δ18O and δ13C in carbonate

Main content

Sample material: carbonates (e.g. foraminifera, corals, otoliths, spaleothems, inorganic precipitates, human/animal tooth & bone, etc.)

Precision: long term external precision (1standard deviation) is normally 0.02-0.03‰ for δ13C and 0.06-0.08‰ for δ18O in samples between 10-100 mg.  

Instrument: Thermo Scientific MAT253 and online Kiel IV carbonate device with microvolume. Gasbench-Delta V and/or DeltaRay may be used for slower reacting carbonates (e.g. dolomite). δ13C and δ18O are acquired simultaneously from each sample analyzed. 

Sample requirements: we typically request ≥20mg of carbonate but have run with high precision down to 5 mg. Sample sizes can vary greatly depending upon the material and the experimental requirements. We recommend you contact us so that we can discuss and provide advice regarding the ideal sample size for meeting your specific requirements.  

Routines: most samples are analyzed on the dedicated MAT253-Kiel IV system. Cleaning/purification of sample carbonate may be required, and the specific methods depend upon the material to be analyzed. Dry carbonate is weighed into individual Kiel vials. The Kiel IV automatically reacts cleaned carbonate samples in a vacuum with phosphoric acid, H2O is removed and the resulting COis dried cryogenically (H2O removed) and concentrated in a microvolume for analysis. Each run takes approximately one day and contains around 36 sample aliquots and 10 standards. Masses 44-46 are measured. The data are transferred into the absolute reference frame (‰VPDB) using international carbonate standards (e.g. NBS-19, NBS-18) and an in-house control standard for assessing long-term stability and external precision.   

The Delta Ray CO2 isotope analyzer is equipped with a universal reference inlet and autosampler with heated sample tray for temperature controlled reaction of carbonates with phosphoric acid. The system is able to provide high precision measurements in the laboratory and in the field, for example when deployed on a ship for isotope results in near real time during scientific expeditions.