Identifying Drivers of the Meridional Overturning Circulation from Observations in Drake Passage

南大洋的南极绕极流（ACC）连接着世界上所有的主要海洋。因此，ACC对于热量、淡水以及影响海洋生态系统的碳和营养物质等其他属性的转移和交换非常重要。南大洋对气候变化特别敏感，它对过去几十年里风的增加和转移以及ACC核心的显著变暖做出了反应。然而，当洋流在南大洋周围流动时，是什么控制着洋流的整体强度，以及洋流及其所携带的特性如何随着海洋的深度而变化，我们仍然知之甚少。这项提议的工作旨在利用南大洋德雷克海峡20年的洋流、温度和盐的时间序列，研究可能在一系列时空尺度上控制强度和深度分布变化的过程。这项工作将改善我们对这一关键地区如何应对未来气候变化的预测。由于数据稀少，一般使用全球气候模式来研究南大洋在气候系统中与全球变暖和二氧化碳吸收的影响有关的作用。在粗分辨率模型中，涡效应必须参数化，而参数化通常是在非常有限的观测数据库上进行测试的。德雷克通道的精细尺度观测允许对这些参数化进行评估，并为识别模型错误或缺失的物理提供线索，从而建立对ACC系统内过程和动力学的详细模型表示的信心。该项目增加了代表性不足的群体对科学和技术的参与。它通过研究生的参与来促进培训和学习。本研究旨在了解南大洋环流的物理过程，重点关注德雷克海峡内的三个中心研究主题：(1)混合：表征内波场，并从速度、温度和盐度观测推断混合，以了解混合的垂直和水平分布的决定因素；(2)能量和输运：确定高空1000 m环流的平均输运和时变输运，并确定其变率与风强迫变化和涡旋存在的关系；(3)性质搅拌：了解涡旋能量分布及其与地形特征、ACC锋面、风和浮力的关系。拟议的分析将利用正在进行的船上温度、盐度和速度剖面的测量数据，这些数据是过去20年里，美国南极补给队（United States Antarctic Supply）的研究船在德雷克海峡（Drake Passage）全年例行收集的。在同一平台上以相似的高分辨率时间和空间尺度进行同期测量，为探索驱动南大洋环流的过程的统计特征、特征、机制和影响提供了显著的好处。来自Argo浮标和卫星风和海面高度数据的额外测量将提供区域背景，以帮助解释船上的时间序列。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。

The Antarctic Circumpolar Current (ACC) in the Southern Ocean links all the major oceans of the world. The ACC is therefore very important for the transferring and exchanging of heat, freshwater and other properties like carbon and nutrients that impact the marine ecosystem. The Southern Ocean is particularly sensitive to climate variability, responding to winds that have increased and shifted over the past several decades and a significant warming in the core of the ACC. Yet we still have little understanding about what controls the overall strength of the current as it flows around the Southern Ocean or how the flow and the properties it carries change with depth in the ocean. The proposed work aims to study the processes that might control the changes in strength and depth distribution over a range of temporal and spatial scales using a 20-year time series of currents, temperature and salt in the Drake Passage sector of the Southern Ocean. This work will improve our predictions of how this critical region will respond to future climate change. Given the sparsity of data, the Southern Ocean's role in the climate system in relationship to the impact of global warming and the uptake of carbon dioxide are generally examined using global climate models. Eddy effects must be parameterized in coarse-resolution models, and the parameterizations are generally tested on a very limited observational database. The fine-scale observations in Drake Passage allow for an evaluation of these parameterizations and provide clues for identifying model errors or missing physics so as to build confidence in the detailed model representation of processes and dynamics within the ACC system. The project increases the participation of underrepresented groups in science and technology. It promotes training and learning through the involvement of a graduate student.The research aims to understand the physical processes that contribute to the circulation in the Southern Ocean, focusing on three central research themes within Drake Passage: (1) Mixing: Characterize the internal wave field and infer mixing from velocity, temperature and salinity observations to understand what determines the vertical and horizontal distribution of mixing; (2) Energy and transport: Determine the mean and time-varying transport of the ACC in the upper 1000 m and determine how the variability relates to changes in wind forcing and presence of eddies; and (3) Property stirring: Understand the eddy energy distribution and its relationship to topographic features, ACC fronts, wind and buoyancy forcing. The proposed analysis will take advantage of underway shipboard measurements of temperature, salinity and velocity profiles that have been routinely collected year-round from the United States Antarctic Supply research vessels in the Drake Passage over the past two decades. Contemporaneous measurements at similar high-resolution time and space scales from the same platform offer significant benefit for exploring the statistical characteristics, features, mechanisms and impacts of the processes that drive the Southern Ocean circulation. Additional measurements from Argo floats and satellite wind and sea surface height data will provide regional context to help interpret the shipboard time series.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.