IntCal20 calibration curves

From this week, all radiocarbon dating results by GNS Science will be calibrated using the new IntCal20 calibration curves. We’re excited about this new dataset, which will help us date materials with even greater accuracy.

Calibration curves are essential for translating measured radiocarbon values into calendar ages. They’re important because radiocarbon levels in the atmosphere have fluctuated significantly over time. Calibration curves provide scientists with a way to take these fluctuations into account, and accurately transform radiocarbon measurements into a calendar age.

The IntCal curves are agreed upon by the international radiocarbon community, and are the internationally accepted calibration curves. There are three calibration curves, for use depending on where the object was found: Northern Hemisphere, Southern Hemisphere and Marine.

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Radiocarbon dating has revolutionised many areas of science, and it’s developing all the time – helping us to learn more about our past, and look ahead into our future

Dr Jocelyn Turnbull

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IntCal20 uses measurements from almost 15,000 samples from known-age objects. These include tree rings, stalagmites found in caves, corals and lake and ocean sediments. IntCal20 expands and refines the datasets used in previous calibration curves, and now extends back to 55,000 years ago.

SHCal20 is a separate dataset for the Southern Hemisphere, and is a refinement of the previous SHCal datasets, also extending to 55,000 years ago. NZ kauri measurements are the backbone of the SHCal20 dataset. 

Marine20 is the updated version of the marine calibration curve, based primarily on ocean radiocarbon modelling. Marine calibration requires an extra input, the local “marine reservoir” correction. Our current research is contributing to those corrections for New Zealand’s coastal margins.

“The IntCal calibration curves help us work out what the climate was like in the past, so we can better understand and prepare for future changes,” Jocelyn Turnbull from GNS Science says.

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“Radiocarbon dating and calibration are also critical to understanding the timing of past earthquakes and how often they might happen in the future.

“The new calibration curves also give our radiocarbon dating clients confidence that GNS Science is using the latest developments to deliver the most accurate results.

“Radiocarbon dating has revolutionised many areas of science, and it’s developing all the time – helping us to learn more about our past, and look ahead into our future.”

On request, we will recalibrate previously reported results with the new calibration curves.  You can also do this yourself: calib.org is the simplest online calibration tool; https://c14.arch.ox.ac.uk/oxcal/ allows more sophisticated calibration.