| 摘要: | 本研究利用位於臺灣西南海域，水深1,315公尺的MD18-3568岩心（岩心總長20.7公尺），透過浮游性有孔蟲的種屬與豐度變化及主成分分析，探討南中國海東北部所受之古環境變化的影響。岩心的浮游性有孔蟲碳十四定年結果顯示，本岩心自38,000年以來為連續、穩定沉積。本研究採集51個樣本，將樣本處理為含有300隻以上的浮游性有孔蟲化石並鑑定其種屬，共分辨出44種浮游性有孔蟲。優勢種屬為Globigerina bulloides、Globigerinoides ruber、Trilobatus sacculifer、Neogloboquadrina dutertrei 、Neogloboquadrina incompta、Pulleniatina obliquiloculata、Globigerinita glutinata，七個種屬相對豐度總和可達84%。主成分分析得到四個較高的主成分，依據種屬得分大於0.4所顯示，PC1（+G. glutinata、-N. dutertrei、-N. incompta）、PC2（-G. bulloides）、PC3（+P. obliquiloculata、-G. ruber）、PC4（+N. incompta、-N. dutertrei），四個主成分可得87%以上的總變方（variance）。在七個優勢種屬中，G. ruber的相對豐度變化和同岩心的G. ruber及N. dutertrei的氧同位素差值（δ18Odut-δ18Orub）趨勢相似，可對應夏季季風的強度變化。P. obliquiloculata在距今約4,000-2,500年有發生一普林蟲最小事件（Pulleniatina Minimum Event, PME），在此期間P. obliquiloculata的相對豐度銳減至幾乎消失。G. bulloides可能為冬季表層水營養鹽的指標，在末次最大冰期（Last Glacial Maximum; LGM）時期豐度來得較小。PC1中得分大於0.4的G. glutinata、N. dutertrei、N. incompta三者皆為生活在次表水層中的種屬，推測PC1可對應到次表水層的變化，而影響南海東北部次表水鹽度變化的應為黑潮侵入及呂宋西北外海之湧升流所造成，且PC1的主成分分數在PME時期亦有較低的值出現。G. glutinata、N. dutertrei、N. incompta及P. obliquiloculata四個種屬棲息深度相似，可分為G. glutinata + P. obliquiloculata及N. dutertrei + N. incompta兩組，呈現此消彼漲的趨勢。;This study examines the core MD18-3568 located in offshore southwest Taiwan of 1,315 m and with a total core length of 20.7 m. The AMS 14C dating on planktonic foraminifera of this core shows that the core has been deposited continuously since 38,000 years ago. In this study, 51 samples were collected, and the samples were processed to contain more than 300 planktonic foraminifera and their species were identified. A total of 44 planktonic foraminifera species were identified. The dominant species are Globigerina bulloides、Globigerinoides ruber、Trilobatus sacculifer、Neogloboquadrina dutertrei 、Neogloboquadrina incompta、Pulleniatina obliquiloculata、Globigerinita glutinata, the total relative abundance of there 7 species is around 84%. Among the seven dominant species, the relative abundance changes of G. ruber and the oxygen isotope difference of G. ruber and N. dutertrei（（δ18Odut-δ18Orub） in the same core have similar trend, which may correspond to the changing intensity of summer monsoon. The abundance of P. obliquiloculata show a Pulleniatina Minimum Event（PME） around 4,000-2,500 years BP, during which the relative abundance of P. obliquiloculata decreased sharply and almost disappear. The results show G. bulloides may be an indicator of nutrients in winter surface water, and its relative abundance was lowered during the Last Glacial Maximum（LGM）. Four principle components, PC1（+G. glutinata, -N. dutertrei, -N. incompta）, PC2（-G. bulloides）, PC3（+P. obliquiloculata, -G. ruber）, PC4（+N. incompta, -N. dutertrei）, reaching more than 87% of the total variance, are identified through principle component analysis on foram abundance. G. glutinata, N. dutertrei, and N. incompta with scores greater than 0.4 in PC1, all of them live in the nutrient-rich subsurface water. It is speculated that PC1 may correspond to the subsurface water layer, and affect the northeastern South China Sea. The changes in the salinity of subsurface water should be caused by the intrusion of the Kuroshio current, and the principal component fraction of PC1 also had a lower value during the PME period. G. glutinata, N. dutertrei, N. incompta and P. obliquiloculata have similar dwelling depths and can be divided into two groups: G. glutinata + P. obliquiloculata and N. dutertrei + N. incompta., and the trend of G. glutinata + P. obliquiloculata is inversely to N. dutertrei + N. incompta. |
