CALIBRATION OF CARBON AND OXYGEN ISOTOPE VALUES OF MODERN TREE-RING CELLULOSE FROM SASKATCHEWAN WITH METEOROLOGICAL RECORDS

Carbon and oxygen isotope values of tree-ring cellulose record annual variations in environmental conditions such as temperature, relative humidity, soil moisture, and precipitation; however, these parameters conflate in a complex manner to yield the observed δ¹³C and δ¹⁸O values of cellulose. In order to assess the applicability of δ¹³C and δ¹⁸O values of tree-ring cellulose to the modeling of paleometeorological conditions, it is therefore necessary to evaluate the relationship between isotope values of cellulose and multiple environmental parameters. We present a 55-year record of δ¹³C and δ¹⁸O values of tree-ring cellulose in modern tree species (Pinus banksiana and Larix laricina) from Limestone Lake in north central Saskatchewan (54°40'37N, 103°11'11W). Isotope values in early- and late-wood cellulose components have been compared to temperature, relative humidity, and precipitation records from meteorological stations in Prince Albert, Saskatchewan located 300 km to the southwest. Carbon isotope values display a total variability of ~2.5 permil, whereas oxygen isotope values vary by ~6 permil.

δ¹³C_cellulose values are well correlated with relative humidity during the growing season, where growth years characterized by high relative humidity correlate with low δ¹³C_cellulose values. δ¹⁸O_cellulose values primarily reflect winter precipitation amount and precipitation δ¹⁸O values. However, growing season temperature and relative humidity also influences δ¹⁸O_cellulose values as these parameters modulate the amount of evaporative enrichment through moisture loss in the leaves or indirectly as moisture loss from soils. During growing seasons characterized by higher than normal temperature and/or precipitation, late-wood isotope values of both carbon and oxygen are less correlative with early-wood values and reflect the late summer growing conditions. Isotope studies of tree-ring cellulose, when properly calibrated with modern meteorological data, can therefore provide a record of multiple atmospheric conditions beyond the spatial and temporal limitations of instrumental records.