INFLUENCE OF WATER DEPTH ON PHYTOLITH ASSEMBLAGES AND TAPHONOMY IN SURFACE SEDIMENTS FROM LAKE TANGANYIKA, EAST AFRICA

Phytolith assemblages can be preserved in terrestrial and lacustrine sediments and serve as a useful proxy for paleo-vegetation patterns and dynamics. Phytoliths can also be a significant source of biogenic silica in lake sediments. In order to address paleoenvironmental questions, fossil phytolith analysis relies on understanding patterns of phytolith taphonomy across different environments. However, in most large and deep lakes, little is known about phytolith transport and preservation. Here, we show that phytolith assemblages in modern surface sediments of Lake Tanganyika change depending on the water depth (D_min=72m and D_max=795m) and distance to the shoreline. Grass silica short cell phytoliths are more abundant in the nearshore and decline farther offshore. In contrast, the phytoliths of woody dicotyledons (trees and shrubs) and palm trees are relatively more abundant in deep-water, offshore environments. Changes in these modern assemblages also impact common vegetation-hydroclimate indices derived from phytoliths, including the dicotyledons-to-Poaceae tree cover index (D/P) and aridity (Iph) index, which represents Chloridoideae short cell phytolith types relative to the sum of Panicoideae and Chloridoideae short cell phytolith types. Our results have implications for interpreting paleo-vegetation and hydroclimate dynamics from phytoliths in lake core studies, as well as for optimizing coring survey design to effectively capture information from these microfossils.