Rain, wind or fire: which led the PAH fallout in Northern Madagascar across the Holocene?

Abstract. The interactions between wildfire, human and climate variability are not well understood. To have better predictions, past studies are useful for observing their behaviours on a long-time scale. To infer past fire activity, studies used charcoal and molecular biomarkers derived from biomass burning, such as Polycyclic Aromatic Hydrocarbons (PAHs). In the north of Madagascar, charcoals are of local origin and have shown increased abundance since 1000 cal a BP. In contrast, PAH are present throughout the Holocene. Therefore, PAHs likely provide a more regional information. Due to the seasonal wind regime, they are thought to originate from East Africa. However, the PAH signal pattern differs from the fire activity record of East Africa. Instead, it shows a similar pattern to precipitation variability in northern Madagascar. Higher PAH concentrations are observed during wetter period, whereas lower concentrations occur during drier periods. This suggest that PAH preservation is enhanced, which may facilitate leaching processes prior to their deposition in sediments. These results challenge the direct interpretation of PAH as straightforward indicators of fire events and dry periods.