In 1992, a 60 miles long iceberg in the Southern Ocean, named B-9B, that had calved from an even larger iceberg — B9 – ran aground off the coast of Antarctica, not far in nautical miles from the Mertz Glacier Tongue. In February of this year, B-9B was back at sea and rammed into the glacier tongue. The result is a new iceberg named C-28, measuring 50 miles long and 25 miles wide, and weighing in at 860 billion tons.

The collision is shown in an animation from eight radar images made by Envisat, the largest earth observation spacecraft ever built. A press release from the European Space Agency, accompanying the animation, reports that the B-9B and C-28 have drifted together into a area of open water surrounded by sea ice, which is called a polynya.

Sea ice is formed in polynyas, along with a dense, salty brine that sinks to the sea bottom and drives ocean circulation around the globe. Scientists are concerned that the icebergs could block formation of the “bottom water,” which carries oxygen to the deep currents.

An agency that will watch what the two icebergs do in the weeks ahead is the National Ice Center in Maryland. Operated by the Navy, Coast Guard, and NOAA (National Oceanic and Atmospheric Administration), the center provides information on snow and ice conditions around the world and tracks icebergs. In the Antarctic, icebergs must be 10 nautical miles long and a set distance from the South Pole to be named and tracked.

Dividing the continent in four quadrants, the center names icebergs for the quadrant where they calved and assigns a number according to their sequence in breaking away. C-28 is the 28^th iceberg to be formed in the C quadrant, which faces Australia.