An installation for the preparation of foraminifera micro samples for the isotopic analysis of carbon and oxygen

摘要

A technical modification of the traditional method of decomposition of carbonates in phosphoric acid was proposed for the determination of δ~(13)C and δ~(18)O in organogenic carbonate samples weighing 10-30 μg with an accuracy of 0.05%. The extraction of CO _2 was carried out under a vacuum at 95°C in 105% phosphoric acid. The isotopic composition of CO_2 was measured by CG-IRMS. The used feed-motion of samples to the reactor provides a consecutive delivery of the samples from the sample holders to the acid. This sample feeding method prevents the contamination of the acid with impurities from the surface of the sample, obviates the necessity of removing the sample holders from the acid, and allows the use of the same acid for performing a very large numbers of analyses. The accuracy and reproducibility of the δ~(13)C and δ~(18)O values was estimated by measuring international standards and comparing with the δ~(13)C and δ~(18)O values for organogenic carbonate samples obtained by the proposed method of analysis at a microgram level and the traditional method at a milligram level. The proposed technology was successfully used to study the isotopic composition of oxygen and carbon in the plankton and benthos foraminifers in order to reconstruct the Okhotsk Sea palaeotemperatures.