Assessing tree-ring carbon and oxygen stable isotopes for climate reconstruction in the Canadian northeastern boreal forest.

• Published in: Palaeogeography, Palaeoclimatology, Palaeoecology
• Main Authors: Bégin, Christian, Gingras, Mathieu, Savard, Martine M., Marion, Joëlle, Nicault, Antoine, Bégin, Yves
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2015
• Subjects: black spruce; stable isotopes; tree-rings; dendroclimatology; boreal forest; Subarctic
• Online Access: https://espace.inrs.ca/id/eprint/3802/; https://doi.org/10.1016/j.palaeo.2015.01.021

In this study, we analyzed stable isotopes of oxygen (δ¹⁸O) and carbon (δ¹³C) of five black spruce (Picea mariana (Mill.) BSP) trees growing in the Québec boreal forest. We then produced the first dendroisotopic series covering the last two centuries (1800-2003) for this region where climatic records are particularly scarce and of short duration. Our aim was to evaluate the isotope sensitivity to climate and their potential as proxies for past climate conditions. The δ¹⁸O results show a strong coherence between all trees indicating that these values express a homogenous response at the site scale. For the δ¹³C series, slight inter-tree differences suggest the influence of micro-site conditions. Isotopic values were compared to climatic data for the period 1944-2003. These statistical analyses indicate that the δ¹³C and δ¹⁸O ratios are directly influenced by summer maximum temperatures but also correlate with parameters that integrate temperatures and moisture status. In all cases, the climate effects on δ¹³C values are weaker than the ones recorded by the δ¹⁸O series. Moreover, because the δ¹⁸O and δ¹³C values are sensitive to climatic variables that are linked and commonly associated in typical subarctic climate ambiances (warm-dry, cold-wet), the patterns of their joint response show stronger correlations with climatic parameters. Then, a temperature reconstruction was developed based on a regression model that calibrates the combined δ¹³C and δ¹⁸O series against summer maximum temperature (TmaxJJA). The reconstructed summer temperatures indicates that the first half of the 19th century was the coldest period in the past 200 years and that a steadily change throughout milder conditions started in the early 1940’s. These trends are consistent with other reconstructed values from independent proxies available for the same region. This research confirms that C and O dendroisotopic series of black spruce trees in high latitudes can document adequately past climatic conditions.