FN Archimer Export Format
PT J
TI Iron mineral structure, reactivity, and isotopic composition in a South Pacific Gyre ferromanganese nodule over 4 Ma
BT 
AF MARCUS, Matthew A.
   EDWARDS, Katrina J.
   GUEGUEN, Bleuenn
   FAKRA, Sirine C.
   HORN, Gregory
   JELINSKI, Nicolas A.
   ROUXEL, Olivier
   SORENSEN, Jeffry
   TONER, Brandy M.
AS 1:1;2:2;3:3,4,5;4:1;5:2;6:6;7:3;8:6;9:6;
FF 1:;2:;3:;4:;5:;6:;7:PDG-REM-GM-LGM;8:;9:;
C1 Univ Calif Berkeley, Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA 94720 USA.
   Univ So Calif, Dept Biol Sci, Los Angeles, CA 90089 USA.
   IFREMER, Ctr Brest, Unite Geosci Marines, F-29280 Plouzane, France.
   Univ Brest, Inst Univ Europeen Mer, UMR 6538, F-29280 Plouzane, France.
   Yale Univ, Dept Geol & Geophys, New Haven, CT 06520 USA.
   Univ Minnesota, Dept Soil Water & Climate, St Paul, MN 55108 USA.
C2 UNIV CALIF BERKELEY, USA
   UNIV CALIF LOS ANGELES, USA
   IFREMER, FRANCE
   UBO, FRANCE
   UNIV YALE, USA
   UNIV MINNESOTA, USA
SI BREST
SE PDG-REM-GM-LGM
UM LGO
IN WOS Ifremer jusqu'en 2018
   copubli-france
   copubli-univ-france
   copubli-int-hors-europe
IF 4.315
TC 33
UR https://archimer.ifremer.fr/doc/00278/38965/37505.pdf
LA English
DT Article
AB Deep-sea ferromanganese nodules accumulate trace elements from seawater and underlying sediment porewaters during the growth of concentric mineral layers over millions of years. These trace elements have the potential to record past ocean geochemical conditions. The goal of this study was to determine whether Fe mineral alteration occurs and how the speciation of trace elements responds to alteration over ∼3.7 Ma of marine ferromanganese nodule (MFN) formation, a timeline constrained by estimates from 9Be/10Be concentrations in the nodule material. We determined Fe-bearing phases and Fe isotope composition in a South Pacific Gyre (SPG) nodule. Specifically, the distribution patterns and speciation of trace element uptake by these Fe phases were investigated. The time interval covered by the growth of our sample of the nodule was derived from 9Be/10Be accelerator mass spectrometry (AMS). The composition and distribution of major and trace elements were mapped at various spatial scales, using micro-X-ray fluorescence (μXRF), electron microprobe analysis (EMPA), and inductively coupled plasma mass spectrometry (ICP-MS). Fe phases were characterized by micro-extended X-ray absorption fine structure (μEXAFS) spectroscopy and micro-X-ray diffraction (μXRD). Speciation of Ti and V, associated with Fe, was measured using micro-X-ray absorption near edge structure (μXANES) spectroscopy. Iron isotope composition (δ56/54Fe) in subsamples of 1-3 mm increments along the radius of the nodule was determined with multiple-collector ICP-MS (MC-ICP-MS). The SPG nodule formed through primarily hydrogeneous inputs at a rate of 4.0 ± 0.4 mm/Ma. The nodule exhibited a high diversity of Fe mineral phases: feroxyhite (δ-FeOOH), goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and poorly ordered ferrihydrite-like phases. These findings provide evidence that Fe oxyhydroxides within the nodule undergo alteration to more stable phases over millions of years. Trace Ti and V were spatially correlated with Fe and found to be adsorbed to Fe-bearing minerals. Ti/Fe and V/Fe ratios, and Ti and V speciation, did not vary along the nodule radius. The δ56/54Fe values, when averaged over sample increments representing 0.25 to 0.75 Ma, were homogeneous within uncertainty along the nodule radius, at -0.12 ± 0.07 ‰ (2sd, n=10). Our results indicate that the Fe isotope composition of the nodule remained constant during nodule growth and that mineral alteration did not affect the primary Fe isotope composition of the nodule. Furthermore, the average δ56/54Fe value of -0.12 ‰ we find is consistent with Fe sourced from continental eolian particles (dust). Despite mineral alteration, the trace element partitioning of Ti and V, and Fe isotope composition, do not appear to change within the sensitivity of our measurements. These findings suggest that Fe oxyhydroxides within hydrogenetic ferromanganese nodules are out of geochemical contact with seawater once they are covered by subsequent concentric mineral layers. Even though Fe-bearing minerals are altered, trace element ratios, speciation and Fe isotope composition are preserved within the nodule.
PY 2015
PD DEC
SO Geochimica Et Cosmochimica Acta
SN 0016-7037
PU Pergamon-elsevier Science Ltd
VL 171
UT 000364822100005
BP 61
EP 79
DI 10.1016/j.gca.2015.08.021
ID 38965
ER

EF