Geochemical Journal, Vol. 43 (No. 2), pp. e5-e9, 2009EXPRESS LETTER
Martin Novak, Leona Zemanova, Iva Jackova, Frantisek Buzek and Marie Adamova
Department of Geochemistry, Czech Geological Survey, Geologicka 6, 152 00 Prague 5, Czech Republic
(Received November 11, 2008; Accepted January 31, 2009; Online published March 27, 2009)
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.
Key words: peat, Sphagnum , carbon, C sequestration, isotopes