Award: OCE-1234166

Iron is an essential micronutrient for biological production in the ocean, and the scarcity of water soluble, bioavailable iron limits production in major portions of the worldÆs oceans. This production fuels oceanic food webs and draws carbon dioxide from the atmosphere providing a counter to anthropogenic carbon dioxide emissions that impact climate. The continents are major sources of iron to the ocean via atmospheric transport and deposition with mineral dusts and fossil fuel emissions. Recently, it has been discovered that iron from combustion sources is considerably more soluble than iron from mineral dusts, and therefore may have a bigger impact on ocean productivity on a per gram of iron basis. The reason for the different iron solubilities has, however, confounded the oceanography community. Aerosol particle acidity, photochemistry, mineralogy, and associations with organic matter have all been hypothesized to affect iron solubility. With this project, great progress has been made toward understanding the relationships between iron quantity and solubility and organic matter quantity and composition. This work took advantage of new state-of-the-art analytical instrumentation and statistical techniques that previously limited organic matter characterization. These techniques have allowed an assessment of whether water soluble organic matter (WSOM) in air particles from combustion sources can bind with co-emitted iron enabling that iron to be delivered to the ocean in a soluble form that phytoplankton can use. The intellectual merit of this study lies in it being the first of its kind to extensively characterize the various compounds in WSOM (the "molecular characteristics") and iron solubility on concurrently collected marine aerosol samples. Aerosol particles collected in the North Atlantic Ocean during two US GEOTRACES cruises that were influenced by aerosol particle emissions coming from the European, North African, and North American continents as well as marine aerosols were examined, and the following conclusions were drawn: 1) The amount of WSOM in aerosols from combustion-influenced continents (Europe and North America) is sufficient for WSOM-iron binding to raise iron solubility in a meaningful way. However, iron is so much more abundant than WSOM in North African-influenced aerosols that WSOM-iron binding could not have an impact on iron solubility. 2) The WSOM in aerosols coming from the European and North American continents has a very different composition than that coming from the North African continent. Those differences are due to combustion versus mineral dust sources and are manifest by the presence of compounds in WSOM that have components (carbonyl and carboxyl functional groups) known to bind with iron. 3) Statistical analyses identified the contributions of various sources of iron and other elements to aerosol particles over the ocean and showed that as pollution-related iron contributions and iron solubility increase for a given sample so does the abundance of the potential iron-binding components in WSOM compounds. In combination, these results demonstrate the probable associations of organic matter with iron and their impact, along with factors such as particle acidity and photochemistry, on iron solubility and bioavailability. This studyÆs broader impacts extend to its value for other scientific fields, the development of several young scientists, and outreach activities exposing young students to careers in oceanography. The use of the advanced analytical and statistical techniques in this project provided detail on the source-specific (N. America, marine, N. Africa, Europe) molecular composition of aerosol WSOM that cannot be acquired using other techniques. This information is invaluable for understanding organic matter impacts in the atmosphere and environment because the composition of this material both depends on its source and processing and determines its impact on climate, human h...