bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil Moisture Patterns in an artificial water catchment – A machine learning approach from geophysical measurements
Authors: Badorreck Annika , Moghadas Davood
Published: March 2020

The Chicken Creek catchment (Brandenburg, Germany) was built 2005 in a post-mining landscape in Eastern Germany and was left for an unmanaged primary ecosystem succession. During the following years this artificially created system was subject to a series of fast changes with regard to morphology, hydrology or vegetation cover. Soil water content plays a major role since it mediates the water and energy exchange between the surface and atmosphere. In this respect, time‐lapse electrical resistivity tomography measurements were carried out along a transect in the Chicken Creek catchment.

Electrical and electromagnetic geophysical techniques have been widely used to estimate soil electrical conductivity (σ) and soil moisture (θ). However, obtaining the relationship is not straightforward due to the non‐linearity and also dependency on many different soil and environmental properties. To ensure proper retrieval of the σ and θ, reference values were measured near the beginning of the transect via an excavated pit using 5TE capacitance sensors installed at different depths.

The purpose of this contribution is to determine if artificial neural network is an appropriate machine learning technique for relating electrical conductivity to soil water content. We explored robustness and pertinence of the artificial neural network approach in comparison with Rhoades model (as a commonly used petrophysical relationship) to convert the inversely estimated σ from electrical resistivity tomography to the θ. The proposed approach was successfully validated and benchmarked by comparing the estimated values with the reference data. This study showed the superiority of the artificial neural network approach to the Rhoades model to obtain relationship. In particular, artificial neural network allowed for more accurate estimation of the temporal wetting front than the petrophysical model. The proposed methodology thus offers a great promise for deriving spatiotemporal soil moisture patterns from geophysical data and obtaining the in situ relationship, taking into account the non‐linear variations of the soil moisture.
Experimental constraints on mylonite formation
Authors: Skemer Philip , Bollinger Caroline , Cross Andrew , Couvy Helene
Published: March 2020

Mylonites are ubiquitous structural features of dynamic plate boundaries, and are widely assumed to represent the product of localized deformation at high pressure and temperature. There are two features of mylonites that distinguish them from typical host rocks: grain-sizes that may be reduced by orders of magnitude and mineral phases that generally well-mixed.  Together, these microstructural characteristics are thought to promote rheological weakening over long geologic intervals, an essential feature of Earth-like plate tectonics.  In this contribution we describe experiments that seek to reproduce deformation processes and resulting microstructures that occur during mylonitization. Experiments were conducted at high pressure (1-2 GPa) and temperature (500-750 C) on dense synthetic composites of calcite (Ca) and quartz (Qz), anhydrite (An), or fluorite (Fl).  These composites were selected to investigate the influence of viscosity contrast on the phase mixing process. Shear strains of γ > 50 were produced using the Large Volume Torsion Apparatus (LVT) at Washington University in St. Louis.  Ex situ microstructural analysis was performed with optical microscopy, SEM, EBSD, and TEM. Experiments are interpreted to have deformed by either viscoplastic (Ca+Fl and Ca+An) or semi-brittle mechanisms (Ca+Qz). We show that the evolution of the protolith towards recrystallized and well-mixed microstructures occurs over a large range of shear strains. The critical strain depends on the mechanism of mixing, the viscosity contrast between the two phases, and the microstructure of the starting material. Phase mixing is determined to be the product of several independent mechanisms, the relative importance of which depends on pressure, stress, strain, composition, viscosity contrast, and the ratio of the initial grain-size to the recrystallized grain size.
Tidally influenced iceberg motion: sub-metre resolution imaging of iceberg ploughmarks using autonomous underwater vehicles in the Weddell Sea
Authors: Montelli Aleksandr , Batchelor Christine , Ottesen Dag , Dowdeswell Julian , Evans Jeff , Dowdeswell Evelyn
Published: March 2020

Linear to curvilinear depressions interpreted as iceberg ploughmarks are identified on the continental shelf beyond Larsen C Ice Shelf in about 350 m water depth using multibeam echo-sounding at sub-metre horizontal resolution. Detailed imaging of ploughmark morphology demonstrates the presence of irregularly spaced ridges extending across the full ploughmark width. These ridges have an arcuate shape in plan-view, are up to 2 m high, 20-40 m wide, show occasional presence of subdued debris-flow lobes on their distal side and have an asymmetric cross-profile in which the seafloor deepens beyond their slightly steeper side. The ridges are interpreted to have been produced when the iceberg moved backwards under the falling tide, which pushed up a ridge of sediment behind the iceberg keel, before it continued on its original trajectory under the rising tide. Similar features, which we term ‘iceberg tidal ridges’, can be identified at lower resolution on bathymetric and three-dimensional seismic data from the mid-Norwegian margin, suggesting the broader implications of the interpretations presented here. For example, the mapping of delicate ridges preserved within iceberg ploughmarks can be used to reconstruct past oceanic circulation including the former direction and strength of ocean currents.
Is there warming in the pipeline? A multi-model analysis of the zero emission commitment from CO2
Authors: MacDougall Andrew H. , Frölicher Thomas L. , Jones Chirs D. , Rogelj Joeri , Matthews H. Damon , Zickfeld Kirsten ,   Zero Emissions Commitment Model Intercomparison Project
Published: March 2020

The Zero Emissions Commitment (ZEC) is the change in global mean temperature expected to occur following the cessation of net CO2 emissions, and as such is a critical parameter for calculating the remaining carbon budget. The Zero Emissions Commitment Model Intercomparison Project (ZECMIP) was established to gain a better understanding of the potential magnitude and sign of ZEC, in addition to the processes that underlie this metric. Eighteen Earth system models of both full and intermediate complexity participated in ZECMIP. All models conducted an experiment where atmospheric CO2 concentration increases exponentially until 1000 PgC has been emitted. Thereafter emissions are set to zero and models are configured to allow free evolution of atmospheric CO2 concentration. The inter-model range of ZEC 50 years after emissions cease for the 1000 PgC experiment is -0.36 to 0.29 oC with a model ensemble mean of -0.06 oC, median of -0.05 oC and standard deviation of 0.19 oC. Models exhibit a wide variety of behaviours after emissions cease, with some models continuing to warm for decades to millennia and others cooling substantially. Analysis shows that both ocean carbon uptake and carbon uptake by the terrestrial biosphere are important for counteracting the warming effect from reduction in ocean heat uptake in the decades after emissions cease.

 

Overall, the most likely value of ZEC on decadal time-scales is assessed to be close to zero, consistent with prior work. However substantial continued warming for decades or centuries following cessation of emission is a feature of a minority of the assessed models and thus cannot be ruled out.
Divergent consensuses on Arctic amplification influence on mid-latitude severe winter weather
Authors: Cohen Judah , Zhang Xiangdong ,   Arctic mid-latitude linkages review paper
Published: March 2020

The Arctic has warmed more than twice as fast as the global average since the late 20th century, a phenomenon known as Arctic amplification (AA).  Recently, there have been significant advances in understanding the physical contributions to AA and progress has been made in understanding the mechanisms linking AA to mid-latitude weather variability.  Observational studies overwhelmingly support that AA is contributing to winter continental cooling.  While Arctic warming is strongest at the surface, it extends throughout the mid-troposphere. In addition, the sea ice loss and associated warming is not uniform across the Arctic, but rather regionally focused including in the Barents-Kara Seas, a key region for disrupting the polar vortex.  The probability of severe winter weather increases across the Northern Hemisphere continents following polar vortex disruptions.  While some model experiments support the observational evidence, the majority of modeling results show little connection between AA and severe mid-latitude weather. Rather the excess warming generated in the Arctic due to sea ice loss and other mechanisms is not redistributed vertically in model simulations, but rather horizontally suggesting the export of excess heating from the Arctic to lower latitudes.  Divergent conclusions between model and observational studies, and even intra-model studies, continue to obfuscate a clear understanding of how AA is influencing mid-latitude weather.
Methane emissions and origin in tree stems in an upland forest
Authors: Barba Josep , Poyatos Rafael , Capooci Margaret , Vargas Rodrigo
Published: March 2020

Trees can exchange methane (CH4) with the atmosphere through their stems. However, the magnitudes, patterns, drivers and origin of these emissions as well as the biogeochemical pathways that might result in net CH4 production or uptake are still poorly understood. One of the most important constraints is the limited information on the spatial and temporal variability of these emissions. Manual measurements are useful for measuring spatial variability of stem emissions (both within and between trees), but their low temporal frequency hinders our understanding of temporal patterns. In contrast, high-frequency measurements capture temporal variability, but instrumentation cost and complex technical logistics preclude high number of spatial replicates. In this study we combined manual and automated measurements of tree stem emissions in 18 different bitternut hickory trees (Carya cordiformis) in an upland forest during one growing season. Methane emissions were measured at two stem heights (75 and 150 cm) in three trees every 30 min, whereas the other 15 trees were measured once every two weeks at three different stem heights (50, 110 and 170 cm). Additionally, sap flow, soil temperature, soil water content, ground water level, and CH4 concentrations in the heartwood and in the soil profile were measured. Finally, we performed incubations of stem cores to test its potential for producing CH4. All trees were net sources of methane during the experiment, but some of them showed sporadic capture of CH4. High-frequency measurements revealed large temporal variability of stem emissions even within hours. Trees showed a seasonal trend of CH4 emissions partially explained by sap flow, soil moisture and temperature, but the pattern and the magnitudes were not consistent between and within trees. Even when a larger number of trees were studied (15 trees with manual measurements every two weeks), no consistent spatial pattern emerged among trees or with stem height, with emissions differing up to two orders of magnitude among trees. We found high CH4 concentrations in the heartwood of the trees (up to 75,000 ppm), no relevant concentrations in the soil profile (<6 ppm in all cases), and methanogenic capacity in all trees (stem cores were able to produce CH4 in laboratory incubations), supporting the interpretation that CH4 emitted by treestems was likely produced in the heartwood of the trees rather than being produced in soils and transported by the roots. Our results provide evidence on the potential origin of CH4 emitted by tree stems, but also indicate that the spatial and temporal patterns of stem emissions should be better described in order to assess the role of trees in local-to-global CH4 budgets.
Self-organisation of morphology and sediment transport in alluvial rivers
Authors: Lajeunesse Eric , Abramian Anais , Devauchelle Olivier
Published: March 2020

The coupling of sediment transport with the flow that drives it shapes the bed of alluvial rivers. The channel steers the flow, which in turns deforms the bed through erosion and sedimentation. To investigate this process, we produce a small river in a laboratory experiment by pouring a viscous fluid on a layer of plastic sediment. This laminar river gradually reaches its equilibrium shape. In the absence of sediment transport, the combination of gravity and flow-induced stress maintains the bed surface at the threshold of motion (Seizilles et al., 2013). If we impose a sediment discharge, the river widens and shallows to accommodate this input. Particle tracking reveals that the grains entrained by the flow behave as random walkers. Accordingly, they diffuse towards the less active areas of the bed (Seizilles et al., 2014). The river then adjusts its shape to maintain the balance between this diffusive flux, which pushes the grains towards the banks, and gravity, which pulls them towards the center of the channel. This dynamical equilibrium results in a peculiar Boltzmann distribution, in which the local sediment flux decreases exponentially with the elevation of the bed (Abramian et al., 2019). As the sediment discharge increases, the channel gets wider and shallower. Eventually, it destabilizes into multiple channels. A linear stability analysis suggests that it is diffusion that causes this instability, which could explain the formation of braided rivers (Abramian, Devauchelle, and Lajeunesse, 2019).

 

References:

Abramian, A., Devauchelle, O., and Lajeunesse, E., “Streamwise streaks induced by bedload diffusion,” Journal of Fluid Mechanics 863, 601–619 (2019).

Abramian, A., Devauchelle, O., Seizilles, G., and Lajeunesse, E., “Boltzmann distribution of sediment transport,” Physical review letters 123, 014501 (2019).

Seizilles, G., Devauchelle, O., Lajeunesse, E., and M ́etivier, F., “Width of laminar laboratory rivers,” Phys. Rev. E. 87, 052204 (2013).

Seizilles, G., Lajeunesse, E., Devauchelle, O., and Bak, M., “Cross-stream diffusion in bedload transport,” Phys. of Fluids 26, 013302 (2014).
Dynamics of a subglacial meltwater plume revealed by continuous subsurface monitoring directly on the calving front
Authors: Podolskiy Evgeny A. , Kanna Naoya , Sugiyama Shin
Published: March 2020

Recent literature has highlighted the great importance of subglacial meltwater plumes in a variety of processes including subaqueous ice melting, enhanced fjord-scale circulation, nutrient and heat mixing, foraging ground formation, and the movements of seals that apparently use plumes for returning to the sea surface.

However, direct measurements of plume water properties are scarce due to the difficulty of conducting observations near unstable glacier calving fronts. A few studies have succeeded in obtaining snapshot views of plume structures using bio-logging, remotely operated vessels, or helicopter-borne eXpendable Conductivity Temperature Depth (XCTD) probes, but continuous data time-series remain elusive and technically challenging.

In this study, we overcame these limitations by deploying mooring-based equipment between major calving events from a calving front of Bowdoin Glacier, an ocean-terminating glacier in Northwest Greenland. In July 2017, a first-of-its-kind 10 d dataset of plume dynamics was obtained by attaching instruments to the ice cliff for the logging of conductivity, temperature, and pressure at depths of ~5 m and ~100 m, with a sampling interval of 10 s.

Nonlinear and spectral time-series analysis revealed a chaotic system, an extremely turbulent environment, the presence of coherent structures, tide-modulated signals, and a non-intuitive transition in the dynamics of the plume due to a witnessed glacial lake outburst flood. Our observations should provide an important reference for the glacier-science community, including modellers interested in the evolution of ocean-terminating glaciers, fjord-scale circulation, and glacier fjord ecosystems.
Brittle Deformation and Neotectonics of the Serra da Cantareira Ridge, Pico do Jaraguá Hill, and Perus Region – Southeastern Brazil
Authors: Pinheiro Marcos , Cianfarra Paola
Published: March 2020

Classical geomorphological and geological researches state that the Brazilian landscapes are mostly influenced by the old tectonics (Pre Cenozoic), considering that such region is currently far away from the South America plate border, where seismic activity is higher. On the other hand, recent studies are pointing out present-day tectonic activity in the southeast Brazil thus revealing that Neotectonics, the tectonic regime acting since Neogene, has an important role on the evolution of the Brazilian landforms, including the Continental Rift of Southeastern Brazil, which comprises a set of 900 km length of ENE-WSW tectonic lines and tertiary basins. However, information about Neotectonic activity in the nearby zones of the rift are still missing, such as in the Serra da Cantareira Ridge, Pico do Jaraguá Hill and Perus region, both of them characterized by outcrops of Pre Cambrian igneous and metamorphic rocks. In this way, the objective of this research is to study the brittle deformation of these areas in order to identify possible traces of Neotectonics. This young tectonic was explored through lineament domains, which were automatically detected by SID software and statistically analyzed through Daisy 3 software. In the field, 712 structural data were surveyed in 51 outcrops and cumulated into databases of the Daisy 3 software, in order to identify the main fault azimuthal trends, fault kinematics, and compute the paleostresses. The lineament analysis show the presence of a principal E-W lineament domain, coincident and possibly related to an old (Neoproterozoic), shear zone probably reactivated in the current tectonic regime.  The field data indicate the predominance of NW-SE, E-W, and NE-SW strike-slip faults, compatible with the left and right-lateral kinematics of the E-W shear corridor. The computed paleostresses are similar to the Neotectonic stress regime identified in the surrounding areas by other researches: NE-SW compression and NW-SE extension (Neogene); Nearly N-S compression and E-W extension (Holocene). On the other hand, only some of the studied faults present evidence of Neotectonic activity. In fact, most of the surveyed faults are closed or mineral-filled, suggesting they are old or were not recently reactivated. The preliminary results of this work suggest the important role of inherited (Pre-Cambrian) crustal weakens crustal zone probably reactivated in Cenozoic and also in the Neotectonic stress regime. Further detailed studies and field surveys are still necessary to highlight the role of the current Neotectonic regime on the present-day Brazilian landscape as well as to better define the geographic extent and location of the E-W shear corridor.
Projected 21st Century changes in extreme wind-wave events
Authors: Meucci Alberto
Published: March 2020

Extreme ocean waves shape world coastlines and significantly impact offshore operations. Climate change may further exacerbate these effects increasing losses in human lives and economic activities. Studies generally agree on the trends in the mean values, yet there is no consensus on the extreme events, and whether their magnitude and/or frequency are changing. The present work applies an innovative extreme value analysis approach to a multi-model ensemble wind-wave climate dataset, derived from seven global climate models, to evaluate projected extreme wave height changes towards the end of the 21st century. Under two greenhouse gas emission scenarios, we find that at the end of the 21st century, the one in 100-year wave height event increases across the scenarios by 5 to 15 % over the Southern Ocean. The North Atlantic shows a decrease at low to mid-latitudes (5 to 15 %) and an increase at the high latitudes (10 %). The extreme wave heights in the North Pacific increase at the high latitudes by 5 to 10 %. The present work suggests that pooling an ensemble of future projected ocean storms from different GCMs might significantly improve uncertainty estimates connected to future coastal and offshore wave extremes, thereby improving climate adaptation strategies.
Analysis of physicochemical characteristics in the atmospheric boundary layer over the North Plain China based on large tethered balloon and Doppler wind lidar
Authors: Sun Haijiong , Shi Yu , Hu Fei , Zhang Zhe , Ding Weichen
Published: March 2020

Physicochemical characteristics of the atmospheric boundary layer over North Plain China during the comprehensive observation experiment from 10 to 21 December 2018 were investigated in this paper. The observation data are obtained from the large tethered balloon, Doppler wind lidar, ground-level instruments. The maximum concentration of PM2.5 exceeded 200 µg m-3, and the ratio value of PM2.5/PM10 was basically around 0.4 (maximum has reached approximately 0.8) during the whole observation period, indicating that explosive growth of fine ode dominant aerosols during the winter heating season. The peak solar irradiance was slightly larger on the clean day, compared with the value during the pollution process. The correlation coefficient between the concentration of PM2.5 and CO was highest (0.725) among the gas pollutants, and the relationship between O3 and PM2.5 was basically negative correlated, not simple linear relationship. Three distinctly different vertical profile types of the PM2.5 were categorized according to the vertical changes based on the total 33 vertical profiles obtained by the tethered balloon. Type 1 was mainly observed in the daytime, accounted for nearly 51.5%, the PM2.5 concentration decreased nearly linearly as a function of height below approximate 600 m; Type 2 shows a sharp decreasing trend from the ground to about 200 m; Type 3 shows multi-layer structure of pollutants, some pollutants suspended aloft in upper air. The vertical profile of PM2.5 was closely related to the atmospheric vertical structure such as the wind, temperature and turbulent kinetic energy, caused by the diurnal variation of the boundary layer. Small wind layer and the weak turbulence activities contributed to the accumulation of pollutants. Vertical patterns of the concentration of PM2.5 were also greatly affected by the local ground emission sources and regional transport processes.
Analysis of flooding potential with different return periods-A case study of Dianbao River in Kaohsiung City, Taiwan
Authors: Hsieh Tien-Hsiang , Liu Wen-Cheng
Published: March 2020

　　In Taiwan, when the rainy season comes, the extreme rainfall and typhoon events cause floods and economic losses in the middle and lower reaches, which impacts on the safety of people's lives. In this study, we took Dianbao River in Kaohsiung City as an example and simulated the rainfall-runoff in the upstream water catchment area based on the HEC-HMS model and used its results as the flow input condition of the FLO-2D model. The two models were validated by the Kongrey typhoon event in 2013 and the Megi typhoon event in 2016. In terms of upstream watershed, the analysis results of the HEC-HMS rainfall-runoff errors for the Kongrey typhoon and the Megi typhoon were as follows: percent errors of peak discharge (EQP) were 0.6% and 4.6%, respectively; errors of time to peak (ETP) were 0 hour and 2 hours, respectively; coefficients of efficiency (CE) were 0.89 and 0.91, respectively. In the Dianbao River, the FLO-2D model error analysis results of Kongrey typhoon and Megi typhoon events were as follows: percent errors of peak water level (EWP) were 13.51% and 4.71%, respectively; errors of time to peak (ETP) were 1 hour and 0 hour, respectively; coefficients of efficiency (CE) were 0.69 and 0.79, respectively. The simulation and validation of the two typhoon-inundated areas were reasonable and then the model was applied to explore the flood potential of the Dianbao River during different flood return periods.

Keywords：HEC-HMS、FLO-2D、rainfall-runoff、error analysis、flooding potential
Recent Progress of APSOS-Tibet System Observation-Current Status and Future Plan
Authors: Lyu Daren , Wang Yinan , Pan Weilin , Xuan Yuejian , Wang Xin , Tian Yufang , Bi Yongheng
Published: March 2020

To understand the dynamics-physics-chemistry processes of the whole atmosphere, from earth surface to lower thermosphere, a synthetic observation system was established over the Tibetan Plateau at the end of 2017. This system consists of 5 lidars, 2-micrometer wave cloud radars, a THz spectrometer, and a set of surface meteorological observation instruments as well as atmospheric environmental instruments. The system, we call it as APSOS, is located in central Tibet, Yangbajing, at the altitude of 4300m ASL. During the last 2 years, quasi-continuous observations are made for different realms. A set of observation data have been collected for future analysis. Some of the system ability and case study has been achieved and further work plan will be presented in this paper.
The mantle flow below the Alps from isolated mantle anisotropy based on differential Ps – XKS Splitting
Authors: Link Frederik , Rümpker Georg
Published: March 2020

SKS-splitting measurements in the European Alps show an anisotropic fast axes parallel/subparallel relative to the mountain-belt. This indicates a mantle flow with a rotational component according to the orogeny under the assumption that the fast axes directly reflect the flow direction. This might be misleading due to a possible crustal contribution of anisotropy. Therefore, we isolate the crustal anisotropy using an improved receiver function method that accounts for anisotropic and structural properties.

The analysis for the crustal anisotropy is based on the stacking method proposed by Kaviani & Rümpker (2015). We modify their approach by introducing a time-selective splitting analysis of the crustal Ps- and PpPs-phases. The stacking is performed to the phases after correction of the anisotropic effect according to the model parameters H, the crustal thickness,  κ, the P-to S-wave velocity ratio, a, the percentage of anisotropy and φ, the fast axis orientation.

The Alps show a considerable Moho-topography due to its mountain root and its complex tectonic history. This can significantly deflect the crustal phases introducing a dominating appearance in the receiver functions. We therefore analyse for a dipping interface (not accounting for anisotropy) and then use an improved model in our analysis to infer the anisotropic properties of the crust.

Knowing the crustal anisotropic contribution we correct for this effect on the XKS-waveforms to isolate the anisotropy of the mantle. The remaining splitting shows an improved approximation of the flow patterns in the asthenosphere, while complexities might still imply an effect of the lithospheric mantle.

We apply our approach to stations of the AlpArray network resulting in a detailed distribution of the crustal anisotropy in the European Alps and show first results for the isolated mantle anisotropy from the corrected XKS-waveforms and the crustal anisotropy from the receiver-function analysis.
Phosphorus dynamics associated with partitioning of organic carbon oxidation pathways in the surface sediments of the deep Ulleung Basin, East Sea
Authors: Mok Jin-Sook , Kim Bomina , Cho Hyeyoun , An Sung-Uk , Lee Hyun-Ji , Hyun Jung-Ho
Published: March 2020

As sediments play an important role as either a sink or a source of phosphorus (P) for water column, it is important to elucidate the major P fractions and behaviors (i.e., mobilization and immobilization) in the sediments to better understand P cycles in local and global scale. We investigated major P speciation associated with the partitioning of organic carbon (Corg) oxidation in the sediments to elucidate the P dynamics at two contrasting sediments in the continental shelf (EB1) and rise (EC1) in the Ulleung Basin (UB), East Sea. Sulfate reduction (SR) pre-dominated Corg oxidation at shelf site (EB 1), comprising % of Corg oxidation, whereas Mn- and Fe-reduction combined accounted for >80% of Corg oxidation in Mn-oxide and Fe-oxide-rich basin site (EC 1). Under SR-dominated condition (EB 1), H2S oxidation coupled to reductive dissolution of FeOOH to form precipitation of FeS induced the accumulation of dissolved iron and phosphate in the pore water. On the other hand, phosphate in the Mn- and Fe-oxide-rich basin sediments (EC 1) was depleted because the P released through organic matter decomposition or reductive dissolution of Fe oxide/Mn oxide was effectively adsorbed to the metal-oxides in the surface sediments. Sequential extraction of P phases revealed that Fe bound P (52-65% of total P) was the major phase in the surface sediments of both sites. Interestingly, the organic P (Porg) fraction was 2.4-times higher at the basin site (12 μmol g-1) than at the shelf site (5 μmol g-1). Corg : Porg ratios presented as redox proxies in sediments were 644 and 191 for EB1 and EC1, respectively,. The results indicate that Porg has an effective preservation relative to Corg under sub-oxic conditions (EC1), whereas Porg was preferentially regenerated under anoxic conditions (EB1). Overall, the dynamics of P in the UB sediments were largely regulated by the partitioning of Corg oxidation pathways (i.e., sulfate reduction vs. metal reduction) and resultant interaction between Fe/Mn-S-P.
Estimation of terrestrial latent heat flux over Qilian Mountains by the fusion of five satellite-derived products using Extremely Randomized Trees
Authors: Shang Ke , Yao Yunjun , Yang Junming , Chen Xiaowei , Bei Xiangyi , Guo Xiaozheng
Published: March 2020

The latent heat flux (LE) governs the associated heat flux from the interactions between the land surface and its atmosphere and plays an important role in the surface water and energy balance. The Qilian Mountains is the largest marginal mountain system in the northeast of the Qinghai-Tibet Plateau. An accurate representation of spatio-temporal patterns of LE over Qilian Mountains is essential in many terrestrial biosphere, hydrosphere, and atmosphere applications. Various satellite-derived LE products have been widely used to estimate terrestrial LE, yet each individual LE product exhibits large discrepancies. To reduce uncertainties from individual product and improve terrestrial LE estimation over Qilian Mountains, we produced five satellite-derived LE products using traditional algorithms based on Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI, LAI products and China Meteorological Forcing Dataset (CMFD), and implemented the fusion of these five LE products using Extremely Randomized Trees (Extra-Trees) combining information from ground-based measurements. A validation using ground-based measurements was applied at different plant function types and the validation results demonstrate that the fusion product using Extra-Trees outperformed all the LE products used in the fusion method. Comparing with three other machine learning fusion models such as Gradient Boosting Regression Tree (GBRT), Random Forest (RF) and Gaussian Process Regression (GPR), Extra-Trees exhibits the best performance in terms of both training and validation accuracy. This fusion LE product also outperformed when compared against two state-of-the-art global LE products such as Global Land Surface Satellite (GLASS) and Moderate Resolution Imaging Spectroradiometer (MODIS). The fusion LE product showed improvements in the linear correlation, bias and RMSE at different plant function types. Our results suggest that the fusion method using Extra-Trees could be successfully applied to other region and to enhance the estimation of other hydrometeorological variables.
A Bayesian Approach to Improve Regional and Global Ionospheric Maps using GNSS Observations
Authors: Farzaneh Saeed , Forootan Ehsan
Published: March 2020

The Global Ionosphere Maps (GIMs) are generated on a daily basis at the Center for Orbit Determination in Europe (CODE) using the observations from about 200 Global Positioning System (GPS)/GLONASS sites of the International GNSS Service (IGS) and other institutions. These maps contain Vertical Total Electron Content (VTEC) values, which are estimated in a solar-geomagnetic reference frame using a spherical harmonics expansion up to degree and order 15. Although these maps have wide applications, their relatively low spatial resolution limits the accuracy of many geodetic applications such as those related to Precise Point Positioning (PPP) and navigation. In this study, a novel Bayesian approach is proposed to improve the spatial resolution of VTEC estimations in regional and global scales. The proposed technique utilises GIMs as a prior information and updates the VTEC estimates using a new set of base-functions (with better resolution than that of spherical harmonics) and the GNSS measurements that are not included in the network of GIMs. To achieve the highest accuracy possible, our implementation is based on a transformation of spherical harmonics to the Slepian base-functions, where the latter is a set of bandlimited functions that reflect the majority of signal energy inside an arbitrarily defined region, yet they remain orthogonal within this region. The new GNSS measurements are considered in a Bayesian update estimation to modify those of GIMs. Numerical application of this study is demonstrated using the ground-based GPS data over South America. The results are also validated against the VTEC estimations derived from independent GPS stations.

Key words: Spherical Slepian Base-Functions, Spherical Harmonics, Ionospheric modelling, Vertical Total Electron Content (VTEC)
Application of artificial intelligence method to develop a reliable model for spatially assessing the health risk from arsenic exposure via drinking groundwater
Authors: Liang Ching-Ping , Sun Chi-Chien , Chen Jui-Sheng , Xie Yi-Yu
Published: March 2020

Lanyang Plain in northwestern Taiwan is an intensively productive agricultural area, most from the cultivation of crops and aquaculture. Groundwater fi
	Seasonal variability of fast ice edge in the McMurdo Sound between 2017 and 2019 based on Sentinel-1 SAR
Authors: Dai Liyun
Published: March 2020

The fast ice in the McMurdo Sound plays an important role in the coastal ecological systems and climate changes, but its seasonal and interannual variations are poorly understood. In this study, the fast ice phenology and extent variation are investigated using Sentinel-1 Synthetic Aperture Radar (SAR) images from 2017 to 2019, and the factors controlling the fast ice development are explored. The results showed that the fast ice edge presented obvious seasonal change. In 2017/2018 and 2018/2019 years it arrived at northernmost during May – July, and keeps north until the end of December or January, and then moves south, arriving at most south on February or March. However, there are some difference between these two years. The date the fast ice edge arrived at northernmost in 2018 was about two months later than in 2017, but the ending time at the northern edge was about one month earlier (31 Dec 2018 vs 30 Jan 2018). The time when it retreated to the southernmost in 2019 was about one month before that in 2017 or 2018. It seems the longer the edge stays in the northernmost, the later it retreats to the southernmost, and it may not completely disappear; the shorter the edge stays in the northernmost, the earlier it retreats to the southernmost, and it may completely disappear. The dominant factor controlling the beginning and end dates are air temperature. This statement still needs to be confirmed when more data will be processed and analyzed in near future.
Combination of Earth Observation and Seismic Reflection Data Analysis for The Definition of Strike Slip Fault Zones in Central Crete
Authors: Vassilakis Emmanuel , Alexopoulos John , Farangitakis Georgios-Pavlos
Published: March 2020

The general understanding of the major tectonic structures that are traced on Crete Island is of great importance to decipher the geodynamic regime of the leading edge of the overriding Aegean microplate and consequently Eurasia’s southernmost active margin. The aim of this multi-disciplinary methodology is to provide useful information for more reliable mapping of buried structures, which in turn supplement the dynamic and kinematic model of this key area of high interest.

Several indicators for the existence of oblique fault block displacement were identified with the use of earth observation data, as strike slip faulting expressions on the surface are more efficiently identified by vertical observations. Tectonic structures which are usually created along lateral displacements require different working scales. Hence, earth observation data (satellite images, aerial photographs) with various spatial characteristics need to be included.

Therefore, the methodology presented in this paper involves high spatial resolution digital elevation models and several remote sensing multispectral datasets, in many cases merged with higher spatial resolution panchromatic aerial photographs. The co-registration and ortho-rectification of all datasets proved to be a very significant part of this work in order to produce high resolution coloured 3D scenes at selected sites in central Crete, where the observed N-S trending strike slip fault zones crosscut arc parallel low angle normal faults and higher angle fault scarps.

Additionally, deep seismic reflection datasets along the major geomorphic structure of Messara basin were combined and highlighted the strike slip mechanism, since the continuation of the sub-vertical structures in depth has become clearer after the exact positioning of the sections and further interpretation.
The connectivity framework: a way forward in understanding the surface processes and dynamics
Authors: Sinha Rajiv , Singh Manudeo
Published: March 2020

The surface processes are dynamic and act at multiple spatio-temporal scales and contain embedded hierarchies to generate complex landscapes.  It is, therefore, necessary to understand the linkages or ‘connections’ of landscapes across various scales and levels to gain insights on their interactions and feedbacks in association with such processes. Recently, there has been a surge in the application of the concept of connectivity to the multitude of geomorphic systems with varying scales, objectives, and field of study. A large number of review articles and special issues published in the last few years is a testament to the utility of this concept. It, therefore, implies that the connectivity concept could be a way forward to understand the earth’s surface processes and dynamics and their associations with the landforms. This work presents a ‘connectivity framework’ by establishing (a) the interrelationship and interdependencies among its types (sediment connectivity, hydrological connectivity, landscape connectivity), components (structural and functional connectivity), and dimensions (spatial and temporal), (b) the inherent feedback among various components under a process-response framework and under varying terrain characteristics, and (c) its utility in different geomorphic systems at variable scales and physical settings.

In a geomorphic system, connectivity accounts for static and dynamic properties of the landscape, and therefore, establishes structural and functional frameworks of the landscapes and process-response systems. This concept is applicable at all spatial and temporal scales and can be used to understand evolutionary pathways of landscapes and their dynamics. Further, the connectivity approach has the potential to be applied extensively to the hydro-geomorphic systems to understand their complexity as well as for designing effective management practices for river systems and wetlands, water resources for agriculture, and for assessment of ecological flows in rivers. It can also be aligned to a multitude of problems from river basin management to hazard and risk assessment to wetland management and restoration. We, therefore, argue that the connectivity concept is emergent as well as a fundamental property of landscapes and the connectivity framework presents a robust tool to understand the surface processes and dynamics.
Modelling the impact of biogenic particle flux intensity and composition on sedimentary Pa/Th
Authors: Missiaen Lise , Menviel Laurie , Meissner Katrin J. , Bouttes Nathaelle , Roche Didier M. , Dutay Jean-Claude , Quiquet Aurélien , Lhardy Fanny , Waelbroeck Claire , Pichat Sylvain
Published: March 2020

There is compelling evidence of a strong relation between the Atlantic Meridional Overturning Circulation (AMOC) and millennial scale climate variability during the last glacial period. Part of the advances in understanding the underlying mechanisms rely on the analysis of the sedimentary Pa/Th ratio, which can be used to qualitatively infer past flow rates in the Atlantic. The compilation of existing North Atlantic records indicates repeated, consistent and significant Pa/Th increases across millennial-scale events, indicating significant reductions of deep-water formation in the Northwest Atlantic. However, the use of sedimentary Pa/Th as a pure kinematic circulation proxy is challenging because Pa and Th are also highly sensitive to changes in particulate flux intensity and composition that have probably occurred across these millennial scale events. A primary control of particles on the available Pa/Th records has been ruled out ensuring the absence of correlation between the reconstructed particle fluxes (e.g. Th-normalized opal fluxes) and the sedimentary Pa/Th. However, quantitative estimates of the impact of particles on the available paleo Pa/Th are still missing.

In this study, we use the Pa/Th enabled iLOVECLIM Earth System Model of Intermediate Complexity to decipher the impact of particles on the sedimentary Pa/Th. We evaluate the impact of imposed changes in biogenic particle flux intensity and composition on the Atlantic Pa/Th in a 3-D geographical perspective. We find that up to 30% of the observed Pa/Th increase across Heinrich Stadial 1 could be explained by changes in particle fluxes and composition. Besides, changes in the Particulate Organic Carbon (POC) most efficiently affects the sedimentary Pa/Th, followed by biogenic opal. Last but not least, the global Atlantic sedimentary Pa/Th response is very sensitive to shifts in the geographical distribution of particles and high scavenging areas. In our simulations, a decrease of the opal production in the Northwest Atlantic can induce a far field Pa/Th increase in a large part of the North Atlantic basin, suggesting that a local monitoring of the particle fluxes might not be enough to rule out any influence of the particles on paleo sedimentary Pa/Th records.
On the use of near-neutral backward Lyapunov vectors to get reliable ensemble forecasts in coupled ocean-atmosphere systems
Authors: Vannitsem Stéphane , Duan Wansuo
Published: March 2020

The use of coupled Backward Lyapunov vectors (BLv) for ensemble forecast is demonstrated in a coupled ocean-atmosphere system of reduced order, the Modular Arbitrary Order Ocean-Atmosphere sytem (MAOOAM). It is found that the best set of BLvs to build a coupled ocean-atmosphere forecasting system are the ones associated with near-neutral or slightly negative Lyapunov exponents. This counter intuitive result is related to the fact that these sets display larger projections on the ocean variables than the others, leading to an appropriate spread for the ocean, and at the same time a rapid transfer of these errors toward the most unstable BLvs affecting predominantly the atmosphere is experienced. The latter dynamics is a natural property of any generic perturbation in nonlinear chaotic dynamical systems, allowing for a reliable spread with the atmosphere too. The implications of these results for operational ensemble forecasts in coupled ocean-atmosphere systems are discussed.  
Improving 2-km drought monitoring by assimilating satellite and in-situ soil moisture into a distributed hydrological model in the Yangtze River basin
Authors: Yang Han , Xiong Lihua , Xu Chong-Yu
Published: March 2020

Hydrological drought is increasing due to the collaborative influence of climate change and human activities, especially in populated river basins. Despite drought monitoring skills are improved over the last decade for the development of satellite technology and global measuring networks, there are still challenges for an accurate simulation and prediction of hydrological drought in small spatial scale. In this study, in order to improve small scale drought monitoring, soil moisture datasets with different spatial scales, including multi-satellite-retrieved soil moisture dataset released by the Europe Space Agency’s Change Initiative (ESA CCI) with a spatial resolution of 0.25° and in-situ soil moisture dataset measured in dots, are considered to assimilate into the 2-km Digital Elevation Model (DEM) based distributed rainfall-runoff model (DDRM). The 2-km soil moisture simulations coupled with outlet streamflow simulations are used to identify hydrological drought in the Yangtze River basin. Three assimilation scenarios, including (i) only assimilating satellite soil moisture; (ii) jointly assimilating satellite and in-situ soil moisture; (iii) correcting satellite soil moisture by in-situ data firstly, and assimilating the corrected satellite soil moisture into the model, are developed to identify the influence of different scenarios on drought monitoring. Results indicate that all assimilation scenarios significantly improve 2-km soil moisture drought monitoring, and slightly improve streamflow drought monitoring. The scenario of assimilating corrected satellite soil moisture dataset into the model has the best performance, and the scenario of only assimilating satellite data has the worst. This study recommends a valuable assimilation scenario of the distributed hydrological model for better improving drought monitoring in a small spatial scale.

 
Role of vegetation on fire behaviour in Fennoscandia forests during the Holocene
Authors: Molinari Chiara , Bradshaw Richard H.W. , Carcaillet Christopher , Hannon Gina , Lehsten Veiko
Published: March 2020

The relationship between Holocene changes in Fennoscandia biomass burning (reconstructed by means of sedimentary charcoal records from lake and peat bogs) and main forest composition (based on pollen reconstructions from the same sites) divided into three different fire sensitivity classes is explored based on the hypothesis that fire-prone species are more abundant during periods characterized by higher fire disturbance, while fire-intolerant species dominate when biomass burning is low.

The overall patterns found across Fennoscandia suggest that there was low but increasing fire activity during the early Holocene, while a low and decreasing trend characterized the middle Holocene. During the late Holocene biomass burning increased, with a peak around 500 cal yr BP. This maximum is then followed by a downturn during the last centuries.

Generally, fire-prone species are strongly positively correlated with multi-millennial variability of biomass burning in Fennoscandia forests. A positive - but much weaker - relationship also exists between fire-tolerant species and long-term fire trends. On the contrary, a quite strong negative correlation is detected between biomass burning and fire-intolerant species.

The results presented in this large-scale analysis demonstrate that biomass burning was highly linked to fuel type (according to different fire sensitivity classes) during the Holocene, underlying the fact that all past fire-climate studies must consider key functional interactions between fuel type and long-term changes in fire regime.