In the seabed, there are numerous microorganisms that play an important role in the global carbon cycle. Until now, however, it has not been understood to what extent geodynamic processes such as the subduction of oceanic plates influence this microbial activity and, in turn, impact the carbon balance. A study carried out by an international team of researchers, including scientists from the GFZ German Research Centre for Geosciences, now provides new evidence. They drilled down to a depth of 200 meters into an underwater mud volcano. Based on the recovered samples, they found that the microorganisms in the sediment are extremely active and form about 90 percent of the methane released from that depth. Apparently, the role of mud volcanoes in the global methane cycle has been significantly underestimated, the authors now conclude.