Three in one: Antarctica is more than just a heap of ice

The hits keep coming. A new report from the British Antarctic Survey tells us what many of us already suspected: the West Antarctic Ice Sheet’s days are numbered. The report covers melting of key ice shelves in the Amundsen Sea driven by warmer ocean waters and how the differences in projections where greenhouse gas emissions are slashed and those that are “business as usual” are minimal. This means that melting is “baked in” to the future and short of dramatically cooling the oceans, the ice shelves could disintegrate in the coming decades. Ice shelves float on the ocean, so their melting has no direct effect on sea level. But they hold back large glaciers like the cork in a champagne bottle. Once gone there would be nothing to stop the West Antarctic Ice Sheet from sliding into the ocean, possibly raising sea level by about 5 meters.

But you might ask: what about ice gains in East Antarctica and volcanoes in the Antarctic Peninsula? At first glance, these points seem like valid questions; however, the facts on the ground are a bit more complicated.

Antarctica is a Big Place

Antarctica is roughly the size of the continental United States, and although it may look like a single mass of ice in pictures, the geography of Antarctica is anything but simple. Under the ice there are mountains and valleys, which affect how ice moves as it slides from the interior toward the sea. But at a very high level it can be helpful to think of Antarctica as three continents in one. The Antarctic Peninsula is one of these three. It is the part that sticks up toward South America, and is mountainous. Being at lower latitude and surrounded by the Southern Ocean means that the climate in the Antarctic Peninsula is different than the rest of the continent. A large mountain range extends down the Antarctic Peninsula and across the rest of the continent as the Transantarctic Mountains. These mountains act like America’s Rocky Mountains in a way, serving as a continental divide.

The Great Divide

The Transantarctic Mountains separate East and West Antarctica. Just as water falling on the western side of the Continental Divide in America would flow toward the Pacific Ocean, snow falling on the western side of the Transantarctics will slowly form into ice that flows to the west into places like the Amundsen Sea. Snow on the eastern side of the Transantarctics will flow to the east.

Mountains, valleys, and plains

Another big difference between East and West Antarctica is the shape of the bedrock beneath. West Antarctica is more steeply sloped toward the ocean, whereas East Antarctica is largely a plateau. This means ice flows much more slowly east of the Transantarctic Mountains. This slower flow gives ice more time to accumulate, even if you discount weather differences. Throw in more precipitation and you have a recipe for increased ice mass. But extra snow in East Antarctica would have no effect on West Antarctica and vice versa. And anything that happens on the Antarctic Peninsula stays has no bearing on East or West Antarctica. So a volcano erupting on the Antarctic Peninsula would only affect ice there and not in other parts of the continent.

This simple fact, that the three main parts of Antarctica are basically separated, is important to remember. Asking a question about how there can be a drought in Colorado and a flood in Mississippi at the same time would get you funny looks at least. The same is true about ice growth in East Antarctica, volcanoes on the Antarctic Peninsula, and melting in West Antarctica. These places are on the same continent, but they are separate regions with different characteristics and different conditions.