Suction dynamics-induced bubbly sand under groundwater table fluctuations     

Shinji Sassa  Soonbo Yang 《Sedimentology》2023,70(1):280-288

Bubbly sand is found in intertidal zones and has been considered to be closely related to swash and tides. Unlike bubble structures that arise from in situ methane gas production and bubble growth in river and marine sediments due to organic matter decomposition, the formation mechanism and conditions of bubbly sand remain unresolved. The present study aims to resolve them on the basis of a conceptual model and controlled laboratory experiments. The study demonstrates that bubbly sand is a consequence of the cyclic expansion of sand under groundwater table fluctuations. The varying intensity of dynamics of suction, which is sand moisture tension defined by negative pore water pressure relative to atmospheric pressure, controls the manifestation of a full spectrum of sand behaviour relevant to the formation of bubbly sand. Namely, with increasing intensity of suction dynamics under larger groundwater table fluctuations, the sand behaviour varies from enhanced cyclic contraction, to weak contraction, loosening and expansion resulting in bubbly sand. The suction dynamics-induced cyclic expansion of sand occurs under conditions where the maximum suction developed exceeds the air-entry suction of sand such that the degree of saturation becomes lower than 60%, while the groundwater tables cyclically rise to and fall from the sediment surface. Accordingly, the sand porosity changes remarkably from dense to super-loose states of bubbly sand. These findings account for previously unanswered questions with respect to bubbly sand, both qualitatively and quantitatively, and will lead to a renewed understanding of the geological record and morphological features at waterfronts that are subject to groundwater table fluctuations.  相似文献   

Effects of raised CO2 concentration on the egg production rate and early development of two marine copepods (Acartia steueri and Acartia erythraea)     

Kurihara H  Shimode S  Shirayama Y 《Marine pollution bulletin》2004,49(9-10):721-727

Direct injection of CO(2) into the deep ocean is receiving increasing attention as a way to mitigate increasing atmospheric CO(2) concentration. To assess the potential impact of the environmental change associated with CO(2) sequestration in the ocean, we studied the lethal and sub-lethal effects of raised CO(2) concentration in seawater on adult and early stage embryos of marine planktonic copepods. We found that the reproduction rate and larval development of copepods are very sensitive to increased CO(2) concentration. The hatching rate tended to decrease, and nauplius mortality rate to increase, with increased CO(2) concentration. These results suggest that the marine copepod community will be negatively affected by the disposal of CO(2). This could decrease on the carbon export flux to the deep ocean and change the biological pump. Clearly, further studies are needed to determine whether ocean CO(2) injection is an acceptable strategy to reduce anthropogenic CO(2).  相似文献   

Ecological aspects of hydrothermal vent animals in captivity at atmospheric pressure     

Hiroshi Miyake  Mitsugu Kitada  Shinji Tsuchida  Yoko Okuyama  & Ko-ichi Nakamura 《Marine Ecology》2007,28(1):86-92

Hydrothermal vent animals were kept and displayed at atmospheric pressure with an artificial hydrothermal vent system in Enoshima Aquarium, Fujisawa, Kanagawa, Japan. The artificial hydrothermal vent system was composed of a main rearing tank, a heating tank, a hot water outlet with added Na₂S as the source of H₂S, and added CO₂ for chemosynthetic bacteria and pH regulation. When the need arises, a dissolved oxygen control unit and submersible heaters can be attached. We are now rearing hydrothermal vent crabs (Austinograea yunohana), hydrothermal vent galatheid crabs (Shinkaia crosnieri), vestimentiferan tubeworms (Lamellibrachia satsuma), hydrothermal vent shrimp (Opaepele spp.), hydrothermal vent barnacles (Ashinkailepas seepiophilia and Neoverruca sp.), and tonguefish (Symphurus sp.). In the artificial hydrothermal vent tank, shrimp and crabs have been observed to cluster close to the artificial hydrothermal vent. In particular, large (adult) crabs needed a heat source to live in the aquarium over a long term. Additionally, some species (A. yunohana, S. crosnieri, Opaepele sp. and Symphurus sp.) have spawned and hatched in captivity. It is likely higher water temperatures are needed for egg and larval development compared with temperatures for adult requirements.  相似文献   

Sub-Lethal Effects of Elevated Concentration of CO<Subscript>2</Subscript> on Planktonic Copepods and Sea Urchins   总被引：2，自引：0，他引：2  

Haruko Kurihara  Shinji Shimode  Yoshihisa Shirayama 《Journal of Oceanography》2004,60(4):743-750

Data concerning the effects of high CO₂ concentrations on marine organisms are essential for both predicting future impacts of the increasing atmospheric CO₂ concentration and assessing the effects of deep-sea CO₂sequestration. Here we review our recent studies evaluating the effects of elevated CO₂ concentrations in seawater on the mortality and egg production of the marine planktonic copepod, Acartia steueri, and on the fertilization rate and larval morphology of sea urchin embryos, Hemicentrotus pulcherrimus and Echinometra mathaei. Under conditions of +10,000 ppm CO₂ in seawater (pH 6.8), the egg production rates of copepods decreased significantly. The survival rates of adult copepods were not affected when reared under increased CO₂ for 8 days, however longer exposure times could have revealed toxic effects of elevated CO₂ concentrations. The fertilization rate of sea urchin eggs of both species decreased with increasing CO₂ concentration. Furthermore, the size of pluteus larvae decreased with increasing CO₂ concentration and malformed skeletogenesis was observed in both larvae. This suggests that calcification is affected by elevated CO₂ in the seawater. From these results, we conclude that increased CO₂ concentration in seawater will chronically affect several marine organisms and we discuss the effects of increased CO₂ on the marine carbon cycle and marine ecosystem. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Geographical Variations in Prosome Length and Body Weight of Neocalanus Copepods in the North Pacific     

Toru Kobari  Kazuaki Tadokoro  Akihiro Shiomoto  Shinji Hashimoto 《Journal of Oceanography》2003,59(1):3-10

Geographical variations in prosome length and body weight of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were investigated on samples from North-South and East-West transects in the North Pacific during spring to early summer in 1998 and 1999. Southward and eastward increasing patterns were pronounced for water temperature, although no significant pattern was observed for chlorophyll a concentrations. All Neocalanus species showed large geographical variations in prosome length and body weight, being smaller in the southern and eastern waters. Comparing the relationship between prosome length and body weight, large deviations (lower body weight at a given prosome length) were evident for the eastern specimens of N. cristatus and N. plumchrus. In stepwise regression analysis, the geographical variations of prosome length and body weight revealed a significantly negative correlation with temperature variations. These results suggest that temperature is a more important environmental factor than chlorophyll a concentration in its effect on geographical variations in prosome length and body weight of Neocalanus copepods in the North Pacific. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Evolution of the composition of seawater through geologic time, and its influence on the evolution of life   总被引：2，自引：2，他引：0  

Tsuyoshi Komiya  Takafumi Hirata  Kouki Kitajima  Shinji Yamamoto  Takazo Shibuya  Yusuke Sawaki  Tomoko Ishikawa  Degan Shu  Yong Li  Jian Han 《Gondwana Research》2008,14(1-2):159

The redox state of the surface environment of the early Earth is still controversial, and a detailed and quantitative estimate is still lacking. We carried out in-situ analyses of major, trace, and rare-earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea-deposits, in order to eliminate secondary carbonate and contamination of detrital materials, and to estimate the redox condition of seawater through time. Based on the Ce content and anomalies of the carbonate minerals at given parameters of atmospheric CO₂ content (pCO₂) and Ca content of seawater, we calculated the oxygen contents of shallow and deep seawater, respectively. The results show that the oxygen content of the deep sea was low and constant until at least 1.9 Ga. The oxygen content of shallow seawater increased after 2.7 Ga, but fluctuated. It became quite high at 2.5 and 2.3 Ga, but eventually increased after the Phanerozoic. In addition, the calculation of a high pCO₂ condition shows that seawater was more oxic even in the Archean than at present, suggesting a relatively low pCO₂ through geologic time.Our detailed calculations from compositions of carbonate minerals in Three Gorge area, south China show a low oxygen content of seawater after the Snowball Earth until the late Ediacaran, an increase in the late Ediacaran, and a significant decrease around the Precambrian–Cambrian and Nemakit/Daldynian–Tommotian boundaries. These variations were possibly caused by global regression and dissolution of methane hydrates.  相似文献   

Classification of magnetic reconnection during two current-loop coalescence     

Jun-ichi Sakai  Shinji Koide 《Solar physics》1992,142(2):399-402

We present a classification of magnetic reconnection during two current loop coalescence, which may be quite important for the physical process of both solar flares and coronal loop heating in the solar active region. It is suggested that different kinds of the current loop coalescence processes could be identified from the soft X-ray telescope(SXT) of the Yohkoh satellite and the magnetic field data in the active region.  相似文献   

A quadratic element method for evaluating groundwater flow by the inversion of surface tilt with application to the Tono Area, Japan     

Koji Matsuki  Katsuya Nakatani  Takashi Arai  Kazuo Ohmura  Ryuji Takeuchi  Yasushi Arai  Shinji Takeuchi 《Journal of Hydrology》2008,360(1-4):217-229

By modifying a previous method with constant elements, we developed a quadratic element method for more accurately estimating groundwater flow by the inversion of tilt data. In this method: (1) a region of groundwater flow is divided into quadratic elements in which the change in groundwater volume per unit volume of rock (Δv) and the Skempton coefficient (B) vary in a quadratic manner with the coordinates, (2) the values of Δv are set to zero at the boundaries of the region of groundwater flow and (3) the sum of the squared second derivatives of Δv is adopted as a constraining condition that is weighted and added to the sum of the squared errors in tilt. First, analyses were performed for a flow model to determine the accuracy of this method for estimating groundwater flow and also to clarify the effect of the assumed size of a region of groundwater flow. These analyses showed that the quadratic element method proposed in this study gives a much better estimation of Δv than the constant element method and that a large region of groundwater flow should be assumed, rather than a small region, since the values of Δv at points outside of the actual region of groundwater flow are estimated to be nearly zero when a large region is assumed while these values are greatly overestimated when an excessively small region is assumed. Finally, the quadratic element method was applied to the site of the Mizunami Underground Research Laboratory in the Tono area, Japan. Inverse analyses were performed for tilt data measured by four tiltmeters with a resolution of 10⁻⁹ radians during the excavation of two shafts under the assumption that the rock mass is an isotropic and homogeneous half- space. The results showed that the method proposed in this study reproduced the tilt data very accurately. Thus, the distribution of Δv was estimated without sacrificing the reproducibility of the tilt data. The contour maps of B(1 + ν)Δv (ν: Poisson’s ratio) showed that the heterogeneous flow of groundwater occurred at the site and that groundwater volume decreased mainly in the area surrounded by two faults. The latter result is consistent with the finding obtained by previous investigations that these faults have low permeability in the direction perpendicular to the strike and may act as a flow barrier.  相似文献   

Primary productivity and solar radiation off Sanriku in May 1997     

Akihiro Shiomoto  Shinji Hashimoto  Takayuki Murakami 《Journal of Oceanography》1998,54(5):539-544

We measured the in situ primary production at four stations from the surface to 80 m off Sanriku in late May 1997. The depth-integrated daily primary production in the upper 80 m was estimated to be 391, 468, and 855 mgC m⁻²d⁻¹ in water from the Oyashio, and 336 mgC m⁻²d⁻¹ in the warm-core ring. The variation in the primary production was primarily due to the variation in phytoplankton activity (chlorophyll α-specific primary production). A combination of previous and present studies in water from the Oyashio and the warm-core ring suggested that phytoplankton activity is proportional to light intensity between 12 and 50 Ein m⁻²d⁻¹ which is close to the usual light condition (61–75 Ein m⁻²d⁻¹) off Sanriku in May and June. Light may be a limiting factor for phytoplankton off Sanriku in late spring and early summer.  相似文献   

西南日本秋吉带石炭系高山(Ko-yama)灰岩群的褶皱构造     

Noriyuki INADA  Shigeyuki SUZUKI  Keisuke ISHIDA  Shinji YAMASHITA 《地球学报》2012,33(S1):24-24

The study area is located in Kawakami-cho, Okayama Prefecture, which is occupied by Lower Carboniferous to Middle Permian Ko-yama Limestone Group (Yokoyama et al., 1979), Permian Yoshii Group (Sano et al., 1987) and Triassic Nariwa Group (Tera-oka, 1959). The Nariwa Group unconformably covers the Paleozoic successions (Otoh, 1985). These succes-sions belong to the Akiyoshi Belt. The Ko-yama Limestone Group is composed mainly of massive limestone, with basic volcanic rocks, acidic tuff and chert. The group was dated by foraminifer and fusu-linid as Lower Carboniferous to Middle Permian (Yo-koyama et al., 1979).  相似文献