Collaborative Research: Mixing and the Meridional Overturning Circulation in the Modern and Glacial Ocean

海洋内部的小尺度混合影响全球大尺度经向翻转环流和示踪剂分布。然而，人们对过去混合如何以及为什么发生变化知之甚少，也不知道这些变化对环流、气候和生物地球化学循环有什么影响。该项目将结合数值模拟和现有观测资料，研究现代和末次极盛期（LGM）海洋中的海洋混合。过去，只考虑了湍流源附近的混合（近场效应），但现在可以包括由内波或波/电流/涡流相互作用带走的离湍流源较远的混合（远场效应）。在中等复杂气候模式的全球粗分辨率海洋分量中，将探索新的准周期混合参数化概念。还将评估中尺度涡旋的参数化。该模型将根据现代海洋进行校准，包括物理和生物地球化学示踪剂分布，以及基于微观结构的扩散率估计。随后，将其应用于冰川海洋的一系列实验中，这些实验涵盖了强迫、环流状态和内波场潮汐能量输入的不确定性。冰川沉积物数据将用于评估模式模拟和检验关于分层、环流几何和潮汐对河床混合的影响以及南半球风变化对碳循环和大气二氧化碳的影响的假设。该项目将改进古气候和未来气候的建模，并促进物理海洋学家和古海洋学家之间的合作。带有用户指南和文档的新模型代码将在网上发布，并提供关于模型使用的网络研讨会。该项目将支持一名早期职业博士后研究员和一名学生。工作人员将参与当地博物馆和公共论坛的外联活动。末次冰期的混合和经向翻转环流仍有争议。北大西洋深水和南极底水之间界面的浅滩化和层积的增加是已提出的减少底水混合的两种机制。另一方面，由于海平面下降，潮汐能量输入从大陆架向深海的转移已经被假设为增加了潜流混合。远场混合效应的参数化将被纳入俄勒冈州立大学（OSU）版本的中等复杂性维多利亚大学（UVic）全球气候模式。利用现代观测资料调整到现代海洋条件，然后利用现有的古观测资料评估LGM的性能，将允许检查这些科学目标：研究LGM的底周期混合与现代量级的比较；电位差如何影响LGM MOC；以及这些影响对全球碳循环的影响。代表远场效应的参数化，在OSU-UVic模型中进行了测试和调整，也将被移植到社区地球系统模型（CESM）的模块化海洋模型（MOM6）的最新版本中，尽管CESM没有计划进行广泛的调整、测试和评估。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Small-scale mixing in the ocean interior affects the large-scale global meridional overturning circulation (MOC) and tracer distributions. However, little is known about how and why mixing has changed in the past, nor what the effects of those changes were on circulation, climate and biogeochemical cycles. This project will examine ocean mixing in the modern and last glacial maximum (LGM) ocean using a combination of numerical modeling and existing observations. In the past, only mixing near sources of turbulence have been considered (near-field effects), but mixing more distant from turbulence sources, carried away by internal waves or wave/current/eddy interactions (far field effects) are now possible to include. New parameterization concepts of diapycnal mixing will be explored in the global coarse-resolution ocean component of an intermediate complexity climate model. Parameterizations of mesoscale eddies will also be evaluated. The model will be calibrated for the modern ocean with modern observations including physical and biogeochemical tracer distributions, and microstructure-based diffusivity estimates. Subsequently, it will be applied to the glacial ocean in a suite of experiments that cover uncertainties in forcing, circulation state and tidal energy input to the internal wave field. Glacial sediment data will be used to evaluate the model simulations and test hypotheses regarding effects of stratification, circulation geometry and tides on diapycnal mixing and effects of southern hemisphere wind changes on the carbon cycle and atmospheric carbon dioxide. The project would improve modeling of paleoclimate and future climate, and foster collaborations between physical oceanographers and paleoceanographers. New model code with user guide and documentation will be posted online with a webinar on model use provided. The project will support an early career post-doctoral investigator and a student. Personnel will be involved in outreach activities at a local museum and in public discussion forums.Mixing and the meridional overturning circulation during the last glacial period remain controversial. Shoaling of the interface between North Atlantic Deep Water and Antarctic Bottom Water and increased stratification are two mechanisms that have been suggested to reduce diapycnal mixing. On the other hand, a shift of tidal energy input from the continental shelves to the deep ocean due to sea level lowering has been hypothesized to increase diapycnal mixing. A parameterization of far field mixing effects will be incorporated into the Oregon State University (OSU) version of the intermediate-complexity University of Victoria (UVic) global climate model. Tuning to modern ocean conditions using modern observations followed by assessment of LGM performance using available paleo observations will permit the examination of these science goals: to investigate how diapycnal mixing in the LGM compares to modern magnitudes; how potential differences may have affected the LGM MOC; and what the consequences of such effects would have been for the global carbon cycle. The parameterizations representing far field effects, tested and tuned in the OSU-UVic model, will also be ported to the newest version of the Modular Ocean Model (MOM6) of the Community Earth System Model (CESM), though extensive tuning, testing and evaluation with CESM is not planned.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.