Explore the vast range of titles available.

Among natural energy resources, methane clathrate has attracted tremendous attention because of its strong relevance to current energy and environment issues. Yet little is known about how the clathrate starts to nucleate and disintegrate at the molecular level, because such microscopic processes are difficult to probe experimentally. Using surface-specific sum-frequency vibrational spectroscopy, we have studied in situ the nucleation and disintegration of methane clathrate embryos at the methane-gas–water interface under high pressure and different temperatures. Before appearance of macroscopic methane clathrate, the interfacial structure undergoes 3 stages as temperature varies, namely, dissolution of methane molecules into water interface, formation of cage-like methane–water complexes, and appearance of microscopic methane clathrate, while the bulk water structure remains unchanged. We find spectral features associated with methane–water complexes emerging in the induction time. The complexes are present over a wide temperature window and act as nuclei for clathrate growth. Their existence in the melt of clathrates explains why melted clathrates can be more readily recrystallized at higher temperature, the so-called “memory effect.” Our findings here on the nucleation mechanism of clathrates could provide guidance for rational control of formation and disintegration of clathrates.

This research studies the structure of flames that use laboratory-produced methane hydrates as fuel, specifically for the purpose of identifying their key combustion characteristics. Combustion of a methane hydrate involves multiple phase changes, as large quantities of solid clathrate transform into fuel gas, water vapor, and liquid water during burning. With its unique and stable fuel energy storage capability, studies in combustion are focused on the potential usage of hydrates as an alternative fuel source or on their fire safety. Considering methane hydrate as a conventional combustion energy resource and studying hydrate combustion using canonical experimental configurations or methodology are challenges. This paper presents methane hydrate flame geometries from the time they can be ignited through their extinguishment. Ignition and burning behavior depend on the hydrate initial temperature and whether the clathrates are chunks or monolithic shapes. These behaviors are the subject of this research. Physical properties that affect methane hydrate in burning can include packing density, clathrate fraction, and surface area. Each of these modifies the time or the temperature needed to ignite the hydrate flames as well as their subsequent burning rate, thus every effort is made to keep consistent samples. Visualization methods used in combustion help identify flame characteristics, including pure flame images that give reaction zone size and shape and hydrate flame spectra to identify important species. The results help describe links between hydrate fuel characteristics and their resulting flames.

Abstract Methane clathrates on continental margins contain the largest stores of hydrocarbons on Earth, yet the role of biomolecules in clathrate formation and stability remains almost completely unknown. Here, we report new methane clathrate-binding proteins (CbpAs) of bacterial origin discovered in metagenomes from gas clathrate-bearing ocean sediments. CbpAs show similar suppression of methane clathrate growth as the commercial gas clathrate inhibitor polyvinylpyrrolidone and inhibit clathrate growth at lower concentrations than antifreeze proteins (AFPs) previously tested. Unlike AFPs, CbpAs are selective for clathrate over ice. CbpA3 adopts a nonglobular, extended structure with an exposed hydrophobic surface, and, unexpectedly, its TxxxAxxxAxx motif common to AFPs is buried and not involved in clathrate binding. Instead, simulations and mutagenesis suggest a bipartite interaction of CbpAs with methane clathrate, with the pyrrolidine ring of a highly conserved proline residue mediating binding by filling empty clathrate cages. The discovery that CbpAs exert such potent control on methane clathrate properties implies that biomolecules from native sediment bacteria may be important for clathrate stability and habitability.

The primary volatile ‘rock-forming’ minerals in the icy satellites of the outer solar system include water-ice and various hydrated crystals of methane and ammonia. The rich polymorphism of these substances as a function of pressure and temperature are described in this chapter. This polymorphism has a fundamental influence on the exchange of mass and energy between the core and the surface of icy satellites. We describe the current state-of-the-art in our understanding of the high pressure phase behaviour and the measurements of thermoelastic and transport properties of these substances. In addition we describe the structures and properties of hydrated phases of methanol, sulfuric acid, and various sulfate salts.

Europa and Callisto are two “extreme members” in a sequence of the Galilean ice satellites formed at different distances from Jupiter. The difference in their mean density probably reflects the material density gradient that appeared even in the subplanetary disk of Jupiter. At the same time, general peculiarities in the composition of the surfaces of Europa and Callisto apparently characterize the accumulated effect of all subsequent evolutionary processes, including current volcanic activity on the satellite Io and its ionized material transfer in Jovian magnetosphere, as well as chemical reactions taking place under low-temperature (within ~90–130 K) and irradiation conditions. In 2016–2017, we observed the leading and trailing hemispheres of Europa and Callisto in the spectral range of 1.0–2.5 μm at 2-m telescope of Caucasian Mountain Observatory (CMO) of Sternberg Astronomical Institute (SAI) of Moscow State University (MSU). We found that, on a global scale, Europa and Callisto exhibit similar spectral characteristics and, particularly, the maxima in the distributions of sulfuric acid hydrate in the trailing hemispheres of the both moons, which agrees with the data of previous measurements. This can be considered as evidence for general ion implantation on these and other moons in the radiation belts of Jupiter. Moreover, our spectral data suggest that water ice and hydrates (clathrates) of other compounds are dominant or abundant in the leading hemispheres of Europa and Callisto. Specifically, we detected a weak absorption band of CH4 clathrate centered at ~1.67 μm in the reflectance spectra of the leading (the band is more intense) and trailing (the band is less intense) hemispheres of Europa. Weak signs of the same absorption band are also in the reflectance spectra of Callisto measured at its different orientations.

Vast quantities of methane are trapped in oceanic hydrate deposits, and there is concern that a rise in the ocean temperature will induce dissociation of these hydrate accumulations, potentially releasing large amounts of methane into the atmosphere. The recent discovery of active methane gas venting along the landward limit of the gas hydrate stability zone (GHSZ) on the shallow continental slope west of Spitsbergen could be an indication of this process, if the source of the methane can be confidently attributed to dissociating hydrates. In the first large‐scale simulation study of its kind, we simulate shallow hydrate dissociation in conditions representative of the West Spitsbergen margin to test the hypothesis that the observed gas release originated from hydrates. The simulation results are consistent with this hypothesis, and are in remarkable agreement with the recently published observations. They show that shallow, low‐saturation hydrate deposits, when subjected to temperature increases at the seafloor, can release significant quantities of methane, and that the releases will be localized near the landward limit of the top of the GHSZ. These results indicate the possibility that hydrate dissociation and methane release may be both a consequence and a cause of climate change.

The human impact on Earth's climate is often treated as a hundred-year issue lasting as far into the future as 2100, the year in which most climate projections cease. In The Long Thaw, David Archer, one of the world's leading climatologists, reveals the hard truth that these changes in climate will be \"locked in,\" essentially forever.If you think that global warming means slightly hotter weather and a modest rise in sea levels that will persist only so long as fossil fuels hold out (or until we decide to stop burning them), think again. In The Long Thaw, David Archer predicts that if we continue to emit carbon dioxide we may eventually cancel the next ice age and raise the oceans by 50 meters. A human-driven, planet-wide thaw has already begun, and will continue to impact Earth's climate and sea level for hundreds of thousands of years. The great ice sheets in Antarctica and Greenland may take more than a century to melt, and the overall change in sea level will be one hundred times what is forecast for 2100. By comparing the global warming projection for the next century to natural climate changes of the distant past, and then looking into the future far beyond the usual scientific and political horizon of the year 2100, Archer reveals the hard truths of the long-term climate forecast.Archer shows how just a few centuries of fossil-fuel use will cause not only a climate storm that will last a few hundred years, but dramatic climate changes that will last thousands. Carbon dioxide emitted today will be a problem for millennia. For the first time, humans have become major players in shaping the long-term climate. In fact, a planetwide thaw driven by humans has already begun. But despite the seriousness of the situation, Archer argues that it is still not too late to avert dangerous climate change--if humans can find a way to cooperate as never before. Revealing why carbon dioxide may be an even worse gamble in the long run than in the short, this compelling and critically important book brings the best long-term climate science to a general audience for the first time.With a new preface that discusses recent advances in climate science, and the impact on global warming and climate change, The Long Thaw shows that it is still not too late to avert dangerous climate change--if we can find a way to cooperate as never before. David Archer is professor of geophysical sciences at the University of Chicago. He is the author of many books, including The Global Carbon Cycle (Princeton).

This paper highlights the similarity in the timing between the 8.2 ka cold event across the North Atlantic region and one of the world’s largest underwater slides, the Storegga submarine landslide that took place on the continental slope west of Norway. We argue on the basis of a reinterpretation of the age of tsunami deposits that date the slide, as well as published ages of sediment directly resting upon the slide surface, that the slide occurred between 8100 and 8200 cal. yr, near the end of the 8.2 ka cold event. Because sediment exposed at the base of the slide contained less methane-gas-hydrate c. 8200 years ago than exists today and because Greenland ice cores do not show an increase in methane at the time of the slide, it is argued here that the slide did not release significant volumes of methane to the atmosphere and did not contribute to any change in temperature during or after the 8.2 ka cold event.

For twenty-five years following the Voyager mission, scientists speculated about Saturn's largest moon, a mysterious orb clouded in orange haze. Finally, in 2005, the Cassini-Huygens probe successfully parachuted down through Titan's atmosphere, all the while transmitting images and data. In the early 1980s, when the two Voyager spacecraft skimmed past Titan, Saturn's largest moon, they transmitted back enticing images of a mysterious world concealed in a seemingly impenetrable orange haze.Titan Unveiledis one of the first general interest books to reveal the startling new discoveries that have been made since the arrival of the Cassini-Huygens mission to Saturn and Titan. Ralph Lorenz and Jacqueline Mitton take readers behind the scenes of this mission. Launched in 1997, Cassini entered orbit around Saturn in summer 2004. Its formidable payload included the Huygens probe, which successfully parachuted down through Titan's atmosphere in early 2005, all the while transmitting images and data--and scientists were startled by what they saw. One of those researchers was Lorenz, who gives an insider's account of the scientific community's first close encounter with an alien landscape of liquid methane seas and turbulent orange skies. Amid the challenges and frayed nerves, new discoveries are made, including methane monsoons, equatorial sand seas, and Titan's polar hood. Lorenz and Mitton describe Titan as a world strikingly like Earth and tell how Titan may hold clues to the origins of life on our own planet and possibly to its presence on others. Generously illustrated with many stunning images,Titan Unveiledis essential reading for anyone interested in space exploration, planetary science, or astronomy. A new afterword brings readers up to date on Cassini's ongoing exploration of Titan, describing the many new discoveries made since 2006.

Methane clathrates are widespread on the ocean floor of the Earth. A better understanding of methane clathrate formation has important implications for natural-gas exploitation, storage, and transportation. A key step toward understanding clathrate formation is hydrate nucleation, which has been suggested to involve multiple evolution pathways. Herein, a unique nucleation/growth pathway for methane clathrate formation has been identified by analyzing the trajectories of large-scale molecular dynamics (MD) simulations. In particular, ternary water-ring aggregations (TWRAs) have been identified as fundamental structures for characterizing the nucleation pathway. Based on this nucleation pathway, the critical nucleus size and nucleation timescale can be quantitatively determined. Specifically, a methane hydration layer compression/shedding process is observed to be the critical step in (and driving) the nucleation/growth pathway, which is manifested through overlapping/compression of the surrounding hydration layers of the methane molecules, followed by detachment (shedding) of the hydration layer. As such, an effective way to control methane hydrate nucleation is to alter the hydration layer compression/shedding process during the course of nucleation.