Data for U-Th dated coral from reef matrix cores and death assemblage from Mazie Bay, North Keppel Island, Southern Great Barrier Reef (NERP TE 1.3, UQ)

This dataset provides the results of U-Th dating of coral samples obtained from reef matrix percussion cores and death assemblages from Mazie Bay, North Keppel Island, Southern Great Barrier Reef. Data is presented for 117 coral samples ranging in age from 6900 years before present (yr.BP) to modern. A U-Th dating approach to understanding past coral reef dynamics and geomorphological constraints on future reef growth potential; Mazie Bay, Southern Great Barrier Reef - Reconstructing coral reef histories at multiple temporal scales provides a window of understanding into their response to changing environments. Using high precision Uranium-Thorium dating of corals from various reef zones we have reconstructed a complete growth history of Mazie Bay reef (North Keppel Island) in the Southern Great Barrier Reef. Our results show that Mazie Bay reef has been dominated by fast-growing branching Acropora spp. corals for the past 7000 years, and that during the mid-Holocene coral growth rapidly filled available accommodation space. The modern veneer of living coral is subject to periods of disturbance and recovery driven by various climatic influences including cyclones, floods and bleaching. Although loss of coral at Mazie Bay in the past was followed by relatively rapid recovery (~15 years), continued or chronic decimation of adult Acropora spp. coral populations could be catastrophic for this region due to the lack of connectivity to reefs outside of the Keppel Islands region.Methods:This tables contain data for U-Th dating of coral samples collected in February 2012 and June 2013 from a fringing reef in Mazie Bay, North Keppel Island, Southern Great Barrier Reef, including reef flat and slope matrix percussion cores and death assemblage (coral rubble at the sea/sediment interface next to the reef slope). For reef matrix percussion cores, ten-centimetre diameter aluminium cores were manually percussed into the reef matrix in November 2012 and November 2013. Four cores (two proximal to the beach and two distal) were taken from the emergent reef flat. Nine reef slope matrix cores from three discrete location across ~400 m of the modern reef slope were manually percussed on SCUBA at a depth of ~3 metres below lowest astronomical tide (mLAT) following methods described by Roff et al. (2015). Coral fragments were selected for U-Th dating from the base of each core where coral material was present, then up core where suitable skeletal material was available (i.e. from corals with enough unaltered aragonite for U-Th dating purposes). As compaction of the reef matrix occurs during percussion coring internal and external measurements of the cores were taken in the field prior to extracting the cores. Compaction of the cores was calculated as; core length = (Total Length of the core (initial) - External) and percentage compaction of the reef material inside the cores [(Internal-External)/((Total Length (initial) -External) – (Internal-External))*100]. Coral depths are based on linear uncompacted core length and reported relative to depth metres lowest astronomical tide (mLAT) based on 2012/2013 tide data from Maritime Safety Queensland for Rosslyn Bay (Station-024011A). Death assemblages were collected at three sites, adjacent to the reef slope cores, along four consecutive 20 m transects running parallel to the reef front at depths of ~- 3 to - 6 mLAT. Coral rubble was excavated from the benthos within 5 metre intervals of each transect and placed into calico bags (40 cm x 20 cm). Samples of death assemblages for U-Th dating were selected randomly from the calico bags, with sub-samples for U-Th dating being taken as close to the top (most recent) growth section of the corals so as to represent the timing of mortality.U-Th datingAll coral samples were prepared and U-Th dated on a Nu Plasma Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC ICP-MS) at the Radiogenic Isotope Facility, The University of Queensland following methods described in detail in Clark et al. (2014) and Leonard et al. (2016). U-Th data was calculated using Isoplot 3.75 (Ludwig, 2012). Activity ratios were calculated from atomic ratios using decay constants; lambda 238 = 1.55125 × 10-10 yr-1 (Jaffey et al., 1971), lambda 234 = (2.8262 ± 0.0057) × 10-6 yr-1, lambda 230 = (9.158 ± 0.028) × 10-6 yr-1 (Cheng et al., 2000) and corrected using the two component mixing equation of Clark et al. (2014) with a detrital 230Th/232Th value of 0.62 based on Keppel Islands specific isochron data from Leonard et al. (2016). For ease of comparison to previously reported data from reef matrix cores we report all dates prior to 1950 as yr.BP (years before present; where present is 1950), but consider all ages >1950 from slope core tops and death assemblage as “modern” and report as AD. Format:The dataset consists of three excel spreadsheets; one for samples U-Th dated to older than 1950 AD (calculated as years before present where present is 1950), and the second is calculated as years AD (post 1950 samples). The third spreadsheet provides lat/long of sample sites.Data Dictionary:•    Labcode – sample specific labcode in Radiogenic Isotope Facility, The University of Queensland•    Sample Name – Sample field name – NK = North Keppel; S = site number; AB/CD = core section followed by uncompacted core depth where samples was taken. •    Genus – Genus of coral•    Date of Chemistry – Date column chemistry was completed•    U (ppm) – Uranium concentration in parts per million•    232Th (ppb) – Thorium 232 concentration in parts per billion •    (230Th/232Th); (230Th/238U); (234U/ 238U) - activity ratios calculated from atomic ratios using decay constants; lambda 238 = 1.55125 × 10-10 yr-1 (Jaffey et al., 1971), lambda 234 = (2.8262 ± 0.0057) × 10-6 yr-1, lambda 230 = (9.158 ± 0.028) × 10-6 yr-1 (Cheng et al., 2000).•    uncorr. 230Th Age (ka) - Uncorrected 230Th age was calculated using Isoplot/EX 3.75 program (Ludwig, 2012). All values have been corrected for laboratory procedural blanks and all errors are 2 sigma.•    corr. 230Th Age (ka) - 230Th ages were corrected using the two-component correction method of Clark et al. (2014) using 230Th/232Thhyd and 230Th/232Thdet activity ratios of 1.08 ± 0.23 and 0.62 ± 0.14, respectively.•    delta 234U - = [(234U/238U) - 1] × 1000•    Depth (mLAT) – Uncompacted core sample depth relative to metres lowest astronomical tide References:Cheng, H., Edwards, R.L., Hoff, J., Gallup, C.D., Richards, D.A. and Asmerom, Y., 2000. The half-lives of uranium-234 and thorium-230. Chemical Geology, 169(1): 17-33.Clark, T.R., Roff, G., Zhao, J.-x., Feng, Y.-x., Done, T.J. and Pandolfi, J.M., 2014. Testing the precision and accuracy of the U–Th chronometer for dating coral mortality events in the last 100 years. Quaternary Geochronology, 23(0): 35-45.Jaffey, A., Flynn, K., Glendenin, L., Bentley, W.t. and Essling, A., 1971. Precision measurement of half-lives and specific activities of U 235 and U 238. Physical review C, 4(5): 1889.Leonard, N.D., Zhao, J.-x., Welsh, K.J., Feng, Y.-x., Smithers, S.G., Pandolfi, J.M. and Clark, T.R., 2016. Holocene sea level instability in the southern Great Barrier Reef, Australia: high-precision U–Th dating of fossil microatolls. Coral Reefs, 35(2): 625-639.Ludwig, K., 2012. Isoplot/Ex Version 3.75, a Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center. Special Publications. Berkeley Geochronology Center, Berkeley, CA.Roff, G., Zhao, J.-x. and Pandolfi, J.M., 2015. Rapid accretion of inshore reef slopes from the central Great Barrier Reef during the late Holocene. Geology, 43(4): 343.Data Location:This dataset is filed in the eAtlas enduring data repository at: data\NERP-TE\1.3_Coral_Cores

本数据集包含采自南太平洋大堡礁北凯珀尔岛马齐湾的礁基质冲击取心样（reef matrix percussion cores）与死亡堆积（death assemblages）的珊瑚样本铀钍测年（U-Th dating）结果。本次研究共涉及117个珊瑚样本，测年范围为距今6900年（yr.BP，以1950年为基准的距今年数）至现代。

采用U-Th测年方法解析古珊瑚礁动态及未来礁体生长潜力的地貌约束，是本次研究的核心方向；本数据集通过多时间尺度下的珊瑚礁历史重建，为理解马齐湾礁体对环境变化的响应提供了研究窗口。研究团队通过对不同礁带珊瑚样本开展高精度铀钍测年，重建了南大堡礁北凯珀尔岛马齐湾礁体完整的生长历史。结果显示，过去7000年间马齐湾礁体一直以快速生长的分枝状鹿角珊瑚属（Acropora spp.）珊瑚为主导，全新世中期珊瑚生长快速填充了可利用的容纳空间。现代活珊瑚表层受到气旋、洪水与珊瑚白化等多种气候驱动因素引发的扰动与恢复周期影响。尽管历史上马齐湾珊瑚礁损失后可实现约15年的快速恢复，但由于凯珀尔群岛区域外缺乏礁体连通性，持续或长期消减成年鹿角珊瑚属种群可能对该区域造成灾难性影响。

## 研究方法
本次采样于2012年2月与2013年6月采集自北凯珀尔岛马齐湾的岸礁，涵盖礁坪与礁坡基质冲击取心样，以及礁坡毗邻的海-沉积物界面处的珊瑚碎块死亡堆积。
对于礁基质冲击取心样：2012年11月与2013年11月，研究人员使用直径10厘米的铝制取心管手动冲击打入礁基质。共采集4个岩心（2个靠近海滩，2个远离海滩），取自出露的礁坪区域；在现代礁坡约400米范围内的3个离散点位，通过水肺潜水（SCUBA）在最低天文潮位（metres lowest astronomical tide, mLAT）下约3米深度处，手动采集了9个礁坡基质岩心，采样方法参考Roff等（2015）的方案。
研究团队从每个岩心的底部（若存在珊瑚物质）开始向上选取适合U-Th测年的珊瑚碎块，要求珊瑚骨骼具有足够的未蚀变文石结构以满足测年需求。由于冲击取心过程中礁基质会发生压实作用，研究人员在野外提取岩心前对取心管的内部与外部尺寸进行了测量。岩心压实率计算公式如下：
岩心长度 = 初始总岩心长度 - 外部长度
礁基质压实百分比 = [(内部长度 - 外部长度) / ((初始总岩心长度 - 外部长度) - (内部长度 - 外部长度))] × 100
珊瑚样本深度基于未压实岩心的线性长度计算，以2012/2013年昆士兰海事安全局罗斯林湾（站点编号024011A）的潮汐数据为基准，报告为相对于最低天文潮位的米数（mLAT）。
死亡堆积样本于3个点位采集，紧邻礁坡岩心点位，沿4条平行于礁前的连续20米样带布设，采样深度约为-3至-6 mLAT。在每条样带内以5米为间隔从底栖生境中挖掘珊瑚碎块，装入40 cm × 20 cm的棉布袋中。U-Th测年用的死亡堆积样本从棉布袋中随机选取，测年子样本优先选取珊瑚顶部（最新生长层）附近的材料，以准确反映珊瑚死亡的时间。

## U-Th测年方法
所有珊瑚样本的制备与U-Th测年均在昆士兰大学放射性同位素实验室的多接收杯电感耦合等离子体质谱仪（Multi-Collector Inductively Coupled Plasma Mass Spectrometer, MC-ICP-MS）上完成，测试方法参考Clark等（2014）与Leonard等（2016）的详细方案。U-Th数据通过Isoplot 3.75（Ludwig, 2012）计算得到。活度比通过原子比结合衰变常数计算得到：λ238 = 1.55125 × 10^-10 yr^-1（Jaffey等, 1971），λ234 = (2.8262 ± 0.0057) × 10^-6 yr^-1，λ230 = (9.158 ± 0.028) × 10^-6 yr^-1（Cheng等, 2000），并采用Clark等（2014）提出的二组分混合方程进行校正，碎屑相230Th/232Th值为0.62，该值基于Leonard等（2016）针对凯珀尔群岛的等时线数据得到。为便于与已发表的礁基质取心样数据对比，本数据集将1950年之前的测年结果报告为yr.BP（距今年，以1950年为基准），将礁坡岩心顶部与死亡堆积样本中年龄大于1950年的样本标记为“现代”，并以公元（AD）年份报告。

## 数据集格式
本数据集包含3个Excel电子表格：第一个表格对应年龄早于1950 AD的样本（以1950年为基准的距今年计算），第二个表格对应公元后（AD）样本（1950年之后的样本），第三个表格提供采样点位的经纬度坐标。

## 数据字典
• Labcode（实验室编号）：昆士兰大学放射性同位素实验室为样本分配的专属编码
• Sample Name（样本名称）：样本野外编号规则为：NK = 北凯珀尔（North Keppel）；S = 样点编号；AB/CD = 取心段编号，后接样本采集处的未压实岩心深度
• Genus（属名）：珊瑚所属的属
• Date of Chemistry（化学分析日期）：完成化学前处理的日期
• U (ppm)：铀元素浓度，单位为百万分之一（parts per million）
• 232Th (ppb)：钍-232浓度，单位为十亿分之一（parts per billion）
• (230Th/232Th); (230Th/238U); (234U/238U)：活度比，通过原子比结合衰变常数计算得到，衰变常数参数同前文所述
• uncorr. 230Th Age (ka)：未校正230Th测年年龄，通过Isoplot/EX 3.75程序（Ludwig, 2012）计算得到，所有数值均已校正实验室流程空白，误差为2σ
• corr. 230Th Age (ka)：校正后230Th测年年龄，采用Clark等（2014）的二组分校正方法，其中230Th/232Thhyd与230Th/232Thdet活度比分别为1.08 ± 0.23与0.62 ± 0.14
• delta 234U：计算公式为[(234U/238U) - 1] × 1000
• Depth (mLAT)：相对于最低天文潮位的未压实岩心样本深度，单位为米

## 参考文献
1. Cheng, H., Edwards, R.L., Hoff, J., Gallup, C.D., Richards, D.A. and Asmerom, Y., 2000. The half-lives of uranium-234 and thorium-230. Chemical Geology, 169(1): 17-33.
2. Clark, T.R., Roff, G., Zhao, J.-x., Feng, Y.-x., Done, T.J. and Pandolfi, J.M., 2014. Testing the precision and accuracy of the U–Th chronometer for dating coral mortality events in the last 100 years. Quaternary Geochronology, 23(0): 35-45.
3. Jaffey, A., Flynn, K., Glendenin, L., Bentley, W.t. and Essling, A., 1971. Precision measurement of half-lives and specific activities of U 235 and U 238. Physical review C, 4(5): 1889.
4. Leonard, N.D., Zhao, J.-x., Welsh, K.J., Feng, Y.-x., Smithers, S.G., Pandolfi, J.M. and Clark, T.R., 2016. Holocene sea level instability in the southern Great Barrier Reef, Australia: high-precision U–Th dating of fossil microatolls. Coral Reefs, 35(2): 625-639.
5. Ludwig, K., 2012. Isoplot/Ex Version 3.75, a Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center. Special Publications. Berkeley Geochronology Center, Berkeley, CA.
6. Roff, G., Zhao, J.-x. and Pandolfi, J.M., 2015. Rapid accretion of inshore reef slopes from the central Great Barrier Reef during the late Holocene. Geology, 43(4): 343.

## 数据存储位置
本数据集存储于eAtlas长期数据仓库中，路径为：dataNERP-TE1.3_Coral_Cores