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是水柱中颗粒物质和远洋沉积物中普遍存在的成分。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域的生产力之间存在相关性。重晶石显然在巴的地球化学循环中起着重要作用，而且它也很难溶解，因此阻碍了沉积物中的溶解和成岩交换。此外，海水同位素组成对解决许多古海洋学问题具有重要意义的三种元素(锶、S和钕)赋存于重晶石中，其数量使人们能够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的重要示踪物，例如气候、构造、海平面变化和海洋热液活动速率。然而，目前对重晶石在沉积柱中的形成、迁移和归宿的位置和机制的认识还很不完整，需要澄清重晶石、重晶石和碳通量之间的联系。在这项研究中，将用物质平衡、形态、地球化学和同位素方法研究赤道太平洋上层沉积层中重晶石的旋回及其与C旋回的关系。这项工作的新方面包括利用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、过滤和底部沉积物样品，并将与其他工作人员对水柱进行的地球化学和同位素调查密切协调。还将密切关注重晶石作为同时代矿物的潜力，以及对海水生物地球化学和同位素特征的古监测。

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.