Pandora Reef, Havannah Island - Ba/Ca Data ----------------------------------------------------------------------- World Data Service for Paleoclimatology ----------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! DESCRIPTION: Extended Description of Methods and Study Sites All metadata and data for this study can be accessed via: https://doi.org/10.25921/c3w9-2c39 ----------------------------------------------------------------------- Methods and Study Sites: Two coral reef sites have been examined in this study, Havannah and Pandora Reefs. At Havannah Reef a Porites core of 5.3 metres length that extends back to the late 1600ís, was collected by Dr Isdale from AIMS in 1988. Additional shorter cores were collected by the authors in 1998 from both Havannah and Pandora Reefs. Although these shorter cores only extend back to the late 1960ís, they nevertheless enable crosschecks to be made on reproducibility of the coral records both within and between reefs. Coral cores were slabbed into ~6 mm slices, x-rayed and photographed under UV light. The UV light illuminates luminescent bands caused by river flood plumes, with floods generally occurring in the months of January and February. Luminescent flood bands therefore provide excellent chronological markers for the inner GBR. A luminescent chronology was established by counting of individual flood bands, which was crosschecked using x-ray density bands. The translation from distance to time in the coral was undertaken independently, using Sr/Ca and U/Ca ratios (determined with laser ablation ICP-MS) and assuming that the winter minimum sea surface temperature (i.e. maximum Sr/Ca and U/Ca ratios) occurred on the 20th July of each year. Time was interpolated linearly between winter minimums. The chronology of the Ba/Ca records was thus determined independently from the luminescent flood band chronology. The coral slices were cut into 20 mm x 50 mm pieces for analysis in the laser ablation cell and cleaned in distilled water using a high intensity ultra-sonic probe. Slices were then scanned beneath an ArF excimer laser in a mixed He, Ar cell with ablated material being carried in an Ar stream to the ICP-MS plasma. The laser operates at a wavelength of 193 nm and has the unique feature of having a large depth of field, a consequence of the extended focal length optics. This is important for analyses of corals, as it enables the laser beam to remain in focus despite the relatively irregular coral surface and hence minimise elemental fractionation. Prior to analysis the coral slice was pre-ablated using a 100x800 micron slit with the Ar gas stream disconnected from ICP-MS. Elemental analysis of the coral pieces were undertaken with a 50x500 micron slit with backgrounds and standards being determined at the beginning and end of the analysis of each piece. High abundance minor elements B, Mg, Sr and U were standardised against a pressed powder coral standard. The isotopes 11B, 25Mg, 31P, 46Ca, 55Mn, 84Sr, 138Ba and 238U were measured with 46Ca being used as an index isotope to correct for signal fluctuations. Samples were scanned at a rate of ~1 mm per minute, with data being collected in 1 second cycles. To improve counting statistics data was averaged into 10 second blocks, representing a spatial resolution of ~0.15 mm equivalent to a temporal resolution of 3-4 days. See Sinclair et al and Fallon et al for more details. Determination of the Magnitude of pre-European Floods: For the Burdekin River, daily discharge data is available from 1921 to the present. Prior to that time there are occasional records of the maximum height of flood peaks (measured near Home Hill) that extend back to 1870, when European settlers first arrived. Two methods have been used to estimate the magnitude of pre-European floods. The first approach is based on the method of Lough et al., using visual determination of flood band intensity under UV light. Based on this approach, flood bands were divided into three categories, strong, average, and weak. The modern coral record (i.e.1921 to 1988) was used to calibrate these categories against the measured Burdekin River flow discharge. This modern calibration was then applied to the pre-European flood bands. To crosscheck this semi-quantitative approach, a limited number of flood-bands were also sampled at high resolution (0.25 mm intervals) for Sr/Ca and d18O isotope ratio measurements. Following the approach of McCulloch et al., the salinity change at the coral reef due to freshwater input by the river flood plumes can be determined by subtracting the temperature component from the d18O signal using Sr/Ca ratios. This is because d18O ratios in corals reflect changes in both temperature and salinity (i.e. the d18O composition of seawater), whereas Sr/Ca ratios are mainly dependent on sea surface temperature. In the Havannah coral, d18O-Sr/Ca systematics were determined for the floods of 1958, 1968, 1970, 1972, 1974 and 1981 and then compared with the weekly averaged records of Burdekin River flow. For the modern part of the coral record there is a reasonable correlation between salinity changes derived from d18O-Sr/Ca ratios in the coral and the Burdekin River discharge records of flood events. This approach was then extended to the older part of the coral record for the floods of 1819, 1826, 1831, 1859, 1860 and 1864. The flood magnitudes determined using this approach are shown in the supplementary figure and are consistent with those obtained using the intensity of luminescent bands. Flood plume events were recorded throughout the entire coral record with their magnitude being dependent on salinity changes inferred from d18O-Sr/Ca ratios and the intensity of luminescent flood bands.