Scientists celebrate 60 years of radiocarbon measurements
Scientists will next month celebrate the diamond anniversary of the world’s longest continuous record of atmospheric
radiocarbon measurements.
Sixty years ago, New Zealand scientists started the world’s first long timeseries of atmospheric radiocarbon
measurements. Measurements have continued through the years, incorporating improved techniques, and now this
world-renowned timeseries is a joint effort between NIWA and GNS Science.
Radiocarbon occurs naturally and is present in small amounts in carbon dioxide. The radiocarbon atoms then decay slowly
over time, a process that enables scientists to carry out carbon dating.
The measurements, which require a high level of precision, were started to help scientists understand how carbon
molecules cycle through the atmosphere, oceans, and plants. The radiocarbon content of atmospheric carbon dioxide
contains information about carbon exchange between the atmosphere and the oceans and land, as well as emissions from
burning fossil fuels.
Baring Head, southeast of Wellington, is a world-renowned “clean air” site, providing a global state of the atmosphere
removed from human influences. NIWA atmospheric scientist Dr Sara Mikaloff-Fletcher said the site was particularly well
suited for observing the Southern Ocean, a region that plays a key role in absorbing fossil fuel carbon dioxide.
Large-scale testing of nuclear bombs saw a dramatic increase in the amount of radiocarbon in the atmosphere to the point
it almost doubled. Fortunately, atmospheric radiocarbon never reached a dangerous level for human health. It peaked in
1966 in Wellington, three years after the introduction of the Limited Test Ban Treaty, which prohibited nuclear testing
above ground.
From then the radiocarbon produced by the nuclear tests has slowly been absorbed by plants, animals, soils and the
oceans.
Dr Mikaloff-Fletcher said over the next few years atmospheric radiocarbon levels are predicted to continue to decline,
prompted by growing amounts of radiocarbon-free fossil fuel carbon dioxide.
“The record of changes in radiocarbon at Wellington offer scientists a window on where carbon dioxide produced by
burning fossil fuel goes in the environment and how quickly it can be absorbed,” says GNS Science senior scientist Dr
Jocelyn Turnbull.
“We are extraordinarily lucky to have such a long, uninterrupted span of records.”
The radiocarbon in carbon dioxide molecules arriving at Baring Head carries the signatures of its origin. Analysing
these signatures reveals information about the Earth’s ability to slow climate change.
Following the establishment of the Wellington record, other scientists around the world followed suit. Subtle
differences between these international records provide a better understanding of the global picture.
Scientists from NIWA collect the samples and extract the carbon dioxide, then the carbon dioxide is measured for
radiocarbon at GNS Science. This process results in the highest precision radiocarbon measurements available anywhere in
the world.
Methods have advanced over the past 60 years and accelerator mass spectrometry is now used which requires only a few
litres of air to do the measurement.
Data are freely available and new modelling tools have been developed to use this record to understand underlying
processes.
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