The concentration of total metal sulfide throughout a water column over a submarine hydrothermal vent in Kikai Caldera south of Kyushu Island, Japan, at ~350 pmol/kg, was higher than that reported in previous studies, at <50 pmol/kg below the halocline. Seawater filtered at 0.2 μm pore size and unfiltered seawater exhibited almost identical metal sulfide concentrations throughout the water column, indicating that most metal sulfide existed in dissolved and particulate forms with diameters <0.2 μm. By using a mass balance calculation with the observed sulfide species of free and metal sulfides and carbonyl sulfide, we showed that ~70% of the metal sulfide supplied from hydrothermal vents were contained in the water column beyond the halocline without undergoing oxidative loss even after mixing into overlying oxic seawater. Our findings clearly indicate that sulfide and trace metals emitted from hydrothermal vents form a stable metal-sulfide complex with diameters <0.2 μm. These results also strongly support the recently proposed theory such that metal-sulfide complexation/nanoparticles play an important role in the long-distance transportation of trace metals in the ocean.
Pore waters at the depths of 0-590 cm below seafloor (bsf) were collected from four core samples at four different sites in a mud volcano off Tanegashima Island between Ryukyu trench and Ryukyu arc of Japan. Concentrations of Cl-, SO42-, CH4, C2H6 and stable isotopic composition of δ13CCH4, δ18OH2O, δDH2O in the pore waters vary as a function of distance from seafloor. This paper reports and discusses the pore waters collected at the summit (CV) site. The concentrations of Cl- decrease from 540 at the seafloor to 375 mmol/kg at a depth of ∼200 cm and remain constant at around 350 mmol/kg (64% of the concentration of seawater) below the depth. The concentrations of CH4 are two to three orders of magnitude higher than those at other sites and have a maximum value of 715 μmol/kg at around 120-140 cm bsf. Core samples collected at depths deeper than 180 cm bsf show collapsing gas bubbles and empty voids when they were split open. It was also observed that liquid seeped out from the surface of the split core. Considering the physical condition is favorable for the formation of methane hydrate, the observations suggest the existence of methane hydrates. High concentration of C2H6, which had similar depth profile to that of CH4, was also observed. C2H6/CH4 ratio remained larger than 10-3 and δ13CCH4 also remained around -45‰ below 180 cm bsf. The data suggest presence of thermogenic methane in the CV site. δ18OH2O and δDH2O profiles exhibited an opposite depth dependence, and only δDH2O showed a decreasing depth profile similar to the concentration profile of Cl-. They were inversely correlated with the concentration of Cl-. The data of these two isotope compositions suggest a dilute fluid originates mainly from clay mineral dehydration but meteoric water. A simple mixing model of fluids from three sources (ambient seawater, water dissociated from methane hydrates, and diagenetic water ascending from deeper depth) with isotopic fraction during methane hydrate dissociation was applied for the observation result below 280 cm bsf to constrain ranges of δ18OH2O and δDH2O of diagenetic water. Using the observed depth profile of Cl- as a conservative component of ambient seawater, contribution of ambient seawater is estimated to be 64% whereas 36% from other two sources. Considering an isotopic fractionation during methane hydrate dissociation and using the estimated source fractions and observed isotopic composition of pore water, δ18OH2O and δDH2O of the diagenetic water were estimated to range from +15 to +22‰ and from -103 to -43‰, respectively, which are in good agreement with isotopic compositions of water formed from clay minerals during their dehydration but quite different from those of meteoric water, supporting negligible contribution of meteoric water in the Tanegashima mud volcano fluid.
The rapidly rising levels of atmospheric and oceanic CO 2 from the burning of fossil fuels has lead to well-established international concerns over dangerous anthropogenic interference with climate.Disposal of captured fossil fuel CO 2 either underground, or in the deep ocean, has been suggested as one means of ameliorating this problem.While the basic thermodynamic properties of both CO 2 and seawater are well known, the problem of interaction of the two fluids in motion to create a plume of high CO 2 /low pH seawater has been modeled, but not tested.We describe here a novel experiment designed to initiate study of this problem.We constructed a small flume, which was deployed on the sea floor at 4 km depth by a remotely operated vehicle, and filled with liquid CO 2 .Seawater flow was forced across the surface by means of a controllable thruster.Obtaining quantitative data on the plume created proved to be challenging.We observed and sensed the interface and boundary layers, the formation of a solid hydrate, and the low pH/high CO 2 plume created, with both pH and conductivity sensors placed downstream.Local disequilibrium in the CO 2 system components was observed due to the finite hydration reaction rate, so that the pH sensors closest to the source only detected a fraction of the CO 2 emitted.The free CO 2 molecules were detected through the decrease in conductivity observed, and the disequilibrium was confirmed through trapping a sample in a flow cell and observing an unusually rapid drop in pH to an equilibrium value.
We have carried out series of remotely operated vehicle–controlled oceanic CO 2 system perturbation experiments off the coast of California at depths down to 1000 m to observe reaction rates and pathways with both HCl and HCO 3 − addition. The work was done to evaluate possible barriers to carrying out future Free Ocean CO 2 Enrichment experiments to simulate the chemistry of the emerging high CO 2 –lower pH ocean. A looped 460 mL flow cell with a pH sensor was used to monitor the time to equilibrium for 900 μL additions of 0.008 N HCl and for small slugs of HCO 3 − enriched seawater. The results were compared to equivalent experiments at the same temperature and 1 atm pressure. In each case the experiments at depth showed significantly faster time to equilibrium than those at 1 atm. These results are consistent with the low partial molal volume of CO 2 in seawater, favoring the hydration reaction rate. The results imply, but do not prove, a significant effect of pressure on the rate constants. The relatively rapid equilibration times observed in seawater of 4°C and at 10 MPa indicates that there are no fundamental physical chemistry limits for carrying out small‐scale free‐ocean CO 2 enrichment experiments.
Type A N-fold supersymmetry of one-dimensional quantum mechanics can be constructed by using sl(2) generators represented on a finite-dimensional functional space. Using this sl(2) formalism we show a general method of constructing type A N-fold supersymmetric models. We also present systematic generation of known models and several new models using this method.
N-fold supersymmetry is an extension of the ordinary supersymmetry in one-dimensional quantum mechanics. One of its major property is quasi-solvability, which means that energy eigenvalues can be obtained for a portion of the spectra. We show that recently found type A N-fold supersymmetry can be constructed by using sl(2) algebra, which provides a basis for the quasi-solvability. By this construction we find a condition for the type A N-fold supersymmetry which is less restrictive than the condition known previously. Several explicitly known models are also examined in the light of this construction.
