Can palaeohydrological changes in peat bogs be inferred by Sphagnum δ13C values?

Julie Loisel, Michelle Garneau
GEOTOP-UQAM-McGill and Department of Geography,
Université du Québec à Montréal

Organic sequences in peat bogs constitute a high-resolution record of Holocene climatic changes. These palaeoclimatic archives are closely related to the moisture content of the peatland. Surface assemblages and four peat sequences from two boreal peatlands (James Bay area, Québec, Canada) were examined in order to reconstruct surface-moisture changes that occured during the late Holocene. A multi-proxy approach was prefered to prevent erroneous interpretation derived from a single proxy. Because they are sensitive to hydrological changes, testate amoebae assemblages were used to reconstruct surface moisture conditions. Similarly, peat humification analyses, as well as bulk density and C/N ratio measurements, provided semi-quantitative measurements of the summer effective rainfall by estimating the state of decomposition of the peat.  The record of changes in vegetation assemblages, using macrofossils, also allowed the reconstruction of moisture variations of the bog surface. Chronology of peat accumulation was obtained by 210Pb and AMS radiocarbon dating.

Since carbon isotopic composition of plants records information about climatic conditions during plant growth, the hypothesis of a relationship between Sphagnum δ13C values and peatland’s surface moisture is suggested. To verify the potential of this method, results are compared to hydrological changes that have been reconstructed with proxies presented above. δ13C measurements were performed on the bulk material of the following Sphagnum species: S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. Preliminary results show isotopic patterns related to the water table depth of sampling sites.


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