Miracle-dz/UniFAR-FTUs huggingface dataset:
The δ18O of atmospheric O2 from air inclusions in the Vostok Ice Core: Timing of CO2 and ice volume changes during the penultimate deglaciation

One important question about the CO2-climate connection is how increasing atmospheric pCO2 levels affect climate and thereby the mass balance of continental ice sheets. A record of atmospheric CO2 variations over the last 160,000 years has recently been constructed by analyzing the trapped gas in the Vostok ice core [Barnola et al., 1987]. The relationship between changes in atmospheric CO2 and the size of the continental ice sheets has been difficult to ascertain because the CO2 record is obtained from ice cores while the ice volume record has been constructed from the stable isotopic composition of biogenic CaCO3 in deep-sea sediment cores. In order to compare these two records in a more precise manner, we present a record of the isotopic composition (δ18O) of atmospheric O2 trapped in the Vostok ice core, and propose that it may be considered a proxy for the δ18O of seawater and hence ice volume. Having a record of atmospheric CO2 along with a continental ice volume proxy in trapped air in the same ice core allows us to compare the timing of changes in these two parameters with little uncertainty in the relative ages of important events. Our results suggest that, during the penultimate glacial termination, atmospheric CO2 began to increase at least 3 kyr before the initial introduction of meltwater to the oceans. Possible errors in the relative age-depth curve of the Vostok ice core and uncertainties in the influence of biological and hydrologic processes on the δ18O of atmospheric O2 introduce some uncertainty into our conclusions. However, our results are in general agreement with the observed phase relationship between atmospheric CO2 and ice volume [Imbrie et al., 1984; Imbrie et al., 1989] (inferred from changes in the δ13C difference between contemporaneous planktonic and benthic forams deposited in deep-sea cores and the SPECMAP ice volume record).
Micro‐X‐ray diffraction assessment of shock stage in enstatite chondrites

Abstract– A new method for assessing the shock stage of enstatite chondrites has been developed, using in situ micro‐X‐ray diffraction (μXRD) to measure the full width at half maximum (FWHMχ) of peak intensity distributed along the direction of the Debye rings, or chi angle (χ), corresponding to individual lattice reflections in two‐dimensional XRD patterns. This μXRD technique differs from previous XRD shock characterization methods: it does not require single crystals or powders. In situ μXRD has been applied to polished thin sections and whole‐rock meteorite samples. Three frequently observed orthoenstatite reflections were measured: (020), (610), and (131); these were selected as they did not overlap with diffraction lines from other phases. Enstatite chondrites are commonly fine grained, stained or darkened by weathering, shock‐induced oxidation, and metal/sulfide inclusions; furthermore, most E chondrites have little olivine or plagioclase. These characteristics inhibit transmitted‐light petrography, nevertheless, shock stages have been assigned MacAlpine Hills (MAC) 02837 (EL3) S3, Pecora Escarpment (PCA) 91020 (EL3) S5, MAC 02747 (EL4) S4, Thiel Mountains (TIL) 91714 (EL5) S2, Allan Hills (ALHA) 81021 (EL6) S2, Elephant Moraine (EET) 87746 (EH3) S3, Meteorite Hills (MET) 00783 (EH4) S4, EET 96135 (EH4–5) S2, Lewis Cliff (LEW) 88180 (EH5) S2, Queen Alexandra Range (QUE) 94204 (EH7) S2, LaPaz Icefield (LAP) 02225 (EH impact melt) S1; for the six with published shock stages, there is agreement with the published classification. FWHMχ plotted against petrographic shock stage demonstrates positive linear correlation. FWHMχ ranges corresponding to shock stages were assigned as follows: S1 < 0.7°, S2 = 0.7–1.2°, S3 = 1.2–2.3°, S4 = 2.3–3.5°, S5 > 3.5°, S6—not measured. Slabs of Abee (EH impact‐melt breccia), and Northwest Africa (NWA) 2212 (EL6) were examined using μXRD alone; FWHMχ values place both in the S2 range, consistent with literature values. Micro‐XRD analysis may be applicable to other shocked orthopyroxene‐bearing rocks.
Mesozoic dipole low: Myth or reality?

Study of the long-term variation of polarity and paleo-direction of the Earth's magnetic field in the Precambrian and Phanerozoic has proved valuable in geosciences. Magnetic polarity in the Mesozoic and Cenozoic is fairly well established, with some first-order trends defined for older times. Defining Earth's comparable long-term dipole moment variation has proved far more difficult [e.g., Selkin and Tauxe, 2000]. Among many other findings, magnetic polarity studies have defined several first-order features like the Permo-Triassic and Cretaceous superchrons, characterized by constant reverse and normal polarity, respectively, over long intervals.
Right-side cooling and phytoplankton bloom in the wake of a tropical cyclone

The rightward tendency (in northern hemisphere) of enhanced phytoplankton bloom often observed in the wake of a tropical cyclone has commonly been attributed to the rightward bias of mixing due to stronger wind and wind-current resonance. We demonstrated using a high-resolution biophysical model that vertical mixing alone resulted only in weak asymmetry after the passage of the storm. The enhanced bloom was caused instead by decreased turbulence due to restratification by submesoscale recirculation cells preferentially produced on the right side, rightward shift of cool isotherms, and spin-up of a subsurface jet. We showed using a two-time scale asymptotic expansion that these slower-evolving features were forced by resonance Reynolds stresses of the energetic and rapidly oscillating near-inertial internal waves.
High resolution sequence stratigraphy; the East Coulee Delta, Alberta

ABSTRACT The fundamental concept on which sequence stratigraphy is based is that stratal architectures develop in response to the interaction between base-level change and sediment flux. A small lacustrine fan-delta at East Coulee, Alberta, illustrates these principles and demonstrates that sequence stratigraphic concepts are scale- and time-independent. This fan-delta formed in a matter of days in a roadside drainage ditch as water level rose and then fell. Changes in the subaqueous space available for sediment to fill (i.e., accommodation) resulted in the development of a succession of systems tracts analogous to those formed within sedimentary basins over much longer time frames. Deposition began during lake-level rise with progradation of a fan-deltaic wedge. Accelerating lake-level rise resulted in a backstepping of the shoreline and deposition of a transgress systems tract. Subsequent lake-level fall resulted in subaerial exposure of the relatively steep delta front and caused incised valley formation and deposition of a lowstand delta. This stratigraphic response to base-level fall is typical of lowstand systems tract development on basin margins characterized by high-relief slopes (e.g., passive margins). Further lake-level fall resulted in minor additional valley incision and development of a second lowstand delta on a surface characterized by lower relief as lowering water level exposed a flatter physiography. This development of lowstand deltas and coa tlines during base-level fall constitutes a forced regression of Posamentier et al. (1990) and is typical of lowstand systems tracts on basin margins characterized by gentle slopes. In spite of its small size, this example clearly illustrates that sequence stratigraphic principles apply to lacustrine as well as marine settings and at all spatial and temporal scales.
Climate fluctuations during the past two millennia as recorded in sediments from Maxwell Bay, South Shetland Islands, West Antarctica

Abstract The climate evolution of the South Shetland Islands during the last c. 2000 years is inferred from the multiproxy analyses of a long (928 cm) sediment core retrieved from Maxwell Bay off King George Island. The vertical sediment flux at the core location is controlled by summer melting processes that cause sediment-laden meltwater plumes to form. These leave a characteristic signature in the sediments of NE Maxwell Bay. We use this signature to distinguish summer and winter-dominated periods. During the Medieval Warm Period, sediments are generally finer which indicates summer-type conditions. In contrast, during the Little Ice Age (LIA) sediments are generally coarser and are indicative of winter-dominated conditions. Comparison with Northern and Southern Hemisphere, Antarctic, and global temperature reconstructions reveals that the mean grain-size curve from Maxwell Bay closely resembles the curve of the global temperature reconstruction. We show that the medieval warming occurred earlier in the Southern than in the Northern Hemisphere, which might indicate that the warming was driven by processes occurring in the south. The beginning of the LIA appears to be almost synchronous in both hemispheres. The warming after the LIA closely resembles the Northern Hemisphere record which might indicate this phase of cooling was driven by processes occurring in the north. Although the recent rapid regional warming is clearly visible, the Maxwell Bay record does not show the dominance of summer-type sediments until the 1970s. Continued warming in this area will likely affect the marine ecosystem through meltwater induced turbidity of the surface waters as well as an extension of the vegetation period due to the predicted decrease of sea ice in this area.
Analysis on Environmental Impact of Deep Excavation in Shenzhen, China

A 30-m-deep foundation pit is excavated into 10-m-thick weathered granite strata in Shenzhen, China. The upper ground over weathered granite is a 20-m strata composed of loose sandy soil and clayey soil with high water content. To evaluate the impact on the surroundings caused by the excavation of the pit, a numerical simulation is performed by finite element method (FEM). Taking account of the interaction of excavation process, retaining structures and soil, simulation is conducted for the process of progressive excavation, support system assembling, and disassembling. Simulation results agree well with measured values and meet the requirements of construction criterion. The FEM model offers an available analysis method for the deformation prediction and design of similar ultra-deep excavation in Shenzhen.
Deformation of an incompressible viscoelastic flat earth with powerlaw creep: a finite element approach

SUMMARY Extrapolating experimental creep data to mantle conditions indicates that the upper mantle may deform as a power-law medium. In all of the previous models of loading/unloading in a power-law medium, some simplifying assumptions were made to keep the calculation tractable. Unfortunately, some of these assumptions are invalid while others are too restrictive. In this paper, the finite element method is used to study the deformation of incompressible linear and non-linear rheological earth models that are subject to constant gravitational acceleration. The advantage of this new approach is that none of these simplifying assumptions has to be made—thus the solution is much more rigorous. The deformation of a non-linear half-space due to Heaviside loading and unloading of a boxcar load is shown to be characterized by: (i) ubiquitous updoming/sinking outside the load; (ii) a very high initial rate of deformation followed by a much slower rate inside the load; and (iii) the load history is fully coupled with the rheology of the earth because the state of stress, caused by the magnitude of the load and the sequence of loading or unloading events, determines the effective viscosity and thus the deformation. It is also demonstrated that the usual assumption of ‘self-similarity’ and ‘proportional relaxation’ are invalid. Moreover, the relaxation time is a function of both space and time. The effect of an elastic lithosphere on a linear or non-linear channel is shown to be much larger than that for a half-space even at small t. The effects of a non-linear channel, a parabolic load and a depth-dependent creep parameter A are also studied. When the observed uplift data near the rebound centre in Fennoscandia are compared to the predicted uplift curves, it is demonstrated that for the instantaneous removal of a 15 MPa boxcar load, power-law rheological models cannot fit the observations as well as the linear models can. However, more work has to be done before one can decide whether the rebound process actually involves a mantle with linear rheology or power-law rheology.
Runoff, soil loss and soil physical property changes of light textured surface soils from long term tillage treatments

A long-term tillage trial was conducted (1981 to 1987) on loamy textured soils to quantify changes in runoff, soil loss and some soil physical properties due to conservation tillage practices. Two sites were established, one at Cowra on a sandy loam textured soil, and the other at Grenfell on a loamy textured soil. The tillage treatments imposed were direct drilling (DD), reduced tillage (RT) and traditional tillage (TT), with grazing at both sites, and a direct drilling ungrazed (NT) treatment at Cowra only. Runoff and soil loss were measured using a rainfall simulator, and sorptivity (S), saturated hydraulic conductivity (Ksat), bulk density to 40 mm (BD4) and 100 mm (BD10), organic carbon (OC) and water stable aggregates (WSA) were measured annually. Runoff decreased significantly in the minimum soil disturbance treatments (NT and DD) at Cowra. Runoff did not decrease in the stubble incorporation treatments despite a significant increase in OC and WSA. Decreases in runoff were due to the development and maintenance of porosity, particularly macropores. Changes in other soil physical properties were generally not significant owing to temporal variability. The regression relationship between OC and WSA, although significant, had little practical value because of high prediction error. Although improvements in soil physical properties were measured, a period of at least five years of cropping at both sites was required before they became significant and consistent.
Accumulation of fallout cesium 137 in soils and sediments in selected watersheds

The fallout of certain radioisotopes produced in nuclear explosions and their subsequent dispersion over the earth provide tracers for following the movement of soil particles in the sedimentation cycle. Cesium 137, which is strongly adsorbed by most soil particles, was identified in sampled soils and sediments by gamma differential spectrometric analysis using a 1024-channel pulse height analyzer ancl a 10- × 12.5-cm NaI (thallium) scintillation crystal detector. The concentration of 137Cs measured ranged from 0.01 to 3.28 pci/g in soils and from 0.01 to 10.05 pci/g in sediments. Uranium, thorium, and potassium were determined simultaneously with 137Cs. Total potassium ranged from a trace to 5.4%, uranium from 0.5 to 9.4 ppm, and thorium from 1.9 to 42.0 ppm. The concentration of 137Cs in reservoir sediments varied with depth. In some reservoirs the years of greatest 137Cs fallout were correlated with layers containing peak concentrations of 137Cs in the sediment profile. The occurrence of 137Cs in sediments was significantly correlated with the amount of clay and of organic matter present. The amount of 137Cs was greater per unit area in sampled sediments than in the contributing watersheds, and the relative concentration factor was as large as 24. This accumulation of 137Cs in reservoir sediments is indicative of the pollution possible in reservoirs as a result of fallout within the watershed but not necessarily within the reservoir.
Simulations of Doppler spectra in the melting layer of precipitation

A new technique for simulating the full Doppler spectrum in the melting layer of precipitation is presented. Simulated results are shown to agree well with S‐band Doppler radar observations, despite the many simplifying assumptions used in the microphysical and scattering models. The technique has significant potential for radar studies of the melting layer.
Force measurements between particles and the air‐water interface: Implications for particle mobilization in unsaturated porous media

Capillary forces acting at the air‐water interface play an important role in colloid fate and transport in subsurface porous media. We quantified capillary forces between different particles (sphere, cylinder, cube, disk, sheet, and natural mineral particles) and a moving air‐water interface. The particles had different sizes and contact angles (ranging from 14° to 121°). Theoretical calculations using the Young‐Laplace equation were used to support and generalize the experimental data. When the air‐water interface moved over the particles, there were strong capillary forces acting on the particles in the direction of the moving interface. The measured maximum capillary forces were similar to those calculated by the Young‐Laplace equation. The larger the contact angles and the larger the particle size, the stronger were the capillary forces. Particles with irregular shape and sharp edges experienced greater forces than smooth particles. Generalization of the results indicates that capillary forces exerted by a moving air‐water interface can readily exceed attractive Derjaguin‐Landau‐Verwey‐Overbeek (DLVO) and gravity forces for typical subsurface particles, and a moving air‐water interface is therefore an effective mechanism for mobilization of particles in porous media. Particles in the colloidal size range are particularly susceptible for mobilization by a moving air‐water interface.
Separating physical and biological controls on long‐term evapotranspiration fluctuations in a tropical deciduous forest subjected to monsoonal rainfall

Evapotranspiration (ET), especially in the mainland of the Indochina Peninsula, can impact and is impacted by the Asian monsoonal (AM) system, thereby prompting interest in its long‐term variability. To separate the physical and biological factors controlling ET variability in a tropical deciduous forest under the AM influence, 7 year eddy covariance and ancillary measurements were collected and analyzed. The 7 year mean rainfall (Pr) and ET along with their standard deviations were 1335 ± 256 and 977 ± 108 mm (about 73% of Pr), respectively, suggesting close coupling between these two hydrologic fluxes. However, other physical and biological drivers decouple seasonal and annual variations of ET from Pr. To explore them, a big‐leaf model complemented by perturbation analysis was employed. The big‐leaf model agreed well with the measured ET at daily to multiyear time scales, lending confidence in its ability to separate biological and physical controls on ET. Using this formulation, both first‐order and second‐order Taylor series expansions of the total ET derivatives were applied to the big‐leaf model and compared with measured changes in ET (dET). Higher‐order and joint terms in the second‐order expansion were necessary for matching measured and analyzed dET. Vapor pressure deficit (D) was the primary external physical controlling driver of ET. Leaf area index (LAI) and bulk stomatal conductance (gs) were shown to be the main significant biological drivers of the transpiration component of ET. It can be surmised that rainfall variability controls long‐term ET through physical (mainly D) and biological (mainly LAI and gs) factors in this ecosystem.
REVIEW ON SEEPAGE RESEARCHES OF FISSURED ROCK MASS(II)

Seepage in fissured rock mass is a very important issue in geotechnical engineering and should be considered in civil engineering such as hydraulic electricity, traffic and building constructions. Most of stability of slopes and dam base and rock mass bearing capacity of building foundations and dam base are influenced and /or controlled by seepage in these media. Based on the documents regarding the analysis of seepage for 40 years, this paper sums up the chief research results in the aspects of seepage in rock mass, including analytical models of seepage for fissured rock mass, permeability, value simulation of seepage field and coupling between seepage and stress. The first two aspects are analysed in detail, and application efficiencies and some existing questions are summed up.
Statistical Analysis and Computer Modelling of Volcanic Eruptions

Volcanism is an important mechanism by which internal heat is transported to the Earth’s surface and volcanic eruptions are the results of the dynamics of a complex system and are characterized by non-trivial temporal correlations. Understanding the processes involved in volcano formation and magma ascent are crucial to develop better hazard assessment techniques. This study focuses on three main points: understanding caldera formation in the solar system, investigating the global temporal behaviour of volcanic eruptions and understanding the nonlinear interactions taking place in the solid crust which lead to an eruption. In chapter 2, I first examine the distribution of caldera diameters on Earth, Mars, Io and Venus by performing a scaling analysis using the mean caldera diameter as a scaling factor. I find that their probability densities can be described by a universal distribution that can be approximated by a Generalized Extreme Value distribution. This scaling implies that a similar process governs caldera formation throughout the solar system. In chapter 3, I investigate the distribution of interevent times between eruptions for active volcanoes on Earth. When rescaling the axis using the mean rate of volcanism, the distributions collapse into a single one, the log-normal distribution. This scaling implies that the processes governing volcanic eruptions on Earth are similar and are independent of the type of volcanism and location, which emphasizes the importance of studying volcanism by modelling a universal behaviour. In the last chapter, I take a modelling approach to study the interactions between the magma and the crust. I define a lattice gas cellular automata model where the magma is represented by discrete particles. In this model, magma propagates through the crust and fracturing occurs until it reaches the top of the crust and an eruption or a cascade of eruptions occur. I study the statistical behaviour of eruptions in the model and observe similar size and temporal behaviours that have been