Reading the tea-tree leaves: Melaleuca quinquenervia leaves as a palaeoclimate proxy
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Date
2019-07-30
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Publisher
International Union for Quaternary Research (INQUA)
Abstract
The analysis of organic material preserved in sedimentary records is a useful tool in reconstructing past climatic conditions. It has been suggested that the carbon isotope discrimination (Δ) calculated from the bulk leaf δ13C of the modern Melaleuca quinquenervia tree responds to local precipitation in south-east Queensland, Australia [1]. The preservation of these leaves in lake sediments on Minjerribah (North Stradbroke Island) dating to the mid-Holocene presents the opportunity to produce species-specific stable isotope-based records of precipitation.
Here, we test the potential for M. quinquenervia to be used as a palaeoclimate proxy by examining the preservation of the bulk leaf δ13C over time and the relationship of Δ values to historical records of precipitation. Due to the varying rates of degradation of the different chemical constituents of plant matter, it is possible δ13C ratios to be altered by early diagenetic processes before, or during, the incorporation of leaves into the sediment. Therefore, modern studies are needed to establish what factors influence the discrimination derived precipitation record.
Focusing on the M. quinquenervia growing at Swallow Lagoon on Minjerribah, we studied the changes to the bulk leaf δ13C ratios of exposed leaves over an eighteen-month field study. We then applied our findings to the measured δ13C ratios of bulk leaf material retrieved from a core taken from the lagoon. The Δ values calculated based on these measurements were then compared to instrumental rainfall data from the past century to test the established relationship with modern precipitation through time.
By bisecting each leaf used in this study, we were able to compare the experimentally degraded leaves directly to their corresponding control halves. We observed that decay causes an approximate decrease of 1 ‰ in δ13C, as the leaves become more 13C depleted relative to the control leaf halves that were dried immediately. Quantifying this offset enables adjustment of values to be comparable to the calibration equation established using natural fall leaves from modern M. quinquenervia. Comparing the adjusted Δ values for lake core leaves from the last century to corresponding rainfall data the relationship to local precipitation seems to be preserved.
Understanding exactly how early diagenesis changes the stable isotope composition of M. quinquenervia leaf material over time allows us to adjust for the offset between modern and sub-fossil bulk leaf δ13C and advances the potential to use this species as a reliable climate proxy in the future. © The authors.
Description
Keywords
Leaves, Trees, Precipitation, Climates, Queensland, Australia, Carbon isotopes, Quaternary period, Rain
Citation
Greer, J., McInerney, F., Tibby, J., Hua, Q., Chulz, C., Barr, C., Marchall, J., & McGregor, G. (2019). Reading the tea-tree leaves: Melaleuca quinquenervia leaves as a palaeoclimate proxy. Poster presented to the 20th INQUA Congress 25th - 31st July 2019, Dublin, Ireland. Retrieved from: https://virtual.oxfordabstracts.com/#/event/public/574/submission/890