Collaborative Research: Assessing the Impact of Tidal Mixing on the Meridional Overturning Circulation of the Oceans during the Last Glacial Maximum

合作研究：评估末次盛冰期潮汐混合对海洋经向翻转环流的影响

• 批准号: 1559166
• 负责人: Gokhan Danabasoglu
• 金额: $ 6.19万
• 依托单位: University Corporation For Atmospheric Res
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-02-01 至 2019-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1559166&HistoricalAwards=false
• 关键词: Collaborative; Research; Assessing; Impact; Tidal

In the contemporary ocean, most of the tidal energy is dissipated on shallow continental shelves, whereas a smaller portion causes mixing in the deep ocean, which powers the Meridional Overturning Circulation (MOC). Studies of paleo-tides suggest that during the Last Glacial Maximum (LGM), due to the sea level drop of about 120 m, this situation was drastically different and dissipation was shifted from the shallow shelves into the deep ocean. This finding has prompted the hypothesis that the meridional overturning circulation during the Last Glacial Maximum must have been stronger. However, recent research results aimed at quantifying the effects of this dissipation shift on the LGM MOC came to conflicting conclusions, ranging from negligible effects to a large increase in the MOC. This project seeks to resolve these differences and test the aforementioned hypothesis. It will also provide the first quantification of the effects of realistic, data constrained, LGM stratification on turbulent diffusivities, mixing and the MOC. Other uncertainties will also be quantified thus leading to a comprehensive estimate of changes in tidal mixing and its impacts on the LGM MOC. Thus this project will lead to a better understanding of the processes that control planetary-scale ocean circulation changes and their associated biogeochemical cycles in fundamentally different climates. A better understanding of the driving mechanisms for the MOC during the LGM has the potential to improve its quantification with important implications for efforts to quantify the glacial ocean?s carbon cycle and the resolution of the great puzzle of the glacial - interglacial variations in atmospheric carbon dioxide. A beneficial side effect of this project may also be that it improves the present day simulation of tidal mixing, diffusivities and circulation in two climate models that are widely used by the scientific community and influence the design of future Paleoclimate Modeling Intercomparison Projects. A post-doctoral scientist will be supported and trained in running and analyzing a tide model. An undergraduate student will be exposed to research through a summer internship. A conference session will be organized with the goal to bring together modern physical oceanographers and paleoceanographers to foster interdisciplinary exchange of ideas.A detailed modeling study to investigate effects of tidal mixing on the present day and Last Glacial Maximum (LGM) Meridional Overturning Circulation (MOC) will be conducted using a hierarchy of numerical models. Simulations with a global tide model will calculate distributions of tidal energy dissipation, which will be supplied to two global climate/ocean circulation models to quantify their effects on mixing and the MOC. Sensitivity experiments will explore uncertainties due to different proposed parameterizations of internal wave drag, tide model resolution, LGM stratification, floating ice, spatial variations in sea level, and the vertical decay of mixing above the sea floor on the results. Climate model simulations will be conducted with an intermediate complexity model and a state-of-the-science earth system model. Present day simulations will be evaluated by comparison to observational estimates of diapycnal diffusivities and tracer distributions. The effects of different circulations on biogeochemical cycles and isotopes of carbon and nitrogen will also be simulated. Finally, the LGM model results will be compared to paleo-reconstructions from available proxy records in order to evaluate the simulated circulations.

在现代海洋中，大部分潮汐能在浅大陆架上消散，而一小部分在深海中引起混合，这为经向翻转环流（MOC）提供动力。古潮汐的研究表明，在末次盛冰期（LGM），由于海平面下降约120米，这种情况是截然不同的，耗散从浅海架转移到深海。这一发现促使人们假设，末次冰盛期的纬向翻转环流一定更强。然而，最近的研究结果旨在量化这种耗散转变对LGM MOC的影响，得出了相互矛盾的结论，从可忽略的影响到MOC的大幅增加。本项目旨在解决这些差异，并测试上述假设。它还将提供第一个量化的现实，数据约束，末次大冰期分层湍流扩散率，混合和MOC的影响。还将量化其他不确定性，从而全面估计潮汐混合的变化及其对LGM MOC的影响。因此，该项目将导致更好地了解控制行星尺度海洋环流变化的过程及其在根本不同的气候中的相关地球化学循环。 更好地了解在末次盛冰期的MOC驱动机制，有可能提高其量化的重要影响，努力量化冰川海洋？的碳循环和大气中二氧化碳的冰川-间冰期变化的大谜团的解决。该项目的一个有益的副作用也可能是，它改善了目前的模拟潮汐混合，扩散率和环流在两个气候模型，被广泛使用的科学界和影响未来的古气候建模相互比较项目的设计。一名博士后科学家将在运行和分析潮汐模型方面得到支持和培训。本科生将通过暑期实习接触研究。将组织一次会议，目的是汇集现代物理海洋学家和古海洋学家，促进跨学科的思想交流。将使用一个层次的数值模式进行详细的模拟研究，以探讨潮汐混合对当今和末次冰期最大（LGM）经向翻转环流（MOC）的影响。全球潮汐模型的模拟将计算潮汐能耗散的分布，并将其提供给两个全球气候/海洋环流模型，以量化它们对混合和MOC的影响。敏感性试验将探讨由于内波阻力、潮汐模型分辨率、LGM分层、浮冰、海平面空间变化以及海底以上混合的垂直衰减对结果的不同拟议参数化而产生的不确定性。气候模式模拟将使用一个中等复杂性模式和一个最新科学地球系统模式进行。目前的模拟将进行评估比较观测估计diapycnal扩散率和示踪剂分布。模拟了不同环流条件下的地球化学循环和碳、氮同位素的变化。最后，LGM模型的结果将进行比较，从现有的代理记录的古重建，以评估模拟环流。