Kauri chemistry tells a tempestuous tale

NIWA scientists will use geochemistry of precisely-dated kauri tree rings to examine New Zealand's climate during the last millennium. The highly-detailed chemical signatures contained in the iconic kauri may reveal an untold story about temperatures, storms, droughts, and winds that our country faced centuries before instruments were around. The findings from this research project will provide information on New Zealand’s past climate variability as a context against which to consider potential future changes in climate and their impacts.

Two major climate intervals during the last millennium include the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). In parts of Europe, the MCA was characterised by warmth comparable or greater than today, while the LIA was a time of cooler temperatures and glacial advances in the Alps. As such, the impact these intervals had on the Northern Hemisphere is widely documented.

NIWA’s Dr Andrew Lorrey is leading a team of collaborators to define what these climate intervals, and their intervening shift, were like from a Southern Hemisphere perspective. Few studies have been done in this area for New Zealand.

“We know very little from this part of the world. What types of changes occurred and when they occurred, and the timing and rate of changes, are very important. This information will help us better understand the factors influencing our regional climate. We are building a holistic picture of what happened in the past,” says Dr Lorrey.

The relationship between the hemispheres, and how the atmosphere and oceans interact, is becoming increasingly important as scientists’ understanding of climate improves. A better understanding of what occurred in the Southern Hemisphere during critical climate intervals, and interrogating climate shifts, will help us understand the causes and ramifications for future climate changes.

“If you are dealing with limited information - just a Northern Hemisphere perspective - there is very little that can be drawn out about the dynamics of our climate system here. To gain a full view of ‘global climate change’ the whole picture needs to be presented,” says Dr Lorrey.

Kauri trees grow old enough to have an embedded chemical record that can be used as a proxy for climate stretching back in time for centuries. Calendar-dated kauri samples from living and recently dead trees, as well as building timbers, have been archived for research and contain valuable information.

“Previous geochemistry work has been done on one tree, but what does one tree tell you? - Probably not a lot. That’s why we need to investigate and determine what mix of material is needed to tell an accurate story about the past,” says Dr Lorrey.

While previous work to reconstruct climate has largely focused on mature kauri, information from juvenile kauri may even prove very valuable. Analysis of a wide mixture of samples will allow the scientists to calibrate and interpret the chemical signatures for the MCA and LIA.

“We are interested in honing in on the modern trees to understand what the signatures in the past mean. Is it precipitation amount? Is it soil moisture? It’s those things that we are going to figure out with this research,” says Dr Lorrey.

This Marsden funded work will commence in March 2012 and finish in Feb 2015. The key collaborators across New Zealand and in the United States include:

Dr. Andrew Lorrey, Mr. Christian Hyde, Petra Chappell (NIWA)
Dr. Travis Horton and Mr. Tom Brookman (University of Canterbury)
Professor Michael Evans (University of Maryland)
Professor Daniel Schrag (Harvard University)
Dr. Anthony Fowler (University of Auckland)
Ms. Sarah Muir (WaterCare Services Ltd.)