Massive Icebergs Once Floated Around the UK

Deep tracks in the floor of the North Sea are hugely exciting to scientists in the UK, who say the grooves not only confirm that an ice sheet once covered Britain and Ireland, but also that it calved icebergs as large as cities. As the giant tabular icebergs with wide, flat tops and narrow keels scraped along the seafloor between 18,000 and 20,000 years ago, they left behind "deep, comblike grooves" that scientists from the British Antarctic Survey uncovered using detailed 3D seismic data, per the BBC. "These have not been seen before, and it shows definitively that the UK had ice shelves, because that's the only way to produce these gigantic tabular icebergs," says BAS marine geophysicist James Kirkham, lead author of a study published Thursday in Nature Communications.

The size of the grooves indicates the icebergs reached tens of kilometers wide and between 165 feet and 590 feet meters thick, "comparable in size to some of the smaller icebergs found off present-day Antarctica," per the BBC. The evidence suggests at least some came within 90 miles of Scotland's east coast. Because satellite data only covers 10 cases of ice shelves collapsing, researchers say that looking to the past could eliminate some of the uncertainty around ice loss and sea level rise, per the BBC. They hope that in studying evidence of the ancient UK ice sheet, they could learn more about how Antarctica's ice sheets and shelves might respond to climate change.

In the UK, giant icebergs were produced occasionally up until about 18,000 years ago, when the cold climate warmed, researchers say. Smaller icebergs—identified by single grooves in the seafloor, per the Guardian—then became more frequent, in a possible sign that ice shelves broke up. Ice shelves, extensions of thick land ice over water, are key to the stability of ice sheets, keeping continental ice from reaching the ocean. Researchers are now interested to learn whether the UK's ice shelves disappeared first, leading to the retreat of the ice sheet, or whether the ice shelves fell into the sea only after the ice sheet began melting. Precise dating of the North Sea's sediment tracks could offer a rough timeline for how it happened, researchers note. (More icebergs stories.)