SCOTLAND鈥橲 coastline may seem tranquil today, but 55 million years ago it was anything but. Hot rock flowing beneath the Earth鈥檚 crust caused the region to rise and fall by hundreds of metres. Similar activity could be responsible for dramatic changes in sea level elsewhere in the world.
Global sea levels can change by more than 100 metres in only tens of thousands of years as land ice accumulates or melts. Now of the University of Cambridge and colleagues say that evidence from Scotland shows that changes in the Earth鈥檚 mantle may produce similarly dramatic changes in local sea levels, albeit on a slightly longer timescale.
The team has accumulated measurements from oil well cores and seismic imaging around the coast of Scotland. These show that 55 million years ago, the western flank rose and fell by at least 490 metres within 2 million years or so. A similar event seems to have occurred about a million years later on the eastern flank. The team suggests that a pulse of hot, solid rock rose from a hotspot beneath Iceland and travelled east beneath the Earth鈥檚 crust. Since the pulse was hotter than surrounding rock, it had a greater volume, lifting the land it passed under it (Journal of the Geological Society, ). 鈥淚t鈥檚 as though a giant hand pushed the surface up and then after a while pulled it down again,鈥� Lovell says.
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鈥淎s the pulse of hot rock travelling under Scotland had a greater volume, it lifted the land as it passed鈥�
The idea that circulation in the Earth鈥檚 mantle can significantly affect sea levels has been gaining momentum, says of the University of Hawaii in Honolulu. Changes like those seen in Scotland may mean that records of global sea levels on Earth, which track climate swings and plate tectonics, may need to be re-examined to take account of this mechanism.
