Behavior of air molecules in polar ice sheets (review)

Ancient atmospheric gases are trapped in polar ice sheets. The gas molecules are stored in air bubbles at shallower depth. The air bubbles are gradually compressed with depth and begin to transform into clathrate hydrates below a level at which the hydrostatic pressure becomes greater than the formation pressure of the phase of air clathrate hydrate. Air bubbles and clathrate hydrates coexist in the deep ice over a long period of time. Significant gas fractionations during the transition process have been found from measurements of the depth profile of the N2/O2 composition ratios in clathrate hydrates and air bubbles in the Dome-Fuji ice and the Vostok ice. Analyzing the molecular diffusion process in ice, the gas fractionation is attributed to a larger mass flux of O2 molecules from air bubbles to clathrate hydrates through the ice matrix than that of N2. We review the process of gas fractionation caused by the formation of clathrate hydrates in polar ice sheets

Catalytic role of the calcium ion in GH97 inverting glycoside hydrolase

AbstractThe role of calcium ion in the active site of the inverting glycoside hydrolase family 97 enzyme, BtGH97a, was investigated through structural and kinetic studies. The calcium ion was likely directly involved in the catalytic reaction. The pH dependence of kcat/Km values in the presence or absence of calcium ion indicated that the calcium ion lowered the pKa of the base catalyst. The significant decreases in kcat/Km for hydrolysis of substrates with basic leaving groups in the absence of calcium ion confirmed that the calcium ion facilitated the leaving group departure

Crystal Growth of air hydrate and resulting air diffusion in deep ice sheet

第2回極域科学シンポジウム　氷床コアセッション 11月16日（水） 国立極地研究所 2階大会議

Average time scale for Dome Fuji ice core, East Antarctica

Three different approaches to ice-core age dating are employed to develop a depth-age relationship at Dome F: (1) correlation of the ice-core isotope record to the geophysical metronome(Milankovich surface temperature cycle) inferred from the deep borehole temperature profile at Vostok,(2) importing a known chronology from another(Devils Hole) paleoclimatic signal, and(3) direct ice sheet flow modeling. Inverse Monte Carlo sampling is used to constrain the accumulation rate reconstruction and ice flow simulations in order to find the best-fit glaciological time scale matched with the two other chronologies. General uncertainty of the different age estimates varies from 2 to 6kyr on average and reaches 6-14kyr at maximum. Whatever the causes of this discrepancy might be, they are thought to be of different origins, and the age errors are assumed to be independent. Thus, the average time scale for the Dome F ice core down to a depth of 2500m(ice age of 335kyr) is deduced consistently with all three age-depth relationships within the standard deviation limits of ±3.3kyr, and its accuracy is estimated as 1.4kyr on average. The constrained ice-sheet flow model allows extrapolation of the ice age-depth curve further to the glacier bottom and predicts the ages at depths of 2800, 3000, and 3050m to be 615±70, 1560±531, and 2985±1568kyr, respectively

Air-hydrate crystal growth in polar ice

Based on the theory of precipitation from supersaturated solutions proposed by Lifshitz and Slyozov (J. Phys. Chem. Solids 19 (1/2) (1961) 35), we develop a mathematical description of post-formation growth (ripening) of mixed air clathrate-hydrate crystalline inclusions in polar ice sheets. The growth is controlled by oxygen and nitrogen diffusion through the ice matrix. Hydrate populations in general go through three sequential stages: (1) a short transient characterized by the rapid composition relaxation and dissolution of the smallest hydrates, (2) a slow transformation of the resulting size distributions towards a steady-state pattern that is an attribute of (3) the asymptotic stage of ripening. A regularization procedure is used to numerically solve the initial value problem. Computer simulations of the hydrate size distributions are compared to the data from a 3300-m ice core from Vostok Station, East Antarctica. The asymptotic stage is likely unattainable in natural conditions. Data from the GRIP ice core (central Greenland) suggest that the activation energy of hydrate growth increases at the elevated temperature near the ice-sheet bottom. The theory predicts extinction of the climatically induced fluctuations in the hydrate number-concentration and mean-radius profiles in ice sheets with depth. © 2003 Elsevier B.V. All rights reserved

Mechanical anisotropy of deep ice core samples by uniaxial compression tests (scientific paper)

Mechanical anisotropy of ice core samples has been observed in various uniaxial compression tests. The c-axis orientation distribution is the primary influence on the mechanical behavior of ice cores. A strong single-maximum fabric pattern is observed in the deep parts of the ice sheet. In this region, polycrystalline ice is very hard along the vertical axis; however, it easily shears along the horizontal plane. Thus, by acquiring the distribution of c-axis orientations throughout the ice sheet, the mechanical anisotropy of ice sheet flow behavior can be understood. Analysis of fabric measurements on the Dye 3, GRIP, and Dome F ice cores suggests that the c-axis orientation distribution depends primarily on vertical strain. Therefore, if the ice thickness at some point in the ice sheet is known, it should be possible to predict the distribution of c-axis orientations at that depth. Uniaxial compression tests were carried out along various directions of the Dye 3, GRIP, and Dome F ice cores. A contour map of mechanical anisotropy was then made to relate the compression direction to the vertical strain. This clarified the flow enhancement factor in every compression direction at a given vertical strain

X-ray diffraction study on the structure of the ice of the Dome Fuji ice core

第2回極域科学シンポジウム　氷床コアセッション 11月16日（水） 国立極地研究所 2階大会議

Precipitant-Free Lysozyme Crystals Grown by Centrifugal Concentration Reveal Structural Changes

The three-dimensional (3D) structure of a protein molecule in its crystal need not correspond to that found in vivo in many cases, since we usually crystallize protein molecules using precipitants (salts, organic solvents, polymeric electrolytes, etc.), and the precipitants are often incorporated into crystals along with the protein molecules. Although precipitant-free crystallization methods would solve these problems, such methods had not yet been established. We have achieved a novel precipitant-free crystallization method by liquid-liquid phase separation during the centrifugal concentration of lysozyme in ultra-pure water. In the 3D structure of the precipitant-free crystal, lysozyme loses a sodium cation and changes the position of Ser 72. Deionization of the solution also appears to induce a change in the position of Asp 101 and an increase in the activity of lysozyme