B-15 broke off from the Ross Ice Shelf in Antarctica. It was the largest iceberg ever documented, with a surface area of more than 4,200 square miles — more than twice the size of the state of Delaware. After it started breaking up, the largest of its pieces, B-15a, drifted along the coast of Antarctica, lingered on a shallow seamount, and collided with an ice tongue, before running aground and breaking again. Late in 2007, the largest remaining chunk floated out into the South Pacific where, in the warmer water, it began to disintegrate.
For the whole of the next year, the ocean was noisier than usual. All the way up past the equator, 4,350 miles or so away from where B-15a broke apart, hydrophones that scientists from the National Oceanic and Atmospheric Administration (NOAA) had suspended underwater were picking up strange signals. Another set of hydrophones, this one in the Juan Fernández Islands, off the coast of Chile, picked up the noise, too, even louder. When the scientists used the two sets of data to determine the source of the noise, they found the most likely culprits: B-15a and C-19a, another giant iceberg.
Twenty years ago, not so long before B-15 broke off from Antarctica, “we didn’t even know that icebergs made noise,” says Haru Matsumoto, an ocean engineer at NOAA who has studied these sounds. But in the past few years, scientists have started to learn to distinguish the eerie, haunting sounds of iceberg life — ice cracking, icebergs grinding against each other, an iceberg grounding on the seafloor — and measure the extent to which those sounds contribute to the noise of the ocean. While they’re just now learning to listen, the sounds of ice could help them understand the behavior and breakup of icebergs and ice shelves as the poles warm up.