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Climate in Southwestern Ontario, Canada, between AD 1610 and 1885 Inferred from Oxygen and Hydrogen Isotopic Measurements of Wood Cellulose from Trees in Different Hydrologic Settings

Abstract Oxygen and hydrogen isotopes were measured in wood cellulose and cellulose-nitrate from trees that grew in different hydrologic settings in southwestern Ontario, Canada. An isotope model that accounts for isotopic fractionations associated with photosynthesis in plants was applied to the stable isotope data to infer past meteoric water isotopic composition and seasonal air moisture variations. The model-inferred climate data was rationalized in terms of the trees' hydrologic environment and weather characteristics of the Great Lakes region. The result is an account of summer and winter conditions in southwestern Ontario for 275 years (1610 to 1885) prior to instrumental climate records. Conditions between 1610 and 1750 are inferred to have been cooler and drier than present. This was followed by a warm-moist climate interval between 1750 and 1885 during which there was an increase in winter precipitation. Cool-dry conditions were recorded instrumentally in this region at the end of the nineteenth century.