Collaborative Research: Dynamics of Cross-shore Thermally Driven Exchange

与研究充分的大陆架相比，人们对岛屿海岸线上典型的陡峭水深和狭窄大陆架的跨陆架循环知之甚少。跨陆架环流导致水团交换，并控制沿海海洋中热、盐、营养物质、污染物、沉积物和浮游生物(如幼虫或浮游植物)的分布。此外，就珊瑚礁而言，跨陆架环流的水平热量再分配缓和了珊瑚虫经历的每日温度变化，从而有可能减少热应力。这项研究将利用两个地点的现有资料和高分辨率数值模拟来研究热力驱动的交换流动及其如何随着跨岸距离的变化以及如何受到涌浪能量、陆架坡度、近岸地形、风况和季节变化的调制。以色列埃拉特和夏威夷瓦胡岛的两个珊瑚礁的观测突出了热力强迫斜压交换在跨岸输送中的作用。在每个地点，白天情况的特点是，随着近岸较浅水域温度的升高，表面出现离岸流动。夜间的冷却导致了海底附近的离岸水流。然而，这两个地点的流动响应的显著差异表明了不同的动力机制。来自瓦胡岛的时间序列数据进一步表明，该交易所对整个跨岸交易所的贡献是一阶的。本研究将审查热力驱动流动的动力学结构，并确定其对热带海岸的影响程度和一般性，办法是利用现有的数据集进行全面的历史分析，并进行高分辨率的数值模拟，所涉参数范围很广，范围从通常采用二维水深测量的相对简单的楔形情况(类似于Eilat)，到复杂的(更典型的)具有显著波浪强迫的礁-泻湖环境(瓦胡岛Kilo Nalu天文台)。它将提供对珊瑚礁环境中的跨岸输送过程的基本了解，并应揭示热力驱动的斜压交换在多大程度上有助于热带海岸线的跨岸环流。更好的理解应该导致建立能够对这些流动做出准确预测的模型。拟议研究的结果将特别适用于生态丰富和经济重要的珊瑚礁和其他陡峭的热带沿海环境，例如了解珊瑚礁生态系统将如何应对海洋酸化或海洋温度上升等环境变化，以及建立海洋保护区等保护珊瑚礁的努力。

In contrast to well-studied continental shelves, relatively little is known about cross-shelf circulation on island coastlines typically characterized by steep bathymetry and narrow shelves. Cross-shelf circulation results in the exchange of water masses and controls the distribution of heat, salt, nutrients, contaminants, sediment, and planktonic organisms like larvae or phytoplankton in the coastal ocean. In addition, in the case of coral reefs, the horizontal redistribution of heat by cross-shelf circulation moderates the daily variations in temperature experienced by coral polyps, thus potentially reducing thermal stress. This study will use existing data sets from two locations and high resolution numerical modeling to study the thermally driven exchange flows and how they vary with cross-shore distance and are modulated by swell energy, shelf slope, nearshore morphology, wind regimes and seasonal changes.Observations at two reefs at Eilat, Israel and Oahu, Hawaii have highlighted the role of thermally forced baroclinic exchange in cross-shore transport. At each site, daytime conditions were characterized by offshore flow at the surface in response to increased temperatures in shallower water nearshore. Nighttime cooling resulted in offshore flow near the bottom. Significant differences in flow response at the two sites indicate distinct dynamic regimes, however. Time series data from Oahu further indicates that the exchange provides a first order contribution to the overall cross-shore exchange. This study will examine the dynamical structure of thermally driven flows and establish the extent of their influence and generality for tropical coasts by leveraging existing data sets in a comprehensive historical analysis coupled with high-resolution numerical modeling spanning a wide parameter space ranging from a relatively simple wedge case with generally two-dimensional bathymetry (similar to Eilat) to a complex (more typical) forereef-lagoon environment with significant wave forcing (Kilo Nalu Observatory, Oahu). It will provide fundamental understanding of cross-shore transport processes in reef environments and should reveal the extent to which thermally driven baroclinic exchange contributes to cross-shore circulation for tropical coastlines in general. Improved understanding should lead to the construction of models capable of making accurate predictions of these flows. The results of the proposed research will have particular applicability to ecologically rich and economically important coral reefs and other steep, tropical, coastal environments, such as understanding how reef ecosystems will respond to environmental changes like ocean acidification or rising ocean temperatures, as well as to efforts to protect them like the establishment of marine reserves.