Background/Question/Methods This project attempts to quantify the resilience of prairie ecosystems to climate change in the Pacific Northwest (PNW). In this region, prairie ecosystems currently sustain ~1.3 million beef cows and calf production costs are expected to increase to offset drought-induced plant productivity loss. Here, we investigate patterns of asymbiotic nitrogen fixation (ANF) and biogeochemical controls, that also influence plant community composition and prairie productivity, under experimental drought to address a major challenge for sustainable agriculture in the region. We hypothesize that the effect of drought on prairie vegetation cover increases soil asymbiotic N inputs by diminishing the dominance of symbiotic root-fungal networks. To test this hypothesis, we quantified the impacts of decadal drought stress on soil ANF using 15N-labeled dinitrogen (15N2) incubations of soils from high- and low-diversity prairies across a 520-km latitudinal gradient (i.e., southern Oregon-SOR, central Oregon-COR, and central Washington-CWA) representing increasingly severe Mediterranean conditions. We also quantified total soil organic carbon-C, total, and available N, and available phosphorus-P and iron-Fe pools to better understand underlying mechanisms governing drought-induced changes in ANF. At each site, composite soil samples (n = 3) were collected from five co-located high- and low-diversity prairie plots under control (ambient) and drought (-40% precipitation) conditions. Results/Conclusions We found that soil ANF response to drought increased with the PNW Mediterranean drought intensity gradient; while ANF rates increased nearly two-fold in the southernmost site (SOR), a significant decrease in ANF was verified in the northernmost site (CWA). ANF response to drought also varied depending on plant diversity, where low-diversity prairies had a more predictable response to drought than high-diversity prairies. For instance, ANF in SOR high-diversity prairies was suppressed but no change was verified in COR high diversity prairies. Soil C and N contents were generally higher in high-diversity prairies whereas treatment had no significant effect across sites. Soil P availability, also affected by drought, and pH were the most important variables explaining ANF variability across vegetation types and sites. Based on our findings, low-diversity prairies in central WA may be those most severely impacted by increased climate change-induced drought stress. Our study highlights the importance of using soil-plant-atmosphere interactions to assess prairie ecosystem resilience to drought in the PNW.

Klinkenberg-corrected gas permeability (k) estimation in tight-gas sandstones is essential for gas exploration and production in low-permeability porous rocks. Most models for estimating k are a function of porosity (ϕ), tortuosity (τ), pore shape factor (s) and a characteristic length scale (lc). Estimation of the latter, however, has been the subject of debate in the literature. Here we invoke two different upscaling approaches from statistical physics: (1) the EMA and (2) critical path analysis (CPA) to estimate lc from pore throat-size distribution derived from mercury intrusion capillary pressure (MICP) curve. τ is approximated from: (1) concepts of percolation theory and (2) formation resistivity factor measurements (F = τ/ϕ). We then estimate k of eighteen tight-gas sandstones from lc, τ, and ϕ by assuming two different pore shapes: cylindrical and slit-shaped. Comparison with Klinkenberg-corrected k measurements showed that τ was estimated more accurately from F measurements than from percolation theory. Generally speaking, our results implied that the EMA estimated k within a factor of two of the measurements and more precisely than CPA. We further found that the assumption of cylindrical pores yielded more accurate k estimates when τ was estimated from concepts of percolation theory than the assumption of slit-shaped pores. However, the EMA with slit-shaped pores estimated k more precisely than that with cylindrical pores when τ was estimated from F measurements.

Tikhonov’s regularization method is the standard technique applied to obtain models of the subsurface conductivity dis- tribution from electric or electromagnetic measurements by solving UT (m) = ||F(m) - d||^2 + P(m): The second term correspond to the stabilizing functional, with P(m) = ||m||^2 the usual approach, and the regularization parameter. Due to the roughness penalizer inclusion, the model developed by Tikhonov’s algorithm tends to smear discontinuities, a feature that may be undesirable. An important requirement for the regularizer is to allow the recovery of edges, and smooth the homogeneous parts. As is well known, Total Variation (TV) is now the standard approach to meet this requirement. Recently, Wang et.al. proved convergence for alternating direction method of multipliers in nonconvex, nonsmooth optimization. In this work we present a study of several algorithms for model recovering of Geosounding data based on Inmal Convolution, and also on hybrid, TV and second order TV and nonsmooth, nonconvex regularizers, observing their performance on synthetic and real data. The algorithms are based on Bregman iteration and Split Bregman method, and the geosounding method is the low-induction numbers magnetic dipoles. Non-smooth regularizers are considered using the Legendre-Fenchel transform.

The coupled operation of fracture, diffusion, and intracrystalline-plastic micromechanisms during semibrittle deformation of rock is directly relevant to understanding crustal processes such as earthquake rupture at the base of the seismogenic zone and failure of salt caverns for energy storage. Triaxial stress-cycling experiments are used to investigate elastic-plastic and viscoelastic behaviors in two synthetic salt-rocks deformed at room temperature and low confinement. During semibrittle flow at high differential stress, porous, granular, work-hardened samples deform predominantly by grain boundary sliding and opening accompanied by minor intragranular cracking and dislocation glide. In contrast, fully annealed, near-zero porosity samples deform at lower differential stress by dislocation glide, grain-boundary sliding and opening accompanied by minor intragranular cracking. During high-stress cycling and semibrittle flow, grain boundary sliding is predominantly frictional; but, associated dispersal of water previously trapped in fluid inclusions can activate fluid-assisted diffusional sliding along grain boundaries at low strain rates. Young’s modulus and Poisson’s ratio are largely controlled by the behavior of closed grain boundaries. Grain boundary sliding accommodated by fluid-assisted diffusion leads to nearly complete stress relaxation after semibrittle flow, and in subsequent low-stress cycling both viscoelasticity and pronounced hysteresis are observed. However, such time-dependent effects vanish with grain boundary healing over days-long holds at low differential stress. Experimental results suggest that within the semibrittle regime, high-stress events can lead to significant transient reduction in viscosity and related phenomena.

The Early Cretaceous Jehol Biota evolution has remarkable spatiotemporal correlation with the destruction of the North China craton though the coupling mechanism remains enigmatic. The craton destruction was accompanied by intense magmatic activity and the released volatiles and nutrients might have had climatic and environmental impacts on the biotic evolution. In this study, we investigated the mentioned hypothetical causal link by determining concentrations and total emissions of volatile elements (S, F, Cl) and bulk-rock P contents of volcanic rocks that were erupted during the pre-flourishing, flourishing and post-flourishing stages of the Jehol Biota. Our results show that the volcanism near the flourishing stage has lower S (1083-2370 ppm), Cl (1277-5608 ppm) and higher P2O5 contents (0.48-0.84 wt.%) than that in non-flourishing stages with S of 1991-3288 ppm, Cl of 7915-12315 ppm and P2O5 of 0.17-0.23 wt.%. Fluorine contents in the three stages vary from 893 to 3746 ppm. The total volatile emissions are minor in the flourishing stage (3.6-6.6 Gt S, 2.2-4.6 Gt Cl and 2.1-4.0 Gt F) but elevated in the non-flourishing stages (1-690 Gt S, 4-934 Gt Cl and 1-308 Gt F). Our data suggest that regional climatic and environmental impacts of volcanism in the non-flourishing stages probably hindered the species diversification. The high P flux released from lithospheric mantle-derived lavas during the peak time of craton destruction might enhance primary productivity and contribute to the flourishing of the Jehol Biota. Our study provides insights into the relationship between the biosphere and deep geodynamic processes driven by volcanism.

Despite the importance of turbidity currents in environmental and resource geology, their flow conditions and mechanism are not well understood. To resolve this issue, a novel method for the inverse analysis of turbidity current using deep learning neural network (DNN) was proposed. This study aims to verify this method using artificial and flume experiment datasets. Development of inverse model by DNN involves two steps. First, artificial datasets of turbidites are produced using a forward model based on shallow water equation. To develop a inverse model, DNN then explores the functional relationship between initial flow conditions and characteristics of the turbidite deposit through the processing of artificial datasets. The developed inverse model was applied to 200 sets of artificial test data and four sets of experiment data. Results of inverse analysis of artificial test data indicated that the flow conditions can be precisely reconstructed from depositional characteristics of turbidites. For experimental turbidites, spatial distributions of grain size and thickness were accurately reconstructed. With regard to hydraulic conditions, reconstructed values of flow heights, sediment concentrations, and flow durations were close to the measured values. In contrast to the other values, there was a larger discrepancy between the measured and reconstructed values of flow velocity, which may be attributed to inaccuracies in sediment entrainment functions employed in the forward model.

The Braiding Index (BI), defined as the average count of intercepted channels per cross-section, is a widely used metric for characterizing multi-thread river systems. However, it does not account for the diversity of channels (e.g., in terms of discharge) within different cross-sections, omitting important information related to system complexity. Here we present a modification of BI (the Entropic Braiding Index, eBI) which augments the information content in BI by using Shannon Entropy to encode the diversity of channels in each cross section. eBI is interpreted as the number of “effective channels” per cross-section, allowing a direct comparison with the traditional BI. We demonstrate the superior capabilities of eBI via analysis of synthetic, numerical and field examples. In addition, we show that interrogating cross-sections via the ratio BI/eBI has the potential to quantify channel disparity, differentiate types of multi-thread systems, and inform about cross-section stability to forcing variability (e.g., seasonal flooding).

The shallow 1971 Mw 6.6 San Fernando, California earthquake involved a complex rupture process on an immature thrust fault with a non-planar geometry, and is notable for having a higher component of left-lateral surface slip than expected from seismic models. We extract its 3-D coseismic surface displacement field from aerial stereo photographs and document the amount and width of the vertical and strike-parallel components of distributed deformation along strike. The results confirm the significant left-lateral surface offsets, suggesting a slip vector rotation at shallow depths. Comparing our offsets against field measurements of fault slip, we observe that most of the offset was accommodated in the damage zone, with off-fault deformation averaging 68% in both the strike-parallel and vertical components. However, the magnitude and width of off-fault deformation behave differently between the vertical and strike-parallel components, which, along with the rotation in rake near the surface, can be explained by dynamic rupture effects.

Modern Ocean is characterized by the formation of deep-water in the North Atlantic (i.e. NADW). This feature has been attributed to the modern geography, in which the Atlantic Ocean is a large basin extending from northern polar latitudes to the Austral Ocean, the latter enabling the connection of the otherwise isolated Atlantic with the Pacific and Indian Oceans. Sedimentary data date the establishment of the NADW between the beginning of the Eocene (∼49 Ma) and the beginning of the Miocene (∼23 Ma). The objective of this study is to quantify the impact of Miocene geography on NADW through new simulations performed with the earth system model IPSL-CM5A2. We specifically focus on the closure of the eastern Tethys seaway (dated between 22 and 14 Ma), which allowed the connection between the Atlantic and Indian Oceans, and on the Greenland ice sheet, whose earliest onset remains open to discussion but for which evidence suggest a possible existence as early as the Eocene. Our results show that the closure of the eastern Tethys seaway does not appear to impact the establishment of NADW, because waters from the Indian Ocean do not reach the NADW formation zone when the seaway is open. Conversely, the existence of an ice sheet over Greenland strengthens the formation of NADW owing to topography induced changes in wind patterns over the North Atlantic, which in turn, results in a larger exchange of water fluxes between the Arctic and the North Atlantic, and in a re-localization of deep-water formation areas.

Topographic features are commonly interpreted to represent interactions between tectonic and climate-driven processes. However, recent work has highlighted how drainage reorganization from river capture may produce landscapes that resemble those generated by changing tectonic conditions and emphasized the importance of developing tools and metrics to identify the source of landscape transience (Yang et al., 2015; Whipple et al., 2017). While few studies have sought to estimate the rates and magnitudes of increased transient incision resulting from river capture (e.g. Prince et al., 2011, Yanites et al., 2013), the ability to quantify river capture-related incision is vital to improve our characterization of landscape responses to transience. This work tests the hypothesis that the observed incision and distribution of knickpoints in the Sutlej river network of the western Himalaya is the result of an ongoing transient response to a large-scale river capture event that occurred in the late Pleistocene. A combination of topographic analyses using digital elevation models, knickpoint propagation modeling, 1-D numerical incision modeling, and landscape evolution modeling are used in conjunction with new and existing field-derived data (e.g. cosmogenic radionuclide-derived erosion rates and (U-Th)/He and fission track thermochronology) to quantify the magnitude and timing of the transient landscape response. Redistribution of drainage area and the subsequent enhancement of incision along the Sutlej may explain the increased amounts of Himalayan detritus delivered to the Indus fan since 5 Ma (Clift and Blusztajn, 2005). Similar large-scale river capture events proposed throughout the Himalaya (e.g. Garzione et al., 2003; Van Der Beek et al., 2018), suggest that capture events may be a regional phenomenon inherent to the Himalayan orogen and imply that river capture may be an important contributor to the distribution of sediment along collisional margins.

Densely spaced GPR and complex resistivity measurements on a 30,000 square meters site in a region of enigmatic sinkhole occurrences in unconsolidated Quaternary sediments have featured unexpected and highlighting results from both a meteorite impact research and an engineering geology point of view. The GPR measurements and a complex resistivity/IP electrical imaging revealed extended subrosion depressions related with a uniformly but in various degrees of intensity deformed loamy and gravelly ground down to at least 10 m depth. Two principle observations could be made from both the GPR high-resolution measurements and the more integrating resistivity and IP soundings with both petrophysical evidences in good complement. Subrosion can be shown to be the result of prominent sandy-gravelly intrusions and extrusions typical of rock liquefaction processes well known to occur during strong earthquakes. Funnel-shaped structures with diameters up to 25 m near the surface and reaching down to the floating ground water level at 10 m depth were measured. GPR radargrams could trace prominent gravelly-material transport bottom-up within the funnels. Seen in both GPR tomography and resistivity/IP sections more or less the whole investigated area is overprinted by wavy deformations of the unconsolidated sediments with wavelengths of the order of 5 - 10 m and amplitudes up to half a meter, likewise down to 10 m depth. Substantial earthquakes are not known in this region. Hence, the observed heavy underground disorder is considered the result of the prominent earthquake shattering that must have occurred during the Holocene (Bronze Age/Celtic era) Chiemgau meteorite impact event that produced a 60 km x 30 km sized crater strewn field directly hosting the investigated site. Depending on depth and size of floating aquifers local concentrations of rock liquefaction and seismic surface waves (probably LOVE waves) to produce the wavy deformations could develop, when the big disintegrated meteoroid (a loosely bound asteroid or a comet of roughly estimated 1 km size) hit the ground. The observations in the Chiemgau area emphasize that studied paleoliquefaction features and wavy deformations (e.g. seismites) need not necessarily have originated solely from paleoseismicity but can provide a recognizable regional impact signature.

Pore water freshening (i.e., decreases in dissolved Cl) has been documented in marine sediments along most active margins, with the migration of deep fluids or methane hydrate dissociation often invoked as sources of freshening in the sediment column. During D/V JOIDES Resolution Expedition 379T in 2019, two new sites (J1005 and J1006) were cored near ODP Site 1233 (41°S), adjacent to a seafloor mound venting structure. The three sites are less than 10 km apart but show marked differences in pore water chemistry and methane hydrate occurrence. The extent of Cl decrease is a function of distance from the mound, with the strongest freshening occurring at the closest site (J1006), which is the only site where methane hydrate was observed. Methane fluxes follow the same pattern, suggesting a common control. Increasing oxygen and decreasing hydrogen isotopes point to deep mineral bound water as the primary source of freshening near the mound, with fluids originating ~2.5 km below seafloor near the décollement. Secondary influences from methane hydrate dissociation and ash diagenesis also appear to influence regional pore water chemistry. The variability in pore water freshening suggests that fluid migration and eventual expulsion at the venting structure follows narrow pathways, likely along faults within the forearc complex. The migration of deep, gas-charged fluids may also support methane hydrate saturations greater than in situ organic carbon diagenesis would allow, but nonetheless consistent with geophysical estimates. Together, the data highlight an important link between fluid migration and methane hydrate formation on the Chilean Margin.

Lava tubes can offer protection for human crews and their equipment on other solar system bodies, in particular from radiation threats and extreme surface temperatures. Developing strategies to survey regions of other terrestrial bodies (such as the Moon or Mars) for tubes suitable for potential habitation will likely become an important part in planning future space exploration projects. A variety of surface geophysical techniques, such as ground penetrating radar (GPR) have the potential to help recognize and map tubes. GPR shows promise for providing high resolution information on tube geometries. To investigate GPR’s capacity and limitations, we use GPR, as well as comparative methods of seismic and magnetic surveys, in conjunction with LiDAR mapping of tube interiors at the Lava Beds National Monument (LBNM) in California, USA. LBNM offers a wide variety of tube geometries and textures. We have collected 2D GPR profiles and small 3D GPR grids (of parallel 2D lines) with antenna frequencies of 100 and 200 MHz on four lava tubes with different geometries, textures and at different depths. Challenges in recovering tube geometries include wave scattering in fractured rock covering tubes, irregular and “drippy” ceilings and walls, and blocky floors. Our primary results show that the top of the LBNM tubes can generally be resolved in the GPR data, while resolving the bottom is more challenging. The utility of various GPR processing techniques can be directly assessed by comparing resolved GPR images against the LiDAR-measured tube geometries.

If a kick is not detected and circulated properly out of the wellbore with heavier mud weight, it leads to blowouts. In this case, reservoir fluids gush out of the well uncontrollably without restriction leading to loss of control. This may lead to fractures initiating in the post-blowout capping stages, just below the casing shoe, propagating upwards creating a channel through which reservoir fluids can flow to the ocean floor. Being able to model these fracture failures will help understand wellbore integrity problems from loss of control situations and predict the possibility of broaching preventing many ecological disasters like the 1969 Santa Barbara oil spill from Union Oil’s A-21 well. The hypothesis tested is that fracture initiation from a wellbore in a loss of control situation can be predicted through analysis of the near-wellbore stress field, with knowledge of the in-situ stress state and the properties of the formation and the borehole assembly. A 3D numerical model is employed to assess whether a fracture will initiate. This is done by considering the stressfield at the casing shoe; the point most vulnerable to tensile fracture failure downhole. In-situ stress state, wellbore pressure, casing shoe depth and the casing, cement, and formation’s mechanical properties are independent variables that are shown to control fracture initiation; the dependent variable. A reservoir model is used to predict pressure build-up during capping procedures. A case study on Gulf of Mexico is presented with input wellbore pressure data generated using a worst case discharge model. Wellbore pressure drop during uncontrolled discharge from a well can cause casing collapse failures and subsequently pressure build-up in the post-blowout capping stage, may initiate fractures which can lead fluid leakage to the surface either through the cement or the interfaces with the casing and the formation. The region of the in-situ stress states where fracture initiation will occur is shown in dimensionless plots. This is useful for drilling and wellbore integrity teams. When targeting highly-pressured formations as in deepwater, wellbore architecture must be made with considerations of the wellbore pressures generated from loss of control situations like blowouts. Research reported in this publication was supported by an Early-Career Research Fellowship from the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine.

Equatorial Guinea’s Bioko Island is located in the Atlantic Ocean off the west coast of Cameroon. It is a volcanic island and the first off-shore expression of the Cameroon Volcanic Line. It is home to three shield volcanoes: Pico de Basile, Pico Biao, and Gran Caldera de Luba. Eruptive history is only known for Pico de Basile which erupted within the past 100 years, and steam vents were observed as recently as 2012. There is no permanent seismic monitoring; the closest seismic stations are in Cameroon and have not reported data since 2015. In Nov. 2017 Drexel University researchers, supported by the Bioko Biodiversity Protection Program (BBPP) and the Universidad Nacional de Guinea Ecuatorial (UNGE), installed 4 broadband seismometers. Two more stations were installed in March of 2019. Due to the COVID-19 pandemic data from the two most recent stations has yet to be retrieved and analyzed. Local collaborators reported a station was vandalized. It is unknown at this time how much data was recorded by this station. Preliminary earthquake detection and location was completed using an automated STA/LTA algorithm. S wave arrivals were added manually. Initial locations use the global IASP91 model and events were relocated using a local model. Events cluster into two areas: those near Bioko Island and those near Cameroon. Between 12-Dec-2017 and 17-Feb-2018, 77 events were recorded. Local magnitudes range between 0.16 and 2.61. Of these events, 49 are located near Cameroon and 28 are near Bioko. Most of the depths are upper to mid-crust. Analysis of the entire data set yields 458 events with 367 near Bioko Island and 91 near Cameroon. The range in local magnitude is -0.28 – 3.86. Our preliminary results show seismicity associated with Bioko Island as well as Cameroon. Locations match well with events recorded by a regional network in Cameroon. Stations were serviced in Feb. and Nov. 2018 and March 2019. Failures have been due to water infiltration, vandalism, and heavy cloud cover. Enclosures were redesigned after the Feb. 2018 service. All stations were upgraded to the new design in Nov. 2018 and solar panels were upgraded (20 to 35 watt) in March 2019. The next anticipated service was to be completed in March 2020 but was canceled due to the COVID-19 pandemic. The next anticipated service will occur in March 2022 if travel restrictions allow.

The conglomerate is characterized by multiscale grain packing structure and various pore distribution morphology, which is also named as multimodal structure. However, artificial conglomerate applying the experimental investigation differs significantly from natural conglomerates in terms of pore structure, due to centralized pore distribution and lack of nano-scale pores. Hence, we present an experimental method for controlling the pore structure in the artificial conglomerate. First of all, Portland cement was adopted as the main cementing agent, which could generate wider pore distribution and more proportion of nano-scale pores. Next, the grain size distribution design model was applied to realize the various pore structure. Finally, Genetic Programing was adopted to quantify the relationship between grain size distribution and pore structure. The results demonstrated that grain size distribution is composed of coarse grain peak (CGP) and fine grain peak (FGP), various morphology of grain distribution could be realized by adjusting the width and granularity of CGP and FGP. Moreover, lithology is determined by the average value μ1 of CGP, while permeability is determined by the average value μ2 of FGP. As the granularity difference between CGP and FGP performs larger, the morphology of pore distribution transforms from steep peak to hills in the conglomerate, most frequent and average radius of pore decrease, and capillary curve morphology transforms from concave to convex. In comparison with natural cores within alluvial fan of Karamay conglomerate reservoir, pore distribution morphology of artificial conglomerates has high similarity with natural cores.

The 2004-2009 uplift episode is the largest recorded episode of unrest at Yellowstone caldera. We use GPS and InSAR time series spanning 2004-2015, with a focus in the aforementioned event to understand the mechanisms of unrest. InSAR data recorded ~25 and ~20 cm of uplift at the Sour Creek (SCD) and Mallard Lake (MLD) resurgent domes during 2004-2009, and ~8 cm of subsidence at the Norris Geyser Basin (NGB). The SCD/MLD uplift was followed by subsidence across the caldera floor with a maximum at MLD of ~1.5-2.5 cm/yr and no deformation at NGB. The best-fit source models are two horizontal sills at depths of ~8.7 and 10.7 km for the caldera source and NGB respectively, with volume changes of 0.354 and -0.121 km3, and an overpressure of ~0.1 MPa. The InSAR and GPS time series record an exponential increase followed by exponential decrease in the uplift, which is indicative of magma injection into the caldera reservoir, with no need for other mechanisms. However, magma extraction from NGB to the caldera is unable to explain the subsidence coeval with the caldera uplift. The GPS time series of the 2014-2015 episode of caldera uplift can also be explained by a magma injection model. Distributed sill opening models show that magma is stored across the caldera source with no clear boundary between MLD and SCD. Since the magma overpressure is orders below the tensile strength of the encasing rock, historical episodes of unrest like these are very unlikely to trigger an eruption.

Differentiation and contamination of silicic magmas are common phenomena characterizing the granite batholiths and large igneous provinces that build up most of the continental crust. Although they can be identified by means of geochemical relations of igneous rocks exposed in the continents, the mechanisms allowing magmas to undergo the necessary crystal–liquid separation and digestion of country rocks for differentiation and contamination are poorly constrained. In this paper we show two independent approaches that are essential to understand fractionation and contamination of magmas. These are (1) the study and interpretation of field relations in exposed deep sections of batholiths, and (2) the results of laboratory experiments carried out at middle–upper crust pressure. Experiments support that fractionation is intrinsic to crystallization of water-bearing magmas in thermal boundary layers created at the sidewalls of ascent conduits and walls of magma chambers. Gravitational collapse and fluid migration are processes identified in experimental capsules. Similarly, reaction experiments in mixed capsules support reactive bulk assimilation as a plausible mechanism that is compatible with field and petrographic observations in contaminated granitic rocks.

Ceres’ regolith contains water ice that has receded in response to insolation-driven sublimation. Specially targeted, high spatial-resolution measurements of hydrogen by Dawn’s Gamma Ray and Neutron Detector reveal elevated hydrogen concentrations in and around Occator, a young, 90-km diameter, complex crater located at 19.82N where near-surface ice is not expected. The excess hydrogen is explained by impact excavation of water-rich outer crustal materials and their emplacement in the crater floor and ejecta blanket. This is supported by thermophysical models that show water ice could survive at sub-meter depths, given Occator’s relatively young age (~20 Myr). We hypothesize that the regolith can be replenished with ice from large impacts and that this process partially controls the distribution and depth of near surface ice. This is supported by results from Occator and similarities in the global distribution of hydrogen and the pattern of large craters (20-100 km diameter).

Sputnik Planitia on Pluto is a vast plain consisting of a nitrogen ice deposit filling a broad topographic depression, likely an impact basin. The basin displays a broad, raised rim and is surrounded by numerous extensional fracture systems, each with characteristic orientations with respect to the basin center. The nitrogen ice exerts a large mechanical load on the water ice outer shell crust (here also containing the lithosphere). We calculate models of stress and deformation related to this load, varying dimensional, mechanical, and boundary condition properties of the load and Pluto’s lithosphere, in order to constrain the conditions that led to the formation of the observed tectonic and topographic signals. We demonstrate that the tectonic configuration is diagnostic of a particular set of conditions that hold for the Sputnik basin and Pluto, including moderate elastic lithosphere thickness (50 ± 10 km) and a wide load set into a basin that was pan-shaped and shallow (~3 km) at the time of nitrogen deposition initiation. These tectonic systems show the contributions of both flexural (bending) and membrane (stretching) responses of the lithosphere, with the latter dominating in proportion to the importance of spherical geometry effects (i.e., wide loads). Rim topography may also show an influence of primordial annular trans-basin ice shell thickening from the impact process. Analysis of stress-driven cryomagma transport shows that loading stresses can facilitate ascent of cryomagmas in annular zones around the basin, the locations of which overlap the observed distances from Sputnik of several candidate cryovolcanic sites.

A key feature of subduction zone geodynamics and thermal structure is the point at which the slab and mantle mechanically couple. This point defines the depth at which traction between slab and mantle begins to drive mantle wedge circulation and also corresponds with a major increase in temperature along the slab-mantle interface. Here we consider the effects of the backarc thermal structure and slab thermal parameter on coupling depth using two-dimensional thermomechanical models of oceanic-continental convergent margins. Coupling depth is strongly correlated with backarc lithospheric thickness, and weakly correlated with slab thermal parameter. Slab-mantle coupling becomes significant where weak, hydrous antigorite reacts to form strong, anhydrous olivine and pyroxene along the slab-mantle interface. Highly efficient (predominantly advective) heat transfer in the asthenospheric mantle wedge and inefficient (predominantly conductive) heat transfer in the lithospheric mantle wedge results in competing feedbacks that stabilize the antigorite-out reaction at depths determined primarily by the mechanical thickness of the backarc lithosphere. For subduction zone segments where backarc lithospheric thickness can be inverted from surface heat flow, our results provide a regression model that can be applied with slab thermal parameter to predict coupling depth. Consistently high backarc heat flow in circum-Pacific subduction zones suggests uniformly thin overriding plates likely regulated by lithospheric erosion caused by hydration and melting processes under volcanic arcs. This may also explain a common depth of slab-mantle coupling globally.

Low-grade Ni-laterite deposits are well-developed over the mafic/ultramafic protoliths in the northern Oman Mountains. Concentrations, distribution patterns and mobility of platinum-group element (PGE) are investigated in some Ni-laterite profiles of the Oman ophiolite as a possible unconventional PGE resource. The ultramafic protolith displays the lowest PGE content (average total PGE = 35 ppb), which is almost similar to the PGE content in the overlying saprolite zone. The PGE content substantially increased upward in the laterite profile, where the highest total PGE content (up to 253 ppb) is recorded in the oxide and ferricrete/clay-rich zones. The highest PGE content corresponds to Pt > Ru > Pd, while the lowest PGE content is mostly corresponding to Os < Rh < Ir, There is a general positive correlation between PGE contents and both Cr2O3 and Fe2O3 contents in the Ni-laterite profiles. This may reflect the formation of PGE-Fe nanoparticle alloys that are hosted by Fe-rich oxyhydroxides or due to the residual accumulation of chromite in the oxide and ferricrete/clay-rich zones during the lateritization process. The PGE distribution patterns and positive correlation with the ultramafic index of alteration (UMIA) indicate that PGE can be mobilized in different proportions in the surficial environment upon progressive lateritization processes. The high concentration of total PGE in the Oman Ni-laterite is in good agreement with the PGE-rich laterite deposits worldwide, which can be considered as an unconventional PGE resource if adequate extraction and refining processes can be applied for their recovery from the possible upcoming Ni production.

The paper is to detect the leakage inlets, determine the leakage pathways through the dam, and ensure that the amount of the leakage in the upstream and downstream is consistent, and that there is no leakage around the concrete face rockfill dam. The injection of a pseudo-random current in the water between two aluminum sheets A and B generates a current field that can be measured in the water with sensitive current sensors. When the current is channeled along leakage pathways, the flow-field fitting method can be used to detect these inlets of the leakage pathways. We first review the background equations for the seepage field and the current field in the flow-field fitting method, and we also use an approach to calculate the discharge and ensure the consistency of the upstream and downstream leakage based on the Doppler effect in physics. Moreover, to illustrate how the flow-field fitting method works, we use numerical simulation method to verify the feasibility of the flow-field fitting method. Lastly, we proceed with a case study for which the flow-field fitting method and the acoustic Doppler flow velocity measurement are used to identify and map potential leakage pathways bypassing upstream into the flow measurement weir of the downstream. The approaches proposed in this paper successfully detect three leakage areas and obtain the discharge. The results of detected in a case study provide engineering geology information for optimizing the layout of grouting holes.

The current study presents new bed-by-bed brachiopod δ13C and δ18O records from Öland, Sweden, which together with previously published data from the East Baltic region, constitutes a high-resolution paired brachiopod and bulk rock carbon and oxygen isotope archive through the Lower to Upper Ordovician of Baltoscandia. This new dataset refines the temporal control on the global Ordovician δ18O-trend considerably, improving paleoenvironmental reconstructions through the main phase of the Great Ordovician Biodiversification Event (GOBE). The new brachiopod carbon and oxygen isotope records from Öland display strong similarity with the East Baltic records, elucidating the regional consistency as well as global correlation utility of the ensuing composite Baltoscandian Early to Middle Ordovician carbon and oxygen isotope record. The carbon isotope record from Öland indicates that prominent carbon cycle perturbations are recorded in both brachiopods and bulk carbonates, most notably the MDICE (Mid-Darriwilian Carbon Isotope Excursion). The oxygen isotope record reveals a long-term Early to Late Ordovician trend of increasingly heavier brachiopod δ18O values, with a pronounced increase during the Middle Ordovician Darriwilian Age. We interpret this trend as dominantly reflecting a paleotemperature signal indicating progressively cooler Early to Middle Ordovician climate with glacio-eustasy. Our Baltic δ18O values are therefore consistent with postulations that the biotic radiations during the GOBE and climatic cooling during the Darriwilian were strongly linked.