Ninth international conference on - Marum

Abstracts of posters 95
oxidation (AMO) and methanogenesis. For each reactive type, a constant C fractionation was assumed with δ 13 C
values in the produced DIC of -15‰, -35‰, and +15‰, respectively. As source terms, the directly measured
turnover rates from radiotracer incubations were applied. An additional downward advection term was always
included in the diffusion equation in order to simulate sedimentation rate.
Preliminary model runs show initially a sharp increase of δ 13 C values at the sulphate methane boundary due to
isotopically heavy DIC produced during methanogenesis. However, this effect is rapidly outcompeted by
downward diffusion of DIC with negative δ 13 C values that is produced at much higher rates by sulphate
reduction. Applying the present activity rates to the model allowed to partially reproduce the trends in modern
DIC isotopic signatures, but do not explain the more positive δ 13 C values preserved in the carbonates. In order
to simulate the dynamics that occurred in the past, a further refinement of the model is necessary that integrates
organic matter reactivity, sulphate and methane diffusion, and isotope specific DIC production. In particular,
organic matter (OM) reactivity needs to be represented as an exponential decay process including a fixed decay
constant and a distribution factor for OM reactivity. This model provides a theoretical basis necessary to
understand δ 13 C patterns in dynamic diffusive systems and to postulate conditions of past deep biospheres from
δ 13 C records of early diagenetic carbonate.
Reference
Meister, P., McKenzie, J.A., Vasconcelos, C., Bernasconi, S., Frank, M., Gutjahr,.M., and Schrag, D.P. (2007)
Dolomite formation in the dynamic deep biosphere: results from the Peru Margin. Sedimentology 54,
1007–1031.
Isotopic and chemical analyses of gas hydrate- and pore- water samples obtained from gas
hydrate-bearing sediment cores retrieved from mud volcanoes in Lake Baikal
H. Minami 1 , A. Krylov 1,2 , A. Hachikubo 1 , H. Sakagami 1 , H. Tomaru 1 , K. Hyakutake 1 , S. Kataoka, S. Yamashita,
N. Takahashi 1 , S. Nishio 3 , H. Shoji 1 , O. M. Khlystov 4 , T. I. Zemskaya 4 , T. V. Pogodaeva 4 , and M. Grachev 4
1 Kitami Institute of Technology, 165 Koen-cho, Kitami 090-8507, Japan
2 VNIIOkeangeologia, 1 Angliyskiy pr., St. Petersburg 190121, Russia
3 Institute of Technology, Shimizu Corp, 3-4-17 Etchujima, Koto-ku, Tokyo 135-8530, Japan
4 Limnological Institute SB RAS, 3 Ulan-Batorskaya st., Irkutsk 664033, Russia
International cooperative research projects for the natural gas hydrate sampling operation and isotopic/chemical
core analyses at the mud volcanoes such as Malenky (southern basin) and Kukuy K-2 (central basin) in Lake
Baikal, Eastern Siberia, Russia were conducted during 2005 to 2007. The gas hydrate-bearing sediment cores
were retrieved from the bottom of the lake floors by using steel gravity corers. The pore water sampling was
conducted on board by a squeezer designed and constructed at Kitami Institute of Technology. The hydrate
water sample was obtained by the dissociation of the hydrate on board. In order to clarify the origin and
composition of the gas hydrates-forming fluid, the isotopic and chemical analyses of the gas hydrate-, pore-, and
lake water samples were conducted. Stable isotope ratios of oxygen and hydrogen of the water samples were
analyzed by using a mass spectrometer (Model Finnigan Delta plus XP, Thermo Fisher) equipped with a gasbench
system (Model Gas-Bench II, Thermo Fisher).
The δ 18 O and δD values of the hydrate water samples obtained were up to +2.7‰ (δ 18 O) and +10‰ (δD) heavier
than those of the lake bottom water sampled from 50 cm above the lake floor.
The concentrations of major ions in samples of water obtained by decomposition of different hydrate samples are
broadly variable, and do not correlate with the composition of the pore water of the in-filled sediments.
Remarkable are the extremely high concentrations of Cl - , Na + , SO4 2- in some of them. This fact suggests that the
concentrations of salts in hydrate-forming gas-saturated fluids change in the course of upward migration of
hydrates which carry away pure water and leave salts behind.
Effect of methane gas phase dynamics on the coupled methane-sulfur cycles in the subsurface
J. Mogollón 1 , I. L’Heureux 2 , A. Dale 1 , and P. Regnier 1
1 Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3508TA Utrecht, The Netherlands
2 Department of Physics, University of Ottawa, Macdonald Hall, 150 Louis Pasteur, Ottawa, ON, Canada
Reactive-transport models of geomicrobiological dynamics in subsurface environments have largely ignored the
role of biogenic gas generation, transport, and dissolution. In natural systems characterized by high rates of