HR: 14:10h
AN: V13F-03 INVITED    [Abstracts]
TI: Use of Multiple Isotopic Systems to Interpret Ecosystem Processes in Hawaii
AU: * Chadwick, O
EM: oac@geog.ucsb.edu
AF: University of California, Department of Geography, Santa Barbara, CA 93106-4060,
AU: Derry, L
EM: lad9@cornell.edu
AF: Cornell University, Department of Geological Sciences, Ithaca, NY 14853,
AU: Vitousek, P
EM: vitousek@stanford.edu
AF: Stanford University, Department of Biological Sciences, Stanford, CA 94305,
AB: The Hawaiian Islands are an excellent natural laboratory for studying the way in which ecosystems develop and function under varying climates. The mantle-derived basalt parent material provides a constant reaction matrix, the trade winds provide an asymmetric climate pattern that means that the same-age lava flows can be studied under different forcing factors, the relatively few plant species that made it to Hawaii provide a simplified biotic influence on substrate. In essence, we find that the geochemical evolution of basalt weathering provides shifting boundary conditions that constrain ecosystem potentialities, and allows us to apply a number of isotopic systems to enhance the specificity of our interpretation of ecosystem processes. We have applied the following isotopes to assist us in understanding the processes that impact ecosystems: O, C, Sr, Ca, N, Si and Be, and are presently exploring the use of S and Mg. We use these isotopic systems within a matrix of controls that allows us to focus on specific questions. The isotopic signatures from different isotopic systems can define climate- response patterns that are non-linear with each defining different threshold and plateau in rainfall space. Measurement of these isotopic systems allows us to evaluate multiple chemical behaviors at once and to evaluate expected responses to perturbations to any of these tracers in response to past or future changes in climate or other ecosystem drives such as land cover change. For instance, based on deep-soil samples, the plants that grew before humans reached Hawaii have C13 values that drop from -14 per mil to -26 per mil as rainfall increases from 200 mm to 3000 mm. Today the surface-soil values remain close to -14 per mil throughout the rainfall gradient due to the introduction of C4 grasses for pasture. Along the same rainfall gradient, Sr isotopes demonstrate that as C3 plants began to predominate there was a fundmental shift in nutrients supplied from rocks to those supplied by rainfall.
DE: 1099 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting