Spatial and particle size distributions of atmospheric dissolvable iron in aerosols and its input to the Southern Ocean and coastal East Antarctica

To characterize atmospheric dissolvable iron over the Southern Ocean (SO) and coastal East Antarctica (CEA), bulk and size-segregated (0.056-18 μm in diameter) aerosols were collected from 34°S, 109°E to 69°S, 76°E and between 69°S, 76°E and 66°S, 110°E during a cruise during November 2010 to March 2011. Aerosols were analyzed for total dissolvable Fe and Fe(II) by UV/Visible spectroscopy and total Fe by inductively coupled plasma-mass spectrometry. The average concentrations of total Fe were 19 ng m^-3 (range: 10-38 ng m^-3) over the SO and 26 ng m ^-3 (range: 14-56 ng m^-3) in CEA. The average Fe(II) concentrations were 0.22 ng m^-3 (range: 0.13-0.33 ng m^-3) over the SO and 0.53 ng m^-3 (range: 0.18-1.3 ng m^-3) over CEA; the total dissolvable Fe followed the same trend. Over the SO, a single-peak size distribution of Fe(II) existed. Over CEA, a bimodal size distribution of Fe(II) appeared, with the first peak at 0.32-0.56 μm and the second peak at 5.6-10 μm. Higher Fe concentrations over CEA than over the SO and the existence of coarse mode Fe(II) over CEA suggest potential dust sources in Antarctica. The fractional Fe(II) solubility ranged from 0.58% to 6.5% and decreased with total Fe concentration increase. The estimated atmospheric fluxes of Fe(II) were 0.007-0.092 mg m^-2 yr^-1 over the SO and 0.022-0.21 mg m^-2 yr^-1 in CEA. Total dissolvable Fe fluxes were 0.007-0.52 mg m^-2 yr^-1 over the SO. The atmospheric dissolvable Fe input contributes to the dissolved Fe pool in the SO surface waters. Key Points Dissolved Fe in aerosols is accumulated in fine-mode particles Fe solubility and Fe concentration are higher in coastal Antarctica Air-to-sea fluxes of dissolved Fe is dominated by Fe(II) deposition