A new oscillopolarographic method for the determination of Si (Ⅳ) is described in this paper. In the system HCl-Sb(Ⅲ)-Mo(Ⅵ)-NaCl-ethyl alcohol, Si (Ⅳ) with Sb (Ⅲ) and Mo (Ⅵ) form ternary heteropoly acid. The anion of ternary heteropoly is adsorbed on the dropping mercury electrobe and under proper electric potentials reduced quickly into heteropoly blue. The process of electrochemical reaction will produce a sensitive polarographic wave with peak potential at -0.30(Vs. SCE). The lower limit of determination is 8×10-8 mol/dm3. This method is sensitive, accurate and extremely rapid for the determination of micro-silicon in seawater.
The early diagenesis processes of several redox-sensitive trace metals (RSMs) (Mo, U and V) were studied with several short sediment cores (~25 cm) collected in the northern Okinawa Trough (OT). Pore water vertical profiles indicated that the sedimentary environments in all cores were between oxic and suboxic, not yet reaching anoxic sulfidic conditions. The recycling process of Mo in sediments was clearly associated with Mn and yielded little authigenic accumulation, while U showed a downcore increase in sediment and its authigenic mass accumulation rate (MAR) was estimated to be ~23% of the Changjiang (Yangtze) and Huanghe (Yellow) riverine flux. Benthic diffusive fluxes and MAR were calculated and the comparison of them showed that U and V fluxes matched relatively well both in direction and in magnitude, implying that diffusion processes at the sediment-water interface is the dominant process controlling the remobilization or burial of V and U in northern OT. This work provided a systematic study (both in pore water and solid phase) on the RSMs geochemical behaviors during early diagenesis process, yielding a quantitative assessment of the remobilization or burial fluxes of the RSMs in northern OT. Such studies are in general lacking in the coastal margin of Northwest Pacific Ocean.
Tungsten and molybdenum in seawater can be sensitively and accurately determined by the polarographic catalytic wave.In a supporting electrolyte containing HCl-benzilic acid-Nad, tungsten has a clear and stable catalytic wave.Then, the peak current of molybdenum increases as KClO3 is added into the above medium.The sensitivity of the proposed method is 5×10-2M for W and 6×10-10M for Mo, respectively. This method is an extremely quick, sensitive one and is suitable for the analysis of various kinds of water.
In the system HCl-Sb (Ⅲ)-ammonium molybdatc-acetone-butanone, PO43-, Sb (Ⅲ) and Mo (VI) form ternary heteropoly acid. This ternary heteropoly acid anion is adsorbed on the dropping mercury electrode and reduced quickly into heteropoly blue. The process of electrochemical reaction will produce a sensitive polarographic wave with peak potential -0.42V (vs S.C.E.). The detection limit is 6×10-8 mol/l. Variable coefficients are 10% and 3% for 0.1 μmol/l and 1 μmol/l respectively. This method is sensitive, accurate and extremely rapid for analysis of seawater.
In this paper,the following important problem is answered:Under what condition can the Hilbert transform be put in the simple form.Then,using the Hilbert technique,it is demonstrated that,with some relative weak restrictions,the particle motion at the sea surface and energy transmission may be obtained from a wave record.The analysis shows that for the two-dimensional and narrow-band mo tion (or a physical phenomena,such as capillary waves breaking,which satisfy the narrow-band approx imation) the local kinetic energy fluctuates in time as the envelope squared multiplied by a constant factor and can be obtained directly from a wave record.It is pointed that the local fluctuations of the potential energy as well as the local fluctuations of the total energy can be separated into a slowly varying part and a more rapid oscillating part.Both parts can be evaluated by means of the Hilbert transform.Finally,a physical interpretation of the envelope of the two-dimensional capillary waves as well as the method for wave group analysis is presented.
Trace elemental associations and Sr-Nd isotopic compositions are of important to recognition of biogenic material from mixed marine sediments.The foraminifera shell from the Okinawa Trough strongly enrichesSr, P, Mn andBa, enriches Li, U, Th, Sc, Co, Cu, Pb, Zn, Cr, Rb, Y, Sb and light rare earth elements, slightly enriches V, Ga, Zr, Nb, Cd and middle rare earth elements, is short of Mo, In, Sn, Cs, Hf, Ta, W, Ti, Bi and heavy rare earth elements.The mechanism of elemental enrichment in forminifera is the concentrations of trace elements in sea water and selective absorption of trace elements during foraminifera living, as well as the geochemical affinity between major elements and trace elements.The REE (rare earth elements) partition pattern of foraminifera shell of the Okinawa Trough shows enrichment of middle rare earth elements with slightly negative Ce anomaly, which are different from those of foraminifera of the Pacific Ocean.The Sr, Nd isotopic ratios of the Okinawa Trough foraminifera are 0.709 769 and 0.512 162, respectively, which are different not only from those of oceanic water, but also from those of river water of China's Mainland, the former is slightly higher than those of oceanic water, but much lower than those of river water; the latter is slightly lower than those of oceanic water, but higher than those of river water, demonstrating that the Okinawa Trough sea water has been influenced by river water of China's Mainland.
Recent studies have shown that specific geochemical characteristics of sediments can be used to reconstruct past methane seepage events. In this work, the correlation between the Sr/Ca and Mg/Ca ratios of sediment samples is analyzed and the sulfate concentration profile in Site C14 from cold-seep sediments in the Qiongdongnan Basin in northern South China Sea is obtained. The results confirmed that, sulfate at 0-247 cm below sea floor (Unit I) is mainly consumed by organic matter sulfate reduction (OSR), while sulfate at 247-655 cm (Unit Ⅱ) is consumed by both the OSR and the anaerobic oxidation of methane (AOM). In addition, the bottom sediment layer is affected by weak methane seepage. The Mo and U enrichment factors also exhibit similar trends in their respective depth profiles. The responses of trace elements, including Co/Al, Ni/Al, Cr/Al and Zn/Al ratios to methane seepage allowed the study of depositional conditions and methane seepage events. Based on the results, it is speculated that the depositional conditions of Unit Ⅱ changed with depth from moderate conditions of sulfidic and oxic conditions to locally anoxic conditions, and finally to suboxic conditions due to methane fluid leakage. The stable isotope values of chromium-reducible sulfide produced by AOM and those of sulfide formed by OSR in the early diagenetic environment suffered serious depletion of 34S. This was probably due to weak methane leakage, which caused the slower upward diffusion and the effect of early diagenesis on the samples. It is necessary to consider the effects of depositional environments and diagenesis on these geochemical parameters.