QUANTIFYING THE ROLES OF CHEMICAL AND MICROBIAL WEATHERING IN ACID-SULFATE HYDROTHERMAL SYSTEMS

Although the roles of microbial and chemical processes are relatively well-studied in neutral-chloride hydrothermal systems, very few studies have addressed these processes in acid-sulfate hydrothermal systems. This study aims to survey the roles of chemical and microbial weathering in acid-sulfate hydrothermal systems in order to provide greater understanding of the geochemical processes operating in low pH (2-4) and relatively high temperature (43-90oC) enviroments. These data provide insight into both modern and ancient life in extreme environments, as well as which processes are abiotically controlled. Field microcosm experiments indicate initial dissolution in Las Pailas hydrothermal system, located on the southwest flank of Rincón de la Vieja, Costa Rica, is likely driven by microorganisms. These microorganisms increase the short-term volumetric weathering rate of anorthoclase containing Fe-oxide and apatite mineral inclusions by an order of magnitude relative to abiotic controls. However, weathering of other silicates by microorganisms appeared to be relatively similar to abiotic controls. These results indicate that microbially induced silicate dissolution facilitates phosphate solubulization in acid-sulfate hydrothermal systems. These results are similar to previous research conducted in low temperature (T), circum-neutral pH systems, despite the higher reaction rates due to increased T and acid attack in this extreme environment. The net result of increased weathering is the mobilization of trace metals into solution. Hydrothermal fluid fluxes contain abundant trace metals, however, these metals preferentially partition into the sediments at Las Pailas. In other hydrothermal systems and acid mine drainage environments, trace metals preferentially bind to iron oxides. Microorganisms in these systems typically facilitate the formation of Fe-oxides to which trace metals bind. In circum-neutral hydrothermal systems, associated with low-sulfidation epithermal ore deposits, microorganisms form shallow epithermal ore deposits. Sequential extraction of Las Pailas sediments indicates microorganisms also concentrated trace metals, particularly copper, gold and silver in the Las Pailas sediments, despite the acidic pH. However, microorganisms in this acid-sulfate system appear to sequester trace metals by binding them to microbial cell surfaces, exopolymeric substances, and iron oxides produced and entrained within biofilm. These data suggest microorganisms may create shallow/surficial indicators of epithermal Au-Ag ore formation at depth. Moreover, the association of microbial biomarkers and influences on the isotopic record suggest microorganisms may play a role in ore formation that occurs below the limit for life (~121oC) and that microorganisms may have been involved in ore formation throughout geologic time. Not all processes in acid-sulfate hydrothermal systems, however, are microbially controlled. Weathering not only concerns itself with the dissolution of primary mineral phases, but also the formation of secondary mineral phases, particularly nontronite and kaolinite formation. Pailas de Agua I, one of the hot springs in the Las Pailas hydrothermal field, contains abundant clay minerals. To assess the influence of microorganisms on secondary mineral formation in Las Pailas, a model hydrothermal solution, based on the solution geochemisty of Pailas de Agua I, was created. Experiments using this solution were performed at high (80oC) and low (25oC) temperatures, with and without the addition of fluoride and microbial surrogates to determine the influence of temperature, Al-complexation by fluoride and microbial processes on clay formation. Results indicate that high temperature experiments form nontronite and kaolinite regardless of experimental conditions. However, in low temperature solutions, fluoride plays a key role in Al-complexation and aids in authigenic nontronite precipitation. Microbial surrogates play little role in clay formation in acidic pH systems, in contrast to, clay mineral formation in many circum-neutral pH systems, which is microbially influenced. Acid-sulfate hydrothermal systems have been proposed as an analog for Mars because of mineralogical similarities between the two systems. These data indicate that while clay minerals on Mars may be good indicators of water in Mars' history, they do not specifically indicate an environment of formation, nor should they be used as an indicator of past life on Mars. Moreover, these data suggest that the kickstarting of the "clay mineral factory" on early Earth may not be the result of microbial processes. These results indicate that many microbial processes, including microbially induced mineral dissolution and trace metal immobilization, may be ubiquitous in nature regardless of whether exceptional preservation of microbial structures occurs. However, the mechanisms that underpin these processes may differ between environments. Most importantly, despite the common association between microorganisms and clay minerals in modern environments, authigenic clay formation may occur in the absence of microbial surrogates, if/when Al-complexing ligands are present in solution. Both abiotic and biological processes influence weathering in acid-sulfate hydrothermal systems and these processes may likely be differentiable in the rock record through examination of associations between biomarker associations with sediments, even in the absence of exceptional preservation

Deciphering the diagenetic history of the El Abra Formation of eastern Mexico using reordered clumped isotope temperatures and U-Pb dating

Carbonates form ubiquitously throughout the history of deposition, burial, and uplift of basins. As such, they potentially record the environmental conditions at the time of formation. Carbonate clumped isotopes provide the temperature of precipitation but can be internally reordered if the host rock is exposed to elevated temperatures over geologic time scales. Here, we exploited this kinetic behavior by analyzing multiple generations of cements that capture the range of environments experienced by the El Abra Formation from eastern Mexico. From this, we developed a quantitative diagenetic history for these different phases of cementation. We observed a 70 °C range in clumped isotope temperatures from 64 °C to 134 °C for these cements, which is not compatible with their inferred precipitation environments. This suggests that bond reordering occurred during burial but did not fully reorder all cements to a common apparent temperature. We reconstructed original cement growth temperatures and the isotopic signature of the parent fluids to show that precipitation from a marine pore fluid began at 125 Ma, contemporaneous with deposition, and continued throughout burial to temperatures of at least 138 °C at 42 Ma. We show that precipitation of equant cements, which occluded 90% of the pore space, was coincident with Laramide-related burial to depths greater than 3800 m. A U-Pb age of diagenetic calcite of 77.1 ± 3.6 Ma provides independent support for our estimates of the absolute timing of precipitation of two distinct phases of the paragenesis. This is the first demonstration of the utility of integrating U-Pb age dating with reordered clumped isotope temperatures to provide quantitative constraints on the time-temperature history of cementation. Such information may ultimately lead to advances in our understanding of the formational environments and geological processes that drive diagenesis in carbonates for temperatures below the clumped isotope “blocking temperature.

A conservation roadmap for the subterranean biome

The 15th UN Convention on Biological Diversity (CBD) (COP15) will be held in Kunming, China in October 2021. Historically, CBDs and other multilateral treaties have either alluded to or entirely overlooked the subterranean biome. A multilateral effort to robustly examine, monitor, and incorporate the subterranean biome into future conservation targets will enable the CBD to further improve the ecological effectiveness of protected areas by including groundwater resources, subterranean ecosystem services, and the profoundly endemic subsurface biodiversity. To this end, we proffer a conservation roadmap that embodies five conceptual areas: (1) science gaps and data management needs; (2) anthropogenic stressors; (3) socioeconomic analysis and conflict resolution; (4) environmental education; and (5) national policies and multilateral agreements.Peer reviewe

Fundamental Science and Engineering Questions in Planetary Cave Exploration

32 páginas.- 3 figuras.- 2 tablas.- 260 referenciasNearly half a century ago, two papers postulated the likelihood of lunar lava tube caves using mathematical models. Today, armed with an array of orbiting and fly-by satellites and survey instrumentation, we have now acquired cave data across our solar system-including the identification of potential cave entrances on the Moon, Mars, and at least nine other planetary bodies. These discoveries gave rise to the study of planetary caves. To help advance this field, we leveraged the expertise of an interdisciplinary group to identify a strategy to explore caves beyond Earth. Focusing primarily on astrobiology, the cave environment, geology, robotics, instrumentation, and human exploration, our goal was to produce a framework to guide this subdiscipline through at least the next decade. To do this, we first assembled a list of 198 science and engineering questions. Then, through a series of social surveys, 114 scientists and engineers winnowed down the list to the top 53 highest priority questions. This exercise resulted in identifying emerging and crucial research areas that require robust development to ultimately support a robotic mission to a planetary cave-principally the Moon and/or Mars. With the necessary financial investment and institutional support, the research and technological development required to achieve these necessary advancements over the next decade are attainable. Subsequently, we will be positioned to robotically examine lunar caves and search for evidence of life within Martian caves; in turn, this will set the stage for human exploration and potential habitation of both the lunar and Martian subsurface.The following funding sources are recognized for supporting several of the contributing authors: Human Frontiers Science Program grant #RGY0066/2018 (for AAB), NASA Innovative Advanced Concepts Grant #80HQTR19C0034 (HJ, UYW, and WLW), and European Research Council, ERC Consolidator Grant #818602 (AGF), the Spanish Ministry of Science and Innovation (project PID2019-108672RJ-I00) and the "Ramon y Cajal" post-doctoral contract (grant #RYC2019-026885-I (AZM)), and Contract #80NM0018D0004 between the Jet Propulsion Laboratory, California Institute of Technology and the National Aeronautics and Space Administration (AA, MJM, KU, and LK).Peer reviewe

A roadmap for planetary caves science and exploration

2 páginas.- 1 figura.- 16 referenciasTo the Editor — 2021 is the International Year of Caves and Karst. To honour this occasion, we wish to emphasize the vast potential embodied in planetary subsurfaces. While researchers have pondered the possibility of extraterrestrial caves for more than 50 years, we have now entered the incipient phase of planetary caves exploration....Peer reviewe

The Enceladus Orbilander Mission Concept: Balancing Return and Resources in the Search for Life

Enceladus's long-lived plume of ice grains and water vapor makes accessing oceanic material readily achievable from orbit (around Saturn or Enceladus) and from the moon's surface. In preparation for the National Academies of Sciences, Engineering and Medicine 2023–2032 Planetary Science and Astrobiology Decadal Survey, we investigated four architectures capable of collecting and analyzing plume material from orbit and/or on the surface to address the most pressing questions at Enceladus: Is the subsurface ocean inhabited? Why, or why not? Trades specific to these four architectures were studied to allow an evaluation of the science return with respect to investment. The team found that Orbilander, a mission concept that would first orbit and then land on Enceladus, represented the best balance. Orbilander was thus studied at a higher fidelity, including a more detailed science operations plan during both orbital and landed phases, landing site characterization and selection analyses, and landing procedures. The Orbilander mission concept demonstrates that scientifically compelling but resource-conscious Flagship-class missions can be executed in the next decade to search for life at Enceladus