Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water.

Glacial meltwater stops bottom-water formation, allowing warm ocean waters to reach Antarctic ice shelves and drive rapid melting. Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise.

冰川融水阻止了底层水的形成，使得温暖的海水能够抵达南极冰架并导致快速融化。 在沿海冰间湖中海冰形成期间，强烈的热量散失和盐分释放会使南极大陆架上的海水冷却并盐化。因此，冰间湖活动既限制了海洋向南极冰盖的热通量，又促进了高密度陆架水（DSW）的形成，而高密度陆架水是南极底层水的前身。然而，尽管存在强烈的冰间湖活动，在东南极的萨布丽娜海岸和西南极的阿蒙森海却并未形成高密度陆架水。通过使用一个由观测强迫驱动的简单海洋模型，我们发现，来自冰架底部融化的淡水输入，部分抵消了这两个区域冰间湖中因海冰形成而产生的盐通量，从而阻止了水体的全深度对流以及高密度陆架水的形成。在缺乏深层对流的情况下，抵达大陆架底层的温暖海水不会向大气散失太多热量，因此能够导致萨布丽娜海岸的托滕冰架以及阿蒙森海的多森冰架和盖茨冰架出现快速的底部融化。我们的研究结果表明，在气候变暖的情况下，冰川融水输入的增加既会减少南极底层水的形成，又会引发南极冰盖质量损失加剧，进而对全球经向翻转环流和海平面上升产生影响。