Processes Affecting the Riverine Flux of Uranium Isotopes from Coastal Margins to the Ocean: A Study of the Mississippi River and Adjacent Shelf

沿海和陆架环境中的地球化学过程影响海洋中的铀浓度，并影响了过去冰期/间冰期旋回期间海洋的铀同位素组成。这项研究的总体目标是提高对影响铀从沿海边缘到开阔海洋的通量的循环过程的理解。本研究的重点是密西西比河和邻近的大陆架，以实现以下目标。(1)表征河/海混合过程中铀的行为；并且，确定控制铀河口行为的过程。(2)查明影响陆架沉积物作为铀净源或净汇作用的条件和过程；并且，为了评估河流主导的大陆架在铀的整体海洋化学中所起的一般作用。水柱和海床样本将从密西西比河附近的大陆架收集。水样将被分割成溶解，胶体和颗粒部分使用过滤和超滤技术。将检查所有馏分的铀浓度和同位素比率，以评估江河/海洋混合过程中铀的命运。将从陆架岩心中提取间隙水，检查底部沉积物中铀的成岩吸收或释放情况，并将利用河水和海水的混合实验来研究河口混合对铀的影响。

Geochemical processes in coastal and shelf environments affect uranium concentrations in the ocean, and have influenced the uranium isotope composition of the ocean during past glacial/interglacial cycles. The overall aim of this research is to improve understanding of the cycling processes that affect the flux of uranium from coastal margins to the open ocean. This study focuses specifically on the Mississippi River and the adjacent continental shelf to achieve the following objectives. (1) To characterize the behavior of uranium during river/ocean mixing; and, to identify the processes that govern the estuarine behavior of uranium. (2) To identify the conditions and processes that influence the role of shelf sediments as net sources or sinks for uranium; and, to evaluate the general role that river dominated shelves play in the overall ocean chemistry of uranium. Water-column and Seabed samples will be collected from the continental shelf adjacent to the Mississippi River. Water samples will be partitioned into dissolved, colloidal and particulate fractions using filtration and ultrafiltration techniques. Uranium concentrations and isotope ratios will be examined in all fractions to evaluate the fate of U during river/ocean mixing. Interstitial waters will be extracted from shelf cores and examined for diagenetic uptake or release of uranium from bottom sediments, and mixing experiments between river water and seawater will be used to study effects of estuarine mixing on uranium.