Greenland ice core data offer clues to last big melt

by Nora Schultz, NewScientist.com new service, 20 June 2008

The most detailed Greenland ice-core analysis yet offers important clues about what caused the climate to change so rapidly at the end of the last ice age.

"We can now read the climate's history at unprecedented resolution, going 15,000 years into the past", says Jim White at the University of Colorado at Boulder, who studied the new ice core as part of an international team.

Around this time, temperatures in Greenland rose by 10 °C in just 50 years. The new ice-core data suggests that this change began with a very rapid retreat of the ice covering the Atlantic. It also shows that it was preceded by dramatic climate change on the other side of the planet.

Damper deserts

White and his colleagues analysed the amount of dust and heavy oxygen and hydrogen isotopes in small sections of the ice core that each represent a few months of climate history.

This approach is only made possible using an automated analysis tool that continuously melts an ice core and measures its composition at the extraction site, not in the lab.

Most of the dust found in Greenland drifts there from China. The core reveals a sharp drop in dust levels at the end of the ice age, suggesting the Asian deserts suddenly became much wetter.

Following this, levels of the heavy hydrogen isotope deuterium indicate that atmospheric circulation in the North probably led to a retreat in the ice covering the Atlantic all the way from Portugal to Iceland over just one to three years. This was followed by a more gradual rise in Greenland temperatures over the next few decades.

Mystery connection

White says that the rapid ice melt was most likely triggered by a sudden recuperation of the warm North Atlantic deep water circulation.

However, he is surprised that the climate changed in Asia just before or at the same time. Although he does not yet know how the two events could be connected, White says the data strongly suggest that we should take a broader view when looking for warning signs of rapid climate change today.

"Otherwise, if we are just staring at the North Atlantic looking for change then we may get smacked in the rear by something that happens on the other side of the world," he says.

Katrin Meissner at the Climate Modelling Lab at the University of Victoria in Canada says the study presents groundbreaking insights into the existence of tipping points in the planet's climate system.

"This knowledge is crucial to understand and predict future climate changes due to man-made perturbations such as greenhouse gas emissions", she says.

Journal Reference: Science Express (DOI: 10.1126/science.1157707)