What Makes Sea Ice?

Sea ice forms when ocean water cools to its freezing point.

The Formation Process Explained

The creation of sea ice is a fascinating process driven by cold temperatures. Here's a breakdown:

Cooling Ocean Surface: The process begins when very cold air chills the surface of the ocean.
Reaching Freezing Point: As the surface water temperature drops to the freezing point of seawater (around -1.8°C or 28.8°F), ice crystals begin to form.
Density Increase and Sinking: As the water cools towards freezing, its density increases. This denser, colder water sinks.
Upwelling and Further Cooling: Warmer water then rises to replace the sinking cold water. This warmer water also needs to be cooled to allow ice formation. Therefore, sea ice formation isn't just about the surface; a column of water needs to be near freezing.
Ice Crystal Growth: Initially, small ice crystals, known as frazil ice, form. These crystals clump together to form larger, pancake-shaped pieces of ice.
Consolidation: Over time, these pancake ice pieces freeze together, creating a more solid ice cover. This process can be rapid, particularly in very cold conditions.
Ice Thickening: The sea ice continues to thicken as more water freezes onto its underside. The rate of thickening depends on the air temperature, snow cover, and the salinity of the water.

Several factors influence the formation and extent of sea ice:

Air Temperature: Extremely cold air is crucial for initiating and maintaining sea ice formation.
Ocean Salinity: Saltwater freezes at a lower temperature than freshwater. Higher salinity means a lower freezing point.
Ocean Currents: Ocean currents can transport heat, influencing the temperature of the water and impacting ice formation.
Wind: Wind can break up existing ice, creating open water where new ice can form rapidly, or it can compact ice, increasing its thickness.
Snow Cover: Snow on top of sea ice insulates it, slowing down the rate of ice growth.

Sea ice plays a critical role in the Earth's climate system:

Reflects Sunlight: Sea ice has a high albedo (reflectivity), meaning it reflects a large portion of incoming solar radiation back into space, helping to regulate Earth's temperature.
Insulates the Ocean: Sea ice acts as a barrier between the ocean and the atmosphere, reducing heat exchange and influencing regional climates.
Habitat: It provides habitat for various species, including polar bears, seals, and walruses.