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

Kenji M Matsuzaki,Shin-Ichi Kamikuri,Takuya Itaki,Ryuji Tada

doi:10.1186/s40645-018-0204-7

Kenji M Matsuzaki, Shin-Ichi Kamikuri + Show 2 more

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https://doi.org/10.1186/s40645-018-0204-7

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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.

Highlights

The Japan Sea is a back-arc basin opened by continental rifting during the late Oligocene to middle Miocene Epoch, ca. 28–13 million years ago (Ma) (e.g., Tamaki et al 1992; Jolivet et al 1994)
Kamikuri and Motoyama (2007) showed that, at Deep-Sea Drilling Program (DSDP) Site 302, radiolarian species related to the North Pacific deep water occurred in the Japan Sea between 8 and ca. 3 Ma, which suggests inflow of deep water of the North Pacific into the Japan Sea. These findings showed that the hypothesis proposed by Tada (1994) for that time is plausible, some concern remains about the ecology of the radiolarian species associated with the North Pacific deep water
Ation caused by glacial/interglacial cyclic climate changes (e.g., Elderfield et al 2012; Lisiecki and Raymo 2005). At both sites (U1425 and U1430), the preservation of Relative abundances of dominant species radiolarian fossils fluctuated between good to moderate We have defined a species or species group as dominant for the time interval between the late Miocene and late if their relative abundance exceeded 30% of the total

Summary

Introduction

The Japan Sea is a back-arc basin opened by continental rifting during the late Oligocene to middle Miocene Epoch, ca. 28–13 million years ago (Ma) (e.g., Tamaki et al 1992; Jolivet et al 1994). In the northern Japan Sea (corresponding to the southern to central part of Hokkaido Island), several geological studies suggested that a bathyal environment prevailed since the beginning of the late Miocene until the late Pliocene (e.g., Fukusawa 1988; Iijima and Tada 1990; Itaki 2016; Kosaka et al 1992; Kano et al 1991; Sagayama 2002; Suzuki 1989; Ogasawara 1994; Yahata 2002) (Fig. 2). A southward shift of the Okhotsk plate likely caused a southward migration of the Kuril basin and a progressive shoaling and closure of the Sakhalin seaways during the early to late Pliocene (Takeuchi et al 1999; Kharakhinov 2010)

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