bluuebunny/crossref_metadata_2025 huggingface dataset:
Understanding monsoon controls on the energy- and mass-balance of glaciers in High Mountain Asia
Authors: Fugger Stefan , Miles Evan , McCarthy Michael , Fyffe Catriona , Kneib Marin , Fatichi Simone , Yang Wei , Pellicciotti Francesca
Published: March 2020

The Indian Summer Monsoon (ISM) shapes the melt and accumulation patterns of glaciers in large parts of High Mountain Asia (HMA) in complex ways due to the interaction of persistent cloud-cover, large temperature amplitudes, high atmospheric water content and high precipitation rates. While the ISM dominates in the southern and eastern regions, it progressively loses influence westward towards the Karakoram, where the influence of westerlies is predominant. Previous applications of energy- and mass-balance models for glaciers in HMA have been limited to single study sites (in Khumbu, Langtang and Parlung) and a few attempted to link model results to large-scale weather patterns. While these studies have helped to understand the energy- and mass-balance of glaciers in HMA under specific local climates, a regional perspective is still missing. In this study, we use a full energy- and mass-balance model together  with eight on-glacier AWS datasets around HMA to investigate how ISM conditions influence glacier-surface energy and mass balance. In particular, we look at how debris-covered and debris-free glaciers respond differently to the ISM, validating our results against independent in-situ measurements. This work is fundamental to the development of parameterizations of glacier melt for long-term hydrological studies and to the understanding of the present and future HMA cryosphere and water budget evolution.
Fault opening related to free surface interaction on reverse faults: insights from numerical modeling
Authors: Bruhat Lucile , Rougier Esteban , Okubo Kurama , Bhat Harsha S.
Published: March 2020

Thrust faults are commonly known to produce significant amounts of slip, damage and ground acceleration, especially close to the free surface. The effect of the free surface on faulting has always been a standing issue in theoretical mechanics. While static solutions exist, they still cannot explain the large amounts of slip, damage and ground acceleration observed on low dipping faults. Dynamics effects raised by the presence of a free surface were first evaluated by Brune [1996] using analog experiments, which hinted at a torque mechanism induced in the hanging wall leading to a natural reduction in elastic compressive normal stress as the rupture approaches the surface. This solution was recently supported by preliminary work from Gabuchian et al. [2017], which, combining numerical and experimental simulations, also showed that the earthquake rupture, propagating up dip, induces rotation of the hanging wall, and might promote fault opening.

In this work, we take advantage of new numerical algorithms for dynamic modeling of earthquake rupture to confirm and document this opening effect. We use enhanced numerical solutions for earthquake rupture, based on the Combined Finite-Discrete Element Methodology (FDEM), which were recently developed by the Los Alamos National Laboratory. Through a systematic analysis of case studies, we investigate the effect of fault geometry, friction parameters and rupture behavior on the deformation pattern. Fault opening is observed in all simulations, growing dramatically as the rupture reaches the surface. Evolution of slip, fault-normal displacement and velocities, and of the predicted surface displacements and velocities are documented for each simulation. These predictions will serve as synthetic data when comparing with recorded surface deformation from real-case earthquakes.
Magnetic fabric and rock magnetic studies of the ~1.78 Ga large igneous province in the North China Craton and its implication for the configuration of the supercontinent Nuna/Columbia
Authors: Xu Huiru , Yang Tao , Dekkers Mark , Peng Peng , Ge Kunpeng , Deng Chenglong
Published: March 2020

The paleo-position of the North China Craton (NCC) within the Supercontinent Nuna/Columbia is controversial. Hindered by ubiquitous alteration of the very ancient rocks, paleomagnetic studies have not been able yet to conclusively solve this puzzle. Comprehensive analysis on the relatively limited Precambrian records is essential to understand the geological history of these cratons. Within the NCC, the tectonic setting of a ~1.78 Ga large igneous province (LIP) is long debated. It is considered to be related to a paleoplume, post-collision extension, or an Andean continental margin. Knowing its mode of formation constrains the geological evolution of the NCC and its paleo-position within the Supercontinent Nuna/Columbia. Here we conduct a study into the anisotropy of magnetic susceptibility (AMS) in the dykes and lavas of the ~1.78 Ga LIP, together with systematic rock magnetic experiments, to constrain the geological background of the igneous event(s), to understand the tectonic evolution of the NCC, as well as its paleo-position within the assembly of the Nuna/Columbia supercontinent.

Thirty-three dykes in the northern and middle parts and thirty lavas in the southern part of the NCC were collected. Detailed rock magnetic analyses indicate PSD magnetite to be the dominant magnetic mineral in the samples, occasionally with pyrrhotite in the dykes and hematite in the lavas. The often observed relatively weak anisotropy degree suggests that the AMS ellipsoids probably portray magma flow-related fabrics. The inferred directions from the AMS fabrics of the lavas reveal a radial flow pattern with an eruption center located on the south margin of the NCC. The studied dykes show a predominance of horizontally to subhorizontally northward magma flow, with only few vertical intrusions. These observations imply that the ~1.78 Ga LIP may have formed by magma source(s) at the south margin of the NCC. Some localized magma sub-chambers may have formed during the propagation of the magma and could have been responsible for the less common vertically intruded dykes and the EW-trending dykes. Therefore, we favor a plume-related tectonic setting for the ~1.78 Ga LIP with the eruption center along the margin of the NCC. It can serve as an essential criterion to search for possible neighbour(s) of the NCC within Nuna/Columbia, which should preserve the relics of the ~1.78 Ga LIP. Our study, in combination with extant geological and paleomagnetic results suggests a close linkage of the NCC with the São Francisco-Congo, Rio de la Plata and Siberia cratons in the Nuna/Columbia supercontinent.
Validity of the hydrostatic approximation at convection-resolving scales: Diagnostic analysis and model intercomparison
Authors: Zeman Christian , Ban Nikolina , Wedi Nils , Schär Christoph
Published: March 2020

The increasing availability of computing power allows the use of kilometer-scale convection-resolving weather and climate models for operational forecasts. One of the open questions at these scales concerns the validity of the hydrostatic approximation, which assumes that vertical accelerations are small compared to the balancing forces of gravity and the vertical pressure gradient. This assumption is valid as long as the ratio of vertical to horizontal length scales of motion is small. Results from previous studies suggest that the horizontal resolution at which the hydrostatic approximation becomes invalid is highly dependent on the particular model, model configuration, and case setup.

 

While most of the previous studies have been conducted with an idealized setup, this work will concentrate on a real-world case. To this end, a few summer days with strong convection over complex terrain in Europe are simulated with the nonhydrostatic regional Consortium for Small-scale Modelling (COSMO) model with horizontal resolutions ranging from 12 km to 275 m. To assess the validity of the hydrostatic approximation, we developed a hydrostatic reconstruction technique and diagnose the vertical wind using the hydrostatic set of equations. The diagnosed values are then compared to the actual nonhydrostatic up- and downdrafts with a statistical analysis of vertical wind speed frequencies for the different resolutions.

 

Results suggest that the diagnosed hydrostatic vertical velocities are very similar to the nonhydrostatic vertical velocities up to horizontal resolutions of 1 km and thus the use of the hydrostatic approximations at these scales still seems to be a valid option.

 

Furthermore, the study contains an intercomparison of precipitation and vertical winds produced by the nonhydrostatic COSMO model and the hydrostatic Integrated Forecast System (IFS) from ECMWF for the same case. The intercomparison supports the previous findings that at resolutions of ∼2 km and ∼4 km the effect of the hydrostatic approximation is negligible. The results also show that a small enough timestep size is essential in order to properly resolve the high vertical velocities associated with convection.
The role of subsurface storage on departures from the Budyko curve
Authors: Pfister Laurent , Schymanski Stan , Nijzink Remko , McDonnell Jeffrey
Published: March 2020

The Budyko framework is a widely used empirical concept in hydrology and climatology. However, catchment water balances that plot along the curve are often noisy and scattered, with some catchments plotting above the curve and some below the curve. Here we examine one of the possible causes for such scatter: subsurface storage. We bring together data from 38 experimental catchments in Luxembourg where all climate and landuse factors are roughly constant, except for subsurface storage.

We leverage diverse catchment geology represented by the large differences in bedrock porosity and permeability with resulting large differences in storage and streamwater transit times across our set of nested catchments. This setting enables us to test the null hypothesis that departures (offset) from the Budyko line along the evaporative index (i.e. actual evapotranspiration / potential evapotranspiration) axis has no relation to below ground storage. We then ask the following questions:

Where do the 38 Luxembourg catchments plot in the Budyko space?

How do subsurface storage metrics vary across the 38 Luxembourg catchments?

How are these subsurface storage metrics related to the Budyko offset?

And secondarily,

What might explain scatter on the precipitation / PET axis in the Luxembourg catchments and how is this related to catchment area?

Our main finding is that subsurface storage—driven by differences in catchment geology—explains approximately 60% of the departure from the Budyko curve. Furthermore, scatter along the aridity index axis (i.e. precipitation / potential evapo-transpiration) is explained by an east-west gradient in precipitation amount within an otherwise low seasonality environment.
The intertidal sanding up of the Seine-Maritime coast (Normandy, France): Sedimentological and geochemical approaches.
Authors: Peuziat Bastien , Costa Stéphane , Tessier Bernadette , Murat Anne , Gregoire Gwendoline
Published: March 2020

The Seine-Maritime coastline (France) is a macro-tidal environment (8 m tidal range), developing along an epicontinental sea, the English Channel. The SW-NE coast is opened to westerly atmospheric flows, generating occasionally wind sea with energetic waves (Hs: 4.65 m decennial return). High chalk cliffs and a wide marine erosion platform partially hidden on its upper part by a flint pebble beach, characterise this 130 km long coast.

Observations since the end of the 1990’s show a recent and massive sanding up of the marine erosion platform. This raises the question of the origin of the sandy fraction and the sedimentary dynamics on the intertidal area.

We present herein an innovative method that combine grain-size and geochemical analysis in order to highlight sand sources and transport direction along these rocky coast.

Sixteen beaches were sampled during low tide and fair-weather conditions. At each site, 3 samples were collected along the cross-shore beach profile (from the pebbly upper beach to the low tide limit).

Grain-size results show that for all sites, medium to coarse-grained sands dominate in the upper beach (mode 315-400µm) while fine sands dominate in the middle and low foreshore (mode 160-250µm). A decrease in grain-size is thus evidenced from the upper beach to the low foreshore.

The geographical variability of the sand composition and consequently sources was determined on the basis of geochemical data. In order to avoid the granulometric effect on the data, X-Ray fluorescence analysis (xSORT, SPECTRO AMETEK) were performed on the two major grain-size modes of each sample. Eighteen calibrated chemical elements (Si, S, K, Ca, Ti, V, Mn, Fe, Ni, Ga, As, Br, Rb, Sr, Y, Pb, Th and U) were measured at each station. Statistical processing performed step by step on the data allows to gradually reduce the number of significant geochemical parameters. Finally, 4 major elements (Si, Ca, Sr, K) as well as the ratio Sr/Ca have been considered as the best proxies of sample discrimination and potential source.

The first results indicate a longshore gradient of Si and Ca, especially for the finest sands (160-200µm). From SW to NE, i.e. in the direction of the littoral drift, and whatever the position across the beach profile, there are an enrichment in Si (sands are more siliciclastic) and an impoverishment in Ca.

This gradient highlights differentiated longshore sediment transport and sorting, in relation probably with sediment sources (siliclastic sands vs bioclastics sands).
Non-monotonic relationship of sun-induced fluorescence to photosynthesis
Authors: Wieneke Sebastian , Balzarolo Manuela , Asard Han , AbdElgawad Hamada , Peñuelas Josep , Rascher Uwe , Ven Arne , Verlinden Melanie , Janssens Ivan , Vicca Sara
Published: March 2020

Due to its close link to the photosynthetic process, sun-induced fluorescence (SIF) is one of the most promising signals to assess spatio-temporal variation in photosynthesis. Yet the positive linear relationship between SIF and photosynthesis, often reported from satellite and proximal remote sensing, contradicts findings from leaf-level studies, particularly under stress conditions. In two separate experiments, we grew Mays (Zea mays L.) under increasing phosphorus limitation and potato (Solanum tuberosum L.) under increasing drought stress to assess whether SIF can detect the phosphorus and drought induced reduction in photosynthesis. We demonstrate that the relationship between photosynthesis and APAR (absorbed photochemical active radiation) normalized SIF (FY) is non-monotonic under increasing environmental stress conditions, rendering the prediction of photosynthesis by FY alone unfeasible. The use of FY in combination with a pigment corrected photochemical reflectance index (PRI) as an indicator of the stress stage, allows the estimation of photosynthesis. However, this approach is strongly affected by uncertainties in PRI and we therefore propose the pigment-corrected ratio of the two SIF peaks (cFratio) as a precise and robust estimator of photosynthesis (R² = 0.90, rRMSE = 10%). Due to its independence on the absorbed photosynthetic active radiation, the cFratio is a promising novel estimator of spatio-temporal variation in photosynthesis.
The effect of plasmaspheric material on magnetopause reconnection
Authors: Fuselier Stephen , Haaland Stein , Tenfjord Paul , Malaspina David , Burch James , Denton Michael , Giles Barbara , Trattner Karlheinz , Petrinec Steven , Strangeway Robert , Toledo-Redondo Sergio
Published: March 2020

The Earth’s plasmasphere contains cold (~eV energy) dense (>100 cm-3) plasma of ionospheric origin. The primary ion constituents of the plasmasphere are H+ and He+, and a lower concentration of O+. The outer part of the plasmasphere, especially on the duskside of the Earth, drains away into the dayside outer magnetosphere when geomagnetic activity increases. Because of its high density and low temperature, this plasma has the potential to modify magnetic reconnection at the magnetopause. To investigate the effect of plasmaspheric material at the magnetopause, Magnetospheric Multiscale (MMS) data are surveyed to identify magnetopause crossings with the highest He+densities. Plasma wave, ion, and ion composition data are used to determine densities and mass densities of this plasmaspheric material and the magnetosheath plasma adjacent to the magnetopause. These measurements are combined with magnetic field measurements to determine how the highest density plasmaspheric material in the MMS era may affect reconnection at the magnetopause.
Keeping Up the Momentum: Early Career Scientists in Policy-making and Community Science
Authors: Hall Caitlyn , Howley Ethan , Morton Evvan , Murphy Erin , Bercovici Hannah , Tindell Kevin , McCutcheon Griffin , Solves Jean-Phillipe , Kurtz Liza , Phillips Mitchell , Bersson Jessica , Bernard Miranda , Dirks Blake , Weller Nicholas
Published: March 2020

To make an impact on science policy, a relationship between scientists, community leaders, and decision-makers cannot stop at one successful event – it must grow and evolve. The Arizona Science Policy Network aims to facilitate collaboration between early career scientists and decision-makers to draft science-informed policy. Beyond providing interactive and cross-disciplinary training and curriculum to scientists, we facilitate opportunities to practice in real situations, including speaking at town halls and public hearings, organizing public science science cafes and science days, writing policy memos and briefs, and advising on bills. In 2019, we successfully brought more than 60 early career scientists to the Arizona State Capitol to discuss drafts of the complex, multi-state Drought Contingency Plan with decision-makers. Since then, the state government has invited us to help draft sustainability- and climate change-focused legislation. We consider issues like climate change, water quality and availability, heat adaptation and mitigation, science education, ecological and social impacts of mining and industry, waste management, and emerging technologies. As we worked in impacted communities, we soon realized that we were missing the voices of community leaders in the conversation between scientists and policy-makers. In order to correct this, we hosted several science forums in breweries and cafes throughout Arizona. The science cafes initiated collaboration between policy-makers, scientists and community stakeholders, including Native American tribes. These meetings gave scientists, community members, and policy-makers a platform to discuss the environmental and socio-economic  impact of mining sites specific to each forum’s location. Early career scientists contributed their scientific expertise to explain how we can address region-specific problems. Community members also shared their knowledge of each unique area and context of the impact of current business and policy. Policy-makers brought their perspective on how science is used to enact change. From these efforts, we have fostered a more equitable and inclusive environment to ensure that all perspectives and knowledge are included in new bills and policies. Our program has provided a unique experience for scientists to further understand the broader impacts of science on communities and society. This presentation will reflect on the lessons learned in drafting policy with decision-makers and community leaders.
Lake trophic states shape microbial community structure in sediments
Authors: Han Xingguo , Schubert Carsten , Fiskal Annika , Dubois Nathalie , Lever Mark
Published: March 2020

Lake sediments are globally important carbon sinks, and play a critical role in the global carbon cycle. Although the fate of organic carbon in lake sediments depends mostly on sedimentary microorganisms, the environmental controls on the microbial community structure in lake sediments are still poorly understood.

Here we investigate the relationships of lake trophic state, sediment redox chemistry, sediment organic matter (OM) sources and microbial community structure in sediment records across five lakes with different eutrophication histories and trophic states in central Switzerland. Our results show that, across all five lakes, bacterial and archaeal communities based on 16S rRNA gene sequencing analyses show similar sediment depth-dependent zonations at the phylum- and class-level, which appears to be primarily driven by vertical distributions of electron acceptors and secondarily by differences in the contributions of aquatic and terrestrial OM revealed by biomarkers. Yet, there are clear differences in microbial communities between lakes, most notably the higher abundances of putatively aerobic nitrifying Bacteria (Nitrospirae) and Archaea (Marine Group I, Thaumarchaeota) in anoxic sediments of oligotrophic Lake Lucerne. Furthermore, at the level of Zero-radius Operational Taxonomic Unit (ZOTU), eutrophication-related trends are more pronounced, in which microbial communities in the sediments of eutrophic lakes are more similar and share more ZOTUs with each other than with the oligotrophic lake. Notably, deep sediment layers of presently eutrophic lakes that were deposited prior to the era of eutrophication show high similarities in bacterial communities to equivalent depths in the oligotrophic lake. By contrast, archaeal communities are clearly differentiated according to trophic state only in recently deposited sediment layers, and independent of trophic state converge toward high similarities over time.

Our study indicates a significant role of trophic status in driving lacustrine sediment microbial communities and reveals fundamental differences in the temporal responses of bacterial and archaeal communities to anthropogenic eutrophication.
Reconstructing past lake water total phosphorus concentration using sediment geochemical records
Authors: Moyle Madeleine , Boyle John , Chiverrell Richard
Published: March 2020

To understand current phosphorus (P) cycling, which encompasses disturbances caused by human activity, it is necessary to quantify the long-term natural P cycles on which modern drivers act. The shortness of monitored P records renders this difficult by only covering the post-disturbance period and therefore fail to capture pre-disturbance baselines. Target driven management of sensitive ecosystems suffering from eutrophication uses baselines for P that cannot be reliably quantified at present. Recovery will only be possible if P loadings can be brought under control and this requires an understanding of what water quality targets are both desirable and achievable on a site-specific basis. This matters because a well-functioning ecosystem will be more resilient under future climate change and increasing human pressure on the landscape.

Where lakes are present in the landscape, there is the opportunity to use the sediment archive to provide long records of past P concentration.  At present, these reconstructions rely on diatoms or related microfossil indicators. These require time and resource intensive tailored training sets and furthermore the records do not preserve in all lakes. Here we present a novel geochemical method for reconstructing water P concentrations based on lake sediment P burial fluxes, which in principle is universally applicable.

Tested at six published lake sites, the method produces results that agree very well with overlapping monitoring data for those lakes (r2 = 0.8). We want to share our method with the research community to identify additional sites to further verify the general applicability.

To illustrate the value of this approach to site-specific management, we compare past lake water total P reconstructions at Crosemere (UK) with a record of Holocene land cover change to identify the drivers of acceleration in the P cycle. Wider application of this lake sediment geochemical method will allow more critical evaluation of the human and natural drivers of the P cycle and be of benefit to ‘systems understanding’ spanning terrestrial and aquatic ecosystems.
Unravelling and quantifying natural and anthropogenic subsidence drivers in a mega delta
Authors: Minderhoud Philip S.J. , Erkens Gilles , Kooi Henk , Zoccarato Claudia , Teatini Pietro , Stouthamer Esther
Published: March 2020

Unraveling the contribution of different natural and anthropogenic drivers to total subsidence can be a main challenge when studying changes of land elevation in a coastal-deltaic area. In fact, the contribution of a single driver often varies both in time and space and segmented land subsidence measurements only provide part of the solution. However, it is a crucial step required to facilitate the development of effective mitigation and adaptation strategies for sinking coastal-deltaic areas. This presentation highlights recent and future advances towards unravelling the contribution of different subsidence drivers for one of the largest deltas on the planet, the Mekong delta.

The multidisciplinary approach combined estimates of subsidence rates, both remotely-sensed (PS INSAR) and from field observations, with spatial data analysis and two complementary numerical modelling approaches, which bring together information and expertise from amongst others geology, hydrogeology and geomechanics. This multi-year effort provides insights in several significant natural (i.e. natural compaction) and anthropogenic subsidence (i.e. aquifer systems compaction due to groundwater extraction) processes that play a role in the Mekong delta system. Combining various advances enabled the creation of future elevation projections following groundwater-extraction scenarios, which provides valuable insights for Mekong delta’s policymakers but also shows the dire situation of the low-lying delta. Efforts towards further unraveling and quantification different subsidence drivers in the Mekong delta are ongoing and new Sentinel’s PS INSAR data provide exciting opportunities for detailed quantification of depth-depending sinking rates.

Present results make clear that the effectiveness of mitigation measures to reduce groundwater extraction-induced sinking rates will predominantly determine elevation evolution and thereby faith of the low-lying Mekong delta in the coming decades.
Machine learning for detection of climate extremes: New approaches to uncertainty quantification
Authors: Collins William , O'Brien Travis , Prabhat Mr , Kashinath Karthik
Published: March 2020

Machine learning (ML) has proven to be a very powerful body of techniques for identifying rare but highly impactful weather events in huge volumes of climate model output and satellite data.  When these events and the changes in them are studied in the context of global warming, these phenomena are known as climate extremes.  This talk concerns the challenges in applying ML to identify climate extremes, which often center on how to provide suitable training data to these algorithms.  The challenges are:

In many cases, the official definitions for the weather events in the current climate are either ad hoc and/or subjective, leading to considerable variance in the statistics of these events even in literature concerning the historical record; 

Operational methods for identifying these events are also typically quite ad hoc with very limited quantification of their structural and parametric uncertainties; and

Both the generative mechanisms and physical properties of these events are both predicted to evolve due to well-understood physics, and hence the training data set  should but typically does not reflect these secular trends in the formation and statistical properties of climate extremes.  

We describe several approaches to addressing these issues, including:

The recent creation of the first labeled data set specifically designed for algorithm training on atmospheric extremes, known as ClimateNet;

Probabilistic ML algorithms that identify events based on the level of agreement across an ensemble of operational methods;

Bayesian methods for that identify events based on the level of agreement across an ensemble of human expert-generated labels; and 

The prospects for physics-based detection using fundamental properties of the fluid dynamics (i.e., conserved variables and Lyapunov exponents) and/or information-theoretic concepts.
Exploring nitrogen losses from urine patches between upland and lowland grazing systems
Authors: Hunt Danielle , Jones David , Cardenas Laura , Chadwick David
Published: March 2020

Urine patches in grassland ecosystems present unique environments where extreme nitrogen (N) loading occurs. This results in N losses into the atmosphere or leaching from soil. N losses vary due to climate conditions, soil conditions, and management practices. However, we do not fully understand how these factors influence N cycling and nitrous oxide (N2O) emissions from urine patches. Much of the current literature on urine patch N cycling has focused on typical lowland agricultural systems. Very little work has explored other grazing systems, such as upland farming which is conducted across much of Wales. We have investigated this by using a catena sequence crossing both upland and lowland agricultural grazing systems. The range of soil types allowed us to explore how N2O emissions and N losses vary under different conditions. Here we report on both a laboratory incubation and a mesocosm experiment examining these issues. This work should help to fill the knowledge gap around how emissions from urine patches could vary between UK uplands and lowlands. We hope to improve understanding of N losses and provide more realistic, regional, and accurate emission factors for upland farming systems.
Understanding preservation of primary signatures in apatite by comparing matrix and zircon-hosted crystals from the Eoarchean Acasta Gneiss Complex (Canada)
Authors: Bruand Emilie , Antoine Clementine , Guitreau Martin , Devidal Jean-Luc
Published: March 2020

A novel way to investigate the petrogenesis of ancient poly-metamorphosed terranes is to use zircon as a vessel and study protected mineral inclusions which are sensitive to melt evolution such as apatite. Recent contributions have shown that zircon-hosted apatite inclusions of unmetamorphosed granitoids can provide valuable petrogenetic information about a given pluton and, in turn, represent a way to circumvent effects of metamorphism. Yet, the impact of metamorphism on apatite inclusion has never been studied in detail. To address the issue of chemical and isotopic preservation of primary signals in apatite crystals both in the matrix and armored within zircons, we have studied apatite crystals from four 3.6-4.0 Ga orthogneisses of TTG affinity from the Acasta Gneiss Complex (Canada). Our results demonstrate that U-Th-Pb isotope systematics in matrix apatite crystals are reset at the time of the Wopmay orogen (1.8-1.7 Ga) whereas primary REE signatures were preserved in many crystals. On the contrary, zircon-hosted apatite inclusions all preserved primary REE signatures despite U-Th-Pb isotope systematics giving ages between 1.7 and 4.0 Ga. We interpret the variable resetting of these ages as a consequence of radiation damage accumulation in zircon lattice. Only the most pristine zircon has an apatite inclusion with a concordant age consistent with the magmatic age of the zircon (4.0 Ga). In addition, our results show that apatite crystals from TTG have distinct REE composition from post-Archean granitoids apatites, and that even apatites with reset ages preserved some of the chemical signatures characterizing TTG compositions (e.g. HREE). This capacity to retain primary information together with its discriminating power for granitoids makes apatite a very valuable tool for reconstructing the nature and evolution of ancient crustal rocks through the use of either detrital minerals or detrital-zircon hosting inclusions.
Investigation of strongly enhanced methane Part II: Slow climate feedbacks.
Authors: Stecher Laura , Winterstein Franziska , Dameris Martin , Jöckel Patrick , Ponater Michael
Published: March 2020

Methane (CH4) is the second most important anthropogenic greenhouse gas and its atmospheric abundance is rising rapidly at the moment (e.g. Nisbet et al., 2019). 

We assess the effects of doubled and fivefold present-day (2010) CH4 lower boundary mixing ratios on the basis of sensitivity simulations with the
chemistry-climate model EMAC. As a follow-up on Winterstein et al. (2019) we investigate slow adjustments by applying a mixed layer ocean (MLO) model
instead of prescribed oceanic conditions. In the simulations with prescribed oceanic conditions, tropospheric temperature changes are largely suppressed,
while with MLO tropospheric temperatures adjust to the forcing. In the present study we compare the changes in the MLO sensitivity simulations to the
sensitivity simulations with prescribed oceanic conditions (Winterstein et al., 2019). Comparing the responses of these two sets of sensitivity simulations separates rapid adjustments and the effects of slow climate feedbacks associated with tropospheric warming.

The chemical interactions in the stratosphere in the MLO set-up (slow adjustments) compare in general well with the results of Winterstein et al. (2019) (rapid adjustments). The increase of stratospheric water vapor is albeit 5 % (15 %) points weaker in the MLO doubling (fivefolding) experiment compared to the doubling (fivefolding) experiment with prescribed oceanic conditions in line with a weaker increase of stratospheric OH. Stronger O3 decrease and CH4
increase in the lowermost tropical stratosphere in the MLO sensitivity simulations compared to the sensitivity simulations with prescribed oceanic conditions indicate a more distinct strengthening of tropical up-welling due to tropospheric warming in the MLO set-up. The MLO simulations also show evidence of a strengthening of the Brewer-Dobson Circulation. When separating the quasi-instantaneous chemically induced O3 response from the O3 response pattern in the MLO set-up, the O3 response to slow climate feedbacks remains. This pattern is consistent with the O3 response to slow climate feedbacks induced by increases of CO2.

This first of its kind study shows the climatic impact of strongly enhanced CH4 mixing ratios and how the slow climate response of tropospheric warming potentially damp instantaneous chemical feedbacks.
2D thermo-mechanical-chemical coupled numerical models of interactions between a cooling magma chamber and a visco-elastic host rock
Authors: Kiss Dániel , Moulas Evangelos , Rummel Lisa , Kaus Boris
Published: March 2020

A recent focus of studies in geodynamic modeling and magmatic petrology is to understand the coupled behavior between deformation and magmatic processes. Here, we present a 2D numerical model of an upper crustal magma (or mush) chamber in a visco-elastic host rock, with coupled thermal, mechanical and chemical (TMC) processes. The magma chamber is isolated from deeper sources of magma and it is cooling, and thus shrinking. We quantify the mechanical interaction between the shrinking magma chamber and the surrounding host rock, using a compressible visco-elastic formulation, considering several geometries of the magma chamber.

We present a self-consistent system of the conservation equations for coupled TMC processes, under the assumptions of slow (negligible inertial forces), visco-elastic deformation and constant chemical bulk composition. The thermodynamic melting/crystallization model is based on a pelitic melting model calculated with Perple_X, assuming a granitic composition and is incorporated as a look-up table. We will discuss the numerical implementation, show the results of systematic numerical simulations, and illustrate the effect of volume changes due to crystallization on stresses in the host rocks.
A spatial emergent constraint on the sensitivity of soil carbon turnover time to global warming
Authors: Varney Rebecca , Cox Peter , Chadburn Sarah , Friedlingstein Pierre , Burke Eleanor , Koven Charles , Hugelius Gustaf
Published: March 2020

Carbon cycle feedbacks represent large uncertainties on climate change projections, and the response
of soil carbon to climate change contributes the greatest uncertainty to this. Future changes in soil
carbon depend on changes in litter and root inputs from plants, and especially on reductions in the
turnover time of soil carbon (τs) with warming. The latter represents the change in soil carbon
due to the response of soil turnover time (∆Cs,τ), and can be diagnosed from projections made with
Earth System Models (ESMs). It is found to span a large range even at the Paris Agreement Target
of 2◦C global warming. We use the spatial variability of τs inferred from observations to obtain a
constraint on ∆Cs,τ . This spatial emergent constraint allows us to greatly reduce the uncertainty in
∆Cs,τ at 2◦C global warming. We do likewise for other levels of global warming to derive a best
estimate for the effective sensitivity of τs to global warming, and derive a q10 equivalent value for
heterotrophic respiration.
About determination of coordinates of sources of geomagnetic perturbations according to the world network of magnetic observatories
Authors: Zhumabayev Beibit , Vassilyev Ivan , Protsenko Vladimir , Zhumabayeva Saltanat
Published: March 2020

A method for determining the coordinates of geomagnetic perturbation sources based on joint data processing of the world network of magnetic observatories is proposed. A large statistical material showed the relationship of large geomagnetic storms with the interaction of two or more magnetic clouds formed as a result of coronal mass ejections. To determine the coordinates of the sources of perturbations, it is proposed to use the data of magnetic observatories of the "INTERMAGNET" international network, which has more than 100 observation points distributed around the world and equipped with modern identical hardware. The results of geomagnetic field measurement obtained by magnetic observatories are brought to a single coordinate system. It was achieved by rotation of the axes of local stations, which allows determining the coordinates of the sources of perturbations and evaluating the accuracy of specifying the coordinate system of each local observatory.
Using Earth observation data of vegetation to improve global hydrological simulations
Authors: Trautmann Tina , Koirala Sujan , Carvailhais Nuno , Güntner Andreas , Kim Hyungjun , Jung Martin
Published: March 2020

Vegetation structure and activity are the crucial links between the water, carbon and energy cycles. However, their representation remains a major source of uncertainty in large-scale models. Hydrological models not only vary in the way they include vegetation and its interaction with water, but also become less tangible when their complexity increases. This poses a challenge in validating these models, as shown by several comparisons of dynamic vegetation models.

In this context, the increasing availability and quality of Earth observation-based data provides a new avenue and valuable information to improve model simulations and gain insights into the role of vegetation within the global water cycle. On the one hand, such observations can be used to calibrate model parameters. On the other hand, more vegetation related data allows new approaches to describe in-model vegetation characteristics beyond the values that are traditionally defined for plant functional types.

In this study, we use a simple and highly transparent global hydrological model and constrain its vegetation related parameters against diverse Earth observation-based data. We include GRACE terrestrial water storage anomalies, GlobSnow snow water equivalent, ESA CCI soil moisture as well as estimates of evapotranspiration from FLUXCOM and gridded runoff from GRUN in a multi-criteria calibration approach that considers the strengths and uncertainties of each data stream.

Further, we conduct several factorial experiments to test alternative approaches for representing vegetation characteristics that influence processes like infiltration, root water uptake and transpiration. The approaches range from the simple differentiation of vegetated and non-vegetated areas over applying plant functional type-specific parameters to defining vegetation characteristics as functions of Earth observation-based data such as EVI, tree cover and estimates of plant rooting depth.

For each of the experiments, the model is calibrated and the results are finally compared with each other and against observations to quantify the ability to reproduce observational patterns and to assess the effects of vegetation on simulated hydrological processes across spatio-temporal scales.
Accounting for non-stationary effects in the model of the Earth’s pole motion
Authors: Wai Yan
Published: March 2020

Accounting for non-stationary effects in the model of the Earth’s pole motion

Wai Yan Soe, Rumyantsev D.S., Perepelkin V.V.

 

Nowadays the problem of constructing a model of the Earth pole motion is relevant both in theoretical and in applied aspects. The main difficulty of accurately describing the Earth pole motion is that it has non-stationary perturbations leading to the changes in both the average parameters of its motion and the motion as a whole.

The main process of the Earth pole coordinates fluctuations is the sum of the quasi periodic Chandler component and annual one. The approximation of the Earth pole motion is generally accepted to be a few parametric two-frequency model with constant coefficients. Relatively slow changes in the parameters of the Chandler and annual components make it possible to use this approximation in the time intervals of 6–7 years, that is, during the period of the Chandler and annual components modulation. This model has low algorithmic complexity and describes the main process of pole oscillations with acceptable accuracy.

However, due to the non-stationary perturbations there are effects in the Chandler and annual components that are not typical for a simple dynamical system that is described by linear differential equations with constant coefficients. Such changes can also be observed in the dissipative systems with not only with the amplitude variations but also when oscillation process is in steady-state condition [1].

In this work the effect of changing in the Earth pole oscillatory mode is revealed, which consists in a jump-like shift in the average frequency of the pole around the midpoint (the motion of the Earth pole midpoint is a pole trend of a long-period and secular nature), which leads to a change in the average speed of its motion.

A method is proposed to determine the moment when the average frequency is shifted, which is important for refining the forecast model of the Earth pole motion. Using this method a modified model of pole motion is developed and the dynamic effects in its motion are considered, caused by the change in the amplitudes ratio of the Chandler and annual harmonics.

References

[1] Barkin M.Yu., Krylov S.S., Perepelkin V.V. Modeling and analysis of the Earth pole motion with nonstationary perturbations. IOP Conf. Series: Journal of Physics: Conf. Series 1301 (2019) 012005; doi:10.1088/1742-6596/1301/1/012005

 
Landslide Early Warning Systems Considering Impulse Waves – a Case Study of the Jiuxianping Landslide in the Three Gorges Reservoir Area, China
Authors: Zhang Yu , Yin Yunkong , Evers Frederic , Liang Xin
Published: March 2020

Landslides along river, lake, reservoir and ocean shorelines may trigger impulse waves when they slide into the water body with a high velocity. This secondary process can extremely expand the area threatened by the landslide beyond its primary impact zone. Since the impoundment of the Three Gorges Reservoir in 2003, several landslides have caused huge property damage and several casualties due to an insufficient understanding of and reaction to impulse waves as a secondary process in landslide disaster risk management. This contribution aims to provide an integrative approach for risk perception and mitigation of a local landslide considering impulse waves as a secondary disaster risk.

Jiuxianping landslide is located in the middle part of the Three Gorges Reservoir in China. Featuring a large thick layer of rock slope, the elevation of the landslide ranges from 95 to 385 m a.s.l., and the volume is approximately 5.7×107 m3. The trailing edge of the landslide appeared as a more than 100 meters transverse tensile crack with an opening width of at least 25 cm in 2008, leading to damaged housing. The landslide stability is strongly influenced by rainfall and the reservoir water level. More than 300 people still live at the landslide site and there is a shipyard in operation at its toe.

As a new perspective to detect secondary disasters, the areas with the highest risk and probability of damage under different conditions were estimated using an auto search function in GeoStudio and the Morgenstern-Price method. Then, we simulated the landslide runout as well as wave generation and propagation using Tsunami Squares to predict the risk intensity and impact area of the generated impulse waves. Lastly, we evaluated the warning levels for different scenarios and proposed the area restricted for navigation at corresponding warning levels. Our case study demonstrates the necessity and the importance of considering secondary disaster risks such as impulse waves in landslide early warning system.
Spatial and temporal evolution of micro-earthquakes during Multi-cycle operation of the Hutubi underground gas storage, Xinjiang, China
Authors: Zhang Bo , Wang Baoshan , Ji Zhanbo , Hou Jinxin , Li Lu , Wei Bin , Wu Nier , Wu Zhide
Published: March 2020

Underground Gas Storages (UGSs) are important large-scale industrial facilities used to bridge the gap between the natural gas demand and supply. The UGS production can cause periodical changes of the subsurface stresses and probably change the seismicity pattern. The UGS operation related seismicity has important affects on the UGS, but is rarely reported. Hutubi UGS is the largest Underground Gas Storage in China and well equipped with seismic observations from the beginning of the UGS operation in Jun. 2013. The Hutubi UGS provides an unprecedented opportunity to study the seismicity related gas injection. The seismicity around the Hutubi UGS was detected and located by using matched filter and double difference relocation techniques. More than 7000 earthquakes were detected and located within 20 km of the UGS from Jan. 2011 to Dec. 2018 (i.e., 2 years before the operation and 6 injection-extraction cycles). The seismicity can be clustered into three groups South of, North of, and beneath the UGS. Two (South and North) of three groups occurred along two south-dipping planes with dipping angle ~40 degree, corresponding to local geological structures. While the underlaying group occurred along the direction conjugate to the other two groups, which was in accordance with the starting of the second injection stage and gradually migrated deeper. The northern cluster occurred mainly after the Murghob earthquake (M7.2) and the Hutubi earthquake (M6.2), which may be related to dynamic stress triggering from these two earthquakes. The seismicity in the southern cluster persists, but the rate shows seasonality, which is likely modulated by the gas operation and underground water exploitation. The seismicity in the Hutubi UGS area may have different origins. Understanding the mechanism of the impact of UGS operation on different clustering seismicity will help us to optimize the production parameters and reduce the risk of induced earthquake.