Yes, sea ice is mostly freshwater.
When seawater freezes to form sea ice, the salt is largely excluded from the ice crystal structure. This process results in sea ice that is significantly less saline than the surrounding ocean water. Here's a breakdown:
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Initial Formation: As seawater begins to freeze, tiny ice crystals called frazil ice form. These crystals are nearly pure freshwater because salt doesn't readily incorporate into the ice structure. The salt is expelled into the surrounding water.
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Brine Channels: Although the ice is mostly freshwater, some pockets of highly concentrated salt water, called brine, can become trapped within the ice structure, forming brine channels.
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Desalination Over Time: Over time, the brine slowly drains out of the ice through these channels, further reducing the salinity of the sea ice. Older sea ice is therefore fresher than newly formed sea ice.
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Melting: When sea ice melts, it releases primarily freshwater back into the ocean. This can contribute to localized areas of lower salinity in the surface waters.
In summary, while newly formed sea ice may contain some brine, the freezing process largely excludes salt, making sea ice predominantly freshwater. As the ice ages, desalination continues, further reducing the salinity.
