- 1School of Environmental and Life Sciences, University of Newcastle Australia, Australia
- 2School of Geography, Environment and Earth Sciences, Victoria University of Wellington, New Zealand
- 3ANSTO, Lucas Heights, NSW, Australia
- 4Xi'an Jiaotong University, Xi'an, China
- 5School of Geography, Earth and Atmospheric Sciences, the University of Melbourne, VIC, Australia
Insufficient palaeoclimate data from the South Pacific lead to conflicting theories regarding the region's responses to Holocene climate fluctuations. To address this gap in knowledge we present preliminary results from five stalagmites collected from two different caves in the Kingdom of Tonga.
Despite their vicinity, Ana Hulu (on Tongatapu Island) and Ana Maui (on ‘Eua Island) caves differ significantly in their microclimatic settings. Ana Hulu is a warm (24.2 °C) and shallow coastal cave, whereas Ana Maui is a deep and relatively cooler cave opening deep in the forest at 188 m above sea level. These differences are likely underpinned in the formation of the well-laminated and coloured stalagmites retrieved from Ana Hulu and the colourless, faint-laminated stalagmites from Ana Maui.
The set of U-series dated stalagmites provides an almost continuous record spanning the entire Holocene up to the end of the Younger Dryas (ca. 12,500 years ago). The stalagmites show different growth rates varying from 50 to 300 µm/year. The high-resolution chronology can offer the potential for annually resolved records of infiltration (rainfall) variability, which are likely to be related to shifts of the South Pacific Convergence Zone (SPCZ), the most important tropical South Pacific cloud belt..
However, an interpretation of SPCZ shifts based solely on speleothem δ13C and δ18O values is challenging. The potential influence of enhanced evaporation and degassing effects, which may arise from warm temperatures and low cave air pCO2, must be accounted for. A multi-proxy approach on coeval stalagmites has been shown to provide critical information about the role of local hydrology. Thus, we combined the stable isotope ratios values time-series with petrographic observations, high-resolution LA-ICP-MS trace elements data, and synchrotron-radiation XRF elemental mapping. This multi-proxy approach, along with an assessment of crystallization pathways leading to fabrics, is expected to enable robust reconstructions of coeval changes in infiltration regimes and hydroclimate dynamics across the South Pacific.
How to cite: Zareh Parvar Ghoochani Nejad, H., Borsato, A., Verdon-Kidd, D., Frisia, S., Sinclair, D., C. Treble, P., Cheng, H., and Drysdale, R.: Palaeoclimate reconstruction using high-resolution proxy data from Holocene stalagmites from the Kingdom of Tonga, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8924, https://doi.org/10.5194/egusphere-egu25-8924, 2025.
