Virginia Panizzo, George Swann, Anson W. Mackay, Vanessa Pashley, Matthew S. A Horstwood

Throughout the Quaternary, lake productivity has been shown to be sensitive to drivers such as climate change, landscape evolution and lake ontogeny. In particular, sediments from Lake Baikal, Siberia, provide a valuable uninterrupted and continuous sequence of palaeoproductivity, which document orbital and sub-orbital frequencies of regional climate change. Here we augment these records through the application of silicon stable isotope analyses of diatom opal (δ30Sidiatom), from sediments spanning the Last Interglacial cycle (approximately equivalent to Marine Isotope Stage [MIS] 5e; c. 130 to 115 ka BP) as a means to test the hypothesis that diatom nutrient utilisation was greater, than during the
Holocene. Results show that diatom dissolved silicon (DSi) utilisation, was significantly greater (p=0.001) during MIS 5e than the current interglacial, which reflects increased diatom productivity over this time (concomitant with higher biogenic silica and warmer pollen-inferred vegetation reconstructions). Diatom biovolume accumulation rates (BVAR) are used, in tandem with δ30Sidiatom data, to model DSi supply to Lake Baikal surface waters. When constrained by sedimentary mineralogical archives of catchment weathering indices (e.g. the Hydrolysis Index), data highlight the small degree of weathering intensity and therefore representation that catchment-weathering DSi sources had, over the duration of MIS 5e. Changes to DSi supply during the Last Interglacial are attributed to variations in within-lake conditions (e.g. turbulent mixing) over the period, where periods of both high productivity and modeled-DSi supply (e.g. strong convective mixing) account for the decreasing trend in δ30Sidiatom compositions (after c. 124 ka BP).