Search

Polycyclic aromatic hydrocarbons (PAHs), originating mainly from the incomplete combustion of fossil fuels and biomass and the leakage of petroleum products, are hazardous pollutants with adverse carcinogenic and mutagenic potential for marine organisms. The Yangtze River estuarine–inner-shelf area in the East China Sea is one of the largest reservoirs of PAHs and connected with the semi-enclosed Sea of Japan through the shallow, narrow Tsushima Strait. The main sources of PAHs in the Sea of Japan are the East Asian landmass and East China Sea, with the major PAH transport pathways being atmospheric transport of the westerly and northwesterly winter monsoon and marine transport in the Tsushima Warm Current. Investigation of the environmental behavior of PAHs in the Sea of Japan is critical in assessing the ecological risks of PAHs, as the sea is among the most fertile fishing grounds, however, the contributions of surface PAHs transported via atmosphere and ocean current are unclear. This study aimed to elucidate variation factor of dissolved PAHs in the surface Sea of Japan during 2017–2022, and analyzed 1) surface PAH distribution, 2) PAH source, 3) air-sea PAH exchange flux, and 4) ocean current driven PAHs flux through the Tsushima Strait. Surface seawater samples of 10–15 L were collected at 148 sites in the Sea of Japan, and its adjacent seas including the Tsushima Strait and Kuroshio Current area (Sesoko, Okinawa Island) from 2017 to 2022. Particulate and dissolved phases were separated by filtration through 0.5 µm glass fiber filter (GFF), and the latter was concentrated in C18 disks. Particulate and dissolved PAHs were respectively extracted from the GFF and C18 disks with dichloromethane and measured by HPLC system with fluorescence detector. Total concentrations of the 14 dissolved PAHs (Σ14PAHdiss) in the central Sea of Japan were in range 0.26–5.87 ng L−1, with the mean of 3.26±0.36 ng L−1 in 2017, 3.70±1.44 ng L−1 in 2019, 0.51±0.10 ng L−1 in 2020, 1.29±0.53 ng L−1 in 2021, and 0.69±0.35 ng L−1 in 2022. In 2020, although atmospheric PAH deposition flux were increased to 4.0 ton month−1 from 2019 (3.4 ton month −1) at the Sea of Japan, mean Σ14PAHdiss in the surface seawater were parallelly decreased to 0.51 ng L−1 at the central Sea of Japan, 0.86 ng L−1 at the Tsushima Strait, and 0.46 ng L−1 at the Kuroshio Current area. The contribution of PAH-rich and low salinity continental shelf water from the East China Sea in the Tsushima Strait was decreased to 36% in 2020 from 58% in 2019 on the basis of salinity mass-balance and ocean current simulation. Moreover, PAHs inflow flux through the Tsushima Strait were in range 2.2–8.8 ton month−1, and decreased to 2.2 ton month−1 in 2020. Thus, the decrease in surface Σ14PAHdiss levels at the central Sea of Japan in 2020 was mainly caused by the decrease in PAHs flux via the Tsushima Warm Current, which flow into the Sea of Japan from the East China Sea.

PAHs have high dissolved concentrations (Σ13PAHdiss) at the northern area off the Sakhalin Island (33-78 ng L−1) where oil and natural gas is extracted (Chizova et al.,2013). East Sakhalin Current (ESC) starting northern of the Sakhalin Island and reaching the southern Okhotsk Sea during autumn-winter, presents a latent risk of PAHs transboundary pollution. The southern Okhotsk Sea is also fed by Soya Warm Current (SWC, Summer) originating in the Sea of Japan. The seasonal interchange of SWC and ESC makes the area an excellent fishing ground, with 352,000 tons of scallops, crabs, salmon, and other major species of fish caught annually. 50+ seawater samples (~10 L) were collected from 2017 to 2022 with collaboration of the Japan Fisheries Research and Education Agency to evaluate the PAHs migration around southern Okhotsk Sea. Dissolved PAHs were concentrated, from pre-filtered (0.5 µm) samples, using C18 membranes and measured with a HPLC-fluorescence. Low-background γ-spectrometry of 234Th and 228Ra were measured at the Ogoya-Underground Laboratory, Kanazawa University using HPGe-detectors. 129I was measured using accelerator mass spectrometry at the University of Tsukuba. 234Th is constantly produced from 238U in seawater, thus the disbalance of the particle-reactive 234Th (t1/2=24.1 d) tells the scavenging due to new production. 228Ra (t1/2=5.75 y) is produced by the decay of 232Th, in the shallow continental shelves. 129I (t1/2=15.7x 106 y) is released from nuclear fuel reprocessing facilities and transported by the westerlies to the West-Pacific’s marginal seas. The Σ13PAHdiss averaged 2.59 (0.87−5.56) ng L−1. Using isomers ratios and statistical analyses, PAHs’ sources were inferred as primarily pyrogenic for all samples. Oceanographic structure was characterized by a coastal area [high salinity (>33.0 PSU), high 228Ra (0.80−1.90 mBq L−1) and low PAHs (−1)], dominated by the SWC and an offshore area [low salinity (228Ra (0.25−0.80 mBq L−1) and high PAHs (>2 ng L−1)], dominated by the ESC-influenced Okhotsk Sea Surface Water. Σ13PAHdiss were not necessarily low (1.71−5.15 ng L−1) at the endmember of SWC, and thus surface migration and isopycnal mixing does not fully explain PAHs distribution. 234Th/238U ratio was 0.65 at the endmember of SWC, 0.51 ± 0.03 in the offshore area, but only 0.36 ± 0.10 in the coastal area. Chlorophyll-a, PO43-, and SiO2 at the coastal (1.38 ± 0.76 mg m3, 0.07 ± 0.05 μM, 1.77 ± 0.65 μM, respectively) and offshore (0.61 ± 0.57 mg m3, 0.20 ± 0.08 μM, 3.64 ± 1.44 μM, respectively) areas also indicated higher primary productivity at the former, and thus scavenging of dissolved PAHs at the coastal area of southern Okhotsk Sea was nominated as a major geochemical process at the southern Okhotsk Sea. The high primary productivity and downward carbon export is key for the successful of scallop farming, but the co-scavenging of organic pollutants found by this study emphasizes the environmental risk that Sakhalin I, II present. 228Ra’s origins are multiple at the West-Pacific’s marginal seas, therefore a multiple-tracer assessment including the seaice’s role will be prepared when 129I analysis are completed.

Concentration data of soluble radionuclides in the southern South Indian Ocean and Southern Ocean transition zone are rare or insufficient for the study of its current system. We examined the lateral surface variations in soluble natural (

From August 2019 to August 2020, particulate and dissolved polycyclic aromatic hydrocarbons concentrations (PAHs) were analyzed in the water body of West Nanao Bay, Japan, to determinate their levels, environmental pathways, and ecological risks at this remote but shallow and semi-enclosed bay. The 14 targeted PAHs were analyzed by high performance liquid chromatography-fluorescence detector. Even when water column stratifies, the summatory of 14 targeted dissolved PAHs did not follow significantly change with depth. Results agreed with our previous findings in the surface distribution at the bay and can be attributed to long retention time of the water mass of the semi-enclosed bay. Suspended solids start precipitating according to their size; with biggest particles rapidly settling in the proximities of river mouths. Partition coefficients (Kp) varied from 10

In the Kaluxung River catchment of the southeastern Tibetan Plateau in China, we identified three Ephedra gerardiana communities on different soils and glacial landforms from 4842 to 4899 m above sea level: a moraine community located on constantly collapsing sandy gravel alpine steppe slopes with exposed bedrock on the outer slope of the terminal moraine of the Qiangyong Glacier on Mt. Kaluxung; an outwash plain community located on a gentle alpine steppe slope with exposed bedrock at the terminal end of the outwash plain in the glacial valley of the southeast side of Mt. Noijinkangsang; and a river terrace community located in an alpine meadow on a rock-scattered flat river terrace along a glacier-fed river in the outwash plain in the glacial valley of the southeast side of Mt. Noijinkangsang. Based on the finding of identical DNA sequences of the intergenic spacers of chloroplast trnT-trnF and trnS-trnfM regions for all Ephedra specimens examined in this study, the E. gerardiana in this study were considered to comprise a genetically homogeneous population. Analysis of the relationship between ephedrine alkaloid profiles of these three communities and soil characteristics showed that the river terrace community in wet alpine meadow had significantly lower ephedrine content than did the moraine and outwash plain communities in dry alpine steppe (moraine community, 1.52 ± 0.44; outwash plain community, 1.42 ± 0.68; river terrace community, 0.33 ± 0.65%DW), but pseudoephedrine content showed the reverse pattern (moraine community, 0.86 ± 0.30; outwash plain community, 0.73 ± 0.60; river terrace community, 1.50 ± 0.71%DW). In addition, total alkaloid (ephedrine and pseudoephedrine) content in the river terrace community (1.83 ± 0.24%DW) was significantly lower than that in the moraine community (2.38 ± 0.64%DW) and outwash plain community (2.15 ± 0.55%DW).

Concentrations of 13 phase-partitioned polycyclic aromatic hydrocarbons (PAHs) in seawater were monitored monthly off Oki Island, Japan, during 2015-2019 to elucidate seasonal variations, main source, and transport pathways of PAHs in the southwestern Sea of Japan. Total PAH (dissolved plus particulate) concentrations in surface seawater at 36°09.0'N, 133°17.3'E (site OK) were in the range 0.49-9.36 ng L

The Guangxi Zhuang Autonomous Region in southern China is one of the most typical karst relief areas with various forms, and tiankeng is one of the most typical karst relief forms of the Quaternary Period. In this work, accurate measurements of tiankeng exposure ages were made. The exposure ages of carbonate rocks from the five largest tiankengs in the world, the DaShiwei, HuangJing, ChuanDong, DaTuo, and DaCao tiankengs, were determined by accelerator mass spectrometry to be at least 20–400 thousand years, which provides significant proof for activity of new tectonic movement of the Eurasian continent in the Quaternary.

Tiankeng, a typical Karst relief of the Late Quaternary Period, in the south of China, plays an important role when researching the surface shape and evolution of the Karst relief. The accumulation of Chlorine-36 (T1/2 = 301 ka) through the interaction of cosmic ray particles with Ca, K and Cl in rocks allow it to be used as the ideal nuclide for determination of the exposure age and erosion rate of limestone. In this work, an improved 36Cl sample preparation method for Tiankeng limestone was presented. The Isotope Dilution-AMS technique allows for the simultaneous measurement of 36Cl and Cl with a single AMS sample preparation. The barium introduced during the sample preparation was removed to avoid ionizer poisoning and attain a higher and more stable beam current. The method is particularly suitable for limestone samples, as well as for soil, sediment and water samples.

The jungles of Linyun and Longlin Autonomous Prefecture, located in the heart of the southwestern Guangxi Zhuang Autonomous Region of China, are home to the oldest tea trees (Camellia sinensis) in the world. In the absence of regular annual rings, radiocarbon (14C) dating is one of the most powerful tools that can assist in the determination of the ages and growth rates of these plants. In this work, cores were extracted from large ancient tea trees in a central Longlin rain forest; extraction of carbon was performed with an automated sample preparation system. The 14C levels in the tree cores were measured using accelerator mass spectrometry (AMS) at the University of Tsukuba. These measurements indicated that contrary to conventional views, the ages of trees in these forests range up to ~700 years, and the growth rate of this species is notably slow, exhibiting a long-term radial growth rate of 0.039±0.006 cm/yr. It was demonstrated that 14C analyses provide accurate determination of ages and growth rates for subtropical wild tea trees.

The first preliminary test of the 14C-accelerator mass spectrometry (AMS) system at the University of Tsukuba was successfully performed using a gas/solid hybrid ion source and an automated sample preparation system with an elemental analyzer (EA). The maximum 12C− current of ∼11 µA was achieved using the optimized CO2 flow rate to the hybrid ion source. The machine background of 14C/12C for the AMS system reached to ∼2.4 × 10−16 (∼0.02 percent modern carbon, pMC) using unprocessed mineral graphite. Moreover, the blank level of 14C/12C including the combustion process for an IAEA-C1 graphite sample was 4.6 × 10−16 (0.05 pMC), demonstrating the low blank level of the automatic sample preparation system. In contrast, the blank level of 14C/12C including the combustion process for an IAEA-C1 CO2 sample was 5.0 × 10−15 (0.49 pMC), an order of magnitude worse than that for the graphite sample. The measurement uncertainty for the gas ion source was 0.6%, 2–3 times worse than that for the solid ion source (0.2%–0.3%).

Radioiodine is one of the most important radionuclides released by the accidents of Fukushima Dai-ichi nuclear power plant (FDNPP). Iodine-131 elevated ambient radiation dose rate immediately after the accident, but it is extinguished due to its short half-life. The long-lived 129I can be used as a tracer to retrospectively infer the level of 131I. Understanding of environmental behavior of 129I is important for preparedness against nuclear disaster. This study presents sampling campaigns on the Abukuma River during two high flow events, and discusses riverine 129I behavior based on comparisons with that of 137Cs. The study site was the Kuroiwa site locating at midstream of the Abukuma river. Its catchment area was 2886 km2 and mean 129I inventory in the catchment was 0.041 Bq m-2. Five and seven river water samples were taken during high-flow events in July 2018 (JUL18) and October 2018 (OCT18), respectively. Suspended sediment and filtrate samples were obtained by decantation and subsequent filtration with 0.45 μm-mash membrane filter, respectively. The suspended sediment and filtrate samples were measured for 137Cs activity concentrations with HPGe detector and then measured for 129I/127I ratio with accelerator mass spectrometer and for 127I concentration with ICP-QQQ-MS. Mean 129I activity concentration in suspended sediment during JUL18 and OCT18 were 1.0 and 0.43 mBq kg-1, respectively. In terms of temporal trends, 129I activity concentration in suspended sediment lowered in the peak water discharge phase, contrastive to those of 137Cs which were the highest at peak water discharge phase. Mean dissolved 129I activity concentrations during JUL18 and OCT18 were 0.18 and 0.067 μBq L-1, respectively. Both 129I and 137Cs activity concentrations in dissolved form tended to decrease with time during two high-flow events. Mean apparent distribution coefficient (Kd) during JUL18 and OCT18 were 4.3 ×104 and 6.1 ×103 L kg-1, respectively. The Kd values of 129I were lower than those of 137Cs and it reveal relatively-high solubility of 129I. Total exportation of 129I from the catchment during JUL18 and OCT18 were estimated as 1.0 × 104 and 2.3 × 104 Bq, respectively. Exported 129I in dissolved form accounted for 80 and 27% of total exportations, respectively. By contrast, more than 95% of 137Cs was exported in particulate form in the events. These results indicated an importance of dissolved form for understanding environmental behavior of radioiodine.

To evaluate the environmental impact of 14C discharged to the atmosphere from the Tokai nuclear facility during normal operational periods, cores were extracted from an 80-yr-old pine tree that grew close to the Tokai Nuclear Power Plants (Tokai NPP and Tokai-2 NPP) and the Tokai Reprocessing Plant (Tokai RP), and the 14C levels in the annual rings were measured using accelerator mass spectrometry (AMS). The 14C activity ranged from 232 to 403 Bq kg−1 C in the tree rings formed during the period 1959–2013. The activities in the periods 1959–1965 and 2011–2013 represent the background levels, and the activities recorded between 1966 and 2010 are significantly elevated compared with these background levels, indicating uptake by the tree of 14C discharged from the Tokai nuclear facility. The excess 14C activity values of 1.1–70 Bq kg−1 C for the period 1966–2010 are positively correlated with the estimated total annual 14C discharges of 0.019–2.0 TBq from the Tokai NPP, Tokai-2 NPP, and Tokai RP (R2 = 0.72; n = 40). This activity of

A horizontal-type 6 MV Pelletron tandem accelerator was installed at the University of Tsukuba, Japan, in September 2014. The first test of the multi-nuclide accelerator mass spectrometry system was performed in March 2016, after two years of construction. This is the first report of its performance. The particle detection system was designed for high-sensitivity detection of 10Be, 14C, 26Al, 36Cl, 41Ca, and 129I. A five-electrode ΔE-E gas-ionization detector was installed as the end station of the detection system. The system background for 14C measurements, with the 4+ charge state at 5.0 MV, has a 14C/12C ratio of ∼2.4 × 10−16. 10Be, 26Al, 36Cl, 41Ca, and 129I have also been successfully detected. The 41Ca/Ca background is ∼3 × 10−15 as a result of improved isobaric separation techniques.

The anthropogenic long-lived radionuclide 129I is receiving increased attraction as a new oceanic tracer in addition to usage as a fingerprint of radionuclide contamination of the marine environment. To demonstrate the robustness of 129I as an oceanic tracer in the Northwest Pacific area, specifically in the Japan Sea, the input history of 129I to surface seawater was reconstructed using a hermatypic coral core sample from Iki Island in the Tsushima strait. Iodine isotopes in each annual band were measured using AMS and ICP-MS after appropriate pre-treatments of small amounts of coral powder. The 129I/127I ratios in the 1940s were almost at background levels (

A series of nuclides (14C, 26Al, and 36Cl) was measured using the 12UD Pelletron tandem accelerator before replacement by the horizontal 6 MV tandem accelerator at the University of Tsukuba Tandem Accelerator Complex (UTTAC). This paper considers the modification of the accelerator mass spectrometry (AMS) measurement parameters to suit the current 6 MV tandem accelerator setup (e.g., terminal voltage, detected ion charge state, gas pressure, and entrance window material in detector). The Particle and Heavy Ion Transport code System (PHITS) was also used to simulate AMS measurement to determine the best conditions to suppress isobaric interference. The spectra of 41Ca and 41K were then successfully separated and their nuclear spectra were identified; the system achieved a background level of 41Ca/40Ca ∼ 6 × 10 - 14 .

Environmental contaminations of 129I were continuously monitored in various sample preparation rooms for accelerator mass spectrometry at the University of Tsukuba. Monitoring of 129I was performed in the rooms used for the treatment of samples in the past, in order to compare with the results obtained in the sample preparation rooms. Ambient levels of atmospheric 129I in each room were estimated from the measured concentrations in the alkali trap solutions. This article reports the results of one year of monitoring the temporal changes of stable iodine (127I) and 129I contamination rates in the alkali trap solutions. It was found that 129I contamination rates were lower than approximately 104 atoms cm-2 day-1 in the rooms where ether no samples or only samples with environmental background levels of 129I were handled. Values from 104 to 105 atoms cm-2 day-1 were recorded in another room where environmental samples, such as the samples derived from nuclear power plant accidents, were treated. Higher levels of 129I, ranging from 106 to 107 atoms cm-2 day-1, were recorded in rooms used for treating neutron-activated iodine. The experimental results show that the 129I level depended on the 129I sample-preparation histories for the respective rooms. It is possible to estimate the 129I contamination risk from the atmosphere to the samples by knowing the 129I level in the preparation room.

To better understand the reported paleoclimate features and underlying mechanisms in the lowest-latitude region (~28°N to 29°30′N), where 12 major river gorges cross the Himalayas, of the southern Tibetan Plateau, we aim to elucidate the major sources and behavior of modern monsoon air masses in the region based on spatial variations in the δ18O and δ2H of stream water and precipitation, and vegetation during the summer monsoon season. Our main findings were following: The river gorges, high mountain ranges bearing extensive dense vegetation, and stronger solar insolation characteristic of the lowest-latitude region may have functioned for an extended period as the essential geological settings for strongly drawing significant amounts of moisture from the Indian Ocean toward the region without passing through the Yarlung Zangbo basin. The combination of such geological settings specific to this region may have caused its earlier response to the climate amelioration after a cold/dry event, such as the Younger Dryas and Heinrich-1, compared to other regions on the Plateau. Furthermore, gorge-derived monsoon air masses that blew through the lowest-latitude region are highly likely to have more significantly influenced the onset of the climate amelioration after a cold/dry event even in the southwestern, south-central, and southeastern regions, rather than the Yarlung Zangbo-derived monsoon air masses. Therefore, this caused the subsequent expansion of the Indian summer monsoon (ISM) over the Plateau. Thus, with its unique geological setting, the lowest-latitude region has presumably played a critical role as the key region, i.e. the initiator, for the early evolution of the ISM on the Tibetan Plateau by responding to climate amelioration after cold/dry events more rapidly than any other region and drawing gorge-derived monsoon air masses strongly toward the region.

The anthropogenic long-lived radionuclide

To evaluate the deposition density and extent of subsurface infiltration of (129)I and (137)Cs in the restricted area that was highly contaminated by the accident of Fukushima Dai-ichi Nuclear Power Plant, cumulative inventories of (129)I and (137)Cs, concentrations of (129)I and (137)Cs, and (129)I/(137)Cs ratio in 30-cm-long soil columns were compared with pre-accident levels from the same area. The cores were collected before and after the accident from locations of S-1 (4 km west of FDNPP) and S-2 (8 km west of FDNPP). Deposition densities of (129)I and (137)Cs in the soil following the accident were 0.90-2.33 Bq m(-2) and 0.80-4.04 MBq m(-2), respectively, which were 14-39 and 320-510 times larger than the pre-accident levels of (129)I (59.3-63.3 mBq m(-2)) and (137)Cs (2.51-7.88 kBq m(-2)), respectively. Approximately 90% of accident-derived (129)I and (137)Cs deposited in the 30-cm soil cores was concentrated in the surface layer from 0 to 44-95 kg m(-2) of mass depth (0-4.3-6.2 cm depth) and from 0 to 16-25 kg m(-2) of mass depth (0-1.0-3.1 cm depth), respectively. The relaxation mass depths (h0) of 10.8-11.2 kg m(-2) for (129)I estimated in the previous study were larger than those of 8.1-10.6 kg m(-2) for (137)Cs at both sites, owing to the larger infiltration depth of radioiodine mainly by the gravitational water penetration in the surface soil in our study sites. Approximately 7-9% of the accident-derived (129)I was present in the lower layer from 44 to 100 kg m(-2) (4.3-8.6 cm depth) at S-1, and from 95 to 160 kg m(-2) (6.2-10.2 cm depth) at S-2. Approximately 1% of (137)Cs seems to infiltrate deeper than (129)I in the lower layer at each site in contrast to the surface layer.

Accelerator mass spectrometry (AMS) is one of method used for 90 Sr determination. It would enable rapid 90 Sr measurements from environmental samples such as water, soil, and milk. However, routine analysis of 90 Sr using AMS has not yet been achieved because of difficulties associated with isobaric separation and production of intense negative ion beams characterized by currents from hundreds of nanoamperes to several microamperes. We have developed a rapid procedure for preparing samples with optimum compositions for use with AMS, which enables production of intense Sr beam currents from an ion source. Samples of SrF 2 were prepared from a standard Sr solution and agricultural soil. The time required to prepare a SrF 2 sample from a soil sample was 10 h. Negative 88 SrF 3 − ions were successfully extracted at 500 nA from mixed samples of SrF 2 and PbF 2 . In the present work, negative ions of 90 Zr, included as an impurity, were accelerated with a tandem accelerator operated at a terminal voltage of 5 MV. Ions characterized by a charge state of 6+ were channeled into a gas counter. An atomic ratio of 90 Zr/ 88 Sr of 3 × 10 −8 was estimated for the soil sample. No signal was detected from the assay of PbF 2 , which was pressed in an aluminum cathode, for a mass number of 90. PbF 2 revealed good performance in the production of negative SrF 3 − molecular ion beams and detection of 90 Sr with a gas counter.

The deposition density and extent of subsurface infiltration of 129I were investigated within the area highly contaminated by the March 2011 accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in Japan. Depth profiles of 129I activity and 129I/127I ratios were measured in 5-cm-long soil cores that were collected 20–27 months after the accident from three sites (S-1, S-2, and S-3) within 10 km to the west and northwest of the FDNPP. These profiles were compared with the background levels of 129I from the same areas. The deposition densities of 129I were 2.17 Bq m−2 at S-1, 0.80 Bq m−2 at S-2, and 1.41 Bq m−2 at S-3, which are, respectively, about 160, 60, and 100 times larger than the background level (12.8–14.8 mBq m−2). The average 129I/127I ratios in each soil core after the accident (S-1: 2.1 × 10−6; S-2: 4.2 × 10−7; S-3: 2.3 × 10−6) were similar to the value typically found in contaminated surface soil within 80 km of the FDNPP. Therefore, accident-derived 129I deposited at S-1 (4.3 km west of the FDNPP) was 2.7 times larger than at S-2 (8.2 km west of the FDNPP), and 1.5 times larger than at S-3 (7.5 km northwest of the FDNPP). Depth profiles showed that the 129I activity and 129I/127I ratios decayed exponentially with depth. ∼90% of accident-derived 129I deposited in the soil cores was concentrated in the upper 25.2–26.4 kg m−2 of mass depth (2.1–3.1 cm depth). The relaxation mass depths (h0) of 129I were 9.49–11.2 kg m−2 at the three sampling sites, and these values are comparable to those of accident-derived 131I (10.4 kg m−2) at a site 40 km northwest of the FDNPP.

To improve the understanding of the emission sources and pathways of polycyclic aromatic hydrocarbons (PAHs) in the coastal environments of remote areas, their particulate and dissolved concentrations were analyzed on a monthly basis from 2015 to 2018 in surface waters of Nanao Bay, Japan. The concentration of the targeted 13 species of PAHs on the United States Environmental Protection Agency (USEPA) priority pollutant list in dissolved and particle phases were separately analyzed by high-performance liquid chromatography (HPLC) coupled to a fluorescence detector. Particulate and dissolved PAHs had average concentrations of 0.72 ng∙L&minus, 1 and 0.95 ng∙L&minus, 1, respectively. While most of the samples were lower than 1 ng∙L&minus, 1, abnormally high levels up to 10 ng∙L&minus, 1 were observed in the winter of 2017&ndash, 2018 for particulate PAHs. Based on the isomer ratios of Flu to Flu plus Pyr, it was possible to determine that the pyrogenic loads were greater than the petrogenic loads in all but four out of 86 samples. The predominant environmental pathway for PAHs in winter was determined to be long-range atmospheric transportation fed by the East Asian winter monsoon, while for the summer, local sources were more relevant. By the risk quotients method, it was determined that PAHs in surface seawater presented a very low risk to marine life during the interannual survey.

Concentrations of phase-partitioning 13 polycyclic aromatic hydrocarbons (PAHs) in seawater were investigated in the Tsukumo Bay, Noto Peninsula, Japan, during 2014&ndash, 2018, to improve the understanding of the environmental behavior of PAHs in the coastal areas of the Japan Sea. Total PAH (particulate plus dissolved) concentrations in surface seawater were in the range 0.24&ndash, 2.20 ng L&minus, 1 (mean 0.89 ng L&minus, 1), an order of magnitude lower than the mean values observed in the Japan Sea in 2008 and 2010. Although the PAH contamination levels during 2014&ndash, 2018 were significantly lower than those in the East China Sea, the levels increased from 2014 to 2017 and were maintained at the higher level during 2017&ndash, 2018. The main sources of particulate and dissolved PAHs during 2014&ndash, 2018 were combustion products, of which the former were more influenced by liquid fossil-fuel combustion and the latter by biomass or coal combustion. The increase in particulate PAH concentrations in October&ndash, December during 2014&ndash, 2018 was due to the impact of PAH-rich airmasses transported from the East Asian landmass in the northwesterly winter monsoon winds. The increase in dissolved PAH levels during July&ndash, September in 2014, 2016, 2017, and 2018 indicates that the Tsukumo Bay is possibly impacted by the PAH-rich summer continental shelf water transported by the Coastal Branch of the Tsushima Warm Current, which flows into the Japan Sea from the East China Sea.

The paleoclimatic changes in the southern region on the Tibetan Plateau (TP) after the LGM were studied by multi-proxy analysis, including pollen, Ca-carbonates, TOC, δ 13 C TOC , plant macrofossils and sands with sediment cores from Lake Pumoyum Co, close to the east end of the Himalayas. The following paleoclimatic changes characteristic of the southern TP were suggested by comparing with the paleoclimatic records from various regions within the Southwest (SW) monsoon domain on the TP. Soon after the LGM, deglaciation in the southern TP had already started at 18.5 ka BP, and more actively increased after ca. 16.5 ka BP, with the hydrological circulation oscillating in ca. 1200-, 2000- and 4000-year periods. An abrupt increase in humidity under the reduced SW monsoon intensity occurred at 15.0 ka BP as part of further deglaciation processes. Subsequently, the climate amelioration in the southern region started from 15.0 ka BP a few centuries earlier than other regions of the TP and then was further intensified by synchronizing with the Bolling/Allored (B/A) event. Over the B/A period, the SW monsoon intensity in the southern region almost continuously and sharply increased. Unlike many regions on the TP, the southern region experienced almost no or substantially small impact of the Younger Dryas (YD) event and also other major dry/cold reversals, such as Heinrich 1 event, the 8.2 kyr event, and an abrupt spell occurring between 5 and 4 ka BP. The monsoon intensity in the southern region after the YD event started to rapidly increase from 11.4 ka BP and reached a maximum between 10.8 and 10.0 ka BP after the LGM which lagged about 1200 years behind the maximum insolation in the northern hemisphere. From ca. 9.6 ka BP, the gradual decrease in humidity in the southern TP started and continued until 4.2 ka BP. It's aridification trend was characterized by three-stepwise transition observed at 9.6, 7.7 and 5.5 ka BP. However, the aridification in the southern TP was rather weak, and the climatic conditions were sustained fairly humid and comparably stable. The humidity between 4.2 and 2.5 ka BP essentially increased despite the weakened SW monsoon intensity at that time, whereas from 2.5 ka BP to the present, the climatic conditions became most arid and instable during the Holocene. As a consequence, the Holocene climate optimum in the southern region lasted from 11.4 ka BP until 2.5 ka BP and was marked by the earliest start and the latest end timings within the SW monsoon domain on the TP. The comparison of the start timings from various paleoclimatic records indicated that the first SW monsoon on the TP after the YD event generated at 11.4 ka BP in the southern region. Subsequently, according to the degree of the recovery of positive vegetation-albedo feedback system in each region, the monsoon probably extended from the southern TP over the entire TP taking 3000–4000 years. Based on these results, the possible key factors and mechanisms responsible for the paleoclimatic changes in the southern region and also the possible processes as to the evolution of the SW monsoon over the TP are discussed.

Paleoclimatic records from the Tibetan Plateau provide important clues for understanding the Asian monsoon and Asian climate systems. To reconstruct climatic and environmental changes in the southern Tibetan Plateau, a 3.77-m-long sediment core (PY608E–PC) was taken from the southeastern part of Lake Pumoyum Co in August 2006. Because terrestrial plant residues are extremely rare in this core, we performed radiocarbon dating on the total organic carbon fraction. We also estimated the old carbon effect and radiocarbon reservoir age of the total organic carbon fraction. Using these estimates, we propose a new radiocarbon chronology for past climatic changes from ca. 12,500 to 700 cal BP. The linear sedimentation rate of the core was founded to be constant at 32.0 cm/kyr, indicating stable sedimentation conditions in Lake Pumoyum Co from the period of the Younger Dryas to the Holocene.

We obtained three sediment cores from a high-altitude lake (Lake Pumoyum Co; altitude, ~ 5020 m asl) on the southern Tibetan plateau for reconstruction of environmental changes during the last glacial–Holocene transition. In this study, we established the first reliable chronology for sediment cores from Lake Pumoyum Co, ca. 18.5 cal ka BP at the bottom, by 14C analyses of terrestrial plant residue concentrates (PRC, > 125 μm) and aquatic plant residues. The calibrated ages of the PRC fraction in the surface sediment were nearly modern (0.1 ± 0.1 cal ka BP), and the δ13C values (− 22‰ to − 24‰) were agreed well with those of modern terrestrial C3 plants. In addition, we estimated 14C reservoir ages of macrophyte remains from changes in their δ13C values. The major climate boundary layers in the cores (transitions to Bolling–Allerod, 14.5 ± 0.5 cal ka BP; Younger Dryas, 12.8 ± 0.1 cal ka BP; and Preboreal, ~ 11.6 cal ka BP) were confirmed by our new 14C chronology. The transition to the Bolling–Allerod warm phase from the last glacial (14.5 ± 0.5 cal ka BP) coincided with an obvious lithologic boundary (a rapid decrease in the abundance of the macrophyte remains) in the Lake Pumoyum Co sediment cores.

Further discussion about the limnological features of Lake Puma Yum Co, South Tibet, China, is provided based on the results of several investigations. By using depth data from all over the lake, the whole submarine topography has been compiled. Horizontal analysis of the water's physicochemical features indicates that compared with the relatively uniform water features at other lake areas, apparent spatial heterogeneity exists in the water of the subaquatic alluvial fan induced by the Jiaqu River, the biggest inflow. Vertical analysis of water characteristics using two-factor analysis of variance with no re-experiment indicates that temperature, dissolved oxygen, and pH of the water vary with water depth rhythmically, whereas other parameters demonstrate no evident vertical variation, which shows that chemical stratification is not obvious. But this does not exclude slightly higher concentrations of Ca2+ induced by lower pH at the bottom of deep lake water. The hydrochemistry difference between inflow water and lake water reveals the loss of Ca2+ in lake water, which indicates calcite deposition may be an important characteristic of lake sediment.

A new continuous sediment core (PY608W-PC; 3.8 m length) for reconstruction of climatic and environmental changes in the southeastern Tibetan Plateau was taken from the eastern part of Lake Pumoyum Co in August 2006. Sediment layers of the lower part of PY608W-PC (380–300 cm depth) were composed mainly of relatively large plant residues (up to ∼3 cm in length) with an admixture of fine sand and sandy silt. The large plant residues disappeared at ∼300–290 cm depth in core PY608W-PC and were replaced by silt-silty clay. The large plant residues from the lower part of PY608W-PC could be aquatic, because the plant residues were extremely enriched in 13C (up to –3.0‰, −5.6 ± 2.3‰ on average). On the other hand, the plant residue concentrates (PRC fractions) from the upper part of the core (290–0 cm in depth) could be terrestrial C3 plants (δ13C = –21.8 ± 1.7‰ on average). Radiocarbon dating was performed on the large plant residues and PRC fractions from the PY608W-PC sediment core, which represented the chronology from ∼19,000 cal BP to present.

Soil samples from an 85-cm-long continuous section (PY608ES) were collected from an island in Lake Pumoyum Co (southeastern Tibetan Plateau, ∼5020 m asl) in August 2006. To estimate past environmental conditions of Lake Pumoyum Co during the Holocene, we analyzed radiocarbon ages, stable carbon isotope compositions, and total organic carbon/total nitrogen (TOC/TN) atomic ratios of the soil samples. The 14C measurements were performed with the Tandetron accelerator mass spectrometry system at the Center for Chronological Research, Nagoya University. The 14C concentration in the surface layer (101 pMC; 5–10 cm soil depth) was nearly modern. A 14C chronology of the sequence indicated that continuous soil development began on the island in Lake Pumoyum Co at ∼5800 cal BP (at 63 cm soil depth, the top of a gravel layer). These results may reflect a decrease in the lake level in the middle Holocene. The age of the obvious lithologic boundary (∼5800 cal BP) corresponds to the end of Holocene climate optimum.

We constructed a new age model based on high-time-resolution 14 C data sets from three sediment cores from Academician ridge, Lake Baikal, for reconstruction of environmental and biological changes in southern Siberia during the last ca. 30 kyr. We used 14 C ages of total organic carbon (TOC) for the model, because terrestrial plant residues and biogenic carbonate were not observed in the sediments. For accurate dating and age models based on 14 C ages of TOC, the freshwater 14 C reservoir effect and the effect of dead carbon from land-derived organic materials must be estimated. In this study, we estimated the correction factor for these effects to be 2100 ± 90 yr, on the basis of a key layer, the “ 14 C plateau”, caused by changes in the atmospheric 14 C concentration during the Younger Dryas (YD) cooling event. The new age scale, along with the TOC mass accumulation rate (MAR TOC ) and stable carbon isotope ratio in the sediment cores, clearly indicate a rapid decrease in lake productivity and reduced influx of terrestrial organic materials into the lake during the YD (12.8–11.6 cal ka BP). Productivity was high (MAR TOC , up to 19.7 mg/cm 2 ·kyr) in and around Lake Baikal during 9.3–6.4 cal ka BP (Holocene climate optimum). Moreover, paleoproductivity changes during the last ca. 30 kyr in and around the Lake Baikal were clearly associated with fluctuations in the East Asian monsoon intensity, as inferred from the δ 18 O record from Sanbao and Hulu caves, China, during the late Quaternary (Wang et al., 2008. Nature 451, 1090–1093).

This study investigates the source and flux of particulate 129I in the downstream reaches of the Niida River system in Fukushima. The upper watershed is a relatively highly contaminated zone located 30–40 km northwest of the Fukushima Daiichi Nuclear Power Plant. Samples of total suspended substance (SS) were collected continuously at Haramachi (5.5 km upstream from the river mouth) from December 2012 to January 2014 using a time-integrative SS sampler. Activity of 129I and the 129I/127I ratio in SS were 0.9–4.1 mBq kg−1 and (2.5–4.4) × 10−8, respectively, and were strongly correlated with the total dry weight of SS samples with R2 of 0.79–0.88. High SS 129I activity and 129I/127I ratios were found in March, April, September, and October 2013. SS 129I activity and 129I/127I ratios are considered to reflect the SS source, i.e., the more contaminated upper watershed or the less contaminated downstream area. The flux of particulate 129I at the Haramachi site was estimated to be 7.6–9.0 kBq month−1 during September–October 2013. A relatively high amount of particulate 129I may have been transported from the upstream to the downstream reaches of the Niida River by high rainfall over this period.

Limnological features of Lake Puma Yum Co, a typical alpine lake located at the altitude of 5030 m in the Tibetan Plateau, China, are described based on the findings of the second expedition in September 2004. The lake surface is about 280km2 and maximal depth is 65 m. Total inflow just after the rainy season was estimated to be about 860 000m3 day−1, and the lake water was drained from a newly excavated channel at a rate of 960 000m3 day−1. We may have to expect undesirable lowering of the water level by this new drainage, especially in the dry season. Thermocline developed from 20 to 30 m depth, and the euphotic zone reached the 50 m depth. Dissolved oxygen in surface water was supersaturated as in productive lakes, although there were no large point and nonpoint sources of nutrient in the catchment. Vertical distribution of phytoplankton biomass and primary production suggested the presence of photoinhibition. What should be noted about the flora and fauna is that a Chara zone and a shell zone were distributed at about 30 or 40 m of depth.

Lake Pumoyum Co is on the southeastern Tibetan plateau (altitude, ∼5030 m asl; lake surface area, 281 km2; maximum water depth, 65 m). We obtained 14C dates on total organic carbon (TOC) for three sediment cores from Lake Pumoyum Co, covering the period from the last glacial to the Holocene, and compared them with 14C ages on plant residue concentrates (PRC fraction, mainly terrestrial plant residues) and aquatic plant fragments in the cores. The calibrated ages of TOC were older than those of the PRC fraction in the sediment cores by ca. 0.6–11.3 kyr. The calculated dead carbon fraction (fdead carbon) values for TOC increased during 9.5–5.5 cal ka BP, and fluctuations of fdead carbon paralleled variations in Asian monsoon intensity [Y. Wang et al., Nature 451 (2008) 1090]. One possible explanation for these results is that large amounts of terrestrial organic materials containing old carbon were supplied to the lake (“old carbon effects” from lake terrace, paleosol and/or stratum with dead 14C) when the lake level rose rapidly and its catchment area expanded during the Holocene climate optimum (9.5–5.5 cal ka BP).