Ninth international conference on - Marum

80
Abstracts of posters
experience in gas hydrates research and investigations allow us to continue not only large-scale basic research,
but also testing of instruments and equipment for their studies and technology of gas exploration from subaquatic
nearsurface hydrates.
References
Kalmychkov G. V., Egorov A. V., Kuz’min M. I.., Khlystov O.M. Genetic Types of Methane from Lake Baikal
// Doklady Earth Sciences, 2006. V. 411A. No. 9. P. 1462–1465.
Kida M., Khlystov O., Zemskaya T., et al Coexistence of structure I and II gas hydrates in Lake Baikal
suggesting gas sources from microbial and thermogenic origin // Geophysical Research Letter, 33.
L24603. 2006. doi:10.1029/2006GL028296.
Khlystov O. M., Gorshkov A. G., Egorov A. V. et al. Oil in the Lake of World Heritage // Doklady Earth
Sciences, 2007. Vol. 415. No. 5. P. 682–685.
Crystal size distributions of naturally occurring gas hydrates
S. A. Klapp 1 , S. Hemes 2 , H. Klein 2 , G. Bohrmann 1 , W. F. Kuhs 2 and F. Abegg 1
1 MARUM, University of Bremen, PO Box 330440, 28334 Bremen, Germany
2 GZG, Abt. Kristallographie, Universität Göttingen, Goldschmidtstrasse 1, 37077 Göttingen
Gas hydrates are considered to host a large reservoir of volatile hydrocarbons. Hydrates crystallize at sites of gas
seepage both from gases percolating through pore space as well as from pore waters.
Many gas hydrate-related processes involve the hydrate surface area or grain boundaries, for instance gas
exchange reactions, mass transport or hydrate dissociation. But due to experimental difficulties, size distributions
of gas hydrate crystallites are largely unknown in natural samples.
Here, we report on crystallite size distributions of several natural gas hydrates for samples retrieved from the
Gulf of Mexico, the Black Sea and from Hydrate Ridge offshore Oregon from varying depth below the sea floor.
High-energy synchrotron radiation provides high photon fluxes as well as high penetration depth and thus allows
the investigation of bulk sediment samples. The gas hydrate crystallite sizes measured with a newly developed
diffraction technique, utilizing the excellent beam collimation, appear to be (log-) normally distributed in the
natural samples and to be of roughly globular shape. This could be confirmed by measurements conducted on
differently positioned and rotated samples.
The mean crystallite sizes are typically in the range from 200-300 µm for hydrates recovered from near the sea
floor while a tendency for bigger grains was noticed in greater depth for the Hydrate Ridge samples, indicating a
difference in the formation age or formation process. Laboratory produced methane hydrate, starting from ice
and aged for 3 weeks, shows half a lognormal curve with a mean value in the order of 40µm. This one order-ofmagnitude
smaller grain sizes suggests that care must be taken when transposing crystallite-size sensitive (petro-
) physical data from laboratory-made gas hydrates to natural settings.
Regulation of anaerobic oxidation of methane in diffusive sediments of the Black Sea
N. J. Knab 1,2 , B. Cragg 3 , E. Hornibrook 4 , R. J. Parkes 3 , C. Borowski 1 , B. B. Jørgensen 1
1 Max-Plank Institute for Marine Microbiology, Department of Biogeochemistry, Bremen, Germany
2 University of Southern California, Department of Biological Sciences, Los Angeles, USA
3 Cardiff University, School of Earth, Ocean & Planetary Sciences, Cardiff, Wales, U.K.
4 University of Bristol, Department of Earth Sciences, Bristol, U.K.
Anaerobic oxidation of methane (AOM) and sulfate reduction (SRR) were investigated in sediments of the
western Black Sea, where methane transport is controlled by diffusion. To understand the regulation and
dynamics of methane production and oxidation in the Black Sea, rates of methanogenesis, AOM, and SRR were
determined using radiotracers in combination with pore water chemistry and stable isotopes. On the shelf of the
Danube paleo-delta (P771GC) and the Dnjepr Canyon (P806GC), AOM did not consume methane effectively
and upwards diffusing methane created an extended sulfate-methane transition zone (SMTZ) that spread over
more than 2.5 m and was located in formerly limnic sediment. Measurable AOM rates occurred mainly in the
lower part of the SMTZ, sometimes even at depths where sulfate seemed to be unavailable. The incomplete
oxidation of methane in the major AOM zone and resulting methane tailing is a common feature of diffusion
dominated methane rich sediments of the western Black Sea. The reason for the sluggish and inefficiency
oxidation seems to be related with the location of the SMTZ inside the sediment with a limnic history (below the