bluuebunny/crossref_metadata_2025 huggingface dataset:
First steps to bridging the gap between CryoSat-2 and ICESat2: retrackers and slope induced error.
Authors: Sejan Katarzyna , Wouters Bert , van den Broeke Michiel
Published: March 2021

Satellite radar altimetry is one of the most important tools for monitoring changes in the mass balance of the world's ice sheets. Different altimetry techniques however, come with their own pitfalls. In radar altimetry, signal penetration into the snowpack introduces ambiguity in the origin of reflected echo, a major issue not present in laser altimetry. Fine tuning the developed processing algorithms for the CryoSat-2 radar altimetry data, using the IceSat2 laser altimetry data as a benchmark, may allow for a more precise surface elevation and snowpack depth estimations. Furthermore, bridging the gap between radar and laser altimetry will result in larger spatial and temporal data coverage when the two data sets are combined.  Focusing on Greenland Ice Sheet (GIS), we have developed a processing chain for the estimation of surface elevations and elevation changes from the ESA level-1 product (L1b) Baseline D. We investigated the importance of a retracker type, retracker threshold, Digital Elevation Model (DEM) in the slope correction, and how these affect the estimated surface elevation as compared to the ICESat2 data.

Firstly, ESA L1b Baseline-D data was processed at several different thresholds and with various waveform retracker algorithms, including threshold first maxima retracker algorithm (TFMRA) (Helm, 2012; Nilsson, 2015) and the offset center of gravity (OCOG) retracker algorithm (Bamber, 1994; Ricker et al. 2014). We then apply slope correction to adjust for the slope induced error in the radar altimetry data (Hurkmans, 2012), the correction was applied using three different DEMs, ArcticDEM Release 7 (Porter et al., 2018), Greenland Ice Mapping Project (GIMP) DEM (Howat et al., 2017) and ‘Helm’ DEM (Helm, 2014). We checked all of the produced data sets against IceSat-2 data (Smith et al., 2019) corresponding to the same time period, and selected by nearest neighbor calculation for specified maximum distance. We analyze and discuss the differences between IceSat-2 data and CryoSat-2 data and their dependence on several radar altimetry processing parameters and methodologies.

 
Evidences of melt water control on crevasse propagation using dense array seismic observations
Authors: Gimbert Florent , Urruty Benoit , Roux Philippe , Gilbert Adrien , Nanni Ugo , Lecointre Albanne
Published: March 2021

Crevasses are inherent features of glaciers and Ice Sheets. They exert a primary control on glacier dynamics, such as, for example, along shear margins through reducing the overall glacier ice viscosity, or at glacier and Ice Sheet fronts through controlling the onset of serac falls and of ice sheet instabilities (calving, ice shelf disintegration). However, our understanding of crevasse formation and propagation, and in particular the effect of melt water, remains limited due to lacking observations. Here we provide novel observational insights into englacial fracturing, the depth of crevasses and their depth propagation rates using dense seismic array monitoring on an Alpine glacier. We systematically detect and locate englacial seismic events through applying matched-field-processing on a particularly dense seismic array of 98 sensors deployed on the Glacier d’Argentière during 1-month in spring 2018. We observe rupture fronts along crevasses, which propagate from the glacier center to the glacier side at typical velocities of few hundreds of meters per day, i.e. at velocities that are much lower than those of seismic waves but much higher than those of glacier flow. We argue based on a dedicated spatial and temporal analysis that crevasse rupture propagation is set by the migration of water along the crevasse tip. We also observe that crevasses are associated with a wide range of depths, varying from the near surface to the glacier base, which at the present site is located about a hundred meters below the surface. This observation is particularly interesting, since it provides evidences that (i) crevasses are water filled and (ii) crevasses play a role in the supply of water to the bed. These findings are further supported by the observation that surface melt modulates the seismic activity of crevasses including those reaching the bed. Finally, by evaluating coherent structures in the crevasse population, we are able to infer their depth propagation rate, which we find is constant through the ice column, as expected if the surrounding ice stress field is counterbalanced by the water pressure in the crevasse. These observationally-derived findings provide useful grounds to test and improve theories of crevasse dynamics and their control in the overall transfer of water from the surface to the bed.
Experiments on the grain size gap across gravel-sand transitions
Authors: Dingle Elizabeth , Venditti Jeremy
Published: March 2021

An abrupt transition in river bed grain size occurs from gravel to sand over a short downstream distance, often only a few channel widths, and is termed the gravel-sand transition (GST). At this point, the bed structure also changes from framework- to matrix-supported. Whether the GST is externally imposed, a result of internal dynamics (sediment sorting, abrasion, suspension deposition) or due to some other emergent property is unclear. There is also a general absence of rivers beds with median surface grain sizes between ~1 and 5 mm, often referred to as the grain size gap. Here we present two sets of new laboratory experiments, examining changes in fluid and sediment dynamics across the GST. In the first set, we created stable GSTs with a 10 mm gravel and 0.5 mm sand that show GST formation is consistent with  previous theory suggesting that at shear velocities of ~0.1 m/s, sand particles rapidly fall out of suspension as a result of a particle Reynolds number dependency (i.e. a viscous effect). In a second set of experiments, we explored the fate of grain size gap material. We formed a gravel wedge composed of ~2 to 5 mm sediment, then fed 0.5 mm sand.  Our observations indicate that where sand rapidly starts to fall out of suspension, the gravel bed becomes inherently unstable. Gravel is transported downstream until the grain size gap material is largely exhausted from the system (e.g. buried under sand or rafted out of the flume). This occurs because sand sized particles fill or bridge interstitial pockets in the fine gravel bed surface, generating fluid acceleration in the near-bed region (i.e. a geometric effect specific to these grain sizes). As such, particles in the grain size gap do not form the dominant mode in river bed sediments. 
Enhancing subtle seafloor relief variation: relief visualisation techniques for bathymetric data 
Authors: Novak Ana , Poglajen Sašo , Vrabec Marko
Published: March 2021

Bathymetric data is commonly visualized as a simple shaded relief, where features oriented parallel to the light source are prone to false topographic perception or are even obscured to the viewer. On the other hand, many relief visualisation techniques developed in past decades are extensively used in visualisation and analysis of high-resolution digital elevation models, especially in geomorphological and archaeological studies. We tested and assessed the suitability of relief visualisation techniques provided by the Relief Visualisation Toolbox (RVT) software for representation of bathymetric data. We used a multibeam-sonar derived bathymetric model with a 10 x 10 m cell size from the Gulf of Trieste (northern Adriatic) characterised by a shallow low-relief seabed. Our results clearly demonstrate the effectiveness of relief visualisation techniques for exposing subtle relief variation in bathymetric data. We find that small-scale features (outcrops, wrecks, pockmarks, reefs, etc.) and negative linear features are best highlighted by “visualization for archaeological topography” (VAT) and “openness” techniques. High-relief features and topographic infection points are pronounced by “hillshade from multiple directions” and “sky-view factor” (SVF). Finally, “principal components analysis” (PCA), “prismatic openness”, “simple local relief model”, “anisotropic SVF” and “local dominance” algorithms show best results when we want to highlight both high- and low-relief features in one image. The tested techniques are far superior to a simple hillshade visualisation especially when imaging low-gradient relief (common on continental shelves and abyssal plains) where topographic details are often not adequately pronounced by hillshading. To our knowledge, this study represents the first attempt to test and compare several relief visualisation techniques for bathymetric data.  
Integrative hydrogeo-ecological assessment of the quantitative and qualitative response of groundwater to hydrological extremes
Authors: Birk Steffen , Haas Johannes , Retter Alice , Collenteur Raoul , Brielmann Heike , Stumpp Christine , Griebler Christian
Published: March 2021

An integrative interdisciplinary approach is currently developed to investigate groundwater systems in alpine and prealpine environments and how they respond to hydrological extremes such as droughts, heavy rain and floods in terms of water quantity, hydrochemical quality, and ecological status. The new approach is aimed at improving the understanding of the interaction between physical, chemical, and biological processes in groundwater responses to extreme events as well as developing indicators suitable for an integrative monitoring and management of the aquifers. For this purpose, observation wells of the existing state hydrographic monitoring net have been selected within the Austrian part of the Mur river basin, stretching from the alpine origin to the national border in the foreland. The investigation area thus comprises diverse hydrogeological settings and land-use types. The selected observation wells have long-term records of groundwater levels and are used for sampling campaigns under different hydrological conditions. Groundwater level fluctuations are evaluated using drought indices and statistical approaches, such as auto-correlation and cross-correlation with precipitation and stream stages. Our hydrochemical analyses of groundwater and surface waters also consider compounds indicative of agricultural sources (e.g., nitrate), wastewater-borne micro-pollutants, and stable isotopes of water. These indicators are used to identify different drivers controlling water origin and quality. The ecological status is characterized using microbiological measures, such as total number of bacteria and microbial activity, groundwater fauna, and the qualitative composition of dissolved organic matter (DOM). First results demonstrate a deterioration of water quality from groundwater to surface water and from the alpine region towards the foreland, corresponding to the more intense agricultural and urban land use in the foreland. Linkages between water quality and hydrological conditions are currently being evaluated and will be further examined using UV-Vis spectrometry for high-resolution in-situ monitoring of water quality changes (DOM and nitrate) at selected observation wells.
Observations of shock propagation through turbulent plasma in the solar corona
Authors: Carley Eoin , Cecconi Baptiste , Reid Hamish , Briand Carine , Raja K. Sasikumar , Masson Sophie , Dorovskyy Vladimir , Tiburzi Caterina , Zucca Pietro
Published: March 2021

Eruptive activity in the solar corona can often lead to the propagation of shockwaves. In the radio domain the primary signature of such shocks are type II radio bursts, observed in dynamic spectra as bands of emission slowly drifting towards lower frequencies over time. These radio bursts can sometimes have inhomogeneous and fragmented fine structure, but the cause of this fine structure is currently unclear. Here we observe several type II radio bursts on 2019-March-20th using the New Extension in Nancay Upgrading LOFAR (NenuFAR), a radio interferometer observing between 10-85 MHz. We show  that the distribution of size-scales of density perturbations associated with the fine structure of one type II follows a power law with a spectral index of -1.71, which closely matches the value of -5/3 expected of fully developed turbulence. We determine this turbulence to be upstream of the shock, in background coronal plasma at a heliocentric distance of ~2 Rsun. The observed inertial size-scales of the turbulent density inhomogeneities range from ~62 Mm to ~209 km. This shows that type II fine structure and fragmentation can be due to shock propagation through an inhomogeneous and turbulent coronal plasma, and we discuss the implications of this on electron acceleration in the coronal shock.
Evaluation of water resources management and agronomic scenarios using an integrated modelling system for coastal agricultural watersheds: The case of Almyros Basin, Thessaly, Greece
Authors: Lyra Aikaterini , Loukas Athanasios , Voudouris Konstantinos , Mylopoulos Nikitas
Published: March 2021

Coastal agricultural watersheds face complex problems of water quantity and quality.  In many coastal agricultural watersheds, the problems arise from: i) the limited use of surface water, ii) the excessive groundwater abstractions for irrigation, and iii) the over-fertilization practices for crop yield magnification. These complex and interrelated problems may be studied by using an integrated modelling system of surface water and groundwater able to simulate the processes regarding the quantity and quality of water. In this study, water resources management and agronomic scenarios are developed for the evaluation of the quantity and quality of the groundwater system of the semi-arid coastal agricultural Almyros Basin, in Thessaly, Greece. The historical and current unsustainable irrigation and fertilization practices, the groundwater abstractions, and the limited use of surface water reservoirs have caused a large water deficit of the aquifer system, groundwater nitrate contamination and seawater intrusion, resulting in severe degradation of water resources. Land use change and agronomic scenarios, as well as, reservoir operation scenarios, are combined and simulated using an integrated modelling system.   The Integrated Modelling System consists of coupled models of: surface hydrology (UTHBAL), groundwater flow (MODFLOW), agronomic practices and nitrate leaching (REPIC, an R-ArcGIS based EPIC model), nitrate transport (MT3DMS), and seawater intrusion (SEAWAT). The models have been calibrated and validated against observations/measurements of various variables, e.g. groundwater table levels, crop yields, nitrate concentrations and chloride concentrations.  The feasibility of the simulation of the various scenarios have been, also, evaluated with indices of Crop Water Productivity (CWP), Nitrogen Use Efficiency (NUE) and Economic Water Productivity (EWP).
The geology of King George Island, South Shetland Islands: uniting local geological maps and stratigraphical columns
Authors: Lopez Bastian , Bastias Joaquin , Matus Daniela , Jaña Ricardo , Leppe Marcelo
Published: March 2021

King George Island is the largest one of the South Shetland Islands group distributed parallel to and separated by the Bransfield Strait of the northern tip of Antarctic Peninsula. The archipelago of the South Shetlands is mainly composed of the products of the active margin developed as a result of the subduction of the Phoenix Plate beneath the continental crust of the Antarctic Peninsula (e.g. Barker, 1982; Bastias et al., 2019). The lithologies are largely dominated by Mesozoic and Cenozoic sedimentary and volcanic successions that are cut by a few hypabyssal plutons. While some authors have suggested a southwest to northeast trend along the archipelago from older to younger magmatic activity (e.g. Haase et al., 2012), others have indicated that some of the magmatic events may have been recorded along the entire archipelago (e.g. Valanginian arc rocks; Bastias et al., 2019). Regardless, King George Island hosts an exceptional stratigraphical record of the Cenozoic period. Moreover, this island is mostly covered by an ice cap at the present day, which is commonly terminated with ice cliffs around much of the island. The southern edge of the island host Mesozoic and Paleogene successions, these rocks are dominated by volcanic and volcaniclastic units. The rocks in King George Island are generally young to the east and to the north ends. Cape Melville, the southeast extreme of the island, hosts the youngest sedimentary rocks known on the island: the Moby Dick Group (Birkenmajer, 1985).

While several authors have presented local studies in the King George Island over the last three decades, an integrated assessment of the outcropping units in the entire island remains unexplored. A new geological map for King George Island will allow to update the current understanding of the stratigraphy of the South Shetland Islands, which will help to support not only the geological studies but also those focused on the environmental and paleontological record.

Barker, 1982. Journal of the Geological Society 19, 787-801. (DOI: 10.1144/gsjgs.139.6.0787)

Bastias et al. (2019). International Geology Review 62 (11), 1467-1484. (DOI: 10.1080/00206814.2019.1655669)

Birkenmajer (1985). Bulletin Polish Academic Earth Sciences 33:15-23.

Haase et al. (2012). Contributions to Mineralogy and Petrology 163, 1103-1119. (DOI: 10.1007/s00410-012-0719-7).
Development and Assembly of a MEMS Based High-Sensitivity Relative Gravimeter for Multi-Pixel Imaging Applications 
Authors: Toland Karl , Prasad Abhinav , Noack Andreas , Anastasiou Kristian , Middlemiss Richard , Paul Douglas , Hammond Giles
Published: March 2021

The manufacture and production of a high-sensitivity cost-effective gravimeter has the potential to change the methodology and efficiency of gravity measurements. Currently, the most common method to conduct a survey is by using a single gravimeter, usually costing tens of thousands of Dollars, with measurements taken at multiple locations to obtain the required data. The availability of a cost-effective gravimeter however would allow the user to install multiple gravimeters, at the same cost of a single gravimeter, to increase the efficiency of surveys and long-term monitoring.  

 

Since the previous reporting on a low-drift relative MEMS gravimeter for multi-pixel imaging applications (Prasad, A. et al, EGU2020-18528), significant progress has been made in the development and assembly of the previously reported system. Field prototypes have been manufactured and undergone significant testing to investigate the stability and robustness of the system in preparation for the deployment of multiple devices as part of the gravity imager on Mount Etna. The device, known as Wee-g, has several key features which makes it an attractive prospect in the field of gravimetry. Examples of these features are that the Wee-g is small and portable with the ability to connect to the device remotely, can be powered through a mains connected power supply, or through portable batteries, weighs under 4kg, has a low power consumption during normal use of 5W, correct for tilt through manual adjustments or remotely through integrated stepper motors with a total tilt correction range of 5 degrees, the ability to read out tilt of the device through an inclinometer for either alignment or long term monitoring and numerous temperature sensors and heater servos to control the temperature of the MEMS to <1mK.

 

This presentation aims to report on the progress that has been achieved in the development and manufacturing of the prototype devices, various testing of the devices under various laboratory conditions (such as the measurements of the Earth tides, and a relative measurement of gravity at various floor levels), as well as additional applications that are to be explored in 2021. 
Quantification of fluvial-peat interactions in the Pikeville formation Central Appalachian Basin, USA.
Authors: Wooldridge Peter , Duller Robert , Jerrett Rhodri , Straub Kyle
Published: March 2021

Basin-scale fluvial architecture is, to a large extent, determined by the ability of river systems to migrate and avulse across their own floodplain. River avulsion takes place when a river aggrades by one channel depth to achieve super-elevation above the surrounding floodplain. However, peat enhancement of floodplain aggradation is likely to affect this fluvial behaviour and has received little attention. The interaction between river channels and peat-dominated floodplains is likely to have the effect of inhibiting or prolonging the conditions required for river avulsion, and so will impact on basin scale architecture during prolonged peat accumulation on floodplains. To elucidate and quantify the nature of this channel-floodplain interaction we investigate the coal-bearing clastic interval of the Carboniferous Pikeville Formation, Central Appalachian Basin, USA. Using a combination of well data and outcrop data, two coal horizons and intervening sand bodies, were mapped across an area of 5700 km2 to ascertain overall basin-scale architecture. Comparison of the accumulation rate of the coal units (corrected for decompaction) with the synchronously deposited sand bodies suggests that extensive and rapid peat accumulation can increase avulsion timescales by 3 orders of magnitude and dramatically alter basin-scale fluvial architecture.
A new Last Glacial-Interglacial Transition varve record from Chilean Patagonia
Authors: Pike Joshua , Palmer Adrian , Thorndycraft Varyl , Matthews Ian
Published: March 2021

High-resolution sedimentary archives, such as glaciolacustrine varve sequences formed in proglacial lakes, can enable detailed reconstructions of past glacier dynamics, assess regional to global climate (a)synchronicity and disentangle oceanic and atmospheric climatic forcing mechanisms. Specifically, glaciolacustrine varved sequences can be utilised to investigate, at an annual resolution, the rates and/or duration of change during deglaciation of a former glacial basin, significantly refining models of ice-sheet deglaciation. Additionally, the identification of tephra layers deposited within varved sequences offer the potential to provide isochronous marker layers, enabling high-precision correlations between sites and palaeoenvironmental archives, and an independent means of generating an absolute age for the varve chronology.

We present new varve data obtained from sediment sections in Chile Chico (-46.53oS, -71.73oW) in the Lago General Carrera (Chile)/Buenos Aires (Argentina) basin in central Patagonia. Here, an ice-contact, proglacial lake formed during the recession of an ice lobe of the former Patagonian Ice Sheet from its local Last Glacial Maximum position (18,778 ± 615 to 18,086 ± 2141). Sequences of laminated glaciolacustrine sediment accumulated in the palaeolake and have subsequently been exposed following lake drainage. We report on the detailed macro- and micro-facies of the Chile Chico sediments as well as an updated tephrostratigraphy for the region. In particular we (1) develop a process model for the formation of melt season and non-melt season components that suggest a varved origin; (2) present a ~3.5 kyr varve thickness record for Chile Chico that post-dates (<17 ka BP) the Fenix Chico Master Varve Chronology, and (3) detail pilot tephrochronological assessment of the sequences. Consideration is also given to the challenges associated with developing both the varve chronology, where detection of varves is variable and hiatuses and deformation exist within the sequences, and tephrochronology, where distinguishing between eruptive events with this level of stratigraphic resolution is unparalleled in the region.

1Bendle, J.M., Palmer, A.P., Thorndycraft, V.R., Matthews, I. P. (2019) Phased Patagonian Ice Sheet response to Southern Hemisphere atmospheric and oceanic warming between 18 and 17 ka. Sci Rep 9, 4133
How to upscale reaction-diffusion models
Authors: Zawallich Jan , Frohloff Daria , Spanner Tobias , Horn Marcus A. , Dörsch Peter , Ippisch Olaf
Published: March 2021

Denitrification is an important microbial process and potential source for nitrous oxide (N2O), an important greenhouse gas and destructor of stratospheric ozone. Quantitative predictions of denitrification in soils are difficult as denitrification, an anaerobic respiration process,  appears to occur even in well-areated soils. It is assumed that denitrification is active in dense aggregates over short time periods - so called hot spots and hot moments. While soil microbial metabolism occurs at the pore scale, the interest in denitrification is mostly at the field and landscape scale. Simulating both scales simultaneously is not feasible. Therefore, denitrification has to be upscaled from the pore to the aggregate scale without losing essential properties of the aggregates. An important key to effectively upscale is the anaerobic aggregate volume fraction.

In order to compare different upscaling techniques we conducted pure culture experiments with varying spatial structures. To avoid confounding effects associated with the transition of bacteria switching from oxic respiration to denitrification, we used bacteria only capable of the former. The investigated upscaling techniques include simplifying the microbial reaction as well as creating an effective one-dimensional diffusion model. We compare computation intensity and approximation quality of experimental results.
Mechanism of salt flux transport in a tidal dynamic delta
Authors: Sun Yujuan , Bricheno Lucy , Horsburgh Kevin
Published: March 2021

The annual mean combined river discharge from the Ganges-Brahmaputra-Meghna (GBM) riverine system is 100,000 – 140,000 m3/s (EGIS 2000), draining to Bay of Bengal, covering 83% of total area of Bangladesh, and making Bangladesh delta more vulnerable to both the freshwater and the mixing with sea water. This estuarine environment varies spatially and temporally, over all multiple time scales, due to its funnel-shaped vast river networks, strong tides, and saltwater intrusion. Recent studies reported a drastic salinity increasing at the end of the dry season in the past 20 years (Murshed et al., 2019). Significant salinity intrusion appears from the Sundarbans (over 20ppt in 2015), and then extends inland, which makes salinity a key factor for changing land use and demographic migration.

We examine volume and salt flux transports at multi-river channels where the GBM drains to the Bay of Bengal, using our unstructured-grid Bangladesh-FVCOM model (Bricheno et al., 2016). This realistic simulation of the whole delta has been shown to reproduce the present-day river flow circulation, tidal dynamics, and salinity stratification.

We then summarise results from the detailed hydrodynamic numerical model into a simplified flow budget, to summarise the climate impacts on salt-intrusion in the delta. In this way, we can investigate the mechanism of salt flux transports in Bangladesh delta, and improve our understanding of the controlling processes driving salinity intrusion in this region.
Warming affects seasonal dynamics of microorganisms and reduces the N storage capacity of soil microbes in winter
Authors: Gündler Philipp , Canarini Alberto , Marañón Jiménez Sara , Gunnarsdóttir Gunnhildur , Sigurðsson Páll , Peñuelas Josep , Janssens Ivan A. , Sigurdsson Bjarni D. , Richter Andreas
Published: March 2021

Seasonality of soil microorganisms plays a critical role in terrestrial carbon (C) and nitrogen (N) cycling. The asynchrony of immobilization by microbes and uptake by plants may be important for N retention during winter, when plants are inactive. Meanwhile, the known warming effects on soil microbes (decreasing biomass and increasing growth rates) may affect microbial seasonal dynamics and nutrient retention during winter.

We sampled soils from a geothermal warming site in Iceland (www.forhot.is) which includes three in situ warming levels (ambient, +3 °C, +6 °C). We harvested soil samples at 9 time points over one year and measured the seasonal variation in microbial biomass carbon (Cmic) and nitrogen (Nmic) and microbial physiology (growth and carbon use efficiency) by an 18O-labelling technique.

We observed that Cmic and Nmic peaked in winter, followed by a decline in spring and summer. In contrast growth and respiration rates were higher in summer than winter. The observed biomass peak at lower growth rates, suggests that microbial death rates must have declined even more than growth rates. Soil warming increased biomass-specific microbial activity (i.e., growth, respiration, and turnover rates per unit of microbial biomass), prolonging the period of higher microbial activity found in summer into autumn and winter. Microbial carbon use efficiency was unaltered by soil warming. Throughout the seasons, warming reduced Cmic and Nmic, albeit with a stronger effect in winter than summer and restrained winter biomass accumulation by up to 78% compared to ambient conditions. We estimated a reduced microbial winter N storage capacity by 45.5 and 94.6 kg ha-1 at +3 °C and +6 °C warming respectively compared to ambient conditions. This reduction represents 1.57% and 3.26% of total soil N stocks, that could potentially be lost per year from these soils.

Our results clearly demonstrate that soil warming strongly decreases microbial C and N immobilization when plants are inactive, potentially leading to higher losses of C and N from warmed soils over winter. These results have important implications as increased N losses may restrict increased plant growth in a future climate.
Back arc basin unveiled at South Pole along an irregular East Antarctic craton margin
Authors: Ferraccioli Fausto , Dunn Aisling , Green Chris , Jordan Tom , Forsberg Rene , Eagles Graeme , Matsuoka Kenichi , Casal Tania
Published: March 2021

An Andean-style convergent margin was active between ca 580 and 460 Ma along the margin of Gondwana. It led to the emplacement of a major magmatic arc, which is in parts exposed along the much younger Transantarctic Mountains (TAM). Arc magmatism, thrusting, deformation and metamorphism are hallmarks of the long-lived subduction-related Ross Orogen (RO).

Despite the wealth of knowledge on the RO, the location, structure and evolution of the unexposed boundary between the Precambrian Mawson Craton and the RO remains very poorly known, particularly in the South Pole (SP) region- one of the largest poles of ignorance in the whole of East Antarctica.  

Here we combine new aeromagnetic data collected during the ESA PolarGAP campaign with vintage ADMAP 2.0 (Golynsky et al., 2018- GRL) aeromagnetic datasets in the SP region and level these using the satellite magnetic LCS-1 model to investigate the craton margin and RO. The final levelled data were draped at 2800 m above the bedrock topography (Morlighem et al., 2020, Nature Geo.) and reduced to the pole.  

To enhance magnetic signatures and reveal subglacial basement terranes we applied pseudo-gravity transforms, derivatives and upward continuation. We also computed new airborne gravity residual maps and compared these with enhanced magnetic anomaly images. We applied a variety of depth to source of the magnetic and gravity residual anomalies, including tilt depth, Werner and Euler Deconvolution and constructed simple 2D models of the crustal architecture of the RO and the adjacent Precambrian craton margin.  

Using the information from enhanced aeromagnetic imaging and combined magnetic and gravity modelling we propose a new tectonic model for the region. In our model, a former late Neoproterozoic rifted margin that developed along an irregular cratonic margin of the Mawson continent evolved during the Ross Orogen in a wide back-arc basin tectonic setting, linked to a predominantly retreating accretionary subduction-related setting from ca 530 Ma to 500 Ma. This led to the emplacement of magnetite-rich ribbons of arc crust, which are magnetically imaged for the first time in this sector of the active margin. Complex deformation of these ribbons is also imaged from aeromagnetic signatures and appears to resemble some of the deformation patterns observed in the Tasmanides in Australia in evolving retreating accretionary arc and back arc systems (e.g Moresi et al., 2014, Nature).
No “Abrupt increase in harvested forest area over Europe after 2015” – How the misuse of a satellite-based map led to completely wrong conclusions
Authors: Breidenbach Johannes , Ellison David , Petersson Hans , Korhonen Kari , Henttonen Helena , Wallerman Jörgen , Fridman Jonas , Gobakken Terje , Astrup Rasmus , Næsset Erik
Published: March 2021

In a recent Nature article, the satellite-based Global Forest Change (GFC) map was used to estimate the yearly harvest area in each of the EU26-states over the period 2004 to 2018 (Ceccherini et al. 2020). Finland and Sweden were identified as the countries with the largest harvest increases and the biggest effect on the EU’s climate policy strategy. Here, we employ more than 45,000 field observations from the Finnish and Swedish national forest inventories as reference observations to analyze the accuracy of GFC data. We find that harvested area increases only marginally, if at all, after 2015. What did increase abruptly after 2015, however, was GFC’s sensitivity to detect harvested areas and thinnings.

The results of the Nature article are therefore a consequence of an inconsistent time series in GFC due to a change in the mapping algorithm or the sensor system and are thus both incorrect and misleading. The article is thus a good example for how wrong results based on satellite data can be, if no adequate estimators utilizing reference data are used.

 

References

Ceccherini, G. et al. Abrupt increase in harvested forest area over Europe after 2015. Nature 583, 72-77 (2020).
Analysis of water quality time series for improving the measurement strategy in the Brantas basin, Indonesia
Authors: Willard Tijmen , Pramana Reza , Pande Saket , van Breukelen Boris , Ertsen Maurits
Published: March 2021

Water quality in the rivers and tributaries of the Brantas catchment (about 12.000 km2; East Java, Indonesia), which is deteriorating due to various reasons, is measured by different agencies involved in water resource development and management. We discuss how different time series of water quality data from three local agencies in the Brantas basin (differing in specific parameters and measurement frequency) have been used to provide recommendations on the improvement of (using) the different measurement strategies (in policy recommendations). In general, monthly to quarterly data were available from 2009 until 2019 at 104 locations. Data were analyzed with Principal Component Analysis (PCA) to show which parameters vary significantly across the catchment. Preliminary results suggested how parameters were related, based on series of box plots of the PCA scores. This provided insights on the first order processes that control the physical-chemical status of the Brantas River, of each agency and for all the data sets combined. Applying Python and QGIS to separate the parameters and map the hot spots in terms of eigen functions allowed relating water levels with hot spots to estimate the fluctuations in the concentrations of different parameters in time and space. These data elaborations allow improving the different measurement campaigns, and to address specific policy questions related to water quality monitoring more efficiently.
Effects of aging and transformation of Fe(III)-precipitates on the retention of co-precipitated phosphate
Authors: Nenonen Ville , Kaegi Ralf , Hug Stephan J. , Mangold Stefan , Göttlicher Jörg , Winkel Lenny , Voegelin Andreas
Published: March 2021

The cycling of phosphorus in terrestrial and aquatic systems is tightly coupled to the redox-cycling of iron (Fe). The oxidation of dissolved Fe(II) in natural waters leads to the precipitation of amorphous to poorly crystalline Fe(III)-solids that can bind phosphate (P) and other nutrients as well as toxic compounds. The EU project P-TRAP is aimed at developing methods to reduce diffuse P inputs into surface waters to mitigate eutrophication, by using Fe-rich byproducts from water treatment (https://h2020-p-trap.eu/). Within this project, we study mechanistic aspects of the formation and transformation of P-containing Fe(III)-precipitates and their implications for P retention in soils and water filters.

Freshly formed Fe(III)-precipitates are metastable and can transform into more stable phases over time. This may lead to the release of co-precipitated P. In laboratory experiments, we assessed how Ca, Mg, silicate (Si) and P impact on the formation and transformation of Fe oxidation products (at 0.5 mM Fe) and their P retention in synthetic bicarbonate-buffered groundwater. The time-resolved experiments were performed in electrolyte solutions containing Na, Ca, or Mg as electrolyte cation, without or with Si (at molar Si/Fe of 1), and P (P/Fe of 0.3 and 0.05). Changes in dissolved element concentrations over time were linked to changes in the structure and composition of the Fe(III)-solids; with Fe coordination probed by X-ray absorption spectroscopy, mineralogy by X-ray diffraction, and nano-scale morphology and composition heterogeneity by transmission electron microscopy with energy-dispersive X-ray detection.

The freshly-formed Fe(III)-precipitates were mixtures of amorphous Fe(III)-phosphate with either poorly-crystalline lepidocrocite (without Si) or Si-containing ferrihydrite (with Si). Increases in dissolved P during aging were largest in Na electrolytes without Ca, Mg or Si, and were linked to the transformation of amorphous Fe(III)-phosphate into lepidocrocite with a lower P retention capacity than Fe(III)-phosphate. In Ca- and to a lesser extent Mg-containing electrolytes, the Ca or Mg stabilized the amorphous Fe(III)-phosphate and thereby reduced P release over time. The presence of Si increased initial P uptake and inhibited P release during aging by causing the formation of Si-ferrihydrite with higher P sorption capacity than lepidocrocite formed in the absence of Si. In conclusion, the extents to which P is trapped by fresh Fe(III)-precipitates and released during aging can be attributed to the individual and coupled impacts of Ca, Mg and Si on Fe(III)-precipitate structure, stability and transformation.

In continuing work, we aim to expand our work to study how organic compounds impact on the formation and colloidal stability of Fe(III)-precipitates and P retention.
Stochastic stress-testing approach for assessing resilience of urban water systems from source to tap
Authors: Nikolopoulos Dionysios , Kossieris Panagiotis , Makropoulos Christos
Published: March 2021

Urban water systems are designed with the goal of delivering their service for several decades.  The infrastructure will inevitably face long-term uncertainty in a multitude of parameters from the hydroclimatic and socioeconomic realms (e.g., climate change, limited supply of water in terms quantity and acceptable quality, population growth, shifting demand patterns, industrialization), as well as from the conceptual realm of the decision maker (e.g., changes in policy, system maintenance incentives, investment rate, expansion plans). Because urban water systems are overly complex, a holistic analysis involves the use of various models that individually pertain to a smaller sub-system and a variety of metrics to assess performance, whereas the analysis is accomplished at different temporal and spatial scales for each sub-system. In this work, we integrate a water resources management model with a water distribution model and a water demand generation model at smaller (household and district) scale, allowing us to simulate urban water systems “from source to tap”, covering the entire water cycle. We also couple a stochastic simulation module that supports the representation of uncertainty throughout the water cycle. The performance of the integrated system under long term uncertainty is assessed with the novel measure of system’s resilience i.e. the degree to which a water system continues to perform under progressively increasing disturbance. This evaluation is essentially a framework of systematic stress-testing, where the disturbance is described via stochastically changing parameters in an ensemble of scenarios that represent future world views. The framework is showcased through a synthesized case study of a medium-sized urban water system.

Acknowledgement

This research is carried out / funded in the context of the project “A resilience assessment framework for water supply infrastructure under long-term uncertainty: A Source-to-Tap methodology integrating state of the art computational tools” (MIS 5049174) under the call for proposals “Researchers' support with an emphasis on young researchers- 2nd Cycle”. The project is co-financed by Greece and the European Union (European Social Fund- ESF) by the Operational Programme Human Resources Development, Education and Lifelong Learning 2014-2020.”
Cyclonic eddies in the West Greenland boundary current system
Authors: Pacini Astrid , Pickart Robert S. , Le Bras Isabela A. , Straneo Fiammetta , Holliday N. Penny , Spall Michael A.
Published: March 2021

The Labrador Sea is an important site for deep convection, and the boundary current surrounding the Sea impacts the strength of this convection and the subsequent restratification. As part of the Overturning of the Subpolar North Atlantic Program, ten moorings have been maintained on the West Greenland shelf and slope that provide hourly, high-resolution renderings of the boundary current. These data reveal the presence and propagation of abundant mid-depth intensified cyclonic eddies, which have not previously been documented in the West Greenland boundary current system. This study quantifies these features and their structure and demonstrates that they are the downstream manifestation of Denmark Strait Overflow Water (DSOW) cyclones. Using the mooring data, the statistics of these features are presented, a composite eddy is constructed, and the velocity and transport structure are described. A synoptic survey of the region captured two of these features, and provides further insight into their structure and timing. This is the first time DSOW cyclones have been observed in the Labrador Sea, and their presence, propagation, and transport must be accounted for in order to assess their contribution to the heat and freshwater budgets of the Labrador Sea interior.
Hydrogeological simulation of sedimentary basin evolution during a glacial cycle
Authors: Silbermann Christian
Published: March 2021

Co-authors: Francesco Parisio, Thomas Nagel

Glaciation cycles affect the long-term evolution of geosystems by crustal deformation, ground freezing and thawing, as well as large-scale hydrogeological changes. In order to properly understand the present and future conditions of potential nuclear waste repository sites, we need to simulate the past history. 
For this, a sedimentary basin is considered here as a large-scale hydrogeological benchmark study. The long-term evolution during one glacial cycle is simulated using the open-source multi-field finite element code OpenGeoSys. The impact of the glacial loading (weight and induced shear) is taken into account using appropriate time-dependent stress boundary conditions. As a preliminary study, the hydro-mechanically coupled problem and the thermal problem are considered separately. For comparison with a previously published study by Bense et al. (2008), the entire displacement field is prescribed and the groundwater evolution (hydraulic problem) is regarded. Then, the displacement is only prescribed by means of boundary conditions. The impact of different constitutive assumptions on the deformation and hydraulic behavior is analyzed. The thermal problem is used to simulate the evolution of frost bodies in the subsurface beneath and ahead of the glacier.

V. F. Bense and M. A. Person. Transient hydrodynamics within intercratonic sedimentary basins during glacial cycles. Journal of Geophysical Research,
113(F4):F04005, 10 2008.
Ionospheric shadowing signatures of ringlets and plateaus in Saturn's C Ring
Authors: Dreyer Joshua , Vigren Erik
Published: March 2021

During the Grand Finale of the Cassini mission, the southern hemisphere of Saturn was shadowed by its rings and the substructures within, whose more intense shadows can be mapped to specific ionospheric altitudes. We successfully connect small-scale variations (dips) in the ionospheric H2+ density below 2500 km, measured by the Ion and Neutral Mass Spectrometer (INMS) during orbits 288 and 292, to the shadows of individual ringlets and plateaus in the C Ring. From the H2+ density signatures we estimate lower limits of the associated ringlet or plateau opacities. These will be compared with results obtained from stellar occultations and potential implications/constraints on the ionospheric dynamics will be discussed. The ringlet and plateau shadows are not associated with obvious dips in the electron density.
Local Impact of Stochastic Shallow Convection on Clouds and Precipitation in the Tropical Atlantic
Authors: Sakradzija Mirjana , Senf Fabian , Scheck Leonhard , Ahlgrimm Maike , Klocke Daniel
Published: March 2021

Local impact of a stochastic shallow convection scheme on clouds and precipitation is tested in a case study over the tropical Atlantic on 20th December 2013 using the Icosahedral Nonhydrostatic Model (ICON) of the German Weather Service. ICON is used at a grid resolution of 2.5 km and is tested in several configurations that differ in their treatment of shallow convection. Two versions of a scale-aware stochastic shallow convection scheme are compared to the operational deterministic scheme and a case with no representation of shallow convection. The model is evaluated by comparing synthetically generated irradiance data for both visible and infrared wavelengths against actual satellite observations. The experimental approach is designed to distinguish the local effects of parameterized shallow convection (or lack thereof) within the trades versus the ITCZ. 
The stochastic cases prove to be superior in reproducing low-level cloud cover, deep convection and its organization, as well as the distribution of precipitation in the tropical Atlantic ITCZ. In these cases, convective heating in the subcloud layer is substantial, boundary layer depth is increased as a result of the heating, while evaporation is enhanced at the expense of sensible heat flux at the ocean’s surface. The stochastic case where subgrid shallow convection is deactivated below the resolved deep updrafts shows that local boundary-layer convection is crucial for a better representation of deep convection. Based on these results, our study points to a necessity to further develop parameterizations of shallow convection for the use at the convection-permitting resolutions and to assuredly include them in weather and climate modelling efforts. 