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

合作研究：南大洋的 DIMES、双重和等重混合

• 批准号: 0622825
• 负责人: James Ledwell
• 金额: $ 284.83万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0622825&HistoricalAwards=false
• 关键词: Collaborative; Research; DIMES; Diapycnal; Isopycnal

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.

由于海洋容纳热量和二氧化碳的巨大能力，海洋倾覆在地球气候中起着控制作用。围绕南极洲的南洋在这种倾覆的循环中起着不成比例的作用，因为这是深水升到地面以将热和二氧化碳与大气交换的主要区域之一。尽管南极绕极电流（ACC）系统将深水带到表面，但动态约束抑制了子午交换。据信，海洋涡流在将水向南运输到深脊上的ACC上，从而由巨大的风向北驱动水。通过跨密度层混合来“短路”的程度对气候模型很重要，但未知。智慧优点：全球子午倾覆的概念模型和未来气候的数值预测的概念模型非常敏感，这些方法对代表整个南极循环循环的方法都非常敏感，在此处添加了浓度（ACC）（ACCASC）（ISOPYCN）。在南大洋中，均未以系统的方式测量二元性和异型混合。南大洋（Dimes）在南海（Dimes）中的杂质和等距混合实验的目标是在地下海洋中的密度表面（等距混合）以及跨这些密度层（DiapyCnal混合）的涡流混合，并确定这些过程如何取决于海洋规模动力学的数字循环，以确定循环的循环和循环。为了揭示ACC中工作中的这些过程，将在2008年初在ACC附近的ACC，60 s和110 W的ACC中释放出一个沿等速度表面的水的化学示踪剂和75个浮子。在同一时间将在同一时间释放the-Tracture T，S，S和速度的浮点。浮子和示踪剂将由ACC在SE太平洋相对光滑的底部携带，并在它们行驶时遍布电流和沿电流。一年后，示踪剂的前沿将开始越过德雷克通道的山脊进入斯科舍省。此时，将在示踪剂贴片的中心附近释放另外75个异植物浮子。用一系列声源测量的浮子的轨迹将用于研究和测量同型分散。示踪剂的传播将提供同配量和二细分散体的综合度量。涡流及其垂直结构将通过卫星高度计测量的海面高度，以及从研究容器中获取的水文剖面以及用示踪剂绘制的自动仪仪器。可以估计湍流的耗散耗散，将用基于船舶的自由落体剖面师测量，以研究混合的空间和时间尺度，并检查可疑的混合热点。剪切驾驶这种混合将通过自由落体的剖道师和特殊的浮子进行测量，并在表面和示踪剂层之间介绍的示踪剂和浮子。将提供混合结果，以帮助改善气候模型中混合的表示。此外，分析角色浮标将增加南大洋的Argo数据库。该项目将涉及博士后研究员，佛罗里达州立大学的研究生和Scripps海洋学研究所，并将为每年一到两个本科生提供研究机会。该项目是对美国Clivar（气候变异性和可预测性）计划的贡献。