High-resolution climate stratigraphy across the Matuyama–Brunhes transition from palynological data of Osaka Bay sediments in southwestern Japan

Abstract

This study presents a high-resolution palynological analysis of a sedimentary core from Osaka Bay (Japan) straddling Marine Oxygen Isotope Stage (MIS) 19, i.e. across the Matuyama–Brunhes magnetic polarity Boundary (MBB). Comparison with the standard marine oxygen isotope curve ([Bassinot, F.C., Labeyrie, L.D., Vincent, E., Quidelleur, X., Shackleton, N.J., Lancelot, Y., 1994. The astronomical theory of climate and the age of the Brunhes–Matuyama magnetic reversal. Earth and Planetary Science Letters 126, 91–108.]) demonstrates that variations in vegetation and the basinal environment coincided with global ice volume changes. The late MIS 20 is characterized by boreal climate with coniferous forest. In MIS 19, the forest was generally dominated by Fagus and Quercus ( Lepidobalanus), suggesting onset of humid climatic conditions slightly cooler than the present. Excluding coastal vegetation components, climate during MIS 19 can be subdivided into three stages. The early stage, including substage 19.3, is characterized by high seasonality in precipitation. This contrasts with the very abundant, year-round precipitation that is inferred for the late stage, from substage 19.2 to substage 19.0, which is characterized by cool-temperate coniferous taxa including Cryptomeria. The very high precipitation rates of the latter persisted at least up to substage 18.4. There was no apparent vegetational response to the sea level highstand of 19.3. In contrast, a short-lived thermal maximum event took place ca. 6–7 kyr later, i.e. in middle MIS 19. This event is characterized by increases in the warm-temperate element Quercus ( Cyclobalanopsis). The MBB, the recommended criterion for defining the Lower–Middle Pleistocene boundary, took place in middle MIS 19. These lines of evidence indicate that the occurrence of the MBB corresponded with a shift towards warmer and wetter climatic conditions. Similar warming and wetting events across the MBB are also observed in pollen records from southern Italy and central Japan. This possibly provides long-distance correlation, and may suggest a connection between the Earth's magnetic field and climate.