In frontal zones, water masses that are tens of kilometers in extent with origins in the mixed layer can be identified in the pycnocline for days to months. Here, we explore the pathways and mechanisms of subduction, the process by which water from the surface mixed layer makes its way into the pycnocline, using a submesoscale-resolving numerical model of a mesoscale front. By identifying Lagrangian trajectories of water parcels that exit the mixed layer, we study the evolution of dynamical properties from a statistical standpoint. Velocity and buoyancy gradients increase as water parcels experience both mesoscale (geostrophic) and submesoscale (ageostrophic) frontogenesis and subduct beneath the mixed layer into the stratified pycnocline along isopycnals that outcrop in the mixed layer. Subduction is transient and occurs in coherent regions along the front, the spatial and temporal scales of which set the scales of the subducted water masses in the pycnocline. As a result, the tracer-derived vertical transport rate spectrum is flatter than the vertical velocity spectrum. An examination of specific subduction events reveals a range of submesoscale features that support subduction. Contrary to the forced submesoscale processes that sequester low potential vorticity (PV) anomalies in the interior, we find that PV can be elevated in subducting water masses. The rate of subduction is of similar magnitude to previous studies (~100 m/year), but the pathways that are unraveled in this study along with the Lagrangian evolution of properties on water parcels, emphasize the role of submesoscale dynamics coupled with mesoscale frontogenesis.

Near-Earth asteroids and meteoroids constitute various levels of impact danger to our planet. On the one end, billions of events associated with small-sized meteoroids have resulted in trivial effects. On the other end, the occurrences of large-sized asteroidal collisions that can cause mass extinctions and may wipe out the modern human civilization are extremely rare. In addition, large near-Earth asteroids are being monitored constantly for accurate and precise predictions of potential hazardous visits to our planet. However, small asteroids and large meteoroids can still often go under the radar and cause bolide explosions with potential of significant damage to communities on the ground. To facilitate management of bolide hazard, a number of scholarly works have been dedicated to estimation of frequencies of bolide events from a global perspective for planetary defense and mitigation. Nevertheless, few of the existing bolide frequency models were developed for local hazard management. In this presentation, the author introduces two recently developed frequency models for local management of bolide hazard. The first one, called the Dome model, computes the expected frequency of bolide explosions within a dome-shaped volume around a location. The second one, called the Coffee Cup model, is for a column-shaped volume above an area. Both models are based on empirical calibrations with historical data on energy, latitude, altitude, and frequency of bolide events. The modeling results indicate a linearly decreasing trend of frequency of bolide events from south to north latitudinally around the globe. The presented models can be applied to any location or area on Earth, including the entire surface of the planet.

The final published version of the paper is available (open-access) in the Aerosol Science & Technology JournalLow-cost sensors for the measurement of fine particulate matter mass (PM2.5) enable dense networks to increase the spatial resolution of air quality monitoring. However, these sensors are affected by environmental factors such as temperature and humidity and their effects on ambient aerosol, which must be accounted for to improve the in-field accuracy of these sensors. We conducted long-term tests of two low-cost PM2.5 sensors: Met-One NPM and PurpleAir PA-II units. We found a high level of self-consistency within each sensor type after testing 25 NPM and 9 PurpleAir units. We developed two types of corrections for the low-cost sensor measurements to better match regulatory-grade data. The first correction accounts for aerosol hygroscopic growth using particle composition and corrects for particle mass below the optical sensor size cut-point by collocation with reference Beta Attenuation Monitors (BAM). A second, fully-empirical correction uses linear or quadratic functions of environmental variables based on the same collocation dataset. The two models yielded comparable improvements over raw measurements. Sensor performance was assessed for two use cases: improving community awareness of air quality with short-term semi-quantitative comparisons of sites and providing long-term reasonably quantitative information for health impact studies. For the short-term case, both sensors provided reasonably accurate concentration information (mean absolute error of 4 µg/m3) in near-real time. For the long-term case, tested using year-long collocations at one urban background and one near-source site, error in the annual average was reduced below 1 µg/m3. Hence, these sensor scan supplement sparse networks of regulatory-grade instruments, perform high-density neighborhood-scale monitoring, and be used to better understand spatial patterns and temporal air quality trends across urban areas.

The Southern California Bight (SCB), an eastern boundary upwelling system, is impacted by global warming, acidification and deoxygetation, and receives anthropogenic nutrients from a coastal population of 20 million people. We describe the configuration, forcing, and validation of a realistic, submesoscale resolving ocean model as a tool to investigate coastal eutrophication. This modeling system represents an important achievement because it strikes a balance of capturing the forcing by U.S. Pacific Coast-wide phenomena, while representing the bathymetric features and submesoscale circulation that affect the vertical and horizontal transport of nutrients from natural and human sources. Moreover, the model allows to run simulations at timescales that approach the interannual frequencies of ocean variability, making the grand challenge of disentangling natural variability, climate change, and local anthropogenic forcing a tractable task in the near-term. The model simulation is evaluated against a broad suite of observational data throughout the SCB, showing realistic depiction of mean state and its variability with remote sensing and in situ physical-biogeochemical measurements of state variables and biogeochemical rates. The simulation reproduces the main structure of the seasonal upwelling front, the mean current patterns, the dispersion of plumes, as well as their seasonal variability. It reproduces the mean distributions of key biogeochemical and ecosystem properties. Biogeochemical rates reproduced by the model, such as primary productivity and nitrification, are also consistent with measured rates. Results of this validation exercise demonstrate the utility of fine-scale resolution modeling in support of management decisions on local anthropogenic nutrient discharges to coastal zones.

Halogen atoms affect the budget of ozone and the fate of pollutants such as hydrocarbons and mercury. Yet their sources and significances in polluted continental regions are poorly understood. Here we report the observation of unprecedented levels (averaging to 60 parts per trillion) of bromine chloride (BrCl) at a mid-latitude site in North China during winter. Widespread coal burning in rural households and a photo-assisted process were the primary source of BrCl and other bromine gases. BrCl contributed about 55% of both bromine (Br) and chlorine (Cl) atoms. The halogen atoms increased the abundance of ‘conventional’ tropospheric oxidants (OH, HO2, and RO2) by 26-73%, and enhanced oxidation of hydrocarbon by nearly a factor of two and the net ozone production by 55%. Our study reveals the significant role of reactive halogen in winter atmospheric chemistry and the deterioration of air quality in continental regions where uncontrolled coal combustion is prevalent.

We combine earthquake spectra from multiple studies to investigate whether the increase in stress drop with depth often observed in the crust is real, or an artifact of decreasing attenuation (increasing Q) with depth. In many studies, empirical path and attenuation corrections are assumed to be independent of the earthquake source depth. We test this assumption by investigating whether a realistic increase in Q with depth (as is widely observed) could remove some of the observed apparent increase in stress drop with depth. We combine event spectra, previously obtained using spectral decomposition methods, for over 50,000 earthquakes (M0 to M5) from 12 studies in California, Nevada, Kansas and Oklahoma. We find that the relative high-frequency content of the spectra systematically increases with increasing earthquake depth, at all magnitudes. By analyzing spectral ratios between large and small events as a function of source depth, we explore the relative importance of source and attenuation contributions to this observed depth dependence. Without any correction for depth-dependent attenuation, we find a systematic increase in stress drop, rupture velocity, or both, with depth, as previously observed. When we add an empirical, depth-dependent attenuation correction, the depth dependence of stress drop systematically decreases, often becoming negligible. The largest corrections are observed in regions with the largest seismic velocity increase with depth. We conclude that source parameter analyses, whether in the frequency or time domains, should not assume path terms are independent of source depth, and should more explicitly consider the effects of depth-dependent attenuation.

Millennial scale East Asian monsoon variability is closely associated with natural hazards through long-term variability in flood and drought cycles. Here we present a new East Asian summer monsoon (EASM) rainfall reconstruction from the northwest Chinese loess plateau spanning the past 650,000 years. The magnitude of millennial monsoon variability (MMV) in EASM rainfall is strongly linked to ice volume and greenhouse gas (GHG) at the 100,000-year earth-orbital eccentricity band and to GHG and summer insolation at the 23,000-year precession band. At the precession band, times of stronger insolation and increased atmospheric GHG lead to increases in the MMV of EASM rainfall. These findings indicate increased extreme precipitation events under future warming scenarios, consistent with model results.

Global-scale Observations of Limb and Disk (GOLD) disk measurements of far ultraviolet molecular nitrogen band emissions are used to retrieve column integrated disk temperatures (Tdisk), which are representative of the lower-and-middle thermosphere. The present work develops a new approach to assimilate the Tdisk in the Whole Atmosphere Community Climate Model with thermosphereâ\euro?ionosphere eXtension (WACCMX) using the Data Assimilation Research Testbed (DART) ensemble adjustment Kalman filter. Nine days of data,1 to 9 November 2018, are assimilated. Analysis state variables such as thermospheric effective temperature (Teff, airglow layer integrated temperature), ratio of atomic oxygen to molecular nitrogen column densities (O/N2), and column electron content are compared with a control simulation that is only constrained up to ~50 km. It is observed that assimilation of the GOLD Tdisk improves the analysis states when compared with the control simulation. The analysis and model states, particularly, Teff, O/N2, and Electron Column Density (ECD) are also compared with their measurement counterparts for a validation of the assimilation. Teff and O/N2 are compared with GOLD Tdisk and O/N2. While, the ECD is compared with ground based Total Electron Content (TEC) measurements from Global Navigational Satellite System (GNSS) receivers. Root Mean Square Error (RMSE) improvements in Teff and O/N2 are about 10.8% and 22.6%, respectively. The RMSE improvement in analyses ECD is about 10% compared to control simulation.

The Alto Tiberina normal fault (ATF) in Central Italy is a 50 km long crustal structure that dips at a low angle (15-20◦). Events on the fault plane are about ten times less frequent than those located in its shallower syn- and antithetic hanging-wall splays. To enhance ATF catalogue and achieve a better understanding of the degree of coupling in the fault system, we apply a template matching technique in the 2010-2014 time window. We augment by a factor 5 the detections and decrease the completeness magnitude to negative values. Contrary to what previously observed on ATF, we highlight intermittent seismic activity and long-lasting clusters interacting with sequences on the shallower splays. One of these episodes of prolonged seismic activity, detected at the end of 2013 on a 30 km long ATF segment, suggest the ATF active role during an aseismic transient unravelled by geodetic data.

Satellite data reveal widespread changes in Earth’s vegetation cover. Regions intensively attended to by humans are mostly greening due to land management. Natural vegetation, on the other hand, is exhibiting patterns of both greening and browning in all continents. Factors linked to anthropogenic carbon emissions, such as CO2 fertilization, climate change, and consequent disturbances such as fires and droughts, are hypothesized to be key drivers of changes in natural vegetation. A rigorous regional attribution at the biome level that can be scaled to a global picture of what is behind the observed changes is currently lacking. Here we analyze different datasets of decades-long satellite observations of global leaf area index (LAI, 1981–2017) as well as other proxies for vegetation changes and identify several clusters of significant long-term changes. Using process-based model simulations (Earth system and land surface models), we disentangle the effects of anthropogenic carbon emissions on LAI in a probabilistic setting applying causal counterfactual theory. The analysis prominently indicates the effects of climate change on many biomes – warming in northern ecosystems (greening) and rainfall anomalies in tropical biomes (browning). The probabilistic attribution method clearly identifies the CO2 fertilization effect as the dominant driver in only two biomes, the temperate forests and cool grasslands, challenging the view of a dominant global-scale effect. Altogether, our analysis reveals a slowing down of greening and strengthening of browning trends, particularly in the last 2 decades. Most models substantially underestimate the emerging vegetation browning, especially in the tropical rainforests. Leaf area loss in these productive ecosystems could be an early indicator of a slowdown in the terrestrial carbon sink. Models need to account for this effect to realize plausible climate projections of the 21st century.

The fate of organic carbon (C) in permafrost soils is important to the climate system due to the large global stocks of permafrost C. Thawing permafrost can be subject to dynamic hydrology, making redox processes an important factor controlling soil organic matter (SOM) decomposition rates and greenhouse gas production. In iron (Fe)-rich permafrost soils, Fe(III) can serve as a terminal electron acceptor, suppressing methane (CH4) production and increasing carbon dioxide (CO2) production. Current large-scale models of Arctic C cycling do not include Fe cycling or pH interactions. Here, we coupled Fe redox reactions and C cycling in a geochemical reaction model to simulate the interactions of SOM decomposition, Fe(III) reduction, pH dynamics, and greenhouse gas production in permafrost soils subject to dynamic hydrology. We evaluated the model using measured CO2 and CH4 fluxes as well as changes in pH, Fe(II), and dissolved organic C concentrations from oxic and anoxic incubations of permafrost soils from polygonal permafrost sites in northern Alaska, United States. In simulations of higher frequency oxic-anoxic cycles, rapid oxidation of Fe(II) to Fe(III) during oxic periods and gradual Fe(III) reduction during anoxic periods reduced cumulative CH4 fluxes and increased cumulative CO2 fluxes. Lower pH suppressed CH4 fluxes through its direct impact on methanogenesis and by increasing Fe(III) bioavailability. Our results suggest that models that do not include Fe-redox reactions and its pH dependence could overestimate CH4 production and underestimate CO2 emissions and SOM decomposition rates in Fe-rich, frequently waterlogged Arctic soils.

This article is composed of one integrated commentary about the state of ICON principles (Goldman et al., 2021) in natural hazards and a discussion on the opportunities and challenges of adopting them. Natural hazards pose risks to society, infrastructure, and the environment. Hazard interactions and their cascading phenomena in space and time can further intensify the impacts. Natural hazards’ risks are expected to increase in the future due to environmental, demographic, and socioeconomic changes. It is important to quantify and effectively communicate risks to inform the design and implementation of risk mitigation and adaptation strategies. Multihazard multisector risk management poses several nontrivial challenges, including: i) integrated risk assessment, ii) Earth system data-model fusion, iii) uncertainty quantification and communication, and iv) crossing traditional disciplinary boundaries. Here, we review these challenges, highlight current research and operational endeavors, and underscore diverse research opportunities. We emphasize the need for integrated approaches, coordinated processes, open science, and networked efforts (ICON) for multihazard multisector risk management.

Organic matter (OM) sulfurization can enhance the preservation and sequestration of carbon in anoxic sediments, and it has been observed in sinking marine particles from marine O2-deficient zones. The magnitude of this effect on carbon burial remains unclear, however, because the transformations that occur when sinking particles encounter sulfidic conditions remain undescribed. Here, we briefly expose sinking marine particles from the eastern tropical North Pacific O2-deficient zone to environmentally relevant sulfidic conditions (20C, 0.5 mM [poly]sulfide, two days) and then characterize the resulting solid-phase organic and inorganic products in detail. During these experiments, the abundance of organic sulfur in both hydrolyzable and hydrolysis-resistant solids roughly triples, indicating extensive OM sulfurization. Lipids also sulfurize on this timescale, albeit less extensively. In all three pools, OM sulfurization produces organic monosulfides, thiols, and disulfides. Hydrolyzable sulfurization products appear within ≤ 200-m regions of relatively homogenous composition that are suggestive of sulfurized extracellular polymeric substances (EPS). Concurrently, reactions with particulate iron oxyhydroxides generate low and fairly uniform concentrations of iron sulfide (FeS) within these same EPS-like materials. Iron oxyhydroxides were not fully consumed during the experiment, which demonstrates that organic materials can be competitive with reactive iron for sulfide. These experiments support the hypothesis that sinking, OM- and EPS-rich particles in a sulfidic water mass can sulfurize within days, potentially contributing to enhanced sedimentary carbon sequestration. Additionally, sulfur-isotope and chemical records of organic S and iron sulfides in sediments have the potential to incorporate signals from water column processes.

Factors influencing data reproducibility of fission-track (FT) thermochronology can be summarized into three main categories associated with data acquisition steps. (1) Sample preparation involves mineral separation, mounting, polishing and etching; (2) data revelation relates to instrumentation (microscope, LAICPMS, etc.) and software settings; and (3) execution depends on feature selection by the analyst. Previous committee reports and studies (Hurford A.J. 1990; Ketcham et al. 2009; Ketcham et al. 2015; Ketcham et al. 2018) have contributed significant insights into the reproducibility of fission-track data by comparing length and age measurements produced by several laboratories using their own preparation and revelation procedures. A recent attempt to isolate analyst-specific factors in length measurement using an image-based approach (Tamer et al. 2019) found that when two analysts observe the same feature and agree it is a valid track, measurement reproducibility was very good, though impacted by etching. Dispersion of individual length measurements was 0.7-1.0 µm (2 for weaker etching and 0.5-0.8 µm for stronger etching, but mean lengths were always within 0.1 µm of each other. Where the analysts disagreed more significantly, however, was in finding tracks and evaluating whether they were valid, sufficiently clear, and sufficiently etched for measurement, which led to differences of up to ~0.8 µm in mean track length. This study builds on the image-based approach to encompass more aspects of the measurement process and increase the number of analysts being compared. We will look at confined track selection in greater detail, and also study analyst decisions behind age determination, including the selection of the region of interest for counting, and identification of grain-surface features as tracks appropriate for counting. Reflected and transmitted light image stacks for 41 grains and graticules are available on a cloud platform Participants will carry out analyses of these images using their preferred approach, e.g. suitable analytical software, manual measurements or AI-based analysis. A limited license for FastTracks (v3.2) will be available for those who would like to participate but do not have measurement software. Analysts are asked to fill out a questionnaire about their fission track experience, conduct track density estimations, confined track length and Dpar measurements, and especially provide comments on all grains being analyzed or skipped. FastTracks users are asked to send the .xml files produced by the software, while other participants are asked to submit the results using a template. The results will be entirely anonymous unless the analyst states otherwise. The deadline for the submission of the results is June 1st, 2022. The results will be shared on 18th International Conference on Thermochronology.

The uncertainty in polar cloud feedbacks calls for process understanding of the cloud response to climate warming. As an initial step toward improved process understanding, we investigate the seasonal cycle of polar clouds in the current climate by adopting a novel modeling framework using large eddy simulations (LES), which explicitly resolve cloud dynamics. Resolved horizontal and vertical advection of heat and moisture from an idealized general circulation model (GCM) are prescribed as forcing in the LES. The LES are also forced with prescribed sea ice thickness, but surface temperature, atmospheric temperature, and moisture evolve freely without nudging. A semigray radiative transfer scheme without water vapor and cloud feedbacks allows the GCM and LES to achieve closed energy budgets more easily than would be possible with more complex schemes. This enables the mean states in the two models to be consistently compared, without the added complications from interaction with more comprehensive radiation. We show that the LES closely follow the GCM seasonal cycle, and the seasonal cycle of low-level clouds in the LES resembles observations: maximum cloud liquid occurs in late summer and early autumn, and winter clouds are dominated by ice in the upper troposphere. Large-scale advection of moisture provides the main source of water vapor for the liquid-containing clouds in summer, while a temperature advection peak in winter makes the atmosphere relatively dry and reduces cloud condensate. The framework we develop and employ can be used broadly for studying cloud processes and the response of polar clouds to climate warming.

A 24-hour 2D time-lapse electrical resistivity imaging (ERI) survey was conducted in an altered mangrove forest on a barrier island in southeast Florida, USA, to (1) assess the method’s utility in hypersaline conditions and (2) understand how trees respond to hypersaline conditions. ERI measurements serve as a proxy for pore water salinity and saturation. Here, resistivity changes suggest a lag between the tidal cycle and changes in ground resistivity. ERI data show that overall changes within 24 hours are very small, but there is more variability in resistivity in the root zone of mangroves than in open salt flat portions along a fixed transect. Two to three hours after sunset, root zone resistivity increased from initial, midday conditions. Overnight, the root zone was less resistive than midday. By sunrise, root zone resistivity was once again higher than initial conditions. Measurements from the salt flat where roots are absent remained generally constant throughout the survey. Thus, changes in resistivity over time are inferred to reflect mangrove tree physiological influences related to diel water use. A mechanistic explanation for the decreased resistivity two hours after sunset from the re-distribution of salts to the soil around the roots is the Cohesion-Tension Theory, which suggests that trees continue water uptake after sunset to balance the pressure after leaf stomates have closed. The corresponding overnight drop in ground resistivity just prior to sunrise may be explained by redistribution of freshwater from the tree to the soil that was delayed until the early morning hours. The limited period of data acquisition limits definitive data interpretations, but the study illustrates the monitoring potential of ERI in hypersaline environments such as a mangrove forest.

In this study, 27 soil samples were collected for laboratory pretreatment and the total concentration of heavy metal Cd, Cr, Cu, Ni, Pb, Zn, As and Hg was measured. Pearson correlation analysis was carried out on the measured data after removing outliers, and the comparison groups with a significant correlation at the level of 0.01 between the concentration of several groups of elements were obtained. In order to identify effectively source of soil heavy metals by PMF analysis (Positive Matrix Factorization), we drew the location map in the study area and the concentration distribution of heavy metals. Combining Pearson correlation analysis, distribution of heavy metal concentration and PMF analysis, we obtained convincing identification results of heavy metal sources. With C# language and ArcGIS Engine development components, we developed a soil heavy metal database management system to manage the spatial and attribute data needed in source apportionment for soil heavy metals, which will provide data support for the latter sustainable research. In this paper, we proposed a sustainable heavy metal pollution identification research process, SSAPD (sustainable source analysis process based on database), which includes data collection in the field, laboratory measurement, pretreatment, PMF pollution source analysis and database establishment. The process can not only effectively identify the source of soil heavy metal pollution, but also realize the continuity of research and the sharing of data.

Rubble pile asteroids such as (162173) Ryugu have large bulk porosities, which are believed to result from void spaces in between the constituent boulders (macroporosity) as well as void spaces within the boulders themselves (microporosity). In general, both macroporosity and microporosity are estimated based on comparisons between the asteroid bulk density and both the bulk and grain density of meteorite analogues, and relatively large macroporosities are usually obtained. Here we use semi-empirical models for the macroporosity of multi-component mixtures to determine Ryugu’s macroporosity based on the observed size-frequency distribution of boulders on the surface. We find that Ryugu’s macroporosity can be significantly smaller than usually assumed, as the observed size-frequency distribution allows for an efficient packing of boulders, resulting in a macroporosity of $16 \pm 3$~\%. Therefore, { we confirm that} Ryugu’s high bulk porosity is a direct consequence of a very large boulder microporosity. Furthermore, using estimates of boulder microporosity of around { 50~\%} as derived from in-situ measurements, the average grain density in boulders is { $2848 \pm 152$ kg m$^{-3}$, similar to values obtained for CM and the Tagish lake meteorites}. Ryugu’s bulk porosity corresponding to the above values is { 58~\%.} { Thus, the macroporosity of rubble pile asteroids may have been systematically overestimated in the past.}