Variable Depths Research Articles

Effect of Embedded Basement Stories on Seismic Response of Low-Rise Building Frames Considering SSI via Small Shaking Table Tests

The dynamic soil-structure interaction is a combination of phenomena caused by the flexibility of soil foundation in structure response. The structure response may be changed by embedded basement stories. Thus, this study seeks to assess the dynamic response of seven-story concrete frame type buildings without a basement, one basement story, and two basement stories, considering fixed and flexible bases. For this purpose, the experimental tests on the small shaking table were executed with a small scaling coefficient of 1:50. Consequently, three scaled models of steel skeleton structures with variable embedded depths have been constructed with fixed and flexible bases. These models are exposed to three seismic input motions: Northridge (1994), Kobe (1995), and Chi-Chi (1999) at the base of the structure as a fixed base and the bedrock level in the soil structure system as a flexible base. The finite element technique is carried out for scaled and real models. Both the scaled and real numerical models are in good agreement with the obtained experimental observations with reasonable accuracy. It is concluded that the lateral deflections are overestimated by excluding embedded depths of structural elements. In the flexible prototype model, the lateral deflections of the superstructure with embedded depths (3 m, 6 m) decrease compared with no embedded depth, in which the maximum reduction percentages of 7-story with embedded depths 3 m and 6 m at the roof floor level are 21% and 42% compared with no embedded depth, respectively, under Northridge earthquake. Otherwise, ignoring the SSI effects (fixed base case), the lateral displacements are underestimated compared with the flexible base. The maximum amplification percentages at the roof floor level between flexible and fixed bases models with variable embedded depths are 35%, 37%, and 65% under Northridge, Kobe, and Chi-Chi earthquakes, respectively. The amplification and reduction percentages may be high or low, mainly depending on soil condition (fixed, flexible), variable embedded depths, characteristics of seismic motion, travel pass, and source of seismic motion. These items are summarized as the frequency domain of the coupled system compared with the frequency domain of the earthquake motion.

Breast Cancer Classification From Histopathological Images Using Resolution Adaptive Network

A histopathological analysis performed by pathologists plays a key role in the diagnosis of breast cancer. A novel approach based on an image processing technique is proposed to help pathologists efficiently produce accurate diagnoses, that is composed of two modules, namely, anomaly detection with a support vector machine (ADSVM) method and a resolution adaptive network (RANet) model. The ADSVM method screens mislabeled patches to improve the training performance of the RANet model. In the RANet model, subnetworks with variable resolutions and depths are utilized to classify images according to the classification difficulty. This adaptive mechanism potentially increases the computational efficiency and prediction accuracy. The proposed RANet-ADSVM approach is evaluated using two public datasets: the BreaKHis and BACH 2018 datasets. Binary and multiclass classifications of patient and image levels at different magnification factors are conducted on the BreaKHis dataset. The best accuracies of 98.83% and 99.14% are obtained for the binary classification at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200\times $ </tex-math></inline-formula> magnification at the patient and image levels, respectively. For the BACH 2018 dataset, binary and multiclass classifications on patch and image levels are performed. Experimental results show that the best accuracies for multiclass and binary classifications at the image level are 97.75% and 99.25%, respectively. Additionally, comparative experiments are performed and indicated that the proposed approach achieves significant improvements in both the classification accuracy and computational efficiency. Compared with similar networks (ResNet and DenseNet), the computational time is reduced by approximately 50%.

Single crystal monolithic upconverter solar cell device tandems with integrated optics

Solar photons possessing energy less than the bandgap of a single-junction solar cell can be utilized via the upconversion (UC) of two or more photons, resulting in the emission of a single above-bandgap photon. Due to the non-linear nature of UC, highly concentrated light is required, which is typically much greater than the practical concentration limits of a solar cell. It has been proposed that concentrating upconversion solar cells (UC-SC) with optical elements integrated into the device could help realize the high solar irradiance required. To avoid scattering problems arising from common UC materials based on micro-crystalline powders, in this work, concentrators are investigated with mono-crystalline upconverters in silicon-based tandem devices. An external quantum efficiency (EQE) of 6% with 1493 nm infrared illumination at 876 W / m 2 was obtained in upconverter device with concave integrated optics. At an irradiance higher than 90 W / m 2 (equivalent to 2.95 × in the 1450–1600 nm range), the non-concentrating UC-SC exhibited 1 . 5 × higher EQE than the UC-SC with a compound parabolic concentrator (CPC), while below 90 W / m 2 the CPC UC-SC exhibited 1.95 × higher EQE than the non-concentrating reference device. Due to the negligible scattering of the UC layer, the distribution of localized irradiance is revealed along with its effect on the performance of devices. It is found that irradiance is accumulated within the first 1 mm of the UC layer with peaks at variable depths according to the concentrating scheme. These results suggest ample space for improved UC devices by using integrated optics.

Stratigraphic signature of the Perito Moreno ice-dammings during the Little Ice Age (southern Patagonia, Argentina)

The spectacular water outburst occurring semi-periodically when the ice-dam formed by the external front of the Perito Moreno glacier collapses, is one of the most attracting events in the UNESCO ‘Parque Nacional Los Glaciares’ of southern Patagonia. These occurrences have been documented since 1936. Instead, evidence of previous events has been only indirectly provided by dendrochronology analysis. Here we show for the first time radiocarbon-dated sediment cores collected within a small inlet of Brazo Sur, that is, the southern arm of Lago Argentino that record ice-dammings in the Little Ice Age, at 324–266 cal yrs BP, as measured on a vegetal fragment sampled at ca. 14 cm from the top of a core. A common characteristic of the three sediment cores is the abrupt change in the stratigraphic record found at variable depths of 14–18 cm from the top of the cores. This change is marked by a hiatus spanning ca. 3200 years, separating planar-laminated sediments below from an alternation of erosional and depositional events above it, indicating recurring high-energy conditions generated by the emptying of the lake basin. In addition, we observed significant changes in the abundance of environmental indicators as testate amoebae below and above the hiatus. These well-preserved stratigraphic records highlight the key role of glaciolacustine deposits in reconstructing the glacial dynamics and palaeoclimate evolution of a glaciated region.

Transition from slab roll-back to slab break-off in the central Apennines, Italy: Constraints from the stratigraphic and thermochronologic record

ABSTRACTStratigraphic and thermochronologic data are used to study the processes that shaped the topography of the central Apennines of Italy. These are part of a major, active mountain belt in the center of the Mediterranean area, where several subduction zones control a complex topography. The Apennines were shaped by contraction at the front of the accretionary wedge overlying the subducting Adria microplate followed by extension at the wedge rear in response to eastward slab roll-back. In the central Apennines, intermontane extensional basins on the western flank rise eastward toward the summit. We contribute with new data consisting of 28 (U-Th-Sm)/He and 10 fission track ages on apatites to resolve a complex pattern of thermal histories in time and space, which we interpret as reflecting the transitional state of the orogen, undergoing a two-phase evolution related to initial slab retreat, followed by slab detachment. Along the Tyrrhenian coast, we document cooling from depths ≥3–4 km occurring between 8 and 5 Ma and related to the opening of marine extensional basins. Post–5 Ma, a broader region of the central Apennines exhibits cooling from variable depths, between &amp;lt;2 km in most areas and ≥3–4 km in the northeast, and with different onset times: at ca. 4 Ma in the west, at ca. 2.5 Ma in the center and northeast, and at ca. 1 Ma in the southeast. Between 5 and 2.5 Ma, exhumation is associated with modest topographic growth during the late stages of thrusting. Since 2.5 Ma, exhumation has concurred with the opening of intermontane basins in the west and in the east, with regional topographic growth and erosion, that we interpret to be associated with the locally detaching slab.

Integrating observations and models to determine the effect of seasonally frozen ground on hydrologic partitioning in alpine hillslopes in the Colorado Rocky Mountains, USA

AbstractThis study integrated spatially distributed field observations and soil thermal models to constrain the impact of frozen ground on snowmelt partitioning and streamflow generation in an alpine catchment within the Niwot Ridge Long‐Term Ecological Research site, Colorado, USA. The study area was comprised of two contrasting hillslopes with notable differences in topography, snow depth and plant community composition. Time‐lapse electrical resistivity surveys and soil thermal models enabled extension of discrete soil moisture and temperature measurements to incorporate landscape variability at scales and depths not possible with point measurements alone. Specifically, heterogenous snowpack thickness (~0–4 m) and soil volumetric water content between hillslopes (~0.1–0.45) strongly influenced the depths of seasonal frost, and the antecedent soil moisture available to form pore ice prior to freezing. Variable frost depths and antecedent soil moisture conditions were expected to create a patchwork of differing snowmelt infiltration rates and flowpaths. However, spikes in soil temperature and volumetric water content, as well as decreases in subsurface electrical resistivity revealed snowmelt infiltration across both hillslopes that coincided with initial decreases in snow water equivalent and early increases in streamflow. Soil temperature, soil moisture and electrical resistivity data from both wet and dry hillslopes showed that initial increases in streamflow occurred prior to deep soil water flux. Temporal lags between snowmelt infiltration and deeper percolation suggested that the lateral movement of water through the unsaturated zone was an important driver of early streamflow generation. These findings provide the type of process‐based information needed to bridge gaps in scale and populate physically based cryohydrologic models to investigate subsurface hydrology and biogeochemical transport in soils that freeze seasonally.

Metamorphic CO2 emissions from the southern Yadong-Gulu rift, Tibetan Plateau: Insights into deep carbon cycle in the India-Asia continental collision zone

Extensional rift systems provide important pathways for the release of large amounts of deeply-sourced CO2 into the atmosphere. Continental rifting zones (e.g., East African rift) are thus invoked to be important for understanding the links between CO2 outgassing and global climate change associated with continental breakup. However, deeply-sourced CO2 emissions from extensional rift systems in continental collision zones remain poorly understood. Here, we focus on hydrothermal CO2 emissions from the southern segment of the Yadong-Gulu rift (YGR), the largest extensional rift in southern Tibetan Plateau, aiming at delineating rift-related CO2 emissions from the India-Asia continental collision zone. In-situ measurements of diffuse soil CO2 emissions indicate that average soil CO2 fluxes from the Kangbu, Mengzha, and Chaduo hydrothermal fields are 40, 700, and 255 g m−2 d−1, respectively. Combined with average soil CO2 fluxes (20–437 g m−2 d−1) from central and northern YGR, we speculate a relatively steady-state CO2 degassing pattern for the entire rift. The magnitude of soil CO2 fluxes of the YGR is higher than that of representative areas of the East African rift system. Evidence from 3He/4He reveals a pure crustal origin for CO2-bearing fluids in southern YGR, while the involvement of mantle CO2 is recognized in the central and northern rift segments. We suggest that metamorphic decarbonation of crustal rocks at variable depths is the primary cause for CO2 origin in southern YGR, which differs from the magma‑carbonate interaction model of central and northern YGR. Ternary mixing calculation based on He-CO2 systematics of hydrothermal gases indicates dominant contributions from carbonate rocks to total carbon inventory, with mantle CO2 contributions absent in southern YGR but discernible in northern YGR. The characteristic high proportions of crustal CO2 (>90%) distinguish the YGR from extensional rifts fed primarily by mantle CO2 in continental rifting zones. Our results reveal a crustal-scale carbon cycle in accretionary wedge of the India-Asia continental collision zone, together with magmatic front setting of the central and northern YGR, outlining a transect of the rift-related CO2 emissions across continental collision zones. This would contribute to better understanding the role of continental assembly in deeply-sourced CO2 emissions and global carbon budget.

Zircon geochronology and geochemistry of pre-Bushveld sills in the eastern Transvaal Supergroup, South Africa

Abstract An extensive suite of sills occurring in the eastern and western Transvaal Supergroup has been termed the Marico Diabase Suite. As a result of their overall geographic proximity to the Bushveld Complex and occurrence in the Transvaal Supergroup they have been assumed to be related to the Bushveld Complex. Previous studies have identified two different types of rocks within this suite, namely the Maruleng and Lydenburg types, based on geochemical and metamorphic characteristics. The Maruleng type has mineralogical (orthopyroxene-bearing) and geochemical affinities with the mafic rocks of the Bushveld Complex, and rocks belonging to this type are much more closely spatially related to the Bushveld Complex. The Lydenburg type, on the other hand, is much more extensive spatially and was emplaced at variable depths within the Transvaal Supergroup. The latter type of rock is variably metamorphosed, far beyond the likely thermal effects arising from emplacement of the Bushveld Complex. Using LA-SF-ICPMS and LA-MC-ICMS for U-Pb-Hf isotope ratio and REE+Ti concentration analysis, we demonstrate that zircon grains from this latter type were subjected to hydrothermal alteration, which caused the introduction of common lead. Despite compositional and isotopic overprinting, an age of 2 083 ± 18 Ma (MSWD = 12, n = 16) is obtained, suggesting a pre-Bushveld in age. We suggest that the original term Marico Diabase Suite encompasses two different events. The Maruleng Suite should be grouped as part of the Bushveld Complex, whereas the Lydenburg Suite should be given a status that is independent from the Bushveld event.

Tracing the subducting Pacific slab to the mantle transition zone with hydrogen isotopes

Hydrogen isotopes have been widely used as powerful tracers to understand the origin of terrestrial water and the water circulation between the surface and the deep interior of the Earth. However, further quantitative understanding is hindered due to a lack of observations about the changes in D/H ratios of a slab during subduction. Here, we report hydrogen isotope data of olivine-hosted melt inclusions from active volcanoes with variable depths (90‒550 km) to the subducting Pacific slab. The results show that the D/H ratio of the slab fluid at the volcanic front is lower than that of the slab fluid just behind the volcanic front. This demonstrates that fluids with different D/H ratios were released from the crust and the underlying peridotite portions of the slab around the volcanic front. The results also show that the D/H ratios of slab fluids do not change significantly with slab depths from 300 to 550 km, which demonstrates that slab dehydration did not occur significantly beyond the arc. Our estimated δD‰ value for the slab materials that accumulated in the mantle transition zone is > − 90‰, a value which is significantly higher than previous estimates.

3D Printed Chest Wall: A Tool for Advanced Microsurgical Training Simulating Depth and Limited View.

Summary:The deep inferior epigastric perforator (DIEP) flap has become the free flap of choice for autologous breast reconstruction. However, anastomoses of DIEP pedicles to internal mammary vessels in the chest wall are difficult due to restricted access and the depth of the vessels. Successful performance of such demanding procedures necessitates advanced requirements for microsurgical training models. The current chicken thigh model has been used to acquire microsurgical skills, allowing early learning curve trainees to practice repeatedly in inconsequential environments. Despite the increasing use of this model for training purposes, the resemblance to a clinical environment is tenuous. Such models should include anastomosis practice within the depth where the recipient vessels are located. To address this, we developed a three-dimensional (3D) printed chest wall as an addition to the current chicken thigh model, which reliably mimics the complexity of the anastomosis performed during DIEP breast reconstruction. This form of rapid prototyping facilitates a newfound ability for early learning curve trainees to exercise end-to-end anastomoses on vessels located with variable depths. Our enhancement of the current chicken thigh model is simple, cost-effective and offers a significantly more realistic resemblance to a clinical situation.

Free flexural vibrations of homogeneous beams with symmetrically variable depths

The subject of the paper are homogeneous beams of symmetrically variable depth and bisymmetrical cross sections. Free flexural vibrations of these beams are analytically and numerically studied. Based on Hamilton’s principle, the differential equations of motion of these beams are obtained. The equations of motion are analytically solved with consideration of the bending lines of these beams subjected to their own weight. The fundamental natural frequency for exemplary beams is derived and presented in Tables and Figures.

Experimental and clinical evaluation of a new intra-lingual suture pattern for management of lingual wounds in farm animals

A pre-clinical experimental study is used to evaluate a new intralingual suture pattern, for treating farm animal’s tongue-wounds. Experimental section was performed on 36 fresh goat’s tongue-samples, to compare the new suture pattern with the traditionally used two patterns (double rows simple interrupted pattern; and tension relieve vertical mattress with deep row simple interrupted pattern that is followed by superficial opposing vertical mattress). Comparison involved the required stitches number, duration of suturing, and pattern’s tensile strength. The main clinical study was carried out on recent lingual wounds of variable depths which involved 30-50% of tongue width in one horse, one camel, one buffalo-calf, and three donkeys. In addition to three donkeys had old lacerations which failed to heal by first intension. Wounds sutured by the new pattern were covered by one row of cruciate mattress to oppose the mucosa. Results revealed that the new pattern required fewer stitches numbers, consume lesser time, had higher tensile strength, it could be applied easily, achieved proper apposition of both the muscular layer and mucosa, and it induced minimal scar formation and deformity. The technique is widely acceptable by the owners than the other traditional merhods. The technique is advised to be used as alternative suture pattern for repair of lingual wounds of farm animals.

Application of β-Tricalcium Phosphate in Adhesive Dentin Bonding.

The study aimed at synthesizing β-tricalcium phosphate (β-TCP) nanoparticles and comparing the mechanical properties and dentin interaction of two adhesives: experimental adhesive (EA) and EA with 5 wt.% β-TCP nanoparticles (β-TCP-5%). These filler nanoparticles were synthesized and then characterized with scanning electron microscopy (SEM) and micro-Raman spectroscopy. The β-TCP nanoparticles were incorporated in the adhesives to form two groups: gp-1: EA (control) and gp-2: β-TCP-5%. These adhesives were characterized by SEM, energy-dispersive X-ray (EDX) spectroscopy and were also assessed for their micro-tensile bond strength (μTBS) with (TC) and without thermocycling (NTC). Fourier Transform Infrared (FTIR) spectroscopy was performed to evaluate the degree of conversion (DC) of two adhesives. The β-TCP filler was seen as irregularly shaped agglomerates on SEM. The micro-Raman spectra revealed characteristic peaks associated with β-TCP nanoparticles. Both adhesives presented suitable dentin interaction, which was demonstrated by the formation of resin tags of variable depths. The EDX analysis verified the existence of calcium (Ca) and phosphate (P) for the β-TCP-5% group. The greatest μTBS values were shown by β-TCP-5% group samples when they were non-thermocycled (NTC) (β-TCP-5%-NTC: 34.11 ± 3.46) followed by the thermocycled (TC) samples of the same group (β-TCP-5%-TC: 30.38 ± 3.66), compared with the EA group. Although the DC presented by β-TCP-5% group was comparable to the EA group, it was still lower. The addition of β-TCP nanoparticles in the adhesive improved its μTBS and resulted in a suitable dentin interaction, seen in the form of hybrid layer and resin tag formation. Nonetheless, a decreased DC was observed for the β-TCP-5% adhesive. Future studies probing the effect of different filler concentrations on various properties of the adhesive are warranted.

Do soil depth and plant community composition interact to modify the resistance and resilience of grassland ecosystem functioning to drought?

While the effect of drought on plant communities and their associated ecosystem functions is well studied, little research has considered how responses are modified by soil depth and depth heterogeneity. We conducted a mesocosm study comprising shallow and deep soils, and variable and uniform soil depths, and two levels of plant community composition, and exposed them to a simulated drought to test for interactive effects of these treatments on the resilience of carbon dioxide fluxes, plant functional traits, and soil chemical properties. We tested the hypotheses that: (a) shallow and variable depth soils lead to increased resistance and resilience of ecosystem functions to drought due to more exploitative plant trait strategies; (b) plant communities associated with intensively managed high fertility soils, will have more exploitative root traits than extensively managed, lower fertility plant communities. These traits will be associated with higher resistance and resilience to drought and may interact with soil depth and depth heterogeneity to amplify the effects on ecosystem functions. Our results showed that while there were strong soil depth/heterogeneity effects on plant‐driven carbon fluxes, it did not affect resistance or resilience to drought, and there were no treatment effects on plant‐available carbon or nitrogen. We did observe a significant increase in exploitative root traits in shallow and variable soils relative to deep and uniform, which may have resulted in a compensation effect which led to the similar drought responses. Plant community compositions representative of intensive management were more drought resilient than more diverse “extensive” communities irrespective of soil depth or soil depth heterogeneity. In intensively managed plant communities, root traits were more representative of exploitative strategies. Taken together, our results suggest that reorganization of root traits in response to soil depth could buffer drought effects on ecosystem functions.

Volatile Element Evidence of Local MORB Mantle Heterogeneity Beneath the Southwest Indian Ridge, 48°–51°E

AbstractThe mantle source beneath the Southwest Indian Ridge (SWIR) reflects a complex history of contamination. Magmatic volatile contents are vital tracers of these kinds of heterogeneities, which may fractionate otherwise constant volatile/non‐volatile elemental ratios, such as the H2O/Ce ratio. Although several studies have recently used trace element and isotopic data to address mantle source heterogeneity and magmatic processes at SWIR 48°–51°E region, volatile element constraints provide a valuable test of models for the origins of mantle heterogeneities in this region. Here, we present new data for nine rare basaltic glass samples from the 48°–51°E region, which enable careful assessment of the effects of primary versus secondary processes on the glass volatile contents. These samples are strongly affected by variable extents of carbon degassing, and shallow assimilation of Cl‐rich fluid, but also reveal consistently high H2O/Ce ratios (458.8 ± 14.9), among the highest in MORBs, that cannot be explained by late‐stage secondary processes, crustal assimilation, or simple melting of peridotite mantle at variable depths. Instead, the high H2O/Ce ratios are features of the mantle source composition. The 48°–51°E region is notably more depleted in highly incompatible trace elements relative to other regions of the SWIR, although this depletion is not apparent in H2O, which is similarly abundant throughout the SWIR. We link the high H2O/Ce ratios in these glasses with other trace element characteristics diagnostic of subduction and fluid addition, suggesting that the mantle source reflects signatures of a refractory mantle residue that previously melted within a subduction zone.

Nitrous oxide surface fluxes in a low Arctic heath: Effects of experimental warming along a natural snowmelt gradient

Climate change is profound in the Arctic where increased snowfall during winter and warmer growing season temperatures may accelerate soil nitrogen (N) turnover and increase inorganic N availability. Nitrous oxide (N2O) is a potent greenhouse gas formed by soil microbes and in the Arctic, the production is seen as limited mainly by low inorganic N availability. Hence, it can be hypothesized that climate change in the Arctic may increase total N2O emissions, yet this topic remains understudied. We investigated the combined effects of variable snow depths and experimental warming on soil N cycling in a factorial field study established along a natural snowmelt gradient in a low Arctic heath ecosystem. The study assessed N2O surface fluxes, gross N mineralization and nitrification rates, potential denitrification activity, and the pools of soil microbial, soil organic and soil inorganic N, carbon (C) and phosphorus (P) during two growing seasons. The net fluxes of N2O averaged 1.7 μg N2O–N m−2 h−1 (range −3.6 to 10.5 μg N2O–N m−2 h−1), and generally increased from ambient (1 m) to moderate (2–3 m) snow depths. At the greatest snow depth (4 m) where snowmelt was profoundly later, N2O fluxes decreased, likely caused by combined negative effects of low summer temperatures and high soil moisture. Positive correlations between N2O and nitrate (NO3−) and dissolved organic N (DON) suggested that the availability of N was the main controlling variable along the snowmelt gradient. The maximum N2O fluxes were observed in the second half of August associated with high NO3− concentrations. The effect of growing season experimental warming on N2O surface flux varied along the snowmelt gradient and with time. Generally, the experimental warming stimulated N2O fluxes under conditions with increased concentrations of inorganic N. In contrast, warming reduced N2O fluxes when inorganic N was low. Experimental warming had no clear effects on soil inorganic N. The study suggests that if increased winter precipitation leads to a deeper snow cover and a later snowmelt, total emissions of N2O from low Arctic heath ecosystems may be enhanced in the future and, dependent on dissolved N availability, summer warming may stimulate or reduce total emissions.

Moment Analysis for Modeling Soil Water Distribution in Furrow Irrigation: Variable vs. Constant Ponding Depths

Despite increasing use of pressurized irrigation methods, most irrigation projects worldwide still involve surface systems. Accurate estimation of the amount of infiltrating water and its spatial distribution in the soil is of great importance in the design and management of furrow irrigation systems. Moment analysis has previously been applied to describe the subsurface water distribution using input data from numerical simulations rather than field measured data, and assuming a constant ponding depth in the furrow. A field experiment was conducted in a blocked-end level furrow at Maricopa Agricultural Center, Arizona, USA, to study the effect of time-variable ponding depths on soil water distribution and the resulting wetting bulb under real conditions in the field using moment analysis. The simulated volumetric soil water contents run with variable and constant (average) ponding depths using HYDRUS 2D/3D were almost identical, and both compared favorably with the field data. Hence, only the simulated soil water contents with variable ponding depths were used to calculate the moments. It was concluded that the fluctuating flow depth had no significant influence on the resulting time-evolving ellipses. This was related to the negligible 10-cm variation in ponding depths compared to the high negative matric potential of the unsaturated soil.

Geomorphometric analysis of seabed pockmarks, offshore western Niger Delta: A case study of the Freeman Field

The morphometry and spatial distribution of seabed pockmarks have been used as proxies for subsurface conditions and local hydrodynamics. We have characterized and analyzed the distribution of seabed pockmarks in the Freeman Field, offshore western Niger Delta using a high-resolution 3D seismic data to understand the relationships between pockmarks and their controlling factors. We identified a total of 684 pockmarks in the Freeman Field at water depths between 1461 and 2395 m. The pockmarks are circular, elliptical, and elongated in plan view, having U-, V-, and W-shaped geometries in cross-sectional view. The average length, width, and depth of the pockmarks are 210, 111, and 15 m, respectively. More than 80% of the pockmarks were randomly distributed. From statistical analysis, most of the pockmarks occurred within a water depth range of 1600–2100 m. The randomly distributed pockmarks occurred at variable water depths whereas the pockmarks that were aligned along fault planes occurred at shallow water depths (approximately 1400–1700 m). However, those confined within the canyon occurred at deeper water depths (approximately 1700–2400 m). Our results show no correlation between the water depth and any of the pockmark dimensions; therefore, we hypothesize that changes in water depth had no effect on any of the pockmark dimensions because the Freeman Field is located at water depths greater than 1000 m where the current velocity range is lower (0.2 and 0.42 m/s). Hence, pockmark dimensions were comparatively uniform throughout the study area. We suggest that the variation in pockmark morphometry is linked to seafloor currents and the activity history of the pockmarks whereas the spatial distribution is linked to structural and stratigraphic discontinuities. Furthermore, our results give insights to the factors that should be considered during risk assessment before hydrocarbon exploration and production.

Overwintering distribution, inflow patterns and sustainability of Calanus finmarchicus in the North Sea

Calanoid copepods are key taxa in the North Sea as they are the main food source for many fish stocks, such as herring, mackerel and cod. In this study we use an individual-based model for Calanus finmarchicus embedded in the NORWegian ECOlogical Model system (NORWECOM) to investigate important population parameters such as biomass and abundance, distribution and interannual variability of the overwintering population, as well as the inflow of C. finmarchicus into the North Sea from adjacent areas for the 2000–2016 period. The modelled spatial–temporal patterns of C. finmarchicus abundance is comparable with the Continuous Plankton Recorder (CPR) Survey data in the northern North Sea. The simulated annual mean biomass of C. finmarchicus amounts to 0.94 million-tonnes of carbon. High overwintering biomass appears in the Norwegian Trench as well as in the north-west shelf region of the North Sea. A decreasing trend in the overwintering biomass has been detected on the path of the East Shetland Atlantic Inflow (ESAI) over the simulated period. The inflow of C. finmarchicus biomass into the North Sea from the north constitutes on average 41% of the annual mean biomass in the North Sea during the simulated 17 years, and thus determines the interannual variability of the biomass. We conclude that the C. finmarchicus population in the North Sea is not self-sustained and is highly dependent on the inflow of C. finmarchicus from the Faroe-Shetland Channel and south of the Norwegian Sea. C. finmarchicus enter the North Sea via three branches of the North Atlantic current with variable depths depending on seasons and topography. Beside the western flank of the Norwegian Trench (carrying 57% of the inflow biomass), we suggest that the ESAI is also an important agent carrying 37% of the total C. finmarchicus inflow biomass through the shelf area into the north-west of the North Sea. The annual mean outflow biomass is larger than the inflow biomass (0.52 versus 0.39 million-tonnes carbon per year), which indicates that the North Sea serves as a feeding ground and growth region for C. finmarchicus. This study is a first step towards a better understanding and quantification of the exchange of C. finmarchicus between the open seas, coastal waters and the fjords.

Trace element and isotope Geochemistry of Neoarchean carbonate rocks from the Dharwar craton, southern India: Implications for depositional environments and mantle influence on ocean chemistry

Neoarchean carbonate rocks of the Vanivilas Formation (2.7 Ga) occur extensively in greenstone belts of western Dharwar craton, are associated with banded Fe-Mn formations and clastic sediments including diamictites, preserve well-developed stromatolitic structures. We intend to understand the depositional environments of these carbonates, extent of oxygenation in shallow oceans and to examine the mantle and continent inputs to Neoarchean oceans. Depleted LREESN and slightly enriched HREESN patterns, Y/Ho > 28, La, Y and Eu spiking and varying Ce anomalies shown by most of the samples, are consistent with their marine origin. However, 4 samples exhibit negative Ce anomaly indicating presence of oxygen supporting the hypotheses of localised, protected, shallow marine oxygenation in redox stratified late Meso- to Neoarchean oceans. δ13C values are well preserved (mean = -0.27‰ (PDB)) similar to other Archean marine carbonates from other cratons and show no correlation with δ18O and Mn/Sr ratios. Whereas, the δ18O values (mean= -10.78‰) show considerable depletion and can be attributed to later interactions with diagenetic/meteoric fluids. The mantle dominated, yet continental affected Neoarchean ocean chemistry is apparent from Sr-Nd isotope systematics. The lowest 87Sr/86Sri of carbonates, 0.7024 reflects ocean water Sr isotopic composition at 2.7 Ga, is higher than the model seawater evolution curve of Shields and Veizer, (2002). Similarly, other recent studies on Archean carbonates and barites reported higher 87Sr/86Sri values. This is due to the existence of Paleoarchean continental crust subjected to chemical weathering resulting in increased continental flux than previously thought of. Range of ℇNd values (-8.39 to 5.83) suggest that the carbonates had variable contributions of Nd from a long term depleted mantle through hydrothermal fluids, as well as, from 3.5 Ga old continental crust in the Dharwar craton. The carbonates were deposited in the Neoarchean ocean at variable depths within the shelf and those deposited at shallower and deeper environments are characterized respectively, by inputs derived from chemical weathering of ≥3.5 Ga old continental crust and mantle through hydrothermal fluids associated with submarine volcanic activity.