Resolved 𝛿13C Signatures in Metrosideros Polymorpha as an Indicator of Hydroclimate Variability on Mauna Kea

Abstract

High-resolution 𝛿13C data in perennial plants can be associated with changes in annual to inter-annual hydroclimate variability. Analysis of 𝛿13C in native evergreen Sophora chrysophylla (māmane) from Mauna Kea, Hawai‘i demonstrated that variations in the 𝛿13C signature correlated with changes in July precipitation, illustrating the strong relationship between photosynthetic carbon isotope discrimination and hydroclimate. Using similar methodology, this study analyzes the 𝛿13C signature of high elevation Metrosideros polymorpha (‘ōhi’a) from Hakalau, Mauna Kea, Hawai‘i. A wedge of ‘ōhi‘a was processed and cut into thin slices with an industrial razor and combusted in an EA-CRDS Stable Isotope Analyzer, producing a full resolution of 𝛿13C values across the wedge. The measured 𝛿13C values were then compared to the visible ring structure and to independent 𝛿13C values measured from māmane on Mauna Kea, in order to evaluate potential trends and annual to inter-annual signals of hydroclimate variability. This study shows that variability in the 𝛿13C signature of ‘ōhi‘a is most likely driven by regional changes in climate, suggesting that ‘ōhi‘a may act as a proxy for past climate conditions on Mauna Kea.