Sea ice works by forming when ocean temperatures drop to the freezing point, acting as an insulator between the ocean and atmosphere once it starts to grow.
Here's a more detailed explanation:
The Freezing Process
As ocean water nears its freezing point (around -1.8°C or 28.8°F for seawater, due to its salinity), several key processes occur:
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Density Increase and Sinking: As water cools, its density increases, causing it to sink. This process mixes the water column, meaning the entire water column, not just the surface, must cool to near freezing.
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Ice Crystal Formation: Once the surface water reaches its freezing point, ice crystals begin to form. These crystals initially appear as frazil ice – small, needle-like crystals.
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Consolidation and Growth: Frazil ice coalesces to form larger structures, eventually forming a continuous sheet of ice. This sheet can grow both horizontally and vertically.
The Insulating Effect
The critical function of sea ice comes into play after it begins to form:
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Barrier to Heat Transfer: Sea ice acts as an insulator between the relatively warmer ocean water below and the colder atmosphere above. Ice has a much lower thermal conductivity than water, meaning it doesn't transfer heat as effectively.
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Slowing Down Freezing: This insulating effect dramatically slows down the rate at which the ocean loses heat to the atmosphere. Without sea ice, the ocean would lose heat much more quickly, and significantly more ice would form.
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Albedo Effect: Sea ice has a high albedo, meaning it reflects a large percentage of incoming solar radiation back into space. This further contributes to cooling the polar regions. Less solar energy is absorbed by the ocean, helping to maintain colder temperatures and promote ice formation and persistence.
The Cycle Continues
As sea ice grows thicker, its insulating effect becomes even stronger. This allows the ice to survive through the winter months and potentially last for multiple years, becoming multi-year ice. In the summer, some of the sea ice melts, reducing its extent, but the presence of sea ice helps to keep polar temperatures cooler than they would otherwise be.
In summary, sea ice formation is driven by decreasing ocean temperatures, and once formed, it acts as a crucial insulator, slowing further ice formation and impacting regional and global climate.
