The Ca Isotopic Evolution of the Oceans

通过确定海水的44Ca/40Ca同位素比率及其随地质时间的变化，本研究将扩展对自然界Ca稳定同位素变化的研究。海洋中44Ca/40Ca比值的变化对应于河流向海洋输送Ca与钙质沉积物中Ca的转移之间平衡的变化。Ca平衡反映了风化作用与碳酸盐沉积之间的关系，碳酸盐沉积控制着大气中二氧化碳的含量，从而影响全球气候。因此，这项研究将提高我们对哪些地球过程在决定地球全球气候方面最具影响力的理解。先前的研究表明，由于生物过程，44Ca/40Ca的比例发生了变化；当钙通过食物链向更高的营养水平移动时，这个比例就会降低。由于Ca主要通过生物过程从海洋中去除，因此对海洋的44Ca/40Ca有影响，这就产生了古海洋Ca同位素组成与全球Ca循环之间的关系。最近的地质记录部分，追溯到最古老的海底时代（大约2亿年），将是研究的重点。在这部分地质记录中，我们可以了解到最多，因为我们可以将观测到的钙同位素变化与过去气候和海洋化学的其他指标进行比较。44Ca/40Ca比值将在碳酸钙样品上测量。这些样品将从DSDP和ODP岩心、意大利陆地剖面和其他陆地剖面获得。还将对现代海洋环境进行一项有限的调查，以调查现代碳酸盐之间的变化，并描述海洋中Ca的现代来源。

9909639DePaoloThe proposed research will extend studies of Ca stable isotope variations in nature by determining the 44Ca/40Ca isotopic ratio of seawater and how it has changed over geologic time. Variations of the 44Ca/40Ca ratio in the oceans correspond to changes in the balance between delivery of Ca to the oceans by rivers and its removal into calcareous sediments. The Ca balance in reflects the relationship between weathering and carbonate sedimentation, which control the amount of carbon dioxide in the atmosphere and hence affect global climate. Consequently, this study will improve our understanding of which earth processes have been most influential in determining the global climate of the earth. Previous work shows that the 44Ca/40Ca ratio is shifted as a result of biological processes; the ratio decreases as Ca moves through food chains to higher trophic levels. Because Ca is removed from the oceans mainly by biological processes, there is an effect on the 44Ca/40Ca of the oceans, which produces the relationship between the Ca isotopic composition of the paleo-oceans and the global Ca cycle. The more recent part of the geologic record, back through the age of the oldest ocean floor (about 200 million years) will be the focus of the study. During this part of the geologic record, we can learn the most because we can compare the observed Ca isotopic variations to other indicators of past climate and ocean chemistry. The 44Ca/40Ca ratio will be measured on samples of calcium carbonate. These samples will be obtained from DSDP and ODP cores, from on-land sections in Italy, and other on-land sections. A limited survey of modern marine environments will also be done to investigate variability among modern carbonates and to characterizing the modern sources of Ca in the oceans.