Jensen, P.; Aagaard, I.; Burke, Jr. R. A.; Dando, P. R.; Jorgensen, N. O.; Kuijpers, A.; Laier, T.; O'Hara, S. C. M.; Schmaljohann, R. (1992). 'Bubbling reefs' in the Kattegat: submarine landscapes of carbonatecemented rocks support a diverse ecosystem at methane seeps. Marine Ecology Progress Series. 83: 103-112.
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Jensen, P.; Aagaard, I.; Burke, Jr. R. A.; Dando, P. R.; Jorgensen, N. O.; Kuijpers, A.; Laier, T.; O'Hara, S. C. M.; Schmaljohann, R.
1992
'Bubbling reefs' in the Kattegat: submarine landscapes of carbonatecemented rocks support a diverse ecosystem at methane seeps
Marine Ecology Progress Series
83: 103-112
Publication
NeMys doc_id: 17998
Available for editors
Methane seeps in shallow waters In the northern Kattegat off the Danish coast form
spectacular submarine landscapes - the 'bubbling reefs' - due to carbonate-cemented sandstone
structures which are colonized by brightly coloured animals and plants. These structures may be
100 m2 in area and consist of pavements, complex formations of overlying slab-type layers, and pillars
up to 4 m high. The carbonate cement (high-magnesium calcite, dolomite or aragonite) is 13C-depleted,
indicating that it originated as a result of microbial methane oxidation. It is believed that the cementation
occurred in the subsurface and that the rocks were exposed by subsequent erosion of the
surrounding unconsolidated sediment. The formations are interspersed with gas vents that intermittently
release gas, primarily methane, at up to 25 1 h-' The methane most likely originated from the
microbial decomposition of plant material deposited during the Eemian and early Weichselian periods,
i.e. l00 000 to 125 000 years B.P. Aerobic methane oxidation in the sediment was restricted Lo the upper
4 cm in muddy sand and to the upper 13 cm In coarse sand. Maximum aerobic methane oxidation rates
ranged from 4.8 to 45.6 pm01 dm-3 d". The rock surfaces and epifauna around the seeps were also sites
of methane-oxidizing activity. Integrated sulphate reduction rates for the upper 10 cm of muddy sand
gave 4.2 to 26.6 mm01 m-2 d-' These rates are higher than those previously reported from similar
water depths in the Kattegat but did not relate to the sediment methane content. Since gas venting
occurs over several km2 of the sea floor in the Kattegat it is likely to make a significant local contribution
to the cycling of elements in the sediment and the water column. The rocks support a diverse
ecosystem ranging from bacteria to macroalgae and anthozoans. Many animals live within the rocks in
holes bored by sponges, polychaetes and bivalves. Stable carbon isotope composition (6'") of tissues
of invertebrates from the rocks were in the range -17 to -24 'A, indicating that methane-derived
carbon makes little direct contribution to their nutrition. Within the sediments surrounding the seeps
there is a poor metazoan fauna, in terms of abundance, diversity and biomass. This may be a result of toxicity due to hydrogen sulphide input from the gas.
