PLIO-PLEISTOCENE WILDFIRES ACCELERATED SOIL EROSION OVER SOUTH ASIA, BURYING TERRESTRIAL ORGANIC MATTER IN THE NICOBAR FAN

Modern-day observation suggests the production of Pyrogenic Carbon (PyC) and the proliferation of grassland after the fire is a long-term carbon sink via accelerated erosion across the continent and the burial of Terrestrial Organic Carbon (TOC) in the Ocean. The excess burial of PyC, expansion of C₄ grassland, and enhanced soil erosion was observed during the Plio-Pleistocene boundary. However, the role of Wildfire in the burial of TOC is unscrutinized. We have chosen the past 4-million-year sedimentary succession record from the Nicobar fan IODP exp here. 362 site U1480 received sediments primarily from the Eastern Himalayas and Indo-Burma. The river draining out from South Asia contributes 27.4% of suspended sediments,10-20% of TOC, and ⁓20.5% of Black Carbon (PyC & fossil fuel combustion)to the global Ocean and making Nicobar fan sediments as an archetypal to the test the hypothesis. We reconstructed paleo-wildfire changes by analyzing stable nitrogen isotope of fixed ammonium in the clay and PyC Mean Accumulation Rate (MAR). Our paleo-wildfire proxies suggest frequent wildfire activity during the Plio-Pleistocene boundary and sporadic wildfire activity before and after the boundary. We analyzed the stable carbon isotope of TOC to constrain the vegetational type of burning biomass. We observed a tandem between Wildfire and concomitant grassland growth similar to modern-day during Plio-Pleistocene boundary. Furthermore, we reconstructed the wildfire kindred erosion rate using the abundance of fixed NH₄⁺ MAR. Our results indicate Wildfire increased the erosion rate by 7.3±1.1 times during the Plio-Pleistocene boundary compared to Late Pleistocene. We also quantified the Terrestrial Organic Carbon buried in the Nicobar fan using TOC MAR. The temporal association between erosion rate and TOC MAR shows that wildfire-related soil erosion accelerated TOC burial, which coincides with the CO₂ reduction in the atmosphere. Comparing the carbon burial rate and wildfire proxies indicates that the recurrent Wildfire during the Plio-Pleistocene boundary might have caused TOC's heightened burial and played a significant role in CO₂ drawdown.