HR: 0800h
AN: C51B-1029    [Abstracts]
TI: Stable Isotopes in Precipitation and Groundwater as Tracers for Climate Change in Central Australia
AU: McGuffie, K
EM: Kendal.McGuffie@uts.edu.au
AF: Department of Applied Physics, University of Technology Sydney, Broadway, NSW 2007 Australia
AU: Airey, P L
EM: pla@ansto.gov.au
AF: ANSTO Environment, Provate Mail Bag, MENAI, NSW 2234 Australia
AU: Henderson-Sellers, A
EM: ahssec@ansto.gov.au
AF: ANSTO Environment, Provate Mail Bag, MENAI, NSW 2234 Australia
AU: * Tadros, C V
EM: ckh@ansto.gov.au
AF: ANSTO Environment, Provate Mail Bag, MENAI, NSW 2234 Australia
AU: Stone, D M
EM: dms@ansto.gov.au
AF: ANSTO Environment, Provate Mail Bag, MENAI, NSW 2234 Australia
AB: The IAEA GNIP listings of stable isotopes in precipitation reflect the cumulative effects of isotopic shifts accompanying the evaporative and condensation history of the sample, and are increasingly being used in the evaluation of General Circulation Models. At the same time, the properties of age-dated groundwater reflect the isotopic composition of precipitation at recharge and are contributing to paleoclimate studies in warm arid zones. In high latitudes, the isotope ratios in groundwater respond principally to paleo-temperature changes. However, in warm arid zones rainfall distribution patterns become increasingly important. Under these conditions, it is assumed that effective recharge occurs when rainfall intensities (mm/month) exceed a threshold value, and that the stable isotope ratios of the groundwater samples predominantly reflect the weighted mean of rainfall exceeding this threshold. Experimental evidence is presented to support this hypothesis, derived from a detailed comparison of GNIP data from Melbourne and Alice Springs and from a general survey of data from a range of inland stations around the globe. Results from the observational analysis indicate that: 1) the variance of the stable isotope ratio distribution in rainfall increases with aridity; 2) the more intense the rainfall (mm/month), the more depleted are the isotopes; and 3) the magnitude of this intensity effect increases with aridity. From a detailed comparison of the stable isotope ratios in rainfall and in age-dated groundwater from the Alice Springs region, it is concluded that the rainfall intensity threshold (mm/month) leading to effective recharge is about 80 mm/month but has been decreasing over the past 4000 years or so. This is consistent with independent paleoclimate evidence that conditions around Lake Eyre in Central Australia were more benign in the past. The use of stable isotopes to link rainfall distribution patterns with effective recharge in warm arid zones provides a basis for evaluating isotope enabled GCMs, and for assessing their potential in predicting the impact of climate change scenarios on groundwater sustainability in these critical regions.
DE: 1829 Groundwater hydrology
DE: 1833 Hydroclimatology
DE: 1610 Atmosphere (0315, 0325)
DE: 1620 Climate dynamics (3309)
DE: 1655 Water cycles (1836)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting