Comparison of radiocarbon ages from different planktic foraminifera species

考虑到一个强大的年龄模型的古海洋学研究的基础作用，这是至关重要的，以更好地了解海洋沉积物芯的放射性碳测年的潜在陷阱。几项研究报告了共存的浮游有孔虫年龄的显著差异> 2ka。然而，令人惊讶的是，迄今为止，很少有研究以系统的方式解决这个问题。虽然，有几个因素已经被强调，可能会引入一个物种依赖的抵消在明显的14 C年龄，如生物扰动和优先溶解和碎裂，较少关注，但是，有孔虫的生境偏好是否以及如何在产生有文献记载的种间年龄偏移中起决定性作用的问题一直受到关注。底栖和浮游有孔虫是深海通风的一个公认的代用指标，如果确定表层和温跃层有孔虫的14C年龄，预计也会产生类似的效果，因为溶解无机碳的天然14C含量低于季节性温跃层。因此，将温跃层居民与混合层居民相结合可能会增加14C测年的偏差，即使在沉积速率高的地点也是如此。缺乏比较混合层和更深温跃层居民14C年龄的研究，主要是因为深层居民相对丰度较低，这阻碍了系统的深入分析。然而，最近的分析进展允许调查非常少量的碳酸盐物质，基本上使单一有孔虫测试的日期。本文提出的研究将利用这一新的分析可能性，旨在仔细检查不同深度钙化的南极有孔虫物种的14C年龄。为此，我们将比较物种依赖的放射性碳年龄从时间片的明显不同的状态的海洋环流从两个良好的检查高沉积速率沉积物岩心，包括各种浅和深居住有孔虫物种。

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.