Oxygen isotope ratios (δ18O) of tree-ring cellulose in pine (Pinus densiflora) and oak (Quercus serrate and Quercus variabilis) growing in central Japan from 1970 to 2011 share a common inter-annual variance among different cores in a tree, different trees in a species, and different species in a forest. The high mean correlation between the two radii (r = 0.738) of individual trees and the mean standard deviation of two measurements for the same year from the two radii of eight trees (σ = 0.361‰) reveals the reliability and representativeness of single cores. The significant correlation (r = 0.667, p < 0.01) between pine and oak cellulose δ18O suggests that δ18O in tree-ring cellulose is controlled by common external factors, and that it is possible to establish a unique δ18O chronology using different tree species. The δ18O values of tree-ring cellulose in pine and oak trees are negatively correlated with precipitation from June to August (correlation coefficients are −0.679 for pine and −0.583 for oak), which is attributable to the precipitation amount effect, mainly caused by the stagnant rain front (Baiu) in early summer and typhoons in late summer in this region. The δ18O values are negatively correlated with relative humidity from April to September for pine (r = −0.632, p < 0.01), and in June and July for oak (r = −0.437, p < 0.01); these correlations probably reflect different lengths of the growing season. Multiple regression analysis reveals that tree-ring δ18O values of pine and oak in this region are largely governed by summer precipitation. Relative humidity does not appear to greatly affect tree-ring δ18O of oak, in contrast to pine, which may be interpreted in terms of differences in leaf morphology and/or cellulose synthesis processes. Our results indicate that δ18O values of tree-ring cellulose can provide a potential crossdating tool, irrespective of the physiological differences between gymnosperms and angiosperms. In central Japan, tree-ring δ18O values of both pine and oak can act as reliable proxies of June–August precipitation, while pine trees tend to exhibit more potential for reconstruction of relative humidity.
Characterization and in vacuo crushing 40Ar/39Ar dating have been performed on four quartz veins within ultrahigh pressure (UHP) metamorphic rocks from the Yuka terrane, North Qaidam Orogen, western China. The data are used to decipher the nature, origin and age of the vein-forming fluids during the exhumation of UHP rocks. By using petrography and microthermometry analyses, three principal types of fluid inclusions have been identified: (1) hypersaline inclusions (type-a), (2) intermediate to high-salinity inclusions (type-b), and (3) low-salinity aqueous inclusions (type-c). The type-a and partly type-b inclusions occur as isolated, suggesting a primary origin. Most of the type-b inclusions occur as cluster in crystal micro-fracture, but never crosscut the crystal boundaries between individual quartz grains, indicating they are pseudo-secondary inclusions. The type-c inclusions commonly distributed in trails along the micro-fracture, suggesting a secondary origin. Quartz samples dated by 40Ar/39Ar in vacuo crushing method yield monotonic declining release patterns: anomalously old apparent ages are obtained at the first steps and relative flat age plateaus (429–411 Ma) over the final several steps. The gases liberated in the final steps are most derived from radiogenic and trapped argon in small primary fluid inclusions and pseudo-secondary fluid inclusions and also atmospheric argon from the crusher. Consequently, the plateau ages are concluded as the best estimate for the ages of quartz veining during the UHP rocks exhumation. Meanwhile, we ascribe the extremely high initial apparent ages to the most easily crushed and excess 40Ar (40ArE) dominated secondary fluid inclusions, because they generally distributed along crystal fractures. On the plots of 40Ar*/39ArK vs. 38ArCl/39ArK, the early data points yield well-defined isochrons and with two group ages: 392 Ma and ∼344 Ma, representing two episodes of post-collisional fluid flow activities. Microthermometry analyses and 40Ar/39Ar in vacuo crushing dating suggest that the secondary inclusions may be originated from the excess 40Ar rich post-hydrothermal fluid from the depth. In contrast, the primary inclusions have more complex origins, including meteoric waters transported by fault/shearing zones, retrograde decomposition of hydrous minerals and partial melt of HP/UHP rocks.
Due to lack of precise geochronological data, the Late Paleozoic tectonic evolution in the eastern segment of the Central Asian Orogenic Belt (CAOB) is poorly constrained. We present geochronological and geochemical data of newly identified Middle–Late Permian mafic–ultramafic intrusions (Hongqiling Nos. 4, 5 and 6) in the central area of Jilin Province, southeastern margin of the CAOB, aiming to provide important information for understanding the tectonic processes during their emplacement. Gabbros from the Hongqiling Nos. 5 and 6 intrusions give SHRIMP zircon U–Pb ages of 272.0 ± 3.6 Ma and 258.8 ± 3.4 Ma, respectively. Rocks from the Nos. 4, 5 and 6 intrusions have low SiO2, high TFe2O3 and MgO contents. In addition, they are characterized by enrichment in large ion lithophile elements (Ba, Rb, Sr) relative to high field strength elements (Ta, Nb, Zr), indicating that they were derived from a metasomatized lithospheric mantle. On the other hand, they show E-MORB-like geochemical compositions such as Nb/Yb (1.87∼5.33) and Th/Yb (0.18∼1.67) ratios, suggesting that an asthenospheric mantle was involved. Therefore, the dual geochemical characteristics of the Nos. 4, 5 and 6 intrusions may reflect an extensional environment, in which upwelling asthenospheric mantle decompressionally melted and triggered partial melting of overlying metasomatized lithospheric mantle. Recently, another pulse of mafic-ultramafic magmatism (240–212 Ma) representing by the Nos. 1 and 8 intrusions has been identified in the Hongqiling area. In contrast, the Middle–Late Permian (272∼258 Ma) mafic magmas have higher Sm/Yb ratios than those of the Middle–Late Triassic (240∼212 Ma) mafic magmas, suggesting the first pulse of magmatism (272∼258 Ma) derived from a relatively deeper mantle. Thus, two stages of magmatism that derived from different depth have been proposed, namely, Middle–Late Permian (272∼258 Ma) magmatism (Hongqiling Nos. 4, 5 and 6 intrusions) with a greater depth, and Middle–Late Triassic (240∼212 Ma) magmatism (Hongqiling Nos. 1 and 8 intrusions) with a shallow depth. Taking into account the regional tectonic and magmatic data, we correlate the first stage magmatism to a slab break-off regime following the initial collision between the North China Block and the Songnen–Zhangguangcai Range Massif (SZRM), and the second stage of magmatism to a post-orogenic extensional environment associated with delamination. These two stages of magmatism with different geochemical characteristics suggest that the final closure of the Paleo- Asian Ocean (PAO) occurred during Late Permian to Early Triassic.
We examined the molecular weight distribution of the fluorescence intensity of FDOMM and dissolved organic carbon (DOC) concentrations in the subtropical western North Pacific, in order to characterize photoreactivity of FDOMM and understand the relationship between FDOMM and DOC pool. DOC concentrations in a hydrophobic fraction (O-DOC),which is extracted by solid phase extraction, accounted for 34 and 38% of bulk organic carbon in the surface and deep layer. FDOMM in a hydrophobic fraction (O-FDOMM) accounted for 78 and 37% of FDOMM in the surface and 1000-m depth seawater, respectively. Molecular weight distribution of O-FDOMM and O-DOC showed that ratio of the fluorescence intensity to the DOC concentration of each MW fraction increased with depth. This suggests that the contribution of O-FDOMM to O-DOC in the deeper seawater is higher than that in the surface layer. When deep-seawater samples were irradiated by natural sunlight for 5 days, the fluorescence intensity of O-FDOMM decreased to almost half and its molecular weight shifted to lower one, whereas the O-DOC concentration did not decrease. It implies that a part of O-FDOMM remains as photobleached FDOMM (no-fluorescence DOM) after photobleaching.
We estimated the contributions of source regions in East Asia to PM2.5 mass concentrations over Japan for the year 2010 using a regional chemical transport model with an emission sensitivity approach. The horizontal distributions and temporal variations of PM2.5 concentrations were generally well reproduced by the model. The relative contribution of China to the annual mean PM2.5 concentration was estimated to be 50–60% in western Japan (from Kyushu to Kinki), and 40% in the Kanto area. Central north China (105°E–124°E, 34°N–42°N) made a particularly significant contribution, accounting for 20–40% of the annual mean PM2.5 concentration for the whole of Japan. The contribution from foreign sources increased in spring, autumn, and winter in western Japan, and in spring in the Kanto area. The domestic contribution was estimated to be 20–50%. The sum of contributions from foreign anthropogenic sources was greater than the domestic pollution in each receptor region except the Kanto region. The results were obtained from sensitivity simulations with reduced anthropogenic emissions from each source region by 20%. The uncertainties in the source-receptor relationship for annual mean PM2.5 concentrations were estimated to be within a few percent, from additional sensitivity simulations with different perturbations (a 20% increase and a 50% reduction). The model results suggest that regional-scale transport in East Asia has a significant impact on the attainment of the PM2.5 environmental standard in Japan.
The Rexiang hydrothermal Cu deposit, a newly discovered medium-sized deposit, is located in the central Yidun Island Arc (YIA) in northeastern Tibet. Zircon LA-ICP-MS U–Pb dating for a Rexiang copper-bearing monzogranite sample gives a crystallization age of 79.3 ± 0.7 Ma (MSWD = 3.8). Geochemical data indicate that Rexiang copperbearing monzogranite has high-K calc-alkaline to shoshonitic compositions, moderate A/CNK values (lying primarily within 1.02–1.06), high differentiation index (DI = 86–94), and moderate amounts of corundum (0.34–2.19%), indicating an affinity to weakly peraluminous and highly fractionated I-type granite. REE patterns show enrichment in LREE relative to HREE. The monzogranite is characterized by moderately negative Eu anomalies (δEu = 0.22–0.77), strong enrichment in Rb, Th, U and Ta, depletion in Ba, Sr and P, and higher initial 87Sr/86Sr ratios (0.70957–0.7114). Combined with the analysis of its tectonic setting, the monzogranite is interpreted as resulting from partial melting of supracrustal rocks in the postorogenic stage after the collision orogenesis of the YIA in the Late Yanshanian. A Late Cretaceous porphyry (hydrothermal) Cu–Mo-polymetallic mineralization event not only exists in the southern segment of the YIA (the Zhongdian arc) but also in the central segment of the YIA.
This survey was conducted to analyze particle-associated atmospheric polycyclic aromatic hydrocarbons (PAHs) at a rural site (Kamihaya) in Tanabe, Wakayama Prefecture, central Japan from 2012–2013. Analysis of particulate matter revealed that total PAHs ranged from 0.036 to 10.16 ng m−3 with an average concentration of 3.20 ng m−3. The highest PAHs concentration of 10.16 ng m−3 was observed on September 19, 2012. Significant seasonal variations in PAHs concentrations were observed at the site, with higher values during winter/spring and lower values during summer/autumn. Trajectory analyses suggest that PAHs produced domestically have a greater impact on Kamihaya than those transported from other countries. Molecular diagnostic ratios and principal component analysis showed that atmospheric PAHs primarily arose from industrial and traffic emissions, while wood combustion appeared to be a minor source. Overall, the results of this study suggest that atmospheric PAHs in Kamihaya present a potential threat to the underlying vegetation and may cause damage to plants if combined with other air pollutants.
We conducted a sequential chemical extraction experiment for radiocesium (134Cs + 137Cs) using 21 surface sediment samples and two sets of size-fractionated surface sediment samples collected offshore Fukushima. Our results support earlier reports in this area that organic substances in marine sediments have an apparently higher preference for radiocesium than mineral substances. Observations suggest that mineral and organic substances in the marine sediments offshore Fukushima have the same order of preference for radiocesium, primarily because of the existence of ionic competitors in seawater. The apparent preference of radiocesium for organic material is greater because of the partial coverage of sediment mineral surfaces by organic substances. By using these relationships, we created a 2-D map of radiocesium concentration in sediment organic fraction in offshore-Fukushima region. Combining our results with existing monitoring data of marine benthos in offshore-Fukushima sediments, we estimated a transfer coefficient of radiocesium from sediment organic materials to benthic polychaetes as less than 0.03–0.008.
We assess the usefulness of the empirical boron partition coefficient, KD and B/Ca measured from planktonic foraminifera in estimation of pCO2 using three different relationships between KD and temperature derived from various studies. Two sediment cores spanning the last 22 kyr were utilised, one from the intense CO2 source region of the Western Arabian Sea (WAS) and another from the Eastern Arabian Sea (EAS). The sea-air difference in pCO2 at these sites shows results contrary to the present day scenario. Moreover the reconstructions using the three KD relationships lead to assorted results which suggests that the KD approach may not be suitable in paleo-pCO2 reconstructions.