A Holocene temperature (brGDGT) record from Garba Guracha, a high-altitude lake in Ethiopia. Biogeosciences Discussions 1–33. https://doi.org/10.5194/bg-2022-95 (Accepte
Eastern Africa has experienced strong climatic changes since the last deglaciation (15,000 years ago). The driving mechanisms and teleconnections of these spatially complex climate variations are yet not fully understood. Although previous studies on lake systems have largely enhanced our knowledge of Holocene precipitation variation in eastern Africa, few such studies have reconstructed the terrestrial temperature history of eastern Africa from lake archives. Here, we present (i) a new branched glycerol dialkyl glycerol tetraether (brGDGT) temperature calibration that includes Bale Mountain surface sediments and (ii) a quantitative record of mean annual temperature (MAT) over the past 12 cal ka BP using brGDGTs in a sediment core collected from Garba Guracha (3950 m a.s.l.) in the Bale Mountains. After adding Bale Mountain surface sediment (n=11) data to the existing East African lake dataset, additional variation in 6-methyl brGDGTs was observed, which necessitated modifying the MBT'5ME calibration by adding 6-methyl brGDGT IIIa' (resulting in the MBT-Bale Mountain index, r2=0.93, p<0.05). Comparing the MBT’5ME and the new MBT-Bale Mountain index, our high altitude Garba Guracha temperature record shows that significant warming occurred shortly after the Holocene onset. The temperature increased by more than 3.0 °C in less than 600 years. The highest temperatures prevailed between 9 and 6 cal ka BP, followed by a temperature decrease until 1.4 cal ka BP. The reconstructed temperature history is strongly linked to supraregional climatic changes associated with insolation forcing and the African Humid Period (AHP), as well as with local anomalies associated with catchment deglaciation and hydrology.