Published Papers - SHINJO Ryuichi

Geochemical characteristics of hydrothermal fluids at Hatoma Knoll in the southern Okinawa Trough

Toki Tomohiro, Itoh Michihiro, Iwata Daigo, Ohshima Shogo, Shinjo Ryuichi, Ishibashi Jun-ichiro, Tsunogai Urumu, Takahata Naoto, Sano Yuji, Yamanaka Toshiro, Ijiri Akira, Okabe Nobuaki, Gamo Toshitaka, Muramatsu Yasuyuki, Ueno Yuichiro, Kawagucci Shinsuke, Takai Ken

ＧＥＯＣＨＥＭＩＣＡＬ　ＪＯＵＲＮＡＬ ( 一般社団法人日本地球化学会 )  50 ( 6 ) 493 - 525   2016

Type of publication: Research paper (scientific journal)

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<p>Chemical and isotopic compositions of hydrothermal fluids from Hatoma Knoll in the southern Okinawa Trough were investigated. The hydrothermal fluids were derived from a single pure hydrothermal fluid source, but they underwent phase separation beneath the seafloor prior to venting. Only vapor-like fluids vent at the Hatoma system, and the most active area is around the center of the crater, based on the location of the maximum temperature and the lowest Cl^– concentrations. Compared with other hydrothermal systems in the world, at Hatoma the pH and alkalinity, as well as the B, NH₄⁺, K, Li, CO₂, and CH₄ concentrations, were higher, and the Fe and Al concentrations were lower, suggesting that the characteristics of the Hatoma hydrothermal fluids are comparable to those of the other Okinawa Trough hydrothermal fluids. Helium isotope ratios were lower than those of sediment-starved hydrothermal systems, suggesting that ⁴He derived from the sediment is supplied to the hydrothermal fluids in Hatoma Knoll. The carbon isotope ratios of CO₂ in the hydrothermal fluids indicate an influence of organic carbon decomposition. The carbon isotope ratios of CH₄ in the hydrothermal fluids imply that most of the CH₄ originated from microbial methane produced in a recharge zone of the hydrothermal system. Although sediment influences are a typical feature of Okinawan Trough hydrothermal fluids, the Hatoma hydrothermal system has the lowest carbon isotope ratios of CH₄ among them, which suggests that Hatoma is the most highly influenced by the sediments in the recharge zone. Thus, the degree of the sediment influences has a variable in each hydrothermal field in the Okinawa Trough.</p>

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Geology and Formation of Ryukyu Arc

SHINJO Ryuichi

Pedologist ( Japanese Society of Pedology )  60 ( 1 ) 47 - 54   2016 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Response of Acropora digitifera to ocean acidification: constraints from δ11B, Sr, Mg and Ba compositions of aragonitic skeletons cultured under variable seawater pH

Tanaka, K, Holcomb, M, Takahashi, A, Kurihara, H, Asami, R, Shinjo, R, Sowa, K, Rankenburg, K, Watanabe, T, McCulloch, M

Coral Reef ( Coral Reefs )  34 ( 4 ) 1139 - 1149   2015.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The response of Acropora digitifera to ocean acidification is determined using geochemical proxy measurements of the skeletal composition of A. digitifera cultured under a range of pH levels. We show that the chemical composition (delta B-11, Sr/Ca, Mg/Ca, and Ba/Ca) of the coral skeletons can provide quantitative constraints on the effects of seawater pH on the pH in the calcification fluid (pH(CF)) and the mechanisms controlling the incorporation of trace elements into coral aragonite. With the decline of seawater pH, the skeletal delta B-11 value decreased, while the Sr/Ca ratio showed an increasing trend. The relationship between Mg/Ca and Ba/Ca versus seawater pH was not significant. Inter-colony variation of delta B-11 was insignificant, although inter-colony variation was observed for Ba/Ca. The decreasing trend of pH(CF) calculated from delta B-11 was from similar to 8.5, 8.4, and 8.3 for seawater pH of similar to 8.1, 7.8, and 7.4, respectively. Model calculations based on Sr/Ca and pH(CF) suggest that upregulation of pH(CF) occurs via exchange of H+ with Ca2+ with kinetic effects (Rayleigh fractionation), reducing Sr/Ca relative to inorganic deposition of aragonite from seawater. We show that it is possible to constrain the overall carbonate chemistry of the calcifying fluid with estimates of the carbonate saturation of the calcifying fluid (Omega (CF)) being derived from skeletal Sr/Ca and pH(CF) (from delta B-11). These estimates suggest that the aragonite saturation state of the calcifying fluid Omega (CF) is elevated by a factor of 5-10 relative to ambient seawater under all treatment conditions.

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Solid phase below the seafloor estimated from Li isotope ratio in hydrothermal fluids from Okinawa Trough

Toki Tomohiro, Heshiki Sawako, Shinjo Ryuichi, Ishibashi Jun-ichiro

Abstracts of Annual Meeting of the Geochemical Society of Japan ( GEOCHEMICAL SOCIETY OF JAPAN )  62 ( 0 ) 4   2015

Type of publication: Research paper (research society, symposium materials, etc.)

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Li isotope ratios in Okinawa Trough hydrothermal fluids show higher concentrations and lower isotopic ratios than those in MOR hydrothermal fluids. It suggests Okinawa Trough hydrothermal fluids react with sediment and volcanic rocks.

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Data report: Boron isotope ratios in interstitial waters from Sites C0021 and C0022

Toki, T, Higa, K, Shinjo, R

Proceedings of the Integrated Ocean Drilling Program   338   2015 [ Peer Review Accepted ]

Type of publication: Research paper (other science council materials etc.)

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Damage zone propagation and support pressure estimation around two access tunnels of the Barapukuria coal mine in Bangladesh: a two-dimensional numerical modeling approach

Rafiqul, M. I, Faruque, M. O, Shinjo, R

International Journal of Advanced Geosciences   3   14 - 24   2015 [ Peer Review Accepted ]

Type of publication: Research paper (other science council materials etc.)

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Late Holocene coral reef environment recorded in Tridacnidae shells from archaeological sites in Okinawa-jima, subtropical southwestern Japan

Asami R, Konishi M, Tanaka K, Uemura R, Furukawa M, Shinjo R

Island Arc   24 ( 1 ) 61 - 72   2015 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Seasonally resolved records of carbon and oxygen isotopic composition (δ18O) in fossil shells of giant clams (Tridacnidae) recovered from the Kogachibaru Shell Mound (26°26'N, 127°49'E) and the Second Aragusuku-Shichabaru Ruin (26°18'N, 127°46'E) in Okinawa-jima, southwestern Japan, were investigated to reconstruct subtropical coral reef environments of the past. The samples, mainly composed of aragonite shells with limited amounts of diagenetically-altered calcite cements, were selected for geochemical analyses. The radiocarbon dating of the samples for stable isotope analyses yields about 4000yr cal. BP for the Kogachibaru Shell Mound and about 1900-1700yr cal. BP for the Second Aragusuku-Shichabaru Ruin, respectively, that correspond to the early and middle Shell Mound periods in Okinawa-jima. These show good agreement with the respective ages inferred from excavation. The shell δ18O values roughly show seasonal variations, coincident with the occurrence of annual growth bands. Applying corrections for the effect of diagenetic alteration, the averages of annual, summer, and winter δ18O values of fossil shells were significantly lower (by 0.1-0.7‰) than those of aragonite theoretically precipitated in present-day coral reef water of Okinawa-jima. These results demonstrate that annual mean seawater temperature and salinity at the sites where the Tridacnida spp. lived were about 1-3°C higher and/or about 1-2 lower than at present. This variation cannot be fully explained by global climate change, sea level change, and topographic growth of coral reef. Therefore, it is likely that the giant clams lived in extremely small and/or closed coral-reef lagoons with less water circulation where seawater is highly susceptible to insolation-induced temperature increase and input of fresh water; the effect could be enhanced by the fisheries lifestyle that stonewalling would be constructed at shallow waters through the use of tidal variation during the early and middle Shell Mound period in Okinawa-jima.

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沖縄島の地質と成り立ち

新城竜一

琉球列島の自然講座 サンゴ礁・島の生き物たち・自然環境     150 - 159   2015

Type of publication: Research paper (other science council materials etc.)

δ11B, Sr, Mg and Ba in Acropora digitifera cultured under acidified seawater: Effects of seawater pH on trace element incorporation into coral aragonite

Tanaka, K, Holcomb M, Takahashi, A, Kurihara, H, Asami, R, Shinjo, R, Sowa, K, Rankenburg, K, Watanabe, T, McCulloch, M

Coral Reefs     2015 [ Peer Review Accepted ]

Type of publication: Research paper (other science council materials etc.)

The geology of Okinawa-jima Island

Shinjo, R

Nature in the Ryukyu Archipelago: Coral Reefs, Biodiversity, and the Natural Environment     112 - 119   2015

Type of publication: Research paper (other science council materials etc.)

Sr-Nd-Pb-Hf isotopic constraints on the diversity of magma sources beneath the Aden Ridge (central Gulf of Aden) and plume-ridge interaction

Shinjo R.

岩石礦物礦床學 ( 一般社団法人　日本鉱物科学会 )  110 ( 3 ) 97 - 110   2015

Type of publication: Research paper (scientific journal)

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This paper presents new Sr–Nd–Pb–Hf isotopic compositions of tholeiitic basalts dredged along the Aden Ridge of the central Gulf of Aden (45.5°E–49°E). Two groups of basalts are identified based on their contrasting spatial distributions and geochemical signatures. Basalts dredged from east of 46.2°E (Group 1) are LREE–depleted but have relatively wide variations in ⁸⁷Sr/⁸⁶Sr (0.70278–0.70304) and ²⁰⁶Pb/²⁰⁴Pb (18.21–19.03) and limited ¹⁴³Nd/¹⁴⁴Nd (0.51301–0.51309) and ¹⁷⁶Hf/¹⁷⁷Hf ranges (0.283224–0.283276; εHf = 15.98–17.83), analogous to the geochemical signature of enriched to depleted normal mid–oceanic ridge basalts (N–MORB). In contrast, the basalts dredged between 45.6°E and 46.2°E (Group 2) are more enriched in incompatible elements [ocean island basalt (OIB)–like] but have little variation in ⁸⁷Sr/⁸⁶Sr (0.70323–0.70341), ²⁰⁶Pb/²⁰⁴Pb (19.33–19.49), and ¹⁴³Nd/¹⁴⁴Nd (0.51285–0.51292) and a wide variation in ¹⁷⁶Hf/¹⁷⁷Hf (0.283020–0.283155; εHf = 8.77–13.54). Isotopic and trace element variations can be attributed to the mixing of three types of mantle source: depleted MORB–type mantle (Component i), matrix mantle of the Afar plume (Component ii), and recycled oceanic crust (Component iii) occurring as blobs, streaks, or ribbons within the plume matrix. Mixing between Components i and ii would have produced Group 1 basalts, and Components ii and iii produced Group 2 basalts. Our data suggest that the Afar plume components were involved in magma genesis westward from 48°E in the Aden Ridge.

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Determination of rare earth elements in small-volume seawater by off-line preconcentration system and inductively coupled plasma mass spectrometry

Shinjo　Ryuichi,

No.92 (2011/9) ( 琉球大学理学部 )  ( 92 ) 17 - 22   2011.11

Type of publication: Research paper (bulletin of university, research institution)

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An analytical method was developed for determining rare earth element (REE) concentrations in seawater using inductively coupled plasma mass spectrometry (ICP-MS). A relatively small-volume seawater sample (25 ml) was used for chemical separation. REE concentrations in 20-fold preconcentrated solution by an off-line preconcentration system were analyzed by ICP-MS with microflow nebulizer. The recoveries were mostly higher than 95%. To assess the analytical method, REE concentrations of the North Atlantic Surface Seawater (NASS-5), a seawater certified reference material, were measured with the proposed preconcentration procedure. Results obtained in this study are consistent with those of previous studies with good precision. （管理者追加）リポジトリ登録情報を移行しました。確認のうえ、加除修正をしてください。

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The tectonic stress field and deformation pattern of northeast India, the Bengal basin and the Indo-Burma Ranges: A numerical approach

Islam, M.S., Shinjo, R. and Kayal, J.R.

Journal of Asian Earth Sciences ( その他の出版社 )  40   121 - 131   2011

Type of publication: Research paper (scientific journal)

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Pop-up tectonics of the Shillong Plateau in northeastern India: Insight from numerical simulations

Islam, M.S., Shinjo, R., Kayal, J.R.

Gondwana Research ( その他の出版社 )  (in press)   2011

Type of publication: Research paper (scientific journal)

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Extracellular Matrix Protein in Calcified Endoskeleton: A Potential Additive for Crystal Growth and Design

Rahman, M.A., Fujimura, H., Shinjo, R. and Oomori, T.

Journal of Crystal Growth ( その他の出版社 )  (in press)   2011

Type of publication: Research paper (scientific journal)

Geochemistry and geochronology of the mafic lavas from the southeastern Ethiopian rift (the East African Rift System): Assessment of models on magma sources, plume-lithosphere interaction and plume evolution

Shinjo, R., Chekol, T., Meshesha, D., Itaya, T. and Tatsumi, Y.

Contributions to Mineralogy and Petrology ( その他の出版社 )  (in press)   2011

Type of publication: Research paper (scientific journal)

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New supplemental activator for lead isotope analysis with TIMS

Nohda, S., Wang, B.-S., You, C.-F. and Shinjo, R.

Geochemical Journal ( その他の出版社 )  (in press)   2011

Type of publication: Research paper (scientific journal)

Barite geochemistry from hydrothermal chimneys of the Okinawa Trough: insight into chimney formation and fluid/sediment interaction

Noguchi, T., Shinjo, R., Ito, M., Takada, J. and Oomori, T.

Journal of Mineralogical and Petrological Sciences ( その他の出版社 )  106   26 - 35   2011

Type of publication: Research paper (scientific journal)

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Report on RN97 Cruise by T/S Nagasaki Maru in the Southern Okinawa Trough

Motoyama　Isao,Nakamura　Mamoru,Takaki　Yasuaki,Nishida　Hideaki,Morii　Yasuhiro,Tanaka　Hitoshi

No.65 (1998/3) ( 琉球大学理学部 )  ( 65 ) 39 - 51   2010.02

Type of publication: Research paper (bulletin of university, research institution)

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As a part of the educational cruise (RN97 Cruise) for students of College of Science, University of the Ryukyus, by T/S Nagasaki Maru, the scientific survey is carried out during November 15 to 24, 1997. We dredge seafloor samples at several seaknolls which locate in the southern Okinawa Trough. Pumices and dacitic lava fragments are dredged. The rocks are quite fresh, and thus appear to be Quaternary eruptives, confirming the presence of continuous volcanic front from the northern Ryukyu Arc to the southern Ryukyu Arc. Surface sediment type varies depending on depositional settings. Sediments recovered by a grab sampler are composed of quartz sand in the continental shelf, biogenic calcareous sand in the Hokuto-Sekibi Bank and the Ryukyu Ridge, and mud in the Okinawa Trough. The radiolarian assemblage from the surface sediment sample in the Okinawa Trough is characterized by warm water species in accord with the oceanographic setting. （管理者追加）リポジトリ登録情報を移行しました。確認のうえ、加除修正をしてください。

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Hafnium isotope variations in Bure volcanic rocks from the northwestern Ethiopian volcanic province: a new insight for mantle source diversity

Meshesha, D. and Shinjo, R.

Journal of Mineralogical and Petrological Sciences ( その他の出版社 )  105   101 - 111   2010

Type of publication: Research paper (scientific journal)

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