Abstract The C 4 Fire Hypothesis posits that an increase in fire catalyzed late Miocene C 4 grass expansion by clearing forest canopies to create open landscapes preferred by C 4 grasses, creating a positive feedback loop. However, few analyses have directly resolved the fire feedback, though components of the Fire Hypothesis have been supported. We reconstructed the fuel type of the late Miocene fire regime by analyzing the morphological and morphometric characteristics of charcoal found in Ocean Drilling Program Leg 184 Site 1146 (South China Sea; 19°27.40′N, 116°16.37′E) legacy cores and compared it to published paleoclimate data to understand the extent of the role of fire in the C 4 grass expansion. Charcoal accumulation rates (CHAR) show an increase of fire around the time of the expansion (7.3–6.9 Ma) and several statistical techniques demonstrate the robustness of this interval of increased CHAR. However, charcoal morphology and L:W ratio show no discernible transition in fuel type during this period, suggesting neither woody nor grassy vegetation were preferentially burnt. The CHAR increase aligns with regional climatic changes, including a decrease in monsoon intensity and increased aridification starting around 7 Ma. Though our data do not directly resolve the most dramatic C 4 increase in the region dating to 20 Ma, they do provide perspective on the final C 4 transition wherein modern vegetation conditions were established. Our findings partially support the Fire Hypothesis in that we see evidence for an increase in fire activity, but not preferential burning recorded in the South China Sea as initially argued.
Barney et al. (Mon,) studied this question.