Revelation 8:8 And the
second angel sounded, and as it were a great
mountain burning with fire was cast into the
sea: and the third part of the sea became
blood;
9 And the third
part of the creatures which were in the sea,
and had life, died; and the third part of
the ships were destroyed.
The
verse sounds like it will be one particular
sea rather than all the oceans. You
mentioned the Mediterranean Sea, Red Sea and
the Black Sea as possibilities. If the great
mountain burning with fire that is cast into
the sea is a volcanic mountain, then it would
have to be near the coastline. There are
some volcanoes near the coastline of the
Mediterranean Sea and the Red Sea, but none
near the Black Sea.