bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparatory analysis and development for the ITRF2020
Authors: Altamimi Zuheir , Rebischung Paul , Metivier Laurent , Collilieux Xavier , Chanard Kristel , Teyssendier-de-la-Serve Maylis
Published: March 2021

In preparation for ITRF2020, we developed a number of software tools and analysis strategies aiming at improving the quality, consistency and accuracy of the new frame. Our target is to enhance the modelling of the nonlinear station motions, including post-seismic deformation models for stations subject to major earthquakes, and periodic signals embedded in the station position time series. In addition to the classical annual and semi-annual signals, we foresee to simultaneously adjust some satellite draconitic harmonics and evaluate their impact on the estimated frame parameters.  The ITRF2020 is expected to be provided in the form of an augmented reference frame so that in addition to station positions and velocities, parametric models for both PSD and periodic signals (expressed in the CM frame of satellite laser ranging) will also be delivered to the users. Depending on the availability of the input data of the four techniques at the time of this presentation, we expect to show and discuss some early results and give some indications regarding the specifications of the final ITRF2020 solution.
The past and future dynamics of salt intrusion in the Mekong Delta
Authors: Eslami Sepehr , van der Vegt Maarten , Minderhoud Philip , Nguyen Trung Nam , Hoch Jannis , Sutanudjaja Edwin , Do Doc Dung , Tran Quang Tho , Voepel Hal , Woillez Marie-Noëlle
Published: March 2021

In the context of global rising temperatures, rapid urbanization and excessive demand for natural resources (e.g., freshwater and sand) stress the livelihood of the world deltas. Sea Level Rise, land subsidence, discharge anomalies, floods, drought, and salt intrusion are common challenges facing these ecologically essential and economically crucial coastal landscapes. Climate change projections in deltas regularly isolate climate-driven stressors and disregard anthropogenic environmental drivers. This often leads to insufficient socio-political drive at times when the short window of opportunity to save the world’s largest deltas is closing. Here, by integrating both climatic and anthropogenic drivers of exposure and vulnerability, we project salt intrusion within the Mekong mega-Delta for the next three decades. Leveraging modern numerical codes and computation capacity, by applying a high-resolution 3D model we capture the 3D dynamics of saline water intrusion, and by covering the entire delta (from 400 km upstream to 70 km offshore) we eliminate/minimize the boundary effects at the areas of interest. We differentiate the relative effects of various drivers and demonstrate that while sea level rise can increase areas affected by salinity by 5-19%, anthropogenic drivers such as extraction-induced subsidence and riverbed level incisions due to sediment starvation can further amplify that by additional 10-27%. The results are crucial input for climate adaptation policy development in the Mekong Delta and provides a blueprint for systemic assessment of environmental changes and developing environmental pathways at scale of a delta.
Greenland land-terminating glaciers velocity trends during the last two decades
Authors: Halas Paul , Mouginot Jeremie , de Fleurian Basile , Langebroek Petra
Published: March 2021

Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise. Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding. The sliding component of glaciers has been observed to be strongly related to surface melting, as water can eventually reach the bed and impact the subglacial water pressure, affecting the basal sliding.  

The link between ice velocities and surface melt on multi-annual time scale is still not totally understood even though it is of major importance with expected increasing surface melting. Several studies showed some correlation between an increase in surface melt and a slowdown in velocities, but there is no consensus on those trends. Moreover those investigations only presented results in a limited area over Southwest Greenland.  

Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.  

Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration. This trend however does not seem to be observed on the whole ice sheet and is probably specific to this region’s climate forcing. 

Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.
Blocking phloem transport triggers bimodal radial growth in Pinus sylvestris at a xeric site
Authors: Oberhuber Walter , Landlinger-Weilbold Anton , Gruber Andreas , Wieser Gerhard
Published: March 2021

A bimodal radial grow pattern, i.e. growth peaks in spring and autumn, was repeatedly found in trees in Mediterranean regions, where summer drought causes reduction or cessation of cambial activity. In a dry inner Alpine valley of the Eastern Alps (Tyrol, Austria, c. 750 m asl), which is characterized by drought periods at the start of the growing season in spring and more favorable conditions during summer, Pinus sylvestris shows an unimodal growth pattern with onset and cessation of cambial activity in early April and late June, respectively. Although xylem cell differentiation (cell wall thickening) may last until end of August, a resumption of cambial activity after intense summer rainfall was not observed in this region. In a field experiment we therefore tested the hypothesis that early cessation of cambial activity under drought is an adaptation to limited water availability during the growing season (April through June), leading to an early and irreversible switch of carbon (C) allocation to belowground. To accomplish this, the C status of c. 20 year old Pinus sylvestris saplings (mean stem height 1.5 m) was manipulated at a xeric site by physical blockage of phloem transport (girdling) in mid-July (doy 199), i.e. c. four weeks after cessation of cambial cell division. The influence of manipulated C availability on radial growth was continuously recorded by stem dendrometers, which were mounted 5 cm above girdling. In response to blockage of phloem flow, resumption of radial growth was detected above the girdling zone after about 2 weeks, i.e., bimodal growth could be triggered above girdling by increasing C availability. Although the experimentally induced second growth surge lasted for the same period as in spring (i.e., c. 2 months), the increment was more than twice as large. Below girdling radial growth was not affected (i.e., no reactivation of cambial activity occurred), but cell wall thickness of last latewood cells was significantly reduced indicating lack of C after girdling. Intense radial growth resumption in Pinus sylvestris saplings after girdling indicates that cessation of stem cambial activity can be reversed by manipulating the C status of the stem suggesting a high belowground C demand on the drought-prone, nutrient deficient site. This work highlights the need of in-depth experimental studies in order to understand the impact of endogenous and exogenous factors on cambial activity more clearly.

The research was funded by the Austrian Science Fund (FWF; project number P25643-B16).
Atmospheric influences on water stable isotopes in Antarctic water vapor and surface snow – implications for ice core interpretation
Authors: Schlosser Elisabeth , Bagheri Saeid , Powers Jordan G. , Manning Kevin W. , Hoerhold Maria , Behrens Melanie , Werner Martin
Published: March 2021

In Austral summer 2017/18 daily surface snow samples were taken (weather allowing) at two depths, 0-1cm and 6-7cm, at Neumayer III Station, Dronning Maud Land DML, Antarctica. Stable isotope ratios (18O, D, d-excess) of the snow samples were analysed in the AWI isotope lab. In parallel, water vapor stable isotopes were measured continuously on a routine base with a Picarro cavity ring-down spectroscope analyser (CRDS). Neumayer III is also a full meteorological observatory measuring all important meteorological variables including upper-air data. Meteorological data were directly compared to both snow and vapor isotope data. The corresponding synoptic situations were analysed using data from AMPS (Antarctic Mesoscale Prediction System), which employs WRF (Weather Research and Forecasting Model), a mesoscale atmospheric model that has been successfully used in earlier studies in DML. AMPS is run operationally at NCAR for Antarctic weather forecasting, particularly for flight operations of the US Antarctic Program (USAP). Additionally, back-trajectory calculations to investigate moisture sources and transport were carried out using FLEXPART, an open-source Lagrangian particle dispersion model. Due to logistical problems, the measuring period during the expedition was too short for statistical analysis, thus we focus on case studies here. In particular, periods with no precipitation were investigated, since earlier studies in Greenland have shown that the interaction of snow surface and atmosphere is important for the stable isotope ratio in the snow, thus in later ice cores that are used to derive paleo temperatures. A better understanding of the highly complex relationship between water vapor stable isotopes and meteorological conditions (including moisture source and transport) as well as the interaction between surface snow and water vapor is necessary for a correct paleoclimatic interpretation of ice cores.
Flagella and their property affect the transport and deposition behaviors of Escherichia coli in quartz sand
Authors: Zhang Mengya , He Lei , Tong Meiping
Published: March 2021

The effects of bacterial flagella as well as their property on the transport and deposition of bacteria were examined by using four types of Escherichia coli (E.coli) with or without flagella, as well as with normal or sticky flagella. Packed column, quartz crystal microbalance with dissipation (QCM-D), visible parallel plate flow chamber system, as well as visible flow chamber system packed with porous media system were utilized to investigate the deposition behaviors and the deposition mechanisms of bacteria with different property of flagella. We found that the presence of flagella favored E.coli deposition onto quartz sand/silica surfaces. Moreover, by changing the porous media porosity and directly observing the deposition process of bacteria in porous media, grain-to-grain contacts were found to be major sites for bacterial deposition. Particularly, flagella could help bacteria swim near and then deposit at grain-to-grain contacts. In addition, we found that due to the stronger adhesive forces, sticky flagella could further enhance bacterial deposition onto quartz sand/silica surfaces. Elution experiments showed that the portion of bacteria with flagella depositing onto secondary energy minima was relatively lower than bacteria without flagella, indicating that flagella could help bacteria attach onto sand surfaces more irreversibly. Clearly, flagella and their property would have obvious influence on the transport and deposition behaviors of bacteria in porous media. By removing the flagella or changing their property, the transport and deposition of bacteria in porous media can be altered. Particularly, bacterial flagella can be removed to facilitate the transport of bacteria in remediation system requiring high mobility of bacteria, while in system requiring the immobilization bacteria in porous media, bacteria with sticky flagella can be employed.
Core-log-seismic integration in metamorphic rocks at the ICDP drilling project COSC-1, Sweden
Authors: Elger Judith , Berndt Christian , Kästner Felix , Pierdominici Simona , Kück Jochem , Almqvist Bjarne S. G. , Juhlin Christopher , Lorenz Henning
Published: March 2021

Continental collision causes deformation in the crust along shear zones. However, the physical and chemical conditions at which these zones operate and the deformation processes that enable up to hundreds of km of tectonic transport are still unclear because of the depth at which they occur and the challenges in imaging them. Ancient exhumed collision zones allow us to investigate these processes much better, for example at the COSC-1 borehole in the central Scandinavian Caledonides. This study combines data from the COSC-1 borehole, such as downhole logging and zero-offset vertical seismic profile data, with 2D and 3D seismic measurements to provide constraints on the spatial lithological and textural configuration of the Seve Nappe Complex. This is one of the few studies that shows that core-log-seismic integration in metamorphic rocks allows to identify the spatial distribution of major lithological units, even though the methodology was originally developed for sedimentary basins in the hydrocarbon industry. Especially gamma ray logs in combination with density data are powerful tools to distinguish between mafic and felsic lithologies in log-core correlation. Reflections in the Seve Nappe Complex are not as distinct as in greater depths but continuous, and our results indicate that they are primarily caused by compositional rather than textural changes. Several of the reflections can be linked to magmatic intrusions, which have been metamorphically overprinted. Their setting indicates that the Seve Nappe Complex consists of the remnants of a volcanic continental margin. It appears that in spite of the metamorphic overprint around 417+/-9 Ma, the original configuration of the volcanic passive margin is partly preserved in the Seve Nappe Complex and that it outlasted continent-continent collision, including the nappe emplacement. Thus, an integration of borehole and three-dimensional geophysical data can image lithological changes that can then be extrapolated in three dimensions to arrive at a better understanding of the composition and geometry at mid-crustal levels. Furthermore, our results suggest that ductile-deformed middle crustal reflectivity is primarily a function of pre-orogenic lithological variations which has to be considered when deciphering mountain building processes.
Ongoing biogenic silica diagenesis — Interstitial-water chemical signals
Authors: Varkouhi Shahab , Tosca Nicholas J. , Cartwright Joseph A.
Published: March 2021

Biogenic silica diagenesis leads to abrupt changes in the physical properties of host sediment across the depth of an opal-A to opal-CT transition zone. Predicting the present-day diagenetic state of this reaction boundary, i.e., active versus arrested opal-A to opal-CT transition zones, is imperative to constraining the diagenetic factors that impact dramatic variations in the physical state of sediment. This study assesses whether there are present-day signatures of active silica diagenesis in the interstitial water, and corroborates the potential for pore-water chemistry for distinguishing between ongoing precipitation of diagenetic opal and arrested reaction fronts. Interstitial-water chemistry, mineralogy, and thermodynamic analyses of the Ocean Drilling Program Sites 794 and 795 demonstrate that solubility equilibrium is reached with respect to opal-CT in the transition zones accommodated by the Neogene biosiliceous sediments in the Sea of Japan. Even though the dissolution of biogenic opal is triggering reverse-weathering processes, the equilibrium reached with respect to diagenetic opal strongly suggests that the dissolved silica depression across the transition zones is essentially influenced by ongoing transformation of opal-A to opal-CT. Owing to abrupt petrophysical variations linked to opal-CT precipitation, the interstitial profiles of major ions and primary parameters have also been impacted by silica diagenesis. The extremely low dissolved-silica diffusion fluxes in the sediment, the very low permeability of the sediment capturing silica diagenetic transformations, and the marked pore-water loss at the depth of the transition zone all support the fact that the dissolved species have not been diffused in the sediment at rates comparable to those by pore-water advection due to sediment porosity drop. Advective and diffusive mechanisms, however, appear to have ceased recently because they have failed to smooth out the traces of ongoing biogenic silica diagenesis.
Geoethics in a scheme: a simplified way to represent its definition, vision, and theoretical structure
Authors: Peppoloni Silvia , Di Capua Giuseppe
Published: March 2021

Geoethics arises from the awareness that, only partly consciously, human beings have irreversibly modified and are continuing to modify the natural environments and territories in which they live and operate. Humans alter not only physical, chemical and biological characteristics of their niche, but also social and cultural traits that connote social–ecological systems today as in the past, which in turn, in a feedback mechanism, influence people’s economic development, social perspectives and sense-making. It then becomes a responsibility for geoscientists to look beyond their traditional areas of work and each interact proactively with civic communities to promote changes that are needed. The key concepts of geoethics constitute a cultural proposal for the whole society, on which to base new perspectives for the human agent.
Ten years ago, the first session dedicated to geoethics was organized at the EGU General Assembly in order to widen the discussion on ethics in geosciences. Nowadays the theoretical framework of geoethics has consolidated and it has become the proposal on which to base a global ethics of the human agent towards the Earth system. This work synthetizes in a scheme the reference framework on which geoethics developed, its definition, foundations, and main characteristics, highlighting the importance of sharing values and actions among planetary human communities to manage global changes and threats.
Stratospheric cirrus clouds related to deep convection over North America observed by satellite measurements
Authors: Zou Ling , Hoffmann Lars , Griessbach Sabine , Wang Lunche
Published: March 2021

Cirrus clouds in the stratosphere (SCCs) regulate the water vapor budget in the stratosphere, impact the stratosphere and tropopshere exchange, and affect the surface energy balance. But the knowledge of its occurrence and formation mechanism is limited, especially in middle and high latitudes. In this study, we aim to assess the occurrence frequencies of SCC over North America based on The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) instrument during the years 2006 to 2018. Possible driving forces such as deep convection are assessed based on Atmospheric Infrared Sounder (AIRS) observations during the same time. 

Results show that at nighttime, SCCs are most frequently observed during the thunderstorm season over the Great Plains from May to August (MJJA) with maximum occurrence frequency of 6.2%. During the months from November to February (NDJF), the highest SCCs occurrence frequencies are 5.5% over the North-Eastern Pacific, western Canada and 4.4% over the western North Atlantic. Occurrence frequencies of deep convection and strong storm systems from AIRS show similar hotspots like the SCCs, with highest occurrence frequencies being observed over the Great Plains in MJJA (4.4%) and over the North-Eastern Pacific, western Canada and the western North Atlantic in NDJF (~2.5%). Both, seasonal patterns and daily time series of SCCs and deep convection show a high degree of spatial and temporal correlation. As further analysis indicates that the maximum fraction of SCCs generated by deep convection is 74% over the Great Plains in MJJA and about 50% over the western North Atlantic, the North-Eastern Pacific and western Canada in NDJF, we conclude that, locally and regionally, deep convection is a leading factor for the formation of SCCs over North America. Other studies stressed the relevance of isentropic transport, double tropopause events, or gravity waves for the formation of SCCs. 

In this study, we also analyzed the impact of gravity waves as a secondary formation mechanism for SCCs, as the Great Plains is a well-known hotspot for stratospheric gravity waves. In case of SCCs that are not directly linked to deep convection, we found that stratospheric gravity wave observations correlate in as much as 30% of the cases over the Great Plains in MJJA, about 50% over the North-Eastern Pacific, western Canada and maximally 90% over eastern Canada and the north-west Atlantic in NDJF. 

Our results provide better understanding of the physical processes and climate variability related to SCCs and will be of interest for modelers as SCC sources such as deep convection and gravity waves are small-scale processes that are difficult to represent in global general circulation models. 
Amplified Arctic precipitation increases are driven by atmospheric radiative cooling
Authors: Pithan Felix , Jung Thomas
Published: March 2021

As the climate warms, the amount of water vapour in the atmosphere increases by about 7 % per K, following the clausius-clapeyron relation. Globally averaged precipitation only increases by about 1-2 % per K of warming, as it is constrained by the atmospheric energy budget rather than the availability of moisture in the atmosphere. In the Tropics, zonally averaged precipitation mostly increases in the ITCZ near the equator and decreases in the subtropical dry zones (rich get richer, poor get poorer). A fundamental explanation of extratropical precipitation change has yet to be provided.

Here, we show that the structure of zonal mean mid-latitude precipitation changes is largely controlled by circulation changes, whereas amplified Arctic precipitation change is linked to increased atmospheric radiative cooling. The relative change in precipitation per unit of local warming is greater at high latitudes than anywhere else.
The effects of assimilating a sub-grid scale sea ice thickness distribution in a new Arctic sea ice data assimilation system
Authors: Williams Nicholas , Byrne Nicholas , Feltham Daniel , Van Leeuwen Peter Jan , Bannister Ross , Schroeder David , Shepherd Andrew
Published: March 2021

A modified, standalone version of the Los Alamos Sea Ice Model (CICE) has been coupled to the Parallelized Data Assimilation Framework (PDAF) to produce a new Arctic sea ice data assimilation system CICE-PDAF, with routines for assimilating many types of recently developed sea ice observations. In this study we explore the effects of assimilating a sub-grid scale sea ice thickness distribution derived from Cryosat-2 Arctic sea ice estimates into CICE-PDAF. The true state of the sub-grid scale ice thickness distribution is not well established, and yet it plays a key role in large scale sea ice models and is vital to the dynamical and thermodynamical processes necessary to produce a good representation of the Arctic sea ice state. We examine how assimilating sub-grid scale sea ice thickness distributions can affect the evolution of the sea ice state in CICE-PDAF and better our understanding of the Arctic sea ice system.
Contemporary crustal deformation in Georgia (Caucasus)
Authors: Khazaradze Tsilosani Giorgi , Sokhadze Giorgi , Hahubia Galaktion , Kachakhidze Manana
Published: March 2021

The Republic of Georgia is located in the Caucasus, between the Black and Caspian seas from the west and the east, and the Greater and Lesser Caucasus mountains from the north and the south. Tectonically, the region belongs to the Alpine-Himalayan collisional zone, formed during the late Cenozoic period as a result of a collision between the Arabian and Eurasian plates. The deformation zone due to this collision is broad and extends from Zagros mountains in southern Iran to the Greater Caucasus in the north. The GPS studies conducted during the last decade suggest a convergence rate of up to 20 mm/yr between the Arabia and Eurasia plates. Although majority of this convergence occurs in the southern part of the deformation zone, important part of this convergence takes place in Georgia, implying an elevated seismic risk in the region. This is corroborated by a presence of significant historical and instrumental earthquakes in the country.

As part of the project dealing with the detection of possible low frequency electromagnetic emissions proceeding earthquakes, in summer of 2016 we have installed a continuous GNSS station MTSK between Mtskheta and Tbilisi. The station consists of Leica GRX1200 GNSS receiver with an AS10 antenna. It is mounted on top of the building, anchored to the existing brick wall. In contrast, principal convergence between the Lesser and Greater Caucasus across the Tbilisi segment, occurs along the northern boundary of the Lesser Caucasus. To constrain the velocity gradient to the northern boundary of the lesser Caucasus, in 2019 an additional continuous GNSS station MKRN was installed in this deformation zone by the GTDI near the settlement of Mukhrani. It consists of Trimble 5700 receiver with a Zephyr Geodetic antenna.

The analysis of the data is performed using the Gamit/Globk software package from MIT and it is processed in conjunction with 26 continuous GNSS stations of the GEO-CORS network operated by National Agency of Public Registry of Georgia (geocors.napr.gov.ge). In addition, we analyze data form the stations located on Eurasia, Arabia and Africa plates. The main objective of the given work is to monitor a millimeter level deformation of the crust due to the collision of Arabia and Eurasia tectonic plates and identify the regions of higher deformation and relate them to individual faults.

This work has been partially supported by Shota Rustaveli National Science Foundation of Georgia (grant DI/21/9-140/13) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) project, financed by the Spanish MINEICO. We are grateful to the Andronikashvili Institute of Physics (www.aiphysics.tsu.ge) for letting us use their facility for the installation of the GNSS station.
Stochastic Modeling of Diffusivity and Constant-Rate Pumping Tests in Heterogeneous Aquifers in a Tomographic Setup and Its Application to Field Measurements
Authors: Cheng Kan Bun , Dagan Gedeon , Rabinovich Avinoam
Published: March 2021

Characterization of spatially variable aquifer properties is a necessary first step towards modeling flow and transport. An emerging technique in hydraulic tomography, known as diffusivity tests, consist of injecting (or pumping) a volume of water through short segments of a well for a short time and measuring the travel time of the peak of the head signal at different points in the surrounding aquifer volume. In our stochastic model, the specific storage is assumed to be constant, while the hydraulic conductivity of the heterogeneous aquifer is modeled as a random lognormal field. The axi-symmetric anisotropic structure is characterized by a few parameters (logconductivity mean and variance and horizontal and vertical integral scales). The mean and variance of the peak travel time are then determined as a function of distance from an instantaneous source by solving the flow equation using a first-order approximation in the logconductivity variance. The mean travel time is recast in terms of the equivalent conductivity, which decreases from the harmonic mean near the source to the effective conductivity in uniform flow for a sufficiently large distance. Similarly, the variance drops from its maximum near the source to a small value.

A different type of tomographic test is the constant-rate pumping one. We propose to apply the first order stochastic approach to the data from the Boise Hydrogeophysical Research site (BHRS) to characterize the aquifer properties by estimating heterogeneity statistical parameters. Equivalent properties are first calculated by matching a homogeneous aquifer solution to the pointwise data to obtain a spatially varying hydraulic conductivity (Keq) and storativity (Ss,eq). Then the statistical properties of K and Ss are to be computed by a best fit between the theoretically derived statistical moments of the equivalent random properties (Keq, Ss,eq) and those from field measurements. Our preliminary results indicate that the proposed stochastic methodology is robust and reliable as well as computationally more efficient than the conventional hydraulic tomography techniques.
Comparison of empirical noise models for GRACE Follow-On derived with the Celestial Mechanics Approach
Authors: Lasser Martin , Meyer Ulrich , Arnold Daniel , Jäggi Adrian
Published: March 2021

A key component of any model is the accurate specification of its quality. In gravity field modelling from satellite data, as it is done with the observation collected by GRACE Follow-On, usually least-squares adjustments are performed to obtain a monthly solution of the Earth’s gravity field. However,
the jointly estimated formal errors usually do not reflect the error level that could be expected but provides much lower error estimates. We take the Celestial Mechanics Approach (CMA), developed at the Astronomical Institute, University of Bern (AIUB), and extend it by an empirical modelling of the noise based on the post-fit residuals between the final GRACE Follow-On orbits, that are co-estimated together with the gravity field, and the   observations, expressed in position residuals to the kinematic positions and in K-band range-rate residuals. We compare and validate the solutions that employ empirical modelling with solutions that do not contain sophisticated noise modelling by examining the stochastic behaviour of the respective post-fit residuals, by investigating areas where a low noise is expected and by inspecting the mass trend estimates in certain areas of global interest. Finally, we investigate the influence of the empirically weighted solutions in a combination of monthly gravity fields based on other approaches as it is done in the COST-G framework.
Comparative analysis of TMPA and IMERG precipitation datasets in the arid environment of El- Qaa Plain, Sinai
Authors: Morsy Mona , Scholten Thomas , Michaelides Silas , Borg Erik , Sherief Youssef , Dietrich Peter
Published: March 2021

The replenishment of aquifers depends mainly on precipitation rates, which is of vital 19 importance for determining water budgets in arid and semi-arid regions. El-Qaa Plain in Sinai 20 Peninsula is such a region which experiences a constant population growth. The local water budget 21 equilibrium is negatively affected by relatively frequent light rain events. This study compares the 22 performance of two sets of satellite-based data of precipitation and in situ rainfall measurements. The 23 dates selected refer to rainfall events between 2015 and 2018. For this purpose, 0.1° and 0.25° spatial 24 resolution TMPA (TRMM Multi-satellite Precipitation Analysis) and IMERG (Integrated Multi-25 satellitE Retrievals for GPM) data were retrieved and analyzed, employing appropriate statistical 26 metrics. The best-performing data set was determined as the data source capable to most accurately 27 bridge gaps in the limited rain gauge records, embracing both frequent light-intensity rain events 28 and rarer heavy-intensity events. With light-intensity events the corresponding satellite-based data 29 sets differ the least and correlate more, while the greatest differences and weakest correlations are 30 noted for the heavy-intensity events. The satellite-based records best match those of the rain gauges 31 during light-intensity events, when compared to the heaviest ones. IMERG data exhibit a superior 32 performance than TMPA, in all rainfall intensities.
The effect of cultivation with reed canary grass on methane emissions from different Danish wet agricultural peatlands and the correlation with biogeochemical soil properties
Authors: Nielsen Claudia , Elsgaard Lars , Jørgensen Uffe , Lærke Poul Erik
Published: March 2021

Drainage of peatlands for agriculture causes substantial degradation and finally loss, including associated ecosystem functions, but also creates emission hotspots of carbon dioxide (CO2). Mean CO2 emission from drained temperate grassland on peat was reported by IPCC as 22.4 (18.3-26.7) Mg
CO2-eq ha-1 y-1 (95% CI) while methane (CH4) emissions were close to zero. Rewetting of peatlands reduces CO2 emissions while at the same time favouring CH4 emissions. From wet or rewetted nutrient-rich grassland, emissions of CO2 and CH4 were reported by IPCC as 1.8 (-2.8-2.8) and
9.8 (0-39) Mg CO2-eq ha-1 y-1, respectively (GWP CH4 = 34). The uncertainties of the estimates reflect the large variation among the reported studies, which could be caused by different climate conditions, vegetation, groundwater table (GWT), peat composition and biogeochemistry. A mesocosm experiment was established to assess biogeochemical causes of variation in CO2 and CH4 flux dynamics under controlled GWT for peatsoils derived from five different Danish bogs and fens. A total number of 75 mesocosms were grouped into three treatments: GWT -40 cm, bare; GWT -5 cm, bare; and GWT -5 cm, cultivated with reed canary grass (RCG). GHG fluxes were measured using opaque chambers at biweekly intervals from July 2019 to 2020 and extrapolated to annual values. Preliminary results indicate significant differences regarding CO2 and CH4 fluxes across all sites and depending on soil biogeochemical and physical properties. Rewetting raised the contribution of CH4 most on soils from Store Vildmose and Vejrumbro with 1.9 to 12.9 t CO2eq ha-1 yr-1 and 0.1 to 5.7 t CO2eq ha-1 yr-1, respectively. On an annual average, these high emissions were with 69 % and 48 % mitigated by the cultivation of RCG in a paludiculture scenario. Further, the results show that CH4 spikes of up to 37.5 mg m-2 h-1 at elevated GWT during warmer summer months may be mitigated by cultivation with RCG, with maximum peaks of 2.1 mg m-2 h-1. Soil analyses highlighted distinct differences in the soil mineralogical composition across sites and soil depths.
An easy-to-use, low-cost evaporation protection to collect more reliable stable water isotope data with Teledyne ISCO portable samplers
Authors: von Freyberg Jana , Knapp Julia L. A. , Rücker Andrea , Studer Bjørn , Zappa Massimiliano , Kirchner James W.
Published: March 2021

Off-the-shelf portable automatic water samplers, such as the 6712 full-size portable sampler (Teledyne ISCO, Lincoln, USA), are often used in remote locations to collect precipitation or streamwater for subsequent analysis of deuterium and oxygen-18.  The bottles inside these automatic samplers remain open during the full duration of sampler deployment and the collected water samples can thus be subjected to evaporation and vapor exchange.  Both processes are known to alter the isotope composition of the water sample, and thus the questions arise as to 1) how credible the isotope measurements from automatically collected water samples are and 2) how can these isotope effects in the automatic water sampler be reduced?

We evaluated these questions through laboratory and field experiments in which we quantified the change in isotope composition in the water samples with respect to ambient conditions (air temperature and relative humidity), storage duration, and sample volume.  We found that isotope fractionation in the water samples was substantial under very warm and dry condition, when sample volumes are small or when sample storage exceeded 10 days.  To address these problems, we have designed an evaporation protection method which modifies autosampler bottles using a syringe housing and silicone tube.  We performed paired experiments with open vs. evaporation-protected bottles in Teledyne ISCO 6712 full-size portable samplers to evaluate our design.  We could show that the evaporation protection successfully reduced isotope fractionation in the water samples for storage durations of up to 24 days and for a wide range of ambient conditions; e.g., while deuterium concentrations in the water samples in open bottles changed by ca. 3‰ under very warm and dry conditions, no isotope effect was measured in the bottles equipped with the evaporation protection. Because our design is very cost efficient it can easily be implemented to upgrade Teledyne ISCO’s 6712 full-size portable samplers or other similar devices for collecting more reliable isotope data.
A novel marine phosphorus record from Lower Jurassic belemnites?
Authors: Roper Ailsa , Ullmann Clemens , Little Crispin , Poulton Simon , Wignall Paul , He Tianchen , Newton Robert
Published: March 2021

Studying the long-term evolution of nutrient cycles and their interaction with other biogeochemical cycles is essential to understand Earth’s history. Marine nutrient cycling forms a key control on the cycling of carbon and oxygen in the bio- and geospheres. Here, we focus on phosphorus, which is the ultimate limiting nutrient on geological timescales and a potential driver of past intervals of marine anoxia/euxinia. Despite its importance, obtaining direct information on spatial and temporal variations in marine phosphorus concentrations has proved challenging. Recent work has demonstrated the potential for calcium carbonate-associated phosphorus in corals to record water-column phosphorus (e.g., LaVigne et al., 2008; 2010). Building on this approach, we are investigating the use of other calcitic fossils as a proxy for water column phosphorus concentration, focussing on belemnites, an extinct group of nektic molluscs.

We have developed and optimised a method to quantify phosphorus in the belemnite rostrum, and initially applied this method to samples from the upper Sinemurian to the Toarcian in the Lower Jurassic. During this time there were major climatic and environmental events in the latest Pliensbachian and early Toarcian, which are thought to have been driven by large scale volcanism of the Karoo-Ferrar Large Igneous Provinces (LIP). Of particular interest are an icehouse event during the Pliensbachian, and a warming event during the Toarcian which coincided with widespread ocean anoxia (the Toarcian Ocean Anoxic Event [TOAE]) and a second order mass extinction event (the Early Toarcian Mass Extinction).

We will present P/Ca results from method development tests and collections of belemnites from the Sinemurian to the Toarcian from a number of sites in the European Epicontinental Sea (EES). Pilot data show similar trends in belemnite phosphorus concentrations at different sites in the EES, including a sharp peak during the TOAE. We will also discuss the impact of inter-species variation on belemnite phosphorus concentrations, as well as internal variability in phosphorus concentrations in individual belemnites, to determine the potential impact of these variables on the reconstruction of water column phosphorus concentrations. 

LaVigne, M., Field, M. P., Anagnostou, E., Grottoli, A. G., Wellington, G. M., Sherrell, R. M. (2008). Skeletal P/Ca tracks upwelling in Gulf of Panamá coral: Evidence for a new seawater phosphate proxy. Geophysical Research Letters 35.

LaVigne, M., Matthews, K. A., Grottoli, A. G., Cobb, K. M., Anagnostou, E., Cabioch, G., Sherrell, R. M. (2010). Coral skeleton P/Ca proxy for seawater phosphate: Multi-colony calibration with a contemporaneous seawater phosphate record. Geochimica et Cosmochimica Acta 74: 1282–1293.
Wave-current interactions representation by coupling spectral wave and coastal hydrodynamics models
Authors: Fragkou Anastasia , Old Christopher , Angeloudis Athanasios
Published: March 2021

A parallelized unstructured coupled model is developed to investigate wave-current interactions in coastal waters at regional scales. This model links the spectral wave model Simulating Waves Nearshore (SWAN; Booij et al., 1999) with the coastal hydrodynamics shallow-water equation model Thetis (Kärnä et al., 2018). SWAN is based on the action density equations encompassing the various source-terms accounting for deep- and shallow-water phenomena. Thetis solves the non-conservative form of the depth-averaged shallow water equations implemented within Firedrake, an abstract framework for the solution of Finite Element Method (FEM) problems. In resolving wave-current interactions in the proposed model, Thetis predicts water elevation and current velocities which are communicated in SWAN, while the latter provides radiation stresses information for the former. The numerical domain is prescribed by an unstructured mesh allowing higher resolution to areas of interest, while maintaining a reasonable computational cost. As the models share the same mesh, interpolation errors and certain computational overheads can be contained, whereas the choice to employ a sub-mesh for SWAN model is being considered to reduce the overall cost.

The model is initially validated and its performance assessed by a slowly varying-bathymetry. Predictions are compared against the analytical solutions for the wave setup and significant wave height (Longuet-Higgins and Stewart, 1964). Comparisons also extend to results from a coupled 3-D hydrodynamics model with a spectral wave model (Roland et al., 2012). The results of the proposed coupled model exhibit good correlations with the analytical solutions showcasing the same level of eﬃciency as the 3-D coupled model.

 

References

[1] Booij N, Ris RC, Holthuijsen LH. A third-generation wave model for coastal regions: 1. Model description and validation. Journal of geophysical research: Oceans 1999;104(C4):7649–7666.

[2] Kärnä T, Kramer SC, Mitchell L, Ham DA, Piggott MD, Baptista AM. Thetis coastal ocean model: discontinuous Galerkin discretization for the three-dimensional hydrostatic equations. Geoscientific Model Development 2018;11(11):4359–4382.

[3] Longuet-Higgins MS, Stewart R. Radiation stresses in water waves; a physical discussion, with applications. In: Deep sea research and oceanographic abstracts, vol. 11 Elsevier; 1964. p. 529–562.

[4] Roland A, Zhang YJ, Wang HV, Meng Y, Teng YC, Maderich V, et al. A fully coupled 3D wave-current interaction model on unstructured grids. Journal of Geophysical Research: Oceans 2012;117(C11).
Measuring plant hydraulic conductivity: Should we push or should we pull?
Authors: Krieger Louis , Schymanski Stan , Jansen Steven
Published: March 2021

Usually hydraulic conductance and vulnerability are measured under extreme conditions never experienced by living plants (e. g. centrifugation, bench dehydration, and large pressure gradients). A common factor that is known to inhibit the water transport in plants is embolism, which is believed to occur either by air entry through the pit valves on the walls of the xylem, or by ex-solution of dissolved gases, or vaporization of water at very low pressures.

Here we explore possibilities to measure hydraulic conductance and induce embolism under close to natural conditions. The setup consists of a syringe pump to control water flow, where a twig is inserted in the flow path to measure its hydraulic conductivity using pressure and flow meters. This setup has enabled us to imitate natural conditions where transpiration rate induces a pressure difference between the sink (leaf) and source (root) along the flow path. It has also allowed us to induce flow in both directions through the twig without having to rotate or change out the sample. Using our setup, we found that the conductivity of the same twig was 50% lower when pulling compared to pushing. This can be explained by the emptying and filling of cut end vessels and the pressure gradient along the twig, which is induced by the flow rate and flow direction. Our findings are discussed in the context that currently employed methods for measuring wood hydraulic conductance employ either centrifugation, where water is pulled on both ends, or pushing of water by applying positive pressure on one end.
A flexible method for determining decorrelation ranges in rainfall applied to Ghana
Authors: Israelsson Jennifer , Black Emily , Neves Cláudia , Torgbor Francis Feehi , Greatrex Helen , Tanu Michael , Lamptey Patrick Nii Lante
Published: March 2021

The spatial structure of rainfall events over west Africa is not very well understood, and a major limitation for improving this understanding is the generally sparse rain gauge network. This lack of spatial knowledge makes it difficult to describe the state between the rain gauges, something that is important if one wants to determine which locations are likely to have received rainfall and not. Earlier work on estimating correlation structures has been limited by the long distances between rain gauges, which often has been longer than the actual correlation range. 

In this talk, we will describe a simple and easily adapted method developed for calculating the decorrelation range in daily rainfall. Thanks to a new, dense daily rain gauge data set from Ghana Met agency, the spatial structure of rainfall for the different phases of the West African monsoon has been investigated. Previous studies have only considered a general decorrelation range, ignoring rainfall intensity as a factor when determining the rainfall extent. For the results presented in this talk, the decorrelation range has been estimated for 4 different rainfall intensities to explore the difference between low and high intensity events. This is analysed separately for each month at a fine spatial scale. Results on the anisotropic, i.e correlation changing with direction, pattern at the subweekly and local scale for several aggregation periods will also be presented.

It is found that the spatial correlation structure of rainfall vary greatly with the intensity of the rainfall event and the phase of the monsoon. In particular, it was determined that the intensity rather than the time of the year had the largest influence at the local scale. The westward propagation of convective systems, a well known phenomena over weekly to monthly time scales, was detected even at short aggregation periods.
Predict depth constraints for lithospheric modelling by machine learning 
Authors: Holzrichter Nils , Guy Alexandra , Ebbing Jörg
Published: March 2021

Machine learning applications in geophysical studies are often used to predict geophysical observations in areas with sparse or not data or recognize patterns and similarities in data. In our study, we test different techniques to improve the information of constraining data by machine learning and to improve strengthen the modelling of lithospheric structures with potential field data. Constraining data like seismic information, surface geology, rock classifications etc. is often used during the interpretation step of lithospheric modelling to aid the qualitative interpretation. Consensus between additional data and the own model is assessed by comparison and used to describe the model goodness consistency. First Wwe test, how this additional data can be used before the modelling by using machine learning techniques to quantify the data. We focus on supervised learning to predict crustal structure in areas with little constraints, on trained learning in data-rich areas. Second, we test the spatial analysis of surface data to determine lithospheric boundaries in depth. These tests are performed in North America and the Central Asian Orogenic belt (CAOB) to compare the results in areas with respectively good and spare data coverage. That approach can be used to link the large variety of surface and deep information in the CAOB region.

The combination of the different geophysical data available with the geological data should improve our tectonic modelling.