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Abstract:
The Ha°kon Mosby Mud Volcano is a highly active methane seep hosting different chemosynthetic
communities such as thiotrophic bacterial mats and siboglinid tubeworm assemblages. This study focuses on in
situ measurements of methane fluxes to and from these different habitats, in comparison to benthic methane and
oxygen consumption rates. By quantifying in situ oxygen, methane, and sulfide fluxes in different habitats, a
spatial budget covering areas of 10–1000-m diameter was established. The range of dissolved methane efflux (770–
2 mmol m22 d21) from the center to the outer rim was associated with a decrease in temperature gradients from
46uCm21 to , 1uCm21, indicating that spatial variations in fluid flow control the distribution of benthic habitats
and activities. Accordingly, total oxygen uptake (TOU) varied between the different habitats by one order of
magnitude from 15 mmol m22 d21 to 161 mmol m22 d21. High fluid flow rates appeared to suppress benthic
activities by limiting the availability of electron acceptors. Accordingly, the highest TOU was associated with the
lowest fluid flow and methane efflux. This was most likely due to the aerobic oxidation of methane, which may be
more relevant as a sink for methane as previously considered in submarine ecosystems.
