scholarly journals Biomarkers in the rock outcrop of the Kazusa Group reveal paleoenvironments of the Kuroshio region

2020 ◽  
Author(s):  
HIROTO KAJITA ◽  
Ayumi Maeda ◽  
Masayuki Utsunomiya ◽  
Toshihiro Yoshimura ◽  
Naohiko Ohkouchi ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Kuroshio Current ◽  
Sea Surface ◽  
Average Chain Length ◽  
Rock Outcrop ◽  
Central Japan ◽  
Sedimentary Succession ◽  
Atmospheric Changes ◽  
The Kuroshio ◽  
Kuroshio Region

Abstract The classical biomarkers of long-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct paleoenvironments. Here, we detected these biomarkers are preserved in the rock outcrop of the Kazusa Group exposed in central Japan, the most continuous sedimentary succession in the world, covering almost the entire Pleistocene. The alkenone unsaturation ratio and average chain length of n-alkanes appeared to reflect the glacial-interglacial changes in the sea surface temperature (SST) and terrestrial climate, respectively. Alkenone-based SSTs during 1.1–1.0 Ma were significantly higher than present-day SSTs in the same area, as supported by foraminiferal Mg/Ca-based temperatures, possibly reflecting the direct intrusion of the warm Kuroshio Current. Applying these biomarkers, which might be circumstantially preserved owing to their immunity to high temperature and consolidation stress during burial and uplift, we expect that the Kazusa Group should reveal detailed oceanic and atmospheric changes of the Kuroshio region.

scholarly journals Biomarkers in the rock outcrop of the Kazusa Group reveal palaeoenvironments of the Kuroshio region

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Hiroto Kajita ◽  
Ayumi Maeda ◽  
Masayuki Utsunomiya ◽  
Toshihiro Yoshimura ◽  
Naohiko Ohkouchi ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Kuroshio Current ◽  
Sea Surface ◽  
Average Chain Length ◽  
Rock Outcrop ◽  
Diagenetic Alteration ◽  
Organic Biomarkers ◽  
The Kuroshio ◽  
Kuroshio Region ◽  
Long Chain

AbstractLong-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct palaeoenvironments. However, applying this technique to exposed sedimentary rock sequences is relatively challenging due to the potential for the diagenetic alteration of organic biomarkers. Here, we extract long-chain alkenones and n-alkanes from an exposed outcrop of the Kazusa Group in central Japan, one of the most continuous sedimentary successions in the world, covering almost the entire Pleistocene. We find that the alkenone unsaturation ratio and average chain length of n-alkanes appears to reflect the glacial-interglacial changes in sea surface temperature and terrestrial climate, respectively. Alkenone-based sea surface temperatures between 1.1 and 1.0 million years ago concur with foraminiferal Mg/Ca-based temperature estimates and may reflect an intrusion of the Kuroshio Current. We suggest that the preservation of these biomarkers in the Kazusa Group demonstrates its potential to provide a detailed palaeoenvironmental record.

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

scholarly journals Impacts of the Kuroshio Intrusion through the Luzon Strait on the Local Precipitation Anomaly

2021 ◽  
Vol 13 (6) ◽  
pp. 1113
Author(s):  
Wen-Pin Fang ◽  
Ding-Rong Wu ◽  
Zhe-Wen Zheng ◽  
Ganesh Gopalakrishnan ◽  
Chung-Ru Ho ◽  
...  
Keyword(s):  
Kuroshio Current ◽  
Precipitation Anomaly ◽  
Luzon Strait ◽  
Sea Surface ◽  
Research Quality ◽  
Northwestern Pacific ◽  
Kuroshio Intrusion ◽  
Vertical Advection ◽  
Budget Analysis ◽  
The Kuroshio

The Kuroshio Current has its origin in the northwestern Pacific, flowing northward to the east of Taiwan and the northern part of Luzon Island. As the Kuroshio Current flows northward, it quasi-periodically intrudes (hereafter referred to as Kuroshio intrusion (KI)) into the northern South China Sea (SCS) basin through the Luzon Strait. Despite the complex generation mechanisms of KI, the purpose of this study is to improve our understanding of the effects of KI through the Luzon Strait on the regional atmospheric and weather variations. Long-term multiple satellite observations, including absolute dynamic topography, absolute geostrophic currents, sea surface winds by ASCAT, multi-scale ultra-high resolution sea surface temperature (MURSST) level-four analysis, and research-quality three-hourly TRMM multi-satellite precipitation analysis (TMPA), was used to systematically examine the aforementioned scientific problem. Analysis indicates that the KI is interlinked with the consequential anomalous precipitation off southwestern Taiwan. This anomalous precipitation would lead to ~560 million tons of freshwater influx during each KI event. Subsequently, independent moisture budget analysis suggests that moisture, mainly from vertical advection, is the possible source of the precipitation anomaly. Additionally, a bulk formula analysis was applied to understand how KI can trigger the precipitation anomaly through vertical advection of moisture without causing an evident change in the low-level flows. These new research findings might reconcile the divisiveness on why winds are not showing a synchronous response during the KI and consequential anomalous precipitation events.

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).

Characterization of diversity and community structure of small planktonic copepods in the Kuroshio region off Japan using a metabarcoding approach

2021 ◽  
Vol 657 ◽  
pp. 25-41
Author(s):  
J Hirai ◽  
K Yamazaki ◽  
K Hidaka ◽  
S Nagai ◽  
Y Shimizu ◽  
...  
Keyword(s):  
Community Structure ◽  
Environmental Changes ◽  
Fish Larvae ◽  
Size Fraction ◽  
Kuroshio Current ◽  
Taxonomic Resolution ◽  
Immature Stages ◽  
Small Copepod ◽  
The Kuroshio ◽  
Kuroshio Region

Small copepods are important prey for fish larvae in the Kuroshio region off southern Japan. However, revealing entire community structures of small copepods is difficult using conventional methods. We applied a metabarcoding method to size-fractionated community samples of epipelagic copepods (small: 0.1-0.5 mm, medium: 0.5-1.0 mm, and large: 1.0-2.0 mm). Samples were collected from 2013 to 2016 from the shoreward (Kuroshio Slope, KS) and oceanic (Kuroshio Gyre, KG) sides of the Kuroshio Current at 138° E; the results were compared with those in the center of the subtropical gyre (SG). The KS and KG sites showed both spatial differences and seasonal changes, with distinct differences between winter-spring and summer-autumn in each size-fractionated community. Water temperature markedly influenced copepod diversity and community structure, especially in the small size fraction. Warm-water species in the SG intruded into the Kuroshio regions during high-temperature periods, leading to high diversity in summer-autumn. Inter-annual environmental variations influenced by temperature and productivity were evident in KS, leading to clear changes in the sequence proportions of dominant small copepods including Paracalanus sp. and immature stages of the large copepod Calanus sinicus. Immature stages of medium/large copepods formed a substantial proportion of small-copepod communities in the Kuroshio regions (KS: 28.8%; KG: 24.7%; SG: 11.9%; based on average proportions of sequence reads). Because of their ecological importance and sensitivity to environmental changes, monitoring communities of small copepods with high taxonomic resolution may provide further insights into marine ecosystems, including fish recruitment, in the Kuroshio region.

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