Carbon and oxygen isotope dendrochronology in sub-fossil bog oak tree rings - A preliminary study

Abstract

Isotope dendroclimatology is a relatively new field investigating environmental factors that control the radial growth of trees. Tree-ring series of sub-fossil bog oaks can be dated from sites across northwest Europe indicating that the environmental change(s) were regional rather than local. Bog oaks show characteristic periods of suppressed growth thought to have resulted from changes in the hydrological status of bogs towards either wetter or drier conditions. This study investigates relative changes in stable carbon (δ13C) and oxygen (δ18O) isotope content in phases of suppressed and normal growth in three bog oaks dated as c. 200 BC to 150 AD from Zwolle, eastern Netherlands. Bog oaks show no clear relationship between tree-ring width and isotopic composition although one tree exhibited relatively depleted values of 13C and 18O with suppressed growth. Suppressed ring growth is characterised by the formation of early wood only, possibly as a result of hydrologic alterations that limited the formation of latewood, which would otherwise have locked up a detectable signal in stable isotopic shift.