Collaborative Research: 800-Year Trends in Anthropogenic and Marine Biogenic Sources of Arctic Sulfate Aerosol

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In recent decades, the Arctic has experienced the most rapid rate of warming around the globe. Satellite observations show that sea ice has been declining since at least 1980. The Arctic is projected to be ice-free during summer starting between 2050-2100 C.E. Both the open ocean and sea ice host a range of microscopic algal or phytoplankton communities, and the response of these algal communities to melting sea ice can be important to both the marine and atmospheric environment, but is unknown. This project aims to detect, describe and understand such response by studying sulfur-containing substances preserved in a Greenland ice core. Oceanic phytoplankton are the largest natural source of sulfur aerosol to the atmosphere. Sulfur-containing aerosol has a cooling impact on climate because it efficiently reflects sunlight back to space. As the emission of sulfate from combustion of fossil fuels has declined due to effective air pollution mitigation, natural sources are becoming more important. However, it is unclear how decreasing sea ice affects the abundance of natural sulfate aerosol in the Arctic. This project will measure two indicators of the phytoplankton source of sulfur aerosol in a Greenland ice core record dating from 1200 - 2006 C.E. These measurements will reveal any trends in the phytoplankton source of sulfur aerosol resulting from melting sea ice, and will inform future predictions of Arctic primary productivity and climate. Insight from this project will prove valuable for forecasting the future response of phytoplankton emissions and climate-cooling aerosols to melting sea ice. This award will provide training for two graduate and several undergraduate students at the University of Washington and South Dakota State University, and will support outreach activities such as demonstrations at the annual Polar Science Weekend at the Pacific Science Center in Seattle, WA.This award will support measurements of the sulfur isotopic composition of sulfate and the concentration of methanesulfonic acid (MSA) in a Greenland ice core dating from 1200 - 2006 C.E. Oceanic phytoplankton emit dimethylsufide (DMS) into the atmosphere. Once in the atmosphere, DMS is oxidized to the sulfur aerosols sulfate and MSA. Sulfur isotopes of sulfate originating from DMS oxidation are distinct from other sources of sulfate, while MSA originates only from DMS oxidation. This project will provide the first observational constraint on variations in the phytoplankton source of sulfur aerosol over the past 800 years, with a particular focus on the last 35 years of the record when we know that Arctic sea ice has declined. Global model sensitivity studies will complement the ice-core record by providing insight into the sensitivity of the abundance of Arctic sulfur aerosol to phytoplankton emissions and transport, and provide quantitative insight into the climate impacts of this natural source of sulfur aerosol.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.