What biome is Antarctica?

I was asked a good question by somebody through the "Ask A Biologist" website:
"What is the biome of Antarctica? Some say it is a Tundra Biome and some say it is a Desert or Ice Biome. What is the right answer?"
It's a great question, so I thought I'd put my answer here, too! (It's also on the Ask A Biologist website.)

The important thing to remember about Antarctica is that it's a big continent. It's larger than the United States, which has many different biomes! Most of Antarctica is a desert, yes. Of course, it is a very different type of desert than most people think about, because most people think of deserts as being hot places with a lot of cacti, and that's not what Antarctica looks like! So, I think a lot of people call Antarctica a tundra because they don't know that a desert could be very cold. Scientists that work in Antarctica mostly refer to the majority of the continent as being cold desert or polar desert. The difference between cold and polar desert is very technical, mainly dealing with mineral salt chemistry. Some say that the coastal soils around the bulk of the continent are polar deserts while the rest of the continent (not near the ocean) is cold desert. Some people, though, use the terms interchangeably.

McMurdo Dry Valleys: a polar desert

However, some locations in and around Antarctica have a slightly milder climate, which we call the "maritime" climate region. This includes the islands along the Antarctic Peninsula (which is the part that reaches up towards South America on the Western side of the continent), as well as the sub-Antarctic islands. Because it's less harsh, there are more plants (mostly moss and algae, but also some grass). The soils therefore have more organic matter (aka rotting dead plant stuff), making these locations more like a tundra ecosystem. However, there are no woody plants in Antarctica, and only two species of vascular plants (a grass and a pearlwort), so it is not as diverse or complex as the Arctic tundra.

King George Island: a tundra-like ecosystem on the Peninsula

So, yes, some areas of Antarctica are considered tundra (or at least tundra-like), but it's not the entire outside of the continent. Most Antarctic scientists would consider the tundra ecosystems to just be the "maritime climate" region of the Antarctic Peninsula in West Antarctica and the sub-Antarctic islands, and the rest of West and East Antarctica as polar or cold desert. And, of course, much of the desert areas are covered by ice, with less than 2% of the continent being ice-free. In my opinion, organisms still live in these regions (like bacteria), so it's still an ecosystem. Whether it's called an "ice biome" or desert probably isn't official. The ice covered regions still meet the criteria for being a desert, because while there is water, it is frozen and unavailable to biology! Precipitation is low and moisture easily lost to the atmosphere. But obviously ice is a very different habitat from soil, so it could make sense to differentiate between the two.

There's a lot of ice in Antarctica!