Sensitivity of whole wood stable carbon and oxygen isotope values to milling procedures.

RATIONALE Milling of wood samples is a widely applied preparation method for pooling tree-rings from different trees or periods of several years for determination of δ¹³C and δ¹⁸O values. In this study, whole wood samples were milled using different procedures in order to evaluate potential effects of this preparation method on δ¹³C and δ¹⁸O values. METHODS Subsamples of a 5 cm³ wood piece of a single tree-ring from a lowland white fir were used. The samples were milled with different setups: (i) two and three stainless-steel balls, (ii) 3, 5 and 8 min milling time, and (iii) discontinuous and continuous milling. The δ¹³C values were measured using an elemental analyser connected to an IsoPrime mass spectrometer and δ¹⁸O values using a Thermo Scientific MAT 253 mass spectrometer and a TC/EA connected by a ConFlo IV. RESULTS The results show that varying the milling procedure does not alter the δ¹³C and δ¹⁸O values in comparison to non-milled blank samples. For shorter milling times, an increased variance of δ¹⁸O values is recorded, probably caused by isotopic gradient between early- and latewood portions of the tree-ring and thereby biasing the insufficiently homogenised samples. No overheating effects on the δ¹³C and δ¹⁸O values were detected. CONCLUSIONS Milling of wood samples for carbon and oxygen isotope analyses is an appropriate preparation method. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]