Paleoceanographic history of the Japan Sea over the last 9.5 million years inferred from radiolarian assemblages (IODP Expedition 346 Sites U1425 and U1430)

Abstract

Previous studies showed that the evolution of the Japan Sea paleoceanography since the Miocene has been influenced by the regional tectonism (e.g., opening/closing of the connecting seaways) and regional/global climate. In the Japan Sea, Expedition 346 of the Integrated Ocean Drilling Program (IODP) retrieved core sediments dating back to the Miocene at two sites (U1425 and U1430). In this study, we reconstruct shallow-to-deep-water hydrography of the Japan Sea during the Mio-Pliocene based on radiolarian assemblages at Sites U1425 and U1430 considering the local tectonism and changes in global/regional climate. Our data suggest that glacioeustatic sea-level changes have probably had an influence on the local paleoceanography between 9.5 and 7.0 Ma. Indeed, warm water probably flowed from the North Pacific into the Japan Sea when sea level was high via shallow central and eastern seaways. In addition, the sill depth of the northern seaway was probably close to 1000 m between 9.5 and 7.8 Ma and had probably allowed inflow of oxygen minimum zone water from the North Pacific to the Japan Sea when sea level was high. In contrast, our data imply that Cycladophora nakasekoi, an endemic species to the Japan Sea, dominated between 9.5 and 7.3 Ma when sea level was low. Our data also suggest a progressive shoaling of the sill for the period since 7.8 Ma and that global climatic events such as such the late Miocene cooling (7.5-5.5 Ma) and the early Pliocene warmth have had a sustained influence on the Japan Sea. During the mid-Pliocene, a deep cooling of the subsurface to intermediate water of the Japan Sea likely occurred because species related to subarctic subsurface to intermediate waters were dominant between 5 and 3.8 Ma. The Northern Hemisphere Glaciation (ca. 3.0-2.7 Ma) and Mid-Pleistocene Transition (1.2-0.8 Ma) have both likely intensified the cooling of the Japan Sea.

Aeolian delivery to Ulleung Basin, Korea (Japan Sea), during development of the East Asian Monsoon through the last 12 Ma

“…We integrate several age models for Site U1430 (Kamikuri et al 2017;Matsuzaki et al 2018;Kurokawa et al 2019) that are of similar sampling resolution and cover the same age range as our study. We therefore use these models rather than, for example, a higherresolution age model for only the youngest 1 Ma (Tada et al 2018).…”

“…We therefore use these models rather than, for example, a higherresolution age model for only the youngest 1 Ma (Tada et al 2018). Matsuzaki et al (2018) identified a hiatus between c. 4 Ma and 7.3 Ma. Bulk accumulation rates (BAR; g cm −2 ka −1 ) for individual samples were calculated from the dry bulk density and linear sedimentation rates.…”

Paleoceanographic changes in the Northern East China Sea during the last 400 kyr as inferred from radiolarian assemblages (IODP Site U1429)

“…The microfossil group of radiolarians is the only abundant group bearing skeletons composed of amorphous silica (SiO 2 •nH 2 O) and inhabiting deep to shallow water depths (e.g., Suzuki and Aita 2011;Suzuki and Not 2015). Numerous studies of radiolarians in the Northwest Pacific and its adjacent marginal seas have demonstrated the suitability of this microfossil group as a paleoceanographic proxy (e.g., Itaki et al 2007Itaki et al , 2009Kamikuri et al 2007;Matsuzaki et al 2014aMatsuzaki et al , 2018Okazaki et al 2004). Recently, Integrated Ocean Drilling Program (IODP) Expedition 346, which aimed to reconstruct changes in EASM intensity since the Pliocene at high resolution, retrieved sediment cores at Site U1429 in the Danjo Basin of the northern ECS.…”

Cyclostratigraphy of the Late Miocene to Pliocene sediments at IODP sites U1425 and U1430 in the Japan Sea and paleoceanographic implications

“….45 Ma were too low (~1 cm/kyr) to detect meaningful orbital-scale changes in GRA, and the radiolarian datums and the occurrence of a glauconite layer suggest a hiatus during the time interval from 7 to 5 Ma (Kamikuri et al 2017;Matsuzaki et al 2018;Tada et al 2015c). For this reason, we conducted an orbital tuning only for 11.8 to 7.3 Ma.…”

“…The presence of parallel laminations only at site U1425 in the upper part of unit IIIA signifies euxinic or anoxic conditions in the bottom water there and oxic or suboxic conditions at site U1430, whereas the presence of parallel laminations only at site U1430 in the lower part of unit IIIA (~9.0 Ma) may indicate the development of an oxygen minimum zone within the Japan Sea, because site U1430 was at the appropriate paleo-water depth. Another line of evidence that an oxygen minimum zone developed or expanded in the Japan Sea around 8 Ma is radiolarian data indicating the presence of North Pacific type deep-water species at that paleo-water depth (Matsuzaki et al 2018).…”