An iceberg in theArctic OceanTabular icebergIceberg from overhead showing above and submerged ice
Aniceberg is a piece offresh water ice more than 15 meters (16 yards) long[1] that has broken off aglacier or anice 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 aserious maritime hazard.
Icebergs vary considerably in size and shape. Icebergs thatcalve from glaciers inGreenland are often irregularly shaped whileAntarctic ice shelves often produce large tabular (table top) icebergs. The largest iceberg in recent history, namedB-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 ofScott Island, in the South Pacific Ocean, by theUSSGlacier on November 12, 1956. This iceberg was larger thanBelgium.[7]
Typically about one-tenth of the volume of an iceberg is above water, which follows fromArchimedes's Principle of buoyancy; thedensity of pure ice is about 920 kg/m3 (57 lb/cu ft), and that ofseawater 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.
Northern edge ofIceberg B-15A in the Ross Sea, Antarctica, 29 January 2001
Iceberg size classifications according to the International Ice Patrol[1]
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 beencalved, or broken off, from theRoss Ice Shelf ofAntarctica. 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 theNorth Atlantic was 168 metres (551 ft) above sea level, reported by the USCG icebreakerEastwind 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
wherem is the iceberg mass,v the drift velocity, and the variablesf,k, andF correspond to theCoriolis 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 massm, as well as the surface area, volume, and stability of the iceberg.[12][13] Iceberg deterioration and drift, therefore, are interconnected. Fracturing must be considered when modelling iceberg drift.[12]
Winds and currents may move icebergs close to coastlines, where they can become frozen intopack ice (one form ofsea ice), or drift into shallow waters, where they can come into contact with the seabed, a phenomenon calledseabed gouging.
Icebergs lose mass due to melting, andcalving. 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 thesea 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 "BergieSeltzer". 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 thecenter 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 evenrainbow-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 aretabular andnon-tabular. Tabular icebergs have steep sides and a flat top, much like aplateau, with a length-to-height ratio of more than 5:1.[24]
Wedge: An iceberg with a steep edge on one side and a slope on the opposite side.
Dry-dock: An iceberg that haseroded to form a slot orchannel.
Blocky: An iceberg with steep, vertical sides and a flat top. It differs from tabular icebergs in that itsaspect ratio, the ratio between its width and height, is small, more like that of a block than a flat sheet.
Prior to 1914 there was no system in place to track icebergs to guard ships against collisions[citation needed] despitefatal 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 ofwatertight compartmentalization in ship construction led designers to declare their ships "unsinkable".
During the1912 sinking of theTitanic, theiceberg 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, theUnited States Navy patrolled the waters and monitored ice movements. In November 1913, theInternational Conference on the Safety of Life at Sea met inLondon to devise a more permanent system of observing icebergs. Within three months the participating maritime nations had formed theInternational Ice Patrol (IIP). The goal of the IIP was to collect data onmeteorology andoceanography to measure currents, ice-flow,ocean temperature, and salinity levels. They monitored iceberg dangers near theGrand 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 ofradar 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 ofsatellite photographs of ice in Antarctica. Systems for optical satellites had been developed but were still limited by weather conditions. In the 1980s, driftingbuoys were used in Antarctic waters for oceanographic andclimate research. They are equipped with sensors that measure ocean temperature and currents.
Acoustic monitoring of an iceberg
Side looking airborne radar (SLAR) made it possible to acquire images regardless of weather conditions. On November 4, 1995,Canada launchedRADARSAT-1. Developed by theCanadian Space Agency, it provides images of Earth for scientific and commercial purposes. This system was the first to usesynthetic aperture radar (SAR), which sendsmicrowave energy to the ocean surface and records the reflections to track icebergs. TheEuropean Space Agency launchedENVISAT (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 launchedRADARSAT-2 in December 2007, which uses SAR and multi-polarization modes and follows the sameorbit 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 ofArctic,Antarctic,Great Lakes andChesapeake 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 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.[32] In 2017, a business from theUAE announced plans to tow an iceberg from Antarctica to the Middle East; in 2019 salvage engineerNick Sloane announced a plan to move one to South Africa[33] at an estimated cost of $200 million.[32] In 2019, a German company, Polewater, announced plans to tow Antarctic icebergs to places like South Africa.[34][35]
Companies have used iceberg water in products such asbottled water, fizzy ice cubes and alcoholic drinks.[34] For example, Iceberg Beer byQuidi Vidi Brewing Company is made from icebergs found aroundSt. John's, Newfoundland.[36] Although annual iceberg supply inNewfoundland 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.[34]
The freshwater injected into the ocean by melting icebergs can change the density of the seawater in the vicinity of the iceberg.[37][38] Fresh melt water released at depth is lighter, and therefore more buoyant, than the surrounding seawater causing it to rise towards the surface.[37][38] Icebergs can also act as floatingbreakwaters, impacting ocean waves.[39]
Icebergs contain variable concentrations of nutrients and minerals that are released into the ocean during melting.[40][41] Iceberg-derived nutrients, particularly the iron contained in sediments, can fuel blooms of phytoplankton.[40][42] Samples collected from icebergs in Antarctica, Patagonia, Greenland, Svalbard, and Iceland, however, show that iron concentrations vary significantly,[41] complicating efforts to generalize the impacts of icebergs on marine ecosystems.
Iceberg B15 calved from theRoss 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.[43] It has been hypothesized that this breakup may also have been abetted by ocean swell generated by anAlaskan storm 6 days earlier and 13,500 kilometres (8,400 mi) away.[44][45]
2010, Ice sheet, 260 km2 (100 sq mi), broken off ofPetermann Glacier in northern Greenland on August 5, 2010, considered to be the largest Arctic iceberg since 1962.[48] About a month later, this iceberg split into two pieces upon crashing into Joe Island in theNares Strait next to Greenland.[49] In June 2011, large fragments of the Petermann Ice Islands were observed off the Labrador coast.[50]
One of the most infamous icebergs in history is theiceberg that sank theTitanic. The catastrophe led to the establishment of anInternational Ice Patrol shortly afterwards. 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 ofManhattan Island.[58][59][60][61][62]
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.[63]Caspar David Friedrich,The Sea of Ice, 1823–1824 is a polar landscape with an iceberg and ship wreck depicting the dangers of such conditions.[64]William Bradford created detailed paintings of sailing ships set in arctic coasts and was fascinated by icebergs.[65]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.[66]
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 anAurora Borealis. The ship made it through unscathed to the next morning, when the sun rose and "touched the crowns, Of all those arctic kings".[67]
Because much of an iceberg is below the water's surface and not readily visible, the expression "tip of [an] iceberg" is often used to illustrate that what is visible or addressable is a small part of a larger unseen issue.Metaphorical references to icebergs include theiceberg theory or theory of omission in writing adopted, for example, byErnest Hemingway,Sigmund Freud's iceberg model of thepsyche,[68] the "behavioural iceberg",[69] and models analysing the frequencies of accidents and underlying errors.[70]
^Meroni, Agostino N.; McConnochie, Craig D.; Cenedese, Claudia; Sutherland, Bruce; Snow, Kate (10 January 2019). "Nonlinear influence of the Earth's rotation on iceberg melting".Journal of Fluid Mechanics.858:832–851.Bibcode:2019JFM...858..832M.doi:10.1017/jfm.2018.798.S2CID126234419.
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