Paleoceanographic evolution of the Japan Sea over the last 460 kyr – A coccolithophore perspective

• Published in: Marine micropaleontology 2019-09, Vol.152, p.101720, Article 101720
• Main Authors: Saavedra-Pellitero, Mariem, Baumann, Karl-Heinz, Gallagher, Stephen John, Sagawa, Takuya, Tada, Ryuji
• Format: Article
• Language: English
• Subjects: Assemblage; Biogeography; Coccolith; Coccolithophores; East China Sea; Japan Sea; Tsushima current
• ISSN: 0377-8398; 1872-6186
• DOI: 10.1016/j.marmicro.2019.01.001

Changes in the intensity of the influx of the Tsushima Warm Current (TWC) in the south-central part of the Japan Sea (JS), or East Sea in Korean, were reconstructed for the last 460 kyr at IODP Site U1427 using the composition and abundance of the coccolithophore assemblage. In addition, the recent distribution of coccolithophore taxa in the JS and the East China Sea was assessed using electron microscopy. Coccolithophore assemblages, dominated by Emiliania huxleyi and Gephyrocapsa species, and coccolith abundance reveal a strong relationship between sea level and ocean variability over the last five glacial/interglacial cycles, in good agreement with planktic foraminiferal data. Three different circulation modes based on calcareous nannofossil and foraminifera TWC indicators were proposed for the JS. Coccolith production was low and TWC indicators (i.e., Gephyrocapsa oceanica, Calcidiscus leptoporus s.l., and Helicosphaera carteri) absent due to the isolation of the JS during glacials in response to global sea level falls (Mode 1). In contrast, coccolith abundance and TWC indicators reach a maximum due to the most intense TWC flow through the Tsushima Strait during interglacials (Mode 3). Intermediate conditions (Mode 2) are characterized by moderate/high coccolith numbers, presence of TWC coccolith indicators, and rare TWC planktic foraminifera indicators. This mode resulted in intermittent variations in the contribution of the TWC and East China Sea coastal water due to relatively low sea level stands (ca. −90 m to −20 m). Coccoliths dominated the carbonate sequence prior to MIS 8 and were major contributors to the total carbonate of the sediment at Site U1427, suggesting high coccolithophore productivity and a bloom-type environment during MIS 11 and 9. These changes in the carbonate chemistry caused by glacio-eustacy in the JS at the northwest margin of the Pacific Ocean should be considered in future paleoceanographic and paleoclimate models. [Display omitted] •Coccolithophores responded to glacio-eustatic sea level changes for the last 460kyr.•Variations in the Tsushima Warm Current were recorded by coccolith&foram indicators.•Coccoliths dominated the sequence & contributed to the total carbonate prior to MIS8.•The 1st occurrence of Emiliania huxleyi is recorded in the Japan Sea at 230 kyr.