HR: 13:40h
AN: C43D-01 INVITED     [Abstracts]
TI: Sources of variability in the multi-isotopic composition of Antarctic snow from climate model simulations
AU: * Noone, D
EM: dcn@colorado.edu
AF: Program in Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Campus Box 311, Boulder, CO 80309 United States
AB: The isotopic composition of Antarctic snow is known to reflect climate variability on all time scales that have been sampled. These robust signals have been of great use in understanding the broad features of past climate variability, however, the desire to understand the changes in the mechanisms responsible for climate variability leads to the need to understand the partitioning of processes contributing to the isotopic signals. Specifically, any number of individual processes can modify the isotopic composition of polar snow, yet different combinations of processes can signify different climate conditions. Information on the set of processes active can be obtained by examining isotope-isotope associations where more than one species exists (such as the ``deuterium exces'' and the ``O17 anomaly''), although there is as yet no consensus on the best application of multi-isotope analyses in climate reconstruction. As different environmental conditions impart differing signals on the set of isotopic species, a mapping can be constructed between different climatic processes and the isotopic state. While such a mapping can not provide an unambiguous method for reconstructing all aspects of climate variability, it does provide quantitative guidance to the confidence one may place on the interpretation of the isotope records. In this manner, we attempt to identify which processes dominate the isotopic signal using numerical simulations. A state-of-the-art atmospheric general circulation model has been fitted with a new isotopic tracer scheme which computes the spatiotemporal distribution of water nuclides, including the four most abundant stable isotopes of glaciological interest (H$_2$O, HDO, H$_2^{18}$O and H$_2$^{17}$O). The isotopic state of atmospheric water vapor, cloud condensate, and precipitation is of principal interest. With the model, a theoretical assessment of the isotopic response to changes in atmospheric processes is determined. Building on previous work for a single isotope, we establish the sensitivity of isotope-isotope associations to changes in the condensation history of moist parcels by considering 1) the conditions affecting cloud microphysics (ice/liquid partitioning), and 2) changes in dilution of the isotopic signal by both large-scale and turbulent mixing.
DE: 3344 Paleoclimatology
DE: 1704 Atmospheric sciences
DE: 1719 Hydrology
DE: 1854 Precipitation (3354)
DE: 1040 Isotopic composition/chemistry
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting