U-Th dating of deep-sea corals
U-Th dating of deep-sea corals
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DOI：
10.1016/s0016-7037(99)00422-6
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发表时间：
2000-07-01
影响因子：
5
通讯作者：
Boyle, EA
中科院分区：
文献类型：
--
作者：
Cheng, H;Adkins, J;Boyle, EA
用热电离质谱(TIMS)测定了几种深海孤立珊瑚的Th-230、Th-232、U-234和U-234组分。对低[Th-232](5到几百ppt)的现代原始珊瑚进行高精度测年是可能的。然而，由于较老的深海珊瑚往往比表层珊瑚具有更高的[232Th]，而且初始的Th-230/Th-232比率不确定，因此较老的深海珊瑚具有更大的年龄不确定性(对于含有几千ppt Th-232的样品，年龄为+/-几百年)。因此，精确的U-Th测年的关键障碍是去除或解释含有升高的Th-232和相关的Th-230的污染物，这些污染物不是由于珊瑚晶格内的闭合系统衰变而引起的。对用于有孔虫和表面珊瑚的痕量金属清洗方法进行修改，可以显著减少这种污染。通过计数可见的生长带和测量单个隔膜的平均年龄，估计克里斯蒂安吸虫的延伸率在0.1~3.1 mm/年之间。从平均意义上讲，波带似乎每年都在减少，但这一估计存在很大的不确定性。因此，如果能够建立适当的示踪剂校准，这些珊瑚适合记录其一生中的十年或亚十年海洋学变化。所有不同地点、不同深度的现代样品的(234U)值相似(平均为145.5+/-2.3ppm)，与从表层珊瑚获得的数据没有区别。精度约为千分之二。我们在水柱顶部2000米以上的三角洲(234)U比的海洋剖面上没有发现任何构造。版权所有(C)2000爱思唯尔科学有限公司。
Th-230, Th-232, U-234 and U-234 compositions of several deep-sea solitary corals, mainly the species Desmophyllum cristagalli, were determined by thermal ionization mass spectrometry (TIMS). It is possible to obtain high precision ages on modern pristine corals that have low [Th-232] (5 to a few hundred ppt). However, because older deep-sea corals tend to have higher [232Th] compared to surface corals, and the initial Th-230/Th-232 ratio is uncertain, older deep-sea corals have larger age uncertainties (+/-several hundred years for samples with a few thousand ppt Th-232). Therefore, the key hurdle for precise U-Th dating is to remove or account for contaminants which contain elevated Th-232 and associated Th-230 not due to closed system decay within the coral lattice. A modification of the trace metal cleaning methods used for foraminifera and surface corals can significantly reduce this contamination. By counting the visible growth bands and measuring the mean age of a single septum, the extension rate of D. cristagalli was estimated to be between 0.1 and 3.1 mm/year. In a mean sense, bands appear to be precipitated annually, but this estimate has a large uncertainty. If appropriate tracer calibrations can be established, these corals are therefore suitable to record decadal or sub-decadal oceanographic changes over the course of their lifetime. The delta(234)U values of all modern samples from different localities and different depths are similar (mean 145.5 +/- 2.3 parts per thousand) and indistinguishable from the data obtained from surface corals. At a precision of about +/-2 parts per thousand. we find no structure in the oceanic profile of delta(234)U ratios over the top 2000 m of the water column. Copyright (C) 2000 Elsevier Science Ltd.