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Tamiji Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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The Seto Inland Sea––eutrophic or oligotrophic?
Marine Pollution Bulletin, 2020Co-Authors: Tamiji YamamotoAbstract:The present water quality conditions in the Seto Inland Sea of Japan are described along with an historical background before and after the measures taken to reduce eutrophication. The directive to reduce phosphorus discharge into this area was very effective, reducing the number of red tides from about 300 cases per year at their peak in 1976 to the recent level of about 100 cases per year, indicating the improvement of Seawater quality. However, the hastiness of the measures taken to reduce phosphorous seems to have led to a depletion of dissolved inorganic phosphorus that is an essential nutrient for the growth of phytoplankton. Fishery production has also decreased with the reduction of phosphorus, showing a time lag, and the relationship between them shows a hysteresis-like pattern indicating that the condition of fishery production is currently in a critical stage of collapse. This implies that the phosphorus reduction could have lowered the phytoplankton primary production and also caused a detrimental effect on the fishery production. Noteworthy is the change in the phytoplankton species composition. The dominant species that form red tides have changed from non-harmful diatoms to harmful raphidophytes in the eutrophication process and then finally to harmful/toxic dinoflagellates in the oligotrophication process. This indicates that the measures to reduce phosphorus have caused a change in phytoplankton species composition, thereby altering the food web structure, suggesting that this might be the major cause of the reduction of fishery production. In conclusion, the Seto Inland Sea of Japan is apparently in an oligotrophic condition, and it could be said to be in the state of ‘‘cultural oligotrophication’’ caused by the hasty reduction of phosphorus loading. Dam construction, as another possible cause of the cultural oligotrophication, is also discussed, and evidence relating to the existence of numerous dams in this area is also shown. Stress is placed on the regulation of the level of nutrients and their elemental ratio in the Seawater, because these factors are considered to be effective in preventing the generation of harmful algae and in sustaining the fishery production through preservation of the natural environment. A proposal is also described regarding howthese factors could be controlled. 2003 Elsevier Science Ltd. All rights reserved.
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An estimation of net ecosystem metabolism and net denitrification of the Seto Inland Sea, Japan
Ecological Modelling, 2008Co-Authors: Tamiji Yamamoto, Naoyuki Hiraga, Kuniaki Takeshita, Toshiya HashimotoAbstract:Abstract Net ecosystem metabolism (NEM) and net denitrification (ND) of the Seto Inland Sea were estimated from monthly budgets of dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN) according to the method proposed by the Land Ocean Interaction in the Coastal Zones (LOICZ) Working Group. In the model, the Seto Inland Sea was separated into 16 boxes in terms of geographic features (eight regions) and was vertically stratified into two layers. Monthly computation of the DIP budget revealed that the regional characteristics of each strait and basin reflected the hydrography, geography and vegetation of each box. The amount of particulate phosphorus (PP) formed from DIP was estimated to be 12.2 t P year−1, which accounted for 99.6% of the total DIP load. This indicates that the Seto Inland Sea is a very efficient system in terms of the transfer efficiency of material. By converting the amount of formed PP to carbon, the NEM of the Seto Inland Sea was estimated to be 0.08 g C m−2 day−1 (0.47 Mt C year−1 for the whole area), which accounted for about 12% of the reported primary production. The net denitrification of the Seto Inland Sea was estimated from the difference between the DIP budget and the DIN budget. Particulate nitrogen formed from DIN was ca. 50% (88 × 103 t N year−1), and the remaining 50% was estimated to be released to the air by the denitrification process.
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the seto Inland Sea eutrophic or oligotrophic
Marine Pollution Bulletin, 2003Co-Authors: Tamiji YamamotoAbstract:The present water quality conditions in the Seto Inland Sea of Japan are described along with an historical background before and after the measures taken to reduce eutrophication. The directive to reduce phosphorus discharge into this area was very effective, reducing the number of red tides from about 300 cases per year at their peak in 1976 to the recent level of about 100 cases per year, indicating the improvement of Seawater quality. However, the hastiness of the measures taken to reduce phosphorous seems to have led to a depletion of dissolved inorganic phosphorus that is an essential nutrient for the growth of phytoplankton. Fishery production has also decreased with the reduction of phosphorus, showing a time lag, and the relationship between them shows a hysteresis-like pattern indicating that the condition of fishery production is currently in a critical stage of collapse. This implies that the phosphorus reduction could have lowered the phytoplankton primary production and also caused a detrimental effect on the fishery production. Noteworthy is the change in the phytoplankton species composition. The dominant species that form red tides have changed from non-harmful diatoms to harmful raphidophytes in the eutrophication process and then finally to harmful/toxic dinoflagellates in the oligotrophication process. This indicates that the measures to reduce phosphorus have caused a change in phytoplankton species composition, thereby altering the food web structure, suggesting that this might be the major cause of the reduction of fishery production. In conclusion, the Seto Inland Sea of Japan is apparently in an oligotrophic condition, and it could be said to be in the state of ‘‘cultural oligotrophication’’ caused by the hasty reduction of phosphorus loading. Dam construction, as another possible cause of the cultural oligotrophication, is also discussed, and evidence relating to the existence of numerous dams in this area is also shown. Stress is placed on the regulation of the level of nutrients and their elemental ratio in the Seawater, because these factors are considered to be effective in preventing the generation of harmful algae and in sustaining the fishery production through preservation of the natural environment. A proposal is also described regarding howthese factors could be controlled. 2003 Elsevier Science Ltd. All rights reserved.
Akira Hoshika - One of the best experts on this subject based on the ideXlab platform.
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carbon sources for demersal fish in the western seto Inland Sea japan examined by δ13c and δ15n analyses
Limnology and Oceanography, 2002Co-Authors: Noriyuki Takai, Yasufumi Mishima, Akemi Yorozu, Akira HoshikaAbstract:The relative importance of benthic and pelagic primary production for demersal fish and some invertebrates in the western Seto Inland Sea of Japan was examined using carbon and nitrogen stable isotope analyses. A few fishes, such as juvenile black rockfish Sebastes inermis and large Japanese anchovies Engraulis japonicus, had isotopic carbon signatures similar to pelagic particulate organic matter ( 220.1 6 1.7‰), which indicates that their food was derived from production in the water column. However, 92% of the 401 demersal fish that were analyzed hadd 13 C signatures (217.0 to 213.0‰) similar to those of benthic crustaceans, epilithic microphytobenthos, and macroalgae and unlike the signature of pelagic particulate organic matter or zooplankton. These results suggest that in the Seto Inland Sea there is not a tight coupling between pelagic primary production and the food web of demersal fishes, but rather that these fishes are dependent on carbon from benthic primary production.
Hiroshi Sakugawa - One of the best experts on this subject based on the ideXlab platform.
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Determination of Daytime Flux of Nitric Oxide Radical (NOâ¢) at an Inland Sea-Atmospheric Boundary in Japan
2020Co-Authors: Adebanjo Jacob Anifowose, Hiroshi SakugawaAbstract:The flux of nitric oxide radical (NO•) during the daytime at the Seto Inland Seaatmosphere boundary was measured during the Sea cruises embarked upon in September, 2013 and June, 2014. Atmospheric concentration of NO• over the Seto Inland Sea and that present in the Sea surface were measured. Results showed that average atmospheric NO• concentrations measured over the Inland Sea in 2013 and 2014 were 4.4 × 10-10 and 5.2 × 10-10 atm, respectively. Also during the cruises, average wind speed of 2.0 and 3.2 m s-1 were measured in 2013 and 2014, respectively. In the surface Seawater, the average NO• concentrations measured were 2.1 × 10-11 and 1.9 × 10-11 mol NO• L-1 in 2013 and 2014, respectively. Using appropriate formula, a daytime efflux of 0.22 pmol NO• m-2 s-1 from the Sea to the atmosphere was estimated for the two year-study. Assuming 8 h of solar intensity per day, about 1.54 × 106 g NO• y-1 efflux from the 23,000 km2 Seto Inland Sea surface was determined. The study confirmed that, during the day, Sea could be an additional source of NO• to the atmosphere.
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distribution and source estimation of polycyclic aromatic hydrocarbons in coastal sediments from seto Inland Sea japan
Environmental Chemistry, 2020Co-Authors: Hiroaki Tsuji, Kazuhiko Takeda, Satoshi Asaoka, Waqar Azeem Jadoon, Yoko Nunome, Hideo Yamazaki, Hiroshi SakugawaAbstract:Environmental context Polycyclic aromatic hydrocarbons are carcinogenic environmental contaminants that tend to migrate into the sediments in oceans and Seas. Their vertical distribution in sediments from the Seto Inland Sea matched their emission over time, which in turn reflected changes in energy sources and industrial activities in Japan. This study shows that human activities on land directly and significantly influence the concentration of polycyclic aromatic hydrocarbons in sediments. Abstract Seventeen polycyclic aromatic hydrocarbons (PAHs) were identified in sediment cores collected at several locations in the Seto Inland Sea in 2015 and 2016 to understand their spatial distribution and potential emission sources. PAHs were analysed using gas chromatography–mass spectrometry. The age of the sediment cores was analysed using radioisotopic dating techniques to reconstruct historical PAH emissions. The total concentrations of 17 PAHs in the sediment cores of Osaka Bay in 2015 were in the range of 108–2810 ng g−1 dry weight (dw) with a mean concentration of 1050 ng g−1 dw. The total concentrations of 17 PAHs in sediment cores from the Seto Inland Sea in 2016 were in the range of 52.6–941 ng g−1 dw with a mean concentration of 313 ng g−1 dw. The spatial distribution of PAHs showed the highest concentration in Osaka Bay and the lowest in Kii Channel in 2016. The horizontal PAH distribution showed a decreasing trend in concentrations from the estuary offshore to Osaka Bay and Aki-Nada. The vertical PAH distribution revealed that levels were higher before the 1980s–1990s, when oil consumption and industrial activities in the Osaka region reached a maximum in the 20th century. The diagnostic ratios of PAHs and a principal component analysis revealed three main emission sources of PAHs, industry, biomass burning and traffic activities.
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Carbaryl residue concentrations, degradation, and major sinks in the Seto Inland Sea, Japan
Environmental Science and Pollution Research, 2020Co-Authors: Aly Derbalah, Russel Chidya, Chikumbusko Kaonga, Yoko Iwamoto, Kazuhiko Takeda, Hiroshi SakugawaAbstract:The fate of carbaryl in the Seto Inland Sea (west Japan) was predicted using a mass distribution model using carbaryl concentrations in river and Sea water samples, degradation data, and published data. The predicted carbaryl concentrations in water in Kurose River and the Seto Inland Sea were 4.320 and 0.2134 μg/L, respectively, and the predicted concentrations in plankton, fish, and sediment were 0.4140, 2.436, and 1.851 μg/g dry weight, respectively. The carbaryl photodegradation and biodegradation rates were higher for river water (0.330 and 0.029 day^−1, respectively) than Sea water (0.23 and 0.001 day^−1, respectively). The carbaryl photodegradation rates for river and Sea water (0.33 and 0.23 day^−1, respectively) were higher than the biodegradation rates (0.029 and 0.001 day^−1, respectively). The hydrolysis degradation rate for carbaryl in Sea water was 0.003 day^−1, and the half-life was 231 days. Land (via rivers) was the main source of carbaryl to the Seto Inland Sea. The model confirmed carbaryl is distributed between sediment, plankton, and fish in the Seto Inland Sea. Degradation, loss to the Open Ocean, and sedimentation are the main carbaryl sinks in the Seto Inland Sea, accounting for 43.81, 27.90, and 17.68%, respectively, of total carbaryl inputs. Carbaryl source and sink data produced by the model could help in the management of the negative impacts of carbaryl on aquatic systems and human health.
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occurrence of diuron and irgarol in Seawater sediments and planktons of seto Inland Sea japan
Geochemical Journal, 2012Co-Authors: Sarangaraja Balakrishnan, Kazuhiko Takeda, Hiroshi SakugawaAbstract:Copyright © 2012 by The Geochemical Society of Japan. but may have a potential to impact the coastal ocean via surface runoff due to their solubility (Lamoree et al., 2002). Diuron (3-[3,4-dichlorophenyl]-1,1-dimethylurea) is an herbicide derived from urea that is considered to be a priority hazardous substance by the European commission (Malato et al., 2002). Accordingly, countries including the UK, Sweden, Denmark and France have restricted the use of Diuron in antifouling paints (Konstantinou and Albanis, 2004). In Japan, Diuron has long been used in agricultural and other activities, and a large amount of Diuron discharged into river water has been transported into the Seto Inland Sea with little or no degradation (Sakugawa et al., 2010). Furthermore, extensive quantities of Diuron are used as antifouling paints by the shipping industry and the highest concentration occurred in Seawater of Japan was 3.05 μg/L (Okamura et al., 2003). In addition urban areas of Okinawa Island, Japan apply a significant amount of Diuron as a weed control (Kitada et al., 2008). Irgarol (2-[tert-butylamino]-4-[cyclopropylamino]-6[methylthio]-1,3,5-triazine) is a protective algaecide widely used in antifouling paints and has a wide range of action against a number of algal organisms. Irgarol belongs to the s-triazine group of compounds, which act as photosystem-II (PSII) inhibitors, with the inhibition of photosynthetic electron capture transport in chloroplasts as their biochemical mode of action (Dahl and Blanck, 1996). Okamura et al. (2003) found the highest concenOccurrence of Diuron and Irgarol in Seawater, sediments and planktons of Seto Inland Sea, Japan
Kazuhiko Takeda - One of the best experts on this subject based on the ideXlab platform.
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distribution and source estimation of polycyclic aromatic hydrocarbons in coastal sediments from seto Inland Sea japan
Environmental Chemistry, 2020Co-Authors: Hiroaki Tsuji, Kazuhiko Takeda, Satoshi Asaoka, Waqar Azeem Jadoon, Yoko Nunome, Hideo Yamazaki, Hiroshi SakugawaAbstract:Environmental context Polycyclic aromatic hydrocarbons are carcinogenic environmental contaminants that tend to migrate into the sediments in oceans and Seas. Their vertical distribution in sediments from the Seto Inland Sea matched their emission over time, which in turn reflected changes in energy sources and industrial activities in Japan. This study shows that human activities on land directly and significantly influence the concentration of polycyclic aromatic hydrocarbons in sediments. Abstract Seventeen polycyclic aromatic hydrocarbons (PAHs) were identified in sediment cores collected at several locations in the Seto Inland Sea in 2015 and 2016 to understand their spatial distribution and potential emission sources. PAHs were analysed using gas chromatography–mass spectrometry. The age of the sediment cores was analysed using radioisotopic dating techniques to reconstruct historical PAH emissions. The total concentrations of 17 PAHs in the sediment cores of Osaka Bay in 2015 were in the range of 108–2810 ng g−1 dry weight (dw) with a mean concentration of 1050 ng g−1 dw. The total concentrations of 17 PAHs in sediment cores from the Seto Inland Sea in 2016 were in the range of 52.6–941 ng g−1 dw with a mean concentration of 313 ng g−1 dw. The spatial distribution of PAHs showed the highest concentration in Osaka Bay and the lowest in Kii Channel in 2016. The horizontal PAH distribution showed a decreasing trend in concentrations from the estuary offshore to Osaka Bay and Aki-Nada. The vertical PAH distribution revealed that levels were higher before the 1980s–1990s, when oil consumption and industrial activities in the Osaka region reached a maximum in the 20th century. The diagnostic ratios of PAHs and a principal component analysis revealed three main emission sources of PAHs, industry, biomass burning and traffic activities.
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Carbaryl residue concentrations, degradation, and major sinks in the Seto Inland Sea, Japan
Environmental Science and Pollution Research, 2020Co-Authors: Aly Derbalah, Russel Chidya, Chikumbusko Kaonga, Yoko Iwamoto, Kazuhiko Takeda, Hiroshi SakugawaAbstract:The fate of carbaryl in the Seto Inland Sea (west Japan) was predicted using a mass distribution model using carbaryl concentrations in river and Sea water samples, degradation data, and published data. The predicted carbaryl concentrations in water in Kurose River and the Seto Inland Sea were 4.320 and 0.2134 μg/L, respectively, and the predicted concentrations in plankton, fish, and sediment were 0.4140, 2.436, and 1.851 μg/g dry weight, respectively. The carbaryl photodegradation and biodegradation rates were higher for river water (0.330 and 0.029 day^−1, respectively) than Sea water (0.23 and 0.001 day^−1, respectively). The carbaryl photodegradation rates for river and Sea water (0.33 and 0.23 day^−1, respectively) were higher than the biodegradation rates (0.029 and 0.001 day^−1, respectively). The hydrolysis degradation rate for carbaryl in Sea water was 0.003 day^−1, and the half-life was 231 days. Land (via rivers) was the main source of carbaryl to the Seto Inland Sea. The model confirmed carbaryl is distributed between sediment, plankton, and fish in the Seto Inland Sea. Degradation, loss to the Open Ocean, and sedimentation are the main carbaryl sinks in the Seto Inland Sea, accounting for 43.81, 27.90, and 17.68%, respectively, of total carbaryl inputs. Carbaryl source and sink data produced by the model could help in the management of the negative impacts of carbaryl on aquatic systems and human health.
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Persistent organic pollutants are still present in surface marine sediments from the Seto Inland Sea, Japan.
Marine Pollution Bulletin, 2019Co-Authors: Satoshi Asaoka, Akira Umehara, Yuki Haga, Chisato Matsumura, Ryosuke Yoshiki, Kazuhiko TakedaAbstract:Abstract Although persistent organic pollutants (POPs) are currently banned or strictly controlled under the Stockholm Convention on Persistent Organic Pollutants, POPs are still distributed worldwide due to their environmental persistence, atmospheric transport, and bioaccumulation. Herein we investigated the current concentrations of POPs in the sediments from Seto Inland Sea, Japan and sought to clarify the factors currently controlling the POPs concentration of the surface sediments from Seto Inland Sea. The concentrations of hexachlorocyclohexane isomers (HCHs), dichlorodiphenyltrichloroethane and its metabolites (DDTs), and chlordane isomers (CHLs) in sediments from Seto Inland Sea were
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The Iodide and Iodate Distribution in the Seto Inland Sea, Japan
Aquatic Geochemistry, 2017Co-Authors: Kazuhiko Takeda, Kengo Yamane, Yuuta HoriokaAbstract:We report the vertical and horizontal distributions of inorganic iodine (iodide and iodate) and their related species (bromide nitrate and nitrite) in the Seto Inland Sea, which is a semi-enclosed coastal Sea area of western Japan. In this study, ion chromatography with ultraviolet detection was employed to determine the iodide, iodate, bromide nitrate, and nitrite levels simultaneously in a single run. Iodide was higher at inshore sites than at offshore sites. Vertical profiles showed that iodide increased in the bottom layer of inshore sites of Osaka Bay and Hiroshima Bay, but were low in the bottom layer of the Kii Channel, the main channel connecting Osaka Bay with the Pacific Ocean. Iodates were low in the low-salinity inshore surface, but were high in the bottom layer of the Kii Channel. The riverine flux of iodine to the coastal marine environment was negligible. The vertical profiles of total inorganic iodine (iodide + iodate) looked uniform; however, plots of total inorganic iodine versus salinity demonstrated a net loss of total inorganic iodine in the low-salinity inshore surface. The iodine distributions in the Seto Inland Sea could be explained by three-end-member mixing, with one member being non-iodine river water, another high-salinity and high-iodate water of the open ocean, and the final high-iodide and low-iodate Inland water with a salinity of around 32–33.
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occurrence of diuron and irgarol in Seawater sediments and planktons of seto Inland Sea japan
Geochemical Journal, 2012Co-Authors: Sarangaraja Balakrishnan, Kazuhiko Takeda, Hiroshi SakugawaAbstract:Copyright © 2012 by The Geochemical Society of Japan. but may have a potential to impact the coastal ocean via surface runoff due to their solubility (Lamoree et al., 2002). Diuron (3-[3,4-dichlorophenyl]-1,1-dimethylurea) is an herbicide derived from urea that is considered to be a priority hazardous substance by the European commission (Malato et al., 2002). Accordingly, countries including the UK, Sweden, Denmark and France have restricted the use of Diuron in antifouling paints (Konstantinou and Albanis, 2004). In Japan, Diuron has long been used in agricultural and other activities, and a large amount of Diuron discharged into river water has been transported into the Seto Inland Sea with little or no degradation (Sakugawa et al., 2010). Furthermore, extensive quantities of Diuron are used as antifouling paints by the shipping industry and the highest concentration occurred in Seawater of Japan was 3.05 μg/L (Okamura et al., 2003). In addition urban areas of Okinawa Island, Japan apply a significant amount of Diuron as a weed control (Kitada et al., 2008). Irgarol (2-[tert-butylamino]-4-[cyclopropylamino]-6[methylthio]-1,3,5-triazine) is a protective algaecide widely used in antifouling paints and has a wide range of action against a number of algal organisms. Irgarol belongs to the s-triazine group of compounds, which act as photosystem-II (PSII) inhibitors, with the inhibition of photosynthetic electron capture transport in chloroplasts as their biochemical mode of action (Dahl and Blanck, 1996). Okamura et al. (2003) found the highest concenOccurrence of Diuron and Irgarol in Seawater, sediments and planktons of Seto Inland Sea, Japan
Tadashi Hibino - One of the best experts on this subject based on the ideXlab platform.
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INTER-ANNUAL FLUCTUATION OF WATER QUALITY IN SETO Inland Sea: RELATIONSHIP WITH Sea LEVELS AT THE ENTRANCES OF THE Inland Sea
Coastal Engineering Journal, 2020Co-Authors: Tadashi Hibino, Katsuyoshi ShimizuAbstract:The comprehensive water quality survey in the Seto Inland Sea has been operated by the Ministry of Land, Infrastructure and Transport (MLIT), Japan. The water quality survey Program was established for the purpose of making data sets available to know actual conditions of water pollution, and to generate products that would be valuable for scientific analysis of climate-related processes. The program started in May 1981. Water qualities (salinity, water temperature, DO, pH, turbidity and clearness) were observed in February, May, August and October. The observations were carried out at 200 points (142 points in 1989–1999) located on 8 km × 8 km grid. We examined the physical factors affecting inter-annual and Seasonal changes in water quality of the Seto Inland Sea by using the data (salinity, temperature, Sea level etc.) measured/collected by several institutions, mainly MLIT and JMA (Japan Meteorological Agency). From the present study, it is revealed that the water mass inside the Inland Sea is strongl...
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Influence of Kuroshio Path on Salinity Distribution in Seto Inland Sea
Journal of Coastal Research, 2018Co-Authors: Shinya Nakashita, Tadashi HibinoAbstract:Nakashita, S.; Woo, H.; Kim, K.; Kim, K.; Lee, I.-C.; Kim, D.-S., and Hibino, T., 2018. Influence of Kuroshio path on Salinity distribution in Seto Inland Sea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal ReSearch, Special Issue No. 85, pp. 21–25. Coconut Creek (Florida), ISSN 0749-0208.This study analyzes residual current and salinity distribution in Seto Inland Sea induced by Kuroshio Path variation. The salinity ranged 30 - 34 PSU and it decreased by approximately 1 - 2 PSU at near center of Bisanseto during non-meandering period. Sea level height variations at both boundary of Seto Inland Sea which induces residual current mainly depends on distance between boundaries and Kuroshio Path because of higher Sea level hight at Kuroshio path than than that at northern part of Kuroshio path approximately 1 m. Westward residual flow during the non-meandering period (year 1997) was estimated to be faster than that during the meandering period with maximum relative velocity of 4.5 cm/sec. Decrease of salinity at near center of Bisanseto is due to the westward movement of the river water plume from the eastern Bisanseto. From the results obtained above, it is concluded that location of low salinity water at Bisanseto is mainly depends on the residual current due to variation of Kuroshio Path.
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ESTIMATION OF MEAN Sea LEVEL IN SETO Inland Sea
PROCEEDINGS OF HYDRAULIC ENGINEERING, 2001Co-Authors: Tadashi Hibino, Katsuaki Komai, Tadashi AsaiAbstract:In this analysis, Seto Inland Sea level is defined as the standard Sea level of reference datum during zero Sea level gradientbetween North Pacific and West Pacific, and zero atmospheric pressure gradient in North West Pacific Ocean.Based on the assumption, the difference between Seto Inland Sea level and Pacific Ocean level depends on the summation oftwo components of Sea level fluctuation; such as, local atmospheric pressure gradient and Sea water density. It seems reasonable tosuppose that the mean Sea level in Seto Inland Sea can be estimated by global Sea level fluctuation.It is concluded that the Sea level fluctuation in Seto Inland Sea is mainly caused by variation of Sea water density during winter, and by Sea water exchange during summer. The mean Sea level in Seto Inland Sea is lower than that of the Pacific Ocean, especially in Kii Channel and Suo Sea of Seto Inland Sea.