Deep tectonic tremors occur in the Nankai subduction zone, defining a belt-like zone with a width of a few ten km located at depths between 30 and 55 km along upper surface of the subducting Philippine sea slab. We interpret the geometry of the tremor belt based on temperature calculations. Time evolution of temperature is calculated using a 3-D heat conduction assuming constant geometry of the slab and the present-day plate convergence velocity. The results show that the tremors occur along the 450°C isotherm along the slab surface where the mantle wedge can be non-convective and already well-serpentinized. Two gaps of the tremor belts are explained by different mechanisms. The Ise gap is where the hanging wall is not mantle wedge but crust. The Kii Gap is not a gap orthogonal to the plate convergence direction, but only appears to be a gap because the isotherm of the plate surface steps in the plate convergence direction. The tremors can be caused by high pore-fluid pressure conditions due to aqueous fluids released by dehydration reactions in blueschist-facies oceanic crust to form eclogite facies. The depth of the tremor belt corresponds to that of decoupled, non-convective mantle wedge. Since the temperature and pressure are within the serpentinite stable condition, the released fluid would normally be absorbed by serpentinization of the mantle wedge peridotite. However, since the non-convective mantle wedge is already well serpentinized from exposure to previously released fluids, the newly released fluid is not absorbed and increases the pore pressure.

Subglacial seismicity presents the opportunity to monitor inaccessibleglacial beds at the epicentral location and time. Glaciers can beunderlain by rock or till, a first order control on bed mechanics.Velocity-weakening, necessary for unstable slip, has been shown for eachbed type, but is much stronger and evolves over more than an order ofmagnitude longer distances for till beds. Utilizing a de-stiffeneddouble direct shear apparatus, we found conditions for instability atfreezing temperatures and high slip rates for both bed types. Duringstick-slip stress-drops, we recorded acoustic emissions withpiezoelectric transducers frozen into the ice. The two populations ofevent waveforms appear visually similar and overlap in their statisticalfeatures. We implemented a suite of supervised machine learningalgorithms to classify the bed type of recorded waveforms and spectra,with prediction accuracy between 65% - 80%. The Random ForestClassifier is interpretable, showing the importance of initialoscillation peaks and higher frequency energy. Till beds have generallyhigher friction and resulting stress-drops, with more impulsive firstarrivals and more high frequency content compared to rock emissions, butrock beds can produce many till-like events. Seismic signatures couldenhance interpretation of bed conditions and mechanics from subglacialseismicity.

Wind-excited near-inertial waves (NIWs) rapidly propagate towards the equator on a β-plane. In this letter, we model the evolution of NIWs under the β-effect by imposing initial zonal velocity in the mixed layer. We varied the background stratification strength and observed the changes in wave characteristics and also quantified the decay rate of the mixed layer kinetic energy. Varying the interior stratification strength leads to higher vertical modes and faster decay of mixed layer kinetic energy. We observed a strong double-inertial frequency signal in the FFT spectrum, which could result from the nonlinear interactions between near-inertial waves. The faster decay of mixed layer kinetic energy at higher stratifications is due to the increasing vertical wave flux at the base of the mixed layer. We also observed strong shear at the base of the mixed layer with $Ri_g$ values dropping below 0.25 in this region.

It was recently proposed (Franco et al., Nature 2021) that methanediol (MD, HOCH2OH ) formed by hydration of formaldehyde in liquid cloud droplets is outgassed to a larger extent than previously estimated, and reacts in the gas phase with the hydroxyl radical (OH), leading to formic acid (HCOOH). Whereas the resulting global production of formic acid is greatly dependent on poorly constrained parameters, such as the Henry’s law constant (HLC) of methanediol and the rate constant of its reaction with OH, Franco et al. suggest, based on global model calculations and on newly conducted chamber experiments (for the rate constant) and on statistical prediction methods (for the HLC), that this mechanism explains the large “missing source” of HCOOH in the atmosphere (e.g. Stavrakou et al. 2012). If true, this finding would be of tremendous importance for our understanding of the biogeochemical cycling of oxygenated organic compounds. For this reason, it is of utmost importance to double check the validity of thehypotheses and parameterizations behind this assessment. Here we examine two critical aspects of this determination: the HLC (taken equal to either 10^4 or 10^6 M atm^-1 in model simulations by Franco et al.) and the rate of the MD+OH reaction (taken equal to 7.5 × 10^12 cm^3 s^-1 ). The representation of chemical processing in liquid clouds in global models is also briefly discussed. Plausible ranges for those parameters are proposed , and causes of uncertainty are discussed . The potential consequences for the resulting production of formic acid are briefly explored.

Beaches are thought to contain a large part of plastics entering the marine environment. Here, they can cause harm to biota, and can potentially break down into smaller fragments over time. To protect vulnerable beaches, it is advantageous to have information on the sources of this plastic. Here, we develop a universally applicable Bayesian framework to map sources for plastic arriving on a specific beach, applied to a beach in southwest the Netherlands. In this framework, we combine Lagrangian backtracking simulations of drifting particles with data of plastic input from coastlines, rivers and fishing activity. This facilitates spatiotemporal source attribution for plastic arriving at the specified beach. We show that the main sources are the east coast of the UK, the Dutch coast, the English channel (fisheries) and the Thames, Seine, Rhine and Trieux (rivers). We also show that particle age is a major uncertainty in source attribution using backtracking.

A high-resolution 3-D crustal and upper-mantle shear-wave velocity model of Northeast China is established by joint inversion of receiver functions and Rayleigh wave group velocities. The teleseismic data for obtaining receiver functions are collected from 107 CEA permanent sites and 118 NECESSArray portable stations. Rayleigh wave dispersion measurements are extracted from an independent tomographic study. Our model exhibits unprecedented detail in S-velocity structure. Particularly, we discover a low S-velocity belt at 7.5-12.5 km depth covering entire Northeast China (except the Songliao basin), which is attributed to a combination of anomalous temperature, partial melts and fluid-filled faults related to Cenozoic volcanism. Localized crustal fast S-velocity anomaly under the Songliao basin is imaged and interpreted as late-Mesozoic mafic intrusions. In the upper mantle, our model confirms the presence of low velocity zones below the Changbai mountains and Lesser Xing’an mountain range, which agree with models invoking sub-lithospheric mantle upwellings. We observe a positive S-velocity anomaly at 50-90 km depth under the Songliao basin, which may represent a depleted and more refractory lithosphere inducing the absence of Cenozoic volcanism. Additionally, the average lithosphere-asthenosphere boundary depth increases from 50-70 km under the Changbai mountains to 100 km below the Songliao basin, and exceeds 125 km beneath the Greater Xing’an mountain range in the west. Furthermore, compared with other Precambrian lithospheres, Northeast China likely has a rather warm crust (~480-970 °C) and a slightly warm uppermost mantle (~1200 °C), probably associated with active volcanism. The Songliao basin possesses a moderately warm uppermost mantle (~1080 °C).

We present PetroChron Antarctica, a new relational database including petrological, geochemical and geochronological datasets along with computed rock properties from geological samples across Antarctica. The database contains whole-rock geochemistry with major/trace element and isotope analyses, geochronology from multiple isotopic systems and minerals for given samples, as well as an internally consistent rock classification based on chemical analysis and derived rock properties (i.e., chemical indices, density, p-velocity and heat production). A broad range of meta-information such as geographic location, petrology, mineralogy, age statistics and significance are also included and can be used to filter and assess the quality of the data. Currently, the database contains 11,559 entries representing 10,056 unique samples with varying amounts of geochemical and geochronological data. The distribution of rock types is dominated by mafic (36%) and felsic (33%) compositions, followed by intermediate (22%) and ultramafic (9%) compositions. Maps of age distribution and isotopic composition highlight major episodes of tectonic and thermal activity that define well known crustal heterogeneities across the continent, with the oldest rocks preserved in East Antarctica and more juvenile lithosphere characterising West Antarctica. PetroChron Antarctica allows spatial and temporal variations in geology to be explored at the continental scale and integrated with other Earth-cryosphere-biosphere-ocean datasets. As such, it provides a powerful resource ready for diverse applications including plate tectonic reconstructions, geological/geophysical maps, geothermal heat flow models, lithospheric and glacial isostasy, geomorphology, ice sheet reconstructions, biodiversity evolution, and oceanography.

The high temperature of the corona, 2 x 106 K, recognized by the presence of highly ionized atoms, such as FeXIV, is caused by the ionization of accelerated electrons by a double layer which tends to form along magnetic field-aligned currents; ions could also be accelerated. It is shown that electric currents of intensity of about 10 mA, consisting of 10 Kev electrons, accelerated by the double layer along magnetic field-aligned currents, could provide the ionization rate of 6.2 x 109/cm3s in the middle level of the corona, where the density of hydrogen atoms is about 1010/cm3; the ionization is thus about 60 %, as is known. A dynamo process of the photosphere may be responsible for generating the field-aligned currents. A double layer might be formed in a prominent discontinuity of the electron density at about the height of 2 x 103 km, where the above estimates are made.

In this paper, THz channel propagation characterization and modeling for a desktop environment is presented. Path loss and PDPs measured on the motherboard in both free-space and desktop resemble metal cavity are compared. To characterize the large scale fading of the channel, mean path loss model as a function of antenna height is proposed by treating the motherboard desktop environment as a partially dielectric filled resonant cavity. Good match between the measured and modeled path loss proves the model validity. For the shadowing across the frequency, Gamma-mixture model is applied to characterize the oscillations of in-cavity measured path loss. Results show that with proper choice of the number of mixed Gamma distributions $k$, the goodness of fit between the model and the probability density function (PDF) of path loss oscillations can reach more than 97\%. Multipath components are characterized by cluster-based channel modeling. Modifications were made on the conventional S-V model to accurately characterize the channel by rewriting the cluster power decay with step-wise functions and each sub-function is expressed exponentially in dB, and the ray power decay with power law approach. A good agreement can be observed between the model and the measurements.

The carbonate chemistry of Arctic Ocean seafloor and its vulnerability to ocean acidification remains poorly explored. This limits our ability to quantify how biogeochemical processes and bottom water conditions shape sedimentary carbonate chemistry, and to predict how climate change may affect such biogeochemical processes at the Arctic Ocean seafloor. Here, we employ an integrated model assessment that explicitly resolves benthic pH and carbonate chemistry along a S—N transect in the Barents Sea. We identify the main drivers of observed carbonate dynamics and estimate benthic fluxes of dissolved inorganic carbon and alkalinity to the Arctic Ocean. We explore how bottom water conditions and in-situ organic matter degradation shape these processes and show that organic matter transformation strongly impacts pH and carbonate saturation (Ω) variations. Aerobic organic matter degradation drives a negative pH shift (pH < 7.6) in the upper 2—5 cm, producing Ω < 1. This causes shallow carbonate dissolution, buffering porewater pH to around 8.0. Organic matter degradation via metal oxide (Mn/Fe) reduction pathways further increases pH and carbonate saturation state. At the northern stations, where Ω > 5 at around 10–25 cm, model simulations result in authigenic carbonate precipitation. Furthermore, benthic fluxes of dissolved inorganic carbon (12.5—59.5 µmol cm−2 yr−1) and alkalinity (11.3—63.2 µmol cm−2 yr−1) are 2—3-fold greater in the northern sites due to greater carbonate dissolution. Our assessment is of significant relevance to predict how changes in the Arctic Ocean may shift carbon burial and pH buffering into the next century.

Convective turbulence driven by gravitational instability is a fundamental mixing mechanism in geophysical flows, but in situ estimation of its characteristics is obscured by the background flows and the relatively slow temporal scales. We present characteristics of the full Reynolds tensor from a convective surface boundary layer of an ice-covered lake. The results were obtained by using an original method of measuring the full set of turbulent stresses by a combined use of two ADCPs. The strong horizontal shear stress was revealed as a characteristic feature of free convection differing from the “conventional” turbulent boundary flows. The ratio of normal stresses along vertical and horizontal axes remained below 1/4, suggesting strongly anisotropic character of turbulence. The vertical r.m.s. velocity fluctuations obeyed the buoyancy flux scaling with the coefficient of 1/3, which is at lower boundary of the previously reported values.

Using borehole strainmeters, we detected a 13-day long slow slip event on the Longitudinal Valley Fault, Taiwan. It is located between 8 to 15 km depth and has an equivalent moment magnitude of 5.5. The slow event has likely been promoted by the significant Coulomb stress changes (∼ + 1 MPa) imparted by a combination of coseismic and postseismic slip of the M w 6.8 Chengkung earthquake. Besides, insignificant coseismic slip is observed in the slow event region, suggesting that the latter could have acted as a barrier during the Chengkung earthquake. We also found a spatiotemporal correlation between the slow event and a cluster of repeating microearthquakes, suggesting aseismic slip as a possible driven mechanism of repeating ruptures. These results highlight the complex interplay between seismic and aseismic processes along the fault.

We use GPS observations to investigate the magnitude and spatial distribution of vertical coseismic and postseismic deformation of the Australian continent and compare these with elastic and viscoelastic model outputs. We observe and model surface deformation in Australia caused by six recent large far-field events: 2004 Mw 8.1 Macquarie Ridge, 2004 Mw 9.3 Sumatra-Anderman, 2005 Mw 8.6 in northern Sumatra, the 2007 series of Mw 8.5 and 7.9 in southern Sumatra, two events in 2012 of Mw 8.6 and 8.2 in northern Sumatra, and the 2009 Mw 7.8 south of New Zealand. Observed vertical coseismic deformation reaches 3 mm, with the magnitude varying spatially and by earthquake in broad agreement with modelling of coseismic deformation. Postseismic deformation is observed in all three coordinate components at Australian GPS sites nearest to these earthquakes, with deformations reaching several mm/yr in the vertical over multiple years. In particular, the Sumatran sequence produces observed subsidence in north-western Australia of up to 4 mm/yr over 2004.9-2010.0 where predictions based on one-dimensional viscoelastic Earth models replicate the subsidence but underpredict the vertical rate by a factor of two. Across all earthquakes, the models often fit one or two coordinate components of the observations, but rarely all three. Unmodeled lateral rheological structure likely contributes to this given the difference between the oceanic location of the earthquakes and the Australian continental setting of the GPS sites. The magnitude and spatial extent of these coseismic and postseismic deformations warrant their consideration in future updates of the geodetic terrestrial reference frame.

Flux transfer events (FTEs), as flux ropes (FRs), are considered key agents for solar wind energy to enter the terrestrial magnetosphere. Recent observations identify entangled flux tubes that collide and pull against each other. Reconnection occurs to disentangle and produce a new pair of flux ropes with different connectivity. In this paper, we examine how such an entanglement process evolve in time by comparing 17 entanglements observed by the Magnetospheric Multiscale (MMS) mission. The By-dominated interplanetary magnetic field (IMF) distribution of the entangled tubes agrees with previous findings. We have identified three evolutionary stages characterized by the magnetic field and pressure enhancement. Our study confirms the flux rope nature of these events and explains how a disparate pair of ropes is formed from two entangled flux tubes, each initially connected to a different hemisphere of the magnetosphere.

High energy electrons observed in the magnetosheath must be accelerated by some mech- anism that is as yet undetermined. We present observations of high-energy electrons trapped in diamagnetic cavities as measured by Magnetospheric Multiscale from 2015-2018. The observations support the notion of local acceleration in the reconnection quasi-potential as many of events show particles with pitch angles that are increasingly closer to 90 de- grees with increasing energy. It is suggested that these particles can end up in the loss cone and be transported to the magnetosheath. We also characterize each diamagnetic cavity as formed due to low- or high-latitude reconnection based on prevailing solar wind conditions. The character of the ions in the diamagnetic cavity is only briefly mentioned as their properties warrant another stand-alone investigation.

Rooting depth is an ecosystem trait that determines the extent of soil development and carbon cycling. Recent hypotheses propose that human-induced changes to Earth’s biogeochemical cycles propagate deeply due to rooting depth changes from agricultural and climate-induced land cover changes. Yet, the lack of a global-scale quantification of rooting depth responses to human activity limits knowledge of hydrosphere-atmosphere-lithosphere feedbacks in the Anthropocene. Here we use land cover datasets to demonstrate that global rooting depths have become shallower in the Anthropocene, and are likely to become yet shallower this century. Specifically, globally averaged depths above which 99% of root biomass occurs (D99) are 8.7%, or 16 cm, shallower relative to those for potential vegetation. This net shallowing results from agricultural expansion truncating D99 by 82 cm, and woody encroachment linked to anthropogenic climate change extending D99 by 65 cm. Projected land cover scenarios in 2100 suggest further D99 shallowing of 63 to 72 cm, exceeding that experienced to date and suggesting that the pace of root shallowing will quicken in the coming century. Losses of Earth’s deepest roots—soil-forming agents—suggest unanticipated changes in fluxes of water, solutes, and carbon. Our work constrains rooting depth distributions for global models, allowing the land modeling community to explore cascading effects of rooting depth changes on water, carbon, and energy dynamics, and can guide design of field-based efforts to quantify deep anthropogenic influences. Understanding human influence on biota’s reach into Earth’s subsurface will improve predictions of interactive functioning of the biosphere, lithosphere, and hydrosphere.

Probing the flow permeability of porous media with elastic waves is a formidable challenge, also because the wave-induced oscillatory motion renders the permeability frequency dependent. Existing theoretical models for such a dynamic permeability assume that the frequency dependence is primarily controlled by a single characteristic length scale of the pore space. However, the fact that in most natural porous media there exists a distinct range of pore sizes is ignored. To overcome this limitation, we develop a dynamic permeability model that explicitly incorporates the pore size distribution. We show that the pore size distribution has a first-order effect on the dynamic permeability. Since the pore size distribution is measurable from techniques such as nuclear magnetic resonance, the results indicate the possibility to jointly use remote-sensing technologies for improved geomaterial characterization and optimized permeability manipulation of manufactured porous media.

Erosion, transport, and deposition of a river-bed has attracted attentions from various disciplines. To understand those issues, bed shear stress should be evaluated first. However, calculating bed shear stress with existing formulas have certain limitations because uniform and/or gradually-varied flow was assumed in their studies, which is hardly found in an actual river. Therefore, direct applying them into three-dimensional complex flow field, such as flow around a bridge obstruction or a large-rock, is questionable. Thus, laboratory experiment was conducted in a flume and the results were used to suggest a method of bed shear stress estimation in the complex flow field. To generate the complex flow field, three different width of obstruction was constructed and installed in one side of the flume. Water depth, velocities, and turbulence intensities were measured, and the measurements were used as input variables of four different widely used existing shear stress formulas for their evaluation. Then, the effects of local turbulence on the shear stress were discussed in terms of Reynolds stress and turbulent kinetic energy (TKE) measured under a wide range of flow variables. Based on the findings, bed shear stress can be estimated with an empirical correction factor for the local turbulence around the obstruction where elevated region of bed shear stress is found, and the experimental result shows that the correction factor is function of the value of flow contraction ratio. The results are expected to be a useful outcome to understand the mechanism of geomorphological change under rapidly-varied non-uniform flow.