西太平洋暖池南緣MD05-2925岩芯55萬年以來浮游有孔蟲氧碳同位素記錄

Stable carbon and oxygen isotope records of planktonic foraminifera of core MD05-2925, South margin of western Pacific Warm Pool during the last 550 ka

林怡君(Yi-chun Lin)

指導教授 ： 米泓生 ； 李孟陽

國立臺灣師範大學/理學院/地球科學系/碩士(2009年)

摘要

本研究分析位於所羅門海南部MD05-2925岩芯(9°20.61'S, 151°27.61'E，全長28.43公尺，水深1642公尺)上部10公尺Globigerina sacculifer、Globigerinoides ruber及Pulleniatina obliquiloculata三種浮游有孔蟲之氧碳同位素組成以探討西太平洋暖池南緣所羅門海域之古海洋演變。整根岩芯年代模式由G. sacculifer氧同位素記錄比對「低緯度區氧同位素綜合曲線」，佐以五個碳十四定年點，建立氧同位素地層第1階至第14階約55萬年的記錄。
不同種屬浮游有孔蟲各有不同偏好生存深度，故可以之重建上層水體古水文變化。混合層種G. ruber (白色)與G. sacculifer，上部溫躍層P. obliquiloculata之氧同位素數值依照生存之水層位置與溫度由表水往溫躍層變重。而G.ruber碳同位素則因生機效應而與海水無機碳同位素產生偏移，導致G.ruber碳同位素並無依照生存水層深度分布。
將G. sacculifer與P. obliquiloculata之氧同位素記錄與西太平洋暖池中心ODP 806B岩芯作比較，呈現出暖池南緣分布範圍於冰消期向北偏移，溫躍層深度於冰期進入冰消期時明顯變深。而在MIS 5.5時暖池中心與南緣間海表溫差極小，由於暖池中心與南緣氧同位素差異大，應為鹽度效應所致。
冰期進入間冰期的冰消過程中，南濱洋受日照量影響產生暖化現象，釋放出大量二氧化碳，而融冰則造成南極中層水(AAIW)及亞南極模態水(SAMW)生成量的增高，西風帶往南極移動引起南極湧升作用增加，藉通氣作用將深海之高營養鹽及低碳同位素海水帶至南極中層水及亞南極模態水生成區，隨之傳送至赤道太平洋區。東赤道太平洋湧升流區岩芯記錄提供代表南極區氣候變遷的碳同位素數值偏低之訊號，並以多數岩芯具有碳同位素極小事件為特色。過去研究認為西赤道太平洋區於冰消期並無明顯碳同位素極小值事件發生，但MD05-2925岩芯之溫躍層浮游有孔蟲P. obliquiloculata於冰消期時則記錄到明顯的碳同位素極小值事件，與東赤道太平洋碳同位素極小值事件皆於10~11ka發生，顯示西赤道太平洋與南極高緯度區間，有著遙相關。

關鍵字

西太平洋暖池 ； 氧碳同位素 ； 浮游性有孔蟲 ； 所羅門海

並列摘要

Stable isotope data from Solomon Sea core MD05-2925 (9°20.61'S, 151°27.61'E, 28.43m in length, 1642m water depth) are presented from planktonic foraminifera Globigerinoides ruber, Globigerina sacculifer and Pulleniatina obliquiloculata (top 10m) . The age model for core MD05-2925 is based on correlation of the G. sacculifer oxygen isotope record to the Low Latitude Stake chronology and five radiocarbon dating.
In order to reconstruct the hydrology during the last two glacial terminations in the south margin of the Western Equatorial Pacific Warm Pool, we use multiple species approach of planktonic foraminifera as the proxy of water column structure. We compare the oxygon and carbon isotope records of the surface-dwelling foraminifers G. ruber and G. sacculifer and thermocline dwelling P. obliquiloculata with the cores in the eastern equatorial Pacific upwelling region, central Western Equatorial Pacific Warm Pool, and Antarctica. We demonstrate that during the last two glacial terminations, there are obvious 13C minimum events related to the South Ocean warming and CO2 concentration increment. With the support like the oxygen isotope records , we demonstrate that thermocline in the south region of the western Pacific Warm Pool was deepen and was warmer during the last two terminations.

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