2005 Fiscal Year Final Research Report Summary
Impacts of freshwater originating from the Changjiang discharge flowing from the East China Sea on the thermohaline circulation in the Japan Sea
| Project/Area Number |
15540422
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
SENJYU Tomoharu Kyushu University, Research Institute for Applied Mechanics, Associate Professor, 応用力学研究所, 助教授 (60335982)
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| Co-Investigator(Kenkyū-buntansha) |
MORIMOTO Akihiko Nagoya University, Hydrospheric Atmospheric Research Center, Associate Professor, 地球水循環研究センター, 助教授 (80301323)
ONITSUKA Goh National Fisheries University, Department of Fishery Information and Management, Research associate, 水産情報経営学科, 助手 (40399647)
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| Project Period (FY) |
2003 – 2005
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| Keywords | Tsusuma Strait / low salinity water / Changjiang discharge / interannual variability / Japan Sea / Japan Sea Proper Water / deep circulation |
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| Research Abstract |
1.Salinity variation in the Tsushima Strait
(1)Interannual salinity variations in the Tsushima Strait were investigated based on the historical observation data. The EOF analysis revealed that the most dominant mode is the in-phase variation between the eastern and western channels. This mode correlates with the Changjiang discharge variation, and salinity in the strait tends to decrease over summer related to a large discharge of the Changjiang. The multi-regression model to estimate the Changjiang discharge from precipitation anomalies was developed.
(2)An observation of surface temperature and salinity was carried out by a TS-meter moored at Futaoi Island in the Tsushima Strait in 2004-2005. Salinity shows a clear seasonal variation with a rapid decrease in mid-July and a minimum in mid-August in each year. However, salinity in 2005 decreased faster than that in 2004 by about 20 days and the minimum in 2005 was lower than that in 2004 by 1-2 psu. The TS-meter records suggest a periodic passage of water masses with a higher temperature and lower salinity in the strait in June-July.
2.Thermohaline circulation in the Japan Sea
(1)The abyssal circulation in the Japan Sea was investigated based on the direct current measurements. The distribution of mean flow vectors indicates relatively strong cyclonic circulations along the basin periphery. In contrast, sluggish mean flows are found in the interior region because of eddy motions dominancy.
(2)The Yamato Basin Bottom Water (YBBW) exhibits higher temperature and lower dissolved oxygen than those in the Japan Basin Bottom Water (JBBW). Both bottom waters meet around the boundary between the Yamato and Japan Basins, forming a clear benthic front. The YBBW is the modified JBBW flowing into the Yamato Basin. A box-model estimated the turnover time and vertical diffusivity for the YBBW as 9.1 years and 3.4×10^<-3> m^<-3>s^<-1>, respectively.
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