The hydrodynamics of Lake Tanganyika are quite complex and driven by several factors occurring both on the water surface and in the deeper water layers. The lake is meromictic, meaning it usually has two main distinct layers that differ in terms of temperature, nutrient concentration, and water density. Twice a year, winds trigger the upwelling or downwelling of the deeper layers, altering the thickness of the layers and their physical (temperature and density) and chemical (nutrient concentration) compositions. This characteristic of the lake plays a crucial role in shaping its hydrodynamics and ecosystem, influencing the productivity of fishery activities.
Furthermore, within the complexity of the lake's hydrodynamics, three main water movements can be distinguished. Firstly, waves occur on the surface of the water and are caused by winds, storms, or other external forces. Secondly, tides are periodic changes in the water level caused by the gravitational interaction between the Earth and the Moon, and, to a lesser extent, the Sun. Thirdly, seiches are standing waves that are caused by changes in atmospheric pressure, wind, and water density variations.
More details can be found in the references listed below:
- Sterckx, The impact of seasonal variability and climate change on lake Tanganyika's hydrodynamics (2023). It refers that the thermocline is subject to an internal seiche, which is controlled by topography, atmospheric pressure and wind stress. The authors then point out that the winds have a cyclic pattern, with a period of 3-4 weeks, which is close to the first free mode of oscillation of the lake and results in a quasi-resonance of the seiche.
- Naithani, Analysis of wind-induced thermocline oscillations of Lake Tanganyika (2003). This focuses mainly on the internal seiche, whose oscillations range from 15 to 45 m and whose period varies from 3 to 4 weeks (modeling results).
- Naithani, Origin of intraseasonal variability in Lake Tanganyika (2002). Here the same authors of the previous paper emphasise that the wind forces are in resonance with the free mode of oscillations of the lake.
- Huttula, Tanganyika Lake: Strong in Hydrodynamics, Diverse in Ecology (2012). The authors refer to some measurements of the surface and internal seiche made by buoys in Bujumbura and in Mpulungu (southern extreme). Apparently the surface seiche has a period of 4.7 h with a phase shift of 180° between Bujumbura and Mpulungu, while the internal seiche has longer period: 23.4 days in the dry season and 34.8 days in the wet season.