ABSTRACT

Several processes may contribute to systematic downcore trends in δ¹³C of bulk Sphagnum peat. Whereas changes in water availability during C assimilation may change δ¹³C values in both a negative and positive direction, other processes would always cause a uni-directional shift in δ¹³C. Selective preservation of isotopically light lignin C may lead to more negative δ¹³C values with an increasing depth and age of peat. Anthropogenic change toward lower δ¹³C of atmospheric CO₂ due to massive coal burning since the beginning of the Industrial Revolution would result in lower δ¹³C of the youngest peat layers, and in higher δ¹³C of older peat layers. Emissions of low-δ¹³C methane from wetlands should result in a progressive enrichment of the residual peat substrate in the heavier isotope ¹³C. Consequently, deeper peat would have higher δ¹³C. In a specific peat profile, the downcore trend in δ¹³C will be the result of an interplay between all these isotope-sensitive processes. Most Central European wetlands studied previously show a ¹³C enrichment (i.e., higher δ¹³C values) with an increasing depth and age. Here we focus on sites which showed lower δ¹³C with an increasing depth and age when a single peat core was taken. Replication did not confirm this negative downcore δ¹³C shift. A positive downcore δ¹³C shift is more widespread than previously believed. We suggest that decreasing δ¹³C of atmospheric CO₂ and emissions of low-δ¹³C methane belong to the main controls of the downcore δ¹³C trends in young peat substrate.