Dissolved inorganic nitrogen (DIN), such as NO2– and NH4+, is known to react abiotically with organic matter to form organic N under specific conditions. However, the contribution of abiotic processes to the dynamics of DIN in marine environments has not been sufficiently evaluated. In this study, I demonstrated using 15N-labeled tracers that abiotic immobilization of DIN (particularly NO2–) occurred in coastal marine sediments after samples were autoclaved or treated with HgCl2, and compared it with the biotic immobilization (bacterial assimilation) of DIN in terms of reaction rate, product yield, and the degradability of the organic N produced. Abiotic and biotic immobilization of N from DIN into solid sediment occurred within a period of days to a few weeks. NH4+, NO2–, and NO3– were significantly immobilized by biotic processes in the sediment investigated, although microbial dissimilatory reduction seemed to be the primary sink for NO2– and NO3–. In contrast, only NO2– was significantly immobilized in the sediment by abiotic processes. Abiotic immobilization of NO2– apparently obeyed first-order kinetics when the concentration of NO2– was <200 μM. Decomposition experiments with natural sedimentary bacteria demonstrated that organic N formed biotically from NH4+ and abiotically from NO2– was operationally separated into a readily decomposable fraction and a refractory fraction. The refractory fraction of immobilized N ranged from 22% to 68% and was apparently dependent on the physical nature of the sediment (e.g., specific surface area), rather than whether it had been produced biotically or abiotically. This observation suggested that abiotically immobilized N can be preserved in sediment to a similar extent, and by similar mechanisms, as biotically produced organic N.
Understanding catfish ecology is important because catfish constitute one of the largest fish stocks in the coastal Indo-Pacific regions. Recent technological advances have enabled the use of biological electric sensors to understand fish ecology, but their application requires catch and release. Fish otoliths can record ecological changes, and oxygen isotopes and Sr/Ca ratios along the growth direction are independently used to reconstruct the migration history of the fish. Here we report high-resolution measurements of both oxygen isotopes and Sr/Ca ratios of a modern otolith from a marine catfish (Plicofollis tenuispinis) collected from the Gulf of Khambhat, western India. Both sets of data suggest that the catfish migrated from an estuarine environment to the sea during its lifetime. Migration history of the catfish was estimated with monthly resolution aided by numerical modeling. Potential applications of this analysis as an environmental recorder for variables such as temperature and water chemistry are examined.
The origin of the abundant salt resources in the Gasikule salt lake in the northwest Qaidam Basin in China remains highly contested. We performed a detailed study of the hydrochemical characteristics and material sources of the Gasikule brines based on their chemical composition and hydrogen-oxygen isotopes, together with high-resolution remote sensing imagery of the stream water, surface brine, and intercrystalline brine. Stream waters within the catchment were found to be weakly alkaline and dominated by HCO3–, Cl–, and Na+ ions. The Gasikule surface brine was also weakly alkaline and classified as chloride type. The average total dissolved solid (TDS) was 366.19 g L–1; Cl– and SO42– were the dominant anions, and Mg2+ and Ca2+ were the dominant cations. The intercrystalline brine was weakly acidic and classified as a magnesium sulfate subtype. The average TDS was 381.80 g L–1; Cl– was the dominant anion, and K+ and Mg2+ were the dominant cations. The surface and intercrystalline brines were enriched in K+ because of the annual formation of “dry salt lake” conditions. Using Enhanced Thematic Mapper (ETM) and Satellite Probatoire Pour l’Observation de la Terre 5 (SPOT5) remote sensing data, two (approximately) north-south trends in salinity in the eastern area of the Gasikule surface brine were identified (referred to as “water swell annular anomalies”). These two anomalies were found to be located (approximately) above an existing buried fault from which Ca-Cl type deep water recharged the surface brine. Three main sources were identified for the recharge of the surface and intercrystalline brines of the Gasikule salt lake: (a) stream water sourced from rainfall and melting ice; (b) leaching of Pliocene salt-bearing host rocks that contain sulfate minerals such as gypsum, mirabilite, and celestite at the northern end of the salt lake; and (c) Ca-Cl type deep water, associated with a buried fault.
δ13C was measured in two species of Sphagnum moss (Sphagnum palustre and Sphagnum fimbriatum), collected from the Genseinuma-fen in Unzen, Northern Kyushu in March, 2010. From examination of several specimens of the two species near the sampling site, the growth rates were determined to be sufficiently high to allow interpretation of annual δ13C variation through comparison with locally recorded climatic information. The δ13C values of different organs (stems and branches) and components (bulk and cellulose) exhibit consistent variations, although the differences between them appear to be species-specific. Both species, but in particular S. palustre, exhibited smooth increases in δ13C towards the central part of the sample length (total 16–17 cm), corresponding to approximately half a year’s of growth. Temperature is considered to be the primary factor affecting the δ13C values of both species, with the observed δ13C maximum corresponding to the summer of the previous year. However, the positions of the peaks in branches and stems differed by 2 or 3 cm, reflecting the fact that stem growth was preceded by branch growth. Considering the relationship between δ13C and temperature, a rise of 1‰ in δ13C is seen to correspond to a rise of 14°C and 10°C for S. palustre and S. fimbriatum, respectively.
During the 5th China Arctic Research Expedition of the R/V Xuelong (June–September, 2012) total gaseous mercury (TGM) in the marine boundary layer along the route was measured. The spatial distribution of TGM was determined from Shanghai to the Bering Strait along the Northwestern-Pacific volcanic belt and around Iceland outside the Arctic Ocean. TGM ranged from 0.17 to 9.03 ng/m3 with a mean of 1.86 ± 1.21 ng/m3 (median: 1.55 ng/m3). Several peaks along the cruise exceeded 4.0 ng/m3. TGM means in leg1 and leg4 (near Japan) were 1.99 ± 0.71 ng/m3 and 2.56 ± 1.39 ng/m3, respectively. In leg2 and leg3 near the Kamchatka peninsula, TGM was 1.23 ± 0.55 ng/m3 and 2.78 ± 1.42 ng/m3, respectively. In leg5 near Iceland TGM was 1.39 ± 1.02 ng/m3 with relatively high value in Reykjavik harbor (mean: 1.91 ± 1.27 ng/m3). Based upon backward air trajectory, trace gas CO, meteorological/hydrologic data, and volcanic degassing information, relatively greater TGM values were associated with the role of ocean emissions, volcanic, and other geothermal activities.
The effects of artificial deforestation in the 1970s and the subsequent recovery process on the transport of particulate organic matter were investigated using reservoir sediments obtained from the Noto Peninsula in Japan. In 1975, the sedimentation rate increased to about 2.7 times its previous value because of deforestation and plantation activities in the catchment. The sedimentation rate remained high until 1991, suggesting that the erosion rate of soil and organic matter increased during the 15 years after the deforestation. This intensive erosion was induced by exposure of bare soil, forest management activities to remove understory vegetation, and heavy rainfall. Conversely, the δ13C and δ15N of the sediment organic matter has continued to decrease from the mid-1980s to the present time, despite the fact that the sedimentation rate has recovered to pre-deforestation levels. The decrease of the δ13C and δ15N of the sediment organic matter reflects a decrease in the contribution of soil organic matter, although post-depositional diagenesis and variability of the isotopic composition of the aquatic organic matter also affect the δ13C and δ15N. The decrease in the soil organic matter contribution suggests gradual recovery of vegetation, accumulation of forest floor organic matter, and reduction of soil erodibility. These results indicate that the change in the transport of organic matter continued for at least 35 years after the deforestation and plantation.
The 500 m long section through the upper part of the Permo-Carboniferous Landsberg laccolith (Halle Volcanic Complex) was sampled every 25 meters. The modal proportions between plagioclase and K-feldspar phenocrysts vary in the section and the laccolith may be divided into four parts with different proportions of Pl/Kfs, which, in subvolcanic rocks, should reflect different proportions of these minerals in the magma plumbing system. Chemical composition of whole rock samples is uniform, but the correlations of Si and other elements with depth within all of the four sections suggest that the sections based on modal composition are also reflected in chemical composition of the rock. Also, the uppermost 100 meters of the laccolith has slightly higher contents of Fe, Ti, Zr and Nb compared to those in the rest of the laccolith and this is consistent with it being a separate magma pulse derived from a distinct source. Detailed analyses of chemical variations within each section are consistent with the model that the upper 500 meters of the Landsberg laccolith was formed by three successive pulses with slightly different chemical compositions. The best documented is the uppermost pulse, which was over-accreted on the first pulse. Another pulse was probably emplaced in the middle of the first pulse. The thickness of the pulses was 100–300 m, which is consistent with previous 2D and 3D emplacement models of the Halle laccoliths. However, the contacts between the pulses based on modal and chemical compositional variations are not always concurrent with the presence of shearing zones, the discrepancy that is not yet well understood. In general, because silica-rich laccoliths are relatively small bodies that cool quickly due to high level of emplacement, they may preserve better evidence for separate magma pulses compared to plutonic batholiths.
Determination of adsorption coefficient of strontium (Sr), one of the major elements of low and intermediate level radioactive wastes, is an important step to assess the performance of a waste repository. The adsorption coefficient of strontium on rhyolitic type pumice tuff, already selected as a potential host rock for radioactive waste repositories in Japan, was investigated with batch adsorption experiments. Some parts of the pumice tuff were oxidized and this redox effect was compared with fresh tuff. The distribution coefficient yielded negative values ranging from –0.3 to –9.6 mL/g at low initial concentration of 10–6 and 10–7 mol/dm3, because a higher strontium concentration over the initial one was found in the aqueous phase at equilibrium. Batch dissolution experiment revealed that pumice tuff releases considerable amount of strontium, 8.27 × 10–7 and 4.76 × 10–6 mol/dm3, respectively for fresh and oxidized tuff. Incorporating the dissolved strontium concentration in equilibrium, major changes in distribution coefficient values were found for the oxidized tuff. Considering the dissolution effect is thus necessary, especially for redox zone solid, to properly evaluate the distribution coefficient of easily soluble nuclides when a lower initial concentration is used. To incorporate the dissolution effect, a slight modification of the existing equation was made to determine the distribution coefficient.
The dissolution rate of minerals is affected by not only physical factors but also chemical factors, such as temperature, solid applied stress, pore water pressure and pH. In general, previous studies on mineral dissolution have dissociated these physical and chemical factors. In this paper, we propose a new dissolution rate equation for quartz dissolution that considers the physical and chemical effects of dissolution. Therefore, the reaction rate constant (k), which is the most important factor in the calculation of the reaction rate, was separated into three individual terms: temperature, solid applied stress and pore water pressure. Finally, the theoretical dissolution rate equation is proposed in this study; the equation contains all of the parameters that are related to the dissolution mechanism, such as temperature, solid applied stress at contact zone, pore pressure and pH conditions. To verify the proposed equation, it is compared with the experimental results, which were collected under various physical and chemical conditions; the equation is found to fit the experimental data well.
The distribution of solar-wind ions in Genesis mission collectors, as determined by depth profiling analysis, constrains the physics of ion-solid interactions involving the solar wind. Thus, they provide an experimental basis for revealing ancient solar activities represented by solar-wind implants in natural samples. We measured the first depth profile of 4He in a Genesis collector; the shallow implantation (peaking at <20 nm) required us to use sputtered neutral mass spectrometry with post-photoionization by a strong field. The solar wind He fluence calculated using depth profiling is ~8.5 × 1014 cm–2. The shape of the solar wind 4He depth profile is consistent with TRIM simulations using the observed 4He velocity distribution during the Genesis mission. It is therefore likely that all solar-wind elements heavier than H are completely intact in this Genesis collector and, consequently, the solar particle energy distributions for each element can be calculated from their depth profiles. Ancient solar activities and space weathering of solar system objects could be quantitatively reproduced by solar particle implantation profiles.
Trace element geochemistry for dolomitic limestones was carried out by chemical separation of the constituent calcite and dolomite. A five-minute treatment for fine-grained dolomitic limestone with 0.5 M acetic acid differentially dissolves the calcite, but 82–90% of dolomite remained undissolved. The fraction of dissolved dolomite contributed 2–17% to the calcite fraction, depending on the calcite/dolomite ratios of the samples. The residue of the acetic acid treatment was treated with 0.5 M HCl and an almost pure dolomite fraction was obtained. Comparison of the trace element concentrations in the calcite and dolomite fractions for four dolomitic limestones revealed that the REE abundances in both the fractions were similar, while the Fe, Mn, P, and Al concentrations in the dolomite fractions were higher than those in the calcite fractions. The method developed in this study can be used for trace element studies of dolomitic limestones.
Nitrogen isotopes are widely used to trace volatile sources in volcanic/hydrothermal systems. However, the nitrogen isotope composition of dissolved N2 may not be the same as N2 gas, due to minor isotope fractionation. In order to evaluate N isotope fractionation during dissolution of N2 gas in water as a function of temperature, we measured δ15N values of dissolved N2 over a temperature range of 5 to 60°C. Our experiments show that δ15N values are 0.91, 0.73, –0.04, and –0.42‰ at 5, 20, 40, and 60°C, respectively. The temperature dependent fractionation is stronger than published results and indicates an isotopic “crossover” at 40°C. A possible explanation for the steep temperature dependence is that a kinetic-based incorporation of the light isotope (14N) into water increases as temperature rises. We show that small negative δ15N values in natural springs could be due to kinetic fractionation between dissolved N2 and N2 in air.