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

合作研究：现代和冰川海洋中的混合和经向翻转环流

• 批准号: 2049499
• 负责人: Gokhan Danabasoglu
• 金额: $ 8.32万
• 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: 2021
• 资助国家: 美国
• 起止时间: 2021-06-15 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2049499&HistoricalAwards=false
• 关键词: Collaborative; Research; Mixing; Meridional; Overturning

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.

海洋内部中的小规模混合会影响大规模的全球子午倾覆循环（MOC）和示踪剂分布。然而，关于过去如何以及为什么混合发生变化，也不了解这些变化对循环，气候和生物地球化学周期的影响。该项目将使用数值建模和现有观测值的结合来检查现代和最后冰川最大（LGM）海洋中的海洋混合。过去，仅考虑了附近湍流来源的混合（近场效应），但是将内部波浪或波/电流/涡流相互作用（远场效应）带走的湍流来源更遥远。 Diapynal混合的新参数化概念将在中间复杂性气候模型的全球粗分辨率海洋组件中探索。也将评估中尺度涡流的参数化。该模型将通过现代海洋进行校准，包括现代观测，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值。随后，它将在一系列实验中应用于冰川海洋，这些实验涵盖了强迫，循环状态和潮汐能输入到内波场中的不确定性。冰川沉积物数据将用于评估模型模拟和测试假设，内容涉及分层，循环几何形状和潮汐对二比混合的影响以及南半球风变对碳循环和大气二氧化碳的影响。该项目将改善古气候和未来气候的建模，并促进物理海洋学家和古平均学者之间的合作。使用用户指南和文档的新模型代码将在网上发布有关提供的模型使用的网络研讨会。该项目将支持早期职业博士后调查员和学生。人员将在当地博物馆和公共讨论论坛上参与外展活动。在最后一个冰川时期的混合和子午线推翻循环仍然存在争议。北大西洋深水和南极底水之间的界面和增加分层的浅滩是两种机制，这些机制被认为是减少二比混合的两种机制。另一方面，由于降低了海平面的潮汐能量输入从大陆货架转移到深海，以增加二比混合。遥远的现场混合效应的参数化将纳入俄勒冈州立大学（OSU）版本的维多利亚大学（UVIC）全球气候模型。使用现代观察结果对现代海洋条件进行调整，然后使用可用的古观察评估LGM性能，将允许检查这些科学目标：研究LGM中的Diapycaln混合与现代大小相比如何；潜在差异如何影响LGM MOC；这种影响的后果将带来全球碳周期。 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 标准。