Subterranean Estuarine Chemistry: The Role of the Fe/Mn Redox Cycles on the Transport of U, Ra and Th Isotopes to the Coastal Ocean

伍兹霍尔海洋研究所的两位地球化学家将进行一项研究，以更好地了解地下河口发生的化学转化。地下水占地球淡水水库的近97%，可通过“地下河口”向海洋输送大量溶解的化学物质。地下河口是海水和新鲜地下水的混合状态，是许多沿海地区的基础)。由于对与海底地下水有关的化学反应和通量知之甚少，量化其对沿海海洋的影响需要对一个封闭的河口进行集中和深入的研究，该河口接受有充分记录的地下水通量。研究人员已经确定马萨诸塞州的瓦奎特湾——国家河口研究保护区系统的一部分——是对这些过程进行初步研究的理想地点。该项目将包括两个部分：o建立整个地下河口化学成分的时间变化。外部强迫功能，如潮汐泵送和含水层的降雨补给，可能在地下水/海水界面的位置和结构中发挥重要作用。(1)氧化还原敏感元素（Fe， Mn和U），(2)清除元素（P， Th同位素）和(3)流动元素（Ra同位素）在地下河口的地球化学反应和转化研究。地下河口中这三类元素的添加和移除过程有多重要？地下河口沉积物中“铁/锰幕”的形成是否对被清除元素和流动元素的运输和转化具有重要意义？重点将放在铁和锰的氧化还原化学和U-Th-Ra系列同位素的系统学上。该项目结合了与重要社会问题相关的基础海洋学和地球化学问题的研究，这些问题与复杂界面中的运输和反应性有关。

ABSTRACTOCE-0095384Two geochemists at the Woods Hole Oceanographic Institution will conduct a study to gain a better understanding of the chemical transformations that take place in a subterranean estuary. Groundwater, nearly 97% of the Earth's freshwater reservoir, may contribute significant fluxes of dissolved chemical species to the oceans via transport through "subterranean estuaries". Subterranean estuaries are mixing regimes of seawater and fresh ground water that underlie many coastal regions). Since little is known about chemical reactions and fluxes associated with submarine groundwater, quantifying its impact on the coastal oceans requires a focused and in-depth study of an enclosed estuary that receives a well documented flux of ground waters. The investigators have identified Waquoit Bay, Massachusetts -- part of the National Estuarine Research Reserve system -- as an ideal location for an initial study of these processes. The project will consist of two parts: o Establishment of the temporal variability in chemical compositions across the subterranean estuary. External forcing functions such as tidal-pumping as well as rainfall recharge of the aquifer will likely play important roles in the location and structure of the groundwater/seawater interface. o Study of the geochemical reactions and transformations in subterranean estuaries of three important classes of elements - (1) redox sensitive elements (Fe, Mn and U), (2) scavenged elements (P, Th isotopes) and (3) mobile elements (Ra isotopes). How significant are the addition and removal processes operating on these three classes of elements in subterranean estuaries? Is the formation of an "Fe/Mn Curtain" in the sediments of a subterranean estuary an important process with respect to the transport and transformation of scavenged and mobile elements? Particular focus will be on the redox chemistries of Fe and Mn and on the systematics of U-Th-Ra series isotopes. This project combines relevance to important societal problems with the study of fundamental oceanographic and geochemical problems associated with the transport and reactivity in a complex interface.