Studies of authigenic phosphorus (P) minerals in marine sediments typically focus on authigenic carbonate fluorapatite, which is considered to be the major sink for P in marine sediments and can easily be semi-quantitatively extracted with the SEDEX sequential extraction method. The role of other potentially important authigenic P phases, such as the reduced iron (Fe) phosphate mineral vivianite (Fe(II)3(PO4)*8H2O) has so far largely been ignored in marine systems. This is, in part, likely due to the fact that the SEDEX method does not distinguish between vivianite and P associated with Fe-oxides. Here, we show that vivianite can be quantified in marine sediments by combining the SEDEX method with microscopic and spectroscopic techniques such as micro X-ray fluorescence (μXRF) elemental mapping of resin-embedded sediments, as well as scanning electron microscope–energy dispersive spectroscopy (SEM–EDS) and powder X-ray diffraction (XRD). We further demonstrate that resin embedding of vertically intact sediment sub-cores enables the use of synchrotron-based microanalysis (X-ray absorption near-edge structure (XANES) spectroscopy) to differentiate between different P burial phases in aquatic sediments. Our results reveal that vivianite represents a major burial sink for P below a shallow sulfate/methane transition zone in Bothnian Sea sediments, accounting for 40–50% of total P burial. We further show that anaerobic oxidation of methane (AOM) drives a sink-switching from Fe-oxide bound P to vivianite by driving the release of both phosphate (AOM with sulfate and Fe-oxides) and ferrous Fe (AOM with Fe-oxides) to the pore water allowing supersaturation with respect to vivianite to be reached. The vivianite in the sediment contains significant amounts of manganese (∼4–8wt.%), similar to vivianite obtained from freshwater sediments. Our results indicate that methane dynamics play a key role in providing conditions that allow for vivianite authigenesis in coastal surface sediments. We suggest that vivianite may act as an important burial sink for P in brackish coastal environments worldwide

ID21 beamline (ESRF) offers combination of μXRF, μXANES (2.0–9.1 keV), μXRD and μFTIR, increasingly used to analyse artistic and ancient materials.

Subduction zone magmas are more oxidised on eruption than those at mid-ocean ridges. This is attributed either to oxidising components, derived from subducted lithosphere (slab) and added to the mantle wedge, or to oxidation processes occurring during magma ascent via differentiation. Here we provide direct evidence for contributions of oxidising slab agents to melts trapped in the sub-arc mantle. Measurements of sulfur (S) valence state in sub-arc mantle peridotites identify sulfate, both as crystalline anhydrite (CaSO₄) and dissolved SO₄²⁻ in spinel-hosted glass (formerly melt) inclusions. Copper-rich sulfide precipitates in the inclusions and increased Fe³⁺/∑Fe in spinel record a S⁶⁺–Fe²⁺ redox coupling during melt percolation through the sub-arc mantle. Sulfate-rich glass inclusions exhibit high U/Th, Pb/Ce, Sr/Nd and δ³⁴S (+ 7 to + 11‰), indicating the involvement of dehydration products of serpentinised slab rocks in their parental melt sources. These observations provide a link between liberated slab components and oxidised arc magmas.

We investigate the relationship between sulfur and oxygen fugacity at Erta Ale and Masaya volcanoes. Oxygen fugacity was assessed utilizing Fe³⁺/∑Fe and major element compositions measured in olivine‐hosted melt inclusions and matrix glasses. Erta Ale melts have Fe³⁺/∑Fe of 0.15–0.16, reflecting fO₂ of ΔQFM 0.0 ± 0.3, which is indistinguishable from fO₂ calculated from CO₂/CO ratios in high‐temperature gases. Masaya is more oxidized at ΔQFM +1.7 ± 0.4, typical of arc settings. Sulfur isotope compositions of gases and scoria at Erta Ale (δ³⁴S_gas − 0.5‰; δ³⁴S_scoria + 0.9‰) and Masaya (δ³⁴S_gas + 4.8‰; δ³⁴S_scoria + 7.4‰) reflect distinct sulfur sources, as well as isotopic fractionation during degassing (equilibrium and kinetic fractionation effects). Sulfur speciation in melts plays an important role in isotope fractionation during degassing and S⁶⁺/∑S is 0.67 in Masaya melt inclusions. No change is observed in Fe³⁺/∑Fe or S⁶⁺/∑S with extent of S degassing at Erta Ale, indicating negligible effect on fO₂, and further suggesting that H₂S is the dominant gas species exsolved from the S²⁻‐rich melt (i.e., no redistribution of electrons). High SO₂/H₂S observed in Erta Ale gas emissions is due to gas re‐equilibration at low pressure and fixed fO_2. Sulfur budget considerations indicate that the majority of S injected into the systems is emitted as gas, which is therefore representative of the magmatic S isotope composition. The composition of the Masaya gas plume (+4.8‰) cannot be explained by fractionation effects but rather reflects recycling of high δ³⁴S oxidized sulfur through the subduction zone.

The origin(s) and role(s) of metal soaps in paints are a worldwide concern today. These hybrid compounds, containing both fatty acid chains and metals associated with a carboxylate function, are increasingly identified in paints. As reviewed in the first part of this work, the presence of metal soaps in paints is differently interpreted in scientific publications: metal soaps are sometimes considered to play a positive role as anchor points, during paint drying processes; they can also be considered as responsible for many degradation processes (protrusions, efflorescences, darkening, etc.). Their origins are also interpreted in various ways. In some paintings (in particular from the twentieth century), they have sometimes introduced on purpose, as additives, to modify the physical properties of the painting materials. In older paintings, metal soaps are usually thought to result from an uncontrolled reaction of oil with lead-based pigments, in particular lead white, red lead, and lead tin yellow. In the second part of this work, the review of historical recipes of lead-based paint shows an important number of recipes based on controlled mixing of oil with lead driers. In the third part, the experimental reproduction of such traditional recipes using walnut oil and litharge (PbO) shows that lead soaps can be formed, both in about one hour at ∼100°C, or in about one month at room temperature. It shows as well that after a few years, litharge is no longer detected in the paint medium, while different lead carbonates are. Finally, the micro-infrared spectroscopy and micro-X-ray diffraction re-analysis of protrusions from a nine-year model painting shows together with lead soaps, the presence of Pb₅(CO₃)₃(OH)₂O (‘synthetic plumbonacrite’), an unusual phase recently observed in a protrusion from a painting by Vincent Van Gogh. This work highlights (i) the multiple origins and roles of metal soaps in paints and (ii) the importance of combining the analysis of fragments from historical paintings with the analysis and reproduction of historical recipes. In particular, we show that the components detected today in historical paintings may severely differ from those originally used or prepared by the painter, complicating the assessment of the painter's intentions. More than the presence of metal soaps, the key questions to be tackled should be about their origins and (re)mobilization.

In this study, we investigate the interactions between the cellulose surface and Ag nanoparticles (AgNPs) for the purpose of manufacturing hybrid nanomaterials using bacterial cellulose nanocrystals (BCNs) as a model substrate. We focus on the role of the BCN surface chemistry on the AgNP nucleation obtained by chemical reduction of Ag+ ions. Homogeneous hybrid suspensions of BCN/AgNP are produced, regardless of whether the BCNs are quasi-neutral, negatively (TBCNs) or positively charged (ABCNs). The characterization of BCN/AgNP hybrids identifies the -OH surface groups as nucleation points for AgNPs, of about 20 nm revealing that surface charges only improve the accessibility to OH groups. X-ray Absorption technics (XANES and EXAFS) revealed a high metallic Ag0 content ranging from 88% to 97%. Moreover, the grafting of hydrophobic molecules on a BCN surface (HBCNs) does not prevent AgNP nucleation, illustrating the versatility of our method and the possibility to obtain bifunctional NPs. A H2O2 redox post-treatment on the hybrid induces an increase in AgNPs size, up to 90 nm as well as a shape variation (i.e., triangular). In contrast, H2O2 induces no size/shape variation for aggregated hybrids, emphasizing that the accessibility to -OH groups ensures the nucleation of bigger Ag nano-objects.