Before getting too deeply into how Antarctica produced its own accent, a discussion of what even makes an accent is in order.
Broadly speaking, an accent is simply the way words sound when they come out of your mouth, as the Linguistic Society of America explains. Things such as the way you pronounce vowel and consonant sounds (or if you’re capable of pronouncing them at all), the positions of the tongue and lips in the mouth in relation to each other, the order of words in which a sentence is constructed; all of these things, and others, define an accent.
One of the key factors that makes and maintains an accent is the speaker’s contact with other speakers. Prior to mass communication, speaker groups were largely isolated, which allowed one accent to develop in, say, Newcastle, England, and another to develop in, say, Ypsilanti, Michigan.
Linguistics look at accents in two contexts. The first is accents within native speakers of the same language. The aforementioned Newcastle speakers and Ypsilanti speakers, for example, though they all speak English as a first language, are still going to have wildly different accents. The second context is that of speakers of foreign languages speaking a language they might not speak naturally. A native German speaker trying to speak English, for instance, is going to have a German accent.
It was this stew of isolation mixed with some foreign accents that led to the discovery of the Antarctic accent.