Decadal-scale variation in COD and DIN dynamics during the summer in the inner area of the Ariake Sea,Japan     

Yuichi Hayami  Naoki Fujii 《Journal of Oceanography》2018,74(6):551-563

More than 30 years of chemical oxygen demand (COD) and dissolved inorganic nitrogen (DIN) data for the inner area of the Ariake Sea were analyzed with a box model to show the changes in the average seasonal budget and the decadal-scale variation during the summer. The COD peaked in August and March on average. This summertime peak can be explained by an enhanced riverine load and increased primary production. The peak in March suggested additional organic matter production. There were also two peaks in DIN concentration on average: a summertime peak that could be explained by an enhanced riverine load, and a peak in December that was more complicated to explain. From the 1970s to the early 1990s, the bottom water in this area became increasingly hypoxic due to increased COD during the summer, even though there were minimal increases in terrestrial COD and nutrient loads and there were tidal flats covering a widespread area during this period. The increase in COD was caused by increased net ecosystem production, which was due to enhanced primary production induced by an increased freshwater residence time and decreased bivalve grazing. There was a negative feedback control in which hypoxia progressively increased, leading to declines in bivalve biomass, which in turn decreased the grazing pressure limiting primary production, meaning that primary production increased and the area became even more hypoxic. The net DIN production decreased during the 1980s and the 1990s. This was consistent with the change in net ecosystem production according to the COD.  相似文献   

The effects of possible contamination by sample holders on samples to be returned by Hayabusa2     

Naoki Shirai  Yuzuru Karouji  Kazuya Kumagai  Masayuki Uesugi  Kaori Hirahara  Motoo Ito  Naotaka Tomioka  Kentaro Uesugi  Akira Yamaguchi  Naoya Imae  Takuji Ohigashi  Toru Yada  Masanao Abe 《Meteoritics & planetary science》2020,55(7):1665-1680

Chemical compositions of materials used for new sample holders (vertically aligned carbon nanotubes [VACNTs] and polyimide film), which were developed for the analysis of Hayabusa2‐return samples, were determined by instrumental neutron activation analysis and/or instrumental photon activation analysis, to estimate contamination effects from the sample holders. The synthetic quartz plate used for the sample holders was also analyzed. Ten elements (Na, Al, Cr, Mn, Fe, Ni, Eu, W, Au, and Th) and 14 elements (Na, Al, K, Sc, Ti, Cr, Zn, Ga, Br, Sb, La, Eu, Ir, and Au) could be detected in the VACNTs and polyimide film, respectively. The VACNT data show that contamination by this material with respect to the Murchison meteorite is negligible in terms of the elemental ratios (e.g., Fe/Mn, Na/Al, and Mn/Cr) used for the classification of meteorites due to the extremely low density of VACNTs. However, for the Au/Cr ratio, even small degrees (1.7 wt%) of contamination by VACNTs will change the Au/Cr ratio. Elemental ratios used for the classification of meteorites are only influenced by large amounts of contamination (>60 wt%) of polyimide film, which is unlikely to occur. In contrast, detectable effects on Ti isotopic compositions are caused by >0.1 and >0.3 wt% contamination by VACNTs and polyimide film, respectively, and Hf isotopic changes are caused by >0.1 wt% contamination by VACNTs. The new sample holders (VACNTs and polyimide film) are suitable for chemical classification of Hayabusa2‐return samples, because of their ease of use, applicability to multiple analytical instruments, and low contamination levels for most elements.  相似文献   

Coastal ecosystem change in Asia: hypoxia,eutrophication, and nutrient conditions     

Guo  Xinyu  Morimoto  Akihiko  Zhou  Feng  Yoshie  Naoki  Damar  Ario  Takikawa  Tetsutaro 《Journal of Oceanography》2021,77(6):829-830

Journal of Oceanography -  相似文献   

Spatial distribution and cell size of aerobic anoxygenic phototrophic bacteria in the Uwa Sea,Japan     

Yuki Sato-Takabe  Shotaro Suzuki  Ryuki Shishikura  Koji Hamasaki  Yuya Tada  Takafumi Kataoka  Taichi Yokokawa  Naoki Yoshie  Satoru Suzuki 《Journal of Oceanography》2015,71(1):151-159

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Nutrient interleaving below the mixed layer of the Kuroshio Extension Front   总被引：1，自引：1，他引：0  

Takeyoshi Nagai  Sophie Clayton 《Ocean Dynamics》2017,67(8):1027-1046

Nitrate interleaving structures were observed below the mixed layer during a cruise to the Kuroshio Extension in October 2009. In this paper, we investigate the formation mechanisms for these vertical nitrate anomalies, which may be an important source of nitrate to the oligotrphoc surface waters south of the Kuroshio Extension Front. We found that nitrate concentrations below the main stream of the Kuroshio Extension were elevated compared to the ambient water of the same density (σ _?? = 23.5–25). This appears to be analogous to the “nutrient stream” below the mixed layer, associated with the Gulf Stream. Strong turbulence was observed above the vertical nitrate anomaly, and we found that this can drive a large vertical turbulent nitrate flux \(>\mathcal {O}\) (1 mmol N m^?2 day^?1). A realistic, high-resolution (2 km) numerical simulation reproduces the observed Kuroshio nutrient stream and nitrate interleaving structures, with similar lateral and vertical scales. The model results suggest that the nitrate interleaving structures are first generated at the western side of the meander crest on the south side of the Kuroshio Extension, where the southern tip of the mixed layer front is under frontogenesis. Lagrangian analyses reveal that the vertical shear of geostrophic and subinertial ageostrophic flow below the mixed layer tilts the existing along-isopycnal nitrate gradient of the Kuroshio nutrient stream to form nitrate interleaving structures. This study suggests that the multi-scale combination of (i) the lateral stirring of the Kuroshio nutrient stream by developed mixed layer fronts during fall to winter, (ii) the associated tilting of along-isopycnal nitrate gradient of the nutrient stream by subinertial shear, which forms vertical interleaving structures, and (iii) the strong turbulent diffusion above them, may provide a route to supply nutrients to oligotrophic surface waters on the south side of the Kuroshio Extension.  相似文献   

Distribution of <Emphasis Type="Italic">Nemopilema nomurai</Emphasis> in the southwestern Sea of Japan related to meandering of the Tsushima Warm Current     

Satoshi?KitajimaEmail author  Naoki?Iguchi  Naoto?Honda  Tatsuro?Watanabe  Osamu?Katoh 《Journal of Oceanography》2015,71(3):287-296

We investigated the horizontal distribution of Nemopilema nomurai medusae using a midwater trawl in the southwestern Sea of Japan from September to October of each year from 2006 to 2012. Numerous medusae of this species found in 2006, 2007, and 2009 were mainly distributed far (>40 km) from the mainland of Japan in the western part of the survey area, but were distributed in the stations closest (<25 km) to the mainland in the eastern part, particularly in 2006 and 2009. These distribution patterns were associated with the path of the second branch of the Tsushima Warm Current (TWC) that flows offshore to the west of Oki Islands and usually approaches the mainland of Japan to the east of Oki Islands. Differences in jellyfish distribution across the survey periods were related to the distribution of the second branch being associated with types, position and intensity of eddies in the eastern part of the survey area. Hence, the formations of eddies and consequent variation in the path of the TWC would be responsible for transporting medusae from offshore to near the mainland to the east of Oki Islands. Individuals with large bells accumulated in the northwestern part of the survey area, where a cyclonic eddy was present downstream of the third branch of the TWC. This variation in bell size distribution may be ascribed to differences in the physical and/or biological factors among the three branches of the TWC.  相似文献   

西南日本地区地壳P、S波速度结构与地震活动的关系   总被引：2，自引：1，他引：1       下载免费PDF全文

孙安辉  赵大鹏  池田伦治  陈颙  山田朗  陈棋福  大野裕记  西坂直树 《地球物理学进展》2008,23(4):1013-1022

选用密集的高精度地震台网Hi-net 2002～2004年记录的836个地震事件的23,895条P波和21,969条S波的到时资料,计算得到了日本西南地区水平分辨率约33 km,垂直分辨率4～15 km的三维地壳P波和S波速度结构,并进一步获得泊松比分布.研究表明,在大山火山下存在显著的低速异常,表明该火山可能是一个潜在的活火山.速度异常图像清楚地显示了菲律宾板块俯冲至西南日本地区下,其上方存在的低速高泊松异常表明可能有流体的存在,分析得出可能来自板块俯冲过程中的脱水作用.并进一步探讨了流体在地震孕育及触发的过程中可能起的重要作用.  相似文献   

Possibility of recent changes in vertical distribution and size composition of chlorophyll-a in the western North Pacific region     

Hiroshi Ishida  Yutaka W. Watanabe  Joji Ishizaka  Toshiya Nakano  Naoki Nagai  Yuji Watanabe  Akifumi Shimamoto  Nobuhiro Maeda  Michimasa Magi 《Journal of Oceanography》2009,65(2):179-186

Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a (Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season, as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4 and 2.3% year⁻¹ in the subtropical area along 137°E (STA₁₃₇) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA₁₇₅) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year⁻¹ in STA₁₃₇ and KEA₁₇₅; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. Water density (σ _θ ) at 75 m depth had also decreased by 0.006 and 0.05 year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. The ratio of biogenic opal to biogenic CaCO₃ in the sinking flux decreased by 0.015 year⁻¹ in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density of surface water caused by warming in the western North Pacific, especially in the summer.  相似文献   

Chemical characteristics of the lherzolitic shergottite Yamato 000097: magmatism on Mars inferred from the chemical compositions of shergottites   总被引：1，自引：1，他引：0  

Naoki Shirai  Mitsuru Ebihara 《Polar Science》2009,3(2):117-133

As a part of a consortium study, we analyzed the Martian meteorite Yamato (Y) 000097 by prompt gamma-ray analysis, instrumental neutron activation analysis, and instrumental photon activation analysis. For comparison, we also analyzed Allan Hills (ALH) 77005 using the same methods. The data confirm that Y000097 belongs to lherzolitic shergottites in terms of chemical composition. Although there exist slight differences in elemental abundances among lherzolitic shergottites due to differences in the modal abundances of constituent minerals, they have essentially the same chemical compositions, suggesting they are genetically related and experienced similar formation histories.Zr/Hf ratios obtained for Y000097 and ALH 77005 are subchondritic, consistent with values reported for other lherzolitic shergottites and olivine-phyric shergottites. Such fractionation can be explained by invoking clinopyroxene, ilmenite, or majorite in the petrogenesis of the shergottites' source material. CI-normalized Hf/Sm ratios obtained for Y000097 and ALH 77005 are 1.52 and 1.37, respectively, consistent with superchondritic Hf/Sm ratios reported for shergottites. Based on experimentally derived partition coefficients, majorite is the best candidate mineral for the fractionation of Hf and Sm in shergottites.  相似文献   

Foraminiferal evidence of submarine sediment transport and deposition by backwash during the 2004 Indian Ocean tsunami     

Daisuke  Sugawara  Koji  Minoura  Naoki  Nemoto  Shinji  Tsukawaki  Kazuhisa  Goto  Fumihiko  Imamura 《Island Arc》2009,18(3):513-525

Micropaleontological analysis of nearshore to offshore sediments recovered from the southwestern coast of Thailand was performed to clarify the submarine processes of sediment transport and deposition during the 2004 Indian Ocean tsunami. The distribution pattern of benthic foraminifers showed seaward migration after the tsunami event. Agglutinated foraminifers, which are characteristic of an intertidal brackish environment, were identified in the post-tsunami samples from foreshore to offshore zones. These suggest that sediments originally distributed in foreshore to nearshore zones were transported offshore due to the tsunami backwash. On the other hand, the distribution pattern of planktonic and benthic species living in offshore zones showed slight evidence of landward migration by the tsunami. This suggests that landward redistribution of sediments by the tsunami run-up did not occur in the offshore seafloor of the study area. Our results and a review of previous studies provide an interpretation of submarine sedimentation by tsunamis. It is possible that tsunami backwashes induce sediment flows that transport a large amount of coastal materials seaward. Thus, traces of paleotsunami backwashes can be identified in offshore sedimentary environments as the accumulation of allochthonous materials. This can be recognized as changes in benthic foraminiferal assemblages.  相似文献