Distribution of Trace Bioelements in the Subarctic North Pacific Ocean and the Bering Sea (the R/V Hakuho Maru Cruise KH-97-2)

A column concentration-high resolution inductively coupled plasma mass spectrometry (ICP-MS) determination was applied to measure the total dissolved concentrations of Fe, Co, Ni, Cu and Zn in seawater collected from the subarctic North Pacific (~45°N) and the Bering Sea in July–September 1997. Total adsorbable Mn was determined on board by column electrolysis preconcentration and chemiluminescence detection. The vertical profiles for Fe, Ni and Zn were nutrient-like. The deep water concentration of Fe was ~0.5 nM in the northeast Pacific (18°-140°W) and increased to ~1 nM in the northwest Pacific (161°E) and ~2 nM in the Bering Sea (57°N, 180°E). The deep water concentrations for Ni and Zn in the Bering Sea were also 1.3–2 times higher than in the North Pacific. The profiles for Co and Cu were examined in the subarctic North Pacific, and results obtained were consistent with previous reports. There was a significant correlation between the concentrations of Co and Mn except for surface mixed layer. The profiles for total adsorbable Mn were similar to the reported profiles for total dissolvable Mn. The deep water concentration of Mn in the Bering Sea was also 4 times higher than in the North Pacific. Iron and zinc were depleted in surface water of the subarctic North Pacific. The relationship between these trace elements and nutrients suggests that these elements could be a limiting factor of phytoplankton productivity. In the Bering Sea, surface water contained ~0.3 nM of Fe. The Zn concentration, which was less than the detection limit in surface water, increased at shallower depths (~30 m) compared with the subarctic North Pacific. These results imply a higher flux of Fe and Zn to surface water in the Bering Sea. This in turn may cause the ecosystem in the Bering Sea characterized by a dominance of diatoms and high regenerated production.     

Distribution of particulate organic carbon and nitrogen in the Bering Sea and northern North Pacific Ocean

Particulate matter was collected in the Bering Sea and the northern North Pacific Ocean during the cruise of R. V. Hakuho-maru, Ocean Research Institute of Tokyo University in summer of 1975. The particulate matter was analyzed for organic carbon and nitrogen, chlorophylla and amino acids.The concentrations of particulate organic carbon and nitrogen were measured with the range of 16–422gC l^–1 and 1–85gN l^–1, 19–186gC l^–1 and 1–26gN l^–1, 46–1,038gC l^–1 and 6–79gN l^–1 and 19–246gC l^–1 and 2–25gN l^–1 in the Oyashio, the Deep Bering Sea, the continental shelf of Bering Sea and the northern North Pacific, respectively. Particulate organic carbon and nitrogen decreased with depth throughout the areas. The average concentrations of organic carbon and nitrogen in the entire water column tended to decrease in the following order; the continental shelf > Oyashio > northern North Pacific > Deep Bering Sea.C/N of particulate matter varied in the range of 3–15 (7 on average) in surface waters throughout the areas and these values tended to increase with depth to 5–20 (11 on average) in deep waters without significant regional variability.Linear regressions between chlorophylla and particulate organic carbon in the euphotic layers indicate that detrital organic carbon accounted for 34.2, 44.9, 49.1 and 25.2 % of particulate organic carbon in the Oyashio, the Deep Bering Sea, the continental shelf and the northern North Pacific, respectively.Particulate amino acid was determined in the range of 10.3–78.0g l^–1, 104–156g l^–1 and 10.4–96.4g l^–1 in the Deep Bering Sea, the continental shelf and the northern North Pacific, respectively. Aspartic acid, glutamic acid, serine, glycine and alanine were found as dominant species of amino acid of particulate matter.     

New discoveries in dynamics of an M8 earthquake-phenomena and their implications from the 2003 Tokachi-oki earthquake using a long term monitoring cabled observatory

At the 2003 Tokachi-oki earthquake of M8, seafloor phenomena such as a generation process of tsunami, seafloor uplifts, turbidity current, etc., were observed using a cabled observatory installed on the seafloor. The turbidity current was observed as a benthic storm caused presumably by the mainshock. The seafloor uplifts were observed at the mainshock and continuously after the mainshock. The uplifts were 0.35, 0.37, and 0.12 m for epicentral distances of 25.5, 31.4, and 81.7 km, respectively. After the mainshock, a continuous uplift of the seafloor is observed at all three pressure gauge locations indicating that there was a change in the state of friction on the plate boundary interface by the mainshock. In this paper, we first show what was observed using the cabled observatory installed right above the focal area of the earthquake, and then we discuss to summarize these phenomena associated with the earthquake, its possible causes, and future directions in long term monitoring of seismogenic processes.     

Missing role of groundwater in water and nutrient cycles in the shallow eutrophic lake Kasumigaura,Japan

A process‐based model was developed, NICE‐LAKE (NIES (National Institute for Environmental Studies) Integrated Catchment‐based Ecohydrology), which includes interactions between surface water, canopy, unsaturated water, aquifer, lake and rivers, and used it to model the shallow eutrophic Lake Kasumigaura in Japan. By estimating the spatial distribution of the hydrological cycle, the model shows that groundwater withdrawal greatly affects groundwater distribution and seepage and indirectly influences lake water level. The simulated seepage agrees excellently with the budget‐derived value calculated from the observed groundwater level, lake level and isotope analyses. The model showed that groundwater seepage and groundwater concentrations are important contributors to the eutrophication of Lake Kasumigaura, an important contribution not recognized in previous studies of the lake. Groundwater entering the lake from the north side is contaminated with high concentrations of nitrate and ammonia from intensive pig and cattle raising and cultivated fields. The simulation showed that this high nitrogen load plays an important role in the eutrophication of the lake (the nitrogen load in inflowing groundwater is 30% of river inflow and 4 times that from wastewater treatment plants) in spite of government policies to prevent overland flow of nutrients into the lake. Our results show that NICE‐LAKE is a powerful tool for forecasting how the water quality of the lake will be affected by the (illegal) disposal of animal excreta in the surrounding open fields. Copyright © 2007 John Wiley & Sons, Ltd.     

Does heavy oil pollution induce bacterial diseases in Japanese flounder Paralichthys olivaceus?

As basic research for the effect of heavy oil on the fish immune system, in this study, the number of leukocyte was counted in Japanese flounder Paralichthys olivaceus, after exposure to heavy oil at a concentration of 30 g/8 L for 3 days. To compare the numbers of bacteria in the skin mucus between oil-exposed and control fish, viable bacteria were enumerated by counting colony forming unit (CFU). Compared with 5.79 ± 1.88 × 10⁷ leukocytes/mL in the controls, the exposed fish demonstrated higher counts, averaging 1.45 ± 0.45 × 10⁸ cells/mL. The bacterial numbers of control fish were 4.27 ± 3.68 × 10⁴ CFU/g, whereas they were 4.58 ± 1.63 × 10⁵ CFU/g in the exposed fish. The results suggest that immune suppression of the fish occurred due to heavy oil stressor, and bacteria could invade in the mucus, resulting in the increasing leukocyte number to prevent infectious disease.     

Toxicogenomic analysis of immune system-related genes in Japanese flounder (Paralichthys olivaceus) exposed to heavy oil

Heavy oil contamination is one of the most important environmental issues. Toxicities of polycyclic aromatic hydrocarbons (PAHs), including immune toxicities, are well characterized, however, the immune toxic effects of heavy oil, as a complex mixture of PAHs, have not been investigated. In the present study, we selected Japanese flounder (Paralichthys olivaceus) as a model organism, and observed alteration of immune function by the exposure to heavy oil. To analyze the expression profiles of immune system-related genes, we selected 309 cDNAs from our flounder EST library, and spotted them on a glass slide. Using this cDNA array, alteration of gene expression profiles was analyzed in the kidneys of flounders exposed to heavy oil. Six Japanese flounders (mean body weight: 197 g) were acclimated to laboratory conditions at 19–20 °C. Three fish were exposed to heavy oil C (bunker C) at a concentration of 3.8 g/L for 3 days, and the others were kept in seawater without heavy oil and used as the control. After the exposure period, the fish were transferred into control seawater and maintained for 4 days, and then they were dissected and their kidneys were removed. Total RNA was extracted from the kidney samples to use in gene expression analyses. The microarray detected alteration of immune system-related genes in the kidneys of heavy oil-exposed flounders, including down-regulation of immunoglobulin light chain, CD45, major histocompatibility complex class II antigens and macrophage colony-stimulating factor precursor, and up-regulation of interleukin-8 and lysozyme. These results suggest that pathogen resistance may be weakened in heavy oil-exposed fish, causing a subsequent bacterial infection, and then proinflammatory genes may be induced as a defensive response against the infection. Additionally, we found candidate genes for use as biomarkers of heavy oil exposure, such as N-myc downstream regulated gene 1 and heat shock cognate 71 kDa proteins.     

Comparison of landslide susceptibility based on a decision-tree model and actual landslide occurrence: The Akaishi Mountains, Japan

This paper proposes a statistical decision-tree model to analyze landslide susceptibility in a wide area of the Akaishi Mountains, Japan. The objectives of this study were to validate the decision-tree model by comparing landslide susceptibility and actual landslide occurrence, and to reveal the relationships among landslide occurrence, topography, and geology. Landslide susceptibility was examined through ensemble learning with a decision tree. Decision trees are advantageous in that estimation processes and order of important explanatory variables are explicitly represented by the tree structures. Topographic characteristics (elevation, slope angle, profile curvature, plan curvature, and dissection and undissection height) and geological data were used as the explanatory variables. These topographic characteristics were calculated from digital elevation models (DEMs). The objective variables were landslide occurrence and reactivation data between 1992 and 2002 that were depicted by satellite image analysis. Landslide susceptibility was validated by comparing actual data on landslides that occurred and reactivated after the model was constructed (between 2002 and 2004).This study revealed that, from 2002 to 2004, landslides tended to occur and reactivate in catchments with high landslide susceptibility. The landslide susceptibility map thus depicts the actual landslide occurrence and reactivation in the Akaishi Mountains. This result indicates that the decision-tree model has appropriate accuracy for estimating the probabilities of future landslides. The tree structure indicates that landslides occurred and reactivated frequently in the catchments that had an average slope angle exceeding ca. 29° and a mode of slope angle exceeding 33°, which agree well with previous studies. A decision tree also quantitatively expresses important explanatory variables at the higher order of the tree structure.     

Pyrene induces a reduction in midbrain size and abnormal swimming behavior in early-hatched pufferfish larvae

Spills of heavy oil (HO) have an adverse effect on marine life. We have demonstrated previously that exposure to HO by fertilized eggs of the pufferfish (Takifugu rubripes) induces neural disruption and behavioral abnormality in early-hatched larvae. Here, two kinds of polycyclic aromatic hydrocarbons, pyrene and phenanthrene, were selected to examine their toxic effects on larval behavior of another pufferfish species (T. niphobles). Larvae exposed to pyrene or phenanthrene exhibited no abnormalities in morphology. However, those exposed to pyrene but not phenanthrene swam in an uncoordinated manner, although their swimming distance and speed were normal. The optic tectum, a part of the midbrain, of pyrene-exposed larvae did not grow to full size. Thus, these findings are indicated that pyrene might be a contributor to the behavioral and neuro-developmental toxicity, although there is no indication that it is the only compound participating in the toxicity of the heavy oil mixture.     

Horizontal distribution and population dynamics of the dominant mysid Hyperacanthomysis longirostris along a temperate macrotidal estuary (Chikugo River estuary, Japan)

The estuarine turbidity maximum (ETM) that develops in the lower salinity areas of macrotidal estuaries has been considered as an important nursery for many fish species. Mysids are one of the dominant organisms in the ETM, serving as a key food source for juvenile fish. To investigate the horizontal distribution and population dynamics of dominant mysids in relation to the fluctuation of physical conditions (temperature, salinity, turbidity, and freshwater discharge), we conducted monthly sampling (hauls of a ring net in the surface water) along the macrotidal Chikugo River estuary in Japan from May 2005 to December 2006. Hyperacanthomysis longirostris was the dominant mysid in the estuary, usually showing peaks of density and biomass in or close to the ETM (salinity 1–10). In addition, intra-specific differences (life-cycle stage, sex, and size) in horizontal distribution were found along the estuary. Larger males and females, particularly gravid females, were distributed upstream from the center of distribution where juveniles were overwhelmingly dominant. Juveniles increased in size toward the sea in marked contrast with males and females. The findings suggest a possible system of population maintenance within the estuary; gravid females release juveniles in the upper estuary, juveniles grow during downstream transport, young males and females mature during the upstream migration. Density and biomass were primarily controlled by seasonal changes of temperature, being high at intermediate temperatures (ca. 15–25 °C in late spring and fall) and being low at the extreme temperatures (ca. 10 °C in midwinter and 30 °C in midsummer). High density (up to 666 ind. m⁻³) and biomass (up to 168 mg dry weight m⁻³) of H. longirostris were considered to be comparable with those of copepods in the estuary.     

Iron, manganese and aluminum in upper waters of the western South Pacific Ocean and its adjacent seas

Total dissolvable iron, manganese and aluminum distributions in upper waters were determined in the western South Pacific, Solomon Sea, Coral Sea, and Tasman Sea. In these oceanic regions, the surface aluminum distributions well reflect the atmospheric deposition pattern of mineral dust in the western South Pacific reported previously. Surface manganese distributions derive mainly from lateral transportation from the coastal sediments of western tropical islands. Compared to Mn and Al, the Fe distributions reflect the nutrient cycle in upper waters. Iron limitation over the vast South Pacific, as revealed by physiological features of phytoplankton, seems to be caused by low atmospheric dust deposition and low Fe:N ratios in deep waters. In the western South Pacific, with its unique geographic and oceanographic settings, the local sources of trace metals might considerably affect their biogeochemical cycles.