Weakened pacific overturning circulation, winter monsoon dominance and tectonism re-organized Japan Sea paleoceanography during the Late Miocene global cooling

Abstract

The Late Miocene global cooling (LMGC; approximately 7.9–5.8 Ma) was associated with remarkable changes in monsoon dynamics, biogenic bloom in the global oceans, and the rise of modern ecosystems at the expense of old biota. However, the possible linkage between the environmental changes and ecosystem shifts during the LMGC is still debated. In this paper, we show the high-resolution changes in the fluxes of selected radiolarian species, suggesting a drastic reorganization in the paleoceanography and ecosystem in the Japan Sea during the LMGC. The endemic radiolarian Cycladophora nakasekoi dominated the Japan Sea until 7.4 Ma when the Japan Sea sediment changed from dark radiolarian-rich sediment to organic-poor diatom ooze. Changes in the fluxes of C. nakasekoi and Tricolocapsa papillosa, the latter related to changes in the Pacific central water (PCW), show 100, 200, and ~ 500 ka cycles with their high flux mostly within the darker sediment intervals during the low-eccentricity period until 7.4 Ma, suggesting that orbitally paced PCW inflow might have been the major nutrient source into the Japan Sea. At about 7.4 Ma, these species decreased at the expense of increased Larcopyle weddellium, a radiolarian related to the North Pacific intermediate water (NPIW), and Cycladophora sphaeris, a subarctic radiolarian species, implying a decrease in PCW inflow and an increase in the inflow of NPIW and subarctic shallow water. Such a change would have been related to the LMGC-induced weakening in the Pacific Meridional overturning circulation and the southward shift of the subarctic front due to intensified East Asian winter monsoon. Such a drastic reorganization in the hydrography in the Japan Sea probably caused changes in nutrient provenance from the PCW to the NPIW and resulted in faunal turnover, marked by the disappearance of the old regional and endemic faunal components, such as C. nakasekoi.

Evolution of Oceanography of the Central Northwest Pacific Over the Past 10 Million Years With Focus on Late Miocene Global Cooling

“…Large changes can also be observed in the relative abundances of species related to PCW, dropping from 5% to <1% at ∼7.8 Ma at the onset of LMGC (Figure 2). A similar decrease between 8.0 and 7.8 Ma was recorded in PCW radiolarians from site U1425 in the Sea of Japan (Matsuzaki et al., 2022). Therefore, in the Northwest Pacific, there was likely a significant change in the North Pacific deep‐water system at the onset of LMGC.…”

“…Miocene deep-water circulation schemes by Holbourn et al (2013) suggest that a weakening of the ventilation of Southern Ocean intermediate water will weaken PMOC and lead to decreased productivity in PCW. Contextually, Matsuzaki et al (2022) suggested that there was a weakening of PMOC at the onset of LMGC. The results of the current study confirm this hypothesis, showing there was a decrease in PCW influence at site 1208 in the central North Pacific, and it is likely that PMOC weakened at the onset of LMGC and affected the whole Northwest Pacific.…”

“…To trace PCW changes, the relative abundances of Carponanistrum microdon Haeckel and Carpocanarium papillosum (Ehrenberg) were grouped because these species inhabit water depths between 1,000 and 3,000 m in the Northwest Pacific. These depths correspond to PCW (Matsuzaki, Itaki & Sugisaki, 2020;Matsuzaki et al, 2022).…”

“…Recent studies in the Sea of Japan based on key ecological properties of radiolarians (Matsuzaki et al., 2018; Matsuzaki, Suzuki, & Tada, 2020; Matsuzaki et al., 2022) tried clarify the oceanographic changes that occurred during LMGC. Numerous studies published since 2000 have shown that radiolarian microfossils are suitable proxies for the reconstruction of paleoceanography of the North Pacific Ocean from Neogene to Holocene (Dong et al., 2021; Hernandez‐Almeida et al., 2017, 2020; Itaki & Ikehara, 2004; Itaki et al., 2007, 2012, 2022; Kamikuri & Motoyama, 2020; Kamikuri & Moore, 2017; Matsuzaki, Nishi, Suzuki, Cortese, et al., 2014; Matsuzaki, Nishi, Suzuki, Kawate, et al., 2014, Matsuzaki et al., 2015, 2018, 2019; Matsuzaki, Suzuki, & Tada, 2020; Matsuzaki et al., 2022). Based on the ecology of radiolarian species extant since ∼10 Ma, Matsuzaki, Suzuki, and Tada et al.…”

“…Matsuzaki, Suzuki, and Tada (2020) and suggested that 8°C cooling exhibited by the radiolarian‐based SSTs during LMGC was caused by EAWM intensification. In addition, radiolarians also inhabit deep‐water masses such as the North Pacific intermediate water (NPIW) and Pacific central water (PCW) (Matsuzaki, Itaki & Sugisaki, 2020; Matsuzaki et al., 2022). During LMGC, a decrease in the fluxes of deep‐sea radiolarian species occurred; this can be linked to the weakening of the Pacific meridional overturning circulation (PMOC) and increasing production of NPIW (Matsuzaki et al., 2022; Zhai et al., 2021).…”