Tabular icebergs are away from Antarctica ice shelves
James Kirkham
When the ice sheets covering much of Northern Europe were rapidly retreating about 18,000-20,000 years ago, urban-sized icebergs once drifted through the British coast.
James Kirkham During a survey in the Antarctic of England, his colleagues discovered preserved scour marks created by these giants, which were created when they ploughed underwater sediments. The long comb-like features are buried under the mud of the North Sea, but are still visible in seismic survey data collected for searches for oil and gas.
“We know about the degree of scouring and ancient sea level, so we can estimate that these bergs are probably five to tens of kilometers wide, and perhaps hundreds of meters thick.
In Antarctica, table-form or table-top icebergs are a spectacular sight. Some will rival even small states in the US from a regional standpoint, like the recent giants known as the A23A and A68A. They listen from the ice shelf – a wide floating protrusion of a glacier flowing from the glacier.
Therefore, the perception that tabular icebergs once existed in the North Sea clearly shows that they had both the sea edges of the British and Ireland ice sheets and ice shelves. And that means there may be some lessons for the future decline of Antarctica, says Keycam.
In the North Sea, the large iceberg’s straight trams are written by wavy valleys made by narrow keels of much smaller blocks of ice. In other words, there is a “change of administration” in which large icebergs are replaced by countless small icebergs when ice shelves are crushed in response to rising temperatures, says Keekam.
Radiocarbon dating of sediments indicates that this shift occurs between 20,000 and 18,000 years ago.
Observations question the idea that labours of megabergs like the A23A and A68A may signal the widespread collapse of Antarctic ice shelves.
Emma Mackey The University of Florida tracks tabular iceberg sizes with satellite data since the mid-1970s, finding this trend to be inherently flat.
“James’ research highlights the mines, which means that major birth events are not necessarily signs of instability or cause of alarm,” says McKee. “In fact, ice shelves are disintegrated by death by 1,000 cuts. You need to worry when you stop watching large-scale birth events.”
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Source: www.newscientist.com
