Temporal variability of rainwater iron speciation at the Bermuda Atlantic Time Series Station

Abstract

[1] Diurnal and seasonal variations in rainwater iron speciation were investigated during a summer and winter cruise aboard the RV Endeavor at the Bermuda Atlantic Time Series Station. Concentrations of total Fe, Fe(II), and Fe(III) were all higher in rainwater falling at BATS during the summer relative to winter cruise. Iron speciation displayed marked diel variability with a 200-fold higher Fe(II)(aq)/Fe(III)(aq) ratio in rain received between 1200 and 1800 local time (LT) relative to late evening or early morning summer rain. The higher Fe(II)/Fe(III) ratio in the afternoon indicates Fe(II) is produced at the expense of Fe(III) during the course of the day, suggesting photochemical processes are important in controlling iron speciation in marine rains falling over the open ocean. Experiments utilizing authentic rainwater collected at BATS during both summer and winter cruises demonstrate that rainwater Fe(II)(aq) is stabilized against oxidation and precipitation for more than 4 hours after mixing with BATS seawater. Preliminary results suggest this stabilization is the result of organic complexation of Fe in rainwater. Owing to the isolation of BATS from riverine sources of Fe, rainwater is the predominant source of soluble and stable Fe(II) in this region of the North Atlantic.

Impact of natural organic matter on H2O2-mediated oxidation of Fe(II) in a simulated freshwater system

“…Increasing the pH of such samples to that of seawater in mixing experiments has also demonstrated the continued stability of ferrozinelabile Fe(II) on the timescale of several hours (Kieber et al, 2001b(Kieber et al, , 2003. The Fe(II)L 2 complex proposed in this model is suggested to behave similarly.…”

Impact of anthropogenic combustion emissions on the fractional solubility of aerosol iron: Evidence from the Sargasso Sea

“…In this context, the soluble fraction of iron in wet deposition is an important unknown. The inorganic and organic acids present in rainwater are thought to promote the reductive dissolution of aerosol iron [ Zhu et al , 1993; Pehkonen et al , 1993; Siefert et al , 1994; Spokes et al , 1994; Spokes and Jickells , 1995; Kieber et al , 2003; Hand et al , 2004]. On this basis, one might predict that the fractional solubility of iron in wet deposition to the Sargasso Sea is considerably higher than that estimated for dry aerosols at any one time.…”

The role of air masses on iron concentrations in wet atmospheric deposition over the urbanized coastal zone of the Gulf of Gdańsk

“…This method requires little water and few manual activities, minimising the risk of contamination. Moreover, this method is recommended in the latest available publications concerning the determination of iron speciation in rainwater (Kieber et al 2001a(Kieber et al , 2001b(Kieber et al , 2003.…”