Variability in the uranium isotopic composition of the oceans over glacial-interglacial timescales
Variability in the uranium isotopic composition of the oceans over glacial-interglacial timescales
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DOI：
10.1016/j.gca.2006.06.013
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发表时间：
2006-08-15
影响因子：
5
通讯作者：
Yokoyama, Yusuke
中科院分区：
文献类型：
--
作者：
Esat, Tezer M.;Yokoyama, Yusuke
对来自巴布亚新几内亚胡翁半岛上升的末次冰期阶地的珊瑚进行的铀系质谱分析显示，与现代珊瑚相比，珊瑚生长时的U-234/U-238值系统性较低。当与其他研究的珊瑚数据相结合时，出现了一种系统的趋势，表明在涉及海平面大幅变化的重大冰川-间冰期过渡时期，U-234/U-238比率发生了变化。从末次冰期到全新世，三角洲中U-234的变化率约为每千年千分之一。海洋中铀收支的变化似乎是由于在温暖气候和高海平面时期，在靠近海岸的缺氧和亚氧沉积物中、盐沼和红树林中、河口和大陆边缘中积累了过量的U-234。这些近岸地区在低海平面期间暴露，导致铀迅速氧化成高度可溶的相。随后，随着海平面上升，铀-234浓缩铀在一段持续的时间内释放到海洋中。(c)2006年爱思唯尔公司All rights reserved.
Uranium-series mass spectrometric analyses of corals from the uplifted last glacial terraces at Huon Peninsula, Papua New Guinea, that grew from 50,000 years ago to 30,000 years ago show systematically low values of U-234/U-238, at the time of coral growth, compared with modern corals. When combined with coral data from other studies a systematic trend emerges indicating shifts in the U-234/U-238 ratio at times of major glacial-interglacial transitions that involve large variations in sea-levels. From last glacial to Holocene, the rate of change in delta U-234 is approximately 1 parts per thousand per thousand years. The variations in the U budget of the oceans appear to be due to accumulation of excess U-234 in near shore areas in anoxic and suboxic sediments, in salt marshes and mangroves, in estuaries, and in continental margins during periods of warm climate and high sea-levels. These near-shore areas are exposed during periods of low sea level resulting in rapid oxidation of U into highly soluble phases. The subsequent release of U-234-enriched uranium into the oceans occurs over a sustained period, in step with rising sea-levels. (c) 2006 Elsevier Inc. All rights reserved.