Abstract The objectives of this study were to investigate the distribution and chemical characteristics of cations in annual rings of Japanese cedar ( Cryptomeria japonica D. Don) grown in a healthy stand of an unindustrialized region in Japan and discuss the possibility of using cations in tree‐rings as a chronological index of acidic deposition. Radial distributions of some cations and P at different vertical positions of the stem were analyzed for five trees from the same mountain. Each cation and P in all trees showed a specific distribution in its radial pattern but similar distribution trends were observed at all vertical positions. The cations and P were classified into three groups: (I) constant radial concentrations (Ca 2+ , Sr 2+ , Na + , and probably Ba 2+ ), (II) high concentrations in the heartwood and low in the sapwood (Mg 2+ , K + , Rb + , Cs + ), and (III) increasing concentrations in the sapwood (P, Mn 2+ , Cu 2+ ). The total concentration of cations exceeded the calcium‐binding capacity (CBC) of the wood, and the excess was attributed to K + in a salt form. The CBC increased from the sapwood/heartwood boundary toward the pith in the heartwood but remained constant in the sapwood. The increase of CBC in the heartwood was consistent with the profile of Mg 2+ , indicating a transfer of Mg 2+ into heartwood and fixation on the acquired binding site. The radial distribution of 90 Sr was closely related to the cumulative deposition of fallout from the nuclear weapon tests, but that of 137 Cs was unrelated. This suggests immobility of Sr 2+ and mobility of Cs + in the horizontal direction of wood. The conservation of the historical 90 Sr/Sr 2+ change indicated that no influence of heartwood formation on the chemical environment of Sr 2+ in cedar xylem and a possibility of using Sr 2+ as a chronological index of nutrient availability. A steady‐state in nutrient availability is speculated for trees growing in this mountain because all of the trees analyzed show constant radial distributions of Sr 2+ for decades.
This study aimed to explore the transport patterns of reactive materials under the Tsushima Warm Current (TWC) in the Sea of Japan. Fine-resolution seasonal and lateral variations in 228Th/228Ra activity ratio were examined along with 228Ra/226Ra ratio in surface seawater samples from the Sea of Japan, East China Sea (ECS), and Pacific Ocean in 2015–2020. Significant 228Th/228Ra ratio variations were observed in surface seawaters (<∼0.02–0.3), which partially correlated with the mixing ratios of the low-228Th/228Ra continental shelf side waters from the western ECS and high-228Th/228Ra Kuroshio Warm Current of the Pacific Ocean, in addition to the contributions of the subarctic current of the northern Sea of Japan. Conversely, in the Sea of Japan, local variation of 228Th/228Ra ratios were observed in samples with a similar fraction of the ECS continental shelf side waters. It is reasonable to speculate that these variations are due to local scavenging during the TWC circulation.
A total of 150 surface seawater samples were collected from around the Japanese Archipelago between July 2009 and February 2012, with sample collection peaking in July and October 2011. Low-background measurements revealed that, except for coastal and offshore areas around western Japan, 134Cs and 137Cs concentrations in surface waters were significantly higher than those recorded before the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, although their concentration levels were generally very low (<~0.1 to 1 mBq/L for 134Cs). In June 2011, concentration peaks of 1 mBq/L for 134Cs and 2.5 mBq/L for 137Cs were recorded in the Tsugaru Strait and off western Hokkaido, toward the Japan Sea approximately 150-300 km north of the high-deposition area of Akita in northern Honshu. In October 2011, 134Cs was detected only in the surface waters off western Hokkaido at a concentration of 0.2 mBq/L, which is markedly lower than the values observed in June 2011. These findings indicate that the observed radionuclide distributions could primarily be attributed to the atmospheric deposition of radionuclides emitted from the FDNPP and transported by ocean currents.
Japanese cedar rings sampled from Aomori Prefecture, Japan, were measured to obtain tree-ring radiocarbon data covering a period of the latter half of the 20th century in the northernmost area of Honshu (mainland Japan), to obtain records of variation in atmospheric 14 C concentration caused by past atmospheric nuclear testing, and to study any possible local effects. This work, carried out on a partial disk, was also intended to provide a reference for data obtained by core sampling of live, standing Japanese black pines as a part of marine environmental studies.
Abstract In this study, we investigated diurnal coastal trapped waves in the eastern coastal area of the Shimokita Peninsula near the Tsugaru Strait. The coastal trapped waves in this area have not yet been observed. We observed current velocities at three sites on the coast to clarify the propagation and seasonal features. We also used an ocean general circulation model to determine the detailed structure and the causes underlying the seasonal characteristics of the waves. The coastal trapped waves propagated southward along the coast from the strait, where significant tidal currents exist. Coastal trapped waves depend on cross-shelf length and stratification strength. The coastal trapped waves propagate as internal Kelvin waves from summer to early winter in the northern part of the peninsula (where the shelf is narrow) and as shelf waves in the southern part (where the shelf is wide). From late winter to spring, the coastal trapped waves practically disappear in the northern part of the peninsula owing to the vertical uniform density off the east coast and the small cross-shelf width in the northern part. In autumn, the tidal current flows north of the sill near Cape Shiriya at the eastern mouth of the straits owing to the northward shift of the Tsugaru Warm Current in the strait; thus, the coastal trapped waves along the Shimokita coast weaken.
