Whitecaps, Bubbles and Advection: Insights From Concurrent Measurements in the Open Ocean

Field measurements of breaking waves and bubble depths were obtained using a stereo video system collocated with a submerged acoustic Doppler current profiler (ADCP) in the central North Sea. We discriminate between two bubble depths that define an active near-surface layer and a deeper layer. The active layer intermittently sees short-lived injected bubble depths from breakers whereas the deeper layer is dominated by persistent passive bubble plumes that remain visible for more than 50 mean wave periods. We augment traditional single-beam bubble detection methods by utilizing all five beams of the ADCP to achieve broader spatial coverage of bubble plume measurements. The combined wave and bubble observations reveal that deep bubble plumes often occur offset spatially from surface whitecaps, suggesting that Langmuir-type circulation plays a role in the formation and persistence of deep bubble plumes through vertical and horizontal advection.