The concentrations of the herbicide Diuron and algaecide Irgarol in the Seto Inland Sea, Japan, were assessed for October 2008 and October 2009. Overall, 29 seawater, sediment and plankton samples were collected from off-shore areas around the sea. The Diuron levels were 0.01-0.062 μg/L, 0.01-0.09 μg/g dry weight (dw) and 0.075-0.45 μg/g dw in seawater, sediments and planktons respectively. Irgarol levels were 0.011-0.055 μg/L, 0.011-0.068 μg/g dw and 0.02-0.36 μg/g dw in seawaters, sediments and planktons respectively. This is the first study to report the presence of Diuron and Irgarol in plankton from aquatic environments. The concentrations of Diuron and Irgarol were similar in both years and the highest levels of concentration were found near the coastal area of Osaka bay, second largest metropolitan region in Japan. The distribution of Diuron and Irgarol in seawaters, sediment and plankton would be largely determined by riverine discharge or uses of these pesticides as antifouling agent at harbors and ports and then transport to offshore from coastal waters by water flows.

View full abstract

Sulfur isotopes in vein sulfides (galena, sphalerite, and pyrite) and pyrite sulfur derived from overprinting hydrothermal systems in the altered volcanic host rocks of the Toyoha-Muine area are determined. Miocene and Pliocene-Pleistocene systems are found and are both characterized by Pb and Zn mineralization. The δ³⁴S values for the vein sulfides in both systems show a similar range, i.e., 1.7~7.5‰ and 1.3~7.7‰ for the Miocene and Pliocene-Pleistocene systems, respectively. The δ³⁴S values of pyrite sulfur in the Miocene altered rocks show a wider range (-4.0~10.5‰) than the contemporaneous ores, while Pliocene-Pleistocene values (0.8~6.3‰) show a narrow range, similar to the contemporaneous ores. Miocene ore deposits were formed from hydrothermal fluids under reduced conditions; aqueous sulfur in the solutions was predominated by dissolved H₂S. From the δ³⁴S of the Miocene sulfide minerals, δ³⁴S_H2S is calculated to be in the range 2.8~6.2‰, indicating that the sulfide sulfur was arc magmatic in origin. Although previous studies suggest that the source of sulfur and metals for the Pliocene-Pleistocene system can also be attributed to the contemporaneous arc magma, this study proposes another source. Combined with a previous study of tectonic setting, the common presence of Pb and Zn in the ores and the similar δ³⁴S of the vein sulfides for distinct hydrothermal systems suggest that minor amounts of sulfide sulfur and base metals (Pb, Zn, and Fe) from the Pliocene-Pleistocene ores were introduced by dissolution and remobilization of sulfur and metals from the Miocene ores and altered rocks. The wide range of δ³⁴S from pyrite sulfur in the Miocene altered rocks may be a result of the contribution of magmatic sulfur contaminated by reduced seawater sulfate; however, the narrow range of δ³⁴S in the Pliocene-Pleistocene altered rocks is a result of the major contribution of magmatic sulfur and minor contribution of recycled sulfur from the Miocene ores and altered rocks, as in the case of the contemporaneous vein mineralization.

View full abstract

To elucidate the isotope geochemistry of CH₄ production in deep subsurface environments, we investigated the relation between H₂ concentration and hydrogen and carbon isotope fractionation by CO₂ reduction using microbial communities obtained from groundwater in a deep aquifer associated with an accretionary prism. Incubation experiments were conducted under anaerobic culture conditions of two types. In one experiment, a coculture of H₂-producing fermenters and hydrogenotrophic methanogens was established in groundwater treated with organic substrates. The other experiment used groundwater under H₂ + CO₂ (80:20, v/v) to produce CH₄ under high H₂ concentrations. In the cocultures, H₂ concentrations increased in the initial phases, then decreased gradually and remained low during CH₄ production, indicating H₂ consumption by hydrogenotrophic methanogens to produce CH₄. This study revealed for the first time that cocultures with fermenters and hydrogenotrophic methanogens producing CH₄ in low H₂ concentration cause smaller hydrogen isotope fractionations (0.663 < α_H < 0.725) than in monocultures under high H₂ concentrations (0.629 < α_H < 0.656). Carbon isotope fractionation in cocultures was greater (1.052 < α(CO₂-CH₄) < 1.074) than in monocultures under high H₂ concentrations (1.021 < α(CO₂-CH₄) < 1.023). The large carbon fractionation was thought to result from low levels of H₂, supporting the hypothesis of differential reversibility of multiple enzymatic processes in CH₄ production. Although lack of agreement remains between results of incubation experiments and field observations especially in hydrogen isotope fractionations, both hydrogen and carbon isotope fractionation in cocultures were close to the fractionations of field observation in which CO₂ reduction is a dominant pathway in CH₄ production compared with those in monoculture.

View full abstract

Experiments were carried out to determine molybdenum isotope fractionation associated with adsorption to pyrite. Results show that the Mo isotope composition of the aqueous solution becomes progressively heavier as Mo is adsorbed, with a Mo isotope fractionation as large as 2.9‰. This fractionation is larger than observed for typical anoxic continental margin marine sediments (e.g., ~0.7‰), suggesting that Mo adsorption to pyrite is not the dominant process operating in these environments. However, our adsorption results do suggest the possibility that anoxic fractionation processes could impart an isotope signature within the geologic record similar to the isotope fractionation observed under oxygenated conditions. Additional experiments were conducted at high (~100 μM) dissolved Mo concentrations, but at varying pH and ∑H₂S concentrations, and in each case these experiments promoted Mo-sulfide precipitation. Even though the experiments were conducted under differing conditions and produced different amounts of precipitate, the results suggest a constant fractionation of ~0.9‰ associated with this Mo removal process. This fractionation is more consistent with that inferred for anoxic continental margin marine sediments, suggesting that a process similar to Mo-sulfide precipitation, rather than an adsorption process, may be responsible for the Mo isotope compositions observed in these environments. The findings of this study suggest that, regardless of the geochemical mechanism employed, sediment Mo sequestration under anoxic conditions may impart a significant isotopic fractionation relative to parent seawater.

View full abstract

Main objectives of this study were to investigate whether humic substances (HS) exist in hot groundwater from deep basinal aquifers waters and to provide basic knowledge on humic (HA) and fulvic acids (FA) isolated from these fluids. Water sampling and HS isolation was carried out in three consecutive years from wells tapping the aquifers of the Pannonian Basin (Southeast Hungary). The isolated humic acid and fulvic acid samples were studied by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR/MS). We found that modified sampling (acidification of water samples either immediately or after cooling down) had no traceable effect on the properties of isolated HAs and FAs. The quantity and quality of humic materials did not change in three years. The analytical results clarified distinctive chemical characters of HS in the deep aquifer groundwater compared to the Suwannee river fulvic acid (SRFA) as a reference. In addition, we stated that aliphatic content of isolated HAs and FAs increased with increasing aquifer depth and temperature, but the aromaticity and heteroatom content decreased in both fractions.

View full abstract

The historical trend of the concentrations of carotenoids originating from phytoplankton in sediment cores collected at two sites in Lake Shinji, a eutrophic oligohaline lake was investigated to clarify the changes in phytoplankton community structures in the lake over the last 100 years. Eight kinds of carotenoids were detected in the sediments, i.e., astaxanthin and lutein from chlorophytes, alloxanthin from cryptophytes, canthaxanthin, echinenone and zeaxanthin from cyanobacteria, diatoxanthin from diatoms, and β-carotene from unspecified algal groups. On the basis of the stoichiometric relation between total organic carbon (TOC) and total sulfur (TS), the historical changes in the TOC concentration of sediment cores since circa 1970 have been attributable to the decomposition of organic matter by sulfate reduction, confirming the importance of diagenetic processes in Lake Shinji sediments. It was found that labile chlorophyll a is transformed diagenetically to more stable pheophytin a and pyropheophytin a within the upper 5 cm of the cores. Similarly, the concentrations (μg g^-1 TOC) of carotenoids, other than diatoxanthin, in the cores decreased rapidly within this zone, and in the cores lower than 5 cm below lake floor, their concentrations showed a decreasing or fixed trend with depth. This suggests that these carotenoids have been degraded in sediments depending on their stabilities. Among the diatoxanthin, lutein and zeaxanthin of which the stability is similar, the relative abundance of lutein (chlorophytes) has increased since circa 1970, and, conversely, the relative abundance of diatoxanthin (diatoms) has decreased. Diatoms are likely a staple food for the shellfish Corbicula japonica in Lake Shinji, because they are rich in lipids, which are needed for the growth and survival of C. japonica. Hence, the relative decrease in the number of diatoms may have some effect on the decrease in the population of C. japonica since the 1970s in the lake.

View full abstract

A cultured strain of Isochrysis galbana UTEX LB 2307 was grown at 20°C and 15°C under salinity of 35‰, 32‰, 27‰, 20‰, and 15‰, and analyzed for long chain (C₃₇-C₃₉) alkenones and (C₃₇-C₃₈) alkyl alkenoates. It was characterized by abundant C₃₇ alkenones and C₃₈ ethyl alkenoates (fatty acid ethyl ester: FAEEs) and a lack of C₃₈ methyl alkenones. There were no tetra-unsaturated (C_37:4) alkenones, which are frequently found in natural samples from low salinity waters. The alkenone unsaturation index (U^K′₃₇) did not vary in response to change in salinity at 15°C. The alkenone unsaturation index (U^K′₃₇) clearly changed in response to change in salinity at 20°C, but not at 15°C, where algal growth was and was not limited by temperature at 15°C and 20°C, respectively. The U^K′₃₇-temperature calibration for I. galbana UTEX LB 2307 is quite different from those of E. huxleyi and another strain of I. galbana (CCMP1323), while is resemble to that reported for C. lamellosa isolated from a Chinese lake. Also, variation in the alkenone chain length ratio values (K₃₇/K₃₈) did not correlate with salinity. These results implied that a high abundance of tetra-unsaturated alkenone and high K₃₇/K₃₈ values might be attributed to a taxonomic factor rather than a physiological response to salinity change. Interestingly, our culture experiments showed that the ethyl alkenoates/alkenones ratio (EE/K₃₇) correlates with salinity. Hence, it is suggested that the EE/K₃₇ ratios are affected by the cellular and physiological factors against salinity condition in single haptophyte cells.

View full abstract

Nitrogen isotopic analyses were conducted on two kerogenous samples from the Gunflint Formation (ca. 1.9 Ga) using the stepwise combustion technique to evaluate a potential analytical problem for the carbonaceous samples and to assess if this method is appropriate for the analysis of ancient rocks. Two discriminated δ¹⁵N plateaux are identified for each sample with mean values of +5.0‰ and +7.3‰ for sample 0708, and +6.1‰ and +5.2‰ for sample 0704, respectively. The direction of the δ¹⁵N shift is opposite in each sample. This characteristic excludes the possibility of analytical artifact as the source of isotope fractionation and metamorphism isotope fractionation. The two δ¹⁵N plateaux observed for each of the samples are characterized by different activation energies for the co-released carbon. These results suggest that similarly aged sedimentary rocks may contain at least two types of organic matter that record different source information for δ¹⁵N.

View full abstract

A simple gas chromatographic method has been developed for the simultaneous and sensitive analysis of inorganic (H₂, CO, and CO₂) and organic gaseous compounds (CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, iso-C₄H₁₀, and n-C₄H₁₀). The analysis of these gases generally requires multi-columns and/or multi-detectors, whereas the proposed method uses a single micropacked column and a single pulsed discharge helium ionization detector (PDHID). All of the investigated peaks (except for the N₂ and O₂ peaks, which are the major components of air) show good separation when using an oven temperature program from 40°C to 300°C. This gas chromatography-PDHID system yielded good linearity and a relative standard deviation of less than 5%. This sensitive and convenient method shows great potential in analyses of various types of gaseous compounds.

View full abstract

A swarm of quartzofeldspathic dykes extensively intruded the Permian-Triassic Yeongdeok pluton and xenoliths therein in southeastern Korea. Zircons from the dyke intruding a diorite xenolith yield sensitive high resolution ion microprobe ²⁰⁶Pb/²³⁸U dates ranging from Middle Permian (ca. 260 Ma) in the crystal cores to Late Cretaceous (ca. 82 Ma) in the outermost rim, with a negative correlation between U contents and dates. Such systematic variations can be explained by an initial mixing between inherited zircons from the host Permian diorite and overgrowth rims with various U/Pb ratios crystallized during intrusion of the dyke in the Cretaceous. This study shows that zircon U-Pb data from dyke rocks need to be treated with caution for geochronological interpretation.

View full abstract

We measured helium-3 (³He), sulfur (S), fluorine (F), chlorine (Cl) and bromine (Br) concentrations in vesicles of Mid Ocean Ridge Basalts (MORBs) and Back-Arc Basin Basalts (BABBs). The aim of this study was to characterize the MORB-source composition and to estimate the fluxes of S, F, Cl and Br from the mantle. A newly developed gas extraction method called the “Frozen Crushing Method” was applied. Measured concentrations in vesicles were (4-31) × 10^-15 mol/g of ³He, (20-420) × 10^-9 mol/g of S, (60-5000) × 10^-9 mol/g of F, (160-450) × 10^-9 mol/g of Cl and (10-1300) × 10^-9 mol/g of Br. We estimated global fluxes of S, F, Cl and Br at Mid Ocean Ridges using the molar ratio of each element on the ³He in the samples and the known mantle ³He flux of 527 mol/yr. Estimated fluxes using element concentrations measured in vesicles are (1.2 ± 0.7) × 10¹⁰ mol/yr of S, (1.4 ± 1.0) × 10¹¹ mol/yr of F, (1.4 ± 0.5) × 10¹⁰ mol/yr of Cl and (3.1 ± 2.8) × 10¹⁰ mol/yr of Br. In addition, fluxes calculated on the basis of estimated concentrations in the bulk basalts are (1-26) × 10¹⁰ mol/yr of S, (2-120) × 10¹¹ mol/yr of F, less than (2-120) × 10¹⁰ mol/yr of Cl and (4-240) × 10¹⁰ mol/yr of Br.

View full abstract

The relative warmth and stability of the Holocene was punctuated by several brief cold events. Whereas these cold events on a global scale are widely reported, the lack of records from regions such as the East China Sea (ECS) results in an incomplete understanding of the underlying cooling mechanism. Here, we present a coral-based paleo-SST (sea-surface temperature) reconstruction from the ECS to constrain Holocene variability in the Kuroshio Western Boundary Current and the East Asian Monsoon (EAM). Our new data confirm that cold conditions prevailed at 3.8 cal kyr BP, which is consistent with the previously-reported Pulleniatina Minimum Event (PME). While this previous reconstruction could not reveal seasonal differences, our high-resolution data indicate a differing seasonal SST response between summer and winter. This result provides an important insight into understanding the mechanism of the millennium scale cold event in the ECS, the region affected by EAM.

View full abstract