105 results on '"Jun Nishioka"'
Search Results
2. Next steps for assessing ocean iron fertilization for marine carbon dioxide removal
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Ken O. Buesseler, Daniele Bianchi, Fei Chai, Jay T. Cullen, Margaret Estapa, Nicholas Hawco, Seth John, Dennis J. McGillicuddy, Paul J. Morris, Sara Nawaz, Jun Nishioka, Anh Pham, Kilaparti Ramakrishna, David A. Siegel, Sarah R. Smith, Deborah Steinberg, Kendra A. Turk-Kubo, Benjamin S. Twining, Romany M. Webb, Mark Wells, Angelicque White, Peng Xiu, and Joo-Eun Yoon
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marine carbon dioxide removal ,ocean iron fertilization ,carbon sequestration ,climate ethics ,exploring ocean iron solutions ,centennial tonne ,Environmental sciences ,GE1-350 - Abstract
There are many potential approaches to marine carbon dioxide removal (mCDR), of which ocean iron fertilization (OIF) has the longest history of study. However, OIF studies to date were not primarily designed to quantify the durability of carbon (C) storage, nor how wise OIF might be as an mCDR approach. To quantify C sequestration, we introduce a metric called the “centennial tonne,” defined as 1,000 kg of C isolated from atmospheric contact for on average at least 100 years. We present the activities needed to assess OIF from a scientific and technological perspective, and additionally, how it might be responsibly studied and potentially deployed. The five activities include: field studies in the Northeast Pacific; improved modeling for field studies, data assimilation and predictions at larger scales; improvements in monitoring, reporting and verification (MRV) for C, and also MRV for tracking ecological and environmental impacts; and developing new iron sources and their delivery, to increase efficiencies and reduce costs. The fifth activity is to understand whether public and community support exists for OIF, and what governance structures might support further research and possible deployment of OIF. This article is written by a multidisciplinary experts group called Exploring Ocean Iron Solutions (ExOIS) that is organized around a responsible code of conduct. Of the mCDR approaches, OIF has the potential to be low cost, scalable, and rapidly deployable. Reducing CO2 emissions must lead the way, but there is also an urgency to decide under what conditions and whether OIF might be deployed or not.
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- 2024
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3. Asian dust-deposition flux to the subarctic Pacific estimated using single quartz particles
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Kana Nagashima, Hajime Kawakami, Koji Sugie, Tetsuichi Fujiki, Jun Nishioka, Yoko Iwamoto, Toshihiko Takemura, Takuma Miyakawa, Fumikazu Taketani, and Maki Noguchi Aita
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Medicine ,Science - Abstract
Abstract Iron availability limits marine ecosystem activities in large areas of the ocean. However, the sources and seasonal supply of iron, critically important for controlling surface ocean biogeochemistry and carbon cycling, are poorly understood. The western subarctic Pacific is a high-nutrient and low-chlorophyll region, and despite high concentrations of macronutrients, iron limits phytoplankton production in summer. Here, we determine the seasonal deposition flux of Asian dust using scanning electron microscope–cathodoluminescence analysis of single quartz particles derived from the western subarctic Pacific during 2003–2022 to trace provenance. We found a high (up to 6.9 mg m−2 day−1) deposition flux of Asian dust in May, June, and early July, with an annual average of 1.0 ± 0.2 mg m−2 day−1. The supply of dissolved-iron flux calculated from Asian dust was 0.9 ± 0.3 µg m−2 day−1 during the high productivity season (April–July), which is approximately half that from the deeper part of the ocean, calculated from vertical profiles of dissolved iron. Our study provides a reliable approach for estimating iron supply from dust to the surface ocean that may be critical for sustaining biological productivity under future ocean stratification, which suppresses nutrient supply from the subsurface ocean.
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- 2023
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4. High biomass turnover rates of endosymbiotic nitrogen‐fixing cyanobacteria in the western Bering Sea
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Shunyan Cheung, Kailin Liu, Kendra A. Turk‐Kubo, Jun Nishioka, Koji Suzuki, Michael R. Landry, Jonathan P. Zehr, Szeki Leung, Lixia Deng, and Hongbin Liu
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Oceanography ,GC1-1581 - Abstract
Abstract Recent studies have described active nitrogen fixation in high‐latitude waters, but the ecological controls on the occurrence or activity of nitrogen‐fixing organisms (diazotrophs) in such systems remain unknown. Turnover rates and top‐down controls are also general knowledge gaps for marine diazotrophs. We detected abundant UCYN‐A (endosymbiotic nitrogen‐fixing cyanobacteria) in the Gulf of Anadyr, western Bering Sea, which correlated with high dissolved iron to dissolved inorganic nitrogen ratios (Fe : DIN) due to riverine input. Growth and grazing mortality of UCYN‐A sublineages were almost balanced with higher biomass‐turnover rates compared to the whole phytoplankton community, indicating selective grazing of UCYN‐A in nitrogen‐depleted waters. Grazing rates on UCYN‐A1 (small cells) were higher than for UCYN‐A2/3/4 (large cells), consistent with the general size dependence of phytoplankton growth and grazing mortality. We found that Fe : DIN is a major determinant of UCYN‐A abundances in high‐latitude waters, where UCYN‐A could make substantial contributions to plankton food‐web cycling.
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- 2022
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5. Fate of dissolved black carbon in the deep Pacific Ocean
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Youhei Yamashita, Motohiro Nakane, Yutaro Mori, Jun Nishioka, and Hiroshi Ogawa
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Science - Abstract
Black carbon is a product of incomplete combustion and is distributed everywhere on the Earth’s surface due to its recalcitrant nature. Here the authors show the removal process and flux of dissolved black carbon in the deep sea, its ultimate repository.
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- 2022
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6. Vertical Profiles of 226Ra and 228Ra Activity Concentrations in the Western Subarctic Gyre of the Pacific Ocean
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Hirofumi Tazoe, Hajime Obata, Takuya Hara, Mutsuo Inoue, Takahiro Tanaka, and Jun Nishioka
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radium-228 ,radium-226 ,Subarctic Gyre of the Pacific Ocean ,vertical flux ,lateral transport ,Science ,General. Including nature conservation, geographical distribution ,QH1-199.5 - Abstract
The vertical activity concentration distributions of the radium isotopes, 226Ra and 228Ra, which are useful as radiotracers, were obtained for the first time in the western Subarctic Pacific Gyre (WSAG). It was possible to detect short-lived 228Ra present from the surface to 400 m depth by analyzing large seawater samples. Low 228Ra and high 226Ra activity concentrations in the surface layer in the WSAG were strongly influenced by upwelled deeper water with nutrients. The activity concentration distribution of 226Ra especially was in good agreement with the silicate concentration distribution, which was consistent with previous reported findings. These distributions were uniform from the surface to 100 m of the dichothermal layer due to vertical mixing in winter. 228Ra activity concentration decreased with water depth below the pycnocline and reached the undetectable level at 600 m which was within the oxygen minimum layer. Estimations of vertical fluxes of 228Ra and nitrate according to 228Ra decay indicated that the vertical transport by eddy diffusion was a minor process for the 228Ra and nitrate fluxes, and lateral transport mainly affected 228Ra in the intermediate warm water, that is, the mesothermal layer below the main pycnocline. Vertical mixing or submarine underground water and lateral transport to the WSAG could yield this 228Ra in the intermediate depth.
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- 2022
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7. Distinct profiles of size-fractionated iron-binding ligands between the eastern and western subarctic Pacific
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Yoshiko Kondo, Rise Bamba, Hajime Obata, Jun Nishioka, and Shigenobu Takeda
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Medicine ,Science - Abstract
Abstract Iron (Fe) is well known as a limiting factor to control primary productivity especially in high-nutrient and low chlorophyll area such as the subarctic Pacific. The solubility of Fe is believed to be controlled by its complexation with natural organic ligands, while the distribution of organic ligands is poorly understood. Here, we report that dissolved (
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- 2021
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8. Author Correction: New index of organic mass enrichment in sea spray aerosols linked with senescent status in marine phytoplankton
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Yuzo Miyazaki, Koji Suzuki, Eri Tachibana, Youhei Yamashita, Astrid Müller, Kaori Kawana, and Jun Nishioka
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Medicine ,Science - Published
- 2021
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9. Response to Sea Ice Melt Indicates High Seeding Potential of the Ice Diatom Thalassiosira to Spring Phytoplankton Blooms: A Laboratory Study on an Ice Algal Community From the Sea of Okhotsk
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Dong Yan, Kazuhiro Yoshida, Jun Nishioka, Masato Ito, Takenobu Toyota, and Koji Suzuki
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ice algae ,diatom bloom ,Thalassiosira ,osmotic stress ,photophysiology ,seeding effect ,Science ,General. Including nature conservation, geographical distribution ,QH1-199.5 - Abstract
Phytoplankton communities in seasonally ice-covered areas are largely affected by ice algae. The Okhotsk Sea is the southernmost sea ice zone in the northern hemisphere with a sizeable seasonal ice cover, thus ice algae of the Okhotsk sea ice have a large potential to seed the early spring bloom. Little is known about the Okhotsk ice algal communities and their seeding effects. We investigated the dynamics of the composition and the photophysiological performances of an Okhotsk ice algal community in a 6-day laboratory incubation experiment that simulated the natural ice melt conditions. Centric diatoms, especially Thalassiosira spp., overwhelmingly dominated the ice algal community throughout incubation, whereas pennate diatoms, mostly Navicula and Nitzschia, showed little growth with much higher mortality. The maximum photochemical efficiency of Photosystem II (Fv/Fm) was the lowest at the beginning of the ice melt, suggesting a suppressed photosynthetic functioning by changes in salinity. The cellular pigment contents decreased by 30% due to osmotic stress, evidenced by deformed plastids under a microscope. The transcript level of the rbcL gene that encodes the large subunit of RubisCO was significantly higher during ice melt and decreased in the no-ice period, suggesting an urgent need for carbon fixation under the melt condition. Full recovery of photosynthesis and growth was also made after complete ice melt. Our results indicated high seeding potential of Thalassiosira to spring blooms owing to their photophysiological plasticity to dynamic salinity changes.
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- 2020
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10. Geographic Distribution of Ammonia-Oxidizing Archaea along the Kuril Islands in the Western Subarctic Pacific
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Hongmei Jing, Shunyan Cheung, Xiaomin Xia, Koji Suzuki, Jun Nishioka, and Hongbin Liu
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AOA ,amoA ,pyrosequencing ,geographic distribution ,Microbiology ,QR1-502 - Abstract
Community composition and abundance of ammonia-oxidizing archaea (AOA) in the ocean were affected by different physicochemical conditions, but their responses to physical barriers (such as a chain of islands) were largely unknown. In our study, geographic distribution of the AOA from the surface photic zone to the deep bathypelagic waters in the western subarctic Pacific adjacent to the Kuril Islands was investigated using pyrosequencing based on the ammonia monooxygenase subunit A (amoA) gene. Genotypes of clusters A and B dominated in the upper euphotic zone and the deep waters, respectively. Quantitative PCR assays revealed that the occurrence and ammonia-oxidizing activity of ammonia-oxidizing archaea (AOA) reached their maxima at the depth of 200 m, where a higher diversity and abundance of actively transcribed AOA was observed at the station located in the marginal sea exposed to more terrestrial input. Similar community composition of AOA observed at the two stations adjacent to the Kuril Islands maybe due to water exchange across the Bussol Strait. They distinct from the station located in the western subarctic gyre, where sub-cluster WCAII had a specific distribution in the surface water, and this sub-cluster seemed having a confined distribution in the western Pacific. Habitat-specific groupings of different WCB sub-clusters were observed reflecting the isolated microevolution existed in cluster WCB. The effect of the Kuril Islands on the phylogenetic composition of AOA between the Sea of Okhotsk and the western subarctic Pacific is not obvious, possibly because our sampling stations are near to the Bussol Strait, the main gateway through which water is exchanged between the Sea of Okhotsk and the Pacific. The vertical and horizontal distribution patterns of AOA communities among stations along the Kuril Islands were essentially determined by the in situ prevailing physicochemical gradients along the two dimensions.
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- 2017
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11. Methods for biogeochemical studies of sea ice: The state of the art, caveats, and recommendations
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Lisa A. Miller, Francois Fripiat, Brent G.T. Else, Jeff S. Bowman, Kristina A. Brown, R. Eric Collins, Marcela Ewert, Agneta Fransson, Michel Gosselin, Delphine Lannuzel, Klaus M. Meiners, Christine Michel, Jun Nishioka, Daiki Nomura, Stathys Papadimitriou, Lynn M. Russell, Lise Lotte Sørensen, David N. Thomas, Jean-Louis Tison, Maria A. van Leeuwe, Martin Vancoppenolle, Eric W. Wolff, and Jiayun Zhou
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sea ice ,biogeochemistry ,methods ,Environmental sciences ,GE1-350 - Abstract
Abstract Over the past two decades, with recognition that the ocean’s sea-ice cover is neither insensitive to climate change nor a barrier to light and matter, research in sea-ice biogeochemistry has accelerated significantly, bringing together a multi-disciplinary community from a variety of fields. This disciplinary diversity has contributed a wide range of methodological techniques and approaches to sea-ice studies, complicating comparisons of the results and the development of conceptual and numerical models to describe the important biogeochemical processes occurring in sea ice. Almost all chemical elements, compounds, and biogeochemical processes relevant to Earth system science are measured in sea ice, with published methods available for determining biomass, pigments, net community production, primary production, bacterial activity, macronutrients, numerous natural and anthropogenic organic compounds, trace elements, reactive and inert gases, sulfur species, the carbon dioxide system parameters, stable isotopes, and water-ice-atmosphere fluxes of gases, liquids, and solids. For most of these measurements, multiple sampling and processing techniques are available, but to date there has been little intercomparison or intercalibration between methods. In addition, researchers collect different types of ancillary data and document their samples differently, further confounding comparisons between studies. These problems are compounded by the heterogeneity of sea ice, in which even adjacent cores can have dramatically different biogeochemical compositions. We recommend that, in future investigations, researchers design their programs based on nested sampling patterns, collect a core suite of ancillary measurements, and employ a standard approach for sample identification and documentation. In addition, intercalibration exercises are most critically needed for measurements of biomass, primary production, nutrients, dissolved and particulate organic matter (including exopolymers), the CO2 system, air-ice gas fluxes, and aerosol production. We also encourage the development of in situ probes robust enough for long-term deployment in sea ice, particularly for biological parameters, the CO2 system, and other gases.
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- 2015
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12. Long-Term Observation of the Soya Warm Current Combining HF Ocean Radars with Coastal Tide Gauges and Satellite Altimetry.
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Naoto Ebuchi, Yasushi Fukamachi, Kay I. Ohshima, Toru Takatsuka, H. Mitsudera, Jun Nishioka, K. Ono, Masao Ishikawa, Takaharu Daibo, K. Shiwasawa, and Masaaki Wakatsuchi
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- 2023
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13. Role of nutrients and temperature in shaping distinct summer phytoplankton and microzooplankton population dynamics in the western North Pacific and Bering Sea
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Kailin Liu, Jun Nishioka, Bingzhang Chen, Koji Suzuki, Shunyan Cheung, Yanhong Lu, Huijun Wu, and Hongbin Liu
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Aquatic Science ,Oceanography - Published
- 2023
14. Dissolved Iron Concentration and the Solubility Inferred by Humic‐Like Fluorescent Dissolved Organic Matter in the Intermediate Water in the North Pacific Including the Marginal Seas
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Youhei Yamashita and Jun Nishioka
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Atmospheric Science ,Ecology ,Paleontology ,Soil Science ,Forestry ,Aquatic Science ,Water Science and Technology - Published
- 2023
15. Subarctic Pacific Intermediate Water: An Oceanic Highway for the Transport of Trace Metals in the North Pacific
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Kuo Hong Wong, Hajime Obata, Jun Nishioka, Youhei Yamashita, Yoshiko Kondo, Taejin Kim, Asami Mashio, and Hiroshi Hasegawa
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Aquatic Science ,Oceanography ,Water Science and Technology - Published
- 2022
16. The interannual variability of sea ice area, thickness, and volume in the southern Sea of Okhotsk and its likely factors
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Takenobu Toyota, Noriaki Kimura, Jun Nishioka, Masato Ito, Daiki Nomura, and Humio Mitsudera
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ASPeCt visual observation ,Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,seasonal sea ice ,Earth and Planetary Sciences (miscellaneous) ,Oceanography ,ice rheology ,sea of okhotsk - Abstract
The lowest latitude sea ice in the world (excluding coastal freezing) is in the southern Sea of Okhotsk (south of 46°N), where it has significant impacts on freshwater input and primary production. This region is subject to climate change, and accordingly the monitoring of sea ice conditions is important. However, the interannual variability of the region’s sea ice is poorly understood due to its logistical challenges. Sea ice observations have been conducted in this region every winter for the period 1996-2020. The interannual variability of the ice conditions and the likely factors responsible for it were investigated using visual observations following the international ASPeCt protocol, combined with satellite SSM/I-SSMIS ice concentration data (1988-2020). AMSR-derived ice drift data sets and ERA5 meteorological reanalysis data sets were also analyzed to examine the effects of dynamic and thermodynamic processes. Our analysis revealed that 1) sea ice area in this region varies differently from that in the central and northern Sea of Okhotsk, where decreasing trends are reported, 2) sea ice volume has remarkable interannual variation and the peaks appeared much to more affected by dynamically deformed ice than freezing conditions, and 3) prominently deformed ice can be explained by taking shear components into account based on sea ice rheology. These results suggest the importance of including the proper sea ice rheology in numerical sea ice models to reproduce the realistic sea ice volume and deformation processes, and thereby the realistic primary production for all seasonal ice zones., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)
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- 2023
17. Decadal vision in oceanography 2021: Coastal oceans
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Shinichiro Kida, Haruko Kurihara, Yumiko Obayashi, Michiyo Yamamoto-Kawai, Yoshiko Kondo, and Jun Nishioka
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- 2021
18. Decadal vision in oceanography 2021: Polar oceans
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Michiyo Yamamoto-Kawai, Takeshi Tamura, Eiji Watanabe, Jun Nishioka, Daiki Nomura, Ryusuke Makabe, Kohei Mizobata, and Yasunaka Sayaka
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- 2021
19. Decadal vision in oceanography 2021: Mid-latitude ocean
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Fuminori Hashihama, Shinya Kouketsu, Yoshiko Kondo, Yoshi N. Sasaki, Shusaku Sugimoto, Kazutaka Takahashi, Takeyoshi Nagai, Jun Nishioka, Hakase Hayashida, and and Junya Hirai
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- 2021
20. Decadal vision in oceanography 2021: Air―sea boundary
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Yoko Iwamoto, Hidenori Aiki, Osamu Isoguchi, Yumiko Obayashi, Fumiyoshi Kondo, Yoshiko Kondo, and and Jun Nishioka
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- 2021
21. Number‐Size Distribution and CCN Activity of Atmospheric Aerosols in the Western North Pacific During Spring Pre‐Bloom Period: Influences of Terrestrial and Marine Sources
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Kaori Kawana, Yuzo Miyazaki, Yuko Omori, Hiroshi Tanimoto, Sara Kagami, Koji Suzuki, Youhei Yamashita, Jun Nishioka, Yange Deng, Hikari Yai, and Michihiro Mochida
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Atmospheric Science ,Geophysics ,Space and Planetary Science ,Earth and Planetary Sciences (miscellaneous) - Published
- 2022
22. A review: iron and nutrient supply in the subarctic Pacific and its impact on phytoplankton production
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Kazuhiro Misumi, Youhei Yamashita, Toru Hirawake, Yoshiko Kondo, Ichiro Yasuda, Hajime Obata, and Jun Nishioka
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0106 biological sciences ,Biogeochemical cycle ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,North Pacific High ,Atmospheric dust ,Oceanography ,01 natural sciences ,Subarctic climate ,chemistry.chemical_compound ,Nutrient ,chemistry ,Chlorophyll ,Phytoplankton ,Environmental science ,0105 earth and related environmental sciences - Abstract
One of the most important breakthroughs in oceanography in the last 30 years was the discovery that iron (Fe) controls biological production as a micronutrient, and our understanding of Fe and nutrient biogeochemical dynamics in the ocean has significantly advanced. In this review, we looked back both previous and updated knowledge of the natural Fe supply processes and nutrient dynamics in the subarctic Pacific and its impact on biological production. Although atmospheric dust has been considered to be the most important source of Fe affecting biological production in the subarctic Pacific, other oceanic sources of Fe have been discovered. We propose a coherent explanation for the biological response in subarctic Pacific high nutrient low chlorophyll (HNLC) waters that incorporates knowledge of both the atmospheric Fe supplies and the oceanic Fe supplies. Finally, we extract future directions for Fe oceanographic research in the subarctic Pacific and summarize the uncertain issues identified thus far.
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- 2021
23. Enhanced vertical turbulent nitrate flux in the intermediate layer of the Kuroshio in the Tokara Strait
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Jun Nishioka, Hirohiko Nakamura, Takahiro Tanaka, Shinzo Fujio, Daisuke Hasegawa, Daigo Yanagimoto, Ryuichiro Inoue, and Ichiro Yasuda
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010504 meteorology & atmospheric sciences ,010505 oceanography ,Turbulence ,Flow (psychology) ,Internal wave ,Oceanography ,Mooring ,Atmospheric sciences ,01 natural sciences ,Eddy diffusion ,chemistry.chemical_compound ,North Pacific Intermediate Water ,Nitrate ,chemistry ,Hotspot (geology) ,Geology ,0105 earth and related environmental sciences - Abstract
Vertical mixing in the ocean is an important physical process that brings deep nutrients to the upper layer. The Tokara Strait, where the Kuroshio flows out to the North Pacific from the East China Sea, is known for a mixing hotspot, but the associated vertical nutrient transport has not been well quantified yet, especially in the intermediate layer below 200 m depth. This study involved flow, turbulence, and nitrate observations to quantify the vertical turbulent nitrate flux in the Tokara Strait and discuss its impact on the Kuroshio nutrient transport. Temporal variation of current velocity, derived from a 3.5-day mooring observation, captured semi-diurnal internal waves propagating vertically at depths between 200 and 400 m. Vertical shear associated with the semi-diurnal flow was elevated at this depth range. Vertical shear due to the mean and the diurnal flow was also elevated at about 220 m and 400 m depths, respectively. Mean vertical eddy diffusivity was elevated to O(10–3–10–2 m2 s−1) at the density layers of 25.2–26.4 σθ (200–450 m depth). Associated vertical turbulent nitrate flux reached O(10 mmol m−2 day−1), especially at around 25.6 σθ (250 m depth) and 26.2–26.4 σθ (400–450 m depth). The enhanced vertical turbulent nitrate flux suggests a large amount of nitrate is injected vertically to the nutrient stream from the layer just above the North Pacific Intermediate Water and is transported throughout the core of the Kuroshio nutrient stream situated at 25.0–26.2 σθ.
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- 2021
24. New insights into the biogeochemical cycling of copper in the subarctic Pacific: Distributions, size fractionation, and organic complexation
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Kuo Hong Wong, Taejin Kim, Jun Nishioka, Yoshiko Kondo, and Hajime Obata
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Biogeochemical cycle ,chemistry ,Environmental chemistry ,chemistry.chemical_element ,Fractionation ,Aquatic Science ,Organic complexation ,Oceanography ,Copper ,Subarctic climate - Published
- 2021
25. Observations of anticyclonic eddies in the western subarctic North Pacific
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Yuki Okada, Hideharu Sasaki, Ryo Dobashi, Toru Hirawake, Hiromichi Ueno, Takahiro Tanaka, Ichiro Yasuda, Daisuke Hasegawa, Atushi Ooki, Sachihiko Itoh, Jun Nishioka, and Yoshikazu Sasai
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geography ,Chlorophyll a ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,010505 oceanography ,Oceanography ,01 natural sciences ,Subarctic climate ,Mesoscale eddies ,chemistry.chemical_compound ,Eddy ,chemistry ,Anticyclone ,Peninsula ,Satellite data ,Submarine pipeline ,Geology ,0105 earth and related environmental sciences - Abstract
We conducted a ship observation of two anticyclonic mesoscale eddies (Eddies A and B) between June and July 2016 in the offshore region of the western subarctic North Pacific to clarify the impact of anticyclonic eddies on biological production. Analysis of satellite data reveals that Eddy A formed south of the Alaskan Peninsula on May 2011 while Eddy B formed in the observation area on November 2015. Iron concentration was low both inside and outside Eddies A and B, and there were no large differences between chlorophyll a (chl-a) concentration inside and outside eddies. Satellite-derived chl-a concentration inside Eddy A had been high compared with that in the surrounding area when the eddy was located along the Aleutian Islands and just after it detached from the islands, suggesting that iron originating from the coastal region was consumed during the two-year journey from the coastal region to the observation area. Field measurements also reveal that vertical diffusivity was low both inside and outside Eddies A and B, which could be another factor underlying low iron both inside and outside Eddies A and B and small differences between chl-a concentration inside and outside the eddies.
- Published
- 2021
26. Long‐Range Lateral Transport of Dissolved Manganese and Iron in the Subarctic Pacific
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Kuo Hong Wong, Jun Nishioka, Taejin Kim, and Hajime Obata
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Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,Earth and Planetary Sciences (miscellaneous) ,Oceanography - Published
- 2022
27. New index of organic mass enrichment in sea spray aerosols linked with senescent status in marine phytoplankton
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Eri Tachibana, Koji Suzuki, Kaori Kawana, Youhei Yamashita, Astrid Müller, Jun Nishioka, and Yuzo Miyazaki
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0301 basic medicine ,010504 meteorology & atmospheric sciences ,lcsh:Medicine ,01 natural sciences ,Article ,03 medical and health sciences ,chemistry.chemical_compound ,Phytoplankton ,Atmospheric science ,Organic matter ,lcsh:Science ,Relative species abundance ,0105 earth and related environmental sciences ,chemistry.chemical_classification ,Multidisciplinary ,fungi ,lcsh:R ,Biogeochemistry ,Sea spray ,Aerosol ,030104 developmental biology ,chemistry ,Productivity (ecology) ,Chlorophyll ,Environmental chemistry ,Seawater ,lcsh:Q - Abstract
Linking the amount of organic matter (OM) in sea spray aerosols (SSAs) to biological processes in ocean surface is essential for understanding marine aerosol formation and their potential to affect cloud formation. To date, chlorophyll (Chl) a concentration has been widely used as a surrogate for surface phytoplankton biomass or productivity to predict the relative abundance of OM in SSAs (OMSSA). Here we show a new index to present OMSSA using concentrations of Chl a and chlorophyllide (Chllide) a, which is a breakdown product of Chl a and has been used as a biomarker of senescent algal cells. The index was compared with submicrometer OMSSA, based on surface seawater and aerosol samples obtained during the pre-bloom in the western subarctic Pacific. Our results showed that the OMSSA was highly correlated with this unique index, suggesting that the OMSSA was closely linked with senescent algal cells and/or cell lysis. Furthermore, the hygroscopicity parameters κ derived from water-extracted SSA samples implied a reduction in the SSA hygroscopicity with increasing senescent status of phytoplankton. The index can represent OMSSA on a timescale of a day during the pre-bloom period, which should be further examined over different oceanic regions.
- Published
- 2020
28. Subpolar marginal seas fuel the North Pacific through the intermediate water at the termination of the global ocean circulation
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Jun Nishioka, Keunjong Lee, Kazuya Ono, Ichiro Yasuda, Hajime Obata, Shigenobu Takeda, Youhei Yamashita, and Hiroshi Ogawa
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0106 biological sciences ,North Pacific Ocean ,Multidisciplinary ,010504 meteorology & atmospheric sciences ,macronutrients ,010604 marine biology & hydrobiology ,Geotraces ,Ocean current ,island chains mixing ,01 natural sciences ,Deep sea ,Subarctic climate ,Earth, Atmospheric, and Planetary Sciences ,dissolved iron ,GEOTRACES ,Oceanography ,Nutrient ,Productivity (ecology) ,Physical Sciences ,Environmental science ,Thermohaline circulation ,Thermocline ,0105 earth and related environmental sciences - Abstract
Significance A correct understanding of the iron and macronutrient dynamics at the termination of the global ocean conveyor belt circulation is critical for understanding the global carbon cycle and its changes in geological timescale. Newly obtained and compiled datasets of iron and macronutrients with the vertical mixing magnitude in the subarctic Pacific and marginal seas indicate the processes that determine the nutritional status of intermediate waters and the mechanisms by which subpolar marginal seas fuel the North Pacific Ocean through the intermediate water. The intermediate water formation processes play a major role in the connection of nutrients between the deep water and the surface water above it, and sustain biological production, at the termination of the global nutrient circulation., The mechanism by which nutrients in the deep ocean are uplifted to maintain nutrient-rich surface waters in the subarctic Pacific has not been properly described. The iron (Fe) supply processes that control biological production in the nutrient-rich waters are also still under debate. Here, we report the processes that determine the chemical properties of intermediate water and the uplift of Fe and nutrients to the main thermocline, which eventually maintains surface biological productivity. Extremely nutrient-rich water is pooled in intermediate water (26.8 to 27.6 σθ) in the western subarctic area, especially in the Bering Sea basin. Increases of two to four orders in the upward turbulent fluxes of nutrients were observed around the marginal sea island chains, indicating that nutrients are uplifted to the surface and are returned to the subarctic intermediate nutrient pool as sinking particles through the biological production and microbial degradation of organic substances. This nutrient circulation coupled with the dissolved Fe in upper-intermediate water (26.6 to 27.0 σθ) derived from the Okhotsk Sea evidently constructs an area that has one of the largest biological CO2 drawdowns in the world ocean. These results highlight the pivotal roles of the marginal seas and the formation of intermediate water at the end of the ocean conveyor belt.
- Published
- 2020
29. Meltwater Discharge From Marine-Terminating Glaciers Drives Biogeochemical Conditions in a Greenlandic Fjord
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Naoya Kanna, Shin Sugiyama, Takuto Ando, Yefan Wang, Yuta Sakuragi, Toya Hazumi, Kohei Matsuno, Atsushi Yamaguchi, Jun Nishioka, and Youhei Yamashita
- Subjects
protists ,Atmospheric Science ,Global and Planetary Change ,glacier ,nutrients ,Greenland ,trace metals ,Environmental Chemistry ,dissolved organic matter ,General Environmental Science - Abstract
An increasing body of work has shown the potential impacts of subglacial discharge from marine-terminating glaciers on the marine environment around Greenland. Upwelling of nutrients associated with rising buoyant plumes near the front of marine-terminating glaciers plays a key role in maintaining the high productivity of connected fjords. The response of protist communities to subglacial discharges into fjords nevertheless remains poorly understood. Here we show data of water properties, nutrients, and protist communities during two summers in 2018 and 2019 in a Greenlandic fjord system fed by marine-terminating glaciers. This study included the period of intense summer melting of the Greenland Ice Sheet in 2019. The data revealed high nutrient concentrations in 2019 that were attributed to intensified upwelling of nutrients and dissolved iron into the subsurface layer. The source of the iron and the nutrients was subglacial discharge and deep fjord water, respectively. Intense glacial discharges in 2019 mitigated nitrate and phosphate limitations of phytoplankton in the fjord and resulted in an increase of chlorophyll a in the subsurface layer and growth of large diatoms. Heterotrophic protists such as dinoflagellates, tintinnids, and nanoflagellates were more abundant in the summer of 2019. We concluded that nutrient upwelling by subglacial discharges was the major driver of the structure of lower trophic levels in fjord ecosystems. We hypothesize that the more intense melting of glaciers and related increase in subglacial discharge will enhance nutrient upwelling, and increased summer productivity in fjords until the glaciers retreat and terminate on land.
- Published
- 2022
30. Author Correction: New index of organic mass enrichment in sea spray aerosols linked with senescent status in marine phytoplankton
- Author
-
Kaori Kawana, Koji Suzuki, Youhei Yamashita, Eri Tachibana, Astrid Müller, Yuzo Miyazaki, and Jun Nishioka
- Subjects
Multidisciplinary ,Index (economics) ,Oceanography ,Science ,Phytoplankton ,Medicine ,Environmental science ,Sea spray ,Author Correction - Abstract
Linking the amount of organic matter (OM) in sea spray aerosols (SSAs) to biological processes in ocean surface is essential for understanding marine aerosol formation and their potential to affect cloud formation. To date, chlorophyll (Chl) a concentration has been widely used as a surrogate for surface phytoplankton biomass or productivity to predict the relative abundance of OM in SSAs (OM
- Published
- 2021
31. Influence of Coastal Oyashio water on massive spring diatom blooms in the Oyashio area of the North Pacific Ocean
- Author
-
Tsuyoshi Watanabe, Yuko Toya, Akira Kuwata, Jun Nishioka, Hiroshi Kuroda, Yukiko Taniuchi, and Daisuke Hasegawa
- Subjects
0106 biological sciences ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,biology ,010604 marine biology & hydrobiology ,Geology ,Aquatic Science ,biology.organism_classification ,01 natural sciences ,Algal bloom ,Boundary current ,Salinity ,Oceanography ,Nutrient ,Diatom ,Spring (hydrology) ,Environmental science ,Submarine pipeline ,Transect ,0105 earth and related environmental sciences - Abstract
We hypothesized that the characteristics of Coastal Oyashio water in the North Pacific Ocean during winter–spring have a major influence on the generation of massive spring diatom blooms throughout the Oyashio area. To test this hypothesis, we analyzed in situ data from May during 1990–2016 along a transect known as the “A-line” to monitor conditions in the Oyashio off the southeast coast of Hokkaido, Japan. Chlorophyll-a concentrations were high (≥5 mg m−3) on the shelf and in the offshore Oyashio areas around the First and Second Oyashio Intrusions. About 80% of the high chlorophyll-a concentrations in the Oyashio area were linked with low-salinity (≤33.0) water that was associated with the Coastal Oyashio water and its modified waters. For the remaining Oyashio area, the so-called “Oyashio water” with a high salinity of 33.0–33.7 was near the sea surface and associated with low chlorophyll-a concentrations with a frequency distribution mode at 1–2 mg m−3. Diatom communities with high abundance and diversity were also connected (disconnected) between the shelf and the offshore Oyashio areas with low (high) salinity and high (low) chlorophyll-a concentrations. Analysis of historical temperature–salinity data near the sea surface revealed that the Coastal Oyashio water and its modified waters appear most frequently around the shelf along Hokkaido and the Kuril Islands, and that the frequency of appearance decreases with increasing distance offshore. We suggest that the transport and pathway around the islands of the Coastal Oyashio water and its modified waters, which contain high nutrient concentrations and the seeds for massive spring blooms, are the primary factors regulating the generation and spatial extent of the massive spring blooms over the Oyashio area.
- Published
- 2019
32. Accumulation processes of trace metals into Arctic sea ice: distribution of Fe, Mn and Cd associated with ice structure
- Author
-
Jun Nishioka and La Kenya Evans
- Subjects
0106 biological sciences ,Biogeochemical cycle ,010504 meteorology & atmospheric sciences ,Oceanography ,01 natural sciences ,Trace metals ,Brining ,Sea ice ,Environmental Chemistry ,Trace metal ,0105 earth and related environmental sciences ,Water Science and Technology ,Frazil ice ,geography ,geography.geographical_feature_category ,Sea ice structure ,010604 marine biology & hydrobiology ,General Chemistry ,Particulates ,Snow ,Arctic ice pack ,Labile particulate ,Environmental chemistry ,Environmental science ,Dissolved - Abstract
Biogeochemical cycling of trace metals in sea ice is important to the productivity of the Arctic Ocean. Unfortunately, the processes by which trace metals accumulate into sea ice are poorly understood. To gain a clearer understanding of the mechanisms behind trace metal accumulation, dissolved (D, < 0.2 mu m), and labile particulate (LP = Total Dissolvable Dissolved) iron (Fe), manganese (Mn), and cadmium (Cd) concentrations were compared to the structure observed in sea ice. Samples were pre-concentrated via solid-phase extraction on NOBIAS Chelate PA-1 resin and analyzed on a Graphite Furnace Atomic Absorption Spectrometer. Using photographic analysis for the percentage of pore microstructure and delta O-18 analysis, sea ice structure was determined to be snow ice, granular ice (frazil ice), mixed ice (granular and columnar ice) and columnar ice. Salinity and nutrients were low, indicating brine drainage and multi-year ice. High trace metal concentrations in snow ice indicated meteoric snow was a source of trace metals to sea ice. High concentrations of LPFe in granular ice indicated entrainment of suspended particulate trace metals by frazil ice during the formation of the granular ice structure. Whereas the high concentrations of DFe and DMn in granular ice may have been due to reduction from LPFe and LPMn after particle entrainment, indicating chemical transformation processes. Low dissolved and labile particulate trace metal concentrations in mixed and columnar ice indicated a release due to brine drainage. Our study clearly indicates that the differences observed in trace metals among sea ice structures, showed that sea ice formation, chemical reduction and brine release were the processes driving trace metal accumulation and release in the Arctic sea ice.
- Published
- 2019
33. Winter microalgal communities of the southern Sea of Okhotsk: A comparison of sea ice, coastal, and basinal seawater
- Author
-
Dong Yan, Jun Nishioka, Takenobu Toyota, and Koji Suzuki
- Subjects
Geology ,Aquatic Science - Published
- 2022
34. Enhanced vertical turbulent nitrate flux in the Kuroshio across the Izu Ridge
- Author
-
Yasutaka Goto, Daisuke Hasegawa, Takahiro Tanaka, Ichiro Yasuda, Shinzou Fujio, H. Tsuji, and Jun Nishioka
- Subjects
geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,010505 oceanography ,Turbulence ,Biogeochemistry ,Oceanography ,01 natural sciences ,chemistry.chemical_compound ,North Pacific Intermediate Water ,Sill ,Nitrate ,chemistry ,Phytoplankton ,Ridge (meteorology) ,Crest ,Geology ,0105 earth and related environmental sciences - Abstract
The first direct measurements of vertical turbulent nitrate flux, FluxNO3, were conducted in the Kuroshio across the Izu Ridge and revealed large FluxNO3 near the sill crest at the 1% light depth. This large FluxNO3 possibly enhances downstream phytoplankton growth. Extremely large FluxNO3 was also observed at 26.0–26.6 σθ between the core of the Kuroshio nutrient stream and the North Pacific Intermediate Water. We hypothesize that strong vertical mixing in the Izu Ridge draws sufficient nitrate upward from the North Pacific Intermediate Water to the nutrient stream, which eventually impacts the downstream biogeochemistry in the western North Pacific.
- Published
- 2018
35. Slowly Sinking Particles Underlie Dissolved Iron Transport Across the Pacific Ocean
- Author
-
Kazuhiro Misumi, J. K. Moore, Takaki Tsubono, Matthew C. Long, Jun Nishioka, Keith Lindsay, Daisuke Tsumune, and Hajime Obata
- Subjects
Atmospheric Science ,Global and Planetary Change ,Nutrient ,Oceanography ,Dissolved iron ,Environmental Chemistry ,Environmental science ,Pacific ocean ,General Environmental Science - Published
- 2021
36. Iron and nutrients supply to a fjord from glacier-induced pumping in northwestern Greenland
- Author
-
Naoya, Kanna, Shin, Sugiyama, Yasushi, Fukamachi, Daiki, Nomura, and Jun, Nishioka
- Abstract
The 11th Symposium on Polar Science/Special session: [S] Accelerating Arctic research: Recent progress and future prospect of Arctic research, Tue. 1 Dec.
- Published
- 2020
37. The Cold Water Upwelling Near the Anadyr Strait: Observations and Simulations
- Author
-
Yusuke, Kawaguchi, Jun, Nishioka, Shigeto, Nishino, Shinzou, Fujio, Keunjong, Lee, Amane, Fujiwara, Daigo, Yanagimoto, Humio, Mitsudera, and Ichiro, Yasuda
- Abstract
The 11th Symposium on Polar Science/Special session: [S] Accelerating Arctic research: Recent progress and future prospect of Arctic research, Tue. 1 Dec.
- Published
- 2020
38. Determination of Nd isotopic composition in seawater using newly developed solid phase extraction and MC-ICP-MS
- Author
-
Katsuhiko Suzuki, Jun Nishioka, Hajime Obata, Hirofumi Tazoe, Hiroshi Amakawa, and Takuya Hara
- Subjects
Chelating resin ,Elution ,Coprecipitation ,Chemistry ,Geotraces ,010401 analytical chemistry ,Extraction (chemistry) ,Analytical chemistry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Analytical Chemistry ,Column chromatography ,Seawater ,Solid phase extraction ,0210 nano-technology - Abstract
Determination of neodymium (Nd) isotopic composition in seawater is useful for tracing water masses and geochemical cycles for lithogenic elements in the ocean. A new separation procedure for determination of the Nd isotopic composition of in seawater samples was developed that offers enhanced sample throughput and improved measurement reliability. The procedure consists of conventional Fe hydroxide coprecipitation, solid phase extraction using DGA chelating resin column chromatography, and Ln Resin column chromatography to preconcentrate samples. High selectivity in HNO3 medium and elution by low concentration HCl medium for Nd are characteristics of extraction using DGA Resin®, and they allowed an evaporation step to be omitted between the chromatographic steps. These chromatographic steps, using DGA Resin to separate REEs and Ln Resin® to remove Sm, were refined from a previous study. The procedural blank value of Nd was obtained as 2 pg (n = 6) from 3 L of water samples. Chemical yield of Nd from 3 L of seawater ranged within 90–95%. The developed procedure was combined with multiple collector-ICP-MS and applied to analysis of vertical seawater samples obtained from the western subarctic gyre of the North Pacific Ocean, where eNd ranged from −1.29 ± 0.42 at the surface to −3.80 ± 0.41 at 4000 m depth. These results were validated by comparing them with results obtained by the conventional method verified in the GEOTRACES inter-calibration program.
- Published
- 2020
39. Biogeochemical and physical linkages between the Arctic Ocean and Sub-Arctic Pacific through marginal seas
- Author
-
Jun Nishioka, Ichiro Yasuda, Toru Hirawake, Tomohiro Nakamura, Yoshiko Kondo, and Yuri N. Volkov
- Subjects
Geology ,Aquatic Science - Published
- 2022
40. Community composition and photosynthetic physiology of phytoplankton in the western subarctic Pacific near the Kuril Islands with special reference to iron availability
- Author
-
Koji Suzuki, Jun Nishioka, Kazuhiro Yoshida, Stanford B. Hooker, and Suzu Nakamura
- Subjects
Atmospheric Science ,Water mass ,010504 meteorology & atmospheric sciences ,Ecology ,biology ,Paleontology ,Soil Science ,Forestry ,Chaetoceros ,Aquatic Science ,biology.organism_classification ,01 natural sciences ,Subarctic climate ,Article ,chemistry.chemical_compound ,Oceanography ,Diatom ,Nitrate ,chemistry ,Phytoplankton ,Environmental science ,Seawater ,Photic zone ,0105 earth and related environmental sciences ,Water Science and Technology - Abstract
The western subarctic Pacific (WSP) is known as one of the most productive regions among the world’s oceans in spring. However, its oceanic waters are also known as a High Nutrient, Low Chlorophyll (HNLC) region during summer due to low iron (Fe) availability in seawater. Indeed, recent studies have demonstrated that the distribution of Fe in the WSP is complex and heterogeneous. This study thus investigated the effects of Fe availability on the community composition and photophysiology of surface phytoplankton from coastal to offshore waters in the WSP in the summer of 2014. Although relatively high concentrations (>2 mg m(−3)) of chlorophyll (chl) a were found in the Sea of Okhotsk and some coastal waters, low chl a concentrations (
- Published
- 2020
41. Distinct profiles of size-fractionated iron-binding ligands between the eastern and western subarctic Pacific
- Author
-
Shigenobu Takeda, Rise Bamba, Jun Nishioka, Yoshiko Kondo, and Hajime Obata
- Subjects
Water mass ,Multidisciplinary ,010504 meteorology & atmospheric sciences ,Science ,Size fractionated ,Significant difference ,010501 environmental sciences ,01 natural sciences ,Subarctic climate ,Article ,Environmental sciences ,chemistry.chemical_compound ,Colloid ,Ocean sciences ,chemistry ,Chlorophyll ,Environmental chemistry ,Medicine ,Solubility ,Primary productivity ,0105 earth and related environmental sciences - Abstract
Iron (Fe) is well known as a limiting factor to control primary productivity especially in high-nutrient and low chlorophyll area such as the subarctic Pacific. The solubility of Fe is believed to be controlled by its complexation with natural organic ligands, while the distribution of organic ligands is poorly understood. Here, we report that dissolved (
- Published
- 2020
42. Iron Supply by Subglacial Discharge Into a Fjord Near the Front of a Marine‐Terminating Glacier in Northwestern Greenland
- Author
-
Daiki Nomura, Shin Sugiyama, Naoya Kanna, Yasushi Fukamachi, and Jun Nishioka
- Subjects
Atmospheric Science ,Global and Planetary Change ,geography ,Oceanography ,geography.geographical_feature_category ,Front (oceanography) ,Environmental Chemistry ,Environmental science ,Fjord ,Glacier ,General Environmental Science - Abstract
Glacial fjords in Greenland show high productivity owing to the runoff of meltwater from the glaciers. Macronutrient dynamics (of nitrate, phosphate, and silicate) associated with subglacial discharge plumes in front of marine-terminating glaciers are widely cited as important drivers of summer phytoplankton blooms in the fjords. However, the dynamics of iron (Fe), an essential micronutrient for primary production, remain largely unstudied in glacial fjords. To investigate the role of subglacial discharge plumes in Fe supply processes in glacial fjords, a comprehensive survey of Bowdoin Fjord, adjacent to the marine-terminating Bowdoin Glacier in northwestern Greenland, was conducted. The subglacial discharge of Fe-rich meltwater induces a buoyancy-driven upwelling plume in front of the glacier that entrains nutrient-rich Arctic- and Atlantic-origin waters. The plume water potentially carried 4.5-8.7 x 10(7) g day(-1) of total dissolvable Fe out of Bowdoin Fjord in summer. The concentration of dissolved Fe (dFe) in the plume water (similar to 15.6 nmol kg(-1)) was 4 times higher than that in the water in the outer part of the fjord (similar to 3.8 nmol kg(-1)). The dFe:nitrate + nitrite ratio (mmol mol(-1)) in the plume water varied between 0.58 and 3.2, several orders of magnitude higher than the phytoplankton cellular Fe:nitrate ratio estimated using the hypothetical Fe:C ratio and observed particulate organic carbon:nitrate ratio of the fjord. Hence, the plume water is replete with Fe with respect to phytoplankton demands. Subglacial discharge drives the upwelling of Fe and macronutrients toward the euphotic zone, which is vital for the generation of summer phytoplankton growth in glacial fjords.
- Published
- 2020
43. Global oceanic iron distribution estimated by dynamic interpolation
- Author
-
Hajime Obata, Shuhei Masuda, Andrew R. Bowie, Toshimasa Doi, Jun Nishioka, Eric P. Achterberg, Kazuhiro Misumi, and Satoshi Osafune
- Subjects
Ocean observations ,Distribution (number theory) ,13. Climate action ,Dissolved iron ,Environmental science ,Soil science ,14. Life underwater ,Interpolation - Abstract
The availability of dissolved iron (dFe) exerts an important control on primary production. Recent ocean observation programs have provided information on dFe in many parts of the ocean, but knowledge is still limited concerning the rates of processes that control the concentrations and cycling of dFe in the ocean and hence the role of dFe as a determinant of global primary production. We constructed a three-dimensional gridded dataset of oceanic dFe concentrations by using both observations and a simple model of the iron cycle, and estimated the difference of processes among the ocean basins in controlling the dFe distributions. A Green's function approach was used to integrate the observations and the model. The reproduced three-dimensional dFe distribution indicated that iron influx from aeolian dust and from shelf sediment were 7.6 Gmol yr and 4.4 Gmol yr in the Atlantic Ocean and 0.4 Gmol yr and 4.1 Gmol yr in the Pacific Ocean. The residence times were estimated to be 12.2 years in the Atlantic and 80.4 years in the Pacific. These estimates imply large differences in the cycling of dFe between the two ocean basins that would need to be taken into consideration when projecting future iron biogeochemical cycling under different climate change scenarios. Although there is some uncertainty in our estimates, global estimates of iron cycle characteristics based on this approach can be expected to enhance our understanding of the material cycle and hence of the current and future rates of marine primary production.
- Published
- 2020
44. Importance of Intermediate Water Formation for Suplying Iron and Macro-Nutrient in the North Pacific
- Author
-
Jun Nishioka, Hajime Obata, and Ichiro Yasuda
- Published
- 2020
45. Responses of phytoplankton assemblages to iron availability and mixing water masses during the spring bloom in the Oyashio region, NW Pacific
- Author
-
Koji Suzuki, Hiroshi Hattori, Robert Michael L. McKay, Yoshiko Kondo, Hiroaki Saito, Kenshi Kuma, Ai Hattori-Saito, Jun Nishioka, and Tomonori Isada
- Subjects
0301 basic medicine ,Water mass ,010504 meteorology & atmospheric sciences ,Aquatic Science ,Spring bloom ,Oceanography ,01 natural sciences ,03 medical and health sciences ,030104 developmental biology ,Phytoplankton ,Environmental science ,Mixing (physics) ,0105 earth and related environmental sciences - Published
- 2018
46. Quantitative analysis of Fe, Mn and Cd from sea ice and seawater in the Chukchi Sea, Arctic Ocean
- Author
-
La Kenya Evans and Jun Nishioka
- Subjects
0106 biological sciences ,geography ,Biogeochemical cycle ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Ecology ,010604 marine biology & hydrobiology ,Sea ice ,Aquatic Science ,01 natural sciences ,Oceanography ,Arctic ,Trace metals ,Labile particulate ,General Earth and Planetary Sciences ,Environmental science ,Seawater ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Dissolved - Abstract
Sea ice is important for the health of the polar oceans yet its role in the biogeochemical cycling of trace metals is not so clear. To understand the geochemical behaviour of trace metals and their accumulation into sea ice, dissolved (D, < 0.2 mu m), and labile particulate (LP, Total Dissolvable - Dissolved) Fe, Mn, and Cd were examined in sea ice and seawater collected from the Chukchi Sea in the Arctic Ocean. Samples were pre-concentrated utilizing the solid-phase extraction NOBIAS Chelate PA-1 resin (Hitachi High-Technologies Corporation) and analyzed on a Graphite Furnace Atomic Absorption Spectrometer. Chukchi seawater showed high percentage for DMn (71.5%) and DCd (66.3%) with a high percentage of LPFe (94.1%). In seawater, DCd was the only metal to correlate with phosphate (R-2 = 0.78) indicating a biogeochemical cycling source. Chukchi seawater concentrations of Fe and Mn may have been controlled through external sources such as sediments (shelf or river) and/or sediment reductive processes. Trace metal concentrations in Chukchi sea ice were heterogeneous. Sea ice showed high percentages for the LP fraction (99.2% Fe, 63.6% Mn and 71.2% Cd). This data indicated that, regardless of the trace metal behaviour in Chukchi seawater, Chukchi sea ice was observed to have a preference for the LP trace metal fraction.
- Published
- 2018
47. Cold water upwelling and entrainment near the Anadyr Strait: Implications to the North Pacific-Arctic interaction
- Author
-
Yusuke, Kawaguchi, Jun, Nishioka, Shigeto, Nishino, Shinzou, Fujio, Amane, Fujiwara, Daigo, Yanagimoto, and Ichiro, Yasuda
- Abstract
The Tenth Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Wed. 4 Dec. / Entrance Hall (1st floor) , National Institute of Polar Research
- Published
- 2019
48. Sea ice melt affects algal photosynthesis and growth: A laboratory study on an ice algal community from the Sea of Okhotsk
- Author
-
Dong, Yan, Kazuhiro, Yoshida, Jun, Nishioka, Masato, Ito, Takenobu, Toyota, and Koji, Suzuki
- Abstract
The Tenth Symposium on Polar Science/Ordinary sessions: [OB] Polar Biology, Wed. 4 Dec. / 3F Multipurpose conference room, National Institute of Polar Research
- Published
- 2019
49. Determination of the freshwater origin of Coastal Oyashio Water using humic-like fluorescence in dissolved organic matter
- Author
-
Koji Suzuki, Atsuko Sugimoto, Youhei Yamashita, Yuya Tada, Takahiro Tanaka, Yuta Tsuzuki, Jun Nishioka, and Yu Mizuno
- Subjects
0106 biological sciences ,Water mass ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,Freshwater end-member ,Oceanography ,Sea-ice melt water ,01 natural sciences ,River water ,Pacific ocean ,Salinity ,Coastal Oyashio Water ,Environmental chemistry ,Spring (hydrology) ,Phytoplankton ,Dissolved organic carbon ,Sea ice ,Environmental science ,Dissolved organic matter ,Humic fluorescence ,0105 earth and related environmental sciences - Abstract
Coastal Oyashio Water (COW), defined as a water mass with a temperature lower than 2 degrees C and a salinity lower than 33.0, is distributed in the North Pacific Ocean off southeastern Hokkaido, Japan, from winter to spring. COW is rich in macronutrients and dissolved iron and is thus considered to affect the spring phytoplankton blooms in the Oyashio region. Although river water and sea-ice melt water have been considered freshwater end-members of COW, the contributions of these freshwater sources to COW have not been well described. In this study, the humic-like components in dissolved organic matter were first applied as a parameter to evaluate the freshwater end-members of COW in March 2015. Linear regressions with negative slopes were determined between the humic-like components and the salinity of COW. The intercepts of the regressions against the humic-like components were within the ranges of those observed for the local rivers of Hokkaido but were very different from those of sea ice. These findings suggest that river water contributed to the COW observed here as a freshwater end-member, although the contribution of sea-ice melt water to COW could not be evaluated. This novel approach also highlighted two different less-saline water masses in COW. The first was characterized by a lower temperature and relatively high levels of humic-like components, while the second was higher in temperature and had higher levels of humic-like components. It is suggested that these different characteristics are due to the contributions of water from different rivers and/or different effects of sea-ice melt water.
- Published
- 2018
50. Dynamics of particulate and dissolved organic and inorganic phosphorus during the peak and declining phase of an iron-induced phytoplankton bloom in the eastern subarctic Pacific
- Author
-
Jun Nishioka, Takeshi Yoshimura, Atsushi Tsuda, and Hiroshi Ogawa
- Subjects
Inorganic matter ,Biogeochemical cycle ,010504 meteorology & atmospheric sciences ,Phytoplankton bloom ,chemistry.chemical_element ,Aquatic Science ,010402 general chemistry ,Oceanography ,01 natural sciences ,Algal bloom ,chemistry.chemical_compound ,Phytoplankton ,POPOP ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Chemistry ,Phosphorus ,fungi ,Spring bloom ,Subarctic climate ,0104 chemical sciences ,Environmental chemistry ,Organic matter ,Bloom - Abstract
Phosphorus (P) is an essential element for all organisms and thus the P cycle plays a key role in determining the dynamics of lower trophic levels in marine ecosystems. P in seawater occurs conceptually in particulate and dissolved organic and inorganic (POP, PIP, DOP, and DIP, respectively) pools and clarification of the dynamics in these P pools is the basis to assess the biogeochemical cycle of P. Despite its importance, behaviors of each P pool with phytoplankton dynamics have not been fully examined. We measured the four operationally defined P pools (POPop, PIPop, DOPop, and SRP) during an iron-induced phytoplankton bloom (as part of the subarctic ecosystem response to iron enrichment study (SERIES)) in the eastern subarctic Pacific in summer 2002. During our observations of the iron-enriched patch from day 15 to day 26 after the iron infusion, chlorophyll-a concentration in the surface layer decreased from 6.3 to 1.2 μg L− 1, indicating the peak through decline phase of the phytoplankton bloom. At the bloom peak, P was partitioned into POPop, PIPop, and DOPop in proportions of 60, 27, and 13%, respectively. While chlorophyll-a and POPop showed similar temporal variations during the declining phase, PIPop showed a different peak timing with a 2 day delay compared to POPop, resulting in a rapid change in the relative proportion of PIPop to total particulate P (TPP = POPop + PIPop) at the peak (25%) and during the declining phase of the bloom (50%). A part of POPop was replaced by PIPop just after slowing down of phytoplankton growth. This process may have a significant role in the subsequent regeneration of P. We conclude that measurement of TPP alone is insufficient to show the interaction between P and phytoplankton dynamics and fractionation of TPP into POPop and PIPop provides useful insights to clarify the biogeochemical cycle of P.
- Published
- 2018
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