Saturation Depth Research Articles

A method for predicting the factor of safety of an infinite slope based on the depth ratio of the wetting front induced by rainfall infiltration

Abstract. Most landslides in Korea are classified as shallow landslides with an average depth of less than 2 m. These shallow landslides are associated with the advance of a wetting front in the unsaturated soil due to rainfall infiltration, which results in an increase in water content and a reduction in the matric suction in the soil. Therefore, this study presents a modified equation of infinite slope stability analysis based on the concept of the saturation depth ratio to analyze the slope stability change associated with the rainfall on a slope. A rainfall infiltration test in unsaturated soil was performed using a column to develop an understanding of the effect of the saturation depth ratio following rainfall infiltration. The results indicated that the rainfall infiltration velocity due to the increase in rainfall in the soil layer was faster when the rainfall intensity increased. In addition, the rainfall infiltration velocity tends to decrease with increases in the unit weight of soil. The proposed model was applied to assess its feasibility and to develop a regional landslide susceptibility map using a geographic information system (GIS). For that purpose, spatial databases for input parameters were constructed and landslide locations were obtained. In order to validate the proposed approach, the results of the proposed approach were compared with the landslide inventory using a ROC (receiver operating characteristics) graph. In addition, the results of the proposed approach were compared with the previous approach used: a steady-state hydrological model. Consequently, the approach proposed in this study displayed satisfactory performance in classifying landslide susceptibility and showed better performance than the steady-state approach.

Influence of partial saturation on total nitrogen removal in a single-stage French constructed wetland treating raw domestic wastewater

The objective of this research was to evaluate the nitrogen removal performance of vertical flow constructed wetlands implemented with a bottom saturated layer in the treatment of raw wastewater (French system). This research was carried out in two pilot systems over 16 months with different saturation depths (25cm and 15cm) to determine the optimal level for denitrification promotion. Monitoring included regular analysis of the physico-chemical parameters (TSS, dissolved COD, NH4+-N, TKN and NO3−-N) as well as online measurements (redox potential, oxygen and temperature, hydraulic behavior) to explain the filter’s behavior. Statistical performance analysis showed that a higher removal rate was obtained when the filters operated with 25cm saturation in comparison with 15cm saturation depth. The hydraulic study revealed the positive evolution of the system from the winter, where the clogging was observed, to the summer, where this phenomenon was not observed, demonstrating that the hydraulic conditions affect the nitrification efficiency. The redox potential measured at three different depths inside the filters clearly showed the variation in the Eh values as a function of the saturation level and feeding–resting cycles, indicating that such measurements are capable of revealing the existing biogeochemical processes in highly dynamic systems, such as constructed wetlands. The results demonstrated variations in performance according to the saturation condition and the system’s hydraulics; however, improvement of the design or the introduction of an additional treatment stage is necessary to achieve complete TN removal.

A transient phreatic surface mound, evidenced by a strip of vegetation on an earth dam

On the slopes of the embankment of the Al-Khod groundwater recharge–flood protection dam (Oman), a band of scrub vegetation community emerged after torrential rains and temporary filling of the dam reservoir. Species composition differs markedly on both sides of the embankment, with many exotics found on the reservoir side and more typical gravel-desert species on the outside. Hydro-ecologically, the vegetation is interpreted as the footprint of a temporary storage of water, which is a small-sized groundwater mound within the permeable shoulder of the levee. The levee, as an anthropogenic landform, induces a U-turn (gravitational slumping–lateral seepage–transpirational moisture ascent) topology of seepage. The Lembke method of successive variations of steady states is used in modelling the water table dynamics. In the early stage of the mound decay, outflow through a seepage face of the shoulder is modelled by the Barenblatt slumping parabola of the phreatic-zone part of the flow domain, which is perfectly matched with the Youngs exact solution for a purely horizontal flow through a porous wedge. At the stitching cross-section, the flow rates and saturated depths in the two zones coincide. The late stage of mound evolution is characterized by transpiration by the plant roots projected onto a shrinking free surface, with the Barenblatt and Youngs solutions conjugated but without the outcrop of the saturated mound on the levee slope. Ordinary differential equations for the sliding or descending locus of the intersection of the parabola and the triangle hypotenuse are integrated in a closed form or by the Runge-Kutta method. The dwindling saturated volume and the rate of drainage are obtained. They can be used in assessments of the hydro-ecological sustainability of slope-rooted shrubs (vegetation survival between rare rainfall episodes).Editor D. Koutsoyiannis; Associate editor A. Porporato

Influence of the Leachate Drainage Systems on Groundwater Quality in Muntenia Region

Abstract The greatest challenge, as far as landfill designing is concerned, is building a drainage system capable of diminishing the most severe negative effect, i.e., groundwater pollution. Based on waste collection system configuration – drainage conditions for existing landfills, drainage of homogeneity, etc. – the present paper managed to determine the hydraulic conductivity of the drainage layer and the maximum depth of saturation. Drainage system effectiveness is highly dependent on efficient analyses of the leachate collection systems. One of the most important factors of the present study is represented by the maximum saturated depth of infiltration with a net value of 98 cm/year. The hydraulic conductivity determined for this value of net infiltration reveals that, in some cases, the vertical drain leachate drainage is prevalent. The study covered a span of two years. In order to identify groundwater pollution levels in Muntenia region five sampling points were established; their focus was to analyse COD, BOD, pH and TSS values. Study results revealed a lower degree of pollution in the case of industrial waste landfills as compared to domestic waste ones.

Stability and liquefaction analysis of porous seabed subjected to cnoidal wave

Cnoidal wave theory is appropriate to periodic wave progressing in water whose depth is less than 1/10 wavelength. However, the cnoidal wave theory has not been widely applied in practical engineering because the formula for wave profile involves Jacobian elliptic function. In this paper, a cnoidal wave-seabed system is modeled and discussed in detail. The seabed is treated as porous medium and characterized by Biot's partly dynamic equations (u–p model). A simple and useful calculating technique for Jacobian elliptic function is presented. Upon specification of water depth, wave height and wave period, Taylor's expression and precise integration method are used to estimate Jacobian elliptic function and cnoidal wave pressure. Based on the numerical results, the effects of cnoidal wave and seabed characteristics, such as water depth, wave height, wave period, permeability, elastic modulus, and degree of saturation, on the cnoidal wave-induced excess pore pressure and liquefaction phenomenon are studied.

Carrier dynamics in inhomogeneously broadened InAs/AlGaInAs/InP quantum-dot semiconductor optical amplifiers

We report on a characterization of fundamental gain dynamics in recently developed InAs/InP quantum-dot semiconductor optical amplifiers. Multi-wavelength pump-probe measurements were used to determine gain recovery rates, following a powerful optical pump pulse, at various wavelengths for different bias levels and pump excitation powers. The recovery was dominated by coupling between the electronic states in the quantum-dots and the high energy carrier reservoir via capture and escape mechanisms. These processes determine also the wavelength dependencies of gain saturation depth and the asymptotic gain recovery level. Unlike quantum-dash amplifiers, these quantum-dots exhibit no instantaneous gain response, confirming their quasi zero-dimensional nature.

The Numerical and Experimental Analysis of Heat Transport and Water Infiltration in a Granular Packed Bed Due to Supplied Hot Water

The characteristics of heat transport and water infiltration in a granular packed bed due to supplied hot water are investigated experimentally and numerically. The distributions of water saturation and temperature are focused on one-dimensional models assuming the local thermal equilibrium between water and particles at any specific space in a vertical granular packed bed column. This study describes the dynamics of heat transport and water infiltration in various testing condition. The calculated water saturation, temperature distribution, and infiltration depth are compared with the experimental results. Experimentally and numerically, the influence of particle sizes and supplied water flux on heat transport during unsaturated flow are clarified in detail. The results showed that the granular packed bed with a larger particle size results in a faster infiltration rate and forms a wider infiltration depth. However, an extension of the heated layer is not as much as that of the infiltration layer because the temperature of water infiltration gradually drops due to upstream heat transport. It is found that a greater supplied water flux corresponds to a higher water saturation and temperature along a granular packed bed for each time increment. The numerical results closely match the experimental results.

Contaminant Transport in Capped Deformable Partially Saturated Sediments

ABSTRACT Zhang, H.; Yang, H., and Jeng, D.-S., 2015. Contaminant transport in capped deformable partially saturated sediments. Contaminated sediment tends to consolidate in response to the loading imposed by an overlying cap layer. The form of transient solute advection through sediments and caps is consequently changed. Therefore, the contaminant discharge into the overlying water is expected to increase and the effectiveness of the in situ capping system will be strongly affected. In this study, a one-dimensional sediment–cap model coupling consolidation and advection–dispersion equation was established. A simplified model was proposed through the sensitivity analysis, and then a parametric study was conducted. Numerical examples concluded that the absorption, degree of sediment saturation, cap thickness, and sediment depth significantly affect the contaminant discharge from the top of the cap. Therefore, these parameters should be considered carefully during cap design.

The volatile flushing triggers eruptions at open conduit volcanoes: Evidence from Mount Etna volcano (Italy)

At the Mount Etna volcano (Italy) the massive release of magmatic gasses (especially H2O, CO2 and SO2) during explosive eruptions and through the persistent gas plume, raises important issues: i) the volume of magma erupted at given periods is insufficient to feed the gas plume of the related periods; ii) gas-dominated, explosive eruptions do not emit differentiated products, but relatively Mg-rich magmas; iii) H2O measured in melt inclusions (~3.5wt.% at about 0.4GPa) exceeds what is expected from intraplate mantle-derived melts (<1.4wt.%).Literature data on melt inclusions (MIs) along with textural and compositional analyses of plagioclase and phase stability constrained by MELT calculations, enabled us to build a model that reconciles the abovementioned discrepancies with the high variability of the water content along the Etnean feeding system.We propose that along an open magma conduit, continuous gas loss from the free surface of magma at depth promotes an almost steady stream of H2O-rich fluid extending well below the gas saturation depth. The velocity of volatile migration might be enhanced by the huge amount of CO2 present at Mount Etna, because the CO2 exsolved at high-pressure conditions may act as carrier for other volatile species.In this way the H2O-undersaturated primitive magma present in the plumbing system, may undergo a volatile “flushing” proportional to the residing time. This process is fundamental to increase the originally low H2O content of primitive magma (≤1.4wt.%) allowing it to overcome the saturation threshold, to exsolve as gas and to promote the eruption of Mg-rich lavas. Such mechanism would also account for the unexpectedly high amount of magmatic water released during non-eruptive periods.

Estimation of maximum saturated depth in two-layered drainage blankets over the barrier in landfill cover system

For accurately calculating the maximum saturated depth over the landfill barrier and analyzing the variation of liquid head with inflow time, a new method is presented that considers the unsteady-state condition. Based on the principle of water balance and the extended Dupuit assumption, the solution of the new method can be calculated. Also, this method is capable of revealing the effect of the multilayered drainage media. One of the advantages of the method presented in this paper is that it can be used to draw a phreatic surface in layered drainage media under unsteady-state condition and estimate the location of the maximum liquid depth, for both homogeneous conditions and two-layered drainage conditions. Based on the developed analysis method, the effects of a parametric variation on the maximum saturated depth and the variation of saturated depth with time are presented. The calculated results show that with the increase of slope gradients of cover system, the saturated depth of cover system is easy to reach a stable value. Moreover, when the drainage layer consists of two layers with different thickness and hydraulic conductivity, the increase of hydraulic conductivity of the upper drainage layer will make it easier for the saturated depth of cover system to reach a stable and lower value.

Infiltration regulation and stability analysis of soil slope under sustained and small intensity rainfall

Rainfall infiltration depth and mode can severely influence slope stability. With the sustained rainfall, the influenced region of slope gradually expands. By using the Green-Ampt model to the soil slope, infiltration regulation was discussed under sustained and small intensity rainfall. And the infiltration rate of unsaturated soil was proposed according to the saturated infiltration theory. Because of the changing of initial moisture content in depth of slope, the saturated or unsaturated infiltration rate and depth could also be changeable with the sustained rainfall infiltration. Based on the principle of strength reduction, the calculation model of slope safety factor was established under different initial moisture contents and infiltration modes. Then, the slope stability was quantitatively analyzed through software FLAC3D. The calculation results of soil slope engineering show that there is a shorter period for slope stability under different initial moisture contents and unsaturated infiltration ways at the slope wetting front. The stability period of slope is 33.3% according to different initial moisture contents of wetting front less than that of the same initial moisture content of wetting front. And the slope is easier to fail under the unsaturated infiltration. The results agree well with the actual situation under sustained and small intensity rainfall.

Observed Microphysical Evolution for Two East Coast Winter Storms and the Associated Snow Bands

AbstractThis paper presents the observed microphysical evolution of two coastal extratropical cyclones (19–20 December 2009 and 12 January 2011) and the associated passage of heavy snowbands in the cyclone comma head. The observations were made approximately 93 km east of New York City at Stony Brook, New York. Surface microphysical measurements of snow habit and degree of riming were taken every 15–30 min using a stereo microscope and camera, and snow depth and snow density were also recorded. A vertically pointing Ku-band radar observed the vertical evolution of reflectivity and Doppler vertical velocities. There were rapid variations in the snow habits and densities related to the changes in vertical motion and depth of saturation. At any one time, a mixture of different ice habits was observed. Certain ice habits were dominant at the surface when the maximum vertical motion aloft occurred at their favored temperature for depositional growth. Convective seeder cells above 4 km MSL resulted in relatively cold (less than −15°C) ice crystal habits (side planes, bullets, and dendrites). Needlelike crystals were prevalent during the preband period when the maximum vertical motion was in the layer from −5° to −10°C. Moderately rimed dendritic crystals were observed at snowband maturity associated with the strongest frontogenetical ascent on the warm (east) side of the bands. Riming rapidly decreased and more platelike crystals became more numerous as the strongest ascent moved east of Stony Brook. Snow-to-liquid density ratios ranged from 8:1 to 13:1 in both events, except during the period of graupel, when the ratio was as low as 4:1.

The effect of spatial variability on the sensitivity of passive microwave measurements to snow water equivalent

Passive microwave (PM) remote sensing measurements are routinely utilized to estimate snow depth and water equivalent (SWE). Both vegetation and physical snowpack variables including snowpack grain size, snow depth, and stratigraphy influence the observed brightness temperature. The natural heterogeneity of snowpack and vegetation states within the microwave footprint occurs at spatial scales shorter than PM observation scales. In this study, we analyze the relationship between PM brightness temperature measurements and the heterogeneity of snowpack and vegetation. Specifically, we explore the question of whether PM observations are sensitive to changes in snow depth even given sub-pixel variability in snow and vegetation. To examine this question, densely sampled, spatially distributed in situ snow properties from multiple study areas made during the NASA Cold Land Processes Experiment (CLPX) are employed in a forward modeling scheme to study the effect of highly variable snow and vegetation properties on the observed PM measurement.In all test cases, this study finds that there exists sensitivity of microwave brightness temperature (Tb) to total snow depth contained within the measurement footprint, regardless of the heterogeneous nature of snow pack properties. Across three study areas, Tb decreases by 23–35K as depth increased up to the signal saturation depth, which ranged from 70 to 120cm. With regard to vegetation sensitivity, forest fractions (F) as little as 0.2 can modify the PM measurement by up to 10K, and F greater than 0.6 mask virtually all of the microwave signal attributable to snow. Finally, with respect to the measurement scale, our results indicate that the scale at which the PM measurement is made does not affect the sensitivity of the Tb to mean snow depth, to the scale (1km) examined herein.

Statistical Spatial Models for Soil Parameters: A Comparative Analysis of Several Methods Applied to Dobrovăţ Basin (Eastern Romania)

This study compares the performance of several statistical methods (multiple linear regression, analysis of covariance, geographically weighted regression, regression kriging, and ordinary kriging) for deriving spatial models of soil parameters. The applications were carried out within a 186-km2 hydrographic basin situated in eastern Romania. Statistical models were computed from a sample of approximately 180 soil profiles, scattered in the eastern half of the basin. Two independent samples, each of 50 soil profiles, were used for validation inside (interpolation) and outside (extrapolation) the main sampling area. The predictors included X and Y coordinates of soil profiles, geomorphometrical parameters (altitude, slope, aspect, wetness index, terrain curvature), climate parameters (mean annual temperatures, precipitation, global radiation), the normalized difference vegetation index, the main soil types, land use, and surface lithology. For only three soil variables the geostatistical approach proved to be useful: occurrence depth of calcium carbonates, pH, and base saturation. The best spatial models were achieved using analysis of covariance, geographically weighted regression, and ordinary kriging. The most relevant continuous predictor is the mean annual precipitation, whereas the most relevant qualitative factor is the soil type.

비탈면 침투해석시 지반 및 강우조건에 의한 포화깊이 분석

우리나라는 기후변화에 따른 국지성 호우의 증가로 비탈면 붕괴와 같은 재해 가능성이 높아지고 있으며, 이러한 재해를 사전에 예방하기 위해 "건설공사 비탈면 설계기준"에 관련 지침사항을 규정하고 있다. 최근에는 관련 지침 중 기존의 우기시 비탈면 안정성 검토 방법이 강우의 침투를 고려하여 보다 현실적으로 수행할 수 있도록 개정되었다. 본 연구에서는 이러한 동향에 따라 통일분류법에 따른 흙의 종류와 강우강도별 포화깊이를 분석하였다. 분석 결과, 전반적으로 투수계수와 강우강도가 클수록 포화깊이도 비례하여 증가하는 양상을 보였으나 MH, CL에서는 포화영역이 발생하지 않았다. 또한 선행강우를 해석상에 반영한 경우에 포화깊이가 전반적으로 증가하였으며, 강우량이 많은 경우 보다 적은 경우에 포화영역의 증가율이 높은 것으로 나타났다. Climate change, according to the country to increase locality of slope collapse of heavy disaster, such as increasing the likelihood and prior in order to prevent these disasters, "Slope construction design standards (Ministry of Land, 2011)," is prescribed in the relevant guidelines. In recent years, guidelines Slope Stability Analysis of the existing methods when the rainy season infiltration of rainfall, taking into account have been revised to perform more realistic. In this study, according these trends to the analysis of saturation depth by rainfall intensity and soil conditions. Results as a whole, the larger the saturated hydraulic conductivity and depth of rainfall intensity also showed a tendency to rise in proportion but MH, CL did not occur in the saturation region. Analysis of antecedent rainfall case also reflects an overall increase of depth in the saturated, rainfall in many cases is less than the growth rate was higher in the saturation region.

불포화토 내 강우침투에 따른 포화깊이비를 고려한 사면안정해석

본 연구는 기존에 제안된 무한사면 안정해석식을 바탕으로 불포화토 내에 강우침투 시 지표로부터 시간에 따른 토층의 포화깊이비를 새로운 변수로 삽입하여 무한사면 안정해석 수정식을 제안하고자 하였다. 이를 위해 기존에 고려하지 못했던 시간에 따른 포화깊이비와 지표하 흐름 깊이의 개념을 새로이 도입하였으며, 유사동력학적 습윤지수 이론에서 도출되는 해석대상 지역의 유효상부기여면적, 지표하흐름 깊이, 포화깊이비를 계산하고, 이를 토대로 시간에 따른 포화깊이비를 반영한 무한사면 안정해석을 수행하도록 하였다. 이를 통해 실질적인 시간에 따른 강우의 변화양상과 사면 안전율 변화를 계산할 수 있게 되었다. 한편, 본 연구에서는 Park et al. (2011 a)가 실시한 불포화토 칼럼시험을 통한 강우침투 속도분석 결과를 바탕으로 본 연구에서 제안한 식을 이용하여 토층의 포화깊이비를 고려한 사면안정해석을 실시하였다. 이 해석을 통해 편마암 풍화토의 토층 내 강우 침투속도를 고려하여 포화깊이비가 변화함에 따른 안전율의 변화를 파악할 수 있었다. 해석결과에 의하면, 연속강우의 경우 안전율이 1.3 이하로 감소하는 시간이 강우강도 20 mm/h 조건에서 2.86 ~ 5.38시간이고, 강우강도 50 mm/h 조건에서는 1.34 ~ 2.92시간으로 나타났다. 반복강우의 경우, 안전율이 1.3 이하가 되는 시간은 강우조건별로 3.27 ~ 5.61시간으로 나타났다. 따라서, 토층 내 강우침투속도 차이에 따른 포화깊이비 변화를 고려한 무한사면의 안전율 변화 파악이 가능하였다. This study proposes a modified equation to calculate the factor of safety for an infinite slope considering the saturation depth ratio as a new variable calculated from rainfall infiltration into unsaturated soil. For the proposed equation, this study introduces the concepts of the saturation depth ratio and subsurface flow depth. Analysis of the factor of safety for an infinite slope is conducted by the sequential calculation of the effective upslope contributing area, subsurface flow depth, and the saturation depth ratio based on quasi-dynamic wetness index theory. The calculation process makes it possible to understand changes in the factor of safety and the infiltration behavior of individual rainfall events. This study analyzes stability changes in an infinite slope, considering the saturation depth ratio of soil, based on the proposed equation and the results of soil column tests performed by Park et al. (2011 a). The analysis results show that changes in the factor of safety are dependent on the saturation depth ratio, which reflects the rainfall infiltration into unsaturated weathered gneiss soil. Under continuous rainfall with intensities of 20 and 50 mm/h, the time taken for the factor of safety to decrease to less than 1.3 was 2.86-5.38 hours and 1.34-2.92 hours, respectively; in the case of repeated rainfall events, the time taken was between 3.27 and 5.61 hours. The results demonstrate that it is possible to understand changes in the factor of safety for an infinite slope dependent on the saturation depth ratio.

GEOCHEMICAL CONTROLS ON CARBONATE SHELL TAPHONOMY IN NORTHERN GULF OF MEXICO CONTINENTAL SHELF AND SLOPE SEDIMENTS

Abstract We examine the linkage between the sediment geochemical milieu and the process of carbonate degradation over a wide range of continental shelf and slope sediments using molluscan shells deployed for 13 years by the Shelf and Slope Experimental Taphonomy Initiative (SSETI). Geochemical characterization of the environment of preservation included the breadth of the pore-water carbonate undersaturation window, a depth-integrated carbonate dissolution index, the depth of minimum pore-water saturation, diffusive fluxes of oxygen and calcium, average sulfate and chloride concentration in the upper 5 cm, and the carbonate and organic carbon fractions in the same sedimentary horizon. Taphonomic indices included the maximum degree of dissolution; average dissolution; the incidences of chalkiness, pitting, deep dissolution, and a soft shell surface; the maximum degree of discoloration; the incidences of fading, gray-to-black discoloration, brown discoloration, and orange discoloration; the presence of pyri...

GEO-Environmental Suitability Evaluation of Land for Urban Construction Based on A Back-Propagation Neural Network and GIS: A Case Study of Hangzhou

Evaluating the geo-environmental suitability of land for urban construction is an important step in the analysis of urban land use potential. Using geo-environmental factors and the land use status of Hangzhou, China, a back-propagation (BP) neural network model for the evaluation of the geo-environmental suitability of land for urban construction was established with a geographic information system (GIS) and techniques of grid, geospatial, and BP neural network analysis. Four factor groups, comprising nine separate subfactors of geo-environmental features, were selected for the model: geomorphic type, slope, site soil type, stratum steadiness, Holocene saturated soft soil depth, groundwater abundance, groundwater salinization, geologic hazard type, and geologic hazard degree. With the support of the model, the geo-environmental suitability of Hangzhou land for urban construction was divided into four suitability zones: zone I, suitable for super high-rise and high-rise buildings; zone II, suitable for multi-story buildings; zone III, suitable for low-rise buildings; and zone IV, not suitable for buildings. The results showed that a BP neural network can capture the complex non-linear relationships between the evaluation factors and the suitability level, and these results will support scientific decision-making for urban-construction land planning, management, and rational land use in Hangzhou.

Submarine Slope Failure Primed and Triggered by Bottom Water Warming in Oceanic Hydrate-Bearing Deposits

Many submarine slope failures in hydrate-bearing sedimentary deposits might be directly triggered, or at least primed, by gas hydrate dissociation. It has been reported that during the past 55 years (1955–2010) the 0–2000 m layer of oceans worldwide has been warmed by 0.09 °C because of global warming. This raises the following scientific concern: if warming of the bottom water of deep oceans continues, it would dissociate natural gas hydrates and could eventually trigger massive slope failures. The present study explored the submarine slope instability of oceanic gas hydrate-bearing deposits subjected to bottom water warming. One-dimensional coupled thermal-hydraulic-mechanical (T-H-M) finite difference analyses were performed to capture the underlying physical processes initiated by bottom water warming, which includes thermal conduction through sediments, thermal dissociation of gas hydrates, excess pore pressure generation, pressure diffusion, and hydrate dissociation against depressurization. The temperature rise at the seafloor due to bottom water warming is found to create an excess pore pressure that is sufficiently large to reduce the stability of a slope in some cases. Parametric study results suggest that a slope becomes more susceptible to failure with increases in thermal diffusivity and hydrate saturation and decreases in pressure diffusivity, gas saturation, and water depth. Bottom water warming can be further explored to gain a better understanding of the past methane hydrate destabilization events on Earth, assuming that more reliable geological data is available.

Synthesis towards a global-bathymetric model of metabolism and chemical composition of marine pelagic chaetognaths

Respiration (=oxygen consumption) and chemical composition [water content, ash, carbon (C) and nitrogen (N)] were determined for seven chaetognaths (Parasagitta elegans, Caecosagitta macrocephala, Pseudosagitta scrippsae, Solidosagitta zetesios, Eukrohnia hamata, Eukrohnia bathypelagica and Eukrohnia fowleri) from the epipelagic through bathypelagic zones (<3000m) in the western subarctic Pacific Ocean. Enzyme activities of the electron transfer system (ETS) were also determined on mesopelagic and bathypelagic chaetognaths, and ETS:Respiration ratios were calculated to confirm the validity of respiration rates measured at near in situ temperature but under normal pressure (1atm). These data were combined with literature data from Arctic, Antarctic, temperate and tropical waters, and epipelagic through bathypelagic zones. A total of 25 data sets on 17 chaetognaths for respiration, and a total of 18–34 data sets on 18–21 chaetognaths for chemical composition were used to explore important parameters affecting their respiration rates and chemical composition. Designating body mass (dry mass, C or N), ambient temperature, oxygen saturation and sampling depth as independent variables, stepwise multiple regression analyses revealed that body mass, habitat temperature and sampling depth were significant, attributing 82–93% of the variance of respiration rates. No significant effect of sampling depth and habitat temperature was detected in the chemical composition. These results are compared with those of copepods to highlight unique features of chaetognaths.