Preface The expedition ARK XIX/3 with the German icebreaking RV ...

mediated by the two syntrophic partners, which rely on interspecies hydrogen
transfer: methanogenic archaea mediating the oxidation of methane with water
(reaction 1), and sulfate reducing bacteria scavenging the intermediate hydrogen
(reaction 2):
CH 4 + 2 H 2 O CO 2 + 4 H 2 (1)
SO 2- 4 + 4 H 2 + H + HS - + 4 H 2 O (2)
The net reaction of methane oxidation can thus be formulated as:
CH 4 + SO 4 2- HCO 3 - + HS - + H 2 O
In the methane budget proposed by Reeburgh (1996), more than 80% of the methane
produced annually in anoxic marine sediments is consumed before it can reach the
atmosphere. The previously estimated 75 Tg/yr (not including the high AOM rates at
methane seeps) indicate that methane consumption is nearly twice the annual
increase in the atmospheric inventory of CH 4 (40 Tg/yr). In several sedimentary
environments, AOM can be the dominant sulfate-consuming process, e.g., in
sediments above gas hydrate and at methane seeps, as well as in the deep
biosphere. No data are yet available from mud volcanoes which are another important
geological source of methane. An updated compilation of AOM rates shows that the
consumption of methane in gassy sediments is probably several times higher than
previously estimated (Hinrichs and Boetius, 2002). Hence, even if the area affected
by methane seepage at continental margins is below 1%, this might have a significant
impact on the total methane budget. Thus, measurements of methane turnover rates
in sediments and bottom water and methane emission to the hydrosphere are
extremely important for realistic calculations of methane consumption in the sea.
Thus, measurements of methane and sulfate turnover rates in sediments and bottom
water and methane emission to the hydrosphere are extremely important for realistic
calculations of methane consumption in the sea. The main questions for this
investigation are:
- Where are the hot spots of methane turnover at the Håkon Mosby Mud
Volcano ?
- How much methane is oxidized anaerobically in the sediments ?
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