It's neither! It is a Continent.
The Antarctic Circle is not a country, state, province, or territory, so it does not have a capital. Also, since Antarctica has no permanent inhabitants and does not belong to any country, Antarctica does not have a capital. In fact, neither Antarctica nor the Antarctic Circle has any cities.
Antarctica is governed by the Antarctic Treaty: there are no countries there, as you state. Australia is a single country.
There are no countries in the Antarctic.
No country owns any part of the Antarctic continent.
No.
The Antarctic Circle does not pass through any country.
The Antarctic is a region that contains the continent Antarctica.
Chile is.
Mount Erebus is a Antarctic volcano. There are no countries on the Antarctic continent..
There are no countries on the Antarctic continent.
Chile has.
There aren't any.