In cold polar waters, temperatures sometimes drop below the freezing point, a process referred to as supercooling. However, observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon. We here provide observational evidence that supercooled waters are much more widespread in the seasonally ice‐covered Southern Ocean than previously reported. In 5.8% of all analyzed hydrographic profiles south of 55° S, we find temperatures below the surface freezing point ('potential' supercooling), and half of these have temperatures below the local freezing point ('in‐situ' supercooling). Their occurrence doubles when neglecting measurement uncertainties. We attribute deep coastal‐ocean supercooling to melting of Antarctic ice shelves, and surface‐induced supercooling in the seasonal sea‐ice region to winter‐time sea‐ice formation. The latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes‐‐‐an important mechanism for vertical tracer transport and water‐mass structure in the polar ocean.

中文翻译：

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过冷的南大洋水域

在寒冷的极地水域，温度有时会降至冰点以下，这一过程称为过冷。然而，极地地区的观测挑战限制了我们对这种现象的时空范围的理解。我们在这里提供的观察证据表明，在季节性冰覆盖的南大洋中，过冷水比以前报道的要广泛得多。在 55° S 以南的所有分析的水文剖面中，有 5.8% 的温度低于地表冰点（“潜在”过冷），其中一半的温度低于局部冰点（“原位”过冷）。当忽略测量不确定性时，它们的出现会加倍。我们将深层沿海海洋过冷归因于南极冰架的融化，季节性海冰区地表引起的过冷对冬季海冰形成的影响。由于对流下沉羽流，后一种过冷类型可以向下延伸到永久的偏斜层——这是极地海洋中垂直示踪剂传输和水团结构的重要机制。