Collaborative Research: DIMES, Diapycnal and Isopycnal Mixing in the Southern Ocean

海洋的翻转环流在地球气候中起着支配作用，因为海洋具有巨大的容纳热量和二氧化碳的能力。环绕南极洲的南大洋在这一翻转环流中发挥了不成比例的作用，因为这是深层沃茨上升到表面与大气交换热量和二氧化碳的主要区域之一。虽然南极绕极流（ACC）系统将深层水带到表层，但动力学约束抑制了南极绕极流交换。据信，海洋涡旋在将水向南输送穿过深脊上方的ACC方面发挥了主导作用，为强风向北输送的水提供了补给。在何种程度上，这种等密圈环流是“短路”的混合密度层是很重要的气候models.Intellectual优点：概念模型的全球纬向翻转和未来气候的数值预测是非常敏感的方法来表示mixingalong和整个南极绕极流（ACC），在等密圈是陡峭的倾斜。在南大洋，无论是横密度混合还是等密度混合都没有系统地测量过。南大洋底膜和等密度混合实验（DIMES）的目标是测量地下海洋中沿着密度表面（等密度混合）和跨越这些密度层（底膜混合）的涡旋混合，并确定这些过程如何依赖于更大尺度的海洋动力学，以便它们可以在海洋环流和气候的数值模型中得到正确的表示。为了揭示ACC中的这些工作过程，将于2008年初在ACC近1300 m深度、60 S和110 W处释放一种化学示踪剂和75个沿等密度面跟踪水的浮子。测量示踪云内部和上方的精细结构T、S和速度的浮子将同时释放。漂浮物和示踪剂将由ACC携带在东南太平洋相对光滑的底部，在它们行进时横跨并沿着水流传播。一年后，示踪剂的前缘将开始越过德雷克海峡的山脊进入斯科舍海。另外75个等密度浮标将在此时在示踪剂补丁的中心附近释放。用声源阵列声学测量的浮标轨迹将用于研究和测量等密度线散布。示踪剂的扩散将给出等密度和透密度弥散的综合测量。将利用卫星高度计测量的海面高度，以及从研究船和携带示踪剂的自主仪器上取得的水文剖面图，研究涡流场及其垂直结构。湍流耗散，从其中可以估计diapycnal混合，将测量船基自由降落剖面仪研究混合的空间和时间尺度，并检查可疑的混合热点。剪切驱动这种混合将通过自由下落剖面仪和与示踪剂一起漂移的特殊浮子以及在表面和示踪剂层之间剖面的浮子进行测量。更广泛的影响：DIMES将部署各种仪器，包括微观结构和精细结构剖面仪以及等密度线跟踪自主浮子，其中一些是首次在南大洋使用。将提供混合结果，以帮助改进气候模式中混合的表示。此外，对DIMES浮标进行剖面分析将扩大Argo南大洋数据库。该项目将涉及一名博士后研究员、佛罗里达州立大学和斯克里普斯海洋学研究所的研究生，并将每年为一到两名本科生提供研究机会。该项目是对美国CLIVAR（气候变化和可预测性）计划的贡献。

The overturning circulation of the ocean plays a governing role in the earth's climate because of the enormous capacity of the ocean to hold heat and carbon dioxide. The Southern Ocean, which surrounds Antarctica, plays a disproportionate role in this overturning circulation because this is one of the main areas where deep waters rise to the surface to exchange heat and carbon dioxide with the atmosphere. Although the Antarctic Circumpolar Current (ACC) system brings deep water to the surface, dynamical constraints inhibit meridional exchanges. Ocean eddies are believed to play a dominant role in transporting water south across the ACC above deep ridges, feeding water driven northward by the intense winds. The extent to which this Isopycnal circulation is "short-circuited" by mixing across density layers is important to climate models but is unknown.Intellectual Merit: Conceptual models of global meridional overturning and numerical predictions for future climate are strongly sensitive to the methods used to represent mixingalong and across the Antarctic Circumpolar Current (ACC), where isopycnals are steeply tilted. Neither diapycnal nor isopycnal mixing has been measured in the Southern Ocean in a systematic way. The goals of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) are to measure eddy mixing along density surfaces in the subsurface ocean (isopycnal mixing), and across those density layers (diapycnal mixing), and to determine how those processes depend on the larger scale dynamics of the ocean, so that they can be properly represented in numerical models of ocean circulation and of climate. To reveal these processes at work in the ACC, a chemical tracer and 75 floats that follow the water along isopycnal surfaces will be released in the ACC near 1300 m depth, 60 S, and 110 W, early in 2008. Floats that measure fine-structure T, S, and velocity within and above the tracer cloud will be released at the same time. The floats and tracer will be carried by the ACC over the relatively smooth bottom of the SE Pacific, spreading both across and along the current as they travel. After a year, the leading edge of the tracer will just start to pass over the ridges of Drake Passage into the Scotia Sea. Another 75 isopycnal floats will be released near the center of the tracer patch at this time. Trajectories of the floats, measured acoustically with an array of sound sources, will be used to study and to measure isopycnal dispersion. Spreading of the tracer will give integrated measures of both isopycnal and diapycnal dispersion. The eddy field, and its vertical structure, will be studied with sea surface height measured by satellite altimeters, and with hydrographic profiles taken from research vessels and from autonomous instrumentsdrifting with the tracer. Turbulent dissipation, from which diapycnal mixing can be estimated, will be measured with ship-based free-falling profilers to study the spatial and temporal scales of the mixing and to examine suspected hot spots of mixing. Shear driving this mixing will be measured with the free-falling profilers and with special floats drifting with the tracer and floats that profile between the surface and the tracer layer.Broader Impact: DIMES will deploy a variety of instruments including microstructure and finestructure profilers and and isopycnal-following autonomous floats, some for the first time in Southern Ocean. The mixing results will be made available to aid in improving representations of mixing in climate models. In addition, profiling DIMES floats will augment the Argo database for the Southern Ocean. The project will involve a postdoctoral investigator, graduate students at Florida State University and Scripps Institution of Oceanography and will offer research opportunities to one to two undergraduates per year. This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) program.