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The Mechara caves and speleothems, Southeastern Ethiopia: high-resolution palaeoclimate archives

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Among the various climate proxies in speleothems (δ18O, δ13C, growth rate, trace elements, lipids) calcite δ18O is routinely used as rainfall proxy. However, many studies including some from Ethiopia indicated that a variety of climatic, environmental and hydrologic parameters influence the geochemical and physical properties of speleothems, and multi-proxy approach is crucial as the various proxies respond to single climate forcing in different manners. Calcite δ18O records from U-Th dated, Holocene and late Pleistocene speleothems from Ethiopia are discussed in this context. Since 2004, we have been conducting multi-stalagmite, multi-proxy analysis of speleothems from the Mechara karst system in the southeastern Ethiopian highlands and have derived high-resolution paleoclimate parameters such as precipitation. Both δ18O and growth rate parameters of Holocene speleothems indicate marked decadal scale rainfall variability in this climatically sensitive region, implying persistent decadal-scale variability for the large-scale atmospheric and oceanic driving factors throughout the Holocene. On the other hand, the same two proxies from late Pleistocene speleothems from the same region respond non-linearly. In conclusion, calcite δ18O could be a robust rainfall proxy; however, coupling it with other proxies (such as growth rate parameters) is crucial, as any single proxy analysis could lead to an over-simplified interpretation of past climatic / environmental change.

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