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Oxygen isotopes from biogenic apatite: An attempt to calibrate IRMS and SIMS generated data

Oxygen isotopes (δ18O) from biogenic apatite are used for the calculation of seawater temperatures in paleoclimatic reconstructions. While conventional δ18O analyses by IRMS (isotope ratio mass spectrometry) requires sample quantities of more than 1 mg, in situ SIMS (secondary ion mass spectrometry) minimizes sample size and thus the risk of contamination of the primary δ18O signal. Despite this obvious advantage, there are some critical points that could influence the final δ18O values and their interpretation: (1) The conventional IRMS method exclusively measures the δ18O from the isolated PO43− group of biogenic apatite (Ca5(PO4, CO3, F)3(OH, F, Cl, CO3)). In contrast, SIMS releases the oxygen from all molecular groups and from organics. But, to what extent do these non-PO43− bound oxygen isotopes bias the final δ18O values? (2) Thermometer equations are based on IRMS analyses. Are these equations also applicable to SIMS data? (3) Thermometer equations assume, that the δ18O of seawater signature is –1‰ or 0‰ (VSMOW) for ice-free or ice-covered oceans, respectively. These data are based on sub-recent glacial-interglacial cycles and the associated δ18O seawater signatures. Whether the oxygen isotopic composition of seawater has changed during the earth history is still under debate.

Clarification of these aspects is crucial for a reliable assessment of δ18O values and the calculation of seawater temperatures. For this reason, we compare δ18O data of recent shark teeth analyzed by IRMS and SIMS. Our sharks lived during documented seawater temperatures, ph-values, and δ18O signatures and are therefore the ideal subjects for our study.

Details

Author
Thomas Wotte1, Anja Wotte1, Robert Haenel1
Institutionen
1TU Bergakademie Freiberg, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/jsqf-e813