Fault-zones significantly influence the migration of fluids in the subsurface and can be important controls on the local as well as regional hydrogeology. Hence, understanding the evolution of fault porosity-permeability is critical for many engineering applications (like geologic carbon sequestration, enhanced geothermal systems, groundwater remediation, etc.) as well as geological studies (like sediment diagenesis, seismic activities, hydrothermal ore deposition, etc.). The highly heterogeneous pore structure of fault-zones along with the wide range of hydrogeochemical heterogeneity that a fault-zone can cut through make conduit fault-zones a dynamic reactive transport environment that can be highly complex to accurately model. In this paper, we present a critical review of the possible ways of modeling reactive fluid flow through fault-zones, particularly from the perspective of chemically driven “self-sealing” or “self-enhancing” of fault-zones. Along with an in-depth review of the literature, we consider key issues related to different conceptual models (e.g. fault-zone as a network of fractures or as a combination of damaged zone and fault core), modeling approaches (e.g. multiple continua, discrete fracture networks, pore-scale models) and kinetics of water-rock interactions. Inherent modeling aspects related to dimensionality (e.g. 1D vs 2D) and the dimensionless Damköhler number are explored. Moreover, we use a case-study of the Little Grand Wash Fault-zone from central Utah as an example in the review. Finally, critical aspects of reactive transport modeling 2 like multiscale approaches and chemo-mechanical coupling are also addressed in the context of fault-zones.

The combination of strontium (87Sr/86Sr) and uranium (234U/238U) isotopes is an especially useful tool to track and quantify mixtures of water sources in arid wetlands, where chemistry and lighter isotopic tracers are strongly influenced by evaporation and transpiration. Those isotopes were used to understand modern water supply to the Pahranagat National Wildlife Refuge (PNWR) in southern Nevada (Paces & Wurster, 2014, J. Hydrol. 517). We investigate the possibility that this isotopic combination might also track paleohydrological changes in such settings. Here, we present Sr and U isotope data for authigenic carbonates in a sediment core spanning 5800 14C cal years from Lower Pahranagat Lake (LPAH), a shallow, alkaline lake within the PNWR. Modern surface waters in the PNWR are comprised of mixtures of discharge from two high volume springs from the regional carbonate aquifer in the northern valley, and smaller amounts of local discharge from the shallow volcanic aquifer in the southern valley. Modern surface water from LPAH has U isotopic values similar to the most recently formed LPAH carbonates; however, Sr isotopic values in LPAH surface water are somewhat lower than values in those same carbonates. Combined Sr and U isotope values in Holocene LPAH carbonates fall within the range defined by the three primary spring sources and reflect varying mixtures of those sources supplying LPAH from mid-Holocene to modern time. Values in the oldest samples (~5800 14C cal yr BP) have distinct 87Sr/86Sr and 234U/238U values that nearly match the local spring end member, suggesting that LPAH water at that time was dominated by proximal volcanic aquifer sources. By ~5300–5200 14C cal yr BP, LPAH water was comprised of a nearly equal mixture of the three spring sources, marking a dramatic shift in hydrologic conditions that allowed contributions of surface flow from distal carbonate springs to the north. Values in samples from ~1,000–3,000 14C cal yr BP indicate decreased contributions from distal carbonate springs during two drought intervals; however, by 730 14C cal yr BP, surface flow from carbonate springs had resumed. Our results indicate that combined Sr and U isotopes preserve evidence of past changes in water sources in arid wetlands useful for interpreting evolving hydrologic conditions.

Northern high latitudes are projected to get warmer and wetter in the future which will affect rates of permafrost thaw and the mechanisms by which thaw occurs. To better understand these changing thaw dynamics, we instrumented an isolated permafrost plateau in south-central Alaska with climate conditions that currently mirror those expected in more northern permafrost regions in the future. Using preliminary 2019 measurements of temperature from the soil surface into permafrost, depth to frost table, water level, groundwater temperature, and meteorological variables, we tracked soil and permafrost warming throughout the season, and identified how environmental factors, such as water table elevation, microtopography, and warm rain events, affected rates of warming and thaw. Additionally, we present the extent of permafrost degradation since the last observations at this site in 2015. Permafrost thaw and resultant landscape change has a net warming effect on the climate. Understanding of the environmental factors that lead to thaw and rates at which permafrost will thaw under future climate conditions will allow for better preparation, modeling, and policy making for the future.

Tectonic models as a universal outcome generate predictions regarding the travel time paths of rocks as they are displaced due to the application of particular input parameters and boundary conditions. A need for most of these models, either as a constraint for realistic input conditions or to gauge their relevance to a particular natural system, is pressure‐temperature‐time (P‐T‐t) paths from individual rock samples that track the conditions they experienced during displacement. Although arguments can be made that P‐T paths and absolute peak P‐T conditions may not necessarily be diagnostic of processes involved, this type of information is clearly a valuable addition to other types of data, such as timing and microstructural information regarding strain recorded during rock deformation. Low‐resolution P‐T paths can be limited in their ability to test ideas regarding lithospheric response to perturbations, including motion within fault zones. Here we apply advances in thermodynamic modeling to acquire high‐resolution P‐T paths that show the conditions responsible for garnet growth within one of the Himalayas’ major fault systems. The approach we outline can be applied to any garnet‐bearing assemblage using bulk rock and mineral compositions and have the potential to significantly increase the understanding of the dynamics of field areas that contain garnet, from the mineral’s crystallization to erosion‐driven or tectonically-driven exhumation. Overall, high-resolution garnet-based P-T paths were generated for two transects across the Himalayan Main Central Thrust (MCT) spaced ~850 km apart (along the Bhagirathi and Marsyangdi drainages) and monazite grains were dated in situ to help constrain crystallization time. Rocks collected at equivalent structural positions to the MCT along both transects show similar paths and a shear zone imbrication model suggest the MCT zone has very high exhumation rates, up to 12 mm/yr since the Pliocene.

Iron isotope compositions (δ56Fe) of ferromanganese (Fe-Mn) crusts and nodules are reliable proxies for understanding the biogeochemical cycling of Fe in the ocean. Fe-Mn nodules/crusts are characterized by low δ56Fe values (–0.8 to –0.05 ‰ IRMM 014), while the dissolved Fe in the deep ocean is 56Fe enriched (d56Fe range from +0.2 to +0.8 ‰). Here, we report Fe isotope compositions of top scrapings of sixteen Mn nodules and three Fe-Mn crusts and their geochemical compositions from the Central Indian Basin (CIB) to understand Fe isotope compositions. Based on their morphology and elemental compositions, the CIB nodules are divided into three groups: ‘hyrogenetic,’ ‘diagenetic,’ and ‘mixed’ types. The range of δ56Fe values (-0.63 to -0.06 ‰) for CIB nodules and crusts is similar to those from different parts of the world ocean. The δ56Fe values of the hydrogenetic group of CIB nodules are consistent with a fractionation model involving selective adsorption 56Fe onto organic ligands (siderophore complexes). Using a fractionation factor of -0.77 ‰ between seawater and nodules, we estimate that δ56Fe of the CIB deep seawater dissolved Fe range between +0.28 and +0.63 ‰ similar to the Atlantic deep seawater. The δ56Fe values of mixed nodules correlate positively with Mn/Fe and concentrations of Mn, Cu, Zn, Mo, Cd, Sb, and Tl, and negatively with Fe, Be, Sc, Co, Zr, Nb, and rare earth elements (REE). These mixing lines attest to variable proportions of metals from diagenetic and hydrogenetic sources.

Although iron and light are understood to regulate the Southern Ocean biological carbon pump, observations have also indicated a possible role for manganese. Low concentrations in Southern Ocean surface waters suggest manganese limitation is possible, but its spatial extent remains poorly constrained and direct manganese limitation of the marine carbon cycle has been neglected by ocean models. Here, using available observations, we develop a new global biogeochemical model and find that phytoplankton in over half of the Southern Ocean cannot attain maximal growth rates because of manganese deficiency. Manganese limitation is most extensive in austral spring and depends on phytoplankton traits related to the size of photosynthetic antennae and the inhibition of manganese uptake by high zinc in Antarctic waters. Importantly, manganese limitation expands under the increased iron supply of past glacial periods, reducing the response of the biological carbon pump. Overall, these model experiments describe a mosaic of controls on Southern Ocean productivity that emerge from the interplay of light, iron, manganese and zinc, shaping the evolution of Antarctic phytoplankton since the opening of the Drake Passage.

Coal fly ash has long been considered a potential resource for recovery of valuable elements, such as rare earth elements (REE), which are retained and concentrated upon combustion of coal feedstocks. Understanding REE occurrence within fly ash is a key to developing possible recovery methods. Recent results using modern analytical approaches shed light on the distribution REE in fly ash and the approaches required for their recovery. Some of the highest REE contents occur in fly ash derived from U.S. Appalachian Basin coals, and among these, coals influenced by input volcanic ash (Fire Clay coal, Kentucky) are especially enriched. Leaching studies of bulk fly ash show that, as a proportion of the total REE present, samples from eastern U.S. coals are generally less readily extractible than fly ash derived from western U.S. coals having lower REE contents. Direct determinations by ion microprobe show that REE in a range of fly ash samples are partitioned into aluminosilicate glasses formed during melting at boiler temperatures. These glasses comprise the largest mass fraction of coal fly ash. REE-enriched domains are present locally in fly ash at the nanometer scale (as shown by TEM), and these REE coexist with the glass phase. To enable systematic study of these REE, Ce has been proposed as a proxy for the trivalent lanthanides, as supported by speciation determinations demonstrating that Ce occurs in the trivalent form in fly ash. Despite a decreasing proportion of coal use for electric power generation in the U.S. and elsewhere, annual fly ash production, combined with coal ash already in storage, make up a large resource for potential recovery of rare earths and associated critical elements. Further developments in extraction technologies are needed to overcome difficulties in REE concentration and purification to produce REE materials of saleable purity derived from coal ash.

Magnetic particles including ferrimagnetic (FM) and antiferromagnetic (AFM) particles are ubiquitous in the surface of Earth and Mars. The FM particles dominating soil magnetism usually coexist or compete with AFM hematite due to their comparable thermodynamic stability. The uncertain correlation can be modulated by phosphorous (P) absorption during aging of precursor amorphous iron (Fe) oxides. We investigated two Ferralsol sequences around a P mining field with comparable content of hematite but contrasting P/Fe ratio. The FM particles accompanying the formation of hematite are enriched stably at accelerating rates under high P/Fe but at unstably even rates under low P/Fe. The FM particles became less abundant and coarser while the iron oxide crystallinity increased monotonically as P/Fe decreased. We attribute it to more rapid grain growth of FM particles and transformation into hematite without P retarding the crystallization of iron oxides.

Although ~10% of Earth’s water resides within continents, HO distribution throughout the continental lithosphere and partitioning of HO in nominally anhydrous minerals (NAMs) remain poorly constrained. Models of continent formation and destruction depend on HO content. We report HO contents in NAMs measured on petrographic thin sections by secondary ion mass spectrometry (SIMS) of Proterozoic deep crustal xenoliths from Colorado, USA. Clinopyroxene, orthopyroxene, and garnet contain average HO contents of 560, 347, and 85 ppm, respectively; reconstructed bulk rock HO ranges from ~75 to ~600 ppm. Inter-mineral HO ratios overlap experimental mineral/melt D values, and are used to calculate HO of melts last in equilibrium with the xenoliths. We propose that these xenoliths represent cumulates fractionated from a primitive, hydrous (≥1 wt.% HO) melt at high (~1 GPa) pressures, similar to conditions in modern subduction zones, and potentially associated with widespread arc accretion that formed the core of North America in the Precambrian.

Radiocarbon (14C) is commonly used as a tracer of the carbon cycle to determine how fast carbon moves between different reservoirs such as plants, soils, rivers or oceans. However such studies mostly emphasize the mean value (as Δ14C) of an unknown probability distribution. We introduce a novel algorithm to compute Δ14C distributions from knowledge of the age distribution of carbon in compartmental systems at equilibrium. Our results demonstrate that the shape of the distributions might differ according to the speed of cycling of ecosystem compartments and their connectivity within the system, and are mostly non-normal. The distributions are also sensitive to the variations of Δ14C in the atmosphere over time, as influenced by the counteracting anthropogenic effects of fossil-fuel emissions (14C-free) and nuclear weapons testing (bomb 14C). Lastly, we discuss insights that such distributions can offer for sampling and design of experiments aiming to capture the precise variability of Δ14C values in ecosystems.

The Noerdlinger Ries is regarded as one of the best studied terrestrial impact craters. Because of its accessibility and its excellent preservation this area continues to be a research target for numerous international students, geoscientists and impact researchers. Here astronauts from the Apollo 14 and 17 missions studied the identification and sampling of impact rocks to prepare for their trip to the Moon. Today it is a regular training area for ESA astronauts and project planners. As an ‘In-crater museum’, the Ries Crater Museum offers insights into the spectacular event 15 million years ago. It illuminates the significance and the larger context of the Ries event to a wider audience: our Solar System, comets, asteroids, meteorites, and the special role of impacts in the evolution of our Solar System and Earth. Permanent didactic challenges in this context are: Most of the relevant processes cannot be observed directly. The time scale considered is very large and very different from that of a human being. Large impact-events took place long ago (Millions and billions of years ago) and were/are very rare events by human standards. Also, only remains of large and relatively new impacts are preserved and visible to some extent. All this often leads to the conclusion that impact processes are part of the past without actual relevance except at the cinema. In reality objects from space hit Earth every day, every hour, every minute, every second. But since they are usually very small, their fall is rarely spectacular and usually not noticed. We are currently working on the renewal of the meteorite area in our museum. In this context we plan to draw visitors’ attention to recent fall events and to show their special importance for science and society. To demonstrate the ongoing bombardment of the earth we present online or ‘near online’ observations to make visible the usually invisible to the ‘normal’ eye. We try to overcome the restrictions of timescale and take a sharp look into the present by reducing time slots and using a ‘magnifying glass’. We present concepts and approaches. Suggestions and comments are welcome!

We have used Mars Exploration Rover Opportunity data to investigate the origin and alteration of lithic types along the western rim of Noachian-aged Endeavour crater on Meridiani Planum. Two geologic units are identified along the rim. The Shoemaker formation consists of two types of polymict impact breccia: clast-rich with coarser clasts in upper units; clast-poor with smaller clasts in lower units. Comparison with observations at terrestrial craters show that the lower units represent more distal ejecta from one or more earlier impacts, and the upper units are ejecta from Endeavour crater. Both are mixtures of target rocks of basaltic composition. Subtle compositional differences are caused by differences in post-impact alteration along the crater rim. The lower Shoemaker units and the Matijevic formation represent pre-Endeavour geology, which we equate with the regionally mapped Noachian subdued cratered unit. An alteration style unique to these rocks is formation of Si- and Al-rich vein-like structures crosscutting outcrops, and formation of smectite. Post-Endeavour alteration is dominated by sulfate formation. Rim-crossing fracture zones include regions of alteration that produced Mg-sulfates as a dominant phase, plausibly closely associated in time with the Endeavour impact. Calcium-sulfate vein formation occurred over an extended time period, including pre-Endeavour impact and after the Endeavour rim had been substantially degraded, likely after deposition of the Burns formation that surrounds and embays the rim. Differences in Mg, Ca and Cl concentrations on rock surfaces and interiors indicate mobilization of salts by transient water that has occurred recently and may be ongoing.

Large wildfires generate smoke that greatly compromises air quality over a wide area. Limited studies have suggested that smoke constituents may enter natural water bodies. In an 18-year water monitoring study, we examined whether smoke from distant wildfires had a detectable effect on ion content in a mountain river in an unburned watershed. Significant local wildfire smoke occurred in six years as traced by MODIS satellite data of fires, regional and local atmospheric fine particulate matter (PM2.5), and the amount of potassium (K+) in PM2.5 as a marker of vegetation combustion. Rainwater had elevated K+ and calcium (Ca2+, also associated with wildfire smoke) in smoke years compared to no-smoke years, and was the primary route of atmospheric deposition. Similarly, river water in smoke years had elevated concentrations of K+ and Ca2+, with a higher ratio of K+ to Ca2+ compared to no-smoke years. River concentrations were generally unrelated to river discharge and observed K+ concentrations in smoke and no-smoke years could be accounted for atmospheric deposition. Our study provides early evidence that wildfires affect water quality far beyond the watersheds where they occur. Wildfires are increasing in frequency and extent worldwide, widely distributing vast quantities of smoke containing nutrients, toxins and microbes. Potassium is a routinely-measured water quality parameter that can act as a sentinel of smoke inputs. Further work is needed on the patterns and processes by which wildfire smoke enters water as well as on the consequences for ecosystems and human health.

Expedition NBP1808 on the R/V Nathan B. Palmer completed 32 dredges between October and December, 2018 from locations across the Rio Grande Rise (RGR)—a largely unstudied oceanic plateau on the South American plate—and several seamounts located between RGR and the Mid-Atlantic Ridge (MAR). Eighteen samples from 10 dredge locations on RGR were dated to better understand the geochronological history of this large igneous province and to provide clues to its relationship with the Walvis Ridge and Tristan-Gough hotspot(s) on the conjugate African plate. 40Ar/39Ar results from plagioclase separates (and one biotite) show a prolonged emplacement history throughout RGR ranging from ~84 to 48 Ma. Ages in general decrease towards the MAR in accord with plate motions showing that RGR as a whole was emplaced over at least several Ma and not as a single pulse like some other oceanic plateaus. Using the recently published tectonic reconstruction of Sager et al., most volcanism in the NW and NE sectors on RGR was emplaced off-axis while that in the SE sector was erupted on-axis. This suggests that the plume source for RGR changed from more intraplate to more ridge-centered as the system evolved through time. There is evidence of a possible reversed age progression in the NE RGR which could provide evidence for micro-plate activity that has been suggested in this region, though more ages are needed to confirm this trend. Geochemistry studies are ongoing and will be used in the future to better understand the eruptive processes. Additional age analyses are also ongoing and will focus on the other dredge locations throughout RGR as well as the seamounts to complete the geochronological picture of the emplacement of RGR.

A key question pertaining to Europa’s habitability is whether hydrothermal activity could be sustained for long periods of time, enabling redox and nutrient exchange between the ocean and rocky interior [e.g. 1, 2]. Europa’s early ocean, if formed during differentiation, could have been infused with gases [3]. A consequence of this initial infusion is that clathrate hydrates may have been stable within the ocean. These clathrates could then rise to the bottom of the ice shell, or blanket the seafloor, depending on their density relative to the ocean. Accumulations of floating and sinking clathrates would affect the geological and thermal evolution of Europa because of their high heat capacity and low thermal conductivity compared to ice Ih, but sinking clathrates could also inhibit chemical exchange between the ocean and the rocky interior. We calculate the stability and density of CH4 and CO2 clathrates, and predict the volumes precipitated at the seafloor or accumulated at the base of the ice shell, for ocean compositions evolved from the interior of Europa during metamorphism on the path towards formation of a metallic core [3]. For a chemically reduced ocean derived from heating a mix of chondritic material near Jupiter [4], plus cometary volatiles, ~2 x 10^7 km^3 of methane clathrates form. These are less dense than the ocean (Fig. 1), and float to the base of the ice shell. However, for a CO2-rich ocean derived from CI or CM chondrites, ~3 x 10^8 – 2 x 10^9 km^3 of CO2 clathrates could form, i.e., sufficient feedstock to form a 13–77 km global layer on the seafloor. A salty ocean (e.g. 10 % MgSO4) or a warm seafloor (316 K) may be needed to prevent the accumulation of a CO2 clathrate blanket (Fig. 1), although the blanketing effect would thin the equilibrium thickness of the clathrate layer to ~500 m for allowable heat fluxes (~50 mW/m^2). [1] Vance, S. et al. (2007). Astrobiology, 7(6), 987–1005. https://doi.org/10.1089/ast.2007.0075 [2] Klimczak, C. et al. (2019). 50th Lunar. Planet Sci. Conf., Abstract #2132, p. 2912. https://ui.adsabs.harvard.edu/abs/2019LPI….50.2912K [3] Melwani Daswani, M. et al. (2021). A metamorphic origin for Europa’s ocean (preprint). https://doi.org/10.1002/essoar.10507048.1 [4] Desch, S. J. et al. (2018). Astrophys. J., Suppl. Ser., 238(1), 11. http://dx.doi.org/10.3847/1538-4365/aad95f

This paper discusses the mathematical aspects of band fitting and introduces the mathematics of the Asymmetric Gaussian shape and its tangent space for the first time. First, we derive an equation for an Asymmetric Gaussian shape. We then use this equation to derive a rule for the resolution of two Gaussian shaped bands. We then use the Asymmetrical Gaussian equation to derive a Master Equation to fit two overlapping bands. We identify regions of the fitting space where the Asymmetric Gaussian fit is optimal, sub optimal and not optimal. We then demonstrate the use of the Asymmetric Gaussian to fit four overlapping Gaussian bands, and show how this is relevant to the olivine spectral complex at 1 ?m. We develop a new model of the olivine family spectrum based on previous work by Runciman and Burns. The limitations of the asymmetric band fitting method and a critical assessment of three commonly used numerical minimization methods are also provided.

Being a complex environment subject to coastal and marine processes, little is understood concerning the evolution of northern Beibu Gulf and the human impacts on its ecosystem. Since various environmental information can be stored in the deposited sediments, it is considered to be useful tracers for natural and anthropogenic processes. The aim of this study is to determine a detailed reconstruction of the sedimentation rates in the past decades by applying the 210Pb dating method. To achieve this, 3 sediment cores located in different regions along the coast of northern Beibu Gulf were collected. 226Ra and 210Pb were measured using gamma spectrometry and age determination was analyzed by the CRS model. Physical parameters (water content, grain size and bulk density) and TOC were determined for each core. The results showed that the average sediment mass accumulation rates (dry mass) calculated from 210Pb profiles was 0.043-0.008 g cm-2 yr-1in core of Sanniang Bay and 0.028?0.003 g cm-2 yr-1 in core of Lianzhou Bay. Sediment mass accumulation rates decreased with increasing water depth. The sedimentation rate was 0.54 cm/y in Sanniang Bay and 0.38 cm/y in Lianzhou Bay. Water content and grain size did not change much with age variation, while TOC showed a general decline during past decades, probably due to the terrigenous input. This study provides a chronological framework for comparing the depositional histories and inventories of various pollutants that have been measured in the same sediment cores. This information will be useful for resolving scientific environmental quality and coastal management in northern Beibu Gulf.

We have to face an important and urgent problem: even though according to spectral detection, we cannot conclude that there is much water ice on the Moon as the prevailing theory claims. We might have overlooked the widespread presence of methanol on the Moon. After the interstellar methanol ice fell onto the Moon, the methanol in it was retained due to the strong adsorption of methanol in the carbon-rich lunar regolith and the water in it could be divided into two situations: one involved in catalytic reactions with methanol on lunar surface and another one escaped to the deep space because of harsh environment. The rest of methanol might still be widespread on lunar surface. M3 is unable to distinguish between hydroxyl radicals from water ice and hydroxyl groups from methanol because the absorption strengths of the two are all 2.9 μm, and there are no established methods to distinguish them using the 2.9μm band. Thus, most of the lunar water detected by M3 might be lunar methanol. Attention should be paid to previous misreading of the spectrum. The so-called surficial water illogically appeared at lunar equator, seriously shaking the credibility of M3 spectra data analysis. The vast quantities of hydrogen found in lunar polar craters should be hydrogen ice, which easy to confuse with water ice. The author has also made a preliminary study of the physical / chemical process chains on lunar surface. It is necessary to conduct in-depth research in this field in the future.

Soil organic matter (SOM), the accumulated, decaying debris of biota living on or in the soil, represents the largest of the active terrestrial C pools, holding about 1500 Pg C to a depth of 1 m. In aquatic ecosystems, SOM is a storehouse of inorganic nutrients which, after mineralization, are released to the stream and used by planktonic and benthic microorganisms. Here we present the results of a study designed to elucidate the controls on the spatial and temporal variations of the SOM distribution along the Clear Fork River, which drains a mixed urban-agricultural landscape in north-central Ohio. Fluvial bed sediments were sampled monthly (March to October) in eight stations along the river. Organic matter (OM) and carbonate content were determined by loss-on-ignition (LOI). Sediments from all stations were analyzed in triplicate to account for intrasample variation and to provide a measure of precision. Textural analysis was also performed in all samples. Results show OM content varying between 14 and 109 g kg-1, with highest values observed during spring, and lower values during summer. Sediments from stations where the stream flow is high generally presented lower OM concentration. In addition, stations located within urban landscapes presented the highest OM concentrations.

The ocean plays a critical role in reducing human impact on the global climate by absorbing and sequestering CO2 from the atmosphere. To quantify the ocean’s role in the global carbon budget, we need surface ocean pCO2 across space and time, but only sparse observations exist. The typical approach to reconstructing pCO2 is to train a machine learning approach on a subset of the pCO2 data and available physical and biogeochemical observations. Though the variables are all related to the pCO2, these approaches are often perceived as black boxes, as it is unclear how inputs are physically linked to pCO2 outputs. Here, we add physics by incorporating our knowledge of the direct effect of temperature on surface ocean pCO2. We use the machine learning algorithm XGBoost to develop a function between satellite and in-situ observations and the difference between observed pCO2 and the pCO2 that would exist if temperature variations were the only driver of variability. We show the resulting model is physically consistent, and performs at least as well as other data approaches. Uncertainty in the reconstructed pCO2 and its impact on the estimated CO2 fluxes are quantified. Uncertainty in piston velocity drives flux uncertainties. The historical reconstructed CO2 fluxes show larger interannual variability than the smoother neural network approaches, but a lesser trend since 2005. We estimate an air-sea flux of -2.3 +/- 0.5 PgC/yr for 1990-2018, agreeing with other data products and the Global Ocean Carbon Budget models of 2021 estimate of -2.3 +/- 0.4 PgC/yr.

Eastern Africa contains a well-preserved pedogenic carbonate record, useful for contextualizing the paleoenvironment associated with key fossil and archeological evidence. One significant paleoanthropological discovery from the Turkana Basin in Kenya was Nariokotome Boy, one of the most complete examples of Homo erectus discovered to date. This site is directly associated with a paleo-Vertisol and the Natoo tuff, enabling stratigraphic correlation into outcrop records. Leveraging this opportunity, we analyzed stable isotopes of pedogenic carbonates (n=74) to study the paleoenvironmental conditions in the Turkana Basin for three time slices between 1.9 and 1.2 Ma. We interpret that the narrow range of δ18O values implies the presence of one main water source throughout the time interval. Variation in δ13C, with a standard deviation of 1.5‰ and range of 6.9‰, can thus be considered a function of landscape heterogeneity rather than changing water source. Woody cover estimates from the paleosols within this study interval suggest this area was a wooded grassland despite a significant first-order paleoenvironmental change from a marginal lacustrine environment to a fluvially-dominated one. While our record cannot resolve variability on a millennial scale, the lack of significant long term trends in percent woody cover suggest that Nariokotome Boy and other hominin communities inhabited a paleoenvironment which was relatively stable in terms of vegetation composition despite a major lacustrine regression.

Elevated organic matter (OM) concentrations are found in hadal surface sediments relative to the surrounding abyssal seabed. However, the origin of the biological material remains elusive. Here, we report the composition and distribution of cellular membrane intact polar lipids (IPLs) extracted from surface sediments around the deepest points of the Atacama Trench and adjacent bathyal margin to assess and constrain the sources of labile OM in the hadal seabed. Multiscale bootstrap resampling of IPLs’ structural diversity and abundance indicates distinct lipid signatures in the sediments of the Atacama Trench that are more closely related to those found in bathyal sediments than to those previously reported for the upper ocean water column in the region. While the overall number of unique IPL structures in hadal sediments is limited and they contribute a small fraction of the total IPL pool, they include a high contribution of phospholipids with mono- and di-unsaturated fatty acids that are not associated with photoautotrophic sources. The diversity of IPLs in hadal sediments of the Atacama Trench suggests the presence of in situ microbial production and biomass that resembles traits of physiological adaptation to high pressure and low temperature, and/or the transport of labile OM from shallower sediment. We argue that the export of the most labile lipid component of the OM pool from the euphotic zone and the overlying oxygen minimum zone into the hadal sediments is neglectable. Our results contribute to the understanding of the mechanisms that control the delivery of labile OM to this extreme deep-sea ecosystem. Furthermore, they provide insights into some potential physiological adaptation of the in situ microbial community to high pressure and low temperature through lipid remodeling.

Abiotic efflux of CO2 from soil is often attributed to dissolution of carbonates, and therefore not expected to occur in soils with a low pH. However, another abiotic source of CO2, less constrained by pH, may arise from reactions that oxidize natural soil organic matter and reduce metal oxides. Studies of redox reactions between phenolic compounds and Fe and Mn oxides in soil have been focused mainly on the environmental fate of both oxidants and reductants and formation of organic matter. We measured CO2 formed during 3-hour, room temperature (22±2 oC), incubations of samples of archived soils and from an ongoing crop diversity study. Subsamples (8 g. ODE) of each soil, were treated (5 ml) with water, or solutions of glucose (0.029 M), or gallic acid (0.025 M). For each soil, subsamples amended with H2O or with the glucose solution produced little CO2 and were nearly identical to each other, while CO2 quickly formed after treatment with gallic acid regardless of pH. The net increase in CO2 due to gallic acid, observed from the 18 archived soils, ranged from less than 0.5 to more than 80 mg CO2-C kg-1 soil. Significant treatment effects were observed in samples from the crop diversity study with more (Tukey’s P≤0.05) net CO2 from a small grain-fallow treatment compared a 5-year rotation treatment, 19.04 and 15.77 mg CO2-C kg-1 soil, respectively. This study suggests abiotic reactions capable of rapidly producing a burst of CO2 can occur in a wide range of soils following inputs of simple phenolic compounds and be impacted by management regimes. We suggest these are redox reactions in soil linked to Mn or Fe metal oxides and when considered together with fluctuations of carbon inputs to soil and redox cycling, might be a larger contributor to C emissions than previously accounted for.

Serpentinites play a vital role in subduction zone processes: as one of the dominant carriers of water in downgoing plates, they are critical constituents in the global volatile cycle and add complexity to the bulk rheology and density of downgoing and overlying plates, with strong implications for seismicity and mechanical mixing. These rocks can form in a number of tectonic settings where water reacts with peridotite under certain conditions, including at or near mid-ocean ridges and in mantle overlying dehydrating subducted plates. In the HP/LT terrane preserved on the island of New Caledonia, serpentinites outcrop as meter-scale resistant blocks and as highly deformed “matrix” that hosts a range of metasedimentary, metamafic, and meta-ultramafic lenses. The origin of these HP serpentinites has been debated, with competing hypotheses linking protolith to nearby obducted ophiolite or to the subducted oceanic plate. We analyzed 30 serpentinites and associated hybrid rocks from across the HP terrane to discern the tectonic origin of their protoliths and to better understand their reaction history through subduction and exhumation. Whole rock major and trace element and stable isotope geochemistry reveal the existence of at least two distinct types of serpentinites in the HP terrane. Serpentinites in the far NE exhibit elevated HREE’s, δ18O values of 6-10‰, and scatter in major element concentrations. In the SE, a ~1 km2 ultramafic massif contains serpentinites with relatively more depleted REE, δ18O values of 5-7‰, and a more restricted range of major element concentrations, with distinctly higher MgO and lower Al2O3 than samples from the NE. We compare these data to a global geochemical compilation of serpentinites from various tectonic settings. Ongoing Raman spectroscopy work will determine serpentine polymorph(s) and electron probe microanalysis will target isolated relict pyroxene grains and oxide minerals to retrieve additional protolith information. The recognition of multiple types of serpentinites in this HP/LT terrane adds important information to debate about the origin of the ultramafic material, and may speak to complex interactions between the downgoing plate and overlying mantle or to systematic spatial differences in protolith composition or degree of metamorphism or deformation.