Bubble-mediated transport of benthic microorganisms into the water column and its implication on pelagic biogeochemical cycles.

Benthic microorganisms transported into the water column potentially influence biogeochemical cycles and the pelagic food web structure. In our present study in the coastal waters of the Coal Oil Point seep field (California) and the Blowout site in the North Sea (abandoned well site 22/4b), we proved the dislocation of microorganisms from the sediment into the water column via gas bubbles released from the seabed. These studies showed that the transport efficiency of benthic methanotrophic bacteria into the water column was dependent on the gas flux intensity from the gas-releasing vent site. Cold seeps represent hot spots of seabed-derived methane emissions to the water column, where physical and biological barriers regulate transport of methane to the atmosphere. In our study, we combined field measurements with a particle-tracking model and demonstrated that sediment resuspension and gas-bubble-mediated inoculation of the water column with methane oxidizing bacteria decreased the methane turnover time by a factor of five. Our findings impressively demonstrate that the bubble-mediated transport of microorganisms influences the pelagic microbial abundance and community composition at gas-releasing seep sites. For cold seeps sites this newly discovered bentho-pelagic transport mechanisms creates a positive feedback on the pelagic methane sink and it seems obvious that this mechanism influences other biogeochemical processes in the vicinity of gas seeps, too.