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.

在当代海洋中，大部分潮汐能在浅层大陆架上消散，而一小部分则在深海中引起混合，从而为经向翻转环流（MOC）提供动力。古潮汐研究表明，在末次盛冰期（LGM）期间，由于海平面下降了约120 m，这种情况发生了很大的变化，消散从浅层陆架转移到深海。这一发现提出了这样的假设：末次盛冰期期间的经向翻转环流一定更强。然而，最近旨在量化这种耗散变化对 LGM MOC 影响的研究结果得出了相互矛盾的结论，从影响可以忽略不计到 MOC 大幅增加。该项目旨在解决这些差异并测试上述假设。它还将首次量化现实的、数据受限的、LGM 分层对湍流扩散、混合和 MOC 的影响。其他不确定性也将被量化，从而对潮汐混合的变化及其对末次盛宴 MOC 的影响进行全面估计。因此，该项目将有助于更好地了解控制行星规模海洋环流变化的过程及其在根本不同的气候下相关的生物地球化学循环。 更好地了解末次盛冰期期间 MOC 的驱动机制有可能改善其量化，对量化冰川海洋碳循环和解决大气二氧化碳冰川-间冰期变化的巨大难题具有重要意义。该项目的一个有益的副作用还可能是，它改进了当今科学界广泛使用的两种气候模型中潮汐混合、扩散和环流的模拟，并影响了未来古气候模拟比对项目的设计。博士后科学家将获得运行和分析潮汐模型的支持和培训。本科生将通过暑期实习接触研究。将组织一次会议，旨在将现代物理海洋学家和古海洋学家聚集在一起，促进跨学科的思想交流。将使用一系列数值模型进行详细的模型研究，以调查潮汐混合对当今和末次盛冰期 (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量耗散的分布，该分布将提供给两个全球气候/海洋环流模型，以量化其对混合和 MOC 的影响。灵敏度实验将探索由于内波阻力、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垂直衰减等不同建议参数化对结果的影响。气候模型模拟将使用中等复杂性模型和最先进的地球系统模型进行。目前的模拟将通过与径流扩散率和示踪剂分布的观测估计进行比较来进行评估。还将模拟不同环流对生物地球化学循环以及碳和氮同位素的影响。最后，LGM 模型结果将与可用代理记录的古重建进行比较，以评估模拟环流。