Author ORCID Identifier

https://orcid.org/0000-0001-8477-1010

Date Available

6-16-2025

Year of Publication

2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Arts and Sciences

Department/School/Program

Earth and Environmental Sciences (Geology)

Faculty

Michael Matthew McGlue

Abstract

Understanding the long-term responses of ecosystems to climate variability is crucial for predicting and mitigating future changes in the Afrotropics, a region where a significant portion of the population is highly vulnerable to extreme climatic events. Lake Tanganyika, the largest rift lake in East Africa, offers a unique sedimentary archive that can be used to investigate the limnological changes, hydroclimatic shifts, and vegetation dynamics across various timescales. A multi-proxy approach was employed to assess the landscape responses to hydroclimatic fluctuations in the Late Holocene, integrating paleoenvironmental records from radiocarbon-dated sediment cores. This approach involved sedimentology, mineralogy, geochemistry, phytolith analysis, and macrocharcoal analysis. In Chapter 1, sedimentological and geochemical analyses from the Kavala Island Ridge (KIR) revealed a shift from detrital-rich, river-borne sediment influx during the termination of the African Humid Period (AHP, ~5880–4640 cal yr BP) to laminated, organic-rich deposits reflecting enhanced primary production in response to cooler and seasonally dry conditions from ~3680 to 1100 cal yr BP. Variability in magnetic susceptibility, carbon isotopes, and total organic carbon content during the Common Era suggests dynamic hydroclimate changes, including those associated with the Medieval Climate Anomaly (~950–1250 CE) and Little Ice Age (~1250–1850 CE). These findings highlighted the importance of sedimentary records in constraining long-term hydroclimatic and nutrient flux patterns. In Chapter 2, paleoecological reconstructions using phytolith and macrocharcoal data from Lake Tanganyika elucidated vegetation and fire regime shifts in the surrounding Zambezian miombo woodlands. Grassland expansion was facilitated by reduced precipitation and increased fire activity, particularly during the Medieval Climate Anomaly (~950–1250 CE), while cooler and wetter conditions promoted woodland encroachment during the early LIA (~1250–1530 CE). Our results suggest that fire activity worked as both a disruptive force and a stabilizing factor in shaping the grassland-woodland mosaic. These vegetation shifts can provide insights for biodiversity conservation and sustainable land-use practices in the Lake Tanganyika basin. In Chapter 3, an assessment of modern phytolith assemblages from lake and catchment sediments further refines our understanding of vegetation reconstruction in large rift lake systems using this proxy. Distinct phytolith compositions from Kungwe Bay (Tanzania) and Nsumbu Bay (Zambia) indicate varying contributions of C3- and C4-grasses influenced by regional climate and land use. The D/P° and Iph indices offer lake-wide signals of tree cover and aridity, while water stress and climatic indices respond more sensitively to localized vegetation changes. These phytolith-based proxies provide a crucial baseline for deciphering past vegetation and hydroclimate history, but they also reflect the most recent changes in watershed land use. Together, our findings highlight the importance of lake sediments in refining our understanding of past hydroclimate variability, vegetation dynamics, and ecosystem resilience in the Afrotropics. This knowledge is critical for developing conservation strategies, sustainable land-use practices, and long-term ecosystem management plans for the Lake Tanganyika basin.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.257

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