Barite in the Central Equatorial Pacific: Implications for Marine Chemistry, Productivity, and Circulation of the Modern and Past Oceans

矿物重晶石（BaSO4）是水柱和远洋沉积物中普遍存在的颗粒物质成分。许多工人已经注意到沉积物中重晶石的丰度与上覆地表水的生产力之间的相关性。重晶石在钡的地球化学循环中具有重要的作用，它也具有很强的不溶性，因此在沉积物中难以溶解和成岩交换。此外，海水同位素组成对解决许多古海洋学问题很重要的三种元素（Sr、S和Nd）存在于重晶石中，其数量允许对极少量的分离相进行精确的同位素测量。由于所有这些原因，重晶石似乎是生产力、地球化学循环和一系列可能影响海水化学和同位素组成的过程（如气候、构造、海平面变化和海洋热液活动速率）的重要示踪剂。然而，目前对沉积柱中重晶石的形成、运输和命运的位置和机制的认识非常不完整，Ba、重晶石和C通量之间的联系需要澄清。本研究将采用质量平衡、形态、地球化学和同位素等方法研究赤道太平洋上部沉积层重晶石的循环及其与碳循环的关系。本研究的新方面包括利用Nd、Sr和S同位素作为重晶石形成环境和可能的再循环的线索。这项研究将利用沉积物捕集器、过滤后的底泥样品，并将与其他工作人员对水柱的地球化学和同位素调查密切协调。在进行这项工作时，还将密切注意重晶石作为海水生物地球化学和同位素特征的当代和古监测的潜力。

The mineral barite BaSO4) is an ubiquitous component of particulate material in the water column, and of pelagic sediments. Many workers have noted a correlation between the abundance of barite in sediments and productivity in overlying surface waters. Barite is clearly important in the geochemical cycle of Ba, and it is also quite insoluble and therefore resists dissolution and diagenetic exchange in sediments. Furthermore, three elements for which the seawater isotopic composition is important for solving many paleoceanographic problems (Sr, S and Nd) occur in barite in amounts that permit precise isotopic measurements to be made on very small amounts of the separated phase. For all of these reasons, barite appears to be an important tracer of productivity, geochemical cycling, and a host of processes that may affect seawater chemical and isotopic compositions, e.g. climate, tectonics, sealevel change and rates of marine hydrothermal activity. Nevertheless, the present understanding of the sites and mechanisms of barite formation, transport, and fate in the sedimentary column is very incomplete and the linkage between Ba, barite and C fluxes need to be clarified. In this research a mass- balance, morphological, geochemical and isotopic approach to the study of the cycling of barite in upper sedimentary layers of the equatorial Pacific and its relation to the C cycling will be made Novel aspects of the work include the use of Nd, Sr and S isotopes as clues to the environment of formation and possible recycling of barite. This study will make use of sediment trap, filtered and bottom sediment samples, and will be closely coordinated with geochemical and isotopic investigations of the water column by other workers. It will also be undertaken with close attention to the potential of barite as a contemporary as well as a paleo monitor of biogeochemical and isotopic characteristics of seawater.