Why don’t Oceans Freeze? Are Icebergs Made of Salt water or Fresh water?

Many people fall overboard for some of the most enduring myths about the largest area of our world, the oceans. Some people believe the oceans don’t freeze solid because of the deep currents.

Although the water around the Arctic and Antarctica is freezing cold, oceans don’t freeze solid for several reasons. Oceans contain a lot of water, which circulates all around the world. Water from warmer oceans and from underground volcanoes flows into the Arctic, which warms it up a bit. But the main reason oceans don’t go into a deep freeze is the salt in the water.

The freezing point of saltwater is lower than that of freshwater, and as ocean water reaches the freezing point, the salt crystals themselves interfere with the formation of ice crystals. This water is also more dense (in other words heavier because it is full of salt) and therefore it sinks, allowing warmer water to come up to the top, below the surface ice. The surface ice actually insulates this warmer water, in the same way an igloo insulates the air inside of it. The ice also reflects the sun’s rays, and this helps warm the surface and prevents the ice from thickening further. Nearly all the ice in the Antarctic is seasonal, which means that it melts and reforms annually.

Another myth that some people believe is that icebergs are made of frozen seawater. This seems like it might be common sense, because icebergs float in the sea water, but many natural phenomena don’t seem immediately to be common sense until you think about it for a few minutes.

Oceanographers agree that icebergs are made of freshwater, in the form of snow, that has compacted over hundreds or thousands of years. True icebergs are huge pieces of ice that have broken off from the glaciers that make up the Continental ice sheets, as found in Antarctica or Greenland. Seawater, with its salt content, doesn’t mix with the fresh water in the iceberg. The freshwater iceberg doesn’t contain the heavy salt so it’s lighter weight, and floats in the sea water.

To test this theory at home, put saltwater and freshwater in the freezer at the same time. Check on it regularly and see which one solidifies faster.

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