Ice sheet collapse led to dramatic sea level rise

Posted by Kate Taylor

Scientists studying coral off the coast of Tahiti have linked a collapse of the world's ice sheets 14,600 years ago to a sudden 14-meter rise in global sea-levels.

Until now, the date of the sea-level rise was unknown. But the new evidence dates it to 14,650 to 14,310 years ago, just when the Earth was experiencing a period of rapid climate change known as the Bølling warming.

During this period, high latitudes of the Northern hemisphere warmed as much as 15 degrees Celsius in less than 350 years - possibly  much more quickly.

"It is vital that we look into Earth's geological past to understand rare but high impact events, such as the collapse of giant ice sheets that occurred 14,600 years ago,' says Dr Alex Thomas of Oxford University.

"Our work gives a window onto an extreme event in which deglaciation coincided with a dramatic and rapid rise in global sea levels - an ancient 'mega flood'. Sea level rose more than ten times more quickly than it is rising now!"

The Tahitian coral is helpful because samples thousands of years old can be dated to within plus or minus 30 years. And because Tahiti is an ocean island, far away from major ice sheets, it's close to the  average of sea levels across the globe. While it's gradually subsiding into the ocean, this is happening at a steady pace that can easily be adjusted for.

What exactly caused the Bølling warming is unclear; right now, the leading theory is that the ocean's circulation changed so that more heat was transported into Northern latitudes.

The new sea-level evidence suggests that a lot of the water causing the sea-level rise must have come from melting of the ice sheets in Antarctica, which sent a 'pulse' of freshwater around the globe.

"This is an excellent test bed for climate models: if they can reproduce this extraordinary event, it will improve confidence that they can also predict future change accurately," says Thomas.