Comparison of radiocarbon ages from different planktic foraminifera species

考虑到稳健的年龄模型在古海洋学研究中的基础作用，更好地理解海洋沉积物岩心放射性碳测年的潜在陷阱是至关重要的。几项研究报告了浮游有孔虫共存年龄的显著差异。然而，令人惊讶的是，到目前为止，很少有研究系统地讨论这一主题。虽然已经强调了几个因素，如生物扰动和优先溶解和碎裂，可能在表观14C年龄中引入与物种有关的偏移，但对于有孔虫的栖息地偏好是否以及如何在产生已记录的种间年龄偏移中起决定性作用的问题关注较少。虽然共生的底栖有孔虫和浮游有孔虫之间的14C年龄差是一个公认的深海通风指标，但如果在表层和温跃层确定居住在有孔虫上的14C年龄，那么应该可以预期类似的影响，因为溶解无机碳的自然14C含量下降到季节性温跃层以下。因此，即使在沉积速率较高的地点，将温跃层居民与混合层居民结合起来也可能增加对14C测年的偏差。缺乏对混合层和深层温跃层居民14C年龄进行比较的研究，主要是因为深层居民的丰度相对较低，这阻碍了系统的深入分析。然而，最近的分析进展允许研究非常少量的碳酸盐物质，基本上能够对单个有孔虫测试进行测年。这项拟议的研究将利用这一新的分析可能性，旨在仔细研究不同深度的浮游有孔虫物种的14C年龄。为此，我们将比较来自两个经过充分研究的高沉积速率沉积岩芯的明显不同海洋环流状态的时间片的物种依赖的放射性碳年龄，其中包括各种浅海和深部栖息的有孔虫物种。

Considering the fundamental role of a robust age model for paleoceanographic research, it is of utmost importance to better understand the potential pitfalls of radiocarbon dating of marine sediment cores. Several studies reported significant differences of > 2 ka in the ages of co-existing planktonic foraminifera. However, surprisingly few studies have addressed this topic in a systematic way so far. While, several factors have been highlighted that could introduce a species-depended offset in apparent 14C ages like bioturbation and preferential dissolution and fragmentation, less attention, however, has been paid on the question if and how the habitat-preferences of the foraminifera play a decisive role in generating the documented inter-specific age offsets.While the 14C age difference between co-occurring benthic and planktonic foraminifera is a well-established proxy for deep ocean ventilation a similar effect should be expected if 14C ages are determined on surface and thermocline dwelling foraminifera as the natural 14C content of dissolved inorganic carbon decreases below the seasonal thermocline. Thus, combining thermocline dwellers with mixed-layer dwellers may thus add a bias to 14C dating even in sites with high sedimentation rates.The lack of studies comparing mixed layer and deeper thermocline dweller 14C ages largely originates from the relatively low abundance of deep dwellers which prohibited systematic in-depth analyses. However, recent analytical advance allows to investigate very small amounts of carbonate material essentially enabling dating of single foraminiferal tests. The here proposed study will take advantage of this new analytical possibility and aims to scrutinize the 14C ages of planktonic foraminiferal species calcifying in different depths. For this we will compare species-dependent radiocarbon ages from time slices of distinctly different states of ocean circulation from two well examined high sedimentation rate sediment cores comprising a variety of shallow and deep dwelling foraminifera species.