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Journal Articles

Iron distributions in the water column of the Japan Basin and Yamato Basin (Japan Sea)

Fujita, Satoshi*; Kuma, Kenshi*; Ishikawa, Satoko*; Nishimura, Shotaro*; Nakayama, Yuta*; Ushizaka, Satomi*; Isoda, Yutaka*; Otosaka, Shigeyoshi; Aramaki, Takafumi*

Journal of Geophysical Research, 115(C12), p.C12001_1 - C12001_12, 2010/12

 Times Cited Count:14 Percentile:39.46(Oceanography)

Vertical distributions of dissolved iron (D-Fe, less than 0.22 micrometer fraction), total iron (T-Fe, unfiltered), and chemical and biological components (e.g., nutrients) in seawater were determined at seven stations in the Japan Sea to understand the mechanisms that control iron behavior. Distributions of the D-Fe were characterized by surface depletion, mid-depth maxima, then slight decrease with depth in deep water and uniform concentration in bottom water because of biological uptake in the surface water and release from microbial decomposition of sinking organic matter in mid-depth water. The T-Fe concentrations in the deep-water column were variable with different T-Fe levels among stations and depths. We found a significant relationship of the exponential increase in the T-Fe concentrations with decreasing water transmittance, resulting from the iron supply into the deep and bottom waters due to the lateral transport of resuspended sediment from the continental slope.

Journal Articles

Iron in the Japan Sea and its implications for the physical processes in deep water

Takata, Hyoe*; Kuma, Kenshi*; Isoda, Yutaka*; Otosaka, Shigeyoshi; Senju, Tomoharu*; Minakawa, Masayuki*

Geophysical Research Letters, 35(2), p.L02606_1 - L02606_5, 2008/01

Concentrations of iron in seawater (dissolved and labile dissolved phases) in the two basins (Yamato Basin and Japan Basin) of the Japan Sea are measured and the origin and behavior of iron were discussed. Extremely high vertically integrated total dissolvable Fe inventories (300-350 $$mu$$mol m$$^{-2}$$) were observed at the surface water in both basins (0-200 m depth), and was probably resulting from high atmospheric Fe input to the surface water. Labile dissolved Fe in both basins was characterized by mid-depth (1-2 km depth) maxima, which were regulated by the competition between dissolved Fe input from the microbial decomposition of sinking biogenic organic matter and Fe removal by particulate scavenging. The distributions of Fe in the Japan Sea would play an important role in understanding the biogeochemical cycle of iron in the ocean.

Journal Articles

Variation of volume transport of the Tsugaru Warm Current in the period from 2000 to 2002

Ito, Toshimichi; Kawamura, Hideyuki; Nakayama, Tomoharu*; Shima, Shigeki*; Onishi, Mitsuyo*; Isoda, Yutaka*

Proceedings of International Workshop on Monitoring and Forecasting of the Rapid Change in Ocean-Atmosphere Environment in the East Asia, p.13 - 14, 2007/11

The volume transport of the Tsugaru Warm Current (TgWC) from April 2000 to June 2002, which was estimated based on the ferry-borne ADCP observation was examined in this study. The estimated transport varied from about 0.6 Sv to 2.5 Sv (=10$$^{6}$$ m$$^{3}$$s$$^{-1}$$), and the mean value was estimated to be about 1.3 Sv with $$pm$$ 0.3 Sv showing the similar level as that in the preliminary result. The temporal variation with a period of about 20-30 days seemed to be remarkable in the anterior half of this observation period rather than seasonal variation. By contrast, the seasonal variation was dominant in the posterior half in which the minimum and maximum values appear in the spring and autumn, respectively. The temporal change of the transport showed good correlation with the sea level differences around the strait as expected. In addition, the present result suggests that the change of local wind around the strait also lead in part of the change of the transport.

Journal Articles

Variation of volume transport of the Tsugaru Warm Current in the period from 2000 to 2002

Ito, Toshimichi; Kawamura, Hideyuki; Onishi, Mitsuyo*; Isoda, Yutaka*; Nakayama, Tomoharu*; Shima, Shigeki*

Proceedings of 14th PAMS/JECSS Workshop, p.222 - 223, 2007/05

no abstracts in English

Journal Articles

Benthic front and the Yamato Basin Bottom Water in the Japan Sea

Senju, Tomoharu*; Isoda, Yutaka*; Aramaki, Takafumi*; Otosaka, Shigeyoshi; Fujio, Shinzo*; Yanagimoto, Daigo*; Suzuki, Takashi; Kuma, Kenshi*; Mori, Kosuke*

Journal of Oceanography, 61(6), p.1047 - 1058, 2005/12

 Times Cited Count:8 Percentile:18.19(Oceanography)

The detail structure of the Bottom Water in the Japan Sea was revealed by the hydrographic observations. The Yamato Basin Bottom Water (YBBW) exhibits higher temperature, lower dissolved oxygen, and higher nutrients concentrations than those in the Japan Basin Bottom Water (JBBW). Both Bottom Waters meet around the boundary region between the Yamato and the Japan Basins, and form a clear benthic front. It is inferred from the property distributions that the JBBW flowing into the Yamato Basin is trapped by the cyclonic circulation in the basin, and modified to the YBBW in the course of the circulation through the vertical diffusion, geothermal heating and oxygen consumption. The thermal balance of in the YYBW was examined using a box-model. The results show that the effect of geothermal heating has about 70 per-cent of magnitude to the vertical thermal diffusion and both terms cancel the advection term of the cold JBBW from the Japan Basin. The box-model also estimated the averaged residence time for the YBBW was 9.1 years.

Journal Articles

Examination of Harmonic analysis methods using semi-regular sampling data from an ADCP installed on a regular ferry; Evaluation of tidal and residual currents in the eastern mouth of the Tsugaru strait

Kuroda, Hiroshi*; Isoda, Yutaka*; Onishi, Mitsuyo*; Iwahashi, Masayuki*; Sato, Chizuru*; Nakayama, Tomoharu*; Ito, Toshimichi; Iseda, Kenichi*; Nishizawa, Keisuke*; Shima, Shigeki*; et al.

Umi No Kenkyu, 13(6), p.553 - 564, 2004/11

no abstracts in English

Journal Articles

Winter transport and tidal current in the Tsugaru Strait

Onishi, Mitsuyo*; Isoda, Yutaka*; Kuroda, Hiroshi*; Iwahashi, Masayuki*; Sato, Chizuru*; Nakayama, Tomoharu*; Ito, Toshimichi; Iseda, Kenichi*; Nishizawa, Keisuke*; Shima, Shigeki*; et al.

Hokkaido Daigaku Suisan Kagaku Kenkyu Iho, 55(2), p.105 - 119, 2004/10

Transport variations and characteristics of tidal currents in the Tsugaru Strait (TS) are investigated using the ship-mounted ADCP data obtained during October 29, 1999 - March 31, 2000. The Tsugaru Strait connects the North Pacific Ocean (NPO) and Japan/East Sea (JES), and is a main output for Tsushima Warm Current (TWC) in the JES. The strong northeastwards mean current was found in the center of the strait, and counter flows exist near the Hokkaido and Honshu coasts. The estimated mean net eastward transport is 1.8 Sv (1Sv=10$$^{6}$$m$$^{3}$$s$$^{-1}$$). In the TS, the transports of K1 and M2 across the strait are 0.72 Sv and 0.52 Sv, respectively. From the phase analysis, it is understood the K1 is progressive wave-like while the M2 is standing wave-like. We also find a significant barotropic fortnightly oscillation. The Mf tide is more energetic along the JES coast with the amplitude of 1-3cm, while the Mf tide amplitudes in the NPO are less than 1 cm. It is inferred that observed fortnightly oscillation may be generated by the difference of Mf tide amplitude between both sides of the TS.

Journal Articles

Benthic front between the Japan Basin and the Yamato Basin in the Japan Sea

Senju, Tomoharu*; Isoda, Yutaka*; Aramaki, Takafumi; Otosaka, Shigeyoshi; Suzuki, Takashi; Kuma, Kenshi*; Mori, Kosuke*

Proceedings of 12th PAMS/JECSS Workshop, p.3_4_1 - 3_4_4, 2003/11

Abyssal water mass distribution from the Yamato Basin to the Japan Basin in the Japan Sea was observed on the R/V Hakuho-Maru cruise, KH02-3 (October 14-19, 2002). The bottom layer in the Yamato Basin was occupied by the water of higher temperature and lower oxygen compared to that in the Japan Basin. As a result, a benthic front of potential temperature and dissolved oxygen was formed between the Yamato and Japan Basins. Dissolved oxygen and nutrients concentrations show that the bottom water in the Yamato Basin is older than that in the Japan Basin. This indicates the existence of the Yamato Basin Water, which is modified bottom water by the closed circulation in the Yamato Basin. The structure of the benthic front suggests an estuary-like circulation around the mouth of the Yamato Basin; outflow from the Yamato Basin lying on the inflow from the Japan Basin. The highest oxygen water was found on the slope of southern periphery of the Japan Basin. This is considered to be the bottom water from the west transported by the cyclonic circulation in the Japan Basin.

Journal Articles

Variation of velocity and volume transport of the Tsugaru warm current in the winter of 1999-2000

Ito, Toshimichi; Togawa, Orihiko; Onishi, Mitsuyo*; Isoda, Yutaka*; Nakayama, Tomoharu*; Shima, Shigeki*; Kuroda, Hiroshi*; Iwahashi, Masayuki*; Sato, Chizuru*

Geophysical Research Letters, 30(13), p.11_1 - 11_4, 2003/10

The variation of velocity and volume transport of the Tsugaru Warm Current (TWC) is investigated based on the data of continuous and cross-sectional current monitoring in the Tsugaru Strait. During November 1999 - March 2000, the structure of the velocity transection across the strait was almost stable in which the TWC occupied the central part of the strait, while the returning flows existed in the northern and southern part of the strait, and these indicate a totally declining trend. The volume transport of the TWC varies from 2.1 to 1.1 Sv, with the mean value of 1.5 Sv, following the variation of the TWC. The temporal variation of the volume transport shows a linear correlation with that of the sea level difference between the Japan Sea and the Pacific Ocean. The contribution of the sea level difference to the volume transport is estimated to be roughly 70 %.

Journal Articles

10-, 25- and 60-day periodical current variations on the western shelf in Hidaka Bay

Kuroda, Hiroshi*; Isoda, Yutaka*; Onishi, Mitsuyo*; Iwahashi, Masayuki*; Sato, Chizuru*; Nakayama, Tomoharu*; Ito, Toshimichi; Iseda, Kenichi*; Nishizawa, Keisuke*; Shima, Shigeki*; et al.

Umi No Kenkyu, 12(2), p.195 - 214, 2003/03

Variabilities of the periodical current fluctuations on the shelf in Hidaka Bay were examined with use of ferry-mounted ADCP data obtained during 2000-2001. As the result of analysis, (1) three periodical variations around 10-, 25- and 60-day period are found, (2) the horizontal phase lag of these variations is little along the ship track, and the vertical phase lag is little at 10- and 25-day variations while several-day at 60-day variation, and (3) the 10-day variation shows coherent cross-correlation between current and wind.

Oral presentation

Behavior of iron in the Yamato Basin and the Japan Basin, Japan Sea

Takata, Hyoe*; Kuma, Kenshi*; Isoda, Yutaka*; Nishioka, Jun*; Otosaka, Shigeyoshi; Chikira, Mitsuru*; Takagi, Shogo*; Kamei, Yoshihiko*; Sakaoka, Keiichiro*

no journal, , 

The authors discussed on the difference of behavior of iron between two basins (the Yamato Basin and Japan Basin) in the Japan Sea by measurements of iron (dissolved and labile dissolved phases) and nutrients in seawater. Concentration of labile dissolved iron in the surface water was about 1.0 nM and did not show difference between the basins. On the other hand, concentration of labile dissolved iron in the Japan Basin increased to 4.5 nM at 1-2 km depth and decreased to 4 nM in the bottom layer. In the Yamato Basin, concentration of labile dissolved iron in deep water increased uniformly and was about 6 nM at the bottom layer. The difference in distribution of iron in seawater indicates that the transport processes of biogenic elements in the deep layers are different between the basins of the Japan Sea.

Oral presentation

Estimation of volume transport of the Tsugaru throughflow based on the shipboard ADCP measurement; Result of the observation during 2000-2002

Ito, Toshimichi; Kawamura, Hideyuki; Nakayama, Tomoharu*; Shima, Shigeki*; Isoda, Yutaka*; Onishi, Mitsuyo*

no journal, , 

no abstracts in English

Oral presentation

Vertical profile of DOC-14 in the Japan Sea

Tanaka, Takayuki; Otosaka, Shigeyoshi; Amano, Hikaru; Togawa, Orihiko; Senju, Tomoharu*; Isoda, Yutaka*; Kuma, Kenshi*

no journal, , 

no abstracts in English

Oral presentation

Temporal variation of volume transport in the Tsugaru strait; An Estimation from the ADCP observation between 2000 and 2002

Ito, Toshimichi; Kawamura, Hideyuki; Nakayama, Tomoharu*; Shima, Shigeki*; Onishi, Mitsuyo*; Isoda, Yutaka*

no journal, , 

The volume transport through the Tsugaru Strait, which was estimated from ADCP observation data, in the period between Apr. 2000 and Jun. 2002 was examined. Through the analysis, following features were elucidated: (1) The range of volume transport with mean value, (2) The prevailing periods in the variation, (3) the correlation with the sea level differences (along and across direction of the Strait) and its seasonal dependency, and (4) relationships with the Tsushima Warm Current.

Oral presentation

Temporal variation of volume transport in the Tsugaru Strait, 2; An Estimation from the ADCP observation between 2002-2004

Ito, Toshimichi; Kawamura, Hideyuki; Nakayama, Tomoharu*; Shima, Shigeki*; Onishi, Mitsuyo*; Isoda, Yutaka*

no journal, , 

During Nov. 1999-Dec. 2007, JAEA carried out an observation of the Tsugaru Strait Throghflow using a ship-board Acoustic Doppler Current Profiler with voluntary cooperation by Higashi-Nihon Ferry Co. Ltd.,. From the analysis of volume transports estimated at 20 current monitoring points, it is elucidated in the period between Apr. 2002 and Mar. 2004 that; (1) most of the transport occurred in the part of the opening mouth of the strait, (2) in the area south of the main stream, west of Shimokita Peninsular, a topographically generated returning flow system was established by the wake of Shimokita Peninsular and a part of its volume transport was expected to join together with the transport of main stream, and (3) the minimum appeared in spring while the maximum was in fall showing significant amplitude of variation with 20-30 days period. The volume transport in this period varied in the range 0.5-1.8 Sv (1 Sv = 1$$times$$10$$^{6}$$ m$$^{3}$$ s$$^{-1}$$) and the mean transport was estimated to 1.2 $$pm$$ 0.2 Sv, slightly smaller than previously reported value.

Oral presentation

Throughflow in the Tsugaru Strait; Variation of volume transport and its mechanism

Ito, Toshimichi; Kawamura, Hideyuki; Onishi, Mitsuyo*; Isoda, Yutaka*; Nakayama, Tomoharu*; Shima, Shigeki*

no journal, , 

The results of JAEA's observation and study on the throughflow in the Tsugaru Strait is reviewed for the period of Apr. 2000 - Jun. 2002. In this period, the volume transport varied in the range of 0.6-2.5 Sv (10$$^{6}$$m$$^{3}$$s$$^{-1}$$) with mean value of 1.3$$pm$$0.3 Sv. The transport showed the maximum around autumn. Additionally, the variability with period of 20-30 days was observed. The variation was closely connected with that of sea-level difference arround the strait and correlation between the both more significant in wintertime implying the effect of baroclinic velocities became small. The transport is also connected with that in the Tsushima Strait with delay of 4 months in maximum. The transport in Tsugaru Strait corresponded 40-50% of that in the Tsushima Strait. It is required to elucidate the effect of wind and/or stratification on the transport and to study the variation with 20-30 days period.

Oral presentation

Variation of volume transport in the Tsugaru Strait; An Estimation based on ADCP observation in the period of 2002-2004

Ito, Toshimichi; Kawamura, Hideyuki; Nakayama, Tomoharu*; Shima, Shigeki*; Onishi, Mitsuyo*; Isoda, Yutaka*

no journal, , 

We had measured the 3-D velocity distribution of throughflow in the Tsugaru Strait during Nov. 1999 and Dec. 2007. In this observation, an ADCP (RDI, 150 kHz) had been mounted on the bottom of voluntary ferry (VIRGO, Higashi-nihon Ferry co. ltd.,) regularly operated in the strait. Main results of the observation for the period of Apr. 2002-Mar. 2004 are as follows; (1) velocity distribution was elucidated, (2) volume transport of the throughflow ranged 0.77-1.80 Sv (1Sv=1$$times$$10$$^{6}$$ m$$^{3}$$s$$^{-1}$$) and its mean was 1.30 Sv with standard deviation 0.24 Sv, (3) the volume transport showed relatively weak seasonal variation and relatively strong periodicity with period of 20-30 days, (4) the variation was controlled by sea level difference around the strait, and (5) mean volume transport for in this period, in which missing data were filled using sea level difference data around the strait, was estimated to be 1.34$$pm$$0.24 Sv.

Oral presentation

Circulation and properties of deepwater in the Japan Sea inferred from distribution of multiple tracers

Aramaki, Takafumi*; Otosaka, Shigeyoshi; Takahata, Naoto*; Isoda, Yutaka*; Kuma, Kenshi*; Senju, Tomoharu*

no journal, , 

Deep part of the Japan Sea ($$>$$ 2000m depth) consists of seawater with uniform salinity and temperature. This structure complicated us to understand the transport processes of the deepwater circulation in the sea. By the Japan Sea Expeditions carried out by JAEA from 1997 to 2002, the authors measured isotopic ratio of radiocarbon in seawater as a tracer of seawater movement. As a result, it has been inferred that the deep water is formed in the plural regions of the sea and that the northwestern region is primary region of deep water formation. In the present study, we obtained data of tritium concentration and isotopic ratio of helium as additional indicators, and discussed the detailed deepwater circulation to describe another origin of the deep water.

Oral presentation

Variation of volume transport in the Tsugaru Strait; An Estimation for the years 2004-2007

Ito, Toshimichi; Kawamura, Hideyuki; Onishi, Mitsuyo*; Isoda, Yutaka*; Nakayama, Tomoharu*; Shima, Shigeki*

no journal, , 

no abstracts in English

Oral presentation

Variation of volume transport of Tsugaru Strait throughflow

Ito, Toshimichi; Kawamura, Hideyuki; Onishi, Mitsuyo*; Isoda, Yutaka*; Nakayama, Tomoharu*; Shima, Shigeki*

no journal, , 

no abstracts in English

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