霞ヶ浦と東京湾における混合状態と貧酸素水塊
増永英治; 到津春樹; 北村立実; 大内孝雄; 川口悠介; 伊藤幸彦, Lead
沿岸海洋研究, Aug. 2026
〔Major achievements〕Wind-induced coastal upwelling off southeast Japan supplying surface nutrients to the Kuroshio downstream
Eiji Masunaga; Yusuke Uchiyama; Xu Xhang, Lead
Journal of Geophysical Research: Oceans, 2026, [Reviewed]
黒潮流路変動および季節風に伴う冬季の遠州灘海域における表層一次生産空間変動について
鯰江 岳; 内山雄介; 張旭; 増永英治
土木学会論文集(B2海岸工学), Nov. 2025, [Reviewed]
夏季鹿島灘浅海域における内部ケルビン波による南下流の強化について
浅木雄登; 内山雄介; 渡辺萌斗; 佐野朝昭; 橋本孝治; 伴野雅之; 増永英治; 山崎秀勝
土木学会論文集(B2海岸工学), Nov. 2025, [Reviewed]
Effects of internal tides on GNSS-A seafloor crustal deformation observationYusuke Yokota; Tadashi Ishikawa; Shun-ichi Watanabe; Koya Nagae; Yuto Nakamura; Eiji Masunaga, Abstract
Internal tides are crucial in ocean dynamics and are a source of error in marine acoustic measurements. In Global Navigation Satellite System-Acoustic combination technique (GNSS-A) seafloor crustal deformation observations, which contribute to earthquake and plate subduction sciences, the effect of internal tides has never been estimated, even though it has been predicted. In this study, we quantitatively evaluated the impact of internal tides on GNSS-A observations by numerical reproduction and used data from the GNSS-A observation network around Japan to quantitatively identify the effect of internal tides on GNSS-A observations for the first time. As a result, we clarified the mechanism of internal tidal effects for GNSS-A. Long-term sound speed disturbances during GNSS-A observations were generally explained by a semidiurnal internal tide in modes 1 to 3. GNSS-A is affected by the horizontal wavelength, mode, and direction of the internal tides and can be used to grasp those features. In future, these results are expected to contribute to progress in multidisciplinary research, such as the construction of advanced physical models and analytical methods., Springer Science and Business Media LLC
Progress in Earth and Planetary Science, 28 Jul. 2025,
[Reviewed] 〔Major achievements〕The Influence of Horizontal Dispersion on Residence Times in Shallow LakesEiji Masunaga; Oliver B. Fringer; Tatsumi Kitamura; Takao Ouchi, Lead, Abstract
This study presents results of circulation and residence time in lakes influenced by wind‐induced mixing investigated with numerical simulations. The study area is Lake Kasumigaura, a continuous lake system primally consisting of two lakes, West Lake and North Lake. Although metrological conditions and depths are similar for both lakes, the surface area and shape of the lakes are very different. A numerical model resolves the primary features of the wind‐driven circulation in the lake system and is forced by observed river discharges and wind stress. A passive tracer released from the river mouths is used to estimate the residence time and evaluate mixing processes. Wind‐driven flow dominates the kinetic energy in the lakes and induces chaotic motions leading to tracer dispersion which is largely influenced by the shape of the lakes. Results indicate that the residence time is much longer in the well‐mixed middle basin of West Lake than North Lake. The estimated horizontal tracer diffusivity is approximately three times larger for the large West Lake than for the small‐narrow North Lake. This study suggests that the surface area and shape of lakes in which the flow is predominantly wind driven largely influences circulation, water exchange processes and residence times in lakes., American Geophysical Union (AGU)
Water Resources Research, 17 Feb. 2025,
[Reviewed] Variability of nutrient transport and associated upper ocean primary production induced by Kuroshio meanders in the Enshu-nada Sea, JapanGaku Namazue; Yusuke Uchiyama; Xu Zhang; Eiji Masunaga, Towards the desirable preservation of the marine environment under a changing global climate, this study aims to investigate the coastal biological response to varying oceanic conditions, namely the Kuroshio meander, and associated nitrate transport on the Pacific coast of Japan around the Enshu-nada Sea, using a coupled three-dimensional regional ocean circulation model with a nitrogen-based ecosystem model. A prominent difference was found in nitrate transport processes between for a period when the Kuroshio took a meandering path and for a non-meandering period, leading to about 1.5 times higher surface primary production measured by chlorophyl-a concentration during the non-meandering period than during the meandering period. The upper ocean nitrate flux budget analysis showed that the subsurface nitrate was transported upward as a vertical diffusive flux around the north (shoreward) of the Kuroshio path and as a mean vertical advective flux in the Kuroshio downstream region around the Izu-Ogasawara Ridge. In contrast, high-frequency eddy vertical advective fluxes caused downward transport, but to a degree about 20% smaller than the other fluxes. After nitrate was supplied to the upper layer, it was transported horizontally by the counterclockwise rotating cyclonic eddy formed between the coast and the Kuroshio and supplied to phytoplankton in the Enshu-nada Sea. These results suggest that carbon sequestration due to biological pump may also vary in response to the Kuroshio that is influenced by basin-scale oceanic conditions., EDP Sciences
E3S Web of Conferences, 15 Jan. 2025
海底凸地形上を伝播する 内部潮汐の砕波動態に関する研究
針間 虎次朗; 増永 英治, Last
土木学会論文集(B2海岸工学), 2025, [Reviewed]
領域海洋モデルを用いた 日本周辺海域における沿岸湧昇に関する研究
柳澤 晃; 増永 英治; 内山 雄介, Corresponding
土木学会論文集(B2海岸工学), 2025, [Reviewed]
衛星観測データを用いた日本本州東岸における 夏季の沿岸湧昇に関する研究
柴田 楓; 増永 英治, Last
土木学会論文集(B2海岸工学), 2025, [Reviewed]
〔Major achievements〕Mechanisms of internal tide-induced turbulent mixing observed from mooring data in a shallow steep submarine canyon
Eiji Masunaga; Matthew; H. Alford; Charlotte Bellerjeau, Lead
Journal of Physical Oceanography, 2025, [Reviewed]
Turbulent mixing layers and associated diffusive fluxes across the epilimnion and metalimnion in stratified large Lake BiwaHikaru Homma; Eiji Masunaga; Ilia Ostrovsky; Hidekatsu Yamazaki, Abstract
Stratification and turbulent mixing have an immense impact on biogeochemical regimes and ecosystem dynamics in stratified large lakes. This study investigates the physical properties of the epi‐ and metalimnion of Lake Biwa (Japan), focusing on the persistent vertical diffusive fluxes due to turbulent mixing in the lower metalimnion and their effects on upward nitrate transport. We conducted 24‐h observations at an offshore station in the summer for three consecutive years to examine the temporal and vertical variations of stratification and turbulence. A mooring system provided long‐term data on stratification and current velocity, while thermal profiles along two offshore transects were collected to investigate lateral changes. Our findings revealed strong stratification in the upper metalimnion, where vertical diffusive fluxes were essentially suppressed. Distinct turbulent mixing layers were identified near the water surface and within the moderately stratified lower metalimnion. Field data and numerical model suggested that the turbulence in the lower metalimnion was driven by shear instability, straining, and/or wave–wave interactions linked with the persistent internal waves that occur even during weak winds. Vertical eddy diffusivity of > 10
−5 m
2 s
−1 in the lower metalimnion was associated with rather strong turbulence, which has not been reported in other large lakes. The elevated turbulence resulted in an upward nitrate flux of 0.2 mmol N m
−2 d
−1 across the lower metalimnion, indicating that the upward nutrient transport could support primary productivity and play an important ecological role in deep stratified lakes., Wiley
Limnology and Oceanography, 2025,
[Reviewed] 遠州灘沿岸域における黒潮流路変動に伴う栄養塩輸送および表層一次生産の変 動特性について
鯰江 岳; 内山雄介; 張 旭; 増永英治
土木学会論文集B2（海岸工学）, Nov. 2024, [Reviewed]
海岸地形に影響される浅水域における吹送流モニタリングと数値計算を用いた再現検証
吉田 壮汰; 増永 英治; 北村 立実; 大内 孝雄, Corresponding
土木学会論文集(B2海岸工学), Nov. 2024, [Reviewed]
領域海洋モデル全域から放流した粒子追跡実験を用いた東日本南岸海域の物質輸送過程の評価
佐近 淳平; 増永 英治; 内山 雄介, Corresponding
土木学会論文集(B2海岸工学), Nov. 2024, [Reviewed]
粒子追跡モデルとドリフターデータを用いた日本海における物質輸送過程の研究
原田 一宏,増永 英治,内山 雄介, Corresponding, 土木学会
土木学会論文集(B2海岸工学), Nov. 2023, [Reviewed]
傾圧と順圧的運動に関連する東京湾における運動エネルギーの評価
渡邉 暦,到津 春樹,増永 英治, Corresponding, 土木学会
土木学会論文集（B2海岸工学）, Nov. 2023, [Reviewed]
沖合から伝播する内部潮汐の砕波による河川水の混合に関する研究
門馬 宏典,増永 英治, Corresponding, 土木学会
土木学会論文集（B2海岸工学）, Nov. 2023, [Reviewed]
夏季の気象変化による成層の発達が及ぼす霞ヶ浦への影響の評価
松本 大樹,増永 英治,横木 裕宗, Corresponding, 土木学会
土木学会論文集（G環境）, Sep. 2023, [Reviewed]
Effect of Oxygen Consumption by Bottom-Layer Water and Sediment on Formation of Hypoxic Water in Lake Kitaura
北村 立実,増永 英治,鮎川和 泰,大内 孝雄,湯澤 美由紀,佐藤 和貴,清家 泰,福島 武彦, 水環境学会
水環境学会誌, Jul. 2023, [Reviewed]
領域海洋モデルを用いた洋上風力発電施設の適地選定システム開発に関する基礎的研究
玉井 駿壮・内山 雄介・Xu Zhang・増永 英治・辻 一洋・山崎 秀勝
土木学会論文集（B2海岸工学）, Nov. 2022, [Reviewed]
複数定点観測データを用いた東京湾における水平物理構造と混合状態の評価
到津 春樹・増永 英治, Last
土木学会論文集(B2海岸工学), Nov. 2022, [Reviewed]
沿岸地形が影響する風応力による鉛直混合の観測と評価
佐藤 和貴・増永 英治・北村 立実, Corresponding
土木学会論文集(B2海岸工学), Nov. 2022, [Reviewed]
定常流，振動流及び密度成層を考慮した海洋構造物周辺の数値実験
山﨑 彩花・増永 英治・内山 雄介・辻 一洋・山崎 秀勝, Corresponding
土木学会論文集（B1水工学）, Sep. 2022, [Reviewed]
Seasonal variability of upper ocean primary production along the Kuroshio off Japan: Roles of eddy-driven nutrient transportXu Zhang; Yusuke Uchiyama; Eiji Masunaga; Yota Suzue and Hidekatsu Yamazaki, We assessed spatial and seasonal variabilities of eddy-driven vertical nutrient fluxes, which are essential for maintaining primary production in the upper ocean. A climatological model based on a Regional Oceanic Modeling System (Regional Oceanic Modeling System) coupled with a Nutrient Phytoplankton Zooplankton and Detritus (NPZD) biogeochemical model at a submesoscale eddy-permitting resolution was used to investigate the mechanisms driving such variabilities around the Kuroshio, off the coast of Japan. The model realistically reproduced the spatial segmentations in primary production on both sides of the Kuroshio path with a higher chlorophyll-a concentration on the northern side than the southern side. In winter, downward eddy-induced nitrate flux is predominantly provoked in the upstream Kuroshio region (KR), while upward nitrate fluxes prevail in the downstream Kuroshio Extension (KE) region, due to both shear and baroclinic instabilities. Baroclinic instability plays a crucial role in inducing seasonal variability, leading to enhancement (reduction) of the eddy flux in winter (summer), particularly in regions away from the Kuroshio axis. Furthermore, we found that the influence of the Izu-Ogasawara Ridge, located in the KR, on regional dynamics and resultant spatial variability of the biogeochemical response are mostly confined in the KR. The Kuroshio is less turbulent in the upstream of the ridge, while it becomes unstable to shed mesoscale eddies in laterally wider and vertically deeper regions downstream. Consequently, although the near-surface nitrate concentration is lower downstream, the upward eddy-driven nitrate flux is more effective in maintaining active primary production due to the shear and baroclinic instabilities in winter., Frontiers Media SA
Frontiers in Marine Science, Aug. 2022,
[Reviewed] 自動昇降装置を用いた夏季における北浦の水温成層と貧酸素水塊の形成・消失およびリン溶出過程の検討
北村 立実; 鮎川 和泰; 増永 英治; 小室 俊輔; 大内 孝雄; 湯澤 美由紀; 浅岡 大輝; 三上 育英; 清家 泰; 福島 武彦
水環境学会誌, Jun. 2022
粒子追跡モデルを用いた相模湾及び駿河湾周辺の物質輸送過程の解析
井上孝義・増永英治・小硲大地・Xu Xhang・内山雄介, Corresponding
土木学会論文集(B2海岸工学), Nov. 2021, [Reviewed]
東京湾湾奥部における貧酸素水塊に関わる物理構造と混合状態
到津春樹・増永英治, Last
土木学会論文集(B2海岸工学), Nov. 2021, [Reviewed]
領域海洋モデルを用いた黒潮・親潮混合水域における水塊分布に関する研究
池田雅・増永英治・鈴江洋太・伊藤幸彦・内山雄介, Corresponding
土木学会論文集(B2海岸工学), Nov. 2021, [Reviewed]
北浦における貧酸素水塊の詳細分布と貧酸素水域面積の推計
小室俊輔,北村立実,大内孝雄,増永英治,浅岡大輝,鮎川和泰,三上育英,清家泰,湯澤美由紀,福島武彦, 水環境学会
水環境学会誌, Sep. 2021, [Reviewed]
Diel vertical migration promotes zooplankton horizontal patchiness
Bingzhang Chen; Eiji Masunaga; S. Lan Smith; Hidekatsu Yamazaki
Journal of Oceanography, Feb. 2021, [Reviewed]
TIME-SCALES OF WIND-INDUCED MIXING PROCESSES ASSOCIATED WITH THE TOPOGRAPHY AND STRATIFICATION
浅岡 大輝; 増永 英治; 小室 俊輔; 北村 立実, Corresponding
土木学会論文集(B2海岸工学), Nov. 2020, [Reviewed]
〔Major achievements〕Stratification and mixing processes associated with hypoxia in a shallow lake (Lake Kasumigaura, Japan)
Eiji Masunaga; Shunsuke Komuro, Lead
Limnology, Apr. 2020, [Reviewed]
沿岸地形と風応力が形成する複雑な密度構造と混合状態の高精度計測
増永英治; 浅岡 大輝; 小室 俊輔; 松本 俊一; 小野 正人; 番場 泰彰, Lead
土木学会論文集B2(海岸工学), Nov. 2019, [Reviewed]
Mixing processes associated with hypoxia in Lake Kasumigaura
Eiji Masunaga; Tomoko Ozawa., Lead
7th World Lake Conference proceedings, Oct. 2018, [Reviewed]
A three-dimensional numerical study of river plume mixing processes in Otsuchi Bay, Japan
Sasmal; K.; Masunaga; E.; Webb; A.; Fringer; O. B.; Gross; E. S.; Rayson; M. D.; & Yamazaki; H.
Journal of Oceanography, 2018, [Reviewed]
複数気候モデルによる海面上昇に伴う浸水影響の不確実性評価
土田 晃次郎; 田村 誠; 熊野 直子; 増永 英治; 横木 裕宗
土木学会論文集G（環境）, 2018, [Reviewed]
高解像度数値計算技術を用いた東京湾湾奥の物理構造の解明
増永英治; 木村和久; 鯉渕幸夫, Lead
土木学会論文集B2（海岸工学）, 2018, [Reviewed]
珊瑚環礁内における流動構造と物質輸送過程の解明
小池海; 増永英治; 横木裕宗, Corresponding
土木学会論文集B2(海岸工学), 2018, [Reviewed]
内部潮汐を考慮した伊豆大島周辺海域における潮流予測システムの開発と運用
増永英治; 山崎秀勝; 山口邦久, Lead
土木学会論文集B2(海岸工学), 2018, [Reviewed]
〔Major achievements〕Sediment resuspension and the generation of intermediate nepheloid layers by shoaling internal bores
Eiji Masunaga; Robert S. Arthur; Oliver B. Fringer and Hidekatsu Yamazaki, Lead
Journal of Marine Systems, Feb. 2017, [Reviewed]
日本における海面上昇への適応を目的とした防護費用の将来推計熊野直子; 土田光次郎; 田村誠; 増永英治; 桑原祐史; 横木裕宗, Sea level rise due to climate change may threaten those who live near the coastal area. It is important to examine the cost of coastal protection in the context of climate change and its adaptation. This paper constructed the database of installed cosatal protection around the world, and it tried to estimate the future cost of protection such as constructing new dykes and elevating them in Japan, baesd on SSP scenarios. It is feasble to install new dyke along the major coasts if the related budget keeps a certain level. However, the combination of constructing new dykes and elevating them enables us to cut down more protection cost., Japan Society of Civil Engineers
土木学会論文集B3（海洋開発）, 2017,
[Reviewed] 黒潮と内部波が影響する伊豆諸島周辺海域における流動場の解明増永英治; 鈴江洋太; 内山雄介; 山崎秀勝, Lead, Regional Oceanic Numerical simulations using ROMS with tidal forcing were conducted to investigate tidally induced internal waves (internal tides) in the vicinity of the Izu-chain Islands. The tides enhance the enrgy flux of internal waves by about 10 times as large around the islands. Therefore, in the study region, the internal waves are considerably enargized by the tidal forcing. Although the total and baroclinic components of kinetic eneygy increase due to the tides, the barotropic kinetic energy component decreased by the tidal forcing. The internal waves accompanied by strong baroclinic flows largely contribute to the flow compared to the currents due to winds and the Kuroshio. The numerical simulateons also revealed the enhanced eddy motiions due to the tidal forcing, suggesting that the tides contiribute to lateral mixing or transports via meso- and submesoscale eddies., 土木学会
土木学会論文集B2（海岸工学）, 2017,
[Reviewed] Coastal observation systems to monitor physical, chemical, and biological parametersHidekatsu Yamazaki; Eiji Masunaga; Scott Gallager; Mamoru Tanaka; Marika Takeuchi; Kazuo Amakasu; Hayato Kondo, We have developed a free-fall multi-parameter profiler (YODA Profiler) to measure various physical and biological parameters in coastal ocean. We found internal bores create a strong mixing event. Sediment resuspension is associated with the mixing event and also AZFP detected fish school at the front of bore. We have deployed a cable observatory system (Oshima Coastal Environment data Acquisition Network System, OCEANS) in a coastal area to monitor coastal ecosystem continuously. OCEANS can measure various physical, chemical and biological parameters simultaneously, and operates a plankton imaging system (Continuous Plankton Imaging and Classification System, CPICS). Based on acquired images of phytoplankton and zooplankton, we are investigating how planktonic biodiversity is affected by multi-scale physical processes, such as Kuroshio and internal waves. We are developing a technique to predict the biodiversity of plankton from three-dimensional hydrodynamic model using a newly developed plankton ecosystem model. We are also developing a AUV (MEMO-pen) that carries CPICS as well as microstructure profiler (TurboMAP) in order to simultaneously observe turbulence and plankton. We will introduce the most recent results from these observation systems., Acoustical Society of America (ASA)
Journal of the Acoustical Society of America, 01 Oct. 2016
Development of Monitoring Technologies to Observe Plankton Ecosystem in Coastal Oceans
Yamazaki; H.; E. Masunaga; H. Foloni-Neto; S. Gallager
Bulletin on Coastal Oceanography, Jan. 2016, [Reviewed]
〔Major achievements〕Mixing and sediment resuspension associated with internal bores in a shallow bay
Masunaga; E.; H. Homma; H. Yamazaki; O. Fringer; T. Nagai; Y. Kitade and A. Okayasu, Lead
Continental Shelf Research, Sep. 2015, [Reviewed]
Resuspension and lateral dispersal of sediments due to shoaling internal waves
Masunaga; E.; H. Yamazaki; T. Nagai and O.; Fringer, Lead
IMBER newsletter, Dec. 2013, [Reviewed]
