At least 15 percent of the ocean is covered by sea ice some part of the year. On average, sea ice covers almost about 10 million square miles of the Earth.
Ocean water can freeze just like freshwater, but it requires much lower temperatures. Fresh water freezes at 32 degrees Fahrenheit but seawater freezes at about 28.4 degrees Fahrenheit, because of the salt in it.
When does the ocean water freeze?
Ocean water does freeze when it gets cold enough. Consider The North Pole polar ice cap which is a massive sheet of frozen ocean water.
Without a melting season, fresh water in the air freezes as snow and falls onto the land over frigid places such as Antarctica, Greenland, and Canada. This snow accumulates and compacts over time, becoming an ice mass known as a glacier. Gravity gradually drives the glacier downhill until it reaches the ocean and forms an ice shelf.
As a result, glaciers, ice shelves, and icebergs are all composed of thick sheets of frozen fresh water rather than frozen ocean water.
When ocean water freezes, it creates a thin flat layer called sea ice or pack ice. Sea ice has long been an adversary of sailors seeking an unobstructed route across freezing seas, yet contemporary icebreaker ships have little trouble carving a way through frozen ocean fields.
What prevents the ocean water from freezing?
Despite the fact that the seas do freeze when temperatures drop low enough, ocean water remains liquid in far lower temperatures than one might imagine. There are four major causes that maintain the ocean far more liquid than predicted.
Salt
Ocean water’s significant salt content reduces its freezing point from 32° F (0° C) to 28° F (-2° C). This freezing-point depression effect is why we apply salt to ice sidewalks in the winter. The salt causes the ice to melt by lowering its freezing point below the ambient temperature. If this were the only impact, the ocean water would be ice if the ambient temperature was less than 28° F. This is not the case, thus there must be other factors at work.
Ocean Currents
Ocean currents are large-scale flows of ocean water caused by the moon’s gravitational pull, the earth’s rotational motion, and thermal convection. Ocean currents constantly transport warm water from the equatorial areas to the cooler ocean regions.
This continual circulation of ocean water keeps water molecules from freezing into the fairly immobile state of ice crystals.
High Volume
The greater the volume of water, the more heat must be evacuated to freeze it. More precisely, for a given external temperature, the surface area to volume ratio controls the rate of heat loss and hence the pace of freezing. The oceans’ huge volume and depth protect them from freezing too soon, allowing the heating systems to have a greater effect.
Earth’s Internal Heating
Because the earth’s insulating crust is significantly thinner beneath the seas than beneath the continents, the oceans absorb the majority of the planet’s internal heat. Although the air above the ocean’s top may be cold, the water deep within the ocean is substantially warmer owing to internal heating.
The Crux
Because of the mix of salt, ocean currents, enormous volume, and internal warmth, the majority of the ocean remains liquid even during frigid winters.
