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Studies on metal contamination in 25 de Mayo Island, Antarctica, yielded controversial results. In this work, we analyzed Antarctic marine sediments and Antarctic clam (Laternula elliptica) tissues to investigate the possible use of this mollusk as a biomonitor of metals and to identify the sources of metal pollution. Different types of paint from several buildings from Carlini Station were examined to assess their contribution to the local and random metal pollution. Five sediment samples, 105 L. elliptica specimens (40.2-78.0mm length) and four types of paint were analyzed to quantify Cd, Cr, Cu, Fe, Mn, Pb and Zn using inductively coupled plasma-optical emission spectrometry. Metal concentrations in sediments were lower than the global averages of the earth's crust, with the exception of Cd and Cu. These results were related to the contribution of the local fresh-water runoff. The different varieties of paint showed low levels of Cu, Mn, Fe and Zn, whereas a broad range of values were found in the case of Cr and Pb (20-15,100μg·g-1 and 153-115,500μg·g-1 respectively). The remains of the paint would be responsible for the significant increases in Cr and Pb which are randomly detected by us and by other authors. High levels of Fe and Cd, in comparison to other Antarctic areas, appear to be related to the terrigenous materials transported by the local streams. Accumulation indexes suggested that kidney tissue from L. elliptica could be an adequate material for biomonitoring pollution with Cd, Zn and probably also Pb. In general, relationships between size and metal contents reported by other authors were not verified, suggesting that this issue should be revised. elliptica could be adequate for biomonitoring pollution with Cd and Zn. Fil: Vodopivez, Leopoldo Cristian. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Curtosi, Antonio. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Villaamil Lepori, Edda Cristina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina Fil: Smichowski, Patricia Nora. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Pelletier, Emilien. Université du Québec à Rimouski; Canadá Fil: Mac Cormack, Walter Patricio. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Nanobiotecnología. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Nanobiotecnología; Argentina

Abstract The physical characteristics and impermeability of diamonds allow them to retain radiogenic 4He produced in-situ from radioactive decay of U, Th and Sm. This study investigates the U-Th/He systematics of fibrous diamonds and provides a first step in quantification of the uncertainties associated with determining the in-situ produced radiogenic 4He concentration. Factors determining the total amount of measured helium in a diamond are the initial trapped 4He, the in-situ produced radiogenic 4He, α-implantation, α-ejection, diffusion, and cosmogenic 3He production. Alpha implantation is negligible, and diffusion is slow, but the cosmogenic 3He component can be significant for alluvial diamonds as the recovery depth is unknown. Therefore, samples were grouped based on similar major and trace element compositions to determine possible genetically related samples. A correlation between the 4He and U-Th concentrations approximates the initial 4He concentration at the axis-intersect and age as the slope. In this study, the corrections were applied to eight fibrous cubic diamonds from the Democratic Republic of the Congo and two diamonds from the Jwaneng kimberlite in Botswana. A correlation exists between the 4He and U-Th concentrations of the group ZRC2, 3, and 6, and of the group CNG2, 3, and 4 and both correlations deviate significantly from a 71 Ma kimberlite eruption isochron. The U-Th/He dating method appears a promising new approach to date metasomatic fluid events that result in fibrous diamond formation and this is the first evidence that some fibrous diamonds can be formed 10s to 100s Myr before the kimberlite eruption.

AbstractWe report on the first common volume ground‐based and space measurements of the mesospheric front in noctilucent clouds (NLCs). The detailed ground‐based observations were performed with automated digital cameras located at the Athabasca University Geophysical Observatory (Canada) on the night of 29–30 June 2012, while simultaneous space measurements were conducted onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite using the Sounding of the Atmosphere using Broadband Emission Radiometry instrument. The large temperature difference of 20–25 K between two different air masses at about 85 km altitude was responsible for the front jump separating the area filled with NLCs from the area with no NLCs. The front jump (soliton) had a pronounced elevation of 12 km up to the altitude of 96 km relative to the undisturbed NLC layer located between 84.5 and 86.3 km. Considering present and previous ground‐based measurements of the NLC height, we conclude that altitude of 96–97 km is the upper limit of possible heights of NLCs.

The continental Pleistocene Laurentide Ice Sheet (LIS) had far-reaching marine influence in shaping the ocean-floor adjacent to ice margin. The basinwide submarine-canyon and deep-sea channel system of the Northwest Atlantic Mid-Ocean Channel (NAMOC) of the Labrador Sea is the submarine continuation of the drainge system of the LIS on land, forming an interconnected land/sea drainage system 6,000 km long, one of the word’s longest drainage systems of Pleistocene age. The submarine portion forms a dual system, consisting of the mud-dominated NAMOC with its tributaries and a submarine sandy braid-plain.

Upland peat soils in close proximity to urban and industrial areas can be contaminated with high concentrations of atmospherically deposited lead. The peat soils of the Peak District (UK) are characterised by extensive eroding gullies. Fine-resolution digital topographic data were used to map the extent and depth of these gullies. Peat samples from eroding gully walls and suspended sediments were collected and analysed for lead content. Variability in lead concentrations of gully wall material and suspended sediments can be explained by differences in mean upslope gully depth. The lead content of suspended sediment exported from catchments characterised by shallow peat gullies is higher than that exported from catchments with deep peat gullies. The empirical relationship between sediment-associated lead concentration and mean upslope gully depth was combined with the gully depth mapping to produce a predictive spatial model of suspended sediment lead concentrations across the Peak District. This model may be particularly useful for catchment managers who are currently involved in the restoration of eroding peat soils in the Peak District uplands.

Compared with Phanerozoic strata, sulfate minerals are relatively rare in the Precambrian record; this is probably due to the lower concentrations of sulfate in dominantly anoxic oceans. Here, we present a compilation of sulfate minerals that are stratigraphically associated with the Ediacaran Shuram excursion (SE) – the largest negative δ13C excursion in Earth history. We evaluated 15 SE sections, all of which reveal the presence of sulfate minerals and/or enriched carbonate-associated sulfate concentrations, suggesting a rise in the sulfate reservoir. Notably, where data are available, the SE also reveals considerable enrichments in [Ba] relative to pre- and post-SE intervals. We propose that elevated seawater sulfate concentrations during the SE may have facilitated authigenesis of sulfate minerals. At the same time, the rise in Ba concentrations in shelf environments further facilitated barite deposition. A larger sulfate reservoir would stimulate microbial sulfate reduction and anaerobic oxidation of organic matter (including methane), contributing to the genesis of the SE. The existence of sulfate minerals throughout the SE suggests that oxidant pools were not depleted at that time, which challenges previous modelling results. Our study highlights the dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event. Supplementary material: SEM and EDS data and figures S1-S4 and tables S1-S3 are available at: https://doi.org/10.6084/m9.figshare.c.5602560 Thematic collection: This article is part of the ‘Sulfur in the Earth system’ collection available at: https://www.lyellcollection.org/cc/sulfur-in-the-earth-system

The Mesozoic Marine Revolution (MMR) was a major evolutionary episode involving the large-scale restructuring of shallow-marine benthic communities and the rise to dominance of the Modern Evolutionary Fauna. Although the majority of studies published on the MMR have been based on the body-fossil record, the ichnologic record yields valuable insights into this evolutionary event, most notably regarding the degree of infaunalization, complexity of infaunal tiering structures, and predation intensity. The main groups of bioturbators involved in the MMR were crustaceans, bivalves, echinoids, and “worms,” whereas the most important bioeroders were sponges, gastropods, bivalves, echinoids, and “worms.” The Triassic, encapsulated between two major mass extinctions, can be regarded as setting the stage for the MMR. The sparse ichnologic information available suggests that full recovery from the end-Permian mass extinction had taken place in equatorial carbonate settings by the Middle Triassic, although ichnofaunas show limited infaunalization and relatively simple tiering structures. However, a few key players, most notably some decapod crustaceans, were already dominant in carbonate settings. Jurassic ichnofaunas reveal a compositional turnover, signaling the rise to dominance of the Modern Evolutionary Fauna. This faunal turnover occurred by the Early Jurassic, as indicated by the taxonomic composition and increased diversity of bioturbation structures and the complexity of infaunal tiering. During the Cretaceous, a continuation of the trends established in the Jurassic was recorded. However, by the end of the Cretaceous, a modern-style benthic–pelagic coupling pattern was established, accompanied by an increase in global ichnodiversity. Rapid development of coccolithophores provided a new substrate (chalk) and an increasing flux of organic matter to the seafloor, enabling establishment of complex tiering structures, unknown in older deposits. The degree of macrobioerosion indicates an increasing participation of some players typical of modern communities. Paleogene bioturbation structures are similar to those of the late Mesozoic. Macrobioerosion styles also persisted across the Cretaceous–Paleogene boundary, albeit with an increased role for bioerosion by sponges and fishes later in the Paleogene. Predation pressures (drilling and durophagy) increased during the Eocene. Ichnofaunas in shallow-marine sediments record continued expansion of diversity during the Neogene, as well as more complex tiering structures. Predation pressure continued to rise, involving primarily marine mammals. Although the MMR for the most part took place in shallow, fully marine settings, the trace-fossil record also provides evidence for its expression in the deep sea and marginal-marine, brackish-water settings. Irregular echinoids and decapod crustaceans apparently had migrated to the deep sea by the Late Jurassic, whereas most of the main players of the MMR in fully marine settings (e.g., decapod crustaceans, bivalves, worms) were also dominant in brackish-water settings since the beginning of this major evolutionary event. Trace-fossil data indicate that infaunalization predates an increase of predation pressures by approximately 50 Myr, suggesting a complex set of feedback mechanisms between predation and infaunalization rather than simple cause and effect between the two. Turnover in ichnofaunal composition and the increased infaunalization that took place during the MMR strongly supports the “bulldozing hypothesis” (the notion that biological disturbance increased through the Phanerozoic), indicating a dramatic rise in bioturbational sediment processing by elements of the Modern Evolutionary Fauna. Fil: Buatois, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. University of Saskatchewan; Canadá Fil: Carmona, Noelia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina Fil: Curran, H. Allen. Smith College. Department of Geosciences; Estados Unidos Fil: Netto, Renata G.. Universidad de Vale do Rio dos Sinos; Brasil Fil: Mangano, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Saskatchewan; Canadá Fil: Wetzel, Andreas. Universität Basel. Geologisch-Paläontologisches Institut; Suiza

Abstract The transmission of stress induced by agricultural machinery within an agricultural soil is typically modelled on the basis of the theory of stress transmission in elastic media, usually in the semi-empirical form that includes the “concentration factor” (v). The aim of this paper was to measure and simulate soil stress under defined loads. Stress in the soil profile at 0.3, 0.5 and 0.7 m depth was measured during wheeling at a water content close to field capacity on five soils (13–66% clay). Stress transmission was then simulated with a semi-analytical model, using vertical stress at 0.1 m depth estimated from tyre characteristics as the upper boundary condition, and v was obtained at minimum deviation between measurements and simulations. For the five soils, we obtained an average v of 3.5 (for stress transmitting from 0.1 to 0.7 m depth). This was only slightly different from v = 3 for which the elasticity theory-based classical solution of Boussinesq (1885) is satisfied. We noted that the estimated v was strongly dependent on (i) the reliability of stress measurements, and (ii) the upper stress boundary condition used for simulations. Finite element simulations indicated that the transmission of vertical stresses in a layered soil is not appreciably different from that seen in a homogeneous soil unless very high differences in soil stiffness are considered. Our results highlight the importance of accurate stress readings and realistic upper model boundary conditions, and suggest that the actual stress transmission could be well predicted according to the theory of elasticity for the conditions investigated.