Dramatic warming at the end of the last ice age produced an intense rise in sea level and a massive ice sheet collapse in the Antarctic.
The sea level rise is known as Melt-Water Pulse 1A, and new research indicates it increased sea level by about 45 feet (14 meters) sometime between 14,650 and 14,310 years ago, during the same time as a period of rapid climate change known as the Bølling warming.
Understanding the impacts of earlier warming and sea-level rise is important for predicting the effects of future warming.
"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," study researcher Alex Thomas of Oxford University said in a statement. "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.'"
During this period, "sea level rose more than ten times more quickly than it is rising now," Thomas said, with the rising seas resulting from melting ice sheets that had formed during the ice age. "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." [The Reality of Climate Change: 10 Myths Busted]
Coral cores
The expedition brought the scientists off the coast of Tahiti to collect fossilized coral cores going back thousands of years.
"Tahiti is located at a sufficiently considerable distance from the major former ice sheets to give us close to the average of sea levels across the globe, as a non-volcanic island it is also subsiding into the ocean at a steady pace that we can easily adjust for," study researcher Pierre Deschamps, of the Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement, said in a statement.
The researchers used radioactive dating and species analysis of the coral samples to reconstruct the rise in sea level over the last deglaciation. Different species of corals live at different depths, so by analyzing the coral makeup in cores and comparing that with the coral's age, researchers can get an idea of the sea level during those time periods.
"Corals are outstanding archives to reconstruct past sea-level changes as they can be dated to within plus or minus 30 years stretching back thousands of years," Deschamps said.
They found that the sea level rose about 45 feet (14 meters) in less than 350 years.
To figure out where all that water came from, the researchers compared sea-level rise in Tahiti with previous measurements of sea-level rise for the same time period in Barbados. With the two islands showing similar rises in sea level, the researchers say the water must have come from the Antarctic ice sheet. If the water had come from the Laurentide ice sheet, which covered a large area of North America during the Ice Age (the other main theory), there would have been a sea-level rise of about 40 percent less in Barbados due to its location, the researchers said. [Antarctica Album: The Iceberg Maker]
Changing climate
The researchers warn that more research is needed to understand the sequence of events that led to this drastic rise in the seas.
Even so, "insights into past sea-level changes may help to better constrain future changes," Deschamps said. "Our work sheds light onto an extreme event of rise in global sea levels in which ice-sheet collapse coincided with a rapid warming."
"Whether the freshwater pulse was a result of an already warming world or helped to warm the climate is currently unclear," Deschamps said. "However, our finding will help scientists currently modeling future climate-change scenarios to factor in the dynamic behavior of major ice sheets and finally to provide more reliable predictions of ice-sheet responses to a warming climate."
The study was published March 29 in the journal Nature.
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