Kauri provide a unique climate change record

Kauri provide a unique climate change record

Northland’s long summer drought has brought benefits for international climate change researchers, says the Director of the Waikato Radiocarbon Dating Laboratory, Dr Alan Hogg.

When they can be found, New Zealand swamp kauri provide a unique source of information about past climate change unmatched in the world, and the drought has made these ancient trees visible from the air.

As the grass dies above ancient swamp kauri trunks buried within a metre of the surface, they appear like giant matchsticks scattered across areas of Northland farmland, allowing researchers to undertake aerial reconnaissance missions to find them.

Seventy to 80 sub-fossil kauri have been discovered over the past summer providing an invaluable resource for climate records said Dr Hogg.

Dr Hogg of Waikato University is collaborating on dendrochronology (tree-ring dating) research being led by Dr Gretel Boswijk of Auckland University and assisted by Dr Jonathan Palmer of the Gondwana Tree-ring Lab in Christchurch, with funding of $500,000 from the Foundation of Research, Science and Technology (FRST). The New Zealanders are also working alongside a team of UK scientists from Exeter and Oxford Universities led by Exeter Professor Chris Turney with funding from Britain’s Natural Environment Research Council.

Dr Hogg says tree rings from swamp kauri reveal climate change information including annual rainfall and temperatures from thousands of years ago. Radiocarbon dating not only calibrates the age of specimens but also helps confirm palaeoclimate records, since radiocarbon (C14) levels are influenced by sunspot activity.

Trees add a ring of growth every year and the width of each ring reflects the conditions in which the tree grew.

Northern hemisphere climate research often focuses on ancient oak or pine trees providing growth records spanning about 300 years per tree. But in New Zealand, kauri preserved in peat bog provide records spanning thousands of years. The most long-lived found by the New Zealand researchers is a 25,000-year-old sub-fossil kauri with growth rings spanning 2,200 years.

The Waikato Radiocarbon Dating Laboratory has developed techniques to stretch the limits of radiocarbon dating from 50,000 years ago to upwards of 60,000 years – although other methods have had to be used to date older sub-fossil kauri forests, Dr Hogg says.

Dr Hogg is currently focussing research on five ancient kauri found at Towai, north of Whangarei, which grew 12,000-13,000 years ago and span a short and very rapid cooling period in the earth’s climate – a mini-ice age which lasted about 1,000 years and saw temperatures in Greenland drop seven degrees in only 10 years. This period, known as the Younger Dryas cooling interval, occurred in the middle of a longer period of global warming and has aroused curiosity among the world’s climate change researchers who theorise this sudden global cooling was connected with changing ocean circulation patterns in the North Atlantic.

Dr Hogg says the five ancient kauri are matched to the same era and represent a unique find anywhere in the world, enabling researchers to study southern hemisphere conditions during this cooling interval. The principal tree in the group lived for 1,350 years, spanning the whole period under review.

This FRST-funded research is expected to take another 18 months. It will augment the findings of two other research projects undertaken by the Waikato Radiocarbon Dating Laboratory, with Marsden funding totalling $975,000, to use kauri to develop records of climate change in New Zealand from 200BC to 1950AD. The second of these Marsden projects is due for completion in June this year.

ENDS

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