Collaborative Research: NSFGEO-NERC: Recent changes in Arctic biogenic sulfur aerosol from a central Greenland ice core

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This is a project jointly funded by the National Science Foundation’s Directorate for Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award recommendation, each Agency funds the proportion of the budget that supports scientists at institutions in their respective countries.Sulfur aerosols cool the climate. The amount of sulfur aerosol in the Arctic has varied dramatically in the recent past due mostly to sulfur aerosol from coal combustion. Sulfur emissions from coal combustion increased at the onset of the Industrial Revolution and have been decreasing since the 1970s because of the implementation of policies in the US and Europe to reduce air pollution. As human emissions decline, natural sulfur sources, such as from microscopic plants in the ocean, are becoming more important. The ocean biological source of sulfur aerosol may also be changing with a changing Arctic climate, particularly due to the melting of sea ice. This project will measure the two main chemical sources of sulfur aerosol in the Arctic, methane sulfonic acid (MSA) that is only from ocean biology, and sulfate, that originates from ocean biology, volcanoes, and combustion of coal and oil. The project will measure the sulfur isotopic composition of the chemicals in order to distinguish the ocean biological source from the other two sources and determine how large each source is and how fast each is changing. These measurements will provide a way to determine if and how ocean microscopic plants and their sulfur emissions are responding to Arctic climate change. This project will support the training of two graduate students and several undergraduate students. The students and PIs will participate in local outreach events in Seattle, WA and in Brookings, SD. We will work with the School of Ice to produce a new Virtual Field Lab geared towards students from middle school through early college. Ice-core observations of methane sulfonic acid (MSA) are used as a proxy for past oceanic biogenic productivity because MSA originates solely from the oxidation of dimethyl sulfide (DMS) emitted by ocean phytoplankton. Previous research using Greenland ice cores showed a detectable MSA decline since the 1800s, implying decreasing oceanic biogenic productivity. The use of MSA as a proxy for biogenic productivity relies on the assumption that the branching ratio of production of MSA versus sulfur dioxide (SO2) from DMS oxidation remains constant over time. However, recent examination of MSA and isotopic composition of sulfate in Greenland ice cores over the last 800 years shows that the ratio of MSA-to- biogenic sulfate (MSA/bioSO4) has not remained constant. This project hypothesizes that recent trends in MSA are driven by changes in oxidant abundances (e.g., NOx) that lead to a reduced yield of MSA and increased yield of SO2 during oxidation of DMS. The project will test this hypothesis by measuring ion and MSA concentrations and sulfur isotopes of sulfate in Greenland snow accumulated over the last 30 years. The last 30 years will cover the time when anthropogenic NOx emissions from North America and Europe began to decline (after the mid-1990s). In collaboration with University of St. Andrews in United Kingdom, the project will also measure sulfate isotopes at sub-seasonal resolution over the last 30 years from the proposed shallow ice cores in addition to select, discrete samples from archived ice in the preindustrial. Measuring biogenic sulfate at seasonal resolution since the preindustrial will allow for investigation of changes in the seasonality of biogenic sulfur aerosol in the Arctic resulting from changes in Arctic climate. To assist data interpretation, the global chemical transport model GEOS-Chem will be used to quantify the role of different oxidants on DMS oxidation as these oxidants have changed due to anthropogenic emissions. This project has broad implications for the ice-core, climate, and atmospheric chemistry communities because the results will improve our understanding of the impacts of Arctic climate change and anthropogenic emissions on biogenic sulfur aerosols, and thus our understanding of a potentially important climate feedback at high latitudes and future climate projections. This project will support the training of two graduate students and several undergraduate students at the UW and SDSU in ice-core processing, chemical and isotopic analysis, global modeling, and international collaboration. The students and PIs will participate in local outreach events in Seattle, WA and in Brookings, SD. The team will work with the School of Ice to produce a new Virtual Field Lab geared towards students from middle school through early college. The first-time partnership with University of St. Andrews will enhance scientific outcomes.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.