bluuebunny/crossref_metadata_2025 huggingface dataset:
The magnetic flux rope structure of coronal mass ejections – 2021 Julius Bartels Medal Lecture at vEGU
Authors: Bothmer Volker
Published: March 2021

Magnetic clouds are transient solar wind flows in the interplanetary medium with smooth rotations of the magnetic field vector and low plasma beta values. The analysis of magnetic clouds identified in the data of the two Helios spacecraft between 0.3 and 1 AU showed that they can be interpreted to first order by force-free, large-scale, cylindrical magnetic flux tubes. A close correlation of their occurrences was found with disappearing filaments at the Sun. The magnetic clouds that originated from the northern solar hemisphere showed predominantly left-handed magnetic helicities and the ones from the southern hemisphere predominantly right-handed ones. They were often preceded by an interplanetary shock wave and some were found to be directly following a coronal mass ejection towards the Helios spacecraft as detected by the Solwind coronagraph on board the P78-1 satellite. With the SOHO mission unprecedented long-term observations of coronal mass ejections (CMEs) were taken with the LASCO coronagraphs, with a spatial and time resolution that allowed to investigate their internal white-light fine structure. With complementary photospheric and EUV observations from SOHO, CMEs were found to arise from pre-existing small scale loop systems, overlying regions of opposite magnetic polarities. From the characteristic pattern of their source regions in both solar hemispheres, a generic scheme was presented in which their projected white-light topology depends primarily on the orientation and position of the source region’s neutral line on the solar disk. Based on this interpretation the graduated cylindrical shell method was developed, which allowed to model the electron density distribution of CMEs as 3D flux ropes. This concept was validated through stereoscopic observations of CMEs taken by the coronagraphs of the SECCHI remote sensing suite on board the twin STEREO spacecraft. The observations further revealed that the dynamic near-Sun evolution of CMEs often leads to distortions of their flux rope structure. However, the magnetic flux rope concept of CMEs is today one of the fundamental methods in space weather forecasts. With the Parker Solar Probe we currently observe for the first time CMEs in-situ and remotely at their birthplaces in the solar corona and can further unravel their origin and evolution from the corona into the heliosphere. This lecture provides a state-of-the-art overview on the magnetic structure of CMEs and includes latest observations from the Parker Solar Probe mission.
Formation of non-thermal electron velocity distribution functions in kinetic magnetic reconnection
Authors: Yao Xin , Muñoz Patricio A. , Büchner Jörg
Published: March 2021

Magnetic reconnection can convert magnetic energy into non-thermal particle energy in the form of electron beams. Those accelerated electrons can, in turn, cause radio emission in environments such as solar flares. The actual properties of those electron velocity distribution functions (EVDFs) generated by reconnection are still not well understood. In particular the properties that are relevant for the micro-instabilities responsible for radio emission. We aim thus at characterizing the electron distributions functions generated by 3D magnetic reconnection by means of fully kinetic particle-in-cell (PIC) code simulations. Our goal is to characterize the possible sources of free energy of the generated EVDFs in dependence on an external (guide) magnetic field strength. We find that: (1) electron beams with positive gradients in their parallel (to the local magnetic field direction) distribution functions are observed in both diffusion region (parallel crescent-shaped EVDFs) and separatrices (bump-on-tail EVDFs). These non-thermal EVDFs cause counterstreaming and bump-on-tail instabilities. These electrons are adiabatic and preferentially accelerated by a parallel electric field in regions where the magnetic moment is conserved. (2) electron beams with positive gradients in their perpendicular distribution functions are observed in regions with weak magnetic field strength near the current sheet midplane. The characteristic crescent-shaped EVDFs (in perpendicular velocity space) are observed in the diffusion region. These non-thermal EVDFs can cause electron cyclotron maser instabilities. These non-thermal electrons in perpendicular velocity space are mainly non-adiabatic. Their EVDFs are attributed to electrons experiencing an E×B drift and meandering motion. (3) As the guide field strength increases, the number of locations in the current sheet with distributions functions featuring a perpendicular source of free energy significantly decreases.
Carbon allocation of mature spruce upon drought release – results from a whole-tree 13C-labeling study 
Authors: Hikino Kyohsuke , Danzberger Jasmin , Riedel Vincent , Hafner Benjamin D. , Hesse Benjamin D. , Rehschuh Romy , Ruehr Nadine K. , Brunn Melanie , Lehmann Marco , Weikl Fabian , Pritsch Karin , Grams Thorsten E. E.
Published: March 2021

This contribution presents the result of a free-air 13C labeling experiment on mature Norway spruce (P. abies [L.] KARST.) upon watering after five years of recurrent summer drought in southern Germany, focusing on whole tree allocation processes. Mature spruce trees had been exposed to recurrent summer drought from 2014 to 2018 through complete exclusion of precipitation throughfall from spring to late fall (i.e., March to November).  In early summer 2019, the drought stressed spruce trees were watered to investigate their recovery processes. In parallel with the watering, we conducted a whole-tree 13C labeling in canopies and traced the signal in various C sinks, i.e. stem phloem and CO2 efflux, tree rings at different heights, coarse roots, fine root tips, mycorrhiza, root exudates, and soil CO2 efflux.

We hypothesize that drought stressed spruce preferentially allocates newly assimilated C to belowground sinks upon drought release. Conversely to our expectations, allocation to belowground C sinks was not stimulated in drought stressed compared to control spruce. Likewise, the relative amount of recently fixed C allocated to aboveground sinks did not differ between treatments. Our findings suggest that the belowground C sinks are not of higher priority for the allocation of newly assimilated C upon watering after long-term drought. The observed allocation pattern is discussed taking total above- and belowground biomass as well as C source/sink relations into account.
Local temperature forecasts based on post-processing of Numerical Weather Prediction data
Authors: Kaas Eigil , Alerskans Emy
Published: March 2021

Six adaptive post-processing methods for correcting systematic biases in forecasts of near-surface air temperatures, using local meteorological observations, are assessed and compared. The methods tested are based on the simple moving average and the more advanced Kalman filter - constructed to remove the longer-term bias, the very short-term errors or a combination of the two. Forecasts from a coarser-resolution global model and a regional high-resolution model are post-processed and the results are evaluated for one hundred private weather stations in Denmark. Overall, the postprocessing method for which a moving average is combined with a Kalman filter, constructed to remove the very short-term errors, performs the best. The biases of both the global coarserresolution forecasts and the regional high-resolution forecasts are reduced close to zero for all forecast lead times. The standard deviation is reduced for all forecast lead times for the coarser resolution model, whereas for the high-resolution model the most significant reduction is seen for the first six forecast lead hours. This shows that the application of a relatively simple postprocessing method, based on a short training period, can give good results.
Delineation of S-wave velocity profiles across the Himalayan Frontal Thrust (HFT) using metaheuristic approaches.
Authors: Kumar Prabhakar , Ghosal Dibakar
Published: March 2021

The continent-continent collision between the Indian and Asian Plate formed a series of major faults from north to south along the Himalayan belt. Among these Himalayan Frontal Thrust (HFT) is the southernmost and youngest one and is tectonically very active. Any information on the shear wave velocity distribution across the fault is therefore very important. In this study, we have used the Wide Angle Multichannel Analysis of Surface Wave (WAMASW) to estimate the subsurface shear wave velocity profiles across HFT at Pawalgarh in Uttarakhand, India, using widely used stochastic global search Particle Swarm Optimization (PSO) and Grey wolf Optimization (GWO) algorithms. To gain confidence on the accuracy of the inversion results, we first generated an elastic synthetic seismic shot gather with ground rolls by using the forward modelling scheme of SOFI2D for a two-layer velocity depth model overlying a half-space. The generated gather was then processed in MATLAB to generate the experimental dispersion curve using the Phase shift method. We then extracted the fundamental mode for the gather and inverted it using the standard PSO and GWO algorithms and estimated 1D shear wave velocity profile. After getting acceptable results for the synthetic dataset, we then applied the PSO algorithm to generate the 1D S-wave velocity (Vs) profile across the Himalayan Frontal Thrust (HFT). In the study area, the Rayleigh wave phase velocity for the first shot varies from 444 to 743 m/s. We then obtained the 1D shear wave velocity profiles and a jump in Vs is observed across the HFT indicating variation in the sediment stiffness across the fault.

Keywords: WAMASW, dispersion, Meta- Heuristic, PSO, GWO, 1D Shear wave velocity

 
Trace metal variability in Puerto Rican speleothems and drip waters: Indicators for (past) tropical cyclone activity?
Authors: Warken Sophie , Frank Norbert , Schorndorf Nils , Mielke Aaron , Kuchalski Lea , Keppler Frank , Vieten Rolf , Förstel Julius , Therre Steffen , Winter Amos , Schröder-Ritzrau Andrea , Hartland Adam
Published: March 2021

In the tropical Americas, extreme precipitation events such as hurricanes are responsible for enormous damage and numerous fatalities each year. However, projections of hydro-climatic change and tropical cyclone (TC) activity in Central America and the Caribbean for the next decades are still challenging, requiring more reconstructions of past precipitation and TC activity. In tropical speleothems, stable oxygen isotope values (δ18O) are an often used proxy for precipitation amount, and in some cases TC activity, but may be masked by various effects such as evaporation or kinetic effects inside the cave, temperature, or variable moisture sources and trajectories.

Here we investigate the potential of trace metals in speleothems and drip waters from Larga Cave, Puerto Rico, as complementary proxies for past effective infiltration, and hence precipitation amount. The analysis of transition metal ratios in drip waters from 2014 to 2019 reveal a seasonal variation, with peaks in the Cu/Ni (and Cu/Co) ratios potentially reflecting the intensity of the prior wet season. The suggested imprint of Hurricanes Bertha (2014) and Maria (2017) in the drip water suggests that transition metal ratios might be even indicators of (past) tropical cyclone activity.

Laser ablation ICPMS analyses of speleothems from the same cave support the interpretation of a potential climate signal in the transition metal ratios. Both higher Cu/Ni and Cu/Co values are found during presumably warmer and wetter phases, such as e.g. during the late Holocene, as well as at the onsets of Dansgaard/Oeschger interstadials including the Bolling/Allerod (14.6-12.8 ka BP). Replicated records of the past 400 years combined with stable isotope values of oxygen and carbon (δ13C) will provide a test of the underlying mechanisms driving the observed variability on different timescales. Comparison with other reconstructions highlights the potential of Cu/Ni (and Cu/Co) ratios in speleothems for hydro-climate and past precipitation variability reconstruction.
The challenge of monitoring volcanic unrest processes in small oceanic islands: the case of Tagoro volcano (Canary Islands)  
Authors: del Fresno Carmen , Felpeto Alicia , Domínguez Cerdeña Itahiza , García-Cañada Laura , Meletlidis Stavros , González-Alonso Elena , Torres Pedro A. , Luengo-Oroz Natividad , Sainz-Maza Sergio , López-Díaz Rubén , Moure David , Casas Benito
Published: March 2021

Monitoring the activity of a volcanic unrest in an archipelago is always a challenging task. Difficulties are even greater if we are also dealing with monogenetic volcanism, without a defined magma chamber, where each unrest can be related to a different magma intrusion, following different ascending paths towards an eruptive vent that can arise both on land or at sea. Moreover, if the repose time between eruptions is long, the historical eruptive record contains very few eruptions, and hence few data that allow an in-depth characterization of the dynamics of the volcanism in the area. 

This year marks the tenth anniversary of the beginning of the last eruption in the Canary Islands (submarine eruption of Tagoro volcano, 2011-2012). In this work we review the main difficulties, concerns and uncertainties that arose in the monitoring of this phenomenon. Some of these problems were solved during the crisis, throughout a multiparametric monitoring and the collaboration of different institutions; others would not be a major problem today, thanks to recent technological advances. On the other hand, there are still some unsolved monitoring difficulties when studying an event similar  to the one which lead to Tagoro volcano ten years ago. Part of the complexity is inherent to the spatial distribution of the islands in the archipelago and the limitations on the knowledge of the volcanic phenomenon. It is in these last challenges where the key to improve the volcano monitoring in oceanic islands is. 
Towards a multi-risk, multi-sector, systemic approach to risk management
Authors: Ward Philip ,   MYRIAD-EU team
Published: March 2021

Whilst the last decade saw huge scientific advances in understanding natural hazard risks, most research and policy still addresses risk from a single-hazard, single-sector, perspective. This presents obstacles for addressing real-world challenges faced by risk managers and other decision-makers. Firstly, multiple hazards can have interrelated effects on risk. How can risk be better managed by considering these interrelated effects? Secondly, disaster risk management (DRM) measures taken to reduce risk from one hazard may increase risk from another hazard. How can we better account for these dynamic feedbacks between risk drivers? Thirdly, these interrelated effects have impacts across sectors. How can we account for these trade-offs and synergies across sectors, regions, and hazards? The aforementioned challenges exist within the context of an increasingly interconnected world, increased pressure for space, and climate change, in which the magnitude and frequency of single and multi-hazards are changing at an unprecedented rate. A paradigm shift is needed to successfully address these kinds of complex questions and challenges.

 

The vision of the MYRIAD-EU team is to catalyse this paradigm shift required to move towards a multi-risk, multi-sector, systemic approach to risk management. We embark on a research programme that aims to enable policy-makers, decision-makers, and practitioners to develop forward-looking disaster risk management pathways that assess trade-offs and synergies across sectors, hazards, and scales. To do this, we will co-develop a framework for multi-hazard, multi-sector, systemic risk management, and state-of-the-art products and services to operationalise the framework. To test our framework, products and services, we plan to implement them with stakeholders in five Pilots: North Sea, Canary Islands, Scandinavia, Danube, Veneto. In this contribution, we will present the plans and vision for this ambitious research programme and look for links with existing risk multi-risk projects, networks, and activities.
Tourmalinisation in peraluminous granitic context : from experiment to thermodynamic modelling
Authors: Fort Julien , Sizaret Stanislas , Pichavant Michel , Lassin Arnault , Tuduri Johann , Blein Olivier
Published: March 2021

Tourmaline records the physico chemical conditions during its cristallisation, as its primary chemical zonations are generally unbalanced, its occurrence as alteration product could be used to decipher the physicochemical properties of mineralizing fluids. However, the role of the tourmalinisation in hydrothermal processes remains little studied, if not poorly understood.  The complexity of its thermodynamic properties is related to the presence of four cationic sites allowing the accommodation of a wide variety of elements (Henry and Dutrow, 2018). Moreover the phenomena of deprotonation, Si-IVB and valence state, make the approach of solid solution properties complex (Hughes et al., 2001; Henry et al., 2011; Bačík, 2015; Morgan, 2016). Thus, thermodynamic properties are most often estimated  (Garofalo et al., 2000; Hinsberg and Schumacher, 2007) and only a few measurements could be carried out on a reduced number of near-endmembers crystals (Kuyunko et al., 1984; Ogorodova et al., 2012).

This study aims to investigate experimentally the stability field of schorl (Na-Fe) – dravite (Na-Mg) solid solution at 2 kbar total pressure between 400° and 600°C as a function of the boron content of the fluid and fO2 condition, using an internally heated gas apparatus. Those metasomatic experiments have been conducted on a mixture of naturals crystals of cordierite + albite, representing a peraluminous granite composition in a Na-Mg-Fe-Al-Si-B-O-H system, characterized by a high-Mg, low-Fe content. These experiments were performed in order to simulate a classic aluminous host of these tourmaline alterations in granitic context. The results will be studied, in terms of stability of the tourmaline species, chemistry variation and texture. They will be compared with thermodynamic models build using data from the literature (Korges et al., 2018; Pan et al., 2019 among others) . Ultimately, the objective is to characterize in a P, T, W/R space, the chemical evolution of fluids, the alteration sequence of rocks and the variations in volumes related to the successive reactions.
A modified-boundary condition algorithm for efficient 3D forward modeling of CSEM data
Authors: Dehiya Rahul
Published: March 2021

I present a newly developed 3D forward modeling algorithm for controlled-source electromagnetic data. The algorithm is based on the finite-difference method, where the source term vector is redefined by combining a modified boundary condition vector and source term vector. The forward modeling scheme includes a two-step modeling approach that exploits the smoothness of the electromagnetic field. The first step involves a coarse grid finite-difference modeling and the computation of a modified boundary field vector called radiation boundary field vector. In the second step, a relatively fine grid modeling is performed using radiation boundary conditions. The fine grid discretization does not include stretched grid and air medium. The proposed algorithm derives computational efficiency from a stretch-free discretization, air-free computational domain, and a better initial guess for an iterative solver. The numerical accuracy and efficiency of the algorithm are demonstrated using synthetic experiments. Numerical tests indicate that the developed algorithm is one order faster than the finite-difference modeling algorithm in most of the cases analyzed during the study. The radiation boundary method concept is very general; hence, it can be implemented in other numerical schemes such as finite-element algorithms.
Annual variations of Mars atmosphere, as seen by HEND data since 2002
Authors: Golovin Dmitry , Mitrofanov Igor , Litvak Maxim , Sanin Anton , Malakhov Alexey
Published: March 2021

HEND (High Energy Neutron Detector) onboard NASA’s Mars Odyssey spacecraft performs measurements of neutron emission of Martian surface 2002. HEND uses 3He counters for detection of epithermal neutrons generated by Galaсtic Cosmic Rays interaction with surface and atmosphere of Mars.

Weak Martian atmosphere emits, absorbs and scatters neutrons slightly, and outgoing neutron flux on the orbit is changing depending on atmospheric density along the Martian seasons. We have analyzed the HEND data for seasonal variations of outgoing neutron flux above several areas of Mars for nine Martian annual cycles. Measured seasonal variations, presented as Ls profiles for individual years, are compared with numerically predicted profiles according to the model of Martian atmosphere.
The Radio and Plasma Waves (RPW) Instrument on Solar Orbiter: latest observations and results
Authors: Maksimovic Milan ,   RPW, MAG, SWA and EPD teams
Published: March 2021

We will review the very latest observations and results obtained by the Radio and Plasma Waves (RPW) Instrument on the recently launched Solar Orbiter mission. RPW is designed to measure in-situ magnetic and electric fields and waves from 'DC' to a few hundreds of kHz. RPW is also capable of measuring solar radio emissions up to 16 MHz and link them to solar flares observed by the onboard remote sensing instruments. The latest results we will present concern a wide range of phenomena including: Langmuir and Whistler Waves, dust impacts, Solar Type III bursts and observations during the recently visited Venus environment.
Potential impacts of warming climate on future water resources and hydropower production in a glacierized catchment in Western Himalaya
Authors: Shirsat Tejal , Kulkarni Anil , Momblanch Andrea , Singh Randhawa Surjeet , Holman Ian
Published: March 2021

The Himalayan region has a large hydropower potential due to the natural topographic gradient and abundance of water resource from rainfall, snow and glacier melt. However, future water availability in the Himalayan streams is likely to be altered due to climatic conditions, which necessitates an assessment of hydropower investments, especially for small run-of-the-river projects. Here, we study the future glacio-hydrological changes in a small catchment located in the Upper Beas basin, in Western Himalaya in India, and their impacts on the operation of two small hydropower projects with contrasting hydrological requirements. The Water Evaluation and Planning (WEAP) model is used to integrate and analyse changes in cryosphere, hydrology and hydropower production in the middle and end of the 21st century using multiple climate models representing different types of future scenarios under RCP 4.5 and 8.5. In response to projected climate, the snow and glacier melt contribution to annual discharge declines from 34% in the baseline to 16.5% (RCP4.5) and 13.8% (RCP8.5) by the end of the century. The total streamflow shows broad uncertainty in magnitude and direction of change but shows a noticeable seasonal shift in the hydrological cycle. Of the two hydropower projects, the plant that utilizes high flows with low hydraulic head shows a behaviour similar to streamflow projections resulting in 13% (RCP45) and 19.7% (RCP85) increase in annual power generation by the end of the century arising from the increased hydropower potential of low flows and the rise in precipitation. The second power project that relies on lesser flows with high head maintains its designed power production consistently throughout the century in all the climate change scenarios. The differing sensitivity of the power projects to climate change is influenced by future changes in the runoff as well as by their design. Thus, this study provides insights into the climate-adaptive development and planning of small hydropower projects in the Himalayan region.
Organic soil amendments as a tool to increase biological activity and C sequestration in clay soil
Authors: Heinonsalo Jussi , Salonen Anna-Reetta , Shrestha Rashmi , Kalu Subin , Sietiö Outi-Maaria , Huusko Karoliina
Published: March 2021

Soil C sequestration through improved agricultural management practices has been suggested to be a cost-efficient tool to mitigate climate change as increased soil C storage removes CO2 from the atmosphere. In addition, improved soil organic carbon (SOC) content has positive impacts on farming though better soil structure and resilience against climate extremes through e.g. better water holding capacity. In some parts of the world, low SOC content is highly critical problem for overall cultivability of soils because under certain threshold levels of SOC, soil loses its ability to maintain essential ecosystem services for plant production. Soil organic amendments may increase soil C stocks, improve soil structure and boost soil microbial activities with potential benefits in plant growth and soil C sequestration. Additional organic substrates may stimulate microbial diversity that has been connected to higher SOC content and healthy soils.

We performed a two-year field experiment where the aim was to investigate whether different organic soil amendments have an impact on soil microbial parameters, soil structure and C sequestration.

The experiment was performed in Parainen in southern Finland on a clay field where oat (Avena sativa) was the cultivated crop. Four different organic soil amendments were used (two wood-based fiber products that were leftover side streams of pulp and paper industry; and two different wood-based biochars). Soil amendments were applied in 2016. Soil C/N analysis was performed in the autumns 2016-2018 and soil aggregate in the summer and autumn 2018, as well as measures to estimate soil microbial activity: microbial biomass, soil respiration, enzymatic assays, microbial community analysis with Biolog ®  EcoPlates and litter bag decomposition experiment. The relative share of bacteria and fungi was determined using qPCR from soil samples taken in the autumns 2016, 2017 and 2018.

Data on how the studied organic soil amendments influence soil structure and C content, as well as soil microbial parameters will be presented and discussed.
How forests change transit times of transpiration, evaporation and streamflow – a modeling approach
Authors: Heidbüchel Ingo , Yang Jie , Fleckenstein Jan H.
Published: March 2021

In a recent paper we investigated how different catchment and climate properties influence transit time distributions. This was done by employing a physically-based spatially explicit 3D model in a virtual catchment running many different scenarios with different combinations of catchment and climate properties. We found that the velocity distribution of water fluxes through a catchment is more sensitive to certain properties while other factors appear less relevant. Now we expanded the approach by adding vegetation to the model and thus introducing new hydrologic processes (transpiration and evaporation) to the simulated water cycle. On the one hand we wanted to know how these new processes would influence transit times of the water fluxes to the stream, on the other hand we were interested in how exactly differences in the vegetation itself (e.g. rooting depth and leaf area index) would alter the various flux velocities (including transit times of transpiration and evaporation). It was very interesting to observe that streamflow in forested areas appeared to become older on average. We also found that transpiration was generally younger if the vegetation had shallower roots and/or a larger leaf area index. The biggest difference in the age of evaporation was detected for different amounts of subsequent precipitation (evaporation was generally younger in a wetter climate). In conclusion, we found that forests influence the age of the different water fluxes within a catchment. According to our results the overall hydrologic cycle is decelerated when adding vegetation to a model that otherwise only simulates evaporation.

Still, in order to make meaningful predictions on the age of hydrologic fluxes, it is not constructive to single out specific catchment and climate properties. The multitude of influences from different parameters makes it very challenging to find rules and underlying principles in the integrated catchment response. Therefore it is necessary to look at the individual parameters and their potential interactions and interdependencies in a bottom-up approach.
Continental weathering using combined Hf-Nd isotope system and clay mineralogy: new insights for the Late Cretaceous climate
Authors: Corentin Pauline , Puceat Emmanuelle , Pellenard Pierre , Freslon Nicolas , Guiraud Michel , Blondet Justine , Adatte Thierry , Bayon Germain
Published: March 2021

The Late Cretaceous period records a pronounced decrease in marine temperatures at a global scale initiating the last greenhouse-icehouse transition, whose origin still remains enigmatic. Continental weathering represents a major sink of atmospheric CO2 through silicate weathering reactions yet the importance of this process in the Late Cretaceous cooling has only been scarcely explored.

In this study we explore the impact of the eastern South American margin uplift, concomitant to the long-term Late Cretaceous cooling, on the evolution of chemical weathering of the Brazilian margin, using a new proxy of silicate weathering based on the coupled Lu-Hf and Sm-Nd isotope systems in clays. This proxy, expressed as ΔεHf, has been recently calibrated in modern environments (Bayon et al., 2016) but has only been scarcely applied to deep-time environments. This proxy, applied on sediments from DSDP site 356 on the São Paulo Plateau, highlights a marked increase in silicate chemical weathering of the southeastern Brazilian margin from the Santonian to the Maastrichtian, also supported by the evolution of the chemical index of alteration (CIA) and clay mineralogy.

This increase follows an episode of enhanced mechanical erosion of the margin revealed in the Turonian to Santonian by an increase of primary clay mineral (illite, chlorite) and Ti/Al ratio, linked to the tectonic uplift of the margin. Clay mineral assemblages additionally point to an evolution of local climatic conditions from arid to a more hydrolysing climate following this episode, that we link to a “rain shadow effect” affecting the eastern side of the newly formed relief that would have enhanced chemical weathering of the margin.

Importantly the temporal coincidence of the increase in chemical weathering depicted here with the marked acceleration of the global cooling recorded worldwide during the Campanian points to a potentially important role of this process on the overall climate decline initiating the descent into our icehouse climate mode. Although records from additional sites are needed to establish the spatial extent of the margin affected by this process, our new dataset brings new insights about the impact of tectonic forcing on climate.

Bayon et al. (2016) EPSL 438, p. 25-36.
A close look at the middle Adriatic upwelling: schematized ROMS model simulations
Authors: Beg Paklar Gordana , Pasaric Zoran , Orlic Mirko , Stanesic Antonio
Published: March 2021

Strong upwelling driven by the NNW winds was detected off the eastern middle Adriatic coast in May 2017. High resolution CTD data revealed thermocline doming by about 20 m at approximately 20 km from the coast. Main characteristics of the upwelling event are reproduced in the realistic ROMS model simulation. Adriatic scale ROMS model having 2.5 km horizontal resolution, forced by the air-sea fluxes calculated using surface fields from operational weather forecast model ALADIN-HR (Tudor et al., 2013; Termonia et al., 2018), river discharges, tides and water mass exchange through the Strait of Otranto, reproduces cold water dome and two-layer offshore flow in accordance with CTD and shipborne ADCP measurements. Significant improvement in the upwelling simulations is obtained using increased drag coefficient. The location of upwelling is correctly modelled, although with somewhat lower upper layer temperatures if compared with measurements. Moreover, the surface cyclonic circulation indicated by ADCP measurements along the cross-Adriatic transect is also evident in the model results. In order to improve understanding of the upwelling mechanism, several schematized numerical experiments are conducted. Wind fields from dynamical adaptation (Zagar and Rakovec, 1999; Ivatek-Sahdan and Tudor, 2004) of ALADIN-HR8 (8 km horizontal grid spacing) wind forecast to 2 km grid, are decomposed by the Natural Helmholtz-Hodge Decomposition (HHD) into divergence-free (incompressible), rotation-free (irrotational), and harmonic (translational) component (Bhatia et al., 2014). The components thus obtained and their combinations are used for calculation of the wind stress instead of the total wind field. Simulations with decomposed wind stress are conducted in the Adriatic domains with both flat bottom and realistic topography. Schematized simulations reveal that the positive rotational wind component is responsible for the rising of thermocline through Ekman pumping and it is more pronounced in the flat bottom basin. In the simulations with divergent wind component, the thermocline doming disappears and only coastal upwelling is reproduced. Additional idealised simulations with homogeneous NW wind stress are performed assuming both two-layer and uniform initial density field.
Assessing the Biological Carbon Pump in the Weddell Gyre 
Authors: Douglas Clara , Brown Peter , Briggs Nathan , MacGilchrist Graeme , Naveira Garabato Alberto
Published: March 2021

Biological processes in the subpolar Southern Ocean play a crucial role in the global carbon cycle, mediating CO2 exchange between the atmosphere and the densest waters of the global ocean. While historical perspectives have centred the importance of shelf-sea regions, recent reframing emphasises the role of the open ocean, and the cyclonic gyres. Here, we investigate the operation of the biological carbon pump (BCP) in the Weddell Gyre using satellite ocean colour and bio-Argo floats. We find first that a significant proportion (>54 %) of the inter-annual variability in NPP was explained by the area of open (ice-free) water. Spatial patterns suggest that peak productivity is associated with the ice edge. The seasonal decline in NPP occurs before ice cover returns, suggesting that other controls are limiting annual NPP (e.g. the exhaustion of iron). Comparing the shelf region to the open ocean, the shelf was seen to have higher rates of productivity, but NPP in the relatively less productive open ocean region accounted for ~95% of total carbon uptake each year. The total NPP in the Weddell Gyre (97-197 Tg C yr-1) is sufficient to supply the BCP-derived carbon that was previously observed to be exported from the region in Circumpolar Deep Water (~80 Tg C yr-1). NPP in the open ocean Weddell Gyre could thus provide the major source of carbon exported from the Weddell Gyre to the deep ocean via the horizontal circulation.
Assessment of COSMIC-2 reduced-dynamic and kinematic orbit determination
Authors: Jaeggi Adrian , Arnold Daniel , Weiss Jan , Hunt Doug
Published: March 2021

The Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) mission was launched on June 25, 2019 into six evenly spaced circular orbital planes of 24° inclination with initial altitudes of 725 km. By February 2021 the COSMIC-2 satellites will be lowered to an operational altitude of about 520 km. The satellites carry an advanced Tri‐GNSS (Global Navigation Satellite System) Radio-occultation System (TGRS) instrument to provide high vertical resolution profiles of atmospheric bending angle and refractivity, as well as measurements of ionospheric total electron content, electron density, and scintillation. The TGRS payload tracks GPS and GLONASS signals on two upward looking antennas used for precise orbit determination (POD). We compute one- and two-antenna GPS and GPS+GLONASS POD solutions at both orbit altitudes and assess the orbit quality and systematic orbit errors using different metrics. In particular, we also use different POD setups to compute kinematic solutions employing single-receiver ambiguity fixing and test their contribution to selected months of gravity field recovery based on Swarm GPS data.
Validation of a general microbarom source model using global infrasound observations of the International Monitoring System
Authors: De Carlo Marine , Hupe Patrick , Le Pichon Alexis , Ceranna Lars , Ardhuin Fabrice
Published: March 2021

Between 0.1 and 0.6 Hz, the coherent ambient infrasound noise is dominated worldwide by signals, so-called microbaroms, originating from the ocean. With an energy peaking around 0.2 Hz, microbaroms are generated by second order non-linear interactions between wind-waves at the ocean surface and are able to propagate all around the globe through the stratosphere and thermosphere. Monitoring these signals allows characterizing the source activity and probing the properties of their propagation medium, the middle atmosphere. Here we present the first quantitative validation of global microbaroms modelling against worldwide observations. Modelling microbaroms at ground-based stations is a complex process that requires accounting for sea-wave modelling, infrasound generation from wave interactions, infrasound propagation over thousands of kilometers and infrasound detection at stations. In this study, this process was represented by three main parameters: a wave action model, a source model and an attenuation law through the atmosphere. The global modelling is run for two values of each parameter and the results are quantitatively compared with the global reference database of microbaroms detected by the International Monitoring System over seven years. This study demonstrates that the new source model improves the prediction rate of observations by around 20 percent points compared to existing reference models. The performance is enhanced when combining a wind-dependent attenuation and an ocean wave model that includes coastal reflection.
Characterization of a solid waste landfill through geophysical data fusion
Authors: Steiner Matthias , Katona Timea , Fellner Johann , Flores Orozco Adrián
Published: March 2021

A detailed characterization of the landfill geometry, the waste volume and composition, and the water saturation within and outside the landfill body is critical for an adequate environmental management. To overcome the limited spatial resolution of direct investigations into landfills, geophysical methods have proven to resolve subsurface properties with high spatial resolution in a non-invasive and cost-efficient manner. The joint inversion of different geophysical datasets became increasingly popular in various fields of application since it solves quantitatively for the parameters of interest. Built upon a recently developed framework considering Archie’s law and a time-averaging equation for the seismic slowness, we present here the petrophysical joint inversion (PJI) of electrical and seismic data collected along three profiles at the “Heferlbach” landfill located close to Vienna (Austria). We use the PJI framework to simultaneously invert apparent electrical resistivities and seismic traveltimes to solve for quantitative estimates for porosity, water saturation and air content. Our results show that the shallow geometry of the landfill with an average thickness of 3.5 m is clearly resolved by subsurface areas characterized by an air content of approximately 40 %. Based on the resolved saturation, we were able to identify the known aquifer underneath the landfill (average saturation of 25 %) that is lying on top of an aquiclude formed by tertiary sands. Within the landfill body, the saturation is approximately 10 to 15 %, which is in agreement with available data from the site. The resolved porosity model shows significant lateral variations (between 40 and 60 %) at shallow depths (< 3 m) suggesting a varying degree of compaction of the waste and different types of waste. Our results demonstrate the potential of the proposed PJI to enhance geophysical investigations of landfills by providing plausible quantitative estimates for parameters of interest with an adequate spatial resolution.
Monsoon variability during Mid Pliocene Warm Period: Evidence from oceanic denitrification at eastern Arabian Sea
Authors: Behera Padmasini , Tiwari Manish
Published: March 2021

The variability of the South Asian Monsoon (SoAM) in warmer climatic conditions is not established yet. The Mid-Pliocene Warm Period (MPWP, 3.264 to 3.025 ma) is the most recent such event when the boundary conditions were similar to present with similar CO2 concentration (more than 400 ppmv) and temperature (2-3°C higher than present). It presents the best analogue for understanding the impacts of future global warming on SoAM. The high-resolution study of denitrification from the eastern Arabian Sea can provide an insight into the SoAM variability during MPWP. Denitrification is the process by which nitrate is reduced to nitrogen gas (N2 or N2O) during organic matter decay in oxygen minima zones in the water column. The denitrification process enriches the nitrate pool with 15N, which is incorporated in the particulate organic matter. Denitrification is governed by the surface water productivity related to SoAM strength and the water column ventilation. We analyzed the nitrogen isotopic ratio of sedimentary organic matter (SOM, δ15NSOM) to examine the denitrification in the eastern Arabian Sea. Total nitrogen (TN %) and total organic carbon (TOC%) are used to estimate the surface water productivity from the sediment collected during expedition IODP 355, Hole U1456A. We find that the δ15NSOM values vary between 7-9 ‰ during 3.22-3.15 Ma and 2.9-2.75 Ma indicating high denitrification. High δ15NSOM values coincide with high productivity as shown by both TN and TOC. It shows two major periods in the late Pliocene (3.22-3.15 Ma and 2.92-2.75 Ma) associated with stronger denitrification and high productivity. These results indicate the intensification of SoAM during warmer periods of Late Pliocene and at the start of intensification of Northern hemisphere glaciation. The enhanced denitrification during this period could possibly be due to a reduction in deep water ventilation and monsoon driven upsurge in productivity.
A perspective on Plio-Pleistocene hydrosystems of the northern Turkana Depression (East African Rift System) reconstructed from the study of freshwater mollusk communities
Authors: Andrade Juan , Schuster Mathieu , Nutz Alexis , Van Bocxlaer Bert
Published: March 2021

The northern Turkana Depression of the East African Rift System in Northern Kenya and Southwestern Ethiopia has one of the most complete and well-documented late Cenozoic continental fossil records worldwide, including remarkable finds of early hominins and associated African Cenozoic vertebrates. Most previous paleoenvironmental reconstructions of the depression were developed using terrestrial vertebrate faunas and paleolandscapes, leaving freshwater ecosystems and associated hydrosystems (lakes, tributaries, river deltas, and wetlands) largely unaddressed. African Cenozoic freshwater mollusks were long considered to be good biostratigraphic indicators, given that their communities are able to represent long phases of morphological stability and at other times rapid morphological changes. However, to what extent changes in freshwater mollusk assemblages match with changes in sedimentary landscapes and lake level fluctuations remains unclear. Here, we address this question through integrative studies on Plio-Pleistocene fossil freshwater mollusks assemblages. Specifically, we are developing a taxonomic framework on fossil freshwater bivalves belonging to the families Unionidae, Iridinidae, Etheriidae and Corbiculidae to create a standardized overview of stratigraphically well-characterized fossil assemblages. Subsequently, we integrate this paleontological dataset with sedimentological characterizations of the depositional environments in which shell beds accumulated at high resolution around faunal turnover events. A detailed reconstruction of environmental changes and how these changes affected freshwater ecosystems in the northern Turkana Depression may allow us to recognize key environmental drivers that triggered faunal turnover events. Such an understanding of drivers from the past perhaps provides our best hope to anticipate how future environmental changes will alter freshwater ecosystems in tropical Africa, and, ultimately, the availability of various freshwater resources on which humanity depends.
Kinetic energy generation in cross-equatorial flow and the Somali Jet
Authors: Seshadri Ashwin K , Dixit Vishal
Published: March 2021

In response to the north-south pressure gradients set by the annual march of the Sun, a cross-equatorial flow that turns to become a low-level zonal jet at around 10 ° N (also known as Somali jet) is set in the lower troposphere (around 850 hPa) over the Indian ocean. These flows play a fundamental role in the Indian monsoon. A detailed understanding of small and large scale drivers of this flow is lacking. Here we present the analysis of Kinetic Energy (KE) budget of the low level flow using high spatio-temporal resolution ERA5 reanalysis to identify sources and sinks of KE generation. We find that a significant KE generation occurs over East African highlands, Western Ghats and the Arabian sea. Over the oceans, the KE generation occurs mainly due to cross-isobaric meridional winds in the boundary layer. In contrast, over East African highlands and Western ghats KE generation maximizes just above the boundary layer and mainly occurs due to interaction of flow with the orography. We propose a simple model to decompose lower tropospheric KE generation into contributions from surface pressure, orography and free-tropospheric gradients.
On the current accuracy of altimetry satellite orbits
Authors: Rudenko Sergei , Dettmering Denise , Bloßfeld Mathis , Zeitlhöfler Julian , Alkahal Riva
Published: March 2021

Precise orbits of altimetry satellites are a prerequisite for the investigation of global, regional, and coastal sea levels together with their changes, since accurate orbit information is required for the reliable determination of the water surface height (distance between the altimeter position in space and the water surface). Orbits of altimetry satellites are nowadays usually computed using DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite), SLR (Satellite Laser Ranging), and, of some satellites, GPS (Global Positioning System) observations of a global network of tracking stations. Significant progress in the improvement of altimetry satellite orbit quality has been achieved in the last 30 years. However, the differences of the sea level and its trend computed using up-to-date orbit solutions derived at various institutions using different software packages, types of observations (DORIS+SLR as compared to GPS+DORIS) and different up-to-date models still exceed the requirements of the Global Climate Observing System for the uncertainties of the regional sea level (< 1 cm) and its trend (< 1 mm/year).

In this study, we evaluate the current accuracy of orbits of altimetry satellites derived by various institutions in the state-of-the-art reference frames using up-to-date background models for precise orbit determination by using various observation types. We present some results of our analysis of geographically correlated errors and radial orbit differences for various orbit solutions. We also discuss possible reasons causing the orbit differences and potential ways to reduce them.