2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 28-26
Presentation Time: 9:00 AM-5:30 PM


DELUCA, Nicole M.1, LEVIN, Naomi E.1, BEDASO, Zelalem K.2, ZAITCHIK, Benjamin F.1, WAUGH, Darryn W.1, HARMAN, Ciaran3 and SHANKO, Dula4, (1)Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, (2)Department of Geology, University of Dayton, 300 college park, Dayton, OH 45469-2364, (3)Department of Geography and Environmental Engineering, Johns Hopkins University, 3400 N Charles Street, Baltimore, MD 21218, (4)National Meteorology Agency of Ethiopia, Addis Ababa, Ethiopia, ndeluca1@jhu.edu

Climate change is thought to have played a major role in driving human evolution in eastern Africa, however oxygen and hydrogen isotope records that could help in reconstructions of past climate are poorly understood. In order to expand the utility of these isotopic data, we need to develop a better understanding of how the isotopic composition of waters relates to modern hydrological and climatic processes. The isotopic composition of Ethiopian precipitation is best known from a single, long-term monthly monitoring station at Addis Ababa. The data from this station deviates from expectations given its high altitude and inland location, making the generalized framework usually used to interpret isotopic data from rainfall and geologic materials inappropriate for Ethiopia. We propose that additional sampling campaigns will allow us to better understand what drives isotopic variation in Ethiopia today and in the past. In this study, we collected precipitation samples in monthly, weekly, and daily intervals over a 16-month period from August 2012 to November 2013 at four meteorological stations in Ethiopia (Gondar, Debre Markos, Jimma, and Jijiga) in order to provide a higher spatial and temporal resolution isotope dataset than the long-term data from Addis Ababa. The most distinct trend is a temporally coherent dip in the δ18O values from Gondar, Debre Markos, and Jimma, from +2‰ in June 2013 to a minimum of -8‰ in August 2013, and then rising back to +2‰ by October 2013. Such coherency between three locations with diverse topography, hydroclimates, and vegetation suggests a region-wide phenomenon and indicate that δ18O and δ2H in Ethiopian rainfall integrate regional processes. Precipitation amount does not follow a coherent pattern during this δ18O trend; as such we hypothesize that processes other than the amount effect, such as moisture source, degree of convection, and intensity of the rain event, may be causes for the isotopic variation that we observe.