Cross-Frontal Fluxes in the Antarctic Circumpolar Current near Udintsev Fracture Zone

乌金采夫断裂带附近南极绕极流的锋面通量

• 批准号: 1358470
• 负责人: D. Randolph Watts
• 金额: $ 89.54万
• 依托单位: University of Rhode Island
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-03-15 至 2019-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1358470&HistoricalAwards=false
• 关键词: Cross; Frontal; Fluxes; Antarctic; Circumpolar

Overview: Across the Antarctic Circumpolar Current (ACC), fluxes of heat and momentum and other dynamical quantities establish the heat budget for the whole Southern Ocean, govern the strength of the ACC and its vital inter-ocean exchanges, and arguably govern the main vertical density structure of the world oceans. Yet, theoretical concepts, numerical models, and the sparse observational records give conflicting views of the mechanisms and magnitude of transfers across the ACC. South of about 55° S the puzzle is further confounded, because the heat fluxes associated with wind-driven Ekman transport and its counterbalancing meridional overturning circulation, that are strong and dominant at lower latitudes, become weak. At that latitude, it falls to cross-frontal processes arising from mean and eddying flow to complete the heat budget. It is particularly puzzling how fluxes cross the several ocean fronts, e.g., from Subantarctic Front to Polar Front to Southern ACC Front. Observations of heat and momentum fluxes and mixing are vitally needed at additional sites around the ACC to inform global climate modeling efforts. Of particular interest is how the oceanic meridional overturning circulation absorbs and redistributes heat and carbon that is critical to the earth's climate. In this study, an array of Current and Pressure recording Inverted Echo Sounders (CPIES) will be deployed for a period of two years to observe and quantify exchanges of buoyancy, heat, momentum and potential vorticity across the ACC as it flows near the Udintsev Fracture Zone in the central South Pacific sector of the Southern Ocean. The CPIES have been shown to be particularly well suited for these measurements. The Udintsev Fracture Zone has been selected because the three main fronts (Subantarctic Front, Polar Front, and Southern ACC Front) converge closely together as they deflect equatorward where they encounter complex shallower ridges and exhibit strong eddy variability in the lee. Therefore, the Udintsev Fracture Zone emerges as a likely location for mean and eddy fluxes to combine to cross the entire ACC system. This project is an international collaboration with a team of French and Korean scientists with complementary goals to deploy tall current meter moorings and conduct CTD surveys in this region.Intellectual Merit: Mesoscale eddies are thought to play a key role in ACC dynamics, with cross-frontal exchange by eddies forming the underpinning of the meridional overturning circulation. Recent studies suggest that this exchange occurs locally in "hot spots" found in the lee of bathymetric obstacles, yet direct estimates of eddy fluxes from ocean measurements are scarce, both globally and especially within the Southern Ocean. Two Current and Pressure recording Inverted Echo Sounders (CPIES) arrays are proposed. The northern array is within the strong eddy region between the Subantarctic Front and Polar Front (where they neighbor closely), and the southern array is located near the Southern ACC Front where historically few measurements have been made. These sites have been selected as candidates where eddy and mean cross-frontal fluxes are likely to be strongest. The CPIES arrays will quantify the role of eddies in redistributing heat, momentum and energy throughout the full water column. The French and Korean tall moorings will provide measurements of currents and temperature at fixed levels, providing complementary estimates of mean and eddy fluxes. The knowledge gained regarding eddy fluxes is crucially important for conceptual understanding of the dynamical balances that control the ACC and drive the overturning circulation and to quantitatively guide future modeling efforts.Broader Impacts: A quality-controlled daily time series of density and currents determined from the CPIES measurements will be disseminated broadly. Combined with data from the current meter moorings, data products suitable for validating numerical models and improving prediction of the cross-frontal flux of momentum, heat, and potential vorticity will be produced. New technology for remote transmission of CPIES data via pop-up data capsules will be tested for use in the strong current, high sea state remote Southern Ocean. Dual pressure sensors will be installed in two CPIES to investigate the calibration-drift of these sensors. An engineering undergraduate student will join the University of Rhode Island technical team and assist CPIES upgrades and preparations.

概述：在南极绕极流（ACC）中，热量和动量以及其他动力学量的通量确定了整个南大洋的热量收支，决定了ACC的强度及其重要的海洋间交换，并且可以说决定了世界海洋的主要垂直密度结构。然而，理论概念、数值模式和稀疏的观测记录对横跨ACC的传输机制和量级给出了相互矛盾的观点。在南纬55°以南，这个谜团进一步被混淆，因为与风驱动的Ekman传输及其平衡的纬向翻转环流相关的热通量在低纬度地区很强并占主导地位，变得很弱。在这个纬度上，它福尔斯落在由平均流和涡旋流产生的跨锋面过程上，以完成热量收支。特别令人困惑的是，通量如何跨越几个海洋锋，例如，从亚季风锋到极锋再到南ACC锋。在ACC周围的其他地点观测热量和动量通量以及混合是至关重要的，以告知全球气候建模工作。特别令人感兴趣的是海洋赤道翻转环流如何吸收和重新分配对地球气候至关重要的热量和碳。在这项研究中，一个阵列的电流和压力记录倒置回声探测器（CPIES）将部署为期两年的时间，以观察和量化交换的浮力，热量，动量和潜在的涡度在整个ACC，因为它附近的乌丁采夫断裂带在南太平洋中部的南太平洋部门。CPIES已被证明特别适合这些测量。之所以选择乌金采夫断裂带，是因为三个主要锋（亚南极锋、极锋和南ACC锋）在向赤道偏转时紧密会聚在一起，在那里它们遇到复杂的浅脊，并在背风面表现出强烈的涡流变化。因此，乌金采夫断裂带成为平均通量和涡动通量联合收割机穿过整个ACC系统的可能位置。这个项目是一个国际合作与法国和韩国的科学家团队互补的目标，部署高流速计系泊和CTD调查在这个区域。智力优点：中尺度涡被认为是在ACC动力学中发挥关键作用，跨锋面交换的涡形成的纬向翻转环流的基础。最近的研究表明，这种交换发生在局部的“热点”，发现在背风的水深障碍，但直接估计的涡流通量从海洋测量是稀缺的，在全球范围内，特别是在南大洋。提出了两种海流和气压记录型反向回声测深仪（CPIES）阵列。北方阵列位于亚南极锋和极锋之间的强涡流区域内（它们紧密相邻），南方阵列位于南ACC锋附近，历史上很少进行测量。这些网站已被选为候选人的涡和平均横锋通量可能是最强的。CPIES阵列将量化涡旋在整个水柱中重新分配热量、动量和能量的作用。法国和韩国的高大系泊设施将提供固定水平的海流和温度测量，提供平均通量和涡流通量的补充估计。关于涡通量获得的知识是至关重要的概念理解的动态平衡，控制ACC和驱动翻转环流，并定量指导未来的modeling efforts.Broader Impacts：一个质量控制的每日时间序列的密度和电流确定的CPIES测量将广泛传播。结合海流计系泊的数据，将产生适合于验证数值模型和改进跨锋面动量、热量和位涡通量预测的数据产品。将测试通过弹出式数据舱远程传输CPIES数据的新技术，以便在海流强、海况高的偏远南大洋使用。将在两个CPIES中安装双压力传感器，以研究这些传感器的校准漂移。一名工程本科生将加入罗得岛大学的技术团队，协助CPIES升级和准备工作。