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131.
Taketoshi Kodama Akihiko Morimoto Tetsutaro Takikawa Masashi Ito Yosuke Igeta Shoko Abe Ken-Ichi Fukudome Naoto Honda Osamu Katoh 《Journal of Oceanography》2017,73(6):759-769
To identify water with an excess nitrate concentration to phosphate ratio and its potential source, the nutrient concentrations in the Tsushima Strait (TSS) were investigated over ten cruises in August and September 2007–2014, excluding 2010. On the basis of the Redfield ratio, water with an excess nitrate concentration of >1 μM (positive ExNOx water) was identified below the surface mixed layer during four cruises in 2011–2013. Positive ExNOx water was present mainly in less-saline (<34) waters with a density of 22–25 σ θ , and 25–75 m depth. However, in August 2012, positive ExNOx was detected in dense (25–25.5 σ θ ) and deep (50–110 m depth) waters near the salinity maximum, although the salinity during this period was significantly lower than that in other years. The horizontal length of positive ExNOx water was >100 km across the TSS during two cruises in August 2012 and September 2013, respectively. According to multi-regression analysis conducted on the silicate concentration, temperature, and salinity, the silicate concentration was increased in the less-saline subsurface water. The required amount of original freshwater was 108–9 m3 day?1 based on the excess nitrate concentration. This evidence indicates that the positive ExNOx water originated from large river waters such as the Changjiang. Thus, discharged water from the rivers of the East Asia is contributing to the increased N:P ratio in the Tsushima Warm Current, southern Japan Sea. 相似文献
132.
Osamu Fujiwara Kazuomi Hirakawa Toshiaki Irizuki Shiro Hasegawa Yoshitaka Hase Jun‐ichi Uchida Kohei Abe 《Island Arc》2010,19(3):374-388
A flight of Holocene marine terraces on the southwestern coast of Cape Omaezaki of central Japan provides evidence of recurrent millennium‐scale uplift events. We reconstructed the uplift history of these terraces by using facies analysis of drill core and geoslicer samples, environmental analysis of trace fossils, and 14C age determinations. Coastal uplift can be identified by the displacement of beach deposits such as foreshore deposits, which represent the intertidal swash zone of a wave‐dominated sandy coast. Three levels of former beach deposits facing the Nankai Trough were identified near the coast in the Omaezaki area. The highest of these, dated at about 3020–2880 BC, records a maximum of 2.2–2.7 m of emergence. The middle beach surface, of minimum age 370–190 BC, shows 1.6–2.8 m of emergence. The lowest beach surface, which is older than 1300–1370 AD, records 0.4–1.6 m of emergence. Our analysis of vertical crustal deformation data during the Holocene in this region suggests that rapid and strong uplift was restricted to the southwestern coast of the Omaezaki area and was probably caused by high‐angle thrusting on subsidiary faults branching from the underlying plate boundary megathrust. 相似文献
133.
Seasonal variations of the Hawaiian Lee Countercurrent induced by the meridional migration of the trade winds 总被引:1,自引:0,他引:1
Hideharu Sasaki Shang-Ping Xie Bunmei Taguchi Masami Nonaka Yukio Masumoto 《Ocean Dynamics》2010,60(3):705-715
Seasonal variations of the Hawaiian Lee Countercurrent (HLCC) are investigated using satellite observations of sea surface
height and wind stress as well as eddy-resolving ocean model simulations. The HLCC is strong from summer to winter and weak
in spring between the dateline and the Hawaiian Islands. In response to the seasonal migration of the northeast trade winds
in the meridional direction, the wind curl dipole lee of Hawaii varies in strength, exciting westward-propagating Rossby waves.
The analyses of both observations and simulations show that the propagation of Rossby waves south of the HLCC, driven by the
southern pole of the wind curl dipole in the lee of the islands, contributes the most to the seasonal variations of the HLCC.
Unlike the wind-driven seasonal variations, our analysis suggests that other mechanisms such as mode water intrusion or air–sea
interaction may cause the interannual variations of the HLCC. 相似文献
134.
Osamu Seki Philip A. Meyers Kimitaka Kawamura Yanhong Zheng Weijian Zhou 《Organic Geochemistry》2009,40(6):671-677
Based on paleoclimatic reconstructions using various proxies, the Holocene Climate Optimum (10.5–6 ka) has been characterized as a warmer and wetter period in most of East Asia. The summer monsoons associated with the East Asian Monsoon evidently intensified and extended further inland from the Pacific Ocean, a source region of moisture. A notable exception to this general pattern exists in northeast China, where less wet conditions are recorded. We determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions (δD values) in a radiocarbon-dated peat core recovered from the Hani marsh in Jilin Province (China) and confirmed that the temperature-dependent effective precipitation in northeast China decreased during the Holocene Climate Optimum. A combination of Paq, an indicator of the relative contribution of aquatic to terrestrial plants, and the difference in δD between low (C23, C25 and C27) and high molecular weight (C31) n-alkanes in the Hani peat bog indicates a dramatic change in vegetation from the deglaciation to the Holocene. No significant differences were observed between the δD values of low and high molecular weight n-alkanes with relatively high δD values and low Paq during the early Holocene, indicating that all n-alkanes were produced by evapotranspiration-sensitive terrestrial plants during that time. However, lower δD values of mid-chain n-alkanes (C23, C25 and C27) relative to the long chain n-alkane (C31), together with higher Paq values during the deglaciation (14–11 ka), suggest an increase in the contribution of aquatic plants and a higher water level during the period. The study demonstrates that northeast China was under a markedly wetter climate condition during the late deglaciation. For the 16 kyr record in the Hani peat sequence, we infer that moisture delivery by the East Asian Monsoon was relatively invariable in northeast China, but increased evaporation during the warmer Holocene Climate Optimum reduced the effective precipitation, defined by the balance between precipitation and evaporation. 相似文献
135.
Katsuyuki Sasaki Tsuneo Ono Katsuhisa Tanaka Kiyoshi Kawasaki Hiroshi Saito 《Journal of Oceanography》1998,54(5):593-603
Partial pressure of CO2 in surface sea water (pCO2) was measured continuously off Sanriku in May, 1997 by a new pCO2 measurement system. We have examined the relation of pCO2 to physical factors such as temperature, salinity and density, chemical and biological factors such as nutrients and carbonate
system and chlorophylla. In the Kuroshio region pCO2 was not correlated to physical, chemical and biological factors in the range of 260 to 290 μatom. In transition water (Tr1)
between Kuroshio and the Oyashio second branch, pCO2 was weakly correlated to physical factors and strongly correlated to nutrients. In transition water (Tr2) between the Oyashio
first and second branches, pCO2 was highly correlated to temperature (SD: 10.9 μatom) and salinity (SD: 8.6 μatom) and also to nutrients. In transition water
(Tr1+Tr2), pCO2 was highly multivariately correlated to temperature (T), salinity (S), chlorophylla (CH) (or nitrate+nitrite (N)) as follows, pCO2(μatom)= 10.8×T(°C)+27.7×S+2.57CH(μg/1) −769, R2= 0.86, SD = 20.9, or pCO2(μatom)= 3.9×T(°C)+25.5×S+16.0NO3(μM) −686, R2= 0.99, SD = 6.4. Moreover, pCO2 was predicted by only two factors, one physical (S) and the other chemical/biological (N) as follows: pCO2 (μatom)=32.8×S+19.4N−908, R2=0.97, SD=8.4. The pH measured at 25°C was well correlated with normalized pCO2 at a fixed temperature. In the Oyashio region pCO2 was decreased to 160 μatom, probably because of spring bloom, but was not correlated linearly to chlorophylla. The results obtained showed the possibility of estimating pCO2 of the Oyashio and transition regions in May by satellite remote sensing of SST, but the problem of estimation of pCO2 in Kuroshio water remains to be solved. 相似文献
136.
Misao Sasaki 《Journal of Astrophysics and Astronomy》1999,20(3-4):281-289
In this talk, I review an analytic method for calculating gravitational radiation from a small mass particle orbiting a massive
black hole. This method allows a systematic evalutation of the gravitational radiation to a very high order in post-Newtonian
expansion, hence gives us useful information on the evolution of coalescing compact binary stars. 相似文献
137.
The atmosphere-ocean exchange of climatically important gases is determined by the transfer velocity (k) and concentration gradient across the interface. Based on observations in the northwestern subarctic Pacific and Sagami
Bay, we report here the results of the first ever application of the natural abundance of triple isotopes of dissolved oxygen
(16O, 17O and 18O) for direct estimation of k and propose a new relationship with wind speed. The k values estimated from nighttime variations in oxygen isotopes are found to be higher than the direct estimations at low wind
speed (<5 m s−1) and lower at high wind speeds (>13 m s−1) and showed significant spatial variability. The method presented here can be used to derive seasonal and spatial variations
in k and the influence of surface conditions on the value, leading to improved estimates of biogenic/anthropogenic gas exchange
at the air-sea interface. 相似文献
138.
Tai Sasaki Naro Hashimoto Takayuki Nakato Tomonari Shiraishi Kazuaki Yajima Tomoyuki Hishiya 《Engineering Geology》1998,49(3-4):337-343
As a preliminary step for predicting groundwater flow in a plateau 30–50 m above sea level, a model for three-dimensional analysis of groundwater flow was formulated and its validity was verified. The plateau consists of Neogene sedimentary rocks and a Quaternary deposit. Most of the groundwater originates in precipitation, with the groundwater table lying in the Quaternary deposit. Steady-state analysis was conducted by using the finite element method. The results of pore-water pressure measurement and water examination were useful in verifying the validity of the model. In constructing the model, reducing the hydraulic conductivity according to the depth on the basis of the results of the actual measurement was important. 相似文献
139.
Takayuki Shiozawa Akira Hoshika Osamu Takimura Terumi Tanimoto 《Journal of Oceanography》1982,38(1):15-20
Vertical and horizontal distributions of manganese in Harima Sound (Harima Nada, Seto Inland Sea) were measured in August and December 1979. High concentrations of dissolved and particulate manganese were found in bottom waters in August, suggesting that the bottom enrichment is probably due to the diffusion of dissolved manganese out of the sediment. From measured distributions, we estimate the annual flux of manganese at the sediment-water interface to be more than 800 tons per year, if Harima Sound is a closed system for manganese. 相似文献
140.
Akihiro Shiomoto Katsuyuki Sasaki Toru Shimoda Satsuki Matsumura 《Journal of Oceanography》1994,50(5):515-529
The maximum uptake rate (max) and affinity constant (K
s) for nitrate and ammonium were estimated in the surface water of offshore Oyashio in May (spring) and September (summer), 1990. The average max/Chl.a for ammonium was 2.1 times larger than that of nitrate in both seasons. The average max/Chl.a for both nitrogens were 3.5 times larger in summer than in spring. Water temperature and size composition of phytoplankton population were related to the seasonal difference in the max/Chl.a. Phytoplankton population showed high affinity for both nitrogens in the spring and summer. In addition, the contribution of new production to total production was estimated by max[max–No3/(max–NO3+max–NH4)]. The spring value was in the range of 0.26 to 0.45 (mean±SD=0.35±0.092), and the values in spring bloom were especially a little over 0.4. The summer value was in the range of 0.30 to 0.37 (0.34±0.04). 相似文献