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A 9000-year oxygen and carbon isotope record of hydrological change in a small Ethiopian crater lake

Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, UK, School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK

Melanie J. Leng

NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK

Henry F. Lamb

Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, UK

Mohammed Umer Mohammed

Department of Geology and Geophysics, University of Addis Ababa, Addis Ababa, Ethiopia

The stable isotope composition of authigenic calcites in a core from Lake Tilo, a small crater lake in the Ethiopian Rift Valley, provides a subcentury scale record of lake response to climatic change over the last 8850 ¹⁴C yrs (9850 cal. yrs). An unusually high range of ¹⁸O and ¹³C values (~15,) is attributed, in part, to major changes in hydrothermal groundwater flux. Although hydrothermal groundwater influx to the lake was high during the early Holocene, its flow rate was relatively stable and thus climatically induced changes to the water budget can be inferred from variations in ¹⁸O and ¹³C ratios. A major decline in hydrothermal groundwater input from ~5500 ¹⁴C yrs BP increased lakewater residence time and led to substantial increases in ¹⁸O and ¹³C, before the mid-Holocene transition to more arid conditions. During the last ~2700 ¹⁴C years diagenetic processes have resulted in extremely varied ¹⁸O and ¹³C values. The Holocene isotope record from Lake Tilo challenges the widely held assumption that crater lakes act as ’gigantic rain gauges’, sensitive only to changes in precipitation/evaporation ratios.

Key Words: Lake Tilo • crater lake • groundwater • stable iosotopes • 18O • 13C • palaeolimnology • palaeohydrology • Holocene • Ethiopia

The Holocene, Vol. 10, No. 2, 167-177 (2000)
DOI: 10.1191/095968300677444611


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