Late Pliocene sea surface environments in the Pacific side of central Japan based on calcareous nannofossils from the lower part of the Chikura Group, southernmost part of the Boso Peninsula

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).

Download Full-text

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

10.21203/rs.3.rs-24663/v1 ◽

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).

Download Full-text

Sabellaria isumiensis n. sp. (Annelida: Polychaeta: Sabellariidae) from shallow waters off Onjuku, Boso Peninsula, Japan, and re-descriptions of three Indo-West Pacific sabellariid species

Zootaxa ◽

10.11646/zootaxa.2680.1.1 ◽

2010 ◽

Vol 2680 (1) ◽

pp. 1 ◽

Cited By ~ 4

Author(s):

EIJIROH NISHI ◽

JULIE HELEN BAILEY-BROCK ◽

ANDRE SOUZA DOS SANTOS ◽

HIROYUKI TACHIKAWA ◽

ELENA K. KUPRIYANOVA

Keyword(s):

New Species ◽

Shallow Waters ◽

Subtidal Zone ◽

Rocky Shores ◽

Type Specimens ◽

Boso Peninsula ◽

The Pacific ◽

Pacific Side ◽

Head Morphology ◽

Far Eastern

A new species of the genus Sabellaria Lamarck, 1812, is described from shallow waters off Onjuku, the Pacific side of Boso Peninsula, Chiba, Japan. Sabellaria isumiensis n. sp. is a gregarious species building colonies of tubes made of sand and shell debris over 2 m wide in the intertidal to subtidal zone of the rocky shores. The new species is distinguished by the character combination of having 1 or 2 pairs of nuchal spines, median teeth of outer paleae with 3–5 lateral spines, two kinds (long and short) of opercular paleae in the middle row of the crown, with slender blades of long ones curved outward. Morphological features of the species are described in details and compared to those of congeners from Japan and world-wide. We re-describe three poorly known sabellariid species, Sabellaria javanica Augener, 1934 from Java, Indonesia, S. chandraae de Silva, 1961 from Galle Force, Sri Lanka, and Neosabellaria uschakovi Kirtley, 1994 from the Far Eastern Seas of Russia. The descriptions are based on the type specimens, and we particularly emphasize the head morphology and paleal characters. We provide a summary of diagnostic characters in the genus Sabellaria and propose new morphological groupings that later will be tested in the framework of a formal phylogenetic analysis.

Download Full-text

Geology and age model of the Lower Pleistocene Nojima, Ofuna, and Koshiba Formations of the middle Kazusa Group, a forearc basin-fill sequence on the Miura Peninsula, the Pacific side of central Japan

Island Arc ◽

10.1111/iar.12066 ◽

2014 ◽

Vol 23 (2) ◽

pp. 157-179 ◽

Cited By ~ 13

Author(s):

Atsushi Nozaki ◽

Ryuichi Majima ◽

Koji Kameo ◽

Saburo Sakai ◽

Atsuro Kouda ◽

...

Keyword(s):

Forearc Basin ◽

Central Japan ◽

The Pacific ◽

Pacific Side ◽

Lower Pleistocene ◽

Group A ◽

Age Model ◽

Basin Fill

Download Full-text

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

Progress in Earth and Planetary Science ◽

10.1186/s40645-021-00465-0 ◽

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.

Download Full-text