Occurrences of fossil benthic foraminifera in sediment core PC-11

We investigated fossil planktonic foraminifera from cores ND-02 (Nakdong River delta) and PC-11 (inner shelf off southeast Korea), to assess millennial-scale variations in the surface oceanography. In addition, we also analyzed benthic foraminiferal fauna in core PC-11. The coiling ratio of Neogloboquadrina pachyderma shows five millennial-scale near-cyclic variations (~8.7-8.3, ~7.5-6.2, ~4.7, ~2.8 and ~0.5 ka) since ~9 ka. These variations are similar to warm-water diatom variations at the Oki Ridge where a cyclicity of ~1.6 kyr is present, possibly associated with a Bond event. By contrast, the near-cyclic variations in our planktonic foraminiferal record were not fully consistent with the reported intensity variations of the Tsushima Warm Current in the East Asian margin and the warm Kuroshio Current in the Northwest Pacific. Our records from southeast Korea seem to reflect the more regional oceanographic variations in the marginal seas of East Asia. We suggest that the coastal upwelling of the subsurface cold water along the southeast coast of Korea plays an important role in generating near-cyclic variations of warm-water biota. The occurrence of the bathyal benthic foraminifera, such as Eilohedra nipponica and Psuedoparrella naraensis in core PC-11 also supports the scenario of the upwelling of subsurface water into the shallower depths at the timing of the more common sinistral specimens of N. pachyderma than the dextral specimens that implies the more intense upwelling. These variations may have a connection to the Bond event periodicity in the North Atlantic Ocean.

本研究对采自洛东江河口三角洲的ND-02岩芯以及韩国东南部近海内陆架的PC-11岩芯中的化石浮游有孔虫（planktonic foraminifera）开展分析，以探究表层海洋学环境的千年尺度变化。此外，本研究还对PC-11岩芯中的底栖有孔虫（benthic foraminifera）动物群进行了剖析。自约9 ka以来，厚壳新抱球虫（Neogloboquadrina pachyderma）的壳体旋向比呈现出5次千年尺度的近周期性变化，分别为~8.7~8.3 ka、~7.5~6.2 ka、~4.7 ka、~2.8 ka以及~0.5 ka。这些变化特征与隐岐海岭（Oki Ridge）处的暖水硅藻（warm-water diatom）变化相似，后者存在约1.6 kyr的旋回周期，推测其与邦德事件（Bond event）存在关联。与之形成对照的是，本研究的浮游有孔虫记录所呈现的近周期性变化，与已报道的东亚陆缘对马暖流（Tsushima Warm Current）以及西北太平洋黑潮（Kuroshio Current）的强度变化并非完全吻合。本研究获取的韩国东南部海域记录，似乎更能反映东亚边缘海的区域性海洋学环境变化。本研究认为，韩国东南部沿海的次表层冷水沿岸上升流活动，对暖水生物群的近周期性变化起到了关键调控作用。PC-11岩芯中产出的日本伊洛赫德虫（Eilohedra nipponica）、奈良假帕雷拉虫（Psuedoparrella naraensis）等半深海底栖有孔虫，也佐证了次表层水上升至较浅水深的过程：当厚壳新抱球虫的左旋壳体个体占比高于右旋壳体时，对应着更为强烈的上升流活动。这些变化或许与北大西洋地区的邦德事件旋回周期存在关联。