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.