The overall goal of the GEOTRACES program is to improve our understanding of the sources, distributions, and removal processes of geochemically significant trace elements and isotopes (TEIs) in the worldÆs oceans. The importance of measuring TEI concentrations and deposition to the oceans for aerosols and rainfall is described in the GEOTRACES Science Plan (2006). Atmospheric "dust" (aerosols) and rainfall deposition can be a significant source of TEIs in the North Atlantic, and will be strongly affected by anthropogenic emissions from North America and Europe and dust emission from northern Africa ("Saharan dust"). Desert dust will be a significant source of the essential biologically required element, iron (Fe), despite the relatively lower solubility compared to Fe in anthropogenic (pollutant) aerosols. Significant enrichment in surface waters of the North Atlantic from atmospheric deposition can be seen in the distributions of dissolved aluminum (Al) and Fe, as well as manganese (Mn) and cobalt (Co), while dissolved lead (Pb) is elevated throughout the upper ocean in the North Atlantic. Al is a tracer for atmospheric dust deposition, while Mn and Co are essential trace elements for phytoplankton. Pb isotopes can be used to pollutants in air masses from North America and Europe, while neodymium (Nd) isotopes can be used to constrain the ages of aerosol source rocks. Atmospheric deposition of nitrate and ammonia may also be significant across the North Atlantic, and the isotopic composition of the nitrogen and oxygen in aerosol nitrate can be used to evaluate anthropogenic source contributions. We recognize that atmospheric deposition has strong seasonality, such that ship-board sampling cannot be expected to reflect the average annual aerosol concentration. However, the proposed cruise track and timing should enable us to chemically characterize relatively distinct samples of North American aerosols, European aerosols, and Saharan dust from the beginning, middle, and end of the cruise. The atmospheric deposition research will also complement the water column TEI research, where TEIs with widely different residence times in the upper ocean (such as Mn>Al>Fe=Nd>Th) will be studied. This proposal was funded to collect aerosol and rainfall samples on the GEOTRACES North Atlantic section cruise in 2011. Three high-volume aerosol samplers and two automated rain samplers had already been acquired using previous NSF funding. They were used to collect aerosols on acid-cleaned Whatman-41 (cellulosic) filters (for inorganic trace elements and their isotopes - TEIs) and pre-combusted quartz microfiber (QMA) filters (for organic species, Hg, and nitrogen compounds). One sampler was equipped with a 5-stage Sierra-style slotted cascade impactor to collect size fractionated aerosols (from >7 µm to <0.49 µm). With collaboration from researchers around the world, the 24-hour integrated aerosol samples, and event-based rain samples, are being analyzed for a large suite of TEIs. Because the microbial organisms in the upper ocean respond to the input of dissolved TEIs, we have analyzed all aerosol samples for ultra-pure water soluble, seawater soluble, and total (residual) TEIs. Rain samples have been analyzed both filtered and unfiltered, to quantify the soluble and particulate TEI concentrations. Air mass back-trajectories can help us understand where the aerosols originated, and have been modeled for all sampling days using the NOAA HySplit program. We also requested some funding for the analysis of seawater samples from the towed-fish and GEOTRACES Trace Metal rosette samplers. Those samples, and the seawater aerosol solubility samples, have been analyzed in our lab for Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb using a shore-based column extraction method utilizing isotope dilution and high-resolution magnetic sector ICPMS. Education and training of graduate students are essential compo...
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