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）铀钍测年数据，样品采自大堡礁（Great Barrier Reef, GBR）北部远岸、中部及南部近岸海域的已知年代活体滨珊瑚属（Porites spp.）样本，用于空间约束初始230Th/232Th（230Th/232Th0）的变化特征。
此类信息对于构建精准年代序列至关重要，后者可用于精确定位近期（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珊瑚死亡事件的发生时间。

实验方法：

研究区域：
从大堡礁三个受邻近流域土地改造程度各异的区域采集了块状滨珊瑚岩芯及完整活体珊瑚群落样本，采样区域包括：大堡礁北部远岸、中部大堡礁、南部大堡礁。后续从每个珊瑚群落取样以分析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切片，制备得到7mm厚的切片。在昆士兰大学兽医诊所对每个切片进行X光扫描。在明确现代滨珊瑚样本的年生长纹层结构后，使用直径5mm的台式钻机从单个生长纹层中钻取1-2g样品。沿珊瑚群落的生长方向，针对不同年生长纹层重复该取样步骤3至4次。所有样品随后在去离子水中超声清洗3-4次直至无可见污染物，并在无污染环境下置于40℃电热板上烘干（Shen et al., 2008）。

铀系化学与分析流程：
基于Zhao et al. (2001; 2009b)及Yu et al. (2006)详细描述的分析流程，在昆士兰大学放射成因同位素实验室（Radiogenic Isotope Facility, RIF）使用VG-Sector-54 WARP滤波高丰度灵敏度热电离质谱（TIMS），对来自11个活体滨珊瑚群落的43个子样本进行铀钍测年制样。

初始230Th/232Th比值计算：
以往研究通过计算年生长纹计数得到的珊瑚“真实年龄”与实际铀系测年结果之间的差值，来确定活体珊瑚的230Th0值（Cobb et al., 2003b; Yu et al., 2006; McCulloch and Mortimer, 2008; Burgess et al., 2009）。本研究采用相同方法，利用X光影像得到的珊瑚绝对纹层计数年龄，以及针对年轻样本修正的铀系年龄公式，计算活体珊瑚样本的230Th/232Th0值（