Planktonic foraminifera and microfossil composition of IODP Hole 302-M0004C@en

Calcareous microfossils are widely used by paleoceanographers to investigate past sea-surface hydrology. Among these microfossils, planktonic foraminifera are probably the most extensively used tool (e.g. [1] for a review), as they are easy to extract from the sediment and can also be used for coupled geochemical (e.g; d18O, d13C, Mg/Ca) and paleo-ecological investigations. Planktonic foraminifera are marine protists, which build a calcareous shell made of several chambers which reflect in their chemistry the properties of the ambient water-masses. Planktonic foraminifera are known to thrive in various habitats, distributed not only along a latitudinal gradient, but also along different water-depth intervals within surface waters (0-1000 m). Regarding their biogeographical distribution, planktonic foraminifera assemblages therefore mirror different water-masses properties, such as temperature, salinity and nutrient content of the surface water in which they live. The investigation of the specific composition of a fossil assemblage (relative abundances) is therefore a way to empirically obtain (paleo)information on past variations of sea-surface hydrological parameters. This paper focuses on the planktonic foraminifera record from the Arctic domain. This polar region records peculiar sea-surface conditions, with the influence of nearly perennial sea-ice cover development. This has strong impact on living foraminifera populations and on the preservation of their shells in the underlying sediments.古海洋学家广泛利用钙质微化石（calcareous microfossils）开展古海洋表层水文环境研究。在这类微化石中，浮游有孔虫（planktonic foraminifera）或许是应用最为广泛的载体类群（相关综述可参见文献[1]）：其不仅易于从沉积物中提取，还可用于耦合地球化学（如δ¹⁸O、δ¹³C、Mg/Ca比值）与古生态研究。浮游有孔虫属于海洋原生生物，其外壳由多个房室构成且为钙质成分，壳体的化学组成能够反映其所处水体团的物理化学性质。已知浮游有孔虫可在多样生境中繁衍，它们不仅沿纬度梯度分布，还在表层水域（0~1000米）的不同水深区间内广泛分布。就生物地理分布而言，浮游有孔虫组合能够反映其生存的表层水体的各类水体团属性，例如温度、盐度与营养盐含量。因此，对化石组合的具体组成（即相对丰度）开展分析，是通过实证手段获取古海洋表层水文参数过去变化信息的有效途径。本研究聚焦于北极区域的浮游有孔虫记录。该极地区域具有独特的表层海洋环境，受近乎常年发育的海冰覆盖过程影响，这对现存有孔虫种群及其壳体在下层沉积物中的保存过程均会产生显著影响。