Radio-carbon clock not always on time
Tasmanian-based scientists have found that the 'clock' commonly used to date fossils doesn't always run at the same speed, findings which they say will fundamentally alter our understanding of climate change.
"This research suggests that climate warming and sea level rise in the Southern Hemisphere following the last Ice-Age may have occurred more rapidly than previously thought," says Dr Will Howard. "We calculate that events happened 1,500 years later than we think they did."
The researchers relied on radioactive carbon data collected from volcanic ash which was deposited at the same time in history on the land and seabed adjacent to New Zealand's North Island.
The amount of radioactive carbon (C-14) in organisms reflects the environment they live in. When an organism dies, it stops taking up radioactive carbon and its level slowly decreases over time as it decays. This enables scientists to use the amount of radioactive carbon in a fossil to tell them how old it is.
However, the ocean contains a lower level of radioactive carbon than the atmosphere (from which the C-14 is absorbed), a fact that scientists take into account when they are dating things in the ocean.
To explain this concept, Dr Howard draws an analogy."If you know your watch is five minutes slow then you can make sure you're on time by accounting for it".
To date, however, the assumption has been that past levels of radioactive carbon in the ocean were the same as they are now. The Tasmanian research has proved otherwise.
The researchers have found that when the Earth last cooled, the oceans circulated more slowly and consequently took up carbon from the atmosphere more slowly.
"We've found that during the last Ice-Age, the oceans took up radioactive carbon much more slowly, which means that during this time, the dating 'clock' ran slower," says Dr Howard.
Apart from pointing to the need to "recalibrate" the carbon-dating clock, Dr Howard says the findings have implications for our understanding of how fast natural climate change occurs and how rapidly oceans take up carbon - including carbon from fossil fuels.