EAGER: Improving Ice Core Observations of Large Volcanic Eruptions, and Their Effect on Global Climate Change, with a Novel Sulfur Isotope Method

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The attribution of modern planetary scale warming between forcings associated with solar output, greenhouse gases, and both natural (volcanic) and anthropogenic aerosols is a challenging and important problem. To date the cooling effect of large volcanic eruptions has been determined by measuring sulfate concentrations in ice cores. However, only volcanoes that inject sulfur dioxide into the stratosphere can cause sustained global cooling as the rain out of new aerosols in the troposphere is very efficient. We need a way to distinguish volcanoes with large amounts of sulfate in the ice core record, but no stratospheric impact (like the Mount St. Helens eruption), from those that reached the stratosphere, so that they can be taken out of the volcanic forcing function in climate attribution studies.Fortunately, injection of SO2 into the stratosphere leaves a mass independent isotopic signal on the sulfur of the resulting sulfate aerosols. This research, led by a professor at the California Institute of Technology, builds on a new technique for measuring sulfur isotopes on small samples that lowers the detection limit the relevant isotopic systems by over three orders of magnitude. This new method will be used to generate a time series of sulfur isotope variability in ice cores of the top 100 volcanic events of the last 1,000 years. The researchers will identify which volcanic eruptions actually entered the stratosphere and therefore caused a global climate cooling. These are the events that must be accounted for in climate warming attribution studies. The research will focus on an ice core from South Greenland. Certain events will be cross-checked in ice cores from Antarctic to confirm the global distribution of sulfate aerosol. The results of this work could be potentially transformative in changing our understanding of the sensitivity of climate to CO2 increases. Outcomes will inform educational outreach efforts. Funding also supports an early career scientist.