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81.
The bottom layer in Osaka Bay was occupied in August from 1980 to 1995 by a water mass of relatively low temperature and rich
in nutrients in comparison to previous and following decades. The relationship between Osaka Bay bottom temperature and Kuroshio
axis location south of Kii Peninsula has been investigated using the dataset archived by Osaka Research Institute of Environment
of Agriculture and Fisheries and axis-location data provided by Marine Information Research Center. The correlation between
bottom temperature in the bay and Kuroshio-axis distance from Cape Shionomisaki indicates that the bottom temperature in the
bay decreases when the Kuroshio axis is a long distance from the cape, and vice versa. To investigate why the temperature
distribution depends on the axis location, composite temperature maps are depicted using summer temperature data from 1970
to 2005 archived in the Japan Oceanographic Data Center (JODC) after dividing all data into two groups with different axis
locations. These temperature maps and temperature-salinity plots using the same JODC data suggest a scenario: cold water in
the Kuroshio intermediate layer is first upwelled on the eastern side of the Kii Peninsula and thereafter moves westward as
a coastal boundary current in the Kelvin wave sense of the Northern Hemisphere when the Kuroshio axis is located around 74-km
distance from Cape Shionomisaki. This scenario is validated using internal Froude number maps depicted using the JODC-archived
hydrographic data and geostrophic current fields. In addition, the reanalysis daily data provided by Japan Coastal Ocean Predictability
Experiment are used for the validation. 相似文献
82.
Ken Arai Shigeki Wada Koichi Shimotori Yuko Omori Takeo Hama 《Journal of Oceanography》2018,74(1):39-52
Dynamics of fluorescent dissolved organic matter (FDOM) in ocean environments has received attention over the past few decades. Although it has appeared that in situ production of oceanic FDOM is mainly due to bacteria, the production and bio- and photodegradation processes of bacterial FDOM have not been elucidated. In this study, a culture experiment with bacteria was carried out to assess the production and biodegradation processes of bacterial FDOM. Photodegradation of bacterial FDOM and dissolved organic carbon (DOC) was also examined by exposure to a solar simulator. Bacterial FDOM consists of six components which were determined by parallel factor analysis (PARAFAC). Fluorescence intensities of protein-like FDOM increased with the bacterial biomass, but the increases of humic-like FDOM lagged behind the protein-like FDOM by 5–10 days. Exposure to simulated sunlight caused significant decreases in fluorescence intensities of all components; 52–94% of the initial intensities were lost during 24 h. While, the DOC concentration exhibited a small decrease through the experiment (1.9–11.1%). These results showed that photodegradability of bacteria derived DOC was much less than the fluorescence, indicating that the lifetime of bacteria-derived DOC is much longer than the length estimated by the fluorescence. The role of photobleached FDOM derived from bacteria may be significant in the biogeochemical cycle at the surface layer. 相似文献
83.
Seasonal and interannual variations in physicochemical properties were investigated in the neritic area of Sagami Bay, Kanagawa,
Japan, from December 2000 to December 2005. Physicochemical properties (i.e. temperature, salinity, density, dissolved oxygen
and dissolved inorganic nutrient concentration) revealed clear seasonal variations, which were similar to each other during
all 5 years. Temperature, salinity and dissolved inorganic nutrients showed rapid, drastic variations within a few days and/or
weeks. These variations are related to sea levels, principally due to the shifting effects of the Kuroshio Current axis: they
were strongly affected by the Kuroshio Water and other waters, when sea level difference was greater than ca. 35 cm and lower
than ca. 15 cm, respectively. Temperature difference (DF
T
) increased with sea level difference, and the difference of salinity and dissolved inorganic nutrients (NH4
+-N, NO3
−+NO2
−-N, NH4
++NO3
−+NO2
−-N, PO4
3−-P and SiO2-Si) increased and decreased with DF
T
, respectively. All these correlations are significant. Total dissolved inorganic nitrogen (N), phosphate (P) and silicate
(Si) revealed seasonal variations in the ranges of 0.57–16.08, 0.0070–0.91 and 0.22–46.38 μM, respectively. From the regression equations between these elements allowed the following relation to be obtained; Si:N:P
= 14.8:13.4:1. Dissolved inorganic nutrients were characterized by Si and/or P deficiency, especially in the upper layer (0–20
m depth) during summer. Single and/or combined elements are discussed on the basis of potential and stoichiometric nutrient
limitations, which could restrict phytoplankton (diatom) growth as a limiting factor. 相似文献
84.
Koichi Sakakibara Maki Tsujimura Sho Iwagami Yutaro Sato Kosuke Nagano Yuichi Onda 《水文研究》2019,33(6):892-904
Understanding rainfall‐runoff processes is crucial for prevention and prediction of water‐related natural disasters. Sulfur hexafluoride (SF6) is a potential tracer, but few researches have applied it for rainfall‐runoff process studies. We observed multiple tracers including SF6 in spring water at 1‐ to 2‐hr intervals during rainstorm events to investigate the effectivity of SF6 tracer in rainfall–runoff studies through the clarification of rainfall–runoff process. The target spring is a perennial spring in a forested headwater catchment with an area of 0.045 km2 in Fukushima, Japan. The relationship between the SF6 concentration in spring water and the spring discharge volume was negative trend; the SF6 concentration in spring water becomes low as the spring discharge volume increases especially during rainstorms. The hydrograph separation using SF6 and chloride ion tracers was applied for determining the contribution of principal sources on rainfall–runoff water. It suggested more than 60% contribution of bedrock groundwater at the rainfall peak and high percentage contribution continued even in the hydrograph recession phase. Based on observed low SF6 concentration in groundwater after heavy rainfall, the replacement of groundwater near the spring with bedrock groundwater is indicated as a mechanism for water discharge with low SF6 concentration during rainfall events. Consequently, rainstorm events play an important role as triggers in discharging water stored in the deeper subsurface area. In addition, SF6 tracer is concluded as one of the strongest tracers for examining rainfall–runoff process studies. And, therefore, this study provided new insights into the dynamics of groundwater and its responses to rainfall in terms of SF6 concentration variance in water in headwater regions. 相似文献
85.
Koichi Ara Koh Yamaki Keisuke Wada Satoshi Fukuyama Takeshi Okutsu Sadao Nagasaka Akihiro Shiomoto Juro Hiromi 《Journal of Oceanography》2011,67(1):87-111
Seasonal and interannual variations in physicochemical properties (i.e., temperature, salinity, dissolved oxygen and dissolved
inorganic nutrients), chlorophyll a (Chl-a), particulate carbon and nitrogen (PC and PN, respectively), and primary production were investigated in the neritic area
of Sagami Bay, Kanagawa, Japan, from January 2002 to December 2008. These abiotic/biotic variables, except for NH4
+–N, repeated similar seasonal variations for all 7 years. On the basis of the analysis of data obtained on 167 sampling dates,
depth-integrated primary production in this water can be easily estimated from Chl-a at the surface using the regression equations obtained in the present study. Intermittently high values of dissolved inorganic
nutrients, Chl-a, PC, PN and primary productivity at the surface during the summer stratified period were induced by high freshwater discharge
from the rivers after rainfalls and by the expansion of nutrient-rich Tokyo Bay Water. Temperature, salinity and dissolved
inorganic nutrients showed drastic variations within a scale of a few days and/or weeks, and these variations were related
to sea levels that represent the intrusion of the Kuroshio Water, Intermediate Oyashio Water or deep water from the continental
slope. However, there was no consistent trend in the variations in Chl-a, PC, PN and primary production due to the complex effects of these waters. 相似文献
86.
From 1980 to 1995, in August, the bottom layer of Osaka Bay was occupied by cold, nutrient-rich water compared with that observed
during both previous and subsequent decades. To investigate the mechanisms for the intrusion of bottom-layer cold water into
Osaka Bay, the intrusion into Osaka Bay via the Kii Channel is simulated using a finite-volume coastal ocean model with unstructured
triangular cell grids. The initial conditions, boundary conditions, and surface temperature given to the model are obtained
from daily reanalysis data provided by the Japan Coastal Ocean Predictability Experiment. The model shows that cold water
uplifted on the eastern side of the Kii Peninsula is propagated westward at 1.0 m/s as a coastal boundary current; it reaches
the Kii Channel mouth when the Kuroshio axis is located around 74 km south of Cape Shionomisaki. However, the modeled cold
water mass at the Kii Channel mouth does not intrude further to the north of the Kii Channel; therefore, another mechanism
is required to explain the cold-water intrusion into the bottom layer of Osaka Bay. A plausible explanation is the estuarine
circulation established by the freshwater supply at the bay head. When the river runoff is included in the model without forced
vertical mixing, the temperature in Osaka Bay decreases 6.6 days later than the temperature decreases at the Kii Channel mouth.
Furthermore, the shoreward current speed in the bottom layer of the modeled estuarine circulation is 15 cm/s, which provides
the mechanism required for the cold water mass to pass the Kii Channel. 相似文献
87.
88.
89.
The writers have been studying the origin of porosity in the Neogene calcareous rocks of Akita, Japan, and in the Mississippian Windsor Group carbonate rocks of Nova Scotia, Canada. The former consist mainly of dolomitic clayey-siliceous marls, derived mainly from opaline skeletal debris of microscopic organisms. These marls were deposited in bathyal to inner-neritic environments. The carbonate rocks of Windsor Group, which include both dolostones and limestones, originated from biogenic carbonate debris and were deposited in inner-shelf to shoal environments. 相似文献
90.
Kozo Yuhara Sachio Ehara Koichi Tagomori 《Journal of Volcanology and Geothermal Research》1981,9(1):99-109
Unzen volcano is situated on Shimabara Peninsula, western Kyushu, Japan. On the flank of the volcano, the Obama, Unzen and Shimabara hot springs are aligned in a direction from the southwest to the northeast across the peak. At Obama and Shimabara, heat is transferred mainly by water flow. But at Unzen heat is transferred by the discharge of natural steam and by conduction as well as water flow. In order to estimate the heat discharge by mechanisms other than water flow, infrared measurements by a helicopter-borne thermocamera were conducted over the Unzen hot spring area. The heat discharge was calculated from the thermal image by a method based on heat balance of the ground surface resulting in a value of 1.9 × 106 cal/s (7.9 MW). The heat discharged by all mechanisms including that by water flow is estimated to be 5.0 × 106 cal/s (21 MW). Similar preliminary estimates have been made for heat discharge at the Obama and Shimabara hot springs giving values of about 1.2 × 107 cal/s (50 MW) and 1.0 × 105 cal/s (0.4 MW), respectively. These values indicate that the heat discharge decreases with distance from the southwest to the northeast direction across the volcano. The total heat discharge from three hot spring areas on Unzen volcano is about 1.7 × 107 cal/s (71 MW).The heat balance method appears useful for quantitative analysis of regional trends but its accuracy may not be always sufficient for detailed surveys. Several methods of determining heat flow, including the heat balance method, were compared at a test field in the Unzen hot spring area. The values obtained by the heat balance method coincide roughly with the other results but more detailed analysis is necessary to improve the accuracy of current methods of geothermal measurements. 相似文献