Nickel Isotope Variations in Terrestrial Silicate Rocks and Geological Reference Materials Measured by MC‐ICP‐MS

Although initial studies have demonstrated the applicability of Ni isotopes for cosmochemistry and as a potential biosignature, the Ni isotope composition of terrestrial igneous and sedimentary rocks, and ore deposits remains poorly known. Our contribution is fourfold: (a) to detail an analytical procedure for Ni isotope determination, (b) to determine the Ni isotope composition of various geological reference materials, (c) to assess the isotope composition of the Bulk Silicate Earth relative to the Ni isotope reference material NIST SRM 986 and (d) to report the range of mass‐dependent Ni isotope fractionations in magmatic rocks and ore deposits. After purification through a two‐stage chromatography procedure, Ni isotope ratios were measured by MC‐ICP‐MS and were corrected for instrumental mass bias using a double‐spike correction method. Measurement precision (two standard error of the mean) was between 0.02 and 0.04‰, and intermediate measurement precision for NIST SRM 986 was 0.05‰ (2s). Igneous‐ and mantle‐derived rocks displayed a restricted range of δ^60/58Ni values between ?0.13 and +0.16‰, suggesting an average BSE composition of +0.05‰. Manganese nodules (Nod A1; P1), shale (SDO‐1), coal (CLB‐1) and a metal‐contaminated soil (NIST SRM 2711) showed positive values ranging between +0.14 and +1.06‰, whereas komatiite‐hosted Ni‐rich sulfides varied from ?0.10 to ?1.03‰.     

Rare earth element abundances in hydrothermal fluids from the Manus Basin, Papua New Guinea: Indicators of sub-seafloor hydrothermal processes in back-arc basins

Rare earth element (REE) concentrations are reported for a large suite of seafloor vent fluids from four hydrothermal systems in the Manus back-arc basin (Vienna Woods, PACMANUS, DESMOS and SuSu Knolls vent areas). Sampled vent fluids show a wide range of absolute REE concentrations and chondrite-normalized (REE_N) distribution patterns (La_N/Sm_N ∼ 0.6-11; La_N/Yb_N ∼ 0.6 - 71; ). REE_N distribution patterns in different vent fluids range from light-REE enriched, to mid- and heavy-REE enriched, to flat, and have a range of positive Eu-anomalies. This heterogeneity contrasts markedly with relatively uniform REE_N distribution patterns of mid-ocean ridge hydrothermal fluids. In Manus Basin fluids, aqueous REE compositions do not inherit directly or show a clear relationship with the REE compositions of primary crustal rocks with which hydrothermal fluids interact. These results suggest that the REEs are less sensitive indicators of primary crustal rock composition despite crustal rocks being the dominant source of REEs in submarine hydrothermal fluids. In contrast, differences in aqueous REE compositions are consistently correlated with differences in fluid pH and ligand (chloride, fluoride and sulfate) concentrations. Our results suggest that the REEs can be used as an indicator of the type of magmatic acid volatile (i.e., presence of HF, SO₂) degassing in submarine hydrothermal systems. Additional fluid data suggest that near-seafloor mixing between high-temperature hydrothermal fluid and locally entrained seawater at many vent areas in the Manus Basin causes anhydrite precipitation. Anhydrite effectively incorporates REE and likely affects measured fluid REE concentrations, but does not affect their relative distributions.     

Thermal expansion along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 solid solutions

The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi₂O₆–NaFe³⁺Si₂O₆ and NaAlSi₂O₆–CaFe²⁺Si₂O₆ joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V ₀) = α(T − T ₀). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–aegirine join instead the high-temperature and high-pressure strain are differently oriented.     

Colloidal Control on the Distribution of Rare Earth Elements in Shallow Groundwaters

A 7-year monitoring period of rare earth element (REE) concentrations and REE pattern shapes was carried out in well water samples from a 450 m long transect setup in the Kervidy/Coët-Dan experimental catchment, France. The new dataset confirms systematic, topography-related REE signatures and REE concentrations variability but challenges the validity of a groundwater mixing hypothesis. Most likely, this is due to REE preferential adsorption upon mixing. However, the coupled mixing–adsorption mechanism still fails to explain the strong spatial variation in negative Ce anomaly amplitude. A third mechanism—namely, the input into the aquifer of REE-rich, Ce anomaly free, organic colloids—is required to account for this variation. Ultrafiltration results and speciation calculations made using Model VI agree with this interpretation. Indeed, the data reveal that Ce anomaly amplitude downslope decrease corresponds to REE speciation change, downhill groundwaters REE being mainly bound to organic colloids. Water table depth monitoring shows that the colloid source is located in the uppermost, organic-rich soil horizons, and that the colloid input occurs mainly when water table rises in response to rainfall events. It appears that the colloids amount that reaches groundwater increases downhill as the distance between soil organic-rich horizons and water table decreases. Topography is, therefore, the ultimate key factor that controls Ce anomaly spatial variability in these shallow groundwaters. Finally, the <0.2 μm REE fraction ultimately comes from two solid sources in these groundwaters: one located in the deep basement schist; another located in the upper, organic-rich soil horizon.     

Iron isotope systematics in estuaries: The case of North River, Massachusetts (USA)

Recent studies have suggested that rivers may present an isotopically light Fe source to the oceans. Since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing, it is important to investigate potential fractionation of Fe-isotopes during this process. In this study, we investigate the influence of the flocculation of Fe-rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles. The samples were collected along a salinity gradient from the fresh water to the ocean in the North River estuary (MA, USA). Estuarine samples were filtered at 0.22 μm and the iron isotope composition of the two fractions (dissolved and particles) were analyzed using high-resolution MC-ICP-MS after chemical purification. Dissolved iron results show positive δ⁵⁶Fe values (with an average of 0.43 ± 0.04‰) relative to the IRMM-14 standard and do not display any relationships with salinity or with percentage of colloid flocculation. The iron isotopic composition of the particles suspended in fresh water is characterized by more negative δ⁵⁶Fe values than for dissolved Fe and correlate with the percentage of Fe flocculation. Particulate δ⁵⁶Fe values vary from −0.09‰ at no flocculation to ∼0.1‰ at the flocculation maximum, which reflect mixing effects between river-borne particles, lithogenic particles derived from coastal seawaters and newly precipitated colloids. Since the process of flocculation produces minimal Fe-isotope fractionation in the dissolved Fe pool, we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values. However, this study also suggests that δ⁵⁶Fe composition of rivers can also be characterized by more positive δ⁵⁶Fe values (up to 0.3‰) relative to the crust than previously reported. In order to improve our current understanding of the oceanic iron isotope cycling, further work is now required to determine the processes controlling the fractionation of Fe-isotopes during continental run-off.     

From outcrop and petrographic studies to basin-scale fluid flow modelling: The use of the Albanian natural laboratory for carbonate reservoir characterisation

The Albanian fold-and-thrust belt and the Peri-Adriatic Depression are well documented by means of seismic reflection profiles, GPS reference points, potential data, wells and outcrops. The continuous Oligocene to Plio-Quaternary sedimentary records help to constrain both the burial history of Mesozoic carbonate reservoirs, the timing of their deformation, and the coupled fluid flow and diagenetic scenarios.Since the mid-90s, the Albanian foothills were used as a natural laboratory to develop a new integrated methodology and work flow for the study of sub-thrust reservoir evolution, and to validate on real case studies the use of basin modelling tools as well as the application of new analytical methods for the study petroleum systems in tectonically complex areas.The integration of the interactions between petrographic and microtectonic studies, kinematic, thermal and fluid flow basin modelling, is described in detail. The fracturing of the reservoir intervals has a pre-folding origin in the Albanides and relates to the regional flexuring in the foreland. The first recorded cement has a meteoric origin, implying downward migration and the development of an earlier forebulge in the Ionian Basin. This fluid, which precipitates at a maximum depth of 1.5 km, is highly enriched in strontium, attesting for important fluid–rock interaction with the Triassic evaporites, located in diapirs. From this stage, the horizontal tectonic compression increases and the majority of the fluid migrated under high pressure, characterised by brecciated and crack-seal vein. The tectonic burial increased due to the overthrusting, that is pointed out by the increase of the precipitation temperature of the cements. Afterwards, up- or downward migration of SO₄²⁻, Ba²⁺ and Mg²⁺-rich fluids, which migrated probably along the décollement level, allows a precipitation in thermal disequilibrium. This period corresponds to the onset of the thrusting in the Ionian Zone. The last stage characterised the uplift of the Berati belt, developing a selective karstification due likely to the circulation of meteoric fluid.The main results of the fluid flow modelling show that the Upper Cretaceous–Paleocene carbonate reservoirs in the Ionian zone have been charged from the Tortonian onward, and that meteoric fluid migration should have intensely biodegraded the hydrocarbon in place. Concerning the migration paths, it has been demonstrated that the thrusts act principally as flow barriers in Albania, mainly due the occurrence of evaporites (non-permeable), except in the foreland, where they do not occur.     

Deep‐water Corallium rubrum (L., 1758) from the Mediterranean Sea: preliminary genetic characterisation

The precious red coral Corallium rubrum (L., 1758) lives in the Mediterranean Sea and adjacent Eastern Atlantic Ocean on subtidal hard substrates. Corallium rubrum is a long‐lived gorgonian coral that has been commercially harvested since ancient times for its red axial calcitic skeleton and which, at present, is thought to be in decline because of overexploitation. The depth distribution of C. rubrum is known to range from c. 15 to 300 m. Recently, live red coral colonies have been observed in the Strait of Sicily at depths of c. 600–800 m. This record sheds new light on the ecology, biology, biogeography and dispersal mechanism of this species and calls for an evaluation of the genetic divergence occurring among highly fragmented populations. A genetic characterization of the deep‐sea red coral colonies has been done to investigate biological processes affecting dispersal and population resilience, as well as to define the level of isolation/differentiation between shallow‐ and deep‐water populations of the Mediterranean Sea. Deep‐water C. rubrum colonies were collected at two sites (south of Malta and off Linosa Island) during the cruise MARCOS of the R/V Urania. Collected colonies were genotyped using a set of molecular markers differing in their level of polymorphism. Microsatellites have been confirmed to be useful markers for individual genotyping of C. rubrum colonies. ITS‐1 and mtMSH sequences of deep‐water red coral colonies were found to be different from those found in shallow water colonies, suggesting the possible occurrence of genetic isolation among shallow‐ and deep‐water populations. These findings suggest that genetic diversity of red coral over its actual range of depth distribution is shaped by complex interactions among geological, historical, biological and ecological processes.     

Relationship between heavy metal accumulation and genetic variability decrease in the intertidal crab Pachygrapsus marmoratus (Decapoda; Grapsidae)

The “genetic erosion” hypothesis posits that heavy metal stress is related to a loss of genetic diversity at the population level. The genetic diversity of natural populations can, however, be affected by natural processes as well as by human impact. We studied the relationship between heavy metal bioaccumulation and genetic variability in the intertidal crab Pachygrapsus marmoratus. Tissue samples were collected from 40 individuals inhabiting four polluted and four unpolluted sites along the Tuscan coast (Mediterranean basin), and were examined for four heavy metals (arsenic, As, cadmium, Cd, lead, Pb, and copper, Cu). We also assessed the genetic variability of 235 crabs from the same localities using six microsatellite loci.Our results show that the bioaccumulation levels of these individuals accurately reflect the levels of pollution in their immediate environment, and that heavy metals accumulate more in the hepatopancreas than in the gills. Moreover, populations from polluted sites have significantly less genetic variability, measured as mean standardized d², and a significantly lower percentage of unrelated individuals, than populations from unpolluted sites. This evidence supports the “genetic erosion” hypothesis for metal heavy exposure in natural environments.     

Vertical migrations of the mangrove snail Cerithidea decollata (L.) (Potamididae) through a synodic month

The vertical migration on mangrove trunks of the gastropod Cerithidea decollata was followed for 5 weeks, in a Kenyan mangrove. Most of the times, snails forage on the mud surface, during low tide, and climb back on trees well before the incoming tide. As soon as the sea retreats, the downward migration takes place and the snails spread again on the ground. The migratory behaviour of snails can vary widely, depending on the relative tide intensity, and different strategies can be exhibited. Individuals can spend several days on trees without migrating to the ground, around Spring Tides, or else, they might remain on the ground without bothering to migrate upwards, during Neap Tides, when the study area is not reached by the water. These irregular animal behaviours, relating to the complicated tide succession, can hardly be explained by the sole presence of an internal clock, and direct cues seem necessary to switch between different strategies, tuning the snails migratory behaviour to the actual local sea conditions.