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- 저자 : Naokazu Ahagon (검색결과 2 건)
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현상민,Naokazu Ahagon,Maria Luisa G. Tejada,Mirko Alessandro C. Uy,Alyssa Peleo-Alampay,김길영,Minoru Ikehara 대한지질학회 2022 지질학회지 Vol.58 No.1
Two of alkenone and terrestrial n-alkane biomarkers derived from the South China Sea (SCS) International Ocean Discovery Program (IODP) 349 sediments were investigated to evaluate the relationship between paleoceanography and Asian monsoon variability since the last 400 ka. The average concentration of total alkenones is 0.43μg/g, and the alkenone-based sea surface temperature (SSTalk) ranged from 22.8 to 27.6℃ (average: 25.86℃; n = 73) at studied site U1432C. The concentration of n-alkanes shows high fluctuation through the glacial-interglacial periods with average 27.92 μg/g. Indices including average chain length (ACL) and carbon preferences index (CPI) showed large shifts and fluctuations, likely due to differences of delivery mechanism under the East Asian monsoon conditions. Specifically, spectral analysis of SSTalk shows a 40-kyr obliquity cycle. Therefore, both alkenone and terrestrial n-alkane biomarkers reflect the orbital obliquity cycle, the records of n-alkanes are not linearly associated with SSTalk paleoceanographic evolution in the last 400 ka. The results of this study suggest that the paleoceanography differs within the glacial-interglacial cycle. However, the terrestrial n-alkanes record developed a short-term variation during transportation reflecting paleoclimatic variation in East Asia region.
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Hyun, Sang-Min,Taira, Asahiko,Ahagon, Naokazu,Han, Sang-Joon The Korean Society of Oceanography 1998 Journal of the Korean Society of Oceanography Vol.33 No.3
Three cores were taken from the northwest Pacific Ocean (Shikoku Basin) to determine the accumulation rates of both biogenic and terrigeneous fractions since the last penultimate interglacial period. The sediment is characterized by large amounts of terrigenous materials with low biogenic fractions and intermittent volcanic-ash layers, suggesting a hemipelagic origin. Composition of major elements shows no significant differences among sites. Relatively small variation of TiO$_2$/Al$_2$O$_3$ ratios with respect to SiO$_2$ content is the strong evidence for the common origin of terrigenous materials. The fraction of biogenic carbonates varies from near 0% in ash layers to about 35%, with a gradual increase toward the south (St. 4 through St. 6 to St. 20). However, carbonate contents show step-wise increasing tendency from St. 4 through St. 6 to St. 20, which suggests a southward increase of carbonate production. The color reflectance indicates that the sediment of the southern sites contains relatively higher amounts of biogenic carbonates. The mass accumulation rate of terrigenous fractions during the glacial period was 2-3 times higher than that of interglacial period. This enhanced mass accumulation rate of terrigenous materials was concomitant with the high accumulation rate of biogenic fractions. The total sediment accumulation rate is considered as the most important factor controlling mass accumulation rates of the biogenic and terrigenous materials. The enhanced sediment accumulation during the glacial periods is interpreted as a consequence of climate-induced change in the supply of eolian dust from the Asian continent. Enhanced wind strength during the glacial time may have increased transportation of terrigenous materials to the ocean. Thus, variation of sediment accumulation is highly linked with climatic variations.
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