Ross Sea Polynya

Ross Sea Polynya. It is a large, recurrent area of open water surrounded by sea ice, located in the southern Ross Sea near the coast of Antarctica. This persistent feature is a type of coastal polynya, formed by intense katabatic winds flowing off the Ross Ice Shelf and the Transantarctic Mountains. The polynya is a critical site for the production of Antarctic Bottom Water, one of the densest water masses in the global ocean, and supports a highly productive polar ecosystem.

Formation and dynamics

The primary driver of its formation is the action of strong, persistent katabatic winds that drain cold, dense air from the East Antarctic Ice Sheet and the Transantarctic Mountains. These winds push newly formed sea ice away from the coast, preventing consolidation and continually exposing the ocean surface to the frigid atmosphere. This process, known as latent heat polynya formation, involves significant heat loss from the ocean, leading to rapid ice production in the diverging ice pack. The dynamics are influenced by the topography of the Ross Ice Shelf front and the presence of Ross Island, which can steer wind patterns. The Circumpolar Deep Water upwells in the region, providing a relatively warm subsurface layer that can also inhibit ice formation under certain conditions.

Physical characteristics

It is one of the largest and most consistent polynyas in the Southern Ocean, with its size varying seasonally and interannually. It typically expands to tens of thousands of square kilometers during the austral winter, though it can occasionally briefly disappear under calm conditions. The ocean within the polynya experiences extreme heat loss, sometimes exceeding 200 watts per square meter, resulting in surface water temperatures near the freezing point of seawater. This intense cooling increases the salinity and density of the surface water, a key process in ocean ventilation. The region is characterized by the formation of High Salinity Shelf Water, a precursor to the globally important Antarctic Bottom Water.

Ecological significance

The early exposure of open water and nutrient-rich conditions makes it a site of immense primary production at the start of the austral spring. This massive phytoplankton bloom, often dominated by diatoms, forms the base of a rich food web. The area is a crucial foraging ground for higher trophic levels, including the Antarctic krill (*Euphausia superba*), which in turn supports predators like Adélie penguin, emperor penguin, and minke whale. The McMurdo Sound region adjacent to the polynya is a key scientific observatory for studying this ecosystem. The high productivity also influences the biological pump, sequestering atmospheric carbon dioxide into the deep ocean.

Research and observations

Long-term monitoring has been conducted from bases like McMurdo Station (United States) and Scott Base (New Zealand). Key research programs include the International Southern Ocean Studies and modern initiatives like the ROSS Sea Ecosystem project. Observations utilize a suite of tools including moored instrument arrays, Autonomous Underwater Vehicles, and satellite remote sensing from platforms like NASA's MODIS and the European Space Agency's CryoSat-2. The ANDRILL project has investigated the paleo-history of the region. Significant contributions have come from research vessels such as the RVIB Nathaniel B. Palmer and the RSV Aurora Australis.

Climate change impacts

The stability and size of the polynya are sensitive to changes in wind patterns, which may be altered by shifts in the Southern Annular Mode and the strength of the Amundsen Sea Low. Increased freshwater input from melting ice shelves like the Ross Ice Shelf or the West Antarctic Ice Sheet could stratify the water column, potentially suppressing the deep vertical mixing necessary for bottom water formation. Changes in polynya activity could disrupt the delicate timing of the phytoplankton bloom, with cascading effects on dependent species like Antarctic krill and Adélie penguin. These processes are a major focus of the Intergovernmental Panel on Climate Change assessments and models developed by institutions like the British Antarctic Survey and the Alfred Wegener Institute.

Category:Polynyas Category:Ross Sea Category:Antarctic geography