Isotope composition of bulk carbon in replicated Sphagnum peat cores from three Central European high-elevation wetlands

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