Dissolution of aerosol iron in the surface waters of the North Pacific and North Atlantic oceans as determined by a semicontinuous flow‐through reactor method

Abstract

[1] Aerosol iron dissolution in oceanic waters is determined with a semicontinuous batch-leaching method. In this procedure, aerosol samples that were collected from the marine boundary layer were leached in an all-Teflon flow-through reaction chamber by multiple aliquots of $40 mL 0.4 mm filtered oceanic surface water collected using ultraclean techniques. Each aliquot of seawater is permitted to leach the aerosol sample in the reaction chamber for a predetermined time before the seawater solution is separated from the aerosol sample by a 0.4 mm Nucleopore filter membrane. A new aliquot of seawater is then added to the leaching chamber to continue leaching the same aerosol particles retained on the filter. The procedure is repeated with progressive increases in leaching time. The method allows the Fe released from the aerosol particles to be continuously removed from the system before saturating the complexation capacity of the seawater-leaching solution or adsorbing onto the leaching chamber wall. This method results in accurate measurements of seawater-dissolvable labile aerosol Fe that is independent of the total aerosol Fe concentrations in the sample. The aerosol Fe solubility determined using this method ranges from 3.5 ± 1.5% for the North Atlantic during September 2005 to 5.7 ± 2.0% for the North

Influence of anthropogenic combustion emissions on the deposition of soluble aerosol iron to the ocean: Empirical estimates for island sites in the North Atlantic

“…The composition of and operational solubility of iron in the North African soil dust aerosols are relatively well constrained by previous studies (Eglinton et al, 2002;Baker and Jickells, 2006;Sedwick et al, 2007;Wu et al, 2007). In contrast, the composition of and operational solubility of iron in the putative North American aerosol end member is poorly constrained by the few V-rich FeATMISS aerosol samples, all of which likely contain some proportion of North African soil dust.…”

“…13 has been expanded from Fig. 1 to include additional data on measured aerosol iron solubility vs. total aerosol iron loading from the studies of Baker et al (2006a,b) and Wu et al (2007). We note that the data shown in Fig.…”

“…A wide variety of experimental methods have been used to estimate the proportion or percentage of aerosol iron that dissolves in the surface ocean, which we term the 'fractional solubility of aerosol iron' (e.g., Zhuang et al, 1990;Spokes and Jickells, 1995;Zhu et al, 1997;Bonnet and Guieu, 2004;Chen and Siefert, 2004;Hand et al, 2004;Chuang et al, 2005;Desboeufs et al, 2005;Baker et al, 2006a;Buck et al, 2006;Wu et al, 2007). It is important to recognize that these experimental methods provide operational definitions of the fractional solubility of aerosol iron, and cannot faithfully reproduce the dissolution of aerosol particles in the surface ocean.…”

A review of natural aerosol interactions and feedbacks within the Earth system

“…For example, Joutsensaari et al (2005) and Mentel et al (2009) studied photochemical production of aerosols using living plants in environmental chambers. In the ocean, iron solubility of real aerosol in natural sea water has been studied in a flow reactor (Wu et al, 2007), and the physical and chemical properties of aerosol generated from bubble bursting in natural sea water has been measured (Keene et al, 2007). Mesocosm experiments that probe the response of natural marine (Vogt et al, 2008) and terrestrial (Pegoraro et al, 2005) systems are valuable controlled experiments.…”

The vertical distribution of iron stable isotopes in the North Atlantic near Bermuda

“…We assume that the first pulse of iron release into seawater is Fe(II) or very soluble iron salts, and so it is not representative of iron desorption rates from particles in the water column. By modeling first-order kinetics for the subsequent slower iron release, however, we can use particle leach data from seven aerosol samples from the Gulf of Alaska, equatorial Pacific, and subtropical Pacific [AguilarIslas et al, 2010] [Wu et al, 2007]. Also, the soluble fraction of Saharan dust was found to dissolve entirely in natural seawater within 1 day [Mendez et al, 2010].…”