julilili42/papers huggingface dataset:
Deformation and recrystallization inside the Northeast Greenland Ice Stream &#8211; findings from microstructural analysis of the EastGRIP ice core
2024-03-08

Solid ice discharge from land-based ice masses into the ocean raises the global sea level and accelerates due to anthropogenic climate change. Modelling ice flow dynamics aims to provide better projections of future sea level rise. The Antarctic and Greenland ice sheets are predominantly drained through ice streams, which are regions of higher ice flow velocity than their surroundings, and thus play an important role in ice sheet dynamics. However, little is known about their rheology. Therefore, they may introduce large uncertainties in ice sheet models.In order to study the main deformation and recrystallization mechanisms dominant in an ice stream, we conducted microstructural analyses on samples from the EastGRIP ice core that was drilled in the largest Greenlandic ice stream, the Northeast Greenland Ice Stream (NEGIS).The data set contains 1064 samples, oriented vertically and horizontally to the ice core axis, from depths between 111 and 2121&amp;#160;m. Analyses of the deepest 550 m of the ice core are pending. All samples were scanned with 5&amp;#160;&amp;#181;m resolution under bright-field illumination with a Large Area Scanning Macroscope (LASM). The obtained microstructure, i.e. grain shape, size, and elongation, was extracted using digitalised grain boundary networks by means of a machine-learning based image analysis software. We determined six different rheological regimes through the ice column. Most microstructural changes were interpreted as changes in recrystallization mechanisms, whereas the dominant deformation mode, horizontal extension, appears to remain fairly constant below 500&amp;#160;m of depth. Previous numerical high-strain ice deformation simulations showed strain localisation with the development of visible shear bands. A similar setting was expected inside ice streams, but at the investigated depths of the EastGRIP ice core, no clear shear bands could be discerned so far for the applied sampling resolution.These results indicate that NEGIS has no strong high-strain localisation down to 2121&amp;#160;m depth but probably deforms as a block with extension along flow. The high ice flow velocities, therefore, might have to be compensated either in the lowest 500&amp;#160;m or below the ice.
Resolving volcanic from anthropogenic metal input to modern lake Elmenteita, Kenya
2024-03-08

Lake Elmenteita located in the central Kenyan Rift System is a shallow (ca. 1 m deep on average), hyper-saline and alkaline playa lake of international bio-ecological importance, as emphasized by its classification as RAMSAR site (2005) and UNESCO world heritage site of &amp;#8220;outstanding universal value&amp;#8221; (2011). Unusually high rainfall and anthropogenic influence (deforestation, agriculture, sewage loading) are current drivers of changes in water level, composition and quality as well as the dramatic decline in riparian habitats. Identifying individual sources of both, elemental nutrients (P, N, Mg, Si, Zn) and potentially toxic elements (heavy metals, e.g., Cs, Mo, Pb, Sb, Cu) to the lake is imperative for ecosystem monitorization and development of biodiversity conservation strategies.Here, we present dissolved element concentrations in water samples collected in July 2022 from the 1) central, 2) northern (discharge of rivers Kariandusi and Mereroni), and 3) southern (dominated by tectonically modulated volcanic hot-springs) part of the lake, as well as from 4) river Mereroni and 5) an additional hot-spring in the eastern part of the catchment. Data was acquired in the field and at the laboratories of the Isotope Geochemistry Group, T&amp;#252;bingen University. Results show compositional differences between hot springs and riverine influx (e.g., Cs: 0.03 ng/g Mereroni river vs. 3.3 ng/g S-hot springs), and also between Mereroni river water and northern shore waters (e.g., Sb: 0.063 ng/g Mereroni river vs. 0.92 ng/g N-shore; Cu: 0.925 ng/g Mereroni river vs. 27.3 ng/g N-Shore). Accompanied by observed compositional heterogeneities within the lake itself, our findings suggest that several sources and processes govern the elemental influx and distribution. Using geochemical indices, we will propose elemental dispersion vectors, main sources, and in-lake processes with the aim to unfolding the impact of recent anthropogenic signals from volcano-tectonic elemental origins to the lake.
Computationally efficient evaluation of Earth System Models in the presence of complex uncertainties
2024-03-08

Comparing Earth System Model (ESM) simulations with in-situ, lab, and remote sensing measurements often involves analytically intractable uncertainty structures for example due to observational uncertainties, internal variability in the climate system, and limitations of ESMs. With increasing resolution of models, ensemble sizes, length of simulations, and number of observations, this can create computational bottlenecks. Making use of Monte Carlo techniques in a data cube architecture, we present a python package for efficient propagation of complex uncertainties in model-data comparison. Additionally, the package contains functionalities for visualizations of uncertainties and the computation of probabilistic score functions.Our focus is on measurement operators, in particular so-called proxy system models that map ESM output onto proxy measurements for transient paleoclimate simulations. Proxy system models contain multiple sources of autocorrelated and non-Gaussian uncertainties due to complex proxy-climate relationships, chronological uncertainties, and processes perturbing the recorded climate signal during the sedimentation of the proxy. Thereby, we connect data cube methods for processing climate simulations with analysis techniques for point data such as those stemming from time series of paleoclimate proxy records. We demonstrate our approach by quantifying the discrepancies of temperature and forest cover changes between global proxy networks and transient simulations from the Last Glacial Maximum to present-day. Given the ongoing shift in the paleoclimate modelling community from equilibrium time-slice towards long transient simulations, our work can help integrate the evaluation of simulations from the Paleoclimate Modelling Intercomparison Project (PMIP) into CMIP7 model benchmarking. Additionally, the implemented methods are transferable to other types of observations that are subject to analytically intractable uncertainty structures.
South Atlantic Convergence Zone impacts on climate and vegetation changes over the last 16,000 years in Central Brazil based on a speleothem multi-proxy record
2024-03-08

The South American Monsoon System (SAMS) plays an important role in the hydroclimate variability and rainfall patterns across South America. Stemming from its convective core in the southwestern Amazon basin, the South Atlantic Convergence Zone (SACZ) is a southeastward convection band, being a critical component of SAMS responsible for large-scale moisture transport, particularly over Central Brazil. Previous paleoclimate studies suggest that SACZ has changed over time, usually associated with changes in the SAMS, and there are current debates regarding the nature of SACZ, shifts in position, size, and intensity, and their potential impacts on vegetation changes. Therefore, this study addresses these debates for the last 16,000 years based on a novel multi-proxy paleorecord of &amp;#948;18O, &amp;#948;13C, and Sr isotope ratios (87Sr/86Sr) from a stalagmite collected in S&amp;#227;o Mateus Cave at the northeast limits of SACZ in central Brazil. This site is therefore under the regime of SACZ, with a climate characterized as tropical semi-humid with a rainy summer season and a dry winter.The inclusion of Sr isotope data enhances our interpretation of past local climate variability since changes in 87Sr/86Sr can provide valuable information about the water residence in the epikarst and changes in soil composition. Furthermore, as S&amp;#227;o Mateus Cave lies within the Cerrado biome, it offers a unique insight into the past climate and environmental changes in central Brazil due to its distinct floral compositions influenced by factors such as location, soil, rainfall distribution, and fire frequency. Comparisons with other paleoclimate data from SACZ-influenced sites are made to access climate and vegetation changes in different locations within this convective band, particularly over larger time scales, such as the transition from the Late-Pleistocene to the Holocene and longer trends. We demonstrate that even though there is a common change in the regional &amp;#948;18O signal connected with SACZ variations, differences in vegetation and local moisture between northern and southern SACZ limits are evident albeit being in the same biome. This multi-proxy approach, combining traditional stalagmite proxies with high-resolution LA-MC-ICP-MS Sr isotope analysis, offers a better understanding of SACZ changes and their implications for Central Brazil's climate and environment.&amp;#160;
Interhemispheric teleconnections as drivers of Southern Hemisphere climate in simulations of spontaneous Dansgaard-Oeschger-type events
2024-03-08

Dansgaard-Oeschger (DO) events are a dominant mode of millennial-scale climate variability during the last glacial period. While the influences of DO events are most pronounced in the North Atlantic region, their impacts are detectable on the global scale. In Antarctica, their imprint primarily manifests as a muted and anti-phased response, which can be explained by the bipolar seesaw mechanism. However, the ice core record revealed an additional in-phase component, suggesting the presence of atmospheric teleconnections.Here, we study the propagation of DO-type signals from the North Atlantic to the Southern Hemisphere in a set of simulations with the general circulation model HadCM3, including an isotope-enabled run. The simulations show spontaneous DO-type oscillations under glacial boundary conditions, which allows studying the timing and interaction of atmospheric and oceanic processes under a continuously varying background state. Consistent with the ice core record, we find a muted and anti-phased temperature response over Antarctica that lags the North Atlantic by ~300 years, and global sea surface temperature patterns in agreement with the bipolar seesaw mechanism. Additionally, we identify a robust Southern Hemisphere mode in phase with the North Atlantic. This mode is associated with hydroclimate changes in the tropical Pacific, which modulate the Southern Hemisphere atmospheric circulation, and, thereby, impact Antarctic temperatures. Notably, the dominant millennial-scale circulation pattern exhibits zonal asymmetries that do not resemble the leading modes of inter-annual variability. Preliminary analyses indicate a good agreement of the simulated millennial-scale variability in oxygen isotopes with a global compilation of speleothem and ice core records.
Thermal and thermohaline variable-density flow and salt transport in a 2D flow tank: Experiments, visualization and modelling
2024-03-08

We carried out laboratory experiments of free thermal and thermohaline convection in homogeneous isotropic media using a laboratory-scale two-dimensional tank filled with glass beads representing a porous medium. Glass beads of different diameter were used in different experiments to achieve different permeabilities of the porous medium. Density and viscosity of the fluid were changed by initially introducing a salt (NaCl) solution, and by applying a heating device placed inside the tank. Fluid temperature inside the tank was measured over time on multiple thermocouples placed inside the tank on the inner glass walls. The fluid was dyed with two color tracers in order to visualize the emerging free convective flow pattern. The convective flow pattern was captured using a digital camera for the tracer distribution, and an IR camera for the temperature distribution. In subsequent numerical simulations, the experiments were successfully simulated numerically including density/viscosity variations and heat loss of the tank to the laboratory air across the back and front glass panes. Flow and transport parameters were calibrated using the results of the experiments with constant salinity. The set of calibrated parameter values was applied to successfully validate a thermohaline experiment with no need for further calibration. The processes of salt (NaCl) transport and heat transfer were both very accurately simulated in a single simulation. Analysis of flow velocities and streamlines showed that flow packages in a convection cell mostly follow a closed path such that there is little radial mixing. The approaches and results presented here can be used for interpretation, testing, and analysis of other simulation software of free thermohaline flow and transport.
Air clathrate hydrates of the Antarctic EPICA Dronning Maud Land ice core
2024-03-08

Polar ice cores are a unique climate archive as they provide the most direct record of past atmospheric gas compositions. In the deeper part of polar ice sheets, most of the ancient air molecules are stored in the crystal lattice of clathrate hydrates (air hydrates). Continuous records of air hydrate number concentration, mean size and shape (geometric properties) exist for the Vostok and Dome Fuji ice cores in Antarctica and the GRIP ice core in Greenland. It was found that the geometric properties correlate with past climatic changes, but also evolve with depth due to physicochemical processes within the ice sheet.The EPICA Dronning Maud Land (EDML) ice core is located on an ice divide in the Atlantic sector of East Antarctica which allows for a comparison to Greenland ice cores. Furthermore, it differs from other Antarctic deep ice cores by a higher accumulation rate and higher annual mean temperatures on site. This makes it possible to analyze air hydrates with a higher temporal resolution (compared to the Dome Fuji and Vostok ice cores). These factors make the EDML ice core interesting for studying air hydrates.We use digital image analysis on ice thick section microphotographs to create a high-resolution record of air hydrate geometric properties below the bubble-hydrate transition zone. The image acquisition was done in the field, within a few days after the sample was drilled, in order to record information of the material before relaxation. Using traditional image analysis algorithms, we can confirm the correlation between climate and air hydrate geometrical properties. In addition, we examine the air hydrate spatial distribution and evolution via depth. Digital object segmentation and object analysis offer many advantages, such as fast and efficient analysis, improved statistical data, higher spatial resolution, over the traditionally used manual methods. We are excited to contribute to the future analysis of air hydrates in polar ice cores.
Exploring the interaction between global changes, soil properties and vegetation patterns on soil phosphorus transformation in alpine grasslands of the Tibetan Plateau
2024-03-08

The grassland ecosystems of the Tibetan Plateau have witnessed substantial transformations in recent decades, driven by various global factors, including alterations in temperature and precipitation, nitrogen (N) deposition, and regional effects. Despite documented shifts in species richness and distribution towards higher elevations, there is a scarcity of comprehensive plant and soil data along elevation gradients in alpine grasslands. The intricate interplay of soil properties and nutrient supply on vegetation patterns at high altitudes, particularly the response of the "grass-line" to global warming, remains unexplored. To bridge these knowledge gaps, our research investigated the impacts of global changes, specifically warming and N deposition, and soil properties on soil phosphorus (P) transformation and plant P uptake. Leveraging insights from long-term nutrient addition experiments, random sampling, and open-top chamber experiments along elevation gradients in an alpine grassland on the northeastern Tibetan Plateau, the study delved into soil properties such as texture, bulk density, soil organic carbon (SOC), and soil P fractions. Furthermore, it explores plant and microbial P pools, P acquisition strategies, and biomass. Results revealed that N input had a discernible effect on plant P requirements, particularly under conditions of deficient soil available P. Changes in P acquisition strategies wielded a more substantial influence on community structure and composition than alterations in root traits. The addition of P significantly impacted plant growth, signifying a shift from nitrogen to P limitation with increased N input. Soil properties exhibited variations among sites, while pH remained stable in the 0&amp;#8211;10 cm soil depth due to the adequate levels of calcium and magnesium in the soil, which could buffer the impact of N deposition on soil acidification in the grassland ecosystem. Strong positive correlations observed between organic P pools, SOC, and total N underscored the pivotal role of soil organic matter in sustaining soil P reserves. More importantly, P limitation did not emerge as the primary factor propelling grasses to higher elevations; instead, other soil properties and nutrients might play a key role. These findings underscore the importance of specific combinations of soil properties in constraining plant growth on the northeastern plateau, thereby influencing biodiversity and biomass production. This research highlights the factors influencing effective soil nutrients and provides valuable insights for predicting the impact of global changes on the stability and productivity of alpine grassland ecosystems.
How ice anisotropy contributes to fold and ice stream in large-scale ice-sheet models
2024-03-08

Satellite and airborne sensors have provided detailed data on ice surface flow velocities, englacial structures of ice sheets and bedrock elevations. These data give insight into the flow behaviour of ice sheets and glaciers. One significant phenomenon observed is large-scale folds (over 100 m in amplitude) in the englacial stratigraphy in the Greenland ice sheet. A large population of folds is located at ice streams, where the flow is distinctly faster than in the surroundings, such as the North-East Greenland Ice Stream (NEGIS). While there is no consensus regarding the formation of large-scale folds, unraveling the underlying mechanisms presents significant potential for enhancing our understanding of the formation and dynamics of ice streams.Ice in ice sheets is a ductile material, i.e., it can flow as a thick viscous fluid with a power-law rheology. Furthermore, ice is significantly anisotropic in its flow properties due to its crystallographic preferred orientation (CPO). Here, we use the Full-Stokes code Underworld2 (Mansour et al.,2022) for 3D modelling of the power-law and transversely isotropic ice flow, also in comparison with the isotropic ice models.Our simulated folds with anisotropic ice show complex patterns on a bumpy bedrock, and are classified into three types: large-scale folds (fold amplitudes &gt;100 m), small-scale folds (fold amplitudes
Full-Field Numerical Simulation of Halite Dynamic Recrystallization From Subgrain Rotation to Grain Boundary Migration
2024-03-08

Full-field numerical modelling is a useful method to gain understanding of rock salt deformation at multiple scales, but it is quite challenging due to the anisotropy and complex plastic behavior of halite and other evaporite minerals at the single crystal level, together with dynamic recrystallization processes. We overcome these challenges and present novel results of full-field numerical simulation of dynamic recrystallization of halite polycrystalline aggregates during simple shear deformation, including subgrain rotation and grain boundary migration recrystallization processes. The results illustrate that the approach successfully reproduces the evolution of pure halite microstructures from laboratory torsion deformation experiments at 100-300&amp;#8451; up to shear strain of four. Temperature determines the competition between (i) grain size reduction controlled by dislocation glide and subgrain rotation recrystallization (at low temperature) and (ii) grain growth associated with grain boundary migration (at higher temperature), while the resulting crystallographic preferred orientations are similar for all cases. The analysis of the misorientation reveals that the relationship between subgrain misorientation and strain follows a power law relationship with a general exponent of 2/3. However, with progressive deformation, dynamic recrystallization leads to a gradual deviation from this relationship. Therefore, predicting strain or temperature from microstructures necessitates careful calibration.
Probabilistic Wind Speed Downscaling for Future Wind Power Assessment
2024-03-08

Wind power and other renewable energy sources are essential for the energy supply. However, due to their dependence on both climate and highly local, variable weather conditions, they are less reliable and challenging to forecast.Recent projections of climate models indicate that the mean annual energy density will change in the future [Pryor et al., 2020]. To avoid costly planning mistakes and improve return on investment, predictions of wind conditions with adequate spatial and temporal resolution are thus indispensable, to facilitate efficient planning of renewables. Recent research regarding the temporal resolution of wind speed data shows that inter-daily wind speed variability can be accounted for by instantaneous data of six-hourly resolution [Effenberger et al., 2024]. However, as wind is a very local phenomenon, the spatial resolution of climate and weather data is paramount in wind power forecasting.Simulated climate data generally lacks the spatial resolution needed for highly localized wind power forecasts and needs to be downscaled. The downscaled data is subject to mainly two types of predictive uncertainty that are often ignored, yet non-negligible for decision-making. Firstly, climate projections depend on unknown physical processes, like the evolution of atmospheric CO2 concentration, and are thus inherently uncertain. We account for this uncertainty by ensembling across different climate models and scenarios. The second source of uncertainty, which is the main focus of this work, is that the coarse resolution of the simulated data introduces additional uncertainty, since interpolating wind speeds spatially is non-trivial. By downscaling different wind speed projections using a probabilistic Gaussian process simulation method, we can model the uncertainty that stems from interpolating wind speed data to unseen locations. Leveraging techniques from physics-informed machine learning, e.g. conditioning on partial differential equations [Pf&amp;#246;rtner et al., 2022], allows for a more realistic model, consistent with the actual dynamics of the atmosphere.The resulting, physics-informed Gaussian process models, provide uncertainty-aware, location-specific wind speed predictions on multi-decadal scales. When planning new turbine locations, these wind speed projections based on climate model data can serve as a proxy for expected future wind power generation.References:Effenberger, N., Ludwig, N., and White, R. H. (2024). Mind the (spectral) gap: how the temporal resolution of wind data affects multi-decadal wind power forecasts. Environmental Research Letters, 19.Pf&amp;#246;rtner, M., Steinwart, I., Hennig, P., and Wenger, J. (2022). Physics-informed Gaussian process regression generalizes linear PDE solvers. arXiv preprint arXiv:2212.12474.Pryor, S. C., Barthelmie, R. J., Bukovsky, M. S., Leung, L. R., and Sakaguchi, K. (2020). Climate change impacts on wind power generation. Nature Reviews Earth &amp;amp; Environment, 1(12):627&amp;#8211;643.&amp;#160;&amp;#160;