What controls the influx and mixing of warm waters onto the polar ocean shelves?

下一个世纪的两个主要环境挑战将是全球海平面和海洋生态系统对海洋迅速变暖的反应，特别是在极地地区。最近，在南极洲和格陵兰岛周围的许多地方都记录到了大量的冰融化，人们担心未来几十年可能会发生突然的灾难性冰损失，对全球海平面产生重大影响。尽管如此，对于温暖的近海沃茨输送到冰架和崩解冰川的路径和机制，仍然缺乏足够的知识。一个特别令人关切的地区是西南极半岛。在这里，大部分增加的冰损失似乎是由于温暖的近海水（称为绕极深水或CDW）到达浮动冰架下的空腔的增强流动造成的。此外，该区域海洋温度的上升和海冰的减少可能对南极生态系统的运作产生重大影响，特别是对磷虾和企鹅的种群。了解导致CDW在陆架上横向和纵向混合的机制以及陆架边缘过程在输送这种水团中的作用对于解释正在发生的区域物理，化学和生物变化至关重要。量化、描述和理解西南极半岛陆架横向和垂直混合的空间和时间变化模式。解决驱动横向和垂直热通量的主要机制，特别侧重于了解深海沃茨的热量如何以及在何处转移到上层海洋。了解关键的大陆架边缘过程在控制这些现象方面的作用，特别是了解和量化这些过程在造成温暖、含盐的深海沃茨侵入极地大陆架方面的重要性，该项目将利用传统和新的海洋学平台的数据，目的是说明温暖的沃茨如何从大陆架边缘移向海岸，陆地上的冰会融化在过去十年中得到广泛发展的海洋滑翔机将提供温度、盐度和小规模速度的测量数据，从中可以确定控制机制。首先，在大陆架边缘，将确定CDW如何跨越大陆架断裂移动（例如，通过漩涡，上升流或地形转向）。第二个区域靠近位于罗瑟拉的英国南极调查基地，将研究这一层热量横向和纵向混合的机制。作为直接测量西南极半岛混合的首批项目之一，我们将确定这些过程是由风、潮汐还是与海洋密度变化有关的过程驱动的。为了帮助解释滑翔机的测量结果，将进行系泊速度观测，并将BAS Rothera时间系列的现有气象和水文数据纳入分析。此外，还将在冬季部署直接测量湍流的仪器，以测试海冰的存在是否会削弱垂直混合。在综合数据时，该项目将使用一个新的方法框架来审查横向和横向进程的相对重要性。我们将利用我们对目标2和目标3的新的机理理解，以及目标1中热流的量化，设计一个概念性模型，说明热量如何移动到大陆架上，或者进入近地表层（并消失在大气中）或移动到冰架边缘。了解这些过程将有助于预测快速变暖的极地地区未来冰盖的稳定性，区域气候和生态系统的变化。

Two of the main environmental challenges of the coming century will be the response of global sea levels and marine ecosystems to rapid ocean warming, particularly in the polar regions. Recently, large increases in ice melt have been recorded at many locations around Antarctica and Greenland, raising fears that sudden catastrophic ice loss could occur in the coming decades, with significant impacts on global sea level. Despite this, there is still insufficient knowledge about the pathways and mechanisms by which warm offshore ocean waters are delivered to the ice shelves and calving glaciers. One particular region of concern is the West Antarctic Peninsula. Here, much of the increased ice loss appears to have been caused by an enhanced flow of warm offshore water (termed Circumpolar Deep Water or CDW) reaching cavities under the floating ice shelves. Furthermore, the increase in ocean temperature and reducing sea ice in this region are likely to have significant impacts on the operation of the Antarctic ecosystem, particularly for populations of both krill and penguins. Understanding the mechanisms that cause CDW to be mixed both laterally and vertically on the shelves and the role of shelf-edge processes in delivering this water mass is vital to interpreting the regional physical, chemical and biological changes that are occurring.The key project objectives are thus:1. To quantify, describe and understand the spatial and time-varying patterns of lateral and vertical mixing on the West Antarctic Peninsula shelf.2. To resolve the dominant mechanisms driving lateral and vertical heat fluxes, with a specific focus on understanding how and where heat from the deep ocean waters is transferred to the upper ocean.3. To understand the role of key shelf-edge processes in controlling these phenomena, in particular by understanding and quantifying the importance of these processes in causing intrusions of warm, saline deep-ocean waters onto polar shelves.The project will use data from both traditional and novel oceanographic platforms, with the aim of describing how warm waters move from the edge of the shelf to the coast, where melting of land-based ice can occur. Ocean gliders, which have been developed extensively over the last 10 years, will provide measurements of temperature, salinity and small-scale velocity, from which the controlling mechanisms can be determined.The fieldwork will focus on two regions. The first, at the shelf edge, will determine how CDW moves across the shelf break (e.g. through eddies, upwelling or steering by topography). The second region, close to the British Antarctic Survey base at Rothera, will examine the mechanisms by which heat in this layer is mixed both laterally and vertically. As one of the first projects to measure mixing on the West Antarctic Peninsula directly, we will determine whether these processes are driven by wind, tides or processes relating to changing ocean density. To help interpret the glider measurements, moored velocity observations will be made and existing meteorological and hydrographic data from the BAS Rothera Time Series will be incorporated into the analysis. In addition, a through-ice wintertime deployment of an instrument that directly measures turbulence will be carried out to test whether vertical mixing is weakened by the presence of sea ice. In synthesising the data, the project will use a new methodological framework to examine the relative importance of horizontal and lateral processes.Ultimately, we will use our new mechanistic understanding from objectives 2 and 3 with the quantification of heat flows from objective 1 to devise a conceptual model of how heat moves onto the shelf and either gets into the near-surface layer (and lost to the atmosphere) or moves to the ice shelf edge. Understanding these processes will help to predict future ice sheet stability, regional climate and ecosystem changes in the rapidly warming polar regions.