bluuebunny/crossref_metadata_2025 huggingface dataset:
Fitting a new piece into the Precambrian puzzle: the detrital rutile record and its links to modern plate tectonics
Authors: Pereira Inês , Storey Craig D. , Strachan Robin , Moreira Hugo , Darling James , Cawood Peter A.
Published: March 2020

Plate tectonics is responsible for shaping the Earth’s surface, influencing the geological, hydrological and atmospheric cycles. However, there is no consensus on when plate tectonics initiated: was it fully operational during the Archean or did it not develop until the Proterozoic?

Much of what is currently known about the secular evolution of Earth’s continental crust and its links to plate tectonics has been recovered from detrital minerals. This is related to the incomplete rock record; the detrital record allows access to information from eroded and unexposed terrains. Most studies have relied on the detrital zircon record, but it is still unclear if the coincidence in age peaks with periods of supercontinent assembly reflects episodic continental growth or bias due to selective preservation of new crust within collisional orogenic belts. Furthermore, because zircon mostly grows in high-temperature conditions, it mostly calibrates magmatic cycles. To understand the evolution of plate tectonics and to assess its influence on continental crust preservation, we developed a new proxy, relevant to a range of metamorphic conditions, including HP-LT.

We investigate the U-Pb distribution ages of detrital rutile, from a range of modern stream sediments and siliciclastic units at sub-amphibolite facies metamorphic grade. Rutile mostly forms in collisional orogens and, by comparison with the zircon record, we can test the existence of a preservation bias. Zircon and rutile age distributions from our sample sets show a significant correlation, both peaks and troughs, that can only be reconciled if the detrital zircon record reflects a preservation bias that occurred during supercontinent assembly.

We further present new U-Pb and trace element data from detrital rutile within two clastic sedimentary units, preserved at sub-greenschist facies conditions in NW Scotland. These are the Torridon (Tonian) and the Ardvreck (Cambrian) groups, whose detrital zircon ages span a significant period between 3 and 1 Ga. By applying Zr-in-rutile thermometry and comparing it to the preserved metamorphic record, we show that both low and high dT/dP conditions can be inferred since at least 2.1 Ga.

Combining the existence of paired metamorphism up to 2.1 Ga with the periodic preservation of the continental crust throughout most of the Earth’s history implies that one-sided subduction, a hallmark of plate tectonics, has operated since at least the late Paleoproterozoic, and that supercontinent assembly during and after this period has been driven by plate tectonic mechanisms.
GLONASS R720 transmit power loss
Authors: Steigenberger Peter , Thölert Steffen , Allende-Alba Gerardo , Montenbruck Oliver
Published: March 2020

All GLONASS satellites transmit navigation signals in the L1 and L2 frequency band whereas newer generations (M+ and K1) also utilize the L3 band. Previous studies have shown that the transmit power in the individual frequency bands can significantly differ for dedicated satellites. These differences are visible in the carrier-to-noise density ratio (C/N0) of geodetic GNSS receivers and can be measured with a high-gain antenna. Whereas C/N0 allows for a continuous monitoring, high-gain antenna measurements are only performed on an irregular basis.

In April 2019, a drop in C/N0 could be observed for the GLONASS-M satellite R720. Measurements of the R720 equivalent isotropically radiated power (EIRP) with the 30 m high-gain antenna of the German Aerospace Center show a reduction by up to 9 dB for L1 and 1.5 dB for L2 compared to earlier measurements obtained in June 2017. The 2019 EIRP measurements also show an asymmetry of ascending and descending arcs that was not present before the power loss and indicate a change in the apparent gain pattern of the R720 transmit antenna. The transmit power change is accompanied by discontinuities in the estimated satellite antenna phase center offsets (PCOs) by about 15 cm in the transmit antenna plane and inter-frequency differential code biases (DCBs) by up 0.6 ns. Several GLONASS PCO and DCB changes were already reported by Dach et al. (2019) but they could not show a direct relation to transmit power changes.

This contribution analyzes the impact of the R720 transmit power loss on C/N0 and high gain antenna measurements as well as PCO and DCB estimates. The current transmit antenna gain pattern is reconstructed based on repeated high-gain antenna measurements. Differential gain pattern are obtained from C/N0 measurements of geodetic receivers and low-gain GNSS antennas before and after April 2019. Furthermore, the impact on precise orbit determination is evaluated as transmit power affects the modeling of antenna thrust.
Debris flow hazard mapping considering the effect of mitigation structure – a case study in Taiwan based on numerical simulation
Authors: Hsu Chih-Hao , Huang Chuan-Yi , Tsao Ting-Chi , Yin Hsiao-Yuan , Huang Hsiao-Yu , Cheng Keng-Ping
Published: March 2020

This study added the dams and retain basin according to their dimensions measured with UAV onto the original 5m-resolition DEM to compare the effect of mitigation structures to debris flow hazard. The original and the modified DEMs were both applied to simulate the consequences by using RAMMS::Debris Flow (RApid Mass Movement Simulation) model.

Hazard map is the best tool to provide the information of debris flow hazard in Taiwan. It has an important role to play in evacuating the residents within the affected zone during typhoon season. For the reason, debris flow hazard maps become a useful tool for local government to execute the evacuation. As the mitigation structure is constructed, the intensity of debris flow hazard reduces.

The Nantou DF190 debris flow potential torrent is located in central Taiwan. In 1996 when Typhoon Herb stroke, 470,000 cubic-meter of debris were washed out and deposited in 91,200 square-meter area (Yu et al., 2006), and the event caused the destruction of 10 residential houses with 2 fatalities. After the event the Soil and Water Conservation Bureau constructed a 100-meter long sabo dam and sediment retain basin with capacity of 60,000 cubic-meters. In order to compare the difference of affected zone before and after the construction of mitigation structures, the study applies RAMMS to simulate the above-mentioned event.

The result shows when large-scale debris flow occurs, most of the sediments still overflow and deposit on the fan with shape similar to the 1996 Typhoon Herb event. However, the intensity has reduced significantly with 50% less in area, several meters less in inundation depth and 50% less in flow velocity approximately. The comparison shows the effect of mitigation structures and could provide valuable information for debris flow hazard mapping.

Key Words: Debris flow, RAMMS, Hazard map, Mitigation, Taiwan
Daily and hourly prediction of DO concentration using machine learning algorithm
Authors: lim heesung , an hyunuk
Published: March 2020

In order to perform adequate water quality management, it is important to predict the water quality through measurement and data accumulation of the concentration of contaminants. However, daily measurement of water quality pollutant is unrealistic in practical aspect. In this study, the possibility of daily- or hourly-based water quality prediction through dissolved oxygen (DO) using RNN-LSTM (Recurrent Neural Network-Long Short-term Memory) algorithm, which is well-known for time-series learning, was performed. The research selected Bugok Bridge in Oncheon-stream, Busan, South Korea. Hourly-based DO, temperature, wind speed, relative humidity, rainfall data was collected at the target location and was converted to daily data. To forecast the DO concentration, TensorFlow, a deep learning open source library developed by Google, was utilized. Data of four years (2014-2017) was used for daily learning data and 2018 data was used for verification of the trained model. The performance with the adjusted number of hidden layers, number of repetitions, and the sequence length, as well as the accuracy of the model was analyzed. As a result of this research, it is proven that the performance of the prediction can be improved when weather data and large amount of data is available.
Cenozoic tectonic evolution of the Pamir-Tian Shan convergence zone: evidence from detrital zircon U-Pb provenance analysis
Authors: Jia Yingying , Glotzbach Christoph , Ehlers Todd , Lü Lixing
Published: March 2020

The Pamir is an along-strike continuation of the Tibet-Himalaya orogen and penetrated ~300 km into the Tarim and Tajik basins in Cenozoic times. This northward indentation led to regional paleoenvironmental changes and facilitated northward transport of the far-field stress from the India-Asia plate boundary. Due to the compressional stress from the India-Asia boundary and Cenozoic lithosphere delamination, the Pamir underwent intense exhumations, which well recorded its Late Cenozoic mountain building processes. However, the very rapid Late Cenozoic exhumation also erased earlier cooling records and hinders a clear understanding of the Early Cenozoic tectonic evolution of Pamir. Thus, the onset and magnitude of the northward movement of Pamir are loosely constrained (Eocene-Late Oligocene) and long debated. In particular, the Early Cenozoic tectonic evolution of Pamir is unclear.

Provenance study of sediments in the adjacent sediment basins is a widely used method to reconstruct the tectonic-geomorphologic evolution of a mountain range. We carried out paleocurrent measurements and detrital zircon analysis of the Cretaceous-Pliocene sediments in the northern Pamir-Tian Shan convergence zone. Our study area, the Tierekesazi section, is located immediately south to the southern Tian Shan and is evolved in the present foreland basin of the southwestern Tian Shan. The provenance data show that the Tian Shan was the primary source area of the northwestern Tarim basin in the Cretaceous. The appearance of the Triassic-Jurassic detrital zircon grains and northward paleo-flow directions in the Eocene (~41 Ma) to Middle Miocene sediments suggest the Pamir became an important source area of the northwestern Tarim basin. Combining with the regional crustal shortening and paleoclimate data, we speculate that the northward indentation of the Pamir initiated before ~41 Ma. In contrast with the northward movement and Middle-Late Miocene accelerated exhumation of the Pamir, the source area of the studied section shifted back to the Tian Shan after the Middle Miocene. It consists with the Middle-Late Miocene uplift of the southwestern Tian Shan. Simultaneously, the crustal shortening of Pamir propagated to its northern foreland. Newly formed fold-and-thrust zones probably blocked the sediment transport from Pamir to the Tierekesazi section, and the present-day east flowing drainage system in the Pamir-Tian Shan convergence zone was established. We infer, in this period, the Pamir likely reached its present position, which is consistent with the appearance of an extreme arid climate in the Tarim basin.
Negentropy anomaly analysis of the borehole strain data associated with the Ms 7.0 Lushan earthquake
Authors: Yu Zining , Hattori Katsumi , Zhu Kaiguang , Chi Chengquan , Fan Mengxuan
Published: March 2020

Several YRY-4 borehole strainmeters have been installed in Sichuan province, China, aiming at monitoring the crustal activities associated with earthquakes. In order to verify the existence of strain precursors preceding the Lushan earthquake, we investigate the negentropy of the borehole strain data during 2011-2013.

First, some local factors that could affect the strain are ruled out, such as environmental disturbances, we analyze the strain responses to air pressure as well as solid tides and water level which were recorded on one YRY-4 strainmeter. Based on a state-space model according to the observations of the strainmeter, we remove the strain response to air pressure, in addition to those due to water level changes and the solid tides by Kalman filter. To investigate whether the remained strain changes are related to the Lushan earthquake, we introduce the approximate negentropy as an easily computable non-randomness measure to give evidence of strain changes and illustrate the instability of the underground of the earthquake zone. Generally, the appearance of a pre-catastrophic state can be characterized by significant higher non-randomness in terms of approximate negentropy.

Negentropy analysis of 3 stations of the southwest end of the Longmenshan fault zone have been performed. The nearest GZ station is 77 km away from the epicenter, and the epicenter distances of XM and RH are respectively 270 and 436 km. The statistical results at GZ station of cumulative counts of negentropy anomaly show acceleration about 6 to 4 months and 10 days prior to the earthquake, implying there are non-random changes in the borehole strain data, which is similar to the previous results. In addition, after the earthquake, the anomalies increase briefly and recover to a quiet state. Besides, XM station appears a significant surge from October 2012 to 2013, which is consistent with the first period anomaly extracted from the GZ station. However, RH station doesn’t show anomaly acceleration, probably due to the distance.

Furthermore, we compare the anomaly acceleration rate of each station. The results indicate that as the epicenter distance increases, the acceleration rate becomes less significant, suggesting the negentropy anomalies are more sensitive near the Lushan earthquake epicenter. In other words, the anomalies of the borehole strain data dependent on the epicenter distance. Therefore, we conclude that there may be strain precursors before the Lushan earthquake and the negentropy analysis have potential capability in the study of earthquake precursors.
The influence of surface charge on dust agglomeration growth in the mesosphere
Authors: Mann Ingrid , Baptiste Joshua , Fox John , Stace Anthony J. , Besley Elena
Published: March 2020

The growth of particles is an important consideration toward a better understanding of the role of dust, ice and refractory particles in the upper mesosphere and lower thermosphere: in short, the MLT region (60 to 130 km). We investigate the conditions of dust growth via mutual collisions. It is assumed that meteoric smoke particles (MSP) are the main dust component in the mesosphere. MSP are small condensates that form in the diffusing meteor and are transported in the atmosphere where they grow by condensation. A second dust component are ice particles that form during summer months at mid and high latitude. These Polar Mesospheric Cloud (PMC) particles are composed of water ice and possibly include a fraction of the smaller MSP.

In this work, we investigate the effect of surface charge on the aggregation and growth of particles in the MLT region. The specific materials of the particles considered are similar to those typically found or expected in this region such as silica, metal oxides and ice, with particle sizes of 0.5 nm and larger. To consider the influence of the surface charges, we apply a model of the electrostatic interaction between particles of dielectric materials that, given the right conditions, includes the possibility for an attractive interaction between like-charged particles (Bichoutskaia et al. 2010). This like-charge attraction occurs due to the mutual polarisation of surface charge densities leading to regions of negative and positive surface densities close to the point of contact between the particles (Stace et al. 2011). This general model allows to investigate the interactions between particles of different size, charge and compositions. We simulate the interactions for particles of same charge and pairs of neutral and charged particles under different collision conditions in the MLT.

Bichoutskaia, E., (E. Besley), et al. J. Chem. Phys., 133(2), 024105 (2010).

Stace, A. J., et al. J. Colloid Interface Sci. 354(1), 417-420 (2011).

 
Triple oxygen isotope variations in precipitation from southeast China and its hydrological significance
Authors: Duan Pengzhen , Mahata Sasadhar , Sha Lijuan , Cheng Hai
Published: March 2020

    High precision triple oxygen isotope measurement of meteoric water is a newly added tracer in hydrological and paleoclimate research. However, it is prerequisite to study the controls on precipitation 17O-excess for proper application of it. Here we report two years highly precise precipitation data from Nanjing, a southeast China station dominated by Asian monsoon. All the water isotopes (δ17O, δ18O and δD) reported here are based on mass spectrometer measurements and optical measurements (cavity ring-down spectroscopy). Nanjing receives moisture from different vapor sources and experiences different rainout mechanisms during various monsoonal sessions. Combined use of above parameters can help us to delineate processes occurring during evaporation, transport, condensation and re-evaporation. Year to year 17O-excess variability is observed in the obtained dataset and no notable seasonal variation is observed. However, the 17O-excess seasonal amplitude is little larger in the first year than the subsequent year. So far, it is known that the precipitation 17O-excess depends on three values: 17O-excess of the source water bodies, amount of 17O-excess gain during evaporation and 17O-excess loss during raindrops evaporation. During dry months 17O-excess gain is balanced by 17O-excess loss, which might lead to the near absence of seasonal cycle at Nanjing. From the comparison of observed data and model simulation, the amount of re-evaporation on falling raindrop is estimated to be about 10% at Nanjing. In addition, correlation with available meteorological parameters has been discussed. Except temperature no significant correlation has been found with other metrological variables (relative humidity and rainfall amount). This study will serve as a baseline to understand some of issues in paleoclimate that have puzzled the scientific community for years.
Using global remote sensing and weather data efficiently for agricultural hotspots monitoring anywhere anytime: the ASAP online system
Authors: Meroni Michele , Rembold Felix , Urbano Ferdinando , Lemoine Guido , Kerdiles Hervé , Perez-Hoyos Ana , Csak Gabor , Dimou Maria , Vojnovic Petar
Published: March 2020

Monitoring agricultural production in vulnerable developing countries is important for food security assessment and requires near real-time (NRT) information on crop growing conditions for early detection of possible production deficits. The public online ASAP system (Anomaly hot Spots of Agricultural Production) is an early warning decision support tool based on weather data and direct observation of crop status as provided by remote sensing. Although decision makers and food security analysts are the main targeted user groups, all the information is fully made available to the public in a simple and well documented online platform. The information further contributes to multi-agency early warning products such as the GEOGLAM Crop Monitor for Early Warning and food security assessments following the IPC-Cadre Harmonisé framework.

Low resolution remote sensing (1 km) and meteorological (5-25 km) data are processed automatically every 10 days and vegetation anomaly warnings are triggered at the first sub-national administrative level. The severity of the warnings is based on the observed land surface phenology and three main derived indicators computed at the 1 km grid level: a proxy of the current season biomass production (the cumulative value of the Normalized Difference Vegetation index from the start of season); an indicator of precipitation deficit (the Standardized Precipitation Index at the 3 month scale); and a water-balance model output (the Water Requirement Satisfaction Index).Warning maps and summary information are published on a web GIS every ten days and then further analyzed by analysts every month. This results in the identification of hotspot countries with potentially critical crop or rangelands production conditions.

In addition to the hotspots analysis and the warning explorer, users can also zoom in to the parcel level thank to the so called High Resolution Viewer, a web interface based on Google Earth Engine that allows to visualize Sentinels (1 and 2) and Landsat imagery, plot temporal profiles and perform basic anomaly operation (e.g. current year NDVI anomaly with respect to a reference year).  

In the near future it is planned to make the anomaly warnings available also at the second sub-national level and to integrate meteorological forecasts in the warning system.
Digital rock physics: Segmentation of sub-resolution features
Authors: Balcewicz Martin , Saenger Erik H.
Published: March 2020

Digital rock physics (DRP) became a complementary part in reservoir characterization during the last two decades. Deriving transport, thermal, or effective elastic rock properties from a digital twin requires a three-step workflow: (1) Preparation of a high-resolution X-ray computed tomography image, (2) segmentation of pore and grain phases, respectively, and (3) solving equations due to the demanded properties. Despite the high resolution µ-CT images, the numerical predictions of rock properties have their specific uncertainties compared to laboratory measurements. Missing unresolved features in the µ-CT image might be the key issue. These findings indicate the importance of a full understanding of the rocks microfabrics. Most digital models used in DRP treat the rock as a heterogeneous, isotropic, intact medium which neglect unresolved features. However, we expect features within the microfabrics like micro-cracks, small-scale fluid inclusions, or stressed grains which may influence the elastic rock properties but have not been taken into account in DRP, yet. Former studies have shown resolution-issues in grain-to-grain contacts within sandstones or inaccuracies due to micro-porosity in carbonates, this means the micritic phase. Within the scope of this abstract, we image two different sandstone samples, Bentheim and Ruhrsandstone, as well as one carbonate sample. Here, we compare the mentioned difficulties of X-ray visualization with further analytical methods, this means thin section and focused ion beam measurements. This results into a better understanding of the rocks microstructures and allows us to segment unresolved features in the X-ray computed tomography image. Those features can be described with effective properties at the µ-scale in the DRP workflow to reduce the uncertainty of the predicted rock properties at the meso- and fieldscale.
Application of machine learning to map the global distribution of deep-sea sediments
Authors: Diesing Markus
Published: March 2020

The deep-sea floor accounts for >90% of seafloor area and >70% of the Earth’s surface. It acts as a receptor of the particle flux from the surface layers of the global ocean, is a place of biogeochemical cycling, records environmental and climate conditions through time and provides habitat for benthic organisms. Maps of the spatial patterns of deep-sea sediments are therefore a major prerequisite for many studies addressing aspects of deep-sea sedimentation, biogeochemistry, ecology and related fields.

A new digital map of deep-sea sediments of the global ocean is presented. The map was derived by applying the Random Forest machine-learning algorithm to published sample data of seafloor lithologies and environmental predictor variables. The selection of environmental predictors was initially based on the current understanding of the controls on the distribution of deep-sea sediments and the availability of data. A predictor variable selection process ensured that only important and uncorrelated variables were employed in the model. The three most important predictor variables were sea-surface maximum salinity, sea-floor maximum temperature and bathymetry. The occurrence probabilities of seven seafloor lithologies (Calcareous sediment, Clay, Diatom ooze, Lithogenous sediment, Mixed calcareous-siliceous ooze, Radiolarian ooze and Siliceous mud) were spatially predicted. The final map shows the most probable seafloor lithology and an associated probability value, which may be viewed as a spatially explicit measure of map confidence. An assessment of the accuracy of the map was based on a test set of observations not used for model training. Overall map accuracy was 69.5% (95% confidence interval: 67.9% - 71.1%). The sea-floor lithology map bears some resemblance with previously published hand-drawn maps in that the distribution of Calcareous sediment, Clay and Diatom ooze are very similar. Clear differences were however also noted: Most strikingly, the map presented here does not display a band of Radiolarian ooze in the equatorial Pacific.

The probability surfaces of individual seafloor lithologies, the categorical map of the seven mapped lithologies and the associated map confidence will be made freely available. It is hoped that they form a useful basis for research pertaining to deep-sea sediments.
Prediction ability of machine learning algorithms in Himalaya region of Pakistan for landslide susceptibility mapping
Authors: Shahzad Naeem , Ding Xiaoli , Abbas Sawaid
Published: March 2020

Machine learning has proven most effective in mapping landslide susceptibility. We carry out experiments with two machine learning algorithms, SVM and MaxENT to study their effectiveness for some mountaneous areas in Pakistan. A data set of 112 historic landslides are used in the study with 70% of the landslides are used for training and the rest for validation. 15 landslide casuative factors are used initially and ineffective ones are eliminated based on information Gain Ratio and Multicollinearity test techniques.  The perfromances of the landslides susceptibility maps generated are assessed using receiver operating curves (ROC), confusion matrix (CM) (Kappa, root mean square error, mean absolute error and balanced accuracy), landslide density (LD), R-index and Pearson’s Chi-squared tests. The result show that both of the models work well in this area. However, the lowest significant value ‘p’ (<0.05) during Chi-square test, showed that both the landslide models have statistical significant difference.
The Story of Plate Tectonics: Engaging A level Geologists in the classroom.
Authors: Garcia Hafsa
Published: March 2020

This poster will highlight a range of activities used in one A level Geology classroom to engage students and enable a deeper understanding of the Plate Tectonics paradigm.

Drawing on inspiration from a recent book published on the topic, and, using a variety of resources and ideas produced by UK geology teachers and organisations, this poster will present the approach I have used in my class as a new Geology teacher. I will consider the role of stories and simple, hands-on models to capture my students’ interest and help them develop a secure and confident understanding of current ideas about the theory. Furthermore, I will demonstrate the way I have approached this topic to enable students to appreciate how the theory was developed through the scientific method and to consider the evidence for themselves.
Probabilistic forecasts of the onset of the rainy season using global seasonal forecasts
Authors: Rauch Manuel , Bliefernicht Jan , Laux Patrick , Salack Seyni , Waongo Moussa , Kunstmann Harald
Published: March 2020

Seasonal forecasts for monsoonal rainfall characteristics like the onset of the rainy season (ORS) are crucial in semi-arid regions to better support decision-making in water resources management, rain-fed agriculture and other socio-economic sectors. However, forecasts for these variables are rarely produced by weather services in a quantitative way. To overcome this problem, we developed an approach for seasonal forecasting of the ORS using global seasonal forecasts. The approach is not computationally intensive and is therefore operational applicable for forecasting centers in developing countries. It consists of a quantile-quantile-transformation for eliminating systematic differences between ensemble forecasts and observations, a fuzzy-rule based method for estimating the ORS date and a graphical method for an improved visualization of probabilistic ORS forecasts, called the onset of the rainy season index (ORSI). The performance of the approach is evaluated from 2000 to 2010 for several climate zones (Sahel, Sudan and Guinean zone) in West Africa, using hindcasts from the Seasonal Forecasting System 4 of ECMWF. Our studies show that seasonal ORS forecasts can be skillful for individual years and specific regions like the Guinean coasts, but also associated with large uncertainties, in particular for longer lead times. The spatial verification of the ORS fields emphasizes the importance of selecting appropriate performance measures to avoid an overestimation of the forecast skill. The ORSI delivers crucial information about an early, mean and late onset of the rainy season and it is much easier to interpret for users compared to the common categorical formats used in seasonal forecasting. Moreover, the new index can be transferred to other seasonal forecast variables, providing an important alternative to the common forecast formats used in seasonal forecasting. In this presentation we show (i) the operational practice of seasonal forecasting of ORS and other monsoonal precipitation characteristics, (ii) the methodology and results of the new ORS approach published in Rauch et al. (2019) and (iii) first results of an advanced statistical algorithm using ECMW-SYS5 hindcasts over a period of 30 years (1981-2010) in combination with an improved observational database.

Rauch, M., Bliefernicht, J., Laux, P., Salack, S., Waongo, M., & Kunstmann, H. (2019). Seasonal forecasting of the onset of the rainy season in West Africa. Atmosphere, 10(9), 528.
Asynchronous instability of NE ice streams of the Laurentide Ice Sheet recorded in the marine sediments of Labrador Sea during the last glacial cycle
Authors: Rashid Harunur , Smith Mary , Zeng Min , Wang Yang , Drapeau Julie , Piper David
Published: March 2020

Hughes et al. (1977) hypothesized of a pan-Arctic Ice Sheet that behaved as a single dynamic system during the Last Glacial Maximum. Moreover, the authors suggested a nearly grounded ice shelf in Davis Strait implying that little or no exchange between Baffin Island and the Labrador Sea. Here we present data at 1-cm (<100 years) resolution between ~12 ka and 45 ka that shed light on the discharge from Hudson Strait and Lancaster Sound ice streams of the Late Pleistocene Laurentide Ice Sheet. A reference sediment core at 938 m water depth on the SE Baffin Slope was investigated with new oxygen isotope stratigraphy, X-ray fluorescence geochemistry, and 18 14C-AMS dates and correlated to 14 regional deep-water cores. Detrital carbonate-rich sediment layers H0-H4 were derived principally from Hudson Strait. Shortly after H2 and H3, the shelf-crossing Cumberland Sound ice stream supplied dark brown ice-proximal stratified sediments but no glacigenic debris-flow deposits. The counterparts of H3, H4, and (?)H5 events in the deep Labrador basin are 4–10 m thick units of thin-bedded carbonate-rich mud turbidites from glacigenic debris flows on the Hudson Strait slope. The behavior of the Hudson Strait ice stream changed through the last glacial cycle. The Hudson Strait ice stream remained at the shelf break in H3-H5 but retreated rapidly across the shelf in H0-H2 and did not deglaciate Hudson Bay. During this time, Cumberland Sound ice twice reached the shelf edge. In H3–H5, it remained at the shelf break long enough to supply thick turbidites. Minor supply of carbonate-rich sediment from Baffin Bay allows chronologic integration of the Baffin Bay and Labrador Sea detrital carbonate records, which is diachronous with respect to Heinrich events. The asynchrony of the carbonate events implies an open seaway through Davis Strait. Our data suggest that the maximum extent of ice streams in Hudson Strait, Cumberland Sound, and Lancaster Sound was neither synchronous.
Mantle source characteristics of Triassic alkaline lavas within the Antalya Nappes, SW Turkey
Authors: Aldanmaz Ercan , Güçtekin Aykut , Yıldız-Yüksekol Özlem
Published: March 2020

The Late Triassic basaltic rocks that are dispersed as several lava sheets in a number of different tectonic slices within the Antalya nappes in SW Turkey represent the remnants of widespread oceanic magmatism with strong intra-plate geochemical signatures. The largest exposures are observed around the Antalya Bay, where pillow structured or massif lava flows are interlayered with Upper Triassic pelagic or carbonate platform sediments. Based on bulk-rock geochemical characteristics, the rocks mostly classify as alkaline basalts and display distinctive OIB-type trace element distributions characterized by significant enrichments in LILE and HFSE abundances, as well as LREE/HREE ratios, with respect to average N-MORB. Quantitative modeling of trace element data suggest that the primary melts that produced the alkaline lavas are largely the products of variable proportions of mixing between melts generated by variable, but generally low (<10) degrees of partial melting of more than one compositionally distinct mantle source. The samples, as a whole, display large variations in radiogenic isotope ratios with 87Sr/86Sr = 0.703021–0.70553, 143Nd/144Nd = 0.51247–0.51279, 206Pb/204Pb = 18.049–20.030, 207Pb/204Pb = 15.544–15.723 and 208Pb/204Pb = 38.546–39.530. Such variations in isotopic ratios correlate with the change in incompatible trace element relative abundances and reflect the involvement of a number of compositionally distinct mantle end-members. These include EMI and EMII type enriched mantle components both having lower 143Nd/144Nd than typical depleted MORB source with their contrasting low and high 206Pb/204Pb and 207Pb/204Pb ratios respectively, as well as a high time-integrated 238U/204Pb component with high 206Pb/204Pb at relatively low 87Sr/86Sr and εNd values. The results from trace element and radiogenic isotope data are consistent with the view that the initial melt generation was likely related to partial melting of the shallow convecting upper mantle in response to Triassic rifting events, while continued mantle upwelling resulted in progressively increased melting of mantle lithosphere that contained compositionally contrasting lithological domains with strong isotopic heterogeneities.
Understanding the plastic cocktail using distributions
Authors: Kooi Merel , Koelmans Albert A
Published: March 2020

Plastic pollution proves a complex challenge, given the large variety in the properties of the items and particles. Usually, models and experiments focus on a small, sometimes arbitrary, subset of the total plastic continuum. This inherently implies a limitation, and will never be fully satisfactory if we are to understand the true behavior of plastic of all sizes, shapes and densities in the environment. Here, we present a novel approach, in which plastics are fully characterized by continuous distribution functions. For microplastics, we report and discuss distributions obtained for the marine and freshwater environment, from water and sediment samples. For macroplastics, we report spatial and temporal trends based on distributions that were derived from monitoring data from the OSPAR beach litter program. We discuss how these micro- and macroplastic distributions can feed directly into transport and fate models. Additionally, they can be used to design effect and fate experiments, where mixtures of (environmental) plastic should be used to better represent the real, complex mixture that plastic really is. By using this approach, the often acclaimed problem of complexity as a limiting factor is circumvented, which brings a true understanding of plastic fate and effects within reach.  
Methane emissions from abandoned offshore wells– First data from a 2019 research cruise to the Dogger Bank, German North Sea
Authors: Blumenberg Martin , Schlömer Stefan , Römer Miriam , Heeschen Katja , Müller Hendrik , Barckhausen Udo , Müller Simon , Schwalenberg Katrin
Published: March 2020

Methane is the second most important greenhouse gas and, considering a period of 100 years, has a more than 30 times higher “global warming potential” than carbon dioxide. Emissions from the production, storage, distribution and use of fossil energy resources in recent years sum up to about 15 % of global methane emissions with numbers still being under discussion and topic of numerous research programs.

Abandoned oil and gas wells are one of the sources of methane from the oil and gas sector. Recent studies found escaping methane at selected abandoned drill holes in the central North Sea. Assuming this would hold for one third of the ~11.000 wells in the region, the process would introduce significant amounts of methane at shallow water depth. Interestingly, the collected methane was of biogenic rather than thermogenic origin, potentially escaping from shallow gas pockets. Likely, this methane was mobilized by mechanical disturbance of the sediments through the drilling operation and the well section has served as a pathway thereafter. However, little is known about the number of wells affected and the relevance for the amounts of methane realeased.

During a research cruise with the German research vessel Heincke in July, 2019, we studied seafloor characteristics, water column anomalies and sediment methane geochemistry and further inspected visually nine abandoned well sites at ~40 m water depth in the German sector of the central North Sea (Dogger Bank). The cruise targeted different situations, including known seeps in the Dutch part of the Dogger Bank, well sites of different ages and an area where abandoned wells penetrate shallow gas pockets. First data demonstrate that at none of the studied sites concentrations of dissolved methane were enriched in the upper water column. For most sites, sediment and deep water methane data demonstrate concentrations in the range known as background for that area (i.e., deep water methane close to ~ 10 nM). At one site with high indications for the presence of shallow gas pockets, we observed methane abundances several times enriched compared to background. However, the enrichments also occurred 500 m away from the drill site and did not increase towards the center. Based on our data we argue for an active natural seep situation rather than a leaking well and underline that natural seeps may challenge the identification of potentially leaking wells.
Using Large Strong Motion Datasets to Model Regional Site Response in Seismic Risk Assessment: Examples from Japan and Europe
Authors: Weatherill Graeme , Cotton Fabrice , Kotha Sreeram Reddy
Published: March 2020

Characterisation of seismic risk within a probabilistic framework is dependent upon well-constrained models of the seismic source, the ground motion scaling and the local site response, in addition to both their aleatory variability and epistemic uncertainty. When assessing risk as a large geographical scale such as that of a country or continent, however, complex models of site response that require detailed parameterization of the site conditions are seldom feasible to constrain. Instead, the use of simpler proxies, such as the well-known topographically inferred 30 m averaged shear-wave velocity (VS30), have become widely adopted for this purpose. In practice, the inference of VS30 from topographic and/or geological proxies have substantial limitations in terms of both the geological environments for which they are appropriate and the increased uncertainty in the prediction of site response; limitations that are not always accounted for in existing seismic risk models.

The volume of data reported by both new and well-established stations is increasing at an exponential rate, with hundreds of thousands of strong motion records now available from thousands of stations. Through this enormous and ever-expanding data set it is possible to constrain thousands of station-specific amplifications and utilize this dataset to calibrate the site amplification directly upon regionally mappable parameters, which can be applied across large spatial scales needed for regional seismic risk analysis. In doing so, it is possible not only to adapt the model of site amplification to different geological environments, but also to adjust the uncertainty in the ground motion characterization to ensure that this is captured appropriately in the seismic risk analysis when using the mappable site proxies. Applications of this approach have been made for two case study regions: i) Japan, where detailed station metadata are available and the relative increase in uncertainty from using regionally-mappable parameters instead of well-constrained site properties can be constrained, and ii) Europe, where station metadata more limited but a large number of stations with repeated observations are available. The implications for the estimates of seismic losses when adopting this new approach in place of the existing methodology are illustrated using examples from the 2020 European Seismic Risk model.
Predicting the 2015 North Atlantic Cold Blob
Authors: Drijfhout Sybren , Mecking Jenny , Hirschi Joel , Megann Alex
Published: March 2020

Leading up to and during the summer of 2015 sea surface temperatures (SSTs) in the eastern North Atlantic Subpolar Gyre reached anomalously low values while in the subtropical gyre just to the SSTs were anomalously warm. Recent observation and modelling studies have found evidence showing that these SST anomalies can be linked to the heat wave experienced over Europe that summer.  The latest observation based data still shows anomalously cold temperatures, as well as the anomalously fresh conditions that went along the 2015 cold blob in the upper layers of the eastern North Atlantic Subpolar gyre.  A second heat wave over Europe occurred in the summer of 2018 where the SSTs reached another minimum value.  Therefore, being able to predict the development, enhancement and persistence of such an anomaly is essential for good seasonal and longer predictions.  At present several modelling systems have had difficulties in simulating/maintaining the 2015 cold blob. In this work we apply a novel initialization technique using anomalous initialization from a forced ocean simulation to simulate the 2015 cold blob.  Initial results show that the model is able to maintain the cold blob as well as have a strengthening of the cold blob, however, it has difficulties capturing the timing of this strengthening.
The representation of Northern Hemisphere blocking in current global climate models
Authors: Schiemann Reinhard , Athanasiadis Panos , Barriopedro David , Doblas-Reyes Francisco , Lohmann Katja , Roberts Malcolm J. , Sein Dmitry , Roberts Christopher D. , Terray Laurent , Vidale Pier Luigi
Published: March 2020

Global Climate Models (GCMs) are known to suffer from biases in the simulation of atmospheric blocking, and this study provides an assessment of how blocking is represented by the latest generation of GCMs. It is evaluated (i) how historical CMIP6 (Climate Model Intercomparison Project Phase 6) simulations perform compared to CMIP5 simulations, and (ii) how horizontal model resolution affects the simulation of blocking in the CMIP6-HighResMIP (PRIMAVERA) model ensemble, which is designed to address this type of question. Two blocking indices are used to evaluate the simulated mean blocking frequency and blocking persistence for the Euro-Atlantic and Pacific regions in winter and summer against the corresponding estimates from atmospheric reanalysis data. There is robust evidence that CMIP6 models simulate blocking frequency and persistence better than CMIP5 models in the Atlantic and Pacific and in winter and summer. This improvement is sizeable so that, for example, winter blocking frequency in the median CMIP5 model in a large Euro-Atlantic domain is underestimated by 32 % using the absolute geopotential height (AGP) blocking index, whereas the same number is 19 % for the median CMIP6 model. As for the sensitivity of simulated blocking to resolution, it is found that the resolution increase, from typically 100 km to 20 km grid spacing, in the PRIMAVERA models, which are not re-tuned at the higher resolutions, benefits the mean blocking frequency in the Atlantic in winter and summer, and in the Pacific in summer. Simulated blocking persistence, however, is not seen to improve with resolution. Our results are consistent with previous studies suggesting that resolution is one of a number of interacting factors necessary for an adequate simulation of blocking in GCMs. The improvements reported in this study hold promise for further reductions in blocking biases as model development continues.
Correlation based snapshot models of the archeomagnetic field
Authors: Schanner Maximilian Arthus , Mauerberger Stefan , Korte Monika , Holschneider Matthias
Published: March 2020

For the global time stationary geomagnetic core field, a new modeling concept for Holocene archeomagnetic data is presented. Major challenges consist of the uneven data distribution, missing vector field components and non-linear relations between observations and the geomagnetic potential. Instead of a truncated spherical harmonics approach, we propose a fully Bayesian, Gaussian process based model. Inherently, the Bayesian approach provides location dependent uncertainties.

The geomagnetic potential is assumed to be a Gaussian process whose covariance structure is given by an explicit kernel function, including several hyperparameters. For this kind of non-parametric models, the full Bayesian posterior is numerically intractable. Instead, we propose an approximate computation using a Bayesian update system. In a first step, the full vector records are used to obtain, within Laplace approximation, a rough field estimate. This estimate serves as a point of linearization for the non-linear observations. The approximate posterior is then given by a Gaussian mixture. Marginals for all relevant parameters and the field itself can be computed. We are able to quantify the impact of data coverage on uncertainty reduction.
Evaluation of the analog-based method for the operational implementation in Croatia
Authors: Odak Plenkovic Iris , Panezic Suzana , Keresturi Endi
Published: March 2020

Even the state-of-the-art mesoscale models exhibit noteworthy errors, especially in the complex terrain. Therefore, it is useful to include post-processing methods in the forecasting system to further reduce starting model errors at locations where measurements are available. 
The analog-based method (ABM) is a point-based post-processing approach which consists of two steps. The first step is to find the most similar past numerical weather predictions (analogs) over several variables (predictors) and the second is to form an analog ensemble (AnEn) out of the corresponding observations. 
The ABM is thoroughly tested using the wind speed NWP input, focusing on the complex terrain. Since August 2019 it is used in a test operational mode at Croatian Meteorological and Hydrological Service. The setup includes 15 members wind speed, wind gusts and temperature ensemble predictions for approximately 50 stations using the 2-year training dataset. The preliminary results show that the ABM implementation is successful, reducing the error and improving the skill of the raw model. Additionally, it is found that the ABM predictions of wind speed and gusts optimally need more predictors than the temperature predictions. Finally, the forecasting system shows the best result in the coastal region for the temperature predictions, while the best results for the wind speed are achieved in the nearly flat continental terrain situated more inland. 