As high-resolution global coverage cannot easily be achieved by direct bathymetry, the use of gravity data is an alternative method to predict seafloor topography. Currently, the commonly used algorithms for predicting seafloor topography are mainly based on the approximate linear relationship between topography and gravity anomaly. In actual application, it is also necessary to process the corresponding data according to some empirical methods, which can cause uncertainty in predicting topography. In this paper, we established analytical observation equations between the gravity anomaly and topography, and obtained the corresponding iterative solving method based on the least square method after linearizing the equations. Furthermore, the regularization method and piecewise bilinear interpolation function are introduced into the observation equations to effectively suppress the high-frequency effect of the boundary sea region and the low-frequency effect of the far sea region. Finally, the seafloor topography beneath a sea region (117.25°-118.25° E, 13.85°-14.85° N) in the South China Sea is predicted as an actual application, where gravity anomaly data of the study area with a resolution of 1′×1′ is from the DTU17 model. Comparing the prediction results with the data of ship soundings from the National Geophysical Data Center (NGDC), the root-mean-square (RMS) error and relative error can be up to 127.4 m and approximately 3.4%, respectively.
Volcanic glass and its mixture with smectite are commonly observed in shallow parts of subduction zones. As volcanic glass layers often act as a glide plane to induce mass transportation such as submarine landslides, and because its alteration product, smectite, is one of the frictionally weakest geological materials, the frictional characteristics of volcanic glass-smectite mixtures are important for fault slip behavior in shallow parts of subduction zones. We performed a series of friction experiments on volcanic glass-smectite mixtures with different smectite contents at various velocity conditions from 10 μm/s to 1 m/s under an effective normal stress of 5 MPa and pore pressure of 10 MPa. In general, friction coefficients negatively depend on the smectite content at any velocity tested. We found that samples with smectite contents of 15-30 % showed a drastic slip-weakening behavior at intermediate velocities of 1-3 mm/s with a characteristic slip displacement of ~0.1 m. Finite element method modeling shows that thermal pressurization does not contribute to the observed weakening behavior. We propose that gouge fluidization or compaction-induced pore pressure increase may be the cause of the weakening. The slip-weakening behavior at intermediate velocities enlarges a critical nucleation length for frictional instability to 1-30 km, or prevent acceleration to seismic slip velocities. Therefore, gouges with minor amount of clay, such as subducting volcanic ash layers, may contribute to the occurrence of the at shallow depths in subduction zones.
We use seismic ambient noise correlation and coda wave interferometry to estimate velocity variations at high temporal resolution, during the pre-eruptive period and the onset of the 2018 eruption of Kilauea volcano. A progressive velocity increase is observed from March to the end of April. It is followed by rapid decrease starting a few days before the onset of the East Rift Zone (ERZ) eruption and then by sharp velocity drop when the eruption started. The change of trend from velocity increase to decrease is progressively delayed by a few days from the summit caldera toward the ERZ. The location of the velocity perturbations shows a migration of the sources of velocity changes from the summit caldera toward the ERZ before the eruption. Using a model of pressure source, we show that the simultaneous caldera inflation and velocity increase probably result from an anisotropic distribution of fault and crack orientations. The velocity decrease could be due to damaging processes above the shallow reservoir and to plastic deformations around the caldera. We introduce a forward model of rock damage associated with the volcano-tectonic seismicity to calculate the velocity decrease. The good agreement between the calculated and the observed velocity variations shows that a large part of the velocity decrease results from damage of the medium. The delayed onsets of velocity decrease and the source migration of velocity perturbations are probably related to progressive fault openings in the Southern and Eastern parts of the caldera and to magma transfer toward the ERZ.
The Paleo-Tethys and Panthalassa are two major oceans that witnessed the end-Permian mass extinction, and they have been suggested to have distinct compositions, with the Paleo-Tethys Ocean euxinic, and the much larger Panthalassa Ocean being largely ventilated. Distinctions of these two once-connected oceans imply that interactions between them must have been restricted shortly before the end-Permian extinction. However, detailed geological processes for the disconnection between them along the eastern Paleo-Tethys Ocean due to the collision of North and South China, are still unclear. Previous geochronological studies on eclogite facies rocks in the Dabie–Sulu orogenic belt, which are the metamorphic products of the collision between North and South China, have yielded mainly Triassic metamorphic ages. Nonetheless, new Permian metamorphic ages are identified from southeastern North China, northern Dabie, and the Permo–Triassic intracontinental orogen of South China, which may collectively closely associate this major tectonic event with the end-Permian extinction. New age dating results, as well as a synthesis of recent studies on metamorphic rocks, show that the onset of the collisional orogenesis dates back to the Middle Permian (270–252 Ma). We thereby provide a new tectonic model for the major continents of East Asia, in which the initial collision between North and South China during the Middle Permian critically isolated the Paleo-Tethys Ocean from the Panthalassa Ocean, facilitating the oceanographic transition of the once fossiliferous Paleo-Tethys from a life-giving nutrient-rich ocean into a euxinic death trap, thereby serving as prelude to the end-Permian extinction.
We present a metric for detecting clouds in auroral all-sky images based on single-wavelength keograms made with a collocated meridian spectrograph. The coefficient of variation, the ratio of the sample standard deviation to the sample mean taken over viewing angle, is the metric for cloud detection. After calibrating and flat-field correcting keogram data, then excluding dark sky intervals, the effectiveness of the coefficient of variation as a detector is tested compared to true conditions as determined by Advanced Very High Resolution Radiometer (AVHRR) satellite imagery of cloud cover. The cloud mask, an index of cloud cover, is selected at the corresponding nearest time and location to the site of a meridian spectrograph at Poker Flat Research Range (PFRR). We use events that are completely cloud-free or completely cloudy according to AVHRR to compute the false alarm and missed detection statistics for the coefficient of variation of the greenline 557.7 nm emission and of the redline 630.0 nm emission. For training data of the years 2014 and 2016, we find a greenline threshold of 0.51 maximizes the percent of events correctly identified at 75%. When applied to testing data of the years 2015 and 2017, the 0.51 threshold yields an accuracy of 77%. There is a relatively shallow and wide minimum of mislabeled events for thresholds spanning about 0.2 to 0.8. For the same events, the minimum is narrower for the redline, spanning roughly 0.3-0.5, with a threshold of 0.46 maximizing detector accuracy at 78-79%.
Quantifying tectonic stress magnitudes is crucial in understanding crustal deformation processes, fault geomechanics, and variable plate interface slip behaviors in subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand is characterized by along-strike variation in interface slip behavior, which may be linked to tectonic stress variations within the overriding plate. This study constrains in-situ stress magnitudes of the shallow (<3km) overriding plate of the HSM to better understand its tectonics and how they relate to larger scale subduction dynamics. Results reveal σ3: Sv ratios of 0.6-1 at depths above 650-700 m TVD and 0.92-1 below this depth interval along the HSM and SHmax: Sv ratios of 0.95-1.81 in the central HSM, and 0.95-3.12 in the southern HSM. These stress ratios suggest a prevalent thrust to strike-slip (σ1=SHmax) faulting regime across the central and southern HSM. In the central HSM, the presence of NNE-NE striking reverse faults co-existing with a modern σ1 aligned ENE-WSW (SHmax) suggests that overtime the stress state here evolved from a contractional to a strike-slip state, where the compressional direction changes from perpendicular (NW-SE) to subparallel (ENE-WSW) to the Hikurangi margin. This temporal change in stress state may be explained by forearc rotation, likely combined with development of upper plate overpressures. In the southern HSM, the modern WNW-ESE/ NW-SE σ1 (SHmax) and pre-existing NNE-NE striking reverse faults indicate that stress state remains contractional and subparallel (NW-SE) to the Hikurangi margin overtime. This may reflect the interseismic locked nature of the plate interface.
Marine Isotope Stage (MIS) 5e (130-116 ka) represents a ‘process analogue’ for future anthropogenic warming. Climate model simulations for MIS 5e have previously failed to produce Southern Ocean sea-surface temperatures (SST) and sea-ice extent reconstructed from marine sediment core proxy records. Here we compare state of the art HadGEM3 and HadCM3 simulations of Peak MIS 5e Southern Ocean summer SST and September sea-ice concentrations with the latest marine sediment core proxy data. The model outputs and proxy records show the least consistency in the regions located near the present-day Southern Ocean gyre boundaries, implying that model simulations are currently unable to fully realise changes in gyre extent and position during MIS 5e. Including Heinrich 11 meltwater forcing in Peak MIS 5e climate simulations improves the likeness to proxy data but it is clear that longer (3-4 ka) run times are required to fully test the consistency between models and data.
The Nyasa/ Malawi rift is characterized by poor magma with relatively large earthquakes. There has been a controversy as to the stress kinematics of the rift, some considering it as part of the transform fault and some considering it as a rift structure characterized by normal faulting. To review this controversy, we collect fault slip data from the central to the southern end of the rift and integrate our results with published focal mechanisms fault slip data on the rift. Results show that the central part of the rift is under radial extension whereas the southern half is under oblique NNE-SSW transtensive tectonic regime with the horizontal axis of minimum extension = 020˚. Further south, the obliquity extension rotates by about 15˚ reaching N-S with Shmin = 175˚. The level of structural penetration and intensity of faulting show that the N-S opening is more important and prominent in the south than towards the north. We also find that the faults that dip to the east and trending NW-SE are characterized by sinistral sense of movement whereas those that dip to the southwestern side are characterized by dextral sense of movements. This implies that regionally, the rift is essentially under normal faulting regime but with a significant strike –slip component – hence the obliquity kinematics. Tectonic regimes obtained from fault-slip data are related to lithospheric scale and involve both the crust and the upper mantle. Thus, the pure NNW-SSE extension related to focal mechanism data are crust deformation related events.
Perfluoroalkyl acids (PFAAs), a group of synthetic compounds associated with adverse human health impacts, are commonly found in effluent discharged from wastewater treatment facilities. When that effluent is used for irrigation, the fate of PFAAs depends strongly on vadose zone solute retention properties and loading history. The relative importance of PFAA retention factors under natural conditions remains uncertain, and the historical record of effluent PFAA concentrations is limited. Using soil cores collected from the Penn State Living Filter (irrigated with treated wastewater effluent for nearly 60 years), we evaluated PFAA transport under near-natural conditions, and estimated historical PFAA concentrations in the irrigated effluent. Total perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) masses stored in soils in 2014 were more than 450 times greater than the masses applied during the 2020 effluent irrigation. Equilibrium piston-flow transport models reproduced the observed PFOS and PFOA profiles, allowing us to estimate historical effluent PFOS and PFOA concentrations: 70-170 ng L-1 and 1000-1300 ng L-1, respectively. Estimated concentrations were comparable to concentrations measured in other wastewater effluents in the 1990s and 2000s, indicating that when interpreted with transport modeling, wastewater-irrigated soils function as integrated records of historical PFAA loading. Simulated PFOS breakthrough to groundwater occurred 50 years after the start of wastewater irrigation, while simulated PFOA breakthrough occurred after only 10 years of irrigation. Thus, while wastewater irrigation of soils facilitates retention and reduces effluent PFAA loading to surface waters, the resulting increased PFAA storage in soils potentially creates long-term sources of PFAAs to groundwater.
Estimating dissipation timeframes and contaminant mass discharge rates of dense non-aqueous phase liquids (DNAPLs) source zones is of key interest for environmental-management support. Upscaled mathematical modeling of DNAPL dissolution provides a practical approach for assimilating site characterization and downgradient monitoring data to constrain future system behavior. Yet significant uncertainties on predictions of source zone dissipation rates may arise from inadequate or inaccurate conceptual assumptions in parameterization designs. These implications were investigated through upscaled modeling, sensitivity, and uncertainty analyses of high-resolution flow-cell experiments. Sensitivity results emphasized the role of local groundwater velocity and source dimensions in mass transfer scaling by strongly influencing error with respect to DNAPL persistence and dissolution rates. Linear uncertainty analyses, facilitated by PEST ancillary software, demonstrated the worth of monitoring profiles for constraining DNAPL saturations and dispersive mass transfer rates, responsible for source zone longevity. Nonlinear analyses performed with the iterative ensemble smoother PESTPP-iES, facilitated the quantification of unbiased source dissipation uncertainties from DNAPL delineation data. Conversely, monitoring data assimilation without consideration of flow-field heterogeneity and saturation distribution along the flow path biased model predictions. Our analyses provided practical recommendations on upscaled model design to assimilate available site data and support remedial-decision making.
Reducing flood risk through improved disaster planning and risk management requires accurate and reliable estimates of flood damages. Models can provide such information by calculating the costs of flooding to exposed assets, such as buildings within a community. Computational or data constraints often lead to the construction of such models from coarse aggregated data, the effect of which is poorly understood. Through the application of a novel spatial segregation framework, we are able to show mathematically that aggregating flood grids through averaging will always introduce a systematic error in a particular direction in partially inundated regions. By applying this framework to a case study we spatially attribute these errors and demonstrate how the exposure of buildings can be an order of magnitude more sensitive to these errors than uninhabited regions. This work provides insight into, and recommendations for, upscaling grids used by flood risk models. Further, we demonstrate a positive dependence of systematic error magnitude on scale coarseness, suggesting coarse models be used with caution and greater attention be paid to issues of scale.
The impacts of climate change and increased water use for irrigation make it difficult to manage sustainable water use and food production. Sufficient research has not been conducted on how humans adapt to water risks due to climate change. One of the difficulties in considering adaptation measures is that adaptation actions in one sector conflict with the interests of other stakeholders in the basin and trade-off relationships emerge among various sectors. Here, we examined how an effective adaptation in one sector (agriculture) influences the other (water resources) by calculating the “benefits of agricultural production” and “drought risk” under current and future climate scenarios. We built a framework consisting of two process-based models of hydrology and crop science and evaluated shifting of the transplantation date as a promising measure to avoid the degradation of rice quality in Japan. Shifting the transplantation date had opposing effects on the total yield and quality of rice, with an earlier date increasing the total yield and a later date increasing the quality. Furthermore, an earlier transplantation date reduced the drought risk. Thus, in terms of the preferred adaptation options, total yield and drought were synergistic, whereas rice quality and drought were trade-offs. Our results imply that the current transplantation date has resulted from the farmers’ motivation to maximize total yield, but this motivation may change to other factors, possibly rice quality, due to climate change. Overall, this study contributes to the understanding of how interconnected systems evolve when climate or socio-economic conditions change.
Ponding at the soil surface exerts profound impacts on infiltration. However, the effects of ponding depth on infiltration, especially the development of a saturated zone below the soil surface, have not been considered in present infiltration models. A new general Green-Ampt model solution (GAMS) was derived for a one-dimensional vertical infiltration into soils under a uniform initial moisture distribution with ponding on its surface. An expression was included in the new solution for simulating the saturated layer developed below the soil surface as long as the pressure head at the surface is greater than the water-entry suction. The GAMS simulates the infiltration processes closer to the numerical solution by HYDRUS-1D than the traditional and a recently improved Green-Ampt model. Moreover, an inversion method to improve the estimates of soil hydraulic parameters from one-dimensional vertical infiltration experiments that is based on the GAMS was suggested. The effect of ponding depth (hp), initial soil moisture content, soil texture, and hydraulic soil properties (Ks, hd and n) in the saturated zone was also evaluated. The results indicate that the saturated zone developed at a much faster rate than the unsaturated zone during infiltration. Generally, a larger saturated zone was found for soils with higher initial soil moisture content, coarser texture, higher Ks values and lower hd and n. Our findings reveal that including the saturated zone in the infiltration model yields a better estimate for the soil hydraulic parameters. The proposed GAMS model can improve irrigation design and rainfall-runoff simulations.
Discharge of groundwater-derived pollutants to inland and marine coastal waters is influenced by the transport and reactive processes occurring in nearshore aquifers. The effect of shoreline change on these processes and subsequent discharge of pollutants to coastal waters is unclear. The objective of this study was to evaluate the impact of shoreline recession (landward movement of the mean shoreline) on the transport of nitrogen [N] and phosphorus [P] in a nearshore aquifer and their discharge to coastal waters. Field investigations were conducted on a permeable unconfined nearshore aquifer on Lake Huron, Canada, in years coinciding with historically low and high lake water levels. At the site, a septic system-derived nutrient-rich (N and P) groundwater plume is moving towards the lake and the mean shoreline position moved ~30 m landward between sampling years due coastal erosion and mean lake water level increase. Data indicate PO4-P fluxes to the lake were higher following shoreline recession due to shortened travel pathways. In contrast, NO3-N fluxes were governed by the specific geochemical conditions near the sediment-water interface, which are not only a function of the shoreline position. Further, findings show shoreline recession may modify mineral phases that tend to sequester pollutants (e.g., iron oxides) near the sediment-water interface and this may possibly mediate release of sediment-bound pollutants. The findings provide new insights into potential impacts of shoreline change on chemical discharge to coastal waters as needed to inform long-term water quality predictions and management.
We present a method for forecasting the foF2 and hmF2 parameters using modal decompositions from measured ionospheric electron density profiles. Our method is based on Dynamic Mode Decomposition (DMD), which provides a means of determining spatiotemporal modes from measurements alone. Our proposed extensions to DMD use wavelet decompositions that provide separation of a wide range of high-intensity, transient temporal scales in the measured data. This scale separation allows for DMD models to be fit on each scale individually, and we show that together they generate a more accurate forecast of the time-evolution of the F-layer peak. We call this method the Scale-Separated Dynamic Mode Decomposition (SSDMD). The approach is shown to produce stable modes that can be used as a time-stepping model to predict the state of foF2 and hmF2 at a high time resolution. We demonstrate the SSDMD method on data sets covering periods of high and low solar activity as well as low, mid, and high latitude locations.
Using the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere Volatile and Evolution spacecraft (MAVEN) we analyzed data from Mars Year (MY) 32, 34, and 35 to examine the He bulge during the northern winter solstice (Ls ~180-240) specifically focusing on the effects from the planet encircling dust event (PEDE-2018). He collects on the dawn/nightside winter polar hemisphere of the terrestrial planets (Earth, Mars, and Venus). The seasonal migration of the Martian He bulge has been observed and modeled (Elrod et al., 2017, Gupta et al., 2021). The MAVEN orbit precesses around Mars allowing for a variety of latitude and local time observations throughout the Martian year. MY32, 34 and 35 had the best possible opportunities to observe the He bulge during northern winter (Ls ~180-240). NGIMS observations during MY 32 and MY 35 revealed a He bulge on the nightside to dawn in alignment with modeling and previous publications. However, in MY 34, during the PEDE, the He bulge was not present indicating the PEDE directly impacted upper atmospheric circulation. Updates in modeling indicate changes in circulation and winds can cause He to shift further north and dawn-ward than MAVEN was able to observe. The temperature increases in the thermosphere on the nightside during the dust storm along with changes in gravity waves and eddy diffusion occurring during this event could account for this circulation change.
We investigate the effect of extremely rough bathymetry on energy dissipation and mixing in a coastal region characterized by small-scale seafloor features penetrating a strongly-stratified density interface of comparable vertical scale. Our data from the non-tidal Baltic Sea include shear microstructure measurements and observations from a broadband echosounder, here used to resolve the extreme variability and intermittency of stratified turbulence in the vicinity of obstacles. Scale analysis and acoustic imaging of small-scale turbulent motions suggest that the underlying mixing mechanisms are related to topographic wake eddies and, to a smaller extent, to breaking internal waves near the bathymetric features. Vertical diffusivities exceed those at a nearby reference station with smooth bathymetry by up to two orders of magnitude. Our study emphasizes the importance of rough small-scale (< 1 km) bathymetric features for energy dissipation and vertical turbulent transport in coastal areas shaped by e.g., glacial, tectonic, or volcanic processes.
Vegetation turnover time (τ) is a central ecosystem property to quantify the global vegetation carbon dynamics. However, our understanding of vegetation dynamics is hampered by the lack of long-term observations of the changes in vegetation biomass. Here we challenge the steady state assumption of τ by using annual changes in vegetation biomass that derived from remote-sensing observations. We evaluate the changes in magnitude, spatial patterns, and uncertainties in vegetation carbon turnover times from 1992 to 2016. We found that the forest ecosystem is close to a steady state at global scale, contrasting with the larger differences between τ under steady state and τ under non-steady state at the grid cell level. The observation that terrestrial ecosystems are not in a steady state locally is deemed crucial when studying vegetation dynamics and the potential response of biomass to disturbance and climatic changes.