Ancient kauri trees lie buried in bogs scattered over a 300 kilometre stretch of northern New Zealand. Nowhere else on the planet has such a rich resource of sub-fossil wood for scientific work. The time span preserved within these bogs covers more than 130,000 years. The trees are of vast proportions and almost perfectly preserved: individual trees can measure up to 4 metres across and live for up to 2000 years. Within this precious archive is an annual record of past climate but, equally importantly, changing atmospheric carbon levels.
In the fifteenth century, Leonardo da Vinci realised there was a link between the thickness of tree rings and what the growing conditions were like at the time. Thick rings, he reasoned, must have been when it was a good season for tree growth; narrow or non-existent rings, terrible. Using historic observations we now know kauri thrive in drier conditions; conditions strongly controlled by the El Niño-Southern Oscillation (ENSO), providing a method of reconstructing past variability in the tropical Pacific.
Radiocarbon dating is a way to work out the age of any material that contains carbon and was formed up to 60,000 years ago. It’s one of the best known of all the dating methods and has revolutionized our understanding of the past. 14C forms just one trillionth of all modern carbon; the equivalent of a drop of water in an Olympic-size swimming pool. With a known rate of radioactive decay, it's possible to measure the 14C in ancient kauri trees to back calculate an age. And because changes in the global carbon cycle have a major impact on atmospheric 14C levels, kauri are giving new insights into how our planet works.