Deep water circulation in the South China Sea during the last 40 kyr：Nd isotopic compositions in sedimentary Fe-Mn oxyhydroxides

• Main Authors: Ya-Hui Lin, 林雅慧
• Other Authors: Chen-Feng You
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/02077524348866096541

碩士 === 國立成功大學 === 地球科學系碩博士班 === 96 === With the ability to provide very accurate and precise isotopic ratios, mass spectrometry has become as the most important method in the field of radiometric dating. The precision of dating has been hugely improved in the last decade, in some case less than 1 year error can be achieved. These processes stimulate the study of Quaternary climate change. One of the most important subjects is reconstructing long-term and short-term climate by tracing major ocean currents in the past. The Nd isotopic compositions of ancient seawater deduced from sedimentary Fe-Mn hydroxides have been used extensively to trace short-term variation in the water masses. Two cores, SO17940-2 and MD052914, used in this study were collected from South China Sea. Due to high sedimentation rate in marginal sea, those cores have a good potential to reconstruct century-scale climate variations over the last 30Ka. The sedimentary Nd isotope compositions were carried out by MC-ICPMS after the HH treatment and ion chromatography separation using AG50W-X8 and LN resins. REE pattern also been measured by a HR-ICPMS. Due to the presence of Ca, Na and Mg, the matrix effects were determined to be insignificant. PAAS normalized REE patterns of sedimentary Fe-Mn oxyhydroxides show LREE enrichment and positive Ce anomalies, similar to those in the Atlantic. The 143Nd/144Nd ratio is ranging from -6 to -8εNd and has a minimum value in the period of 10~12Ka (Younger Dryas Event) in core SO17940-2；The 143Nd/144Nd ratio is ranging from -8 to -9.5εNd in MD052914. This can be explained by strengthening. Winter monsoon resulted in high flux of terrestrial input from the continent, which is characterized by low 143Nd/144Nd ratio. The other possibility is the weakening of North Pacific Intermediate Water (NPIW) flow into the South China Sea. However, in the last glacial maximum, the negative anomaly Nd isotope did not observed. This probably is due to lower sedimentary rate and no significant change in the strength of NPIW.