Modern Sphagnum δ13C signatures follow a surface moisture gradient in two boreal peat bogs, James Bay lowlands, Quebec

Carbon isotopic composition of Sphagnum macrofossils can potentially he used as a palaeohydrological tool for peat-based climatic studies since a relationship between Sphagnum delta C-13 Values and peatland Surface moisture has been presented in previous Studies. In order to verify this hypothesis, modern Sphagnum delta C-13 values were measured along a moisture (microtopographic) gradient in two boreal peat bogs, Isotopic measurements were performed oil bulk material of S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. Isotopic variations found within and between Sphagnum species along the microtopographic gradient were compared using analysis Journal of Quaternary Science of variance. A significant Positive Correlation (P < 0.0001) was found between Sphagnum delta C-13 Values and their position along the Surface moisture gradient. Results show that C-13-depleted values are related to low water table depths (WTD), while C-13-enriched values correspond to a water table that is close to the peat surface. Although the mechanisms underlying carbon fractionation processes in mosses are not Well understood, we demonstrate that water resistance to CO2 diffusion is an important fractionation process that is observed in bulk Sphagnum delta C-13 measurements, since drier and wetter samples exhibit consistent and very different isotopic signatures. Copyright (C) 2008 John Wiley & Sons, Ltd.