Isotopic Records of Ancient Wildfires in C-4 Grasses Preserved in the Sediment of the Ross Sea, Antarctica

We report carbon isotopic values in total organic carbon (TOC) and pyrogenic carbon (PyC) preserved in two sediment cores from the Ross Sea, Antarctica. The delta C-13 values of PyC ranged from -10.9 parts per thousand to -17.2 parts per thousand, with distinct differences from the delta C-13 values of TOC (-24.1 parts per thousand to -26.1 parts per thousand) in the sediments. The radiocarbon ages of PyC were 9,128 and 8,410 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 was produced from ancient wildfires predominantly in C-4 vegetation and transported to Antarctica in the atmosphere. We suggest that ancient wildfires in predominantly C-4 grasslands likely frequently occurred on a large scale and at a high intensity in the Southern Hemisphere during the last deglaciation to mid-Holocene period of 14,800-4,200 years ago.