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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Actinium-227 as a deep-sea tracer: sources, distribution and applications
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Actinium-227 as a deep-sea tracer: sources, distribution and applications

机译：Actinium-227作为深海示踪剂：来源，分布和应用

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Actinium is one of the rarest naturally occurring elements on earth. We measured its longest-lived isotope ~(227)Ac (half-life 21.77 yr) for the first time in the water column of the Southeast Pacific, the Central Arctic, the Antarctic Circumpolar Current (ACC) and the Weddell Gyre (WG). Besides the profile in the Southeast Pacific, which confirms earlier findings about the role to diapycnal mixing for ~(227)Ac distribution, we found three other different types of vertical profiles. These profiles point to a prominent role of advection for ~(227)Ac distribution, especially in the Southern Ocean. Depending on the type of profile found, ~(227)Ac is proposed as a tracer for different oceanographic questions. In the Southern Ocean, up to 4.93 250L?0.32 dpm m~(-3) ~(227)Ac is found close to the sea floor, which is the highest concentration ever observed in the ocean. Close to the sea surface in the WG, 0.46 ± 0.05 dpm m~(-3) ~(227)Ac_(ex) (~(227)Ac in excess of its progenitor ~(231)Pa) is detected. We use ~(227)Ac_(ex) there to determine the upwelling velocity in the Eastern WG to be about 55 m yr~(-1). In the ACC, Upper and Lower Circumpolar Deep Water (UCDW and LCDW) are found to differ clearly in their ~(227)Ac_(ex) activity. High ~(227)Ac_(ex) activities are therefore a promising tracer for recent inputs of LCDW to the sea surface, which may help to understand the role of deep upwelling for iron inputs into Antarctic surface waters. The expected release of ~(227)Ac is compared with ~(228)Ra to make sure that the large near-surface excess in the water column of the Southern Ocean is not due to lateral inputs by isopycnal mixing. Data from the Central Arctic and from a transect across the ACC confirm that ~(228)Ra and ~(227)Ac_(ex) differ strongly in their sources. The first measurements of ~(227)Ac on suspended matter (less than 1.7% of total ~(227)Ac close to the sea floor) indicate that the particle reactivity of ~(227)Ac is negligible in the open ocean, in agreement with earlier finding [Y. Nozaki, Nature 310 (1984) 486-488]. Despite the extremely low concentrations of ~(227)Ac, new measurement techniques [2.S. Moore, R. Arnold, J. Geophys. Res. 101 (1996) 1321-1329] point to a comfortable and comparably simple determination of ~(227)Ac in the future. Finally, ~(227)Ac_(ex) may become a widely used deep-sea specific tracer.
机译：in是地球上最稀有的天然元素之一。我们首次在东南太平洋，中北极，南极绕极洋流（ACC）和韦德尔涡流（WG）的水柱中首次测量了其寿命最长的同位素〜（227）Ac（半衰期21.77年） 。除了东南太平洋的剖面，这证实了先前的研究对辉砂混合对〜（227）Ac分布的作用外，我们还发现了其他三种不同类型的垂直剖面。这些剖面图表明对流对〜（227）Ac分布起着重要作用，尤其是在南大洋。根据发现的剖面类型，建议使用（（227）Ac）作为不同海洋学问题的示踪剂。在南大洋靠近海床处发现了高达4.93250L？0.32 dpm m〜（-3）〜（227）Ac，这是海洋中观测到的最高浓度。在WG中靠近海面的地方检测到0.46±0.05 dpm m〜（-3）〜（227）Ac_（ex）（〜（227）Ac超过其祖先〜（231）Pa）。我们在那里使用〜（227）Ac_（ex）确定东部WG的上升流速度约为55 m yr〜（-1）。在ACC中，发现上下极地极深水（UCDW和LCDW）的〜（227）Ac_（ex）活性明显不同。因此，高〜（227）Ac_（ex）活度是LCDW最近向海表层输入的有前途的示踪剂，这可能有助于了解深铁上升对南极地表水的铁输入的作用。将〜（227）Ac的预期释放量与〜（228）Ra进行比较，以确保南大洋水柱中大量的近地表过量不是由于等渗混合引起的横向输入。来自中央北极和横跨ACC的横断面的数据证实〜（228）Ra和〜（227）Ac_（ex）的来源差异很大。 〜（227）Ac对悬浮物的首次测量（不到靠近海床的〜（227）Ac总量的1.7％）表明，〜（227）Ac在开放海洋中的颗粒反应性可以忽略不计有较早的发现[Y. Nozaki，Nature 310（1984）486-488]。尽管〜（227）Ac的浓度极低，但新的测量技术[2.S. Moore，R。Arnold，J。Geophys。 Res。 101（1996）1321-1329]指出了将来〜（227）Ac的舒适且相对简单的测定。最后，〜（227）Ac_（ex）可能成为广泛使用的深海特定示踪剂。

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