ELEVATED PYROGENIC ORGANIC MATTER IN SEDIMENTS FROM LAKE BOSUMTWI, GHANA AS A PROXY FOR THE TERMINATION OF THE AFRICAN HUMID PERIOD
This study investigates the Holocene paleoclimatic history of northern Africa, using total organic carbon (TOC), soot carbon (Csoot), and other markers of pyrolysis in a sediment core from Lake Bosumtwi, Ghana, west Africa. The African climate has been dynamic throughout the Quaternary, influenced by multiple drivers varying in duration and magnitude. One particularly notable period is the transition from the African Humid Period (AHP) (~14 - ~5 ka) to the current arid conditions in northern Africa. Sedimentary records from large African lakes can provide insights into climate-driven landscape changes caused by droughts, wildfires, flooding, and erosion. A key proxy for wildfires is black carbon (BC), formed from the incomplete combustion of organic matter. BC occurs across a size continuum from large charcoal macro-particles which remain near the fire source to smaller sub-micron-sized soot aerosols capable of long-range atmospheric transport. This study hypothesizes that variations in soot concentrations and anhydride sugars from pyrolysis of cellulose served as a proxy for drought and wildfire activity during the AHP termination (~7.4 -~5 ka). Core samples were analyzed using stratigraphic and geochemical techniques, with Csoot isolated through demineralization and chemo-thermal oxidation. The findings of this project show a relative increase in the abundance of pyrogenic organic matter and suggests increased wildfires in northern Africa before the end of the AHP. The proportion of soot to charcoal in Lake Bosumtwi sediments suggests increased distal wildfire activity and aeolian transport of soot before the end of the AHP (7.4 ka – 5 ka). The isotopic range of the soot carbon shows a distinct change in vegetation around 5 ka and 3 ka. These findings do not support our initial hypothesis that suggested there would be an increase in the combustion of C3 vegetation around the termination of the AHP, followed by an increase in the combustion of C4 vegetation. Nonetheless, these results contribute to the understanding of aeolian transport of charred biomass between northern and western Africa, providing constraints on the timing and spatial variability of the AHP termination.
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