LATE HOLOCENE CLIMATE VARIABILITY AND ANTHROPOGENIC IMPACT IN LAKE TANGANYIKA

Abstract

Lake sediment cores act as archives of past environmental change, recording shifts in organic matter sources, aquatic productivity, and watershed dynamics over varying timescales that are driven by climatic or anthropogenic forcings. This study examines two sediment cores from Lake Tanganyika, located in central Africa, to document the impact of Holocene climate change as well as more recent anthropogenic activities on nearshore sedimentation. One core (Luiche) was collected from 79 m water depth offshore of a shoreline with a large river delta and adjacent to towns with high population. The other core (Utinta) was collected from 94 m water depth and offshore of a shoreline with low population density and no apparent delta. The cores were analyzed on a cm-scale to examine changes in sediment input and composition as well as assess differences in organic carbon production, preservation, and nutrient input in relation to climate and land use change. A multi-proxy approach was used, incorporating grain size analysis, sedimentation rates, elemental geochemistry (C%, N%, C/N ratio), and lipid biomarkers including Pyropheophytin a, Bacteriopheophytin a, and Perylene, with chronology established using a Bayesian age-depth model (“rPlum”). The Utinta record extends to ~3005 cal yr BP (~1005 BCE), revealing shifts coinciding with the Medieval Climate Anomaly and the Little Ice Age. The core reveals a transition toward greater microbial productivity in more recent sediments, interpreted as a response to climate-driven changes within the lake and primary productivity. The Luiche core extends to ~983 cal yr BP (~967 CE), therefore beginning during the Medieval Climate Anomaly, and exhibiting trends consistent with the impact of climate variability on watershed sediment flux, texture, and composition of sediment delivered to the lake from the major river. More recent changes in the Luiche core reflect anthropogenic disturbance within the catchment. Across the different proxies, the records demonstrate that climate variability has driven long-term changes across Lake Tanganyika, but the increased land-use change, and human impact has made its mark, highlighting the importance of site comparisons and a multi-proxy approach in paleolimnological research.