Distinctive stable isotope ratios in important zooplankton species in relation to estuarine salinity gradients: Potential tracer of fish migration

To assess the potential of stable isotope ratios as an indicator of fish migration within estuaries, stable isotope ratios in important zooplankton species were analyzed in relation to estuarine salinity gradients. Gut contents from migratory juveniles of the euryhaline marine fish Lateolabrax japonicus were examined along the Chikugo River estuary of the Ariake Sea, which has the most developed estuarine turbidity maximum (ETM) in Japan. Early juveniles in March and April preyed primarily on two copepod species; Sinocalanus sinensis at lower salinities and Acartia omorii at higher salinities. Late juveniles (standard length > 40 mm) at lower salinities preyed exclusively on the mysid Acanthomysis longirostris until July and complementarily on the decapod Acetes japonicus in August. These prey species were collected along the estuary during the spring–summer seasons of 2003 and 2004, and their carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) were evaluated. The δ¹³C values of prey species were distinct from each other and were primarily depleted within and in close proximity to the ETM (salinity < 10); S. sinensis (−26.6‰) < Acanthomysis longirostris (−23.3‰) < Acartia omorii (−21.1‰) < Acetes japonicus (−18.5‰). The overall gradient of δ¹³C with salinity occurred for all prey species and showed minor temporal fluctuations, while it was not directly influenced by the δ¹³C values in particulate organic matter along the estuary. In contrast to δ¹³C, the δ¹⁵N values of prey species did not exhibit any clear relationship with salinity. The present study demonstrated that δ¹³C has the potential for application as a tracer of fish migration into lower salinity areas including the ETM.     

Neural Network-Based Estimation of Principal Metal Contents in the Hokuroku District,Northern Japan,for Exploring Kuroko-Type Deposits

The Hokuroku district, extending over 40 × 40 km² in northern Japan, is known to be dominated by kuroko-type massive sulfide deposits that have a genetic relation to submarine volcanic activity. The deposits are hosted in a specific stratigraphic zone of Miocene volcanic rocks. Because kuroko-type deposits are under exploration in several countries, it is important to integrate the geologic and geochemical data that have been accumulated in the Hokuroku district to characterize the distribution of deposits and produce a map of mineral potential. Thus, we collected data on multiple chemical components from 1917 rock cores at 143 drillhole sites and concentrated on components with relatively large amounts of data, which are SiO₂, Al₂O₃, and Fe₂O₃ as major elements and Cu, Pb, and Zn as trace elements. Although frequencies of these data can be approximated by normal or lognormal distributions, spatial correlation structures cannot be extracted from the semivariograms of each component nor from the cross-semivariograms between two components of the major or minor elements. To handle such complexity, a spatial method of modeling content distribution, SLANS, is developed by applying a feedforward neural network. The principle of SLANS is to train a network repeatedly to recognize the relation between the data value and the location and lithology of a sample point. One-hundred outputs for each element are obtained by changing the numbers of neurons in a middle layer from 1 to 10 and sample data used for training from 3 to 12, and finally one output is selected based on the estimation precision of the network which is restricted near the target point. After constructing a geologic distribution model from the geological column classified into 25 rock codes, three-dimensional distributions of Cu, Pb, and Zn contents are estimated over the study area. The content models are considered to be valid because high-content zones are located on the known mine sites and the margins of ancient volcanoes or calderas. Some zones are distributed along strikes of major deep-seated fractures in the district.     

Seasonal changes in camera-based indices from an open canopy black spruce forest in Alaska,and comparison with indices from a closed canopy evergreen coniferous forest in Japan

Evaluation of the carbon, water, and energy balances in evergreen coniferous forests requires accurate in situ and satellite data regarding their spatio-temporal dynamics. Daily digital camera images can be used to determine the relationships among phenology, gross primary productivity (GPP), and meteorological parameters, and to ground-truth satellite observations. In this study, we examine the relationship between seasonal variations in camera-based canopy surface indices and eddy-covariance-based GPP derived from field studies in an Alaskan open canopy black spruce forest and in a Japanese closed canopy cedar forest. The ratio of the green digital number to the total digital number, hue, and GPP showed a bell-shaped seasonal profile at both sites. Canopy surface images for the black spruce forest and cedar forest mainly detected seasonal changes in vegetation on the floor of the forest and in the tree canopy, respectively. In contrast, the seasonal cycles of the ratios of the red and blue digital numbers to the total digital numbers differed between the two sites, possibly due to differences in forest structure and leaf color. These results suggest that forest structural characteristics, such as canopy openness and seasonal forest-floor changes, should be considered during continuous observations of phenology in evergreen coniferous forests.     

Characteristics of evapotranspiration from a permafrost black spruce forest in interior Alaska

Here, the year 2011 characteristics of evapotranspiration and the energy budget of a black spruce forest underlain by permafrost in interior Alaska were explored. Energy balance was nearly closed during summer, and the mean value of the daily energy balance ratio (the ratio of turbulent energy fluxes to available energy) from June to August was 1.00, though a large energy balance deficit was observed in the spring. Such a deficit was explained partly by the energy consumed by snowmelt. Ground heat flux played an important role in the energy balance, explaining 26.5% of net radiation during summer. The mean daily evapotranspiration of this forest during summer was 1.37 mm day^?1 – considered typical for boreal forests. The annual evapotranspiration and sublimation yielded 207.3 mm year^?1, a value much smaller than the annual precipitation. Sublimation accounted for 8.8% (18.2 mm year^?1) of the annual evapotranspiration and sublimation; thus, the sublimation is not negligible in the annual water balance in boreal forests. The daytime average decoupling coefficient was very small, and the mean value was 0.05 during summer. Thus, evapotranspiration from this forest was mostly explained by the component from the dryness of the air, resulting from the aerodynamically rough surface of this forest.     

JAMSTEC-IARC international collaboration enhancing understanding of the Arctic climate system

Collaborations amongst researchers from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan and the International Arctic research Center (IARC), University of Alaska Fairbanks (UAF), U.S., have been on-going since 1998 and resulted in a great number and magnitude of accomplishments that could not have been achieved without this close partnership. The Arctic represents an important region for Japan, the U.S. and the world, and many opportunities and challenges press for immediate understanding to enable wise decisions and policy making. We have many common interests and our countries face many common problems and goals. Addressing the tremendous scientific challenges of the Arctic requires such massive investment of manpower and resources that sharing efforts, data and working together on expeditions are in our mutual best interests.This issue presents a compilation of selected results on recent analyses conducted in the five-year (2009–2014) research term related to observational studies, model development and remote sensing applications of the Arctic Ocean, adjacent marginal seas, and the surrounding terrestrial regions. All of these studies are intended to provide a better understanding of how individual components and processes interact to form a complex and dynamic arctic system. Through these collaborations, Japanese and UAF Arctic researchers can achieve our goals of developing a quantitative understanding of the Arctic System.     

A new fracture criterion for brittle rocks

A general form of a “fracture function” for isotropic brittle materials is expressed in terms of the three invariants of the stress tensor. The coefficients in the function are determined by use of the small number of experimental data under specific conditions. This function is applicable to an estimate of the fracture condition of brittle rocks under a general stress state i.e., σ₁ ≠ σ₂ ≠ σ₃. The application of this function is attempted for the data of three brittle rocks i.e., Dunham dolomite, Mizuho trachyte, and Westerly granite, reported by previous workers. For the first two, this criterion gives a good estimation of the effect of the intermediate principal stress σ₂ on failure. For the last, the fracture strength at high confining pressure is estimated by use of the several data obtained under very low confining pressures, and the agreement with experimental data is also satisfactory.     

Comprehensive numerical analysis of fault‐structure systems – Computation of the large‐scale seismic structural response to a given earthquake scenario –

The seismic structural response is affected by temporal and spatial variations in strong ground motion. It can be evaluated through the fault‐structure system: the fault mechanism, wave propagation through the crust, amplification near the surface, and soil‐structure interaction. To analyze this system at high resolution and accuracy, we previously proposed a new multiscale analysis method and numerically verified its validity. However, the problem of the extremely large computation cost of constructing a three‐dimensional numerical model and solving the discretized governing equations still remains. Here, we introduce a new method to resolve these difficulties. By combining this new method with our multiscale analysis, we developed a tool for fault‐structure system analysis. The accuracy of this tool is verified by comparing it to a Green's function solution. Finally, we demonstrate the potential utility of the method by estimating the seismic response of a large and complex underground highway junction in a given earthquake scenario. Copyright © 2011 John Wiley & Sons, Ltd.     

U–Pb zircon geochronology of the North Pole Dome adamellite in the eastern Pilbara Craton

Supracrustal rocks around the North Pole Dome area, Western Australia, provide valuable information regarding early records of the evolution of crustal processes, surface environments, and biosphere. Owing to the occurrence of the oldest known microfossils, the successions at the North Pole Dome area have attracted interest from many researchers. The Paleoarchean successions (Warrawoona Group) mainly comprise mafic‐ultramafic greenstones with intercalated cherts and felsic lavas. Age constraints on the sediments have been mainly based on zircon U–Pb geochronology. However, many zircon grains have suffered from metamictization and contain anomalously high contents of common Pb, which makes interpretation of the U–Pb data complicated. In order to provide more convincing chronological constraints, an U–Pb Concordia age is widely accepted as the best estimate. Most zircons separated from two adamellites also suffered from severe metamictization. In our analyses, less metamictized domains were selected using a pre‐ablation technique in conjunction with elemental mapping, and then their U–Pb isotopic compositions were determined with a laser ablation inductively coupled plasma mass spectrometry. Most analyzed domains contained certain amounts of common Pb (²⁰⁴Pb/²⁰⁶Pb > 0.000 1), whereas three and five U–Pb data points with less common Pb (²⁰⁴Pb/²⁰⁶Pb < 0.000 1) were obtained. These U–Pb datasets yielded U–Pb Concordia ages of ca 3 445 Ma and 3 454 Ma, respectively. These ages represent the timing of the adamellite intrusion, and constrain the minimum depositional age of the Warrawoona Group. In addition, a single xenocrystic zircon grain showed a ²⁰⁷Pb/²⁰⁶Pb age of ca 3 545 Ma, supporting the idea that the sialic basement of the Pilbara Craton existed prior to 3 500 Ma. The in situ U–Pb zircon dating combined with the pre‐ablation technique has the potentials to identify non‐metamictized parts and to yield precise and accurate geochronological data even from partially metamictized zircons.     

The peristerite gap in low-grade metamorphic rocks

Coexisting Na-plagioclases from greenschists both in the thermal aureole of the Kasugamura Granite, Japan, and in the low-P metamorphic zone of Yap Island, western Pacific were analyzed in great detail; the peristerite solvus was determined for each suite. The asymmetric solvus has steep albite-rich and gentle oligoclase-rich limbs that are similar to those for higher pressure series. The present results together with those from Vermont, New Zealand, and the Sanbagawa belt indicate that the peristerite solvus shifts toward the albite component and higher temperature with increasing pressure. With increasing pressure, albite co-existing with oligoclase (An=100 Ca/Ca+ Na=20) varies in composition from An 8–9 (in Kasugamura), through An 3 (in Yap Island and Vermont), to An 1 (in New Zealand) and An less than 0.5 (in the Sanbagawa belt). The consolute temperatures for the peristerite solvus estimated from available geothermometry are 420° C in Kasugamura, 450–550° C in Vermont and 550°–600° C in the Sanbagawa belt. The variation of plagioclase composition in progressive metamorphic zones is explained by intersection of a plagioclase-forming reaction and the peristerite immiscibility gap in an isobaric T-X _An diagram. The greenschist zone is characterized by albite, the transition zone by occurrence of peristerite pairs and the amphibolite zone by plagioclase of An 20–50.