Testate amoebae, Sphagnum carbon isotopic composition and other proxy data as palaeoindicators of surface-moisture changes in two boreal peatlands during the late Holocene: preliminary results

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

Jean-François Hélie
GEOTOP-UQAM-McGill and Department of Earth Sciences,
Université du Québec à Montréal

Organic sequences in ombrotrophic peatlands constitute a high-resolution record of Holocene climatic changes. These palaeoclimatic archives are closely related to the moisture content of the sites. Surface assemblages and four peat sequences from two boreal peatlands (James Bay area) were examined in order to reconstruct the surface-moisture changes that occured during the late Holocene. A multi-proxy approach was prefered in order to prevent (enlève:an) erroneous interpretation derived from single proxy.

Because they are sensitive to hydrological changes, Testate amoebae assemblages were used to reconstruct surface moisture conditions. (enlève:of the peatlands). Similarly, bog surface wetness (BSW) values provided semi-quantitative measurements of the summer effective rainfall by estimating the rate (or the state) of decomposition.  (Enlève: state of the peat, the latter depending on the time that the plant remains take to pass into the anoxic portion of the peatland). The record of changes in vegetation assemblages using macrofossils allowed the reconstruction of moisture variations of the bog surface. (enlève: since species have differing humidity tolerances). Chronology of peat accumulation was obtained by 210Pb and AMS radiocarbon dating. Carbon isotopic composition of plants records informations about climatic conditions during plant growth and the hypothesis of a relationship between isotopic composition of Sphagnum species and humidity is suggested. The carbon isotopic composition measurements were performed on the bulk material of these four Sphagnum species: S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. (Enlève: However, the results of many studies are still not concluent and there is a need to develop this tool.)

Preliminary results show isotopic patterns that are respectively related to dry hummocks, lawns and submerged hollows.
 

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