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NASA NTRS2020

The Effect of Europa and Enceladus Analog Seawater Composition on Isotopic Measurements of Volatile CO2

Science goals for icy ocean worlds missions include characterizing the chemical compositionof the surface and interior using remote sensing and in situ techniques. The next class of flightmass spectrometers for these missions will obtain compositional identifications and isotope ratiomeasurements of volatiles evolved from the ice surface (exosphere) and plumes. These massspectra will be combined with data from other flight instruments to infer the composition of theinterior from volatiles. To ensure accurate interpretation of these measurements, it is critical toverify whether the fundamental assumption that volatiles observed in icy ocean world exospheresor plumes will be a direct reflection of the sub-ice ocean. The present study evaluates whether isotopologues from an initial CO2 gas fractionate by interacting with seawater (brine) of varyingsalt composition and concentration. δ13CCO2 are affected by the pH of the brine and subsequentspeciation of {CO2}, where {CO2} represents the combination of CO2, H2CO3, HCO3-, and CO32-.{CO2} for low pH brines hypothesized for Europa will preferentially speciate as CO2. Analyzedδ13CCO2 for low pH brines are within error of the original δ13CCO2, demonstrating that volatile CO2in a low pH system will be a direct reflection of the original CO2. However, Europa’s radiativeenvironment and rapid depressurization due to plume ejection may impose fractionation effects.In contrast, high pH systems relevant to Enceladus or a more alkaline Europa are expected toform all carbonate species, while favoring speciation as HCO3-. High pH brines in theseexperiments include both an original CO2 gas and an isotopically distinct HCO3- (from NaHCO3salt). These alkaline experiments demonstrate that δ13CCO2 values are highly variable, and dependon the concentration of the dominant carbonate species, (Na)HCO3-. Mass balance estimatesindicate that measured δ13CCO2 is a thermodynamically predictable mixture of both carbonsources, suggesting that measurements of δ13C at Enceladus would directly reflect of the sourcesof CO2 and carbonate buffering in the ocean. δ18O measurements for CO2 interacting with KCland MgCl2 follow established models for δ18O-ionic strength. CO2 interacting with MgSO4,Na2SO4, and NaCl demonstrate an offset from established δ18O-ionic strength models dependingon the concentration of initial CO2. These results suggest that current predictive models for δ18Oin brines need to be resolved for changing concentrations of CO2

Ocean Worlds↗

NASA NTRS2021

The abundances of F, Cl, and H2O in eucrites: Implications for the origin of volatile depletion in the asteroid 4 Vesta

We conducted a petrologic study of apatite within eight unbrecciated, non-cumulate eucrites and two monomict, non-cumulate eucrites. These data were combined with previously published data to quantify the abundances of F, Cl, and H2O in the bulk silicate portion of asteroid 4 Vesta (BSV). Using a combination of apatite-based melt hygrometry/chlorometry and appropriately paired volatile/refractory element ratios, we determined that BSV has 3.0–7.2 ppm F, 0.39–1.8 ppm Cl, and 3.6–22 ppm H2O. The abundances of F and H2O are depleted in BSV relative to CI chondrites to a similar degree as F and H2O in the bulk silicate portion of the Moon. This degree of volatile depletion in BSV is similar to what has been determined previously for many moderately volatile elements in 4 Vesta (e.g., Na, K, Zn, Rb, Cs, and Pb). In contrast, Cl is depleted in 4 Vesta by a greater degree than what is recorded in samples from Earth or the Moon. Based on the Cl-isotopic compositions of eucrites and the bulk rock Cl/F ratios determined in this study, the eucrites likely formed through serial magmatism of a mantle with heterogeneous δ37Cl and Cl/F, not as extracts from a partially crystallized global magma ocean. Furthermore, the volatile depletion and Cl-isotopic heterogeneity recorded in eucrites is likely inherited, at least in part, from the precursor materials that accreted to form 4 Vesta and is unlikely to have resulted solely from degassing of a global magma ocean, magmatic degassing of eucrite melts, and/or volatile loss during thermal metamorphism. Although our results can be reconciled with the past presence of wide-scale melting on 4 Vesta (i.e., a partial magma ocean), any future models for eucrite petrogenesis involving a global magma ocean would need to account for the preservation of a heterogeneous eucrite source with respect to Cl/F ratios and Cl isotopes.

Francis M. Mccubbin↗

NASA NTRSDate not supplied

Overview of the Volatiles Investigating Polar Exploration Rover

The Volatiles Investigating Polar Exploration Rover (VIPER) is a lunar volatiles detection and measurement mission. VIPER will be launched to the Moon in late 2023 as a payload on the Commercial Lunar Payload Services(CLPS) flight provided by Astrobotic's Griffin lander. The VIPER rover is a solar powered, mobile robot de-signed to traverse up to 20 km during a mission lasting up to four lunar days. After landing in a south polar region, the VIPER rover will travel to investigate a range of Ice Stability Regions (ISRs) across scales from 100s of meters to kilometers and conduct surface and subsurface assessment of lunar water and other volatiles. VIPER includes a suite of rover-mounted instruments(three spectrometers and a drill), which the VIPER science mission team will use to characterize the nature of the volatiles and to create global lunar water resource maps.

planetary rover↗

NASA NTRS2022

Characterization of Lunar Polar Volatiles for Curation and ISRU - Executive Summary

The goal of this project is to support lunar exploration by simulating and characterizing ice and volatile-rich materials expected to be found at the lunar poles. These materials are highly sensitive to heating, which could significantly alter their composition and prevent scientific studies on lunar samples. During FY19, we obtained materials for and designed a simulated lunar environment, within which volatile-rich simulant could be made. We also refined the procedure for moderate-fidelity lunar simulants at cryogenic temperatures. In FY20, we completed our test setup, and we can now reach cryogenic temperatures and near-lunar pressures with active compositional monitoring of volatiles in the vapor phase. For FY21, we: 1) progressed towards developing sample storage temperature requirements for volatile-rich samples by completing storage testing, along with materials testing for Artemis geologic sampling, 2) obtained instrumentation for solid sample monitoring to characterize solid species, and 3) progressed towards water extraction testing for ISRU. Our test results will directly feed into Artemis science requirements, hardware designs for sample return, vehicle requirements (HLS, Gateway, Orion), and operations planning for lunar exploration activities.

Julie L Mitchell↗

NASA NTRS2024

Volatiles in melt inclusions from lunar mare basalts: Bridging the gap in the H 2 O/Ce ratio between melt Inclusions in lunar pyroclastic sample 74220 and other mare samples

The H2O concentration and H 2 O/Ce ratio in olivine-hosted melt inclusions are high in lunar pyroclastic sample 74220 (H 2 O up to 1410 ppmw; H 2 O/Ce up to 77) but lower (H2O 10 to 430 ppmw; H 2 O/Ce 0.3 to 9.4) in all other lunar samples studied before this work. The difference in H 2 O concentration and in H 2 O/Ce ratio is absent for other volatile elements (F, S, and Cl) in melt inclusions in 74220 and other lunar samples. Because H 2 O (or H) is a critical volatile component with significant ramifications on the origin and evolution of the Moon, it is important to understand what causes such a large gap in H 2 O/Ce ratio between 74220 and other lunar samples. Two explanations have been advanced. One is that volcanic product in sample 74220 has the highest cooling rate and thus best preserved H 2 O in melt inclusions compared to melt inclusions in other samples. The other explanation is that sample 74220 comes from a localized heterogeneity enriched in some volatiles. To distinguish these two possibilities, here we present new data from two rapidly cooled lunar samples with glassy melt inclusions: olivine-hosted melt inclusions (OHMIs) in 79135 regolith breccia (unknown cooling rate but with glassy MIs similar in texture with those in 74220), and pyroxene-hosted melt inclusions (PHMIs) in 15597 pigeonite basalts (known high cooling rate, second only to 74220 and 15421). In addition, we also investigated new OHMIs in sample 74220. If the gap is due to the difference in cooling rates, samples with cooling rates between those of 74220 and other studied lunar samples should have preserved intermediate H2O concentrations and H 2 O/Ce ratios. Our results show that melt inclusions in 79135 and 15597 contain high H 2 O concentrations (up to 969 ppmw in 79135 and up to 793 ppmw in 15597) and high H 2 O/Ce ratios (up to 21 in 79135 and up to 13 in 15997), bridging the big gap in H 2 O/Ce ratio among 74220 and other lunar samples. Combined with literature data, we confirm that H 2 O/Ce ratios of different lunar samples are positively correlated to the cooling rates and independent of the type of mare basalts. We hence reinforce the interpretation that the lunar sample with the highest cooling rate best represents pre-eruptive volatiles in lunar basalts due to the least degassing. Based on Ce concentration in the primitive lunar mantle, we estimate that H 2 O concentration in the primitive lunar mantle (meaning bulk silicate Moon) is 121 ± 15 ppmw. Our new data also further constrain F/P, S/Dy and Cl/Ba ratios in lunar basalts and the lunar mantle. Estimated F, P, and S concentrations in the lunar primitive mantle are 4.4 ± 1.1 ppmw, 22 ± 8 ppmw, and 67 +67 −33 ppmw, respectively.

Xue Su↗

DOE OSTI2025

Secondary Organic Aerosol from OH Oxidation of Acyclic Terpenes Is More Viscous and Less Volatile than That of Their Cyclic Analogs

Biogenic volatile organic compounds (BVOCs), a dominant source of secondary organic aerosol (SOA) globally, exhibit emission rates and composition that are plant species-specific and vary with environmental stressors. A common outcome of plant stress is increased emissions of acyclic terpenes. The paucity of information about acyclic terpene SOA chemistry contributes to uncertainties in predictions of SOA global loadings and impacts on Earth’s radiative budget, particularly in a changing climate where acyclic terpene emissions could become more prominent. This study compared properties of SOA derived from OH oxidation of acyclic and cyclic monoterpenes (ß-ocimene, a-pinene) and sesquiterpenes (ß-farnesene, ß-caryophyllene). Single particle mass spectrometry was used for assessing shape, density, and evaporation kinetics of size-selected SOA particles, and nanospray desorption electrospray ionization high-resolution mass spectrometry (nano-DESI-HRMS) was used to measure molecular composition of SOA. Acyclic terpene SOA exhibited higher viscosity and lower volatility compared to cyclic terpene SOA, and had a greater volume fraction remaining (VFR) after ~24 hours of evaporation - approximately 1.3-1.6 times higher VFR than that of cyclic terpene SOA. Additionally, HRMS analysis revealed greater chemical diversity and higher fractions of extremely low volatility compounds (56-62% ELVOC/LVOC) in acyclic terpene SOA compared to cyclic counterparts (25-37% ELVOC/LVOC). Our findings highlight the potential importance of accounting for acyclic terpene aerosol chemistry under conditions of plant stress to improve predictions of SOA loadings and impacts.

SOA physical properties↗

NASA NTRS1997

Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact

A comprehensive analysis of volatiles in the Chicxulub impact strongly supports the hypothesis that impact-generated sulfate aerosols caused over a decade of global cooling, acid rain, and disruption of ocean circulation, which contributed to the mass extinction at the Cretaceous/Tertiary (K/T) boundary. The crater size, meteoritic content of the K/T boundary clay, and impact models indicate that the Chicxulub crater was formed by a short period comet or an asteroid impact that released 0.7-3.4 x 10(31) ergs of energy. Impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons (Gt) each of SO2 and water vapor, and over 500 Gt of CO2, were globally distributed in the stratosphere by the impact. Additional volatiles may have been produced on a global or regional scale that formed sulfate aerosols rapidly in cooler parts of the vapor plume, causing an early, intense pulse of sulfuric acid rain. Estimates of the conversion rate of stratospheric SO2 and water vapor to sulfate aerosol, based on volcanic production of sulfate aerosols, coupled with calculations of diffusion, coagulation, and sedimentation, demonstrate that the 200 Gt stratospheric SO2 and water vapor reservoir would produce sulfate aerosols for 12 years. These sulfate aerosols caused a second pulse of acid rain that was global. Radiative transfer modeling of the aerosol clouds demonstrates (1) that if the initial rapid pulse of sulfate aerosols was global, photosynthesis may have been shut down for 6 months and (2) that for the second prolonged aerosol cloud, solar transmission dropped 80% by the end of first year and remained 50% below normal for 9 years. As a result, global average surface temperatures probably dropped between 5 degrees and 31 degrees K, suggesting that global near-freezing conditions may have been reached. Impact-generated CO2 caused less than 1 degree K greenhouse warming and therefore was insignificant compare to the sulfate cooling. The magnitude of sulfate cooling depends largely upon the rate of ocean mixing as surface waters cool, sink, and are replaced by upwelling of deep ocean water. This upwelling apparently drastically altered ocean stratification and circulation, which may explain the global collapse of the delta 13C gradient between surface and deep ocean waters at the K/T boundary.

NASA Center JPL↗

NASA NTRS2015

Organic Aerosol Volatility Parameterizations and Their Impact on Atmospheric Composition and Climate

Despite their importance and ubiquity in the atmosphere, organic aerosols are still very poorly parameterized in global models. This can be explained by two reasons: first, a very large number of unconstrained parameters are involved in accurate parameterizations, and second, a detailed description of semi-volatile organics is computationally very expensive. Even organic aerosol properties that are known to play a major role in the atmosphere, namely volatility and aging, are poorly resolved in global models, if at all. Studies with different models and different parameterizations have not been conclusive on whether the additional complexity improves model simulations, but the added diversity of the different host models used adds an unnecessary degree of variability in the evaluation of results that obscures solid conclusions. Aerosol microphysics do not significantly alter the mean OA vertical profile or comparison with surface measurements. This might not be the case for semi-volatile OA with microphysics.

Aerosols↗

NASA NTRS2016

Volatile Analysis by Pyrolysis of Regolith (Vapor) for Planetary Resource Prospecting

Measuring the chemical composition of planetary bodies and their atmospheres is key to understanding the formation of the Solar System and the evolution of the planets and their moons. In situ volatile measurements enable a ground-truth assessment of the distribution and abundance of resources such as water-ice and oxygen, important for a sustained human presence on the Moon and beyond. The Volatile Analysis by Pyrolysis of Regolith (VAPoR) instrument is a compact pyrolysis mass spectrometer designed to detect volatiles released from solid samples that are heated to elevated temperatures and is one technique that should be considered for resource prospecting on the Moon, Mars, and asteroids.

regolith↗

NASA NTRS2022

VESIcal: A Critical Approach to Volatile Solubility Modelling Using the Open-Source Engine Vesical

Accurate models of H(2)O and CO(2) solubility in silicate melts are vital for understanding volcanic plumbing systems. These models are used to estimate the depths of magma storage regions from melt inclusion volatile contents, investigate the role of volatile exsolution as a driver of volcanic eruptions, and track the degassing path followed by a magma ascending to the surface. However, despite the large increase in the number of experimental constraints over the last two decades, many recent studies still utilize an earlier generation of models which were calibrated on experimental datasets with restricted compositional ranges. This may be because many of the available tools for more recent models require large numbers of input parameters to be hand-typed (e.g., temperature, concentrations of H(2)O, CO(2), and 8–14 oxides), making them difficult to implement on large datasets. Here, we use a new open-source Python3 tool, VESIcal, to critically evaluate the behaviors and sensitivities of different solubility models for a range of melt compositions. Using literature datasets of andesitic-dacitic experimental products and melt inclusions as case studies, we illustrate the importance of evaluating the calibration dataset of each model. Finally, we highlight the limitations of particular data presentation methods, such as isobar diagrams, and provide suggestions for alternatives, and best practices regarding the presentation and archiving of data. This review will aid the selection of the most applicable solubility model for different melt compositions, and identifies areas where additional experimental constraints on volatile solubility are required.

magma↗

NASA NTRSDate not supplied

Bessel Tube to Capture Lunar Volatiles

Current arts to create linear motion or acceleration of fine particles and molecules into devices such as mass spectrometers and vacuum pumps rely on the pressure difference created by a pinhole or mechanical processes. However, in an environment of vacuum, these approaches do not create such a pressure differential to drive and move fine particles and molecules. In some cases, electrostatic or magnetic processes may work to create the desired motion. A cylindrical harmonic of electric field, which is widely used in electron accelerators, offers a unique capability to capture and induce a linear motion of molecules and particles when electrically charged. Generally, lunar volatiles are electrostatically charged. The idea to capture and collect the lunar volatiles by creating a drift axis of motion using a cylindrical harmonic field has led to the development of a device concept, called a Bessel Tube. The Bessel Tube concept ingests fine particles, gaseous atoms, and gaseous molecules and guides them along an extraction tube for collection, separation, and analysis. The Bessel Tube concept for lunar volatile collection is discussed.

Bessel Tube↗

NASA NTRS2021

Volatiles and Refractories in Surface-Bounded Exospheres in the Inner Solar System

Volatiles and refractories represent the two end-members in the volatility range of species in any surface-bounded exosphere. Volatiles include elements that do not interact strongly with the surface, such as neon (detected on the Moon) and helium (detected both on the Moon and at Mercury), but also argon, a noble gas (detected on the Moon) that surprisingly adsorbs at the cold lunar nighttime surface. Refractories include species such as calcium, magnesium, iron, and aluminum, all of which have very strong bonds with the lunar surface and thus need energetic processes to be ejected into the exosphere. Here we focus on the properties of species that have been detected in the exospheres of inner Solar System bodies, specifically the Moon and Mercury, and how they provide important information to understand source and loss processes of these exospheres, as well as their dependence on variations in external drivers.

Moon↗

NASA NTRSDate not supplied

Polar Resources Ice Mining Experiment-1 (PRIME-1) NASA’s First Polar Drilling and Volatiles Detection Mission

The US Administration announced in 2019 that NASA would return to the Moon where it would seek to establish a sustainable lunar presence. In Situ Resource Utilization (ISRU) is needed to sustain and grow hu-man surface exploration and it is therefore a vital part of ensuring this bold endeavor. ISRU requires ground-truth on physical, mineral, and volatile characteristics of the resources. Water, a key and game-changing resource, exists in the polar regions of the Moon. Learning to harvest and use this resource first requires understanding where the resource is abundantly located and on what scales. Harvested water, which is usable for life support and fuel, must be identified, quantified, and assessed for its mining feasibility. The project goal for PRIME-1 is to develop a flight-ready instrumentation package that can assess the volatiles at a polar lunar landing location. PRIME-1 is the combination of two instruments; Mass Spectrometer observing lunar operations (MSolo) and The Regolith and Ice Drill for Exploring New Terrain (TRIDENT). TRIDENT is an 1-meter augering drill capable of bringing incremental lunar regolith samples to the surface for volatile analysis. MSolo is a modified, commercial-off-the-shelf (COTS) mass spectrometer capable of qualifying and quantifying atomic species in the 1-100 amu range, including isotopic differentiation. These two lunar flight instruments operating together make up the PRIME-1 instrument suite. PRIME-1 intends to fly on and operate from a static lunar lander acquired by the NASA Commercial Lunar Payload Services (CLPS) acquisition process. The PRIME-1 payload suite was selected to fly on Intuitive Machines Nova-C lander, and is currently targeting a late Fall 2023 landing attempt.

MSolo↗

NASA NTRSDate not supplied

Polar Resources Ice Mining Experiment-1 (PRIME-1) NASA’s First Polar Drilling and Volatiles Detection Mission

MSolo↗

DOE OSTI2026

Shock wave formation in the thermosphere by an earthgrazing fireball: Empirical evidence for volatile-enhanced hydrodynamic shielding

Hydrodynamic shielding is a theoretically well-established but observationally elusive and experimentally difficult-to-replicate phenomenon with implications that extend far beyond meteor physics. Rare earthgrazing meteoroids with infrasound signatures that penetrate to the ground can be used to probe hydrodynamic shielding that leads to strong shock formation at high altitude. Here, we report the first coordinated optical and multi-station infrasound observations of a centimeter-scale earthgrazing fireball that generated sustained cylindrical line shock at thermospheric altitudes near 92 km. The event was recorded by numerous optical stations and three infrasound arrays, allowing trajectory reconstruction, ablation behavior, acoustic source localization, and shock characteristics. Optical observations indicate early mechanical erosion and ablation/evaporation at exceptionally low dynamic pressure, consistent with a cometary or a porous, volatile-bearing CM chondritic object. Independent infrasound detections localize shock generation to multiple points along a 164 km trajectory segment near perigee. Weak-shock modeling yields a consistent blast radius of ∼30 m, implying an acoustic-equivalent source size far exceeding the physical dimensions of the ∼45 g nucleus. We demonstrate that classical gas dynamics and ablation-driven hydrodynamic shielding alone cannot account for these observations under ambient thermospheric conditions. We show that volatile release provides the additional flow-field density enhancement required to amplify hydrodynamic shielding, reduce the effective local Knudsen number, and sustain a shock envelope capable of radiating detectable infrasound. Furthermore, these results demonstrate that small, volatile-rich meteoroids can transiently establish continuum-like flow in rarefied environments.

Astrometry↗

DOE OSTI2024

Comparison of volatiles evolving from selected highland and mare lunar regolith simulants during vacuum sintering

Volatiles evolving from JSC-1A, NU-LHT-4M and CSM-LHT-1G lunar regolith simulants during in vacuo thermal processing were analyzed using mass spectrometry as a function of temperature. Two high-fidelity simulants, JSC-1A (mare) and NU-LHT-4M (highland), were compared to a newly developed CSM-LHT-1G highland simulant, modified to closely match lunar geochemistry. Large autogenous gas loads were observed for all investigated materials. Mineralogical knowledge was used to identify and attribute individual volatile species to reacting, transforming, or decomposing constituents (hydrates, carbonates, sulfates, sulfides, clays, etc.) of the respective regolith simulant in the self-generated gas environment. Cumulative mass losses for individual simulant components as a function of temperature were quantified using mass spectrometry in conjunction with thermogravimetric analysis. Investigation of the four components of CSM-LHT-1G – anorthosite, basalt, augite, and glass – aided the attribution of volatile species to specific compounds and their respective sources. The results showed significant decomposition of non-lunar phases present in the man-made regolith simulants below the typical glass crystallization temperatures, which paves the way to devising methods for enhancing the fidelity of the simulants. Finally, high gas loads and corrosive gases (HF and HCl) were recognized as potential hazards, pertaining to the development of large testbed facilities.

42 ENGINEERING↗

DOE OSTI2024

Volatility Basis Set Distributions and Viscosity of Organic Aerosol Mixtures: Insights from Chemical Characterization Using Temperature-Programmed Desorption–Direct Analysis in Real-Time High-Resolution Mass Spectrometry

Quantitative assessment of gas-particle partitioning of individual components within complex atmospheric organic aerosols (OA) mixtures is critical for predicting and comprehending the formation and evolution of OA particles in the atmosphere. This investigation leverages previously documented data obtained through a temperature programmed desorption - direct analysis in real time – high resolution mass spectrometry (TPD-DART-HRMS) platform. This methodology facilitates the bottom-up construction of volatility basis set (VBS) distributions for constituents found in three biogenic secondary organic aerosol (SOA) mixtures produced through the ozonolysis of a-pinene, limonene, and ocimene. The apparent enthalpies (ΔH*, kJ mol -1 ) and saturated vapor mass concentrations (C T *, µg∙m -3 ) of individual SOA components, determined as a function of temperature (T, K), facilitated an assessment of changes in VBS distributions and gas-particle partitioning with respect to T and atmospheric total organic mass loadings (tOM, µg∙m -3 ). Further, the VBS distributions reveal distinct differences in volatilities among monomers, dimers, and trimers, enabling their categorization into separate volatility bins. At the ambient temperature of T = 298 K, only monomers efficiently partition between gas and particle phases across a broad range of atmospherically relevant total organic mass loadings (tOM) values of 1–100 µg∙m -3 . Partitioning of dimers and trimers becomes notable only at T > 360 K and T > 420 K, respectively. The viscosity of SOA mixtures is assessed using a bottom-up calculation approach, incorporating the input of elemental formulas, ΔH*, C T *, and particle-phase mass fractions of the SOA components. Through this approach, we are able to accurately estimate the variations in SOA viscosity that result from the evaporation of its components. These variations are, in turn, influenced by atmospherically relevant changes in tOM and T. Comparison of the calculated SOA viscosity and diffusivity values with literature reported experimental results shows close agreement, thereby validating the employed calculation approach. These findings underscore the significant potential for TPD-DART-HRMS measurements in enabling the untargeted analysis of organic molecules within OA mixtures. This approach facilitates quantitative assessment of their gas-particle partitioning and allows for the estimation of their viscosity and condensed-phase diffusion, thereby contributing valuable insights to atmospheric models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Volatilized Ammonia Supports Subterranean Ecosystems with Unusual Nitrogen Isotopic Signatures

The Frasassi cave system hosts a robust subterranean ecosystem based on microbial lithoautotrophy. Curiously, acidic biofilms forming above degassing sulfidic cave streams, and the invertebrates that feed on them, are extremely depleted in nitrogen-15 (δ 15 N values less than −20‰). In this study, we tested the hypothesis that these low δ 15 N values result from the volatilization, trapping, and uptake of ammonia degassed from circumneutral streams. We found that dissolved ammonium in the streams had δ 15 N values near +3‰, whereas NH 3(g) in the cave atmosphere above streams exhibited δ 15 N values as low as −27‰, consistent with fractionation by NH 3 volatilization. Extremely acidic condensation droplets on cave walls efficiently trapped airborne NH 3 , accumulating up to 4 mM NH 4 + with δ 15 N values as low as −29‰, thereby confirming volatilized and trapped ammonia as the primary N source to cave wall biofilms and the extensive subsurface ecosystem they support. Airborne ammonia trapping represents a novel mechanism for biological N acquisition and provides abundant N for growth in an extreme subsurface environment that otherwise receives very limited nutrient input.

Nitrogen↗