Influence of cellulose oxygen isotope variability in sub-fossil Sphagnum and plant macrofossil components on the reliability of paleoclimate records at the Mer Bleue Bog, Ottawa, Ontario, Canada

► The δ18Ocel isotopic ratios of different peatland plant taxa were compared. ► Significant difference in δ18Ocel was found between Sphagnum and vascular plants. ► There is no significant difference in δ18Ocel between different Sphagnum species. ► Paleotemperature reconstructions from peatland are best from δ18Ocel of Sphagnum.