Absolute Volume Transports of the Oyashio Referred to Moored Current Meter Data Crossing the OICE

During November 2000–June 2002, both direct current measurements from deployment of a line of five moorings and repeated CTD observations were conducted along the Oyashio Intensive observation line off Cape Erimo (OICE). All the moorings were installed above the inshore-side slope of the Kuril-Kamchatka Trench. Before calculating the absolute volume transports, we compared vertical velocity differences of relative geostrophic velocities with those of the measured velocities. Since both the vertical velocity differences concerned with the middle three moorings were in good agreement, the flows above the continental slope are considered to be in thermal wind balance. We therefore used the current meter data of these three moorings, selected among all five moorings, to estimate the absolute volume transports of the Oyashio referred to the current meter data. As a result, we estimated that the southwestward absolute volume transports in 0–1000 db are 0.5–12.8 × 10⁶ m³/sec and the largest transport is obtained in winter, January 2001. The Oyashio absolute transports in January 2001, crossing the OICE between 42°N and 41°15′ N from the surface to near the bottom above the continental slope, is estimated to be at least 31 × 10⁶ m³/sec. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamics of the Kuroshio large meander

The bimodality of the Kuroshio path is studied numerically with a barotropic inflow-outflow model. The dynamics that determines the path depends on the Rossby number,Ro (proportional to inlet velocity) and the Reynolds number (representing effects of viscosity). At lowRo (<Ro ₁) only a meander path occurs, while at highRo(Ro ₂) only a straight path is developed. Between these critical values (Ro ₁RoRo₂) either of the two paths can occur (multiple states), and the choice of path is determined by its history. Increase (decrease) inRo acrossRo ₂ (Ro ₁) leads to catastrophic transition from one path to the other. In the intermediate range (Ro ₁RoRo₂), the straight path is conditionally unstable to finite amplitude disturbances, and abrupt changes to the meander path take place. Absolute vorticity is almost conserved along the meander path, while along the straight path it is dissipated in large amount near the coast. At low Re, the flow tends to a viscous flow, and steady states are obtained. At highRe, time variations with different periods for the meander and straight paths become dominant. Intermittent transitions from one state to the other without any changes of external parameters are found at intermediateRo and at highRe.     

Silicate darkening in the Kobe CK chondrite: Evidence for shock metamorphism at high temperature

Abstract— The Kobe CK4 chondrite, like most metamorphosed CK chondrites, exhibits pronounced silicate darkening of matrix and chondrule mesostases. Our petrographic and scanning electron microscopic study reveals that the matrix of Kobe consists mostly of intermixtures of two types of fine‐grained olivine. One forms subhedral to anhedral normal crystals. The other fills interstices of the subhedral to anhedral olivine crystals, exhibiting a complex network of veinlets. The latter type of olivine contains high densities of small spherical vesicles (<0.05‐3 μm in diameter) and grains (<0.05‐5 μm) of magnetite and pentlandite as well as round to anhedral grains (1–10 μm) of plagioclase, low‐Ca pyroxene, diopside and chlorapatite. The vesicular olivine is particularly abundant in regions of matrix that exhibit a relatively high degree of darkening and commonly fills chondrule mesostases. The vesicular olivine is clearly the principal cause of the silicate darkening in Kobe. The internal texture of the vesicular olivine closely resembles those of local melts produced from the matrices of experimentally and naturally shocked carbonaceous chondrites. The occurrence and texture of the vesicular olivine suggest that it resulted from recrystallization of partially melted matrix olivine by shock. Kobe exhibits light shock effects in olivine that are consistent with shock stage S2 that is too low to explain the occurrence of olivine melting. We suggest that the vesicular olivine in Kobe was produced by shock metamorphism at a relatively mild shock pressure (<25 GPa) and a high temperature (>600 °C). Thus, it is probable that the shock effects in olivine, manifest as fracturing and deformation, were relatively minor, but heating was strong enough to cause partial melting of matrix olivine.     

Regional variations in trace element concentrations in tissues of black tiger shrimp Penaeus monodon (Decapoda: Penaeidae) from South Vietnam

The goal of the present study was to examine the specific bioaccumulation of 22 trace elements in muscle, exoskeleton and hepatopancreas of black tiger shrimp Penaeus monodon from the Mekong River Delta (MRD), and the South Key Economic Zone (SKEZ), South Vietnam. The general tendency in most trace element concentrations among different tissues were hepatopancreas>exoskeleton>muscle. Comparisons of trace element levels in tissues between the two regions showed that concentrations of Se in muscle and As in all three tissues were higher in SKEZ; whereas in MRD, the higher concentrations of most elements such as Mn, Cu, Cd, Ba, Hg, were observed in tissues. These geographical variations in trace element levels may reflect the differences in human activities between the two regions of South Vietnam. The target hazard quotient (THQ) values for trace elements (<1) indicate that local residents are not exposed to potential health risks via the consumption of shrimp.     

Advances in computational morphodynamics using the International River Interface Cooperative (iRIC) software

Results from computational morphodynamics modeling of coupled flow–bed–sediment systems are described for 10 applications as a review of recent advances in the field. Each of these applications is drawn from solvers included in the public-domain International River Interface Cooperative (iRIC) software package. For mesoscale river features such as bars, predictions of alternate and higher mode river bars are shown for flows with equilibrium sediment supply and for a single case of oversupplied sediment. For microscale bed features such as bedforms, computational results are shown for the development and evolution of two-dimensional bedforms using a simple closure-based two-dimensional model, for two- and three-dimensional ripples and dunes using a three-dimensional large-eddy simulation flow model coupled to a physics-based particle transport model, and for the development of bed streaks using a three-dimensional unsteady Reynolds-averaged Navier–Stokes solver with a simple sediment-transport treatment. Finally, macroscale or channel evolution treatments are used to examine the temporal development of meandering channels, a failure model for cantilevered banks, the effect of bank vegetation on channel width, the development of channel networks in tidal systems, and the evolution of bedrock channels. In all examples, computational morphodynamics results from iRIC solvers compare well to observations of natural bed morphology. For each of the three scales investigated here, brief suggestions for future work and potential research directions are offered. © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd     

Rare gases in a phlogopite nodule and a phlogopite-bearing peridotite in South African kimberlites

Rare gas isotopes in a phlogopite nodule and a phlogopite-bearing peridotite nodule in South African kimberlites were studied to examine the state of rare gases in the deep interior of the kimberlite region.Within the experimental error of 1 ～ 2%, rare gas isotopic compositions are atmospheric except for radiogenic⁴He and⁴⁰Ar. No excess¹²⁹Xe was observed.In phlogopite, Ne is more depleted, whereas the heavier rare gases are more enriched than the atmospheric rare gases relative to³⁶Ar.Together with other data these results suggest that the state of rare gases in the upper mantle of the South African kimberlite region might have been changed from the typical primitive mantle by a process such as mixing of crustal materials.