Anticipating the release of
129I from a new spent nuclear fuel reprocessing plant at Rokkasho in Japan, the levels of
129I in seawater before its operation were measured at the western North Pacific ...Ocean and the Japan Sea from surface to bottom.
Iodine isotopic ratios (
129I/
127I) in surface seawater at the offshore of Kushiro, the Japan Basin and the Yamato Basin were (7.1
±
0.3)
×
10
−11, (5.8
±
0.2)
×
10
−11 and (4.6
±
0.2)
×
10
−11, respectively. The
129I/
127I in the deep layer at the offshore of Kushiro below 1500
m depth was constant and its ratio was (1.5
±
0.4)
×
10
−12. Since this ratio agreed with the natural origin
129I/
127I corresponding to (1.5
±
0.015)
×
10
−12, the anthropogenic
129I have not invaded the deep layer below this depth. On the other hand,
129I/
127I in the bottom layer below 2000
m depth at the Japan Basin and Yamato Basin was also constant but their ratios were (7.1
±
0.8)
×
10
−12 and (9.1
±
0.6)
×
10
−12, respectively. Taking account of the natural
129I/
127I, anthropogenic
129I was intruded into the basin bottom of the Japan Sea, completely. Furthermore, the inventory of anthropogenic
129I for the Japan Basin and Yamato Basin was three times higher than that in the offshore of Kushiro. These results would be due to the characteristics for the ocean circulation and the bottom topography in the Japan Sea.
To investigate the migration of anthropogenic 129I in the environment, we measured 129I concentrations at both subarctic (above 40oN) and subtropical (below 40oN) circulations in the surface seawater ...of the Japan Sea. The averaged concentrations of stations 193, 194, 201, 206 and 210 above 200m were (2.1±0.3)×1010atoms/m3, (2.0±0.2)×1010atoms/m3, (1.6±0.3)×1010atoms/m3, (1.4±0.3)×1010atoms/m3 and (1.7±0.3)×1010atoms/m3, respectively. The averaged concentration at the subarctic circulation in the Japan Sea above 200m (1.9×1010atoms/m3) was higher than that in the subtropical circulation (1.5×1010atoms/m3). This latitudinal distribution pattern of 129I is not consistent with those of bomb-derived radionuclides such as 14C, 90Sr and 137Cs. Taking into account latitudinal location and the total amount of releases from reprocessing plants, this discriminating latitudinal distribution of 129I in the Japan Sea would indicate that a significant amount of 129I originating from active reprocessing plants in Europe is supplied to the surface of the Japan Sea.
The concentrations of
129I in seawater samples from two sites (off Sekine and the Toyama Bay) in the Japan Sea were determined by accelerator mass spectrometry. The observed concentrations exceed ...amounts expected from natural origin and globally distributed fallout due to nuclear weapons testing. Because the fraction of natural origin and global fallout is 2% and 8.9–13.8%, respectively, the residual more than 80% of the concentration must come primarily from nuclear fuel reprocessing plants. This result indicates a rapid distribution of
129I through atmospheric transport on a global scale. The depth distribution of
129I at the Toyama Bay in the Japan Sea shows that the
129I maximum is in the mixed layer and that concentrations decrease with depth. The inventory of
129I in water column is four times higher than that measured in the Gulf of Mexico which has almost the same depth at the Toyama Bay. This higher inventory probably reflects: (1) the rapid water sinking in the Japan Sea, (2) the difference of distance in sampling locations with respect to major
129I releasing plants and (3) the strong increase in emissions from nuclear fuel reprocessing plants after the profile of the Gulf of Mexico was taken.
Radiocarbon in dissolved organic matter in seawater gives information on the dynamics and origin of the dissolved organic matter. Here, we present the vertical profile of Δ
14C of dissolved organic ...carbon in the western North Pacific Ocean. The profile was almost parallel to that for Δ
14C of dissolved inorganic carbon, indicating that the time scale of seawater circulation was the main influence on the Δ
14C signature of dissolved organic carbon. On the basis of the Δ
14C differences between dissolved organic carbon and dissolved inorganic carbon, and a comparison with Δ
14C of dissolved organic carbon in the central North Pacific Ocean, we suggest that there may be a source of younger dissolved organic carbon in the western North Pacific Ocean.
A numerical simulation model system that consists of an ocean current model, Princeton Ocean Model (POM), and a particle random-walk model, SEA-GEARN, has been developed to describe the migration ...behavior of non-conservative radionuclides in a shallow water region. Radionuclides in the ocean are modeled in three phases, i.e., the dissolved phase in seawater, the adsorbed with large particulate matter (LPM) and the adsorbed with active bottom sediment. The adsorption and desorption processes between the dissolved and solid phases are solved by the stochastic method with the kinetic transfer coefficients. Deposition of the LPM and re-suspension from bottom sediment are also considered. The system was applied to simulate the long-term (24-year) dispersion of 137Cs actually released from the BNFL spent nuclear fuel reprocessing plant at Sellafield in United Kingdom. The calculation well reproduced the main characteristics of migration of dissolved
137
Cs concentration in the Irish Sea.
A numerical simulation model system that consists of an ocean current model, Princeton Ocean Model (POM), and a particle random-walk model, SEA-GEARN, has been developed to describe the migration ...behavior of non-conservative radionuclides in a shallow water region. Radionuclides in the ocean are modeled in three phases, i.e., the dissolved phase in seawater, the adsorbed with large particulate matter (LPM) and the adsorbed with active bottom sediment. The adsorption and desorption processes between the dissolved and solid phases are solved by the stochastic method with the kinetic transfer coefficients. Deposition of the LPM and re-suspension from bottom sediment are also considered. The system was applied to simulate the long-term (24-year) dispersion of 137Cs actually released from the BNFL spent nuclear fuel reprocessing plant at Sellafield in United Kingdom. The calculation well reproduced the main characteristics of migration of dissolved 137Cs concentration in the Irish Sea.
An international sampling cruise, the IAEA’97 NW Pacific Expedition, was carried out in 1997 with the primary objective of contributing to better understanding of the present distributions of ...radionuclides in the open ocean and of the processes affecting their distributions in the water column, to study the sources which have introduced radionuclides to the Pacific Ocean, and to compare present results with historical data sets obtained from the previous expeditions (e.g., the Geochemical Ocean Sections Programme, GEOSECS). The observed temperature, salinity, dissolved oxygen, and silicate levels in water samples collected showed differences in the upper 1000
m layer in all studied profiles. Transuranics water profiles showed typical sub-surface maxima, with concentrations less by about a factor of 4 than the GEOSECS results, at depths greater by about a factor of 2 and a decrease in the water column inventory by about 20% over 24 years, which were less a function of particle-driven vertical processes and more in response to water mass circulation in the region. Increases in concentrations were observed in deep water near the sea floor. Transuranics inventories in the water column substantially exceeded those expected from global fallout.
90Sr and
137Cs data confirm that the observed changes in concentration profiles have resulted from physical circulation of the regional water masses and transport of radionuclides to deep waters. The IAEA’97 results present the most comprehensive recent study on the distribution of
239,240Pu,
90Sr and
137Cs in the NW Pacific Ocean with a description of the behaviour of these radionuclides in the water column and the effects of the physical forcing of water mass circulation over the last 24 years.
Seasonal and spatial variations of particulate organic carbon (POC) flux were observed with sediment traps at three sites in the Japan Sea (western and eastern Japan Basin and Yamato Basin). In order ...to investigate the transport processes of POC, radiocarbon (
14
C) measurements were also carried out. Annual mean POC flux at 1 km depth was 30.7 mg m
−2
day
−1
in the western Japan Basin, 12.0 mg m
−2
day
−1
in the eastern Japan Basin and 23.8 mg m
−2
day
−1
in the Yamato Basin. At all stations, notably higher POC flux was observed in spring (March–May), indicating biological production and rapid sinking of POC in this season. Sinking POC in the high flux season showed modern Δ
14
C values (>0‰) and aged POC (Δ
14
C < −40‰) was observed in winter (December–January). The Δ
14
C values in sinking POC were negatively correlated with aluminum concentration, indicating that Δ
14
C is strongly related to the lateral supply of lithogenic materials. The Δ
14
C values also showed correlations with excess manganese (Mn
xs
) concentrations in sinking particles. The Δ
14
C-Mn
xs
relationship suggested that (1) the majority of the aged POC was advected by bottom currents and incorporated into sinking particles, and (2) some of the aged POC might be supplied from the sea surface at the trap site as part of terrestrial POC. From the difference in the Δ
14
C-Mn
xs
relationships between the Japan Basin and the Yamato Basin, we consider that basin-scale transport processes of POC occur in the Japan Sea.
The newly formed bottom water in the Japan Sea was observed in the summer of 2001 after the severe winter 2000–2001. The new bottom water, which was observed in the northwestern Japan Sea, showed low ...temperature, high salinity, high dissolved oxygen and low nutrients concentration compared to the old bottom water. The distribution of the new bottom water indicates that the bottom water was formed in the south off Vladivostok, not in the northern Japan Sea north of 43°N, and was advected to the observation area. It is suggested that the formation event occurred in the late January‐early February 2001, because strong flows of faster than 8 cms−1 appeared abruptly from mid‐February 2001. This formation event may contribute not only the relaxation of the oxygen‐decreasing trend in the bottom layer but also the spin‐up of the thermohaline circulation in the Japan Sea.
We developed an extraction method for accurately and reproducibly determining dissolved organic radiocarbon in seawater by ultraviolet oxidation of dissolved organic carbon and subsequent accelerator ...mass spectrometry. We determined the irradiation time required for oxidation of the dissolved organic carbon. By modifying the experimental apparatus, we decreased contamination by dead carbon, which came mainly from petrochemical products in the apparatus and from the incursion of carbon dioxide from the atmosphere. The modifications decreased the analytical blank level to less than 1% of sample size, a percentage that had not previously been achieved. The recovery efficiency was high, 95±1%. To confirm both the accuracy and reproducibility of the method, we tested it by analyzing an oxalic acid radiocarbon reference material and by determining the dissolved organic carbon in surface seawater samples.
PDF
