Spring molybdenum enrichment in scallop shells: a potential tracer of diatom productivity in temperate coastal environments (Brittany, NW France)

Skeletal molybdenum/calcium ([Mo]/[Ca])_shell ratios were examined in shells of the Great Scallop <i>Pecten maximus</i> collected in temperate coastal environments of Western Europe (42 to 49&deg; N). These ratios were determined by quantitative LA-ICP-MS analyses of daily striae taken every third day (i.e. a temporal resolution of 3 days) in 36 flat valves (2-years old; 3 shells/year). Variations of ([Mo]/[Ca])_shell ratios were significant and reproducible for scallops from the same population, from different years (1998–2004) and temperate coastal locations (NW France). The [Mo]/[Ca])_shell ratios exhibit typical profiles characterized by a background content, below the detection limit for this method (&lt;0.003 &mu;mol/mol) for most of the shell growth period, which is punctuated by a significant transient enrichment (0.031–2.1 &mu;mol/mol) mainly occurring from May to June. The Bay of Brest (France) was investigated in particular because of its long term observations on scallop communities, environmental variables, and high resolution analyses of dissolved Mo in bottom seawater in 2000. In 2000, dissolved Mo exhibited a significant increase in concentration just preceding the maximum ([Mo]/[Ca])_shell ratio. Both the intense monitoring survey in 2000 and over the 7-year period indicates that the ([Mo]/[Ca])_shell maximum is directly influenced by spring changes of environmental conditions at the sediment water interface (SWI), occurring subsequent to the intense and periodic spring bloom. Spring maxima of ([Mo]/[Ca])_shell ratios are closely correlated to the extent of silicic acid and nitrate depletion in seawater between winter and late spring (<i>r</i>²=0.878 and 0.780, <i>p</i><0.05, <i>n</i>=6) that reflects diatom uptake and productivity in the Bay of Brest. The Mo inputs in bottom waters and subsequent shell enrichment are thus suggested to be directly or indirectly influenced by such biogenic material input at the SWI. The [Mo]/[Ca])_shell records thus reveal unexpected biogeochemical cycles of Mo influenced by coastal spring productivity, faithfully recorded in scallop shells

Direct determination of trace elements in powdered samples by in-cell isotope dilution femtosecond laser ablation ICPMS

A method has been developed for the direct and simultaneous multielement determination of Cu, Zn, Sn, and Pb in soil and sediment samples using femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICPMS) in combination with isotope dilution mass spectrometry (IDMS). The in-cell isotope dilution fs-LA-ICPMS method proposed in this work was based on the quasi-simultaneous ablation of the natural abundance sample and the isotopically enriched solid spike, which was performed using a high repetition rate laser and a fast scanning beam device in a combined manner. Both the sample preparation procedure and the total analysis time have been drastically reduced, in comparison with previous approaches, since a unique multielement isotopically enriched solid spike was employed to analyze different powdered samples. Numerous experimental parameters were carefully selected (e.g., carrier gas flow rate, inlet diameter of the ablation cell, sample translation speed, scanner speed, etc.) in order to ensure the complete mixing between the sample and the solid spike aerosols. The proposed in-cell fs-LA-ICP-IDMS method was tested for the analysis of two soil (CRM 142R, GBW-07405) and two sediment (PACS-2, IAEA-405) reference materials, and the analysis of Cu, Zn, Sn, and Pb yielded good agreement of usually not more than 10% deviation from the certified values and precisions of less than 15% relative standard deviation. Furthermore, the concentrations were in agreement not only with the certified values but also with those obtained by ICP-IDMS after the microwave-assisted digestion of the solid samples, demonstrating therefore that in-cell fs-LA-ICP-IDMS opens the possibility for accurate and precise determinations of trace elements in powdered samples reducing the total sample preparation time to less than 5 min. Additionally, scanning electron microscope measurements showed that the aerosol generated by in-cell fs-LA-ICP-IDMS predominantly consisted of linear agglomerates of small particles (in the order of few tens of nanometers) and a few large spherical particles with diameters below 225 nm

Lettre de Arthur C. Nielsen

Barats Florence, Nielsen Arthur C. Lettre de Arthur C. Nielsen. In: Quaderni, n°35, Printemps 1998. Les publics : généalogie de l'audience télévisuelle. pp. 53-62

P–T–X conditions on the genesis of orogenic Au (As, Bi, Ag) deposit in metasedimentary rocks of the Buracão Area, Araí Group, Brasília Fold Belt, Brazil

International audienceThe orogenic Au (As, Bi, Ag) mineralization (up to 31 g/t) of the Buracão area is hosted in the metasedimentary Paleo–Mesoproterozoic Traíras Formation, Araí Group, Brasília Fold Belt, Brazil. In order to discuss the P–T–X conditions that generated this mineralization, we present mineralogical, geochemical and fluid inclusion data of veins, gold and wall rocks. Coupled with previous structural data these additional data allow us to link metamorphism and deformation with fluid migration and ore genesis. The integration of fluid inclusion microthermometry with mineral geothermobarometers and structures show that rocks of the study area evolved from: (i) syn–D1a metamorphic peak (400–560 °C, <6 kbar), through to the (ii) development of syn–D1b type I barren veins from low salinity H2O–NaCl fluids during syn– to late–metamorphic peak; and to the (iii) development of syn–D2a type II veins with the pyritic ore precipitation from low to high salinity H2O–CO2–CH4–NaCl ± HCO3 fluids during post–metamorphic peak (345–285 °C, 2.7–1.6 kbar).The high fineness gold nuggets accompanied by As, Bi and Ag within pyrite–arsenopyrite–bismuthinite association in the pyritic ore allows the Buracão area to be classified as “a gold-only orogenic ore deposit”. Fluid inclusion compounds and the enrichment of As, Bi, Pb, Cu, Te, Se and Ag in pyrite from the pyritic ore point out to metamorphism of carbonaceous phyllites and carbonate rocks of the Traíras Formation as a source for ore–forming fluids. We suggest that sulfur and gold in these fluids were derived by metamorphism of sedimentary rocks and conversion of pyrite into pyrrhotite in a metamorphic–hydrothermal system. The Au(HS)2−–bearing fluids percolated along intrabasinal D2a regional shear zones through the Traíras Formation towards the Buracão area, where they precipitated type II ore–bearing veins within local structures. The ore precipitation was induced by contrasting fO2–fS2 related to the interaction between the sulfur-bearing fluid and host magnetite–graphite phyllites. The lithological control is represented by a series of reactions such as 2FeO(in silicates/magnetite) + 4Au(HS)2−(aq) + 4H+(aq) ↔ 2FeS2(s) + 4Au(s) + 4H2S(aq) + 2H2O(l).The deposits of the Buracão area and other orogenic gold deposits hosted in metasedimentary rocks in the Brasília Fold Belt and worldwide confirm the potential of ore genesis in zones that do not show any relation with (meta)igneous rocks, thus, expanding the exploration possibilities in metasedimentary successions

Oxic and post-oxic chemical changes related to eogenesis and mesogenesis in a Miocene paleolake

International audienc

High frequency Barium profiles in shells of the Great Scallop Pecten maximus: a methodical long-term and multi-site survey in Western Europe

Skeletal barium/calcium ([Ba]/[Ca]) shell ratios were measured every third daily striae in 39 flat valves of the Great Scallop Pecten maximus collected in temperate coastal environments of Western Europe. A methodical evaluation of the ([Ba]/[Ca]) shell ratio was performed for the first time and demonstrates that ([Ba]/[Ca]) shell profiles are reproducible for several scallop individuals from the same population (2-year old; 3 shells/year), over a 7-year period (1998 2004), and from different coastal environments in France (42-49 degrees N). As previously determined in the shells of other bivalve species, ([Ba]/[Ca]) shell profiles generally exhibited a background ratio punctuated by two transient maxima occurring in early and late summer. Background partition coefficient (D-Ba= 0.11 +/- 0.03, in 2000) was similar to that previously reported in P. maximus shells, suggesting a direct shell uptake of dissolved seawater Ba (Gillikin et al., 2008). The 7-year survey in the Bay of Brest of the high frequency ([Ba]/[Ca])(shell) profiles in the scallop's shell was exploited to better constrain both the occurrence and the amplitude of the summer Ba relative enrichments as influenced by environmental processes. Seawater Ba contents in 2000 underlined significant particulate Ba inputs at the sediment water interface (SWI) during ([Ba]/[Ca]) shell peak events. These Ba inputs are thus suggested to be subsequently induced by a pelagic biogenic process, which mainly occurs under summer post-bloom conditions in relationship to the cycling of particulate organic matter and associated Ba. The long term survey reveals that such pelagic Ba cycling processes are responsible for particulate Ba inputs to the sediment water interface (SWI). Subsequent indirect Ba uptake by the bivalve results in higher ([Ba]/[Ca]) shell ratios, in that archived Ba within the shell cannot be used as a direct paleo productivity tracer. Our methodical approach, based on a multi-year and multi-site-survey of ([Ba]/[Ca]) shell ratio in Scallop bivalves, allows us to establish the potential application of such high frequency archives for further biogeochemical and ecological investigations of bivalves in the coastal environment

Arsenic Research and Global Sustainability; Proceedings of the 6th International Congress on Arsenic in the Environment, AS 2016; Stockholm; Sweden; 19-23 June 2016

International audienc

High frequency Barium profiles in shells of the Great Scallop <i>Pecten maximus</i>: a methodical long-term and multi-site survey in Western Europe

Skeletal barium/calcium ([Ba]/[Ca])shell ratios were measured every third daily striae in 39 flat valves of the Great Scallop Pecten maximus collected in temperate coastal environments of Western Europe. A methodical evaluation of the ([Ba]/[Ca])shell ratio was performed for the first time and demonstrates that ([Ba]/[Ca])shell profiles are reproducible for several scallop individuals from the same population (2-year old; 3 shells/year), over a 7-year period (1998–2004), and from different coastal environments in France (42–49&deg; N). As previously determined in the shells of other bivalve species, ([Ba]/[Ca])shell profiles generally exhibited a background ratio punctuated by two transient maxima occurring in early and late summer. Background partition coefficient (DBa=0.11&plusmn;0.03, in 2000) was similar to that previously reported in P. maximus shells, suggesting a direct shell uptake of dissolved seawater Ba (Gillikin et al., 2008). The 7-year survey in the Bay of Brest of the high frequency ([Ba]/[Ca])shell profiles in the scallop's shell was exploited to better constrain both the occurrence and the amplitude of the summer Ba relative enrichments as influenced by environmental processes. Seawater Ba contents in 2000 underlined significant particulate Ba inputs at the sediment water interface (SWI) during ([Ba]/[Ca])shell peak events. These Ba inputs are thus suggested to be subsequently induced by a pelagic biogenic process, which mainly occurs under summer post-bloom conditions in relationship to the cycling of particulate organic matter and associated Ba. The long term survey reveals that such pelagic Ba cycling processes are responsible for particulate Ba inputs to the sediment water interface (SWI). Subsequent indirect Ba uptake by the bivalve results in higher ([Ba]/[Ca])shell ratios, in that archived Ba within the shell cannot be used as a direct paleo productivity tracer. Our methodical approach, based on a multi-year and multi-site-survey of ([Ba]/[Ca])shell ratio in Scallop bivalves, allows us to establish the potential application of such high frequency archives for further biogeochemical and ecological investigations of bivalves in the coastal environment

Groundwater and river baseline quality using major, trace elements, organic carbon and Sr-Pb-O isotopes in a Mediterranean catchment: The case of the Lower Var Valley (south-eastern France),

International audienceDissolved trace and major elements, organic carbon and Pb-Sr-O isotopes have been investigated in surface and groundwater of the Var River Valley (SE France), including alluvial, conglomerate and limestone aquifers, as well as surface water. Boxplots and cumulative frequency distribution diagrams define chemical characteristics of each water group and distinguish between natural and anthropogenic range of concentrations. Low concentration of trace elements, statistical analysis of data and Pb isotopic ratios demonstrate that the measured baseline quality is close to the natural background, mainly influenced by water/rock interaction. Pb and Sr isotopes evidence specific primitive end members, buffering these two elements through leaching late Paleozoic rocks, strongly depleted in U and Rb since their formation. Arsenic undergoes geochemical processes such as sorption on clay minerals of the alluvial deposits. Sr isotopic ratios and high View the MathML sourceSO42-, Sr and Li contents show that Permo-Triassic sediments including evaporites strongly imprint surface waters and alluvial groundwaters. Limestone and conglomerate aquifers are mainly influenced by carbonate minerals, but may be locally affected by evaporite dissolution. High dissolved silica is also specific to conglomerate groundwaters. Limestone and conglomerate groundwaters are characterised by low and heterogeneous trace element compositions that may result from various residence times and rock compositions related to different sampling depth. Even if water quality is generally good for most of the investigated elements, pollution by agricultural activity (fertilisers and pesticides) in the alluvial and some limestone groundwaters has been demonstrated by high View the MathML sourceNO3- and Br− contents. Br− is suspected to originate from methyl bromide fertiliser. In conglomerate aquifers, View the MathML sourceNO3- contents may reach high levels, probably due to both agriculture and residential waste pollution. Despite the industrialization in the Low Var Valley, no significant metallic contamination could be detected and therefore, for trace elements, given parameters (min, max and median values) can be used as a baseline guide to detect future contamination