There are two oceans in Earth’s polar regions: the Arctic Ocean, which occupies most of the north polar region, and the Southern Ocean, which surrounds the continent of Antarctica in the south polar region.
Oceans in the polar regions are a bit different from the other oceans on Earth (the Atlantic, Pacific, and Indian Ocean). There is often sea ice at the surface of polar oceans, especially during the winter months. Both the Arctic Ocean and the Southern Ocean are homes to unique marine ecosystems that thrive in the cold conditions.
Seawater from polar regions can be denser than seawater from other regions. This is because seawater in the polar oceans is often colder than other seawater. It can also become more saline than normal in the winter when sea ice freezes at the ocean surface. The salty part of the water does not freeze, making the remaining seawater saltier. Because it is denser, this seawater sinks to the bottom of the ocean. It travels in slow currents around the bottom of the world’s oceans as an essential part of the pattern of global ocean circulation called thermohaline circulation.
The polar oceans are affected greatly by global warming. Scientists are actively studying how the polar oceans, the sea ice at their surface, and the marine life within them, are changing in response to recent climate change. They have found that sea ice in the Arctic Ocean is melting more rapidly than previously thought, so quickly in fact that by the year 2040 there may not be any sea ice in the Arctic during summer months. Because sea ice reflects a large amount of incoming solar energy, less sea ice means that less solar radiation is reflected back out to space and more of it is absorbed, increasing the rate of warming. The melting sea ice threatens Arctic Ocean species such as polar bears. Scientists are currently studying the effect of less sea ice on polar bears. In the Antarctic, scientists are studying the effect of less sea ice on the penguin breeding season.
Eventually, global warming could also disrupt global ocean circulation. If it gets warm enough that sea ice no longer forms in the polar regions, the seawater would not be extra salty and thus would not be as dense. If the water were warmer it may not be as dense either. This could prevent the formation of deep water, potentially slowing or even stopping global ocean circulation. A shutdown of this circulation could have large consequences for many different aspects of our planet including consequences for regional climates, the severity of weather events, and marine ecosystems.