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) 上，热量和动量通量以及其他动力量确定了整个南大洋的热量收支，控制着 ACC 的强度及其重要的海洋间交换，并且可以说控制着世界海洋的主要垂直密度结构。然而，理论概念、数值模型和稀疏的观测记录对于 ACC 的转移机制和规模给出了相互矛盾的观点。在南纬 55° 以南，这个谜题更加混乱，因为与风驱动的埃克曼输送及其平衡的经向翻转环流相关的热通量（在低纬度地区很强且占主导地位）变得很弱。在该纬度，它落入由平均流和涡流产生的交叉锋面过程来完成热预算。尤其令人费解的是通量如何穿过几个海洋锋面，例如从亚南极锋面到极地锋面再到南大西洋锋面。在 ACC 周围的其他地点迫切需要对热和动量通量以及混合进行观测，以便为全球气候建模工作提供信息。特别令人感兴趣的是海洋经向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，将部署一系列海流和压力记录倒置回声测深仪（CPIES），为期两年，以观察和量化ACC在南大洋中南太平洋区乌金采夫断裂带附近流动时穿过ACC的浮力、热量、动量和位涡的交换。 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，是因为三个主要锋面（亚南极锋面、极地锋面和南部 ACC 锋面）在向赤道偏转时会紧密地汇聚在一起，遇到复杂的浅脊并在背风处表现出强烈的涡流变化。因此，乌金采夫断裂带可能是平均通量和涡通量结合穿过整个 ACC 系统的位置。该项目是一个由法国和韩国科学家组成的团队的国际合作，其目标是在该地区部署高海流计系泊装置并进行 CTD 调查。 智力优点：中尺度涡流被认为在 ACC 动力学中发挥着关键作用，涡流的跨锋面交换形成了经向翻转环流的基础。最近的研究表明，这种交换发生在测深障碍物背风处发现的“热点”局部，但从海洋测量中直接估计涡流通量在全球范围内，尤其是在南大洋内，都很少。提出了两种电流和压力记录倒置回声测深仪（CPIES）阵列。北部阵列位于亚南极锋和极锋（它们紧密相邻）之间的强涡流区域内，南部阵列位于南 ACC 锋附近，历史上很少进行测量。这些地点已被选为涡流和平均横向锋面通量可能最强的候选地点。 CPIES 阵列将量化涡流在整个水柱中重新分配热量、动量和能量的作用。法国和韩国的高系泊装置将提供固定水平的水流和温度测量，从而提供平均和涡流的补充估计。获得的有关涡流的知识对于概念性理解控制 ACC 和驱动翻转环流的动态平衡以及定量指导未来的建模工作至关重要。更广泛的影响：根据 CPIES 测量确定的质量控制的密度和电流每日时间序列将得到广泛传播。结合海流计系泊处的数据，将产生适合验证数值模型和改进动量、热量和位涡的正面通量预测的数据产品。通过弹出式数据胶囊远程传输 CPIES 数据的新技术将在强流、公海状态的偏远南大洋进行测试。双压力传感器将安装在两个 CPIES 中，以研究这些传感器的校准漂移。一名工程本科生将加入罗德岛大学技术团队，协助CPIES升级和准备工作。