po·lyn·ya /pälənˈyä/ noun; a stretch of open water surrounded by ice, especially in Arctic and Antarctic seas.
Formation of Coastal Polynyas
Unobstructed by obstacles, cold, dry winds race down glacial valleys from the high Antarctic plateaus, gaining speed until they shoot off the edge of icy land at up to 200 kilometers per hour. These katabatic winds push the blanket of sea ice away from the edge of the continent, creating pools of open water – polynyas – even when the rest of the sea is covered in ice. The ocean freezes again in the polynya, and eventually more winds push this ice out to sea as well. Thus, polynyas are actually sea ice factories, pumping out sea ice, which is then pushed northward by winds. Since katabatic winds repeatedly flow down the same tracks, coastal polynyas occur in the same place year after year.
Polynyas and the Global Ocean
Processes that begin in the polynya help drive thermohaline circulation, critical to the global ocean health and the ocean’s ability to regulate our climate. As seawater freezes into sea ice in the polynya, it drops most of its salt into the water column below. This extremely cold, salty water will form the densest seawater on Earth – Antarctic Bottom Water – when it sinks and floods off the Antarctic continental shelf, spreading north across the very bottom of the ocean. Another water mass rises offshore, nutrient-rich Circumpolar Deep Water, and the entire Southern Ocean is turned upside down.
These newly available nutrients fuel spectacular blooms of tiny aquatic plants in the polynya regions, taking up vast amounts of carbon dioxide in the process.
Meanwhile, another branch of this Circumpolar Deep Water rises and flows northward in response to strong circumpolar winds and the physics of spinning liquids. As this upwelled water mass spreads away from Antarctica, it absorbs heat, oxygen and carbon dioxide. When it finally begins to sink again, roughly 1500 miles north, it takes the dissolved gasses and heat with it into the ocean interior, thus buffering the effects of climate change while also supplying much-needed oxygen to ocean life at depth. The overturning of the Southern Ocean is linked to all major global oceanic and atmospheric patterns, and polynyas play a key role.
Polynyas and the Ecosystem
Polynyas receive the first daylight as the sun rises in Antarctica, initiating the spring bloom of phytoplankton after winter’s five months of darkness. This phytoplankton is the base of the foodweb, supporting one of the most prolific ecosystems on Earth, despite the frigid water and extreme environment. While polynyas make up less than 5% of the seasonal sea ice area, they are hot spots of Antarctic life all around the continent.
