Holocene black carbon in Antarctica paralleled Southern Hemisphere climate

Black carbon (BC) and other biomass-burning (BB) aerosols are critical components of climate forcing but quantification, predictive climate modeling, and policy decisions have been hampered by limited understanding of the climate drivers of BB and by the lack of long-term records. Prior modeling studies suggested that increased Northern Hemisphere anthropogenic BC emissions increased recent temperatures and regional precipitation, including a northward shift in the Inter-Tropical Convergence Zone (ITCZ). Two Antarctic ice cores were analyzed for BC and the longest record shows that the highest BC deposition during the Holocene occurred ~8-6k years before present in a period of relatively high austral burning season and low growing season insolation. Atmospheric transport modeling suggests South America (SA) as the dominant source of modern Antarctic BC and, consistent with the ice-core record, climate model experiments using mid-Holocene and preindustrial insolation simulate comparable increases in carbon loss due to fires in SA during the mid-Holocene. SA climate proxies document a northward shifted ITCZ and weakened SA Summer Monsoon (SASM) during this period, with associated impacts on hydroclimate and burning. A second Antarctic ice core spanning the last 2.5k years documents similar linkages between hydroclimate and BC, with the lowest deposition during the Little Ice Age characterized by a southerly shifted ITCZ and strengthened SASM. These new results indicate that insolation-driven changes in SA hydroclimate and BB, likely linked to the position of the ITCZ, modulated Antarctic BC deposition during most of the Holocene and suggests connections and feedbacks between future BC emissions and hydroclimate. Plain Language Summary Future anthropogenic-driven climate change may impact wildfires, yet predicting future changes is hampered by few long-term records of natural wildfires, particularly for the Southern Hemisphere. We document large variations in black carbon deposition during the past 14,000 years from an Antarctic ice core. Black carbon is a tracer for wildfires and a significant climate forcing agent. We show that black carbon in Antarctica closely followed Southern Hemisphere hydroclimate and strength of the South American Summer Monsoon. With future predictions showing significant low-latitude changes in precipitation under increased emissions, the climate-fire linkages presented here suggest future changes South American biomass burning

Improved estimates of preindustrial biomass burning reduce the magnitude of aerosol climate forcing in the Southern Hemisphere.

Fire plays a pivotal role in shaping terrestrial ecosystems and the chemical composition of the atmosphere and thus influences Earth’s climate. The trend and magnitude of fire activity over the past few centuries are controversial, which hinders understanding of preindustrial to present-day aerosol radiative forcing. Here, we present evidence from records of 14 Antarctic ice cores and 1 central Andean ice core, suggesting that historical fire activity in the Southern Hemisphere (SH) exceeded present-day levels. To understand this observation, we use a global fire model to show that overall SH fire emissions could have declined by 30% over the 20th century, possibly because of the rapid expansion of land use for agriculture and animal production in middle to high latitudes. Radiative forcing calculations suggest that the decreasing trend in SH fire emissions over the past century largely compensates for the cooling effect of increasing aerosols from fossil fuel and biofuel sources

Bahamian speleothem reveals temperature decrease associated with Heinrich stadials

Temperature reconstructions across Heinrich stadials 1-3 are presented from an absolute-dated speleothem from Abaco Island in the Bahamas to understand the nature of climate change across these intervals in the subtropical Atlantic. The stalagmite carbonate record, dated by the U-Th geochronometry technique, includes higher