Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmgc14a..05m&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #GC14A-05
Mathematics
Logic
0330 Geochemical Cycles (1030), 3004 Gas And Hydrate Systems, 4215 Climate And Interannual Variability (1616, 1635, 3305, 3309, 4513), 5210 Planetary Atmospheres, Clouds, And Hazes (0343)
Scientific paper
Natural processes that separate materials from a mixture may exert a major influence on the development of the atmospheres and surfaces of planets, moons, and other planetary bodies. Natural distillation and gravity separation, amongst others, are well known means of differentiating materials through liquid-gas partitioning. One of the least known attributes of clathrate (gas) hydrates is their potential effect on the evolution of planetary system oceans and atmospheres. Gas hydrates separate gases from mixtures of gases by concentrating preferred hydrate-forming materials (HFM) guests within the water-molecule cage structure of crystalline hydrate. Different HFMs have very different fields of stability. When multiple hydrate formers are present, a preference series based on their selective uptake exists. Compound hydrate, which is formed from two or more species of HFM, extract preferred HFM from a mixture in very different proportions to their relative percentages of the original mixture. These compound hydrates can have different formation and dissociation conditions depending on the evolution of the environment. That is, the phase boundary of the compound hydrate that is required for dissociation lies along a lower pressure - higher temperature course. Compound hydrates respond to variations in temperature, pressure, and HFM composition. On Earth, the primary naturally occurring hydrate of interest to global climate modeling is methane hydrate. Oceanic hydrate on Earth is the largest store of carbon in the biosphere that is immediately reactive to environmental change, and is capable of releasing large amounts of methane into the atmosphere over a short geological time span. Hydrate formation is essentially metastable and is very sensitive to environmental change and to gas flux. Where natural variations in temperature and pressure varies so that hydrate will form and dissociate in some cyclical manner, such as in oceans where sea level is capable of rising and falling, and which warms and cools, and in atmospheres in which temperature swings take place, the compound hydrate system can both sequester and release HFM selectively. When there is strong gas flux hydrate will tend to form; when gas flux falls below a certain level, hydrate may either dissolve or dissociate. On other bodies in the solar system, such as on Titan, ethane, propane, nitrogen, noble gases, and other HFMs may be selectively withdrawn from gas and liquid phases and sequestered within hydrate, or selectively released when climate swings occur, which can cause positive or negative feedback to atmospheric composition and greenhouse intensity. Where carbon-based biosphere conditions exist, the hydrate system will interact with it in the same manner as it does on Earth.
Max Michael D.
Osegovic John P.
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