IODP Hole U1502B penetrates >180 m into the crystalline basement generated at a rifting margin of the South China Sea (SCS), which is the first confirmed intermediate-type margin worldwide. The recovered lavas show petrographic characteristics of mid-ocean ridge basalt (MORB), but suffered pervasively from hydrothermal alteration. This sequence represents the oldest SCS oceanic crust ever drilled in-situ, and offers a globally unique window to explore the hydrothermal processes during continental breakup. Here, 50 whole-rock samples representative of Hole U1502B were analyzed for major & trace elements and Sr–Nd isotopes, presenting the first report of hydrothermally altered basalts for the SCS. The protolith appears to be tholeiite, enriched MORB, and little affected by crustal contamination due to the constant mantle-values of εNd. However, the altered rocks are characterized by significant Ca depletion and 87Sr/86Sr modification. Major processes are identified to be tightly involved with plagioclase: chloritization and albitization. Both reactions are responsible for the Ca-loss and Sr-mobility, and for the resultant Mg- and Na-uptakes, respectively. Environments varying from the peripheral to deep parts within a discharge zone are evidenced by the co-existence of hydro-fracturing brecciation, high water/rock ratios (~1–25), and lower greenschist facies alteration (albite–chlorite–epidote + quartz). This variability can be attributed to detachment-related faulting, which provides permeability allowing deeply channeled pathways of fluids. Such tectonic effects also permit a penetration of Hole U1502B into the lava–dike transition. With a migration from on-axis to off-axis alterations discerned, our results together imply a more complex and longer SCS rifting than previously thought.

Seamounts can be habitats and hazards to submarine navigation, and their distribution reveals the volcanic history of the oceans. As only a few percent of ocean floor has been sounded, seamount distribution must be mapped by satellite altimetry. Wessel (doi:10.1029/2000JB000083) looked at data from an earlier generation of altimeter technology and suggested that all seamounts 2 km and taller had been found, but there might be as many as 50,000 seamounts between 1–2 km tall that were not yet found. The AltiKa altimeter delivers more precise sea level measurements at a higher along-track sampling rate than previous altimeters. These data resolve small seamounts not previously resolvable (Smith, doi:10.1080/01490419.2015.1014950), particularly if repeat-track profiles are “stacked” and band-pass filtered (Marks and Smith, doi:10.1007/s11001-016-9293-0). These two studies looked at only a few isolated locations where multibeam acoustic depth sounding surveys were available for “ground truth” for tuning a band-pass filter to detect the small seamount geoid signal. In the new work we present here we have stacked 32 repeat cycles of SARAL AltiKa data world-wide, and band-pass filtered the stacks, to yield 75,208 potential seamount locations distributed between +/- 81.5 latitude throughout the global ocean. These locations are detected as local maxima in the filtered geoid at least 2 cm above background and with a full-width at half-maximum (FWHM) at least 4 km wide. Of these, 4824 detections were over multibeam surveys. We assign a proxy seamount height to each by subtracting the regional SRTM30 depths from the multibeam depths. These proxy heights follow a Poisson statistical distribution similar to that which fits acoustic bathymetry profiles over seamounts (Jordan et al., doi:10.1029/JB088iB12p10508). We are currently investigating how to derive proxy heights from anomaly amplitude and FWHM, optimizing the trade-off between false negative and false positive detections, and whether it is possible to identify potential seamounts that may pose hazards to submarine navigation.

The Surface Water Ocean Topography (SWOT) mission will launch in 2021 to provide the first global inventory of terrestrial surface water. Although SWOT is primarily a research mission with key science objectives in both the oceanography and hydrology domains, SWOT data is expected to have application potential to address many societal needs. To identify SWOT applications, prepare for the use of SWOT data, and quantify SWOT impacts prior to launch, realistic proxy SWOT observations with representative measurement errors are required. This paper provides a step-by-step description of two methods for deriving proxy SWOT water surface elevations (WSE) from an Observing System Simulation Experiment (OSSE) using the Weather Research and Forecasting hydrological extension package (WRF-Hydro). The first, a basic method, provides a simple and efficient way to sample WRF-Hydro output according to the SWOT orbit and add random white noise to simulate measurement error, similar to many previous approaches. An alternate method using the Centre National d’Etudes Spatiales (CNES) Large-scale SWOT Hydrology Simulator accounts for additional sources of measurement error and produces output in formats comparable to that expected from official SWOT products. The basic method is ideal for river hydrology applications in which a full representation of SWOT measurement errors and spatial resolution are unnecessary, whereas the CNES simulator approach is better-suited for more rigorous scientific studies that require a comprehensive error budget.

One of the goals of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission is to constrain the interior structure of Mars. We present a hierarchical transdimensional Bayesian approach to extract phase velocity dispersion and interior shear-wave velocity (VS) models from a single seismogram. This method was adapted to Mars from a technique recently developed for Earth (Xu & Beghein, 2019). Monte Carlo Markov Chains (MCMC) seek an ensemble of one dimensional (1-D) VS models between a source and a receiver that can explain the observed waveform. The models obtained are used to calculate the phase velocities of fundamental and higher modes at selected periods, and a subsequent analysis is performed to assess which modes were reliably measured. An advantage of our approach is that it can also fit unknown data noise, which reduces the risk of overfitting the data. In addition, uncertainties in the source parameters can be propagated, yielding more accurate model parameter uncertainties. In this paper, we first present our technique and discuss the challenges stemming from using a single station to characterize both structure and the source and from the absence of a Mars reference model. We then demonstrate the method feasibility using the MSS blind test data and our own synthetic data, which included realistic noise levels based on the noise recorded by InSight.

The western region of Bay of Bengal (BoB) is of high importance because of its variability in Western Boundary Current (WBC) pattern, numerous eddy genesis and biogeochemical activities. The WBC is northward in pre–Indian Summer Monsoon (ISM) season and southward in post–ISM season with the presence of anticyclonic and cyclonic gyres respectively. During ISM, the western BoB is dominated by various cyclonic and anticyclonic eddies with discontinuous WBC. The seasonally reversing wind pattern also favors the variation in the circulation pattern of the bay. The mechanism of eddy genesis in the western BoB and their characteristics specially during ISM, when the WBC is discontinuous, is not studied well. Our study uses the Regional Ocean Modeling System (ROMS) to investigate the role of coastal Kelvin wave, which originated from the equatorial wave guide, and local wind on the mesoscale eddies in the western BoB. To better understand the forcing mechanism involved, river influx and modified wind fields are incorporated in the experiments. The simulated Kelvin wave propagation is consistent with the satellite altimetry observations. Two upwelling and two downwelling Coastal Kelvin Wave (CKW) signals are identified. First upwelling signal (UCKW1) exists from January to April whereas the second signal (UCKW2) appears in September. Two downwelling signals are seen from May to August (DCKW1) and October to December (DCKW2), respectively. Depth of 20°C isotherm (D20) shows good correlation with the remote forcing signals as well as surface wind variability. The CKW signals during pre– and post–ISM (UCKW1 and DCKW2 respectively) are dominant. The reversing weaker signals (DCKW1 and UCKW2) contribute to the WBC discontinuity during ISM. Reduction in wind fields results in weak WBC during pre– and post–ISM. Increase in wind field results in strengthening of the weaker CKW modes rather than strengthening the WBC. Average surface eddy kinetic energy along with eddy intensity, radius and lifetime are sensitive to the change in wind field. The eddies are seen to propagate clockwise (anticlockwise) in general due to decrease (increase) in wind field. The study indicates that the CKWs and the local wind have significant impact on seasonally reversing WBC, eddy genesis and their characteristics in the western BoB.

On occasion, tropical cyclones (TCs) have been shown to strengthen over land, provided that the land is warm and moist. The emergent hypothesis is that the moist surface provides sustaining latent heat flux that is reminiscent of an oceanic environment.. To test this hypothesis, numerical simulations of idealized TCs with various profiles of soil moisture availability (SMA) and surface roughness were conducted. SMA gradients are shown to have a large influence on precipitation beyond uniform SMA. The sensitivity of accumulated precipitation to SMA is larger with enhanced friction. The maximum wind speed is more sensitive to differences in SMA under lower surface roughness. Results provide a foundation for refining emerging theories about land –atmosphere interactions with landfalling tropical systems. Additionally, these findings may inform forecasters to consider land-surface conditions when assessing intensity trends for landfalling tropical cyclones, particularly since assimilation of soil moisture and surface characteristics can yield differing impacts.

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.

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.

Southern Alaska is a collage of fault-bounded accreted terranes. The deformation history of these crustal blocks and geometric history of the bounding faults reflect both inherited features and subsequent convergent margin events. Multiple dense (<20-km spacing) arrays of broadband seismometers across southern Alaska has previously allowed for imaging of crustal structure across the region using various seismic imaging methods. Here, we employ S-toP receiver functions to investigate the crustal structure of southern Alaska for signals of dynamic tectonic activity. The subduction zone plate interface and subducting slab Moho are imaged dipping at shallow (<60-km) depths across the southernmost part of the subduction zone. Along two different transects, an inboard-dipping (~15°) boundary is imaged intersecting the trace of the Border Ranges Fault at the surface that we infer represents an unrotated inboard-dipping paleosubduction (Mesozoic) interface. This observation is combined with previous seismic imaging along both the Border Ranges Fault and the next seaward terrane-bounding fault-the Contact Fault-to buttress a known history of convergent tectonics that varies along the margin. Along with large (>10-km) crustal thickness offsets imaged across both the Denali Fault system and the Manuscript in press at upcoming AGU Monograph Tectonics and Seismicity of Alaska and Western Canada: Earthscope and Beyond 2 Eureka Creek Fault, this feature supports a Mesozoic-to-Present inboard-dipping (east and northward) subduction polarity in the region. Additionally, the Sp CCP volume reveals a 100-km x 50-km sized positive velocity gradient with depth (PVG) at ~25-km depth beneath the Copper River Basin, which we interpret as the top of a region of active underplating and/or intrusion of basaltic magmatism into the lower crust. This feature may be related to the generation of a new Wrangell Volcanic Field volcano, resulting from the underlying tear in the subducting slab.

Gas hydrates have been reported to exist in marine sediments from various parts of the world ocean. The hydrates start decomposing soon after recovery of the sediments through coring operations due to changes in ambient pressure and temperature. This decomposition leads to changes in sedimentary structures, and thus complicates physical property related measurements of the sediments by conventional methods. In this study, we used a medical X-ray CT scanner to quickly scan the recovered cores, and then used raw data from the CT, and thus avoided image processing steps, to estimate porosity and density of the sediments. The raw data were in terms of CT numbers, which were obtained by drawing a circular region of interest (ROI) to cover most of the sediments visible in a cross section XCT image of the sediments. The data were weighted for relative contribution of liquid and solid in sediments before estimating porosity. On the other hand, density was estimated by using an average CT number that was automatically calculated by the Osirix software used for drawing the ROI on an XCT image, and by using a calibration equation based on a set of standards. Although some uncertainty in estimation of relative volumes of solid, liquid and gas could not be avoided, the results obtained by this new procedure were in good agreement with those obtained by conventional methods. Since porosity and density estimates by the new procedure can be made in a matter of minutes after core recovery, it can guide progress of coring operation and further processing of hydrate-bearing sediments.

An ensemble of forecasts is necessary to identify the uncertainty in predicting a non-linear system like climate. While ensemble averages are often used to represent the mean state and diagnose physical mechanisms, they can lead to information loss and inaccurate assessment of the model’s characteristics. We highlight an intriguing case in the seasonal hindcasts of the Climate Forecast System version-2. While all ensemble members often agree on the sign of predicted El Nino Southern Oscillation (ENSO) for a particular season, non-ENSO climate forcings, although present in individual members, are disparate. As a result, an ensemble mean retains ENSO anomalies while diminishing non-ENSO signals. This difference between ENSO and non-ENSO predictions and a more decisive impact of ENSO on seasonal climate increases the ensemble mean ENSO-Indian Summer Monsoon Rainfall correlation. Thus, a model’s teleconnection skills, which often help interpret physical mechanisms, should be studied using individual members rather than ensemble averages.

The root system of a plant provides vital functions including resource uptake, storage, and anchorage in soil. The uptake of macro-nutrients like nitrogen (N), phosphorus (P), potassium (K), and sulphur (S) from the soil is critical for plant growth and development. Small signaling peptide (SSP) hormones are best known as potent regulators of plant growth and development with a few also known to have specialized roles in macronutrient utilization. Here we describe a high throughput phenotyping platform for testing SSP effects on root uptake of multiple nutrients. The SSP, CEP1 (C-TERMINALLY ENCODED PEPTIDE) enhanced nitrate uptake rate per unit root length in Medicago trun-catula plants deprived of N in the high-affinity transport range. Single structural variants of M. truncatula and Arabidopsis thaliana specific CEP1 peptides, MtCEP1D1:hyp4,11 and AtCEP1:hyp4,11, enhanced uptake not only of nitrate, but also phosphate and sulfate in both model plant species. Transcriptome analysis of Medicago roots treated with different MtCEP1 encoded peptide domains revealed that hundreds of genes respond to these peptides, including several nitrate transporters and a sulfate transporter that may mediate the uptake of these macronutrients downstream of CEP1 signaling. Likewise, several putative sig-naling pathway genes including LEUCINE-RICH REPEAT RECPTOR-LIKE KINASES and Myb domain containing transcription factors, were induced in 1

Modern bedrock streams and rivers emerged in the Midwestern United States in response to glacial outwash floods ~19,000 years ago and continued to adjust to new drainage patterns over the landscape formed by Wisconsin glaciation events. The Illinois River and corresponding tributaries form a fascinating landscape with canyons carved 50-200 m deep into the St. Peter Sandstone. These geomorphic features are preserved and open to visitors as Starved Rock State Park in Central Illinois. Free access to the state parks and close proximity to the large Chicago metropolitan area result in frequent visitation to this natural attraction. Recently, the rates of natural stream incision appear to be overprinted by direct human influences on the landscape. The St. Peter Sandstone is a weakly cemented, extremely friable quartz arenite, making it susceptible to human disturbance and rapid natural erosion. This study explores how quickly present day changes occur along bedrock surfaces using photogrammetric Structure-from-Motion (SfM). Repeat photographic data were collected once per month from two sites within the park where canyon walls contained human carvings that served as reference features to align photos and monitor change. Photos were merged in Agisoft PhotoScan Pro to construct 3D point clouds and imported into CloudCompare to measure changes to rock surfaces between monthly visits. The photogrammetric SfM analysis detected measurable change on a centimeter to millimeter scale. Changes along footpaths were observed when visitor traffic was high. During winter months when visitor traffic decreased, rainfall and snowmelt runoff primarily caused mobilization and removal of loose sediments covering bedrock surfaces. Bedrock thin sections from each site were studied to assess the influence of cement on erosion rates. Lower cement concentrations were observed at the outcrop site with the greatest measured surface change. Changes detected with SfM analyses demonstrate that human interactions can influence erosion processes in a short time. While both natural and human caused changes occurred on bedrock surfaces, precipitation created greater measurable differences.

Flood risk assessment and the design of protection measures often require the estimation of high water levels of a given probability of exceedance, i.e. design flood levels. The common approach for the estimation of design flood levels has typically three main steps. First, direct measurements of annual maximum water levels in a river cross-section are converted into annual maximum flows by using a rating curve. Second, a probability distribution function is fitted to these annual maximum flows to derive discharges of a desired probability of exceedance, i.e. design peak flows. Third, a hydraulic model is applied to derive the corresponding design flood levels. Each of the three steps is associated with significant uncertainties, affecting the accuracy of estimated design flood levels. In this study, we compare this common approach with an alternative one based on the statistical analysis of time series of annual maximum water levels. The rationale behind this study is that high water levels are directly measured and often come along with higher precision and accuracy than peak flows. While the direct use of high water levels is typical in coastal flood hazard and risk assessment, the potential of this approach in the context of river flooding has not been sufficiently explored. In this study we compare the common approach with an alternative approach based on statistical analysis of annual maximum water levels.

Fine sediment dynamics is an important issue in alpine rivers since it impacts both dam management (decrease of the reservoir capacity, flushing strategy) and river management (interaction between fine sediment and vegetation, gravel bar stabilisation, flood risk). Suspended Particle Matter (SPM) is generally assumed to be transported as washload although significant exchanges with the river bed have been detected in several cases. As a consequence but also due to the variable SPM sources and differences in the discharge and sediment wave velocities, one can often observe a hysteresis behaviour during hydrological events that evolves spatially along the system. In this study, we will present results from a network of hydro-sedimentary stations (measuring both water discharge and sediment concentration) along a reach of 120 km starting from the Arvan River at its confluence and the Arc and Isère rivers, that is part of the ZABR (or Rhône Basin Long Term Environmental Research Observatory). The SPM dynamics is analysed for different types of events (large flood, spring flood, flushing event, debris flow). In particular, we focus on the potential of erosion or deposition between each station by calculating the total SPM flux during each event at each station as well as the hysteresis behaviour using a hysteresis index. The evolution of these parameters is related to input parameters such as discharge and sources and grain size characteristics of the suspension. Indeed, most observed sediment exchanges (erosion or deposition) occur on the gravel bars when inundated, and depend on settling characteristics of the SPM. Also the experimental site provides some useful data for estimating advection and dispersion characteristics of various SPM events that could be used to validate numerical models.

Global-scale Observations of Limb and Disk (GOLD) disk measurements of far ultraviolet molecular nitrogen band emissions are used to retrieve temperatures (T$_{disk}$), which are representative of lower thermospheric altitudes. The present investigation studies the response of lower thermospheric temperatures to geomagnetic activities of varying magnitudes. In this study, it has been observed that T$_{disk}$ increases over all latitudes in response to enhanced geomagnetic activity. The increase in temperature is proportional to the strength of the geomagnetic activity and is greater at higher latitudes. Temperature enhancements vary from 10s to 100s of Kelvins from low- to mid-latitudes. Local time behavior shows that pre-noon enhancements in temperatures, during relatively stronger geomagnetic activities, are greater compared to afternoon, which can be attributed to the combined action of daytime dynamics and geomagnetic forcing. This study thus demonstrates the utility of GOLD T$_{disk}$ measurements investigating the effects of dynamical and external forcings in the thermosphere.

Sorghum is an important cereal crop grown across the globe for its grain and biomass value. It can also efficiently use resources such as nitrogen, and multiple varieties that are nitrogen-use and light-capture efficient are constantly being developed. This study focuses on using the spectral signature of sorghum varieties to predict flowering days, which could be used as a proxy for plants’ growth/productivity and development trends, thus helping breeders make quick decisions about what varieties to move to the next stage. Multiple sorghum varieties from the sorghum association panel were planted in a replicate-design field experiment with the variable supply of nitrogen. The flowering days were monitored and recorded. The hyperspectral reflectance data were collected and used to build a sorghum flowering days predictive model. Although regression models such as partial least square have been used to predict plants’ phenotypes, the non-parametric ensemble machine learning model turned out to perform better on flowering days with an accurate model up to 5 days.

Fire, as a strong disturbance type, can exert significant impacts on biosphere, hydrosphere, geosphere, cryosphere, atmosphere and human society. It can inherently trigger both critical transitions in ecosystems and dramatic changes in landscapes, which can be detected as alternations in land cover types. However, the general changing patterns and possible influential factors of post-fire landscape change remain largely unclear on a global scale. Obtaining such knowledge is of great value in advancing the understanding of fire ecology and promoting sustainable fire management. Here, we combined the satellite observations of long-term land cover and burned areas to assess the global post-fire landscape change patterns from 2005 to 2015. The results showed that the identified areas with post-fire landscape change accounted for approximately 0.36–0.74% of the annual global burned areas during the study period and were most common in countries such as Brazil, Argentina, and the D.R. Congo. The most common landscape change types were “forest-to-agriculture” (31.93%), “forest-to-shrubland” (26.23%) and “agriculture-to-forest” (18.74%) in 2005, 2010 and 2015, respectively. In addition, the conversion between agriculture and forest as well as the shrubland and forest after fire were found to be bidirectional. After assessing 14 fire-related climatic, topographic, ecological and socioeconomic factors that could potentially influence the post-fire landscape change occurrence probability, burned area size and vegetation cover diversity were identified as the two strongest predictors, followed by aspect, fire intensity and slope. Our results provide a global overview of post-fire landscape change patterns and offer guidance for making sustainable fire management policies.