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

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.\nSuch 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).\n\n\nMethods:\n\nStudy area:\nMassive 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.\nSample preparation:\nA 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).\nU-series chemistry and analytical procedures:\nForty-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).\n\nInitial 230Th/232Th calculation:\nPrevious 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 (

本数据集包含43组热电离质谱（thermal ionisation mass spectrometry, TIMS）U-Th测年数据，其样品为已知年龄的活体滨珊瑚属（Porites）样本，采集自大堡礁（Great Barrier Reef, GBR）北部远岸、中部及南部近岸海域，用于空间约束初始230Th/232Th（230Th/232Th0）的变异性。
此类信息对于构建精准年代学框架至关重要，可用于精准定位近期（例如自19世纪50年代澳大利亚北部欧洲殖民以来）珊瑚群落结构变化以及珊瑚死亡事件的发生时间。

研究方法：

研究区域：
从大堡礁三个受邻近流域土地开发程度各异的区域，采集了块状滨珊瑚岩芯以及完整活体珊瑚群落样本。采样区域涵盖大堡礁北部远岸、中部及南部海域。随后从每个珊瑚群落中获取亚样本，用于测定230Th0的空间变异特征。

样品制备：
共对11件现代滨珊瑚样本沿主生长轴进行切片，制备得到厚度为7mm的珊瑚切片。随后在昆士兰大学兽医学院对每块切片进行X光扫描。待现代滨珊瑚样本的年生长纹层特征得到明确约束后，使用直径5mm的台式钻头从单个生长纹层中钻取1~2g的样品。针对珊瑚群落不同的年生长纹层，沿其生长方向重复该步骤3~4次。所有样品随后用去离子水超声清洗3~4次，直至无可见污染物残留，并在无污染环境下以40℃电热板烘干（Shen等，2008）。

U系化学分析与实验流程：
从11个活体滨珊瑚群落中获取的43件亚样本，在昆士兰大学放射性同位素实验室（Radiogenic Isotope Facility, RIF）中，使用VG-Sector-54型WARP滤波高丰度灵敏度热电离质谱（thermal ionisation mass spectrometry, TIMS）完成U-Th测年制样，实验流程遵循Zhao等（2001；2009b）及Yu等（2006）详细描述的分析方案。

初始230Th/232Th计算：
既往研究通过计算校正值来解析初始230Th0，该校正值用于抵消通过年纹层计数得到的珊瑚“真实年龄”与实际U系测年结果之间的差值（Cobb等，2003b；Yu等，2006；McCulloch和Mortimer，2008；Burgess等，2009）。本研究采用类似方法，利用X光影像得到的珊瑚绝对纹层计数年龄，以及适用于年轻样本的修正U系年龄公式，计算活体珊瑚样本的230Th/232Th0值（