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，大多数潮汐能消散在浅大陆货架上，而较小的部分会导致深海混合，从而为子午倾覆的循环（MOC）提供动力。对古潮汐的研究表明，在最后一次冰川最大值（LGM）中，由于海平面下降约为120 m，这种情况截然不同，并且耗散从浅层架子转移到了深海。这一发现促使人们的假设是，在最后一次冰川最大值中的子午倾覆必须更强。但是，最新的研究结果旨在量化这种耗散转变对LGM MOC的影响，这一结论是相互矛盾的，从可忽略的效果到MOC的大幅增加。该项目旨在解决这些差异并检验上述假设。它还将提供对逼真的，数据约束，LGM分层对湍流扩散，混合和MOC的影响的首次量化。其他不确定性也将被量化，从而使潮汐混合变化及其对LGM MOC的影响进行全面估计。因此，该项目将更好地理解控制行星尺度海洋循环变化及其在根本不同气候下的生物地球化学周期的过程。 更好地理解LGM期间MOC的驾驶机制具有改善其量化的潜力，这对量化冰川海的碳循环的努力以及解决了冰川二氧化碳中冰川间变化的极大难题的努力的重要意义。该项目的一个有益的副作用也可能是，它改善了两个气候模型中潮汐混合，扩散性和循环的模拟，这些气候模型被科学界广泛使用，并影响了未来的古气候建模对综合项目的设计。博士后科学家将受到支持和培训，以运行和分析潮汐模型。一名本科生将通过暑期实习接触研究。将组织会议的目标，目的是将现代的物理海洋学家和古文化学家汇集在一起​​，以促进跨学科的思想交流。一项详细的建模研究，以调查潮汐混合对当今和最后一次冰川最大（LGM）子午线倒闭循环（MOC）的影响，将使用数值模型进行。具有全球潮汐模型的仿真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/海洋循环模型，以量化其对混合和MOC的影响。敏感性实验将探索由于内部波浪阻力，潮汐模型分辨率，LGM分层，浮冰，海平面空间变化以及结果在结果上的海底上方混合的垂直衰减而导致的不确定性。气候模型模拟将使用中间复杂性模型和最先进的地球系统模型进行。当今的模拟将通过与Diapynal扩散性和示踪剂分布的观察性估计值进行比较。也将模拟不同循环对碳和氮的生物地球化学周期和同位素的影响。最后，将LGM模型结果与可用代理记录的古重建进行比较，以评估模拟循环。