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

关于潮汐能量的耗散对深海混合有重要贡献的建议，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设联系提出了关于潮汐在过去的作用的有趣的问题。最近的两项研究表明，最近一次冰河时代的北大西洋潮汐比今天的要大得多。冰河时代的潮汐不同于今天的潮汐，因为潮汐是共振现象，因此很可能对海平面的变化和与之相关的盆地几何结构的变化非常敏感。这项建议的主要目标是解决天文潮汐强迫、海平面和海盆几何形状以及耗散如何合力产生观测到的潮汐反应的问题。受最近向前潮汐模型研究进展的推动，这项拟议的研究试图了解当今和冰河时代的潮汐。这项研究的主要内容有三个：(1)在1度分辨率下计算全球海洋的拉普拉斯潮汐方程的简正模；(2)用全球潮汐正演模型模拟海洋对不同强迫频率、盆地几何和海平面的响应；(3)用阻尼式振子理论解释正演模型的结果，使用简正模计算确定的特征频率和相关的空间模式作为输入。增进对潮汐及其如何应对海平面变化的了解，将是朝着能够解决与潮汐对大尺度环流的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河时代的潮汐幅度方面的相对重要性。这项研究具有广泛的影响，因为潮汐和潮汐消散影响海洋环流(通过潮汐混合)、海冰、浮动冰架和大陆冰盖。这项工作对古气候有影响，因为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)。最后，这项研究将为预测未来海平面可能高得多的潮汐提供一个框架，并将其应用于沿海城市。私人投资机构在教学、指导和外展方面发挥积极作用，该项目将继续为这些活动提供支持，包括支持一名将在个人投资机构指导下从事这一项目的本科生。结果和NuMe

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 nume