C04_02

The effect of altitude and latitude on growing season and radiocarbon content in tree rings

Svarva H¹, Grootes P¹, Seiler M¹, Nadeau M¹

¹The National Laboratory for Age Determination, NTNU University Museum, Trondheim, Norway

The construction of high-precision, single-year calibration curves for radiocarbon dating needs to take into account the tree physiological, seasonal, and regional differences in the radiocarbon content of tree rings. ¹⁴C variations can be caused by e.g. carbon stored from previous years and by growing season differences. 

Previous studies have shown that the stored photosynthate component is less important for evergreen conifers. However, the timing of growing season can have a significant impact on the radiocarbon content of tree rings, especially during periods of large atmospheric ¹⁴C fluctuations such as the 1960s bomb spike. The calibration of results from trees that grew during different periods of the year than the trees used for the calibration curve will also be impacted. Cellulose in sub-annual sections of tree rings can be used to trace changes in atmospheric radiocarbon content at a biweekly to monthly resolution.

We present the sub-annual radiocarbon contents of three Scots pines from Norway from 1953 to 1965. One tree grew at a low elevation near Trondheim in central Norway. The others grew nearby at a high elevation and at a low elevation in northern Norway, thus having a generally shorter growing season. Analyses of the differences between the radiocarbon content in the trees through time and comparison with climate records allows us to untangle the differences caused by growing season from inaccuracies in the timing of each increment and potential latitudinal differences in atmospheric ¹⁴C content.