中太平洋与麦哲伦海山富钴结壳中分子化石和碳同位素地球化学及其古海洋对比研究

来源期刊:中南大学学报(自然科学版)2011年第z2期

论文作者:武光海 张海生 李雪富 刘捷红 张宏

文章页码:99 - 107

关键词:太平洋海山;富钴结壳;分子化石;碳同位素;古海洋学

Key words:Mid-Pacific seamounts; Co-rich crusts; molecular marker; carbon isotopes of organic matter δ13C; paleoceanography

摘    要:在中太平洋海山和西太平洋麦哲伦海山的富钴结壳中检出分子化石正构烷烃和类异戊二烯烃,根据分子组合特征指数:主峰碳MH,Σn(C23-)/Σn(C24+),n(C31)/n(C17)、(n(C15)+n(C17)+n(C19))/(n(C27)+n(C29)+n(C31))、CPI、Paq、Pr/n(C17)和Ph/n(C18),其分子组合特征表明富钴结壳中原生有机质主要来自于沉水/漂浮水生大型植物和菌藻类,并混有少量陆源物质;有机碳同位素同样也指示了海洋水生生物的碳同位素特征。研究表明:中太平洋海山与麦哲伦海山相比受陆源物质影响较小。中太平洋海山和西太平洋麦哲伦海山富钴结壳的新壳层Pr/Ph均大于疏松层和老壳层,显示结壳生长后期海水的氧化性增强;麦哲伦海山结壳疏松层的Pr/Ph最低,揭示中间疏松层形成时期的海水氧化程度最低;中太平洋结壳的Pr/Ph值总体上均比麦哲伦结壳的大,表明结壳生长初期和生长过程中,中太平洋海山的海水氧化性要比麦哲伦海山的强。CM3D06结壳从底层到最外层有机碳同位素发生了很大变化,结壳中有机碳同位素组成变化与结壳生长过程中的海洋环境气候变化相符合:富钴结壳生长前期δ13C组成由正变负,对应全球气候变冷,南极底层流向太平洋挺进;而富钴结壳生长后期δ13C逐渐偏正,与全球气候变暖和南极底层流萎缩相关联,即结壳δ13C值偏正。

Abstract: In the molecular markers, n-alkanes and isoprenoid(pristine and phytane),were detected from the Mid-Pacific and western Pacific Magellan seamount Co-rich crusts(hereafter for short as crusts). Some molecular indices are main peak carbon MH, Σn(C23-)/Σn(C24+), n(C31)/n(C17), (n(C15)+n(C17)+n(C19))/(n(C27)+n(C29)+n(C31)), CPI, Paq, Pr/n(C17) and Ph/n(C18), which indicate that the original organic matters are mainly from the sinking or floating hydrophily macrophytes and homonemeaes with little terrigenous matters. The organic carbon isotope (δ13C) characteristics of marine hydrobios were also revealed. The results also show that the mid-Pacific seamounts are less affected by the terrigenous matters than that of the Magellan seamounts. The Pr/Ph ratios of the younger crust layers were higher than those of the older crust layers and middle loosen crust layers both on the Mid-Pacific seamounts and western Pacific Magellan seamounts, indicating the oxidation degree of seawater were enhanced in the late period of the formation of crust. The lowest Pr/Ph ratios, in the loosen crust layers of the Magellan seamount showed that the oxidation degree of seawater is the lowest at that time. The Pr/Ph ratios of the crust on Central Pacific seamounts are higher than those of crust on Magellan seamounts in general, which shows that the seawater oxidation degree of mid-Pacific is stronger than that of Magellan seamount during the crust formation history. The results also show that CM3D06’s organic carbon isotopes had undergone great changes from the bottom to the outer, and the changes of the organic carbon isotopes of crust are consistent with the changes of marine environment and climate during the growth of the crust. In the early period of the growth of the crusts, the δ13C changes from positive to negative, corresponding to the global cooling and the Antarctic bottom water flowing into the Pacific. In the late period of the growth of the crust, the δ13C turns positive gradually, corresponding to the global warming and the shrinkage of the Antarctic bottom water.

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