structure of south-western Honshu, Japan and the nature of the Mohorovicić discontinuity

Summary. Two record sections have been prepared for a series of explosions near Lake Biwa, south-western Honshu, Japan. The record sections cover both the array stations and the network of microearthquake stations that are distributed throughout the area. This enabled us to detect for the first time in the Japanese islands the phase reflected at the Mohorovicić discontinuity. Until now the weakness and obscurity of the phase has made it difficult to detect. We were able to overcome this problem by processing the seismograms to enhance the phase. Our work leads us to propose that the surface of the Mohorović discontinuity may be divided into pieces by a number of deep faults, while a thin layer of ultrabasic rock in the lower crust may account for the weakness of the signal.     

Surface-wave study of the Labrador Sea earthquake 1971 December

Source parameters of an earthquake that occurred on the continental slope off the coast of Labrador, the first earthquake known to have occurred in this region, are determined by using body-and surface-wave data. The focal mechanism is of the dip slip type and the focal depth is 16 km. The local deviatric stress field applied to the region is estimated to be compressional oriented normal to the North American continent. The observed surface-wave spectra are characterized by a sharp fall-off near the period T = 15–20 s. This observed fall-off is attributed to thick sediment at the continental slope. Consequently, when an earthquake is not located within a continental area, the source parameter determination using short-period surface waves is restricted in application.     

TiO2/浮石复合材料降解有机污染物亚甲基蓝的实验研究

利用天然浮石的孔隙结构和小比重等特点,以浮石为原料、TiOSO4为TiO2前驱体,采用水热合成法,在200℃、15 h条件下,制备出可漂浮的TiO2/浮石复合材料.采用10×10-5mol/L亚甲基蓝水溶液,在紫外光下进行光催化实验.并用紫外可见分光光度计检测亚甲基蓝浓度变化.实验结果表明,TiO2/浮石复合材料能够降解亚甲基蓝.该材料的孔隙结构对亚甲基蓝有聚集作用,促进了负载的TiO2的光催化性能的发挥.因为成本低廉,性能优越,TiO2/浮石复合材料在有机污染物治理方面具有很大的应用潜力.     

Western Arctic primary productivity regulated by shelf-break warm eddies

The response of phytoplankton to the Beaufort shelf-break eddies in the western Arctic Ocean is examined using the eddy-resolving coupled sea ice–ocean model including a lower-trophic marine ecosystem formulation. The regional model driven by the reanalysis 2003 atmospheric forcing from March to November captures the major spatial and temporal features of phytoplankton bloom following summertime sea ice retreat in the shallow Chukchi shelf and Barrow Canyon. The shelf-break warm eddies spawned north of the Barrow Canyon initially transport the Chukchi shelf water with high primary productivity toward the Canada Basin interior. In the eddy-developing period, the anti-cyclonic rotational flow along the outer edge of each eddy moving offshore occasionally traps the shelf water. The primary production inside the warm eddies is maintained by internal dynamics in the eddy-maturity period. In particular, the surface central area of an anti-cyclonic eddy acquires adequate light, nutrient, and warm environment for photosynthetic activity partly attributed to turbulent mixing with underlying nutrient-rich water. The simulated biogeochemical properties with the dominance of small-size phytoplankton inside the warm eddies are consistent with the observational findings in the western Arctic Ocean. It is also suggested that the light limitation before autumn sea ice freezing shuts down the primary production in the shelf-break eddies in spite of nutrient recovery. These results indicate that the time lag between the phytoplankton bloom in the shelf region following the summertime sea ice retreat and the eddy generation along the Beaufort shelf break is an important index to determine biological regimes in the Canada Basin.     

Lagrangian ensemble model of Copepoda (Neocalanus cristatus) in the northwestern subarctic Pacific

A Lagrangian ensemble model describing the population dynamics of Neocalanus cristatus was developed. To describe the ecology of N. cristatus, life stage must be included in the model. For this purpose, a new zooplankton compartment, divided into nine life stages, was added to the North Pacific ecosystem model for understanding regional oceanography. In addition, we introduced Lagrangian particles for the copepod population. Each Lagrangian particle represented a population of the same cohort of copepods with information on representative age, developmental stage, growth rate, structural weight, and food satiation. The new model revealed that surviving cohorts are only matched with the phytoplankton bloom after the nauplii stages. The model showed that the existing phytoplankton concentration when copepodites of N. cristatus appear in the surface water determines the development pattern of copepodite stages. The timing of the seasonal phytoplankton bloom depends on climate change, and a sensitivity analysis showed that the multiple spawning strategy through time has an important role in matching the unstable seasonal bloom cycle on a daily basis. The model including the cohorts can collaborate closely with weekly or monthly observations to reveal the rapid response of the marine ecosystem.     

Assessment of mixed layer models embedded in an ocean general circulation model

The atmospheric mixed layer obtained using the Mellor–Yamada model grows slower and becomes shallower than observed, which motivated Nakanishi and Niino (J Meteorol Soc Jpn 87:895–912, 2009) to present a modified version of the Mellor–Yamada model. In this study, incorporating each of the Mellor–Yamada and the Nakanishi–Niino models into an ocean general circulation model, we evaluate its performance in the ocean. Comparing the numerical results with the observed ones in the western North Pacific, the Nakanishi–Niino model is shown to exhibit a better performance than the Mellor–Yamada model under strong wind forcing and sea surface cooling during winter and after passage of typhoons during summer.     

Timescales for the evolution of oxygen isotope compositions in the solar nebula

We review two models for the origin of the calcium-, aluminum-rich inclusion (CAI) oxygen isotope mixing line in the solar nebula: (1) CO self-shielding, and (2) chemical mass-independent fractionation (MIF). We consider the timescales associated with formation of an isotopically anomalous water reservoir derived from CO self-shielding, and also the vertical and radial transport timescales of gas and solids in the nebula. The timescales for chemical MIF are very rapid. CO self-shielding models predict that the Sun has Δ¹⁷O_SMOW ∼ −20‰ (Clayton, 2002), and chemical mass-independent fractionation models predict Δ¹⁷O_SMOW ∼0‰. Preliminary Genesis results have been reported by McKeegan et al. (McKeegan K. D., Coath C. D., Heber, V., Jarzebinski G., Kallio A. P., Kunihiro T., Mao P. H. and Burnett D. S. (2008b) The oxygen isotopic composition of captured solar wind: first results from the Genesis. EOS Trans. AGU 89(53), Fall Meet. Suppl., P42A-07 (abstr)) and yield a Δ¹⁷O_SMOW of ∼ −25‰, consistent with a CO self-shielding scenario. Assuming that subsequent Genesis analyses support the preliminary results, it then remains to determine the relative contributions of CO self-shielding from the X-point, the surface of the solar nebula and the parent molecular cloud.The relative formation ages of chondritic components can be related to several timescales in the self-shielding theories. Most importantly the age difference of ∼1-3 My between CAIs and chondrules is consistent with radial transport from the outer solar nebula (>10 AU) to the meteorite-forming region, which supports both the nebular surface and parent cloud self-shielding scenarios. An elevated radiation field intensity is predicted by the surface shielding model, and yields substantial CO photolysis (∼50%) on timescales of 0.1-1 My. An elevated radiation field is also consistent with the parent cloud model. The elevated radiation intensities may indicate solar nebula birth in a medium to large cluster, and may be consistent with the injection of ⁶⁰Fe from a nearby supernova and with the photoevaporative truncation of the solar nebula at KBO orbital distances (∼47 AU). CO self-shielding is operative at the X-point even when H₂ absorption is included, but it is not yet clear whether the self-shielding signature can be imparted to silicates. A simple analysis of diffusion times shows that oxygen isotope exchange between ¹⁶O-depleted nebular H₂O and chondrules during chondrule formation events is rapid (∼minutes), but is also expected to be rapid for most components of CAIs, with the exception of spinel. This is consistent with the observation that spinel grains are often the most ¹⁶O-rich component of CAIs, but is only broadly consistent with the greater degree of exchange in other CAI components. Preliminary disk model calculations of self-shielding by N₂ demonstrate that large δ¹⁵N enrichments (∼ +800‰) are possible in HCN formed by reaction of N atoms with organic radicals (e.g., CH₂), which may account for ¹⁵N-rich hotspots observed in lithic clasts in some carbonaceous chondrites and which lends support to the CO self-shielding model for oxygen isotopes.     

Cosmogenic nitrogen isotopic disequilibrium observed in meteorites

Abstract— The isotopic disequilibrium of N molecules in meteorites was examined. For a large data-set, consisting of mass compositions of N molecules extracted at 1200 °C by stepped combustion of chondrites and eucrites, we find that a cosmogenic-N-enriched component and a normal air-like N component are isotopically disequilibrated with each other. The isotopic composition of the cosmogenic-N-enriched component seems to be variable, although the cause for the variation is not clear. The abundance of indigenous atomic N in silicate minerals seems to be small. Indigenous N in meteoritic silicates, if present, may be present in the form of N molecules.     

Prediction of monthly mean chlorophylla concentration in Mikawa Bay using GMDH

Data on organic and inorganic nitrogen and phosphorus, and meteorological conditions observed a few times a month at a buoy station in Mikawa Bay (Japan) are averaged on a monthly basis, and monthly transitions of chlorophylla at the station are predicted by GMDH (Group Method of Data Handling, one of the methods of nonlinear system identification) using these monthly mean data. The prediction is successful. GMDH is useful in describing the ecosystem and in predicting transitions within the bay.     

Importance of feeding on regenerable parts of prey for juvenile stone flounder Platichthys bicoloratus in estuarine habitats

Prey availability is one of the most important factors affecting the quality of nursery grounds. Estuaries play an important role as nursery grounds for juvenile stone flounder, but the mechanism behind the consistently high availability of prey has never been examined. This study investigates which prey is mainly selected by juvenile stone flounder (15–55 mm standard length) in the estuary of the Natori River, northern Japan. In a cage experiment, juveniles showed positive selection for the palps of the spionid polychaete Pseudopolydora kempi in March, and for the siphons of the bivalve Nuttallia olivacea in April, May and June in both sandy and muddy-sand habitats. This selective predation showed that sublethal predation on regenerable parts of invertebrates is important for stone flounder. Nuttallia olivacea, the dominant bivalve in the estuary, was more abundant and in better somatic condition in the sandy area in spite of the stronger siphon-cropping pressure by juvenile stone flounder. These results confirm that sublethal predation on highly abundant benthos plays an important role in forming estuarine habitats into areas of high prey availability for juvenile stone flounder, which leads to their high growth rate.