Gas hydrates from the continental margin settings are mostly confined to continental slopes and it is an established fact that their dissociation might trigger submarine slope failures. The present study is carried out to investigate such a scenario in the Krishna Godavari basin where there are proven gas hydrate deposits. We interpret a fault that is generated below the bottom simulating reflector as a result of free gas overpressure in the shale deposits. Gas column height calculated for the KG basin is 51 m and shows that the gas zone is critically over pressured and any further increase in the gas column can potentially trigger slope failure.

Over the 20th and 21st centuries, both anthropogenic greenhouse gas increases and changes in anthropogenic aerosols have affected rainfall in the Sahel. Using multiple characteristics of Sahel precipitation, we construct a multivariate fingerprint that allows us to distinguish between the model-predicted responses to greenhouse gases and anthropogenic aerosols. Models project the emergence of a detectable signal of aerosol forcing in the middle of the twentieth century and a detectable signal of greenhouse gas forcing at the beginning of the twenty-first. However, the signals of both aerosol and greenhouse gas forcing in observations emerge earlier and are stronger than in the models, far stronger in the case of aerosols. The similarity between the response to aerosol forcing and the leading mode of internal variability makes it difficult to attribute this model-observation discrepancy to errors in the forcing, errors in the forced response, model inability to capture the amplitude of internal variability, or some combination of these. For greenhouse gases, however, the forced response is distinct from internal variability as estimated by models, and the observations are largely commensurate with the model projections.

Processes that facilitate the transition between continental rifting and sea-floor spreading remain unclear. Variations in the spatial distribution of extension through Afar and into the Red Sea are indicative of temporal evolution of the rift. We develop a time series of Sentinel-1 interferometric synthetic aperture radar (InSAR) observations of ground deformation covering the whole Afar Rift from 2014-2019, to study the distribution of extension across all magmatic segments. By incorporating GNSS observations, we resolve 3D average velocities in the vertical, rift-perpendicular, and rift-parallel directions. Results show the spatial distribution of long-term plate motions over the rift, as well as deformation at individual volcanic centres, including Dallol, Nabro, and Erta ’Ale. We find that in northern and central Afar, the majority of extension is accommodated within +/- 15-30 km of magmatic spreading centres. In southern Afar, near the Nubia-Arabia-Somalia triple-junction, extension is distributed over 90-180 km, which may indicate an increase in rift focussing with rift maturity. We also observe rapid surface uplift and rift-perpendicular extension at the Dabbahu-Manda-Hararo segment with velocities of 33 +/- 4 mm/yr and 37 +/- 4 mm/yr respectively. These are higher than the background extension rate of 18-20 mm/yr, but have decreased by 55-70 % since 2006-10. The data suggests that this is due to an on-going long-lived response to the 2005-10 rifting episode, with potential continued processes below the segment including a lower-crustal viscous response and magma movement. Continued long-term observations of surface deformation provide key constraints on tectono-magmatic processes in Afar.

In order to explore the cause behind a recently so-called inversion of activation energy between dislocation-diffusion creep, we compress Fangshan dolomite at effective pressures of 50-300 MPa, temperatures of 27-900 ℃, and strain rates of 10-2×10 s using a Paterson-type apparatus. Two end-member deformation regimes, each with respective diagnostic flow law and microstructure, are recognized. At T≤500 ℃, low temperature plasticity (LTP), expressed by an exponential constitutive equation with and , was determined with weakly strain rate dependence and thermal hardening of the strength, and microstructures of predominant undulatory extinctions or f-twinning (Regime 1). At T≥800 ℃, dislocation creep, described by a power law equation ( with , and ), was defined with significant strain rate and temperature sensitivities of strength, and microstructures dominated by smooth undulating extinction and new recrystallized grains (Regime 2). Regime 3, transition from LTP to dislocation creep, is also recognized from ~600 ℃ to 800 ℃ with strain rate dependence of strength changing with temperature and developing microstructures similar to those of regime 2. Overall the medium-grained Fangshan dolomites show similar rheology to coarse-grained Madoc dolomites but a beginning temperature of regime 2 about 50-100 ℃ than the latter, making the dislocation creep of Fangshan dolomite clearly recognized under the condition that dolomite decomposition has no obvious effect. Extrapolated to nature, dislocation creep is expected to occur in a relatively narrow space undergoing high temperatures and relatively high stresses, instead diffusion creep is expected to dominate the deformation of dolomite in low stress tectonic settings.

For the past 5 years, NASA’s Oceans Melting Greenland (OMG) mission has been motivated by the question: “to what extent are the oceans melting Greenland’s ice from below?” Three out of the mission’s four observational components employed aircraft to collect data on and around the ice sheet: (i) airborne gravity above the continental shelf to infer seafloor geometry, (ii) airborne radar (GLISTIN-A) to measure year-to-year glacier elevation changes, and (iii) airborne-deployed oceanographic instruments (AXCTDs, ALAMO and APEX floats, XBTs, and drifters) to measure year-to-year ocean temperature and salinity changes. After highlighting the mission’s operational parameters and key scientific findings, we will detail our rationale for designing the mission to include extensive aircraft-based measurements. Now that OMG has completed its final observational campaign, we will summarize our experience with using aircraft in polar environments and suggest ways in which aircraft could be used to efficiently extend the ocean climate data record started by OMG and the potential for using aircraft in future missions to make similar oceanographic measurements around Antarctica.

Export of Particulate Organic Carbon (POC) is mainly driven by gravitational sinking. Thus, traditionally, it is thought that larger, faster-sinking particles make up most of the POC export flux. However, this need not be the case for particles whose sinking speeds are comparable to the vertical velocities of a dynamic flow field that can influence the descent rate of particles. Particles with different settling speeds are released in two process-oriented model simulations of an upper ocean eddying flow in the Northeast Pacific to evaluate the impact of (1) ocean dynamics on the respective contribution of the different sinking-velocity classes to POC export, and (2) the particle number size-spectrum slope. The analysis reveals that the leading export mechanism changes from gravitationally-driven to advectively-driven as submesoscale dynamics become more active in the region. The vertical velocity associated with submesoscale dynamics enhances the contribution of slower-sinking particles to POC export flux by a factor ranging from 3 to 10, especially where the relative abundance of small particles is large, (i.e., steep particle size-spectrum slope). Remineralization generally decreases the total amount of biomass exported, but its impact is weaker in dynamical regimes where submesoscale dynamics are present and export is advectively-driven.

Does life currently exist, or did life once exist, on other worlds in our solar system? The proximity of the rocky planets of our solar system, Venus and Mars, make them obvious targets for the first attempts to answer these questions via direct exploration, with concomitant implications for, and input to, how we think of exoplanets. Given the limited resources we have to explore our neighbors in space, an ecological assessment (based on terrestrial ecosystem principles) might help us target our search and methodology. Studies of extreme life on Earth consistently reveal adaptability. Mars has been the target of many life-related investigations [1, many others]. Venus has not, yet there may be compelling reasons to think about extant life on the second planet [2], and lessons to learn there about searching for life elsewhere in the solar system and beyond. The Venus Life Equation: Venus may have been habitable for billions of years its history and may still be habitable today. Our current state of knowledge of the past climate of Venus suggests that the planet may have had an extended period – perhaps 1-2 billion years – where a water ocean and a land ocean interface could have existed on the surface, in conditions possibly resembling those of Archaean Earth [3]. At present, Venus’ surface is not hospitable to life as we know it, but there is a zone of the Venus middle atmosphere, ~55 km altitude, just above the sulfuric acid cloud layer, where the combination of pressure, temperature, and gas-mix are more Earth-like than anywhere else in the solar system [2, 4]. The question of whether life could have – or could still – exist on the Earth’s closest neighbor is more open today than it’s ever been. Here we approach the question of present-day life on Venus in a manner analogous to the Drake Equation [5], treating the possibility of current Venus life as an exercise in informal probability – seeking qualitatively the likelihood or chance of the answer being nonzero.The working version of the Venus Life Equation is expressed as: L = O * R * A where L is the likelihood (zero to 1) of there being life on Venus in the present-day, O (origination) is the chance life ever began and “broke out” on Venus, R (robustness) is the potential current and historical size of diversity of the Venus biosphere, A (acceptability) is the chance that conditions amenable to live persisted spatially and temporally to the present. The Venus Life Equation is a work-in-progress as a pre-decadal White Paper [6] and its variables are currently being refined. [1] McKay 1997, Springer, Dordrecht, 1997. 263-289. [2] Limaye et al. 2018 Astrobiology, 18(9), 1181-1198. [3] Way et al. 2016 JGR 43(16) 8376-8383. [4] Schulz-Makuch et al. 2004 Astrobiology 4, 11-18. [5] Burchell 2006, Int. J. Astrobio, 5(3) 243-250. [6] Izenberg et al. 2020, https://is.gd/vd4JE7 (location of Latest version of Venus Life Equation White Paper).

Environmental controls on methane (CH) emission from lakes are poorly understood at sub-daily time scales due to a lack of continuous data, especially for ebullition. We used a novel technique to partition eddy covariance CH flux observed in the littoral zone of a mid-latitude shallow lake in Japan and examined the environmental controls on diffusion and ebullitive CH flux separately at a sub-daily time scale during different seasons. Both diffusive and ebullitive flux were significantly higher in summer than winter. The contribution of ebullitive flux to total flux was 56% on average. Diffusive flux increased with increasing wind speed due to increased subsurface turbulence. For a given wind speed, diffusive flux was higher in summer than in winter due to the higher concentration of dissolved CH in the surface water during summer. The transfer of accumulated dissolved CH from the bottom layer to the surface in summer and the accumulation of dissolved CH under surface ice in winter were important for explaining the variability of diffusive flux. In summer, ebullition tended to occur following triggers such as a decrease in hydrostatic pressure or an increase in wind speed. In winter, on the other hand, the impact of triggers was not obvious, and ebullition tended to occur in the morning when the wind speed began to increase. The low CH production rate in winter slowed the replenishment of bubbles in the sediment, negating the effect of triggers on ebullition.

Flow separation has been observed and studied in sinuous laboratory channels and natural meanders, but the effects of flow separation on along-channel drag are not well understood. Motivated by observations of large drag coefficients from a shallow, sinuous estuary, we found in idealized numerical models representative of that system that flow separation in tidal channels with curvature can create form drag that increases the total drag to more than twice that from bottom friction alone. In the momentum budget, the pressure gradient is balanced by the combined effects of bottom friction and form drag, which is calculated directly. The effective increase in total drag coefficient depends on two geometric parameters: dimensionless water depth and bend sharpness, or the bend radius of curvature to channel width ratio. We introduce a theoretical boundary layer separation model to explain this parameter dependence and to predict flow separation and the increased drag. The drag coefficient can increase by a factor of 2 - 7 in “sharp” and “deep” sinuous channels where flow separation is most likely. Flow separation also enhances energy dissipation due to increased velocities, resulting in greater loss of tidal energy and weakened stratification.Flow separation and the associated drag increase are expected to be more common in meanders of tidal channels than rivers, where point bars that inhibit flow separation are more commonly found. The increased drag due to flow separation affects the tidal amplitude and phasing along the estuary and creates potential morphological feedbacks.

There is little scientific consensus on the importance of external climate forcings—including anthropogenic aerosols, volcanic aerosols, and greenhouse gases (GHG)—relative to each other and to internal variability in dictating past and future Sahel rainfall. We address this query by relating a 3-tiered multi-model mean (MMM) over the Climate Model Intercomparison Project phase 5 (CMIP5) “20th century” and pre-Industrial control simulations to observations. The comparison of single-forcing and historical simulations highlights the importance of anthropogenic and volcanic aerosols over GHG in generating forced Sahel rainfall variability in models. However, the forced MMM only accounts for a small fraction of observed variance. A residual consistency test shows that simulated internal variability cannot explain the residual observed multidecadal variability, and points to model deficiency in simulating multidecadal variability in the forced response, internal variability, or both.

This study proposes the utilization of municipal well records as an alternative dataset for large-scale heterogeneity characterization of hydraulic conductivity () and specific storage () using hydraulic tomography (HT). To investigate the performance of HT and the feasibility of utilizing municipal well records, a three-dimensional aquifer/aquitard system is constructed and synthetic groundwater flow and solute transport experiments are conducted to generate data for inverse modeling and validation of results. In particular, we simultaneously calibrate four groundwater models with varying parameterization complexity using five datasets consisting of different time durations and periods. Calibration and validation results are qualitatively and quantitatively assessed to evaluate the performance of investigated models. The estimated and tomograms from different model cases are also validated through the simulation of independently conducted pumping tests and conservative solute transport. Our study reveals that: 1) the HT analysis of municipal well records is feasible and yields reliable heterogeneous and distributions where drawdown records are available; 2) accurate geological information is of critical importance when data density is low and should be incorporated for geostatistical inversions; 3) the estimated and tomograms from the geostatistical model with geological information are capable in providing robust predictions of both groundwater flow and solute transport. Overall, this synthetic study provides a general framework for large-scale heterogeneity characterization using HT through the interpretation of municipal well records, and provides guidance for applying this concept to field problems.

The ultimate technosignature is an alien artifact. We should look for them near Earth. The great virtue of searching for artifacts is their lingering endurance in space, long after they go dead. I compare a Search for Extraterrestrial Artifacts (SETA) strategy of exploring near Earth for alien artifacts to the existing listening-to-stars SETI strategy. Stars come very close to Earth frequently. About two stars per million years come within a light year. An extraterrestrial civilization that passes nearby can see there’s an ecosystem here, due to the out-of-equilibrium atmosphere. They could send interstellar probes to investigate. The Moon and the Earth Trojans have the greatest probability of a successful search by us, ET archeology. I suggest resources devoted to imaging of our Moon’s surface, the Earth Trojans and Earth co-orbitals, and for probe missions to the latter two. The SETA concept can be falsified: if we investigate these near-Earth objects and don’t find artifacts, the concept is disproven for this region. Close inspection of bodies in these regions, which may hold primordial remnants of our early solar system, yields concrete astronomical research.

We investigate the contributions of emission changes from 10 world regions, as well as the global methane concentration change, on the global tropospheric ozone burden change from 1980 to 2010. The modeled global tropospheric ozone burden has increased by 28.1 Tg, with 26.7% (7.5 Tg) of this change attributed to the global methane increase. Southeast Asia (5.6 Tg) and South Asia (4.0) contribute comparably to the global ozone burden change as East Asia (5.6), even though NO emission increases in each region are less than one third of those in East Asia, highlighting the greater sensitivity of global ozone to these regions. Emission decreases from North America, Europe and Former Soviet Union have led to ozone burden decreases of 2.8, 1.0, and 0.3 Tg. The greater sensitivity of the global ozone burden to emission changes in tropical regions emphasizes the importance of controlling emissions in these regions for global ozone.

The existence of causal constraints introduces a temporal selection effect in the type of technosignatures that we can detect. I discuss the implications of this fact on the characteristic of detectable technosignatures, and in particular their longevity.

Dyson spheres are hypothetical structures that high-level civilizations may build to harvest energy in the form of starlight. As in any thermodynamic process, the conversion of stellar energy would involve the emission of waste heat. For Dyson spheres operating at temperatures in the range 100 - 1000 K, this energy would be emitted primarily in the mid-infrared. Here we present some models to estimate upper limits on the prevalence of Dyson spheres in the Milky Way based on the number of sources with mid-infrared excess. In the present analysis, we are only using 260,000 of the most nearby stars from the Gaia DR2 and AllWISE combined dataset, but the full search will include 10^7 - 10^8 objects, making it the largest search for Dyson spheres in the Milky Way carried out so far. In this small sample, we found that less than 1 in 10,000 stars display the mid-IR excess expected for a Dyson sphere, assuming a Dyson sphere with a temperature of 300 K and a covering factor > 0.9.

The representation of stable boundary layers (SBLs) still challenges turbulence parameterizations implemented in current weather or climate models. The present work assesses whether these model deficiencies reflect calibration choices or intrinsic limits in currently-used turbulence parameterization formulations and implementations. This question is addressed for the ARPEGE-Climat 6.3 CNRM atmospheric model in a single-column model/large-eddy simulation (SCM/LES) comparison framework, using the history matching with iterative refocusing statistical approach. The GABLS4 case, which samples a nocturnal strong SBL observed at Dome C, Antarctic Plateau, is used. The standard calibration of the ARPEGE-Climat 6.3 turbulence parameterization leads to a too deep SBL, a too high low-level jet and misses the nocturnal wind rotation. This behavior is found for low and high vertical resolution model configurations. The statistical tool then proves that these model deficiencies reflect a poor parameterization calibration rather than intrinsic limits of the parameterization formulation itself. In particular, the role of two lower bounds that were heuristically introduced during the parameterization implementation to increase mixing in the free troposphere and to avoid runaway cooling in snow- or ice-covered region is emphasized. The statistical tool identifies the space of the parameterization free parameters compatible with the LES reference, accounting for the various sources of uncertainty. This space is non-empty, thus proving that the ARPEGE-Climat 6.3 turbulence parameterization contains the required physics to capture the GABLS4 SBL. The SCM framework is also used to validate the statistical framework and a few guidelines for its use in parameterization development and calibration are discussed.

The escape of heavy ions from the Earth atmosphere is consequences of energization and transport mechanisms, including photoionization, electron precipitation, ion-electron-neutral chemistry and collisions. Numerous studies considered the outflow of O ions only, but ignored the observational record of outflowing N. In spite of 12% mass difference, N and O ions have different ionization potentials, ionospheric chemistry, and scale heights. We expanded the Polar Wind Outflow Model (PWOM) to include N as well as key molecular ions in the polar wind. We refer to this model expansion as the Seven Ion Polar Wind Outflow Model (7iPWOM), which involves expanded schemes for suprathermal electron impact and ion-electron-neutral chemistry and collisions. Numerical experiments, designed to probe the influence of season, as well as that of solar conditions, suggest that N is a significant ion species in the polar ionosphere and its presence largely improves the polar wind solution, as compared to observations.

The surface of Ganymede is characterized by dark and light terrains. Light terrain, covering two thirds of the surface, is retained to be younger and resulted from resurfacing events, likely correlated to a global expansion of Ganymede [1]. It is typically characterized by several sets of subparallel troughs and ridges, called grooves. They highly modify the dark terrain and the other pre-existing features. Since these areas display two different superposed spacing scales, grooves have been interpreted as the product of extensional tectonism [2] and two different faulting styles have been recognized (horst-graben and domino) [3]. Nevertheless, the stratigraphical relationship, the required conditions to the grooves’ origin and the tectonic mechanisms are still objects of debate. In preparation of the ESA Juice Mission, we are producing DEMs of extended areas of the surface of Ganymede, using both Galileo and Voyager imagery. We use the open-source suite of tools NASA Ames Stereo Pipeline (ASP) [4], by using the photoclinometry-based “shape-from-shading” (SfS) tool. Since SfS needs an input DEM generated preferably with stereo images, and we do not have such data in this area of Ganymede, we used the methodology proposed by Lesage et al. 2021 [5]. Figure 1 shows an example of Digital Elevation Model using a Galileo image (EDR 2878r, with a resolution of 151 m/px) of Anshar Sulcus (167.40° E, 11.50° N). The DEM clearly shows the height variations of the ridge and trough systems included in the study area. These novel Digital Elevation Models can provide new insights on the geological processes of Ganymede. Acknowledgments GM acknowledges support from the Italian Space Agency (contract ASI/2018-25-HH.0). References [1] Pappalardo R.T., et al., 2004. Jupiter: The Planet, Satellites and Magnetosphere, 2:363. [2] Prockter L.M. et al.,2010. Space Sci Rev 153:63-111 [3] Pizzi A. et al., 2017. Icarus 288: 148-159 [4] Beyer, R. A. et al., (2018), Science, 5. [5] Lesage E. et al. (2021), Icarus, 114373.