Brachiopod-based oxygen-isotope thermometer: Update and review

In the early 1950\u2019s, McCrea and Epstein and co-workers laid the foundation for the oxygen isotope-based thermometers. Many variations of the thermometer have been since formulated based on synthetic and biogenic carbonates. Overall, the use and application of oxygen isotope thermometers must consider and be specific as to the mineralogy, and whether it is synthetic, abiogenic or biogenic carbonate. Here, we propose an updated and refined oxygen-isotope thermometer based on a large database of articulated brachiopods from high to low latitudes, cold to warm and shallow to deep-water regimes. In general, brachiopod-based oxygen isotopes are offset from abiogenic calcite precipitated in thermodynamic equilibrium by about -1 . They maintain this offset and that allows for the determination of robust ambient water temperatures over the full marine spectrum. Thus, the specific brachiopod-based oxygen-isotope thermometer applies, with few exceptions, to most modern articulated brachiopods, and potentially their ancient counterparts, and it is as follows: T\ub0C =17.3750 \u2013 4.2535 (\u3b4c-\u3b4w) + 0.1473 (\u3b4c-\u3b4w)2 (N=578, r2 = 0.980) Furthermore, it is imperative that mineralogy and taxa be considered for their appropriateness in the application of oxygen isotope thermometers on synthetic, abiogenic and biogenic marine carbonates. Articulated brachiopods are ideal recorders of oceanographic parameters due to their sessile nature, widespread distribution, high abundance in the Paleozoic and Mesozoic, high resilience to most environmental stresses (e.g., climate change - global warming, ocean acidification), and the resistance of the calcite shell \u2013 the archive \u2013 to post-depositional diagenetic alteration

The influence of glacial cover on riverine silicon and iron exports in Chilean Patagonia

Glaciated environments have been highlighted as important sources of bioavailable nutrients, with inputs of glacial meltwater potentially influencing productivity in downstream ecosystems. However, it is currently unclear how riverine nutrient concentrations vary across a spectrum of glacial cover, making it challenging to accurately predict how terrestrial fluxes will change with continued glacial retreat. Using 40 rivers in Chilean Patagonia as a unique natural laboratory, we investigate how glacial cover affects riverine Si and Fe concentrations, and infer how exports of these bioessential nutrients may change in the future. Dissolved Si (as silicic acid) and soluble Fe (0.45 mu m) phases of both Si and Fe, which are not typically accounted for in terrestrial nutrient budgets but can dominate riverine exports. Dissolved Si and soluble Fe yield estimates showed no trend with glacial cover, suggesting no significant change in total exports with continued glacial retreat. However, yields of colloidal-nanoparticulate and reactive sediment-bound Si and Fe were an order of magnitude greater in highly glaciated catchments and showed significant positive correlations with glacial cover. As such, regional-scale exports of these phases are likely to decrease as glacial cover disappears across Chilean Patagonia, with potential implications for downstream ecosystems

The high-pressure phase of boron, {\gamma}-B28: disputes and conclusions of 5 years after discovery

{\gamma}-B28 is a recently established high-pressure phase of boron. Its structure consists of icosahedral B12 clusters and B2 dumbbells in a NaCl-type arrangement (B2){\delta}+(B12){\delta}- and displays a significant charge transfer {\delta}~0.5- 0.6. The discovery of this phase proved essential for the understanding and construction of the phase diagram of boron. {\gamma}-B28 was first experimentally obtained as a pure boron allotrope in early 2004 and its structure was discovered in 2006. This paper reviews recent results and in particular deals with the contentious issues related to the equation of state, hardness, putative isostructural phase transformation at ~40 GPa, and debates on the nature of chemical bonding in this phase. Our analysis confirms that (a) calculations based on density functional theory give an accurate description of its equation of state, (b) the reported isostructural phase transformation in {\gamma}-B28 is an artifact rather than a fact, (c) the best estimate of hardness of this phase is 50 GPa, (d) chemical bonding in this phase has a significant degree of ionicity. Apart from presenting an overview of previous results within a consistent view grounded in experiment, thermodynamics and quantum mechanics, we present new results on Bader charges in {\gamma}-B28 using different levels of quantum-mechanical theory (GGA, exact exchange, and HSE06 hybrid functional), and show that the earlier conclusion about significant degree of partial ionicity in this phase is very robust

Structural and Vibrational Properties of Silyl (SiH3-) Anions in KSiH3 and RbSiH3: New Insight into Si-H Interactions

The alkali metal silyl hydrides ASiH(3) (A = K, Rb) and their deuteride analogues were prepared from the Zintl phases ASi. The crystal structures of ASiH(3) consist of metal cations and pyramidal SiH3 ions. At room temperature SiH3 moieties are randomly oriented (alpha modifications). At temperatures below 200 K ASiH(3) exist as ordered low-temperature (beta) modifications. Structural and vibrational properties of SiH3- in ASiH(3) were characterized by a combination of neutron total scattering experiments, infrared and Raman spectroscopy, as well as density functional theory calculations. In disordered alpha-ASiH(3) SiH3 ions relate closely to freely rotating moieties with C(3)v symmetry (Si-H bond length = 1.52 angstrom; HSiH angle 92.2 degrees). Observed stretches and bends are at 1909/1903 cm(-1) (nu(1), A(1)), 1883/1872 cm(-1) (nu(3), E), 988/986 cm(-1) (nu(4), E), and 897/894 cm(-1) (nu(2), A(1)) for A = K/Rb. In ordered beta-ASiH(3) silyl anions are slightly distorted with respect to their ideal C-3v symmetry. Compared to a-ASiH(3) the molar volume is by about 15% smaller and the SiH stretching force constant is reduced by 4%. These peculiarities are attributed to reorientational dynamics of SiH3 anions in a-ASiH(3). SiH stretching force constants for SiH3 moieties in various environments fall in a range from 1.9 to 2.05 N cm(-1). These values are considerably smaller compared to silane, SiH4 (2.77 N cm(-1)). The reason for the drastic reduction of bond strength in SiH3- remains to be explored

The shrunk genetic diversity of coral populations in North-Central Patagonia calls for management and conservation plans for marine resources

The Chilean Patagonia is a complex puzzle of numerous fjords, channels, bays, estuaries, and islands. The largest part of it is very remote, hampering the generation of scientific knowledge and effective management planning that could balance conservation of the marine resources with the increasing development of aquaculture activities. The present study focuses on the deep-water emergent cold-water coral Desmophyllum dianthus, dwelling in Chilean Patagonia, with the aim to illustrate its population genetic structure, demography and adaptation of the species along this coast. Microsatellite loci analysis included D. dianthus individuals from twelve sampling localities along bathymetric and oceanographic gradients from the latitude 40°S to 48°S. The results showed a lack of genetic structure with an asymmetric dispersion of individuals, and relevant heterozygosity deficiency in some populations. This study also analyses the natural and human impacts affecting the region (e.g., climate change, increasing salmon farming activities), and stresses the importance of including genetic information in the process of management and conservation of marine resources. In particular, the relevance of using interdisciplinary approaches to fill the gaps in scientific knowledge especially in remote and pristine areas of western Patagonia. Therefore, information on genetic spatial distribution of marine fauna could become pivotal to develop a holistic ecosystem-based approach for marine spatial planning

Oxygen Atom Transfer Reactions from Mimoun Complexes to Sulfides and Sulfoxides. A Bonding Evolution Theory Analysis

In this research, a comprehensive theoretical investigation has been conducted on oxygen atom transfer (OAT) reactions from Mimoun complexes to sulfides and sulfoxides. the joint use of the electron localization function (ELF) and Thom's catastrophe theory (CT) provides a powerful tool to analyze the evolution of chemical events along a reaction pathway. the progress of the reaction has been monitored by structural stability domains from ELF topology while the changes between them are controlled by turning points derived from CT which reveal that the reaction mechanism can be separated in several steps: first, a rupture of the peroxo O-1-O-2 bond, then a rearrangement of lone pairs of the sulfur atom occurs and subsequently the formation of S-O-1 bond. the OAT process involving the oxidation of sulfides and sulfoxides is found to be an asynchronous process where O-1-O-2 bond breaking and S-O-1 bond formation processes do not occur simultaneously. Nudeophilic/electrophilic characters of both dimethyl sulfide and dimethyl sulfoxide, respectively, are sufficiently described by our results, which hold the key to unprecedented insight into the mapping of electrons that compose the bonds while the bonds change.Generalitat ValencianaSpanish Ministry Ministerio de Economiay CompetitividadSpanish-Brazilian programFundacion Bancaixa-Universitat Jaume I (UJI)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)São Paulo State Univ, Inst Chem, Interdisciplinary Lab Electrochem & Ceram, BR-14800900 Araraquara, BrazilUniv Jaume 1, Dept Quim Fis & Analit, Castellon de La Plana 12071, SpainUniversidade Federal de São Paulo, UNIFESP, Dept Ciencias Exatas & Terra, BR-09913030 Diadema, BrazilUniv Fed Sao Carlos, Dept Chem, Interdisciplinary Lab Electrochem & Ceram, BR-13565905 Sao Carlos, SP, BrazilUniversidade Federal de São Paulo, UNIFESP, Dept Ciencias Exatas & Terra, BR-09913030 Diadema, BrazilGeneralitat Valenciana: Prometeo/2009/053Spanish Ministry Ministerio de Economiay Competitividad: CTQ-2012-36253-C03-01Spanish-Brazilian program: PHB2009-0065-PCFundacion Bancaixa-Universitat Jaume I (UJI): P1.1B2010-10FAPESP: 2009/01628-8Web of Scienc

Housing differences in the late Soviet city: the case of Tartu, Estonia

Research on the residential and housing differences of urban populations in post-second world war Central and Eastern Europe has a tradition extending back to the 1960s. Most studies have focused on the Polish, Czech and Hungarian (large) cities using aggregatelevel data and testing simultaneously the impact of a few factors on residential and housing differences. This research clarifies the housing differences in the late Soviet era of Tartu (the second largest city in Estonia). Using the individual-level data of the 1989 Soviet census and multivariate methods, the article demonstrates that several factors (age, education, occupation, employment sector, ethnic origin, place of origin) shape the individual's housing and living conditions in the late Soviet period in Tartu. On the one hand, the results support the importance of the policy of different institutions (state, enterprises) in shaping people's living conditions; on the other hand, they also point to people's resources and desires as the cause. Copyright (c) Joint Editors and Blackwell Publishing Ltd 2003.