In this study, we analyze the circulation patterns in Lake Tanganyika, a large, economically important water body in East and Central Africa, which has experienced significant warming in recent decades. Using the Regional Ocean Modeling System (ROMS) model with a 2.1 km resolution grid and 16 vertical layers, we examine thermal stratification, wind-driven processes, and circulation dynamics. Our results show seasonal variations in surface water temperature caused by changes in air temperature and wind conditions. Primary upwelling occurs in the southern regions from May to August, while secondary upwelling is seen in the northern areas from November to February consistent with previous instrumental studies. Bathymetry affects both upwelling and downwelling circulation. Our findings highlight the interplay between atmospheric and hydrodynamic factors controlling nutrient distribution within the lake driven by internal circulation. These insights underscore the importance of continuous monitoring and collaborative management to protect Lake Tanganyika’s ecosystem amid climate change.

Lake Tanganyika, located in central East Africa, is the longest and second deepest freshwater lake on Earth. Lake Tanganyika’s diverse ecosystem and watershed are under threat today by human activities from extensive deforestation, climate change, and human-induced fires. Therefore, documenting fire and deforestation history in Lake Tanganyika’s surrounding watersheds is crucial for improving watershed management around the lake in the future. Analyzing sediment charcoal records from sediment cores provides high-resolution paleolimnological evidence that reflects the timing and impacts of fire histories and landscape conversion. Macrocharcoal, an incompletely combusted residue that remains when plants materials were burnt by fire, can be transported away from the fire sites and deposited into the lake. We sampled and calculated macro-charcoal (>61 μm) sediment flux from three sediment cores, LT-98-20MR, LT-98-15M, and TANG14-1MC-1A from the lake’s east-central coast. 20MR and 15M are 2.4 km apart, whereas 1A and 15M are 6.97 km apart. We have also compared our results with several previously studied cores from the central part of the lake. Core 15M, which is closest to the shore and has the highest sedimentation rates, showed peaks of charcoal flux from 1830 – 1850, 1896, 1910 – 1914 and 1996 AD based on correlation with a nearby core. Core 20MR, which is further offshore than 15M, has multiple sharp charcoal flux peaks at 1674, 1770, 1848 and 1881 AD, again using correlation with a nearby core. Core 1A, where the watershed has been intensively managed at Kalilani Bay in recent decades (McGlue et al., 2021), shows two significant peaks at 1668 and 1808 AD. The difference in timing of the distributions of sediment charcoal flux peaks from our study indicates these charcoal histories record localized wildfires. Some of these may correlate with the late Little Ice Age dry period in the late 18th – mid 19th C, whereas other more recent ones maybe linked to human activities such as land clearance for cassava cultivation. Low fire frequencies at most sites during the late 19th – mid 20th C may correspond to reduced human populations and disease outbreaks during that period.

Lacustrine, riverine, and spring carbonates are archives of terrestrial climate change and are extensively used to study paleoenvironments. Clumped isotope thermometry has been applied to freshwater carbonates to reconstruct temperatures, however, limited work has been done to evaluate comparative relationships between clumped isotopes and temperature in different types of modern freshwater carbonates. Therefore, in this study, we assemble an extensive calibration dataset with 135 samples of modern lacustrine, fluvial, and spring carbonates from 96 sites and constrain the relationship between independent observations of water temperature and the clumped isotopic composition of carbonates (denoted by Δ47). We restandardize and synthesize published data and report 159 new measurements of 25 samples. We derive a composite freshwater calibration and also evaluate differences in the Δ47-temperature dependence for different types of materials to examine whether material-specific calibrations may be justified. When material type is considered, there is a convergence of slopes between biological carbonates (freshwater gastropods and bivalves), micrite, biologically-mediated carbonates (microbialites and tufas), travertines, and other recently published syntheses, but statistically significant differences in intercepts between some materials, possibly due to seasonal biases, kinetic isotope effects, and/or varying degrees of biological influence. Δ47-based reconstructions of water δ18O generally yield values within 2‰ of measured water δ18O when using a material-specific calibration. We explore the implications of applying these new calibrations in reconstructing temperature in three case studies.