Seawater 187Os/186Os Variation Over Time

187Re是一种放射性同位素，其半衰期约为4.6x1010年。一个体系的187o取决于该体系的年龄、初始的187o / 186o比率和187Re/ 186o（其中186o被用作非放射性的锇示踪剂）。大陆地壳的187Re/186Os比地幔高约100倍，因此平均年龄约为200亿年的大陆地壳的187Re/186Os值约为10.5，而直接从地幔中提取的锇值约为1。187Os/186Os比值为8.5，说明现今供给海洋的锇80%来自大陆，20%来自大洋地幔。根据海洋87Sr/86Sr记录，这一比例预计会随时间变化。地层定年体系中深海氧化沉积物和富有机物还原沉积物的氢组分可以提供过去1870 / 1860年代海水的记录。北太平洋中部的“巨型活塞岩心”（LL GPC-3）以及DSDP和ODP岩心的材料是研究的现成来源。研究了用稀过氧化氢浸出氧化岩心含氢部分的方法。初步结果与海洋97Sr/86Sr记录具有一级相关性，表明大陆和海洋地幔源的相对作用影响了这两个元素。最晚更新世87Sr/86Sr与187Os/186Os呈反比关系，表明这两种元素的来源不同。我们将探索1870 / 1860年代过去1亿年的完整海水记录，并将其与已知的87Sr/86Sr记录进行比较，从而增加我们对两种不同同位素特征与蚀变和风化地质记录之间关系的理解。

187Re is a radioactive isotope that decays with a half- life of about 4.6x1010 years to 187Os. The 187Os of a system depends on the age of that system, the initial 187Os/186Os ratio and the 187Re/186Os (where 186Os is used as the non-radiogenic osmium tracer). The continental crust has 187Re/186Os about 100 times higher than the mantle so that the 187Os/186Os of the average continental crust with a mean age of about 20 billion years is about 10.5 whereas osmium immediately derived from the mantle has a value of about 1. The seawater 187Os/186Os of 8.5 implies that 80% of the present-day osmium supplied to the sea comes from the continents and 20% from oceanic mantle sources. This ratio of sources is expected to vary over time based on the marine 87Sr/86Sr record. The hydrogenous fraction of oxidized deep-sea sediments and organic-rich reduced deposits from stratigraphically dated systems can provide records of past seawater 187Os/186Os. The "giant piston core" from the central North pacific (LL GPC-3) and material from DSDP and ODP cores are ready sources for the study. The procedures involving leaching of the hydrogenous fraction of oxidized cores using dilute hydrogen peroxide have been developed. Preliminary results shows a first order correlation with the marine 97Sr/86Sr record indicating that the relative roles of continental and oceanic mantle source affect both elements. Imposed on this effect is the inverse relationship between 87Sr/86Sr and 187Os/186Os in the latest Pleistocene indicating different sources for the two elements. We will explore the full 187Os/186Os seawater record over the past 100 million years, compare it with the known 87Sr/86Sr record and thereby to add to our understanding of the relationship of two different isotopic signatures to the geologic record of alteration and weathering.