Isotopic records of ancient wildfires in C4 grasses preserved in the sediment of the Ross Sea, Antarctica

We report the carbon isotopic (d¹³C and D¹⁴C) values determined for total organic carbon (TOC) and pyrogenic carbon (PyC) preserved in two sediment cores collected from the slope of the Ross Sea, Antarctica, in 2017. PyC contributed 10-28% of the TOC in the cores. The d¹³C values of PyC ranged from -10.9‰ to -17.2‰, with distinct differences from the d¹³C values of TOC (-24.1‰ to -26.1‰) in the sediments. The radiocarbon ages of PyC were 9540 and 8570 years old on average in the two cores but were thousands of years younger than the ages of TOC at the same core depth. These isotopic records provide strong evidence indicating that the PyC preserved in the sediments of the Ross Sea was produced from ancient wildfires predominantly in C₄ vegetation and that PyC was transported to Antarctica in the atmosphere. These results suggest that ancient wildfires dominated by C₄grasslands likely occurred frequently on a large scale and at high intensity in the Southern Hemisphere during the Holocene period of 5000-12,000 years ago, which was related to climate change.