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.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 (

本数据集包含43组热电离质谱（thermal ionisation mass spectrometry, TIMS）铀钍（U-Th）测年数据，样本为采自大堡礁（Great Barrier Reef, GBR）远北部、中部和南部近岸区域的已知年龄活体滨珊瑚属（Porites spp.）样品，用于在空间上约束初始230Th/232Th（230Th/232Th₀）的变异性。此类信息对于构建精准年代序列至关重要，可用于精准定位近期（例如自19世纪50年代澳大利亚北部被欧洲殖民以来）珊瑚群落结构变化及死亡事件发生的时间。
方法：
研究区域：从大堡礁的三个不同区域采集了大型滨珊瑚岩芯与完整活珊瑚群体，这些区域的邻近流域均经历了不同程度的土地改造。采样区域包括：大堡礁远北部、中部大堡礁、南部大堡礁。随后从每个珊瑚群体中获取子样本，以分析230Th₀的空间变异特征。
样品制备：对共计11个现代滨珊瑚样品沿主生长轴切片，制备7mm厚的切片。在昆士兰大学兽医学院对每个切片进行X光扫描。待现代滨珊瑚样品的年生长带模式得到明确约束后，使用配备5mm钻头的台式钻机，从单个生长带中钻取1~2g样品。沿珊瑚群体的生长长度方向，针对不同年生长带重复该操作3~4次。随后将所有样品用去离子水超声清洗3~4次，直至无可见污染物，并在无污染环境下以40℃电热板烘干（Shen等，2008）。
铀系化学与分析流程：从11个活体滨珊瑚群体中获取的43个子样本，在昆士兰大学放射性同位素实验室（Radiogenic Isotope Facility, RIF）使用VG-Sector-54 WARP滤波高丰度灵敏度热电离质谱仪（TIMS）开展铀钍测年制样，分析流程参照Zhao等（2001；2009b）及Yu等（2006）的详细描述。
初始230Th/232Th比值计算：既往研究通过计算校正值以抵消年生长带计数得到的珊瑚“真实年龄”与实际铀系测年结果间的差异，从而利用活体珊瑚确定230Th₀（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光图像得到的珊瑚绝对生长带计数年龄，以及针对年轻样品修正的铀系年龄公式，计算活体珊瑚样品的230Th/232Th₀值（