The Holocene lake-evaporation history of the afro-alpine Lake Garba Guracha in the Bale Mountains, Ethiopia, based on δ¹⁸O records of sugar biomarker and diatoms

Abstract

Abstract In eastern Africa, there are few long, high-quality records of environmental change at high altitudes, inhibiting a broader understanding of regional climate change. We investigated a Holocene lacustrine sediment archive from Lake Garba Guracha, Bale Mountains, Ethiopia, (3,950 m asl), and reconstructed high-altitude lake evaporation history using δ 18 O records derived from the analysis of compound-specific sugar biomarkers and diatoms. The δ 18 O diatom and δ 18 O fuc records are clearly correlated and reveal similar ranges (7.9‰ and 7.1‰, respectively). The lowest δ 18 O values occurred between 10–7 cal ka BP and were followed by a continuous shift towards more positive δ 18 O values. Due to the aquatic origin of the sugar biomarker and similar trends of δ 18 O diatom , we suggest that our lacustrine δ 18 O fuc record reflects δ 18 O lake water . Therefore, without completely excluding the influence of the ‘amount-effect’ and the ‘source-effect’, we interpret our record to reflect primarily the precipitation-to-evaporation ratio (P/E). We conclude that precipitation increased at the beginning of the Holocene, leading to an overflowing lake between ca. 10 and ca. 8 cal ka BP, indicated by low δ 18 O lake water values, which are interpreted as reduced evaporative enrichment. This is followed by a continuous trend towards drier conditions, indicating at least a seasonally closed lake system.