04 May 2022
04 May 2022
Status: this preprint is currently under review for the journal BG.

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

Lucas Bittner1, Cindy De Jonge2, Graciela Gil-Romera3,4, Henry F. Lamb5,6, James M. Russell7, and Michael Zech1 Lucas Bittner et al.
  • 1Heisenberg Chair of Physical Geography with focus on paleoenvironmental research, Institute of Geography, Technische Universität Dresden, Dresden, Germany
  • 2Geological Institute, Department of Earth Sciences, ETH Swiss Federal Institute of Technology, 8092 Zurich, Switzerland
  • 3Plant Ecology and Geobotany dept., Philipps-Marburg University, Marburg, Germany
  • 4Department of Geo-environmental Processes and Global Change, Pyrenean Institute of Ecology, CSIC, Zaragoza, Spain
  • 5Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, UK
  • 6Department of Botany, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland
  • 7Department of Geological Sciences, Brown University, USA

Abstract. 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.

Lucas Bittner et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-95', Jonathan Raberg, 24 May 2022
  • RC2: 'Comment on bg-2022-95', Anonymous Referee #2, 07 Jun 2022

Lucas Bittner et al.

Lucas Bittner et al.


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Short summary
With regard to global warming, an understanding of past temperature changes is becoming increasingly important. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids used globally to reconstruct lake water temperatures. In the Bale Mountain lakes, we find a unique composition of brGDGT isomers. We present a modified local calibration and a new high altitude temperature reconstruction from the Horn of Africa spanning the last 12500 years.