The last occurrence of Proboscia curvirostris in the North Atlantic marine isotope stage 9-8

Well-preserved diatoms are present in high sedimentation rate Pleistocene cores retrieved on Ocean Drilling Program (ODP) Legs 151, 152, 162 and IMAGES cruises of R/V Marion Dufresne from the North Atlantic. Investigation of the stratigraphic occurrence of diatom species shows that the youngest diatom event observed in the area is the last occurrence (LO) of Proboscia curvirostris (Jousé) Jordan and Priddle. P. curvirostris is a robust species that can easily be identified in the sediments, and therefore can be a practical biostratigraphic tool. We have mapped its areal distribution, and found that it stretches from 40°N to 80°N in the North Atlantic. Further, we have correlated the LO P. curvirostris to the oxygen isotope records of six cores to refine the age of this biostratigraphic event. The extinction of P. curvirostris is latitudinally diachronous through Marine Isotope Stages (MIS) 9 to 8 within the North Atlantic. This is closely related to the paleoceanography of the area. P. curvirostris first disappeared within interglacial MIS 9 (324 ka) from the northern areas that are most sensitive to climatic forcing, like the East Greenland current and the sea-ice margin. It survived in mid-North Atlantic until the conditions of the MIS 8 (glaciation) became too severe (260 ka). In the North Pacific at ODP Site 883 the LO P. curvirostris falls within MIS 8. The observed overlap in age between the North Atlantic and the North Pacific strongly suggests that the extinction of P. curvirostris is synchronous between these oceans.

北大西洋区域获取的沉积速率较高的更新世岩芯中保存有完好的硅藻，这些岩芯来自大洋钻探计划（Ocean Drilling Program, ODP）第151、152、162航次以及“玛丽·迪弗伦号”（R/V Marion Dufresne）执行的IMAGES航次。对硅藻物种地层产出特征的研究表明，该区域观测到的最新硅藻事件为弯喙原角藻（*Proboscia curvirostris* (Jousé) Jordan and Priddle）的末次出现（Last Occurrence, LO）。弯喙原角藻是一种形态粗壮、易于在沉积物中识别的物种，因此可作为实用的生物地层学标志。我们已绘制该物种的区域分布范围，发现其在北大西洋的分布跨度为40°N至80°N。进一步地，我们将弯喙原角藻的末次出现事件与6个岩芯的氧同位素记录进行对比，以精准限定该生物地层事件的年代。弯喙原角藻的灭绝事件在北大西洋范围内随纬度呈现穿时性，发生于海洋同位素阶段（Marine Isotope Stages, MIS）9至8期间，这与该区域的古海洋学特征密切相关。在对气候强迫最为敏感的北部区域（如东格陵兰洋流及海冰边缘地带），弯喙原角藻首先于间冰期MIS 9（324 ka）消失；该物种在北大西洋中部海域存活至MIS 8冰期条件变得极为严酷的时期（260 ka）。在北太平洋的ODP 883站位，弯喙原角藻的末次出现事件处于MIS 8阶段。观测到的北大西洋与北太平洋该事件的年龄重叠现象，强烈表明两个大洋中弯喙原角藻的灭绝事件是同步发生的。