COS 151-4 - Quantifying paleofire emissions from black carbon in Southern hemisphere lake sediments

Background/Question/Methods

Wildfires are an important ecological agent that has driven ecosystem change since millennia. Black carbon aerosols emitted from biomass (and fossil fuel) burning contribute to radiative forcing of climate. Understanding long-term black carbon dynamics is crucial to quantify how humans have modified natural burning regimes and to disentangle biomass and fossil-fuel burning sources during the Industrial Era of the past 150 years. For example, previous charcoal-based studies from New Zealand lakes suggest a strong increase in local fire activity in ecosystems with rare fire activity after the arrival of the Polynesian Māori (1200-1300 CE) that potentially resulted in increased black carbon aerosols over vast areas in the Southern Hemisphere. Existing black carbon records, however, are limited to remote ice core sites far from potential emission sources. This hampers linking black carbon records to local lake sediment records from charcoal analyses. Directly measuring black carbon near the sources in lake sediments may provide an important link between source emissions and the observed black carbon deposition on the Antarctic ice sheet. We developed black carbon records from eight low-latitude lakes across New Zealand, Tasmania, Africa, and Patagonia using an incandescence‐based Single Particle Soot Photometer (SP2)-method for black carbon measurements in lake sediments.

Results/Conclusions

Our data suggest that black carbon in Southern hemisphere lake sediments is spatially variable. While the black carbon record from the sheltered mountain sites, Horseshoe Lake on New Zealand’s South Island and Wombat Pool in Tasmania, shows striking similarities during the past millennium with previous macroscopic charcoal, other sites that are more likely to receive black carbon from long-distance sources show less similarity between black carbon and charcoal trends. Such distal burning emissions are not captured in the larger charcoal fraction. Our black carbon dataset from the Southern hemisphere may provide quantification of a key emission source for black carbon deposition variability on the Antarctic ice sheet and a direct link between black carbon source emissions and black carbon records in remote polar ice archives. Moreover, we close a geographic gap of past Southern Hemisphere mid-latitude black carbon emissions that may improve climate and fire models, and ultimately inform policy decisions.