Millennial-scale oscillations in the Kuroshio\u2013Oyashio boundary during MIS 19 based on the radiolarian record from the Chiba composite section, central Japan

Takuya Itaki,Sakura Utsuki,Yuki Haneda,Yusuke Suganuma,Kentaro Izumi,Yoshimi Kubota,Makoto Okada

doi:10.1186/s40645-021-00465-0

Abstract

Marine isotope stage (MIS) 19 is considered to be the best orbital analog for the present interglacial. Consequently, clarifying the climatic features of this period can provide us with insights regarding a natural baseline for assessing future climate changes. A high-resolution radiolarian record from 800 to 750 ka (MIS 20 to MIS 18) was examined from the Chiba composite section (CbCS) of the Kokumoto Formation, including the Global Boundary Stratotype Section and Point for the lower–middle Pleistocene boundary on the Boso Peninsula on the Pacific side of central Japan. Millennial-scale oscillations in the Kuroshio warm and Oyashio cold currents were revealed by the Tr index, which is estimated using a simple equation based on radiolarian assemblages. The estimated Tr values ranged between 0.1 and 0.8 for MIS 18 through MIS 19, with minimum and maximum values corresponding to values observed off present day Aomori (41°N) and the Boso Peninsula (35°N), respectively. The observed patterns tended to be synchronous with the total radiolarian abundance associated with their production. Multiple maxima in radiolarian abundance occurred during periods of the Oyashio expanded mode before 785 ka and during periods of Kuroshio extension after 785 ka in MIS 19. Such increases in radiolarian abundance with the Kuroshio extension during MIS 19 are likely related to improvements in nutrient and photic environments with the development of a two-layer structure along the Kuroshio–Oyashio boundary zone. A similar pattern of millennial-scale climatic changes was also recognized in a precipitation record from the Sulmona Basin in central Italy, suggesting a close relationship with the CbCS record as a result of a large-scale climate system similar to the Arctic Oscillation in the northern hemisphere.

Highlights

Marine Isotope Stage (MIS) 19 is almost at the midpoint of a transition between progressive increases in the amplitude of climate oscillations with a shift in periodicity from a 41-ky rhythm to a quasi-100 ky rhythm that occurred 1400–400 ka, known as the Early–MiddlePleistocene transition (EMPT) (e.g., Head and Gibbard 2015)
4.1 Millennial‐scale fluctuations The observation of Tr values below 0.4 in MIS 20 and mid-MIS 19a imply that the Chiba composite section (CbCS) was located under conditions similar to those of the present day Oyashio current north of 37°N
Some discrepancies in the low-resolution record are recognized in MIS 20 and MIS 18, the observation of low and high variations in Tr values in the high-resolution record interval during MIS 20 and MIS 19, respectively, is generally consistent with largescale changes in the oxygen isotope ratio of planktonic foraminifera (e.g., Globigerina bulloides d’Orbigny (δ18OGb) and Globorotalia inflata (d’Orbigny) (δ18OGi)), which corresponds to the glacial-interglacial cycles reported by Haneda et al (2020) (Fig. 4a)

Summary

Introduction

Marine Isotope Stage (MIS) 19 is almost at the midpoint of a transition between progressive increases in the amplitude of climate oscillations with a shift in periodicity from a 41-ky rhythm to a quasi-100 ky rhythm that occurred 1400–400 ka, known as the Early–Middle. Pleistocene transition (EMPT) (e.g., Head and Gibbard 2015). MIS 19 has been intensively studied because it is the best orbital analog for the present interglacial (e.g., Tzedakis et al 2012). Itaki et al Progress in Earth and Planetary Science (2022) 9:5 forcing. This orbital configuration is similar to MIS 11 and the present interglacial (MIS 1), only MIS 19 and 1 show an obliquity peak and the precession minimum in-phase (Tzedakis 2010). It is important to obtain a detailed understanding of the climatic features of this period, as doing so could provide insights for establishing a natural baseline for assessing future climate changes (e.g., Tzedakis et al 2012; Giaccio et al 2015; Sánchez Goñi et al 2016; Suganuma et al 2018; Head 2021)

Results

Discussion

Conclusion