Understanding Lake Tanganyika: Insights Into Climate, Circulation Dynamics, and Fishery Productivity Across Time Using Paleolimnological and Modeling Approaches

Abstract

Lake Tanganyika, one of the world’s most biodiverse freshwater lakes and a vital resource for local fisheries, faces significant threats from climate change that jeopardize its ecological integrity and the livelihoods of dependent communities. This dissertation investigates the lake's thermal dynamics, circulation patterns, and historical limnological conditions using the Regional Ocean Modeling System (ROMS) and sediment core analyses. Our simulations show seasonal surface temperatures between ~25.8°C and ~27.8°C, consistent with observations, along with a concerning increase of up to 0.4°C at depths below 150 meters from 2001 to 2020. Primary upwelling occurs in the southern region during the dry season, while secondary upwelling occurs in the northern region during the wet season. Notably, there is previously unrecognized downwelling on the west side of the lake during September to November. Sediment core analyses reveal a warming trend since ~1850 AD, highlighting long-term climate change impacts on the lake's ecosystem. These trends correlate with global climate patterns, raising concerns about future effects on lake stratification and fishery yields. Enhanced productivity in pelagic zones is linked to deep vertical mixing, while productivity in littoral zones is influenced by increased riverine input during wetter phases. Under high-emission climate scenarios projected through 2100, lake surface temperatures could rise by up to 3.9°C, leading to significant changes in isotherm depths and thermal stratification, which may disrupt nutrient transport and adversely affect fish populations that provide approximately 40% of animal protein for local communities. Our findings emphasize the role of hydrodynamic and atmospheric interactions on nutrient distribution and ecological dynamics. They highlight the urgent need for adaptive management strategies, including community involvement in monitoring and international collaboration, to mitigate climate change impacts on Lake Tanganyika's ecosystem. This research offers valuable insights into the interplay between climate, hydrology, and biological productivity, informing strategies to preserve the ecological balance of Lake Tanganyika and support the livelihoods of millions reliant on its resources.