scholarly journals Correction to: A full sequence of the Matuyama–Brunhes geomagnetic reversal in the Chiba composite section, Central Japan

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Yuki Haneda ◽  
Makoto Okada ◽  
Yusuke Suganuma ◽  
Takahiro Kitamura
Keyword(s):  
Central Japan ◽  
Geomagnetic Reversal ◽  
Full Sequence ◽  
Composite Section

An amendment to this paper has been published and can be accessed via the original article.

scholarly journals A full sequence of the Matuyama–Brunhes geomagnetic reversal in the Chiba composite section, Central Japan

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Yuki Haneda ◽  
Makoto Okada ◽  
Yusuke Suganuma ◽  
Takahiro Kitamura
Keyword(s):  
Field Intensity ◽  
Geomagnetic Field ◽  
Central Japan ◽  
Virtual Geomagnetic Pole ◽  
Geomagnetic Reversal ◽  
Full Sequence ◽  
Intensity Index ◽  
Axial Dipole ◽  
Composite Section ◽  
Stratigraphic Position

Abstract Geological records of the Matuyama–Brunhes (M–B) geomagnetic reversal facilitate the development of an age model for sedimentary and volcanic sequences and help decipher the dynamics of the Earth’s magnetic field. However, the structure of the geomagnetic field during the M–B geomagnetic reversal remains controversial due to its complex field behavior. In this study, we conducted paleo- and rock-magnetic analyses of samples from the Chiba composite section (CbCS), a continuous and expanded marine succession in Central Japan, to reconstruct the full sequence of the M–B geomagnetic reversal. We define an average stratigraphic position of the M–B boundary and estimate its age based on three sections in the CbCS and a neighboring drill core, TB-2. The average stratigraphic position of the M–B boundary in the CbCS is established at 1.1 ± 0.3 m above a widespread volcanic ash bed (the Byk-E tephra). Assuming a chronological error associated with orbital tuning of 5 kyr and stratigraphic uncertainty of 0.4 kyr, the M–B boundary in CbCS is at 772.9 ± 5.4 ka (1σ). The virtual geomagnetic pole, which is calculated from the paleomagnetic directions, shows several short fluctuations between 783 and 763 ka, with concomitant decreases in geomagnetic field intensity index. After termination of the field instabilities, the field intensity recovered and became higher than before the M–B boundary, with a stable normal polarity direction. The paleomagnetic records in the CbCS exhibit a field asymmetry between the axial dipole decay and field recovery, providing a full sequence of the M–B reversal, suggesting that the non-axial dipole field dominated several times during periods ca. 20 kyr long across the M–B boundary, due to depletion in the main axial dipole component. Our results provide probably the most detailed sedimentary record of the M–B geomagnetic reversal and offer valuable information to further understand the mechanism and dynamics of geomagnetic reversals. Graphical abstract

scholarly journals Millennial-scale changes in sea-surface temperature and productivity along the Kuroshio–Oyashio boundary during MIS-19 based on the radiolarian record from the Chiba composite section, central Japan

2020 ◽  
Author(s):  
Takuya Itaki ◽  
Sakura Utsuki ◽  
Yuki Haneda ◽  
Kentaro Izumi ◽  
Yoshimi Kubota ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Surface ◽  
Middle Pleistocene ◽  
Central Japan ◽  
High Productivity ◽  
Pacific Side ◽  
Composite Section ◽  
The Kuroshio ◽  
Millennial Scale

Abstract A high-resolution radiolarian record from 800 to 750 ka was examined from the Chiba composite section (CbCS) of the Kokumoto Formation, including the GSSP (Global Boundary Stratotype Section and Point) for the Lower–Middle Pleistocene boundary, on the Boso Peninsula, Pacific side of central Japan. Total radiolarian abundance was closely related to biological productivity in the sea-surface layer and was observed to increase and repeatedly decrease in the millennial-scale period. Summer SST (sea-surface temperature), which was estimated based on the radiolarian assemblage, was 19°C at the end of MIS-20 (790-793 ka) and fluctuated between 21 and 26°C during MIS-19, with the warm periods tending to be synchronous with high productivity. Recent observations have revealed that productivity increases with a northward shift of the Kuroshio along the Kuroshio-Oyashio boundary zone. Therefore, high productivity in the warmer and stratified conditions during MIS-19 can be interpreted as being closely related to millennial-scale oscillations of the Kuroshio Extension. Such millennial-scale climatic changes were also recognized in southern Europe and are likely related to shifts in climate systems such as AO (Arctic Oscillations).

scholarly journals Millennial-scale changes in sea-surface temperature and productivity along the Kuroshio–Oyashio boundary during MIS-19 based on the radiolarian record from the Chiba composite section, central Japan

2020 ◽  
Author(s):  
Takuya Itaki ◽  
Sakura Utsuki ◽  
Yuki Haneda ◽  
Kentaro Izumi ◽  
Yoshimi Kubota ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Surface ◽  
Middle Pleistocene ◽  
Central Japan ◽  
High Productivity ◽  
Pacific Side ◽  
Composite Section ◽  
The Kuroshio ◽  
Millennial Scale

Abstract A high-resolution radiolarian record from 800 to 750 ka was examined from the Chiba composite section (CbCS) of the Kokumoto Formation, including the GSSP (Global Boundary Stratotype Section and Point) for the Lower–Middle Pleistocene boundary, on the Boso Peninsula, Pacific side of central Japan. Total radiolarian abundance was closely related to biological productivity in the surface layer and was observed to increase and repeatedly decrease in the millennial-scale period. Summer SST (sea-surface temperature), which was estimated based on the radiolarian assemblage, was 19°C at the end of MIS-20 (790-793 ka) and fluctuated between 21 and 26°C during MIS-19, with the warm periods tending to be synchronous with high productivity. Recent observations have revealed that productivity increases with a northward shift of the Kuroshio along the Kuroshio-Oyashio boundary zone. Therefore, high productivity in the warmer and stratified conditions during MIS-19 can be interpreted as being closely related to millennial-scale oscillations of the Kuroshio Extension. Such millennial-scale climatic changes were also recognized in southern Europe and are likely related to shifts in climate systems such as AO (Arctic Oscillations) and PDO (Pacific Decadal Oscillations).

scholarly journals Millennial-scale oscillations in the Kuroshio–Oyashio boundary during MIS 19 based on the radiolarian record from the Chiba composite section, central Japan

2022 ◽  
Vol 9 (1) ◽  
Author(s):  
Takuya Itaki ◽  
Sakura Utsuki ◽  
Yuki Haneda ◽  
Kentaro Izumi ◽  
Yoshimi Kubota ◽  
...  
Keyword(s):  
Kuroshio Extension ◽  
The Arctic ◽  
Middle Pleistocene ◽  
Central Japan ◽  
Boso Peninsula ◽  
Precipitation Record ◽  
Pacific Side ◽  
Composite Section ◽  
The Kuroshio ◽  
Millennial Scale

AbstractMarine 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.

scholarly journals Multiproxy sedimentological and geochemical analyses across the Lower–Middle Pleistocene boundary: chemostratigraphy and paleoenvironment of the Chiba composite section, central Japan

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Kentaro Izumi ◽  
Yuki Haneda ◽  
Yusuke Suganuma ◽  
Makoto Okada ◽  
Yoshimi Kubota ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Bottom Water ◽  
Middle Pleistocene ◽  
Oxygen Level ◽  
Terrigenous Material ◽  
Central Japan ◽  
Water Oxygen ◽  
Composite Section ◽  
Geochemical Analyses

AbstractThe Chiba composite section (CbCS) in the Kokumoto Formation, Kazusa Group, central Japan is a thick and continuous marine succession that straddles the Lower–Middle Pleistocene boundary and the well-recognized Matuyama–Brunhes paleomagnetic polarity boundary. Although recent studies extensively investigated the CbCS, its chemostratigraphy, particularly around the Lower–Middle Pleistocene boundary, is poorly understood. Therefore, in this study, we performed multiproxy sedimentological and geochemical analyses of the CbCS, including the Chiba section, which is the Global Boundary Stratotype Section and Point for defining the base of the Middle Pleistocene Subseries. The aim of these analyses is to establish the high-resolution chemostratigraphy and to reconstruct the paleoenvironments of its sedimentary basin in detail. We used the K/Ti ratio as a broad proxy for the clastic material grain size of the sediments. Although the K/Ti ratio generally varies throughout the studied interval, the K/Ti ratio especially during Marine Isotope Stage (MIS) 19a shows a variation pattern like those of the foraminiferal oxygen isotope (δ18O) records. The records of the C/N ratio of bulk samples and carbon isotope ratio of the organic carbon (δ13Corg) suggest that the organic matter in the CbCS sediments during MIS 19c mostly originated from marine plankton, whereas the organic matter during MIS 18 and 19a was characterized by a mixture of marine plankton and terrestrial plants. These records are clearly indicative of changes in mixing ratio of marine vs. terrestrial organic matter in association with glacial–interglacial cycles from the late MIS 20 to the early MIS 18. In addition, we calculated the mass accumulation rates (MARs) of organic carbon, biogenic carbonate, and terrigenous material for quantitative interpretations on the paleoenvironmental changes. MAR calculations revealed that the contribution of marine organic carbon relative to terrestrial organic carbon increased during MIS 19c, and that the contribution of the terrigenous material relative to biogenic carbonate decreased during MIS 19c. Furthermore, we observed relatively large variations in the total organic carbon and total nitrogen contents during MIS 19a. These variations were probably caused by the relative decrease in bottom-water oxygen level, which is also supported by our trace-fossil data, although it is not certain whether the increase in organic-carbon flux at ~ 760 ka was due to the synchronous increase in biogenic productivity in surface water. Such a relative decrease in bottom-water oxygen level was partly due to the increased ocean stratification because of the northward displacement of the Kuroshio Extension Front.

scholarly journals Calcareous nannofossil biostratigraphy of the Lower–Middle Pleistocene boundary of the GSSP, Chiba composite section in the Kokumoto Formation, Kazusa Group, central Japan, and implications for sea-surface environmental changes

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Koji Kameo ◽  
Yoshimi Kubota ◽  
Yuki Haneda ◽  
Yusuke Suganuma ◽  
Makoto Okada
Keyword(s):  
Environmental Changes ◽  
Kuroshio Current ◽  
Sea Surface ◽  
Middle Pleistocene ◽  
Calcareous Nannofossil ◽  
Central Japan ◽  
Composite Section ◽  
Calcareous Nannofossil Biostratigraphy ◽  
The Kuroshio ◽  
Millennial Scale

Abstract The Chiba composite section (CbCS), in the middle of the Boso Peninsula in central Japan, was ratified as the Global Boundary Stratotype Section and Point (GSSP) for the Lower–Middle Pleistocene boundary, accompanied by the Matuyama–Brunhes (M–B) paleomagnetic polarity boundary in January 2020. This study examined the calcareous nannofossil biostratigraphy of the CbCS to describe potential nannofossil events and discuss sea-surface environments around the M–B paleomagnetic polarity boundary. There are no clear biohorizons at the M–B paleomagnetic polarity boundary, although a temporary disappearance of Gephyrocapsa specimens (≥ 5 μm in diameter), an important calcareous nannofossil genus in the Pleistocene, occurs just above the Lower–Middle Pleistocene boundary. Although this is a characteristic event around the M–B paleomagnetic polarity boundary, it is unclear whether the event is globally traceable. Changes in the environmental proxy taxa of calcareous nannofossils in the CbCS revealed that sea-surface environments were driven by glacial-interglacial and millennial-scale climate forces. The time-transgressive change of the Tn value, a calcareous nannofossil temperature index, is mostly concordant with the planktonic foraminiferal oxygen isotope fluctuation. Abundant occurrences of a warm-water species, Umbilicosphaera spp., indicate that the Kuroshio Current was strong after ~ 783 ka. Even the strong influence of the Kuroshio Current, cooling events related to southward movements of the Kuroshio Front occurred every 10,000 years based on the presence of a cold-water taxon, Coccolithus pelagicus. Additionally, the inflow of coastal waters strengthened after ~ 778 ka because of abundant occurrences of Helicosphaera spp. Millennial-scale sea-surface changes were also inferred from detected floral fluctuations of less than 10,000 years. Graphical abstract

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