Engineered and Natural Marine Seep, Bubble-Driven Buoyancy Flows

Bubble-plume upwelling flows were studied in the marine environment through dye releases into engineered plumes and a natural hydrocarbon seep plume. For engineered plumes, these experiments measured the water column-averaged upwelling flow V-up(z(o)) from release depth z(o) to the sea surface, for a wide range of flows Q, and z(o). From V-up(z(o)), the local upwelling flow V-up(z), where z is depth, was calculated and found to vary with Q as V-up(z) similar to Q(0.23) for plumes strong enough to penetrate a shallow, thermally stratified layer, which was in good agreement with published relationships between V-up(z) and Q. These data were used to interpret data collected at a natural marine seep. For the seep, the upwelling flow decelerated toward the sea surface in contrast to the engineered plumes, which accelerated toward the sea surface. Data showed the seep bubble-plume upwelling flow lifted significantly colder and more saline water. The increased density difference between this upwelling fluid and the surrounding fluid most likely caused the deceleration. Midwater-column bubble measurements showed downcurrent detrainment of smaller bubbles from the bubble plume.