Fire response to changes in hydroclimate and vegetation in Pleistocene East Africa

Abstract:

Pleistocene sediments deposited in the Paleolake Olduvai (Olduvai Gorge, Tanzania) record orbitally paced changes in vegetation and hydroclimate, inferred from leaf wax carbon and hydrogen isotopes. Fire feedbacks between vegetation and climate are well-studied in modern savannah ecosystems, but there is less known about how they operate on longer timescales. Using polycyclic aromatic hydrocarbons (PAHs), a suite of molecules produced during biomass fires, we reconstructed paleo-fire activity in the Olduvai paleolake catchment from 1.9-1.8 Ma, and compared it with previous biomarker records of vegetation and hydroclimate. PAH-inferred paleo-fire from Olduvai Gorge Coring Project (OGCP) Core 2A appears to be paced by orbital obliquity (in contrast to the precessional pacing of vegetation change), which points to the influence of the “short rains” (i.e., Oct-Dec precipitation) on paleo-fire activity at Olduvai Gorge from 1.9-1.8 Ma. In modern environments, frequent fires facilitate mineral weathering and enhance landscape erosion. Using bulk organic and inorganic proxies, we assessed the relationship between paleo-fire and the sources, accumulation, and stratigraphic architecture of Paleolake Olduvai sediments. The influence of fire on vegetation and landscape processes may have additionally impacted the distribution and availability of food resources for hominins at Olduvai, potentially exposing exploitable resources such as rodent burrows or plant underground storage organs.