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

概述：在整个南极绕极洋流(ACC)，热量、动量通量和其他动力学量建立了整个南大洋的热量收支，支配着ACC的强度及其重要的海洋间交换，并可以说支配着世界海洋的主要垂直密度结构。然而，理论概念、数字模型和稀少的观测记录给出了关于通过ACC转移的机制和大小的相互矛盾的观点。在约55°S以南，这个谜团变得更加混乱，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变得弱，这两个热通量在低纬地区是强的和主要的。在这个纬度，它下降到由平均和涡流引起的跨锋面过程，以完成热量收支。尤其令人费解的是，通量是如何跨越几个大洋锋面的，例如，从亚南极锋面到极地锋面再到行政协调中心南部锋面。在行政协调会周围的更多地点，迫切需要对热量和动量通量和混合进行观测，以便为全球气候模拟工作提供信息。尤其令人感兴趣的是，海洋经向颠覆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，将部署一组电流和压力记录反向回声探测仪(CPIES)，为期两年，以观测和量化在南太平洋中部Udintsev断裂带附近流动的ACC的浮力、热量、动量和位涡的交换。CPIES已被证明特别适合于这些测量。乌丁采夫断裂带之所以被选中，是因为三个主要锋面(亚南极锋面、极地锋面和南ACC锋面)在向赤道偏转时紧密汇聚在一起，在那里它们遇到复杂的浅脊，并在背风处表现出强烈的涡旋变化。因此，乌丁采夫断裂带很可能是平均通量和涡流通量结合在一起穿过整个ACC系统的地方。该项目是与法国和韩国科学家团队的国际合作，目标相辅相成，目的是在该地区部署大流速计系泊设备并进行CTD调查。智力优势：中尺度涡旋被认为在ACC动力学中发挥关键作用，通过涡旋进行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，这种交换发生在水深测量障碍物背风处的“热点”区域，但对海洋测量的涡流通量的直接估计很少，在全球范围内都是如此，在南大洋尤其如此。提出了两种电流和压力记录反向回声测深(CPIES)阵列。北极阵位于亚北极锋和极锋之间的强涡区域内(它们在那里很接近)，而南阵位于历史上很少进行测量的南极锋附近。这些地点被选为涡旋和平均跨锋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设施将提供固定水平的海流和温度测量，提供对平均和涡流通量的补充估计。获得的有关涡旋通量的知识对于从概念上理解控制ACC和驱动颠覆环流的动态平衡以及定量指导未来的模拟工作至关重要。广泛的影响：由CPIES测量确定的质量控制的密度和电流的每日时间序列将被广泛传播。结合来自海流计系泊的数据，将产生适合于验证数值模式和改进跨锋面动量、热量和位涡通量预报的数据产品。通过弹出数据舱远程传输CPIES数据的新技术将被测试用于强流、高海况的遥远的南大洋。双压力传感器将安装在两个CPIES中，以调查这些传感器的校准漂移。一名工程学本科生将加入罗德岛大学的技术团队，协助CPIES升级和准备工作。

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.