The radiocarbon in leaf fossils, such as those found in Lake Suigetsu, comes directly from the atmosphere.This means the processes that can slightly change the levels found in marine sediments or cave formations do not affect it.However, in cases where there are no low temperature age plateaus, the age of the youngest component can only be estimated by kinetic modeling which introduces model uncertainties to the chronology.

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The team managed this by matching the first 12,200 years of their record with the tree ring data, a well-established record that begins in the present.

They also used other records from the same period and found that they generally aligned.

"Because of the unique combination of a complete radiocarbon record and terrestrial paleo-climate data, Suigetsu can be a benchmark against which other records can be compared," said Professor Takeshi Nakagawa of Newcastle University.

"From a palaeoclimate perspective, this radiocarbon dataset will also allow very high precision direct correlation between Suigetsu and other terrestrial climate records," said Nakagawa in a press release.

"It also allows us to look at the differences between the atmosphere and oceans, and study the implications for our understanding of the marine environment as part of the global carbon cycle." The team measured radiocarbon from terrestrial plant fragments spaced throughout the core to construct a radiocarbon record.

To place the radiocarbon measurements in time, they also counted the dark and light layers throughout the glacial period.

By measuring the radiocarbon levels remaining in samples of ancient organic materials, scientists can work out how old things are.

One element that complicates this calculation is the variability of the amount of environmental radiocarbon from year to year and location to location.

The current team extracted cores of preserved layers of sediment from where they had lain on the bottom of Lake Suigetsu for tens of thousands of years.

The cores contained organic material such as tree leaf and twig fossils.

The method also allows for the resolution of more accurate ages for glacial marine intervals that overlie tills, and hence better estimates for deglaciation.