Nickel and iron partitioning between clay minerals, Fe-oxides and Fe-sulfides in lagoon sediments from New Caledonia

Pauline Merrot; Farid Juillot; Vincent Noël; Pierre Lefebvre; Jessica Brest; Nicolas Menguy; Jean-Michel Guigner; Marine Blondeau; Eric Viollier; Jean-Michel Fernandez; Benjamin Moreton; John R Bargar; Guillaume Morin

doi:10.1016/j.scitotenv.2019.06.274

Nickel and iron partitioning between clay minerals, Fe-oxides and Fe-sulfides in lagoon sediments from New Caledonia

Sci Total Environ. 2019 Nov 1:689:1212-1227. doi: 10.1016/j.scitotenv.2019.06.274. Epub 2019 Jun 21.

Affiliations

¹ Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR 7590 CNRS-SU-IRD-MNHN, Sorbonne Université, case 115, 4 place Jussieu, 75252 Paris Cedex 5, France.
² Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR 7590 CNRS-SU-IRD-MNHN, Sorbonne Université, case 115, 4 place Jussieu, 75252 Paris Cedex 5, France; Institut de Recherche pour le développement (IRD), UMR 206/UMR 7590 IMPMC, 98848 Nouméa, New Caledonia. Electronic address: farid.juillot@ird.fr.
³ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, MS 69, Menlo Park, CA 94025, USA.
⁴ Institut de Physique du Globe de Paris (IPGP), Sorbonne Paris Cité, Univ Paris Diderot, CNRS, F-75005 Paris, France.
⁵ Analytical Environmental Laboratory (AEL), 98800 Nouméa, New Caledonia.

PMID: 31466160
DOI: 10.1016/j.scitotenv.2019.06.274

Abstract

In the tropics, continental weathering and erosion are major sources of trace metals towards estuaries and lagoons, where early diagenesis of sediments may influence their mobility and bioavailability. Determining trace metals speciation in tropical sedimentary settings is thus needed to assess their long-term fate and potential threat to fragile coastal ecosystems. In this study, we determined Fe, Ni and S speciation across a shore-to-reef gradient in sediments from the New Caledonia lagoon that receive mixed contribution from lateritic (iron-oxyhydroxides and clay minerals), volcano-sedimentary (silicates) and marine (carbonate) sources. Sulfur K-edge XANES data indicated a major contribution of pyrite (FeS₂) to S speciation close to the shore. However, this contribution was found to dramatically decrease across the shore-to-reef gradient, S mainly occurring as sulfate close to the coral reef. In contrast, Fe and Ni K-edge XANES and EXAFS data indicated a minor contribution of pyrite to Fe and Ni speciation, and this contribution could be evidenced only close to the shore. The major fractions of Fe and Ni across the shore-to-reef gradient were found to occur as Ni- and Fe-bearing clay minerals consisting of smectite (~nontronite), glauconite and two types of serpentines (chrysotile and greenalite/berthierine). Among these clay minerals, greenalite/berthierine, glauconite and possibly smectite, were considered as authigenic. The low contribution of pyrite to trace metals speciation compared to clay minerals is interpreted as a result of (1) a reduced formation rate due to the low amounts of organic carbon compared to the Fe pool and (2) repeated re-oxidation events upon re-suspension of the sediments top layers due to the specific context of shallow lagoon waters. This study thus suggests that green clay authigenesis could represent a key process in the biogeochemical cycling of trace metals that are delivered to lagoon ecosystems upon continental erosion and weathering.

Keywords: Green clays; Lagoon sediments; Speciation; TEM; Trace metals; XAS.