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

Abstract

This study provides a new understanding of cellulose oxygen (δ 18O cel) isotopic variability in various plant macrofossils, particularly Sphagnum, derived from an ∼9200 year succession of Holocene peat in Mer Bleue Bog, Ottawa, Ontario, Canada. The variation of δ 18O cel isotopic composition, commonly used as a proxy of paleotemperature and paleoprecipitation, was compared between (1) Sphagnum and other plant macrofossils down core and (2) Sphagnum species within and between samples. The most common Sphagnum species encountered was Sphagnum magellanicum von Bridel, 1798 with lesser amounts of Sphagnum capillifolium (Breutel) Steudel, 1824, Sphagnum fuscum Klinggräff, 1872 and Sphagnum angustifolium Jensen, 1896. There is a statistically significant offset in δ 18O cel isotopic values (mean offset: 1.6‰, standard deviation = 3.2‰, n = 19) obtained from Sphagnum in comparison with values obtained from other plant macrofossils, particularly rhizomes. The δ 18O cel isotopic offset (mean offset: 0.1‰, standard deviation = 1.0‰, n = 11) between Sphagnum specimens from the same core horizons, irrespective of the species analyzed, was statistically insignificant at >95%. These results indicate that δ 18O cel isotopic analysis of bulk peat material with high percentage of rhizome and other vascular plants could result in erroneous paleoclimate reconstructions.