Paleoceanographic and paleoclimatic changes in the northeastern Asia: case study
Paleoceanographic history in the northeast Asia, especially in Ulleung Basin, East Sea of Korea, is investigated based on two piston cores 94PC-2 (1,302 m water depth) and 95PC1 (1634 m water depth). Planktonic and benthic foraminifera are analyzed based on 242 samples.Carbonate Compensation Depth in Ulleung Basin shows regional difference. Northern part of Ulleung Basin (core 94PC-2) is characterized by relatively shallow carbonate compensation depth, and shows abrupt changes in the foraminiferal abundance in each core intervals compare to that of the core 95PC-1. On the other hand, southern part of Ulleung Basin (core 95PC-1) contains abundant planktonic and benthic foraminifers in every core intervals.In the East Sea, abrupt climatic shift, called Younger Dryas, is identified. The age of the Younger Dryas cold episode occurred at approximately 10-11ka.. Overall, changes in circulation and bottom water conditions occurred during the Younger Dryas cold episode. Especially, climatic transition from meltwater spike to the Younger Dryas cold episode is characterized by significant shifts of oxygen isotope values, the coiling ratios of Neogloboquadrina pachyderma, and the planktonic foraminifers abundances. In the study area, the calcium carbonate secreting organisms (foraminifers) is replaced by silicon dioxide secreting organisms (diatom, radiolarian) after the abrupt and severe cold climatic event.In the northern part of Ulleung Basin (core 95PC-1), temperature shift occurs around 12.7 ka. Paleotemperature getting colder from older than 12.7 ka toward the 12.7 ka. Then, paleotemperature gradually starts to warm until 10.43 ka. There was an abrupt climatic change between 10.43 to 9.3 ka. Core sediments younger than 9.3 ka do not contain any foraminifers, probably due to the abrupt climate shifts in the study area.