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High-resolution Paleoceanographic Records On The Bifurcation Of The North Equatorial Current In The Northwestern Pacific Since 37ka BP

Posted on:2012-07-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:S X ChenFull Text:PDF
GTID:1100330332996969Subject:Marine geology
Abstract/Summary:PDF Full Text Request
The Kuroshio Source Region (KSR) connects the Western Pacific Warm Pool (WPWP)—the North Equatorial Current (NEC) and the Kuroshio Main Course (KMC)—the Kuroshio Extension (KE). It is on the north edge of the WPWP, and the NEC flows into this area from the east. The paleoenvironment changes in the KSR not only provide hints to the mechanism of paleoenvironment in the KMC—KE area, but also offer evidences for the impacts of the tropical on the northern middle latitudes. The core MD06-3054 (14°30.2816'N, 124°19.2400'E; water depth: 2021 m) is selected to investigate the evolution of paleoenvironment in the KSR, located on the bifurcation of NEC in the northwestern Pacific. Its high-resolution records give valuable information in the KSR and important supplement for the low latitudes.The variations of sea surface temperature, sea surface salinity, the depth of thermocline, inputs of organic carbon, and the planktonic and benthic foraminiferal faunas are reconstructed with geochemical and micropaleontological methods in core MD06-3054. The tests of planktonic foraminifera mixed species of Globigerinoides ruber (G. ruber) and Globigerinoides sacculifer (G. sacculifer) were subjected to AMS 14C measuring, and the tests of planktonic foraminiferal species of G. ruber and Pulleniatina obliquiloculata (P. obliquiloculata) were subjected to carbon and oxygen isotope measuring, and the tests of planktonic foraminiferal species of G. ruber were subjected to Mg/Ca measuring, and the planktonic and benthic foraminifera faunas were identified under a microscope, and the total organic carbon (TOC) and its carbon isotope were also measured. It is found that the high-resolution records from core MD06-3054 agree with the changes of the Kuroshio Current and paleoenvironment in the Kuroshio drainage area, which inferred a robust link between the KSR and the Kuroshio drainage area since 36.7ka BP. The high-frequency variations occurred in the Kuroshio drainage area were also recorded in the KSR, such as the Heinrich events, the Younger Dryas event (YD), the 8.2ka event, and the Holocene events comparable with the Bond events. What is more, the last degalacial broadδ13C minimum event was also recorded, which is originated from the southern high latitudes.Moreover, the records of organic carbon show a response to the changes of sea level since the last glacial to the post glacial. The concentration of TOC is high and the isotope of organic carbon indicates that the main source of organic carbon is from the terrigenous C3 plants with negative values in sediment, responsing the low sea level during the last glacial; while a overall low concentration of TOC and organic carbon with much positive isotope in sediment shows that the main source of organic carbon was producted by marine algas, responsing the high sea level during the post glacial. During the Holocene, the kind of terrigenous inputs may suggest that it was droughty and there were much more C4 plants during 7.3—10.8ka BP, while it was humid and there were much more C3 plants during 1.0—2.3ka BP and 3.2—7.1ka BP, in the adjacent Philippines continent.The planktonic foraminiferal fauna is characteristic by the tropical and sub-tropical species, representing by G. ruber,Globigerinita glutinata (G. glutinata), and G. sacculifer. The variations of the planktonic foraminifera species indicate there were many factors affecting the planktonic fauna, which also suggest a complex and changeable environment on the bifurcation of the NEC since 36.7ka BP. What is more, the variations of the benthic foraminifera accumulation rate and the abundance of U+B show a inhibiting effect of high organic matter influx on the bloom of benthic foraminifera fauna in core MD06-3054.
Keywords/Search Tags:northwestern Pacific, bifurcation of the North Equatorial Current, Kuroshio, foraminifera, organic carbon, high-resolution
PDF Full Text Request
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