Microbial response to organic particle generation by surface coagulation in seawater

Coagulation of organic material onto bubbles and the production of organic particles as the bubbles either dissolve or burst at an air-water interface had a large and well-defined effect on the concentration of dissolved organic carbon (DOC) in a coastal seawater. After only 15 min of bubbling, DOC was reduced by 43 %, and the rapid development of a transient microbial community was associated with the production of labile organic particles. Half of the DOC removed by this surface coagulation was respired to CO₂ within 3 d, and mineralization rates (209 to 212 μgC l⁻¹ d⁻¹) were comparable to primary production rates in even the most productive coastal waters. While surface coagulation is obviously not primary production, it does appear to physically regenerate carbon which remains less accessible to the biota when in the dissolved and colloidal state. This physical regeneration of DOC may be an important part of any pelagic ecosystem based on the consumption of organic particles, but when combined with rapid mineralization of the regenerated material, it could also be a mechanism for recycling a large reservoir of apparently refractory carbon back to CO₂ at the ocean surface.