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標題: | 鈣同位素可做為有用的古海洋學代用指標嗎?
-以西赤道大西洋兩萬年來有孔蟲δ44Ca為例 Can δ44Ca be a proxy for paleoceanography? - A case study of Globigerinoides sacculifer from Western Equatorial Atlantic |
作者: | Shun-Chung Yang 楊順中 |
指導教授: | 魏國彥(Kuo-Yen Wei) |
關鍵字: | 鈣同位素分化,sacculifer,生物礦化,鹽度,加勒比海, Ca isotope fractionation,sacculifer,biomineralization,salinity,Caribbean, |
出版年 : | 2007 |
學位: | 碩士 |
摘要: | 本研究藉由測量加勒比海TT9108-1GC岩芯過去兩萬年以來浮游性有孔蟲G. sacculifer殼體中的δ44Ca、δ18O與Mg/Ca比的比值,來探討δ44Ca和海洋環境因子之間的關係。結果顯示G. sacculifer δ44Ca的變化與海表溫度(SST)和海表鹽度(SSS)有關。經結合有孔蟲之δ18O與Mg/Ca比值,和古海水面變化紀錄所重建的古海表鹽度顯示過去兩萬年以來加勒比海之SSS介於36.5~39.5 psu,呈現顯著變化。扣除溫度分化效應後,G. sacculifer之鈣同位素組成變化與SSS呈現0.27±0.08 ‰/psu之關係,在統計上具有顯著的相關性,但與環境碳酸根離子濃度在統計上並無顯著相關性。此外,G. sacculifer殼體中的鈣同位素比值的變化也可能與Rayleigh fractionation有關。溫度與鹽度控制了G. sacculifer的新陳代謝速率,改變其造殼過程中消耗液泡中鈣離子之比例,間接影響G. sacculifer殼體的鈣同位素比值。基本上本研究無法由Lemarchand et al.(2004)的「速率控制分化」模型來解釋;而支持有孔蟲在造殼過程中會攝取海水,在體內形成獨立的液泡並調節其酸鹼度之模式(Erez, 2003)。 The δ44Ca, δ18O, and Mg/Ca ratios of fossil G. sacculifer over the past 20 ka extracted from a Caribbean core, TT9108-1GC, have been measured in order to examine the possibility of using δ44Ca as a proxy for paleoceanography. Our results indicate that the δ44Ca of G. sacculifer varies as a function of sea surface temperature (SST) and sea surface salinity (SSS). The Caribbean Sea SSS, reconstructed by combining the δ18O and Mg/Ca ratios of G. sacculifer and sea level change data, shows significant fluctuations between 36.5 and 39.5 psu during the last 20 ka. After isolating the temperature effect, the δ44Ca of G. sacculifer exhibits a positive correlation with SSS, ca 0.27±0.02 ‰ per 1 psu. On the other hand, no significant relationship is observed between δ44Ca and seawater [CO3=]. Moreover, variation of G. sacculifer δ44Ca can also be explained using a Rayleigh fractionation model. As a function of temperature and salinity, the metabolic rate may influence the utilization of vacuole Ca++ in G. sacculifer, resulting in different δ44Ca values. The results of this study are inconsistent with the “rate-controlled fractionation model” of Lemarchand et al. (2004), instead, the results are more in-line with the foraminiferal biomineralization model of Erez (2003), where δ44Ca reflects the adjustments of temperature, salinity, and pH of seawater isolated in vacuoles during the growth of G. sacculifer. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/28553 |
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