HR: 0800h
AN: B11A-1011    [Abstracts]
TI: Reconstructing meteorological conditions from tree-ring cellulose at sub-annual resolution using a multi-isotope approach
AU: * Dodd, J P
EM: jpd058@mail.usask.ca
AF: Department of Geological Sciences, University of Saskatchewan, 114 Science Place , Saskatoon, SK S7N 5E2 Canada
AU: Patterson, W P
EM: bill.patterson@usask.ca
AF: Department of Geological Sciences, University of Saskatchewan, 114 Science Place , Saskatoon, SK S7N 5E2 Canada
AU: Holmden, C
EM: chris.holmden@usask.ca
AF: Department of Geological Sciences, University of Saskatchewan, 114 Science Place , Saskatoon, SK S7N 5E2 Canada
AB: General circulation models predict that high latitude climate will change significantly as a result of anthropogenic forcing. However, the relatively short record of meteorological data limits our understanding of natural climate variability. Environmental parameters such as relative humidity, precipitation source, and temperature have been demonstrated to force isotope values of tree-ring cellulose. Thus, isotope time series derived from tree-ring cellulose have the potential to provide high resolution, continuous, precisely dated records of meteorological variability for thousands of years. Here we present seasonally resolved time series of δ¹⁸O, δ¹³C and δD from α-cellulose from modern Black Spruce ( Picea mariana) located in north central Saskatchewan, Canada (54° 40' N, 103° 11'W). Isotopic time series have been compared to the instrumental meteorological data from Prince Albert, Saskatchewan over the period from 1951 to 2004. We have modeled the δ¹⁸O value of water utilized by the tree, which is in turn related to the δ¹⁸O value of precipitation, using a modified leaf-water model (from Anderson et al., 2002). This model accounts for evaporative enrichment of source water in the leaf by incorporating δ¹⁸O values of tree ring α-cellulose, relative humidity, temperature, and ring width measurements. Over the period of meteorological calibration (1951 - 2004) δ¹⁸O α-cellulose values range from 22.1 to 27.4 ‰ and modeled source water δ¹⁸O values demonstrate a high correlation (r = .63) with δ¹⁸O values of March to October precipitation data from the Global Network of Isotopes in Precipitation (GNIP) station in The Pas, Manitoba (approx. 100km to the southeast). In addition, δ¹⁸O cellulose values correlate with snowfall amount over the 3 winters prior to cellulose formation (r = .41). δ¹³C values of α-cellulose range from -27.6 to -24.4 ‰ during the calibration period. δ¹³C values generally display an inverse relationship with relative humidity and positive relationship with temperature, but these relationships alone do not yield a precise measure of either environmental parameter. δ¹³C values of α-cellulose are a result of stomatal conductance and photosynthetic rate. Thus, by incorporating tree ring width measurements as a proxy for net photosynthetic rate and the temperature effect on gas exchange during respiration, we are developing a model that reconstructs relative humidity values from δ¹³C α-cellulose values. Hydrogen isotope values in α-cellulose range from -160 to -120 ‰, and show no significant correlation with δ¹⁸O α-cellulose values (r = .07). In contrast, δ¹⁸O and δD values of GNIP precipitation data display an almost perfect 1:1 relationship (r = .99); therefore, hydrogen isotopes are likely fractionated differently than oxygen prior to incorporation in α-cellulose. Preliminary data indicate that a multiple regression model, incorporating tree ring width measurements, relative humidity, and δD precipitation data as well as δD values of α-cellulose will more accurately model observed temperature variation. Once calibrated, time series of oxygen, carbon, and hydrogen isotopes from tree-ring α-cellulose have the potential provide a record of multiple atmospheric conditions beyond the spatial and temporal limitations of instrumental records.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0476 Plant ecology (1851)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Biogeosciences [B]
MN: Fall Meeting 2005