IMPLICATIONS OF SINGLE-STEP GRAPHITIZATION FOR RECONSTRUCTING LATE HOLOCENE RELATIVE SEA-LEVEL USING RADIOCARBON-DATED ORGANIC COASTAL SEDIMENT
IMPLICATIONS OF SINGLE-STEP GRAPHITIZATION FOR RECONSTRUCTING LATE HOLOCENE RELATIVE SEA-LEVEL USING RADIOCARBON-DATED ORGANIC COASTAL SEDIMENT
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DOI：
10.1017/rdc.2022.55
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发表时间：
2022-08
期刊：
影响因子：
8.3
通讯作者：
J. Sefton;A. Kemp;K. Elder;R. Hansman;M. Roberts
中科院分区：
文献类型：
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作者：
J. Sefton;A. Kemp;K. Elder;R. Hansman;M. Roberts
摘要晚全新世相对海平面的重建通常是利用盐沼和红树林沉积物中保存的代用指标进行的。这些沉积环境以可识别的大型化石（盐沼）和大量有机沉积物（红树林）的形式为放射性碳测年提供了丰富的材料。我们探讨，如果单步石墨化这些样品在准备放射性碳测年可以增加相对海平面重建的数量和时间分辨率，而不会相应增加成本。美国东北部盐沼宏体化石和密克罗尼西亚联邦大量红树林沉积物的年代测定表明，单步石墨化产生的放射性碳年龄与使用传统石墨化制备的重复样品无法区分，但误差略有增加（盐沼宏体化石的平均值/最大值为6.25/15额外的14 C年）。低12 C电流测量散装红树林沉积物单步石墨化后，可能使他们不可靠，尽管他们的明显的准确性。六个盐沼岩心的模拟年表表明，有两倍多的放射性碳年代测定（因为一步石墨化成本为传统石墨化的1.50%）导致年龄深度模型估计的样本年龄的置信区间较窄时，从一步方法的额外误差小于1.50 14 C年（1.30 14 C年，如果年表还利用历史年龄标记）。由于这些阈值大于我们的经验估计的额外误差，我们得出结论，采用单步石墨化的放射性碳测量植物宏体化石的年龄-深度模型的精度可能会增加20/10%以上（没有/有历史年龄标记）。这种改进可以在不增加成本的情况下实现。
ABSTRACT Late Holocene relative sea-level reconstructions are commonly generated using proxies preserved in salt-marsh and mangrove sediment. These depositional environments provide abundant material for radiocarbon dating in the form of identifiable macrofossils (salt marshes) and bulk organic sediment (mangroves). We explore if single-step graphitization of these samples in preparation for radiocarbon dating can increase the number and temporal resolution of relative sea-level reconstructions without a corresponding increase in cost. Dating of salt-marsh macrofossils from the northeastern United States and bulk mangrove sediment from the Federated States of Micronesia indicates that single-step graphitization generates radiocarbon ages that are indistinguishable from replicates prepared using traditional graphitization, but with a modest increase in error (mean/maximum of 6.25/15 additional 14C yr for salt-marsh macrofossils). Low 12C currents measured on bulk mangrove sediment following single-step graphitization likely render them unreliable despite their apparent accuracy. Simulated chronologies for six salt-marsh cores indicate that having twice as many radiocarbon dates (since single-step graphitization costs ∼50% of traditional graphitization) results in narrower confidence intervals for sample age estimated by age-depth models when the additional error from the single-step method is less than ∼50 14C yr (∼30 14C yr if the chronology also utilizes historical age markers). Since these thresholds are greater than our empirical estimates of the additional error, we conclude that adopting single-step graphitization for radiocarbon measurements on plant macrofossils is likely to increase precision of age-depth models by more than 20/10% (without/with historical age markers). This improvement can be implemented without additional cost.