Mesoscale Eddies at the Antarctic Margins

海洋环流就像一个拼图游戏。在海洋中，无数小尺度的物理过程为全球流动做出了贡献，就像许多小拼图必须正确组装才能产生盒子上的图片一样。海洋观测技术和数值模型的改进使海洋学家能够在“拼图”的水平上研究海洋环流。在这一级别发生的物理过程称为海洋中尺度，其典型长度尺度为数十公里。海洋中尺度主要是相干结构，如涡流和急流，它们相当于海洋中的大气风暴和风暴路径。这些特征可以被认为是拼图碎片上的凸起和凹槽，因为它们对于将海洋环流的不同部分连接在一起是必不可少的。在研究海洋环流时，考虑全球气流的部分或组成部分往往是有利的，就像人们在研究大型拼图时可能会专注于一片天空或一件衣服一样。位于南大洋的海洋环流的两个关键组成部分是南极边缘和南极绕极流。前者是海洋中最冷、最密集的水形成的地方。这些水在南极洲周围下沉，进入ACC，最终扩散到覆盖大部分海底。ACC是海洋中最大和最强的洋流系统，负责大洋盆地之间的交换，调节低纬度和极地之间的热量传输，并补充南极洲周围的水域。虽然认识到这两个区域之间的交换有助于调节全球循环，但实现和控制这种交换的机制，特别是涡旋的作用，人们知之甚少。换句话说，连接南极洲周围水域和周围ACC的凸起和凹槽目前在环流拼图中消失了。南大洋对地球气候的演变至关重要；它是世界上生物生产力最高的海洋，也是吸收热量和二氧化碳的主要场所。涡旋过程不仅将ACC和南极边缘联系在一起，而且还决定了该地区如何应对不断变化的气候条件。在过去的几十年里，南极洲周围发生了重大的区域变化，导致更多来自ACC的水渗透到大陆架。这导致西南极冰盖变薄，并导致输出到全球循环的水变得不那么咸。例如，对南极洲周围未来变化及其对海平面上升的影响的准确预测，将需要考虑到涡流。这项提议旨在使用涡旋解析数值模式，或者换句话说，在拼图的水平上研究南极洲周围的海洋环流。需要解决的重要问题包括：旋涡如何确定南极边缘周围水域和行政协调委员会内水域之间交换的位置和频率；旋涡过程如何对模拟南极洲周围观测变化的风和温度模式的变化作出反应？随着流通的个别特征发生变化，拼图将被修改，以新的和有趣的方式组合在一起。仅靠数值模拟不能完全了解连接ACC和南极边缘的过程。因此，这项工作的一个重要组成部分是将模型的结果与激动人心的国家和国际倡议结合起来，以便在实地直接观察这些进程。通过这一共同努力，将更清楚地了解将ACC和南极边缘联系在一起的过程，从而向实现全球图景又迈进了一步。

Ocean circulation is like a jigsaw puzzle. In the ocean a myriad of physical processes with small scales contribute to the global flow, just as many small puzzle pieces must be assembled properly to produce the picture on the box. Improvements in ocean observing techniques and numerical models are just now allowing oceanographers to study ocean circulation at the ``puzzle piece'' level. Physical processes occurring at this level are known as the ocean mesoscale and have typical length scales of tens of kilometres. The ocean mesoscale is dominated by coherent structures, such as eddies and jets, which are the oceanic equivalent of atmospheric storms and storm tracks. These features can be thought of as the bumps and grooves on the puzzle pieces, as they are essential for linking different parts of the ocean circulation together. When studying the ocean circulation, it is often advantageous to consider parts or components of the global flow just as one might focus on a patch of sky or a piece of clothing when working on a large puzzle. Two key components of the ocean circulation located in the Southern Ocean are the Antarctic margins and the Antarctic Circumpolar Current (ACC). The former is the site where the coldest, densest water in the ocean is formed. This water sinks around Antarctica, enters the ACC and eventually spreads to cover most of the ocean floor. The ACC is the largest and strongest current system in the ocean and is responsible for exchange between ocean basins, for regulating heat transport between low latitudes and the pole, and for replenishing the waters around Antarctica. While it is appreciated that exchange between these two regions helps regulate the global circulation, the mechanisms that enable and control this exchange, and especially the role of eddies, is poorly understood. In other words, the bumps and grooves that link waters around Antarctica with the surrounding ACC are presently missing in the circulation jigsaw. The Southern Ocean is crucial for the evolution of the Earth's climate; it is the world's most biologically productive ocean and a major site of heat and carbon dioxide uptake. Eddy processes not only link the ACC and the Antarctic margins, but they also dictate how the region responds to changing climate conditions. Significant regional changes have occurred around Antarctica during the past few decades, which have resulted in more water from the ACC penetrating onto the continental shelf. This has led to a thinning of the West Antarctic Ice Sheet and has caused water exported to the global circulation to become less salty. Accurate predictions of future changes around Antarctica and their impact on sea level rise, for instance, will need to take account of eddies. This proposal aims to study the ocean circulation around Antarctica using an eddy-resolving numerical model, or in other words, at the puzzle piece level. Important questions to be addressed include: How do eddies determine the location and frequency of exchange between waters around the Antarctic margins and those within the ACC; and how do eddy processes respond to changing wind and temperature patterns that mimic observed changes around Antarctica? As individual features of the circulation change, the puzzle pieces will be modified to fit together in new and interesting ways. A complete understanding of the processes linking the ACC and the Antarctic margins can not be achieved by numerical simulations alone. Thus an important component of this work is integrating results from the models with exciting national and international initiatives to observe these processes directly in the field. Through this combined effort, a clearer picture of the processes that couple the ACC and the Antarctic margins will emerge, thus moving another step closer to achieving the global picture on the box.