Stable isotope composition of tropical high-altitude fresh-waters on Mt. Kenya, Equatorial East Africa

The stable isotope composition of equatorial high-altitude precipitation an d surface-water bodies has been studied on Mt. Kenya (0 degrees 10'S; 37 de grees 20'E) in East Africa during July 1997. Regarding the local hydrology, glacier meltwater was identified as the main source of replenishment for t he lakes, while direct precipitation and runoff appear to have a negligible contribution during this period of the year. Two through-flow lakes exhibi t nearly no evaporative isotopic enrichment relative to the inflow isotopic composition, while two longer residence-time lakes display an oxygen and h ydrogen isotopic build-up of 4.0-7.0 parts per thousand and 18.0-34.0 parts per thousand, respectively. The data indicate that stream waters are compo sed of a mixture of high-altitude glacier meltwater and rainfall. The isoto pic composition of an ice-sample obtained directly from the margin of a gla cier is enriched relative to the average composition of the glacier, sugges ting mixing with local rain. Samples of ground-frost crystals have an isoto pic composition similar to the rain or slightly enriched. In addition, the results show the lack of a significant "altitude effect" on the mountain. T his study demonstrates the importance of the characterization of local hydr ological settings when interpreting lacustrine equatorial isotopic records of past climate and confirms that for East Africa, the total range in oxyge n and hydrogen isotopic composition of meteoric waters is smaller than in h igh-latitudes. (C) 2000 Elsevier Science B.V. All rights reserved.