Collaborative Research: Wave driven flow through a shallow, fringing reef

珊瑚礁的生存面临两个重大的长期挑战：(1)海洋酸化，这阻碍了珊瑚钙化的能力；(2)海洋变暖，导致珊瑚漂白。Ofu珊瑚礁(美属萨摩亚)是珊瑚的家园，这些珊瑚似乎具有特殊的抗白化性，是积极研究珊瑚如何能够在生物和生物地球化学方面应对这些挑战的地方。鉴于大堡礁上的碳素系统和温度动态都依赖于水流，本研究的数据和模型的物理见解和定量结果应该会为大堡礁和其他类似珊瑚礁的生态和生物地球化学研究提供重要的输入。此外，该项目还将推进高分辨率珊瑚礁测绘技术。该项目将涉及几名本科生和研究生，以及一名博士后科学家，为大学课程提供独特的材料。这项研究的结果将通过一系列解释水动力过程和珊瑚礁健康之间联系的在线短片向公众公布。该项目的目标是：(1)检验泻湖中摩擦和礁顶上的摩擦的相对重要性决定整个环流结构的概念；(2)检验与局部、空间平均的水流有关的阻力系数可以从珊瑚礁地形数据中估计的假设；(3)使用基于详细水深测量和空间可变阻力参数估计的深度平均环流模型来定量评估Ofu珊瑚礁流动的动力学。这个项目的主要活动将是：(A)使用一架载有照相机的无人机在分米尺度上绘制珊瑚礁水深图，并对产生的图像进行新颖的图像处理；(B)在Ofu珊瑚礁2公里长的区域内部署一套压力记录仪、温度记录仪、声学多普勒海流剖面仪和一个气象站，为期两个月，并对这些观测结果进行分析，以估计阻力等流动特性；(C)使用三维模型进行理想化和现实性的模拟研究。仪器阵列的设计与测绘和建模相结合，既是为了检验概念环流模型，也是为了评估珊瑚礁不同部分上的阻力如何随总体深度、水流和描述珊瑚礁物理结构的几何参数而变化。

Coral reefs face two significant long-term challenges to their existence: (1) Ocean acidification, which hinders the ability of corals to calcify; and (2) Ocean warming, which leads to coral bleaching. The Ofu reef (American Samoa), home to corals that seem to have exceptional bleaching resistance, is the location of active research into how corals may be able to meet those challenges biologically and biogeochemically. Given that both carbon system and temperature dynamics on the reef depend on flow, the physical insights and quantitative results from the data and modeling of this study should provide significant input to studies of ecology and biogeochemistry at Ofu and other similar reefs. In addition, the project will advance the technology for mapping reefs at high resolution. The project will involve several undergraduate and graduate students, as well as a postdoctoral scientist, providing unique material for university courses. The results of this study will be brought to the general public through a series of short online videos, produced to explain the link between hydrodynamic processes and reef health.The goals of this project are: (1) Test the concept that the relative importance of friction in the lagoon and friction on the reef crest determines the structure of the overall circulation; (2) Test the hypothesis that drag coefficients related to local, spatially averaged, flows can be estimated from data on reef topography; (3) Carry out a quantitative evaluation of the dynamics of Ofu reef flows using a depth-averaged circulation model based on detailed bathymetry and estimates of spatially variable drag parameterizations. The primary activities of this project would be: (a) Mapping of reef bathymetry at decimeter scale using an Unmanned Aerial Vehicle carrying cameras and novel image processing of the resulting images; (b) Deploying a set pressure loggers, temperature loggers, acoustic Doppler current profilers and a meteorological station for a 2-km long section of the Ofu reef for two one-month periods and analyzing the results of these observations to estimate flow properties such as drag; (c) Idealized and realistic modeling studies carried out using a three dimensional model. The design of the instrument array in combination with the mapping and modeling is intended to both test the conceptual circulation model and to evaluate how drag on different parts of the reef varies with overall depth, flow and with geometric parameters describing the physical structure of the reef.