BIOMARKER SIGNATURES OF FIRE AND GRASSLAND-FOREST TRANSITIONS ASSOCIATED WITH HOMININS AT OLDVUAI GORGE, TANZANIA
Fire, integral to grassland ecology today, disfavors forests, which re-sprout less vigorously, and fire is widely suspected as a significant agent that links abrupt shifts in vegetation to climate. Fire was likely a factor both in C4-grassland expansion in the Miocene, and in high-frequency variations in eastern tropical Africa during the Quaternary. Materials released during biomass combustion carry organic tracers of fire activity, including the better known solid forms, such as char, black carbon, and soot. Geochemical records built from both polar compounds associated with cellulose and hemi-cellulose combustion (including, levoglucosan, mannosan, galactosan) as well as polycyclic aromatic hydrocarbons (PAH) can also track past fire activities. The taphonomy of each indicator differs. Generally, particulate phases have shorter transport trajectory than compounds borne in aerosols, and more soluble forms are less well preserved under aggressive soil conditions. Biomarker molecules offer power tools to track fire, landscape vegetation, and climate patterns of the past. Here, we compare terrestrial plant biomarkers, molecular carbon and hydrogen isotope records, and fire indicators, especially PAH, in the Lake Olduvai catchment, to evaluate the linkages among fire, climate, and ecosystem stability during hominin occupation, ca. 2 million years ago.