Polynya is an oceanography term borrowed from the Russian (полынья) to refer to an open body of water surrounded by ice. Polynyas are mostly found in the Arctic and the Southern Ocean near Antarctica.
What is the difference between a polynya and a lead?
Polynyas and leads are both openings in sea ice, but they have distinct differences in their formation and characteristics. Polynyas are larger, persistent open water areas within sea ice, found either along coastlines (coastal polynyas) or in the open ocean (open-ocean polynyas). They can last from several days to entire seasons.
Leads are narrower fractures in sea ice. Leads are typically temporary channels that open up within the ice pack, typically due to the shifting and cracking of ice. Leads are primarily formed by the mechanical movement of ice, which creates fractures and openings. These features are essential for navigation in polar regions and provide vital habitats for wildlife, though they are generally smaller and less stable than polynyas.
Types of Polynyas
There are two types of polynyas: coastal polynyas and open-ocean polynyas. Wind and ocean water circulation of warmer waters are the two main mechanisms responsible for their formation.
Wind driven polynyas
Two different types of mechanisms are responsible for the formation of polynyas. The first is wind-driven: strong winds can push ice away from an area, exposing the ocean below. A 2023 study published in The Cryosphere looked a winter polynyas events off of Greenland.
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Analyzing a 42-year period from 1979 to 2020, satellites recorded four major winter polynyas (open-water areas) north of Greenland, with one in 1986 and three more in 2011, 2017, and 2018. The 2018 polynya was the largest and lasted the longest. The study used satellite data, weather station records, and simulations from the Regional Arctic System Model to explore the causes of these events. The results of the study found that strong southern winds were the dominant mechanism, pushing the thick Arctic sea ice out of the region and creating these open-water areas.
Convection-drive polynyas
The second mechanisms for creating polynyas is convection-driven: warmer, saltier water from below rises to the surface, melting the overlying ice. As colder surface waters sink, warmer waters from deeper in the ocean are brought to the surface which also melts sea ice.
A 2019 study published in Nature looked at the underlying mechanisms for the formation of open-ocean polynyas over Maud Rise in 2016 and 2017. The study found that when the ocean surface had high salt levels, strong winter storms triggered a cycle where warm, salty water from deep in the ocean was brought to the surface. The cold air then cooled this water, making it denser and causing it to sink, which in turn brought up more warm water from below. This ongoing cycle prevented the formation of ice on the surface.
Coastal Polynyas
Coastal polynyas occur near coastlines and are usually formed by wind that blows sea ice away from the shore, creating an area of open water. This process of forming a hole in polar sea ice is known as ice advection.
Coastal polynyas can also form through the warm upwelling of seawater. This satellite image taken off the coast of Antarctica, near Ross Island and McMurdo Station on November 16, 2011 shows a coastal polynya. Katabatic winds, hurricane level winds that blow at speeds up to 200 miles (320 kilometers) per hour from Antarctica’s interior, help to create this polynya by blowing sea ice away from the coastline.
The polynya was most likely formed by katabatic winds which blow from Antartica’s high interior and can reach speeds up to 200 miles (320 kilometers) per hour.
Open-Ocean Polynyas
Open-ocean polynyas form when cracks form in the ice sheet far offshore, exposing the seawater. This type of polynyas develop further away from the coast, often over oceanic features like underwater mountains or ridges that influence ocean currents and water mixing.
An example of a open-ocean polynya is Maud Rise polynya, located in the eastern Weddell Sea. This polynya is named after the submerged mountain-like feature over which the opening in the sea ice forms. NASA’s Terra satellite imaged the Maud Rise Polynya on September 25, 2017.
The Maud Rise polynya can vary greatly in size, occurring routinely in early spring and sometimes over the winter. During the fall of 2017, the Maud Rise polynya grew from 9,500 square kilometers in mid-September to 80,000 square kilometers by late October.
Recently published research in ScienceAdvances looked at the mechanism happening during winters of 2016-2017 surrounding the formation of the Maud Rise polynya. Researchers from the University of Gothenburg found that the open-ocean polynyas forming over Maud Rise in the Weddell Sea were caused by deep ocean activity, affecting the local climate through changes in heat and carbon levels.
In 2017 these polynyas formed because early melting of sea ice was triggered by the upward mixing of warm water and salt, making the water lighter and more buoyant. Additionally, a new finding from this study revealed that strong winds helped move salt across nearby ocean currents, further stirring up the upper ocean. During the study period, an Ekman transport of salt moved along the northern flank of the Maud Rise.
The study highlights how specific local interactions among wind, ocean currents, and geographical features can lead to the formation of open-water areas called polynyas in the Southern Ocean.
What are the benefits of polynyas?
Polynyas in Antarctica are important in that they create light and nutrients conditions that enable seasonal, very dense blooms of phytoplankton to flourish. Phytoplankton are significant sources of carbon sinks.
Polynyas are also hotspots of refuge for many Arctic wildlife. Invertebrates, fish, seabirds and marine mammals can often be found congregating around polynyas. Polynyas and leads serve as key wintering grounds for numerous species, such as the entire world population of spectacled eiders, as well as various ice-associated seals and whales. The holes created by polynyas provide wildlife such as the spectacled eiders with direct access to benthic food sources.
Role of polynyas in climate dynamics
While more research is needed into this area, polynyas are believed to create a feedback loop between ocean processes and the atmosphere. During winter, the open water areas of polynyas release significant amounts of heat into the colder atmosphere. This not only affects local weather patterns by warming the air but has the potential to influence climate systems at broader scales.
In coastal polynyas, the dynamic action of strong winds and ocean currents continuously pushes surface ice away, exposing the water beneath which then quickly freezes. This rapid ice formation is a crucial process as it releases salt into the ocean and heat into the atmosphere.
References
Campbell, E. C., Wilson, E. A., Moore, G. K., Riser, S. C., Brayton, C. E., Mazloff, M. R., & Talley, L. D. (2019). Antarctic offshore polynyas linked to Southern Hemisphere climate anomalies. Nature, 570(7761), 319-325. DOI: 10.1038/s41586-019-1294-0
Cheon, W. G., & Gordon, A. L. (2019). Open-ocean polynyas and deep convection in the Southern Ocean. Scientific reports, 9(1), 6935. DOI: 10.1038/s41598-019-43466-2
Cheshire, L. (2020, July 23). Phytoplankton and polynyas. Earthdata. https://earthdata.nasa.gov/learn/sensing-our-planet/phytoplankton-and-polynyas
Deciphering the Maud Rise Polynya. (2019, May 22). Retrieved from https://earthobservatory.nasa.gov/images/145069/deciphering-the-maud-rise-polynya
Lee, Y. J., Maslowski, W., Cassano, J. J., Clement Kinney, J., Craig, A. P., Kamal, S., … & Wang, H. (2023). Causes and evolution of winter polynyas north of Greenland. The Cryosphere, 17(1), 233-253. DOI: 10.5194/tc-17-233-2023
Narayanan, A., Roquet, F., Gille, S. T., Gülk, B., Mazloff, M. R., Silvano, A., & Naveira Garabato, A. C. (2024). Ekman-driven salt transport as a key mechanism for open-ocean polynya formation at Maud Rise. Science Advances, 10(18), eadj0777. DOI: 10.1126/sciadv.adj0777
Polynya off the Antarctic Coast. (2011, November 22). Retrieved from https://earthobservatory.nasa.gov/images/76474/polynya-off-the-antarctic-coast
This article was originally written on January 23, 2020 and has since been updated.
