Lithostratigraphy, physical properties and organic matter variability in Lake Malawi Drillcore sediments over the past 145,000 years

Scientific drill cores recovered from Lake Malawi exhibit a remarkable down-core lithologic variability, and are indicative of radically changing environmental conditions forced by large-amplitude lake-level shifts over the past 150 kyr. Here we present detailed lithologic and sedimentary fabric descriptions of the key sedimentary units, along with down-core physical properties data, down-core organic matter geochemistry (TOC, C/N, and δ13C data sets), and images and descriptions from core sections and from sediment smear slide microscopy. These data reveal a fundamental change in Lake Malawi's limnology and regional climate at ca. 60–70 ka. Prior to this time the lake was characterized by large-amplitude variations in lake level and water chemistry, but after 60 ka the lake remained comparatively high, and the central basin drill site accumulated mainly organic-rich, laminated sediments. Organic matter sources changed dramatically during the different lake stages. During major lake high stands, a mixed assemblage of algal (diatom-dominated), woodland and aquatic macrophyte (C4-pathway), and grassland (C3-pathway) organic matter was deposited, whereas during extreme low lake stages (water depths < 200 m), when saline, alkaline lakes persisted in the basin, sediments with minimal amounts of algal-dominated organic matter accumulated and were preserved.