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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.08.011 Byline: Mathieu Choukroun (a), Olivier Grasset (b), Gabriel Tobie (b), Christophe Sotin (a)(b) Keywords: Titan; Experimental techniques; Interiors; Geophysics; Geological processes Abstract: We have conducted high-pressure experiments in the H.sub.2O-CH.sub.4 and H.sub.2O-CH.sub.4-NH.sub.3 systems in order to investigate the stability of methane clathrate hydrates, with an optical sapphire-anvil cell coupled to a Raman spectrometer for sample characterization. The results obtained confirm that three factors determine the stability of methane clathrate hydrates: (1) the bulk methane content of the samples; (2) the presence of additional gas compounds such as nitrogen; (3) the concentration of ammonia in the aqueous solution. We show that ammonia has a strong effect on the stability of methane clathrates. For example, a 10wt.% NH.sub.3 solution decreases the dissociation temperature of methane clathrates by 14-25K at pressures above 5MPa. Then, we apply these new results to Titan's conditions. Dissociation of methane clathrate hydrates and subsequent outgassing can only occur in Titan's icy crust, in presence of locally large amounts of ammonia and in a warm context. We propose a model of cryomagma chamber within the crust that provides the required conditions for methane outgassing: emplacement of an ice plume triggers the melting (if solid) or heating (if liquid) of large ammonia-water pockets trapped at shallow depth, and the generated cryomagmas dissociate surrounding methane clathrate hydrates. We show that this model may allow for the outgassing of significant amounts of methane, which would be sufficient to maintain the presence of methane in Titan's atmosphere for several tens of thousands of years after a large cryovolcanic event. Author Affiliation: (a) Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., MS 79-24, Pasadena, CA 91109, United States (b) UMR-CRNS 6112 Planetologie et Geodynamique, Universite de Nantes, 2, rue de la Houssiniere, 44322 Nantes Cedex 3, France Article History: Received 6 March 2009; Revised 22 July 2009; Accepted 12 August 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.11.004 Byline: Xin Zhang (a)(b)(c), Peter M. Walz (b), William J. Kirkwood (b), Keith C. Hester (b), William Ussler (b), Edward T. Peltzer (b), Peter G. Brewer (b) Keywords: Pore water; Raman spectroscopy; Laser; Geochemistry; In situ analysis; Deep-sea; Gas hydrate Abstract: We have developed, deployed, and tested a novel probe for study of the geochemistry of sediment pore waters based upon Raman spectroscopy. The Raman technique has already been used successfully for in situ measurements of targets of scientific interest including gas and hydrothermal vents and complex gas hydrates, but sediment geochemistry has so far been an intractable problem since the sediments themselves are strongly fluorescent and typically only very small sample volumes are obtainable. The 35cm long probe extracts pore fluids through a 10[mu]m sintered metallic frit and draws the sample through a 2mm diameter channel into a sapphire windowed optical cell within which the laser beam is focused and the spectrum recorded. The dead volume of the system is [approximately equal to]1ml and the instrument is ROV deployable with activation of probe insertion and sample withdrawal under direct operator control. The unique features of this mode of detection include observation of the sulfate gradient in marine pore waters as an indicator of diagenesis, direct measurement of the dissolved sulfide species H.sub.2S and HS.sup.-, and measurement of dissolved methane; all of which are of primary geochemical interest. Quantitative analysis is achieved by area ratio to known water peaks and from standard calibration curves with a precision of [+ or -]5%. We find only very small fluorescence from pore waters measured in situ, but observe rapid increases in fluorescence from cores returned to the surface and exposed to oxygen. Author Affiliation: (a) Ocean Remote Sensing Institute, Ocean University of China, 5 Yushan Road, Qingdao 266003, PR China (b) Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, USA (c) Key Lab of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, PR China Article History: Received 4 June 2009; Revised 9 November 2009; Accepted 18 November 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.06.016 Byline: Eric Chassefiere Keywords: Atmospheres, chemistry; Atmospheres, evolution; Geological processes; Mars, atmosphere; Mars, polar caps Abstract: The observations of methane made by the PFS instrument onboard Mars Express exhibit a definite correlation between methane mixing ratio, water vapor mixing ratio, and cloud optical depth. The recent data obtained from ground-based telescopes seem to confirm the correlation between methane and water vapor. In order to explain this correlation, we suggest that the source of gaseous methane is atmospheric, rather than at the solid surface of the planet, and that this source may consist of metastable submicronic particles of methane clathrate hydrate continuously released to the atmosphere from one or several clathrate layers at depth, according to the phenomenon of 'anomalous preservation' evidenced in the laboratory. These particles, lifted up to middle atmospheric levels due to their small size, and therefore filling the whole atmosphere, serve as condensation nuclei for water vapor. The observed correlation between methane and water vapor mixing ratios could be the signature of the decomposition of the clathrate crystals by condensation-sublimation processes related to cloud activity. Under the effect of water condensation on crystal walls, metastability could be broken and particles be eroded, resulting in a subsequent irreversible release of methane to the gas phase. Using PFS data, and according to our hypothesis, the lifetime of gaseous methane is estimated to be smaller than an upper limit of 6[+ or -]3months, much smaller than the lifetime of 300yr calculated from atmospheric chemical models. The reason why methane has a short lifetime might be the occurrence of heterogeneous chemical decomposition of methane in the subsurface, where it is known since Viking biology experiments that oxidants efficiently decompose organic matter. If true, it is shown by using existing models of H.sub.2O.sub.2 penetration in the regolith that methane could prevent H.sub.2O.sub.2 from penetrating in the subsurface, and further oxidizing the soil, at depths larger than a few millimeters. The present source of methane clathrate, acting over the last few hundred thousand or million years, could have given rise to the thin CO.sub.2-ice layer covering the permanent water ice south polar cap. The hypothesis proposed in this paper requires, to be validated, a number of laboratory experiments studying the stability of methane clathrates in martian atmospheric conditions, and the kinetics and amplitude of clathrate particle erosion in presence of condensing water vapor. Detailed future observations of methane, and associated modeling, will allow to more accurately quantify the production rate of methane clathrate, its temporal variability at seasonal scale, and possibly to locate the source(s) of clathrates at the surface. Author Affiliation: UPMC Univ. Paris 06; Universite Versailles St-Quentin; CNRS/INSU, LATMOS-IPSL, Universite Pierre et Marie Curie, Boite 102, 4 Place Jussieu, 75005 Paris, France Article History: Received 13 January 2009; Revised 18 June 2009; Accepted 18 June 2009

Femtosecond time-resolved resonance Raman measurements are carried out to examine the relaxation process of the hydrated electron in water. The rise of the intramolecular and intermolecular vibrational Raman bands of the solvating water molecules is successfully time-resolved with a time resolution as high as 250 fs.

Using recorded data of pressure and temperature, we developed a nondestructive method to estimate the precipitation rate of carbon dioxide (C[O.sub.2]) hydrate by considering the C[O.sub.2] solution density equation in association with the mass conservation equation. We applied this method to the investigation of the dynamic process of clathrate hydrate precipitation from C[O.sub.2] solution using a high-pressure dissolution system consisting of a high-pressure vessel and optical detecting instruments. The role of stirring was examined. The temperatures studied in the experiments were from 275 to 288 K over a pressure range of 4-8 MPa. Experimental results showed that our method can quantitatively monitor this dynamic process. The volume ratio of precipitated hydrate to that of the pressure-vessel approached 0.09 when a steady state was reached, which took about 100 seconds; more than 60% of the total clathrate hydrate precipitated within 10 seconds at the cooling rates of this experiment. For precipitation, stirring enhanced the cooling and led to a large hydrate precipitation rate from 0.004 to 0.008 in volume ratio per second. For nucleation, however, the residual structure of the solution decreased the amount of hysteresis in the formation of hydrate nuclei during supercooling, of which induction times were reduced by 4-9 minutes.

The 'in situ' kinetics of the kinetics of the 'hydration' process are studied as a function of time, using neutron scattering to obtain the trend of the fracrtion of free water (free water index, FWI), that is, the fraction of unreacted water. The trend of FWI as a function of Ca3SiO5 paste hydration is reported and the results are compared to recent quasi-elastic neutron scattering experiments.

Four Late Jurassic carbonate successions deposited in the Tethys-Atlantic Ocean record a negative carbon isotope excursion of at least 2 [per thousand]. The excursion is present in both organic and carbonate carbon records and is comparable in magnitude and duration to isotopic changes during the late Paleocene thermal maximum. Our results indicate that during the Late Jurassic, long considered a warm greenhouse time, additional greenhouse gas was input to the atmosphere by a sudden release of methane from buried gas hydrate. A potential triggering mechanism may have been the opening of an oceanic gateway through the early Atlantic between the ancient Tethys and Pacific Oceans. Keywords: Late Jurassic, gas hydrate, carbon cycle, paleoclimate.

The rich molecular electrostatic potential (MESP) topographical features of uracil provide clues on the probable water binding sites and stepwise hydration of uracil. An electrostatics-guided hydration study of uracil is able to bring out the explicit hydration patterns as well as the shell structure.

Analyses of hexasodium diphosphopentamolybdate hydrate using a combination of multiple-quantum magic-angle spinning nuclear magnetic resonace and magic-angle spinning NMR techniques and X-ray powder diffraction reveal that the compound is triclinic, possesses water molecules and two phosphorous sites, and six nonequivalent sodium sites.

Raman spectroscopy studies were performed on tetrahydrofuran (THF) hydrate, a structure II clathrate hydrate (CH) that was produced from THF and a dilute solution of D2O in H2O in a 17:1 ratio. Results showed that the THF ring breathing mode, which is symmetric at high temperatures, widens substantially and becomes asymmetric at low temperature. The reorientational rate of enclathrated THF molecules approaches that of the isolated molecule at about 120 K.

The spontaneous reaction of C3O2 with HCl on the acid hydrate surface was investigated by Fourier transform infrared spectroscopy at low temperature. The first appearing reaction product at 83 K was assigned to chloroformylketene while the second, observed at 145 K, to malonyl dichloride by comparison with previously reported data in matrix isolation spectroscopy. Findings showed that monohydrate H3O+Cl- is more reactive than higher hydrates because of easier C3O2 protonation.

We have observed the process of formation of clathrate hydrates of methane in experiments conducted on the remotely operated vehicle (ROV) Ventana in the deep waters of Monterey Bay. A tank of methane gas, acrylic tubes containing seawater, and seawater plus various types of sediment were carried down on Ventana to a depth of 910 m where methane gas was injected at the base of the acrylic tubes by bubble stream. Prior calculations had shown that the local hydrographic conditions gave an upper limit of 525 m for the P-T boundary defining methane hydrate formation or dissociation at this site, and thus our experiment took place well within the stability range for this reaction to occur. Hydrate formation in free seawater occurred within minutes as a buoyant mass of translucent hydrate formed at the gas-water interface. In a coarse sand matrix the filling of the pore spaces with hydrate turned the sand column into a solidified block, which gas pressure soon lifted and ruptured. In a fine-grained black mud the gas flow carved out flow channels, the walls of which became coated and then filled with hydrate in larger discrete masses. Our experiment shows that hydrate formation is rapid in natural seawater, that sediment type strongly influences the patterns of hydrate formation, and that the use of ROV technologies permits the synthesis of large amounts of hydrate material in natural systems under a variety of conditions so that fundamental research on the stability and growth of these substances is possible.

The crystal-growth behavior of structure I (sI), structure II (sII), and structure H (sH) clathrate hydrates has been studied using a specially designed, pressurized optical cell. Single crystals of each hydrate type, methane sI, methane-propane (95%-5%) sII, and methane-methylcyclopentane sH, were grown in equilibrium with aqueous liquid + vapor [+ or -] liquid hydrocarbon. Each structure type exhibits characteristic crystal morphology, which suggests that crystal habit in natural settings, such as sea-floor outcrops, may allow visual identification of hydrate types. In addition, the relative growth rates for different Miller planes for each crystal type were determined. The relative growth-rate schemes and resulting crystal morphology of each structure can be related to the unit-cell density distribution of the small cages in each structure. Four-phase P-T equilibrium data for methane-methylcyclopentane sH data were also measured using optical methods. Evaluation of these and previously published phase-equilibrium data for all three known hydrate structures strongly suggests that hydrate assemblages of coexisting sII and sH should be common in natural settings.

Selected-area electron diffraction, dark-field images, and high-resolution transmission electron microscope images show that there are pervasive domains in hillebrandite from Mexico. The domains are in thin layers that are almost parallel to (010). They range from one to several unit cells thick across the b direction, with an average thickness of about 10 nm. The actual repetition period (7.28 [angstrom]) along the a crystallographic direction is that of the wollastonite-like chain in the hillebrandite structure. Neighboring superstructure domains are related by stacking faults, with stacking vector of [+ or -]1/2[a.sub.sup.] Nonperiodic arrangements of the superstructure domains give an average structure of hillebrandite with a 3.64 [angstrom] repetition period along the a axis and one-half occupancies of Si atoms in the tetrahedral sites in the two Si-O chains.

Nuclear magnetic resonance (NMR) spectroscopic study of the xenon clathrate hydrate formation at very low temperatures suggests that the initially formed surface phase contains a large number of occupied small cages as compared to the bulk phase at equilibrium. The surface phase is less stable as compared to the bulk phase at higher temperatures. The result also shows that the mobilities of the water molecules are very high and can organize themselves around the xenon atoms even in the absence of transient liquid water.

Visible gas hydrate and possible pore-space hydrate samples have been recovered for the first time in North America from within ice-bonded permafrost in a 451-m-deep core hole in the Mackenzie Delta, Northwest Territories, Canada. The visible hydrate was found as thin icelike layers that released methane gas initially upon retrieval, but stabilized for up to 4 h at atmospheric pressure conditions and subfreezing temperatures. The temporary stabilization of hydrate samples is attributed to the self-preservation phenomenon described by others on the basis of laboratory studies. High methane concentrations in well-ice-bonded sediments and gas releases suggest that pore-space hydrate may be found at depths as shallow as 119 m. Geochemical and isotopic determinations suggest that the methane hydrate observed in the core hole is biogenic (microbial) in origin.

Temperature and pH influence reactions of the product obtained by UV irradiation of cytosine. Cytosine, on irradiation, produces cytosine hydrate that can undergo dehydration or deamination reactions. Low pH favors deamination reaction and Arhenius equations show that activation energy for dehydration is the same at pH 5.4 and 7.4. Stability of cytosine hydrate in DNA and its ability for deamination, producing uracil hydrate, indicate that pyrimidine hydrates can produce mutagenesis and harmful effects on organisms exposed to UV light.

Byline: H. Akbar M. A. Khan M. S. Khan M. A. Khan S. G. Bokhari A. Nasir and A. A. Anjum : ABSTRACT Efficacy of medetomidine HCl anesthesia was evaluated [...]

Air hydrate was observed to be present at a depth of 727m, well above the estimated depth for hydrate stability. This observation was made on the Byrd Station Antarctic core. It was suggested that air hydrate is present 100m above the equilibrium phase boundary at Byrd Station because of 'piezometry.' Flowline trajectories in the ice, based on countless models, reveal that the necessary vertical displacement occurs just upstream of the station.

An analysis of the antitumor drug, cis-dichlorodiammineplatinum(II) with 2'-deoxyuridine reveals a minor product containing some thin plates in a blue precipitate. X-ray diffraction analyses show that the crystals have a novel cyclo tetranuclear platinum cation, ((cis-Pt(NH3)2)4(mu4-CO3)2)4+.

The Department of Energy has responsibility for providing for the long-term energy security of the United States. DOE's Arctic and Subarctic activities support the DOE mission through studies of energy [...]

The experimental arguments for the guest replacement of methane hydrate with carbon dioxide are described using in situ Raman spectroscopy at high pressures. The Raman spectra of the vibration modes of water molecules helps in understanding the phenomena of the coexistence of methane and carbon dioxide hydrates and water phase for guest replacement reactions.

A computational study that is aimed to understand and characterize the structure and behavior of mixed and nitric acid ionic clusters is reported. The geometry optimized structures show that, depending on the cluster arrangement, the nitric acid molecule can dissociate into NO3- and H3O- when the number of water ligands in the cluster is greater than seven.

The magnetic relaxation dispersion analysis of the 2,2,2-trifluoroethanol (TFE) at 27 C reveals structural transformations of N(0% TFE) to I(16%-TFE) and of I(16% TFE) to H(29% TFE) accompanied by protein expansion and loss of long-lived hydration sites. Data demonstrate long-lived association of water and TFE with the expanded protein.

Investigating the magnetic properties, thermal behavior, and structure of copper sulfate pentahydrate, CuSO(sub.4).5H(sub.2)O, in a required two-week first-year graduate course in modern analytical methods is discussed. Students work on a specific solid-state analytical problem that requires use of several methods. They learn about the problem-oriented selection of a method and about expensive equipment not usually used by undergrads . The class involves a bout 45 h in the lab, including computer time, and about 15 h of lecture/discussion.

The molecular geometry and electronic spectra of uracil tautomers, anions, and their hydrated complexes is studied. The excited-state geometry optimization method is used for this purpose and these geometries are predicted to be highly nonplanar.