Hydrodynamics, Hydrochemistry, and Stable Isotope Geochemistry to Assess Temporal Behavior of Seawater Intrusion in the La Yarada Aquifer in the Vicinity of Atacama Desert, Tacna, Peru

The La Yarada aquifer is the primary water resource for municipal, irrigation, and industrial uses in the semi-arid Tacna, Peru. Presently, over-pumping has caused severe groundwater management problems, including the abandonment of saline water wells. This study presents multivariate analysis and chemical–isotopic trends in water to investigate seawater intrusion and hydrogeological processes affecting water quality. The chemical and isotopic analysis of water samples, collected in two campaigns in the dry (August 2020) and wet (November 2020) seasons, together with the 1988 data, were evaluated with a mixing model, cluster, and factor analysis. The hydrochemical and isotopic mixing model suggested the formation of a wedge with 20% seawater intrusion. The heterogeneity of piezometric map isolines corroborates the wedge formation associated with the groundwater movement. The spatial distributions of factors, FA1 and FA2, suggest two processes of seawater front movement: dispersion (diffusion) of chemical elements and different types of water mixing, respectively. At the edge of the La Yarada aquifer, the water head was relatively low, permitting seawater and freshwater mixing. On the other hand, along the sea-land boundary, the water head of the La Yarada aquifer was relatively high, avoiding seawater and freshwater mixing; however, the chemical species were migrating from the seawater to the groundwater due to the diffusion processes. The cluster 4 samples are in the region corresponding to the isotopic mixing process represented by the FA2, while cluster 4 describes the chemical diffusion process represented by the FA2. Thus, the integrated approach is helpful to assess the seawater intrusion mechanisms in coastal aquifers in a semi-arid region.

Water-source contributions to barrier lakes and water-rock interactions in the Wudalianchi volcanic area, Northeast China

Wudalianchi is a typical continental Cenozoic volcanic group rich in potassic volcanic rocks (Northeast China). Five hydrologically connected barrier lakes (Lakes 5 to 1) and upwelling cold mineral springs occur, forming a complex lake-groundwater system. Clarifying the water-source contributions and the role of water-rock interactions in the hydrological cycling for barrier lakes remains a challenge from scientific and engineering perspectives. In this study, seasonal variations of multiple isotopes were analyzed. δ18O and δD data indicate that the Wudalianchi lakes were mainly fed by mineral springs. The values, however, were greatly influenced by precipitation (rain and snow) and varying evaporation intensities. In contrast, 87Sr/86Sr ratios varied little between seasons (0.70701–0.7079), suggesting similar water-rock interactions through time. Nonetheless, Sr isotopic mixing models suggested that shallow mineral springs generally contributed >50% of the water to lower reaches. In contrast, the upstream wetland contributed >50% to Lake 5 and decreased down-valley (10.3–53.6%). Calculations based on the δ18O and δD Rayleigh fractionation equation suggest that evaporation in upper reaches were higher than the lower reaches. The evaporation in July were generally higher than in October. This study demonstrates the homogenous water-rock interactions and the associated water mixing effects on the terrestrial volcanic area.

Solid to superionic transition in iron oxide-hydroxide

<p>At planetary interior conditions, water ice has been proved to enter a superionic phase recently since it was predicted about 30-year ago. Hydrogen in superionic water become liquid-like, and move freely within solid oxygen lattice. Under extreme pressure and temperature conditions of Earth’s deep mantle, the solid-superionic transition can also occur readily in the pyrite-type FeO<sub>2</sub>Hx, a candidate mineral in the lower mantle and probably also in other hydrous minerals. We find that when the pressure increases beyond 73 GPa at room temperature, symmetric hydroxyl bonds are softened and the H<sup>+</sup> (or proton) become diffusive within the vicinity of its crystallographic site. Increasing temperature under pressure, the diffusivity of hydrogen is extended beyond individual unit cell to cover the entire solid, and the electrical conductivity soars, indicating a transition to the superionic state which is characterized by freely-moving proton and solid FeO<sub>2</sub> lattice. The superionic hydrogen will dramatically change the geophysical picture of electrical conductivity and magnetism, as well as geochemical processes of hydrogen isotopic mixing and redox equilibria at local regions of Earth’s deep interiors.</p>

Origin of megacrysts by carbonate-bearing metasomatism – A case study for the Muskox kimberlite, Slave craton, Canada

Low-Cr and high-Cr clinopyroxene, garnet, olivine, and ilmenite megacrysts from the Muskox kimberlite (Canada) have been analyzed for major and trace elements, as well as Sr, Nd, and Pb isotopes. Samples display compositional overlap with respective phases in websterite, while clinopyroxene isotope systematics reveal similarities with both websteritic and metasomatic clinopyroxene in peridotites from the same kimberlite, in addition to Muskox and Jericho kimberlite. All lithologies may represent the products of mixing between EM1 mantle, relic Proterozoic enriched mantle and HIMU carbonatitic fluid. Equilibrium melts calculated from clinopyroxene trace element data using experimental distribution coefficients for feasible proto-kimberlitic melts yield a range of possible metasomatic agents. Conclusion on the carbonate-bearing nature of the metasomatism was based on the presence of a HIMU isotopic signature and results obtained from thermodynamic modeling using the Deep Earth Water model. The latter shows that mineral compositions analogous to megacrysts cannot be produced by metasomatism of mantle peridotite by H2O-rich kimberlitic fluids, or fluids in equilibrium with either asthenospheric or eclogitic mantle. Isotope systematics argue against a strictly cognate relationship between megacrysts and their host kimberlite, instead suggesting megacrysts and websterites may represent products of regional metasomatism by carbonatitic HIMU fluids shortly predating kimberlite magmatism.Supplementary material: Supplementary Table 1 contains the parameters used in isotopic mixing models https://doi.org/10.6084/m9.figshare.c.5255825

A combination of soil water extraction methods quantifies the isotopic mixing of waters held at separate tensions in soil

Measurements of the isotopic composition of separate and potentially interacting pools of soil water provide a powerful means to precisely resolve plant water sources and quantify water residence time and connectivity among soil water regions during recharge events. Here we present an approach for quantifying the time-dependent isotopic mixing of water recovered at separate suction pressures or tensions in soil over an entire moisture release curve. We wetted oven-dried, homogenized sandy loam soil first with isotopically “light” water (δ2H =-130 ‰; δ18O =-17.6 ‰) to represent antecedent moisture held at high matric tension. We then brought the soil to near saturation with “heavy” water (δ2H =-44 ‰; δ18O =-7.8 ‰) that represented new input water. Soil water samples were subsequently sequentially extracted at three tensions (“low-tension” centrifugation ≈0.016 MPa; “mid-tension” centrifugation ≈1.14 MPa; and “high-tension” cryogenic vacuum distillation at an estimated tension greater than 100 MPa) after variable equilibration periods of 0 h, 8 h, 1 d, 3 d, and 7 d. We assessed the differences in the isotopic composition of extracted water over the 7 d equilibration period with a MANOVA and a model quantifying the time-dependent isotopic mixing of water towards equilibrium via self-diffusion. The simplified and homogenous soil structure and nearly saturated moisture conditions used in our experiment likely facilitated rapid isotope mixing and equilibration among antecedent and new input water. Despite this, the isotope composition of waters extracted at mid compared with high tension remained significantly different for up to 1 d, and waters extracted at low compared with high tension remained significantly different for longer than 3 d. Complete mixing (assuming no fractionation) for the pool of water extracted at high tension occurred after approximately 4.33 d. Our combination approach involving the extraction of water over different domains of the moisture release curve will be useful for assessing how soil texture and other physical and chemical properties influence isotope exchange and mixing times for studies aiming to properly characterize and interpret the isotopic composition of extracted soil and plant waters, especially under variably unsaturated conditions.

An Isotopic and Morphometric Examination of Island Dogs (Canis familiaris): Comparing Dietary and Mobility Patterns in the Precolumbian Caribbean

In precolumbian insular Caribbean archaeological sites, domestic dog (Canis familiaris) remains have been recovered from varied contexts, such as formal burials, in refuse deposits, and as modified artifacts, indicating their complex and multifaceted role within indigenous societies. In this study, isotopic and morphometric analyses provide biochemical and morphological correlations to assess this differential treatment. We examined collagen values (n = 21) of carbon (δ13Cco) and nitrogen (δ15N), and enamel values (n = 81) of carbon (δ13Cen), oxygen (δ18Oen), and strontium (87Sr/86Sr) of dog remains from 16 precolumbian sites. Five comparative parameters were used to assess dietary variations between different groups: buried versus nonburied, local versus nonlocal, Greater versus Lesser Antilles, chronology, and modified versus unmodified remains. The only statistically significant difference in diets was between local and nonlocal dogs. Sufficient data were available to conduct isotopic mixing models using the FRUITS statistical program on four individuals for which depositional and morphological data were available. Results of dietary modeling indicate an unexpectedly heavy reliance on plant foods consistent with intentional feeding. This approach highlights the utility of combining isotope analysis, dietary models, morphometrics, and depositional context to provide comprehensive biographic overviews of individual animals.

Mineral reservoirs and behaviors of hydrogen in Earth’s lower mantle

<p>The incorporation of H into minerals imposes profound effects on their physicochemical signatures of the solid Earth. The locations of hydrogen reservoirs are detected by seismology. However, the mineral responsible for storing large quantity of hydrogen, particularly in Earth’s lower mantle is still controversial. Combining a set of in-situ probes at high pressure-temperature and first principles simulation, we investigated the solubility and behaviors of H in silica and hydroxide up to the conditions found at the core-mantle boundary. The solubility of hydrogen keeps high in those minerals even along the mantle geotherm. Under deep lower mantle pressures, hydrogen atoms are free from the hydroxyl bonding and becomes highly diffusive. The swift diffusion of hydrogen ions induces soaring electrical conductivity when the sample is laser heated. Those exotic properties indicate novel transport mechanisms for both charge and mass at Earth’s deep lower mantle. The potential of hydrogen enriched volatile reservoirs may carry major impacts on the electrical and magnetic behaviors, as well as redox, H isotopic mixing, and other geochemical processes in the Earth’s deep interiors.</p>

Combination of soil water extraction methods quantifies isotopic mixing of waters held at separate tensions in soil

Measurements of the isotopic composition of water recovered from soil at different tensions provide a powerful means to identify potential plant water sources and quantify heterogeneity in residence time and connectivity among soil water regions. Yet incomplete understanding of mechanisms affecting isotopic composition of different soil water pools and the interactions between antecedent and new event water hinders interpretation of the isotope composition of extracted soil and plant waters. Here we present an approach for quantifying the time-dependent isotopic mixing of water held at separate tensions in soil. We wetted oven-dried, homogenized sandy loam soil first with isotopically “light” water (𝛿2H = −130 ‰; 𝛿18O = −17.6 ‰) using a sufficient volume to fill only the smallest soil pores, and then with “heavy” water (𝛿2H = −44 ‰; 𝛿18O = −7.8 ‰) to fully saturate the remaining soil regions. Soil water effluents were then sequentially extracted at three tensions (low centrifugation = 0.016 MPa; medium centrifugation = 1.14 MPa; and high cryogenic vacuum distillation at an estimated tension greater than 100 MPa) starting after variable equilibration periods of 0 h, 8 h, 1 d, 3 d and 7 d. We assessed differences in the isotopic composition of extracted effluents over the 7 d equilibration period with a MANOVA and a mixing model describing the time-dependent effects of isotope self-diffusion and exchange. The saturated moisture conditions used in our experiment likely facilitated rapid isotope exchange and equilibration among different pools. Despite this, the isotope composition of waters extracted at medium compared to high tension remained significantly different (MANOVA) for up to 1 day, and that for waters extracted at low compared to high tension remained significantly different for greater than 3 days after soil wetting. Equilibration (assuming no fractionation) predicted from the time-dependent mixing model for water held at high tension occurred after approximately 4.33 days. Our approach will be useful for assessing how soil texture and other physical and chemical properties influence isotope exchange and mixing times for studies aiming to properly characterize and interpret the isotopic composition of extracted soil and plant waters, especially under variably unsaturated conditions.