Spatial variability of initial U-Th in modern Porites from the inshore region of the Great Barrier Reef (NERP TE 1.3, UQ)

Brief description

This dataset consists of 43 thermal ionisation mass spectrometry (TIMS) U-Th dates from living Porites spp. of known ages collected from the far northern, central and southern inshore regions of the Great Barrier Reef (GBR) which were used to spatially constrain initial 230Th/232Th (230Th/232Th0) variability. Such information is essential in providing accurate chronologies used to pinpoint changes in coral community structure and the timing of mortality events in recent time (e.g. since European settlement of northern Australia in the 1850’s). Methods: Study area: Massive Porites coral cores and whole live colonies were sampled from three distinct regions of the GBR that have been subject to varying degrees of land modification in nearby catchment areas. The regions sampled included: far northern GBR, central GBR, southern GBR. Subsamples from each colony were subsequently used to determine the spatial variation of 230Th0. Sample preparation: A total of 11 modern Porites samples were sectioned down the main growth axis and a 7mm thick slice prepared. X-rays of each slab were taken at the University of Queensland Veterinary Clinic. Once annual banding patterns were well constrained in modern Porites samples, a 1-2g sample was drilled from within a single growth band using a bench drill with a 5 mm drill bit. This was repeated three to four times along the length of the colony for different annual growth bands. All samples were then ultrasonically cleaned in deionised water 3-4 times until no visible contaminants were evident and dried at 40°C on a hot-plate under contamination-free conditions (Shen et al., 2008). U-series chemistry and analytical procedures: Forty-three sub-samples from 11 living Porites coral colonies were prepared for U-Th dating using a VG-Sector-54 WARP-filtered high-abundance-sensitivity thermal ionisation mass spectrometer (TIMS) at the Radiogenic Isotope Facility (RIF), University of Queensland, following the analytical protocol described in detail in Zhao et al. (2001; 2009b) and Yu et al. (2006). Initial 230Th/232Th calculation: Previous studies have used living corals to resolve 230Th0 by calculating the value required to account for the difference between the ‘true age’ of the coral determined by annual band counting versus the actual U-series age (Cobb et al., 2003b; Yu et al., 2006; McCulloch and Mortimer, 2008; Burgess et al., 2009). Similarly in this study, 230Th/232Th0 values were calculated for live coral samples using the absolute band-counting ages of the corals obtained from X-ray images and the modified U-series age equation for young samples (<1000 years old) described by Zhao et al. (2009b). Format of the data: The dataset comprises of U-Th data obtained using thermal ionisation mass spectrometry (TIMS). Data is presented in a table in an excel spreadsheet with values for sample weight (g), U concentration (ppm), 232Th concentration (ppb), measured 230Th/232Th (activity ratio), 230Th/238U (activity ratio), ?234U (activity ratio), uncorrected 230Th age (in years), time of chemistry (years AD), growth band age (years AD), initial 230Th/232Th (atomic ratio), initial 230Th/232Th (activity ratio). References: Clark, T.R., Zhao, J.-x., Feng, Y.-x., Done, T., Jupiter, S., Lough, J., Pandolfi, J.M., 2012. Spatial variability of initial 230Th/232Th in modern Porites from the inshore region of the Great Barrier Reef. Geochim. Cosmochim. Acta 78, 99-118. See http://www.sciencedirect.com/science/article/pii/S0016703711007071 for the published paper. Alternatively, please contact the authors for a pdf copy of the paper. Data Location: This dataset is filed in the eAtlas enduring data repository at: data\NERP-TE\1.3_Coral-cores