Miocene fire intensification linked to continuous aridification on the Tibetan Plateau

Although fire is considered an important factor in global vegetation evolution and climate change, few high-resolution Miocene fire records have been obtained worldwide. Here, two independent micro-charcoal-based fire records from the northern Tibetan Plateau were analyzed; both show similar trends in micro-charcoal concentrations through time, with low abundances in the warmer Middle Miocene Climate Optimum (18-14 Ma) followed by a continuous increase throughout the late Miocene (14-5 Ma) cooling. Our detailed statistical analyses show that the micro-charcoal concentration trend is highly positively correlated to the trend in oxygen isotopes (delta O-18, r = 0.94) and xerophytic species (%(Xero), r = 0.95). We propose that the intensified fire frequency on the Tibetan Plateau mainly originated from the forest-steppe ecotone as a result of the continuous aridification in winter driven by the global cooling and decreased atmospheric pCO(2) that occurred during 18-5 Ma, with a secondary control by the tectonic activity of the northern Tibetan Plateau.