Late Glacial and Holocene environmental history of the Ethiopian Highlands inferred from a 12 m long sediment record from Dendi crater lakes

A 12 m long composite sediment sequence from Dendi crater lakes, located on the central Ethiopian Plateau, was recovered during a field campaign in March and April 2012. The sediment sequence was analysed with sedimentological and geochemical methods including XRF scanning, grain size measurements, and the determination of total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN) and total sulphur (TS). Bulk organic carbon samples from 23 horizons throughout the sequence were used for AMS radiocarbon dating and provide the basis for the establishment of a robust age-depth model. The sediment sequence covers almost continuously the last 12.5 ka and indicates high Ca and TIC at the base, which infer relatively high carbonate content and most likely a relatively low lake level. The most prominent sedimentary horizon in the entire sequence is formed by an almost 2 m thick tephra, which was deposited between 11.0 and 10.5 ka BP and probably originates from the Wonchi crater 15 km to the southwest of the Dendi lakes. The sedimentological data indicate that the input of clastic terrigenous matter was highly variable during the African Humid Period (AHP) and was relatively stable during the mid Holocene. Higher variability over the last ca. 4 ka is probably related to increasing human activity in the area or to a changing climate regime. The climate in the area is mainly controlled by variations in solar isolation and atmospheric circulation patterns, which are influenced by the position of the ITCZ and the Congo Air Boundary (CAB). Compared with other sediment records from Ethiopia the influence of the AHP on sedimentation patterns seems to be less pronounced at Dendi crater lakes, which is probably due to their location in the Ethiopian highlands and a more humid climate throughout the Holocene.