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91.
Yuki Sato Naoto Hirano Shiki Machida Junji Yamamoto Masao Nakanishi Teruaki Ishii 《International Geology Review》2018,60(10):1231-1243
The stress field of oceanic lithosphere controls the distribution of submarine petit-spot volcanoes. However, the eruption sites of these petit-spot volcanoes are considered to be limited to concavely flexed regions of lithosphere off the outer rise. Here, we present new data for a recently identified petit-spot lava field on a convexly flexed section of the lithosphere adjacent to the subduction zone offshore of northeast Japan in an area containing more than 80 volcanoes. This area is marked by strongly alkaline lavas that were erupted on the convexly flexed region. As for the concavely flexed region where the petit-spots previously reported, the base of the lithosphere beneath the eruption sites is under extension, whereas the upper part of the lithosphere is under compression. This change in the stress field, from the lower to upper lithosphere, causes ascending dikes to stall in the mid-lithosphere, leading to metasomatic interaction with the surrounding peridotite. The new geochemical data of rocks and xenocrysts presented in this study indicate that strongly alkaline magmas erupted on the convexly flexed region would have ascended more rapidly through the mid-depth of lithosphere because of the extensional regime of the upper lithosphere and decreasing the degree of metasomatic reaction with the surrounding mantle peridotite. The results indicate that the degree of metasomatism and the compositional variations of petit-spot magmas are controlled mainly by the stress field of the lithosphere. 相似文献
92.
93.
High organic carbon deposition in the northern margin of the Aleutian Basin (Bering Sea) before the last deglaciation 总被引:1,自引:0,他引:1
High-resolution geochemical, isotope and elemental data from core PC23A in the northern margin of the Aleutian Basin (Bering Sea) were used to reconstruct distinct paleoceanographic features of the last deglaciation (pre-Boreal[PB], Bølling-Allerød[BA], Younger Dryas[YD]). The PB and BA intervals are characterized by increased siliceous (diatom) and calcareous (coccolithophores and foraminifers) productivity represented by high biogenic opal and CaCO3 contents, respectively. The enhanced productivity can plausibly be attributed to an elevated sea-surface nutrient supply from increased melt-water input and enhanced Alaskan Stream injection under warm, restricted sea-ice conditions. High Corg/N ratios and low δ13C values of sediment organic matter during the PB and BA intervals reflect the contribution of terrestrial organic matters. The PB and BA intervals were also identified by laminated sediment layers of core PC23A, characterized by high Mo/Al and Cd/Al ratios, indicating that the bottom water condition remained anoxic. High δ15N values during the same period were attributed mainly to the increased nutrient utilization and subsequent denitrification of seawater nitrate. Part of high δ15N values may also be due to incorporation of inorganic nitrogen in the clay minerals. It is worthy of note that high total organic carbon (TOC) deposition occurred approximately 3,000 years before onset of the last deglaciation. Simultaneous high Corg/N ratios and low δ13C values clearly suggest that the high TOC content should be related to terrestrial organic carbon input. Low δ15N values during the high TOC interval also confirm the contribution of terrigenous organic matter. Although abundant calcareous phytoplankton production under cold, nutrient-poor conditions represented by Baex data was reported for high TOC deposition preceding the last deglaciation in an earlier study of the Okhotsk Sea, the main reason for the enhanced TOC deposition in the Bering Sea is an increased terrigenous input from the submerged continental shelves (Beringia) with a sea-level rise; this is further supported by Al enrichment of bulk sediments during the high TOC deposition. 相似文献
94.
95.
96.
Simulation of eutrophication and associated occurrence of hypoxic and anoxic condition in a coastal bay in Japan 总被引:1,自引:0,他引:1
A probabilistic method of calculating the occurrence of oxygen-depleted water within a combined hydrothermal and water quality model was presented in this paper to investigate the environmental impact of eutrophication on the living resources. The method was applied to an eutrophicated shallow coastal bay in western Japan, where the occurrence of red tides at the water surface and the onset of bottom hypoxic waters are observed every summer. Both meteorology and freshwater inflow contribute to the development of stratification of the bay, thus limiting the dissolved oxygen supply to bottom waters. The resulting hydrodynamics enhances the development of oxygen-depleted bottom waters by transporting organic matter produced by algal blooms to the inner bay, where it decomposes and exerts high SOD. During August, about 60% of the inner bay is hypoxic for prolonged durations and as a result most of the benthic biota and fish die. The method used here is a very useful and informative way to evaluate the spatial and temporal damage and severity caused by hypoxia on living resources. Moreover, the model results agreed very well with the observed hydrodynamics, thermal structure and water quality data of the stratified bay. The model can be used for other lakes and bays where knowledge of temperature and density stratification is important for assessing water quality. 相似文献
97.
By using data obtained at about 120 XBT stations, cold water regions in the vicinity of the shoal, Kokushô-sone (30°00N, 128°30E), which is located in the current zone of the Kuroshio in the East China Sea, were investigated.The temperature cross-sections obtained were compared with corresponding cross-sections obtained from the four former cruises which were already reported. On the present cruise forced upwelling area was found along the south slope of the shoal, instead of the north slope as was found on the former cruises.The area of the cold water region found along the south slope tends to decrease with decrease in depth, and at depths shallower than 250 m the cold water region extends northward passing the shoal. The area at a depth of 400 m is comparable to that of the shoal itself, and is about 35 km2.Physical parameters and their scales which seem to be related to the dynamics near the shoal are given in the Appendix. 相似文献
98.
Takeshi Kawano Michio Aoyama Terry Joyce Hiroshi Uchida Yasushi Takatsuki Masao Fukasawa 《Journal of Oceanography》2006,62(6):777-792
An updated batch-to-batch difference table of IAPSO standard seawater (SSW) up to P145 is proposed. The batch-to-batch difference
table is based on several recent SSW comparison experiments, including the experiments conducted independently at the Japan
Agency for Marine-Earth Science and Technology (JAMSTEC) and Woods Hole Institute of Oceanography (WHOI) at about the same
time using the same procedure. Proposed batch-to-batch differences range from 1.2 × 10−3 to −1.9 × 10−3 with reference to the average of those from P91 to P102. Batch-to-batch differences from P29 to P145 with reference to the
recent batches and this average over every 5 years since 1960 are also presented, together with standard deviation. This reveals
that inconsistency among batches has improved since 1980s. In particular, the standard deviation was 0.3 × 10−3 in this decade, which is about one-half the value reported previously and almost equal to the modern measurement precision
(0.2 × 10−3) and is within-batch difference (<0.3 × 10−3). Proposed batch-to-batch differences were applied to the observational results of the WOCE hydrographic onetime section
(WHP onetime) in the Indian Ocean. Average absolute salinity differences at 14 crossover points in the Indian Ocean were slightly
larger, from 1.2 × 10−3 to 1.5 × 10−3, when the batch-to-batch difference table was applied; however, when results from the Indian, Pacific, and Atlantic Oceans
were combined, application of the batch-to-batch difference table yielded statistically acceptable salinity differences. The
table was also applied to WHP sections P1 and P17 (revisited about 10 years after the original observations during the WOCE
period) and sections I1, I7, and I8 (visited twice by different research vessels in the same year). In all cases, the table
corrected unrealistically large salinity changes in space and time. The results suggest that the application of the batch-to-batch
table to well-controlled salinity data such as WOCE datasets would be effective in making the datasets more consistent in
space and time. 相似文献
99.
Takashi Midorikawa Sonoki Iwano Kazuhiro Saito Hiroyuki Takano Hitomi Kamiya Masao Ishii Hisayuki Y. Inoue 《Journal of Oceanography》2003,59(6):871-882
We observed the partial pressure of oceanic CO2, pCO2
sea, and related surface properties in the westernmost region of the subarctic North Pacific, seasonally from 1998 to 2001. The
pCO2
sea in the Oyashio region showed a large decrease from winter to spring. In winter, pCO2
sea was higher than 400 μatm in the Oyashio region and this region was a source of atmospheric CO2. In spring, pCO2
sea decreased to extremely low values, less than 200 μatm (minimum, 139 μatm in 2001), around the Oyashio region with low surface
salinity and this region turned out to be a strong sink. The spatial variations of pCO2
sea were especially large in spring in this region. The typical Oyashio water with minimal mixing with subtropical warm water
was extracted based on the criterion of potential alkalinity. The contribution of main oceanic processes to the changes in
pCO2
sea from winter to spring was estimated from the changes in the concentrations of dissolved inorganic carbon and nutrients, total
alkalinity, temperature and salinity observed in surface waters in respective years. These quantifications indicated that
photosynthesis made the largest contribution to the observed pCO2
sea decreases in all years and its magnitude was variable year by year. These year-to-year differences in spring biological contribution
could be linked to those in the development of the density stratification due to the decrease in surface salinity. Thus, the
changes in the surface physical structure could induce those in pCO2
sea in the Oyashio region in spring. Furthermore, it is suggested that the direction and magnitude of the air-sea CO2 flux during this season could be controlled significantly by the onset time of the spring bloom.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
100.
Stable Carbon and Nitrogen Isotopic Characterization of Organic Matter in a Mangrove Ecosystem on the Southwestern Coast of Thailand 总被引:1,自引:0,他引:1
Organic matter in a tropical mangrove ecosystem was characterized by stable carbon and nitrogen isotopic analyze, conducted
on various organic samples, including land and mangrove plants, soils, particulate organic matter (POM), and sea and river
sediments along the southwestern coast of Thailand. The δ13C values of land plants and POM in river water can be explained in terms of a greater influence of C3 plants than C4 plants in this area. The POM and sediments from the Trang River and Ko Talibong area showed systematically higher δ15N values than those from Ko Muk and other coastal areas. Organic matter in the Trang River might be influenced by nitrogen
released from agricultural or human waste, which could affect the isotopic composition of POM and sediments in the Trang River
estuary and along the coast near the river mouth. We used a stochastic method to estimate the contributions of four organic
end-members, identifiable by their δ13C and δ15N values. The results implied that seagrasses were a major source of sedimentary organic matter, contributing 42 ± 5% in the
Ko Muk area and 36 ± 5% in the Ko Talibong area. The contribution of coastal POM to sediments was estimated to be only 13%
in Ko Muk and 19% in Ko Talibong. Mangrove plants contributed approximately 23% in both areas. It was concluded that seagrasses
are an important source of sedimentary organic matter in this coastal region of southwestern Thailand.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献