Osmium Isotopes as a Paleoweathering Tracer

布勒克9314674 Pegram等人论证了海洋沉积物中锇同位素比值作为地球化学示踪剂的潜力。（1992）。 他们表明，在过去的5800万年里，从太平洋红粘土中浸出的锇的187 Os/186 Os比率大幅增加。 他们提出，可浸出的锇是氢的来源，反映了沉淀时海水的同位素组成。 观察到的187 Os/186 Os的变化归因于大陆风化速率的变化;较高的值对应于通过河流增加的放射性成因187 Os供应。 假定的短时间的锇在海水中的滞留时间可能使它能够响应快速（10 Ka）的风化率的变化。 目前，没有具有这种能力的示踪剂。 由于锇同位素在过去的海洋中并不均匀，因此从单一地点的记录中得出的推论并不一致。 这必然适用于整个海洋。 然而，海洋中锇的异质性可能有助于评估当地变化的重要性及其对平均海水化学的影响。 这项研究将通过分析海洋碳酸盐沉积物中的氢（可沥滤）部分来评估海水中锇的时空变化，并阐明在不同时间尺度上控制海洋中锇同位素比值的过程，从而有助于为使用锇作为这些过程的示踪剂奠定基础。

Broecker 9314674 The potential of osmium isotopic ratios of marine sediments as a geochemical tracer was demonstrated by Pegram et. al. (1992). They showed that there has been a large increase in the 187 Os/186 Os ratio of osmium leached from Pacific red clays over the past 58 million years. They proposed that the leachable osmium is hydrogenous in origin, and reflects the isotopic composition of sea water at the time of precipitation. The observed change in 187 Os/186 Os was attributed to changes in continental weathering rates; higher values corresponding to increased supply of radiogenic 187 Os via rivers. The presumed short residence time of osmium in sea water potentially allows it to respond to rapid (10 Ka) changes in weathering rates. At present, no tracer with this capacity exists. Since osmium isotopes have not been homogeneous in the oceans in the past, inferences drawn from the record at a single site do not necessarily apply to the whole ocean. However, the heterogeneity of osmium in the oceans may facilitate evaluation of the importance of local changes and their effect on mean ocean water chemistry. This study will evaluate the spatial and temporal variability of osmium in sea water by analyzing the hydrogenous (leachable) fraction of marine carbonate sediments and elucidate the processes that control osmium isotope ratios in the oceans on various time scales, and thus help to lay the groundwork for the use of osmium as a tracer for these processes.