Iceberg

An iceberg is a piece of freshwater ice more than 15 m 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]

Etymology

The word iceberg is a partial

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.

The largest icebergs recorded have been

Drift

A given iceberg's trajectory through the ocean can be modelled by integrating the equation

${\displaystyle m{\frac {d{\vec {v}}}{dt}}=-mf{\vec {k}}\times {\vec {v}}+{\vec {F}}_{\text{a}}+{\vec {F}}_{\text{w}}+{\vec {F}}_{\text{r}}+{\vec {F}}_{\text{s}}+{\vec {F}}_{\text{p}},}$

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 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.

Mass loss

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

${\displaystyle M_{b}=K\Delta u^{0.8}{\frac {T_{0}-T}{L^{0.2}}},}$

where ${\displaystyle M_{\text{b}}}$ is the melt rate in m/day, ${\displaystyle \Delta u}$ is the relative velocity between the iceberg and the ocean, ${\displaystyle T_{0}-T}$ is the temperature difference between the ocean and the iceberg, and ${\displaystyle L}$ is the length of the iceberg. ${\displaystyle K}$ is a constant based on properties of the iceberg and the ocean and is approximately ${\displaystyle 0.75^{\circ }{\text{C}}^{-1}{\text{m}}^{0.4}{\text{day}}^{-1}{\text{s}}^{0.8}}$ 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

${\displaystyle M_{\text{e}}=cS_{s}(T_{\text{s}}+2)[1+{\text{cos}}(I_{\text{c}}^{3}\pi )],}$

where ${\displaystyle M_{\text{e}}}$ is the wave erosion rate in m/day, ${\displaystyle c={\frac {1}{12}}{\text{m day}}^{-1}}$, ${\displaystyle S_{\text{S}}}$ describes the sea state, ${\displaystyle T_{\text{S}}}$ is the sea surface temperature, and ${\displaystyle I_{\text{c}}}$ is the sea ice concentration.^[17]

Bubbles

Air trapped in snow forms bubbles as the snow is compressed to form firn and then glacial ice.^[18] Icebergs can contain up to 10% air bubbles by volume.^{[18][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.^[19]

Stability

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.^[20] 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.^[21][22]

Color

Icebergs are generally white because they are covered in snow, but can be green, blue, yellow, black, striped, or even rainbow-colored.^[23] 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.^[24]

Shape

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.^[25]

This type of iceberg, also known as an ice island,^[26] 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:^[27]

• Dome: An iceberg with a rounded top.
• Pinnacle: An iceberg with one or more spires.
• Wedge: An iceberg with a steep edge on one side and a slope on the opposite side.
• Dry-dock: An iceberg that has eroded to form a slot or channel.
• Blocky: An iceberg with steep, vertical sides and a flat top. It differs from tabular icebergs in that its aspect ratio, the ratio between its width and height, is small, more like that of a block than a flat sheet.

Monitoring and control

History

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

Technological development

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:^[30]

A – longitude 0° to 90° W (Bellingshausen Sea, Weddell Sea)

B – longitude 90° W to 180° (Amundsen Sea, Eastern Ross Sea)

C – longitude 90° E to 180° (Western Ross Sea, Wilkes Land)

D – longitude 0° to 90° E (Amery Ice Shelf, Eastern Weddell Sea)

The Danish Meteorological Institute monitors iceberg populations around Greenland using data collected by the synthetic aperture radar (SAR) on the Sentinel-1 satellites.

Iceberg management

In Labrador and Newfoundland, iceberg management plans have been developed to protect offshore installations from impacts with icebergs.^[31]

Commercial use

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 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^[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 as

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 floating breakwaters, 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.

Recent large icebergs

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 an Alaskan storm 6 days earlier and 13,500 kilometres (8,400 mi) away.^[44][45]

• 1987, Iceberg B-9, 5,390 km² (2,080 sq mi)
• 1998, Iceberg A-38, about 6,900 km² (2,700 sq mi)^[46]
• 1999, Iceberg B-17B 140 km² (54 sq mi), shipping alert issued December 2009.^[47]
• 2000, Iceberg B-15 11,000 km² (4,200 sq mi)
• 2002, Iceberg C-19, 5,500 km² (2,100 sq mi)
• 2002, Iceberg B-22, 5,490 km² (2,120 sq mi)
• 2003 broke off, Iceberg B-15A, 3,100 km² (1,200 sq mi)
• 2006, Iceberg D-16, 310 km² (120 sq mi)
• 2010, Ice sheet, 260 km² (100 sq mi), broken off of Petermann 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 the Nares Strait next to Greenland.^[49] In June 2011, large fragments of the Petermann Ice Islands were observed off the Labrador coast.^[50]
• 2014, Iceberg B-31, 615 km² (237 sq mi), 2014^[51]
• 2017, Iceberg A-68, (Larsen C) 5,800 km² (2,200 sq mi)^[52]
• 2018, Iceberg B-46, 225 km² (87 sq mi)^[53]
• 2019,
  Iceberg D-28, 1,636 km² (632 sq mi)^[54]
• 2021, Iceberg A-74 from the Brunt Ice Shelf, 1,270 km² (490 sq mi)^[55][56]
• 2021,
  Ronne Ice Shelf, 4,320 km² (1,670 sq mi)^[57]

In culture

One of the most prominently known icebergs in recorded history is that which sank the

Manhattan 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 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]

See also

• List of recorded icebergs by area
• Drifting ice station
• Ice calving
• Sea ice
• Polar ice cap
• Polar ice pack (disambiguation)
• Polynya
• Sea ice
• Seabed gouging by ice
• Shelf ice

References

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External links

Wikimedia Commons has media related to:
Iceberg (category)

• Iceberg Finder Service for east coast of Canada
• Icebergs of The Arctic and Antarctic
• Works related to Iceberg at Wikisource