Studies of Turbulence and Mixing in the Antarctic Circumpolar Current, a Continuation of DIMES

知识价值：南大洋的双极流和等极流混合实验(DIMES)是对南极绕极流(ACC)中海洋混合的研究，绕极流从西向东环绕南极洲大陆，位于其他大陆的南部。目前的系统在某种程度上是热量、二氧化碳和其他重要海洋成分在遥远的南方和海洋其他部分之间传输的障碍，混合过程在这些传输中发挥着重要作用。DIMES是一个由多名调查员合作的项目，由美国和英国的物理海洋学家领导。2009年初，在德雷克海峡以西2000多公里处的亚南极锋和ACC极锋之间的约1500米深的恒定密度表面上部署了被动示踪器和一系列水下浮标。2010年初，美国牵头的一艘研究邮轮对示踪剂、湍流水平以及控制湍流产生的速度和密度分布进行了采样，2011年和2012年，由英国牵头的其他研究邮轮继续进行采样，示踪剂穿过德雷克航道，进入斯科舍海，越过超过3000公里的北斯科舍海脊。初步结果表明，在德雷克海峡以西海底相对平坦的地方，赤潮，即垂直混合，并不比开阔海洋的大多数其他区域大。相比之下，在Drake Passage的崎岖地形上有强烈的速度切变和强烈的湍流水平，在Drake Passage和Drake Passage以东的示踪剂的日扩散系数是Drake Passage的10倍以上。DIMES现场计划继续进行，美国团队在斯科舍海收集了新的速度和湍流数据。预计该示踪剂将至少在2014年初之前继续通过斯科舍海。英国的合作伙伴计划于2013年初和2014年初在北斯科舍海岭和斯科舍海东部和中部的邮轮上对示踪剂进行采样。目前的项目将在2012年底和2013年底继续在德雷克航道的另外两次美国主导的邮轮上使用示踪器的时间序列。根据示踪剂观测、中性浮力漂浮物和数值模型估计的通过斯科舍海的轨迹将被用来准确估计示踪剂的混合速度并确定混合集中的位置。在2013年的巡航中，将测量沿着ACC和德雷克航道海脊的高分辨率横断面上的速度和湍流场，以确定海脊下游多远的地方混合得到增强，并验证通过打破粗糙地形上的气流产生的背风波来增强混合的假设。两名研究生将继续接受这个项目的培训，他们将成为海洋湍流及其产生过程的专家。迪梅斯的工作最终是出于理解全球海洋颠覆环流的需要。这种环流控制着巨大的海洋水库内热量和二氧化碳的运输和储存，因此在调节地球-S气候方面发挥了重要作用。了解环流及其对外部力量的反应如何变化，对于理解过去的气候变化和未来气候可能如何变化是必要的，因此对人类福祉非常重要。DIMES项目收集和分析的数据将在项目结束时汇编并公开。DIMES项目是由美国CLIVAR(气候可变性和可预测性)计划赞助的过程实验。

Intellectual Merit: The Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) is a study of ocean mixing in the Antarctic Circumpolar Current (ACC) which runs west to east all around the continent of Antarctica, south of the other continents. This current system is somewhat of a barrier to transport of heat, carbon dioxide and other important ocean constituents between the far south and the rest of the ocean, and mixing processes play an important role in those transports. DIMES is a multi-investigator cooperative project, led by physical oceanographers in the U.S. and in the U.K. A passive tracer and an array of sub-surface floats were deployed early in 2009 more than 2000 km west of Drake Passage on a surface of constant density about 1500 m deep between the Sub Antarctic Front and the Polar Front of the ACC. In early 2010 a U.S. led research cruise sampled the tracer, turbulence levels, and the velocity and density profiles that govern the generation of that turbulence, and additional U.K. led research cruises in 2011 and 2012 continue this sampling as the tracer has made its way through Drake Passage, into the Scotia Sea, and over the North Scotia Ridge, a track of more than 3000 km. The initial results show that diapycnal, i.e., vertical, mixing west of Drake Passage where the bottom is relatively smooth is no larger than in most other regions of the open ocean. In contrast, there are strong velocity shears and intense turbulence levels over the rough topography in Drake Passage and diapycnal diffusivity of the tracer more than 10 times larger in Drake Passage and to the east than west of Drake Passage.The DIMES field program continues with the U.S. team collecting new velocity and turbulence data in the Scotia Sea. It is anticipated that the tracer will continue passing through the Scotia Sea until at least early 2014. The U.K. partners have scheduled sampling of the tracer on cruises at the North Scotia Ridge and in the eastern and central Scotia Sea in early 2013 and early 2014. The current project will continue the time series of the tracer at Drake Passage on two more U.S. led cruises, in late 2012 and late 2013. Trajectories through the Scotia Sea estimated from the tracer observations, from neutrally buoyant floats, and from numerical models will be used to accurately estimate mixing rates of the tracer and to locate where the mixing is concentrated. During the 2013 cruise the velocity and turbulence fields along high-resolution transects along the ACC and across the ridges of Drake Passage will be measured to see how far downstream of the ridges the mixing is enhanced, and to test the hypothesis that mixing is enhanced by breaking lee waves generated by flow over the rough topography.Broader Impacts: DIMES (see web site at http://dimes.ucsd.edu) involves many graduate students and post-doctoral researchers. Two graduate students, who would become expert in ocean turbulence and the processes generating it, will continue be trained on this project. The work in DIMES is ultimately motivated by the need to understand the overturning circulation of the global ocean. This circulation governs the transport and storage of heat and carbon dioxide within the huge oceanic reservoir, and thus plays a major role in regulating the earth?s climate. Understanding the circulation and how it changes in reaction to external forces is necessary to the understanding of past climate change and of how climate might change in the future, and is therefore of great importance to human well-being. The data collected and analyzed by the DIMES project will be assembled and made publicly available at the end of the project.The DIMES project is a process experiment sponsored by the U.S. CLIVAR (Climate variability and predictability) program.