Iceberg Forensics: Predicting the Planet's Future With Antarctic Ice

There is a new iceberg in the Southern Ocean, and it's big: 50 miles long by 20 miles wide. Until February, it had been the tongue of the Mertz Glacier, sticking out from the East Antarctic ice sheet into the Southern Ocean. Large cracks had been forming over the last few years, crossing the tongue almost from one side to the other, but it took a nudge from a similarly huge iceberg to finally set the chunk of ice free. The new Mertz iceberg will travel westwards on the currents around Antarctica for decades, sometimes running aground on shallow parts of the continental shelf, eventually breaking up into smaller bergs and slowly melting.


Here aboard the scientific drilling ship JOIDES Resolution, which just finished drilling not far from the Mertz glacier in the waters off Wilkes Land, Antarctica, we received daily images from the U.S. National Ice Center to better navigate the ice-infested waters. It was not just the larger icebergs the ship's crew had to keep an eye on, but also the smaller pieces of ice, called growlers (the size of a car) and bergy bits (the size of a house), which were often tricky to spot on radar. But our ship was able to reach most of the planned sites, where we drilled ocean-floor sediments to study, among other things, the glaciological history of icebergs breaking away from the Mertz glacier and this sector of Antarctica.

Today, the 20-mile-wide Mertz Glacier is one of Antarctica's great ice streams, draining the ice from this part of East Antarctica. Snowfall on the highlands upstream is gradually buried and compressed until it becomes ice, and the ice flows downhill into the glacier. The glacier is moving to the ocean at 3000 feet per year and has regularly calved icebergs. Because the snow falling in the hinterland is in balance with the icebergs calving from the glacier, the ice sheet remains stable, neither gaining nor losing mass. At least, this was the case until a few years ago.