Dissolved oxygen supersaturation and its impact on bubble formation in the southern Baltic Sea coastal waters

The dissolved oxygen supersaturation in the surface waters was investigated as a factor influencing bubble formation in the southern Baltic Sea coastal waters in Warszów, Lubiatowo and Hel from 1995 to 2007. To quantify the changes of oxygen supersaturation, data were collected along transects using integrated dissolved oxygen and water temperature sensors, either mounted on a remotely operated platform or deployed manually. Data revealed that an excess of solar energy in the nutrient-rich Baltic Sea coastal waters caused an immediate warming of sea bed and bottom water, which induced gaseous supersaturation and enhanced biological production of oxygen by phytoplankton. Both processes increased the degree of dissolved oxygen saturation, which became highly supersaturated, especially during the spring and summer time. Such conditions are favourable for enhanced formation of bubbles in the water, which enhanced the release of gases (mostly oxygen) into the air. Gaseous evasion is, in particular, enhanced in the presence of breaking waves and whitecaps that are typically formed over coastal ridges and at the shore line. Laboratory experiments indicated that, with the increasing degree of dissolved oxygen supersaturation, both the number of bubbles produced in the water and their sizes increase.