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

The stable isotope composition of authigenic calcites in a core from Lake T ilo, a small crater lake in the Ethiopian Rift Valley, provides a subcentur y scale record of lake response to climatic change over the last 8850 C-14 yrs (9850 cal. yrs). An unusually high range of delta(18)O and delta(13)C v alues (similar to 15 parts per thousand) is attributed, in part, to major c hanges in hydrothermal groundwater flux. Although hydrothermal groundwater influx to the lake was high during the early Holocene, its flow rate was re latively stable and thus climatically induced changes to the water budget c an be inferred from variations in delta(18)O and delta(13)C ratios. A major decline in hydrothermal groundwater input from similar to 5500 C-14 yrs BP increased lakewater residence time and led to substantial increases in del ta(18)O and delta(13)C, before the mid-Holocene transition to more arid con ditions. During the last similar to 2700 C-14 years diagenetic processes ha ve resulted in extremely varied delta(18)O and delta(13)C values. The Holoc ene isotope record from Lake Tilo challenges the widely held assumption tha t crater lakes act as 'gigantic rain gauges', sensitive only to changes in precipiration/evaporation ratios.