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The possibility of life in the venusian clouds was proposed in the 1960s, and recently this hypothesis has been revived with the potential detection of phosphine (PH3) in Venus' atmosphere. These o...

Perchlorate (ClO4−) is globally enriched in Martian regolith at levels commonly toxic to plants. Consequently, perchlorate in Martian regolith presents an obstacle to developing agriculture on Mars. Here, we assess the effect of perchlorate at different concentrations on plant growth and germination, as well as metal release in a simulated Gusev Crater regolith and generic potting soil. The presence of perchlorate was uniformly detrimental to plant growth regardless of growing medium. Plants in potting soil were able to germinate in 1 wt.% perchlorate, however, these plants showed restricted growth and decreased leaf area and biomass. Some plants were able to germinate in regolith simulant without perchlorate, however, they showed reduced growth. In Martian regolith simulant, the presence of perchlorate prevented germination across all plant treatments. Soil column flow-through experiments of perchlorate-containing Martian regolith simulant and potting soil were unable to completely remove perchlorate despite its high solubility. Additionally, perchlorate present in the simulant increased metal/phosphorous release, which may also affect plant growth and biochemistry. Our results support that perchlorate may modify metal availability to such an extent that, even with the successful removal of perchlorate, Martian regolith may continue to be toxic to plant life. Overall, our study demonstrates that the presence of perchlorate in Martian regolith provides a significant challenge in its use as an agricultural substrate and that further steps, such as restricted metal availability and nutrient enrichment, are necessary to make it a viable growing substrate.

Microporous minerals have many industrial applications, from filtration to contaminant immobilization. Natural and synthetic minerals, including zeolites, clays, and silica aerogel, represent a few examples of microporous minerals with distinctive structures, surface charges, and porosity. Analysis and comparison of their crystal structures are necessary to determine how each mineral may be suited for contaminant uptake. Here we assessed the structure of microporous minerals, specifically rowleyite, clinoptilolite, vermiculite, and silica aerogel. Raman spectroscopy, X-ray fluorescence, and X-ray powder diffraction were used to create and model atomic mineral structures to visualize atomic and macroscope features. Taking into account pore size and surface charge each mineral was reviewed to find the best fit with regards to heavy metal uptake, mainly Pb (lead). Overall, we provide a comparative framework to assess microporous minerals that will inform future flow-through experiments for heavy metal uptake.

Water-rock interactions at elevated pressures and temperatures may mobilize chromium from chromite to produce a variety of Cr-silicate minerals. Common Cr-silicates include fuchsite (KCr2(AlSi3O10)(OH)2), kämmererite ((Mg5Cr)(AlSi3)O10(OH)8), tawmawite (Ca2CrAl2Si3O12(OH)), and uvarovite (Ca3Cr2Si3O12). Here we assess the geochemistry and calculate the thermodynamic properties of a variety of Cr-silicates to elucidate their formation as well as how they may contribute chromium to the environment. Chromium-silicates follow an idealized 1:1 relationship with regards to Cr(III) and octahedral Al, except for kämmererite. Kämmererite can have Al in excess of 1:1 to Cr(III), substituting into the Mg site. FTIR and Raman analyses demonstrate that Cr(III) enrichment is distinguishable between respective end member minerals. Thermodynamic properties were calculated using established estimation algorithms and unit-cell measurements. Overall, we provide an extensive assessment of Cr-silicates that addresses the formation of Cr-silicates and fate of chromium in the environment.

Global climate change related to anthropogenic CO2 emissions is one of the most significant challenges for the future of human life on Earth. There are many potential options for reducing or even eliminating atmospheric CO2 emissions including underground sequestration, carbon mineralization and ocean storage. One of the most promising materials for carbon mineralization is Mg(OH)2 which is highly reactive and capable of forming stable carbonates. Here we show a novel low-carbon method of producing Mg(OH)2, from globally abundant olivine-rich silicate rocks. A combination of acid digestion and electrolysis of olivine were used to produce Mg(OH)2 in a fully recoverable system. The use of Mg(OH)2 from olivine provides a viable pathway for significant industrial scale reductions in global anthropogenic greenhouse gas emissions. Magnesium hydroxide is a sustainable material for CO2 sequestration, according to an acid digestion and electrolysis method using olivine-rich silicate rocks in a fully recoverable system.

The French Creek Granite, New Zealand, is an alkaline intrusion with enrichment in rare earth elements (REE). Petrography and whole-rock geochemical signatures demonstrate that the c. 82–84-Ma French Creek Granite is a composite granitoid, dominated by a ferroan, weakly peraluminous biotite alkali feldspar granite to syenogranite, with subordinate quartz-alkali feldspar (QAF) syenite. Maximum total REE + Y contents are higher in the granite and felsic dikes relative to the marginal QAF syenite, cogenetic mafic Hohonu Dike Swarm, and pegmatites. Our findings suggest that REE and high-field-strength element enrichment in the unaltered French Creek Granite is a function of partial melting from an enriched HIMU-like lithospheric mantle source, minor crustal assimilation, and extensive magmatic differentiation. Primary (magmatic) REE enrichment is defined by the occurrence of allanite, zircon, apatite, fergusonite, monazite, perrierite, and loparite, which are commonly associated with interstitial biotite. French Creek Granite samples from a phyllic-sericitic alteration zone in the Eastern Hohonu River are strongly elevated in REE relative to unaltered French Creek Granite, indicating remobilization and secondary REE enrichment by hydrothermal fluids. The REE are hosted in bastnasite group minerals, monazite, xenotime, and zircon. Quartz protuberances, dilatational microfractures, and dike emplacement indicate that this alteration is structurally controlled. The δ13C and δ18O values of secondary carbonate veinlets are consistent with mixed low-temperature (~ 250–260 °C) magmatic hydrothermal fluids containing mantle-derived carbon. These fluids were likely part of a late-stage porphyry-type system operating during the same mantle degassing and extensional episode that was associated with the emplacement of the French Creek Granite and lamprophyric dikes of the Hohonu Dike Swarm, and initial Tasman Sea spreading. Results from this study provide an important insight into the complex processes responsible for REE enrichment in alkaline igneous systems.

Diffuse soil CO2 flux and stable carbon isotope surveys facilitate interpretation of the nature and structure of hydrothermal systems. Although soil CO2 flux measurements are completed in the field, isotopic carbon in CO2 (i.e., δ13C-CO2) analyses are more commonly performed in a stable isotope mass spectrometry laboratory, thereby, increasing the effort, time and resources required to complete the survey. Cavity Ring Down Spectroscopy (CRDS) overcomes these challenges by enabling both CO2 isotopic and flux analyses in field settings. However, H2S interference has limited CRDS applications in H2S-rich hydrothermal settings. Here, we assess the application of a mobile CRDS system equipped with a simple Cu wire trap to complete δ13C-CO2 and CO2 flux surveying in the relatively high H2S Rotorua Hydrothermal System (RHS), North Island, New Zealand. Laboratory experiments demonstrate that the Cu trap was able to remove H2S (~250 ppmv) enabling accurate and precise δ13C-CO2 measurements. In the RHS, the Cu trap successfully removed H2S concentrations during in situ soil gas analyses. Carbon dioxide fluxes determined using the CRDS were found be 102% of those values produced by a traditional soil gas flux meter (i.e., Licor). Carbon dioxide flux determined by CRDS was similar to previous studies in the RHS; however, zones of high CO2 flux in central Kuirau Park have moved ~100–200 m in the past twelve years. Isoscapes of δ13C-CO2 for the RHS were constructed from our soil gas survey results and were used to assess the apportionment of magmatic-hydrothermal versus biogenic CO2 release. Our findings demonstrate that a CRDS enabled system allows for faster in field survey measurement, lower cost, and reactive sampling for both δ13C-CO2 and CO2 flux measurement in H2S-enriched hydrothermal systems.

Thermal springs present rare opportunities to locate and interpret the geological drivers of upper-crustal fluid flow. Interpreting the conditions through which crustal fluids are heated and released to the surface is important for advancing our understanding of crustal deformation and geothermal resource potential across tectonic contexts. In New Zealand, the majority of thermal springs are associated with magmatic-hydrothermal systems in the central North Island or with the rapidly uplifting bedrock in the South Island's convergent fault systems. However, low enthalpy systems outside of these areas represent attractive targets for potential geothermal resource development. The low enthalpy warm springs of Banks Peninsula, located immediately adjacent to Christchurch, represent a highly understudied but potentially significant resource to the South Island's most densely populated metropolitan area. Hosted within the eroded 11–5.8 Ma volcanic complex of Banks Peninsula, these warm springs (14.5–33.6 °C) represent an anomalous hydrothermal system that has been perturbed by the 2010–2016 Canterbury Earthquake Sequence (CES). The February 22, 2011, Mw 6.2 earthquake induced observable changes to the Banks Peninsula warm springs system, including the appearance of new warm springs within the peninsula's north-western Hillsborough Valley. We assess the origins of the volcanically-hosted Banks Peninsula warm springs post-CES using an integrated isotopic, geochemical, and soil gas flux approach. Additionally, we elucidate the tectonic context and geological drivers of upper-crustal fluid flow in the Banks Peninsula warm spring system. Aqueous phase emissions from the springs predominantly plot within the Na+ + K+/HCO3− type waters and exhibit δ 18 O , δ D , and δ 13 C values of −8.30 to −9.26‰ V-SMOW, −60.15 to −64.19‰ V-SMOW, and −12.37 to −15.06‰ V-PDB, respectively. Soil gas flux surveys of the springs at Rapaki Bay revealed CO2 fluxes that average 6.93 ± 10 gm-2 day−1, with an average δ 13 C value of −19.81 ± 5‰ V-PDB, and CH4 fluxes that average 5.58 ± 12 gm-2 day−1, with an average δ 13 C value of −59.52 ± 1‰ V-PDB. Our results suggest that the Banks Peninsula warm springs are a structurally controlled, upper-crustal metamorphic hydrothermal heated system, sourced from high-altitude Southern Alps derived meteoric waters. Carbon isotope compositions of gaseous emissions associated with the Banks Peninsula thermal springs are consistent with an upper-crustal metamorphic decarbonation and decarboxylation carbon source. Based on their geochemistry, we propose that the Banks Peninsula warm springs should be considered an outboard extension of the South Island's plate-boundary hydrothermal system. Such connectivity implies that long-lived low-enthalpy geothermal resources may be associated with permeable and distributed fault networks in the periphery of convergent margins.

Long-term human habitation of Mars will require in situ resources for construction and infrastructure development. In order to determine how to utilize in situ resources, such as Martian regolith, these materials need to be synthesized on Earth for testing and development. Here we address the process of synthesizing a targeted Martian simulant (i.e., Gusev Crater regolith near the Columbia Hills region on Mars) in sufficient quantities required for infrastructure development studies using volcanic material obtained from Banks Peninsula, New Zealand. Martian simulant produced via crushing, sieving, washing and blending of basalts and volcanic glass resulted in accurately reproducing material similar in particle size, chemistry and mineralogy to Gusev Crater regolith. Overall, our applied approach to synthesizing Martian regolith will aid in creating suitable quantities of material that can be used for a variety of research applications such as assessing aggregates for use in the production of construction materials.

Plant nutrients such as potassium (K) may be limited in soil systems and additions (i.e., fertilizer) are commonly required. Glaucony is a widely distributed and abundant marine-derived clay mineral present in soils worldwide which may serve as a source of potassium. The South Island of New Zealand contains numerous deposits of glaucony-rich rocks and related soils providing an opportunity to explore how glaucony might be a beneficial source of potassium. Here, the geochemistry of glaucony and its suitability as a mineral source of soil K from four deposits in New Zealand was examined using spatially resolved chemical analyses and dissolution experiments. Geochemical and morphological analyses revealed that glaucony from all deposits were K-enriched and were of the evolved (6%&ndash, 8% K2O) to highly evolved type (&gt, 8% K2O). Glaucony derived from growth inside pellets contain elevated K and Fe concentrations compared to bioclast-hosted glaucony. Solubility analysis showed that K was released from glaucony at rates higher than any other metal present in the mineral. Additionally, decreasing the pH and introducing an oxidizing agent (i.e., birnessite which is ubiquitous in soil environments) appeared to accelerate K release. Trace metals including Cr, Zn, Cu, and Ni were present in the solid phase analysis, however, further investigation with a focus on Cr revealed that these elements were released into solution at low concentrations and may present a source of soil micronutrients. These results suggest that glaucony may offer a source of slow releasing K into soils, and so could be used as a locally sourced environmentally sustainable K resource for agriculture, whether in New Zealand or worldwide

Hydrothermal systems develop via interspersed thermal events over tens to hundreds of thousands of years. The timing of how these systems evolve is commonly established via application of geochronology to a variety of phases and/or the indirect correlation of dated stratigraphy. Here we report 40 Ar/ 39 Ar results from adularia extracted from a single mineralized fracture in the late Quaternary Tauhara geothermal system of New Zealand. By utilizing both the age and Ar diffusion properties, we demonstrate how adularia can provide reliable temporal and thermal constraints on the evolution of geologically youthful and active geothermal systems. Our results indicate that adularia formation occurred after 30 ka (mean age 15 ± 10 ka), possibly resulting from subsurface fracturing induced by a 25.4 ka hydrothermal eruption. Simulation of transient heat effects upon Ar retention in adularia with respect to the thermal history of the Tauhara geothermal system confirm that this age is consistent with the time of adularia crystallization. Overall, 40 Ar/ 39 Ar dating on geologically young hydrothermal adularia with respect to its thermal history may be used to assess the timing and potential events (e.g., eruptions and fracturing) related to hydrothermal system evolution.

Natural processes and anthropogenic activities may result in the formation and/or introduction of perchlorate (ClO4−) at elevated levels into the environment. Perchlorate in soil environments on Earth and potentially in Mars may modify the dynamics of metal release and their mobilization. Serpentine soils, known for their elevated metal concentrations, provide an opportunity to assess the extent that perchlorate may enhance metal release and availability in natural soil and regolith systems. Here, we assess the release rates and extractability of Ni, Mn, Co and Cr in processed Sri Lankan serpentine soils using a range of perchlorate concentrations (0.10–2.50 w/v ClO4−) via kinetic and incubation experiments. Kinetic experiments revealed an increase of Ni, Mn, Co and Cr dissolution rates (1.33 × 10−11, 2.74 × 10−11, 3.05 × 10−12 and 5.35 × 10−13 mol m−2 s−1, respectively) with increasing perchlorate concentrations. Similarly, sequential and single extractions demonstrated that Ni, Mn, Co and Cr increased with increasing perchlorate concentrations compared to the control soil (i.e., considering all extractions: 1.3–6.2 (Ni), 1.2–126 (Mn), 1.4–34.6 (Co) and 1.2–6.4 (Cr) times greater than the control in all soils). Despite the oxidizing capability of perchlorate and the accelerated release of Cr, the dominant oxidation state of Cr in solution was Cr(III), potentially due to low pH (

The June 2011 eruption of Cordón Caulle volcano, Chile, dispersed tephra over ~ 350,000 km2, including productive agricultural land. This resulted in the death of nearly one million livestock. Two distinct environments were affected: a proximal temperate Andean setting, and the semi-arid Argentine steppe farther from the volcano. The purpose of this study was to better understand the fate and agricultural consequences of leachable elements added to the environment by this large silicic tephra fall. Tephra, soil and surface water samples across the depositional area were collected both immediately after the eruption (tephra and water) and nine months afterwards (tephra, soil and water). Tephra samples were analysed following a new hazard assessment protocol developed by the International Volcanic Health Hazard Network (IVHHN). Water-extractable element concentrations in freshly-collected tephra were very low to low compared to other eruptions, and showed no trends with distance from the volcano. Surface water analyses suggested short-term changes to water composition due to the release of elements from tephra. No effect on the fertility of soils underlying tephra was apparent after nine months. Water-extractable fluorine (F) in freshly-collected tephra ranged from 12 to 167 mg/kg, with a median value of 67 mg/kg. Based on parallels with the 11–12 October 1995 eruption of Ruapehu volcano, New Zealand, we conclude that F toxicity was a possible contributing factor to the large-scale livestock deaths as well as to chronic fluorosis widely reported in wild deer populations across the Cordón Caulle tephra depositional area. Finally, we recommend that effective response to widespread tephra fall over agricultural areas should include: (1) rapid, statistically representative field sampling of tephra, soils, surface water supplies and forage crops; (2) analysis using appropriate and reliable laboratory methods; (3) modelling both short and long-term impacts on the ecosystem, especially for elements that may generate chronic hazard; (4) timely dissemination of results to agricultural agencies; (5) longitudinal sampling and monitoring to adapt impact models; and (6) developing reliable animal fatality diagnoses through autopsies and chemical analysis. Fil: Stewart, Carol. Massey University; Nueva Zelanda Fil: Craig, Heather M.. University Of Canterbury; Nueva Zelanda Fil: Gaw, Sally. University Of Canterbury; Nueva Zelanda Fil: Wilson, Thomas. University Of Canterbury; Nueva Zelanda Fil: Villarosa, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales.; Argentina Fil: Outes, Ana Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales.; Argentina Fil: Cronin, Shane. The University of Auckland; Nueva Zelanda Fil: Oze, Christopher. University Of Canterbury; Nueva Zelanda. Occidental College; Estados Unidos

The Berlins Porphyry located on the South Island of New Zealand provides an opportunity to examine iron concretions formed in a subterranean system. Specifically, an alteration zone within the Berlins Porphyry contains iron concretions similar to sedimentary biologically-mediated iron concretions. Here, we provide evidence for two sources of dissolved Fe (II) that potentially aided in the formation of the iron concretions. Furthermore, we discuss the potential for microbial involvement in the anaerobic oxidation of Fe (II) to Fe (III) to form magnetite. Evidence in support of this hypothesis includes the low concentrations of iron and sulfur in the white hydrothermally altered porphyry outcrop and concretion cores; concentrated pyrite and magnetite mineralisation surrounding the cores; and δ13C values indicative of organic carbon (averaging −26 ‰ ± 4 ‰) within the iron cement, porphyry-core-boundary and outer weathered rinds of the concretions. Overall, these unusually preserved iron concretions could represent a new environmental niche for microorganisms and a potential analogue for microbially induced iron-oxidation. More importantly, this study illustrates the many obstacles involved in analysing and interpreting potential subterranean biosignatures.

Detailed facies analyses of intra-arc basin stratigraphy provide spatial and temporal insights into the nature and timing of past volcanic, sedimentary and tectonic events. Rift and caldera basins hosting lakes in the central Taupo Volcanic Zone (TVZ) continental arc preserve a sequence of locally and regionally sourced volcanic deposits and interbedded lacustrine sediments. A series of new continuous core samples from Wairakei–Tauhara Geothermal Fields in the TVZ intersecting thick Huka Group stratigraphy has provided a unique opportunity to study c. 300 ka of local arc volcanism, sedimentary processes and ancient surface environments. Facies analysis is utilised on 11 cored wells from across Wairakei–Tauhara, including a newly defined Huka Group Reference Section well (WKM15). Interpreted facies identify that the Huka Group commenced with a large ignimbrite (Waiora Ignimbrite Member) emplaced onto faulted relief covered by a pre-existing ancient lake, Lake Huka. Graded volcaniclastic facies, lav...

The transformation of trace metals (TMs) in natural environmental systems has created significant concerns in recent decades. Ultramafic environments lead to potential risks to the agricultural products and, subsequently, to human health. This unique review presents geochemistry of ultramafic soils, TM fractionation (i.e. sequential and single extraction techniques), TM uptake and accumulation mechanisms of ultramafic flora, and ultramafic-associated health risks to human and agricultural crops. Ultramafic soils contain high levels of TMs (i.e. Cr, Ni, Mn, and Co) and have a low Ca:Mg ratio together with deficiencies in essential macronutrients required for the growth of crops. Even though a higher portion of TMs bind with the residual fraction of ultramafic soils, environmental changes (i.e. natural or anthropogenic) may increase the levels of TMs in the bioavailable or extractable fractions of ultramafic soils. Extremophile plants that have evolved to thrive in ultramafic soils present clear examples of evolutionary adaptations to TM resistance. The release of TMs into water sources and accumulation in food crops in and around ultramafic localities increases health risks for humans. Therefore, more focused investigations need to be implemented to understand the mechanisms related to the mobility and bioavailability of TMs in different ultramafic environments. Research gaps and directions for future studies are also discussed in this review. Lastly, we consider the importance of characterizing terrestrial ultramafic soil and its effect on crop plants in the context of multi-decadal plans by NASA and other space agencies to establish human colonies on Mars. Keywords: Soil contamination, Geochemistry, Trace elements, Bioaccumulation, Translocation, Extremophytes

Serpentinization involves the hydrolysis and transformation of primary ferromagnesian minerals such as olivine ((Mg,Fe)2SiO4) and pyroxenes ((Mg,Fe)SiO3) to produce H2-rich fluids and a variety of secondary minerals over a wide range of environmental conditions. The continual and elevated production of H2 is capable of reducing carbon, thus initiating an inorganic pathway to produce organic compounds. The production of H2 and H2-dependent CH4 in serpentinization systems has received significant interdisciplinary interest, especially with regard to the abiotic synthesis of organic compounds and the origins and maintenance of life in Earth's lithosphere and elsewhere in the Universe. Here, serpentinization with an emphasis on the formation of H2 and CH4 are reviewed within the context of the mineralogy, temperature/pressure, and fluid/gas chemistry present in planetary environments. Whether deep in Earth's interior or in Kuiper Belt Objects in space, serpentinization is a feasible process to invoke as a means of producing astrobiologically indispensable H2 capable of reducing carbon to organic compounds. Key Words: Serpentinization—Fischer-Tropsch-type synthesis—Hydrogen formation—Methane formation—Ultramafic rocks. Astrobiology 15, 587–600.

Adularia and sanidine are polymorphs of potassium feldspar commonly present in felsic, hydrothermally altered volcanic deposits. Sanidine is a high-temperature volcanic mineral, whereas adularia forms post deposition by hydrothermal processes. Petrographically differentiating between these polymorphs in hydrothermally altered volcanic rocks may be utilised to distinguish geological units as well as provide insights into fluid–rock interactions. However, petrographic identification may be difficult or not possible in fine-grained drill cuttings. Here, polymorphic-sensitive, Raman spectroscopy and electron microprobe analyses are utilised to characterise adularia and potential sanidine in drill cuttings from the Ngatamariki Geothermal Field, Taupo Volcanic Zone, New Zealand. Differences in Raman spectra are capable of distinguishing between adularia and sanidine whether using peak positions or principal component analysis. All the Ngatamariki Geothermal Field potassium feldspars analysed by Raman spectrosco...

The quantification of heat and mass flow between deep reservoirs and the surface is important for understanding magmatic and hydrothermal systems. Here, we use high-resolution measurement of carbon dioxide flux (φCO2) and heat flow at the surface to characterize the mass (CO2 and steam) and heat released to the atmosphere from two magma-hydrothermal systems. Our soil gas and heat flow surveys at Rotokawa and White Island in the Taupō Volcanic Zone, New Zealand, include over 3000 direct measurements of φCO2 and soil temperature and 60 carbon isotopic values on soil gases. Carbon dioxide flux was separated into background and magmatic/hydrothermal populations based on the measured values and isotopic characterization. Total CO2 emission rates (ΣCO2) of 441 ± 84 t d−1 and 124 ± 18 t d−1 were calculated for Rotokawa (2.9 km2) and for the crater floor at White Island (0.3 km2), respectively. The total CO2 emissions differ from previously published values by +386 t d−1 at Rotokawa and +25 t d−1 at White Island, demonstrating that earlier research underestimated emissions by 700% (Rotokawa) and 25% (White Island). These differences suggest that soil CO2 emissions facilitate more robust estimates of the thermal energy and mass flux in geothermal systems than traditional approaches. Combining the magmatic/hydrothermal-sourced CO2 emission (constrained using stable isotopes) with reservoir H2O:CO2 mass ratios and the enthalpy of evaporation, the surface expression of thermal energy release for the Rotokawa hydrothermal system (226 MWt) is 10 times greater than the White Island crater floor (22.5 MWt).

Diffuse soil CO2 flux surveys are a widely applied approach for delineating zones of elevated heat and mass transfer in areas with geothermal surface features including hot-springs, mud pools, and geysers. However, many geothermal systems are capped by relatively impermeable layers that diminish the surface expression of potential resources present at depth. Here, we report diffuse soil CO2 flux survey results with complementary δ13CO2 values and shallow soil temperatures for the Ngatamariki geothermal system (Taupo Volcanic Zone, New Zealand), a largely surface blind system, in an effort to explore the utility of such data as indicators of magmatic carbon emission in geothermal systems with low CO2 flux. Our results include that: (1) the majority (54%) of the soil CO2 flux measurements are below background levels (15 gCO2 m−2 day−1); (2) only 5.6% of the shallow (10 cm) soil temperatures exceed 30 °C; and (3) no correlation is present between soil temperature and CO2 flux at Ngatamariki. These results belie the fact that a recently developed geothermal resource is present beneath Ngatamariki. Yet, δ13CO2 values when interpreted in the context of soil gas CO2 concentrations, demonstrate that the magmatic-hydrothermal system beneath Ngatamariki can be distinguished from soil-zone carbon sources using diffuse soil gas geochemical tracers. Modeling the Ngatamariki CO2 system as a simple mixture of geothermal biogenic and atmospheric end-members allows for the apportionment of CO2 flux at different locations across the field. Based on these findings, we suggest that delineating potential geothermal sites and assessing the relative contributions of mixed fluid end-members is possible even with low diffuse CO2 flux and limited surface expression of geothermal systems at depth.

Fourier transform infrared spectroscopy (FTIR) is an analytical technique utilized to measure the concentrations of H and C species in volcanic glasses. Water and CO2 are the most abundant volatile species in volcanic systems. Water is present in magmas in higher concentrations than CO2 and is also more soluble at lower pressures, and, therefore it is the dominant volatile forming bubbles during volcanic eruptions. Dissolved water affects both phase equilibria and melt physical properties such as density and viscosity, therefore, water is important for understanding magmatic processes. Additionally, quantitative measurements of different volatile species using FTIR can be achieved at high spatial resolution. Recent developments in analytical equipment such as synchrotron light sources and the development of focal plane array (FPA) detectors allow higher resolution measurements and the acquisition of concentration maps. These new capabilities are being used to characterize spatial gradients (or lack thereof) around bubbles and other textural features, which in turn lead to new insights into the behavior of volcanic feeder systems. Here, practical insights about sample preparation and analysis of the distribution and speciation of volatiles in volcanic glasses using FTIR spectroscopy are discussed. New advances in the field of FTIR analysis produce reliable data at high spatial resolution that can be used to produce datasets on the distribution, dissolution and diffusion of volatiles in volcanic materials.

Hydrous alteration of olivine is capable of producing molecular hydrogen (H-2) under a wide variety of hydrothermal conditions. Although olivine hydrolysis (i.e., serpentinization) has commonly been assessed at elevated temperatures ( greater than 100 degrees C), the nature of these reactions in relation to H-2 production at lower temperatures has not been systematically evaluated, especially with regard to carbonate-rich fluids. Specifically, carbonate formation may kinetically infringe on geochemical routes related to serpentinization and H-2 production at lower temperatures. Here time-dependent interactions of solid, liquid, and gaseous phases with respect to olivine hydrolysis in a carbonate-rich solution (20 mM HCO3-) at 30, 50 and 70 degrees C for 315 days is investigated experimentally. Within the first two months, amorphous Si-rich (i.e., talc-like) and carbonate phases precipitated; however, no inhibition of olivine dissolution is observed at any temperature based on surface chemistry analyses. High-resolution surface analyses confirm that precipitates grew as spheroids or vertically to form topographic highs allowing further dissolution of the free olivine surfaces and exposing potential catalysts. Despite no magnetite (Fe3O4) being detected, H-2 increased with time in experiments carried out at 70 degrees C, indicating an alternative coupled route for Fe oxidation and H-2 production. Spectrophotometry analyses show that aqueous Fe(II) is largely converted to Fe(III) potentially integrating into other phases such as serpentine and talc, thus providing a viable pathway for H-2 production. No increase in H-2 production was observed in experiments carried out at 30 and 50 degrees C supporting observations that incorporation of Fe(II) into carbonates occurred faster than the intertwined processes of olivine hydrolysis and Fe(III) oxidation. Overall, carbonate formation is confirmed to be a major influence related to H-2 production in low-temperature serpentinization systems.

Current and ancestral lakes within the central Taupo Volcanic Zone (TVZ) provide depocentres for pyroclastic deposits, providing a reliable record of eruption history. These lakes can also be the source of explosive eruptions that directly feed pyroclast-rich density currents. The lithofacies characteristics of pyroclastic deposits allow discrimination between eruption-fed and resedimented facies. The most frequently recognised styles of subaqueous eruptions in the TVZ are shallow-water phreatomagmatic and phreatoplinian eruptions that form subaerial eruption columns. However, deeper source conditions (>150 m water depth) could generate subaqueous explosive eruptions that feed water-supported pyroclast-rich density currents, similar to neptunian eruptions. Such deep-water eruptions have not previously been recognised in the TVZ. Here we study a subsurface deposit, the middle Huka Falls Formation (MHFF), in the Wairakei–Tauhara Geothermal Fields (Wairakei–Tauhara), TVZ, which we interpret to be the product...

Metal roofing material is commonly used for residential and industrial roofs in volcanically active areas. Increased corrosion of metal roofing from chemically reactive volcanic ash following ash deposition post-eruption is a major concern due to decreasing the function and stability of roofs. Currently, assessment of ash-induced corrosion is anecdotal, and quantitative data are lacking. Here, we systematically evaluate the corrosive effects of volcanic ash, specifically ash leachates, on a variety of metal roofing materials (i.e. weathered steel, zinc, galvanized steel, and Colorsteel©) utilizing weathering chamber experiments and direct acid treatments. Weathering chamber tests were carried out for up to 30 days, and visual, chemical, and surface analyses did not definitively identify significant corrosion in any of the test roofing metal samples. Direct concentrated acid treatments with hydrochloric (HCl), sulphuric (H2SO4), and hydrofluoric (HF) acids demonstrate that roofing materials are chemically resilient. Our experimental results suggest that ash-leachate-related corrosion is a longer-term process (>1 month), potentially related to a multitude of factors including increased ash leachate concentrations, the dissolution of the glass matrix of the ash, moisture retention at the ash-surface boundary, and potential reactions involving photo-oxidation. Overall, corrosion is not a simple process related to the short-term release of acid and/or salt leachates from the ash surface, but a product of dynamic interactions involving ash and water at the surface of metal roofing material for extended periods.

Crystal growth and crack development in cooling lava domes are both capable of redistributing and mobilizing water. Cracking and hydration decrease the stability of a dome, which may lead to hazards including partial dome collapse and block and ash flows. By examining the distribution of water around crystals and cracks, we identify and confine temperature and timescales of texture development in glassy rocks of volcanic domes. Four generations of textures have been identified: type a: spherulites, type b: cracks associated with spherulite growth, type c: perlitic cracks, and type d: disparate cracks. High-resolution imaging using Fourier Transform Infrared Spectroscopy (FTIR) performed on samples from the Ngongotaha dome, New Zealand, show an increase in H2O of up to 450% along gradients of around 100 μm up to 300 μm in length from perlitic cracks, spherulitic cracks and in haloes around spherulites. No gradients in water concentrations across the disparate cracks are present. Water diffusion models show potential timescale–temperature couples that coincide with textural observations and previous studies, and allow us to develop a conceptual model of spherulite growth and cracking in a cooling lava dome. Spherulite growth starts around the glass transition temperature ( T g ) when the viscous melt cools to a brittle solid and proceeds with cracking related to volume changes at slightly lower temperatures and shorter timescales (days to weeks) compared to spherulite growth. Perlitic cracking happens at T ≪ T g , allowing hydration of a permeable network within weeks to months. Low temperature ( ≲ 50 °C) cracks could not be hydrated in the time since eruption ( ≃ 230 ka). Our data show that textures in cooling glass develop during cooling below T g within days, producing cracks and crystals that create inhomogeneities in the spatial distribution of water. The lengthscales of water diffusion away from spherulites, spherulite cracks, and perlite cracks suggest that most of the rehydration of melt/glass occurs at relatively high temperatures ( > 400 °C). Lack of evidence for water diffusion around other cracks suggests minor low-temperature meteoric water rehydration following emplacement.

Growing pressure on sustainable water resource allocation in the context of global development and rapid environmental change demands rigorous knowledge of how regional water cycles change through time. One of the most attractive and widely utilized approaches for gaining this knowledge is the analysis of lake carbonate stable isotopic compositions. However, endogenic carbonate archives are sensitive to a variety of natural processes and conditions leaving isotopic datasets largely underdetermined. As a consequence, isotopic researchers are often required to assume values for multiple parameters, including temperature of carbonate formation or lake water delta O-18, in order to interpret changes in hydrologic conditions. Here, we review and analyze a global compilation of 57 lacustrine dual carbon and oxygen stable isotope records with a topical focus on the effects of shifting hydrologic balance on endogenic carbonate isotopic compositions.Through integration of multiple large datasets we show that lake carbonate delta O-18 values and the lake waters from which they are derived are often shifted by >+10 parts per thousand relative to source waters discharging into the lake. The global pattern of delta O-18 and delta C-13 covariation observed in >70% of the records studied and in several evaporation experiments demonstrates that isotopic fractionations associated with lake water evaporation cause the heavy carbon and oxygen isotope enrichments observed in most lakes and lake carbonate records. Modeled endogenic calcite compositions in isotopic equilibrium with lake source waters further demonstrate that evaporation effects can be extreme even in lake records where delta O-18 and delta C-13 covariation is absent. Aridisol pedogenic carbonates show similar isotopic responses to evaporation, and the relevance of evaporative modification to paleoclimatic and paleotopographic research using endogenic carbonate proxies are discussed.Recent advances in stable isotope research techniques present unprecedented opportunities to overcome the underdetermined nature of stable isotopic data through integration of multiple isotopic proxies, including dual element C-13-excess values and clumped isotope temperature estimates. We demonstrate the utility of applying these multi-proxy approaches to the interpretation of paleohy-droclimatic conditions in ancient lake systems. Understanding past, present, and future hydroclimatic systems is a global imperative. Significant progress should be expected as these modern research techniques become more widely applied and integrated with traditional stable isotopic proxies. (C) 2015 Elsevier Ltd. All rights reserved.

Ultramafic rocks and their related soils and sediments are non-anthropogenic sources of metal contaminants. In the southeastern region of Sri Lanka, release of Ni and Mn into the surrounding areas and groundwater is an ecological, agricultural and human health concern. Here, we investigate the release and fate of Ni and Mn from serpentine sediment in the Ussangoda ultramafic complex by coupling interpretations garnered from chemical extractions. Sequential extraction experiments, utilized to identify ‘elemental pools,’ indicate Mn is mainly associated with oxides/(oxy)hydroxides, whereas, Ni is bound in silicates and spinels. Both Ni and Mn demonstrate rapid release rates in water (2.4 × 10− 12 and 2.0 × 10− 13 mol m− 2 s− 1, respectively) and release rates increase with increasing ionic strengths. Sediments evaluated from 0.05 to 10 mM with organic (citric, acetic and oxalic) and inorganic (H2SO4, HNO3 and HCl) acids show that the maximum rate of Ni and Mn release occurs with oxalic acid (10 mM) at 7.11 × 10− 11 and 3.56 × 10− 11 mol m− 2 s− 1, respectively. Summarizing chemical extractions, Ni and Mn release rates increase in the order of HNO3 ≈ HCl ≈ acetic

Molecular hydrogen (H 2 ) is derived from the hydrothermal alteration of olivine-rich planetary crust. Abiotic and biotic processes consume H 2 to produce methane (CH 4 ); however, the extent of either process is unknown. Here, we assess the temporal dependence and limit of abiotic CH 4 related to the presence and formation of mineral catalysts during olivine hydrolysis (i.e., serpentinization) at 200 °C and 0.03 gigapascal. Results indicate that the rate of CH 4 production increases to a maximum value related to magnetite catalyzation. By identifying the dynamics of CH 4 production, we kinetically model how the H 2 to CH 4 ratio may be used to assess the origin of CH 4 in deep subsurface serpentinization systems on Earth and Mars. Based on our model and available field data, low H 2 /CH 4 ratios (less than approximately 40) indicate that life is likely present and active.

Laptop computers are vital components of critical infrastructure sectors and a common tool in broader society. As they become more widely used, their exposure to volcanic hazards will increase. Therefore, understanding how laptops will function in volcanic environments is necessary to provide suitable mitigation options. In this study, laptop computers were subjected to volcanic ash and gas in both laboratory and field settings. None of the laptops sustained permanent damage in laboratory experiments; however, ash contamination did reduce the functionality of keyboards, CD drives, and cooling fans. Several laptops shut down temporarily due to overheating following ash contamination. In field experiments, laptops were exposed to high concentrations of volcanic gases at White Island, New Zealand. These laptops did not sustain permanent damage as only a small amount of gas was able to enter the laptops. However, metal components on the outside of the laptop did sustain minor corrosion. Re-examination of the laptops after 6 months indicated they were in full working order. Printed circuit boards suffered significant corrosion damage and ceased working only when in direct and sustained contact with volcanic gases. Simple mitigation techniques such as isolating laptops inside heavy duty polyethylene bags were effective. Overall, our experiments demonstrate that laptops have a relatively low risk of damage from volcanic ash and gas exposure, but have a low-medium risk of loss of functionality in ash environments. We think this has implications for other electronic equipment used extensively in critical infrastructure services.

Chrysotile [Mg 3 Si 2 O 5 (OH) 4 ] and tremolite [Ca 2 Mg 5 Si 8 O 22 (OH) 2 ] asbestos represent two distinct mineralogical categories of regulated asbestos commonly evaluated in epidemiological, toxicological, and pathological studies. Human respiratory and gastric systems are sites of asbestos deposition where chrysotile and tremolite asbestos are undersaturated with respect to biological fluids and dissolution kinetics control the persistence of these minerals in biological environments. Here we examined the biodurabilities (i.e., the resistance to dissolution) of chrysotile and tremolite asbestos in simulated body fluids as a function of mineral surface area over time. Batch experiments in simulated gastric fluid (SGF; HCl and NaCl solution at pH 1.2) and simulated lung fluid (SLF; modified Gamble’s solution at pH 7.4) were performed at 37 °C over 720 h to evaluate the dissolution of chrysotile vs. tremolite asbestos in acidic and near-neutral biological fluids. The rate-limiting step of Si release for both minerals was used to obtain rate constants ( k ) and reaction orders ( n ) allowing comparisons of mineral dissolution rates. Both chrysotile and tremolite asbestos are less biodurable in SGF (low pH) compared to SLF (near-neutral pH). Based on equivalent surface area comparisons, the surface chemistry of tremolite is more reactive in lung fluid than chrysotile and vice versa in digestive fluid. However, the relative biodurabilities of these asbestos silicates (from most to least) are tremolite (SLF) > chrysotile (SLF) > tremolite (SGF) > chrysotile (SGF) when accounting for the greater surface area of chrysotile per mass or per fiber compared to tremolite. Overall, this study illustrates the importance of surface area and fiber morphology considerations when evaluating the biodurabilities of asbestiform minerals.

Serpentine soils derived from the weathering of ultramafic rocks and their metamorphic derivatives (serpentinites) are chemically prohibitive for vegetative growth. Evaluating how serpentine vegetation is able to persist under these chemical conditions is difficult to ascertain due to the numerous factors (climate, relief, time, water availability, etc.) controlling and affecting plant growth. Here, the uptake, incorporation, and distribution of a wide variety of elements into the biomass of serpentine vegetation has been investigated relative to vegetation growing on an adjacent chert-derived soil. Soil pH, electrical conductivity, organic C, total N, soil extractable elements, total soil elemental compositions and plant digestions in conjunction with spider diagrams are utilized to determine the chemical relationships of these soil and plant systems. Plant available Mg and Ca in serpentine soils exceed values assessed in chert soils. Magnesium is nearly 3 times more abundant than Ca in the serpentine soils; however, the serpentine soils are not Ca deficient with Ca concentrations as high as 2235 mg kg −1 . Calcium to Mg ratios (Ca:Mg) in both serpentine and chert vegetation are greater than one in both below and above ground tissues. Soil and plant chemistry analyses support that Ca is not a limiting factor for plant growth and that serpentine vegetation is actively moderating Mg uptake as well as tolerating elevated concentrations of bioavailable Mg. Additionally, results demonstrate that serpentine vegetation suppresses the uptake of Fe, Cr, Ni, Mn and Co into its biomass. The suppressed uptake of these metals mainly occurs in the plants’ roots as evident by the comparatively lower metal concentrations present in above ground tissues (twigs, leaves and shoots). This research supports earlier studies that have suggested that ion uptake discrimination and ion suppression in the roots are major mechanisms for serpentine vegetation to tolerate the chemistry of serpentine soils.

The near-surface inorganic synthesis of molecular hydrogen (H2) is a fundamental process relevant to the origins and to the sustenance of early life on Earth and potentially other planets. Hydrogen production through the decomposition of water is thought to be a principal reaction that occurs during hydrothermal alteration of olivine, an iron–magnesium silicate abundant near planetary surfaces. We demonstrate that copious amounts of H2 are produced only when the olivine undergoing alteration (serpentinization) contains 1 to 50 mol% iron over a variety of planetary surface P–T conditions. This suggests that extrasolar Earth-like planets that are hosted by a star with iron contents up to two times the solar value could support life provided they are hydrothermally active and fall within the habitable zone around the star.

Martian regolith and rock may one day be used for building material to support longterm habitation on Mars. Despite several martian simulants being available, the capability of accurately matching a wide variety of reported grain size distributions coupled to the regolith’s chemical character for specific sites on Mars needs to be advanced before producing large quantities of material for material synthesis experimentation on Earth. Here, we use volcanic material (i.e. olivine basalt and basaltic glass) from Banks Peninsula, New Zealand, to demonstrate an applied approach to matching reported size distributions on Mars. The olivine basalt and basaltic glass were crushed, washed and combined to produce a particle size distribution representative of the Columbia Hills region of the Gusev Crater. As New Zealand has a wide variety of geologic material similar to Mars, we are in the process of acquiring rocks ranging from extrusive volcanics to serpentinites with the intent to provide ‘tailored’ simulant to aid in civil engineering applications.

Dense blue glassy pahoehoe occurs on the lower Kalapana flow field of Hawaii as limited breakouts at the base of tumuli and pressure rises or in localized depressions. Dense blue glassy pahoehoe differs from the more abundant spongy pahoehoe in that it has a distinctive silvery blue color, a poorly vesiculated glassy outer selvage, and lower extrusion temperature (∼10 °C cooler). The color of blue glassy pahoehoe may be attributed to the concentration of iron and magnesium at the surface, whereas the golden color of the spongy pahoehoe is possibly the result of fluorine enrichment. The outer margin of the dense pahoehoe consists of three layers, developed in response to an increased cooling rate toward the surface. The outer glass selvage is less than 1 cm thick containing minor amounts of chromite, olivine, plagioclase, and augite. Inside the glassy rind is a ∼5 mm thick transition zone characterized by increasing numbers and sizes of quenched plagioclase crystals and augite clusters. The interior of dense blue glassy pahoehoe is largely crystalline. Crystal size distribution (CSD) theory demonstrates that the formation and textures of plagioclase, pyroxene, and oxides are related to the cooling rates, growth rates (G), and nucleation rates (J) present in each layer of the dense pahoehoe. In contrast to the outer selvage, the crystalline interior typically contains numerous large coalesced vesicles as compared to the evenly vesiculated spongy pahoehoe. The enigmatic contrast between the poorly vesicular outer glassy selvage and the vesicular interior has been attributed to both lower and higher vapor contents of the dense pahoehoe. The higher density, lower extrusion temperatures, degassed outer glassy selvage, well-developed crystalline interior, and fluorine-deficient surface of dense blue glassy, as compared to spongy pahoehoe, indicate that blue glassy pahoehoe was stagnant long enough to exsolve considerable vapor in the lava tube system before extrusion.

Serpentine soils derived from the weathering of ultramafic rocks, mainly ophiolitic serpentinites, are typically characterized by Cr concentrations in excess of 200 mg kg-1, comparatively higher than non-serpentine soils. We review the chemistry of Cr in serpentine soils and their protoliths, focusing on serpentine soils collected from New Caledonia, Oregon, and California. Overall, serpentine soils are slightly acidic (average pH of ∼6), contain a variety Fe(III) oxides (magnetite and hematite), Fe(III) (oxy)hydroxides, phyllosilicates (serpentine and chlorite), and clays (smectites and vermiculites), and contain concentrations of Cr (> 200 mg kg-1), Ni (> 1,000 mg kg-1), and Mn (> 200 mg kg-1) exceeding values of non-serpentine soils. Although Cr concentrations in serpentine soils have been reported as high as 6 wt% in New Caledonia, Cr values in New Caledonia, Oregon, and California serpentine soils evaluated in this study range from 827 to 9,528 mg kg-1. Chromium(III) is the only valence state observe...

Weathering of ultramafic rocks and serpentinites in the Franciscan Complex of California produces serpentine soils containing high concentrations of Cr as well as other potentially toxic elements including Ni, Co, and Mn. Chromium concentrations in serpentine soils from Jasper Ridge Biological Preserve in the Central Coast Range are as high as 4,760 mg kg−1, nearly three times greater than the serpentinite protolith (∼1800 mg kg−1). Chromium-containing minerals within the bedrock include chlorite (∼0.3 Cr wt. %), enstatite (∼0.4 Cr wt. %), augite (∼0.7 Cr wt. %), chromite (∼10.8 Cr wt. %), magnetite (8.2-10.3 Cr wt. %), and an ultra fine-grained mixture of spinel and a silicate phase containing ∼13.3 Cr weight percent. Chromium concentrations in serpentine soil profiles fluctuate between 1,725 to 4,760 mg kg−1 and do not correspond to variations in soil pH, organic carbon, or electrical conductivity. The enrichment and variability of soil Cr is directly related to the modal abundance and weathering of chromite, Cr-magnetite, and the spinel-silicate mixture. By comparison, Cr silicates account for

Chromium is abundantly and primarily present as Cr(III) in ultramafic rocks and serpentine soils. Chromium(III) oxidation involving chromite (FeCr2O4) via interactions with birnessite has been shown to be a major pathway of Cr(VI) production in serpentine soils. Alternatively, Cr(III)-bearing silicates with less Cr(III) may provide higher Cr(VI) production rates compared to relatively insoluble chromite. Of the potential Cr(III)-bearing silicates, Cr(III)-muscovite (i.e., fuchsite) commonly occurs in metamorphosed ultramafic rocks and dissolution rates may be comparable to other common Cr(III)-bearing phyllosilicates and clays. Here, we examine the formation of Cr(VI) related to Cr(III)-muscovite and birnessite (i.e., acid birnessite) interactions with and without humic matter (HM) via batch experiments. Experimentally, the fastest rate of Cr(VI) production involving Cr(III)-muscovite was 3.8 × 10(-1) μM h(-1) (pH 3 without HM). Kinetically, Cr(III)-muscovite provides a major pathway for Cr(VI) formation and Cr(VI) production rates may exceed those involving chromite depending on pH, available mineral surface areas in solution, and the abundance of Cr(III) present. However, when HM is introduced to the system, Cr(VI) production rates decrease by as much as 80%. This highlights that HM strongly decreases but may not completely suppress the formation and mobilization of Cr(VI). A Sri Lankan serpentine soil was utilized to provide context with regards to the experimental results. Despite Cr(VI) in the soil solids and Cr(VI) formation being favorable from Cr(III)-bearing minerals, no detectable Cr(VI) was released into soil solutions potentially due to the abundance of HM. Overall, the dynamic interactions of Cr(III)-bearing silicates and birnessite provide a kinetically favorable route of Cr(VI) formation which is tempered by humic matter.

Ultramafic rocks and their related soils (i.e., serpentine soils) are non-anthropogenic sources of metal contamination. Elevated concentrations of metals released from these soils into the surrounding areas and groundwater have ecological-, agricultural-, and human health-related consequences. Here we report the geochemistry of four different serpentine soil localities in Sri Lanka by coupling interpretations garnered from physicochemical properties and chemical extractions. Both Ni and Mn demonstrate appreciable release in water from the Ussangoda soils compared to the other three localities, with Ni and Mn metal release increasing with increasing ionic strengths at all sites. Sequential extraction experiments, utilized to identify "elemental pools," indicate that Mn is mainly associated with oxides/(oxy)hydroxides, whereas Ni and Cr are bound in silicates and spinels. Nickel was the most bioavailable metal compared to Mn and Cr in all four soils, with the highest value observed in the Ussangoda soil at 168 ± 6.40 mg kg(-1) via the 0.01-M CaCl2 extraction. Although Mn is dominantly bound in oxides/(oxy)hydroxides, Mn is widely dispersed with concentrations reaching as high as 391 mg kg(-1) (Yudhaganawa) in the organic fraction and 49 mg kg(-1) (Ussangoda) in the exchangeable fraction. Despite Cr being primarily retained in the residual fraction, the second largest pool of Cr was in the organic matter fraction (693 mg kg(-1) in the Yudhaganawa soil). Overall, our results support that serpentine soils in Sri Lanka offer a highly labile source of metals to the critical zone.