ALBERT

Description: U-series ages measured by thermal ionisation mass spectrometry (TIMS) are reported for a Last Interglacial (LI) fossil coral core from the Turtle Bay, Houtman Abrolhos islands, western Australia. The core is 33.4 m long the top of which is approximately 5 m a.p.s.l. (above present sea level). From the232Th concentrations and the reliability of the U-series ages, two sections in the core can be distinguished. Calculated U/Th ages in core section I (3.3 m a.p.s.l to 11 m b.p.s.l) vary between 124±1.7 ka BP (3.3 m a.p.s.l.) and 132.5±1.8 ka (4 m b.p.s.l., i.e. below present sea level), and those of section II (11–23 m b.p.s.l.) between 140±3 and 214±5 ka BP, respectively. The ages of core section I are in almost perfect chronological order, whereas for section II no clear age-depth relationship of the samples can be recognised. Further assessments based on the ϖ234U(T) criteria reveal that none of the samples of core section II give reliable ages, whereas for core section I several samples can be considered to be moderately reliable within 2 ka. The data of the Turtle Bay core complement and extend our previous work from the Houtman Abrolhos showing that the sea level reached a height of approximately 4 m b.p.s.l at approximately 134 ka BP and a sea level highstand of at least 3.3 m a.p.s.l. at approximately 124 ka BP. Sea level dropped below its present position at approximately 116 ka BP. Although the new data are in general accord with the Milankovitch theory of climate change, a detailed comparison reveals considerable differences between the Holocene and LI sea level rise as monitored relative to the Houtman Abrolhos islands. These observation apparently add further evidence to the growing set of data that the LI sea level rise started earlier than recognised by SPECMAP chronology. A reconciliation of these contradictionary observations following the line of arguments presented by Crowley (1994) are discussed with respect to the Milankovitch theory.

Description: A core from a coral colony of Porites lutea was analysed for stable oxygen isotopic composition*. A 200-year proxy record of sea surface temperatures from the Houtman Abrolhos Islands off west Australia was obtained from coral δ18O. At 29′S, the Houtman Abrolhos are the southernmost major reef complex of the Indian Ocean. They are located on the path of the Leeuwin Current, a southward flow of warm, tropical water, which is coupled to Indonesian throughflow. Coral δ18O primarily reflects local oceanographic and climatic variability, which is largely determined by spatial variability of the Leeuwin Current. However, coherence between coral δ18O and the current strength itself is relatively weak. Evolutionary spectral and singular spectrum analyses of coral δ18O demonstrate a high variability in spectral composition through time. Oscillations in the 5–7-y, 14–15-y, and quasi-biennial bands reflect teleconnections of local sea surface temperature (SST) to tropical Pacific climate variability. Deviations between local (coral-based) and regional (instrument) SST contain a cyclic component with a period of 15 y. Coral δ18O suggests a rise in SST by 0.6 ′C since AD 1944, consistent with available instrumental SST records. A long-term warming by 1.4 ′C since AD 1795 is inferred from the coral record