Year

2020

Degree Name

Master of Philosophy

Department

School of Earth, Atmospheric and Life Sciences

Abstract

As anthropogenic warming continues it is important to assess responses in the climate from the climatologically significant West Pacific Warm Pool (WPWP). The warm waters in the WPWP modulate atmospheric convection and rainfall including in the rainfall band known as the South Pacific Convergence Zone (SPCZ). However, these interactions are not fully understood. This study aims to investigate whether corals from the Lau Lagoon seascape, Malaita Province, Solomon Islands, within the WPWP/SPCZ region can be used to extend WPWP/SPCZ climate records and thereby improve understanding of these climate ‘cogs’. Two modern coral samples that span up to twelve years of climate data from the north and south of Lau Lagoon were used to reconstruct present-day variability of the climate and test if the corals are accurate recorders of the local and regional climate. The coral samples were analysed for Sr/Ca to investigate the corals’ potential to record SST variations, luminescence for run-off changes and density to investigate the corals’ growth. Investigations of available instrumental datasets showed that the climatic conditions of Lau Lagoon and the wider regional area had low SST variability and strongly seasonal wind patterns. Comparisons of IGOSS SST grids, tidal data and bathymetry show that Lau Lagoon is an open lagoon that retains an open ocean signal. The coral Sr/Ca results showed a significant but weak relationship with SST (p = <0.01, R2 = 0.32 and p = <0.01, R2 = 0.23). Calibration equations for each coral Sr/Ca with SST were similar, therefore a site-specific calibration equation for Lau Lagoon was developed: Sr/Ca = -0.045 x SST + 10.14. This calibration equation is similar to a composite of southwest Pacific coral calibration equations. Luminescence results showed that the coral from the northern end of Lau Lagoon had a strong runoff signal. Luminescence peaks in the northern coral have a significant and moderate positive relationship with IGOSS SST (R2 = 0.4, p = <0.01), suggesting runoff events in Lau Lagoon occurs during warmer SST, which generally occur in the wet season from September to March. The Lau Lagoon coral had a similar Sr/Ca-SST response to IGOSS SST to ENSO events. The luminescence recorded less runoff during the 2015/2016 El Ni o, one of the largest El Ni o events in the instrumental record. The 2010/2012 La Ni a had a weaker signal in the Lau Lagoon Sr/Ca-SST, however luminescence in the northern core showed an increase of runoff. In conclusion, the Lau Lagoon Sr/Ca-SST and luminescence do appear to track climate events and changes within the WPWP, however ground-truthing of the modern coral signal could be refined by repeat analysis and analysis of other available modern cores from Lau Lagoon.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.