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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
2.
Formation and deformation processes of the late Paleogene sedimentary basins related to a strike–slip fault system in southern central Hokkaido are described by a combination of paleomagnetic study and numerical analysis. After correction of the Miocene counter‐clockwise rotation associated with back‐arc opening of the Japan Sea, paleomagnetic declination data obtained from surface outcrops in the Umaoi and Yubari areas show significant easterly deflections. Although complicated differential rotation is anticipated as a result of recent thrust movements, clockwise rotation in the study areas is closely linked with development of the Paleogene Minami‐naganuma Basin as a pull‐apart depression along the north–south fault system. Numerical modeling suggests that 30 km of strike–slip is required to restore the distribution and volume of the Minami‐naganuma Basin. The relative slip rate on the long‐standing fault system is about 10 mm/yr, which corresponds to global‐scale plate motion. It has inevitably caused regional rearrangement of the eastern Eurasian margin. A rotation field simulated by simplified dextral motion using dislocation modeling basically accords with the paleomagnetic data around the pull‐apart basin. 相似文献
3.
Machiko Yamada Eri Katsuki Mayuko Otsubo Mayumi Kawaguchi Kazuhiko Ichimi Hideki Kaeriyama Kuninao Tada Paul J. Harrison 《Journal of Oceanography》2010,66(6):755-771
Seven Skeletonema species were identified at one station in the industrial harbor Dokai Bay, Japan, in October 2007 and then monthly from January
2008 to December 2009 by morphological scanning electron microscopy observations and molecular analyses of mainly the large
subunit (LSU) rDNA. We refer to one species identified as S. dohrnii using LSU rDNA, but as S. marinoi using the small subunit (SSU) rDNA and consequently we use the term S. marinoi-dohrnii complex. This is the first time that S. ardens, S. costatum s.s., and S. pseudocostatum have been recorded in Japan and that S. menzelii and S. tropicum have been identified by molecular methods in Japan. The S. marinoi-dohrnii complex was isolated with high frequency all year-round, and S. japonicum was also isolated with high frequency but not so in summer. S. Tropicum was isolated from September to December, but S. ardens and S. costatum s.s. were isolated only when the water temperature exceeded 20°C. S. pseudocostatum bloomed just once, in summer, but S. menzelii was isolated in May and again in October. The continuous year-round occurrence of S. costatum s.l. in the bay is supported by the succession of these seven species. Six of the species, except S. menzelii, were important components of algal blooms in the bay. One to four species of Skeletonema were isolated every month. Monthly species diversity was higher when S. ardens, S. costatum s.s., and S. tropicum that are usually associated with tropical or subtropical waters, were isolated. In general, species diversity of the genus
Skeletonema was very high in Dokai Bay. 相似文献
4.
Late Cretaceous to Paleogene tectonic episodes around the eastern Eurasian margin are described utilizing one-dimensional (1D) basin modeling technique on the basis of organic maturation; vitrinite reflectance and Tmax parameter values of the Rock-Eval pyrolysis. Fine-grained marine sediment of the Yezo Supergroup in central Hokkaido is one of the most extensive Cretaceous constituents along the plate margin. To evaluate organic maturation within the Yezo Supergroup, a surface section (Hakkin-zawa) and a deep borehole (MITI Yubari) were selected, from which quite different maturation trends were obtained. Notably low and constant maturation was suggested throughout the thick Hakkin-zawa section, and it was confirmed on the basis of various biomarker analyses. It requires anomalously rapid burial, probably related to thrust-stacking or large-scale slumping, followed by prompt tilting/exhumation event. In sharp contrast, Late Cretaceous strata in the MITI Yubari do not indicate coeval tectonic disturbances in a short period. A wider view of the ancient convergent margin suggests that deformation of the forearc propagated westward during the Cretaceous. High maturation levels in the uppermost thrust sheet around the MITI Yubari are optimized in 1D geochemical modeling on the assumption that a thick missing Paleogene unit has been eroded out as a result of thrust-forming contraction scheme emerged during the Neogene. A similar Cenozoic burial pattern is adopted for the once tilted and exhumed Hakkin-zawa section in order to match the present maturation levels. Although such an active subsidence of a ‘forearc’ is generally interpreted as an effect of the subduction erosion, heavy mineral composition of the shallow marine to fluvial Paleogene implies uplift and exhumation of ultramafic rocks to the east (trench-side). Thus the confined basin-formation in central Hokkaido is to be understood in a different tectonic framework that may reflect transcurrent motions on the plate margin. 相似文献
5.
A history of water pollution and countermeasures for water purification in Dokai Bay, Japan are reviewed. Now, Dokai Bay suffers from the occurrences of red tides and oxygen-deficiency in summer. In order to prevent the occurrences of red tides and oxygen-deficiency, an ecological numerical model has been developed. The model experiments forecast that when the phosphorus or nitrogen load from land will be cut by 90% or 95%, respectively, red tides and oxygen-deficiency will not occur in Dokai Bay. If the industrial and sewage facilities are not sufficient to cut the nutrients load to the necessary degree, we have to consider other countermeasures such as cultivating bivalves and algae in order to decrease the nutrients concentration in the bay. International co-operation related to coastal zone management is also discussed. 相似文献
6.
Kenichiro Hamada Naoko Ueda Machiko Yamada Kuninao Tada Shigeru Montani 《Journal of Oceanography》2012,68(1):173-182
Biologically important nutrient concentrations in Dokai Bay have declined as a result of reductions in anthropogenic inputs
of total nitrogen and total phosphorus. A decrease in nutrient concentrations affects phytoplankton growth, thereby changing
the biochemical characteristics of autochthonous particulate matter. We therefore investigated changes in the C/N/P molar
ratio of suspended particulate matter (SPM) in the summer, when phytoplankton growth is vigorous, before environmental quality
standards (EQSs) were attained (1995–1998) and afterward (2006–2009). We found that the ratio of particulate organic nitrogen
(PON) to particulate phosphorus (PP) changed in conjunction with changes in the ratio of dissolved inorganic nitrogen to dissolved
inorganic phosphorus (DIP) that resulted from reductions in nutrient loading. Furthermore, we suggest that because the DIP
concentration in seawater was high before EQSs were attained, inorganic phosphorus was possibly adsorbed onto SPM. After the
attainment of EQSs, however, the DIP concentration fell, and PON/PP was high. Phosphorus limitation of phytoplankton growth
in the mouth of the bay may explain the high PON/PP ratios after EQS attainment. 相似文献
7.
Abstract Paleomagnetic studies provide constraints on the geometric configuration of the eastern Eurasian margin on geological time scales. Characteristic remanent magnetization components were isolated from eight sites by progressive demagnetization executed on samples from 25 sites in the Oyubari area, central Hokkaido where the Late Cretaceous Yezo Group is distributed. After tilt-correction, all sites show normal polarity site-mean directions, and well-clustered directions pass a positive fold test and a correlation test. Planktonic foraminifera indicate an age range of Cenomanian to Turonian, and the studied section is correlated to the geomagnetic polarity chron C34n. Reliable formation-mean directions that have been corrected for post-depositional shallowing (D = 7.5°, I = 65.9°, α95 = 6.6°) are characterized by inclination data indicative of no significant latitudinal translation since the Late Cretaceous. Central Hokkaido has, therefore, been situated adjacent to easternmost Mongolia including Sikhote Alin around the present latitude since the Late Cretaceous. Declination data require significant differential rotation between Hokkaido and the eastern Asian margin, which may be indicative of rearrangement of crustal blocks along the continental margin. 相似文献
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