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(MOC)和示踪剂分布。然而，关于混合在过去如何以及为什么发生变化，以及这些变化对循环、气候和生物地球化学循环的影响，我们知之甚少。该项目将利用数值模拟和现有观测相结合的方法，研究现代和末次冰盛期(LGM)海洋中的海洋混合。过去，只考虑湍流源附近的混合(近场效应)，但现在可以考虑被内波或波/流/涡相互作用(远场效应)带走的、离湍流源更远的混合。在一个中等复杂性气候模式的全球粗分辨率海洋部分，将探索日周期混合的新的参数化概念。还将评估中尺度涡旋的参数化。该模型将通过现代观测，包括物理和生物地球化学示踪分布，以及基于微观结构的扩散系数估计，为现代海洋进行校准。随后，将在一系列实验中将其应用于冰川海洋，这些实验涵盖了强迫、环流状态和输入到内波场的潮汐能量的不确定性。冰川沉积物数据将用于评估模型模拟和检验关于层化、环流几何形状和潮汐对昼夜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。该项目将改进对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型号代码将在网上发布，并提供关于型号使用的网络研讨会。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的外展活动和公共论坛。混合和上一次冰川时期的子午线颠覆环流仍然存在争议。北大西洋深水和南极底层水之间的界面变浅和层化增加是减少昼夜混合的两种机制。另一方面，由于海平面下降，潮汐能量输入从大陆架转移到深海，这被假设为增加了昼夜混合。远场混合效应的参数化将被纳入到俄勒冈州立大学(OSU)版本的中等复杂性的维多利亚大学(UVic)全球气候模式中。利用现代观测调整到现代海洋条件，然后利用现有的古观测对末次盛冰期的表现进行评估，将使我们能够审查这些科学目标：调查末次盛冰期的昼夜混合如何与现代量级进行比较；位势差异可能如何影响末次盛冰期的MOC；以及这种影响将对全球碳循环产生什么后果。代表远场效应的参数表示，在OSU-UVIC模式中测试和调整，也将被移植到最新版本的社区地球系统模式(CESM)的模块海洋模式(MOM6)，尽管没有计划使用CESM进行广泛的调整、测试和评估。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.