Japanese Exclusive Economic Zone Research Articles

Geochemical insights into secular changes in the depositional environment of ferromanganese nodules in the western North Pacific

Understanding Earth's surface dynamics and biological evolution requires deciphering past marine environmental changes. Hydrogenetic ferromanganese nodules formed by the direct precipitation of Fe–Mn oxide/hydroxide from seawater could record the marine environment at the time of deposition, as in the case of ferromanganese crusts. In this study, petrological and geochemical analyses were conducted on ferromanganese nodules collected from the Japanese Exclusive Economic Zone around Minamitorishima Island in the western North Pacific Ocean. Additionally, the results were compared with those of ferromanganese crusts distributed in the same area to elucidate the secular changes in the depositional environment. The mineralogical features (consisting solely of Fe-vernadite with an absence of 10 Å Mn oxide) and the geochemical characteristics (including positive Ce-anomaly and negative Y-anomaly in rare-earth element patterns, high Co contents, and low Cu and Ni contents) of the nodules suggest that the studied nodules are of a hydrogenetic origin. From the inside to the outside of the nodule, the Mn/Fe and Y/Ho ratios decrease while the Th/U ratio increases, indicating a changing depositional environment over time. A similar trend was observed in ferromanganese crusts from the nearby Takuyo-Daigo Seamount. Furthermore, similar compositional changes were observed on the surfaces of the crust samples (uppermost 1–3 mm), which correlated with depth-related changes in seawater oxygen concentrations. Therefore, the observed cross-sectional changes in the chemical compositions of the nodules and crusts may reflect changes in seawater-dissolved oxygen concentrations over time. The Mn/Fe and Y/Ho trends indicate a shift towards a less oxic environment with increasing age while maintaining the current depth profile, implying an expansion of the oxygen minimum zone (OMZ). Moreover, the observed Ni and Cu enrichment, together with the changes in the Mn/Fe and Y/Ho ratios, suggest that the expansion of the OMZ was caused by increased surface ocean productivity.

Chemostratigraphic Correlations of Deep-Sea Sediments in the Western North Pacific Ocean: A New Constraint on the Distribution of Mud Highly Enriched in Rare-Earth Elements

Deep-sea sediments with total rare-earth elements and yttrium (ΣREY) concentrations exceeding 400 ppm, which are termed REY-rich mud, are widely distributed in the world oceans. Specifically, deep-sea sediments within the Japanese exclusive economic zone (EEZ) surrounding Minamitorishima Island in the western North Pacific have attracted significant attention as a new REY resource, because they contain REY-enriched layers exceeding 2000 ppm of ΣREY. However, neither the sediments deeper than 15 m below the seafloor (mbsf) nor those outside the Minamitorishima EEZ have ever been studied. Recently, a number of distinct geochemical features which are aligned in stratigraphic order were recognized in these sediments, based on multi-elemental composition data. Chemostratigraphy enables us to laterally correlate three REY peaks among apparently featureless pelagic clays. Here, we apply chemostratigraphic correlation to 19 new cores collected from the northern Pigafetta Basin and several small basins within the Marcus-Wake Seamounts. This study revealed that the REY-enriched layers occur at greater depths than the piston core length in a wider area than previously investigated (e.g., ~20.5 mbsf at Ocean Drilling Program Site 801A). This finding suggests that the depositional environments in these areas were basically similar, although local geographic conditions could have affected the continuity of REY peaks.

Chemostratigraphy of deep-sea sediments in the western North Pacific Ocean: Implications for genesis of mud highly enriched in rare-earth elements and yttrium

Deep-sea sediments containing high concentrations of rare-earth elements and yttrium (REY), termed REY-rich mud, are widely distributed in the Pacific and Indian oceans. Mud layers with very high total REY (ΣREY) concentrations (>5000 ppm of ΣREY with ~1000 ppm of heavy rare-earth elements) have been discovered within the Japanese exclusive economic zone surrounding Minamitorishima Island, western North Pacific. The number of highly REY-enriched layers in the sediment column, the depths at which the layers occur, and the maximum ΣREY values of the layers are, however, quite variable on a scale of several tens of kilometers. The factors controlling the formation and distribution of the REY-enriched layers are still poorly understood. Here, we produce a chemostratigraphic scheme for 1240 sediment samples from 49 piston cores collected within the Minamitorishima exclusive economic zone. Detailed investigation of the bulk sediment geochemistry, which exhibits distinctive compositional data structures in multi-elemental subspaces, revealed that the samples can be categorized into five units (Units I to V) in addition to REY peaks (>2000 ppm). These units appear in a consistent stratigraphic sequence in the studied cores. This chemostratigraphy reveals that highly REY-enriched layers formed at least three times, and that almost all of these layers were accompanied by erosion during deposition. Our results suggest that erosion events of deep-sea sediment play an important role in the formation of highly REY-rich mud layers.

Spatiotemporal dynamics of the Pacific chub mackerel revealed by standardized abundance indices

Standardization of catch per unit effort is an effective way to not only extract temporal abundance trends but also understand distribution shifts of fish resources. Chub mackerel in the Northwest Pacific has recently been of great concern to fishermen and fisheries managers because the total catch has been increasing, and fishing grounds have expanded from the Japanese exclusive economic zone eastward to high-sea areas. Understanding the spatiotemporal dynamics of chub mackerel is urgently needed for evaluating the current status (i.e., abundance and distribution) and considering future exploitation. Here we constructed two recruitment indices from pelagic trawl survey data of the Pacific chub mackerel. For recruitment indices of age-0 fish, we integrated an algorithm for automatic area stratification into the delta-GLM that combines two separate generalized linear models (for encounter probability and positive catch rates) to simultaneously investigate changes in relative abundance and distribution. Recruitment indices were high in the recent years of 2013, 2016, and 2017, especially at around 160 °E longitude within the high-sea areas, suggesting simultaneous changes in abundance and distribution. Furthermore, we found that our approach had better predictive ability, especially for positive catch rates, than that of a generalized additive model by cross validation, and the obtained standardized indices mitigated potential bias in stock assessment estimates. Our integrated approach will be useful for understanding the spatiotemporal dynamics of fishes and standardizing abundance indices for stock assessment and management.

南鳥島EEZ南東部全域に分布するマンガンノジュール ～YK16-01航海速報～

南鳥島EEZ南東部全域に分布するマンガンノジュール ～YK16-01航海速報～

Geology and geochemistry of ferromanganese nodules in the Japanese Exclusive Economic Zone around Minamitorishima Island

Geology and geochemistry of ferromanganese nodules in the Japanese Exclusive Economic Zone around Minamitorishima Island

Geochemistry of REY-rich mud in the Japanese Exclusive Economic Zone around Minamitorishima Island

Geochemistry of REY-rich mud in the Japanese Exclusive Economic Zone around Minamitorishima Island

新たな深海底鉱物資源“レアアース泥”の探査と 開発に向けた取り組み<b> </b>

Deep-sea mineral resources have attracted considerable attention in the last few decades as a new source of base metals and rare metals. Recently, we discovered that mud with high rare-earth elements and yttrium (REY) concentrations (termed“ REY-rich mud”) is widely distributed on the deep-sea floor of the Pacific Ocean. REYrich mud has the following great advantages as a mineral resource: (1) high concentrations of REY, (2) remarkable abundance, (3) high exploration efficiency due to homogeneous stratiform distribution, (4) very low concentrations of radioactive elements (e.g., Th and U), and (5) ease of REY extraction and recovery. During the R/V Kairei cruise KR13-02, we discovered extremely high-grade REY-rich mud (the maximum REY content exceeds 6,500 ppm) in the Japanese Exclusive Economic Zone (EEZ) around Minamitorishima. We also found that the distribution of the REY-rich mud can be explored by a shipboard sub-bottom profiler. The REYrich mud within the Japanese EEZ has enormous significance in terms of securing the strategic mineral resource, because REY are critical in the advancement and development of high-tech manufacturing and green technology. Currently, we are continuing to explore the distribution of REY-rich mud in the Minamitorishima EEZ. In addition, together with private-sector corporations, we are also starting to address the challenges for developing the new deep-sea mineral resource, including various technical issues (e.g., how to lift the mud from the seabed deeper than 5000 m of water depth), environmental impact assessments, and economic evaluations. The collaborative efforts of industry, academia, and the government are the key to success of deep-sea mining of REY-rich mud.

Deep-Sea decapod crustaceans (Caridea, Polychelida, Anomura and Brachyura) collected from the Nikko Seamounts, Mariana Arc, using a remotely operated vehicle "Hyper-Dolphin".

Samples and images of deep-water benthic decapod crustaceans were collected from the Nikko Seamounts, Mariana Arc, at depths of 520-680 m, by using the remotely operate vehicle "Hyper-Dolphin", equipped with a high definition camera, digital camera, manipulators and slurp gun (suction sampler). The following seven species were collected, of which three are new to science: Plesionika unicolor n. sp. (Caridea: Pandalidae), Homeryon armarium Galil, 2000 (Polychelida: Polychelidae), Eumunida nikko n. sp. (Anomura: Eumunididae), Michelopagurus limatulus (Henderson, 1888) (Anomura: Paguridae), Galilia petricola n. sp. (Brachyura: Leucosiidae), Cyrtomaia micronesica Richer de Forges & Ng, 2007 (Brachyura: Inachidae), and Progeryon mus Ng & Guinot, 1999 (Brachyura: Progeryonidae). Affinities of these three new species are discussed. All but H. armarium are recorded from the Japanese Exclusive Economic Zone for the first time. Brief notes on ecology and/or behavior are given for each species.

A Discussion paper for the introduction of zoning rules into the Japanese Exclusive Economic Zone and territorial waters area except for port areas

A Discussion paper for the introduction of zoning rules into the Japanese Exclusive Economic Zone and territorial waters area except for port areas

Spatial distributions of floating seaweeds in the East China Sea from late winter to early spring.

Floating seaweeds play an important role as a habitat for many animals accompanying or attaching to them in offshore waters. It was in 2000 that the first report described abundant distributions of floating seaweeds in offshore waters in the East China Sea in spring. Young individuals of the yellowtail Seriola quinqueradiata are captured for aquaculture purposes from floating seaweeds in the East China Sea. Therefore, a sound understanding of the distributions of floating seaweeds in the East China Sea is needed. Detailed information is especially important during the late winter to early spring, which corresponds to the juvenile period of the yellowtail. Thus, field surveys using R/V Tansei-Maru were conducted in the Japanese Exclusive Economic Zone in the East China Sea from late winter to early spring in 2010 and 2011. We obtained positions of the vessel by GPS and transversal distances from the vessel to a raft by visual observation. Distance sampling method (Thomas et al. 2010) was applied to estimation of floating seaweed densities (rafts km−2). Seaweed rafts were also randomly sampled using nets during the research cruises. In the East China Sea, seaweed rafts were distributed mainly on the continental shelf west of the Kuroshio, especially in waters between 26° N and 30° N. Collected rafts consisted of only one species, Sargassum horneri (Turner) C. Agardh. Taking into account surface currents and geographical distribution of S. horneri, it is estimated that these floating seaweeds originated from natural beds along the coast between mid and south China. Considering the approximate travel times, it is suggested that floating patches are colonized by yellowtails early on during their trips, i.e., close to the Chinese coast.

我が国の基盤海洋技術に関する一考察

In order to consider how to strengthen and foster core ocean technologies, current state of ocean technology in Japan is reviewed. The framing of ocean technologies used in the offshore oil and gas development is investigated, and linkage between these technologies and ocean technologies necessary for the ocean renewable energy utilization, the sea floor mining and the methane hydrate development which are expected to be industrialized in Japanese exclusive economic zone (EEZ) in the future. The history of development of ocean technologies in Japan is reviewed to know strength and weakness of Japan's ocean technologies. Summarizing these results, it is found that there is strong linkage between ocean technologies used in the offshore oil and gas development and future projects deployed in Japanese EEZ, and it is important to invest governmental funds in a comprehensive and systematic fashion for developing those core technologies. It is also emphasized that it is important to apply the environment technology and IT to the ocean technology for strengthening Japan's core ocean technologies.

不確実性を考慮した海底熱水鉱床開発の事業性評価

The development of seafloor massive sulfide (SMS) is eagerly investigated for its potential of abundant amount of metal resources in Japanese exclusive economic zone. In order to promote the development of SMS and create new ocean industry, the business feasibility for the decision making of investment are significantly important. In the present study, Monte Carlo DCF and real options valuation were applied to evaluate the business feasibility of a SMS development project. In the analysis, the uncertainty of environmental risk is taken into account by quantifying of experts' opinions. The results of Monte Carlo DCF analysis indicate that the SMS development project has large business risk due to the uncertainties. Then, real options valuations considering decision-making options of abandon and deferment were carried out for two development scenarios. It is clarified that the options values are significant for each scenario of the target project. It is also found that the project will be started easier when the baseline survey for environmental impacts is carried out in earlier stage of the project.

海底熱水鉱床開発の社会受容性に関する研究

The development of seafloor massive sulfide (SMS) is eagerly investigated for its potential of abundant amount of metal resources in Japanese exclusive economic zone. In order to promote the development of SMS and create new ocean industry, the social acceptance for the ecological risk due to the development and the business feasibility for the decision making of investment are significantly important. In the present study, questionnaire survey was conducted about the environmental risks due to SMS development. The results show that the non-specialists feel greater environmental risks than the specialists, which indicates social acceptance could be improved by proper risk communication between them. The economic value of the ecosystem in the vicinity of SMS are also investigated by the questionnaire survey, the result of which is used to determine the scaling factor between ecological and economic values in the inclusive impact index. The environmental risk due to the development of SMS is quantified by analyzing the obtained experts' opinions by means of cross-impact method and species-area relationship. Then the sustainability of the development is investigated by using an inclusive impact index considering both the environmental and the economic factors. From the results, the requirements of the sustainable development are shown for the damaged area and the ratio of species extinction.