Antarctica, on average, is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents. There are no permanent human residents, but anywhere from 1,000 to 5,000 people reside throughout the year at the research stations scattered across the continent. Only cold-adapted organisms survive.
No humans are known to have set foot in Antarctica before the 19th century. In 1912, Roald Amundsen commanded the first expedition to reach the South Pole, narrowly beating out a group led by Robert Falcon Scott.
In most of Harry Turtledove's alternate history works, Antarctica is unchanged from its OTL status. It is referenced in several works, but is rarely relevant to the plot or insightful to the nature of any timeline. E.g., in The War That Came Early: West and East, British soldiers stranded in the wilds of Norway rhetorically compare the local weather to that of Antarctica, and discuss several famous expeditions to that continent.
Antarctica in "The Fillmore Shoggoth"Edit
When Miskatonic University launched a series of expeditions to Antarctica in the 1930s, the world became aware of the existence of the Old Ones and the shoggoths. Humans and the Old Ones were eventually able to achieve co-existence. Nothing, however, could co-exist with the shoggoths.
In 1966, an iceberg broke off from the Ross Ice Shelf, and began traveling north. It survived the trip across the Equator, and landed at San Francisco in 1968. Shoggoths emerged from the iceberg and attacked the city.