Aerosol iron and aluminum solubility in the northwest Pacific Ocean: Results from the 2002 IOC cruise

Abstract

[1] Dust aerosol samples were collected across the western North Pacific Ocean during May-June 2002. Samples were analyzed for soluble aerosol Fe(II), Fe(II) + Fe(III), and Al as well as major cations and anions. The aerosol samples were leached using a 10 second exposure to either filtered surface seawater or ultrapure deionized water yielding a measure of the ''instantaneous'' soluble fraction. A variety of analytical methods were employed, including 57 Fe isotope dilution high-resolution ICP-MS, energy dispersive X-ray fluorescence, graphite furnace AAS, ion chromatography, and the FeLume chemiluminescent technique. Fe was found to be more soluble in ultrapure deionized water leaches, especially during periods of higher dust concentrations. Fe solubility averaged 9 ± 8% in ultrapure water leaches and 6 ± 5% in seawater leaches. Significant correlations were found between both soluble aerosol Fe T and soluble Fe(II) concentrations and aerosol acidity; however, the percentages of soluble aerosol Fe T and Fe(II) did not correlate with aerosol acidity We also did not observe significant correlations between total and soluble aerosol Fe concentrations and the concentrations of either particulate Fe or dissolved Fe in surface waters.

How well can we quantify dust deposition to the ocean?

“…For example, applying a sequential leach method to the aerosol samples used in this study, Shelley et al [54] found the Sol Al obtained using the acetic acid (pH 2) hydroxylamine hydrochloride ('acetate') leach of Berger et al [55] to be about an order of magnitude greater than for the same samples using the instantaneous deionized water ('DI') leach of Buck et al [56]. For the stations between Africa and the Cape Verde Islands, Sol Al obtained using the acetate leach averaged about 10% while Sol Al determined using the DI leach varied between 0.3% and 1.0%.…”

“…In this context, thorium has an advantage because one isotope ( 232 .3)) using measured dissolved 232 Th inventories and estimates of aerosol Th solubility based on (a) the instantaneous deionized water leach (DI, [56]) and (b) the acetate-reducing agent leach (acetate, [55]). In each case, the residence time of Th is derived from the 234 U-230 Th radioactive disequilibrium integrated from the surface to the depth to which the 232 Th inventory is integrated (either 50 m or 500 m).…”

“…For the stations between Africa and the Cape Verde Islands, Sol Al obtained using the acetate leach averaged about 10% while Sol Al determined using the DI leach varied between 0.3% and 1.0%. .2)) following the approach of Measures & Brown [46] using measured dissolved Al inventories in the upper 50 m [50] and estimates of aerosol Al solubility based on the instantaneous deionized water leach (DI, [56]) and the acetate-reducing agent leach (acetate, [55]). A residence time for dissolved Al in the upper ocean of 5 years was assumed for all stations.…”

Seasonal characteristics of tropical marine boundary layer air measured at the Cape Verde Atmospheric Observatory

“…Typical flow rates were 20-30 L min -1 per filter, giving total sample volumes of 50-100 m 3 . Samples were stored frozen (-20 °C) until analysis in the UK, as storage at aerosol solubility decreases when stored at room temperature (Buck et al, 2006) .…”

“…In addition, the metal composition was characterized from the size segregated aerosol samples using total reflection X-ray fluorescence spectrometry (TXRF, Bruker AXS, Germany) (Müller et al, 2010 fraction of metals and nutrients in the samples. 100 ml of ultrapure water was passed through the filter using a filtration apparatus and a small vacuum pump (Buck et al, 2006). The resulting filtrate was analysed for nutrients (NO 3 -, NH 4 + , PO 4 3-, DOC, DON) using a standard nutrient autoanalyser, anions (Cl -and SO 4 2-) using ion chromatography, high temperature combustion TOC-TDN analyser (TOC-V-CPN, Shimadzu), and a broad suite of metals measured using ICP-MS (Thermo, X-series).…”