1,720,982 research outputs found
Linear and weakly nonlinear analyses on morphological instabilities
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Three Years of Field Trials Indicate a Sustained Enhanced Rock Weathering Signal with Limited CO2 Removal
Full text linkEnhanced rock weathering (ERW) is a CO2 removal technology that involves spreading finely ground silicate rock on fields. The chemical weathering of this rock powder removes atmospheric CO2 in the form of bicarbonate ions and secondary carbonates. Despite some promising theoretical simulations and laboratory findings, results from field trials that evaluate the ERW’s impact on soil biogeochemistry and CO2 removal are still scarce. This study investigated the impact of basaltic rock powder applied at the equivalent rate of 20 t per hectare (2 kg m–2) in three temperate vineyard fields in Switzerland over 1000 days. Analyses of soil pore water revealed that most standard ERW monitoring proxies (pH, electrical conductivity, total dissolved inorganic carbon, calcium, and magnesium concentrations) did not increase significantly. By contrast, sodium concentration in soil pore water was on average 3-fold higher in the rock powder-treated plots, indicating active mineral dissolution. Integrating the pore water results with model analyses, we estimated that the average CO2 removal rate was 100 ± 30 kg CO2 ha–1 yr–1, which is 10 to 30 times lower than the upper rates reported in some previous modeling and experimental studies. Future work is now needed to improve our understanding of ERW’s CO2 removal potential and soil contamination under a variety of soils, rock feedstocks, and climate conditions
Stochastic ice stream dynamics
No full textIce streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution
Unexpected Transient Dynamics of Meandering Rivers With Unsteady Flows
Full text linkRiver meandering dynamics are here explored in light of unsteady water flows. While mathematical models have usually focused on constant discharges—a reasonable and widely adopted approach for long-term considerations—we show that varying flows strongly affect the short-term planimetric evolution of meanders, before the cutoff occurrence. In particular, flow variability slows down the meanders' dynamics while does not significantly influence the wavelength selection. We support our arguments with numerical simulations and theoretical (linear and nonlinear) analyses, showing that an interplay between out-of-phase river geometry and flow is responsible for the meander-dynamics slowdown. Our results suggest that accounting for flow variability is critical in assessing yearly to decadal meander dynamics with important implications for river engineering and management strategies.CHANG
Soil Structure and Mixing Controls on Water‐Rock Contact: Implications for Enhanced Weathering
Full text linkEnhanced weathering (EW), the addition of finely ground silicate rock powder (RP) to soil, has
emerged as a promising carbon removal strategy. However, quantifying weathering rates in soils remains
challenging, as most continuum‐scale EW models do not adequately account for the fraction of RP surface area
(SA) that is wet at a given soil moisture and thus actively weathering. Here, we study how soil pore structure, RP
particle size distribution, and RP mixing degree within the soil control water‐rock contact. Using a soil‐physics‐
based framework, we derive a scaling factor that quantifies the wet fraction of RP SA as a function of soil
moisture and mixing degree within soil pores. This scaling factor varies nonlinearly with soil moisture for
typical soil pore structures and RP particle size distributions, countering previous zero‐order (independent of
soil moisture) or linear assumptions. The scaling factor evolves dynamically with hydrological fluctuations and,
for a given pore structure and RP mixing degree, it can span nearly two orders of magnitude with changes in
median particle size. To illustrate its application, we integrate the derived scaling factor into the Soil Model for
Enhanced Weathering and examine the sensitivity of simulated weathering fluxes to mixing degree under
otherwise identical conditions. Under low mixing, results show that average weathering rates are roughly two
orders of magnitude lower than under perfect mixing over 1 year of application. Our work provides a
mechanistic, computationally efficient framework for representing water‐rock contact in soil, offering a
pathway to improve continuum‐scale EW models
Nonlinear and subharmonic stability analysis in film-driven morphological patterns
Full text linkThe interaction of a gravity-driven water film with an evolving solid substrate (calcite or ice) results in the formation of fascinating wavy patterns similar both in caves and in ice-falls. Due to their remarkable similarity, we adopt a unified approach in the study of pattern formation of longitudinally oriented organ-pipe-like structures, called flutings. Since the morphogenesis of cave patterns can evolve for millennia, they have an additional value as silent repositories of past climates. Fluting formation is studied with the aid of gradient expansion and center manifold projection. In particular, through gradient expansion, a Benney-type equation accounting for the movable boundary is obtained. The coupling with a wall evolution equation provides a morphodynamic model for fluting formation, explored through linear and nonlinear analyses. In this way, closed relationships for the selected wave number and for the finite amplitude are achieved. However, as finite-amplitude monochromatic waves may be destabilized by nonlinear interactions with other modes, we verify, through center manifold projection, the stability of the fundamental to subharmonic disturbances. Conclusively, we perform numerical simulations of the fully nonlinear equations to validate the theory results
Calibration of a stochastic model for riparian vegetation dynamics from LiDAR acquisitions
Full text linkThe distribution of phreatophyte riparian vegetation can be described by a stochastic model for vegetation growth. According to this, vegetation dynamics are influenced by the topography of the riparian transect and the randomness of hydrological fluctuations, acting as a dichotomous Markov noise. Also, the response of vegetation to this forcing, i.e. its rate of growth and decay, depends of its intrinsic biological features, which are represented in the model by specific input parameters. Although most of these parameters has already been set and literature values provided for the most common tree species in riparian environments, the one representing the vegetation decay still needs to be properly calibrated.
To this purpose, a segment of Cinca River (Spain) is here modelled, aiming to obtain a calibration of the decay rate of riparian vegetation in temperate climate. The choice of the study river was done according to the availability of hydrological and LiDAR data. The processing of LiDAR raw data allowed to define the digital terrain model of the study area, providing the geometrical input data of the model. Moreover, LiDAR acquisitions returned a measure of vegetation height and its spatial density, thus leading to the estimation of riparian above-ground biomass, which represents the model output. As the decay rate was the sole unknown parameter for the modelling of the study river, its calibration was possible. Furthermore, as LiDAR provided a highly detailed geometry, the outcome of calibration was not a single value of decay rate for the entire riparian corridor, but a set of values for increasing altitude bands, thus allowing the investigation of its relation with topographic positio
Reanalysis of NOAA H2 observations: implications for the H2 budget
Full text linkHydrogen (H-2) is a promising low-carbon alternative to fossil fuels for many applications. However, significant gaps in our understanding of the atmospheric H-2 budget limit our ability to predict the impacts of greater H-2 usage. Here we use NOAA H-2 dry air mole fraction observations from air samples collected from ground-based and ship platforms during 2010-2019 to evaluate the representation of H-2 in the NOAA GFDL-AM4.1 atmospheric chemistry-climate model. We find that the base model configuration captures the observed interhemispheric gradient well but underestimates the surface concentration of H-2 by about 10 ppb. Additionally, the model fails to reproduce the 1-2 ppb yr(-1) mean increase in surface H-2 observed at background stations. We show that the cause is most likely an underestimation of current anthropogenic emissions, including potential leakages from H-2-producing facilities. We also show that changes in soil moisture, soil temperature, and snow cover have most likely caused an increase in the magnitude of the soil sink, the most important removal mechanism for atmospheric H-2, especially in the Northern Hemisphere. However, there remains uncertainty due to fundamental gaps in our understanding of H-2 soil removal, such as the minimum moisture required for H-2 soil uptake, for which we performed extensive sensitivity analyses. Finally, we show that the observed meridional gradient of the H-2 mixing ratio and its seasonality can provide important constraints to test and refine parameterizations of the H-2 soil sink
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