A Holocene temperature (brGDGT) record from Garba Guracha, a high-altitude lake in Ethiopia

[摘要] Eastern Africa has experienced strong climatic changes since thelast deglaciation (15 000 years ago). The driving mechanisms andteleconnections of these spatially complex climate variations are yet notfully understood. Although previous studies on lake systems have enhancedour knowledge of Holocene precipitation variation in eastern Africa,relatively few studies have reconstructed the terrestrial temperaturehistory of eastern Africa from lake archives. Here, we present (i) a newbranched glycerol dialkyl glycerol tetraether (brGDGT) temperaturecalibration that includes Bale Mountains surface sediments and (ii) aquantitative record of mean annual air temperature (MAT) over the past 12 ka cal BP using brGDGTs in a sediment core collected from Garba Guracha (3950 m a.s.l.) in the Bale Mountains. After adding Bale Mountains surface sediment( n =11 ) data (Baxter et al., 2019) to the existing East African lake dataset, additionalvariation in 6-methyl brGDGTs was observed, which necessitated modifying theMBT 5ME ′ calibration (MBT denotes methylation of branched tetraethers) by adding 6-methyl brGDGT IIIa ′ (resulting in theMBT Bale Mountains index, r 2 =0.93 , p <0.05 ). Comparing theMBT 5ME ′ and the new MBT Bale Mountains index, our high-altitude GarbaGuracha temperature record shows that warming occurred shortly after theHolocene onset when the temperature increased by more than 3.0  ∘ C in less than 600 years. The highest temperatures prevailed between 9 and 6  ka cal BP , followed by a temperature decrease until 1.4  ka cal BP . Thereconstructed temperature history is linked to supraregional climaticchanges associated with insolation forcing and the African Humid Period(AHP), as well as with local anomalies associated with catchmentdeglaciation and hydrology.

[学科分类] 大气科学