Holocene productivity of southern Lake Tanganyika inferred from diatom fossils

Description: Lake Tanganyika is the longest freshwater lake in the world, stretching 673 km in the North-South axis. While much research has been conducted to understand how climate influences fishery productivity, much of this research has been restricted to the more accessible northern basin. These studies are insufficient to explain whole-lake dynamics. While there is strong evidence to link reduced productivity to climate change, there is little evidence that this is a lake-wide phenomenon. This study used paleolimnological data from two deep-water sediment cores from the southern basin of Lake Tanganyika to determine whether changes observed in the northern basin are representative of the whole Lake. We infer a decrease in diatom concentration after ~3000 cal yrs BP to reflect a decrease in net primary productivity associated with decreasing convective mixing. The episodic presence of benthic ostracodes and molluscs at these deep sites between ~1800–500 cal yrs BP, along with high Mn, indicates episodic pulses of much deeper ventilation of the southern basin than has been recognized previously. The presence of periphytic diatom species and benthic invertebrates during periods of strong stratification suggests that the lake bottom was periodically ventilated by descending denser (cooler or more sediment-rich) influent waters along the steep slopes of the coastline. Fossil diatom assemblages show P and Si gradients between the two sites. 6A shows a shift in dominance towards lightly silicified taxa (Nitzschia spp.) after ~200 cal yrs BP. 2A shows a reduction in concentration of mostly the lightly silicified taxa, with few periods having heavily silicified taxa. These results are indicative of a relative reduction in convective lake mixing but are not always coincident with temperature trends, suggesting local windiness may also be important for stratification history. Thus, changes in lake productivity in the southern basin appear to be climate mediated, but in ways not previously documented in the northern parts of the lake.

Target audience:
This webinar is directed at a more specialized audience interested in environmental conditions over the past 10,000 years as recorded within the important African lake basin of Lake Tanganyika.