The transient distributions of nuclear weapon-generated tritium and its decay product 3 He in the Mediterranean Sea, 1952–2011, and their oceanographic potential
The transient distributions of nuclear weapon-generated tritium and its decay product 3 He in the Mediterranean Sea, 1952–2011, and their oceanographic potential
复制标题
1952-2011 年地中海核武器产生的氚及其衰变产物 3 He 的瞬态分布及其海洋学潜力
DOI：
--
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
J. Sültenfuss
中科院分区：
文献类型：
--
作者：
W. Roether;P. Jean;E. Fourré;J. Sültenfuss
抽象的。本文介绍了自20世纪50年代和60年代初大气核武器试验产生的氚出现以来，地中海中的氚和~3He的综合情况，基本上是基于所有现有的观测资料。地表水中的氚在1964年上升到20-30TU(TU=1018×[3H]/H])，比自然水平高出约100倍，此后到2011年下降了30倍。这种下降在很大程度上是由于放射性氚的衰变，它产生了大量稳定的子体3He。我们提出了分离~3He的氚部分和从海底释放的部分(陆源部分)的方案。我们表明，在整个地中海水域都可以量化出氚组分，通常为±0.15TU当量，主要是因为陆源部分的3He含量很低。这一事实使地中海独一无二地提供了将氚3He用作示踪剂的潜力。两种示踪剂的瞬时分布由横跨整个海洋的多个剖面显示，并注意到它们的分布的相关特征。到2011年，由于氚浓度下降以及这些水域普遍向西漂移而冲走，顶部数百米处的3He浓度已变得很低。在不同的地点重复获得了黎凡特中水(LIW)中的氚-3He年龄，确定了从罗兹以东的LIW源区经过的时间。年龄随地表水氚最大值以来的时间呈上升趋势，这是因为重复观测代表着LiW全渡越时间谱中移动越来越慢的部分。氚-3He测年的这一新应用揭示了相当大的渡越时间色散。我们发现，到达西西里海峡的平均过境时间为12±2年，到达第勒尼安海的平均过境时间为18年±3年，到达西地中海的平均过境时间为22年±4年。此外，我们还给出了1987年整个东地中海陆源3He和氚-3He年龄，后者同样显示了渡越时间弥散的影响。我们的结论是，现有的氚和~3He数据，特别是如果与其他示踪剂数据相结合，对于限制地中海的地下循环和混合是有用的。
Abstract. We present a comprehensive account of tritium and 3He in the Mediterranean Sea since the appearance of the tritium generated by the atmospheric nuclear-weapon testing in the 1950s and early 1960s, based on essentially all available observations. Tritium in surface waters rose to 20–30 TU in 1964 (TU = 1018 × [3H]/H]), a factor of about 100 above the natural level, and thereafter declined 30-fold up to 2011. The decline was largely due to radioactive tritium decay, which produced significant amounts of its stable daughter 3He. We present the scheme by which we separate the tritiugenic part of 3He and the part due to release from the sea floor (terrigenic part). We show that the tritiugenic component can be quantified throughout the Mediterranean waters, typically to a ± 0.15 TU equivalent, mostly because the terrigenic part is low in 3He. This fact makes the Mediterranean unique in offering a potential for the use of tritiugenic 3He as a tracer. The transient distributions of the two tracers are illustrated by a number of sections spanning the entire sea and relevant features of their distributions are noted. By 2011, the 3He concentrations in the top few hundred metres had become low, in response to the decreasing tritium concentrations combined with a flushing out by the general westward drift of these waters. Tritium-3He ages in Levantine Intermediate Water (LIW) were obtained repeated in time at different locations, defining transit times from the LIW source region east of Rhodes. The ages show an upward trend with the time elapsed since the surface-water tritium maximum, which arises because the repeated observations represent increasingly slower moving parts of the full transit time spectrum of LIW. The transit time dispersion revealed by this new application of tritium-3He dating is considerable. We find mean transit times of 12 ± 2 yr up to the Strait of Sicily, 18 ± 3 yr up to the Tyrrhenian Sea, and 22 ± 4 yr up into the Western Mediterranean. Furthermore, we present full Eastern Mediterranean sections of terrigenic 3He and tritium-3He age in 1987, the latter one similarly showing an effect of the transit time dispersion. We conclude that the available tritium and 3He data, particularly if combined with other tracer data, are useful for constraining the subsurface circulation and mixing of the Mediterranean Sea.