Isotopic Records of Ancient Wildfires in C₄ Grasses Preserved in the Sediment of the Ross Sea, Antarctica

Abstract

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 δ13C values of PyC ranged from −10.9‰ to −17.2‰, with distinct differences from the δ13C values of TOC (−24.1‰ to −26.1‰) 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 C4 vegetation and transported to Antarctica in the atmosphere. We suggest that ancient wildfires in predominantly C4 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.

Fire in the Earth System: Introduction to the Special Collection

“…Evidence of fire is even preserved in sediments of the Ross Sea, Antarctica, from which Ren et al. (2022) presented a pyrogenic carbon record that suggests frequent large fires in South America from late Pleistocene to mid‐Holocene time. Li et al.…”

“…A study by Ren et al. (2022) projected burned area in a semiarid watershed of Idaho, USA. Their model results indicated an increase in burned area by the 2040s followed by a decrease in the 2070s owing to fire‐limiting thresholds of fuel and flammability that vary with complex vegetation responses to increasing CO 2 and temperature in a warming climate.…”

“…Brey et al (2020) examined how future projected increases in vapor pressure deficit and other environmental conditions (precipitation, evaporation, relative humidity, root-zone soil moisture, and wind speed) could affect the U.S. summertime wildfire burn area. A study by Ren et al (2022) projected burned area in a semiarid watershed of Idaho, USA. Their model results indicated an increase in burned area by the 2040s followed by a decrease in the 2070s owing to fire-limiting thresholds of fuel and flammability that vary with complex vegetation responses to increasing CO 2 and temperature in a warming climate.…”