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TitleEvaluating the integrity of C and O isotopes in sub-fossil wood from boreal lakes
AuthorSavard, M M; Bégin, C; Marion, J; Arsenault, D; Bégin, Y
SourcePalaeogeography, Palaeoclimatology, Palaeoecology vol. 348-349, 2012 p. 21-31,
Alt SeriesEarth Sciences Sector, Contribution Series 20120104
Mediapaper; on-line; digital
File formatpdf
NTS23B; 23E; 23J
AreaCaniapiscau River; Nitchequon; Wabush; Schefferville
Lat/Long WENS-71.0000 -66.0000 56.0000 52.0000
Subjectspaleontology; isotopes; carbon isotopes; oxygen isotopes; isotope ratios; petrified wood
Illustrationslocation maps; photographs; plots
ProgramClimate Change Impacts and Adaptation for Key Economic and Natural Environment Sectors, Climate Change Geoscience
AbstractExtending climatic series back to the first millennium using isotopic tree-ring chronologies in northern regions represents a challenge because trees seldom reach the adequate age. Fossil trees deposited in boreal lakes could serve such an endeavor provided that dating the tree-ring series is possible and that the isotopic ratios of sub-fossil wood are preserved. From two boreal lakes in north-eastern Canada, we collected segments of Picea mariana (black spruce) stems with different degrees of wood textural preservation and covering the last millennium. Our main objectives are to assess the selection criteria for wood textures suitable for isotopic reconstruction, and verify the reliability of sub-fossil cellulose carbon and oxygen isotopic series for climatic reconstruction in boreal regions. The isotopic differences between cellulose and lignin obtained for 48 ring pairs of a living tree (delta delta13Cc-l=3.7±0.3permil; delta delta18Oc-l=13±1) and 46 contemporaneous pairs from a subfossil stem (3.5±0.3 and 12.9±0.9permil in the same order), are systematic and matching. For the selection of all sub-fossil samples, we have visually identified three main classes of wood textures for which the degree of alteration is confirmed by secondary electron microscopy: well preserved, slightly altered and highly altered. Slightly altered stem segments have cellulose proportion showing a relative decrease reaching 35%, but delta delta13Cc-l and delta delta18Oc-l values within the range of living trees. Non-altered sub-fossil stems covering the 14th and 11th centuries show systematic and coherent delta delta13Cc-l (3.5±0.2; 3.8±0.4permil) and delta delta18Oc-l results (13.9±0.7; 13.5±0.5permil). Highly altered wood shows a decrease in both cellulose proportion and delta18Ocellulose values, but apparently preserved delta13C ratios. This research shows that it is possible to visually identify the degree of wood preservation and preselect sub-fossil segments holding reliable isotope-ratios, and to use subfossil stems collected from boreal lake floors to reconstruct climate over the last millennia.