Northward indentation of the Qaidam Basin (QB) and southward underthrusting of North China Craton (NCC) lithospheric mantle beneath the Qilian Shan (QLS) are two frequently-cited geodynamic modes for interpreting the evolution of the northeastern Tibetan Plateau. We here aim at understanding the roles of these two dynamic processes in crustal deformation and how they interact during plateau growth in the NE margin by using sandbox experiments that simulate the convergence of the QB-QLS belt through indentation and underthrusting type of boundary conditions individually, alternately or synchronously. Results illustrate that 1) Underthrusting beneath the QLS favors a gently-tapering, one-sided thrust wedge only above the downgoing slab. 2) Indentation of the QB promotes the occurrence of doubly vergent convergent belts with two oppositely-tapering thrust wedges spreading from the slab boundary. 3) Diverse convergence histories lead to distinct deformation patterns for the modelled convergent belts. However, only when indentation and underthrusting occurred synchronously, the modelled thrust wedge resembles current QB-QLS belt in terms of growth sequence, wedge geometry and deformation localization pattern, indicating that bidirectional compression mode maybe the best approximation for the late Cenozoic northeastern Tibetan Plateau. Our experiments further reveal that shift of boundary conditions like alternation of geodynamic drivers and encountered foreland buttress, would result in limited changes in uplift rate of individual structures. Instead, switch between different structural evolutionary stages causes more pronounced variations and should be noted when interpreting thermochronologic data from the northeastern Tibetan Plateau.

Shafaii Moghadam et al. (2020) contribute important new data on Late Cretaceous-Tertiary subduction- related magmatism in Iran, but their plate convergence model, wherein Neotethyan subduction begins in mid-Cretaceous time (c. 100 Ma), overlooks well established facts relating to the tectonic history of Neotethys, in regard to global plate reconstructions, paleolatitude data, the regional stratigraphy, geochronology and geochemistry, and metamorphic history. Based on their model, Neotethys subduction beneath Eurasia began at ~100 Ma, meaning that the Neotethys was spreading and bounded by opposing passive margins during Jurassic and Early Cretaceous time, for ~100 Ma prior to their proposed onset of Neotethyan convergence. Consequently, their subduction model contradicts (1) the Indian Ocean spreading history derived from magnetic anomalies; (2) continental paleolatitude data from paleomagnetism; (3) sedimentary and igneous evolution of the Mesozoic continental margins in Arabia and southern Asia, (4) the age and geochemistry of Jurassic igneous rocks in southernmost Eurasia; and (5) the preservation of Early to Middle Jurassic eclogite metamorphism and exhumation on the northern side of the Arabia-Eurasia suture. Reconciliation of each of these omissions and contradictions of their model would be welcome, and perhaps an advisory that readers may wish to evaluate their concept of Cretaceous subduction initiation with due circumspection.

The 15-20 km crater diameter range on the Moon spans simple to transitional to complex crater morphologies. Simple craters in this range are only in the highlands. Transitional craters that contain localized slumps are scattered across the lunar surface. Most craters with localized slumps in the highlands superpose pre-impact topography with obvious slope breaks. We interpret this as a condition favorable for post-excavation internal slumping. However, some of these craters formed on terrains with topographic variation similar to the settings of simple craters: flat or gradually sloping surface, or degraded structures of older craters such as rims and terraces. To resolve the conundrum of two morphologies on one terrain type, we performed investigations of the local geology and topography of the inferred pre-impact terrains. We assessed if the localized slumping in the craters happened during or well after crater formation, looked for spatial variations in the strength of the highlands crust, detected topographic breaks (through elevation data) that were unnoticeable in the optical data, and examined rim circularity. Our findings corroborate the influence of pre-existing slopes on mass wasting along crater walls. The majority of the craters with localized slumps have walls superposing topographic breaks that slope towards the crater interior. These walls are located near the uphill sector of the rims which initiated localized slumping. Most simple craters were found to have formed on surfaces with topographic breaks/slopes that face away from the adjoining crater walls, so that any immediate mass wasting would likely be outside the crater cavity.

Wettability is one of the key controlling parameters for multiphase flow in porous media and significant for various geoscience applications such as geological storage of CO2, EOR, and energy storage. In this study, by the means of high-resolution imaging, a series of displacement experiments of brine invasion into oil-saturated microfluidic cells under various wettability conditions were conducted to investigate the wettability effects on displacement stability and fluid distributions. Displacements were studied using two oil fluid systems with M (the ratio of the viscosity of the defending fluid to that of the invading fluid) to be 0.85 and 100 respectively under three different flow rates (capillary number Ca ranging from 9.21 × 10−8 to 9.21 × 10−6). Then quantitative analysis of displacement patterns based on fluid distributions images under different flow conditions are performed. Remaining oil distributions are investigated and correlated with capillary forces and wettability conditions. By symmetrically varying the wettability of the flow cell to three different wettability conditions (water-wet, intermediate-wet and oil-wet), we found that as the viscous ratio (M)=0.85, at low capillary number 9.21 × 10−8 when capillary force is dominated, the displacement becomes more efficient as the flow cell becomes more hydrophobic. At small capillary number, residual oil saturation is decreased from 66.89% for water-wet to 59.22% for intermediate-wet and 50.45% for oil -wet. With the capillary number increased to 9.21 × 10−6 , the displacement pattern becomes more compact with 50.62% residual oil saturation. It is noted that with wettability altered from water-wet to oil-wet under the capillary number of 9.21 × 10−7, crossover occurs from stable flow into capillary-dominated flow displacement, resulting in lower displacement efficiency and lager residual oil saturation (Sor=59.77%). When the viscous ratio was increased from 0.85 to 100, the viscous fingering is found to be more obvious, resulting in lower the displacement efficiency as the viscous force dominates the displacement for all the flow conditions compared with fluid flows under M=0.85. Moreover, when the viscous force is increased by increasing flow rates, wettability effect on displacement efficiency and residual oil saturation is suppressed.

Cryospheric data is increasing in size, demanding highly computational analyses. Open science principles, including collaboration, enable efficient, tested, reproducible, and diverse computational resource development. The ICESat-2 science community continues to coalesce around these ideals through contributions to icepyx, a community and open-source Python library for obtaining and working with large (~500 GB/day) data products from the ICESat-2 satellite/ATLAS laser altimeter. Our presentation will focus on the history, motivation, and process of creating this community, developing shared computational tools, and collating a set of example workflows within Jupyter Notebooks focused on ICESat-2 data. We will present new and in-the-works examples and features of the library, including enhanced pre-data-download visualizations, collaborative developments for multi-mission and -sensor data access, and data read-in/merging functionality. We will also highlight the community building events (including hackweeks) that drive this group and showcase some of the research supported and enabled by this software library.

The SW Portuguese margin has been intensively studied, particularly for rifting, tectonic inversion and tectonic reactivation of the Atlantic passive margin. In this work we bring new data on the continental shelf, usually not acquired by the heavier geophysical methods (e.g. airborne or low resolution deep seismic-magnetic surveys). These new data allow casting a clear light bridging between the geological structures onshore and offshore. The geology of this margin went through the Variscan orogeny of Paleozoic age, the North Atlantic rifting, the Late Cretaceous alkaline magmatism (intrusive and extrusive), the Alpine tectonic inversion and the Quaternary reactivation of the passive margin. We present results from the compilation of a series of marine magnetic surveys conducted along the Portuguese nearshore from 2014 to 2019. Magnetic data were acquired with 1 nautic mile line separation, resulting in near full coverage of the nearshore along a 120 km long margin segment, from Sintra to Odeceixe. For a large part of the surveyed area, ultra-high resolution seismics and multibeam bathymetry were simultaneously acquired. Magnetic data were processed to produce high resolution mapping of magnetic anomalies, and also to enhance both shallow and deep structures, using several derivative and filtering techniques. We combine the interpretation of high-resolution magnetic mapping with the interpretation of ultra-high resolution and vintage deep penetration seismic data to infer the local and regional expression of tectonic structures and magmatic bodies. Our results allow: identifying the offshore extension of important faults, e.g. the Grândola, Pinhal Novo and Messejana faults; resolving previously blurry-imaged magmatic structures, e.g. Sines and Cabo Raso anomalies; identifying faults recycled from the Paleozoic through Present; constraining the relation between magmatic intrusions and faults; and bringing constraints to the discussion of magmatic emplacement.

Volcanic tremors and earthquakes must be monitored to gain insights into volcanic activity. Localization of their sources is often challenging because of the unclear onset of seismic waves, particularly during an increasing volcanic activity. Existing alternative techniques are based on the information on the spatial amplitude distribution or travel time difference of seismic waves. We propose a new location method that combines both information, obtained from the cross-correlation of seismic data. Evaluation using known volcanic earthquakes at Tokachidake volcano, Japan, reveals some improvements in location accuracy as compared with existing methods using individual information. We further analyze an episode of volcanic tremors and earthquakes accompanying a rapid tilt change event on 14 September 2020. Source locations are mostly distributed at <1 km depth, with evidence of source movement towards the 62-2 crater. Our method is useful in detecting seismic source changes that may represent volcanic fluid migration at shallow depths.

In the last few years, ALOS/PALSAR (L-band) (HH, HV, VH and VV) images have been widely used due toits ability to penetrate the surface in certain conditions for example of low moisture or dry friable sandysoil. Images from ALOS-1 sensor have been applied to delineate subsurface structures. Optical imagessuch as Landsat-7 ETM+ data are used to discriminate between scatterings from earth surface andsubsurface materials. Thus, Farafra desert is an optimal environment for L-band microwave penetration.Therefore, this research involves mapping and interpretation of lineaments, surface and subsurfacestructures. The interested four spots at Farafara sand sheets display many structures that not have beentraced in the Egyptian official geological maps. Speckle noise is found in radar images due to many reasons, for example, when an object stronglyreflected between itself and the spacecraft causing noise. Refined LEE Filter (RLF) is applied for specklenoise reduction; speckle noise near strong edges is not strongly filtered, leaving the center of the pixelunfiltered, so, this procedure is an essential step in processing of polarimetric data to improve theaccuracy of the data and enhance resolution. ALOS/PALSAR data are processed into circular polarizationfor providing the best viewing of morphological and subsurface lineaments. The ellipse shape governed bytwo axes; semi-major axis ‘a’ and semi-minor axis ‘b’. Orientation angle(ψ) is measured frompositive horizontal axis X counter clockwise direction, orientation angle range from 0° to 180°. Ellipticity(χ) is a shape parameter defined by the degree of oval shape, defined by χ=arctanb/a and can takevalues between -45° to +45°. As, the circular polarization yielded best outputs of subsurface structure indifferent trends, full polarimetric ALOS/PALSAR images (PLR) are transformed into circular polarization, bychanging both angles into orientation angle ψ=0° and elliptical angle χ=45°. Full polarimetric images arerepresented in Pauli RGB. Landsat-7 ETM+ data are freely uploaded with the same date and location ofALOS/PALSAR images. Bands 1, 2, 3, 4, 5 and 7 are merged together, then bands (R:2, G:4, B:7) arechanged to obtain best spatial resolution. Landsat-7 images have some gap areas, which is essentially befilled with Landsat-7 data acquired at the same time of the year by histogram matching technique to fillthe missed pixels of the interested target scenes according to Landsat 7. The obtained rose diagramshows two trends of dominant and secondary; the most dominant direction is North West (NW 330°),while the secondary trend is North (North 10°). This result is confirmed by the field survey. The dominantdirection of lineaments extracted from ALOS/PALSAR images is well fitted with the secondary direction ofthe geological structure in the study area. This work represents a stage of achievement in detecting buried lineaments covered by sand sheets byusing ALOS/PALSAR and Landsat-7 ETM+. Surface and subsurface

Global seismicity on all three solar system’s bodies with in situ measurements — Earth, Moon, and Mars — is due mainly to Rieger resonance (RR) of the solar wind’s macroscopic flapping, driven by the well-known PRg=~154-days Rieger period and detected commonly in most heliophysical data types and the interplanetary magnetic field (IMF). Thus, spectra of InSight B/C-quality marsquakes rates revealed PRg as the only 99%-significant spectral peak in the 1–6 months (385.8–64.3-nHz) band of highest planetary energies. While a very high (>>12) fidelity Φ=2.8·10^6 characterizes PRg at Mars, modular 1/2PRg and 1/3PRg Rieger-type periodicities are co-driving Martian seismicity, at 89%–67% significance, and Φ>>12. A longer (v.9) release of InSight raw data revealed the entire RR, excluding a tectonically active Mars. Previous marsquakes studies showed a preference for higher frequencies, localization, temporal (dusktime) clustering, and annual variation — features that, taken together, are typical of a forced resonator. For check, I analyze rates of Oct 2015–Feb 2019, Mw5.6+ earthquakes, and all the Apollo moonquakes. To decouple magnetosphere and IMF effects, I analyze Earth and Moon seismicity during traversals of the Earth magnetotail vs. IMF separately. As shown with 99–67% confidence and Φ>>12, an unspecified majority of Mw5.6+ earthquakes and moonquakes also recur at RR periodicities, while about half of the spectral peaks split — but also into clusters that average to RR components, where magnetotail reconnecting clears the signal. The repeating of the Mars result for Earth and Moon means the solar wind co-drives geophysics, selenophysics, and areophysics. Without getting into causal mechanisms in detail, previous claims on solar wind/plasma dynamics being seismogenic are confirmed. This result calls for a reinterpretation of the seismicity phenomenon and reliance on global magnitude scales. Predictability of the solar wind threat is beneficial for physics-based seismic prediction and forecasting, and for the safety of space missions and solar system installations.

Mechanisms that control marsh edge erosion include wind-generated waves, vegetation, mudflats, anthropogenic factors, and geotechnical properties of sediments. However, existing models for predicting marsh edge evolution focus primarily on edge retreat rates as a function of wave energy while accounting for other controlling factors as empirical constants. This simplification rises from a lack of high frequency monitoring of marsh evolutions. In particular, marsh erosion is time-scale dependent and conducting field observations on short time and spatial scales could elucidate the progression of erosion, which may improve marsh erosion predictive models. This study developed and validated a near continuous camera monitoring system to document marsh edge erosion at a high frequency in Terrebonne Bay, Louisiana. Erosion pins were monitored with the cameras and daily erosion rates were estimated. This was supplemented with daily wave power to explore the relationships between daily erosion and wave power. The largest magnitude erosion events are driven by a buildup in wave energy over a seven-day time period coupled with a strong one-day wave event, indicating a gradual reduction in marsh edge resistance with continued wave attack. Long-term erosion monitoring methods, including monthly field visits, smooths over the large magnitude short-term erosion events. For example, satellite and aerial imagery provide a long period of record, but they seem to underestimate the average annual erosion rate in the region, the effect of which may become exasperated over the varying temporal scales considered in the planning efforts of projects meant to protect the Louisiana coastline.

Wildfire indices are used globally to quantify and communicate a wide range of fire characteristics, including fire danger and fire behaviour. Wildfire terminologies, definitions and variables used to compute fire indices vary broadly. This makes it difficult to compare them under a common framework for regional assessment and for future improvements under changing climate and land-use/land-cover conditions. This paper reviews 24 fire indices used worldwide and proposes a simple framework within which they can be classified based on constitutive inputs used for their computation. We differentiate between constitutive inputs that are raw or directly measurable variables such as fuel, weather and topography (referred to as Level 1 inputs) and calculated constitutive inputs such as fuel moisture (as a function of ecology and hydrometeorology); fire behaviour (as a function of spread, energy, and ignition); and dynamic meteorology. These six calculated constitutive inputs are referred to as Level 2 inputs. Based on this classification, our findings indicate that the Burning Index from the United States National Fire Danger Rating System (NFDRS) and the Fire Weather Index from the Canadian Forest Fire Danger Rating System (CFFDRS), used by many countries worldwide, utilize the most comprehensive set of Level 2 inputs. In addition, the Level 2 input that is most frequently used by all fire indices is fuel moisture as a function of hydrometeorology and the least integrated input is that of fire ignition. We further group the fire indices in three types: fire weather, fire behaviour, and fire danger indices, according to the open literature definition of their predictant outputs and examine the specific constitutive inputs used in their computation. Most fire indices are based on Level 2 inputs (which use Level 1 inputs) and are predominantly fire danger and fire behaviour indices. This is followed by fire indices that use a combination of both Level 1 and Level 2 inputs, separately and are mostly fire danger indices. Only a few fire indices are computed solely with raw Level 1 inputs and are mainly fire behaviour indices. Providing a comprehensive view of the existing wildfire indices’ utilization and computational structure is expected to be a helpful resource for wildfire researchers and operational experts worldwide. 2

This work presents an integrated methodology for the assessment of threats on spring quality and quantity in poorly investigated Mediterranean semi-arid karst catchments in Lebanon. Pilot investigations, including 1) high-resolution monitoring of spring water and climate, 2) artificial tracer experiments, and 3) analysis of micropollutants in surface water, groundwater, and wastewater samples were conducted to assess flow and transport in three karst catchments of El Qachqouch, El Assal, and Laban springs. First, the high-resolution in-situ spring data allows the quantification of available water volumes, as well as their seasonal and yearly variability in addition to shortages and floodwaters. Moreover, the statistical analysis of hydrographs and chemographs helps assess the karst typology, spring type and hydrodynamic behavior (storage versus fast flow). Furthermore, a series of artificial tracer experiments provides information about key-transport parameters related to the intrinsic vulnerability of the pilot springs, while the analysis of micropollutants gives insight into the specific types of point source pollution as well as contaminant types and loads. On the one hand, the tracer experiments reveal that any potential contamination occurring in snow-governed areas can be observed at the spring for an extensive time due to its intermittent release by gradual snowmelt, even with enough dilution effect. On the other hand, the assessment of persistent wastewater indicators shows that springs in the lower catchment (including El Qachqouch) are highly vulnerable to a wide range of pollutants from point source (dolines and river) and diffuse percolation. Such contaminants breakthrough is challenging to predict because of the heterogenous duality of infiltration and flow, typical of karst systems. Finally, this set of investigations is essential for the proper characterization of poorly studied systems in developing areas, whereby results can be integrated into conceptual and numerical models to be used by decision-makers as support tools in science-evidenced management plans.

Perseverance landed at the Octavia E. Butler landing site next to the Séítah dune region in Jezero crater on 18 February 2021, in close proximity to the largest exposed carbonate deposit on Mars. These carbonate signatures have been shown to be associated with the strongest olivine signatures at Jezero crater (Goudge+ 2015, Brown+ 2020). Alteration of olivine can lead to carbonate+H2 production, an energy source for microbes (Mayhew+, 2013). The question of the origin of the olivine-carbonate unit represents both an opportunity and a challenge for the rover mission and future sample return efforts. Carbonate The landing site is not near the region of carbonate detections (Figure 1), however the rover’s westward traverse will take us over the carbonates on approach to the crater rim. No reliable indications of the 2.5 μm carbonate band have yet been convincingly detected by the SCAM VISIR instrument. Olivine Studies of the olivine-carbonate unit concluded the olivine is relatively Fe-rich and coarse grained (mm: Poulet+ 2007, Clenet+ 2013). The strongest in-situ olivine signatures are found in dune material analysed by LIBS/VISIR (Beyssac+ Mandon+ this conf). This grain size characterization work may be used to investigate the interaction of olivine with water and CO2 (Escamilla-Roa+ 2020). These surface-gas processes are enhanced when olivine is in fine grain form. Ash dispersal modeling is ongoing (Ravanis+ this conf) to determine the range different sized ash particles could have traveled on ancient Mars. We cannot directly compare the 1 μm band for CRISM and VISIR, so we developed a new method that measures the curvature of three points on the absorption bands to assess their relative Fo# shifts and applied it to both datasets. Lab spectroscopy will be used to assess spectral variations with composition versus grain size. Two key factors driving the Fo# are mantle composition and melt temperature. Brown+ (2020) estimated a range of Fo44-65 for the most redshifted olivine observed by CRISM. McGetchin+Smythe (1978) showed that an Fe-rich mantle composition would produce highly viscous lavas and suggested an upper bound of Fo70 for olivine. Understanding the astrobiological potential of the olivine-carbonate unit is a priority of M2020 (Farley+ 2020) and we will speculate on potential formation models in this contribution.

Background: Capillary trapping of gas bubbles and oil blobs within water-saturated media plays an important role for underground gas storage and secondary oil recovery. Wettability and roughness of the surface are elementary properties of a porous medium that determine the trapping efficiency. In previous work [1,2], we demonstrated that glass beads and natural sands display a significant difference (15%) of the trapped gas phase. Here, we carry out a systematic study of the capillary trapping efficiency in dependence of the wettability and surface roughness. Methods: We conducted a series of column experiments to study capillary trapping of gaseous CO2 using both glass beads and natural sands as sediments. Based on the high-resolution non-invasive micro-CT visualization method and subsequent image processing, we quantified capillary trapping efficiency, gas-cluster morphology and gas-cluster size distribution. We used the silanization method for varying degrees of wettability resulting in three different contact angles on microscopic soda lime glass slides: (i) Piranha cleaning (= 7°), (ii) untreated glass (= 30°) and (iii) silanized glass (=100°). Results: We observed that by-pass trapping is the dominant trapping mechanism in glass beads (smooth surfaces). The displacement process is piston-like. For natural sands (rough surface), thick film flow occurs, causing an efficient snap-off trapping mechanism. Our results indicate that the capillary trapping efficiency of natural sands is stronger reduced by a transition from water-wet to CO2-wet 3-phase system (increasing contact angle) when compared to glass beads. [1] H. Geistlinger, I. Ataei-Dadavi, S. Mohammadian, and H.-J. Vogel (2015) The Impact of Pore structure and Surface Roughness on Capillary Trapping for 2D- and 3D-porous media: Comparison with Percolation theory. Special issue: Applications of Percolation theory, Water Resour Res, 51, doi:10.1002/2015WR017852. [2] H. Geistlinger, I. Ataei-Dadavi, and H.-J. Vogel (2016) Impact of Surface Roughness on Capillary Trapping Using 2D-Micromodel Visualization Experiments. Transport in Porous Med., DOI 10.1007/s11242-016-0641-y.

The considerable challenges of accessing unpredictable events at remote seafloor locations make submarine eruptions difficult to study in real time. The serendipitous discovery of two persistently active sites (NW Rota-1 in the Mariana arc, at ~550 m, and West Mata in the NE Lau basin at ~1200 m) resulted in multi-year, multi-parameter studies that included water column plume surveys and direct (ROV) observations. Intense magmatic-hydrothermal plumes rose buoyantly above both sites, while deep particle plume layers, dominated by fine ash and devoid of hydrothermal tracers, were found dispersing laterally on isopycnal surfaces at variable depths below the eruptive vents and above the seafloor. The presence or absence of deep ash plumes was directly correlated with explosive activity or quiescence, respectively. An estimated 0.4-14.6 x 105 m3/yr of fine ash entered the water column surrounding these volcanoes and remained suspended at distances exceeding 10’s of km. We show that deep ash plume layers in the water column are a common feature of explosive submarine eruptions at other sites as well, and that they demonstrate a syn-eruptive mode of transport for fine ash that will result in deposition as “hidden” cryptotephra or fallout deposits in marine sediments at distances greater than previously predicted. Cruise FK171110 extended the time series of observations at West Mata, and resulted in discovery of new lava flows emplaced after September 2012, with one constrained between March 2016 and November 2017. ROV dives confirmed that West Mata was quiescent during this expedition, but widespread deep ash plumes were present. Turbidity in the deep ash plumes decreased by 80% over a 25-day period, with an average loss of 3% (0.15-0.6 g/m2) per day, suggesting the eruption that formed the 2016-2017 eruptive deposits had occurred within 8-121 days prior to the FK171110 expedition. Future studies of submarine volcanic processes will depend on improved exploration and event detection capabilities. In addition to recognizing the characteristic hydrothermal event plumes rising into the water column above actively erupting sites, widespread ash plumes dispersing at depths deeper than eruptive vents can also be diagnostic of ongoing, or very recent, eruptions. We infer the eruptive status at other sites based on these criteria.

Vertical motions of Earth’s surface are used to inform almost all branches of the Earth Sciences, and central role in understanding geological, biological and climatic processes. An important challenge is generating enough information to reliably constrain histories of vertical motion. Significant effort has been expended in generating information about denudation (e.g. from thermochronometry), uplift (e.g. from stable isotopes or drainage analyses) and subsidence patterns. However, a canonical inventory of measurements that determine continental uplift on timescales pertinent to growth and decay of continental topography does not exist. We address this issue using the distribution of unequivocally marine rock recorded in new, detailed, paleobiological inventories. We show that these new compilations of paleobiological and paleoenvironmental data, that were generated to address paleobiological problems, also provide an unprecedented number of self-consistent, high-resolution measurements of continental and ocean island uplift. We focus on the Cretaceous to Recent history, which captures the large-scale marine incursions of the continents. Our results highlight that significant improvements can be made in understanding the histories of the continents in using these measurements of uplift. We present examples from North and South America, southern Africa and Australia to show how this new database can be explored to better understand the processes that generate high topography. They emphasize the importance of large inventories of paleobiological data for understanding long-wavelength uplift and the role tectonic and mantle convective processes play in generating continental topography.

Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, contains a carbonate-bearing rock unit termed the margin fractured unit. Some of the carbonates in these rocks may have formed in a fluviolacustrine environment and therefore could preserve biosignatures of paleolake-inhabiting lifeforms. Here we evaluate whether these margin fractured unit carbonates formed as authigenic precipitates in a fluviolacustrine environment or via alteration of primary minerals by groundwater. We integrate thermal inertia measurements from the Thermal Emission Imaging System (THEMIS), spectral analyses from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), examination of stratigraphic relationships in Jezero crater using High Resolution Science Experiment (HiRISE) and Context Camera (CTX) images and digital elevation models. We also compare the Jezero crater results to observations from the Curiosity rover in Gale crater. We find that margin fractured bedrock with the deepest visible-to-near-infrared carbonate absorptions also has exceptionally high thermal inertia and thickness relative to other carbonate-bearing units in Jezero crater, consistent with enhanced cementation and crystallization by groundwater. Our results indicate that it is equally likely that carbonates in Jezero crater formed via alteration of primary minerals by alkaline groundwater rather than as authigenic precipitates in a fluviolacustrine environment. Jezero crater may have hosted ancient subsurface habitable environments related to these groundwaters, where life-sustaining redox energy was generated by water-rock interactions. The Mars 2020 Perseverance rover could encounter biosignatures preserved from this carbonate-forming environment, whether it was fluviolacustrine or in the subsurface.

The seasonal variation in concentration of transparent exopolymer particles (TEP), particulate organic carbon (POC) and nitrogen (PON) were investigated together with floc size and the concentration of suspended particulate matter (SPM) along the cross-shore gradient, from the high turbid nearshore towards the low-turbid offshore waters in the southern Bight of the North Sea. The analyses of TEP, POC and PON result in a set of parameters that incorporate labile and refractory organic matter (OM) fractions. Our data demonstrate that biophysical flocculation cannot be explained by these heterogeneous parameters, but requires a distinction between a more reactive labile (“fresh”) and a less reactive refractory (“mineral-associated”) fraction. Based on all data we separated the labile and mineral-associated POC, PON and TEP using a semi-empirical model approach. The model’s estimates of fresh and mineral-associated OM show that great parts of the POC, PON and TEP are associated with suspended minerals, which are present in the water column throughout the year, whereas the occurrence of fresh TEP, POC and PON is restricted to spring and summer months. In spite of a constantly high abundance of total TEP throughout the entire year, it is its fresh fraction that promotes the formation of larger and faster sinking biomineral flocs, thereby contributing to reduce the SPM concentration in the water column over spring and summer. Our results show that the different components of the SPM, such as minerals, extracellular OM and living organisms, form an integrated dynamic system with direct interactions and feedback controls.

Predicting the partitioning between aqueous and gaseous C across landscapes is difficult because many factors interact to control CO2 concentrations and removal as DIC. For example, carbonate minerals may buffer soil pH so that CO2 dissolves in porewaters, but nitrification of fertilizers may decrease pH so that carbonate weathering results in a gaseous CO2 efflux. Here, we investigate CO2 production and dissolution in an agricultural, first-order, mixed-lithology humid, temperate watershed. We quantified soil mineralogy and measured porewater chemistry, soil moisture, and pCO2 and pO2 as a function of depth at three hillslope positions for a year. The variation of soil moisture along the hillslope was the dominant control on the concentration of soil CO2, but mineralogy acted as a secondary control on the partitioning of CO2 between the gaseous and aqueous phases. The regression slopes of pCO2 vs. pO2 in the carbonate-bearing soils indicate a deficit of CO2 relative to O2 (p < 0.05). Additionally, we found no abiotic gaseous CO2 efflux from carbonate weathering. We concluded that in the calcareous soils, about a third of respired C dissolves and drains from the soil rather than diffusing out to the atmosphere. To represent the global scope of the reactions we evaluated at our local watershed, we used databases of carbonate minerals and land uses to map types of soil degassing behaviors. Based on our maps, the partitioning of respired soil CO2 to the aqueous phase may be globally common and should be accounted for in ecosystem C budgets and models.

As tides propagate inland, they become distorted by channel geometry and river discharge. Tidal dynamics in fluvial-marine transitions are commonly observed in high-energy tidal environments with relatively steady river conditions, leaving the effects of variable river discharge on tides and longitudinal changes poorly understood. To study the effects of variable river discharge on tide-river interactions, we studied a low-energy tidal environment where river discharge ranges several orders of magnitude, the diurnal microtidal Tombigbee River-Mobile Bay fluvial-marine transition, using water level and velocity observations from 21 stations. Results showed that tidal attenuation was reduced by the width convergence in seaward reaches and height convergence of the landward backwater reaches, with the channel convergence change location ~40-50km inland of the bayhead and seaward of the largest bifurcation (~rkm 90-100). River events amplified tides in seaward regions and attenuated tides in landward regions. This created a region of river-induced peak amplitude seaward of the flood limit (i.e., bidirectional-unidirectional current transition) and passed more tidal energy inland. Tidal currents were attenuated and lagged more with river discharge than water levels, making the phase lag dynamic. The river impacts on the tides were delineated longitudinally and shifted seaward as river discharge increased, ranging up to ~180 km. Results indicated the location and longitudinal shifts of river impacts on tides in alluvial systems can be estimated analytically using the ratio of river discharge to tidal discharge and the geometry convergence. Our simple analytical theory provides a pathway for understanding the tide-river-geomorphic equilibrium along increasingly dynamic coasts.

Through rover missions and martian meteorites received on Earth, the surface of Mars has showed unexpectedly elevated concentrations of transition metals usually measured in minor and trace concentrations in silicate rocks compared to the average crust. Gale crater presents one of the most diverse geological records in terms of its complex fluid and magmatic history described through the sedimentary and igneous records, respectively. Transition metals, such as Mn, Co, Ni, Cu, and Zn, are highly concentrated within various sedimentary rocks and diagenetic features, suggesting their mobilization through fluid circulation. This paper presents the first compilation of elevated concentrations of transition metals measured by the Curiosity rover and reviews the origin of such metals in Gale crater, highlighting the existence of a hydrothermal or magmatic-hydrothermal deposit in its vicinity. The discovery of felsic magmatism on Mars opens up to novel perspectives in terms of the type of metal deposits that current and future exploration could evidence at the surface of Mars and raise questions about the global abundance of such metals. Constraining the abundance of transition metals is also a central question for exobiology purposes. Because on Earth living organisms use transition metals for their survival and functioning, should live have arisen on Mars, the availability of such chemical elements at the surface could have been essential for its development. An accurate assessment of in situ metal resources and potential risks for health will be key for the preparation of human exploration of Mars as recently announced by NASA.

Continental rifting is a critical component of the plate tectonic paradigm, and occurs in more than one mode, phase, or stage. While rifting is typically facilitated by abundant magmatism, some rifting is not. We aim to develop a better understanding of the fundamental processes associated with magma-poor (dry) rifting. Here, we provide an overview of the NSF-funded Dry Rifting In the Albertine-Rhino graben (DRIAR) project, Uganda. The project goal is to apply geophysical, geological, geochemical, and geodynamic techniques to investigate the Northern Western Branch of the East African Rift System in Uganda. We test three hypotheses: (1) in magma-rich rifts, strain is accommodated through lithospheric weakening from melt, (2) in magma-poor rifts, melt is present below the surface and weakens the lithosphere such that strain is accommodated during upper crustal extension, and (3) in magma-poor rifts, there is no melt at depth and strain is accommodated along pre-existing structures such as inherited compositional, structural, and rheological lithospheric heterogeneities. Observational methods in this project include: passive seismic to constrain lithospheric structure and asthenospheric flow patterns; gravity to constrain variations in crustal and lithospheric thickness; magnetics to constrain the thermal structure of the upper crust; magnetotellurics to constrain lithospheric thickness and the presence of melt; GNSS to constrain surface motions, extension rates, and help characterize mantle flow; geologic mapping to document the geometry and kinematics of active faults; seismic reflection analyses of intra-rift faults to document temporal strain migration; geochemistry to identify and quantify mantle-derived fluids in hot springs and soil gases; and geodynamic modeling to develop new models of magma-poor rifting processes. Fieldwork will begin in January 2022 and the first DRIAR field school is planned for summer 2022. Geodynamic modeling work and morphometric analyses are already underway.

The univariate statistics of Potassium (K), Thorium (Th) and Uranium (U) concentrations, in the Earth’s oceanic and continental crust are examined by different techniques. The frequency distributions of the concentrations of these elements in the oceanic crust are derived from a global catalog of mid-ocean ridge basalts (MORB). Their frequency distributions of concentrations in the continental crust are illustrated by the North Pilbara Craton, and the West Africa Craton. For these two cratons, the distributions of K, Th and U derived from geochemical analyses of several thousand whole rock samples differ significantly from those derived from airborne radiometric surveys. The distributions from airborne surveys tends to be more symmetric with smaller standard deviations than the right-skewed distributions inferred from whole rock geochemical analyses. Hypothetic causes of these differences include (i) bias in rock sampling or in airborne surveys, (ii) the differences in the chemistry of superficial material, and (iii) the differences in scales of measurements. The scale factor, viewed as consequence of the central limit theorem applied to K, Th and U concentrations, appears to account for most of the observed differences in the distributions of K, Th and U. It suggests that the three scales of auto-correlation of K, Th and U concentrations are of the same order of magnitude as the resolution of the airborne radiometric surveys (50 – 200 m) and concentrations of K, Th, U are therefore generally heterogenous at smaller scales.

Asteroid 162173 (Ryugu) is a carbonaceous asteroid that was visited by Japan’s Hayabusa2 spacecraft in 2018. The formation mechanism of spinning-top shape of Ryugu is an essential clue to the dynamical history of the near-Earth asteroid. In this study, we address the spin-state evolution of Ryugu induced by the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, i.e., the thermal recoil torque that changes the rotation period and spin-pole direction. Given the current orbit, spin state, and three-dimensional shape observed by Hayabusa2, we computed the YORP torque exerted on Ryugu using a simplified thermal model approximating zero thermal conductivity. Despite differences in meter-scaled topography, all 20 shape models that we examined indicate that the spin velocity of Ryugu is currently decreasing at a rate of (-0.42—6.3)*10-6 deg/day2. Our findings also suggest that the thermal torque on the asteroid is responsible for maintaining the spin pole upright with respect to the orbital plane. Therefore, the YORP effect could explain the significant spin-down from a period of 3.5 h initially to 7.6 h currently. The corresponding time scale of the rotational deceleration is estimated to be 0.58–8.7 million years, depending on the input shape models. This time scale is comparable to e.g., the formation period of the largest crater, Urashima (5–12 Ma) or the western bulge (2–9 Ma) as derived from previous studies on crater statistics in Ryugu. It is considered that the rotation of the asteroid started to decelerate in the wake of the major crater formation or the resurfacing event on the western hemisphere.