julilili42/papers huggingface dataset:
Effects of seasonal variations in vegetation cover and precipitation rates on catchment-scale erosion rates
2022-03-26

&amp;lt;p&amp;gt;Precipitation in wet seasons is the main driver of fluvial erosion and accounts for a significant contribution to annual erosion rates. However, wet seasons also encounter an increase in vegetation cover, which helps to resist erosion. This study quantifies the implications of present-day seasonal variations in rainfall and spatially variable vegetation cover on erosion rates over distinct climate-vegetation settings. We do this using the Landlab-SPACE landscape evolution model modified to account for weathering, rainfall-infiltration-runoff, and the effects of vegetation cover on hillslope and fluvial processes. The input parameters also include present-day SRTM DEM (90m) for the initial condition, MODIS NDVI, and weather station observations of precipitation (between 2000 &amp;amp;#8211; 2019). The soil properties (input parameters) and dynamically evolving soil depths were considered to estimate soil-water infiltration using the Green-Ampt method. Simulations were tuned to four selected catchments in the Chilean Coastal Cordillera (~26 &amp;amp;#176;S &amp;amp;#8211; ~38 &amp;amp;#176;S) which contains a steep climate (from arid to temperate humid) and ecological gradient with similar granodiorite lithology and tectonic forcings. The size (and mean slopes) of the catchments range from 64 (8&amp;amp;#176;) &amp;amp;#8211; 142.5 km&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt; (23&amp;amp;#176;). These catchments are not in steady-state with a background uplift rate of 0.05 mm yr&amp;lt;sup&amp;gt;-1&amp;lt;/sup&amp;gt;. We designed multiple sets of simulations to explore the sensitivity of catchment scale erosion rates to seasonal variations in precipitation and/or vegetation cover. The simulations were conducted for 1,000 years (20 years of vegetation and precipitation observations repeated 50 times) with a time-step of 1 season (3 months). After detrending the results for long-term transient changes, the last 20 years were analyzed. Results indicate that when vegetation cover is varied but precipitation is held constant then the amplitude of change in erosion rates is very low (e.g. 17% in the humid setting). Whereas, in simulations with variable precipitation change and constant vegetation cover, and coupled variations in both precipitation and vegetation cover, the amplitude of change in erosion rates is higher and in a similar range (e.g., 95% in the humid setting). The results during wet seasons also indicate that erosion in the semi-arid region is ~2 times and ~4 times more sensitive than mediterranean and humid regions respectively. However, minimal erosion is observed in the arid setting, due to low precipitation subjected to soil infiltration which leads to lower runoff than the erosion threshold. Overall, we found that at a seasonal scale, erosion rates are significantly influenced by precipitation variations and base vegetation cover (moderately by seasonal variations). Secondly, the vulnerability of erosion rates to weather seasonality increases from humid to semi-arid regions.&amp;lt;/p&amp;gt;
Influence of climate change and CO2 fertilization on vegetation and catchment erosion: A coupled modelling approach
2022-03-26

&amp;lt;p&amp;gt;The Earth&amp;amp;#8217;s surface is shaped by a complex interplay between tectonics, lithology, climate and biota. Previous work has shown that vegetation cover effects on erosion rates are non-linear and depend on the ecosystem investigated. Vegetation cover is not only influenced by climate (via changes in precipitation, temperature and solar radiation) but also by changes in the atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentration through a fertilization effect and increased water use efficiency. However, disentangling the influence of variable climate or atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentrations on vegetation cover, and hence erosion rates, is difficult. Here we present results from a series of coupled model runs aimed at quantifying the non-linear interactions between these different processes.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We apply a landscape evolution model (Landlab) that is coupled to a dynamic vegetation model (LPJ-GUESS) driven by general circulation model predictions of climate change over the last 21 kyr. Three different scenarios are simulated from the Last Glacial Maximum to present-day: 1) Changing climate and changing atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentration; 2) Changing climate but constant atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentration; and 3) Constant climate but changing atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentration. The simulations are adapted to represent four study areas along the extreme climate and ecological gradient of the Chilean Coastal Cordillera (26 &amp;amp;#186; to 38&amp;amp;#186; S). Results indicate that transients in climate and CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; from glacial to interglacial conditions induce a ~10-25% temporal change in catchment erosion, and should be detectable with different measurement techniques. In more detail, we find that precipitation changes exert a stronger influence on erosion rates than changing atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentrations. However, the relative roles of precipitation vs. plant-physiological CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; effects on catchment erosion varies with the climate and ecological zone investigated such that the effects of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fertilization on erosion are larger in temperate than arid settings.&amp;lt;/p&amp;gt;
Time-dependent electromagnetic scattering from thin layers
2022-03-27

Abstract The scattering of electromagnetic waves from obstacles with wave-material interaction in thin layers on the surface is described by generalized impedance boundary conditions, which provide effective approximate models. In particular, this includes a thin coating around a perfect conductor and the skin effect of a highly conducting material. The approach taken in this work is to derive, analyse and discretize a system of time-dependent boundary integral equations that determines the tangential traces of the scattered electric and magnetic fields. In a familiar second step, the fields are evaluated in the exterior domain by a representation formula, which uses the time-dependent potential operators of Maxwell’s equations. The time-dependent boundary integral equation is discretized with Runge–Kutta based convolution quadrature in time and Raviart–Thomas boundary elements in space. Using the frequency-explicit bounds from the well-posedness analysis given here together with known approximation properties of the numerical methods, the full discretization is proved to be stable and convergent, with explicitly given rates in the case of sufficient regularity. Taking the same Runge–Kutta based convolution quadrature for discretizing the time-dependent representation formulas, the optimal order of convergence is obtained away from the scattering boundary, whereas an order reduction occurs close to the boundary. The theoretical results are illustrated by numerical experiments.
The deglacial forest conundrum
2022-03-27

&amp;lt;p&amp;gt;&amp;lt;span&amp;gt;The forest expansion in the Northern Hemispheric extra-tropics during the deglaciation, i.e. the last some 22,000 years, starts earlier and occurs much faster in our model simulation using the MPI-ESM 1.2 than in the recently published synthesis of biome reconstructions by Cao et al. (2019). As a result, the simulated Northern Hemisphere maximum in forest cover is reached at 11ka in the model, whereas &amp;lt;/span&amp;gt;&amp;lt;span&amp;gt;the &amp;lt;/span&amp;gt;&amp;lt;span&amp;gt;forest &amp;lt;/span&amp;gt;&amp;lt;span&amp;gt;distribution&amp;lt;/span&amp;gt;&amp;lt;span&amp;gt; peaks substantially later (at 7ka in the spatial mean) in the reconstructions. The model-data mismatch is largest in Asia, particularly in Siberia and the East Asian monsoon margin. The simulated temperature trend is in line with pollen-independent temperature reconstructions for Asia. Since the simulated vegetation adapt to the &amp;lt;/span&amp;gt;&amp;lt;span&amp;gt;simulated &amp;lt;/span&amp;gt;&amp;lt;span&amp;gt;climate within decades, the temporal model-data mismatch with respect to the forest cover may indicate that pollen records are not in equilibrium with climate on multi-millennial timescales. &amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;span&amp;gt;Our study has some far-reaching consequences. Pollen-based vegetation and climate reconstructions are commonly used to evaluate Earth System Models against past climate states, but to what extent the reconstructed vegetation is in equilibrium with the climate at the reconstructed time slice is still a matter of discussion. &amp;lt;/span&amp;gt;&amp;lt;span&amp;gt;Our results raise the question on which time-scales pollen-based reconstructions are reliable. &amp;lt;/span&amp;gt;&amp;lt;span&amp;gt;Although, it is so far not possible to identify the causes of the mismatch between our simulations and the reconstruction, we suggest critical re-assessment of pollen-based climate reconstructions.&amp;lt;/span&amp;gt;&amp;lt;span&amp;gt; Last, but not least, our&amp;lt;/span&amp;gt;&amp;lt;span&amp;gt; results may also point to a much slower response of forest biomes to current and future ongoing climate changes &amp;lt;/span&amp;gt;&amp;lt;span&amp;gt;than Earth System Models currently predict.&amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;span&amp;gt;References: &amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Cao, X., Tian, F., Dallmeyer, A. and Herzschuh, U.: Northern Hemisphere biome changes (&amp;gt;30&amp;amp;#176;N) since 40 cal ka BP and their driving factors inferred from model-data comparisons, Quat. Sci. Rev., 220, 291&amp;amp;#8211;309, doi:10.1016/j.quascirev.2019.07.034, 2019.&amp;lt;/p&amp;gt;
Integrating Raman spectroscopy and LA-ICP-MS 2D imaging to decipher the localisation and chemistry of impurities on the micro-scale in Greenland ice: Consistencies and open question
2022-03-27

&amp;lt;p&amp;gt;Impurities in polar ice play, among others, a crucial role as a proxy for the paleoclimate while at the same time impacting the internal deformation of ice on the micro-scale. In particular, solid and dissolved impurities can impact grain growth through Zener pinning or the drag of grain boundaries. Recent studies on natural ice from Antarctica and Greenland highlight the need for a multi-method approach to determine the differences in the localisation and chemistry of solid and dissolved impurities comprehensively, in order to ultimately gain a more holistic understanding. Here we report on a recent pilot investigation pursuing the direct integration of complimentary methods: microstructure-mapping, Cryo-Raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with 2D impurity imaging. While LA-ICP-MS enables the fast mapping of cm-size areas with lateral resolution in the order of tens of &amp;amp;#956;m, Raman spectroscopy is more suited to identify the mineralogical composition of individual solid inclusions at the single &amp;amp;#956;m scale. We analysed samples from the Holocene and Last Glacial from the Northeast Greenland Ice Core Project (EGRIP) and the North Greenland Eemian Ice Drilling (NEEM) ice cores. We find that the general localisation patterns of impurities (e.g., low vs. high concentration) are similar for both methods. Furthermore, both methods show (clusters of) inclusions in the grain interior. These findings display that a holistic approach is needed to truly decipher the localisation of impurities in the ice microstructure. Combining the advantages of both methods gives a good overview of the localisation of impurities, both solid and dissolved, on the micro-scale. Localisation patterns are related to the chemistry of the analysed impurities displaying the need for high-resolution methods. For example, Na is strongly located in the grain boundaries, Al is preferentially located within the ice grains and Mg can be located in both regimes. We analyse the role of inclusions in relation to 1) their chemistry and 2) their proximity to grain boundaries. Our approach of 2D impurity imaging in concert with established techniques, such as microstructure mapping and Raman spectroscopy, provides a detailed insight into the impurity distribution throughout a broad range of depths in an ice core. We demonstrate the potential of such an approach to carefully investigate the evolution of impurity localisation in ice cores, with special significance to ice deformation processes and the preservation of the climatic record.&amp;lt;/p&amp;gt;
Thermo-kinematic evolution of the Eastern Alps along TRANSALP: Exploring the transient tectonic state towards slab reversal
2022-03-27

&amp;lt;p&amp;gt;The Eastern Alps are shaped by the indentation of Adria into Europe and exhibit a doubly-vergent lithospheric wedge geometry. Immediately after the subduction of the Penninic ocean, pro- and retro-wedges have been established in the European and Adriatic plates, respectively. Recent tomographic studies, depicting several detached slab fragments beneath the Alps, have been interpreted as evidence of continuous southward subduction, contrary to an often-invoked subduction polarity reversal. Systematic changes in orogen-scale exhumation, driven by rock displacement along active faults, should reflect such change in subduction polarity. Low temperature thermochronology can evaluate upper lithospheric cooling as a response to changes in tectonic and/or erosional boundary conditions. This study investigates whether a potential change in locations of the pro- and retro-wedges is reconcilable with observed crustal re-organisations, exhumation patterns and mantle tomography. A suite of thermo-kinematic forward models driven by a new 2D structural-kinematic reconstruction of continental collision along the TRANSALP profile in the Eastern Alps has been subject to systematic sensitivity analyses encompassing variations in shortening rates, thermophysical parameters and topographic evolution, supplemented by new apatite and zircon fission-track data. Results from the thermo-kinematic modelling reproduce: (i) the orogen-scale structural geometry, (ii) the distribution of low-temperature thermochronometer ages, (iii) independently determined time-temperature paths, and (vi) the present-day surface heat flux. We suggest that the observed thermochronologic record along the TRANSALP profile is primarily driven by cooling through rock displacement along active faults. Our thermo-kinematic reconstruction emphasises a systematic southward shift of deformation, in particular in the Southern Alps, since onset of motion along the Tauern Ramp. Interpreting both, the Tauern Ramp as a mega retro-thrust and the southward shift of deformation in the Southern Alps, as a response to new Coulomb-wedge criterions, then our results are consistent with a Mid-Miocene reversal of continental subduction polarity. This time frame is compatible with a detachment of the European slab and a tectonic re-organisation of the Eastern Alps since ~10-25 Ma.&amp;amp;#160;&amp;amp;#160;&amp;amp;#160;&amp;lt;/p&amp;gt;
Climatic imprint in the mechanical properties of ice sheets and its effect on ice flow. Observations from South Pole and EPICA Dome C ice cores
2022-03-27

&amp;lt;p&amp;gt;The climatic conditions over ice sheets at the time of snow deposition imprint distinctive crystallographic properties to the resulting ice. As it gets buried, its macroscopic structure evolves due to vertical compression and horizontal extension but retains traces of the climatic imprint that generate distinctive mechanical, thermal and optical properties. Because climate alternates between glacial periods, that are colder and dustier, and interglacial periods, the ice sheets are composed from layers with alternating mechanical properties. Here we compare ice core dust content, crystal orientation fabrics, borehole temperature and englacial vertical velocity, measured with phase-sensitive radar (ApRES), at South Pole and EPICA Dome C ice cores. Similarly to previous observations, we show that ice deposited during glacial periods develops stronger crystal orientation fabrics. In addition, we show that ice deposited during glacial periods ice is harder to vertically compress and horizontally extend but softer to shear. These variations in mechanical properties are ignored in ice-flow modelling but they could be critical to interpret ice core records. Also, we show that the changes in crystal orientation fabrics due to transitions from interglacial to glacial conditions can be detected by radar. This information can be used to constrain age-depth in future ice-core locations. Finally, we give our perspective on how radar-detected crystal orientation fabric and englacial vertical velocity can be used to investigate the mechanical properties of ice, its rheology, that are the core of every ice flow model.&amp;lt;/p&amp;gt;
Cytotoxicity as a proxy for particle-associated and dissolved organic contaminant loads in rivers during floods
2022-03-27

&amp;lt;p&amp;gt;Storm events lead to a mobilization of dissolved and particle-associated organic pollutants that pose a risk to river ecosystems. Target screening can hardly capture the broad range of compounds present in stormwater and receiving streams. Thus, an additional monitoring proxy that describes the overall chemical load in stormwater is needed. Each chemical in a mixture contributes, albeit with different potency, to cytotoxicity measured by reduction of cell viability after 24h in four human cell lines. Thus, the aim of this study was to investigate the applicability of cytotoxicity as a proxy for the organic contaminant load of rivers during storm events. Field investigations took place in the Ammer River (annual average discharge 0.87 m&amp;amp;#179; s&amp;lt;sup&amp;gt;-1&amp;lt;/sup&amp;gt;) close to T&amp;amp;#252;bingen, Germany, during intense precipitation events in June 2021. The sampling site was located at the outlet of the gauged catchment (134 km&amp;amp;#178;), thus, integrating inflowing water from all upstream tributaries and sewer overflows. During storm events, high-resolution temporal monitoring of discharge, suspended particles, particle characteristics, as well as dissolved and particle-associated organic contaminants was conducted using both chemical analyses and cell-based &amp;lt;em&amp;gt;in vitro &amp;lt;/em&amp;gt;bioassays. The cytotoxicity in the water phase (expressed as toxic units, TU), was similar among the cell lines. The TU flux followed the course of the hydrograph with highest values at the maximum or slightly after the discharge peak. This finding suggests that the chemical load is controlled by the transported volume of water despite the fact that different contaminant sources are likely to contribute to the water flux and pollutant load in the river at different time points of the hydrograph. For the particle-associated cytotoxicity, the TU flux also followed the course of the events suggesting that the particle-associated cytotoxicity in the river is, similar to the water cytotoxicity, controlled by the particle load in the river. This highlights that the cytotoxicity is a suitable proxy to detect mixtures of organic compounds and, thus, assess the chemical load in rivers during storm events.&amp;lt;/p&amp;gt;
Controls on along-strike variations of basin development: a case study of the Northern Alpine Foreland Basin
2022-03-27

&amp;lt;p&amp;gt;The Northern Alpine Foreland Basin developed in response to the collision between the European and Adriatic plates. During the Oligocene-Early Miocene coeval along-strike deposition of terrestrial and deep marine conditions are recorded in the western and eastern parts of the basin respectively. However, the mechanisms driving the observed variability in along-strike development of the basin are still poorly understood.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;To study the causes of the observed along-strike variability we review published geological data and (re)interpret available 2D and 3D seismic data, constrained by well data. We interpret (1) seismic facies, (2) stratigraphic surfaces and (3) tectonic structures. Our current focus area covers the transitional zone between the western and eastern parts of the basin.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In our study we distinguish 6 stratigraphic surfaces from the Base Tertiary to the Top Aquitanian. From Upper Swabia to the German-Austrian border (along the basin strike) we observe that the top of the crystalline basement is tilted towards the east with an angle of 2-3&amp;amp;#176;. Furthermore, the base of the Tertiary deposits is also tilted towards the east with an angle of 0.3&amp;amp;#176;. The main structural features are E-W and NW-SE striking normal faults. In the western part of our study area the normal faults cut the crystalline basement, Mesozoic and Oligocene deposits. The faults are sealed by Rupelian deposits. Thickness changes (~20 m) occur in Rupelian and overlying Chattian deposits. Maximum offsets of up to 60 m are observed for Mesozoic reflectors. In the eastern part of our study area the normal faults cut the crystalline basement, Mesozoic, Oligocene and Early Miocene deposits. Thickness changes across these faults indicate fault activity during the Rupelian, Chattian and Aquitanian. Maximum offsets (&amp;gt;150 m) are observed for Chattian reflectors. Upper Aquitanian deposits seal these faults, which is younger than observed in the western part of the study area. The NW-SE striking faults confine Paleozoic grabens within the crystalline basement.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We relate the observed normal faulting of the Oligocene and Early Miocene deposits to flexural downbending of the European plate, assumed to have been caused by tectonic loading of the Alps and/or European slab pull. Furthermore, we suggest that the observed temporal variation in termination of fault activity is related to temporal and spatial variations in tectonic loading of the Alps and/or European slab pull. Finally, based on the observed eastward tilt of the top crystalline basement and Base Tertiary along the basin strike, variations in pre-existing crustal architecture must be considered.&amp;lt;/p&amp;gt;