An international team of researchers, led by Dr Christine Batchelor of Newcastle University, UK, used clear pictures of the seafloor to show just how quickly a former ice cover retreated (退去) at the end of the last Ice Age, about 20,000 years ago.
The team mapped more than 7,600 small-scale landforms across the seafloor. The ridges (山脊) are less than 2.5m high and are spaced between about 25 and 300 metres apart. These landforms are understood to have formed when the ice cover’s retreating edge moved up and down with the tides (潮汐), pushing seafloor into a ridge every low tide. Given that two ridges would have been produced each day, the researchers were able to work out how quickly the ice cover retreated. Their results, reported in the journal Nature, show the former ice cover rapidly retreats at a speed of 50 to 600 metres per day.
The seafloor landforms also give light into the way in which such rapid retreat can happen. Dr Batchelor and co-workers noted that the former ice cover had retreated fastest across the flattest parts of its bed.
“An ice can go away from the seafloor and retreat quickly when it becomes buoyant (有浮力的),” explained co-author Dr Frazer Christie. “This retreat only happens across relatively flat beds, where less melting (融化) is required to thin the overlying ice to the point where it starts to float (漂浮).”
The researchers believe that the quick retreat could soon be observed in parts of Antarctica. This includes at West Antarctica’s vast Thwaites Glacier. The authors of this new study suggest that it could go through quick retreat because it has recently retreated close to a flat area of its bed.
“Our findings suggest that present-day rates of melting are enough to cause quick short retreat across flat-bedded areas of the Antarctic Ice Sheet, including at Thwaites,” said Dr Batchelor. “Satellites (卫星) may well know this ice-cover retreat in the near future, especially if we continue our climate warming.”
8. What is the purpose of Paragraph 1?
A.To provide some advice for the readers. |
B.To add some background information. |
C.To make the story interesting. |
D.To bring in the topic. |
9. What does the second paragraph mainly tell us?
A.Where the ice cover’s retreating lies. |
B.Why the ice cover’s retreating is formed. |
C.What the result of ice cover’s retreating is. |
D.How the speed of ice cover’s retreating is worked out. |
10. Why is Thwaites Glacier mentioned in the text?
A.To give an example of quick retreat. |
B.To tell where it is located. |
C.To compare different types of retreat. |
D.To explain why it is important. |
11. What is Dr Batchelor’s attitude to the ice cover’s retreating?
A.Unclear. | B.Anxious. |
C.Positive. | D.Doubtful. |