Location-Dependent Differences in the ¹⁴C Content of Wood

Abstract

ABSTRACT. The long 14C chronologies currently used as calibration curves combine results from wood that grew in the western United States, the British Isles and Germany. Although these results show few significant differences in the 14t content of contemporaneous wood when averaged over the length of the chronology (i.e., the means of overlapping sections of chronology are the same), closer examination shows considerable variability. Separating the sections of chronology according to the provenance of the wood used for calibration reveals patterns that suggest small but finite differences in the i4C content of wood from different locations. We conclude that there is some evidence that German and American wood give dates older by between 20 and 40 yr from those of Irish oak for some periods. Additionally we suggest that the shift of the Belfast 1986 calibration data by ca. 18 yr toward older dates may not be valid and that the resultant offset between the Belfast 1986 and Seattle 1993 data shows a small but real difference in the 14C content of contemporaneous American, German and Irish wood.Intralaboratory measurements made in Belfast on contemporaneous German and Irish oak, and bristlecone pine and Irish oak, give offsets of 39 and 41 yr, respectively, with the Irish oak dating younger. Previous studies, in which sample pairs of American and English and French wood were processed in the same laboratory, also showed American wood to be slightly depleted in 14C. None of the findings of this study would significantly alter calibrated "C dates.

High-Precision Radiocarbon Measurements of Contemporaneous Tree-Ring Dated Wood from the British Isles and New Zealand: Ad 1850–950

“…These measurements essentially repeat, at higher temporal resolution, the Pearson et al (1986Pearson et al ( , 1993) data published in the 14 C special calibration issues. The evolution of the Pearson data was a result of repeated corrections, which were questioned by McCormac et al (1995). Thus, the new data offer the opportunity to test which corrections are appropriate in light of changes made to the calibration data published by Stuiver et al (1998) and commonly known as INTCAL98.…”

Temporal variation in the interhemispheric 14C offset

“…However, contemporaneous wood from different locations within a given hemisphere does not always give identical A14C measurements [Damon, 1995;McCormac et al, 1995;Stuiver and Braziunas, 1998]. Species to species fractionation effects can result in contemporaneous wood having a different specific activity but this is corrected using $13C measurements.…”

Regional Radiocarbon Effect Due to Thawing of Frozen Earth

“…In evaluating this -2.7%o average depression of 0140 at the Grand View site relative to the Pacific Northwest, it should be recalled that there is evidence for a marine west coast USA regional effect involving an average depression of ca. -4% relative to Irish oak or Douglas-fir from the Santa Catalina Mountains near Tucson (Damon 1995;McCormac et al 1995). This has been attributed to the upwelling of 14C-depleted CO2 along the Pacific west coast.…”