Scientists celebrate 60 years of radiocarbon measurements

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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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Dr Jocelyn Turnbull, GNS

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