Marine Radiocarbon Reservoir Values in Southern California Estuaries: Interspecies, Latitudinal, and Interannual Variability
Marine Radiocarbon Reservoir Values in Southern California Estuaries: Interspecies, Latitudinal, and Interannual Variability
复制标题
南加州河口海洋放射性碳储层值：种间、纬度和年际变化
DOI：
10.2458/azu_rc.57.18389
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发表时间：
2015
期刊：
影响因子：
8.3
通讯作者：
G. MacDonald
中科院分区：
文献类型：
--
作者：
J. Holmquist;L. Reynolds;L. Brown;J. Southon;Alexander R. Simms;G. MacDonald
在美国加州，许多研究使用河口贝壳材料的放射性碳年代测定来建立河口沉积物积累的年龄-深度模型。海洋14 C年龄通常比同期陆地碳的年龄更老，需要计算全球平均海洋偏移量的局部偏移量（ΔR），以确保校准日期的准确性。我们使用加速器质谱（AMS）14 C测年40前1950年盐沼蜗牛和蛤蜊贝壳以前收集的四个加州河口。平均ΔR和标准差为217 ± 129 14 C yr，与以前使用河口和海洋混合样品的计算结果一致，尽管我们的河口计算结果的标准差和由此产生的年龄不确定性高于以前的研究。表层动物螺类（ΔR = 171 ± 154 14 C yr）和底层动物蛤类（ΔR = 263 ± 77 14 C yr）之间以及来自各个河口的样本之间的ΔR存在轻微但显著的差异（p = 0.024）。然而，对数据的更仔细的检查表明，即使对于相同的物种，在同一河口，ΔR可以变化高达1500 14 C年。在某些情况下，这种变化的大部分发生在不同采集者在不同时间采集的样品之间，可能表明碳源和ΔR变化的时间依赖性。这些变化也可以归因于在一个单一的河口，并导致碳源的空间差异的收集位置的差异。由于陆地14 C输入的增加，位于高沼泽的潮间带标本的ΔR可能低于完全海洋的标本。ΔR的巨大变化强调了在测定河口源样品的年代时，需要保守的年代学解释，以及广泛的不确定性假设。
Many studies use radiocarbon dates on estuarine shell material to build age-depth models of sediment accumulation in estuaries in California, USA. Marine 14C ages are typically older than dates from contemporaneous terrestrial carbon and local offsets (ΔR) from the global average marine offset need to be calculated to ensure the accuracy of calibrated dates. We used accelerator mass spectrometry (AMS) 14C dating on 40 pre-1950 salt marsh snail and clam shells previously collected from four California estuaries. The average ΔR and standard deviation of 217 ± 129 14C yr is consistent with previous calculations using mixed estuarine and marine samples, although the standard deviation and resulting age uncertainty was higher for our estuarine calculations than previous studies. There was a slight but significant difference (p = 0.024) in ΔR between epifaunal snails (ΔR = 171 ± 154 14C yr) and infaunal clams (ΔR = 263 ± 77 14C yr), as well as between samples from individual estuaries. However, a closer examination of the data shows that even for the same species, at the same estuary, ΔR can vary as much as ∼500 14C yr. In some cases, the bulk of this variation occurs between samples collected by different collectors at different times, potentially indicating time dependence in carbon sources and ΔR variation. These variations could also be attributed to differences in collection location within a single estuary and resulting spatial differences in carbon sources. Intertidal specimens located in the high marsh may have lower ΔR than fully marine counterparts because of increased terrestrial 14C input. The large variations in ΔR here highlight the need for conservative chronological interpretations, as well as the assumption of wide uncertainties, when dating samples from estuarine sources.