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NOAA Reconstruction of
Seasonality of Precipitation and Paleoclimate from Hydrogen and Oxygen
Isotopic Composition of Tree Rings, (NOAA Grant #NA56GP0180 1 April 1995 to 31 March 1997) Principal Investigators: Steven W. Leavitt and Elise Pendall This project was initiated and completed over a period of about 3 years, representing two full growing seasons. In the original proposal, two sites were to be sampled, but early on, we decided to add a third site (in Nevada) to the transect, thereby greatly increasing the range of local climate conditions that would be influencing the isotopic composition of the trees. In part, because of the added expense for travel and analysis of additional samples from a third site, we also decided to forego oxygen isotope analysis of leaf and tree-ring cellulose. We obtained dD and d18O analysis of all of the water samples, but felt dD alone (whose source, like d18O, is environmental water) would provide sufficient primary data from which to infer environmental effects on incorporation of isotopes into leaves and tree rings. The success of the project was predicated on the assistance of the student personnel we hired to work in the field and in the lab, and the people who volunteered help in collecting precipitation samples and in providing space and assistance in sample processing and analysis. As problems were encountered, we were usually able to find solutions, such as our acquisition of water samples from the NADP network to provide precipitation samples for the period prior to the dates at which we initiated precipitation collection at the sites. We assessed the paleoclimatic
significance of dD values of piñon pine (Pinus edulis and P.
monophylla) cellulose nitrate (cn) by developing, testing and applying deterministic and
empirical models, in the context of the soil-plant-atmosphere continuum. In this calibration study, stable
isotope values of precipitation, soil water, xylem sap, leaf water,
atmospheric vapor, annual and sub-annual samples of tree-ring and needle
cellulose, and climatic parameters, were measured along a gradient of
decreasing summer rain in the southwestern U.S. This climatic gradient
allowed us to test the influence of precipitation seasonality and relative
humidity on dD values in tree-ring and leaf cellulose. Average precipitation dD values set the baseline for dDcn values at each site, but interannual variations in relative humidity and precipitation amount altered wood and leaf dDcn values, via leaf water effects. Leaf water (lw) was evaporatively enriched by seasonal moisture stress. dDlw and d18Olw values were strongly correlated with relative humidity on a seasonal basis, but not on a diurnal basis. Measured d18Olw values fit a steady-state model, with an offset attributable to relative humidity. Measured dDlw values were more depleted than predicted by the model, suggesting leaf water - organic matter isotopic exchange. Biochemical fractionation (eB) of hydrogen isotopes between leaf water and cellulose was inversely correlated with relative humidity. Our measurements have quantified this poorly understood component of the most widely used deterministic model for two climatically important species. Empirical models based on linear
regressions demonstrated significant correlations between dDcn values and precipitation seasonality. An
El Niño-Southern Oscillation signal (wood dDcn
values inversely related to winter precipitation amount) was found in In an
application of the empirical and deterministic models, we assessed paleoclimatic conditions over the past 40,000 years in
central Publications and Presentations: Pendall, E., 1999. Precipitation seasonality recorded in D/H
ratios of pinyon pine cellulose in the southwestern
Pendall E, 2000. Influence of precipitation seasonality on pinon pine cellulose delta D values. Global Change Biology 6: 287-301. Pendall, E., Betancourt, J.
and Leavitt, S.W., 1996. Do D/H ratios
in fossil cellulose reflect temperature variations? American Quaternary Association, Annual
Meeting, Pendall, E., Betancourt, J.L. and Leavitt, S.W.,
1999. Paleoclimatic
significance of dD and d13C values
in piñon pine needles from packrat middens spanning the last 40,000 years. Palaeogeography, Palaeoclimatology,
Palaeoecology 147: 53-72. Pendall, E., Betancourt, J.L., Leavitt, S.W., and Toolin, L.J., 1994. Pleistocene-Holocene moisture conditions inferred from H and C stable isotopes in plant matter. American Geophysical Union Fall Meeting, San Francisco, December 5-9, EOS (Nov. 1, 1994, supplement): 349 Pendall, E. and Leavitt, S.,
1995. Seasonal dynamics of stable
isotopes in soil water, pinyon sap, and
precipitation across a climatic transect.
American Geophysical Union Fall Meeting, Pendall, E.G. and Leavitt, S., 1996. Isotopic tracers of water movement through the soil-plant-atmosphere continuum. Conference on Stable Isotopes and the Integration of Biological, Ecological and Geochemical Processes, Association of Applied Biologists, Society for Experimental Biology, and British Ecological Society, Newcastle upon Tyne, UK, 9-11 July. Pendall, E. and Leavitt, S.,
1996. Stable isotopic tracers of water
flux through pinyon pines across a climatic
transect. Ecological Society of
American Annual Meeting, Pendall, E. and Leavitt,
S.W., 1997. El Niño's winter
precipitation recorded in cellulose deuterium/hydrogen ratios. 7th Annual V.M. Goldschmidt Conference, 2-6
June, Pendall, E. and Leavitt,
S.W., 1997. El Niño's winter
precipitation recorded in cellulose D/H.
82nd Annual Meeting of the Ecological Society of Pendall, E. and Leavitt, S.W. 1997. Climate change
deduced from isotopes in tree rings. Invited abstract for the 8th Annual
Conference on Global Change, American Meteorological Society, Pendall, E., Williams, D.G. and Leavitt, S.W., 2005. Comparison of measured and modeled variations in piñon pine leaf water isotopic enrichment across a summer moisture gradient. Oecologia 145: 605-618. |
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