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11.
Tetsuichi Fujiki Kazuhiko Matsumoto Shuichi Watanabe Takuji Hosaka Toshiro Saino 《Journal of Oceanography》2011,67(3):295-303
We deployed a profiling buoy system incorporating a fast repetition rate fluorometer in the western subarctic Pacific and
carried out time-series observations of phytoplankton productivity from 9 June to 15 July 2006. The chlorophyll a (Chl a) biomass integrated over the euphotic layer was as high as 45–50 mg Chl a m−2 in the middle of June and remained in the 30–40 mg Chl a m−2 range during the rest of observation period; day-to-day variation in Chl a biomass was relatively small. The daily net primary productivity integrated over the euphotic layer ranged from 144 to 919 mg C m−2 day−1 and varied greatly, depending more on insolation rather than Chl a biomass. In addition, we found that part of primary production was exported to a 150-m depth within 2 days, indicating that
the variations in primary productivity quickly influenced the organic carbon flux from the upper ocean. Our results suggest
that the short-term variability in primary productivity is one of the key factors controlling the carbon cycle in the surface
ocean in the western subarctic Pacific. 相似文献
12.
Hitomi Yamaguchi Naoto Hirade Miho Kayama Kazuhiko Ichimi Kuninao Tada 《Journal of Oceanography》2014,70(4):355-366
Phytoplankton abundance in the surface waters of Harima Nada, eastern Seto Inland Sea of Japan, decreased after around the late 1970s following a reduction of terrestrial phosphorous inputs, and relatively low levels persisted thereafter. This symptom of de-eutrophication in recent decades might have reduced organic matter storage in surficial sediments. To test this possibility, we examined total organic carbon (TOC) and nitrogen (TN) contents of Harima Nada sediments in 2011, and compared the results to past data from more eutrophic states. In 2011, the TOC and TN varied horizontally within the basin, in relation to physicochemical properties (water and mud content) and phytoplankton remnants (pheo-pigments) of the sediments. These horizontal patterns were fundamentally similar to those of the early 1980s (1982–1983), although discrepancies between the periods were observed in some areas. Differences of mean TOC and TN in the 0–2 cm layer at 63 stations from 1982–1983 to 2011 were consequently <10 %. Hence, the recent de-eutrophication in Harima Nada was associated with little overall change of TOC and TN storage in the sediment. In Harima Nada, changes in water clarity and particle size composition of the sediment seem to have occurred during recent decades. The aforementioned paradoxical phenomenon may therefore be explained by factors that are affected by these environmental changes. Such factors include the ratio of export flux to the seafloor to phytoplankton production, phytoplankton biomass and production in the entire euphotic zone, and accumulation rate of surface sediment. 相似文献
13.
Maung-Saw-Htoo-Thaw Shizuka Ohara Kazumi Matsuoka Tatsuya Yurimoto Shota Higo Khin-Ko-Lay Win-Kyaing Myint-Shwe Sein-Thaung Yin-Yin-Htay Nang-Mya-Han Khin-Maung-Cho Si–Si-Hla-Bu Swe-Thwin Kazuhiko Koike 《Journal of Oceanography》2017,73(3):345-364
Myanmar is tenth among the world’s fish-producing countries and third in ASEAN (Association of Southeast Asian Nations). To understand the mechanisms underlying the high production, oceanographic and phytoplankton surveys, including primary productivity measurements based on pulse amplitude modulation fluorometry, were conducted near an active fishing ground near Myeik City. Three surveys, one in each of the representative seasons and covering the characteristic coastal environments, showed well-defined seasonality in primary production and phytoplankton occurrence. End of the dry season was the most productive, with productivity of 2.59 ± 1.56 g C m?2 day?1 and high concentration of chlorophyll a (3.14 ± 2.64 µg L?1). In this season, the phytoplankton population was dominated by high densities of the diatoms Bellerochea horologicalis and Chaetoceros curvisetus, whereas primary productivity was low at the onset of the dry season, 1.36 ± 0.77 g C m?2 day?1. However, this low primary production might be compensated by activation of microbial food chains originating from high dissolved organic carbon. The rainy season exhibited the lowest production, 6.6% of the end of the dry season, due to the extensive discharge of turbid water from the rivers which lowered euphotic layer depth and resulted in an unusually high diffuse attenuation coefficient of 2.30 ± 1.03 m?1. This incident of turbid water may be related to soil erosion from deforestation and mangrove deterioration. This research reveals the seasonal trend in Myanmar’s coastal productivity and its relationship to the tropical monsoon climate as well as emphasizing the importance of tropical coastal environments to the sustainability of the fisheries. 相似文献
14.
Kuninao Tada Marut Suksomjit Kazuhiko Ichimi Yui Funaki Shigeru Montani Machiko Yamada Paul J. Harrison 《Journal of Oceanography》2009,65(6):885-891
The importance of the nitrogen source for phytoplankton growth in a highly eutrophic embayment, Dokai Bay, was investigated.
The DIN concentration often exceeded 100 μM of which 40–70% was NH4
+. During two incubation experiments, the natural assemblage of mainly diatoms took up NH4
+ instead of NO3
−. The growth of two Skeletonema species isolated in Dokai Bay were significantly faster on NH4
+ (1.86 and 1.27 div. d−1 respectively) than on NO3
− (1.55 and 1.04 div. d−1 respectively). Our results indicated that these diatoms could grow faster by using NH4
+ compared to NO3
− in this eutrophic bay. 相似文献
15.
16.
Takeshi Naganuma Masanori Kyo Tatsuhiko Ueki Kazuhiko Takeda Jun-ichiro Ishibashi 《Journal of Oceanography》1998,54(3):241-246
A new hydrothermal fluid sampler has been developed to provide more maneuverability in underwater operation. The sampler characteristically
employs a shape-memory alloy, which senses high temperature and actuates the suction mechanism. A shape-memory alloy is also
used to switch the intake valve of the sampler, the intention being to avoid missampling when the inlet is in low temperature
water. Prototype samplers were designed to collect the fluids hotter than 80°C. Test sampling was performed at hydrothermal
vents (1372–1374 m deep) in the submarine volcano, Suiyo Seamount, Izu-Bonin Arc, northwestern Pacific. Observed fluid temperature
was between 138 and 298°C, while the ambient seawater temperature was 3.1°C. Each prototype collected about 100 ml fluid as
designed. The magnesium concentration in the samples indicated a seawater content of 47.5–90.8%, which indicates the entrainment
of ambient seawater. Microscopic observatinn revealed the occurrence of microorganisms in the sample fluids at a population
density of 105 to 106 cells ml−1, which is 2–3 orders of magnitude higher than those in seawater at that depth. The use of the newly developed fluid sampler
will greatly facilitate the collection of vent-associated microorganisms, which are of potential biological and biotechnological
interest. 相似文献
17.
The general-relativistic equations of hydrodynamics for a nonideal fluid are derived in the modified Lagrangian form. Together with the zeroth and first moment equations of radiative transfer derived by Morita and Kaneko (1986), the equations provide a complete set of the modified Lagrangian equations of radiation hydrodynamics. The equations of hydrodynamics are specialized for a thermally conducting, Newtonian viscous fluid in the modified Lagrangian form, which are the generalization of the specialrelativistic equations of hydrodynamics derived by Greenberg (1975). 相似文献
18.
In low-lying areas of urban and suburban regions in Asia, the use of landfill has allowed urban land use to encroach onto watery landforms, such as back marshes, which were formerly used as rice fields. To improve understanding of the associations between land-use patterns and landfill development, we carried out a case study in the urban fringe of Metro Manila in the Philippines. We examined landfill volume derived from land-use change using GIS, and field surveyed qualitative aspects of the landfill used. We calculated the rate of application of landfill in low-lying housing development areas to be 5.0 × 103 m3 km?2 year?1, most of which consisted of offsite disposal of construction waste or crushed rock produced by urban development and renewal on the adjoining uplands. The flow of fill material from offsite sources to onsite landfill development areas was on the basis of individual agreements between suppliers and developers. 相似文献
19.
Minoru Kitamura Toru Kobari Makio C. Honda Kazuhiko Matsumoto Kosei Sasaoka Rie Nakamura Kazuyuki Tanabe 《Journal of Oceanography》2016,72(3):387-402
Seasonal changes in mesozooplankton biomass and their community structures were observed at time-series stations K2 (subarctic) and S1 (subtropical) in the western North Pacific Ocean. At K2, the maximum biomass was observed during the spring when primary productivity was still low. The annual mean biomasses in the euphotic and 200- to 1000-m layers were 1.39 (day) and 2.49 (night) g C m?2 and 4.00 (day) and 3.63 (night) g C m?2, respectively. Mesozooplankton vertical distribution was bimodal and mesopelagic peak was observed in a 200- to 300-m layer; it mainly comprised dormant copepods. Copepods predominated in most sampling layers, but euphausiids were dominant at the surface during the night. At S1, the maximum biomass was observed during the spring and the peak timing of biomass followed those of chlorophyll a and primary productivity. The annual mean biomasses in the euphotic and 200- to 1000-m layers were 0.10 (day) and 0.21 (night) g C m?2 and 0.47 (day) and 0.26 (night) g C m?2, respectively. Copepods were dominant in most sampling layers, but their mean proportion was lower than that in K2. Mesozooplankton community characteristics at both sites were compared with those at other time-series stations in the North Pacific and with each other. The annual mean primary productivities and sinking POC fluxes were equivalent at both sites; however, mesozooplankton biomasses were higher at K2 than at S1. The difference of biomasses was probably caused by differences of individual carbon losses, population turnover rates, and trophic structures of communities between the two sites. 相似文献
20.