Measuring hydraulic permeability in a streambed using the packer test

Permeability of a streambed is an important factor regulating nutrient and oxygen availability for aquatic biota. In order to investigate the relationship, an accurate permeability should be measured. However, it is difficult to measure permeability in a coarse gravel bed using a conventional permeability test. Moreover, turbulent flow may occur in coarse bed material, and then deviations from Darcy's law do occur. Thus, permeability calculated following Darcy's law may be overestimated under turbulent flow conditions and should be corrected. The packer test can be used in highly permeable gravel beds. We developed a field method applicable to a gravel bed using the packer test and derived an equation adopting a law of turbulent flow to study the problems under any type of flow condition. The accuracy of the equation was examined using a laboratory flume with a gravel bed. The results suggested that permeability calculated from Hvorslev's equation is overestimated for turbulent flow. In contrast, our equation, developed here, could evaluate permeability accurately under any type of flow condition. Copyright © 2005 John Wiley & Sons, Ltd.     

Meteor Orbit Determinations with Multistatic Receivers Using the MU Radar

The MU radar of RISH (Research Institute for Sustainable Humanosphere, Kyoto University), which is a MST radar (46.5 MHz, 1 MW peak power), has been successfully applied to meteor studies by using its very high versatility. The system has recently renewed with 25 channel digital receivers which significantly improved the sensitivity and precision of interferometer used in meteor observation. The transmission is now synchronized to GPS signals, and two external receiving sites with a ranging capability has additionally been operated in order to determine the trajectories and speeds of meteoroids.     

Effects of balanced impact damper in structures subjected to walking and vertical seismic excitations

This study investigates whether a balanced impact damper (BID) with a vertically suspended impact body colliding with shock absorbing rubber can suppress vibrations of a floor slab subjected to walking and vertical seismic excitations. The impact body is suspended by coil springs to sustain its deadweight and centralize it within the gap, and collides with the stopper when its amplitude exceeds the specified gap width. The stopper is covered by a shock‐absorbing rubber made of polyurethane gel. The installed BID was evaluated in a single degree‐of‐freedom model of a floor slab subjected to vertical excitations. Simulations revealed that the installed BID properly controls the vibrations. Next, the effects of the BID installed on a steel plate were investigated in shaking table tests. The BID effectively suppressed vertical vibrations of the plate subjected to sinusoidal waves, seismic motions, and walking excitations. In addition, the shaking table tests were accurately simulated by the developed mathematical model of the damper. Copyright © 2015 John Wiley & Sons, Ltd.     

A global barotropic ocean model driven by synoptic atmospheric disturbances for detecting seafloor vertical displacements from in situ ocean bottom pressure measurements

A global barotropic ocean model forced by atmospheric disturbances is developed for the detection of seafloor vertical displacements from in situ ocean bottom pressure (OBP) data. The model accuracy is validated by deep-sea OBP data at more than 100 sites obtained over the global ocean. Parameters and boundary conditions including the horizontal resolution incorporated in the ocean model are tested in order to accurately simulate the nontidal (>2 days) OBP variations. The horizontal resolution is found to the factor that most significantly affects the simulated result. The finer the horizontal resolution applied, the smaller the model variability is. The model accuracy is highest when the horizontal resolution is 1/12°, but deteriorates when the horizontal resolution is finer than 1/12°. This may indicate a failure of the energy dissipation parameterization in the barotropic ocean model. Using the developed 1/12° model, the root-mean-square of the observed nontidal OBP component can be reduced by 18 % as an average of all the OBP data used. It is found that the 1/12° model is useful for the detection of a slow seafloor vertical displacement of centimeters related to the 2011 Tohoku-Oki earthquake from in situ OBP records near the hypocenter of the earthquake.     

Transition of solar cycle length in association with the occurrence of grand solar minima indicated by radiocarbon content in tree-rings

In this paper, we review the variation of the 11-year solar cycle since the 15th century revealed by the measurement of radiocarbon content in single-year tree-rings of Japanese cedar trees. Measurements of radiocarbon content in absolutely dated tree-rings provide a calibration curve for accurate dating of archaeological matters, but at the same time, enable us to examine the variations of solar magnetic activity in the pre-historical period. The Sun holds several long-term quasi-cyclic variations in addition to the fundamental 11-year sunspot activity cycle and the 22-year polarity reversal cycle, and it is speculated that the property of the 11-year and the 22-year solar cycle varies in association with such long-term quasi-cycles. It is essential to reveal the details of solar variations around the transition time of solar dynamo for illuminating the mechanisms of the long-term solar variations. We therefore have investigated the property of the 11-year and 22-year cycles around the two grand solar minima; the Maunder Minimum (1645–1715 AD) and the Spoerer Minimum (1415–1534 AD), the periods of prolonged sunspot minima. As a result, slight stretching of the “11-year” and the “22-year” solar cycles was found during these two grand solar activity minima; continuously during the Maunder Minimum and only intermittently during the Spoerer Minimum. On the contrary, normal or slightly shortened 11-year cycles were detected during the interval period of these two minima. It suggests the inverse correlation between the solar cycle length and solar magnetic activity level, and also the change of meridional flow during the grand solar activity minima. Further measurements for the beginning of the grand solar minima will provide a clue to the occurrence of such prolonged sunspot disappearance. We also discuss the effect of solar variations to radiocarbon dating.     

A Method to Suppress Isobaric and Polyatomic Interferences for Measurements of Highly Siderophile Elements in Desilicified Geological Samples

Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Carius tube or high‐pressure asher) is the most common method used to extract highly siderophile elements (HSEs: Ru, Rh, Pd, Re, Os, Ir, Pt and Au) from geological samples. Recently, it has been recognised that additional HF desilicification is necessary to better recover HSEs, potentially contained within silicate or oxide minerals in mafic samples, which cannot be dissolved solely by inverse aqua regia. However, the abundance of interfering elements tends to increase in the eluent when conventional ion‐exchange purification procedures are applied to desilicified samples. In this study, we developed an improved purification method to determine HSEs in desilicified samples. This method enables the reduction of the ratios of isobaric and polyatomic interferences, relative to the measured intensities of HSE isotope masses, to less than a few hundred parts per million. Furthermore, the total procedural blanks are either comparable to or lower than conventional methods. Thus, this method allows accurate and precise HSE measurements in mafic and ultramafic geological samples, without the need for interference corrections. Moreover, the problem of increased interfering elements, such as Zr for Pd and Cr for Ru, is circumvented for the desilicified samples.     

Relative influence of biotic and abiotic processes on travertine fabrics,Satono‐yu hot spring,Japan

The relative influences of biotic and abiotic processes on travertine fabrics are still not well understood, despite increasing interest in the last decade to better understand the record of ancient microbial life and sedimentary fabrics in microbial hydrocarbon reservoirs. This study examines travertines at Satono‐yu hot spring in Japan (the temperature of water flowing over the travertine was ca 35°C), to better understand the interaction between depositional, hydrochemical and microbial parameters at different flow settings. Characteristics of the bulk hydrochemistry, mineralogy (exclusively aragonite) and the driving force for precipitation (primarily abiotic CO₂ degassing with some photosynthetic microbial contribution) were similar among all of the flow settings. Conversely, the increase in flow velocity suppressed the influence of photosynthesis and enhanced the abiotic precipitation due to the thinner diffusive boundary layer at the travertine surface–water interface. Additionally, the increase in flow velocity changed the microbial composition and decreased the bacterial diversity by reflecting their adhesion efficiency on the travertine substrate. The acidity of the cyanobacterial sheaths controls the aragonite nucleation rate and the resulting calcification, even at significantly high equilibrium CO₂ partial pressure (ca 22 to 28 matm), high dissolved inorganic carbon concentration (ca 35 to 38 mmol l^?1), and elevated aragonite saturation state (ca 20‐fold to 34‐fold). Therefore, the increase in flow velocity suppresses the microbial influence with respect to the increase in the saturation state, the nucleation site supply and pore space generation. Overall, this results in the predominance of abiotic precipitation under high flow velocities. Consequently, a sparse‐micritic fabric with abundant interlamina porosity forms under lower flow velocity where the microbial influence is effective, while a dense‐sparitic fabric with little inter‐crystalline porosity forms under higher flow velocity where abiotic precipitation prevails. These findings provide an essential base for assessing the formation processes of ancient travertines and comparable deposits from petrological fabrics.     

Biweekly periodic variation of the Kuroshio axis northeast of Taiwan as revealed by ocean high-frequency radar

An analysis of surface current data obtained from 2002 to 2005 using long-range high-frequency radar provides the first evidence for the presence of biweekly (11–14 day) periodic variations of the Kuroshio axis northeast of Taiwan. This analysis clarifies the spatiotemporal characteristics of these variations and reveals that cyclonic/anticyclonic eddies propagating along the shelf slope from the vicinity of the deep channel east of Taiwan induce these variations northeast of Taiwan. The behavior of the cyclonic/anticyclonic eddies on the shelf slope is well explained by 2nd-mode interior shelf waves advected by the Kuroshio's mean flow. Remote effects from the vicinity of the deep channel east of Taiwan, or from outside the East China Sea, are believed to play an important role in the generation of these biweekly periodic variations of the Kuroshio axis northeast of Taiwan. Moreover, on the shelf slope, these variations cause an onshore current across the shelf slope, suggesting topographically controlled upwelling. Therefore, the biweekly periodic variations of the Kuroshio axis northeast of Taiwan might contribute not only to the onshore transport of Kuroshio surface water but also to transport nutrient-rich Kuroshio subsurface water onto the shelf in the East China Sea.     

Biodiversity loss in benthic macroinfaunal communities and its consequence for organic mercury trophic availability to benthivorous predators in the lower Hudson River estuary, USA

Organic mercury such as methylmercury is not only one of the most toxic substances found in coastal ecosystems but also has high trophic transfer efficiency. In this study, we examined implications of chronically altered benthic macroinfaunal assemblages for organic mercury trophic availability (based on organic mercury intracellular partitioning) to their predators in the Arthur Kill-AK (New York, USA). Despite low species diversity, both density and biomass of benthic macroinvertebrates in AK were significantly higher than those at the reference site. Disproportionately high biomass of benthic macroinvertebrates (mostly polychaetes) in the northern AK resulted in a more than twofold increase (‘ecological enrichment’) in the trophically available organic mercury pool. These results suggest that altered benthic macroinfaunal community structure in AK may play an important role in organic mercury trophic availability at the base of benthic food webs and potentially in mercury biogeochemical cycling in this severely urbanized coastal ecosystem.     

Scale‐dependent controls upon the fluvial export of large wood from river catchments

The annual fluvial export of large wood (LW) was monitored by local reservoir management offices in Japan. LW export per unit watershed area was relatively high in small watersheds, peaked in intermediate watersheds, and decreased in large watersheds. To explain these variations, we surveyed the amount of LW with respect to channel morphology in 78 segments (26 segments in each size class) in the Nukabira River, northern Japan. We examined the differences in LW dynamics, including its recruitment, transport, storage, and fragmentation and decay along the spectrum of watershed sizes. We found that a large proportion of LW produced by forest dynamics and hillslope processes was retained because of the narrower valley floors and lower stream power in small watersheds. The retained LW pieces may eventually be exported during debris flows. In intermediate watersheds, the volume of LW derived from hillslopes decreased substantially with reductions in the proportion of channel length bordered by hillslope margins, which potentially deliver large quantities of LW. Because these channels have lower wood piece length to channel width ratios and higher stream power, LW pieces can be transported downstream. During transport, LW pieces are further fragmented and can be more easily transported. Therefore, the fluvial export of LW is maximized in intermediate watersheds. Rivers in large watersheds, where the recruitment of LW is limited by the decreasing hillslope margins, cannot transport LW pieces because of their low stream power, and thus LW pieces accumulate at various storage sites. Although these stored LW pieces can be refloated and transported by subsequent flood events, they may also become trapped by obstacles such as logjams and standing trees on floodplains and in secondary channels, remaining there for decades and eventually decaying into fine organic particles. Thus, the fluvial export of LW pieces is low in large watersheds. Copyright © 2009 John Wiley & Sons, Ltd.