McMurdo Sound
The McMurdo Sound is a sound in Antarctica, known as the southernmost passable body of water in the world, located approximately from the South Pole.
Captain James Clark Ross discovered the sound in February 1841 and named it after Lieutenant Archibald McMurdo of HMS Terror. The sound serves as a resupply route for cargo ships and airplanes that land on floating ice airstrips near McMurdo Station. The McMurdo seasonal Ice Runway was operated from October to December from the 1950s to the 2010s, then in December the ice breaks up and McMurdo port is opened by an Icebreaker ship and ships can resupply the Antarctic bases.
Physical characteristics
Boundary and extents
The sound extends approximately 55 kilometers in length and width, and opens into the larger Ross Sea to the north. To the south, the sound is bounded by the Ross Ice Shelf cavity, to the west lies the Royal Society Range, and to the east is Ross Island. McMurdo Sound is separated from the McMurdo Ice Shelf by the Haskell Strait. Winter Quarters Bay lies at the south end of the Sound and is the southernmost port on Earth.Navigability
While the sound is navigable, it contains a significant amount of drift ice, especially along the shoreline of Winter Quarters Bay. The pack ice that girdles the shoreline at Winter Quarters Bay and elsewhere in the sound presents a considerable obstacle to surface ships. Vessels require ice-strengthened hulls and often have to rely upon escort by icebreakers. Less than 10 percent of McMurdo Sound's shoreline is free of ice.During austral winter, McMurdo Sound presents a large expanse of surface ice. In summer, ships approaching the sound are often blocked by various amounts of first-year ice, fast ice, and hard multi-year ice. Subsequently, icebreakers are required for maritime resupply missions to McMurdo Station.
Ross Island is the southernmost piece of land in Antarctica that is accessible by ship. In addition, the harbour at McMurdo's Winter Quarters Bay is the world's southernmost seaport. The access by ships depends upon favorable ice conditions.
Tourism is increasingly popular in other parts of Antarctica but remains limited in McMurdo Sound due to the extreme sea conditions.
Temperatures
Cold circumpolar currents of the Southern Ocean shrink the flow of warm South Pacific or South Atlantic waters reaching McMurdo Sound and other Antarctic coastal waters. McMurdo Sound experiences katabatic winds from the Antarctic polar plateau. McMurdo Sound freezes over with sea ice about thick during the winter. During the austral summer when the pack ice breaks up, wind and currents may push the ice northward into the Ross Sea, stirring up cold bottom currents that spill into the ocean basins. Temperatures during the winter months at McMurdo Station have dropped as low as. December and January are the warmest months, with average highs at.Effects of wind
Polar winds are a driving force behind weather systems arising from three surface zones that converge at McMurdo Sound: the polar plateau and the Transantarctic Mountains, the Ross Ice Shelf, and the Ross Sea. These surface zones create a range of dynamic weather systems. Cold, heavy air descending rapidly from the polar plateau at elevations of or more spawns fierce katabatic winds. These dry winds can reach hurricane force when they reach the Antarctic coast. Wind instruments recorded Antarctica's highest wind velocity at the coastal station Dumont d'Urville in July 1972 at .Prevailing winds into McMurdo Sound shoot between mountain passes and other land formations, producing blizzards known locally as "Herbies". Such blizzards can occur any time of year. Residents of McMurdo Station and Scott Base have dubbed the nearby White Island and Black Island "Herbie Alley" due to winds that funnel blizzards between the islands.
Overall the continent's extremely cold air does not hold enough moisture for significant snowfall. The annual snowfall on Ross Island averages only. Snowfall in Antarctica's interior is far less at. Snow seldom accumulates on the McMurdo Dry Valleys on the western shores of McMurdo Sound.
McMurdo Sound provides an important component in Antarctica's global effects upon climate. A key factor is the polar winds that can drive the sound's pack ice into the Ross Sea summer or winter. Frigid katabatic winds rake subsequently exposed water, causing sea ice to form. Freezing surface water excludes salt from the water below; leaving behind heavy, cold water that sinks to the ocean floor. This process repeats along Antarctica's coastal areas, spreading cold sea water into Earth's ocean basins.
According to an interview with climatologist Gerd Wendler, published in the National Science Foundation's Antarctic Sun, one could dive to the ocean floor anywhere in the world and encounter water from the coast of Antarctica. "Seventy-five percent of all the bottom water, wherever you are, comes from Antarctica."
Temperatures
- Average mean sea-level temp:.
- Monthly mean range: in January to in August.
- Stormiest months: February and October.
Wildlife
File:Underwater mcmurdo sound.jpg|thumb|left|Underwater photo showing the diverse animal life in McMurdo Sound, including the scallop Adamussium colbecki, sea urchin Sterechinus neumayeri, sea sponge Homaxinella balfourensis, brittlestar Ophionotus victoriae and sea spider Colossendeis
Antarctic penguins, emperor penguins, and Adélie penguins live in and around the sound. The Weddell seal, leopard seal, and crabeater seal have been spotted, as well as orcas.
Strategic importance
McMurdo Sound's role as a strategic waterway dates back to early 20th-century Antarctic exploration. British explorers Ernest Shackleton and Robert Scott built bases on the Sound's shoreline for their overland expeditions to the South Pole.McMurdo Sound's logistic importance continues today. Aircraft transporting cargo and passengers land on frozen runways at Williams Field on the McMurdo Ice Shelf. Moreover, the annual sealift of a cargo ship and fuel tanker rely upon the sound as a supply route to the continent's largest base, the United States McMurdo Station. Both the U.S. base and New Zealand's nearby Scott Base are on the southern tip of Ross Island.
Iceberg B-15A
In March 2000, the long Iceberg B-15, the largest ever seen at the time, broke off from the Ross Ice Shelf and then suddenly broke up on 27 October 2005.Research based upon measurements retrieved from a seismometer previously placed on B-15 indicated that ocean swells caused by an earthquake away in the Gulf of Alaska caused the breakup, according to a report by the U.S. National Public Radio. Wind and sea currents shifted the smaller, but still massive Iceberg B-15A towards McMurdo Sound. B-15A's girth temporarily blocked the outflow of pack ice from McMurdo Sound.
Iceberg B-15A's grounding at the mouth of McMurdo Sound also blocked the path for thousands of penguins to reach their food source in open water. Moreover, pack ice built up behind the iceberg in the Ross Sea creating a nearly frozen barrier that blocked two cargo ships en route to supply McMurdo Station, according to the National Science Foundation.
The icebreakers USCGC Polar Star and the Russian Krasin were required to open a ship channel through ice up to thick. The last leg of the channel followed a route along the eastern shoreline of McMurdo Sound adjacent to Ross Island. The icebreakers escorted the tanker USNS Paul Buck to McMurdo Station's ice pier in late January. The freighter MV American Tern followed on 3 February.
Similar pack ice blocked a National Geographic expedition aboard the Braveheart from reaching B-15A. However, expedition divers were able to explore the underwater world of another grounded tabular iceberg. They encountered a surprising environment of fish and other sea life secreted within a deep iceberg crevasse. Discoveries included starfish, crabs, and ice fish. The latter were found to have burrowed thumb-sized holes into the ice.
The expedition reported witnessing an iceberg exploding. Shards of ice erupted into the air as if a bomb went off only hours after divers surfaced and after the Braveheart moved away from the iceberg.
Pollution
More than 50 years of continuous operation of the United States and New Zealand bases on Ross Island have left pockets of severe pollution in McMurdo Sound. Until 1981, McMurdo Station residents simply towed their garbage out to the sea ice and let nature take its course. The garbage sank to the sea floor when the ice broke up in the spring, according to news reports.A 2001 survey of the seabed near McMurdo revealed 15 vehicles, 26 shipping containers, and 603 fuel drums, as well as some 1,000 miscellaneous items dumped on an area of some. Findings by scuba divers were reported in the State of the Environment Report, a New Zealand-sponsored study.
The study by the government agency Antarctica New Zealand revealed that decades of pumping thousands of gallons of raw sewage from 1,200 summer residents into the sound had fouled Winter Quarters Bay. The pollution ended in 2003 when a $5 million waste treatment plant went online. Other documented bay water contaminants include leakage from an open dump at the station. The dump introduced heavy metals, petroleum compounds, and chemicals into the water.
A study by the Australian Institute of Marine Science found that anti-fouling paints on the hulls of icebreakers are polluting McMurdo Sound. Such paints kill algae, barnacles, and other marine life that adhere to ship hulls. Scientists found that samples taken from the ocean floor contained high levels of tributyltin, a component of the anti-fouling paints. "The levels are close to the maximum you will find anywhere, apart from ship grounding sites", said Andrew Negri of the institute.
Ships, aircraft, and land-based operations in McMurdo Sound all present hazards of oil spills or fuel leaks. For instance, in 2003, the build-up of two years of difficult ice conditions blocked the U.S. tanker MV Richard G. Matthiesen from reaching the harbour at McMurdo Station, despite the assistance of icebreakers. Instead, shore workers rigged a temporary fuel line over the ice pack to discharge the ship's cargo. The ship pumped more than of fuel to storage facilities at McMurdo.
Officials balance the potential for fuel spills inherent in such operations against the critical need to keep McMurdo Station supplied with oil. A fuel tank spill in an unrelated onshore incident in 2003 spilt roughly of Diesel fuel at a helicopter pad at McMurdo Station. The 1989 grounding of the Argentinean ship Bahía Paraíso and subsequent spillage of of oil into the sea near the Antarctic Peninsula showed the environmental hazards inherent in supply missions to Antarctica.
Zoologist Clive Evans from Auckland University described McMurdo's harbor as "one of the most polluted harbors in the world in terms of oil", according to a 2004 article by the New Zealand Herald.