bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and interpretation of seismic short-duration events inside the Kolumbo submarine volcano in the Southern Aegean
Authors: Schmid Florian , Karstens Jens , Nomikou Paraskevi
Published: March 2021

Kolumbo represents one of the most hazardous, currently active, volcanoes in the eastern Mediterranean. Its last eruption in 1650 AD was associated with a vast explosion, causing a tsunami of regionally devastating impact. The eruption was also associated with the voluminous and rapid release of toxic gases asphyxiating humans and animals on the nearby Islands. Earthquake records from the recent decades document on-going unrest beneath the volcano. Remotely operated vehicle dives revealed several hydrothermal vent sites and bacterial mats at the crater floor, which are concentrated near the northern crater wall. The vents emit mainly CO2, leading to the accumulation of acidic waters in the crater. Accordingly, one of the main volcanic hazards associated with Kolumbo is that rapid overturning of water in the crater may release harmful amounts of toxic gases. Monitoring the hydrothermal processes inside the Kolumbo crater will provide an important contribution to the understanding and evaluation of this and other volcanic hazards.

In October 2019, we deployed an ocean bottom seismometer and hydrophone (OBS/H) inside the Kolumbo crater. During the four days of passive recording we identified about 100 so-called short duration seismic events, which were only present on the seismometer channels, while generally being absent on the hydrophone channels. The events have durations of less than one second with dominant frequencies between 5 to 30 Hz. Most of the events represent well-polarized seismic phases, which enables us to determine their azimuth angle (with a 180-degree bias) and angle of incidence at the OBS/H. We cross-correlated all polarized seismic waveforms and subsequently used the cross-correlation coefficients for a hierarchical cluster analysis to elaborate whether the events have a random origin or originated from a common origin. Our analysis revealed that the majority of events is associated with two clusters. The azimuth angles of all events in the largest cluster coincide with the azimuth angle between station and the field of hydrothermal vents and bacterial mats inside the crater. This coincidence suggests that the origin of the short duration events is associated with the sub-seafloor migration of fluids or the fluid discharge process at the crater floor. In fact, short-duration events of similar characteristics, recorded by OBS/H, were previously attributed to sub-seafloor fluid migration and the discharge of fluids at the seafloor. Our analyses indicate that seismic monitoring of submarine volcanoes should include the detection and analysis of short duration events, which may act as a novel tool in the characterization of volcanic unrests and volcanogenic geohazard monitoring in general.
A self-supervised Deep Learning approach for improving signal coherence in Distributed Acoustic Sensing
Authors: van den Ende Martijn , Lior Itzhak , Ampuero Jean Paul , Sladen Anthony , Richard Cédric
Published: March 2021

Fibre-optic Distributed Acoustic Sensing (DAS) is an emerging technology for vibration measurements with numerous applications in seismic signal analysis as well as in monitoring of urban and marine environments, including microseismicity detection, ambient noise tomography, traffic density monitoring, and maritime vessel tracking. A major advantage of DAS is its ability to turn fibre-optic cables into large and dense seismic arrays. As a cornerstone of seismic array analysis, beamforming relies on the relative arrival times of coherent signals along the optical fibre array to estimate the direction-of-arrival of the signals, and can hence be used to locate earthquakes as well as moving acoustic sources (e.g. maritime vessels). Naturally, this technique can only be applied to signals that are sufficiently coherent in space and time, and so beamforming benefits from signal processing methods that enhance the signal-to-noise ratio of the spatio-temporally coherent signal components. DAS measurements often suffer from waveform incoherence, and processing submarine DAS data is particularly challenging.

In this work, we adopt a self-supervised deep learning algorithm to extract locally-coherent signal components. Owing to the similarity of coherent signals along a DAS system, one can predict the coherent part of the signal at a given channel based on the signals recorded at other channels, referred to as "J-invariance". Following the recent approach proposed by Batson & Royer (2019), we leverage the J-invariant property of earthquake signals recorded by a submarine fibre-optic cable. A U-net auto-encoder is trained to reconstruct the earthquake waveforms recorded at one channel based on the waveforms recorded at neighbouring channels. Repeating this procedure for every measurement location along the cable yields a J-invariant reconstruction of the dataset that maximises the local coherence of the data. When we apply standard beamforming techniques to the output of the deep learning model, we indeed obtain higher-fidelity estimates of the direction-of-arrival of the seismic waves, and spurious solutions resulting from a lack of waveform coherence and local seismic scattering are suppressed.

While the present application focuses on earthquake signals, the deep learning method is completely general, self-supervised, and directly applicable to other DAS-recorded signals. This approach facilitates the analysis of signals with low signal-to-noise ratio that are spatio-temporally coherent, and can work in tandem with existing time-series analysis techniques.

References:
Batson J., Royer L. (2019), "Noise2Self: Blind Denoising by Self-Supervision", Proceedings of the 36th International Conference on Machine Learning (ICML), Long Beach, California
Do tropical islands warm or cool the troposphere?
Authors: Leutwyler David , Hohenegger Cathy
Published: March 2021

Tropical islands are commonly seen as hot spots that heat the troposphere, since during the day, they typically become warmer than the ocean. However, at the same time, they also become dryer (in terms of relative humidity), due to the soil's resistance to evaporate. The surface warm and dry anomaly is then propagated upwards into the troposphere by thunderstorms (deep convection) that frequently form over the islands. The vertical propagation of the anomaly happens because the warmer surface over land tends to push the induced diurnal convection towards a warmer moist adiabat. However, the drying of the land surface also pulls the clouds towards a colder moist adiabat, as more initial lifting along the dry adiabat is needed until saturation is reached. In other words, a dryer island leads to a more elevated cloud base, and thus, to convection at a colder moist adiabat. The formation of convective clouds over land results in a local density anomaly that is then communicated to the island's surroundings by gravity waves since the tropical atmosphere cannot sustain strong horizontal density gradients (WTG theory). Together these ideas allow formulating the hypothesis that surface temperature and humidity anomalies emerging over islands project onto the large-scale temperature profile of the troposphere. Who wins in influencing the troposphere, the surface warming or the drying? Or put differently, do islands heat or cool the troposphere?

 

We assess this hypothesis using a six-member ensemble of double-periodic convection-resolving Radiative-Convective Equilibrium (RCE) simulations (1006x1006x74 grid points), containing an archipelago of flat islands obtained from the Maritime Continent. In contrast to previous RCE simulations, the islands are represented by a land-surface scheme and are thus capable of representing not only the daytime anomaly in temperature but also that in relative humidity. We find that during episodes when precipitation occurs more frequently over land, the domain-mean (virtual) temperature in the mid-troposphere becomes colder. We also find that the drying (i.e, cooling) effect becomes pronounced for larger islands, and thus, removing a large island from the simulation also leads to a systematically colder domain-mean (virtual) temperature profile. The results suggest that islands may rather cool than warm the troposphere and that the inability of evaporation over land to keep up with the daytime surface warming is of key relevance for the temperature profile in the Maritime Continent.
Recent changes of atmospheric composition in background and urban Eurasian regions
Authors: Rakitina Alexandra , Skorokhod Andrey , Pankratova Natalia , Shtabkin Yuri , Wang Gengchen , Vasilieva Anastasia
Published: March 2021

An analysis of the CO and CH4 total column (TC) as well as aerosol optical depth (AOD) data in background and urban Eurasian regions for different time-periods and seasons from 1998 to 2018 years is presented. Trend estimates based on long-term spectroscopic datasets of OIAP RAS for Moscow, Zvenigorod (ZSS, Moscow province), Beijing (joint site of OIAP RAS and IAP CAS) and NDACC stations located in Eurasia are compared between themselves and with similar assessments obtained from satellite data. The comparison of satellite and ground-based trend estimates was provided for the days of synchronous measurements only. Analysis results of the satellite observations of AIRS v6 of CO and CH4 TC and MODIS AOD data are confirmed by ground-based trend estimates. Significant decrease of anthropogenic CO in the megacities Moscow (2.9±0.6%/yr) and Beijing (1.2±0.2%/yr) for autumn months of 1998−2018 was found according to ground-based spectroscopic observations. In spite of total anthropogenic CO emission decrease (for Europe and China) and the decrease of wild-fires emissions in Central North Eurasia (0−90° E, 42−75° N) in 2008−2018 we found CO TC stabilization or even its increase in background regions of Northern Eurasia in summer and autumn months of 2008−2018. Decrease of AOD over Central and Southern Europe as well as over China (1−5%/yr) was observed since 2007. Since 2007-2008 an increase in CH4 TC positive trend values over Northern Europe as well as for tropical belt of Eurasia was obtained.

Additionally some results of comparison of orbital (AIRS, MODIS, TROPOMI) and ground-based spectroscopic diurnal and 10-days averaged data are presented.

This work was supported by the Russian Science Foundation under grant № 20-17-00200 (analysis orbital information and trend distributions).
Detecting early warning signal of the Pacific Decadal Oscillation phase  transition using complex network analysis 
Authors: Lu Zhenghui , Yuan Naiming , Yang Qing , Ma Zhuguo , Kurths Juergen
Published: March 2021

Obtaining an efficient prediction of the Pacific Decadal Oscillation (PDO) phase transition is a worldwide challenge. Here, we employed the climate network analysis to uncover early warning signals prior to a PDO phase transition. This way an examination of cooperative behavior in the PDO region revealed an enhanced signal that propagated from the western Pacific to the northwest coast of North America. The detection of this signal corresponds very well to the time when the upper ocean heat content in the off-equatorial northwestern tropical Pacific reaches a threshold, in which case a PDO phase transition may be expected with the arising of the next El Niño/La Niña event. The objectively detected early warning signal successfully forewarned all the six PDO phase transitions from the 1890s to 2000s, and also underpinned the possible PDO phase transition around 2015, which may be triggered by the strong El Niño event in 2015-2016.
Tortonian Conidae of Crete. New species revealed under UV light. Subgenera Conus (Lautoconus), Conus (Plagioconus) and a possible new subgenus.
Authors: Psarras Christos , Koskeridou Efterpi , Merle Didier
Published: March 2021

Conidae is a very diverse family of carnivorous gastropods with over 900 extant species, that present beautiful colour patterns. These patterns can be useful to biologists for the systematic approach, but lack usually in fossil samples, when they are only observed in natural light. Therefore conid species were difficult to distinguish.
To resolve that problem, we use ultraviolet light to reveal the colour patterns of these fossil shells. Here, we present the second part of a PhD project that attempts to clarify the diversity of the Tortonian Conidae from Crete, Greece. The first part of this project already revealed eleven species of Conilithes Swainson, 1840 and Conus (Kalloconus) da Motta, 1991 five of them being new. In the second part, we found seventeen species, of those seven are considered as new. Among them, ten are attributed to Conus (Lautoconus) Monterosato, 1923 and three in Conus (Plagioconus) Tucker & Tenorio, 2009. Finally, a group of four species with special characteristics is discussed and is proposed as a new subgenus.
This project will greatly enrich the knowledge of the family in  the Tortonian of Eastern Proto-Mediterranean. The results will be compared to similar faunas from the Middle-Miocene to Pliocene of Europe, in order to assess the biogeography of this family.
How can risk mitigation measures for surface runoff and erosion be included in the regulatory environmental risk assessment for pesticides in Germany?
Authors: Klein Michael , Reichenberger Stefan , Spycher Simon , O'Connor Isabel , Thomas Kai , Multsch Sebastian , Sittig Stephan , Großmann Dietlinde , Flade Jens
Published: March 2021

Surface runoff from agricultural fields is a major input pathway of pesticides into surface waters. The aim of this project was to i) analyze the effectiveness of various mitigation measures to reduce pesticide runoff and erosion inputs into surface waters, ii) assess the suitability of the measures found effective for use in the quantitative environmental exposure assessment for authorization of plant protection products (PPP), and iii) make recommendations how the potentially suitable measures could be applied in risk assessment of PPP in Germany.

Following a literature analysis, 16 risk mitigation measures were presented to five experts in the field. Measures finally selected for quantitative analysis belong to 3 groups: vegetative filter strips (VFS), soil conservation measures (including no-till) and microdams in row crops. VFS effectiveness was analysed with CART (Classification and Regression Trees) using the dataset compiled by Reichenberger et al. (2019). CART was performed for three target variables: i) relative reduction of total inflow by the VFS (ΔQ), ii) relative reduction of sediment load (ΔE), and relative reduction of pesticide load (ΔP). The main data sources for soil conservation measures were a plot database with annual runoff volumes and soil losses (Maetens et al., 2012), a literature review (Fawcett et al., 1994) and a field study with event-based data (Erlach, 2005), while for microdams the principal source were the data compiled by Sittig et al. (2020).

The following conclusions were drawn from the analysis:

VFS can be recommended for application in quantitative risk assessment.  However, infiltration and sedimentation should be simulated with a mechanistic model such as VFSMOD.

Due to the high variability of results and limited availability of high-quality data, effectiveness of mulch-till could not be quantified sufficiently well. It can therefore not be recommended for now as a regulatory mitigation measure.

Before recommending no-till as a regulatory mitigation measure for surface runoff and erosion, the question of potentially increased pesticide loss via leaching and drainage should be clarified.

Microdams in row crops can also be recommended as a regulatory mitigation measure, since they have shown to be effective and their effect can be modelled as a reduction of the runoff Curve Number. However, elaborating a CN table for e.g. the FOCUS scenarios would require an in-depth analysis of the available data.
Exploiting large ensembles for a better yet simpler climate model evaluation
Authors: Suarez-Gutierrez Laura , Milinski Sebastian , Maher Nicola
Published: March 2021

We use a methodological framework exploiting the power of large ensembles to evaluate how well ten coupled climate models represent the internal variability and response to external forcings in observed historical surface temperatures. This evaluation framework allows us to directly attribute discrepancies between models and observations to biases in the simulated internal variability or forced response, without relying on assumptions to separate these signals in observations. The largest discrepancies result from the overestimated forced warming in some models during recent decades. In contrast, models do not systematically over- or underestimate internal variability in global mean temperature. On regional scales, all models misrepresent surface temperature variability over the Southern Ocean, while overestimating variability over land-surface areas, such as the Amazon and South Asia, and high-latitude oceans. Our evaluation shows that MPI-GE, followed by GFDL-ESM2M and CESM-LE offer the best global and regional representation of both the internal variability and forced response in observed historical temperatures.
Elevation of the Gangdese Mountains and Their Simulated Impacts on Asian Climate during the Late Cretaceous
Authors: Zhang Jian , Liu Yonggang , Fang Xiaomin , Zhang Tao , Zhu Chenguang , Wang Chengshan
Published: March 2021

The Tibetan Plateau has a significant impact on the Asian climate due to its high topography. However, its uplift history, especially the uplift of the Gangdese Mountains in its early stage, is under intense debate. Most quantitative reconstructions are done for the Cenozoic only, impeding our understanding of the geodynamic and paleoenvironmental evolution during the Cretaceous. How high would the Gangdese Mountains be then, and what effects would they have on Asian climate? In order to explore these two questions, here we model the impacts of the Gangdese Mountains on the Asian climate during the Late Cretaceous by employing the Community Earth System Model version 1.2.2. It is found that the extent of dry land in East Asia is sensitive to the altitude of the Gangdese Mountains; it expands eastwards and southwards with the rise of the mountain range, which is due to the fact that the Gangdese Mountains can significantly reduce the precipitation over the low- to mid-latitude Asia. We then attempt to constrain their paleoaltitude using the available climate indicators in the sediments. The aridity index is further calculated for this region, and its comparison with the climate records suggests that Gangdese Mountains should be higher than 1 km but lower than 3 km during the Late Cretaceous, most likely ~2 km.
Water flow mechanisms and unproductive water losses in rice-based cropping systems in the humid tropics
Authors: Mahindawansha Amani , Kraft Philipp , Külls Christoph , Breuer Lutz
Published: March 2021

In rice production areas in the world, increasing water scarcity is a major problem. Among the water saving techniques, integrating water saving non-flooded crops into the flooded rice system during the dry season is one of the promising water-saving approaches. Therefore, there is a necessity to improve the understanding of the water flow dynamics and losses in crop rotational systems under different climatic conditions in irrigated agricultural fields. That understanding can be used to lower the water requirements to build more efficient water management systems. We experimentally investigated the water flow processes and water losses by introducing non-flooded crops during the dry season (dry rice and maize) followed by flooded rice in the wet season and compared this to flooded rice in both seasons. We measured stable isotopes of water (δ2H and δ18O) in extracted soil water and liquid samples (Groundwater, ponded surface water, rainwater, and irrigation water). The Craig–Gordon equation was applied to estimate the fraction of evaporation losses. Results reveal that the soil isotopic profile patterns reflect the soil water transport processes and differ depending on the irrigation frequencies and crop diversification. Matrix flow and slow soil water infiltration, soil evaporation, and preferential flow via desiccation cracks were identified as the main water flow mechanisms in the irrigated fields. During the dry season, the evaporation effect on soil water is higher and water losses decreased from the beginning towards the end of the seasons. However, greater unproductive water losses were estimated during the wet season compared to the dry season. Finally, the results suggested that introducing dry seasonal crops to the crop rotation system for reducing the unproductive water losses is a good alternative method.

 
Anthropogenic Decline of African Dust inferred from Insights From the Holocene Records and Beyond: are dust purely  natural?
Authors: Yuan Tianle , Yu Hongbin , Chin Mian , Remer Lorraine , McGee David , Evan Amato
Published: March 2021

African dust exhibits strong variability on a range of time scales. Here we show that the interhemispheric contrast in Atlantic SST (ICAS) drives African dust variability at decadal to millennial timescales, and the strong anthropogenic increase of the ICAS in the future will decrease African dust loading to a level never seen during the Holocene. We provide a physical framework to understand the relationship between the ICAS and African dust activity: positive ICAS anomalies push the Intertropical Convergence Zone (ITCZ) northward and decrease surface wind speed over African dust source regions, which reduces dust emission and transport. It provides a unified framework for and is consistent with relationships in the literature. We find strong observational and proxy‐record support for the ICAS‐ITCZ‐dust relationship during the past 160 and 17,000 years. Model‐projected anthropogenic increase of the ICAS will reduce African dust by as much as 60%, which has broad consequences. We posit that dust cannot be thought of as a purely natural phenomenon.
The Potential Applications of Raman Spectroscopy in Unravelling Complex Palaeowildfire Ecosystems
Authors: Theurer Thomas , Muirhead David , Jolley David , Mauquoy Dmitri
Published: March 2021

Raman spectroscopy represents a novel methodology of characterising plant-fire interactions through geological history, with enormous potential. Applications of Raman spectroscopy to charcoal have shown that this is an effective method of understanding intensity changes across palaeofire regimes. Such analyses have relied on the determination of appropriate Raman parameters, given their relationship with temperature of formation and microstructural changes in reference charcoals. Quantitative assessments of charcoal microstructure have also been successfully applied to the assessment of carbonaceous maturation under alternate thermal regimes, such as pyroclastic volcanism. Palaeowildfire systems in association with volcanism may present a complex history of thermal maturation, given interactions between detrital charcoals and volcanogenic deposition. However, whilst palaeofire and volcanic maturation of carbonaceous material are well understood individually, their interaction has yet to be characterised. Here we present the first analysis of palaeofire charcoals derived from volcanic ignition utilising Raman spectroscopy. Our results indicate that complex interactions between volcanism and palaeofire systems may be better understood by the characterisation of charcoal microstructure, alongside palaeobotanical and ecosystem studies. Understanding the unique relationship between wildfires and volcanism, and the impact that this has on the fossil record, may better assist our understanding of wildfire systems in deep history. Further still, this highlights the potential for better understanding the socioecological impacts of modern and future wildfire systems closely associated with volcanic centres. 
Atmospheric Evolution due to impacts during the final stage of planet formation
Authors: Sinclair Catriona , Wyatt Mark
Published: March 2021

We investigate how the bombardment of terrestrial planets by populations of planetesimals left over from the planet formation process, asteroids from the main belt and comets affects the evolution of their atmospheres, through both impact induced atmospheric mass loss and volatile delivery. This work builds on previous studies of this topic by combining prescriptions for the atmosphere loss and mass delivery derived from hydrodynamic simulations with results from dynamical modelling of a realistic population of impactors.

 

The effect on the atmosphere predicted by the hydrodynamical simulations performed by Shuvalov (2009) as a function of the impactor and system properties are incorporated into a stochastic numerical model for the atmospheric evolution. The effects of rare but destructive giant impacts, that can cause non-local atmosphere loss, are also included using the prescription from Schlichting et al. (2015). The effects of aerial bursts and fragmentation of impactors in the atmosphere are included using a prescription based on the work of Shuvalov (2014). These effects are found to be relevant for hot and dense atmospheres analogous to the present day conditions on Venus.

 

We compare the impact induced atmosphere evolution of Earth, Venus and Mars using impact velocities and probabilities inferred from the results of dynamical models of the population of left over planetesimals in the early solar system from Morbidelli et al. (2018), the population of asteroids from Nesvorny et al. (2017a) and comets from Nesvorny et al. (2017b). We use realistic size distributions for these populations based on the main belt asteroids and trans-Neptunian objects. The effect of the variation in the distribution of the impactor material through their bulk density and volatile fraction is investigated, as is the effect of varying the initial conditions assumed for the atmospheres of Earth, Venus and Mars.

 

Our results for the Earth are discussed in light of observational constraints regarding the composition of the material delivered as the late veneer. The results for Venus and Mars are compared to those for the Earth and considered in comparison to observational evidence regarding the past climate of these worlds. A holistic view of the results for all three planets allows constraints on the past atmospheres to be inferred, in the absence of other atmospheric effects.
From monodisperse to polydisperse: the influence of grain size distribution on the mechanical behavior of porous synthetic rocks
Authors: Carbillet Lucille , Heap Michael , Wadsworth Fabian , Baud Patrick , Reuschlé Thierry
Published: March 2021

Sedimentary crustal porous rocks span a wide range of grain size distributions – from monodisperse to highly polydisperse. The distribution of grain size depends on the location and conditions of rock formation, the chemico-physical processes at play, and is influenced by subsequent geological processes. Well-sorted granular rocks, with a grain size distribution close to monodisperse, and granular rocks with a more polydisperse grain size distribution, have repeatedly been subjected to laboratory experiments. And yet the natural variability from sample to sample and structural heterogeneity within single natural samples all conspire to prevent us from constraining the effect of grain size polydispersivity. While a few studies have focused on the influence of grain size, the control of grain size distribution on the mechanical behavior of rocks has scarcely been studied, especially in the laboratory. In this study, we address this knowledge-gap using synthetic samples prepared by sintering glass beads with controlled polydisperse grain size distributions. When heated above the glass transition temperature, the beads act as viscous droplets and sinter together. Throughout viscous sintering, a bead pack evolves from an initial granular discontinuous state into a solid connected porous state, at which the microstructural geometries and final porosity are known. Variably polydisperse individual samples were prepared by mixing glass beads with diameters of 0.2, 0.5, and 1.15 mm in various proportions, which were sintered together to a final porosity of 0.25 or 0.35. Hydrostatic and triaxial compression experiments were performed for each combination of polydispersivity. The samples were water-saturated, deformed at room temperature, and deformed under drained conditions (with a fixed pore pressure of 10 MPa). Triaxial experiments were conducted at a constant strain rate at effective pressure corresponding to the ductile (compactive) regime. Our mechanical data provide evidence that polydispersivity exerts a significant control on the compactive behavior of porous rocks. Insights into the microstructure were gained using scanning electron microscopy on thin sections prepared from samples before and after deformation. These data allow for the observation of the different deformation features, and by extension the deformation micro-mechanisms, promoted by the different type and degree of polydispersivity. Overall, our data show that, at a fixed porosity, increasing polydispersivity decreases the stress required for compactant failure.
Stochastic analysis of time-series related to ocean acidification
Authors: Vagenas Georgios , Iliopoulou Theano , Dimitriadis Panayiotis , Koutsoyiannis Demetris
Published: March 2021

Since the pre-industrial era at the end of the 18th century, the atmospheric carbon dioxide concentration (CO2) has increased by 47.46% from the level of 280 ppmv (parts per million volume) to 412.89 ppmv (Mauna Loa – NOAA Station, November 2020). These increased concentrations caused by natural & anthropogenic activities, interact with the aquatic environment which acts as a safety valve. Nevertheless, the absorbed CO2 amounts undergo chemical transformations, resulting in increasing ionized concentrations that can significantly reduce the water’s pH, a process described as ocean acidification. Here, we use the HOT (Hawaii-Ocean-Time series) to perform time series analysis for temperature, carbon dioxide partial pressure and pH. More specifically, we analyze their temporal changes in month and annual time lag. Then, we proceed in comparisons with relevant studies on atmospheric data to evaluate the produced results. Finally, we make an effort to disentangle the results with simplified assumptions connected with the observed impact of ocean acidification on the aquatic ecosystems.
Variability and changes of drought-relevant circulation types in southern central Europe
Authors: Thanheiser Selina
Published: March 2021

The estimation of regional extreme events (heavy precipitation and droughts) in Central Europe under ongoing climate change especially includes an evaluation of the relationship between atmospheric circulation types and regional droughts taking place in the bilateral research project WETRAX+ (WEather Patterns, Cyclone TRAcks, and related precipitation EXtremes). The study area is located in the south of central Europe, including Austria, parts of Germany, Switzerland, and the Czech Republic.

For a precipitation-conditioned circulation type classification, atmospheric variable fields from gridded daily JRA55 reanalysis data (Japan Meteorological Agency 2018) and gridded daily precipitation data based on 1756 weather stations in the study area (Zentralanstalt für Meteorologie und Geodynamik 2018) were used for the observation period 1961 to 2017. Seven different regional climate model runs of the Euro-Cordex – Initiative and from ReKliEs-De (Regional Climate Projections Ensemble for Germany) as well as three runs of the global climate model ECHAM6 (greenhouse gas scenario RCP 8.5) were used to estimate future changes in two projection periods (2031-2060 and 2071-2100).

The large-scale atmospheric circulation types have been derived using a non-hierarchical cluster analysis provided in the COST733 Classiﬁcation Software. The drought-relevant circulation types are determined according to relative frequencies of circulation type days under a particular percentile of precipitation: If at least 20 percent of the circulation type days are below the 20th percentile of precipitation, the circulation type is defined as drought relevant. Drought-relevant circulation types are examined in terms of trends, persistence, changes in monthly occurrence frequencies, and within-type variability. When transferring the circulation types to the climate model data, each single day of the projection period is assigned to the circulation type to whose centroid fields the respective single fields have the smallest Euclidean distance.

During the observation period, the trend analyses show that the occurrence of drought-relevant circulation types is significantly more often associated with higher temperatures and lower relative humidity. First results of the analysis for the future climate show an increase of central high-pressure areas over Central and Eastern Europe for the months April to September. Anticyclonic weather conditions with a resulting southwesterly flow occur less frequently.
Diachronous exhumation of the Carpathians from low-temperature thermochronology
Authors: Roger Marion , van der Beek Peter , de Leeuw Arjan , Husson Laurent
Published: March 2021

The Carpathians fold-and-thrust belt results from oblique collision of ALCAPA and Tisza-Dacia plates with the eastern European margin. It formed during the Oligocene and Miocene, propagating laterally from NW to SE as clearly demonstrated by balanced-cross sections (Nakapelyukh et al., 2017; Castellucio et al., 2016; Merten et al., 2010). The coeval development of the foreland basin (Roure et al., 1993) is revealed by an axial transport system that prograded from NW to SE, ultimately supplying sediments to the Black Sea (de Leeuw et al., 2020). However, lacking a regional synthesis and integration of thermochronology data, lateral propagation of exhumation in the orogen has not been demonstrated yet.

 We reconstruct the exhumation history of the entire Carpathians from the Oligocene onwards and link it with the development of the Carpathians foreland basin (CFB) using a source-to-sink approach. We compiled more than 500 apatite and zircon fission-track and (U-Th)/He ages from the literature. This comprehensive database was separated by region (Western, Eastern, and South-Eastern Carpathians) and by tectonic domain (as defined in Schmid et al., 2008). This partitioning allows for the inversion of large datasets, reflects the tectonic complexity of the belt, and avoids spurious spatial correlations (Schildgen et al., 2018). The thermochronology data was inverted using Pecube (Braun et al., 2012) to constrain exhumation rates in a Bayesian approach. We thus obtain estimates of exhumation rates through time along the belt (with their uncertainty) and convert these into bulk  sediment fluxes over time, permitting tracking of sediment routing from the eroding belt to the CFB. Ultimately, these data will be used to unravel deeper geodynamics, including the possible effects of slab detachment on the evolution of the belt and its foreland basin.

 

Key words: Low-temperature thermochronology, Carpathians, exhumation, source to sink, Pecube inversions.
A stationary tropospheric sulphur cycle for Earth system models of intermediate complexit
Authors: Eliseev Alexey V. , Gizatullin Rustam D. , Timazhev Alexandr V.
Published: March 2021

A stationary, computationally efficient  scheme, ChAP-1.0 (Chemistry and Aerosol Processes, version 1.0) for the sulphur cycle in the troposphereis developed. This scheme is envisaged to be implemented into Earth system models of intermediate complexity (EMICs). The scheme accounts for sulphur dioxide emissions into the atmosphere, its deposition to the surface, oxidation to sulphates, and dry and wet deposition of sulphates on the surface.
The calculations with the scheme were performed with the anthropogenic emissions of sulphur compounds into the atmosphere for 1850-2000 according to the CMIP5 (Coupled Models Intercomparison Project, phase 5) 'historical' protocol, with the ERA-Interim meteorology, and assuming that natural sources of sulphur into the atmosphere remain unchanged during this period. The model reasonably reproduces characteristics of the tropospheric sulphur cycle known from observations and other simulations (e.g., in the Atmospheric Chemistry and Climate Model Intercomparison Project phase II (ACCMIP) simulations, Copernicus Atmosphere Monitoring Service (CAMS) reanalysis, and the Meteorological Synthesizing Centre–West of the European Monitoring and Evaluation Programme (EMEP MSC-W) data). In particular, in 1980's and 1990's, , when the global anthropogenic emission of sulphur, global atmospheric burdens of SO2 and SO4 account, correspondingly, 0.2 TgS and 0.4 TgS. In our scheme, about half of the emitted sulphur dioxide is deposited to the surface and the rest in oxidised into sulphates. The latter mostly removed from the atmosphere by wet deposition. The lifetime of the SO2 and SO4 in the atmosphere is, respectively, 1.0±0.1 days and 4.1±0.3 days.
Despite its simplicity, our scheme may be successfully used to simulate sulphur/sulphates pollution in the atmosphere at coarse spatial and time scales and an impact of this pollution to direct radiative effect of sulphates on climate, their respective indirect (cloud- and precipitation-related) effects, as well as an impact of sulphur compounds on the terrestrial carbon cycle.
Orbital-scale climatic record in the North China across the Pliocene-Pleistocene transition
Authors: Zhang Ze , Wang Zhixiang , Huang Chunju
Published: March 2021

The Pliocene - Pleistocene period (3.6-1.8 Ma) was a significant global cooling time, from very warm, equable climates to high-amplitude glacial-interglacial cycles. The origin of glaciers in the Northern Hemisphere, and the mechanisms by which glacial cycles have expanded since the late Pliocene, remain a subject of ongoing discussion. The studies of the Pliocene orbital scale climate evolution mainly are focused on marine sediments and loess-paleosoil sequences, however, there are few records of continental lacustrine facies during this period. Here we present a 37.6 m high-resolution Sanmen lacustrine sequences during the Pliocene-Pleistocene transition period that indicates the astronomically controlling East Asian climate transition and the Sanmen paloelake evolution. The Rb/Sr series evolution was divided into two parts for astronomical analysis based on the obvious changes observed in curve shape and Evolutionary spectral analysis through the section: 7.4-19 and 19-45 m. Based on evaluation of average accumulation rates from paleomagnetic results, the dominated ~99-cm cycles in the 7.4 to 19 m intervals represent ~41 kyr obliquity cycles. The 19 to 45 m intervals show obvious cycles at ~232-cm, interpreting as ~100 kyr eccentricity. Astronomical tuning combined with paleomagnetic results has been used to establish the 3.83-2.32 Ma high-precision astronomical scale. Rb/Sr series reveals that ~100 kyr eccentricity was the dominant control on lake expansion for Sanmen paleolake evolutionary before 2.75 Ma, after that, dominant obliquity control. Based on re-established the meridional sea surface temperature (SST) gradient between polar Atlantic borehole ODP 982 and the equatorial Atlantic borehole ODP 662, results show that the meridional sea surface temperature gradients increased significantly at 2.75 Ma, with cyclicity changing from the dominant ~140 kyr and ~95 kyr cycles to ~41 kyr at 2.75 Ma, and is coeval with our Rb/Sr record in the Weihe Basin. Crossspectral analysis show that the Rb/Sr and meridional SST gradient are strongly coherent and almost in-phase at these primary orbital periods in the past between 3.83-2.32 Ma. Thus, we conclude that the reorganization of the East Asian climate system at ~2.75 Ma, which coincided with the expansion of Arctic ice sheet, was a response to a dramatic cooling of the global climate and obliquity-driven changes in meridional SST gradients.
Near‐Complete Local Reduction of Arctic Stratospheric Ozone by Severe Chemical Loss in Spring 2020
Authors: Wohltmann Ingo , von der Gathen Peter , Lehmann Ralph , Maturilli Marion , Deckelmann Holger , Manney Gloria , Davies Jonathan , Tarasick David , Jepsen Nis , Kivi Rigel , Lyall Norrie , Rex Markus
Published: March 2021

In the Antarctic ozone hole, ozone mixing ratios have been decreasing to extremely low values of 0.01–0.1 ppm in nearly all spring seasons since the late 1980s, corresponding to 95–99% local chemical loss. In contrast, Arctic ozone loss has been much more limited and mixing ratios have never before fallen below 0.5 ppm. In Arctic spring 2020, however, ozonesonde measurements in the most depleted parts of the polar vortex show a highly depleted layer, with ozone loss averaged over sondes peaking at 93% at 18 km. Typical minimum mixing ratios of 0.2 ppm were observed, with individual profiles showing values as low as 0.13 ppm (96% loss). The reason for the unprecedented chemical loss was an unusually strong, long-lasting, and cold polar vortex, showing that for individual winters the effect of the slow decline of ozone-depleting substances on ozone depletion may be counteracted by low temperatures.
Spatial patterns of precipitation in shallow convection during EUREC4A
Authors: Radtke Jule , Naumann Ann Kristin , Ament Felix , Hagen Martin
Published: March 2021

Fields of shallow convection exhibit a rich spatial variability forming patterns of various shape, size and arrangement, commonly denoted as organization and often associated with precipitation. To understand either might require understanding both. However, the distribution and patterns of precipitation in shallow convection have received little attention so far.  

We investigate whether spatial patterning matters for the amount or intensity of precipitation in a scene. Are details of the spatial distribution important? Therefore, we analyse if and how the number, size and spatial arrangement of rain objects vary with scene precipitation rates. To do so, we exploit observational data from the C-band radar PoldiRad installed during the EUREC4A measurement campaign scanning a sector with approximately 200 km range east of Barbados in the western tropical Atlantic and compare to storm resolving simulations with ICON.

Our analyses suggest that it is mostly the precipitating area, which is determined by the number and size of rain objects, that regulates scene rainfall amounts. Especially the tail of large objects increases widening the spread in rain object sizes with increasing scene rainfall. While ICON captures this behaviour qualitatively, it overall simulates too small objects that rain too intense. We conclude that the extent of precipitation objects is more relevant for scene precipitation rates than a close spacing of objects.
Toward a quantitative framework for assessing the global severity of Oceanic Anoxic Events
Authors: Clarkson Matthew , Lenton Timothy , Stirling Claudine , Dickson Alexander , Vance Derek
Published: March 2021

Oceanic anoxia is a common response to past climate perturbations and often invoked as a direct cause of mass extinctions and faunal turnover events. During the Phanerozoic, there are numerous events that show qualitatively similar expressions of de-oxygenation, including ‘black shale’ development and distinct geochemical disturbances on global or local scales. These perturbations can be broadly grouped together as Oceanic Anoxic Events (OAEs), but their similarities, and differences, require greater quantification.

Advances in geochemistry over the last decade mean we are approaching a point where such a quantified comparison is possible. In particular, uranium isotopes (δ238U) have become established as an important tool for estimating the global extent of seafloor anoxia, overcoming the geographic limitations of relying on local proxy records. Typically, records from oxic marine carbonates, that are thought to track seawater trends, show negative U isotope excursions that reflect the preferential removal of isotopically heavy 238U into anoxic sediments. Here we present a compilation of δ238U datasets for a series of past climate perturbations, including the Permo-Triassic mass extinction, mid-Cretaceous OAE 2 and the PETM. In combination with a dynamic biogeochemical model, we explore the use of such datasets as a quantitative framework for comparing the ‘severity’ of OAEs. We highlight the strengths and weaknesses of the U isotope approach and outline important guidelines for considering δ238U records and the temporal relationship to other proxy datasets, such as δ13C and temperature.
Short- and long-term evolution of the seismicity associated with the New Volcanic Edifice offshore Mayotte island
Authors: Lavayssière Aude , Retailleau Lise
Published: March 2021

In May 2018, a seismic crisis started in the Comoros archipelago, East of Mayotte, which was widely felt on the Island. The related discovery of a new, 800-m high, submarine edifice 50 km East of Mayotte showed that the seismicity was caused by the birth of a volcano. The eruption is still on going at the time of writing and has sparked a large interest in the scientific community.

The seismicity is still active and is being continuously monitored thanks to several seismic stations installed on the island of Mayotte. The oceanographic campaigns that were carried out since the beginning of the crisis deployed a number of ocean bottom seismometers directly above the seismicity, to accurately understand the crisis and particularly its location. A new technique of automatic detection based on Machine Learning enabled to considerably increase the number of earthquakes that can be used to constrain the extent of the seismicity. Furthermore, the development of a new velocity model for the region allowed a precise location of these earthquakes.

These new developments permitted to reconstruct the seismicity evolution during two years of this seismic crisis and to complete the seismicity map associated with the new seismic activity. These results provide more details on the active structures to study the evolution in time as well as their precise spacial variations, allowing the analysis of the daily-to-yearly timescales of this unprecedented eruption. This is crucial to understand the dynamics of the volcanic and magmatic processes beneath Mayotte island. Linking these spatial and time variations with the real-time data, as well as the deformation and petrology evolutions, will provide crucial details on the dynamics of submarine eruptions.