UC Irvine

Biomass burning plays a major role in atmospheric chemistry, carbon cycling, and climate. To understand and better predict how biomass burning may change in the future, it is important to investigate how biomass burning has varied in the past. Proxy records of biomass burning over long time periods are necessary to identify the link between biomass burning and climate. This information is needed by Earth system models to make accurate projections about future climate change and biomass burning.

In this dissertation, new ice core measurements are used to reconstruct biomass burning variability over the last 2,000 years. The trace gases ethane and acetylene are released to the atmosphere during biomass burning events. New analytical techniques utilizing a wet-extraction method coupled with gas-chromatography and high-resolution mass spectrometry analysis were developed to measure these gases in polar ice cores. The abundance of ethane and acetylene were measured in ice cores from Summit, Greenland, West Antarctic Ice Sheet (WAIS) Divide, Antarctica, and South Pole, Antarctica.

The ice core ethane and acetylene records exhibit similar temporal variability over the 2,000-year period. Over Greenland, little variability is observed in the ethane and acetylene levels. Over Antarctica, they both decline substainitally after 1500 CE, ethane by roughly 30% and acetylene by 50%. Using chemistry transport modeling, this decline in Antarctic ethane and acetylene was attributed to a decline in biomass burning emissions in the non-boreal (tropical) biome, rather than the boreal forests, from the warmer Medieval Period to the cooler Little Ice Age.

My study presents the first millennial scale record of these trace gases in polar ice cores and demonstrates that long-term paleo-climate records from these reactive, trace-level gases are attainable. The results show spatial and temporal variability in biomass burning emissions which were likely driven by climate. More work is needed to extend these records further back in time to periods where there is less influence by human activity and where there is a broader range of climatic variation in order to fully tease apart and quantify the climatic, rather than human, controls over fire in order to aid in validation of Earth system models.