Iron speciation in coastal rainwater: concentration and deposition to seawater |
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| Institution: | 1. CB&I Federal Services, 17 Princess Road, Lawrenceville, NJ 08648, USA;2. Naval Air Warfare Center Weapons Division, China Lake, CA 93555, USA;1. Laboratoire des Sciences de l?Environnement Marin, Technopole Brest Iroise, Place Nicolas Copernic, Plouzané 29280, France;2. Department of Earth, Ocean and Atmospheric Sciences, Florida State University, 117 N. Woodward Avenue, Tallahassee, 32306 FL, USA;1. Environmental Chemical Processes Laboratory, University of Crete, 71003, Crete, Greece;2. Institute for Environmental Research and Sustainable Development, National Observatory of Athens, 15236, Athens, Greece;3. Laboratoire des Sciences du Climat et de l’Environnement, CNRS-CEA-UVSQ, 91191, Gif-sur-Yvette, France;4. The Cyprus Institute, Energy Environment and Water Research Center, Nicosia, Cyprus;5. NCSR “Demokritos”, INRASTES, Environmental Research Laboratory, 15310, Ag. Paraskevi, Greece |
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| Abstract: | More than half of the dissolved iron in rain collected in Wilmington, NC, USA, occurred as Fe(II)(aq). More than 80% of the dissolved iron in marine rain from several marine storms in both North Carolina and New Zealand was Fe(II)(aq). In almost all rain events Fe(II)(aq) was in excess of Fe(III)(aq). Rainwater is a significant source of iron to surface seawater and contributes approximately 1010 mol year?1 of dissolved plus particulate iron to surface seawater on a global scale, which is more than 30 times the amount of iron resident in the surface 10 m of seawater. The length of time atmospherically deposited dissolved iron remains in surface seawater is critical to its role as a phytoplankton nutrient because it is predominately the soluble form of Fe that is bioavailable. Earlier studies have demonstrated that Fe(II)(aq) oxidizes rapidly in seawater. Our experiments utilizing authentic rainwater with ambient concentrations and speciation of iron clearly demonstrate, however, that rainwater Fe(II)(aq) is stabilized against oxidation for more than 4 h in seawater and rainwater Fe(III)(aq) is protected against rapid precipitation when added to coastal or oligotrophic seawater. These results are significant because they show rainwater deposited Fe does not behave as previously thought based on earlier kinetic work on non-rainwater Fe(II) oxidation in seawater. Rainwater, therefore, is an important source of soluble, stable Fe(II)(aq) to surface seawater. |
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