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| McMurdo Sound polynya | |
|---|---|
| Name | McMurdo Sound polynya |
| Location | Ross Sea, Southern Ocean, Antarctica |
| Coordinates | 77°50′S 166°40′E |
| Type | Polynya |
| Area | variable (tens to thousands km²) |
| Depth | surface-open water in sea ice |
| Countries | Antarctica (Research by United States Antarctic Program, New Zealand Antarctic Programme, Australian Antarctic Division) |
McMurdo Sound polynya is a recurrent area of open water within the sea ice of the Ross Sea near McMurdo Sound and Ross Island that plays a central role in Southern Ocean processes, Antarctic ecology, and polar meteorology. It influences exchanges among the Southern Ocean, Ross Ice Shelf, and atmosphere, and has been the focus of sustained programs from United States Antarctic Program, Scott Base, and McMurdo Station. The polynya's behavior is tied to regional winds, ocean currents, and sea-ice dynamics documented by collaborations including National Science Foundation, British Antarctic Survey, and Australian Antarctic Division researchers.
The polynya forms in the lee of Ross Island and adjacent to the McMurdo Sound coastline, lying seaward of the Ross Ice Shelf and near the Dry Valleys and Hut Point Peninsula. Its spatial extent varies seasonally and interannually, sometimes reaching tens to thousands of square kilometres between the grounding line of the Ross Ice Shelf and the Transantarctic Mountains. Bathymetric control from the Victoria Land Basin and interactions with the Antarctic Circumpolar Current sector influence its location, as do coastal features such as Beaumont Bay and Black Island. The polynya typically presents a mosaic of open leads and thin ice within dense pack near permanent features including McMurdo Station and Scott Base logistical areas.
Seasonal opening generally begins in late autumn and winter when katabatic flows from the Transantarctic Mountains and synoptic cyclones linked to the Amundsen Sea Low drive offshore drift of sea ice, exposing open water. The process involves combined forcing from persistent winds, coastal polynya dynamics known from studies at Weddell Sea polynyas, and local interactions with tidal currents near the McMurdo Ice Shelf margins. Freeze–thaw cycles produce dense frazil ice and platelet ice beneath the sea ice cover, while repeated lead formation supports wintertime heat loss to the atmosphere comparable to other active polynyas such as the Ross Polynya and Cape Darnley polynya.
High sensible and latent heat fluxes occur where the polynya exposes Southern Ocean surface waters to the cold Antarctic winter atmosphere, enhancing convection and brine rejection that contributes to formation of dense water masses akin to Antarctic Bottom Water precursors traced toward the Global Conveyor Belt and Meridional Overturning Circulation. Interactions with the Ross Gyre, mesoscale eddies, and the coastal current modulate advection of Circumpolar Deep Water and modified shelf waters. Atmospheric coupling involves katabatic jets, polar cyclones, and radiative cooling documented in campaigns supported by National Oceanic and Atmospheric Administration and European Space Agency remote sensing, while sea-ice thermodynamics follow models developed by groups at Scripps Institution of Oceanography and Lamont–Doherty Earth Observatory.
Repeated opening sustains marine productivity by delivering light and nutrients to the euphotic zone, supporting phytoplankton blooms observed by SeaWiFS and MODIS sensors and surveyed by expeditions from University of Washington and New Zealand Antarctic Programme. This productivity underpins food webs including krill, Antarctic silverfish, and higher trophic levels such as Adélie penguin colonies near Cape Royds, Weddell seal and minke whale foraging grounds, and benthic communities on the Ross Sea shelf. Sea-ice formation and platelet ice influence habitat for sympagic organisms and ice-associated biota investigated by teams from Monash University and University of Canterbury. The polynya also affects nutrient cycling and carbon export, with relevance to Southern Ocean carbon sink estimates advanced by international programs including the Scientific Committee on Antarctic Research.
Long-term observations reveal variability tied to climate modes such as the Southern Annular Mode and El Niño–Southern Oscillation, with decadal shifts influenced by ozone-depletion recovery and greenhouse forcing assessed by the Intergovernmental Panel on Climate Change and regional modeling centers like British Antarctic Survey. Some studies report changing polynya frequency and area associated with altered wind patterns, sea-ice concentration trends, and warming of subsurface waters linked to Circumpolar Deep Water intrusions documented by programs at Woods Hole Oceanographic Institution and NIWA. Projected impacts on local ecosystems, dense-water formation, and global stratification remain subjects of coordinated research in initiatives such as the Southern Ocean Observing System.
The polynya has been observed since early Heroic Age of Antarctic Exploration voyages near Ross Island and featured in logistics for bases like McMurdo Station and Scott Base. Scientific investigation expanded during the International Geophysical Year with oceanographic cruises by United States Antarctic Program and airborne surveys from Royal New Zealand Air Force. Later programs from National Science Foundation, Australian Antarctic Division, British Antarctic Survey, and multinational collaborations have run mooring arrays, CTD transects, autonomous platforms, and ecological studies. Historic ship operations include voyages by RV Nathaniel B. Palmer and research by parties aboard RRS James Clark Ross and RV Tangaroa.
Monitoring uses satellite remote sensing (passive microwave from NASA sensors, optical from MODIS, and altimetry), autonomous vehicles (gliders and Argo-type floats adapted for polar use), moored instruments, ship-based hydrography, and ice-tethered profilers deployed by institutions such as Lamont–Doherty Earth Observatory, Woods Hole Oceanographic Institution, and Scott Polar Research Institute. Time series from coastal observatories, aerial surveys by British Antarctic Survey aircraft, and data assimilation in numerical models from National Centers for Environmental Prediction support analysis of polynya dynamics. Datasets contribute to open repositories maintained by Polar Geospatial Center and the Scientific Committee on Antarctic Research.
Category:Polynyas Category:Ross Sea Category:Antarctic geography