STEM与日常科技·英语30篇（6）

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为何湖面结冰总始于表层，即使下方空气温度更低

Water reaches its maximum density at 4°C, causing colder water near freezing to rise toward the surface.
As air temperature drops below 0°C, surface water loses heat faster and forms ice crystals first.
This insulating ice layer then slows further heat loss from deeper, slightly warmer water below.
Convection currents stop once the top layer freezes, preserving a liquid habitat for aquatic life underneath.
Scientists measure thermal gradients with submerged sensors to model freeze-thaw timing across latitudes.
Lake ice thickness correlates strongly with cumulative degree-days below freezing over winter weeks.
Unlike rivers, still lakes allow uniform surface cooling, making them ideal natural laboratories for phase-change studies.
Wind speed and snow cover significantly alter ice formation rates by affecting heat exchange efficiency.
Remote sensing satellites now track early freeze onset to improve climate models of freshwater systems.
Understanding this process helps predict winter fish survival and methane release from thawing sediments.