HR: 1340h
AN: PP43A-0598    [Abstracts]
TI: A New Model for Interpretation of Carbon Isotope Values of Lacustrine Sediment: Influence of Summer Moisture
AU: * Patterson, W P
EM: Bill.Patterson@usask.ca
AF: University of Saskatchewan, Department of Geological Sciences, 114 Science Place, Saskatoon, SK S7N5E2 Canada
AU: Burnett, A W
EM: aburnett@mail.colgate.edu
AF: Colgate University, Department of Geography, 17 Persson Hall, Hamilton, NY 13346 United States
AU: Mullins, H T
EM: htmullins@syr.edu
AF: Syracuse University, Department of Earth Sciences, 204 Heroy Geology Lab, Syracuse, NY 13244 United States
AU: Kirby, M E
EM: mkirby@fullerton.edu
AF: Cal State University Fullerton, Department of Geological Sciences, Fullerton, CA 92834 United States
AB: We propose that changes in summer moisture stress force variations in terrestrial organic matter $\delta$$^{13}$C values that are recorded in lake calcite. This relationship should be especially strong in small oligotrophic lakes. Lake sediment $\delta$$^{13}$C(CaCO$_{3}$) values serve as a proxy for summer moisture conditions whereby high summer precipitation and low moisture stress yield terrestrial vegetation with lower $\delta$$^{13}$C(organic) values. This variation is superimposed upon aquatic productivity that is related to supply of nutrients, temperature and light availability. Decay of terrestrial vegetation with low $\delta$$^{13}$C(organic) values decrease the $\delta$$^{13}$C value of the lake's dissolved inorganic carbon (DIC) resulting in lower $\delta$$^{13}$C(CaCO$_{3}$) sediment values. $\delta$$^{13}$C(CaCO$_{3}$) values are linked to atmospheric circulation that drives dry/wet periods and therefore high/low $\delta$$^{13}$C(organic) values. Wet periods are associated with mid-tropospheric troughing over the eastern United States, similar to conditions experienced there during summer 2004. To evaluate this hypothesis, we examined the relationship between various measures of summer moisture and $\delta$$^{13}$C(CaCO$_{3}$) values of carbonate varves from a box core recovered at 22 m water depth in Fayetteville Green Lake, central New York State. Calcite $\delta$$^{13}$C(CaCO$_{3}$) values were determined for the historic period (A.D. 1892-1986) on the summer, calcitic portion of individual varves. Multiple correlations were performed between the carbon isotope values and various measures of moisture stress. We compared $\delta$$^{13}$C(CaCO$_{3}$) values to total precipitation, the Palmer drought Z-index, moisture surplus, moisture deficit, and precipitation-potential evapotranspiration (P-PE). Statistically significant correlations include the 5-year auto weighted average for precipitation (-0.357), surplus (-0.432), deficit (0.387), P-PE (-0.409), and Z-index (-0.288). The strength of the five-year weighting reflects the lag in decay and transport of terrestrial organic matter. This carbon isotope-moisture stress hypothesis provides an alternative interpretation, but is not exclusive of, the traditional productivity model.
DE: 4870 Stable isotopes
DE: 3344 Paleoclimatology
DE: 4215 Climate and interannual variability (3309)
DE: 1845 Limnology
DE: 1854 Precipitation (3354)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting