(Table 1) Age determination on various planktonic foraminifera from Ontong Java Plateau core top sediments@en

Shells of coexisting species of planktonic foraminifera from the Ontong Java Plateau reveal radiocarbon age offsets of up to 2200 years. Similar offsets are found between fragments and whole shells of single species. Steady state modelling of dissolution and bioturbation within the sedimentary mixed layer predicts age differences of up to several kiloyears due to the interplay between differential dissolution and fragmentation of foraminifer shells and bioturbation. The observation that fragile foraminiferal shells are systematically older than those of more robust species is more difficult to explain. Mechanisms of chemical erosion, interface dissolution, and sediment redistribution are all apparently unable to explain this phenomenon. A possible solution is presented in which a particular species may be represented by two distinct classes of shells which are more or less robust. In this case, differential dissolution and fragmentation causes an increase in the mean age as the fragile class contributes less to the remaining intact shells. This study highlights the vulnerability of low sedimentation rate cores to the effects of dissolution and bioturbation.取自翁通爪哇海台（Ontong Java Plateau）的共存浮游有孔虫（planktonic foraminifera）壳体，显示出最高可达2200年的碳十四年龄偏差。单一物种的壳体碎片与完整壳体之间也存在类似偏差。通过对沉积混合层内溶解作用与生物扰动（bioturbation）的稳态模拟，预测因有孔虫壳体差异性溶解、破碎与生物扰动的共同作用，可产生最高达数千年的年龄差异。观察发现，脆弱的有孔虫壳体系统性地比壳体更坚固的物种更为古老，这一现象较难解释。化学侵蚀、界面溶解以及沉积物再分配等机制均无法合理解释该现象。本文提出一种可能的解决方案：某一特定物种可通过两类稳健性存在差异的壳体来表征。在此情形下，差异性溶解与破碎作用会导致平均年龄升高，因为脆弱类壳体在剩余完整壳体中的占比降低。本研究凸显了低沉积速率岩芯对溶解作用与生物扰动效应的脆弱性。