Was it H2S? We did not stop around to ask!!!
H2S is toxic (blocks cellular absorption of O2) while methane 'merely' displaces 02 from the air. Pick your poison.
Returning to the matter at hand, tho... Have any of the sea ice photo watchers ever spotted circular polynya over geographically-fixed locations in the continental shelf zone which would be indicative of a persistent upwelling of gas from below?
It would seem to be a likely indicator of outgassing plumes, provided sea conditions are calm enough to let the outward movement of the ice in all directions persist.
I have worked with air lift pumps and they certainly induce a decent horizontal velocity at the surface. I would have thought that a kilometre-scale hydrate emission would be visible among mobile pack ice.
Likewise, the plumes will be bringing up deeper 2 degree water from below and punching it through the ?cooler fresher surface water. Would that show up in thermal imaging as a plume of higher temperature water in the passing current, with a distinct hot-spot as its origin above the plume?
Finally, the rising plume creates a spot of less-dense water. This means the core of the plume will have a water surface which is higher than the surrounding sea. Thus ice thickness / sea surface radars may be able to discern these upwellings, depending on the resolution of the sensors.
We really need to get a handle on this calthrate breakup issue don't we, and any way we can use existing sensor systems to re-look at the sea surface and detect these would be helpful, I would have thought.