The speciation of particulate iron in the Peruvian Oxygen Minimum Zone

Tuesday, 16 December 2014
Maija Iris Heller1, Phoebe J Lam1,2, Brandy M Toner3, Sarah L Nicholas3, James W Moffett4 and Peter Neil Sedwick5, (1)University of California Santa Cruz, Department of Ocean Sciences, Santa Cruz, CA, United States, (2)Woods Hole Oceanographic Inst, Department of Marine Chemistry and Geochemistry, Woods Hole, MA, United States, (3)Univ of MN /Soil Water&Climate, St. Paul, MN, United States, (4)University of Southern California, Department of Biological Sciences, Los Angeles, CA, United States, (5)Old Dominion University, Department of Ocean, Earth and Atmospheric Sciences, Norfolk, VA, United States
Suspended particulate matter (SPM) was collected by in-situ filtration from the Peruvian Oxygen Minimum Zone (OMZ) during the US GEOTRACES Eastern Pacific Zonal Transect cruise. Here, we use X-ray Absorption Near Edge Spectroscopy to examine the redox speciation of marine particulate iron from the Peruvian OMZ to understand the redox cycling processes that generate and maintain elevated Fe concentrations. We hypothesized that Fe(III) oxyhydroxides would be highest at the regions of highest horizontal and vertical oxygen gradients, where dissolved Fe(II) would be lost to oxidization, but found instead that the highest oxyhydroxide concentrations were in oxygen deficient waters on the Peruvian shelf where dissolved Fe(II) was highest. The oxyhydroxides were dominated by the lepidocrocite (gamma-FeOOH) form, which is generally thought to require dissolved Fe(II) for its formation. Although lepidocrocite is relatively common in soils and freshwater systems, there are few reports of its presence in marine systems. Lepidocrocite has been shown to stimulate Fe(II)-dependent nitrite reduction in soils, and we suggest that it may also play a role here in nitrogen cycling.