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Title: Accumulation of Fe oxyhydroxides in the Peruvian oxygen deficient zone implies non-oxygen dependent Fe oxidation

Oxygen minimum zones (OMZs) have been proposed to be an important source of dissolved iron (Fe) into the interior ocean. However, previous studies in OMZs have shown a sharp decrease in total dissolved Fe (dFe) and/or dissolved Fe(II) (dFe(II)) concentrations at the shelf-break, despite constant temperature, salinity and continued lack of oxygen across the shelf-break. The loss of both total dFe and dFe(II) suggests a conversion of the dFe to particulate form, but studies that have coupled the reduction-oxidation (redox) speciation of both dissolved and particulate phases have not previously been done. Here in this work, we have measured the redox speciation and concentrations of both dissolved and particulate forms of Fe in samples collected during the U.S. GEOTRACES Eastern tropical Pacific Zonal Transect (EPZT) cruise in 2013 (GP16). This complete data set allows us to assess possible mechanisms for loss of dFe. We observed an offshore loss of dFe(II) within the oxygen deficient zone (ODZ), where dissolved oxygen is undetectable, accompanied by an increase in total particulate Fe (pFe). Total pFe concentrations were highest in the upper ODZ. X-ray absorption spectroscopy revealed that the pFe maximum was primarily in the Fe(III) form as Fe(III) oxyhydroxides. The remarkable similarity inmore » the distributions of total particulate iron and nitrite suggests a role for nitrite in the oxidation of dFe(II) to pFe(III). Lastly, we present a conceptual model for the rapid redox cycling of Fe that occurs in ODZs, despite the absence of oxygen.« less
Authors:
 [1] ;  [1] ;  [2] ;  [1] ;  [1] ;  [3] ;  [4]
  1. Univ. of California, Santa Cruz, CA (United States). Department of Ocean Sciences
  2. Univ. of Southern California, Los Angeles, CA (United States). Marine Environmental Biology, Department of Biological Sciences
  3. University of Minnesota-Twin Cities, St. Paul, MN (United States). Department of Soil, Water, and Climate
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 211; Journal Issue: C; Journal ID: ISSN 0016-7037
Publisher:
The Geochemical Society; The Meteoritical Society
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 54 ENVIRONMENTAL SCIENCES; Oxygen minimum zone; Oxygen deficient zone; OMZODZ; Fe redox cycling; Synchrotron XAS
OSTI Identifier:
1436158

Heller, Maija I., Lam, Phoebe J., Moffett, James W., Till, Claire P., Lee, Jong-Mi, Toner, Brandy M., and Marcus, Matthew A.. Accumulation of Fe oxyhydroxides in the Peruvian oxygen deficient zone implies non-oxygen dependent Fe oxidation. United States: N. p., Web. doi:10.1016/j.gca.2017.05.019.
Heller, Maija I., Lam, Phoebe J., Moffett, James W., Till, Claire P., Lee, Jong-Mi, Toner, Brandy M., & Marcus, Matthew A.. Accumulation of Fe oxyhydroxides in the Peruvian oxygen deficient zone implies non-oxygen dependent Fe oxidation. United States. doi:10.1016/j.gca.2017.05.019.
Heller, Maija I., Lam, Phoebe J., Moffett, James W., Till, Claire P., Lee, Jong-Mi, Toner, Brandy M., and Marcus, Matthew A.. 2017. "Accumulation of Fe oxyhydroxides in the Peruvian oxygen deficient zone implies non-oxygen dependent Fe oxidation". United States. doi:10.1016/j.gca.2017.05.019. https://www.osti.gov/servlets/purl/1436158.
@article{osti_1436158,
title = {Accumulation of Fe oxyhydroxides in the Peruvian oxygen deficient zone implies non-oxygen dependent Fe oxidation},
author = {Heller, Maija I. and Lam, Phoebe J. and Moffett, James W. and Till, Claire P. and Lee, Jong-Mi and Toner, Brandy M. and Marcus, Matthew A.},
abstractNote = {Oxygen minimum zones (OMZs) have been proposed to be an important source of dissolved iron (Fe) into the interior ocean. However, previous studies in OMZs have shown a sharp decrease in total dissolved Fe (dFe) and/or dissolved Fe(II) (dFe(II)) concentrations at the shelf-break, despite constant temperature, salinity and continued lack of oxygen across the shelf-break. The loss of both total dFe and dFe(II) suggests a conversion of the dFe to particulate form, but studies that have coupled the reduction-oxidation (redox) speciation of both dissolved and particulate phases have not previously been done. Here in this work, we have measured the redox speciation and concentrations of both dissolved and particulate forms of Fe in samples collected during the U.S. GEOTRACES Eastern tropical Pacific Zonal Transect (EPZT) cruise in 2013 (GP16). This complete data set allows us to assess possible mechanisms for loss of dFe. We observed an offshore loss of dFe(II) within the oxygen deficient zone (ODZ), where dissolved oxygen is undetectable, accompanied by an increase in total particulate Fe (pFe). Total pFe concentrations were highest in the upper ODZ. X-ray absorption spectroscopy revealed that the pFe maximum was primarily in the Fe(III) form as Fe(III) oxyhydroxides. The remarkable similarity in the distributions of total particulate iron and nitrite suggests a role for nitrite in the oxidation of dFe(II) to pFe(III). Lastly, we present a conceptual model for the rapid redox cycling of Fe that occurs in ODZs, despite the absence of oxygen.},
doi = {10.1016/j.gca.2017.05.019},
journal = {Geochimica et Cosmochimica Acta},
number = C,
volume = 211,
place = {United States},
year = {2017},
month = {5}
}