Why Does Ice Float on Water?

为什么冰能浮在水面上？

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Unlike most solids, ice floats because frozen water is less dense than liquid water—a rare and vital exception.

与大多数固体不同，冰能漂浮，因为固态水的密度小于液态水——这是一种罕见却至关重要的例外。
When water cools below 4°C, hydrogen bonds begin locking molecules into an open hexagonal lattice.

当水温降至4°C以下时，氢键开始将水分子锁定成疏松的六方晶格。
This crystal structure creates empty spaces between molecules, increasing volume while decreasing density.

这种晶体结构使分子间出现空隙，体积增大而密度降低。
At 0°C, ice is about 9% less dense than liquid water, giving it natural buoyancy.

在0°C时，冰的密度比液态水低约9%，因而具有天然浮力。
If ice sank, lakes and oceans would freeze solid from the bottom up, killing most aquatic life.

如果冰下沉，湖泊和海洋会自下而上完全冻结，导致绝大多数水生生物死亡。
Instead, floating ice insulates the water below, allowing fish and microbes to survive winter beneath the surface.

而实际上，漂浮的冰层能隔绝下方水体，使鱼类和微生物得以在冰面下越冬存活。
This density anomaly also drives ocean circulation, as cold, dense water sinks near poles and flows toward the equator.

这一密度反常现象还驱动着大洋环流：寒冷致密的海水在两极下沉，并向赤道方向流动。
Scientists call this behavior ‘density inversion,’ and it’s one reason Earth supports complex life.

科学家称此现象为‘密度反转’，它也是地球能孕育复杂生命的原因之一。