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

南大洋的南极绕极流（ACC）连接着世界上所有主要的海洋。因此，ACC对于热量，淡水和其他影响海洋生态系统的碳和营养物质的传输和交换非常重要。南大洋对气候变化特别敏感，对过去几十年来风的增加和变化以及ACC核心的显着变暖做出反应。然而，我们仍然不了解是什么控制了南大洋周围流动的总体强度，或者它所携带的流量和属性如何随着海洋深度而变化。拟议工作的目的是利用南大洋德雷克海峡部分的海流、温度和盐份的20年时间序列，研究可能在一系列时间和空间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将如何应对未来气候变化的预测。由于数据稀少，南大洋在气候系统中与全球变暖影响和二氧化碳吸收有关的作用一般使用全球气候模型来研究。涡动效应必须在粗分辨率模式中参数化，并且参数化通常在非常有限的观测数据库上进行测试。在德雷克通道的细尺度观测允许这些参数化的评价，并提供线索，识别模型错误或丢失的物理，以便建立在ACC系统内的过程和动态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。该研究旨在了解影响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：描述内波场的特征，并根据速度、温度和盐度观测结果推断混合，以了解是什么决定混合的垂直和水平分布;（2）能量和输送：确定1000米高空ACC的平均和随时间变化的输送，并确定可变性如何与风强迫和涡旋存在的变化相关;以及（3）性质搅动：了解涡旋能量分布及其与地形特征、ACC锋、风和浮力强迫的关系。拟议的分析将利用正在进行的船上温度、盐度和流速剖面测量，这些测量是过去20年来从德雷克海峡的美国南极供应研究船上全年例行收集的。在同一平台上以类似的高分辨率时间和空间尺度进行同期测量，对于探索驱动南大洋环流的过程的统计特征、特点、机制和影响有很大好处。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，以帮助解释船上时间序列。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.