Comparison of radiocarbon ages from different planktic foraminifera species

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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.