrestrial samples probably will not have enough of a ¹⁷O excess to affect Δ₄₇ measurements, and extra-terrestrial samples will have to be checked.