An Antarctic polynya is an area of persistent open water found within sea ice. These features are notable because they remain unfrozen even during the coldest parts of the year when the surrounding ocean is covered in ice. Ranging in size from small pockets to areas covering thousands of square kilometers, polynyas are recurring phenomena that appear in similar locations year after year, driven by specific local conditions.
Formation of Antarctic Polynyas
Polynyas are created by two physical mechanisms that either prevent ice from forming or melt it from below. The first type, a coastal or latent-heat polynya, forms near the Antarctic coastline. These are caused by cold, dense katabatic winds from the continental interior that sweep across the sea surface. The winds continuously push newly formed ice away from the shore, exposing the water beneath.
This process turns coastal polynyas into “sea ice factories.” The exposed water, subjected to frigid air temperatures, rapidly freezes, only for that new ice to be transported away by the winds. This constant production and export of sea ice leaves a sustained area of open water next to the coast or an ice shelf. The Ross Sea and Weddell Sea are well-known locations for these wind-driven coastal polynyas.
A different process creates open-ocean or sensible-heat polynyas, which form far from land in the middle of the ice pack. These are generated by the upwelling of deeper ocean water that is warmer and saltier than the surface water. This circulation is triggered by the interaction of ocean currents with underwater topography, such as seamounts or ridges.
The Maud Rise polynya, which has appeared intermittently in the Weddell Sea, is a prime example of this type. Here, warmer deep water is forced upward by the Maud Rise seamount, bringing enough heat to the surface. This heat melts the overlying sea ice from beneath and prevents new ice from forming, sustaining the isolated patch of open sea.
Biological Hotspots
Polynyas function as biological hotspots and are among the most productive marine regions in the polar environment. The availability of open water, especially in spring and summer, allows sunlight to penetrate the ocean’s upper layers. This light exposure fuels blooms of phytoplankton, the microscopic plants that form the foundation of the oceanic food web, in a setting where light is normally blocked by ice.
The abundance of phytoplankton directly supports large swarms of Antarctic krill, small crustaceans that graze on the microscopic algae. These krill populations become very dense within polynyas. This concentration of a primary food source is what draws in a host of larger animals, transforming the polynya into a feeding ground.
Consequently, these biological hotspots attract a wide array of predators. Adélie and emperor penguins rely on the open water to access these feeding areas, especially during their breeding seasons. Weddell seals are also frequently found in polynyas, using them for hunting and resting. Various species of whales, from minke to humpbacks, migrate to these locations to feast on the dense aggregations of krill.
Influence on Global Climate
Antarctic polynyas influence both regional weather and the global climate system. The surface of the open water is much warmer than the overlying polar atmosphere, which can be tens of degrees colder. This temperature difference drives a continuous transfer of heat from the ocean into the air, a process that can modify local weather patterns.
Polynya formation also contributes to global ocean circulation. In coastal polynyas, the constant freezing of seawater releases salt into the surface water through brine rejection. This process, combined with cooling from the atmosphere, makes the surface water very cold, salty, and dense.
This dense water, known as Antarctic Bottom Water, sinks from the continental shelf to the deepest parts of the ocean. This sinking process is a driver of the global ocean conveyor belt, a system of deep-ocean circulation that transports heat around the planet and helps regulate Earth’s climate.