Original paper
Oxygen isotope-magnetostratigraphy combined with zircon U–Pb dating for the Upper Pliocene composite marine succession in central Japan: Implications for the warm Pliocene deep-water current system on the northwestern Pacific margin
Haneda, Yuki; Utsunomiya, Masayuki; Iwano, Hideki; Danhara, Tohru; Hirata, Takafumi; Hosoi, Jun; Nakatani, Koretaka; Kubota, Yoshimi; Okada, Makoto
Newsletters on Stratigraphy Volume 58 Number 3 (2025), p. 256 - 289
89 references
published: Oct 14, 2025
published online: Jul 11, 2025
manuscript accepted: May 23, 2025
manuscript revision requested: Apr 8, 2025
manuscript received: Feb 15, 2025
Open Access (paper may be downloaded free of charge)
Abstract
The Late Pliocene was characterized by a warmer climate than today, followed by pronounced cooling toward the Early Pleistocene; thus, the Late Pliocene is a critical period for understanding Earth’s climate evolution and assessing the impacts of future global warming. Although the contribution of the western boundary currents in the northwestern Pacific is essential for the warm climate and subsequent glacial expansion in the Northern Hemisphere, the evolution of these surface/deep current systems remains unclear owing to the lack of continuous paleoceanographic records in this region. In this study, we provide a new Late Pliocene benthic oxygen isotope (δ18O) stratigraphy, with assistance from paleomagnetic polarity transitions and zircon U–Pb dating from on-land marine successions in central Japan that were rapidly deposited in a forearc basin in the northwestern Pacific margin. We measured the stable δ18O composition of four infaunal benthic foraminiferal taxa obtained from three sections in the Boso and Miura peninsulas, Japan. Interspecies offsets and the influence of depositional paleodepth on the benthic δ18O were corrected to construct a composite δ18O stratigraphy. The resultant δ18O stratigraphy, robustly constrained by magnetostratigraphy and zircon U–Pb ages, ranges from Marine Isotope Stage (MIS) Gi1 (3604 ka) to G15 (2898 ka). These sections cover the age interval around the onset of the Northern Hemisphere Glaciation and most of the mid-Piacenzian Warm Period (missing MIS KM6 due to slumping). A clear increase in δ18O during MIS MG4–M2 (3390–3250 ka) is similar to that in the western subpolar Pacific, indicating that cold/high-δ18O deep-water occurred along the northwestern Pacific margin during that period. The change in bottom-water properties coincided with enhancement of the latitudinal thermal gradient in the North Pacific, and recovery of abyssal ventilation into the tropical eastern Pacific in association with cooling around Antarctica and resulting activation of bottom-water formation. These observations suggest that cooling around Antarctica and resulting activation of bottom-water formation in the Southern Ocean during MIS MG4–M2 led to northward expansion of high-density deep-water to the subarctic North Pacific along the western margin and interruption of the weak latitudinal thermal gradient in the North Pacific. Further paleoceanographic and paleoclimatic studies using our δ18O stratigraphy will facilitate understanding of the North Pacific surface and deep western boundary current systems during the Late Pliocene.
Keywords
mid-Piacenzian Warm Period • Northern Hemisphere Glaciation • Chronostratigraphy • Antarctic Bottom Water • western boundary current