An iceberg is a piece of freshwater ice more than 15 meters (16 yards) long [1] that has broken off a glacier or an ice shelf and is floating freely in open water. [2] [3] Smaller chunks of floating glacially derived ice are called "growlers" or "bergy bits". [4] [5] Much of an iceberg is below the water's surface, which led to the expression "tip of the iceberg" to illustrate a small part of a larger unseen issue. Icebergs are considered a serious maritime hazard.
Icebergs vary considerably in size and shape. Icebergs that calve from glaciers in Greenland are often irregularly shaped while Antarctic ice shelves often produce large tabular (table top) icebergs. The largest iceberg in recent history, named B-15, was measured at nearly 300 by 40 kilometres (186 by 25 mi) in 2000. [6] The largest iceberg on record was an Antarctic tabular iceberg measuring 335 by 97 kilometres (208 by 60 mi) sighted 240 kilometres (150 mi) west of Scott Island, in the South Pacific Ocean, by the USS Glacier on November 12, 1956. This iceberg was larger than Belgium. [7]
The word iceberg is a partial loan translation from the Dutch word ijsberg, literally meaning ice mountain, [8] cognate to Danish isbjerg, German Eisberg, Low Saxon Iesbarg and Swedish isberg .
Typically about one-tenth of the volume of an iceberg is above water, which follows from Archimedes's Principle of buoyancy; the density of pure ice is about 920 kg/m3 (57 lb/cu ft), and that of seawater about 1,025 kg/m3 (64 lb/cu ft). The contour of the underwater portion can be difficult to judge by looking at the portion above the surface.
Size class | Height (m) | Length (m) |
---|---|---|
Growler | <1 | <5 |
Bergy bit | 1–5 | 5–15 |
Small | 5–15 | 15–60 |
Medium | 15–45 | 60–122 |
Large | 45–75 | 122–213 |
Very large | >75 | >213 |
The largest icebergs recorded have been calved, or broken off, from the Ross Ice Shelf of Antarctica. Icebergs may reach a height of more than 100 metres (300 ft) above the sea surface and have mass ranging from about 100,000 tonnes up to more than 10 million tonnes. Icebergs or pieces of floating ice smaller than 5 meters above the sea surface are classified as "bergy bits"; smaller than 1 meter—"growlers". [9] The largest known iceberg in the North Atlantic was 168 metres (551 ft) above sea level, reported by the USCG icebreaker Eastwind in 1958, making it the height of a 55-story building. These icebergs originate from the glaciers of western Greenland and may have interior temperatures of −15 to −20 °C (5 to −4 °F). [10]
A given iceberg's trajectory through the ocean can be modelled by integrating the equation
where m is the iceberg mass, v the drift velocity, and the variables f, k, and F correspond to the Coriolis force, the vertical unit vector, and a given force. The subscripts a, w, r, s, and p correspond to the air drag, water drag, wave radiation force, sea ice drag, and the horizontal pressure gradient force. [11] [12]
Icebergs deteriorate through melting and fracturing, which changes the mass m, as well as the surface area, volume, and stability of the iceberg. [12] [13] Iceberg deterioration and drift, therefore, are interconnected ie. iceberg thermodynamics, and fracturing must be considered when modelling iceberg drift. [12]
Winds and currents may move icebergs close to coastlines, where they can become frozen into pack ice (one form of sea ice), or drift into shallow waters, where they can come into contact with the seabed, a phenomenon called seabed gouging.
Icebergs lose mass due to melting, and calving. Melting can be due to solar radiation, or heat and salt transport from the ocean. Iceberg calving is generally enhanced by waves impacting the iceberg.
Melting tends to be driven by the ocean, rather than solar radiation. Ocean driven melting is often modelled as
where is the melt rate in m/day, is the relative velocity between the iceberg and the ocean, is the temperature difference between the ocean and the iceberg, and is the length of the iceberg. is a constant based on properties of the iceberg and the ocean and is approximately in the polar ocean. [14]
The influence of the shape of an iceberg [15] and of the Coriolis force [16] on iceberg melting rates has been demonstrated in laboratory experiments.
Wave erosion is more poorly constrained but can be estimated by
where is the wave erosion rate in m/day, , describes the sea state, is the sea surface temperature, and is the sea ice concentration. [14]
Air trapped in snow forms bubbles as the snow is compressed to form firn and then glacial ice. [17] Icebergs can contain up to 10% air bubbles by volume. [17] [ failed verification ] These bubbles are released during melting, producing a fizzing sound that some may call "Bergie Seltzer". This sound results when the water-ice interface reaches compressed air bubbles trapped in the ice. As each bubble bursts it makes a "popping" sound [10] and the acoustic properties of these bubbles can be used to study iceberg melt. [18]
An iceberg may flip, or capsize, as it melts and breaks apart, changing the center of gravity. Capsizing can occur shortly after calving when the iceberg is young and establishing balance. [19] Icebergs are unpredictable and can capsize anytime and without warning. Large icebergs that break off from a glacier front and flip onto the glacier face can push the entire glacier backwards momentarily, producing 'glacial earthquakes' that generate as much energy as an atomic bomb. [20] [21]
Icebergs are generally white because they are covered in snow, but can be green, blue, yellow, black, striped, or even rainbow-colored. [22] Seawater, algae and lack of air bubbles in the ice can create diverse colors. Sediment can create the dirty black coloration present in some icebergs. [23]
In addition to size classification (Table 1), icebergs can be classified on the basis of their shapes. The two basic types of iceberg forms are tabular and non-tabular. Tabular icebergs have steep sides and a flat top, much like a plateau, with a length-to-height ratio of more than 5:1. [24]
This type of iceberg, also known as an ice island, [25] can be quite large, as in the case of Pobeda Ice Island. Antarctic icebergs formed by breaking off from an ice shelf, such as the Ross Ice Shelf or Filchner–Ronne Ice Shelf, are typically tabular. The largest icebergs in the world are formed this way.
Non-tabular icebergs have different shapes and include: [26]
Prior to 1914 there was no system in place to track icebergs to guard ships against collisions[ citation needed ] despite fatal sinkings of ships by icebergs. In 1907, SS Kronprinz Wilhelm , a German liner, rammed an iceberg and suffered a crushed bow, but she was still able to complete her voyage. The advent of watertight compartmentalization in ship construction led designers to declare their ships "unsinkable".
During the 1912 sinking of the Titanic, the iceberg that sank the Titanic killed more than 1,500 of its estimated 2,224 passengers and crew, seriously damaging the 'unsinkable' claim. For the remainder of the ice season of that year, the United States Navy patrolled the waters and monitored ice movements. In November 1913, the International Conference on the Safety of Life at Sea met in London to devise a more permanent system of observing icebergs. Within three months the participating maritime nations had formed the International Ice Patrol (IIP). The goal of the IIP was to collect data on meteorology and oceanography to measure currents, ice-flow, ocean temperature, and salinity levels. They monitored iceberg dangers near the Grand Banks of Newfoundland and provided the "limits of all known ice" in that vicinity to the maritime community. The IIP published their first records in 1921, which allowed for a year-by-year comparison of iceberg movement.
Aerial surveillance of the seas in the early 1930s allowed for the development of charter systems that could accurately detail the ocean currents and iceberg locations. In 1945, experiments tested the effectiveness of radar in detecting icebergs. A decade later, oceanographic monitoring outposts were established for the purpose of collecting data; these outposts continue to serve in environmental study. A computer was first installed on a ship for the purpose of oceanographic monitoring in 1964, which allowed for a faster evaluation of data. By the 1970s, ice-breaking ships were equipped with automatic transmissions of satellite photographs of ice in Antarctica. Systems for optical satellites had been developed but were still limited by weather conditions. In the 1980s, drifting buoys were used in Antarctic waters for oceanographic and climate research. They are equipped with sensors that measure ocean temperature and currents.
Side looking airborne radar (SLAR) made it possible to acquire images regardless of weather conditions. On November 4, 1995, Canada launched RADARSAT-1. Developed by the Canadian Space Agency, it provides images of Earth for scientific and commercial purposes. This system was the first to use synthetic aperture radar (SAR), which sends microwave energy to the ocean surface and records the reflections to track icebergs. The European Space Agency launched ENVISAT (an observation satellite that orbits the Earth's poles) [27] on March 1, 2002. ENVISAT employs advanced synthetic aperture radar (ASAR) technology, which can detect changes in surface height accurately. The Canadian Space Agency launched RADARSAT-2 in December 2007, which uses SAR and multi-polarization modes and follows the same orbit path as RADARSAT-1. [28]
Iceberg concentrations and size distributions are monitored worldwide by the U.S. National Ice Center (NIC), established in 1995, which produces analyses and forecasts of Arctic, Antarctic, Great Lakes and Chesapeake Bay ice conditions. More than 95% of the data used in its sea ice analyses are derived from the remote sensors on polar-orbiting satellites that survey these remote regions of the Earth.
The NIC is the only organization that names and tracks all Antarctic Icebergs. It assigns each iceberg larger than 10 nautical miles (19 km) along at least one axis a name composed of a letter indicating its point of origin and a running number. The letters used are as follows: [29]
The Danish Meteorological Institute monitors iceberg populations around Greenland using data collected by the synthetic aperture radar (SAR) on the Sentinel-1 satellites.
In Labrador and Newfoundland, iceberg management plans have been developed to protect offshore installations from impacts with icebergs. [30]
The idea of towing large icebergs to other regions as a source of water has been raised since at least the 1950s, without having been put into practice. [31] In 2017, a business from the UAE announced plans to tow an iceberg from Antarctica to the Middle East; in 2019 salvage engineer Nick Sloane announced a plan to move one to South Africa [32] at an estimated cost of $200 million. [31] In 2019, a German company, Polewater, announced plans to tow Antarctic icebergs to places like South Africa. [33] [34]
Companies have used iceberg water in products such as bottled water, fizzy ice cubes and alcoholic drinks. [33] For example, Iceberg Beer by Quidi Vidi Brewing Company is made from icebergs found around St. John's, Newfoundland. [35] Although annual iceberg supply in Newfoundland and Labrador exceeds the total freshwater consumption of the United States, in 2016 the province introduced a tax on iceberg harvesting and imposed a limit on how much fresh water can be exported yearly. [33]
The freshwater injected into the ocean by melting icebergs can change the density of the seawater in the vicinity of the iceberg. [36] [37] Fresh melt water released at depth is lighter, and therefore more buoyant, than the surrounding seawater causing it to rise towards the surface. [36] [37] Icebergs can also act as floating breakwaters, impacting ocean waves. [38]
Icebergs contain variable concentrations of nutrients and minerals that are released into the ocean during melting. [39] [40] Iceberg-derived nutrients, particularly the iron contained in sediments, can fuel blooms of phytoplankton. [39] [41] Samples collected from icebergs in Antarctica, Patagonia, Greenland, Svalbard, and Iceland, however, show that iron concentrations vary significantly, [40] complicating efforts to generalize the impacts of icebergs on marine ecosystems.
Iceberg B15 calved from the Ross Ice Shelf in 2000 and initially had an area of 11,000 square kilometres (4,200 sq mi). It broke apart in November 2002. The largest remaining piece of it, Iceberg B-15A, with an area of 3,000 square kilometres (1,200 sq mi), was still the largest iceberg on Earth until it ran aground and split into several pieces October 27, 2005, an event that was observed by seismographs both on the iceberg and across Antarctica. [42] It has been hypothesized that this breakup may also have been abetted by ocean swell generated by an Alaskan storm 6 days earlier and 13,500 kilometres (8,400 mi) away. [43] [44]
One of the most infamous icebergs in history is the iceberg that sank the Titanic. The catastrophe led to the establishment of an International Ice Patrol shortly after. Icebergs in both the northern and southern hemispheres have often been compared in size to multiples of the 59.1 square kilometres (22.8 sq mi)-area of Manhattan Island. [57] [58] [59] [60] [61]
Artists have used icebergs as the subject matter for their paintings. Frederic Edwin Church, The Icebergs , 1861 was painted from sketches Church completed on a boat trip off Newfoundland and Labrador. [62] Caspar David Friedrich, The Sea of Ice, 1823–1824 is polar landscape with an iceberg and ship wreck depicting the dangers of such conditions. [63] William Bradford created detailed paintings of sailing ships set in arctic coasts and was fascinated by icebergs. [64] Albert Bierstadt made studies on arctic trips aboard steamships in 1883 and 1884 that were the basis of his paintings of arctic scenes with colossal icebergs made in the studio. [65]
American poet, Lydia Sigourney, wrote the poem "Icebergs". While on a return journey from Europe in 1841, her steamship encountered a field of icebergs overnight, during an Aurora Borealis. The ship made it through unscathed to the next morning, when the sun rose and "touched the crowns, Of all those arctic kings." [66]
The climate of Antarctica is the coldest on Earth. The continent is also extremely dry, averaging 166 mm (6.5 in) of precipitation per year. Snow rarely melts on most parts of the continent, and, after being compressed, becomes the glacier ice that makes up the ice sheet. Weather fronts rarely penetrate far into the continent, because of the katabatic winds. Most of Antarctica has an ice-cap climate with extremely cold and dry weather.
The Ross Ice Shelf is the largest ice shelf of Antarctica. It is several hundred metres thick. The nearly vertical ice front to the open sea is more than 600 kilometres (370 mi) long, and between 15 and 50 metres high above the water surface. Ninety percent of the floating ice, however, is below the water surface.
An ice shelf is a large platform of glacial ice floating on the ocean, fed by one or multiple tributary glaciers. Ice shelves form along coastlines where the ice thickness is insufficient to displace the more dense surrounding ocean water. The boundary between the ice shelf (floating) and grounded ice is referred to as the grounding line; the boundary between the ice shelf and the open ocean is the ice front or calving front.
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi). The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice sheets are bigger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are termed an ice cap. An ice cap will typically feed a series of glaciers around its periphery.
The Filchner–Ronne Ice Shelf or Ronne–Filchner Ice Shelf is an Antarctic ice shelf bordering the Weddell Sea.
The Larsen Ice Shelf is a long ice shelf in the northwest part of the Weddell Sea, extending along the east coast of the Antarctic Peninsula from Cape Longing to Smith Peninsula. It is named after Captain Carl Anton Larsen, the master of the Norwegian whaling vessel Jason, who sailed along the ice front as far as 68°10' South during December 1893. In finer detail, the Larsen Ice Shelf is a series of shelves that occupy distinct embayments along the coast. From north to south, the segments are called Larsen A, Larsen B, and Larsen C by researchers who work in the area. Further south, Larsen D and the much smaller Larsen E, F and G are also named.
The Brunt Ice Shelf borders the Antarctic coast of Coats Land between Dawson-Lambton Glacier and Stancomb-Wills Glacier Tongue. It was named by the UK Antarctic Place-names Committee after David Brunt, British meteorologist, Physical Secretary of the Royal Society, 1948–57, who was responsible for the initiation of the Royal Society Expedition to this ice shelf in 1955.
Iceberg B-15 was the largest recorded iceberg by area. It measured around 295 by 37 kilometres, with a surface area of 11,000 square kilometres, about the size of the island of Jamaica. Calved from the Ross Ice Shelf of Antarctica in March 2000, Iceberg B-15 broke up into smaller icebergs, the largest of which was named Iceberg B-15-A. In 2003, B-15A drifted away from Ross Island into the Ross Sea and headed north, eventually breaking up into several smaller icebergs in October 2005. In 2018, a large piece of the original iceberg was steadily moving northward, located between the Falkland Islands and South Georgia Island. As of August 2023, the U.S. National Ice Center (USNIC) still lists one extant piece of B-15 that meets the minimum threshold for tracking. This iceberg, B-15AB, measures 20 km × 7 km ; it is currently grounded off the coast of Antarctica in the western sector of the Amery region.
The Drygalski Ice Tongue, Drygalski Barrier, or Drygalski Glacier Tongue is a glacier in Antarctica, on the Scott Coast, in the northern McMurdo Sound of Ross Dependency, 240 kilometres (150 mi) north of Ross Island. The Drygalski Ice Tongue is stable by the standards of Antarctica's icefloes, and stretches 70 kilometres (43 mi) out to sea from the David Glacier, reaching the sea from a valley in the Prince Albert Mountains of Victoria Land. The Drygalski Ice Tongue ranges from 14 to 24 kilometres wide.
Pine Island Glacier (PIG) is a large ice stream, and the fastest melting glacier in Antarctica, responsible for about 25% of Antarctica's ice loss. The glacier ice streams flow west-northwest along the south side of the Hudson Mountains into Pine Island Bay, Amundsen Sea, Antarctica. It was mapped by the United States Geological Survey (USGS) from surveys and United States Navy (USN) air photos, 1960–66, and named by the Advisory Committee on Antarctic Names (US-ACAN) in association with Pine Island Bay.
Thwaites Glacier is an unusually broad and vast Antarctic glacier located east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. It was initially sighted by polar researchers in 1940, mapped in 1959–1966 and officially named in 1967, after the late American glaciologist Fredrik T. Thwaites. The glacier flows into Pine Island Bay, part of the Amundsen Sea, at surface speeds which exceed 2 kilometres (1.2 mi) per year near its grounding line. Its fastest-flowing grounded ice is centered between 50 and 100 kilometres east of Mount Murphy. Like many other parts of the cryosphere, it has been adversely affected by climate change, and provides one of the more notable examples of the retreat of glaciers since 1850.
Iceberg B-9 was an iceberg that calved from Antarctica in 1987. It measured 154 kilometres (96 mi) long and 35 kilometres (22 mi) wide; it had a total area of 5,390 square kilometres (2,080 sq mi), and is one of the longest icebergs ever recorded. This calving took place immediately east of the future calving site of Iceberg B-15; it carried away Little America V which had been closed in December 1959. Starting in October 1987, Iceberg B-9 drifted for 22 months, covering 2,000 kilometres (1,200 mi) on its journey. Initially, B-9 moved northwest for seven months, before being drawn southward by a subsurface current that eventually led to its colliding with the Ross Ice Shelf in August 1988. It then made a 100-kilometre (62 mi) radius gyre before resuming its northwest drift. It moved at an average speed of 2.5 kilometres (1.6 mi) per day over the continental shelf, as measured by NOAA-10 and DMSP satellite positions, and by the ARGOS data buoy positions. In early August 1989, B-9 broke into three large pieces north of Cape Adare. These pieces were designated as B-9A, 56 by 35 kilometres, B-9B, 100 by 35 kilometres, and B-9C, 28 by 13 kilometres.
The retreat of glaciers since 1850 is a well-documented effect of climate change. The retreat of mountain glaciers provide evidence for the rise in global temperatures since the late 19th century. Examples include mountain glaciers in western North America, Asia, the Alps in central Europe, and tropical and subtropical regions of South America and Africa. Since glacial mass is affected by long-term climatic changes, e.g. precipitation, mean temperature, and cloud cover, glacial mass changes are one of the most sensitive indicators of climate change. The retreat of glaciers is also a major reason for sea level rise. Excluding peripheral glaciers of ice sheets, the total cumulated global glacial losses over the 26 years from 1993 to 2018 were likely 5500 gigatons, or 210 gigatons per year.
Totten Glacier is a large glacier draining a major portion of the East Antarctic Ice Sheet, through the Budd Coast of Wilkes Land in the Australian Antarctic Territory. The catchment drained by the glacier is estimated at 538,000 km2 (208,000 sq mi), extending approximately 1,100 km (680 mi) into the interior and holds the potential to raise sea level by at least 3.5 m (11 ft). Totten drains northeastward from the continental ice but turns northwestward at the coast where it terminates in a prominent tongue close east of Cape Waldron. It was first delineated from aerial photographs taken by USN Operation Highjump (1946–47), and named by Advisory Committee on Antarctic Names (US-ACAN) for George M. Totten, midshipman on USS Vincennes of the United States Exploring Expedition (1838–42), who assisted Lieutenant Charles Wilkes with correction of the survey data obtained by the expedition.
Pobeda Ice Island, original Russian name остров Победы, is an ice island in the Mawson Sea. It is located 160 km (99 mi) off the coast of Queen Mary Land, East Antarctica. This island, which exists periodically, is formed by the running aground of a tabular iceberg.
Ice calving, also known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier. It is a form of ice ablation or ice disruption. It is the sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, ice shelf, or crevasse. The ice that breaks away can be classified as an iceberg, but may also be a growler, bergy bit, or a crevasse wall breakaway.
Petermann Glacier is a large glacier located in North-West Greenland to the east of Nares Strait. It connects the Greenland ice sheet to the Arctic Ocean at 81°10' north latitude, near Hans Island.
Ice mélange refers to a mixture of sea ice types, icebergs, and snow without a clearly defined floe that forms from shearing and fracture at the ice front. Ice mélange is commonly the result of an ice calving event where ice breaks off the edge of a glacier. Ice mélange affects many of the Earth's processes including glacier calving, ocean wave generation and frequency, generation of seismic waves, atmosphere and ocean interactions, and tidewater glacier systems. Ice mélange is possibly the largest granular material on Earth, and is quasi-2-dimensional.
Liu Yan is a Chinese Antarctic researcher best known for her work on iceberg calving. She is an associate professor of geography in the College of Global Change and Earth System Science (GCESS) and Polar Research Institute, Beijing Normal University.
An ice shelf basal channel is a type of subglacial meltwater channel that forms on the underside of floating ice shelves connected to ice sheets. Basal channels are generally rounded cavities which form parallel to ice sheet flow. These channels are found mainly around the Greenland and Antarctic ice sheets in places with relatively warm ocean water. West Antarctica in particular has the highest density of basal channels in the world. Basal channels can be tens of kilometers long, kilometers wide, and incise hundreds of meters up into an ice shelf. These channels can evolve and grow just as rapidly as ice shelves can, with some channels having incision rates approaching 22 meters per year. Basal channels are categorized based on what mechanisms created them and where they formed.
Icebergs float in salt water, but they are formed from freshwater glacial ice.