Climatic and non-climatic effects on the δO and δC compositions of Lake Awassa, Ethiopia, during the last 6.5 ka

A comparison of a 6450 14 Cy rd 18 Oand d 13 C record of authigenic calcite from Lake Awassa, Ethiopia, with other proxy climate records in the area suggests that the lake records long-term regional climate changes. Co-varying and increasing d 18 Oand d 13 C values from B4800 BP suggest an aridification of climate after the early Holocene insolation maximum. After 4000 BP, humid conditions return until after B2800 BP when d 18 Oincreases again, reflecting more arid conditions recorded elsewhere in Ethiopia. In addition to these long-term changes, there are abrupt decreases in both d 18 Ocalcite and d 13 Ccalcite immediately after tephra layers. The likeliest explanation for these abrupt decreases in isotopes is the effect of tephra on the lake’s catchment vegetation. d 18 O, d 13 C and lake-level measurements from Lake Awassa since the 1970s suggest that the lake is currently isotopically sensitive to short-term (annual–decadal) climate change. However, during this period, the catchment has undergone progressive deforestation that may have caused an increase in runoff. Caution is therefore required when reconstructing palaeoclimates as a contemporary lake may not always be a good analogue for lake hydrology in the past. r 2002 Elsevier Science Ltd. All rights reserved.

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