Pictures from the Mariana ArcTop: Bubbles of Molten Sulfur
Sulfur rich plumes emanate from extruded lava. In some places, the liquid sulfur is stable and forms roiling black pools on the seafloor.
Bottom: Champagne Vent (which expels liquid CO2)
Yes, liquid carbon dioxide actually bubbles into the ocean from this vent. The droplets disperse into the ocean less than 200m above the vent site. This is remarkable because the vent is at ~1,600 m depth, but liquid CO2 is lighter than water except between 3,000-3,800 m depth.