Mn-micronodules from the sediments of the Clarion-Clipperton zone (Pacific Ocean): Origin, elemental source, and Fe-Cu-Zn-isotope composition

Type Article
Date 2021-10
Language English
Author(s) Dekov Vesselin M.1, 2, Rouxel OlivierORCID2, Gueguen Bleuenn3, 4, Wegorzewski Anna V.5, Khripounoff AlexisORCID6, Menot LenaickORCID6
Affiliation(s) 1 : Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan
2 : Unité de Géosciences Marines, IFREMER, Z.I. Pointe du diable, BP 70 - 29280 Plouzané, France
3 : CNRS, Univ Brest, UMR 6538 Laboratoire Géosciences Océan, F-29280 Plouzané, France
4 : CNRS, Univ Brest, UMS 3113, F-29280 Plouzané, France
5 : Federal Institute for Geoscience and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany
6 : REM-EEP-LEP, IFREMER, 29280 Plouzané, France
Source Chemical Geology (0009-2541) (Elsevier BV), 2021-10 , Vol. 580 , P. 120388 (34p.)
DOI 10.1016/j.chemgeo.2021.120388
WOS© Times Cited 1
Keyword(s) Fe-Cu-Zn-isotopes, Geochemistry, Mn-micronodules, Mn-nodules, Pore waters, Suboxic diagenesis

Mn- micronodules and nodules of the Clarion-Clipperton zone (Pacific Ocean) are composed of 10 Å and 7 Å phyllomanganates, and δ-MnO2. The Mn-micronodules are built of fine concentric growth layers of three types (1, 2a, and 2b) according to their Mn/Fe ratio and Ni, Cu, and Co content. Applying previously developped geochemical discrimination approaches we found that the Mn-micronodules were diagenetic precipitates that were a result of suboxic diagenesis, whereas the paired Mn-nodules were diagenetic‑hydrogenetic formations. The most common growth layers (type 2) within the Mn-micronodules are suboxic-diagenetic, whereas the rare growth layers (type 1) are mixed diagenetic‑hydrogenetic and hydrogenetic precipitates. The suboxic diagenetic formation of the Mn-micronodules seems to be a result of the fluctuation of the oxic-suboxic front in the sediment since the Last Glacial Period (LGP). The migration of the oxic-suboxic front close to the seawater/sediment boundary during the LGP has likely resulted in suboxic reduction of Mn4+ and other elements in the sediment and their upward diffusion. Post-LGP deepening of the oxic-suboxic front has seemingly led to re-oxidation of Mn2+ in the pore waters and Mn-micronodule precipitation. The suboxic quantitative re-mobilization of seawater-derived Cesolid phase in the sediment (positive Ce anomaly) and its subsequent sequestration by Mn-micronodules resulted in positive Ce anomaly of the Mn-micronodules and Ce-deficient pore water. This Ce deficiency was recorded in the diagenetic Mn-nodules (negative or no Ce anomaly). The sediment pore waters were source of most elements in the Mn-micronodules and to the bottom seawater.

The diagenetic processes were the major control on the Fe-Cu-Zn isotope composition of the Mn- micronodules and nodules. Measured Fe-isotope composition of the Mn-micronodules can equally be explained by hydrogenetic and diagenetic precipitation. Considering our mineralogical and geochemical data we would suggest a rather diagenetic than hydrogenetic control on the Fe-isotope composition of the Mn-micronodules: suboxic diagenetic reduction of the sedimentary Fe in the sediment, fractionation of Fe-isotopes that produces an isotopically light dissolved Fe pool, which leads to light Fe isotope composition of both the Mn- micronodules and nodules (−0.63 to −0.27‰). The preferential scavenging of 63Cu from seawater on the hydrogenetic Mn-Fe-oxyhydroxides accounts for the Cu-isotope composition of the hydrogenetic-diagenetic Mn-nodules (+0.21 − +0.35‰), which is lighter than that of seawater. The identical Cu-isotope composition of the diagenetic Mn-micronodules is a result of oxidative dissolution of the sedimentary Cu-containing minerals, release of isotopically heavy Cuaq2+ in the pore waters and record of this diagenetic Cu-isotope pool in the Mn-micronodules. The hydrogenetic-diagenetic Mn-nodules have Zn-isotope composition (+0.75 − +0.87‰) heavier than that of the seawater which is interpreted to be a result of equilibrium isotope partitioning between dissolved and adsorbed Zn: preferential sorption of 66Zn on Fe-Mn-oxyhydroxides surfaces. Preferential adsorption of 66Zn from the light Zn isotope pool of the pore waters on the Mn-Fe-oxyhydroxides has resulted in heavy Zn-isotope composition of the Mn-micronodules and diagenetic layers of the Mn-nodules.

The lack of robust assessment of the Mn-micronodule abundance in sediment volume unit and the insufficient geochemical data for the Mn-micronodules prevents a meaningful estimation of their resource potential.

Full Text
File Pages Size Access
Author's final draft 75 11 MB Open access
224 KB Access on demand
249 KB Access on demand
281 KB Access on demand
337 KB Access on demand
34 9 MB Access on demand
Top of the page

How to cite 

Dekov Vesselin M., Rouxel Olivier, Gueguen Bleuenn, Wegorzewski Anna V., Khripounoff Alexis, Menot Lenaick (2021). Mn-micronodules from the sediments of the Clarion-Clipperton zone (Pacific Ocean): Origin, elemental source, and Fe-Cu-Zn-isotope composition. Chemical Geology, 580, 120388 (34p.). Publisher's official version : , Open Access version :