GEOTRACES Atlantic Section: Aerosol and Rainfall collection and analysis

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The overall goal of the International GEOTRACES program is to improve our understanding of the sources, distributions, and sinks of geochemically significant trace elements and their isotopes (TEIs) in the world?s oceans. After several years of coordination and planning, and following the 2008 and 2009 intercalibration efforts, US GEOTRACES is ready to move forward with the North Atlantic Ocean Section in 2010. The importance of measuringTEI concentrations and deposition to the oceans for aerosols and rainfall is described in the GEOTRACES Science Plan (2006). Aerosol 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 Fe despite the relatively lower solubility compared to Fe in anthropogenic aerosols. Significant enrichment in surface waters of the North Atlantic from atmospheric deposition can be seen in the distributions of dissolved Al and Fe, as well as Mn and Co (two other important bioactive TEIs), while dissolved Pb is elevated throughout the upper ocean in the North Atlantic. Pb isotopes can be used to distinguish North American and European air masses, while 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 N and O composition of nitrate can be used to evaluate anthropogenic source contributions. With funding under this award, researchers at the Florida State University will collect aerosol and rainfall samples on the GEOTRACES North Atlantic section cruise in 2010. Three high-volume aerosol samplers and two automated rain samplers have already been acquired using previous NSF funding. They are used to collect aerosols on acid-cleaned Whatman-41 (cellulosic) filters (for TEIs) and pre-combusted quartz microfiber (QMA) filters (for organic species, Hg, and nitrogen compounds). One sampler is equipped with a 5-stage Sierra-style slotted cascade impactor to collect size fractionated aerosols (from 7 um to 0.49 um). With collaboration from researchers around the world, the 24-hour integrated aerosol samples, and event-based rain samples, will be analyzed for a large suite of TEIs. The team and other collaborators will analyze all aerosol samples for ultra-pure water soluble, seawater soluble, and total (residual) TEIs. Rain samples will be analyzed, both filtered and unfiltered, to quantify the soluble and particulate TEI concentrations. Air mass back-trajectories for all sampling days will be modeled using the NOAA HySplit program. Additionally, seawater samples from the towed-fish and GEOTRACES Trace Metal rosette samplers will be analyzed 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. Broader Impacts: Education and training of graduate students are essential components of this research. The principal investigator regularly teaches undergraduate and graduate classes and incorporates the results of his fieldwork into lecture materials to motivate the next generation of Earth scientists. The entire research team will benefit from participation in large projects that will create multiple collaborations. The data will be submitted in a timely manner according to the requirements of NSF/OCE and the GEOTRACES Intercalibration program.