Freshwater Export from the Weddell Gyre: Magnitude, Variability and Impacts

淡水是南极洲周围气候系统的关键组成部分。一般来说，海水越新鲜，密度越低，因此向海洋注入淡水控制着一系列过程，包括深水形成和海洋环流。这对全球和区域气候都有影响，最近的研究表明，向威德尔海（南极洲附近）等地区注入淡水，可以在短短几年的时间尺度上影响远至赤道以北的气候。气候模式表明，高纬度地区的淡水储量将随着全球变暖的进展而变化，但这些变化的后果在很大程度上是未知的。事实上，由于在南大洋取样的困难，即使在这里探测到这样的变化也是具有挑战性的。我们建议利用已经安排好的研究巡航，对南大洋威德尔环流边缘的氧同位素进行全面测量。在目前的气候条件下，威德尔环流是一个深水和底水形成强烈的地区，也是一个淡水输出强烈的地区。氧同位素的测量将使我们能够分别确定淡水的来源，将冰川冰融化和降水（雪）的贡献与海冰融化的贡献区分开来。通过将这些测量结果与单独导出的洋流速度计算相结合，我们将提供威德尔环流不同层淡水输出的基准量化。我们将把我们的测量结果与历史测量结果进行比较，以确定任何或所有淡水成分的变化，并在已知和预期的大规模气候变化背景下解释这些变化，包括不断变化的水文循环。这项工作是一项强有力的合作，包括来自佛罗里达州立大学、德克萨斯农工大学和美国伍兹霍尔海洋研究所的工作人员。这些科学家将提供研究巡航后勤，而不仅仅是英国船只提供的后勤，还将进行稀有气体的测量，以补充我们的同位素测量。因此，这项工作有可能为国际科学项目做出非常重大的贡献，同时也与英国的科学优先事项密切相关。

Freshwater is a key component of the climate system around Antarctica. In general, the fresher seawater is, the less dense it is, and so the injection of freshwater into the ocean controls a range of processes that include deep water formation and ocean circulation. This has implications for global and regional climate, and recent studies have shown that injecting freshwater into regions such as the Weddell Sea (adjacent to Antarctica) can influence climate as far north as the equator and beyond on timescales of just a few years. Climate models indicate that the freshwater budget at high latitudes will change as global warming progresses, but the consequences of these changes are largely unknown. Indeed, due to the difficulties of sampling the Southern Ocean, even detecting such a change here is challenging. We propose to take advantage of an already-scheduled research cruise to make comprehensive measurements of oxygen isotopes around the rim of the Weddell Gyre in the Southern Ocean. Under present climate conditions, the Weddell Gyre is a site of strong deep and bottom water formation, and also a region of strong freshwater export. The measurements of oxygen isotopes will enable us to determine the sources of the freshwater separately, with the contributions of glacial ice melt and precipitation (snow) being distinguished from the contribution of sea ice melt. By combining these measurements with ocean current speed calculations being derived separately, we will provide a benchmark quantification of the freshwater export in different layers of the Weddell Gyre. We will compare our measurements with historical measurements to determine change in any or all of the freshwater components, and interpret these changes in the context of known and expected large-scale climate change, including the changing hydrological cycle. This work is strongly collaborative, and includes workers from Florida State University, Texas A&M University and Woods Hole Oceanographic Institution in the United States. These scientists will provide access to research cruise logistics over and above those provided by UK ships alone, and will also make measurements of noble gases to complement our isotope measurements. This work thus has the potential to make very significant contributions to international science programmes, as well as being strongly relevant to UK science priorities.