Water escape on Mars has recently undergone a paradigm shift with the discovery of unexpected seasonal variations in the population of hydrogen atoms in the exosphere where thermal escape occurs and results in water lost to space. This discovery led to the hypothesis that, contradicting the accepted pathway, atomic hydrogen in the exosphere was not only produced by molecular hydrogen but mostly by high altitude water vapor. Enhanced presence of water at high altitude during southern spring and summer, due to atmospheric warming and intensified transport, favors production of H through photolysis ionized chemistry of water molecules and thus appears to be the main cause of the observed seasonal variability in escaping hydrogen. This hypothesis is supported by the observation of large concentrations of water vapor between 50 km and 150 km during the southern summer solstice and global dust events. Using a simplified yet representative air parcel transport model, we show that in addition to the formation of atomic hydrogen from water photolysis above 80 km, a major fraction of the exospheric hydrogen is formed at altitudes as low as 60 km and is then directly advected to the upper atmosphere. Comparing the injection modes of a variety of events (global dust storm, perihelion periods, regional storm), we conclude that southern spring/summer controls H production and further ascent into the upper atmosphere on the long term with direct implication for water escape.
Carbon monoxide is a non-condensable species of the Martian atmosphere produced by the photolysis of CO2. Its mixing ratio responds to the condensation and sublimation of CO2; from the polar caps, resulting in seasonal variations of the CO abundance. Since 2018, all three spectrometers of the Atmospheric Chemistry Suite (ACS) onboard the Trace Gas Orbiter have measured CO in infrared bands by solar occultation. Here we provide the first long-term monitoring of the CO vertical distribution at the altitude range from 0 to 80 km for 1.5 Martian years from Ls=163; of MY34 to the end of MY35. We obtained a mean CO volume mixing ratio of ~960 ppm at latitudes from 45S to 45N, mostly consistent with previous observations. We found a strong enrichment of CO near the surface at Ls=100-200; in high southern latitudes with a layer of 3000-4000 ppmv, corresponding to local depletion of CO2. At equinoxes we found an increase of mixing ratio above 50 km to 3000–4000 ppmv explained by the downwelling flux of the Hadley circulation on Mars, which drags the CO enriched air. The general circulation chemical model tends to overestimate the intensity of this process, bringing too much CO. The observed minimum of CO in the high and mid-latitudes southern summer atmosphere amounts to 700-750 ppmv, agreeing with nadir measurements. During the global dust storm of MY34, when the H2O abundance peaks, we see less CO than during the calm MY35, suggesting an impact of HOx chemistry on the CO abundance.
Terrestrial vegetation is known to be an important sink for carbon dioxide (CO2). However, fluxes to and from vegetation are often not accounted for when studying anthropogenic CO2 emissions in urban areas. This project seeks to quantify urban biogenic fluxes in the Greater Toronto and Hamilton Area located in Southern Ontario, Canada. Toronto is Canada’s most populated city but also has a large amount of green-space, covering approximately 13 % of the city. In addition, vegetation is not evenly distributed throughout the region. We therefore expect biogenic fluxes to play an important role in the spatial patterns of CO2 concentrations and the overall local carbon budget. In order to fully understand biogenic fluxes they can be partitioned into the amount of CO2 sequestered via photosynthesis, gross primary productivity (GPP), and the amount respired by vegetation, ecosystem respiration (Reco). Solar induced chlorophyll fluorescence (SIF) measured from space has been shown to be a valuable proxy for photosynthesis and thus can be used to estimate GPP. Vegetation models, including the Urban Vegetation Photosynthesis and Respiration Model (UrbanVPRM) and the SIF for Modelling Urban biogenic Fluxes (SMUrF) model, have also been used to estimate both GPP and Reco In this study we compare modelled and SIF-derived biogenic CO2 fluxes at a 500 m by 500 m resolution, to ground-based flux tower measurements in Southern Ontario to determine how well these methods estimate biogenic CO2 fluxes. This study works towards determining the importance of biogenic fluxes in the Greater Toronto and Hamilton Area. Furthermore, the results of this work may inform policy makers and city planners on how urban vegetation affects CO2 concentrations and patterns within cities.
The world surrounding us is more over covered with plastics and we are in a “plastic era”. The bigger plastic materials, as the time moves, disintegrate into micro or nano particles may be as a result of radiations or weathering. These are termed as microplastics and nanoplastics. Technically these microparticles do not create a direct impact, instead they make their way to the food chain or rather a complex food chain. These can be through various steps ranging from filter feeding to adherence. They will start to accumulate, as the trophic level increases their accumulations also get increased. These trophic transfer is mainly through ingestion of smaller to higher organisms. Thus they create various damages and diseases to organisms in successive trophic levels. That can be ranging from respiratory disorders to endocrine or oncogenic issues. Not only in the marine world, the terrestrial world is also prone to these microplastics, either by airborne or through sewage water plants. Moreover in a developing or developed country, exposure to these tiny things are much more. The impacts are showing now and will entangle in the near future, unless this is not dealt as a serious issue to be considered. This article focuses on the classification, sources, exposure to food chain or food web, trophic concentrations, health issues, and remedies of microplastics.
To facilitate identification of conditions that lead to the dynamic triggering of seismic events as catalogs of these events keep growing, we applied a machine-learning algorithm (decision tree) to a published data set of known instances of dynamically triggered seismic tremor in central California. To investigate the possible universality of our findings and to further test the algorithm, we also applied it to new observations, presented here, of potentially dynamically triggered seismic activity in three intraplate regions: Raton Basin (CO), Yellowstone, and central Utah. We report potential tremor or local earthquake signals from here during the propagation of surface waves from the 2012 M8.6 Sumatra earthquake. These surface waves also triggered seismic activity along the western boundary of the North American plate and did not trigger seismic activity in the central and eastern USA. We report additional potential dynamic triggering in the three aforementioned intraplate regions from an investigation of seismograms from 37 additional large earthquakes, recorded between 2004 to 2017. Our findings show that transient stresses generated by surface waves from large earthquakes and arriving from favorable directions generally lead to triggered tremor in seismically, volcanically, and hydrothermally active regions like central California and possibly Yellowstone. These stresses do not appear to be decisive factors for the potentially dynamically triggered local earthquakes reported for the Raton Basin and central Utah, while surface waves’ incidence angles do appear to be important there.
Dob’s Linn (Scotland) is a location that has significantly influenced our understanding of how life evolved over the Ordovician to early Silurian. The current chronostratigraphic boundary between the Ordovician and Silurian periods is a Global Boundary Stratotype Section and Point (GSSP) at Dob’s Linn calibrated to 443.8±1.5 Ma, partly based on biostratigraphic markers, radiometric ages, and statistical modeling. Graptolites are used here as relative dating markers. We dated hundreds of zircon grains extracted from defined metabentonites from six horizons exposed at Dob’s Linn using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Each zircon was imaged using cathodoluminescence, and most show igneous zoning with minimal alteration. Sample locations range from 42 meters above to 5 meters below the recognized GSSP for the Ordovician-Silurian. Samples were responsibly collected and analyzed for paleontology and geochemistry in other work. Overall, many 238U-206Pb zircon ages from the section are significantly younger than expected. The youngest zircon in sample DL7, located 5 meters below the GSSP, yielded a 238U-206Pb age of 402±12 Ma (±2s, 5% disc). Nineteen spots on zircons from this sample are younger than the presently assigned GSSP age, including more concordant results of 426±8 Ma (0.8% disc) and 435±5 Ma (0.2% disc). The youngest zircon in sample 19DL12, < 1 m below the GSSP, is 377±8 Ma (2% disc) with a more concordant age of 443±7 Ma (0.6% disc). A sample located directly on the GSSP (19DL09) yields 327±5 Ma (0.8% disc). Eight spots on zircons from this sample are also younger than the presently assigned GSSP age. We also dated two samples (DL24 and BRS23) 8 meters above the GSSP, and the youngest, most concordant zircon ages in these samples are 400±11 Ma (5% disc) and 421±9 Ma (0.4% disc), respectively. Overall, the U-Pb ages would re-assign the Dob’s Linn chronostratigraphic section to Silurian-Devonian. The young age results could be attributed to Pb loss due to hydrothermal alteration during the Acadian and Alleghenian orogenies. Future work will implement Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS) to obtain accurate U-Pb dating and evaluate the potential effects of Pb loss.
Extreme wind-driven autumn wildfires are hazardous to life and property, due to their rapid rate of spread. Recent catastrophic autumn wildfires in the western United States co-occurred with record- or near-record autumn fire weather indices that are a byproduct of extreme fuel dryness and strong offshore dry winds. Here, we use a formal, probabilistic, extreme event attribution analysis to investigate anthropogenic influence on recent extreme autumn fire weather events. We show that while present-day anthropogenic climate change has slightly decreased the prevalence of strong offshore downslope winds, it has increased the likelihood of extreme fire weather indices by 40%, primarily through increased autumn fuel aridity and warmer temperatures during dry wind events. These findings illustrate that anthropogenic climate change is exacerbating autumn fire weather extremes that contribute to high-impact catastrophic fires in populated regions of the western US.
Mechanistic representations of biogeochemical processes in ecosystem models are rapidly advancing, requiring advancements in model evaluation approaches. Here we quantify multiple aspects of model functional performance to evaluate improved process representations in ecosystem models. We compare semi-empirical stomatal models with hydraulic constraints against more mechanistic representations of stomatal and hydraulic functioning at a semi-arid pine site using a suite of metrics and analytical tools. We find that models generally perform similarly under unstressed conditions, but performance diverges under atmospheric and soil drought. The more empirical models better capture synergistic information flows between soil water potential and vapor pressure deficit to transpiration, while the more mechanistic models are overly deterministic. Additionally, both multilayer canopy and big-leaf models were unable to capture the magnitude of canopy temperature divergence from air temperature. Lastly, modeled stable carbon isotope fractionation differed under canopy water stress which illustrates the value of carbon isotopes in helping to characterize ecosystem function and elucidate differences attributable to model structure. This study demonstrates the value of merging underutilized observational data streams with emerging analytical tools to characterize ecosystem function and discriminate among model process representations.
Understanding onset of droughts and its potential linkage to resulting responses like severity (deficit volume) is crucial for providing timely information related to drought sectors including the cultivation planning and monitoring crop productivity. Using high-quality daily observed streamflow records from 82 medium-to-large sized catchments over (tropical) peninsular India, we show that the variability in onset timing drives the severity of hydrological droughts. The strength of onset timing-severity relationships using observed records indicate seasonality of rainfall and catchment characteristics mainly modulate hydrological drought responses in peninsular India, which is not readily apparent from land-surface model simulations. The observed trend for mean onset of drought depicts delayed occurrence for more than half of the catchments. Around one-third of the catchments shows a stronger non-linear significant dependency (>0.7) between severity and onset of drought. The findings of the study highlight the need for accounting feedback between drought onset and severity and their concurrent changes for seasonal-to-sub-seasonal predictability of droughts; and contributes to discussions on building resilience to extreme droughts in a changing climate.
Inland waters are hotspots of greenhouse gas (GHG) emissions, and small water bodies are now well known to be particularly active in the production and consumption of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). High variability in physical, chemical, and environmental parameters affect the production of these GHG, but currently the mechanistic underpinnings are unclear, leading to high uncertainty in scaling up these fluxes. Here, we compare the relative magnitudes and controls of emissions of all three major GHG in twenty pairs of natural wetland ponds and constructed reservoirs in Canada’s largest agricultural region. While gaseous fluxes of CO2 and CH4 were comparable between the two waterbody types, CH4 ebullition was greater in wetland ponds. Carbon dioxide levels were associated primarily with metabolic indicators in both water body types, with primary productivity paramount in agricultural reservoirs, and heterotrophic metabolism a stronger correlate in wetland ponds. Methane emissions were positively driven by eutrophication in the reservoirs, while competitive inhibition by sulfur-reducing bacteria may have limited CH4 in both waterbody types. Contrary to expectations, N2O was undersaturated in both water body types, with wetlands a significantly stronger and more widespread N2O sink than were reservoirs. These results support the need for natural and constructed water bodies for regional GHG budgets and identification of GHG processing hotspots.
A decade (2007-2016) of hourly 6 km resolution maps of the surface currents across the Mid Atlantic Bight (MAB) generated by a regional-scale High Frequency Radar network are used to reveal new insights into the spatial patterns of the annual and seasonal mean surface flows. Across the 10-year time series, temporal means, inter- and intra-annual variability are used to quantify the variability of spatial surface current patterns. The 10-year annual mean surface flows are weaker and mostly cross shelf near the coast, increasing in speed and rotating to more alongshore directions near the shelf break, and increasing in speed and rotating to flow off-shelf in the southern MAB. The annual mean surface current pattern is relatively stable year to year compared to the hourly variations within a year. The ten-year seasonal means exhibit similar current patterns, with winter and summer more cross-shore while spring and fall transitions are more alongshore. Fall and winter mean speeds are larger and correspond to when mean winds are stronger and cross-shore. Summer mean currents are weakest and correspond to a time when the mean wind opposes the alongshore flow. Again, intra-annual variability is much greater than interannual, with the fall season exhibiting the most interannual variability in the surface current patterns. The extreme fall seasons of 2009 and 2011 are related to extremes in the wind and river discharge events caused by different persistent synoptic meteorological conditions, resulting in more or less rapid fall transitions from stratified summer to well-mixed winter conditions.
Seismicity in the Raton Basin over the past two decades suggests reactivation of basement faults due to wastewater injection. In the summer of 2018, 96 short-period three-component nodal instruments were installed in a highly active region of the basin for a month. A machine-learning based phase picker-(PhaseNet) was adopted and identified millions of picks, which were associated with events using an automated algorithm – REAL (Rapid Earthquake Association and Location). After hypocenter relocation with hypoDD, the earthquake catalog contains 9259 M -2.2 – 3 earthquakes focused at depths of 4-6km. Magnitude of completeness (Mc) varies from -1 at night to -0.5 in daytime, likely reflecting noise variation modulated by wind. The clustered hypocenters with variable depths and focal mechanisms suggest a complex network of basement faults. Frequency-magnitude statistics and the spatiotemporal evolution of seismicity are comparable to tectonic systems.
Collisionless shocks in space plasma are regions of heating and acceleration of charged particles and dissipation of kinetic energy. These accelerated particles are the source of electromagnetic emissions from supernova remnants and other astrophysical structures. At high Mach numbers, shocks can be inherently nonstationary and exhibit modulated energy transfer and recurring plasma compression areas in the form of reformation. We use data from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to study reformation of the Martian bow shock which has a relatively high curvature compared to that at Earth and the upstream solar wind is often mass loaded with a population of pickup ions. We show evidence of ion reflection effects in reformation of a supercritical quasi-perpendicular shock.
The overturning tropical Pacific circulation known as the Walker circulation embodies complex interactions between large-scale circulations, deep and shallow convection, stratocumulus clouds, and microphysical cloud processes. The large and multi-scale nature of the Walker circulation has made high resolution modeling costly, while disentangling the relevant circulations and processes in a global model with more parameterizations is often challenging. This work uses the framework of the Walker Circulation as a unifying experiment for both high-resolution and global models with the goal of identifying how deep tropical convective heating and low-level clouds interact with and are influenced by the circulations in which they are embedded. A high resolution model with explicit convection (1km and 2km grid-spacing) is used to examine the system free of the complications inherent in convective parameterizations. The same model is also used at GCM-like resolutions with parameterized convection (25km and 100km grid-spacing) to gain insight into how the clouds and circulations interact in a GCM configuration. We define the idealized Walker circulation with a prescribed sea surface temperature dipole pattern, no rotation, uniform insolation, fully interactive radiation, and a channel domain (100km x 4000km). All simulations use the the same nonhydrostatic dynamical core (FV3) with the physics based on those in the AM4 GFDL atmospheric model. We find large differences in the total condensate between the high-resolution model and the GCM with the high-resolution model tending to have less low-level condensate but more condensate in the deep convective regions. This is reflected in the relative humidity fields as well. The parameterized entrainment of deep convection and the feedbacks of low-level tropical clouds are both leading factors contributing to the large spread of the climate sensitivity. With this in mind experiments are performed with the GCM in which the lateral mixing rate of deep convective plumes is varied. In addition, the detailed representation of cloud fraction between the two models is investigated. Our goal is to determine to what extent deep tropical convection can influence remote low-level clouds in regions with a subsiding free troposphere.
Giant aquifers are capable of storing significant amounts of carbon as a result of immense water volumes, substantial dissolved inorganic carbon (DIC) concentrations and its ubiquitous reactions with matrix, thus contributing the global carbon storage and cycle. However, concentrations of dissolved solutes vary significantly over a distance in the Guarani Aquifer System (GAS) which causes difficulties in process interpretation. To quantify the importance of controlling parameters, we performed reactive transport modeling which combines both hydrological and geochemical inputs. The paper presents a chemical evolution in a two-dimensional aquifer configuration, global sensitivity analysis along with estimates of the DIC flux through the system boundaries. We observed that the DIC flux at recharge as well as plagioclase and olivine hydrolysis rates play an overriding importance in controlling the solute patterns including the DIC concentrations, while soil pH, horizontal hydraulic conductivity, porosity, precipitation of secondary minerals, but calcite, and Mg ratio in carbonates are of minor significance. If released Ca undergoes ion exchange to Na, the storage is delayed in time and space. In conclusion, the capacity of GAS in receiving recharge CO is attributed to the hydrolysis along with advective transport while the global sensitivity analysis informs how the financial resources should be allocated to effectively reduce interpretative uncertainty in large-scale groundwater systems.
The effective implementation of NBS is still hampered by several barriers. Among the others, this work focuses on the collaboration barriers. NBS design and implementation could be conceptualized as a collaborative decision-making process, involving various decision-makers. Nevertheless, differences in problem framings may turn the multi-actors decision-making into a controversial and often futile process, leading to barriers hampering the NBS design and implementation. Contrarily to most of the works on conflict management, mainly based on the reduction of the divergent viewpoints, this work assumes that ambiguity is ineradicable in complex decision-making processes. Therefore, the work demonstrates that enhancing the effectiveness of the networks of interaction, through the implementation of networking interventions, can contribute to reducing the level of conflicts and, thus, enabling the NBS implementation. An integrated SNA-FCM method was developed to this aim and implemented in the Medina del Campo case study, one of the demo-sites in the NAIAD project.
Despite many studies on seafloor hydrothermal systems conducted to date, the generation mechanism of seafloor massive sulfide (SMS) deposits is not yet fully understood. To elucidate this mechanism, this study clarifies the three-dimensional regional temperature distribution and fluid flow of a seafloor hydrothermal system of the Iheya North, middle Okinawa Trough. Lateral flow and boiling of hydrothermal fluids below the seafloor were the main features found by the simulation, leading to an interpretation of two-layered SMS deposit generation as follows. Hydrothermal fluids discharging from black smokers first formed the upper SMS deposits on the seafloor. Caprocks formed below the seafloor, and the above-mentioned occurrences were then induced under the caprocks. In the present system, vapor-rich hydrothermal fluids poor in metals are discharged from the vents as white smokers, whereas liquid-dominated hydrothermal fluids rich in metals flow laterally below the caprocks, forming lower SMS deposits tens of meters below the seafloor.
The strongest Southern Hemisphere minor sudden stratospheric warming (SSW) in the last 40 years occurred in September 2019 and resulted in unprecedented weakening of the stratospheric polar vortex. Ionospheric total electron content (TEC) observations are used to provide an overview of statistically significant anomalies in the low-latitude ionosphere during this event. Quasi-semidiurnal perturbations of TEC are observed in response to the SSW, similar to those seen during Northern Hemisphere SSWs. Analysis indicates the existence of quasi-periodic oscillations in TEC in the crests of the equatorial ionization anomaly, with strong 5-6 day and 2-3 day periodicities. Ionospheric anomalies from the combined effects of multiple mechanisms exceed a factor of 2, comparable to the strongest anomalies associated with Northern Hemisphere SSWs. These results also indicate, for the first time, a remarkable longitudinal variation in the character and magnitude of variations that could be related to a modulation of the non-migrating diurnal tide.