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Topic review
Updated time: 30 Oct 2020
Submitted by: Patrick Meister
Definition: Diagenetic carbonates often show large variations in their carbon isotope compositions. Variations are mainly the result of isotope fractionation effects during microbial metabolic processes, and these processes themselves may induce carbonate formation. Inorganic carbon from dissimilatory microbial activity shows negative carbon isotope values (d13C), in particular if methane is used as a carbon source. In turn, inorganic carbon produced during methanogenesis shows positive d13C values. The range of isotope values preserved in the carbonate phase ultimately depends on the reservoir sizes, diffusive mixing of different carbon sources, and episodic formation of carbonate. The carbon-isotope signature of diagenetic carbonates therefore represents an archive of past biogeochemical activity in the subsurface.
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Topic review
Updated time: 25 Apr 2021
Submitted by: Andrew Wheeler
Definition: Cold-water coral (CWC) habitats are considered important centers of biodiversity in the deep sea, acting as spawning grounds and feeding area for many fish and invertebrates.
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Topic review
Updated time: 02 Jul 2021
Submitted by: Vera Nikolaeva
Definition: E-region Auroral Ionosphere Model (AIM-E) is a numerical model involving both solar EUV radiation and electron precipitation as ionization sources. The AIM-E model allows to evaluate the concentration of the main ionospheric ions N+, N2+, NO+, O2+, O+(4S), O+(2D), O+(2P), electrons and minor neutral components NO, N(4S), N(2D), for quiet and disturbed geomagnetic conditions at specified date, time and geographic location. The model design allows to calculate the ionospheric composition in the entire high-latitude E-region in the retrospective, nowcast and forecast modes and shows good agreement with measurements.
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Topic review
Updated time: 26 Aug 2020
Submitted by: Nikita Chukanov
Definition: Eudialyte-group minerals (EGMs) are typical components of some kinds of agpaitic igneous rocks and related pegmatites and metasomatic assemblages. Crystal-chemical features of these minerals are important indicators reflecting conditions of their formation (pressure, temperature, fugacity of oxygen and volatile species, and activity of non-coherent elements. A unique crystal-chemical diversity of EGMs is determined by a wide variability of their chemical composition involving more than 30 main elements and complex mechanisms of homovalent, heterovalent, and, especially, blocky isomorphism involving groups of atoms having different valency and coordination. The uniqueness of these minerals lies in the fact that they exhibit ability to blocky isomorphism at several sites of high-force-strength cations belonging to the framework and at numerous sites of extra-framework cations and anions.
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Topic review
Updated time: 03 Aug 2021
Submitted by: Rafael M. Santos
Definition: The geochemical computer model is an important innovation that exponentially evolved in the last decades, and that now plays a vital role in several areas of study, ranging from developing new models for surface complexation, reactive transport models, or the generation of thermodynamic data used to simulate or predict solubility reactions. An important application of geochemical modeling involves supporting the explanation or characterization of engineering systems related to waste management, wastewater reuse, evaluation of water quality from a landfill, metal speciation within soils in industrial areas, new technologies or process for waste treatment, and even the evaluation of the potential to use solid wastes in carbon sequestering processes.
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Topic review
Updated time: 15 Sep 2021
Submitted by: Dennis A. Hansell
Definition: Marine dissolved organic matter (DOM) holds ~660 billion metric tons of carbon, making it one of Earth’s major carbon reservoirs that is exchangeable with the atmosphere on annual to millennial time scales. The global ocean scale dynamics of the pool have become better illuminated over the past few decades.
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Topic review
Updated time: 26 Apr 2020
Submitted by: Lutfian Daryono
Definition: Typically, the mitigation of coastal erosion is achieved by amending surface conditions using materials such as concrete. The objective of this study is to evaluate the feasibility of constructing artificial beachrocks using natural materials (e.g., microbes, sand, shell, pieces of coral, and seaweed etc.) within a short time, and to propose the method as a novel strategy for coastal protection. Initially, a survey on resistivity and a multichannel analysis of seismic waves (MASW) were conducted along the coastal lines to characterize and elucidate the subsurface structure of existing beachrocks in the Southeast Yogyakarta coastal area, Krakal–Sadranan beach, Indonesia. The field survey on natural beachrocks suggests that both resistivity and shear wave velocity were higher in the deeper deposits compared to the underlying unconsolidated sand layer within a depth of approximately 1.5 m and covering an area of 210.496 m2 for the α-section and 76.936 m2 for the β-section of beachrock deposit. The results of the sand solidification test in the laboratory showed that treated sand achieved unconfined compressive strength of up to around 6 MPa, determined after a treatment period of 14 days under optimum conditions.
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Topic review
Updated time: 08 Sep 2021
Submitted by: Bopaiah Biddanda
Definition: Extant microbial mats already present on Earth provide useful working analog models for the exploration of life in extraterrestrial hydrospheres.
Entry Collection : Environmental Sciences
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Topic review
Updated time: 27 Aug 2021
Submitted by: Damien Gaboury
Definition: Carbonaceous organic matter occurs under various phases and forms, where its fine characterization is mostly restricted to petroleum and coal geology. As a consequence, few studies have integrated the complete link between various forms of organic matter and metals to decipher hydrothermal ore concentrating processes. The study of Dill et al., integrating the concentration of sulfides and oxides with the interaction of silicates and organic matters, is an example of the next step to reach for defining the complex role of organic matter for the formation of orogenic gold deposits.
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Topic review
Updated time: 05 Jul 2021
Submitted by: Francesco Ciani
Definition: Particulate Bound Hg (PBM) consists of all airborne particulate containing Hg, including both stable condensed and gaseous forms adsorbed on atmospheric particulate matter (PM); it is operationally sampled and quantified by pulling air through a glass fiber or a quartz filter. PBM usually includes all those particles with a diameter <2.5 μm, even if its characterization depends on the pore size of the filter used for its collection. The accurate dimensional characterization is then essential to estimate the dry deposition of PBM, as well as any other particulate pollutant; the particles diameters directly influence gravitational sedimentation and the PBM residence time in the atmosphere. In addition, PBM chemical speciation, as well as for the other Hg forms, is fundamental to understand PBM bioavailability and therefore the effects on human .
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