- Title
- Palaeoclimate reconstructions from geologic archives from the Cook Islands (South Pacific)
- Creator
- Faraji, Mohammadali
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The climate of the South Pacific is highly variable, acting in response to large-scale ocean-atmosphere systems over varying temporal scales. Research has shown that climate-related natural disasters in this region tend to be associated with a contraction or northwest migration of the South Pacific Convergence Zone (SPCZ) and enhanced El Ni˜no Southern Oscillation (ENSO) activity. However, the instrumental records in this region are typically short and incomplete, providing only a snapshot of the range of conditions this region experiences. Further, predictive climate models provide an inconsistent projection of future changes, hampering response planning to anthropogenic climate change. The current project aims to address these knowledge gaps by providing a reconstruction of the past 350 years of effective infiltration (hence rainfall) variability from stalagmites from Atiu island in the Southern Cook Islands and interpreting such variability in terms of ENSO events and shifts in the SPCZ. A combination of laminae counting, U-Th dating and radiocarbon bomb-pulse modelling were utilized to construct accurate chronologies for the stalagmites. These precisely-dated stalagmites then enabled the acquisition of a robust reconstruction of the variability of effective infiltration from a wide range of climate proxy data, including fabrics, δ18O, δ13C and trace elements (Mg, Sr, Na, P, Y, U) all benchmarked against cave monitoring data. Results indicate that speleothem fabrics, when combined with δ13C and δ18O providea great proxy for hydrology. Porous fabrics generally correspond to more negative δ18O and higher infiltration, and compact fabrics coincide with more positive δ18O and lower infiltration. Speleothem data suggests that variability in δ18O of rainfall in the Southern Cooks Islands is driven by a group of climate drivers. Still, it seems that the amount effect explains only 40% of δ18O variability in the rain, and ENSO is an important factor in modulating rainfall and δ18O variability through displacements of SPCZ. This was further supported by trace elements time series that proved to be of great hydroclimate significance, with Mg being the best hydrologically-sensitive element. Trace element proxy data were also indicative of an overarching role of SPCZ and ENSO in driving the rainfall variability in the Southern Cooks Islands. Overall, this study shows that the Southern Cook Islands archipelago is relatively dry when the SPCZ is contracted northeastward following El Ni˜no events (the SPCZ becomes zonal). This displacement drives much of the rainfall variability. However, what drives wet conditions appears to be the upshot of the interplay between different climate drivers of various timescales that cannot be explained only by the SPCZ movements modulated by ENSO. Importantly, the accurately-dated reconstruction presented in this study can assist in evaluating predictive climate models and provide an improved understanding of the baseline climate, particularly in such data poor region as the tropical South Pacific. This is of crucial importance when devising adaptation strategies and testing climate relationships in the climate-vulnerable South Pacific island nations.
- Subject
- palaeoclimate; Cook Islands; South Pacific; geologic archives
- Identifier
- http://hdl.handle.net/1959.13/1513725
- Identifier
- uon:56764
- Rights
- Copyright 2022 Mohammadali Faraji
- Language
- eng
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| View Details Download | ATTACHMENT01 | Thesis | 14 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 149 KB | Adobe Acrobat PDF | View Details Download |