bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Weakly Non-linear Investigation into the Long-term Spatial and Temporal Development of Triadic Resonance Instability
Authors: Grayson Katherine , Dalziel Stuart , Lawrie Andrew
Published: March 2021

With an aim of understanding the role of internal waves to oceanic mixing, various mechanisms have been cited as a possible explanation for how they transfer energy across the wavenumber and frequency spectra and eventually contribute to small-scale turbulence. Triadic Resonance Instability (TRI) has become increasingly recognised as potentially one of these mechanisms. This talk will summarise both experimental work and theoretical modelling (using numerical solutions of a weakly non-linear system) that examines the long-term temporal and spatial evolution of this instability for a finite-width internal wave beam. Experiments have been conducted using a new generation of wave maker, featuring a flexible horizontal boundary driven by an array of independently controlled actuators. We present experimental results exploring the role that a finite width wave beam has on the evolution of TRI. Experimentally, we find that the approach to a saturated equilibrium state for the three triadic waves is not monotonic, rather their amplitudes continue to oscillate without reaching a steady equilibrium. Further theoretical modelling then suggests that part of this variability is due to multiple resonant frequencies interacting with each other, as opposed to a simple triad system. We show how a spectrum of these resonant frequencies in the flow ‘beat’ to cause interference patterns which manifest throughout the instability as slow amplitude modulations.
Hottest drought temperature anomalies in sub-humid regions
Authors: Oh Sungmin , Bastos Ana , Reichstein Markus , Li Wantong , Denissen Jasper , Graefen Hanna , Orth Rene
Published: March 2021

Droughts cause serious environmental and societal impacts, often aggravated by simultaneously occurring heat waves. Climate model projections suggest that droughts and high temperatures will further intensify over the next century. Thus, understanding the underlying mechanisms responsible for drought-induced heat is crucial to inform drought management strategies and to improve prediction of dry-hot extremes, especially under a changing climate. Using observation-based, global data over 2001-2015, we show hottest temperature anomalies during droughts in sub-humid and tree-dominated regions. This is mainly driven by a drought-related net radiation surplus and further amplified by forests’ water saving strategies that result in diminished evaporative cooling. By contrast, in semi-arid and short-vegetation regions, drought-related temperature increases are smaller. The reduction of evaporative cooling is weak and net radiation increases only marginally due to higher albedo over drought-stressed vegetation. As a result, our findings show the relative roles of climate and vegetation in shaping drought-heat extremes across space and highlight the importance of considering all interacting factors in understanding concurrent drought-heat extremes.
Pre-salt rift morphology controls salt tectonics in the Campos Basin, offshore SE Brazil
Authors: B. Amarante Francyne , A-L. Jackson Christopher , M. Pichel Leonardo , M. S. Scherer Claiton , Kuchle Juliano
Published: March 2021

Salt-bearing passive margin basins offshore SE Brazil have been and remain attractive for hydrocarbon exploration and production. In the Campos Basin, major reservoir types include post-salt turbidites, which are located in structural traps related to thin-skinned faulting above salt anticlines and rollers. Classic models of gravity-driven salt tectonics commonly depict kinematically linked zones of deformation, characterised by updip extension and downdip contraction, separated by a weakly deformed zone associated with downdip translation above a relatively smooth base-salt surface. We use 2D and 3D seismic reflection and borehole data from the south-central Campos Basin to show that this does not adequately capture the styles of salt-detached gravity-driven deformation above relict, rift-related relief. The base-salt surface is composed of elongated, broadly seaward-dipping ramps with structural relief reaching c. 2 km. These ramps define the boundary between the External High and the External Low, basement structures related to the rift tectonics. Local deformation associated with the base-salt ramps can overprint and/or influence regional, margin-scale patterns of deformation producing kinematically-variable and multiphase salt deformation. We define three domains of thin-skinned deformation: an updip extensional domain, subdivided into subdomains E1 and E2, an intermediate multiphase domain and a downdip contractional domain. The multiphase domain is composed of three types of salt structures with a hybrid extensional-contractional origin and evolution. These are: (i) contractional anticlines that were subjected to later extension and normal faulting; (ii) diapirs with passive and active growth later subjected to regional extension, developing landward-dipping normal faults on the landward flank; and, lastly, (iii) an extensional diapir that was subsequently squeezed. We argue that this multiphase style of deformation occurs as a consequence of base-salt geometry and relief creating local variations of salt flow that localize extension at the top and along the ramps, and contraction at the base. Translation and extension of salt and its overburden across major base-salt ramps resulted in three ramp syncline basins northeast of the study area, partially bounded by salt-detached listric faults. The temporal and spatial distribution and evolution of these and other key salt and overburden structures, and their relationship to base-salt relief, suggest 30 to 60 km of horizontal gravity-driven translation of salt and overburden.
New geoid models computation in the Southeast part of Brazil
Authors: Silva Valeria , Guimarães Gabriel , Blitkow Denizar , Matos Ana Cristina
Published: March 2021

In the last decade, big efforts have been undertaken in terms of gravity surveys in the Southeast part of Brazil. First of all, São Paulo state has gravity data coverage quite completed in terms of 5’ resolution. Second, in the last few years, some field works have been carried out in Minas Gerais state. The purpose of gravity densification is not only to improve the quality of geoid (quasi-geoid) models in Brazil, but also to contribute to the geodetic infrastructure, in particular, at the moment, for the establishment of the International Height Reference Frame, where two of six planned stations are located in the densification area. These efforts resulted in the computation of two quasi-geoid models in the Southeast region of Brazil. The decision is to compute a quasi-geoid instead of a geoid model, once since 2018, the Brazilian vertical system is based on normal heights. The Minas Gerais model was computed using Least Squares Collocation, via Fast Collocation. The spectral decomposition was employed in the technique for quasi-geoid model computation, where the reference field was represented by XGM2019 up to degree and order 200. The model was compared with GNSS/leveling in order to check the consistency of two different data sets. Two quasi-geoidal models for the São Paulo state have been computed. Numerical integration through the Fast Fourier Transform (FFT) was used to perform the integral. The Molodensky gravity anomaly was determined in a 5’ grid, reduced and restored using the Residual Terrain Model (RTM) technique and the XGM2019 with the degree and order 250 and 720. The validation for the São Paulo quasi-geoid model is based on the GNSS measurements in the leveling network too.  The Digital Terrain Model SRTM15 plus was used in the continent and the ocean areas in both states.
The structure of Indian monsoon low-pressure systems in the subseasonal-to-seasonal prediction models
Authors: Deoras Akshay , Hunt Kieran M. R. , Turner Andrew G.
Published: March 2021

Indian monsoon low-pressure systems (LPSs) are synoptic-scale cyclonic vortices that produce around half of the summer monsoon rainfall over India, and often cause catastrophic floods. Thus, accurate predictions of LPSs are crucial for disaster management and long-term planning. To improve the skill of LPS forecasts, it is important to understand how seasonal forecast models simulate the structure and behaviour of these weather systems. Here we examine in detail the simulation of the structure of LPSs by eleven models of the Subseasonal-to-Seasonal (S2S) prediction project. We use a feature-tracking algorithm to identify LPSs in all S2S models during a common re-forecast period of June–September 1999­­–2010. We then generate composite horizontal and vertical structures and compare them with those of LPSs in ERA-Interim reanalysis. 

The results suggest that LPSs have the weakest intensity as well as precipitation in the Bureau of Meteorology (BoM), Australia, Hydrometeorological Centre of Russia (HMCR) and Japan Meteorological Agency models. Most S2S models simulate the warm-over-cold core structure that is commonly observed in LPSs, except for the BoM and HMCR models, which simulate weak positive temperature anomalies near the LPS centre in the lower troposphere. The vertical structure of relative vorticity is shallower and weaker in all S2S models than in ERA-Interim. In most S2S models, LPS composites feature a drier middle and upper troposphere than in ERA-Interim. There is a strong positive correlation between precipitation and the 925 hPa temperature anomaly in most S2S models and ERA-Interim supporting the hypothesis that evaporative cooling from precipitation and reduced insolation due to significant cloud cover are responsible for the lower-tropospheric cold core.
Disentangling the effect of past and present agroforestry practices in modifying landscapes of Mediterranean mountains
Authors: Lizaga Ivan , Gaspar Leticia , Latorre Borja , Navas Ana
Published: March 2021

Soil erosion and sediment delivery to rivers are important drivers for land degradation and environmental change in mountain agroecosystems.  These factors are especially severe in areas affected by intermittent heavy rainfalls after dry periods, and human practices such as deforestation or clearcutting practices. Many Mediterranean mountain environments underwent conversion of rangelands into croplands during the previous centuries increasing the risk of erosion. After land abandonment the process was gradually reversed during the middle of the 20thcentury, allowing the recovery of natural land cover and reduced soil erosion rates. To further control the high erosion rates, several afforestation programs introduced pine forests at the headwater of most Mediterranean mountain catchments transforming the landscape by terracing and reducing the sediment connectivity. However, nowadays, forests’ different management could lead to high erosion rates and subsequent landscape modifications. To understand the possible effect of these practices together with the current agricultural management, we have combined the strength of empirical data and spatially distributed modelling. Surface soil samples from different land uses were collected in a representative catchment at the foot of Santo Domingo range at the border of the central Ebro River valley. The study catchment was mostly cultivated at the beginning of the 19th century but changed to rangeland and pine afforestation in the last 50 years. The remaining croplands are predominated by rainfed agriculture that leaves soils mostly unprotected from June to January when erosive storms occur. The main land uses are croplands, pine afforestation, scrubland and Mediterranean forest.

In this study, we propose an ensemble technique composed of 137Cs derived soil redistribution rates as specific point values and as a calibration tool for the widely used WaTEM/SEDEM sediment delivery model. Thus, by the use of ground truth and modelled data we aim to i) apply the WaTEM/SEDEM model at the catchment scale and calibrate it with 137Cs derived soil redistribution rates for finding an optimal set of input parameters; ii) examine the effect of clearcutting and agricultural practices on the total erosion; iii) compare the modelled results with recently calculated sediment apportionments by using the sediment fingerprinting technique.

Our findings highlight the use of spatially distributed models combined with 137Cs derived rates as a powerful tool to understand the driving factors of soil erosion in the last decades and to delineate the hotspot areas that could suffer high erosion if subjected to certain management practices.
Quantifying whole tree non-structural carbon dynamics under long-term experimental drought using radiocarbon
Authors: Peltier Drew , Carbone Mariah , Ebert Christopher , Xu Xiaomei , Adams Henry , McDowell Nate , Pockman Will , Richardson Andrew , Trowbridge Amy
Published: March 2021

Under increasingly frequent, persistent, and severe drought events, predicting future forest carbon dynamics necessitates quantitative understanding of the physiological processes leading to tree mortality and physiological impairment. The responses of non-structural carbon (NSC; primarily sugars and starch) pools in mature trees is particularly important, as dynamics in NSC interact with hydraulic damage to perturb future tree growth. However, NSC concentration measurements alone are not suUcient to understand the stress responses of tree NSC pools formed over years to decades. Thus, we are using radiocarbon (14C) to quantify the age of NSC stored within, and used by, piñon pine trees exposed to either severe or long-term drought stress at the Sevilleta LTER, in New Mexico, USA. Measuring the age of NSC allows inference on the storage history of a tree, and how different NSC pools may be altered by drought. Experimental plots are subjected to either 0% (control) or 90% reduction in precipitation. A 45% precipitation reduction plot has also been in place since 2009, offering a chance to study the impacts of a decade of drought. We are measuring Δ14C of NSC in twigs, bole sapwood, and coarse roots, as well as in CO2 respired from the bole and branches. Our goal is to quantify the role of different-aged NSC pools across tree organs in driving whole-tree physiological responses to drought. Preliminary results show that the long-term droughted trees store and respire on average younger NSC than control trees. Ongoing drought treatments and sampling will provide additional information on how NSC dynamics in these trees are influenced by drought.
Predicting Non-Growing Season Net Ecosystem Exchanges of CO2 from a Canadian Peatland 
Authors: Rafat Arash , Rezanezhad Fereidoun , Quinton William , Humphreys Elyn , Webster Kara , Van Cappellen Philippe
Published: March 2021

The world’s cold regions are experiencing some of the fastest warming, especially during the winter and shoulder seasons. Recent studies have further highlighted the significance of carbon dioxide (CO2) emissions during the non-growing season (NGS) to the annual carbon (C) budgets of northern peatlands. Because of the positive feedback of soil microbial respiration to warming, even at sub-zero temperatures, a warmer NGS may be expected to alter the C balance of peatlands, which are estimated to store about one-third of global terrestrial organic C stocks. However, estimates of NGS net ecosystem CO2 exchange (NEE) of peatlands remain highly uncertain. In this study, we use a variable selection methodology and a global sensitivity analysis (GSA) to determine the most influential environmental variables affecting the NGS-NEE of CO2 in a temperate Canadian peatland (Mer Bleue Bog; Ottawa, Canada). A data-driven machine learning model is trained on a 13-year (1998-2010) continuous record of eddy covariance flux measurements at the site. The model successfully reproduces the observed NGS-NEE CO2 fluxes using only 7 variables: soil temperature, soil moisture, air temperature, wind direction and speed, net radiation, and upwelling photosynthetic photon flux density. Of these 7 input variables, NGS-NEE is most sensitive to changes in net radiation, likely through the latter’s strong linkages to variations in plant phenology and snow cover. We further predict how the future NGS-NEE of the Mer Bleue Bog will change under three climate scenarios (RCP2.6, RCP4.5, and RCP8.5). According to the projections, mean NEE during the NGS could increase by up to 103% by the end of the 21st century. Our results thus reinforce the urgent need for a comprehensive understanding of peatlands as evolving sources of atmospheric CO2 in a warming world.
Comparing and Advancing Approaches to Long-Term Flood Projection
Authors: Schlef Katherine , François Baptiste , Brown Casey
Published: March 2021

How should design flood magnitudes be estimated under climate change? Apart from assuming stationarity, the two main approaches are hydrologic simulation and informed-parameter, which is generally based on either trend or climate covariates. Here, we compare these approaches across a large set of hydro-climatologically diverse basins located throughout the contiguous United States, splitting the historic record into a calibration and validation time period. We evaluate performance when the approaches are forced with observed climate as well as simulated climate from general circulation models. We also investigate how the strengths of the climate informed and hydrologic simulation approaches can be combined to improve projections; here, we use the outputs of hydrologic simulation as covariates in the climate informed approach. The results provide a quantitative perspective on key long-term flood projection issues and provide a route forward to improving projections given the identified strengths and weaknesses of each approach.
Nonuniqueness and Uniqueness for Inverse Magnetization Problems
Authors: Gerhards Christian , Kegeles Alexander , Menzel Peter
Published: March 2021

Nonuniqueness is a well-known issue with inverse problems involving geophysical potential fields (typically gravitational or magnetic fields). If no additional assumptions are made on the underlying source, only certain harmonic contributions can be reconstructed uniquely from knowledge of the potential. Such harmonic contributions have no intuitive geophysical interpretation. However, in various applications some specific properties are of particular interest: e.g., the direction of the magnetization in paleomagnetic studies or the lithospheric susceptibility in geomagnetism. In this presentation, we give a brief overview on the characterization of nonuniqueness and on a priori assumptions on the underlying magnetization that might lead to uniqueness or at least partial uniqueness.
HypoSVI: Hypocenter inversion with Stein Variational Inference and Physics Informed Neural Networks
Authors: Smith Jonathan , Ross Zachary , Azizzadenesheli Kamyar , Muir Jack
Published: March 2021

High resolution earthquake hypocentral locations are of critical importance for understanding the regional context driving seismicity. We introduce a scheme to reliably approximate a hypocenter posterior in a continuous domain that relies on recent advances in deep learning.

Our method relies on a differentiable forward model in the form of a deep neural network, which is trained to solve the Eikonal equation (EikoNet). EikoNet can rapidly determine the travel-time between any source-receiver pair for a non-gridded solution. We demonstrate the robustness of these travel-time solutions are for a series of complex velocity models.

For the inverse problem, we utilize Stein Variational Inference, which is a recent approximate inference procedure that iteratively updates a configuration of particles to approximate a target posterior by minimizing the so-called Stein discrepancy. The gradients of this objective function can be rapidly calculated due to the differentiability of the EikoNet. The particle locations are updated until convergence, after which we utilize clustering techniques and kernel density methods to determine the optimal hypocenter and its uncertainty.

The inversion procedure outlined in this work is validated using a series of synthetic tests to determine the parameter optimisation and the validity for large observational datasets, which can locate earthquakes in 439s per event for 2039 observations. In addition, we apply this technique to a case study of seismicity in the Southern California region for earthquakes from 2019.
Disposing of CO2 in basaltic rocks:  opportunities to upscale storage and co-locate sites with offshore renewable (wind) power 
Authors: Goldberg David
Published: March 2021

Continued fossil fuel burning is likely to increase CO2 concentrations in the atmosphere to previously unknown levels and emissions will continue to outpace uptake, unless limiting action is taken. This paper presents new approaches to mitigate emissions and drawdown atmospheric CO2 , that is, new combinations of developing and existing technologies in offshore settings. We consider the permanent and safe geological storage of carbon dioxide (CCS) through in situ carbon mineralization and the potential for CO2  uptake and disposal in offshore basalt formations. The CCS concept in general aims to separate CO2 from industrial emissions, and/or directly remove it from the air, and permanently store it underground. Integrating these technologies with renewable (wind) energy in offshore settings may offer a scalable, long-term climate mitigation choice that warrants early consideration. Current studies of co-located opportunities and new offshore demonstration projects are considered. 

 
Backus-Gilbert style inversions for mantle anisotropy using normal mode data 
Authors: Restelli Federica , Koelemeijer Paula , Zaroli Christophe
Published: March 2021

Seismic tomography is essential for imaging the Earth’s interior in order to better understand the dynamic processes at work. However, robust physical interpretation of tomographic images remain difficult as the inverse problem is under-determined, model amplitudes are biased and uncertainties are usually not quantified.

Commonly-used techniques, such as damped least-square inversions, break the non-uniqueness of the model solution by adding a subjective, ad hoc, regularization, which can lead to biased amplitudes and potential physical misinterpretations. The SOLA method (Zaroli, 2016; Zaroli et al., 2017), based on a Backus-Gilbert approach, removes the non-uniquess by averaging, rather than introducing a subjective regularization. The method explicitly constrains the amplitudes to be unbiased and the computation of the model resolution and uncertainty is inherent and efficient. Instead of aiming to minimize the data fit, the SOLA approach aims to minimize the size of the averaging volume and the associated uncertainties.

We aim to build a new tomographic model of the Earth’s mantle using the SOLA method. We focus our observations on normal mode data, the standing waves of the Earth observed after very large earthquakes, which are not affected by an uneven data distribution. As normal modes are sensitive to multiple seismic parameters, we treat the sensitivity to different parameters as so called “3D noise” within the SOLA framework. We are specifically interested in constraining seismic anisotropy, which provides more direct information on mantle flow.

Here, we report on some forward modelling results, fundamental to understanding normal mode sensitivity to seismic anisotropy at different depths and identifying which modes to focus on during inversions. We also show our initial work towards building a new tomography model, including the calculation of 3D noise and target kernels.

 
Decadal-scale onset and termination of Antarctic ice-mass loss during the last deglaciation
Authors: Weber Michael E. , Golledge Nicholas R. , Fogwill Christopher J. , Turney Chris S.M. , Thomas Zoë A.
Published: March 2021

Emerging evidence suggests retreat of the Antarctic Ice Sheet (AIS) can persist considerably longer than the duration of the forcing. Unfortunately, the short observational record cannot resolve the tipping points, rate of change, and responses on century and longer timescales. New data from Iceberg Alley identifies eight retreat phases after the last Ice Age that de-stabilized the AIS within a decade, contributing to global sea-level rise for centuries to a millennium, which subsequently stabilized equally rapidly. New blue ice records and independent ice-sheet modeling demonstrate the dynamic response of the AIS included a step-wise retreat of up to 400 km across the Ross Sea, accompanied by ice elevation drawdown of the West Antarctic Ice Sheet (>600 m). Together, these long time series support studies that propose the recent acceleration of AIS mass loss may mark the beginning of a prolonged period of ice sheet retreat, associated with substantial global sea level rise.
A new in-situ method to determine the hydrolysis rate constant of adenosine triphosphate (ATP) by application of Raman spectroscopy in a hydrothermal diamond anvil cell
Authors: Moeller Christoph , Schmidt Christian , Guyot Francois , Wilke Max
Published: March 2021

In recent decades increasing evidence was found for life under extreme conditions, e.g., near black smokers on the ocean floor. The synthesis and stability of vital molecules like adenosine triphosphate (ATP) and adenosine diphosphate (ADP) are essential to maintain the metabolism of all known organisms. The lifetime of these molecules in water is limited by the non-enzymatic hydrolysis reaction that becomes dominant at elevated temperatures. A better understanding of this mechanism will provide us insights of life at extreme conditions.

Previous studies determined the hydrolysis rate constants of ATP for several compositions, temperatures and pressures using quench experiments and subsequent analysis. So far, it was not tested whether quench artefacts might have affected those results. Therefore, the current study was performed to develop a method to follow the reaction in-situ with a high sampling rate at elevated temperatures. A confocal micro-Raman spectrometer and a hydrothermal diamond anvil cell were used to perform experiments at elevated temperatures and vapour pressure. Spectra were obtained in the range of 660 cm-1 to 1157 cm-1 as a function of time. Different solutions of ATP and ADP were measured at 353 K, 373 K, and 393 K, at starting pH values of 3 and 7. First findings are consistent with previous studies and show that with decreasing pH value the hydrolysis rate increases. The data indicate hydrolysis rate constants in the magnitude of 10-3 s-1 by 393 K, 10-4 s-1 by 373 K and 10-5 s-1 by 353 K. These initial observations show that this technique produces reliable kinetic data on this reaction. It also provides much better sampling statistics than quench experiments. 

The high reaction rates suggest that a mechanism exists to regulate this reaction at higher temperatures, which is necessary to allow metabolism under extreme conditions. Moreover, it is commonly known that ATP interacts with various metal ions with different effects on the reaction rate. An application of this method would be the quantification of the hydrolysis rate constant in chemically more complex systems.
Plasma waves in Rosetta electric field observations in the plasma environment of comet 67P/Churyumov-Gerasimenko
Authors: Odelstad Elias , Karlsson Tomas , Eriksson Anders , Johansson Fredrik
Published: March 2021

We perform a comprehensive statistical study of plasma wave activity observed in the electric field measurements obtained by the Langmuir probe instrument (RPC-LAP) onboard ESA's Rosetta spacecraft, which followed the comet 67P/Churyumov-Gerasimenko in its orbit around the sun for over two years in 2014-2016. We focus on waves in the range 1-30 Hz, roughly corresponding to the lower-hybrid frequency range. Here, electric field oscillations close to the local H2O+ lower hybrid frequency are common and collocated with sharp plasma density gradients, suggesting generation by the lower hybrid drift instability. We compare statistically the properties of the waves to the theoretical predictions on lower-hybrid wave generation by the lower hybrid drift instability, regarding e.g. amplitude dependence on plasma density gradients. We also examine the data for waves that can be attributed to other instabilities, such as various velocity-space anisotropies that may occur in the cometary plasma. We correlate the comet-related parameters, (relative spacecraft position, solar distance, plasma and neutral gas density, etc.) with wave-related parameters, such as amplitude/spectral density and frequency. This investigation greatly helps to clarify the importance of the plasma waves in different regions of the cometary plasma environment. 
Spatial content and variability of mercury in agricultural soils in the province of Valencia (Spain), with an emphasis on those dedicated to rice crop
Authors: Boluda Rafael , Roca Pérez Luis , Ramos Miras Joaquín , Rodríguez Martín José A. , Bech Borras Jaume
Published: March 2021

Mercury (Hg) is a metal potentially dangerous that can accumulate in soils, move to plants and cause significant ecotoxicological risks. The province of Valencia is the third in Spain and has a great agricultural, industrial and tourist vocation; it has an area of 10,763 km2, of which it devotes 272,978 ha to cultivation, most of which are irrigated soils. To the south of the city of Valencia, is the Albufera Natural Park (ZEPA area and Ramsar wetland) with 14,806 ha dedicated to rice cultivation. Pollution and burning of rice straw in rice paddies are serious problems. Therefore, the concentration of Hg in agricultural soils in the province of Valencia according to use, with an emphasis on rice paddy soils, and spatial distribution were determined; and the effects of rice straw burning on Hg accumulation on rice paddy soils was assessed. Systematic sampling was carried out throughout the agricultural area at an intensity of a grid of 8 x 8 km, in which samples composed of soil between 0 and 20 cm were collected in a total of 98 plots; and a simple random sampling in the case of rice paddies in 35 sites, distinguishing between plots where the incineration of rice straw was carried out and where it was not. The concentration of Hg was determined with a direct DMA-80 Milestone analyzer in the previously pulverized sample. The detection limit was 1.0 g kg-1, the recovery was 95.1% to 101.0% ± 4.0%. The analyses were performed in triplicate. A basic descriptive statistic (means, medians, deviations, and ANOVA) was performed. Samples were grouped according to land use. For geostatistic analysis and in order to obtain the map of the spatial distribution of the concentration of Hg in soils, the classical geostatistic technique was used by ordinary kriging. The concentration of Hg in the soils of the province of Valencia showed great variability. The soils of the rice paddies together with those dedicated to the cultivation of citrus and horticultural of the coastal plain, showed the highest levels of Hg, in contrast to the soils of the interior areas dedicated to dry crops (vineyards, olive, almond and fodder). Spatial analysis reflected a concentration gradient from west to east, suggesting that the Hg in the soils of the interior has a geochemical origin, while in the coast soils it is of anthropic origin. On the other hand, it was observed that the burning of rice straw increased the Hg concentration in rice paddy soils. This research is the first information on the distribution of Hg in the soils of the province of Valencia and a contribution that can help weigh the effects of open burning of rice straw on Valencian rice paddies.
Property of long term (1990-2009) seismicity in the region of L’Aquila Mw6.1 earthquake revealed from machine learning 
Authors: Majstorović Josipa , Poli Piero
Published: March 2021

On April 6th 2009 (01:32 UTC) strong earthquake of magnitude MW6.1 occurred near the city of L’Aquila in the Abruzzo region in the Central Apennines of Italy. Due to the extensional processes the Abruzzo region is characterized by prominent historical seismicity. However, before the 2009 event the background seismic activity is characterised as sparse and mostly clustered in space and time. The general lack of events, especially small magnitude events before the 2009 event motivated us to study the long-term near-fault seismicity before the large earthquake occurrence. To achieve this we first have to extend the existing catalog. We take into consideration the data from the AQU (42.354, 13.405) station that has been recorded in the city of L’Aquila, near Paganica fault responsible for the 2009 event, during an extensive period of 29-years, 19 years before the event itself. The catalog extension is performed by applying the two-stage convolutional neural network pipeline for earthquake detection and characterisation (epicentral distance and magnitude) using three component signal station waveforms. The algorithm allows us to successfully detect ~800 local events (less than 10 km from the AQU station) in the period 1990-2009. We here present a detailed analysis of this catalog including waveforms characterization to derive new insights about the long term preparation processes(es) occuring before the 2009 Mw6.1 earthquake.
The improved representation of underwater radiances and its impact on simulated physics and biogeochemistry in the North Sea
Authors: Skakala Jozef , Bruggeman Jorn , Ford David , Ciavatta Stefano
Published: March 2021

In the presented work we advanced our modelling of in-water optics on the North-West European (NWE) Shelf, with important implications for how we model stratification of the water column, primary productivity, and the underwater radiances. We implement a stand-alone bio-optical module into the existing coupled physical-biogeochemical model configuration. The advantage of the bio-optical module, when compared to the pre-existing light scheme is that it resolves the underwater irradiance spectrally and distinguishes between direct and diffuse downwelling streams. The changed underwater irradiance compares better with both satellite and in-situ observations. We show that both underwater irradiance and model biogeochemistry can be further improved by assimilating suitable ocean-color derived satellite products into the model. We use the light module to introduce feedback from biogeochemistry to physics and demonstrate that the two-way coupled model tends to outperform the one-way coupled model in both physics and biogeochemistry. We discuss the implications of our developments for future modelling of the NWE Shelf.
Mercury vapour haloes in near-surface air above ore deposits and faults on Vancouver Island, British Columbia, Canada
Authors: Rukhlov Alexei S. , Ootes Luke , Hickin Adrian S. , Mashyanov Nikolay R.
Published: March 2021

Volatile geogenic components, such as CO2, He, Rn, and Hg0, form haloes in soil gas and near-surface air directly above mineral deposits. This contrasts with lithochemical, hydrochemical, and biochemical dispersion haloes that can be laterally displaced or obscured by transported overburden. Mercury vapour surveys have been used in exploration, because Hg occurs in most types of enogenic ore deposit types and is highly mobile. Low background concentrations in the atmosphere (1.2 to 1.5 ng/m3) enable detecting even weak Hg emissions directly above buried ore deposits. In this study, we measured Hg vapour in air 1-50 cm above ground at 15 sites on Vancouver Island, British Columbia, Canada. To evaluate the effectiveness of the method across a range of settings, these sites include different types of known mineralized zones, barren rocks, and faults, both buried and exposed. The direct and continuous analysis via a portable RA-915M mercury analyzer reveals Hg vapour concentrations ranging from 0.5 to 54.4 ng/m3. The highest Hg concentration was observed above tailings at the Bentley Au occurrence, possibly due to the amalgamation technique used for fine gold extraction between late 1800s and early 1900s. Prominent Hg vapour haloes mark shear-hosted Cu-Ag-Au sulphides at Mount Skirt (13.4x background Hg), epithermal Au-Ag-Cu at Mount Washington (8.9x background Hg), and sediment-covered polymetallic volcanogenic massive sulphides at the Lara-Coronation occurrence (4.2 to 6.6x background Hg). Basalt-hosted Cu-Ag-Au sulphide zones at the Sunro past producer are marked by weak Hg vapour anomalies relative to local background. Faults, including the Leech River fault, which was active in the Quaternary, are also marked by weak Hg vapour anomalies. The study confirms that, although the Hg level is influenced by weather, the real-time Hg vapour measurement of near-surface air can instantly delineate mineralized zones and fault structures that are buried under overburden 10s of m thick. In contrast to soil gas sampling, this simple and rapid technique can be applied to mineral exploration and geological mapping under overburden above any type of surface, including outcrops, talus, bogs, water bodies, snow, and permafrost.
Atmospheric gaseous hydrochloric and hydrobromic acid in urban Beijing, China: detection, source identification and potential atmospheric impacts
Authors: Yao Lei , Fan Xiaolong , Cai Jing , Yan Chao , Chu Biwu , R. Dällenbach Kaspar , Wang Yonghong , Dada Lubna , Zha Qiaozhi , Kontkanen Jenni , Kurtén Theo , Iyer Siddhart , T Kujansuu Joni , Petäjä Tuukka , Worsnop Douglas , Kerminen Veli-Matti , Liu Yongchun , Bianhi Federico , Tham Yee Jun , Kulmala Markku
Published: March 2021

Gaseous hydrochloric (HCl) and hydrobromic acid (HBr) are vital halogen species that play essential roles in tropospheric physicochemical processes. Yet, majority of the current studies on these halogen species were conducted in marine or coastal areas. Detection and source identification of HCl and HBr in inland urban areas (especially megacities) remain scarce, thus, limiting the full understanding of halogen chemistry and potential atmospheric impacts in the environments with limited influence from the marine sources. Here, both gaseous HCl and HBr were concurrently measured by Chemical Ionization-Atmospheric Pressure interface-Long Time Of Flight-Mass Spectrometer (CI-APi-LTOF-MS) in urban Beijing, China at the BUCT station (39.94° N, 116.30° E) during winter and early spring of 2019. We observed significant HCl and HBr concentrations ranged from a minimum value at 1.3×108 cm-3 and 4.3×107 cm-3 up to 5.9×109 cm-3 and 1.2×109 cm-3, respectively. The HCl and HBr concentrations are enhanced along with the increase of atmospheric temperature, UVB, and levels of gaseous HNO3. Based on the air mass analysis and high correlations of HCl and HBr with the burning indicators (HCN and HCNO), the gaseous HCl and HBr are found to be related to anthropogenic burning aerosols. The gas-aerosol partitioning may also play a dominant role in the elevated daytime HCl and HBr. During the daytime, the reaction of HCl and HBr with OH radicals lead to significant production of atomic Cl and Br, up to 1.7×104 cm-3 s-1and 7.9×104 cm-3 s-1, respectively. The production rate of atomic Br (via HBr + OH) are 2-3 times higher than that of atomic Cl (via HCl + OH), highlighting the potential importance of bromine chemistry in the urban area. Furthermore, our observations of elevated HCl and HBr may suggest an important recycling pathway of halogen species in inland megacities, and may provide a plausible explanation for the widespread of halogen chemistry, which could affect the atmospheric oxidation in China.
Relict basal ice from the Laurentide Ice Sheet near Lac de Gras, Slave Geological Province, N.W.T., Canada
Authors: Gruber Stephan , Subedi Rupesh , Kokelj Steven V.
Published: March 2021

A 2015 drilling campaign near Lac de Gras has recovered permafrost core interpreted to contain preserved basal ice of the Laurentide Ice Sheet (Subedi et al., 2020). Previous samples of basal ice from ice sheets originate from coring, usually beneath modern ice divides, modern margins of Arctic icecaps that have preserved basal ice-sheet ice, or from studies near the margins of former ice sheets. The present study may be the first evidence of basal ice a few hundred kilometers from ice divides. In this intermediate zone, rates of erosion beneath an ice sheet increase and the thermal regime at the base varies. Our finding is of applied relevance because it highlights the mosaic character of a landscape that contains terrain types with non-negligible ground-ice content, poised for climate-driven thaw and landscape change. The occurrence and mosaic character of preserved ice may be reconciled with glaciological theory and observations from mineral prospecting using the theory on the genesis of dispersal plumes in till developed by Hooke et al. (2013). The existence of preserved basal ice opens basic-research opportunities alongside exploration, mining and infrastructure development in the area.  

Hooke, R. L. B., Cummings, D. I., Lesemann, J. E., and Sharpe, D. R.: Genesis of dispersal plumes in till, Can. Jo. Earth Sci., 50, 847–855, https://doi.org/10.1139/cjes-2013-0018, 2013.

Subedi, R., Kokelj, S. V., and Gruber, S.: Ground ice, organic carbon and soluble cations in tundra permafrost soils and sediments near a Laurentide ice divide in the Slave Geological Province, Northwest Territories, Canada, The Cryosphere, 14, 4341–4364, https://doi.org/10.5194/tc-14-4341-2020, 2020.
Searching for new physics: Using explainable AI to understand deep learned parameterizations of turbulent heat fluxes
Authors: Bennett Andrew , Nijssen Bart
Published: March 2021

Machine learning (ML), and particularly deep learning (DL), for geophysical research has shown dramatic successes in recent years. However, these models are primarily geared towards better predictive capabilities, and are generally treated as black box models, limiting researchers’ ability to interpret and understand how these predictions are made. As these models are incorporated into larger models and pushed to be used in more areas it will be important to build methods that allow us to reason about how these models operate. This will have implications for scientific discovery that will ensure that these models are robust and reliable for their respective applications. Recent work in explainable artificial intelligence (XAI) has been used to interpret and explain the behavior of machine learned models.

Here, we apply new tools from the field of XAI to provide physical interpretations of a system that couples a deep-learning based parameterization for turbulent heat fluxes to a process based hydrologic model. To develop this coupling we have trained a neural network to predict turbulent heat fluxes using FluxNet data from a large number of hydroclimatically diverse sites. This neural network is coupled to the SUMMA hydrologic model, taking imodel derived states as additional inputs to improve predictions. We have shown that this coupled system provides highly accurate simulations of turbulent heat fluxes at 30 minute timesteps, accurately predicts the long-term observed water balance, and reproduces other signatures such as the phase lag with shortwave radiation. Because of these features, it seems this coupled system is learning physically accurate relationships between inputs and outputs. 

We probe the relative importance of which input features are used to make predictions during wet and dry conditions to better understand what the neural network has learned. Further, we conduct controlled experiments to understand how the neural networks are able to learn to regionalize between different hydroclimates. By understanding how these neural networks make their predictions as well as how they learn to make predictions we can gain scientific insights and use them to further improve our models of the Earth system.
Testing a Sea Ice Model
Authors: Livings David , Feltham Danny , Schroeder David
Published: March 2021

SI3 (Sea Ice modelling Integrated Initiative) is the sea ice engine of the NEMO ocean model. It incorporates elements of three sea ice models that have been used with NEMO in the past: CICE, GELATO, and LIM. It takes account of sea ice dynamics, thermodynamics, brine inclusions, and subgrid-scale thickness variations.

A process that has historically been poorly represented in sea ice models is the formation and evolution of melt ponds. These ponds accumulate on the surface of sea ice during the melt season and affect the heat and mass balance in various ways, the most important of which is a reduction in albedo. A melt pond scheme that has a significant impact on surface albedo has recently been added to SI3, based on the ideas of Flocco et al (JGR, 2010). This scheme attempts to represent the influence of ice topography on lateral meltwater transport. We present the results of tests of the grid-level conservation of heat and fresh water in this new scheme. To perform these tests we have incorporated a basic mixed-layer ocean model into SI3 as an intermediate complexity alternative to running with the full ocean model or forcing with saved ocean fields.

We also present a comparison of SI3 with the Los Alamos sea ice model (CICE) in multi-decadal simulations. These comparisons cover the sea ice mass balance (sea ice concentration, extent, and thickness) and the sea ice motion.
Evaluating the influence of erosion and tectonic processes on California’s topography by measuring its fractal dimension and anisotropy across scales
Authors: Guillon Hervé , Lane Belize , Byrne Colin F. , Pasternack Gregory B. , Sandoval Solis Samuel
Published: March 2021

Roughness is paramount in Earth sciences, and landscapes, laboratory alluvial fans, river bed elevation, bedload transport and the friction laws of fluid mechanics all exhibit a fractal behavior described by a scale-persistent roughness. Yet, for a given landscape, the exact meaning of statistical roughness, or fractal dimension, remains unclear. The fractal dimension of topography is mainly understood as two end-members: at large spatial scales, it describes tectonic processes; at small spatial scales it describes erosion processes. In this study, we nuance this description by identifying the spatial scale at which erosion processes are inadequately described by fractal dimension and provide quantitative bounds on the meaning of the statistical roughness of topography at scales from 0.25 km to 100 km using three lines of evidence. First, we leverage spatial statistics to evaluate the auto-correlation structure of topographic statistical roughness across the physiographically diverse state of California, USA. Second, we identify the down-slope and across-slope directions using two-dimensional Fourier analysis, and measure the anisotropy of topography by evaluating statistical roughness in each direction. Third, we perform a spatial correlation analysis between statistical roughness and the Péclet number which describes the balance between diffusion and incision processes. Our preliminary results indicate that correlation between statistical roughness and Péclet number fades at scales greater than 4.6 km. In addition, auto-correlation saturation occurs for statistical roughness at scales greater than 16.5 km. Hence our analysis provides a more nuanced description of the statistical roughness of topography: it represents erosion processes at scales up to 4.6 km while being dominated by tectonics at scales greater than 16.5 km.