Ancient coral samples shed light on rising sea levels

28 March 2012


New research involving members of the Oxford Martin School’s 21st Century Ocean Institute is shedding light on ice sheet response to climate change and its relationship to sea-level rise. The findings come from studies of ancient coral off the island of Tahiti, which link the collapse of massive ice sheets 14,650 years ago and a dramatic and rapid rise in global sea-levels of ~14m, to a period known as the Bølling warming.

Dr Alex Thomas and Prof Gideon Henderson were part of an international consortium of researchers whose findings have been published in Nature this week. Their research will help scientists currently modelling future climate change scenarios to factor in the dynamic behaviour of major ice sheets – something that is currently a major source of uncertainty in projected sea-level rise.

“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 14,650 years ago,” said Dr Thomas. “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 10 times more quickly than it is rising now! 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.”

What exactly caused the Bølling warming is a matter of intense debate: a leading theory is that the ocean’s circulation changed so that more heat was transported into Northern latitudes. However, this new sea-level evidence suggests that a considerable portion of the water causing the sea-level rise at this time must have come from melting of the ice sheets in Antarctica, which sent a ‘pulse’ of freshwater around the globe. Whether the freshwater pulse helped to warm the climate or was a result of an already warming world remains unclear.

In explaining the significance of their research, Prof Henderson emphasised, “Understanding this singular event over 14, 000 years ago is important because it sheds light on the dynamic behaviour of large ice sheets in response to changes in the climate system. This topic is crucial in the context of the present warming, as modern ice sheets have been shown to be contributing directly to the recent acceleration in sea level rise.”

The UK’s contribution to this research, and involvement in the Integrated Ocean Drilling Program, was funded through the Natural and Environmental Research Council, and was supported by the Oxford Martin School.