Aromatic acids in a Eurasian Arctic ice core: a 3000-year proxy record of biomass burning

Abstract. Wildfires and their emissions have significant impacts on ecosystems, climate, atmospheric chemistry and carbon cycling. Well-dated proxy records are needed to study the long-term climatic controls on biomass burning and the associated climate feedbacks. There is a particular lack of information about long-term biomass burning variations in Siberia, the largest forested area in the Northern Hemisphere. In this study we report analyses of aromatic acids (vanillic and para-hydroxybenzoic acids) over the past 3145 years in the Eurasian Arctic Akademii Nauk ice core. These compounds are aerosol-borne, semi-volatile organic compounds derived from lignin combustion. The analyses were made using ion chromatography with electrospray mass spectrometric detection. The levels of these aromatic acids ranged from below the detection limit (.01 to .05 ppb) to about 1 ppb, with roughly 30 % of the samples above the detection limit. In the preindustrial late Holocene, highly elevated aromatic acid levels are observed during four distinct periods (1180–660 BCE, 180–220 CE, 380–660 CE, and 1460–1660 CE). The timing of these periods coincides with the episodic pulsing of ice-rafted debris in the North Atlantic known as Bond events. Aromatic acid levels also are elevated during the onset of the industrial period from 1780 to 1860 CE, but with a different ratio of vanillic and para-hydroxybenzoic acid than is observed during the preindustrial period. This study provides the first millennial scale record of aromatic acids. It clearly demonstrates that coherent aromatic acid signals are recorded in polar ice cores that can be used as proxies for past trends in biomass burning.