Collaborative Research: Understanding Tidal Resonances in the Present-Day and Ice-Age Oceans

潮汐能量的耗散对深海海洋的混合起着重要作用，这一建议重新引起了人们对潮汐及其对大尺度海洋环流的影响的兴趣。潮汐、混合和经向翻转环流之间的假定联系提出了关于过去潮汐作用的有趣问题。最近的两项研究表明，最近一次冰河期的北大西洋潮汐比现在大得多。冰河时代的潮汐与今天的潮汐不同，因为潮汐是共振现象，因此可能对海平面的变化和与之相关的盆地几何形状的变化相当敏感。本建议的主要目的是解决天文潮汐强迫、海平面和盆地几何形状以及耗散如何共同产生观测到的潮汐响应的问题。在潮汐正向模拟的最新进展的推动下，提出的研究旨在了解当今和冰河时代的潮汐。研究主要包括3个方面：(1)在1度分辨率下计算全球海洋拉普拉斯潮汐方程的正态模态；(2)利用全球潮汐正演模式模拟海洋对不同强迫频率、盆地几何形状和海平面的响应；(3)根据阻尼驱动振荡器理论解释正演模型结果，使用从正常模式计算确定的特征频率和相关空间模式作为输入。更好地了解潮汐及其对海平面变化的反应，将是朝着能够解决与潮汐对大尺度环流影响有关的一系列问题迈出的重要一步。这项工作将有助于我们理解强迫的空间结构、强迫频率和耗散在确定当今和冰期潮汐振幅方面的相对重要性。这项研究具有广泛的影响，因为潮汐和潮汐耗散影响海洋环流（通过潮汐混合）、海冰、浮冰架和大陆冰盖。由于潮汐混合对海洋环流的影响，也因为冰河时代的潮汐在海因里希事件冰山排放的地点拉布拉多海非常大（潮汐被认为是冰山排放的一个因素），这项工作对古气候有影响。最后，这项研究将为预测未来海平面可能更高的潮汐提供一个框架，并应用于沿海城市。pi在教学、指导和推广方面发挥着积极的作用，本项目将为这些活动提供持续的支持，包括为将在pi指导下从事本项目的本科生提供支持。结果和数字代码将免费提供给研究界。

The suggestion that dissipation of tidal energy contributes significantly to mixing of the abyssal oceans, has renewed interest in tides, and their influence on the large scale ocean circulation. The postulated connection between tides, mixing, and the meridional overturning circulation raises interesting questions regarding the role of tides in the past. Two recent studies have demonstrated that the North Atlantic tides of the most recent ice age were substantially larger than they are today. Ice-age tides differ from those of today because tides are resonant phenomena, and are therefore likely to be quite sensitive to changes in sea level and associated changes in basin geometry. The principal objective of this proposal is to address the question of how the astronomical tidal forcing, sea level and basin geometry, and dissipation conspire to produce the observed tidal response. Motivated by recent advances in forward tide modeling, the proposed research seeks to understand tides of both the present-day and of the ice-ages. There are 3 principal elements to the proposed research: (1) Computation of the normal modes of Laplace's tidal equations for the global ocean at a resolution of 1 degree, (2) Simulations with a global forward model of tides to investigate the oceanic response to different forcing frequencies, basin geometries, and sea-levels; and (3) Interpretation of the forward model results in terms of damped-driven oscillator theory, using, as inputs, the eigenfrequencies and associated spatial patterns determined from the normal mode calculation. An improved understanding of tides and how they respond to sea-level change would be an important step toward being able to address a range of issues related to the impact of tides on the large scale circulation. The work will contribute to our understanding of the relative importance of the spatial structure of the forcing, the forcing frequency, and the dissipation, in setting the amplitude of tides in the present day and in the ice ages. The research has broad impact because tides and tidal dissipation affect oceanic circulation (via tidal mixing), sea ice, floating ice shelves, and continental ice sheets. The work has implications for paleoclimate, because of the effects of tidal mixing on oceanic circulation, and also because ice-age tides were very large in the Labrador Sea, site of the Heinrich event iceberg discharges (tides have been proposed as a factor in the iceberg discharges). Finally, this research will provide a framework for predicting the tides of a future with potentially much higher sea levels, with application for coastal cities. The PIs play an active role in teaching, mentoring, and outreach, and this project will provide continued support for those activities, including support for an undergraduate student who will work on this project under the PIs' direction. Results and numerical code will be made freely available to the research community.