Chemical evidence for the origin of the cold water belt along the northeastern coast of Hokkaido

In the southwestern Okhotsk Sea, the cold water belt (CWB) is frequently observed on satellite images offshore of the Soya Warm Current flowing along the northeastern coast of Hokkaido, Japan, during summertime. It has been speculated that the CWB is upwelling cold water that originates from either subsurface water of the Japan Sea off Sakhalin or bottom water of the Okhotsk Sea. Hydrographic and chemical observations (nutrients, humic-type fluorescence intensity, and iron) were conducted in the northern Japan Sea and southwestern Okhotsk Sea in early summer 2011 to clarify the origin of the CWB. Temperature–salinity relationships, vertical distributions of chemical components, profiles of chemical components against density, and the (NO₃ + NO₂)/PO₄ relationship confirm that water in the CWB predominantly originates from Japan Sea subsurface water.     

Atmospheric correction scheme for GLI with absorptive aerosol correction

The present study proposes an atmospheric correction scheme for Advanced Earth Observation Satellite II (ADEOS-II)/Global Imager (GLI) ocean color retrieval that corrects for the atmospheric absorptive aerosol effect. Radiative transfer simulations were conducted assuming a non-absorptive model aerosol with a soot-type aerosol at various mixture ratios. The results indicate that while the spectral dependency of aerosol reflectance does not change in the longer (>550 nm) wavelength region, the reflectance at shorter wavelengths is highly variable and depends on the mixture ratio. The influence of aerosol absorption was also investigated using GLI data from ocean areas adjacent to Japan in the presence of absorptive Siberian fire smoke aerosol in the spring of 2003. The spectral curvature of the aerosol was estimated from the data obtained. An empirical, iterative scheme that detects and evaluates the influence of absorptive aerosols was developed by comparing 380 nm GLI-observed aerosol reflectance with predicted reflectances derived using an in-water optical model. To evaluate the performance of this scheme, satellite-derived normalized water-leaving radiances were compared with those measured from a ferry servicing Nagasaki and Fukue. The results of data acquired on March 20, 2003, indicate that this absorption correction scheme improved root mean square estimation error for normalized water-leaving radiance by approximately 40% in the 380, 400, and 412 nm bands. This atmospheric correction algorithm was used as a part of the second version of the GLI standard ocean color data process system at Japan Aerospace Exploration Agency (JAXA).     

East-west distribution of POC fluxes estimated from <Superscript>234</Superscript>Th in the northern North Pacific in autumn

Observations of primary productivity, ²³⁴Th, and particulate organic carbon (POC) were made from west to east across the northern North Pacific Ocean (from station K2 to Ocean Station Papa) during September–October 2005. Primary productivities in this region varied longitudinally from approximately 236 to 444 mgC m⁻²d⁻¹ and clearly indicate the West High East Low (WHEL) trend. We estimated east-west variations in the POC flux from the surface layer (0–100 m) by using ²³⁴Th as a tracer. POC fluxes in the western region (44–53 mgC m⁻²d⁻¹) were higher than those in the eastern region (21–34 mgC m⁻²d⁻¹). However, the export ratios (e-ratios) ranged from approximately 8% to 16% and did not show the WHEL trend. Contrary to our expectation, no relation between POC flux (or e-ratio) and diatom biomass (or dominance) was apparent in autumn in the northern North Pacific.     

Particle-tracking simulation for the drift/diffusion of spilled oils in the Sea of Okhotsk with a three-dimensional, high-resolution model

To conduct the simulation of oil spills in the Sea of Okhotsk, we developed a three-dimensional, high-resolution ocean circulation model. The model particularly improved the reproducibility of velocity field during the strong stratification period. Particle-tracking experiments with the effects of evaporation and biodegradation were performed using the combined data of daily ocean currents from the present model and the hourly diurnal tidal currents from the tidal model. The results are shown by the relative concentration of the particles averaged over the 8 years of 1998–2005 based on the ensemble forecast idea. For the case of particles released from the Sakhalin II oil field, the particles deployed in September–January are carried southward by the East Sakhalin Current, finally arriving at the Hokkaido coast, after 60–90 days. The particles deployed in March–August are diffused offshore by the synoptic wind drift, and hardly transported to regions south of Sakhalin. For the case of particles released from the region off Prigorodnoye, the oil export terminal, after the diffusion by the synoptic wind drift, a part of them are carried offshore of Hokkaido by the Soya Warm Current. The particles released in November–April flow out to the Japan Sea through the Soya Strait, mainly by the synoptic wind drift and secondly by the diffusion due to strong tidal currents around the Soya Strait. By considering the effects of evaporation and biodegradation, the relative concentration of the particles is considerably decreased before arriving at the Hokkaido coast, particularly in the case of drift from the Sakhalin II oil field.     

Implementation and evaluation of alternative wave breaking formulas in a coastal spectral wave model

This paper describes methods and results of research for incorporating four different parameterized wave breaking and dissipation formulas in a coastal wave prediction model. Two formulations assume the breaking energy dissipation to be limited by the Rayleigh distribution, whereas the other two represent the breaking wave energy by a bore model. These four formulations have been implemented in WABED, a directional spectral wave model based on the wave action balance equation with diffraction, reflection, and wave–current interaction capabilities. Four parameterized wave breaking formulations are evaluated in the present study using two high-quality laboratory data sets. The first data set is from a wave transformation experiment at an idealized inlet entrance, representing four incident irregular waves in a slack tide and two steady-state ebb current conditions. The second data set is from a laboratory study of wave propagation over a complex bathymetry with strong wave-induced currents. Numerical simulation results show that with a proper breaking formulation the wave model can reproduce laboratory data for waves propagating over idealized or complicated bathymetries with ambient currents. The extended Goda wave breaking formulation with a truncated Rayleigh distribution, and the Battjes and Janssen formulation with a bore model produced the best agreement between model and data.     

Characteristics of Porphyry Cu Mineralization at Waisoi (Namosi District), Viti Levu, Fiji

The porphyry Cu deposits at Waisoi in Namosi district, Viti Levu are separated into two deposits: the Waisoi East deposit and the Waisoi West deposit. In the Waisoi East deposit, quartz porphyry is exposed and in the Waisoi West deposit, diorite porphyry is sporadically exposed in addition to a small body of quartz porphyry. The mineralization in the Waisoi East deposit is characterized by the bornite–chalcopyrite–pyrite assemblage associated with traces of molybdenite and native gold. Polyphase fluid inclusions in stockwork quartz veinlets show homogenization temperatures ranging from 210 to >500°C. The high‐grade Cu mineralization in the Waisoi West deposit is characterized by the bornite–chalcopyrite–pyrite assemblage accompanied with sheeted and stockwork quartz veinlets. Polyphase fluid inclusions occasionally containing hematite flakes in quartz veinlets in the center of the Waisoi West deposit homogenize at temperatures ranging from 450°C to >500°C. However, fluid inclusions in stockwork quartz veinlets in the periphery, homogenize at lower temperatures around 210°C. Both in the Waisoi East and Waisoi West deposits, primary bornite–chalcopyrite–pyrite assemblage in the high Cu‐grade zone was deposited at the upper stability limit of chalcopyrite with respect to sulfur fugacity. Thus, the principal Cu mineralization at the Waisoi deposits occurred at a relatively high sulfur fugacity, that is, in a high‐sulfidation environment.     

土工袋加固地基新技术

介绍了研究开发的土工袋加固地基新技术,内容包括土工袋加固地基的基本原理、基本特性及在日本应用于房屋地基加固、公路路基加固、堤防加固及构筑挡墙等的工程实例。土工袋加固地基的原理在于利用了由于在外荷载作用下袋子周长的伸长而产生的袋子张力, 袋子张力引起了一个附加凝聚力。     

Key species of hermatypic coral for reef formation in the northwest Pacific during Holocene sea-level change

Cores from Holocene reefs provided a growth history and species-level identification of corals and demonstrated the most important reef builders during the formation stage. This knowledge is important to determine a principle for reef formation and to provide preservation plans in the near future. A biological and sedimentological study of sediment cores recovered from the Palau Islands and Yoron Island, northwest Pacific, revealed four major facies: corymbose Acropora, arborescent Acropora, massive Porites, and detritus. Species-level observations show that arborescent Acropora (A. muricata and A. intermedia) contributed to reef growth under low- to moderate-energy conditions, whereas corymbose and tabular Acropora (A. digitifera, A. hyacinthus, and A. robusta/A. abrotanoides) and I. palifera were key species for reef formation under high-energy conditions during Holocene sea-level rise and the ensuing period of sea-level stability. Once sea level had stabilized, massive Porites became restricted to areas subjected to low-energy, turbid conditions. These key species are successful corals because the ecological strategy is rapid growth, determinate growth, a high degree of colony integration, strongly resistant to wave action, and rapid local dispersion via fragmentation. Moreover, the western boundary current (Kuroshio) flows along the reefs in the northwest Pacific and it is easy for key species to distribute throughout the region during the period of Holocene sea-level rise and stabilization. These features are a principle for reef formation during sea-level changes. These key species played a significant role in Holocene reef formation in the northwest Pacific; however, coral mortality, caused by climate change, has recently been widely reported. Moreover, the decrease in key species abundance in present-day reefs has been more severe than that in any other species. These geological findings have important implications regarding the appropriate use of coral transplantation and decisions regarding the optimal location and size of marine protected areas.