Radiation damage in zircon directly impacts diffusion of He from the crystal lattice and is a key factor in defining the kinetics of the zircon (U-Th)/He system. Damage accumulates within a crystal as a function of time and U and Th concentration, but can be thermally annealed as well. The total level of radiation damage in a zircon crystal is governed by a thermally-activated, kinetic process, which in turn influences the interpretation of zircon (U-Th)/He dates for thermal histories. Several annealing models have been defined for the zircon system based on measurements in natural crystals; however, few studies have investigated how multiple levels of radiation damage due to zonation of actinides within a crystal may influence the annealing process. Here we use Raman spectroscopy to map the full width half maximum (FWHM) of then (SiO) band, a proxy for radiation damage, in zircon crystals from the Lucerne pluton (Maine, USA) with heterogeneous distributions of U and Th. We compare FWHM maps before and after annealing these crystals at laboratory times and temperatures. These maps show that each damage zone within a single zircon acts as an isolated domain that is dictated by an independent set of annealing kinetics. Thermally activated annealing decreases radiation damage in all radiation damage zones; however, the rate of annealing is not consistent across all zones. We identify specific modes of damage in probability density plots of all measured FWHM in a crystal that are not present in pre-annealed imagery, but persist in post-annealing Raman maps, regardless of laboratory time temperature conditions: FWHM modes at 2-5 cm, 10-15 cm, and25-30 cm. We attribute these persistent damage modes to variable annealing kinetics that are partially dependent on the level of pre-annealing damage, combined with the inability of high-damage crystals, or zones within crystals, to fully recover their crystallinity. That is, some damage is permanent. These findings therefore show that zircon crystals with non-uniform distributions of U and Th can anneal to create long-lived damage zones at specific damage levels, which has implications for treating the zircon (U-Th)/He chronometer as a multi-domain diffusion system.

Dense polymorphs of silica have been demonstrated experimentally to incorporate from 1.5% to as much as 11.6% weight percent H2O as OH groups, with implications for the hydrogen budgets of Earth and other planets. This OH is thought to enter the SiO2 structure via a charge-balanced substitution in which silicon vacancies (VSi) are compensated by protonating four of the surrounding six oxygen atoms, often referred to as a hydrogarnet-type defect. There are many possible configurations for this defect structure in dense silica, but the nature of these configurations and whether they can be distinguished experimentally is unknown. We present here density functional theory (DFT) calculations that systematically assess the possible configurations of a hydrogarnet-type defect in stishovite (rutile-type SiO2), with direct comparisons to experimental vibrational spectroscopy data. We predict that stishovite synthesized at 450 K and 10 GPa quenched to room temperature is dominated by a single defect type with tetrahedral geometry. This leads to OH stretching modes (2500-3000 cm-1) and SiOH bending modes (~1400 to 1450 cm-1) largely consistent with experimentally observed modes. One remaining issue is that our calculations produce results compatible with experimental data on H to D exchange, but do not explain why a considerable fraction of the 1420 cm-1 mode shifts by only 40 cm-1 in deuterated samples. At elevated pressures and temperatures, we find that a second square planar defect configuration also becomes favorable, leading to modes that should allow differentiation from the tetrahedral configuration.

How the continental crust responds geochemically to progressive extension is one of the interesting questions. The Southern Tibet Rift System (STRS) is one of the active extensional structures. The Yardoi gneiss dome, located within STRS, consists of at least four suites of Miocene granites. As crystallization ages become younger, they are characterized by decrease in Nd(t) and Sr/Y, but increase in 87Sr/86Sr(t) and Rb/Sr. Such temporal trends could be explained by sequential partial melting of first the mafic lower crustal rocks and then progressively shallower metasedimentary rocks. Together with literature data, from north to south along STRS, as the extension proceeds and the heat moves upward, sequential partial melting is common to produce Miocene magmatic rocks. The processes documented in the southern Tibet might be common in other extensional provinces and provides a new insight to unravel the mechanisms for the generation of geochemical variations in contemporaneous granites.

Spectrophotometry using a small sample volume has been developed to measure the alkalinity (or bicarbonate). However, the experimental and calculation processes are complicated, and the atmospheric CO2 has to consider in preparing standard solutions. This study aims to quantify the dissolution of the atmospheric CO2 when using spectrophotometry. Also, the effect on the standard solution in titrating that uses to make calibration curve are calculated to understand the effects of the different CO2 concentrations in a laboratory. The difference between the bicarbonate concentrations and the calculated ones based on the updated chemical equilibrium formula was from 0.038 to 5.4×10-6 mg/L. The maximum difference was found at pH 5.0 in the 10 mg/L HCO3- standard solutions. The bicarbonate concentration without the atmospheric CO2 reaction (C1) and with the atmospheric CO2 reaction (C2) was calculated by the PHREEQC. The difference between C1 and C2 ranged from 0.01 to 0.02 mg/L, but the calculated bicarbonate concentrations between the HCl titration and the PHREEQC output were certainly different, which ranged from 3.1 to 11.5 mg/L at the pH 4.3 endpoint. In contrast, at the pH 4.8 endpoint, the difference was significantly decreased from 0.8 to 1.3 mg/L. The effect of the increasing atmospheric CO2 by human breathing in a laboratory is only 0.05 mg/L in the standard solutions when titrating. From the results of this study, the experimental and calculation processes to correct the bicarbonate concentration by the effect of the atmospheric CO2 in a laboratory may be omitted if natural waters are targeted.

Iron is the fourth most common element found in the earth crust. Although it may not be as important for soil fertility as, e.g., phosphorus, nitrogen and organic matter, its absence would be detrimental to plant growth. At the same time, iron oxides are highly correlated with phosphorus availability. Iron is thus an indicator for soil fertility and the usability of an area for cultivation of crop. A relatively high spectral resolution is needed for mapping iron oxide contents with spectral reflectance data, and remote sensing is the only suitable tool for surveying large areas at a high temporal and spatial interval. Sentinel-2 MSI (MultiSpectral Instrument) is the Landsat-like spatial resolution (10–60 m) super-spectral instrument of the European Space Agency (ESA), aimed at additional data continuity for global land surface monitoring with Landsat and Satellite Pour l’Observation de la Terre (SPOT) missions. Several studies with simulated and real data have been conducted in the last several years to show the potential of Sentinel-2 MSI, including its use for geological remote sensing, mineral mapping in particular. Sentinel-2 has several bands that cover the 0.9 μm iron absorption feature, while space-borne sensors traditionally used for geologic remote sensing, like ASTER and Landsat, had only one band in this feature. In this paper, we show a comparison of Sentinel-2 and AVIRIS to demonstrate the usability of the VNIR bands for mapping the near-infrared iron absorption feature. Next, we present spectral indices for mapping iron minerals that are important in soil fertility and mineral exploration.

With the recent GIEC report about global warming urging humanity to limit the global temperature increase to 2°C maximum, research on the geological storage of carbon dioxide appears more important than ever. However, the injection in geological formations (such as deep saline aquifers and depleted gas/oil fields) of supercritical CO2, stores it in the porosity of the host rock raising legitimate concern about the safety and long-term behavior of such dynamic multiphase hydrosystems. Additionally, the economic and energetic weight of such storage complicates its development at the world scale without strong political incentives. The storage of CO2 in ultramafic formations in some specific contexts appears, on the contrary, as a very appealing technology since it involves the safe mineralization of the carbon by precipitation of carbonates with the major alkaline earth metals (i.e. Mg, Ca…) leached from the formation itself. Moreover, as these rocks contain high amounts of ferrous iron, its oxidation by the water co-injected with CO2 produces dihydrogen, which can be economically valuable rendering the whole process more viable. Large ophiolite formations (Oman, Papua New Guinea, east coast of Adriatic Sea…) are expected to have a storage capacity of several billion tons of CO2 and could produce similar amounts of clean dihydrogen. We present experimental results on the mineral carbonation of natural cores of serpentinites by the continuous percolation of carbon-saturated water. We show that the dimensionless Péclet (relative importance of diffusion and convection processes), and Damköhler (relative importance of convection and chemical processes) numbers as well as the initial geometry of the porosity and permeability control the localization of the silicate dissolution and the carbonate precipitation in the porous medium. We also show that the chemical behavior is principally controlled by the reactivity of calcium-bearing silicates (wollastonite, diopside) and the precipitation of calcite as well as the initial iron content of the different phases. Such results are particularly interesting for the design and the optimization of pilot sites and the development of this technology at industrial scale.

In the subsurface, water content, gas solubility, adsorption on minerals and chemical reactions control gas fluxes between soil and the atmosphere. Because these processes vary in intensity both in time and space, it is very challenging to quantify emissions, specifically when flux measurements are used for detection, identification or monitoring of a subsurface gas source. An experimental setup for gas percolation though soil column experiments under well-controlled conditions was developed and validated at the ECOTRON IleDeFrance research center. Its design included the effect of: i) watering/evaporation cycles, ii) barometric pressure, iii) injection pressure, iv) tracer behaviors and v) plant metabolism. To better understand subsurface processes controlling gas fluxes, we studied transport of multiple tracers across soil columns using long-term and high-resolution monitoring thanks to online low-flow mass-spectrometry. We injected tracer gases into columns containing different porous media, pure sillica sand and zeolite. This set-up allowed us to evaluate the relative contribution of diffusion, solubility and adsorption on various trace gases (SF6, noble gas including Xe). All the experimental data are discussed in conjonction with simulations using the NUFT unsaturated flow and transport code.

The carbonate dissolution plays a major role in the atmospheric CO2 sink and in the riverine transfer of dissolved inorganic carbon from the atmosphere to the critical zone and to the oceans. In this context, the Baget watershed (13.25 km2, altitude 950 m), essentially forested and weakly exposed to local anthropogenic pollution, drains a karst area in the Pyrenees mountains. It has been monitored for more than 40 years to better understand the impact of global changes on carbonate dissolution and hydro-chemistry of streamwaters. The mean annual precipitation exceeds 1500 mm and the air temperature average is 12°C. Calcareous dominates the lithology (around 2/3 of the area), with some flysh and schists. This experimental catchment belongs to the French Karst Network, to the French (OZCAR) and European (LTER) Research Infrastructures. Based on the hydrochemistry survey since 1978, the results focus on carbonate dissolution, stream water chemistry (mainly Ca, Mg and alkalinity) and calcite saturation index (SI) in relation with pCO2, temperature (T) and river discharge (Q). We analysed the long term trends of the instantaneous values but also of the inter-annual fluctuations of the mean monthly values. The long-term hydrochemical survey allows to evidence a net increasing trend in [Ca2++Mg2+] and [HCO3-] that could be related to an increase in air temperature and a decrease in pCO2 and discharge. Indeed, changes in vegetation cover over the period might have been another controlling factor that is currently investigated. Furthermore, mean monthly values based on the long-term trends allow to understand the dynamic of carbonate dissolution and to identify the main key controlling factors such as the water amount (discharge) and the air temperature, which influences pCO2 production. Lastly, the influence of the drainage relative to minor lithology could be evidenced particularly during low water period by an increased proportion of [SO42-] to [HCO3- ] in stream water, due to the relative substitution of [H2CO3] by [H2SO4] from pyrite oxydation.

Continental flood basalts (CFB) in the Karoo large igneous province have been divided into the North and South Karoo groups. Picrites from the Luenha river, Mozambique, have been shown to represent the primitive mantle-like end-member required to explain the geochemical characteristics of the North Karoo CFBs, which have elevated ΔNb compared to the South Karoo CFBs. These picrites exhibit a narrow range of bulk-rock Nd isotope compositions (εNd180Ma -2.0 to +1.4) but a wide range of bulk-rock, plagioclase and groundmass Sr isotope compositions (full range 87Sr/86Sr180Ma 0.704096-0.71061), extending to high values suggestive of crustal contamination in the origin of these rocks. Despite this, preliminary O isotope data for olivine from one sample with elevated 87Sr/86Sr show uniform, mantle-like δ18O values (4.68±0.38‰ to 5.53±0.37‰). New O isotope data to be acquired in November 2019 on the NordSIM Cameca IMS 1280 ion microprobe will determine the O isotope composition of a sample inferred to most closely represent the parental magma as well as test the intra- and inter-sample O-isotopic variability of these picrites. Combined with the available bulk-rock and plagioclase phenocryst compositions, these data allow us to constrain the progress of crustal contamination and evaluate the homogeneity of the parental magmas. Most importantly, we aim to distinguish between the effects upon the samples of crustal contamination versus mantle source heterogeneity.

In the Western Tropical South Pacific, a hotspot of N2-fixing organisms has recently been identified. The survival of these species depends on the availability of dissolved iron (dFe). dFe was measured along a transect from 175 °E to 166 °W near 19-21 °S. The distribution of dFe showed high spatial variability: low concentrations (~0.2 nmol kg-1) in the South Pacific gyre and high concentrations (up to 50 nmol kg-1) west of the Tonga arc, indicating that this arc is a clear boundary between iron-poor and iron-rich waters. An optimal multiparameter analysis was used to distinguish the relative importance of physical transport relative to non-conservative processes on the observed dFe distribution. This analysis demonstrated that distant sources of iron play a minor role in its distribution along the transect. The high concentrations observed were therefore attributed to shallow hydrothermal sources massively present along the Tonga-Kermadec arc. Nevertheless, in contrast to what has been observed for deep hydrothermal plumes, our results highlighted the rapid decrease in dFe concentrations near shallow hydrothermal sources. This is likely due to a shorter residence time of surface water masses combined with several biogeochemical processes at play (e.g., precipitation, photoreduction, scavenging, biological uptake). This study clearly highlights the role of shallow hydrothermal sources on the dFe cycle within the Tonga-Kermadec arc where a strong link to biological activity in surface waters can be assessed. It also emphasizes the need to consider the impact of these shallow hydrothermal sources for a better understanding of the global iron cycle.

Moderate to large earthquakes can increase the amount of water feeding stream flows, raise groundwater levels, and thus grant plant roots more access to water in water-limited environments. We examine tree growth and photosynthetic responses to the Maule Mw 8.8 Earthquake in small headwater catchments of Chile’s Mediterranean Coastal Range. We combine high-resolution wood anatomic (lumen area) and biogeochemical ( of wood cellulose) proxies of daily to weekly tree growth on cores sampled from trees on floodplains and close to ridge lines. We find that, immediately after the earthquake, at least two out of six tree cores show changes in these proxies: lumen area increased and decreased in the valley trees, whereas the sign of change was reversed in trees on the hillslope. Our results indicate a control of soil water on this response, largely consistent with models that predict how enhanced post-seismic vertical soil permeability causes groundwater levels to rise on the valley floor, but fall along the ridges. Statistical analysis with boosted regression trees indicates that streamflow discharge gained predictive importance for photosynthetic activity on the ridges but lost importance on the valley floor after the earthquake. We infer that earthquakes may stimulate ecohydrological conditions favoring tree growth over days to weeks by triggering stomatal opening. The weak and short-lived signals that we identified, however, show that such responses are only valid under water-limited instead of energy-limited tree growth. Hence, dendrochronological studies targeted at annual resolution may overlook some earthquake effects on tree vitality.

Here, we extend the Fisher-Kolmogorov-Petrovsky-Piskunov equation to capture the interplay of multiscale and multiphysics coupled processes. We use a minimum of two coupled reaction-diffusion equations with additional nonlocal terms that describe the coupling between scales through mutual cross-diffusivities and regularise the ill-posed reaction-self-diffusion system. Applying bifurcation theory we suggest that geological patterns can be interpreted as physical representations of two classes of well-known instabilities: Turing instability, Hopf bifurcation, and a new class of complex soliton-like waves. The new class appears for small fluid release reactions rates which may, for negligible self-diffusion, lead to an extreme focusing of wave intensity into a short sharp earthquake-like event. We propose a first step approach for detection of these dissipative waves, expected to precede a large scale instability.

Similar to most West Antarctic ice shelves, those in the Bellingshausen Sea have rapidly thinned by hundreds of cubic kilometers over the last decades yet they remain under-studied compared to other regions. The increased melting rates in the West Antarctic Peninsula (WAP) have been linked to warm Circumpolar Deep Water (CDW) that is able to access the continental shelf due to the absence of the Antarctic Slope Current. The exact pathways of CDW flowing on to the shelf and of meltwater flowing away from the ice shelves are essential to understanding the dynamics in this region and how it will change in the future. Here, we propose that the Bellingshausen Sea plays an important role in connecting circulation between the Amundsen Sea and the WAP and may influence water properties that circulate under floating ice shelves throughout the West Antarctica. Using a combination of hydrographic and isotopic data from a recent cruise to the Bellingshausen Sea (December 2018 to January 2019), multiple methods are applied to identify circulation pathways and to quantify glacial meltwater fractions. The meltwater measurements show that the Belgica and Latady Troughs are important pathways for CDW to reach the ice shelves, though almost twice as much meltwater is transported off the shelf via the Belgica Trough. CDW enters the shelf at the deepest part of the Belgica Trough, moving towards the coast along the trough’s eastern side. The largest meltwater fractions are found along the western flank of the Belgica and Latady Troughs. The meltwater signature can be tracked to the western edge of the Bellingshausen Sea, where it is then entrained into a boundary current system that flows over the continental slope towards the Amundsen Sea.

The North American monsoon (NAM) is an important source of precipitation across the southwestern United States (US). The approximate northern boundary of this feature crosses the Navajo Nation, in the Four Corners region, where NAM rains have long been important to the livelihoods of Native Americans. Relatively little is known about the characteristics and hydrological significance of the NAM in this region. Here we report a new 4-year record of stable H and O isotope ratios in monsoon-season rainfall and water resources across the Navajo Nation. Monthly precipitation samples collected at 39 sites document a characteristic pattern of 2H- and 18O-enrichment associated with monsoonal precipitation. These changes are weakly correlated with local precipitation intensity, however, and the correlation that does exist is dominated by sub-cloud evaporation effects. In contrast to precipitation amount, monsoon-season isotopic values exhibited limited spatial variability across the region, and after correction for sub-cloud evaporation Navajo Nation values were similar to those from a site in southern Arizona. Airmass back-trajectory analysis suggests that the uniformly high NAM isotope values across the region may reflect 1) a region-wide shift from mid-latitude to low-latitude moisture sources at the onset of the peak monsoon, and 2) substantial land-surface recycling of NAM moisture in upwind regions. Comparison of precipitation isotope data with surface and groundwater values implies that, despite its hydroclimatic significance, monsoon rainfall contributes little to rand subsurface water resources. This highlights the monsoon’s importance for warm-season land-surface ecology and hydrology critical to residents of the Four Corners region.

Southeast Asia is a hotspot of riverine export of terrigenous organic carbon to the ocean, accounting for ~10% of the global land-to-ocean riverine flux of terrigenous dissolved organic carbon (tDOC). While anthropogenic disturbance is thought to have increased the tDOC loss from peatlands in Southeast Asia, the fate of this tDOC in the marine environment and the potential impacts of its remineralization on coastal ecosystems remain poorly understood. We collected a multi-year biogeochemical time series in the central Sunda Shelf (Singapore Strait), where the seasonal reversal of ocean currents delivers water masses from the South China Sea first before (during Northeast Monsoon) and then after (during Southwest Monsoon) they have mixed with run-off from peatlands on Sumatra. The concentration and stable isotope composition of dissolved organic carbon, and colored dissolved organic matter spectra, reveal a large input of tDOC to our site during Southwest Monsoon. Using isotope mass balance calculations, we show that 60–70% of the original tDOC input is remineralized in the coastal waters of the Sunda Shelf, causing seasonal acidification by up to 0.10 pH units. The persistent CO2 oversaturation drives a CO2 efflux of 4.1 – 8.2 mol C m-2 yr-1 from the Singapore Strait, suggesting that a large proportion of the remineralized peatland tDOC is ultimately emitted to the atmosphere. However, incubation experiments show that the remaining 30–40% tDOC exhibits surprisingly low lability to microbial and photochemical degradation, suggesting that up to 20–30% of peatland tDOC might be relatively refractory and exported to the open ocean.

As far the ophiolites sequence study has concerned, the characteristics of chromian spinel (Cr-spinel) from mantle rocks (peridotite) and associated chromitite has been a ubiquitous petrogenetic indicator with regard to three tectonic settings (mid-oceanic ridges, subduction zone and arc) in terms of Cr# (= Cr/Cr+Al atomic ratio), Mg# and Ti content. In this study, we attempt to understand the tectonic environment and genetic relationship of mantle peridotites associated chromitites using chromian spinel characteristics from the southern Manipur Ophiolite Complex (MOC) which occupied an integral part of the Indo-Myanmar Orogenic Belt (IMOB), India. The study area mainly consists of peridotites (clinopyroxene-bearing harzburgite and lherzolite) with small pods of podiform chromitite, mafic intrusive - extrusive rocks and oceanic pelagic sediments. The Cr-spinel in peridotites are characterised by high Al2O3 (45.59-50.85), Mg# (89.25-90.48) and low Cr# (19.66 - 23.56) collectively suggest a typical abyssal peridotite derived from fertile mantle at mid-oceanic ridges (MOR) tectonic setting. Whereas, chromitites are low Al2O3 (14.35 to 19.68) and melt compositions (12.01 – 13.69 wt.%) with high Cr# (65.5 to 71.83) suggests that they were crystallized from boninitic magma series in the fore-arc subducting environment. Our petrological and geochemical evidences reveal that two stages of magmatism evolved during the formation of MOC. In the initial stage, magma was generated at the mid - oceanic spreading centre (MOR) by a small degree of partial melting (8–10 %) resulting high Al-rich and low Cr-rich chromian spinel bearing peridotites essentially of lherzolitic composition. At the second stage, high Cr-rich and low Al-rich magma evolved by high degree of partial melting intruded the earlier formed lherzolitic mantle exhibit harzburgite with high Cr# chromitite that formed at the fore-arc related setting above supra-subduction zone. It has been concluded from the present study that the magmatism in the mid-oceanic ridges environment followed by subduction tectonic process were responsible for the evolution of the Nagaland-Manipur Ophiolites that were emplaced along the Eastern plate margin of Indian subcontinent.

Xenoliths of plutonic rocks sporadically torn off by erupting magmas are known to carry valuable information about volcano plumbing systems and the lithosphere in which they emplace. One of the main steps to interpret such information is to quantify the pressure and temperature conditions at which the xenolith mineral assemblages last equilibrated. This chapter discusses some aspects of geothermobarometry of mafic and ultramafic rocks using the xenolith populations of Hualalai and Mauna Kea volcanoes, Hawaii, as case studies. Multiple- reaction geobarometry, recently revisited for olivine + clinopyroxene + plagioclase  spinel assemblages, provides the most precise pressure estimates (uncertainties as low as 1.0 kbar). An example is shown that integrates these estimates with calculated seismic velocities of the xenoliths and the available data from seismic tomography. The results allow to better constrain some km-scale horizontal and vertical heterogeneities in the magmatic system beneath Hawaii. Ultramafic xenoliths at Hualalai are the residuals of magma crystallization at 16–21 km depth, below the pre-Hawaiian oceanic crust. Few available gabbronorites and diorites record instead lower pressures and likely represent conduits or small magma reservoir crystallized at 0–8 km depth. At Mauna Kea, on the other hand, a significant portion of the xenolith record is composed by olivine-gabbros, which crystallized almost over the entire crustal thickness (3– 18 km). Ultramafic xenoliths are less abundant and might represent the bottom of the same magma reservoirs that crystallized in the deeper portion of the magmatic systems (11–18 km). Some unresolved issues remain in geothermometry of mafic and ultramafic rocks representing portions of magma reservoirs that cooled and recrystallized under subsolidus conditions. This suggests that further experimental and theoretical work is needed to better constrain the thermodynamics and kinetics of peridotitic and basaltic systems at low (< 1000 ̵̊C) temperatures.

The key to reproducible data reduction and data processing in scientific research is the ability to faithfully record every step of the process in a reproducible format that is transparent and easy to communicate. This is not an easy task. Most of the time in experimental research that is not primarily computational in nature, it falls victim to the enormous effort required to design experiments well, run complex analytical procedures rigorously and efficiently, and interpret the results in the proper geologic, geochemical or biological context, with little time left to invest in documenting and constructing a reproducible data reduction workflow. While this is understandable, it introduces a high risk for error, makes it extremely difficult to share and discuss one’s approach or review others’, reproduce the calculations at a later point or even just revisit what was done conceptually. Part of the problem lies inherently with most data processing being difficult to document, part of black box process where the inner workings are inaccessible, or simply too divorced from the narrative of the scientific work it represents. One important obstacle that interferes frequently with attempts to remedy this situation in the stable isotope community is the lack of many basic computational and data access tools that enable the kinds of calculations and data processing isotope geochemists need to do on a day to day basis. Here, we introduce a new suite of software packages that provide efficient and transparent access to raw stable isotope ratio mass spectrometry (IRMS) data formats and enable reproducible data processing straight from raw analytical output through data reduction, quality control, visualization and data reporting that retains the necessary flexibility required for the enormous breadth of analytical goals in the stable isotope community. Presented tools will cover aspects of functionality provided by the isoreader (isoreader.kopflab.org), isoviewer (isoviewer.kopflab.org) and isoprocessor (isoprocessor.kopflab.org) software packages and are 100% open-source and freely available to everyone in the geochemical community and beyond.

Europa’s compositional evolution is not well constrained. Observations only provide approximations of the current interior structure of Europa. However, dynamic models [Hussmann & Spohn 2004] resolve the magnitude of interior heating produced by tidal interaction over time. We couple the heat production to thermodynamic and chemical equilibrium models Perple_X [Connolly 2005], Rcrust [Mayne+ 2016] and CHIM-XPT [Reed 1998] to compute compositional changes of the interior and ocean. Assuming that Europa’s interior is not molten now, a Fe core could have accommodated up to 24 wt % S during accretion, assuming chondritic accretion material. However, a metal-silicate segregated magma ocean was needed to allow such high S content in the core. More likely, accretion proceeded with low impact rates that allowed heat dissipation. Based on this and experimental metal-silicate partition behavior, Europa’s core contains ~1 wt % S. Two mantle melting events were calculated corresponding to putative events in Europa’s thermal-orbital evolution: a first event that melted up to 30 vol % of the volatile-rich silicate shell, at pressures of 2.5 – 1.2 GPa ≥4 Ga ago, and a possible melting event ~1.3 Ga ago resulting from increased dissipation as the mantle’s rigidity increased [Hussmann & Spohn 2004]. Melt intrusive to extrusive ratios (I/E) for Europa are unknown, but eruption to the ocean-rock interface would have been hindered by high stress needed to cause fracture propagation and melt migration at depth [Byrne+ 2018]. Assuming I/E = 10, <7 wt % melt would have erupted (Fig 1). Even if lava erupted during the first event, limited heat transfer from, and dehydration of, the mantle may not have prevented the second event from occurring. Considering Europa’s volcanism enables us to predict the minerals likely to have influenced the ocean’s composition and the mineralogy of concurrent water-rock activity. Erupted lava reacting with the ocean results in water-to-rock ratio dependent proportions of sulfides, saponite, chlorite and carbonates. We will describe implications for the ocean’s composition and habitability. A part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2018. All rights reserved.

This article provides a commentary about the state of Integrated, equitable outcomes. GeoHealth research both characterizes and predicts problems at the nexus of earth and human systems like climate change, pollution, and natural hazards. While GeoHealth excels in the area of integrated science, there is a need to improve coordinated and networked efforts to produce open science that is for and with frontline populations that are disproportionately marginalized by environmental injustice or unequal protection from environmental harms and lack of access and meaningful engagement in decision-making for a healthy environment (EPA). GeoHealth practice has the opportunity to advance environmental justice or the “fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income” with respect to how research and collaboration of GeoHealth professionals supports the “development, implementation, and enforcement of environmental laws, regulations, and policies” that produce equal protection from environmental and health hazards and access to the decision-making for a health environment (EPA). Here we highlight barriers and opportunities to apply an equity-centered ICON framework to the field of GeoHealth to advance environmental justice and health equity.

It is now understood that if life had ever erose on Mars, it might have been preserved in the simplest form. Therefore, studying the traces of simple life forms from the rock records of various Earth environments and climatic conditions perhaps helps to narrow down the region of interest while searching for life on the red planet. The Precambrian era covered almost 80% of Earth’s geologic history, witnessed the appearance of life on Earth and experienced prolonged extreme climatic events that delayed biological evolution. During this extreme period, primitive lifeforms such as microbial mats had a strong influence on sedimentation, and they facilitated the formation of a variety of mat-induced sedimentary structures (MISS) in siliciclastic and carbonate sedimentary environments. In the last two decades MISS have been identified from several Precambrian successions of India for example, Vindhyan, Marwar, Chhattisgarh and, Cuddapah Supergroup. In this study we tried to provide an updated catalogue based on the chronologic, stratigraphic and paleoenvironmental occurrences of MISS from the Indian Precambrian successions. We further explore their potential in understanding extreme habitability, searching biomarkers and biosignatures on Mars and propose a few potential sites for astrobiological research.

Inland waters are an important component of the global carbon budget, emitting CO2 to the atmosphere. However, our ability to predict carbon fluxes from stream systems remains uncertain as small scales of pCO2 variability within streams (100-102 m), which makes efforts relying on monitoring data uncertain. We incorporate CO2 input and output fluxes into a stream network advection-reaction model, representing the first process-based representation of stream CO2 dynamics at watershed scales. This model includes groundwater (GW) CO2 inputs, water column (WC), and benthic hyporheic zone (BHZ) respiration, downstream advection, and atmospheric exchange. We evaluate this model against existing statistical methods including upscaling and multiple linear regressions through comparisons to high-resolution stream pCO2 data collected across the East River Watershed in the Colorado Rocky Mountains (USA). The stream network model accurately captures topography-driven pCO2 variability and significantly outperforms multiple linear regressions for predicting pCO2. Further, the model provides estimates of CO2 contributions from internal versus external sources suggesting that streams transition from GW- to BHZ-dominated sources between 3rd and 4th Strahler orders, with GW, BHZ, and WC accounting for 49.3, 50.6, and 0.1% of CO2 fluxes from the watershed, respectively. Lastly, stream network model CO2 fluxes are 4-12x times smaller than upscaling technique predictions, largely due to inverse correlations between stream pCO2 and atmosphere exchange velocities. Taken together, this stream network model improves our ability to predict stream CO2 dynamics and efflux. Furthermore, future applications to regional and global scales may result in a significant downward revision of global flux estimates.

Modeling of the electrical conductivity (EC) of icy moon oceans has previously assumed that chloride, sulfate, and other ions released from rock leaching are the main solutes and carriers of electrical conductivity. Here, we show that accreted volatiles, such as carbon dioxide and ammonia, can add a significant fraction of solutes in bodies whose volatile content was in part supplied from cometary materials. These volatiles can increase the EC of aqueous solutions above 1 S/m. Our salinity and EC estimates can serve as a basis for planning future magnetometer investigations at icy moons and dwarf planets. In particular, oceans expected in some of the Uranian satellites and Neptune’s satellite Triton could have EC above 3 S/m as a result of accretion of large abundances of carbon dioxide and ammonia, even if rock leaching during water-rock separation was limited, and chlorine and sulfur abundances may be at CI carbonaceous chondritic levels.

Ecologists have proposed that montane grassland-shola (stunted evergreen forest) mosaics in the Western Ghats may represent alternative stable vegetation states. But paleoecology investigations seldom consider this framework, especially the role of short-term disturbances (fire, intense drought) other than long-term climatic changes, that can cause vegetation switches in landscapes with alternative vegetation states. The Sandynallah valley that hosts one of the oldest peat accumulations in the world at >50 kyr has been central to the reconstruction of paleovegetation in the montane Nilgiris, Western Ghats. Although the peat-forming vegetation here (dominated by sedges) is a unique vegetation state, its contribution to the paleovegetation signal has not been explicitly considered. We propose a conceptual framework of a tri-stability landscape with sedgeland on the valley floor, grassland on the hill slopes and shola vegetation in the boundary between sedgeland and grassland. While frost prevents shola saplings from establishing in grassland, waterlogging provides a barrier for their establishment in sedgeland, thus maintaining these distinct vegetation states under the same climate. We investigated the stable carbon isotope signatures of the cellulose fraction from two well-dated peat cores (Cores 1 and 2) collected from ~170m apart in the Sandynallah valley within the alternative stable states framework. We find that Core 1, which is closer to the boundary of valley and hill slope, shows dynamic switches between sedgeland and shola whereas Core 2, located in the centre of the valley floor, represents a stable sedgeland state. The vegetation switches and maintenance mechanisms at Core 1 is connected to a disturbance (fire) and to changing climate while Core 2 seems to be responding primarily to climatic changes. The simultaneously distinctive vegetation states in Cores 1 and 2 at such close proximity within the same valley is the first record of alternative stables states in the past in the Western Ghats.