Holocene rainfall runoff in the central Ethiopian highlands and evolution of the River Nile drainage system as revealed from a sediment record from Lake Dendi

Bernd Wagner, Volker Wennrich, Finn Viehberg, Annett Junginger, Anne Kolvenbach, Janet Rethemeyer, Frank Schaebitz, Gerhard Schmiedl

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

A 12 m long sediment sequence was recovered from the eastern Dendi Crater lake, located on the central Ethiopian Plateau and in the region of the Blue Nile headwaters. 24 AMS radiocarbon dates from bulk organic carbon samples indicate that the sediment sequence spans the last ca. 12 cal kyr BP. Sedimentological and geochemical data from the sediment sequence that were combined with initial diatom information show only moderate change in precipitation and catchment runoff during that period, probably due to the elevated location of the study region in the Ethiopian highlands. Less humid conditions prevailed during the Younger Dryas (YD). After the return to full humid conditions of the African Humid Period (AHP), a ~2 m thick tephra layer, probably originating from an eruption of the Wenchi crater 12 km to the west of the lake, was deposited at 10.2 cal kyr BP. Subsequently, single thin horizons of high clastic matter imply that short spells of dry conditions and significantly increased rainfall, respectively, superimpose the generally humid conditions. The end of the AHP is rather gradual and precedes relatively stable and less humid conditions around 3.9 cal kyr BP. Subsequently, slightly increasing catchment runoff led to sediment redeposition, increasing nutrient supply, and highest trophic states in the lake until 1.5 cal kyr BP. A highly variable increase in clastic matter indicates fluctuating and increasing catchment runoff over the last 1500 years. The data from Lake Dendi show, in concert with other records from the Nile catchment and the Eastern Mediterranean Sea (EMS), that the Blue Nile discharge was relatively high between ca. 10.0 and 8.7 cal kyr BP. Subsequent aridification peaked with some regional differences between ca. 4.0 and 2.6 cal kyr BP. Higher discharge in the Blue Nile hydraulic regime after 2.6 cal kyr BP is probably triggered by more local increase in rainfall, which is tentatively caused by a change in the influence of the Indian Ocean monsoon.

Original languageEnglish (US)
Pages (from-to)29-43
Number of pages15
JournalGlobal and Planetary Change
Volume163
DOIs
StatePublished - Apr 2018

Bibliographical note

Funding Information:
The project is funded by the German Research Foundation (DFG) within the scope of the CRC 806 (“Our way to Europe”). Field work was initiated by Dr. Mohammed Umer (University of Addis Ababa) in 2011, but he died unexpectedly some months before the drilling took place. Therefore, we dedicate this paper to him. We would like to thank the entire coring team, Henry Lamb, Tamrat Endale, and the student helpers Jonas Urban and Christian Tourney. Tamrat Endale and Asfawossen Asrat are thanked for the immense logistic support of the field activities. Nicole Mantke, Marvin Preusse, Stephan Opitz, and numerous students carried out the laboratory work.

Publisher Copyright:
© 2018 Elsevier B.V.

Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.

Keywords

  • African humid period
  • Central Ethiopia
  • Holocene
  • River Nile
  • Tephra

Continental Scientific Drilling Facility tags

  • ETP

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