COLLABORATIVE RESEARCH (USC-UW): Evaluating Seawater Circulation Rates Through Permeable Sediments, Using Naturally Occurring Rn and Ra Isotopes

评估可渗透沉积物中的流体流速及其对海洋化学的影响一直是一个具有挑战性的问题。水流可能是由海底的海水环流驱动的，这是由于重力波穿过海面所产生的压力梯度，或者是由于水流流过不规则的海底地形所产生的压力梯度。在一些地区，水流可能是由陆地地下水通过生物灌溉或物理灌溉排放到沿海地区驱动的。在这项研究中，来自南加州大学和华盛顿大学的研究人员将评估加利福尼亚州亨廷顿海滩近海沉积物中的流体循环速率，这些沉积物的循环主要受海浪的影响。这些可渗透沉积物中的循环速率和模式将通过自然发生的放射性同位素分布（222Rn、223Ra、224Ra和228Ra）的反应/输运模型推断出来。该地区以前的工作已经建立了Ra同位素的区域预算，限制了这些浅水沉积物的总体输入。本研究的目的是定义输入如何随水深和波浪特征而变化。观测将为描述通过渗透性沉积物的水流的模型提供一个现场校准点。除了放射性同位素外，还将测量氧、TCO2和营养成分。该数据集将用于根据用放射性同位素开发的模式输运参数确定这些成分的通量。当海水在沙子中循环时，这些通量将有助于限制这些渗透性沉积物在捕获细粒生物颗粒方面的作用。至于更广泛的影响，这项研究的结果将对评估近岸渗透性沉积物过滤水的能力的水质管理人员有价值。该项目还将为本科生提供在实验室和现场工作的研究机会。该研究的实地考察部分将与太平洋科学潜水项目水族馆合作完成。这项合作不仅将为开展这项工作提供重要的后勤援助，而且还将促进海洋学家与沿海地区娱乐用户社区之间的交流。

ABSTRACTOCE-0623413OCE-0623278Evaluating fluid flow rates through permeable sediments, and the impact of this flow on ocean chemistry, has been a challenging problem. Flow may be driven by circulation of seawater through the seabed in response to pressure gradients created by the passage of gravity waves across the sea surface, or by pressure gradients generated as currents flow over irregular bottom topography. In some areas, flow may be driven by terrestrial groundwater discharge into the coastal zone, via bio-irrigation, or physical irrigation. In this study, researcher from the University of Southern California and the University of Washington, will evaluate the fluid circulation rates within offshore sediments off Huntington Beach CA, at sites where circulation is dominated by the influence of waves. Circulation rates and patterns in these permeable sediments will be deduced from reaction/transport modeling of naturally-occurring radioisotope distributions: 222Rn, 223Ra, 224Ra, and 228Ra. Previous work in this region has established regional budgets for Ra isotopes that constrain their overall input from these shallow water sediments. The goal of this study is to define how input varies with water depth and wave characteristics. Observations will provide an in situ calibration point for models describing flow through permeable sediment. In addition to the radioisotopes, oxygen, TCO2, and nutrient profiles will be measured. This data set will be used to establish fluxes of these constituents, based on the model transport parameters developed with radioisotopes. These fluxes will help to constrain the role of these permeable sediments in trapping fine-grained biogenic particles as seawater circulates through the sands. As regards broader impacts, results from this study will be of value to water quality managers who evaluate the ability of nearshore permeable sediments to filter water. The project will also provide research opportunities for undergraduate students to work in laboratory and field settings. The fieldwork component of the research will be done in collaboration with the Aquarium of the Pacific Scientific Diving Program. This collaboration will not only provide an important logistical assistance to carry out the work, but also foster communication between oceanographers and the community of coastal zone recreational users.