Mesoscale Eddies at the Antarctic Margins

海洋环流就像一个拼图游戏。在海洋中，无数小规模的物理过程促成了全球流动，就像许多小拼图必须正确组合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。发生在这一水平的物理过程被称为海洋中尺度，其典型的长度尺度为几十公里。海洋中尺度由连贯的结构主导，如漩涡和喷流，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上的凸起和凹槽，因为它们对于连接海洋环流的不同部分至关重要。在研究海洋环流时，考虑全球流的部分或组成部分通常是有利的，就像人们在解决一个大难题时可能会关注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环极流（ACC）。前者是海洋中最冷、密度最大的水形成的地方。这些水在南极洲周围下沉，进入ACC，最终扩散覆盖大部分海底。太平洋环流是海洋中最大最强的洋流系统，负责海洋盆地之间的交换，调节低纬度和极地之间的热输送，并补充南极洲周围的水域。虽然人们认识到这两个区域之间的交换有助于调节全球环流，但人们对促成和控制这种交换的机制，特别是涡旋的作用却知之甚少。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缺失。南大洋对地球气候的演变至关重要；它是世界上最具生物生产力的海洋，也是吸收热量和二氧化碳的主要场所。涡旋过程不仅将南极大陆和南极边缘联系起来，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，这导致更多的水从ACC渗透到大陆架上。这导致南极西部冰盖变薄，并导致出口到全球环流的水的含盐量降低。例如，要准确预测南极洲周围未来的变化及其对海平面上升的影响，就需要考虑到涡旋。该提案旨在使用一个漩涡解析数值模型，或者换句话说，在拼图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：漩涡如何决定南极边缘水域和行政协调会内部水域之间交换的位置和频率；以及涡旋过程是如何对风和温度模式的变化做出反应的，这些变化模拟了南极周围观察到的变化？随着循环的个别特征的变化，拼图碎片将被修改，以新的和有趣的方式组合在一起。仅靠数值模拟是无法完全了解连接ACC和南极边缘的过程的。因此，这项工作的一个重要组成部分是将模型的结果与令人兴奋的国家和国际倡议结合起来，直接在实地观察这些过程。通过这一共同努力，将出现一幅将行政协调会和南极边缘联系起来的进程的更清晰图景，从而向实现方框上的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.