LDRD Seminar Series: ‘Desert Dust and Pollution: An Iron Recipe for Ocean Biota?’
Atmospheric and Climate Scientist Yan Feng (EVS), will discuss her Laboratory-Directed Research and Development (LDRD) sponsored work at the LDRD Seminar Series presentation Tuesday, June 20, 2017.
“Desert Dust and Pollution: An Iron Recipe for Ocean Biota?” begins at 12:30 p.m. in the Bldg. 203 Auditorium. All are welcome to attend.
Iron is essential for organisms in the ocean. Without iron, chlorophyll cannot be synthesized, nor can atmospheric nitrogen be fixed into bioavailable nutrient for growth. In many oceanic regions, iron deficiency limits the “biological pump” or removal of carbon dioxides (CO2) from the atmosphere by phytoplankton. A major iron supply from the atmosphere to the global ocean is the deposition of dust particles that originate from deserts. Since most photosynthetic aquatic organisms can take up iron only in the dissolved form, it is critical to understand the solubility and in turn, bioavailability of iron in the atmospheric dust particles.
However, at present we lack a fundamental understanding about the iron mineralogy in various dust particles and their chemical processing in the atmosphere influenced by anthropogenic emissions of pollutants. This knowledge gap contributes to a large diversity in predicted global soluble iron deposition to the ocean among the state-of-art Earth System models [ESMs], and the estimated iron lifetime in the ocean ranges from several years to over six hundred years. The LDRD project strives to improve understandings of the chemical transformation processes of iron minerals in dust using the X-ray spectromicroscopy at the Advanced Photo Source (APS).
The synchrotron-based techniques have only recently been applied to the study of atmospheric particles. In the presentation, I will discuss the methodology of using the hard X-ray microscopy at the APS beamlines in the fluorescence mode to quantify elements such as iron, silicon, calcium, and aluminum in micron-sized atmospheric dust particles (10-7 to 10-5 meters) down to the trace level. Using the APS microspectropy beamlines (2-ID-D), we further determine the oxidization states of dust iron (iron (II) or iron (III)), which are closely linked to the iron solubility. Results from analysis of more than a hundred dust samples will be presented. These samples were collected from seven locations around the world: the Southern Ocean, the Mediterranean, the Atlantic Ocean, Hawaii, Bermuda, Patagonia and India. They represent a wide range of dust aerosol characteristics from different source regions and remote oceans.
Across all sampling locations, acidity related to anthropogenic pollutions is identified as the dominating factor controlling iron solubility in dust. When aerosol samples were near the neutral state (pH~6), iron solubility was low, and when samples were more acidic, below a pH of 4, the solubility of iron increased up to 35 percent. Samples near or passing over populated regions tended to contain more soluble iron. In addition, iron mineralogy and reductive iron transformation from iron (III) to iron (II) are also quantified on individual particles. These experimental studies provide observational support to the hypothesis that anthropogenic pollutions may influence the ocean primary productivity and carbon uptake through iron nutrient cycling. Finally, I will discuss ongoing applications of the data sets in atmospheric modeling and ESMs.
Yan Feng is an atmospheric and climate scientist in the Environmental Science Division and a Fellow with the Computation Institute at the University of Chicago. Her research work focuses on global life cycle of both naturally-emitted and man-made atmospheric particles such as dust, soot, sulfate, etc, and their impact on climate and environment. Feng is also interested in improving the accuracy of climate change predictions by Earth System models.
She has extensive experiences of modeling aerosols, clouds, and interactions with climate change, air pollution, and biogeochemical cycles using global and regional climate models. Feng has more than 20 peer-reviewed journal publications including Nature Geoscience, PNAS, and Geophysical Research Letters, and co-authored three book chapters. She contributed to the Third Assessment Report of the International Panel on Climate Change (IPCC), and co-authored “Atmospheric Brown Clouds: Regional Assessment Report with Focus on Asia,” published by the United Nations Environment Programme. Her work has more than 1,700 citations in Google Scholar. Prior to coming to Argonne in 2010, Feng did postdoctoral study at Scripps Institution of Oceanography, University of California, San Diego. She obtained her Ph.D. in Atmospheric Science (2005) and M.S. in Computer Science and Engineering (2002) both from the University of Michigan, Ann Arbor.