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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

基本信息

批准号：
2049357
负责人：
Andreas Schmittner
金额：
$ 61.26万
依托单位：
Oregon State University
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=2049357&HistoricalAwards=false
关键词：
Collaborative Research Mixing Meridional Overturning

项目摘要

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.

海洋内部的小尺度混合影响大尺度全球纬向翻转环流和示踪剂的分布。然而，人们对混合在过去是如何以及为什么发生变化的知之甚少，也不知道这些变化对环流、气候和地球化学循环的影响。该项目将使用数值模拟和现有观测相结合的方法研究现代和末次冰期最大（LGM）海洋中的海洋混合。在过去，只考虑了湍流源附近的混合（近场效应），但现在可以包括离湍流源更远的混合，由内波或波/流/涡流相互作用（远场效应）带走。将在一个中等复杂性气候模式的全球粗分辨率海洋组成部分中探索新的横尺度混合参数化概念。中尺度涡旋的参数化也将被评估。该模型将校准现代海洋的现代观测，包括物理和地球化学示踪剂分布，和微结构为基础的扩散估计。随后，它将在一系列实验中应用于冰川海洋，这些实验涵盖强迫、环流状态和内波场潮汐能输入的不确定性。冰川沉积物数据将用于评价模型模拟，并检验关于分层、环流几何形状和潮汐对纵贯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。该项目将改善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。新的模型代码以及用户指南和文档将在线发布，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的外展活动和公共讨论论坛。末次冰期的混合和经向翻转环流仍然存在争议。北大西洋深层水和南极底层水之间的界面变浅和层化增加是两种被认为可以减少贯向混合的机制。另一方面，由于海平面下降，潮汐能输入从大陆架向深海转移，这被假设为增加了底辟混合。远场混合效应的参数化将纳入俄勒冈州州立大学（OSU）版本的中等复杂性维多利亚大学（UVic）全球气候模式。调整到现代海洋条件下使用现代观测，然后使用现有的古观测评估LGM的性能将允许检查这些科学目标：调查如何在LGM的横周期混合相比，现代的规模;潜在的差异可能会影响LGM MOC;和什么样的后果，这种影响会对全球碳循环。在OSU-UVic模型中测试和调整的代表远场效应的参数化也将移植到社区地球系统模型（CESM）的模块化海洋模型（MOM 6）的最新版本中，尽管进行了广泛的调整，该奖项反映了NSF的法定使命，并被认为是值得通过利用基金会的智力价值和更广泛的影响审查标准。