document_title: Glacier

question_text: explain the behavior and activity of a retreating glacier

question_tokens: explain the behavior and activity of a retreating glacier

text: Glacier

text: Etymology and related terms[edit]

text: The word glacier is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin glaciārium, derived from the Late Latin glacia, and ultimately Latin glaciēs, meaning "ice".[4] The processes and features caused by or related to glaciers are referred to as glacial. The process of glacier establishment, growth and flow is called glaciation. The corresponding area of study is called glaciology. Glaciers are important components of the global cryosphere.

text: Types[edit]

text: Classification by size, shape, and behavior[edit]

text: Glaciers are categorized  by their morphology, thermal characteristics, and behavior. Cirque glaciers form on the crests and slopes of mountains. A glacier that fills a valley is called a valley glacier, or alternatively an alpine glacier or mountain glacier.[5] A large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field.[6] Ice caps have an area less than 50,000 km2 (19,000 sq mi) by definition.

text: Glacial bodies larger than 50,000 km2 (19,000 sq mi) are called ice sheets or continental glaciers.[7] Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces. The only extant ice sheets are the two that cover most of Antarctica and Greenland.[8] They contain vast quantities of fresh water, enough that if both melted, global sea levels would rise by over 70 m (230 ft).[9] Portions of an ice sheet or cap that extend into water are called ice shelves; they tend to be thin with limited slopes and reduced velocities.[10]  Narrow, fast-moving sections of an ice sheet are called ice streams.[11][12] In Antarctica, many ice streams drain into large ice shelves. Some drain directly into the sea, often with an ice tongue, like Mertz Glacier.

text: Tidewater glaciers are glaciers that terminate in the sea, including most glaciers flowing from Greenland, Antarctica, Baffin and Ellesmere Islands in Canada, Southeast Alaska, and the Northern and Southern Patagonian Ice Fields. As the ice reaches the sea, pieces break off, or calve, forming icebergs. Most tidewater glaciers calve above sea level, which often results in a tremendous impact as the iceberg strikes the water. Tidewater glaciers undergo centuries-long cycles of advance and retreat that are much less affected by the climate change than those of other glaciers.[13]

text: Classification by thermal state[edit]

text: Thermally, a temperate glacier is at melting point throughout the year, from its surface to its base. The ice of a polar glacier is always below the freezing point from the surface to its base, although the surface snowpack may experience seasonal melting. A sub-polar glacier includes both temperate and polar ice, depending on depth beneath the surface and position along the length of the glacier. In a similar way, the thermal regime of a glacier is often described by its basal temperature. A cold-based glacier is below freezing at the ice-ground interface, and is thus frozen to the underlying substrate. A warm-based glacier is above or at freezing at the interface, and is able to slide at this contact.[14] This contrast is thought to a large extent to govern the ability of a glacier to effectively erode its bed, as sliding ice promotes plucking at rock from the surface below.[15] Glaciers which are partly cold-based and partly warm-based are known as polythermal.[14]

text: Formation[edit]

text: Glaciers form where the accumulation of snow and ice exceeds ablation. A glacier usually originates from a landform called 'cirque' (or corrie or cwm) – a typically armchair-shaped geological feature (such as a depression between mountains enclosed by arêtes) – which collects and compresses through gravity the snow that falls into it. This snow collects and is compacted by the weight of the snow falling above it, forming névé. Further crushing of the individual snowflakes and squeezing the air from the snow turns it into "glacial ice". This glacial ice will fill the cirque until it "overflows" through a geological weakness or vacancy, such as the gap between two mountains. When the mass of snow and ice is sufficiently thick, it begins to move due to a combination of surface slope, gravity and pressure.  On steeper slopes, this can occur with as little as 15 m (50 ft) of snow-ice.

text: In temperate glaciers, snow repeatedly freezes and thaws, changing into granular ice called firn. Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser and denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice. Glacier ice is slightly less dense than ice formed from frozen water because it contains tiny trapped air bubbles.

text: Glacial ice has a distinctive blue tint because it absorbs some red light due to an overtone of the infrared OH stretching mode of the water molecule. Liquid water is blue for the same reason. The blue of glacier ice is sometimes misattributed to Rayleigh scattering due to bubbles in the ice.[16]

text: Structure[edit]

text: A glacier originates at a location called its glacier head and terminates at its glacier foot, snout, or terminus.

text: Glaciers are broken into zones based on surface snowpack and melt conditions.[17]  The ablation zone is the region where there is a net loss in glacier mass. The equilibrium line separates the ablation zone and the accumulation zone; it is the altitude where the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation.  The upper part of a glacier, where accumulation exceeds ablation, is called the accumulation zone. In general, the accumulation zone accounts for 60–70% of the glacier's surface area, more if the glacier calves icebergs. Ice in the accumulation zone is deep enough to exert a downward force that erodes underlying rock.  After a glacier melts, it often leaves behind a bowl- or amphitheater-shaped depression that ranges in size from large basins like the Great Lakes to smaller mountain depressions known as cirques.

text: The accumulation zone can be subdivided based on its melt conditions.

text:
The dry snow zone is a region where no melt occurs, even in the summer, and the snowpack remains dry.
The percolation zone is an area with some surface melt, causing meltwater to percolate into the snowpack.  This zone is often marked by refrozen ice lenses, glands, and layers.  The snowpack also never reaches melting point.
Near the equilibrium line on some glaciers, a superimposed ice zone develops.  This zone is where meltwater refreezes as a cold layer in the glacier, forming a continuous mass of ice.
The wet snow zone is the region where all of the snow deposited since the end of the previous summer has been raised to 0 °C.

text: The health of a glacier is usually assessed by determining the glacier mass balance or observing terminus behavior. Healthy glaciers have large accumulation zones, more than 60% of their area snowcovered at the end of the melt season, and a terminus with vigorous flow.

text: Following the Little Ice Age's end around 1850, glaciers around the Earth have retreated substantially. A slight cooling led to the advance of many alpine glaciers between 1950 and 1985, but since 1985 glacier retreat and mass loss has become larger and increasingly ubiquitous.[18][19][20]

text: Motion[edit]

text: Glaciers move, or flow, downhill due to gravity and the internal deformation of ice.[21] Ice behaves like a brittle solid until its thickness exceeds about 50 m (160 ft). The pressure on ice deeper than 50 m causes plastic flow. At the molecular level, ice consists of stacked layers of molecules with relatively weak bonds between layers. When the stress on the layer above exceeds the inter-layer binding strength, it moves faster than the layer below.[22]

text: Glaciers also move through basal sliding. In this process, a glacier slides over the terrain on which it sits, lubricated by the presence of liquid water.  The water is created from ice that melts under high pressure from frictional heating.  Basal sliding is dominant in temperate, or warm-based glaciers.

text: Although evidence in favour of glacial flow was known by the early 19th century, other theories of glacial motion were advanced, such as the idea that melt water, refreezing inside glaciers, caused the glacier to dilate and extend its length. As it became clear that glaciers behaved to some degree as if the ice were a viscous fluid, it was argued that "regelation", or the melting and refreezing of ice at a temperature lowered by the pressure on the ice inside the glacier, was what allowed the ice to deform and flow.  James Forbes came up with the essentially correct explanation in the 1840s, although it was several decades before it was fully accepted.[23]

text: Fracture zone and cracks[edit]

text: The top 50 m (160 ft) of a glacier are rigid because they are under low pressure. This upper section is known as the fracture zone and moves mostly as a single unit over the plastically flowing lower section. When a glacier moves through irregular terrain, cracks called crevasses develop in the fracture zone.  Crevasses form due to differences in glacier velocity.  If two rigid sections of a glacier move at different speeds and directions, shear forces cause them to break apart, opening  a crevasse.  Crevasses are seldom more than 46 m (150 ft) deep but in some cases can be 300 m (1,000 ft) or even deeper. Beneath this point, the plasticity of the ice is too great for cracks to form.  Intersecting crevasses can create isolated peaks in the ice, called seracs.

text: Crevasses can form in several different ways.  Transverse crevasses are transverse to flow and form where steeper slopes cause a glacier to accelerate.  Longitudinal crevasses form semi-parallel to flow where a glacier expands laterally.  Marginal crevasses form from the edge of the glacier, due to the reduction in speed caused by friction of the valley walls.  Marginal crevasses are usually largely transverse to flow.  Moving glacier ice can sometimes separate from stagnant ice above, forming a bergschrund.  Bergschrunds resemble crevasses but are singular features at a glacier's margins.

text: Crevasses make travel over glaciers hazardous, especially when they are hidden by fragile snow bridges.

text: Below the equilibrium line, glacial meltwater is concentrated in stream channels.  Meltwater can pool in proglacial lakes on top of a glacier or descend into the depths of a glacier via moulins. Streams within or beneath a glacier flow in englacial or sub-glacial tunnels.  These tunnels sometimes reemerge at the glacier's surface.[24]

text: Speed[edit]

text: The speed of glacial displacement is partly determined by friction. Friction makes the ice at the bottom of the glacier move more slowly than ice at the top. In alpine glaciers, friction is also generated at the valley's side walls, which slows the edges relative to the center.

text: Mean speeds vary greatly, but is typically around 1 m (3 ft) per day.[25] There may be no motion in stagnant areas; for example, in parts of Alaska, trees can establish themselves on surface sediment deposits. In other cases, glaciers can move as fast as 20–30 m (70–100 ft) per day, such as in Greenland's Jakobshavn Isbræ (Greenlandic: Sermeq Kujalleq).  Velocity increases with increasing slope, increasing thickness, increasing snowfall, increasing longitudinal confinement, increasing basal temperature, increasing meltwater production and reduced bed hardness.

text: A few glaciers have periods of very rapid advancement called surges. These glaciers exhibit normal movement until suddenly they accelerate, then return to their previous state. During these surges, the glacier may reach velocities far greater than normal speed.[26] These surges may be caused by failure of the underlying bedrock, the pooling of meltwater at the base of the glacier[27] — perhaps delivered from a supraglacial lake — or the simple accumulation of mass beyond a critical "tipping point".[28] Temporary rates up to 90 m (300 ft) per day have occurred when increased temperature or overlying pressure caused bottom ice to melt and water to accumulate beneath a glacier.

text: In glaciated areas where the glacier moves faster than one km per year, glacial earthquakes occur.  These are large scale earthquakes that have seismic magnitudes as high as 6.1.[29][30]  The number of glacial earthquakes in Greenland peaks every year in July, August and September and is increasing over time. In a study using data from January 1993 through October 2005, more events were detected every year since 2002, and  twice as many events were recorded in 2005 as there were in any other year. This increase in the numbers of glacial earthquakes in Greenland may be a response to global warming.[29][30]

text: Ogives[edit]

text: Ogives (or Forbes bands)[31] are alternating wave crests and valleys that appear as dark and light bands of ice on glacier surfaces.  They are linked to seasonal motion of glaciers; the width of one dark and one light band generally equals the annual movement of the glacier.  Ogives are formed when ice from an icefall is severely broken up, increasing ablation surface area during summer.  This creates a swale and space for snow accumulation in the winter, which in turn creates a ridge.[32]  Sometimes ogives consist only of undulations or color bands and are described as wave ogives or band ogives.[33]

text: Geography[edit]

text: Glaciers are present on every continent and approximately fifty countries, excluding those (Australia, South Africa) that have glaciers only on distant subantarctic island territories. Extensive glaciers are found in Antarctica, Chile, Canada, Alaska, Greenland and Iceland. Mountain glaciers are widespread, especially in the Andes, the Himalayas, the Rocky Mountains, the Caucasus, Scandinavian mountains and the Alps. Mainland Australia currently contains no glaciers, although a small glacier on Mount Kosciuszko was present in the last glacial period.[34] In New Guinea, small, rapidly diminishing, glaciers are located on its highest summit massif of Puncak Jaya.[35] Africa has glaciers on Mount Kilimanjaro in Tanzania, on Mount Kenya and in the Rwenzori Mountains.  Oceanic islands with glaciers include Iceland, several of the islands off the coast of Norway including Svalbard and Jan Mayen to the far North, New Zealand and the subantarctic islands of Marion, Heard, Grande Terre (Kerguelen) and Bouvet. During glacial periods of the Quaternary, Taiwan, Hawaii on Mauna Kea[36] and Tenerife also had large alpine glaciers, while the Faroe and Crozet Islands[37] were completely glaciated.

text: The permanent snow cover necessary for glacier formation is affected by factors such as the degree of slope on the land, amount of snowfall and the winds. Glaciers can be found in all latitudes except from 20° to 27° north and south of the equator where the presence of the descending limb of the Hadley circulation lowers precipitation so much that with high insolation snow lines reach above 6,500 m (21,330 ft). Between 19˚N and 19˚S, however, precipitation is higher and the mountains above 5,000 m (16,400 ft) usually have permanent snow.

text: Even at high latitudes, glacier formation is not inevitable.  Areas of the Arctic, such as Banks Island, and the McMurdo Dry Valleys in Antarctica are considered polar deserts where glaciers cannot form because they receive little snowfall despite the bitter cold.  Cold air, unlike warm air, is unable to transport much water vapor.  Even during glacial periods of the Quaternary, Manchuria, lowland Siberia,[38] and central and northern Alaska,[39] though extraordinarily cold, had such light snowfall that glaciers could not form.[40][41]

text: In addition to the dry, unglaciated polar regions, some mountains and volcanoes in Bolivia, Chile and Argentina are high (4,500 to 6,900 m or 14,800 to 22,600 ft) and cold, but the relative lack of precipitation prevents snow from accumulating into glaciers. This is because these peaks are located near or in the hyperarid Atacama Desert.

text: Glacial geology[edit]

text: Glaciers erode terrain through two principal processes: abrasion and plucking.

text: As glaciers flow over bedrock, they soften and lift blocks of rock into the ice. This process, called plucking, is caused by subglacial water that penetrates fractures in the bedrock and subsequently freezes and expands. This expansion causes the ice to act as a lever that loosens the rock by lifting it. Thus, sediments of all sizes become part of the glacier's load. If a retreating glacier gains enough debris, it may become a rock glacier, like the Timpanogos Glacier in Utah.

text: Abrasion occurs when the ice and its load of rock fragments slide over bedrock and function as sandpaper, smoothing and polishing the bedrock below.  The pulverized rock this process produces is called rock flour and is made up of rock grains  between 0.002 and 0.00625 mm in size.  Abrasion leads to steeper valley walls and mountain slopes in alpine settings, which can cause avalanches and rock slides, which add even more material to the glacier.

text: Glacial abrasion is commonly characterized by glacial striations.  Glaciers produce these when they contain large boulders that carve long scratches in the bedrock.  By mapping the direction of the striations, researchers can determine the direction of the glacier's movement.  Similar to striations are chatter marks, lines of crescent-shape depressions in the rock underlying a glacier.  They are formed by abrasion when boulders in the glacier are repeatedly caught and released as they are dragged along the bedrock.

text: The rate of glacier erosion varies. Six factors control erosion rate:

text:
Velocity of glacial movement
Thickness of the ice
Shape, abundance and hardness of rock fragments contained in the ice at the bottom of the glacier
Relative ease of erosion of the surface under the glacier
Thermal conditions at the glacier base
Permeability and water pressure at the glacier base

text: When the bedrock has frequent fractures on the surface, glacial erosion rates tend to increase as plucking is the main erosive force on the surface; when the bedrock has wide gaps between sporadic fractures, however, abrasion tends to be the dominant erosive form and glacial erosion rates become slow.[42]

text: Glaciers in lower latitudes tend to be much more erosive than glaciers in higher latitudes, because they have more meltwater reaching the glacial base and facilitate sediment production and transport under the same moving speed and amount of ice.[43]

text: Material that becomes incorporated in a glacier is typically carried as far as the zone of ablation before being deposited. Glacial deposits are of two distinct types:

text:
Glacial till: material directly deposited from glacial ice. Till includes a mixture of undifferentiated material ranging from clay size to boulders, the usual composition of a moraine.
Fluvial and outwash sediments: sediments deposited by water. These deposits are stratified by size.

text: Larger pieces of rock that are encrusted in till or deposited on the surface are called "glacial erratics".  They range in size from pebbles to boulders, but as they are often moved great distances, they may be drastically different from the material upon which they are found.  Patterns of glacial erratics hint at past glacial motions.

text: Moraines[edit]

text: Glacial moraines are formed by the deposition of material from a glacier and are exposed after the glacier has retreated.  They usually appear as linear mounds of till, a non-sorted mixture of rock, gravel and boulders within a matrix of a fine powdery material. Terminal or end moraines are formed at the foot or terminal end of a glacier. Lateral moraines are formed on the sides of the glacier. Medial moraines are formed when two different glaciers merge and the lateral moraines of each coalesce to form a moraine in the middle of the combined glacier. Less apparent are ground moraines, also called glacial drift, which often blankets the surface underneath the glacier downslope from the equilibrium line.

text: The term moraine is of French origin.  It was coined by peasants to describe alluvial embankments and rims found near the margins of glaciers in the French Alps. In modern geology, the term is used more broadly, and is applied to a series of formations, all of which are composed of till. Moraines can also create moraine dammed lakes.

text: Drumlins[edit]

text: Drumlins are asymmetrical, canoe shaped hills made mainly of till. Their heights vary from 15 to 50 meters and they can reach a kilometer in length. The steepest side of the hill faces the direction from which the ice advanced (stoss), while a longer slope is left in the ice's direction of movement (lee).

text: Drumlins are found in groups called drumlin fields or drumlin camps. One of these fields is found east of Rochester, New York; it is estimated to contain about 10,000 drumlins.

text: Although the process that forms drumlins is not fully understood, their shape implies that they are products of the plastic deformation zone of ancient glaciers. It is believed that many drumlins were formed when glaciers advanced over and altered the deposits of earlier glaciers.

text: Glacial valleys, cirques, arêtes, and pyramidal peaks[edit]

text: Before glaciation, mountain valleys have a characteristic "V" shape, produced by eroding water. During glaciation, these valleys are often widened, deepened and smoothed to form a "U"-shaped glacial valley or glacial trough, as it is sometimes called.[44]  The erosion that creates glacial valleys truncates any spurs of rock or earth that may have earlier extended across the valley, creating broadly triangular-shaped cliffs called truncated spurs.  Within glacial valleys, depressions created by plucking and abrasion can be filled by lakes, called paternoster lakes.  If a glacial valley runs into a large body of water, it forms a fjord.

text: Typically glaciers deepen their valleys more than their smaller tributaries. Therefore, when glaciers recede, the valleys of the tributary glaciers remain above the main glacier's depression and are called hanging valleys.

text: At the start of a classic valley glacier is a bowl-shaped cirque, which has escarped walls on three sides but is open on the side that descends into the valley. Cirques are where ice begins to accumulate in a glacier.  Two glacial cirques may form back to back and erode their backwalls until only a narrow ridge, called an arête is left. This structure may result in a mountain pass.  If multiple cirques encircle a single mountain, they create pointed pyramidal peaks; particularly steep examples are called horns.

text: Roches moutonnées[edit]

text: Passage of glacial ice over an area of bedrock may cause the rock to be sculpted into a knoll called a roche moutonnée, or "sheepback" rock. Roches moutonnées may be elongated, rounded and asymmetrical in shape. They range in length from less than a meter to several hundred meters long.[45]  Roches moutonnées have a gentle slope on their up-glacier sides and a steep to vertical face on their down-glacier sides. The glacier abrades the smooth slope on the upstream side as it flows along, but tears rock fragments loose and carries them away from the downstream side via plucking.

text: Alluvial stratification[edit]

text: As the water that rises from the ablation zone moves away from the glacier, it carries fine eroded sediments with it.  As the speed of the water decreases, so does its capacity to carry objects in suspension. The water thus gradually deposits the sediment as it runs, creating an alluvial plain. When this phenomenon occurs in a valley, it is called a valley train. When the deposition is in an estuary, the sediments are known as bay mud.

text: Outwash plains and valley trains are usually accompanied by basins known as "kettles". These are small lakes formed when large ice blocks that are trapped in alluvium melt and produce water-filled depressions. Kettle diameters range from 5 m to 13 km, with depths of up to 45 meters.  Most are circular in shape because the blocks of ice that formed them were rounded as they melted.[46]

text: Glacial deposits[edit]

text: When a glacier's size shrinks below a critical point, its flow stops and it becomes stationary. Meanwhile, meltwater within and beneath the ice leaves stratified alluvial deposits. These deposits, in the forms of columns, terraces and clusters, remain after the glacier melts and are known as "glacial deposits".

text: Glacial deposits that take the shape of hills or mounds are called kames. Some kames form when meltwater deposits sediments through openings in the interior of the ice. Others are produced by fans or deltas created by meltwater.  When the glacial ice occupies a valley, it can form terraces or kames along the sides of the valley.

text: Long, sinuous glacial deposits are called eskers.  Eskers are composed of sand and gravel that was deposited by meltwater streams that flowed through ice tunnels within or beneath a glacier. They remain after the ice melts, with heights exceeding 100 meters and lengths of as long as 100 km.

text: Loess deposits[edit]

text: Very fine glacial sediments or rock flour is often picked up by wind blowing over the bare surface and may be deposited great distances from the original fluvial deposition site. These eolian loess deposits may be very deep, even hundreds of meters, as in areas of China and the Midwestern United States of America. Katabatic winds can be important in this process.

text: Isostatic rebound[edit]

text: Large masses, such as ice sheets or glaciers, can depress the crust of the Earth into the mantle.[47]  The depression usually totals a third of the ice sheet or glacier's thickness.   After the ice sheet or glacier melts, the mantle begins to flow back to its original position, pushing the crust back up. This post-glacial rebound, which proceeds very slowly after the melting of the ice sheet or glacier, is currently occurring in measurable amounts in Scandinavia and the Great Lakes region of North America.

text: A geomorphological feature created by the same process on a smaller scale is known as dilation-faulting. It occurs where previously compressed rock is allowed to return to its original shape more rapidly than can be maintained without faulting.  This leads to an effect similar to what would be seen if the rock were hit by a large hammer. Dilation faulting can be observed in recently de-glaciated parts of Iceland and Cumbria.

text: On Mars[edit]

text: The polar ice caps of Mars show geologic evidence of glacial deposits. The south polar cap is especially comparable to glaciers on Earth.[48] Topographical features and computer models indicate the existence of more glaciers in Mars' past.[49]

text: At mid-latitudes, between 35° and 65° north or south, Martian glaciers are affected by the thin Martian atmosphere. Because of the low atmospheric pressure, ablation near the surface is solely due to sublimation, not melting. As on Earth, many glaciers are covered with a layer of rocks which insulates the ice. A radar instrument on board the Mars Reconnaissance Orbiter found ice under a thin layer of rocks in formations called lobate debris aprons (LDAs).[50][51][52][53][54]

text: The pictures below illustrate how landscape features on Mars closely resemble those on the Earth.

text:
Romer Lake's Elephant Foot Glacier in the Earth's Arctic, as seen by Landsat 8.  This picture shows several glaciers that have the same shape as many features on Mars that are believed to also be glaciers.  The next three images from Mars show shapes similar to the Elephant Foot Glacier.

Mesa in Ismenius Lacus quadrangle, as seen by CTX. Mesa has several glaciers eroding it. One of the glaciers is seen in greater detail in the next two images from HiRISE.  Image from Ismenius Lacus quadrangle.

Glacier as seen by HiRISE under the HiWish program. Area in rectangle is enlarged in the next photo. Zone of accumulation of snow at the top. Glacier is moving down valley, then spreading out on plain. Evidence for flow comes from the many lines on surface. Location is in Protonilus Mensae in Ismenius Lacus quadrangle.

Enlargement of area in rectangle of the previous image. On Earth the ridge would be called the terminal moraine of an alpine glacier. Picture taken with HiRISE under the HiWish program.  Image from Ismenius Lacus quadrangle.


document_title: Blood type

question_text: what type of blood is considered the universal donor

root

text: Blood type

text: Blood group systems[edit]

text: A complete blood type would describe a full set of 30 substances on the surface of red blood cells, and an individual's blood type is one of many possible combinations of blood-group antigens.[3] Across the 35 blood groups, over 600 different blood-group antigens have been found.[4]Almost always, an individual has the same blood group for life, but very rarely an individual's blood type changes through addition or suppression of an antigen in infection, malignancy, or autoimmune disease.[5][6][7][8] Another more common cause in blood type change is a bone marrow transplant. Bone-marrow transplants are performed for many leukemias and lymphomas, among other diseases. If a person receives bone marrow from someone who is a different ABO type (e.g., a type A patient receives a type O bone marrow), the patient's blood type will eventually convert to the donor's type.

tag: p

text: Some blood types are associated with inheritance of other diseases; for example, the Kell antigen is sometimes associated with McLeod syndrome.[9] Certain blood types may affect susceptibility to infections, an example being the resistance to specific malaria species seen in individuals lacking the Duffy antigen.[10] The Duffy antigen, presumably as a result of natural selection, is less common in ethnic groups from areas with a high incidence of malaria.[11]

text: ABO blood group system[edit]

text: The ABO blood group system involves two antigens and two antibodies found in human blood. The two antigens are antigen A and antigen B. The two antibodies are antibody A and antibody B. The antigens are present on the red blood cells and the antibodies in the serum. Regarding the antigen property of the blood all human beings can be classified into 4 groups, those with antigen A (group A), those with antigen B (group B), those with both antigen A and B (group AB) and those with neither antigen (group O). The antibodies present together with the antigens are found as follows:

text:
1. Antigen A with antibody B
2. Antigen B with antibody A
3. Antigen AB has no antibodies
4. Antigen nil (group O) with antibody A and B.

text: There is an agglutination reaction between similar antigen and antibody (for example, antigen A agglutinates the antibody A and antigen B agglutinates the antibody B). Thus, transfusion can be considered safe as long as the serum of the recipient does not contain antibodies for the blood cell antigens of the donor.

text: The ABO system is the most important blood-group system in human-blood transfusion. The associated anti-A and anti-B antibodies are usually immunoglobulin M, abbreviated IgM, antibodies. ABO IgM antibodies are produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses.[citation needed] The original terminology used by Karl Landsteiner in 1901 for the classification was A/B/C; in later publications "C" became "O".[12] "O" is often called 0 (zero, or null) in other languages.[12][13]

text:
Phenotype
Genotype

A
AA or AI

B
BB or BI

AB
AB

O
II

tag: table

text: Rh blood group system[edit]

text: The Rh system (Rh meaning Rhesus) is the second most significant blood-group system in human-blood transfusion with currently 50 antigens. The most significant Rh antigen is the D antigen, because it is the most likely to provoke an immune system response of the five main Rh antigens. It is common for D-negative individuals not to have any anti-D IgG or IgM antibodies, because anti-D antibodies are not usually produced by sensitization against environmental substances. However, D-negative individuals can produce IgG anti-D antibodies following a sensitizing event: possibly a fetomaternal transfusion of blood from a fetus in pregnancy or occasionally a blood transfusion with D positive RBCs.[14] Rh disease can develop in these cases.[15] Rh negative blood types are much less common in Asian populations (0.3%) than they are in European populations (15%).[16] The presence or absence of the Rh(D) antigen is signified by the + or − sign, so that, for example, the A− group is ABO type A and does not have the Rh (D) antigen.

text: ABO and Rh distribution by country[edit]

text: As with many other genetic traits, the distribution of ABO and Rh blood groups varies significantly between populations.

text: Other blood group systems[edit]

text: Thirty-three blood-group systems have been identified by the International Society for Blood Transfusion in addition to the common ABO and Rh systems.[17] Thus, in addition to the ABO antigens and Rh antigens, many other antigens are expressed on the RBC surface membrane. For example, an individual can be AB, D positive, and at the same time M and N positive (MNS system), K positive (Kell system), Lea or Leb negative (Lewis system), and so on, being positive or negative for each blood group system antigen. Many of the blood group systems were named after the patients in whom the corresponding antibodies were initially encountered.

text: Clinical significance[edit]

text: Blood transfusion[edit]

text: Transfusion medicine is a specialized branch of hematology that is concerned with the study of blood groups, along with the work of a blood bank to provide a transfusion service for blood and other blood products. Across the world, blood products must be prescribed by a medical doctor (licensed physician or surgeon) in a similar way as medicines.

text: Much of the routine work of a blood bank involves testing blood from both donors and recipients to ensure that every individual recipient is given blood that is compatible and is as safe as possible. If a unit of incompatible blood is transfused between a donor and recipient, a severe acute hemolytic reaction with hemolysis (RBC destruction), renal failure and shock is likely to occur, and death is a possibility. Antibodies can be highly active and can attack RBCs and bind components of the complement system to cause massive hemolysis of the transfused blood.

text: Patients should ideally receive their own blood or type-specific blood products to minimize the chance of a transfusion reaction. Risks can be further reduced by cross-matching blood, but this may be skipped when blood is required for an emergency. Cross-matching involves mixing a sample of the recipient's serum with a sample of the donor's red blood cells and checking if the mixture agglutinates, or forms clumps. If agglutination is not obvious by direct vision, blood bank technicians usually check for agglutination with a microscope. If agglutination occurs, that particular donor's blood cannot be transfused to that particular recipient. In a blood bank it is vital that all blood specimens are correctly identified, so labelling has been standardized using a barcode system known as ISBT 128.

text: The blood group may be included on identification tags or on tattoos worn by military personnel, in case they should need an emergency blood transfusion. Frontline German Waffen-SS had blood group tattoos during World War II.

text: Rare blood types can cause supply problems for blood banks and hospitals. For example, Duffy-negative blood occurs much more frequently in people of African origin,[20] and the rarity of this blood type in the rest of the population can result in a shortage of Duffy-negative blood for these patients. Similarly for RhD negative people, there is a risk associated with travelling to parts of the world where supplies of RhD negative blood are rare, particularly East Asia, where blood services may endeavor to encourage Westerners to donate blood.[21]

text: Hemolytic disease of the newborn (HDN)[edit]

text: Pregnant women may carry a fetus with a blood type which is different from their own. In those cases, the mother can make IgG blood group antibodies. This can happen if some of the fetus' blood cells pass into the mother's blood circulation (e.g. a small fetomaternal hemorrhage at the time of childbirth or obstetric intervention), or sometimes after a therapeutic blood transfusion. This can cause Rh disease or other forms of hemolytic disease of the newborn (HDN) in the current pregnancy and/or subsequent pregnancies. Sometimes this is lethal for the fetus; in these cases it is called hydrops fetalis.[22] If a pregnant woman is known to have anti-D antibodies, the Rh blood type of a fetus can be tested by analysis of fetal DNA in maternal plasma to assess the risk to the fetus of Rh disease.[23] One of the major advances of twentieth century medicine was to prevent this disease by stopping the formation of Anti-D antibodies by D negative mothers with an injectable medication called Rho(D) immune globulin.[24][25] Antibodies associated with some blood groups can cause severe HDN, others can only cause mild HDN and others are not known to cause HDN.[22]

text: Blood products[edit]

text: To provide maximum benefit from each blood donation and to extend shelf-life, blood banks fractionate some whole blood into several products. The most common of these products are packed RBCs, plasma, platelets, cryoprecipitate, and fresh frozen plasma (FFP). FFP is quick-frozen to retain the labile clotting factors V and VIII, which are usually administered to patients who have a potentially fatal clotting problem caused by a condition such as advanced liver disease, overdose of anticoagulant, or disseminated intravascular coagulation (DIC).

text: Units of packed red cells are made by removing as much of the plasma as possible from whole blood units.

text: Clotting factors synthesized by modern recombinant methods are now in routine clinical use for hemophilia, as the risks of infection transmission that occur with pooled blood products are avoided.

text: Red blood cell compatibility[edit]

text:
Blood group AB individuals have both A and B antigens on the surface of their RBCs, and their blood plasma does not contain any antibodies against either A or B antigen. Therefore, an individual with type AB blood can receive blood from any group (with AB being preferable), but cannot donate blood to any group other than AB. They are known as universal recipients.
Blood group A individuals have the A antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the B antigen. Therefore, a group A individual can receive blood only from individuals of groups A or O (with A being preferable), and can donate blood to individuals with type A or AB.
Blood group B individuals have the B antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the A antigen. Therefore, a group B individual can receive blood only from individuals of groups B or O (with B being preferable), and can donate blood to individuals with type B or AB.
Blood group O (or blood group zero in some countries) individuals do not have either A or B antigens on the surface of their RBCs, and their blood serum contains IgM anti-A and anti-B antibodies. Therefore, a group O individual can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group (i.e., A, B, O or AB). If a patient in a hospital situation needs a blood transfusion in an emergency, and if the time taken to process the recipient's blood would cause a detrimental delay, O negative blood can be issued. Because it is compatible with anyone, O negative blood is often overused and consequently is always in short supply.[26] According to the American Association of Blood Banks and the British Chief Medical Officer’s National Blood Transfusion Committee, the use of group O RhD negative red cells should be restricted to persons with O negative blood, women who might be pregnant, and emergency cases in which blood-group testing is genuinely impracticable.[26]

tag: ul

text:
Red blood cell compatibility table[27][28]

Recipient[1]
Donor[1]

O−
O+
A−
A+
B−
B+
AB−
AB+

O−
Y
N
N
N
N
N
N
N

O+
Y
Y
N
N
N
N
N
N

A−
Y
N
Y
N
N
N
N
N

A+
Y
Y
Y
Y
N
N
N
N

B−
Y
N
N
N
Y
N
N
N

B+
Y
Y
N
N
Y
Y
N
N

AB−
Y
N
Y
N
Y
N
Y
N

AB+
Y
Y
Y
Y
Y
Y
Y
Y

text:
Table note
1. Assumes absence of atypical antibodies that would cause an incompatibility between donor and recipient blood, as is usual for blood selected by cross matching.

text: An Rh D-negative patient who does not have any anti-D antibodies (never being previously sensitized to D-positive RBCs) can receive a transfusion of D-positive blood once, but this would cause sensitization to the D antigen, and a female patient would become at risk for hemolytic disease of the newborn. If a D-negative patient has developed anti-D antibodies, a subsequent exposure to D-positive blood would lead to a potentially dangerous transfusion reaction. Rh D-positive blood should never be given to D-negative women of child bearing age or to patients with D antibodies, so blood banks must conserve Rh-negative blood for these patients. In extreme circumstances, such as for a major bleed when stocks of D-negative blood units are very low at the blood bank, D-positive blood might be given to D-negative females above child-bearing age or to Rh-negative males, providing that they did not have anti-D antibodies, to conserve D-negative blood stock in the blood bank. The converse is not true; Rh D-positive patients do not react to D negative blood.

text: This same matching is done for other antigens of the Rh system as C, c, E and e and for other blood group systems with a known risk for immunization such as the Kell system in particular for females of child-bearing age or patients with known need for many transfusions.

text: Plasma compatibility[edit]

text: Blood plasma compatibility is the inverse of red blood cell compatibility.[29] Type AB plasma carries neither anti-A nor anti-B antibodies and can be transfused to individuals of any blood group; but type AB patients can only receive type AB plasma. Type O carries both antibodies, so individuals of blood group O can receive plasma from any blood group, but type O plasma can be used only by type O recipients.

text:
Plasma compatibility table[28]

Recipient
Donor[1]

O
A
B
AB

O
Y
Y
Y
Y

A
N
Y
N
Y

B
N
N
Y
Y

AB
N
N
N
Y

text:
Table note
1. Assumes absence of strong atypical antibodies in donor plasma

text: Rh D antibodies are uncommon, so generally neither D negative nor D positive blood contain anti-D antibodies. If a potential donor is found to have anti-D antibodies or any strong atypical blood group antibody by antibody screening in the blood bank, they would not be accepted as a donor (or in some blood banks the blood would be drawn but the product would need to be appropriately labeled); therefore, donor blood plasma issued by a blood bank can be selected to be free of D antibodies and free of other atypical antibodies, and such donor plasma issued from a blood bank would be suitable for a recipient who may be D positive or D negative, as long as blood plasma and the recipient are ABO compatible.[citation needed]

text: Universal donors and universal recipients[edit]

text: In transfusions of packed red blood cells, individuals with type O Rh D negative blood are often called universal donors. Those with type AB Rh D positive blood are called universal recipients. However, these terms are only generally true with respect to possible reactions of the recipient's anti-A and anti-B antibodies to transfused red blood cells, and also possible sensitization to Rh D antigens. One exception is individuals with hh antigen system (also known as the Bombay phenotype) who can only receive blood safely from other hh donors, because they form antibodies against the H antigen present on all red blood cells.[30][31]

text: Blood donors with exceptionally strong anti-A, anti-B or any atypical blood group antibody may be excluded from blood donation. In general, while the plasma fraction of a blood transfusion may carry donor antibodies not found in the recipient, a significant reaction is unlikely because of dilution.

text: Additionally, red blood cell surface antigens other than A, B and Rh D, might cause adverse reactions and sensitization, if they can bind to the corresponding antibodies to generate an immune response. Transfusions are further complicated because platelets and white blood cells (WBCs) have their own systems of surface antigens, and sensitization to platelet or WBC antigens can occur as a result of transfusion.

text: For transfusions of plasma, this situation is reversed. Type O plasma, containing both anti-A and anti-B antibodies, can only be given to O recipients. The antibodies will attack the antigens on any other blood type. Conversely, AB plasma can be given to patients of any ABO blood group, because it does not contain any anti-A or anti-B antibodies.

text: Antibody-free blood typing[edit]

text: Typically, blood type tests are performed through addition of a blood sample to a solution containing antibodies corresponding to each antigen. The presence of an antigen on the surface of the blood cells is indicated by agglutination. An alternative system for blood type determination involving no antibodies was developed in 2017 at Imperial College London which makes use of paramagnetic molecularly imprinted polymer nanoparticles with affinity for specific blood antigens.[32] In these tests, rather than agglutination, a positive result is indicated by decolorization as red blood cells which bind to the nanoparticles are pulled toward a magnet and removed from solution.

text: Blood group genotyping[edit]

text: In addition to the current practice of serologic testing of blood types, the progress in molecular diagnostics allows the increasing use of blood group genotyping. In contrast to serologic tests reporting a direct blood type phenotype, genotyping allows the prediction of a phenotype based on the knowledge of the molecular basis of the currently known antigens. This allows a more detailed determination of the blood type and therefore a better match for transfusion, which can be crucial in particular for patients with needs for many transfusions to prevent allo-immunization.[33][34]

text: History[edit]

text: Two blood group systems were discovered by Karl Landsteiner during early experiments with blood transfusion: the ABO group in 1901[35][full citation needed] and in co-operation with Alexander S. Wiener the Rhesus group in 1937.[36][37] Development of the Coombs test in 1945,[38] the advent of transfusion medicine, and the understanding of ABO hemolytic disease of the newborn led to discovery of more blood groups, and now 33 human blood group systems are recognized by the International Society of Blood Transfusion (ISBT),[3] and in the 33 blood groups, over 600 blood group antigens have been found;[4] many of these are rare or are mainly found in certain ethnic groups.

text: Czech serologist Jan Janský is credited with the first classification of blood into the four types (A, B, AB, O) in 1907, which remains in use today. Blood types have been used in forensic science and were formerly used to demonstrate impossibility of paternity (e.g., a type AB man cannot be the father of a type O infant), but both of these uses are being replaced by genetic fingerprinting, which provides greater certainty.[39]

text: According to the Austrian Federal Ministry of Health[full citation needed] the original terminology used by Karl Landsteiner in 1901 for the classification is A, B and 0 (zero); the "O" (oh) found in the ABO group system is actually a subsequent variation occurred during the translation process, probably due to the similar shape between the number 0 and the letter O.

text: Society and culture[edit]

text: A popular belief in Japan is that a person's ABO blood type is predictive of their personality, character, and compatibility with others. This belief is also widespread in South Korea[40] and Taiwan. The theory reached Japan in a 1927 psychologist's report, and the government of the time commissioned a study aimed at breeding better soldiers.[40] Interest in the theory faded in the 1930s. Ultimately, the discovery of DNA in the following decades indicated that DNA instead had an important role in both heredity generally and personality specifically. Interest in the theory was revived in the 1970s by Masahiko Nomi, a broadcaster with a background in law rather than science.[40] The theory is widely accepted in Japanese and South Korean popular culture.[41]