LIVERMORE, Calif. Radiocarbon dating is used to determine the age of everything from ancient artifacts to prehistoric corals on the ocean bottom.
But in a recent study appearing in the Aug. 26 edition of the journal, Nature, a Lawrence Livermore scientist and his colleagues used the method to trace the pathway of carbon dioxide released from the deep ocean to the atmosphere at the end of the last ice age.
The team noticed that a rapid increase in atmospheric CO₂ concentrations coincided with a reduced amount of carbon-14 relative to carbon-12 (the two isotopes of carbon that are used for carbon dating and are referred to as radiocarbon) in the atmosphere.
"This suggests that there was a release of very 'old' or low 14/12CO₂ from the deep ocean to the atmosphere during the end of the last ice age," said Tom Guilderson, an author on the paper and a scientist at LLNL's Center for Accelerator Mass Spectrometry.
The study suggests that CO₂ release may speed up the melting following an ice age.
Radiocarbon in the atmosphere is regulated largely by ocean circulation, which controls the sequestration of CO₂ in the deep sea through atmosphere-ocean carbon exchange. During the last ice age (approximately 110,000 to 10,000 years ago), lower atmospheric CO₂ levels were accompanied by increased atmospheric radiocarbon concentrations that have been credited to greater storage of CO₂ in a poorly ventilated abyssal ocean.
"The ocean circulation was significantly different than it is today and carbon was being stored in the deep ocean in a manner that we don't completely understand," Guilderson said.
Using two sediment cores from the sub-Antarctic and subtropic South Pacific near New Zealand, the team dated the cores to be between 13,000 and 19,000 years old. Guilderson was able to use the carbon-14 in the cores as a tracer to determine not only when the large CO₂
|Contact: Anne Stark|
DOE/Lawrence Livermore National Laboratory