Title: Atmospheric records of carbonyl sulfide, methyl chloride, and acetylene during the Holocene from polar ice cores
Abstract: Carbonyl sulfide, methyl chloride, and acetylene are three atmospheric trace gases we measure in air extracted from polar ice cores at the UCI ice core trace gas laboratory. Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere and contributes to stratospheric sulfate aerosols. Methyl chloride (CH3Cl) is a naturally occurring halogenated methane that makes a significant contribution to the stratospheric halogen load. Acetylene (C2H2) is a hydrocarbon, for which wildfires are a major source. In this talk, I will present new data from the most recent US deep ice core drilled at the South Pole (SPICEcore: spicecore.org) covering the Holocene. Both the CH3Cl and COS records are characterized by a modest but sustained long-term increase through the last nine thousand years of the Holocene. What we know about the biogeochemistry of these trace gases point to biomass burning as the most plausible common mechanism that can cause correlated change in atmospheric levels of CH3Cl and COS. However, biomass burning is a relatively small term in the atmospheric budgets of both gases and driving even a modest rise in their global atmospheric levels requires a substantial increase in global fire emission. Acetylene data provide direct evidence for large changes in fire emissions that can drive the observed increases in trace gas levels. There is evidence in the ice core trace gas data for shorter period variability that were likely driven by changes in fire emissions. The results have broader implications as fires are a source of most atmospheric trace gases and aerosols.