SOLVED. Sci-Fi Short/Novella. The Oracle of Delphi is an intelligent gas. SCUBA-diver protagonist. Set in the Mediterranean.

[J.]

I read this short story/novella translated to Swedish in an anthology some time in the late 80s. The original was in English. I don't remember the translated name nor which anthology it was in (most likely one of the ones from Delta in Sweden).

Anyway, I'm looking for the original in English.

What I know:

The protagonist was an expert SCUBA diver working around the Mediterranean.

The main plot revolves around the fact that the Pythia at the Oracle of Delphi was actually breathing in an intelligent alien gas that gave her prophetic visions. The gas is still around in modern times.

The story setting is "real world, post-war", i.e. somewhere around 1950-1980.

What I *think* I know:

The setting and language suggests that the story was written in the late 1950s to the early 70s. It is definitely written well before 1987, which is the latest date when I could have read it the first time,

The gas may have taken control of a dolphin, helping the protagonist at some point.

I (used to) think the original story was called "Dead Pan", and that there were some poker/gambling situations in the story that motivated that title. However, I have not found any story with that name on ISFDB or elsewhere, so I'm beginning to think this could be wrong.

Appreciate any clues!

[Rosa]

“Deadpan,” by Edward Wellen, in Fantasy and Science Fiction, July 1975. You can read it on archive.org.

[J.]

YES!
That's the one. I've been searching for it for 20 years and couldn't find it even though I (almost) knew the name.

A million thanks!

[Rosa]

You’re most welcome! I’m reading it right now.