UC Irvine

Biomass burning plays a major role in climate variability, atmospheric chemistry, carbon cycling, and atmospheric dynamics. In order to understand the drivers of biomass burning and how fire activity will change in the future, it is necessary to investigate how it has varied in the past. Proxy records are needed for understanding the forcing and feedbacks related to fire that are required for developing algorithms for biomass burning in Earth System models. Progress in this field has been limited due to a lack of well-dated proxy records documenting regional variability in burning on millennial and centennial time scales.

In this dissertation, new ice core proxies are utilized to examine past trends in biomass burning. These proxies are organic chemicals (vanillic and p-hydroxybenzoic acids) produced by the incomplete combustion of lignin and commonly found in biomass burning aerosols. New analytical techniques utilizing high performance liquid chromatography, ion chromatography, and mass spectrometry were developed to measure ultra-trace levels of these compounds in polar ice cores. The abundance of these chemicals was measured in Arctic ice cores from Siberia, Greenland, and Svalbard.

The 3,000-year Siberian record shows strong multi-centennial variability in burning with a signal to noise ratio unprecedented in previous proxy burning records. This Siberian ice-core record shows that extended periods of elevated wildfire emissions in Siberia occurred simultaneously with changes in the strength of the Asian Monsoon and the episodic pulsing of ice-rafted debris in the North Atlantic Ocean known as the Bond Events. This is the first clear observational evidence linking wildfire activity to large-scale climate change on millennial timescales.

The 1,700-year Greenland and 750-year Svalbard records exhibit levels of these organic compounds that are considerably lower than those in Siberia, likely reflecting greater distance from the source regions. The variability of the two cores is similar, but quite different from the Siberian record. These differences suggest that the Siberian ice core records regional trends in fire, rather than an average across the high latitude northern hemisphere.

This study represents the first millennial scale ice core records of these organic aerosol tracers. The results show significant spatial and temporal variability that should add significantly to our understanding of the relationship between biomass burning and climate change. Further work will be needed to understand fully these signals and to use such information to compare these biomass burning signals to Earth system models.