Universität zu Köln

Markowska, M., Martin, A. N., Vonhof, H. B., Guinoiseau, D., Fischer, M. L., Zinaye, B., Galer, S. J. G., Asrat, A. and Junginger, A. (2022). A multi-isotope and modelling approach for constraining hydro-connectivity in the East African Rift System, southern Ethiopia. Quat. Sci. Rev., 279. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD. ISSN 1873-457X

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Abstract

During the last African Humid Period (AHP; 15-5 ka), many lakes in the East African Rift System (EARS) experienced pronounced lake-level variations that dramatically transformed the hydrological landscape. Currently dry, saline or marshy-wetland terminal lakes became vast waterbodies, interconnected via overflow sills resulting in the formation of a several thousand-kilometre-long chain of lakes in the EARS. A quantitative, process-based understanding of these hydrological systems can advance our interpretation of past hydroclimate variability from proxy records. Here, we provide a critical modern hydrological dataset for the data-sparse Lake Chew Bahir basin in southern Ethiopia. Driven by modern data, an isotope-enabled hydro-balance model was developed to assess how increases in rainfall modulate delta O-18 and Sr-87/Sr-86 variability. Considering a terminal Lake Chew Bahir scenario, humid conditions resulted in higher lake delta O-18 (similar to+14 parts per thousand) due to increased evaporation and longer water residence times. At the same time Sr-87/Sr-86 Sr decreased from 0.7064 to 0.7061 due to an increased riverine Sr flux characterised by lower, unradiogenic Sr-87/Sr-86 ratios. In a modelling scenario where Lake Chew Bahir became a flow-through system with interconnectivity between lakes Abaya, Chamo, Chew Bahir and Turkana, higher lake delta O-18 (similar to+12 parts per thousand) relative to present was found, but 8 18 0 was lower than in the terminal lake scenario. The lake water Sr-87/Sr-86 ratios (<0.7061) were also slightly lower. A moderate concomitant change in rainfall input delta O-18 of similar to 1 parts per thousand in step with hydrological reorganisation resulted in the lowest lake delta O-18 (similar to+5 parts per thousand). Modelled delta O-18 values were similar to the delta O-18 range of endogenic carbonates from sedimentary cores from Lake Chew Bahir at the onset of the AHP, supporting the validity of our model, and suggesting that evaporation and the lake water residence time strongly influence lake water delta O-18. However, the reported Sr-87/Sr-86 of fossil carbonates from Lake Chew Bahir during the AHP (0.7065-0.7060) could not be reproduced by our modelled scenarios without adjusting the surface-water-to-groundwater ratio, highlighting the potential role of groundwater as a water source in semi-arid regions. These results demonstrate the insights that can be gained from applying a process-based approach using O and Sr isotope hydro-balance modelling to aid interpretation of past hydro-balance and lake interconnectivity from lacustrine sedimentary records. (C) 2022 Elsevier Ltd. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Markowska, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Martin, A. N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Vonhof, H. B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Guinoiseau, D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Fischer, M. L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Zinaye, B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Galer, S. J. G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Asrat, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Junginger, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-689011
DOI:	10.1016/j.quascirev.2022.107387
Journal or Publication Title:	Quat. Sci. Rev.
Volume:	279
Date:	2022
Publisher:	PERGAMON-ELSEVIER SCIENCE LTD
Place of Publication:	OXFORD
ISSN:	1873-457X
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language NORTHERN KENYA; HUMID PERIOD; MASS-BALANCE; LAKE SUGUTA; BLUE NILE; HYDROCHEMICAL CHARACTERIZATION; ENVIRONMENTAL ISOTOPES; GROUNDWATER RECHARGE; WESTERN ETHIOPIA; FLOW DYNAMICS Multiple languages Geography, Physical; Geosciences, Multidisciplinary Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/68901