C04_P09

Origin and age of carbon in cellulose of mid-latitude tree rings

Kromer B¹, Wacker L², Friedrich M³, Lindauer S⁴, Friedrich R⁴, Treydte K⁵, Fonti P⁵, Martinez E⁵

¹Institute of Environmental Physics, Heidelberg, Germany, ²Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland, ³University of Hohenheim, Stuttgart, Germany, ⁴Curt-Engelhorn-Centre Archaeometry, Mannheim, Germany, ⁵WSL Birmensdorf, Birmensdorf, Switzerland

Annual rings of most trees in the middle and high latitudes are composed of the earlywood (EW), formed at the beginning of the growing season, and the latewood (LW), formed from summer onwards. A substantial part of EW in ring-porous deciduous tree species is formed before budburst, i.e. before leaves or needles have unfolded, which is a prerequisite for uptake of atmospheric CO₂. Hence, an essential share of carbon for the construction of EW must come from non-structural, mobile carbon sources (NSC), i.e. from reserve materials formed in the previous year or years. This naturally raises the question to what extent the carbon of an annual ring reflects the atmospheric carbon of the current year.

Here, ¹⁴C measurements on EW and LW tree-ring cellulose from deciduous tree species as well as non-deciduous species in selected years around the ¹⁴C bomb spike in the 1960s are presented. The measured ¹⁴C concentrations of the EW and to a lesser extend of the LW show significant deviations from the atmospheric ¹⁴C values at the time xylem cell wall deposition. With a simple model the fraction of NSC from reserves in addition to carbohydrates photosynthesized in the year of formation is quantified.