Collaborative Research: Dynamics of Cross-shore Thermally Driven Exchange

与研究得很充分的大陆架相比，人们对岛屿海岸线上的跨大陆架环流知之甚少，这些环流通常以陡峭的水深和狭窄的大陆架为特征。跨大陆架环流导致水团交换，控制着沿海海洋中热、盐、营养物、污染物、沉积物和浮游生物（如幼虫或浮游植物）的分布。此外，在珊瑚礁的情况下，通过跨大陆架环流的热量水平再分配缓和了珊瑚虫每天经历的温度变化，从而潜在地减少了热应力。本研究将使用来自两个地点的现有数据集和高分辨率数值模拟来研究热驱动的交换流，以及它们如何随跨岸距离而变化，并受涌能量、陆架坡度、近岸形态、风况和季节变化的调节。对以色列埃拉特和夏威夷瓦胡岛两个珊瑚礁的观测强调了热强迫斜压交换在跨海岸运输中的作用。在每个站点，白天的情况都以近岸浅水温度升高引起的海面流动为特征。夜间的冷却导致了海底附近的近海流。然而，两个地点的流动响应的显著差异表明不同的动力机制。来自瓦胡岛的时间序列数据进一步表明，该交易所为整个跨岸交易所提供了一级贡献。本研究将考察热驱动流的动力结构，并通过综合历史分析中的现有数据集，结合高分辨率数值模拟，确定其对热带海岸的影响程度和普遍性，这些数据集跨越了广泛的参数空间，范围从具有一般二维水深测量的相对简单的楔形情况（类似于埃拉特）到具有显著波浪强迫的复杂（更典型）前礁泻湖环境（基洛纳鲁天文台，瓦胡岛）。它将提供对珊瑚礁环境中跨海岸运输过程的基本理解，并应揭示热驱动斜压交换对热带海岸线跨海岸环流的贡献程度。更好的理解应该导致能够对这些流做出准确预测的模型的构建。拟议的研究结果将特别适用于生态丰富、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它们的努力。

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.