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Journal Articles

$$delta^{13}$$C and $$delta^{15}$$N values of sediment-trap particles in the Japan and Yamato Basins and comparison with the core-top values in the East/Japan Sea

Khim, B.-K.*; Otosaka, Shigeyoshi; Park, K.-A.*; Noriki, Shinichiro*

Ocean Science Journal, 53(1), p.17 - 29, 2018/03

 Times Cited Count:1 Percentile:79(Marine & Freshwater Biology)

Distribution of carbon and nitrogen stable isotope ratios ($$delta$$$$^{13}$$C, $$delta$$$$^{15}$$N) in sinking particles collected in four stations in the Japan Sea was summarized. The $$delta$$$$^{13}$$C and $$delta$$$$^{15}$$N values in the sinking particles showed a clear seasonal variation, which agreed well with the variation in the chlorophyll a concentration in the surface seawater and in the sinking flux of biogenic particles. In particular, during the highly productive season of phytoplankton, a remarkable isotopic fractionation of $$delta$$$$^{13}$$N was found in the sinking particles, and it was inferred that the fractionation indicates the degree of nitrogen uptake by diatoms in the surface layer. These results are helpful information for linking the phenomenon in the ocean surface and the isotopic information recorded in the seafloor.

Journal Articles

Sediment trap record of alkenones from the East Sea (Japan Sea)

Lee, K. E.*; Khim, B.-K.*; Otosaka, Shigeyoshi; Noriki, Shinichiro*

Organic Geochemistry, 42(3), p.255 - 261, 2011/03

 Times Cited Count:13 Percentile:52.99(Geochemistry & Geophysics)

Long chain (C$$_{37}$$) alkenones in sinking particles obtained from the northeastern and the southern regions of the Japan Sea were examined to investigate the characteristics of production, export, and degradation of organic materials in the water column. A comparison of alkenone temperatures with satellite sea surface temperatures (SST) revealed that the alkenone temperatures were higher (6-13 $$^{circ}$$C) than SST during winter time, and lower (2-5 $$^{circ}$$C) during summer time. It indicated that there was a time lag between the SST and the trap records (about 3 months in winter and 1 month in summer). But, the annual average alkenone temperatures are close to annual average SST in the Yamato Basin. The reasons for this time lag can be (1) subsurface production of alkenones in summer and (2) slow settling velocity and long residence time of alkenones in the upper water column especially during winter time.

Journal Articles

Deep sea circulation of particulate organic carbon in the Japan Sea

Otosaka, Shigeyoshi; Tanaka, Takayuki; Togawa, Orihiko; Amano, Hikaru; Karasev, E. V.*; Minakawa, Masayuki*; Noriki, Shinichiro*

Journal of Oceanography, 64(6), p.911 - 923, 2008/12

 Times Cited Count:15 Percentile:61.3(Oceanography)

Transport processes of particulate organic carbon (POC) were inferred from sediment trap experiments in the three regions of the Japan Sea (western and eastern Japan Basin and Yamato Basin) and radiocarbon measurement. Annual mean $$^{14}$$C/$$^{12}$$C isotopic ratio decreased with depth and the vertical changes in the isotopic signature were considered to indicate mixing of two fractions; labile POC produced in the surface and refractory POC. From seasonal variations of POC flux of the two fractions, transport processes of POC in the Japan Sea were summarized as follows: (1) In the Japan Basin, both labile and refractory POC were supplied in spring and a reservoir of refractory POC was formed, and (2) in the Yamato Basin, larger amount of refractory POC were carried the interior and accumulated rapidly.

Journal Articles

Relationship between composition of settling particles and organic carbon flux in the western North Pacific and the Japan Sea

Otosaka, Shigeyoshi; Noriki, Shinichiro*

Journal of Oceanography, 61(1), p.25 - 40, 2005/01

 Times Cited Count:22 Percentile:50.69(Oceanography)

Settling particles play an important role in transport of organic carbon from the surface to the deep ocean. It is known that major components of settling particles are biogenic silicates (opal), biogenic carbonate, lithogenic clays and organic matters. In this study, we estimated organic carbon fluxes that are carried by each component in the western North Pacific Ocean (WNP) including the Japan Sea. Mean organic carbon flux at 1 km depth in the WNP (13.5 mg/m$$^{2}$$/day) was larger than that in the Eastern North Pacific (7.4), central North Pacific (1.1), Equatorial Pacific (4.2), Southern Ocean (5.8) and Eastern North Pacific (1.8). In the WNP, opal was a dominant component and 55 % of particulate organic carbon was carried by opal particles. Opal is known as a major component even in the Eastern North Pacific and Southern Ocean and opal fluxes in these areas are as much as in the WNP. However, organic carbon flux that was carried by opal particles in the WNP was significantly larger than that in the Eastern North Pacific and the Southern Ocean. It was cleared that opal particles in the WNP had great abilities not only to activate the biological pump in the surface ocean but also to transport organic carbon to the deep ocean.

Journal Articles

Lithogenic flux in the Japan Sea measured with sediment traps

Otosaka, Shigeyoshi; Togawa, Orihiko; Baba, Masami*; Karasev, E.*; Volkov, Y. N.*; Omata, Nobutaka*; Noriki, Shinichiro*

Marine Chemistry, 91(1-4), p.143 - 163, 2004/11

 Times Cited Count:32 Percentile:33.15(Chemistry, Multidisciplinary)

Spatial and temporal variations of particulate flux were observed by sediment trap experiments at three areas of the Japan Sea (western Japan Basin, eastern Japan Basin and Yamato Basin) during 1999-2002. Mass flux in the Japan Sea showed remarkable regional distribution. Annual mean mass flux at 1 km depth was 455 mg/m$$_{2}$$/day in the eastern Japan Basin, 252 mg/m$$_{2}$$/day in the eastern Japan Basin and 147 mg/m$$_{2}$$/day in the Yamato Basin. Mass fluxes were especially large in spring (March-May). From the distribution of elemental abundance in sediments, La/Yb and Mn/Al ratios as indicators of the origin of aluminosilicates and the "freshness" of particles, respectively. These proxies suggested three sources of lithogenic material for the Japan Sea, (1) atmospheric input of Kosa particles, (2) lateral transport from the East China Sea, and (3) lateral transport from Island-Arc such as the Japan Islands.

Journal Articles

Organic material of high C/N ratio and heavy metals recorded in Ishikari bay sediment

Hamahara, Kazuhiro*; Shigemitsu, Masahito*; Noriki, Shinichiro*; Fukuyama, Ryuji*; Aramaki, Takafumi; Otosaka, Shigeyoshi

Engan Kaiyo Kenkyu, 41(1), p.53 - 60, 2003/08

no abstracts in English

Oral presentation

Transport processes of particulate materials and biogeochemical cycle of trace elements in the western North Pacific and the Japan Sea

Otosaka, Shigeyoshi; Minakawa, Masayuki*; Noriki, Shinichiro*

no journal, , 

Sediment trap experiments in the Japan Sea are useful in order to know trends of transport processes of particulate materials in the world's ocean, because the Japan Sea is known as a "miniature" of the ocean. In this study, results of sediment trap experiments in the Japan Sea that were carried out by JAEA, Hokkaido University and Fishery Research Association of Japan from 1999 to 2002 were summarized. Particulate fluxes in the Japan Sea were larger in the western Japan Basin where nutrients were effectively supplied to surface layers. Using elemental composition of rare earth elements in settling particles as a indicator of the origin of lithogenic particles, three source materials of lithogenic particles to the Japan Sea were defined. It was also suggested that about 60% of particulate materials supplied to the deep part of the western Japan Basin were transported horizontally to the eastern Japan Basin through the deep layers. The biogeochemical cycle of particulate materials in the "model-ocean" such as Japan Sea would strongly help the study on global cycles of major/trace materials in the ocean by combining long-term observations of particulate flux in the North Pacific.

Oral presentation

Transport process of particulate organic matter in the Japan Sea

Otosaka, Shigeyoshi; Amano, Hikaru; Tanaka, Takayuki; Togawa, Orihiko; Noriki, Shinichiro*; Kaba, Masato*; Minakawa, Masayuki*

no journal, , 

In order to understand biogeochemical cycles of particulate materials in the deep part of the Japan Sea, the authors assessed the processes and a time scale of transport of particulate materials by measurements of organic radiocarbon (C-14) in settling/suspended particles collected in three regions of the Japan Sea; the northwestern, northeastern and southeastern regions. Isotopic ratios of C-14 in settling particles collected at 1 km depth showed little differences between the sampling regions. In the southeastern region, isotopic ratios of C-14 of settling particles collected in the bottom layer (about 0.5 km above the bottom) were similar to those in 1 km depth. On the other hand, the ratios in bottom layer of the northern regions were smaller than those at the shallower layers significantly. These results in indicated that there are different origins of POC between the northern and southeastern regions of the Japan Sea.

Oral presentation

Lateral transport of particulate materials observed with sediment traps

Noriki, Shinichiro*; Otosaka, Shigeyoshi; Maeda, Nobuhiro*

no journal, , 

Origin and lateral transport processes of particulate materials are inferred from sediment trap experiments in the western North Pacific and its marginal seas. We assessed on (1) spatial distribution of aluminum (Al), which is known as a major component of lithogenic aluminosilicates, (2) size-distribution of lithogenic particles, and (3) lanthanum/ytterbium (La/Yb) and thorium/scandium (Th/Sc) ratios that are known as useful indicators of the origin of lithogenic particles in the region. Using these indicators, settling flux of lithogenic particles, which was inferred to originate from the Asian Continent, were estimated. Lithogenic flux of the Asian Continent origin increased with depth. From these results, we could summarize that fine lithogenic particles originated from the Asian Continent would be transported northwardly through the deep part of the western North Pacific.

Oral presentation

Factors controlling an apparent age of particulate organic matter in seawater

Otosaka, Shigeyoshi; Tanaka, Takayuki; Amano, Hikaru; Togawa, Orihiko; Noriki, Shinichiro*; Minakawa, Masayuki*

no journal, , 

An apparent age of particulate organic matter (POM) in seawater that is estimated from isotopic ratio of radiocarbon is convenient indicator for verifying transport processes of POM in the ocean. However, it is suggested that isotopic ratio of radiocarbon also reflects mixing of old POM from the surrounding regions and seafloor as well as an age of the POM. In this study, we discuss the cause of the variation in apparent age of POM from radiocarbon measurements of various particulate materials obtained at the northeastern Japan Sea and the northwestern North Pacific.

Oral presentation

Time-scale of POC cycle in the Japan Sea

Otosaka, Shigeyoshi; Tanaka, Takayuki; Togawa, Orihiko; Amano, Hikaru; Minakawa, Masayuki*; Khim, B.-K.*; Noriki, Shinichiro*

no journal, , 

A time-scale of particulate organic carbon (POC) in the Japan Sea, a marginal sea of the North Pacific, was quantified from radiocarbon (C-14) and stable carbon (C-13) measurements. Delta C-14 in POC decreased with depth, and the value was higher in the order of sinking POC, suspended POC and seabed sediment. delta C-13 values in suspended POC were higher than those in sinking POC obtained from the similar depth. From the radiocarbon signatures and elemental compositions of sinking POC, it was considered that Delta C-14 in sinking POC was determined by a mixing ratio of terrestrial and surface-produced POC. In addition, the difference of Delta C-14 and delta C-13 between the terrestrial and suspended POC was considered to indicate migration process of POC in the water column. From the difference of the C-14 age between terrestrial and suspended POC, it was estimated that an actual age of suspended POC at 3 km depth in the Japan Sea was about 300 years.

Oral presentation

Decadal change of particulate flux in the Japan Sea/East Sea

Otosaka, Shigeyoshi; Oku, Shunsuke*; Minami, Hideki*; Minakawa, Masayuki*; Noriki, Shinichiro*

no journal, , 

The Japan Sea is regarded as a miniature of the ocean because of its bowl-like topography and unique seawater circulation. Recent studies have suggested that biogeochemical processes in the Japan Sea correspond with the global climate change. In this study, we assessed decadal changes in particulate flux and elemental composition of sinking particle in the Japan Sea by comparing results of a sediment trap experiment in September 1984 with those in 1999-2001. Total mass flux did not show remarkable temporal change, however, biogenic opal/carbonate ratios observed recently were lower than those from the previous observation. In addition, relative content of scavenging elements such as manganese and cobalt also showed a decrease between the 15 years. These results may indicate decadal changes in ecological characteristics at the surface and transport processes of particulate materials in the deep water.

Oral presentation

Temporal change in elemental composition of sinking particles in the eastern Japan Sea

Otosaka, Shigeyoshi; Oku, Shunsuke*; Minami, Hideki*; Minakawa, Masayuki*; Noriki, Shinichiro*

no journal, , 

Many researchers pointed out that decadal change in deep-sea circulation in the Japan Sea are strongly related with the global climate change. However, little is known about changes in fluxes and elemental composition of sinking particles in the sea. In this study, we assessed temporal changes in elemental composition of sinking particle in the Japan Sea by comparing results of a sediment trap experiment in middle 1980s with those in end of 1990s. The result indicated that (1) the contribution of Asian dust in sinking particles decreased significantly, (2) horizontal transport of re-suspended particles from the slope regions was weakened, and (3) there was no significant increase in vertical transport of anthropogenic heavy metals to the interior of the Japan Sea.

Oral presentation

Particulate flux of Ba in the Japan Sea; Lateral transport of excess Ba

Oku, Shunsuke*; Otosaka, Shigeyoshi; Minakawa, Masayuki*; Minami, Hideki*; Noriki, Shinichiro*

no journal, , 

Autochthonous Ba (Ba-xs) in seawater is enriched in particulate materials by marine biota and settles down to the seabed. Therefore, Ba-xs is known as a proxy of export production in the surface ocean. However, it is necessary to discuss the effect of lateral transport of Ba-xs for the accurate estimation of the export flux. In this study, the authors investigated the effect of lateral transport of Mn-xs from a sediment trap experiment in the Japan Sea. Particulate fluxes of Ba-xs showed a positive relationship between flux of autochthonous Mn (Mn-xs). The flux of Mn-xs was higher in winter and it might be caused by the lateral transport of particulate materials from the shelf regions. The results indicated that Ba-xs is transported laterally and the effect was on a par with the sinking of biogenic particles.

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