The drivers of tree growth are one critical question in forest ecology and conservation. However, the measurement of tree growth is a difficult task that requires novel methods to improve accuracy and broaden the understanding of the effect of climate on tree metabolism and carbon accumulation. In this context, isotopes variation along woody tissues is a strong tool that provides new information about tree metabolism, growth rate, and the effect of climatic variation on these processes at high temporal resolution. Here, we obtained woody samples of two tree species two individuals per species (n = 4) from the Biogeographic Choco; Region in Colombia, one of the most humid regions of the planet without dry periods (mean annual temperature 25.9C and rainfall over 7200 mm). We measured 18O and 13C on these samples across some rings in each one to obtain intra-annual variation. Using these data, we assessed if isotopes variation in wood is correlated with climatic variation, explicitly precipitation regimen indicators employing Pearson correlation and linear mixed effect models. We found that both isotopes are correlated negatively with ring width. We also found that 18O is high negative correlated with precipitation indicators, rather than 13C. Our results suggest that isotopes variation are surrogates of tree growth in humid and non-seasonal forests. Besides, the 18O accumulation, which is strongly related to rainfall during the less rainy month (February: 370 mm on average), could be a better indicator of the effect of precipitation on the woody tissue rate change. However, 13C is more related to tissue formation processes. In conclusion, we found evidence of intra-annual variation in isotopes and tree growth in one hyper-humid forest challenging the effect of the dry season of tree growth and potentially suggesting the water excess as an additional limiting factor controlling growth rhythms in tropical trees.

My earth science focused PhD research included the analysis of annual fluorescent laminae in cave stalagmites, under the supervision of karst hydrologist Peter Smart (Bristol, UK). At the time, the source of this fluorescence was uncertain, opening new research opportunities characterizing what is now understood to be soil-derived, water-soluble fluorescent dissolved and colloidal organic matter that is transported to the cave by vadose zone percolation waters. Aquatic organic matter fluorescence research benefitted at this time from significant laboratory analytical advances that were commercially driven, including Sony’s Blu-ray technology and the use of fluorescent labelling in the biomedical sciences. Faster analyses at increasingly higher energy excitation energies opened opportunities for novel fingerprinting of organic matter in hydrological science, including landfill leachates and sewage contamination. Today, hand-held fluorescence sensors can instantaneously determine microbial water quality. And back in the field of speleothem (cave deposit) science, annual geochemical laminae are now recognized to be widely preserved in regions where there is a seasonality in recharge, providing a precise chronology for the stalagmite paleoenvironmental archive. Currently, we are utilizing this precise chronology to generate high-resolution fire history records, where the fire proxy is water-soluble ash-derived elements transported from soil to cave by vadose zone percolation waters.

The composition of the lower continental crust is well-studied but poorly understood because of the difficulty of sampling large portions of it. Petrological and geochemical analyses of this deepest portion of the continental crust are limited to the study of high grade metamorphic lithologies, such as granulite. In situ lower crustal studies require geophysical experiments to determine regional-scale phenomena. Since geophysical properties, such as shear wave velocity (Vs), are nonunique among different compositions and temperatures, the most informative lower crustal models combine both geochemical and geophysical knowledge. We explored a combined modeling technique by analyzing the Basin and Range of the United States, a region for which plentiful geochemical and geophysical data is available. By comparing seismic velocity predictions based on composition and thermodynamic principles to ambient noise inversions, we identified three compositional trends in the southwestern United States that reflect three different geologic settings. The composition of the lower crust depends heavily on temperature because of the effect it has on rock mineralogy and physical properties. In the Basin and Range, we see evidence for a lower crust that overall is intermediate-mafic in composition (53.7 +/- 7.2 wt.% SiO2), and notably displays a gradient of decreasing SiO2 with depth.

North Pacific atmospheric and oceanic circulations are key missing pieces in our understanding of the reorganisation of the global climate system since the Last Glacial Maximum (LGM). Here, using a basin-wide compilation of planktic foraminiferal δ18O, we show that the North Pacific subpolar gyre extended ~3 degrees further south during the LGM, consistent with sea surface temperature and productivity proxy data. Analysis of an ensemble of climate models indicates that the expansion of the subpolar gyre was associated with a substantial gyre strengthening. These gyre circulation changes were driven by a southward shift in the mid-latitude westerlies and increased wind-stress from the polar easterlies. Using single-forcing model runs, we show these atmospheric circulation changes are a non-linear response to the combined topographic and albedo effects of the Laurentide Ice Sheet. Our reconstruction suggests the gyre boundary (and thus westerly winds) began to migrate northward at ~17-16 ka, during Heinrich Stadial 1.

Atmospheric input of trace element micronutrients to the oceans is difficult to determine as even with collection of high-quality aerosol chemical concentrations such data by themselves cannot yield deposition rates. To transform these concentrations into rates, a method of determining flux by applying an appropriate deposition velocity is required. A recently developed method based on the natural radionuclide Be has provided a means to estimate the bulk (wet + dry) deposition velocity (V) required for this calculation. Here, water column Be inventories and aerosol Be concentrations collected during the 2018 US GEOTRACES Pacific Meridional Transect are presented. We use these data together with those from other ocean basins to derive a global relationship between rain rate (m/y) and bulk depositional velocity (m/d), such that V= 999±96 x Rain rate + 1040±136 (R=0.81). Thus with satellite -derived rainfall estimates, a means to calculate aerosol bulk deposition velocities is provided.

Magmatic products of the Karoo Large Igneous Province can be divided into a volumetrically dominant, compositionally uniform low-Ti tholeiitic suite, and a subordinate, geographically restricted, compositionally diverse, incompatible-rich high-Ti suite. High-Ti picrites contain up to 2400 ppm Sr, 1900 ppm Ba and 550 ppm Zr, which seems unusual for olivine-enriched mafic rocks. We studied six Karoo picrites to determine the phase(s) in which Sr resides. Samples consist of 10–30% olivine phenocrysts in a groundmass of brown glass, augite, feldspar, ilmenite and apatite. Glass compositions vary, but are generally evolved, ranging from basaltic trachyandesite to trachyte to dacite. X-ray intensity maps demonstrate that most of the Sr resides in the glasses, and to a lesser extent, in feldspars, if present. The highest Sr (up to 9470 ppm) occurs in glasses adjacent to euhedral olivines, suggesting that phenocrysts are genetically related to evolved liquids represented by surrounding groundmasses. Compositional arrays formed by whole rocks (WRs) and bulk groundmasses represent liquid lines of descent. Calculated parental melts have much higher KO and incompatible trace elements (e.g. Sr or Ba >1200 ppm) relative to low-Ti tholeiites. Fractional crystallization modelling yields evolved residual liquid compositions corresponding to those of glasses, and closely follow liquid evolution predicted by mass balance calculations involving mineral and bulk groundmass compositions. The unusual parental melt compositions imply derivation by small degrees of partial melting from SCLM mantle sources enriched in Sr and other incompatibles, and suggest a possible petrogenetic link between the high-Ti Karoo magmas and carbonatites and kimberlites.

Dob’s Linn (Scotland) is a location that has significantly influenced our understanding of how life evolved over the Ordovician to early Silurian. The current chronostratigraphic boundary between the Ordovician and Silurian periods is a Global Boundary Stratotype Section and Point (GSSP) at Dob’s Linn calibrated to 443.8±1.5 Ma, partly based on biostratigraphic markers, radiometric ages, and statistical modeling. Graptolites are used here as relative dating markers. We dated hundreds of zircon grains extracted from defined metabentonites from six horizons exposed at Dob’s Linn using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Each zircon was imaged using cathodoluminescence, and most show igneous zoning with minimal alteration. Sample locations range from 42 meters above to 5 meters below the recognized GSSP for the Ordovician-Silurian. Samples were responsibly collected and analyzed for paleontology and geochemistry in other work. Overall, many 238U-206Pb zircon ages from the section are significantly younger than expected. The youngest zircon in sample DL7, located 5 meters below the GSSP, yielded a 238U-206Pb age of 402±12 Ma (±2s, 5% disc). Nineteen spots on zircons from this sample are younger than the presently assigned GSSP age, including more concordant results of 426±8 Ma (0.8% disc) and 435±5 Ma (0.2% disc). The youngest zircon in sample 19DL12, < 1 m below the GSSP, is 377±8 Ma (2% disc) with a more concordant age of 443±7 Ma (0.6% disc). A sample located directly on the GSSP (19DL09) yields 327±5 Ma (0.8% disc). Eight spots on zircons from this sample are also younger than the presently assigned GSSP age. We also dated two samples (DL24 and BRS23) 8 meters above the GSSP, and the youngest, most concordant zircon ages in these samples are 400±11 Ma (5% disc) and 421±9 Ma (0.4% disc), respectively. Overall, the U-Pb ages would re-assign the Dob’s Linn chronostratigraphic section to Silurian-Devonian. The young age results could be attributed to Pb loss due to hydrothermal alteration during the Acadian and Alleghenian orogenies. Future work will implement Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS) to obtain accurate U-Pb dating and evaluate the potential effects of Pb loss.

Inland waters are hotspots of greenhouse gas (GHG) emissions, and small water bodies are now well known to be particularly active in the production and consumption of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). High variability in physical, chemical, and environmental parameters affect the production of these GHG, but currently the mechanistic underpinnings are unclear, leading to high uncertainty in scaling up these fluxes. Here, we compare the relative magnitudes and controls of emissions of all three major GHG in twenty pairs of natural wetland ponds and constructed reservoirs in Canada’s largest agricultural region. While gaseous fluxes of CO2 and CH4 were comparable between the two waterbody types, CH4 ebullition was greater in wetland ponds. Carbon dioxide levels were associated primarily with metabolic indicators in both water body types, with primary productivity paramount in agricultural reservoirs, and heterotrophic metabolism a stronger correlate in wetland ponds. Methane emissions were positively driven by eutrophication in the reservoirs, while competitive inhibition by sulfur-reducing bacteria may have limited CH4 in both waterbody types. Contrary to expectations, N2O was undersaturated in both water body types, with wetlands a significantly stronger and more widespread N2O sink than were reservoirs. These results support the need for natural and constructed water bodies for regional GHG budgets and identification of GHG processing hotspots.

Carbon isotope (δ13C) records from marine sediments have been extensively used in Cenozoic chemostratigraphy. The early Paleogene interval in particular has received exceptional attention because negative carbon isotope excursions (CIEs) documented in the sedimentary record, e.g. at the Paleocene Eocene Thermal Maximum (PETM), ca ~56 Ma, are believed to reflect significant global carbon cycle perturbations during the warmest interval of the Cenozoic era. However, while bulk-carbonate δ13C values exhibit robust correlations across widely separated marine sedimentary sections, their absolute values and magnitude of CIEs vary spatially. Moreover, bulk-carbonates in open-marine environments are an ensemble of different components, each with a distinct isotopic composition. Consequently, a complete interpretation of the bulk δ13C record requires an understanding of co-evolution of these components. In this study, we dissect sediments, from early Paleogene interval, at ODP Site 1209, Shatsky Rise, Pacific Ocean to investigate how an evolving bulk-carbonate ensemble influences the overall carbon isotope record. A set of 45 samples were examined for δ13C and δ18O compositions, as bulk and individual size fractions. We find a significant increase in coarse-fraction abundance across PETM, driven by a changing community structure of calcifiers, modulating the size of CIE at Site 1209 and thus making it distinct from those recorded at other open-marine sites. These results highlight the importance of biogeography in marine stable-isotope record, especially when isotopic excursions are driven by climate- and/or carbon-cycle changes. In addition, community composition changes will alter the interpretation of weight percent coarse fraction as conventional proxy for carbonate dissolution.

For youth with limited role models in the STEM fields, and restricted summer research opportunities resulting from a lack of financial resources and academic connections, the opportunity to participate in academically connected, community based science research programs can be incredibly empowering. Providing these opportunities is critically important but it takes purposeful work, persistent outreach and strong community networks. We note that while providing these opportunities is incredibly rewarding, but there is a lot of work both up front and ongoing. This work is itself rewarding when networks are humming and enthusiasm for involvement is high, but it can be challenging when ceilings are hit and walls seem to arise unexpectedly. “Early Engagement in Research: Broadening participation through engagement in authentic science research” builds a regional network of summer research experiences for high school students underrepresented in STEM, starting from a successful model that has provided high school summer field research opportunities for New York City youth for over a decade (Secondary School Field Research Program). The program is developed around regional partnerships between various combinations of academic institutions and research centers, community environmental and education centers, state cooperative extensions, high schools and school networks, state and local park systems and land management groups. Each location has a unique approach, but all include some similar attributes. Each tackles an authentic science research issue that affects the local community such as microbiology in the local streams and microplastics in the local bays and biology, and each includes peer and near peer mentoring for the students along with a scientist mentor. Encouraging professional development of each student is central to the program. Technical instruction includes the use of scientific instruments and equipment, data recording and interpretation. Professional discussions include how to successfully read and dissect a science journal article, how to create and present a science poster and most importantly how build a network for themselves in STEM, and how to help us work with them to support the diversity that is needed for all of science to be inclusive and ultimately meet the needs of our future.

Preventing leakage of CO2 along wellbore cement sheaths is a key factor for ensuring success of geologic carbon storage (GCS) operations. Here, we examine a potential alternative cementing material, engineered cementitious composites (ECC), for use in GCS wellbore cementing applications. ECC is a novel fiber-reinforced cementitious composite that exhibits strain hardening and improved tensile ductility in comparison to conventional cement. Improved ductility may prevent wellbore damage caused by CO2 injection pressures and casing expansion/contraction associated with thermal swings. Earlier work examining physical alterations of ECC exposed to CO2 at 10 MPa and 50°C found that damage to ECC was limited to microcracks with apertures less than 60 µm after several weeks of reaction. However, microstructural analysis revealed densification of the fiber/matrix interphase due to calcite precipitation, which could alter the engineered bonding properties between the matrix and fibers. Such alteration following carbonation could negatively impact the long-term ductility of ECC used for GCS wellbore cementing applications. This presentation will discuss recent results from static batch studies investigating the impact of CO2-acidified water on tensile ductility of ECC. Several ECC and ordinary Portland cement (OPC) coupons were exposed to CO2-saturated water under temperature and pressure conditions of 50oC and 10 MPa, respectively, and samples were retrieved after 2, 7, 14, and 28 days. Four-point flexural test and micro-CT analysis were carried out to investigate the impact of carbonation on the ductility and microstructural properties of ECC. Replicate experiments were also conducted under the same conditions but with a N2 headspace to isolate impacts associated with CO­2 exposure. While the samples exposed to N2 continued to exhibit a multiple microcracking behavior with no observable change in tensile ductility, the ductility of the composite exposed to CO2-acidified water showed an increase in the ultimate flexural strength and significant decrease in ductility as the duration of reaction increased. OPC coupons exhibited brittle behaviors under all test conditions. This suggests that the densification of the fiber matrix interface after exposure to CO2 can compromise ECC’s overall ductility.

Fracture dissolution in carbonate rocks is of great interest for the applications of CO2 geological storage and formation of conduits and caves in karst reservoirs. Taking into account the fracture roughness and interporosity fluid exchange between the fracture and the porous host rock, the classical cubic law for parallel-plate channels or Poiseuille's flow for tubes cannot describe the flow within the fracture's opening. The Reynolds number increases along the fracture as a result of the influx crossing the fracture walls. The wavy, irregular, nonparallel-plate shape of the boundaries affects the overall flow regime and the average flow model. The velocity field on the fracture boundaries possesses a slip and a normal component. The nonzero fluid velocity maintains the concentration gradient near the porous host rock and provides a fresh source of the solvent that facilitates dissolution. The aim of this work is to point out the role of fracture roughness and the influx of fluid from the porous host rock on fracture dissolution. The effective model of flow in a single fracture with permeable wavy walls is coupled to transport of dissolved calcite. The asymptotic solutions of the steady-state Navier-Stokes equations with slip boundary condition are used to determine the velocity field in the fracture opening. Two cases of axisymmetric and parallel-plate wavy fractures are considered. The inflow through the walls increases the Reynolds number along the fracture and results in local flow instabilities and formation of reverse flow. The local instabilities arise in relatively higher Reynolds numbers in parallel-plate wavy fractures than in cylindrical wavy fractures. The averaged pressure drop along the fracture is represented as quadratic and cubic corrections to the linear law. The corrections result from the effect of the inflow through the walls and the irregular geometry of channel. Asymptotic solutions to the reactive transport of the dissolved calcite in the acidified brine are derived for rate-limited reactions with a low Damkohler number and high Peclet number. The role of the fracture's walls corrugations, fractures aspect ratio, porous host rock permeability, and the interporosity fluid exchange between the fracture and host rock on the fracture dissolution is investigated.

We performed continuous ramped heating (CRH) on apatites from various tectonic settings and found two major types of 4He outgassing behavior. Apatites with good (U–Th)/He age reproducibility show simple and unimodal incremental gas-release curves that are similar to those predicted by volume diffusion, whereas samples exhibiting greater age dispersion have complex gas-release curves that feature He ‘spikes’ and secondary gas-release peaks deferred to higher temperatures. Age dispersion from the apatites with simple outgassing behavior can be explained by variability in their relative He retentivity observed on Arrhenius arrays—with similar activation energy but different diffusivities, which may be a result of fine-scale crystal imperfections. The observed high-temperature gas component and the resulting “too-old” AHe ages, combined with an attempt at age correction based on secondary peak gas-removal, seem to indicate the existence of sink-like crystal imperfections that can trap 4He both in nature and during laboratory heating. CRH analysis at different heating rates further suggests that the second gas-release peak occurs at varying temperatures, indicating that the sink is kinetically responsive, and if characterizable, may contain additional thermal-history information. These observations suggest that (1) CRH can be deployed as a routine screening tool for (U–Th)/He dating, (2) diffusion of 4He could be complicated by imperfections beyond radiation damage, and (3) if the proposed sinks exist and retain appreciable 4He, there are opportunities to explore additional thermal histories of natural samples.

The rheological properties of Earth’s lower mantle are key for mantle dynamics and planetary evolution. The main rock-forming minerals in the lower mantle are bridgmanite (Br) and smaller amounts of ferropericlase (Fp). Previous work has suggested that the large differences in viscosity between these minerals greatly affect the bulk rock rheology. The resulting effective rheology becomes highly strain-dependent as weaker Fp minerals become elongated and eventually interconnected. This implies that strain localization may occur in Earth’s lower mantle. So far, there have been no studies on global-scale mantle convection in the presence of such strain-weakening (SW) rheology. Here, we present 2D numerical models of thermo-chemical convection in spherical annulus geometry including a new strain-dependent rheology formulation for lower mantle materials, combining rheological weakening and healing terms. We find that SW rheology has several direct and indirect effects on mantle convection. The most notable direct effect is the changing dynamics of weakened plume channels as well as the formation of larger thermochemical piles at the base of the mantle. The weakened plume conduits act as lubrication channels in the mantle and exhibit a lower thermal anomaly. SW rheology also reduces the overall viscosity, notable in terms of increasing convective vigor and core-mantle boundary (CMB) heat flux. Finally, we put our results into context with existing hypotheses on the style of mantle convection and mixing. Most importantly, we suggest that the new kind of plume dynamics may explain the discrepancy between expected and observed thermal anomalies of deep-seated mantle plumes on Earth.

One key question about Mars is whether life has been or still is present on or beneath its surface. For life to flourish, it requires a habitable environment with the appropriate physical and chemical regolith parameters. To better understand the parameters that constitute a habitable environment, leachates of three martian simulants (JSC Mars-1, MMS-1 fine, and MGS-1) were analyzed for their soluble ionic composition, pH, and conductivity in order to determine the presence of any beneficial or toxic elements and their effects on the two bacteria E. coli and Eucapsis. E.coli was cultured in minimal media where acetic acid was the only organic source, and tested its requirements for a carbon source (acetic acid), nitrogen source ((NH4)2SO4) as well as trace elements (Ca, Mn, Zn, Cu, Fe, Co, Mo). In minimal culture media with all nutrients available for healthy growth, E. coli showed substantial growth. In the case of a carbon-only source or nitrogen-only source in MMS-1 soil leachate, E. coli showed limited growth compared to that observed in the full minimal culture media. Assessing Eucapsis growth, among the three leachates tested MMS-1 displayed the best growth. Additionally, we observed that MMS-1+Allen’s minimal and full Allen’s medium groups displayed similar growth curves, indicating that MMS-1 can provide all the trace elements needed for Eucapsis growth. Among all the leachates, MMS-1 showed the most promising results. MMS-1 + Allen’s medium provided the highest Eucapsis growth. MGS-1 + Allen’s minimal media also showed significantly higher growth than MGS-1 alone. However, JSC and JSC + Allen’s minimal did not show any significant difference regarding Eucapsis growth. The results indicated that Eucapsis grew best in both MMS-1 F leachate only and MMS-1 F leachate with Allen’s minimal medium.

We present an interdisciplinary study of observations of pre-earthquake processes associated with major earthquakes based on integrating space and ground- data. Recent large magnitude earthquakes in Asia and Europe have emphasized the various observations of multiple types of pre-earthquake signals recorded either on the ground or from space. Four physical parameters were measured from ground and satellite and used in our simulation models: 1) Ground Radon variation; 2) Outgoing Long-Wavelength Radiation (OLR) obtained from NPOES, NASA/AQUA) on top of the atmosphere (TOA); 3) Atmospheric Chemical Potential (ACP) obtained from NASA assimilation models and; 4) electron density variations in the ionosphere via GPS Total Electron Content (GPS/TEC). For this analysis we selected six large earthquakes from the last decade with differing geographic and seismo-tectonics regions: (1) M9.3, Off the West Coast of Northern Sumatra, Dec 26, 2004; (2) M9.0 Great Tohoku Earthquake, Japan, March 11, 2011; (3) and (4) M7.8 and M7.3 Gorkha, Nepal, 2015; (5); M8.2 Tehuantepec, Mexico, September 8, 2017 and; (6) M7.1, Puebla central Mexico earthquakes, September 19, 2017. Our preliminary results indicate an enhancements of radon (about a week to ten days prior) coincident (with some delay) with an increase in the atmospheric chemical potential measured near the epicenter from both satellite and subsequently with an increase of outgoing infrared radiation (OLR) observed on the TOA from NOAA/NASA (a week in advance). Finally GPS/TEC data indicate an increase of electron concentration 1-4 days before the earthquakes. Although the radon variations and some of satellite OLR anomalies were observed far (>2000km) from the epicenter areas the anomalies were always inside the estimates of the Dobrovolsky-Bowman area of preparation. We examined the possible correlation between magnitude and the spatial size of earthquake preparation zone in the framework of the Lithosphere –Atmosphere -Ionosphere Coupling hypothesis. The reliable detection of pre-earthquake signals for both sea and land earthquakes was possible only by integrating satellite and ground observations. A detail summary of our approach to this study of pre-earthquake research has just been published as AGU/Wiley Geophysical Monograph Series No. 234.

The International Research Laboratory MINERWA (Responsible Mining, West-Africa) has for objective to contribute to the comprehension of the distribution of mineral resources in Ivory Coast, and to their responsible exploration and exploitation, which implies a thorough understanding of environmental and societal impacts. It is co-funded by the French National Research Institute for Sustainable Development (IRD) and by the African Center of Excellence “Mines and Mining Environment” hosted by the INP-HB (Institut National Polytechnique Félix Houphouët-Boigny) in Yamoussoukro, Ivory Coast. It also involves the University Felix Houphouët-Boigny (UFHB, Abidjan), and 4 laboratories in France (Geosciences Environment Toulouse, PRODIG, Hydrosciences Montpellier and Espace-DEV). MINERWA is also part of the world-wide network AMEDEE (Activity of Mining, Environment, Development, Economy, Ethics, https://amedee-network.science/en/), which is an international collaborative R&D platform whose goal is to promote responsible mining in subtropical and intertropical areas in partnership. The approach is interdisciplinary and the research team is composed of specialists in social and environmental sciences and geologists. The focus is placed on a multi-scale analysis, from atomic/mineral to the crustal scale through the scale of territories. It aims to reinforce the analytical capabilities in Ivory coast, with a focus on free remote sensing data and software and low-coast portable instruments for geochemical analysis of rocks and contaminants in the field, including portable XRF, portable LIBS, portable gamma-ray spectrometers and portable visible/NIR spectrometers. The research laboratory shall be funded for 5 years and was initiated in 2019. The activities are divided into 5 work packages, including (1) a platform for continuous exchanges between the different actors, (2) capacity building, (3) geology of mineral ressources, (4) mines, environment and societies, (5) scale transfer. Several preliminary research outcomes in the framework of this laboratory will be presented in the session, in particular in relation to the environmental impact of artisanal mining in West Africa [1,2,3]. [1] Abass Saley, A. et al. , this session. [2] Ngome, M. et al., this session. [3] DAÏ, B.S.M. et al., this session.

The Sandur greenstone belt (SGB) is a distinctive greenstone belt as it is perched within the Closepet granitoid rocks (CG). The emplacement of the CG is attributed to intrusion in a crustal scale transcurrent shear zone towards the end of Archaean (Moyen et al., 2003). The Chitradurga shear zone that forms the eastern margin of the Chitradurga greenstone belt, located west of the Closepet granite, is considered as the boundary between WDC and EDC. As per the division of the Dharwar craton, the domination of volcano-sedimentary sequences in SGB with abundant BIF and considerable greywacke-argillite lithologies, attest their similarity to the greenstone belts of WDC. Closer to the SGB, the rocks of the CG are known to host excellent mafic microgranular enclaves (MME) which might indicate interaction between the granitic magma with the older greenstone belt lithologies during intrusion. It is interesting to note that there is a progressive increase in crustal thickness from north towards south in the Dharwar craton and the SGB is found associated with the CG in the shallow zones of the north (Moyen et al., 2003). The mafic volcanic rocks are predominantly basaltic in composition and are composed of amphibole, pyroxene, plagioclase and quartz with titanite and magnetite as accessory minerals. The rocks are classified as tholeiitic basalts that were metamorphosed to amphibolite grade. Preliminary geochemical studies on these rocks show significant differences in their trace element distribution. The chondrite-normalized REE patterns show moderate to high contents of REE and have unfractionated pattern. The basalts show a flat to slightly LREE enriched pattern. Some samples show slight negative Eu anomaly and some do not show any significant anomaly. Some associated rocks also have complementary enrichment-depletion of certain elements. All of these point to multiple petrogenetic processes involved in the generation of these magmatic precursor rocks.

Native hydrogen (H2) may represent a new carbon free energy resource, but to date there is no specific exploration guide to target H2-fertile geological settings. Here, we present the first soil gas survey specifically designed to explore H2 migration in a region where no surface seepage has been documented so far. We choose the Pyrenean orogenic belt and its northern foreland basin (Aquitaine, France) as a playground to test our strategy. The presence of a mantle body at shallow depth (< 10 km) under the Mauléon Basin connected to the surface by major faults is considered as a preliminary pathfinder for H2 generation and drainage. On this basis, more than 1,100 in situ soil gas analysis (H2, CO, CO2, CH4, H2S, and 222Rn) were performed at ~1 m depth at the regional scale along a 10 x 10 km grid spanning over 7,500 km2. The analysis campaign reveals several hot spots to the north of the Mauléon Basin where H2, CO2 and 222Rn concentrations exceed 1000 ppmv, 10 vol% and 50 kBq m-3, respectively. Most of these hot spots are located along the North Pyrenean Frontal Thrust and other related faults rooted in the mantle body. These results, together with evidence of fluid migration at depth, suggest that H2 may be sourced from mantle rocks serpentinization and carried to the surface along major thrusting faults. Hydrogen traps remain unidentified up to now but the presence of salt-related structures (diapirs) near these hot spots could play this role.

Lakes and reservoirs are a significant source of atmospheric methane (CH4), with emissions comparable to the largest global CH4 emitters. Understanding the processes leading to such significant emissions from aquatic systems is therefore of primary importance for producing more accurate projections of emissions in a changing climate. In this work, we present the first deployment of a novel membrane inlet laser spectrometer (MILS) for fast simultaneous detection of dissolved CH4, C2H6 and d13CH4. During a 1-day field campaign, we performed 2D mapping of surface water of Lake Aiguebelette (France). In the littoral (pelagic) area, average dissolved CH4 concentrations and d13CH4 were 391.9 ± 156.3 (169.8 ± 26.6) nmol L-1 and -67.3 ± 3.4 (-61.5 ± 3.6) ‰, respectively. The dissolved CH4 concentration in the pelagic zone was fifty times larger than the concentration expected at equilibrium with the atmosphere, confirming an oversaturation of dissolved CH4 in surface waters over shallow and deep areas. The results suggest the presence of CH4 sources less enriched in 13C in the littoral zone (presumably the littoral sediments). The CH4 pool became more enriched in 13C with distance from shore, suggesting that oxidation prevailed over epilimnetic CH4 production, that was further confirmed by an isotopic mass balance technique with the high-resolution transect data. This new in situ fast response sensor allows to obtain unique high-resolution and high-spatial coverage datasets within a limited amount of survey time. This tool will be useful in the future for studying processes governing CH4 dynamics in aquatic systems.

Great Salt Lake (UT) is a hypersaline terminal lake in the US Great Basin, and the remnant of the late glacial Lake Bonneville. Holocene hydroclimate variations cannot be interpreted from the shoreline record, but instead can be investigated by proxies archived in the sediments. GLAD1-GSL00-1B was cored in 2000 and recently dated by radiocarbon for the Holocene section with the top 11 m representing ~7 ka to present. Sediment samples every 30 cm (~220 years) were studied for the full suite of microbial membrane lipids, including those responsive to temperature and salinity. The ACE index detects the increase in lipids of halophilic archaea, relative to generalists, as salinity increases. We find Holocene ACE values ranged from 81-98, which suggests persistent hypersalinity with <50 g/L variability across 7.2 kyr. The temperature proxy, MBTʹ5Me,­ yields values similar to modern mean annual air temperature for months above freezing (MAF = 15.7°C) over the last 5.5 kyr. Several GDGT metrics show a step shift at 5.5 ka before which temperature estimates are unreliable due to the shift in lake ecology and likely shallow depth. The step change in lake conditions at 5.5 ka and additional variations within the late Holocene are compared to regional climate records. We find evidence for a dry mid-Holocene in GSL, corroborating other records.

Completely carbonated peridotites represent a window to study reactions of carbon-rich fluids with mantle rocks. Here we present details on the carbonation history of listvenites close to the basal thrust in the Samail ophiolite. We use samples from Oman Drilling Project Hole BT1B, which provides a continuous record of lithologic transitions, as well as outcrop samples from listvenites, metasediments and metamafics below the basal thrust of the ophiolite. 87Sr/86Sr of listvenites and serpentinites, ranging from 0.7090 to 0.7145, are significantly more radiogenic than mantle values, Cretaceous seawater, and other peridotite hosted carbonates in Oman. δ13C in the listvenites and serpentinites range from -10.6‰ to 1.92‰, including a small organic carbon component with δ13C as low as -27‰ that reaffirms the presence of carbonaceous material in Hole BT1B. The source of the radiogenic Sr was probably similar to Hawasina metasediments that underlie the ophiolite, with values up to 0.7241 in clastic lithologies. These results indicate that decarbonation reactions in such clastic sediments, during subduction at temperatures above 500°C, form carbon rich fluids that could have migrated updip, supplying radiogenic 87Sr/86Sr and fractionated δ13C to BT1B serpentinites and listvenites.

Explosive, ash-producing volcanic eruptions are a significant natural hazard with the potential for loss of life, economy, and infrastructure. Turrialba is an active stratovolcano located in the Central Cordillera of Costa Rica. The edifice is located only 35 km east-northeast of Costa Rica's capital city and poses a threat to its central valley, the social and economic hub where more than half of the population resides. The most recent eruption took place in 2016-2017, consisting of four eruption phases. Preliminary observations using SEM show significant morphological differences between the various eruption phases, including the amount of dust and crystals that are present. The morphology of volcanic ash is fundamental to our understanding of magma fragmentation, and in transport modeling of volcanic plumes and clouds. The chemistry of the ash particles produced by fragmenting magmatic foams may affect their evolving morphology throughout the various stages of eruption. In addition, eruption energetics may play a role in ash morphology. Separating the roles of chemical heterogeneity and evolving energetics requires careful examination of ash morphology and its relation to composition. In this way, we take some initial steps in closing the knowledge gap between eruption mechanisms and how and why these mechanisms are exhibited in the morphology of ash during explosive eruptions.

Deep carbon is terrestrial carbon that is not in the atmosphere or oceans or on the surface. We have a great deal of knowledge about the properties of near surface carbon, but relatively little is known about the deep carbon cycle. The Deep Carbon Observatory, was founded in 2009, to address major questions about deep carbon. Where are the reservoirs of carbon? Is there significant carbon flux between the deep interior and the surface? What is deep microbial life? Did deep organic chemistry have a role in the origin of life? This project is directed toward documenting and describing of the history of deep carbon science. The narrative begins in 1601, when William Gilbert suggested that Earth's interior behaves like a giant bar magnet. We trace across three centuries the slow evolution of thought that led to the establishment of the interdisciplinary field of Earth System Science. The concept and then development of the deep carbon cycle of burial and exhumation dates back at least two hundred years. We identify and document the key discoveries of deep carbon science, and assess the impact of this new knowledge on geochemistry, geodynamics, and geobiology. A History of Deep Carbon Science is in preparation for publication by Cambridge University Press in 2019. Its illuminating narrative highlights the engaging human stories of many remarkable researchers who have discovered the complexity and dynamics of Earth's interior.