HR: 1340h
AN: B13B-1204    [Abstracts]
TI: Getting to the Source of the High Isotopic Values of Ethiopian Precipitation
AU: * Levin, N E
EM: levin@earth.utah.edu
AF: Geology & Geophysics, University of Utah, Salt Lake City, UT 84115, United States
AU: Cerling, T E
EM: cerling@earth.utah.edu
AF: Geology & Geophysics, University of Utah, Salt Lake City, UT 84115, United States
AB: Oxygen and deuterium isotopic values of meteoric waters from Ethiopia are unusually high when compared to waters from other high-elevation settings in Africa and worldwide. These high values are well-documented; however, the climate processes responsible the isotopic anomaly in Ethiopian waters have not been thoroughly investigated. Current explanations for the isotopic composition of Ethiopian waters invoke very different moisture transport paths. One model suggests that Ethiopian rainfall originates in the Congo Basin where transpiration returns water to the atmosphere without isotopic differentiation. Another model suggests that Ethiopian rainfall originates in the Indian Ocean and travels westward where the first condensation of ocean moisture in Ethiopia yields precipitation with an isotopic composition close to that of ocean water. Here we present additional isotopic data from Ethiopian waters, use products from the Tropical Rainfall Monitoring Mission (TRMM) and National Centers for Environmental Prediction (NCEP) reanalysis project to evaluate wind directions during precipitation events in Ethiopia, and revisit the question of where the high isotopic values of Ethiopian precipitation originate. Isotopic analyses from more than 250 waters collected in the highlands and rift valleys of Ethiopia all yield values greater than -4 per mil and -22 per mil (VSMOW) for oxygen-18 and deuterium isotopes respectively, which are consistent with results from previous studies of Ethiopian waters. The TRMM and NCEP data show that the majority of low-level winds during precipitation events in Ethiopia are westerly and suggest that the moisture source for Ethiopian rainfall is transpired water from the Congo Basin. We propose that transport of transpired moisture from the Congo Basin is responsible for the high isotopic values of Ethiopian meteoric waters and present a general model for the isotopic and climate dynamics of rainfall in the region.
DE: 0429 Climate dynamics (1620)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting