Implications of strontium isotope and trace element variability in New Zealand kauri (Agathis australis)

Abstract

New Zealand kauri trees are an important dendrochonologic resource in the southern hemisphere due to their long lifespans and the correlation of ring widths to El Niño - Southern Oscillation (ENSO)-events. This study represents the first chronology-constrained dendrochemical investigation of New Zealand kauri. Strontium isotope (87Sr/86Sr) and trace element analyses are combined to determine the potential for provenance (spatial) and environmental (temporal) dendrochemical investigations utilizing the geochemistry of kauri wood. Soil Sr isotopic measurements match 80% of the corresponding analyses from local trees and two of the four study sites have kauri isotopic compositions tightly clustered and distinctive, supportive of provenance investigations. The two sites which record inter-tree isotopic variability, a combination of variables, including geologic, atmospheric (dust and sea spray), and anthropogenic (land-use), all likely influence the isotopic and trace element variations. Discrete annual events or fluctuating conditions are difficult to observe from the isotopic tree ring record, reflecting the potential mobility of Sr within tree rings. However, the preservation of long term geochemical trends suggest processes such as climate change or anthropogenic soil modification may still be preserved in the kauri record.