Optical dating of Holocene extreme flood events in eastern South Africa and their connection to ENSO variability

Wood, Jamie ORCID: https://orcid.org/0000-0003-0923-5511, Toms, Phillip ORCID: https://orcid.org/0000-0003-2149-046X, Grenfell, Michael C and Humphries, Marc S (2026) Optical dating of Holocene extreme flood events in eastern South Africa and their connection to ENSO variability. Quaternary International, 757. p. 110101. doi:10.1016/j.quaint.2025.110101

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Abstract

Existing research examining tributary blocked-valley lake and wetland development upon the Mfolozi River floodplain (South African east coast) has highlighted the potential for blocked-valley lakes to act as mainstem palaeoflood archives. Sand and silt units preserved within the organic deposits of these floodplain-impounded features represent relatively large flood events and provide an opportunity to establish the frequency of extreme flooding in the region beyond the timespan of instrumental and historical records, thereby helping to reduce uncertainty around future tropical cyclone activity in a warming world. However, absolute age estimates for these sequences have been limited to radiocarbon dating of organic units, restricting flood history reconstruction. This study had two inter-related aims. Firstly, to evaluate the use of optically stimulated luminescence (OSL) dating for chronicling clastic sediments associated with the floodplain's blocked-valley lakes. Secondly, in combination with radiocarbon dating and Bayesian age-depth modelling, to reconstruct flood history across three sites on the Mfolozi floodplain and investigate the climatic factors that drove past extreme flooding in the region. The Finite Mixture Model (FMM) applied to single grain OSL data was identified as the most suitable equivalent dose (De) model, producing age estimates that either aligned with historical records and/or accounted for the largest population of grains with a common dose. The deposition models developed provide evidence for the occurrence of multiple extreme floods since the first event identified at 7.2 ka, providing the first long-term flood record for the region. Comparison of the Mfolozi palaeoflood record with independent sedimentary hydroclimatic evidence from the region indicates a historical tendency for more frequent extreme floods during weakened El Niño conditions (i.e., La Niña or neutral ENSO phases). This suggests that variations in ENSO conditions through the mid-to-late Holocene likely played a fundamental role in triggering extreme flooding along South Africa's east coast.

Item Type:	Article
Article Type:	Article
Uncontrolled Keywords:	Blocked-valley lake; Fluvial; OSL; Quartz; Tributary; Wetland
Subjects:	G Geography. Anthropology. Recreation > GB Physical geography G Geography. Anthropology. Recreation > GE Environmental Sciences
Divisions:	Schools and Research Institutes > School of Arts, Culture and Environment Schools and Research Institutes > School of Education, Health and Sciences
Depositing User:	Jamie Wood
Date Deposited:	07 Jan 2026 10:26
Last Modified:	07 Jan 2026 10:45
URI:	https://eprints.glos.ac.uk/id/eprint/15725

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