Dynamic Planet
A. Glacier formation:
a.i. Properties of ice (crystal structure, density, etc)
- Forms at < 0C, 32F, or 273.15K
- Crystal Structure:
Can assume a large number of different crystalline structures, more than any other known material.
It allows ice to flow under pressure and makes ice less dense than liquid water
At ordinary pressures, the stable phase of ice is called ice I; there are various high-pressure phases of ice number up to XIV. Virtually all ice in the biosphere is ice I and phases are based on pressure/temperature variations.
Two closely related variants of ice I:
Hexagonal ice Ih: normal force of ice with hexagonal symmetry
Cubic ice Ic: which has a crystal structure similar to diamond; formed by depositing vapor at very low temperatures (below 140°K).
-Density: Water’s solid form is ~8.3% less dense than its liquid form with a volumetric expansion of 9%.
The density of ice is 0.9167 g/cm^3 at 0 °C and standard atmospheric pressure; water has a density of 0.9998g/cm^3.
Liquid water is densest at 1.00 g/cm^3 at 4 °C and begins to lose its density as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached due to hydrogen bonding, which results in a packing of molecules less compact in the solid.
The density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm^3 at −180 °C (93 K). Density also increases with increased pressure.
-Hardness: Typically 1.5; At its melting point, ice has a Mohs hardness of 2 or less, but the hardness increases to about 4 at a temperature of −44 °C (−47 °F) and to 6 at a temperature of −78.5 °C (−109.3 °F), the vaporization point of solid carbon dioxide (dry ice).
-Specific Heat Capacity: Often varies with temperature and different for each state of matter. Liquid water has one of the highest specific heat capacities among common substances, about 4184 Joules/kgC at 20 °C; but that of ice, just below 0 °C, is only 2093 Joules/kgC.
-Elasticity: Ice is generally very brittle, though some very thin, carefully grown ice microfibers can bend a lot, up to about 11%, and still remain elastic
-Speed of Sound: Speed of sound in ice is ~3669m/s, while in liquid water it is only ~1500m/s.
-Diamagnetism: Ice is diamagnetic, with a mean diamagnetic susceptibility of -12.65 × 10 C.G.S. E.M.U./mole at 0° C. When a diamagnetic sample is placed in a magnetic field, its magnetic moment is always opposite to the direction of the field.
-Color: colourless to white, pale blue to greenish-blue in thick layers
-Streak: White
-Fracture: conchoidal; brittle and doesn’t follow any natural planes of separation
-Luster: Vitreous; reflective properties similar to that of glass
a.ii. formation of glacial ice from snow, neve, and firn
-Snow: Builds up when temperatures are ideal and compresses to form ice. As more snow accumulates, lower, older snow begins to have air bubbles squeezed out. Once the ice lasts through the summer months and achieves enough mass to flow its considered a glacier.
-As snow begins to build up, it compresses the snow below it to form ice. As more and more layers of snow accumulate, lower, older snow begins to have its air bubbles squeezed out. Once this ice lasts through summer months and achieves the critical mass that allows it to flow, it is considered a glacier.
-Névé: First-year glacial snow; partially melted/refrozen, slightly compacted, granular. Minimum density of 500kg/m^3 (~½ the density of liquid water at 1 atm)
-Firn: A state between snow and glacier ice characterized by accumulated granular snow that has survived one melt season; denser and more refrozen than névé, very stiff. Density ranges from 0.35-0.9g/cm^3
-Under the immense pressures of several meters of snow, ice is formed, which is denser than "normal" ice due to the lack of air bubbles (this is also why they’re bluish).
-Individual crystals near the melting point are semi-liquid and slick, allowing them to glide along other crystal planes & fill in spaces between them, thus making them more dense
-The difference in density between glacier ice and regular ice is very minimal—only a few grams per cubic meter.
-In small amounts, debris such as windblown dust and small rocks absorbs more heat due to their darker color. This leads to additional melting at the surface and often can form cryoconite holes.
if the glacier becomes fully encased in debris (from a landslide or similar), the opposite effect takes place, creating a protective shield and preventing sunlight from melting the glacier.
a.iii. Glacial Mass-Balance:
Mass balance: the difference between accumulation and ablation.
Accumulation: addition of snow or ice onto the glacier
A glacier will advance when there’s net positive gain in ice, particularly at the terminus, making it grow further downslope.
The accumulation zone can grow/shrink depending on the season, becoming its largest during the winter months.
Key input is precipitation but also includes wind-blown snow, avalanching, and hoar frost for surface accumulation
Ablation (wastage/wasting): depletion of ice from the glacier, through processes like sublimation and evaporation.
A glacier will retreat when the opposite occurs; it will melt away, leaving the terminus higher up the mountain.
The ablation zone can grow and shrink depending on the season, becoming its largest during the summer months.
Mostly impacted by air temperature and precipitation
Intensified by debris coverage
Zones & Sections
Head: The upper end/beginning of a glacier; only characteristic of mountain glaciers (ice fields, ice caps, and ice sheets don't have a "beginning")
Foot/Terminus: The downhill end of a glacier; term applies more to mountain and outlet glaciers (ice fields, ice caps, and ice sheets exclusively drain into outlet glaciers or terminate as ice shelves).
Zone of Ablation: (Zone of Wastage) The area on the lower "half"/terminus of a glacier where annual melting is greater than accumulation (negative mass balance) and the glacier becomes smaller.
Zone of Accumulation: The area on the upper "half"/head of a glacier where annual accumulation is greater than melting (positive mass balance) and the glacier becomes larger.
Snow/Equilibrium/Firn Line: The line that separates the accumulation/ablation zone; varies in location depending on the time of year, going higher up the glacier during warmer months.
Sensitive to meteorological factors like winter precipitation summer temperature, and wind transport of dry snow
Provides insight into glacier response to climate change and allows for paleoclimatic reconstructions
Glaciers in equilibrium don’t change in steepness or size
Distribution of Glaciers
-Glaciers can form anywhere that the average annual temperature is low enough for snow to last all year round. These locations are typically in high latitudes or at high elevations. Glaciers are found in/around all seven continents.
-The total area that they cover is approximately 15,000,000 square kilometers, around 10% of the world's land area.
-Continental Australia does not have any glaciers, but several islands considered part of Oceania, namely New Zealand, do have some.
Worldwide Coverage (km2)
Antarctica 11,965,000
Greenland 1,784,000
Canada 200,000
Central Asia 109,000
Russia 82,000
United States (with Alaska) 75,000
China & Tibet 33,000
South America 25,000
Iceland 11,260
Scandinavia 2,909
The Alps 2,900
New Zealand 1,159
Mexico 11
Indonesia 7.5
Africa 6
New Guinea 3
a.iv. Glacial Flow
influence of bed (wet/dry, bare rock, and sediment), and relation of flow to elevation and slope/gradient
The driving force to the glacier's flow is attributed to gravity; steeper incline equals faster flow.
Generally unable to on level ground or uphill terrain until reaching 60 m thick. (A glacier can flow uphill to get over obstacles but never towards its own head)
Basal Sliding: Involving the movement of the base of the glacier across the bedrock (incorporating meltwater), when comparing glaciers that undergo basal sliding, thinner, steeper glaciers are more active.
Basal Slip: A thin layer of water between the ice and underlying rock lubricates the glacier to allow it to flow faster, the meltwater coming from pressure-melting, percolation, and water channels like moulins.
Surge: Can occur if enough meltwater is present
Enhanced Basal Creep: When the ice encounters a large obstacle the increase in pressure causes the ice to deform plastically around said obstacle.
Regelation Flow: Occurs when the ice encounters a bedrock obstacle, rather than deforming around it the ice melts under the pressure and refreezes on the other side. (Only if the object is small enough to allow the latent heat on the lee side to be quickly conducted to the stoss side to assist melting).
Lee side: downhill, refreezing
Stoss side: uphill, melting
Internal Deformation/Creep/Plastic Flow/Plastic Deformation: Ice crystals slide across each other within the glacier, the ice deforms as it behaves plastically with extreme pressures (standard condition within glaciers)
Internal deformation is not reliant on meltwater.
Glaciers flow faster near the centers than their periphery. Ice can slide against other ice than a rocky bed, leading to a ‘sagging’ shape.
Bed Deformation/Subglacial Deformation: Allows the shifting of softer sediments to allow the glacier to move downhill. Subglacial till is composed of unsorted sediments with a wide range of sizes from boulders to clay. While finer sediments such as clay or sand deform readily when stress is applied and have high-power water pressure.
Comparison of Basal Sliding/Bed Deformation: Like basal sliding, bed deformation depends on meltwater at the base. Basal sliding is more efficient if the water remains directly under the surface of the ice, whereas bed deformation is more common where the sediment is more saturated with water, reducing its strength.
Thermal Regime: Due to the importance of meltwater in 2 of three methods of glacier flow, the temperature of the glacier (at its base) determines the thermal regime. It’s dependent on basal ice temperature, ice thickness, and the substrate, and is another method of classifying glaciers in addition to morphological characteristics.
Polar; Cold-Based: Glaciers are frozen year-round, excluding seasonal melting near the surface, the base of the ice is frozen, found in high latitudes and have lower seasonal variations in temperatures, minimal to no meltwater.
Temperate; Warm-Based/Wet-Based: Characterized as being warm enough to have meltwater, at or close to their melting point, found at lower altitudes, the movement of these glaciers is through basal sliding (basal slip), meltwater coming from the surface melt channeled to the bottom though moulins, tunnels, crevasses, and more. If basal ice melts through temperature or pressure melting basal slip can occur. During winter months the glacier refreezes to the bedrock, slowing the movement periodically.
Plucking: The meltwater of warm based glaciers can lead to this, causing more sediment transport.
Polythermal/Subpolar: These glaciers will have components of both warm and cold based glaciers (polythermal) depending on the location. Most valley glaciers are these.
Other Factors that Control Movement: Bedrock conditions are frequently the largest force acting against the flow of a glacier. Friction with rougher surfaces will always act to slow the motion of a glacier.
Terminal conditions:
- Debris at the end of a glacier, like terminal moraine, provide an extra buffer to glacial movement.
- Ice shelf buttressing occurs when an ice shelf prevents an outlet glacier from advancing any further into the sea, slowing or stopping its flow and is critical to the stability of the Antarctic and Greenland ice sheets.
Tidewater glaciers, which empty into water without ice shelf buttressing, generally have higher rates of flow and calving.
Relation of flow to elevation and slope:
- At higher elevations, more snow typically falls than melts. The surplus of built-up ice begins to flow downhill. At lower elevations, there is usually a higher rate of melt or icebergs break off that removes ice mass.
- Glaciers flow faster down steeper slopes.
Geothermal Heat Flux
- Geothermal heat is a major heat source to glaciers.
- The amount of heat moving steadily outward from the interior of the earth through a unit area in unit time.
- Increased geothermal heat flux leads to fast glacial erosion rates and expands the area of significant erosion up-valley to high elevations.
- When low, glacial erosion is slow and limited to low elevations within.
- Geothermal heat from underlying bedrock is a major contributor to glacier energy budgets, controlling ice dynamics at the ice-bed interface by changing the basal temperature and the supply of meltwater.
- High geothermal heat flow increases the temperature at the base of glaciers and promotes basal meltwater production.
B. Glacier/Ice Sheet types and forms:
b.i. valley/alpine (cirque, hanging, piedmont)
Constrained: Glaciers constrained by underlying topography are almost always confined by mountains, leading to the nearly synonymous name of mountain glaciers. The only exception is ice fields.
Valley/Alpine: Valley glaciers are a general group of glaciers that flow through the valleys between mountains. Sometimes they originate from cirque glaciers that have spilled out of their cirques and down into the valley.
Branched-Valley: Any valley glacier which has a tributary glacier.
Tributary: Much like tributaries for rivers, are smaller glaciers that merge into larger ones. They are the main contributor to the formation of medial moraines.
Distributary: Opposite of tributaries; they are smaller glaciers which have split apart from the main body.
Piedmont/Foot of Mountain: Valley glaciers that have flowed out beyond the edge of the mountains and into an open plain. Characterized by a fan or mushroom shape at the foot of the mountain. The terminus is often filled with splay crevasses.
Hanging: A valley glacier which terminates at a hanging valley; can create a waterfall down the cliff; formed by avalanches and icefalls
Cirque/Circus/Stadium: Cirque glaciers are generally the smallest type of glacier and form in bowl-shaped depressions in mountains. They can expand beyond their original confines and become a valley glacier.
Niche: A niche glacier is a very small glacier that occupies gullies & hollows on pole-facing slopes of a mountain which are covered by shadows. If the conditions become more favorable, it can develop into a cirque glacier.
Ice Field: Large expanses of glaciers which cover mountains up almost to their peaks, leaving nunataks poking out. This means that ice fields are still partially confined by the mountains they reside in. They can form when a large number of valley glaciers or even smaller ice fields join together.
Outlet: Outlet glaciers are a special form of valley glacier which drain ice from ice caps, ice fields, and ice sheets through narrow mountain passages. These can terminate both on land, into an ice shelf, or simply into the ocean.
Tidewater: Any glacier which terminates in water but does not extend far beyond the coast is considered a tidewater glacier. These are generally valley and outlet glaciers. They calve at very high rates, creating lots of icebergs which can be a hazard to oceangoing vessels. They generally have high flow rates due to the calving.
b.ii. ice sheet/continental (ice stream, ice shelf, ice rise, ice cap, ice tongue, & the geographic distribution of these features)
Unconstrained: Glaciers which not restricted by underlying topography, extending over vast flat areas. The nearly synonymous term continental glaciers generally refers to ice sheets and ice caps only, with the much smaller ice stream being excluded.
Ice Cap: An ice cap is a dome-shaped mass of glacier ice that spreads out in all directions. Ice caps are usually larger than ice fields but always under 50,000 sq. kilometers. The dome shape refers to the fact that accumulation, if it occurs, is generally near the center, leading to a raised area that will flatten out by internal deformation.
Ice Sheet: An ice sheet is the same as an ice cap, except it is greater than 50,000 sq. kilometers. Ice caps and ice sheets are collectively referred to as continental glaciers.
Ice Stream: Ice streams are special areas of ice caps and ice sheets with substantially increased rates of flow, upwards of 500-1000 meters per year. They are important for the mass balance of the ice caps and ice sheets and are often riddled with crevasses and shear margins from the substantial tension and shear stresses.
Ice Tongue/Glacier Tongue: A valley, outlet, or ice stream which extends rapidly out into the sea; exists when there is a narrow floating part of a glacier that extends out into a body of water beyond the glacier's lowest contact with the Earth's crust.
Ice Rise: A clearly defined elevation of the otherwise very much flatter ice shelf, typically dome-shaped and rising several hundreds of meters above the surrounding ice shelf.
Ice Shelf: An ice shelf is a glacier or ice sheet which as flowed out into the ocean. These are very thick and composed of glacial ice. They should not be confused with sea ice, which is thinner and made from seawater. The area where an ice shelf is connected to land is known as the grounding line. They are large and relatively permanent, but have been known to break away and disappear, as was the case with Larsen B in 2002. Ice shelves are also responsible for ice shelf buttressing, where outlet glaciers are held back by the sheer mass of the ice shelf. Ice shelf buttressing are important to controlling the mass balance of outlet glaciers and thus ice caps and ice sheets as well.
C. Glacial Features
c.i. crevasses, ogives, icefalls (what they are & what they indicate about flow and melt)
Crevasses: deep cracks or fractures in a glacier
Form when ice undergoes brittle deformation, splitting apart due to extreme stress in a (relatively) short period of time.
Presence of water in a crevasse can greatly affect the dynamics of a glacier.
If it runs deep enough, it provides a direct connection between surface melt and the bed, providing lots of water to cause or increase basal slip.
Also preserves marks of stress and strain, allowing the movements of a glacier to be deciphered.
Indicates that the glacier is experiencing differential flow and thinning
Crevasse Types & Formation
Form from stresses of all types and are categorized by the stresses that create them.
Marginal Crevasses: form near the sides (margins) of a glacier. As a glacier grinds past the stationary valley walls, the ice in the center flows faster, applying shear and tensional stress. This results in crevasses pointed upslope at around 45 degrees from horizontal.
Longitudinal Crevasses: form parallel to the direction of flow. They form where the glacier expands in width or on the outside edge of a turn where the valley bends. When viewing from downslope, they also form a concave down shape but are generally nearly parallel to the valley walls.
Splashing/Splay Crevasses: typically form near the terminus, where the flow is compressional. The crevasses are approximately parallel to ice flow. They are similar in appearance and orientation to longitudinal crevasses but form from compressional forces pushing ice out laterally. If a glacier spreads out wide enough at the terminus, such as in a piedmont glacier, splay crevasses will radiate outwards from a centerline. They should not be confused with crevasse splay, a non-glacial fluvial deposit.
Transverse Crevasses: are the most common type of crevasse. They form in the zone of extending flow, where the stress is parallel to the direction of flow. The tension stretches the glacier until it fractures. They run side-to-side across the mountain, being nearly perpendicular to flow. They also form where the valley steepens, such as at an icefall. An ice fall, much like a waterfall, is a region of the glacier's flow where there is a sudden change in altitude. This results in heavy amounts of crevassing as the surface layers of ice are stretched more than at the base.
Crevasse Depth: Primarily controlled by compressive pressure from the ice and expansive pressure from water.
The deeper one goes into a glacier, the greater the pressure is keeping a crevasse shut, which is why they usually don't grow to be more than about 3 meters deep—the internal compression from the glacier overpowers the tensile forces pulling it apart. As with the ice, water exerts greater pressure the deeper it is, meaning the crevasse can grow much deeper than before and lead to a crevasse going deep enough to reach the base of the glacier, allowing for significant meltwater drain and an increase in basal slip.
Moulins (Glacier Mills): narrow, near-vertical tubes within a glacier which start at the surface.
-Generally found in a flat section within transverse crevasses.
-Vary greatly in depth but are generally <10 meters wide.
-Carry meltwater down to the base & lubricate the glacier as it slides along.
-More characteristic of mountain glaciers but are not exclusive to them.
Randklufts and Bergschrunds
-Two special types of transverse crevasses.
-Randkluft (German: marginal crevasse): the gap between the headwall of a glacier (the steep back/upper wall of a cirque) and the ice downslope of it. They are formed when the ice directly in contact with the rock is melted and widened in the warmer months. They are generally found in lower-altitude glaciers.
-Bergschrund, sometimes Schrund (German: mountain cleft): a crevasse that forms between a stagnant block of ice above and a moving block of ice below. They generally are found at higher altitudes.
Ogives (Forbes/Alaskan bands):
-Alternating crests and valleys in the glacier ice that appear as dark and light bands of ice.
-Directly linked to the seasonal motion of a glacier.
-The distance across one light and dark band is roughly equal to the annual movement of a glacier.
-Form downslope of icefalls, which contain large transverse crevasses that can be filled with snow, usually over only a couple of seasons. This accumulation will create the visible light-dark pattern which defines ogives, with the light being snow and the dark being ice.
Darker bands lack trapped air bubbles, a result of the way glacier ice forms.
Lighter bands are filled with fresher snow and air pockets and are also much less dense.
-Generally take on a crescent shape, being concave up when viewed from downslope due to the increased rate of flow near the center of the glacier.
-Variations in height of the different bands are caused by uneven melting due to the different colors, with darker bands absorbing more solar radiation and thus melting more.
-Sometimes lack either the undulating surface and even more rarely, the distinct color variations.
-Due to the way they form, ogives are very uncommon on unconstrained ice sheets, ice caps, and ice fields.
Wave Ogive (swell and swale): Alternating crests, convex down ice; each crest equals a year in advancement
Band Ogive: Alternating convex bands of dark and light; color can come from debris or ice density
c.ii. ice shelves and related processes (ie calving, marine ice sheet instability, ice shelf buttressing)
Ice Shelf: An ice shelf is a glacier or ice sheet which as flowed out into the ocean. These are very thick and composed of glacial ice. They should not be confused with sea ice, which is thinner and made from seawater. The area where an ice shelf is connected to land is known as the grounding line. They are large and relatively permanent, but have been known to break away and disappear, as was the case with Larsen B in 2002. Ice shelves are also responsible for ice shelf buttressing, where outlet glaciers are held back by the sheer mass of the ice shelf. Ice shelf buttressing are important to controlling the mass balance of outlet glaciers and thus ice caps and ice sheets as well.
Bedrock conditions: The largest force acting against the flow of a glacier, friction with rougher surfaces will slow the motion of a glacier.
Terminal moraine: debris at the end of a glacier, provide an extra buffer to glacial movement
Ice shelf buttressing: occurs when an ice shelf prevents an outer glacier from advancing any further into the sea by slowing or stopping its flow. It is critical to the stability of the Antarctic and Greenland ice sheets. Without ice shelves, outlet glaciers would drain these ice sheets to cause a change in mass balances.
The mechanical effect of an ice shelf on the stress at the grounding line, where the floating and grounded parts of the ice meet. The presence of an ice shelf affects the stress at the grounding line, and removing it would change the stress and cause the calving front to come into direct contact with the ocean.
Tidewater glaciers: empty the water without ice shelf buttressing, have higher rates of flow and calving.
Calving: The process by which large chunks of ice break off from glaciers and float in the ocean as icebergs.
Marine ice sheet instability: The destabilization of ice sheets grounded below sea level; A low-probability, high-magnitude event that can cause the West Antarctic Ice Sheet to contribute 10 mm of sea level rise per year for 200 years.
Ice shelf disintegration: Ice shelves can disintegrate rapidly due to long-term environmental changes that cause thinning and shrinking. When certain thresholds are passed, the ice shelf can disintegrate catastrophically through iceberg calving.
D. Formation of Landscape Features:
d.i. Erosional
Arête: (French: Rib or Ridge) A sharp parallel ridge of rock that resists erosion, formed by two cirque glaciers coming together but not joining. The glaciers are usually flowing down opposite sides of a mountain. Unsurprisingly, these are characteristic of mountain glaciers only.
Cirque: (French: Circus or Stadium) A large bowl shaped area carved out of a mountain by a moving glacier. They are bounded by a steep cliff know as a headwall. Cirques are also called corries or cwms.
Chatter Marks: (Chatter) Small, curved fracture found in bedrock which has been passed over by a glacier. They are formed by englacial debris acting on the underlying bedrock, typically harder and more brittle rocks. They range in size from submicroscopic marks to over 50 centimeters in length. There are three different types of chatter marks: Crescentic Gouges, Crescentic Fractures, and Lunate Fractures. The features and characteristics of the variations of chatter marks are currently under review due to many conflicting sources.
Crag & Tail: A rocky hill, isolated from other peaks and hills, formed when a glacier passes over a resistant rock formation (often granite or a magmatic intrusion) surrounded by softer material. The softer material behind the block, relative to glacier flow, is sheltered, and creates a shallow, tapering tail on the leeward side of the crag. Post-glacial erosion can often remove the tail. These are found in areas glaciated by continental glaciers.
Hanging Valley: A valley cut across by a deeper valley. This term is not exclusive to glacially-created valleys, as rivers valleys (V-Shaped) can also undercut other valleys. Hanging glaciers can form as a result of this as well.
Horn: A pyramidal peak formed by three or more cirques meeting on a central. They are also called pyramidal peaks. The Matterhorn (Italy & Switzerland, Alps) is a very famous example. Horns are often examples of nunataks.
Outwash Plain: Broad, low-slope angle alluvial plain made of glacially eroded, sorted sediment (outwash) that has been transported by meltwater. While these are generally more associated with continental glaciers, it is not impossible for the meltwater of a mountain glacier to cause it as well.
Roche moutonnée: (French: Sheep (Mutton) Rock) A hard bedrock bump or hill which has been overrun by a glacier to give a smooth side uphill and a rough and plucked surface on the downhill side. The up-glacier surface is often marked with striations.
Striations: (Grooves) Long, narrow channels cut into bedrock by englacial debris. They are parallel to adjacent grooves, and indicate the direction of glacial movement. They must be cut by mid-to-large sized rocks; smaller, fine grained sediments generally polish the entire rock surface, creating a pavement.
U-Shaped Valley: A standard glacially eroded valley. Contrasts with a V-shaped valley, which comes from water erosion. Also called a Glacial Trough. Fjords are U-Shaped valleys which have been opened up to the sea and filled partially with water.
Whalebacks: A sister landform to Roche moutonnée, a whaleback is a knoll of bedrock that has been eroded on all sides.
d.ii. Depositional
Diamictite: Sedimentary rock composed of a range of unsorted or poorly sorted particles. Large rocks and boulders are found in a suspension of finer clay and silt particles. It is typically formed from till or moraines, when in the context of glaciers. In general, diamictite comes from a variety of sources, the most common of which is the non-glacial underwater debris flow. In marine areas subject to cyclical advance and retreat of glaciers (i.e. the coast of Antarctica), diamictite can be contrasted with diatomite, which contains components of fossilized diatom creatures. Repeating layers of diatomite and diamictite are often evidence of glaciers advancing and retreating over a certain location.
Drift: A collective term meaning all sedimentary deposits of glacial origin. Any sediment eroded, transported, and deposited by a glacier is drift.
Dropstones: Larger, irregular, non-marine sediments found embedded in layers of marine sediments. They are carried to their location in oceans or lakes by icebergs in a process known as ice rafting. When the iceberg melts sufficiently for the stone to fall off, it becomes a "marine erratic" of sorts. (Marine erratic is only an analogy, not an actual term). Dropstones are generally much larger than the surrounding sediment, as water can only carry (and deposit) very fine sediments.
Drumlins: Elongated, streamlined hills formed from glaciers acting on till and/or ground moraine. The gently sloped and tapered end points in the direction of glacier flow. They often resemble a crag & tail. Drumlins almost always form in large groups, known as drumlin fields. They are features of continental glaciation.
Erratics: (Glacial erratics) Large, misplaced boulders or rocks transported far from their source by a glacier and left behind upon retreat.
Composition can be used to determine the direction of glacial flow by matching it with potential source rocks.
Typically formed by the transportation of large boulders by glaciers
Eskers: (Eskar, Eschar, Os, Osar, As, Serpent Kame) Long, winding ridges of stratified deposit, left behind by englacial or subglacial meltwater streams. They usually run parallel to the direction of flow of the glacier. They are 5 to 50 meters tall, 50 to 500 meters wide, and can vary in length from only a few dozen meters to several kilometers. They can sometimes appear similar to railway embankments.
They typically form when glacial movement is slow or stagnant, and more so near the terminus, where the ice is thinner. Sometimes, they form in supraglacial areas, such as in crevasses or supraglacial channels.
Kames: An irregularly shaped hill composed of sand, gravel & till that accumulates in a depression on a retreating glacier which is deposited on land upon further retreat. They are formed only by continental glaciers.
Kame Terraces: Formed in the same way as Kames, but along the sides of glacial valleys. They visually similar to lateral moraines in some ways, but differ in their formation method. Kame terraces from from meltwater streams depositing debris along the sides of the glacer (glacio-fluvial deposits) whereas lateral moraines from till being pushed aside.
Kettles: Often found as kettle lakes, they are formed by bits of glacial ice breaking off and forming depressions in the ground, which then melt. Kames and kettles are generally found around and about each other, creating kettle-kame topography. Thus, they are also formed only by continental glaciers.
Moraine: Any ridge or mound of glacial debris that is deposited in glaciated regions; can consist of boulders, gravel, sand, clay, etc.
Terminal moraines: deposited at the terminus (end) of the glacier, marking its furthest advance. The term End moraine refers to both terminal and recessional moraines, as they are formed in the same way.
Recessional moraines: recessional moraines are ridges that are behind the terminal moraine—they mark other locations where the glacier had stopped in the past.
Lateral moraines: are material that have been pushed off to the side of glaciers.
Medial moraines: form between two glaciers with lateral moraines when they converge.
Ground moraine: the layer of till and other sediments underneath a glacier.
Supraglacial moraines: accumulations of debris on top of the glacial ice.
De Geer moraines: (annual, washboard, minor, corrugated, cross-valley, sublacustrine, or lift-off moraines) are narrow, parallel ridges which run across the width of the valley. The ridges are typically irregularly spaced. Their formation method is still unclear. The two main proposals are advance & retreat (similar to recessional moraines) or formation in crevasses. They are found throughout much of Canada and parts of Maine and Alaska, as well as northern Scandinavia.
Interlobate moraines: functionally equivalent to medial moraines but between ice caps or ice sheets (the lobes). Much larger than medial moraines of mountain glaciers and frequently surrounded by kettles.
Pulju moraines: are very similar to Veiki moraines but considerably smaller; exclusive to northern Finland.
Rogen moraines: (ribbed) are regularly and closely spaced, forming perpendicular to the direction of ice flow. They can often be found near drumlin fields. Their formation is unclear, but their close proximity to drumlins has led to the theory that they are formed by glaciers acting on drumlins (and other features) when the glacier changes direction. All theories propose that Rogen moraines are formed directly under the ice.
Veiki moraines: are hummocky and irregular moraines with many ponds and plateaus. They form from the irregular melting of debris-covered ice and are most common in northern Sweden, Canada, and Finland.
Varves: Annual layers of sediment. They form in marine and lacustrine (lake) environments — in the context of glaciers, it is primarily via meltwater lakes. During the summer months, water flow is higher, leading to smaller particles (i.e. clay) remaining suspended while larger particles (i.e. sand) sink to the bottom to form layers. When meltwater flows are reduced in colder seasons, the less turbulent water will deposit the finer particles as well, forming unique bands of (typically) light bands (sand & silt) and dark bands (clay, sand, and silt). Varves can be interrupted by dropstones.
Other: Cover moraines, Hummocky moraines, Sevetti moraines, Kianta moraine, Lee moraine, Vika moraine
d.iii. Lakes - tarns, the Great Lakes, Finger Lakes, kettles, moraine-dammed lake, proglacial lakes
-Glacial Lake: Formed after the melting of glaciers. Formed in depressions or holes created on the surface of the land by glacial erosion. When such depressions fill up with water, lakes are formed. The water in glacial lakes is usually sourced from melting ice left behind by a retreating glacier or rainfall. Landscapes containing glacial lakes usually feature several other glacial landforms like drumlins, moraines, eskers, etc.
-Finger Lakes: eleven long, narrow, roughly north–south lakes located directly south of Lake Ontario in New York; the term in general refers to a long, narrow lake in an overdeepended glacial valley
-Great Lakes: Superior, Michigan, Huron, Erie and Ontario. Though the five lakes lie in separate basins, they form a single, naturally interconnected body of freshwater within the Great Lakes Basin.
-Kettle lakes: Formed in depressions in glacial outwash plains. Such plains are formed by sediments deposited by the meltwater of glaciers, usually at the terminus of the glaciers. Glacial calving often leads to the formation of such lakes. When a detached mass of ice from the glacier gets embedded or partly lodged in the glacial outwash drift, the ice eventually melts to result in the formation of a lake. The depth of the lake increases with the greater accumulation of outwash sediments around the depression. The size of the kettles ranges anywhere from 5 m to 13 km in diameter. The lakes can have depths of up to 45 m. Most of these lakes are circular in shape. Kettles are either found singly or in groups. Kettle Lakes are common in the Yamal Peninsula.
-Moraine/Dammed Lakes: Formed when a terminal moraine acts as a barrier to the flow of meltwater originating from a glacier. As the water is unable to leave the valley, it accumulates to form a lake. A moraine-dammed lake usually appears in the shape of a ribbon. The Calafquén Lake in Chile and Lake Hāwea in New Zealand are examples of lakes of this type.
-Paternoster lake: One of the lakes in a series of glacial lakes that are connected to each other by either a single stream or a network of braided streams. Recessional moraines usually lead to the formation of such lakes. The lakes are named so due to their resemblance to beads on a string or a string of rosary beads. Such lakes usually occur in stepped glacial valleys. Such valleys are formed due to differential bedrock composition and subsequent variability in the erodibility of the underlying bedrock. Thus, places with harder bedrock form the steps of the valley while those with softer bedrock are eroded to form flat plains. Often, the glacier excavates the softer bedrock to considerable depths to create shallow bedrock basins that are occupied by lakes after the glacier retreats. The three Thornton Lakes located in the North Cascades National Park in the US are classic examples of paternoster lakes.
-Proglacial lakes: Lakes that form next to glaciers and are created when meltwater from a glacier pools behind a dam; can form when a glacier retreats and exposes a depression in the bedrock, or when meltwater is trapped by a moraine or ice dam.
-Tarn: A small mountain lake that is located in a cirque (a steep-walled amphitheater-shaped landform formed at the mouth of a valley glacier). In some places like Northern England, the term tarn is used in a broader sense to refer to all ponds in Northern England’s upland areas. However, in glaciology, it refers to a lake left behind by a retreating glacier. The process of overdeepening usually leads to the formation of these lakes. Tarns can be seen in the Tatras Mountains in Slovakia.
E. Periglacial Processes and Landforms
Periglacial: A landscape that undergoes seasonal freezing and thawing, typically on the fringes of past and present glaciated regions. Are able to release large amounts of carbon.
Periglacial processes: The physical processes occur when ground freezes and thaws seasonally, especially in areas with permafrost. These processes are called cryogenic processes.
Permafrost: Permanently frozen ground that remains at or below 0°C for at least two years
Active layer: The uppermost layer of permafrost that freezes and thaws annually. The thickness of the active layer is affected by the geothermal gradient, atmospheric temperature, and the amount of vegetation, snow cover, and organic litter.
Blockfields: A combination of chemical and mechanical weathering can fracture bedrock below the active layer. Over time, these processes produce an uneven bouldery landscape known as a blockfield, which is revealed once ice or permafrost disappears. They potentially began forming up to 23 million years ago during the Neogene, when chemical weathering initiated the slow process of eroding jointed bedrock
Ice Wedges: Vertically-oriented wedge-shaped growths of ice that occur near the surface of permafrost. They form where a temperature differential in the permafrost causes the ground to crack, allowing water to enter, refreeze, and expand. Ice wedges only ever form in periglacial environments. This makes them valuable for identifying former periglacial landscapes and studying past prevailing winter climatic conditions
Patterned Ground: Ordered shapes produced by the organization of sediment and stones are collectively known as ‘patterned ground’. These landforms include polygonal shapes, stone circles and stripes, and labyrinths. Each pattern is produced during the repeated freezing and thawing of the active layer. Initial freezing separates and sorts solid from stones at/ near the ground surface, whilst subsequent thawing once again redistributes these materials into new orientations.
Pingos: Pingo meaning tall, typically circular mounds of former lake sediments in periglacial environments. Over 95% of all pingos are located in the continuous permafrost regions of Arctic North America and northern Asia, where they total >10,000 individuals. Pingos form when growing permafrost uplifts unfrozen sediments (i.e. frost heave) beneath the surface of a draining lake, ultimately creating a stable, predominantly ice-cored mound where the lake was deepest. This process can repeat itself over thousands of years to produce a landscape of multiple buried pingo complexes
Solifluction Lobes: Soils can become highly saturated with moisture when permafrost prevents water percolating deep into the ground. This allows material to start flowing (solifluction) downhill in a lobate structure. These solifluction lobes will flow until they reach a natural barrier (e.g. a knick point) or melting permafrost finally allows water to percolate away from the lobe. Vegetation cover may also stabilize a lobe, ceasing its growth
Terracettes: Wide, stepped hillslopes that have formed naturally in periglacial environments are known as terracettes. It is generally agreed that terracettes form when soil creep processes and periglacial freeze-thaw cycles interact, creating regular step features on >20° slopes. (Habitants may use it as walkways).
Thermokarst: Formed when permafrost and ice-rich ground masses thaw. A variety of landforms are characteristic of thermokarst landscapes. Thermokarst lakes can form as water ponds on the surface of thawing permafrost. They can grow remarkably quickly as a response to warming climate and environmental factors such as forest fires. Thermokarst bogs form as water ponds on ice-rich peat. These bogs are poorly-drained by fluvial activity and groundwater, providing a unique habitat for stale-water plants. Mass movement landforms are also common in thermokarst landscapes.
F. Sea Ice
ice floe, draft vs freeboard, pressure ridge, formation (frazil ice, pancake ice)
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans.[1][2][3] Much of the world's sea ice is enclosed within the polar ice packs in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Polar packs undergo a significant yearly cycling in surface extent, a natural process upon which depends the Arctic ecology, including the ocean's ecosystems. Due to the action of winds, currents and temperature fluctuations, sea ice is very dynamic, leading to a wide variety of ice types and features. Sea ice may be contrasted with icebergs, which are chunks of ice shelves or glaciers that calve into the ocean. Depending on location, sea ice expanses may also incorporate icebergs.
General features and dynamics
Hypothetical sea ice dynamics scenario showing some of the most common sea ice features (the bear provides an approximate scale)
Sea ice does not simply grow and melt. During its lifespan, it is very dynamic. Due to the combined action of winds, currents, water temperature and air temperature fluctuations, sea ice expanses typically undergo a significant amount of deformation. Sea ice is classified according to whether or not it is able to drift and according to its age.
Fast ice versus drift (or pack) ice
"Ice canopy" redirects here. For the pseudoscientific use of the term, see Flood geology § Vapor/water canopy.
Sea ice can be classified according to whether or not it is attached (or frozen) to the shoreline (or between shoals or to grounded icebergs). If attached, it is called landfast ice, or more often, fast ice (as in fastened). Alternatively and unlike fast ice, drift ice occurs further offshore in very wide areas and encompasses ice that is free to move with currents and winds. The physical boundary between fast ice and drift ice is the fast ice boundary. The drift ice zone may be further divided into a shear zone, a marginal ice zone and a central pack.[4] Drift ice consists of floes, individual pieces of sea ice 20 metres (66 ft) or more across. There are names for various floe sizes: small – 20 to 100 m (66 to 328 ft); medium – 100 to 500 m (330 to 1,640 ft); big – 500 to 2,000 m (1,600 to 6,600 ft); vast – 2 to 10 kilometres (1.2 to 6.2 mi); and giant – more than 10 km (6.2 mi).[5][6] The term pack ice is used either as a synonym to drift ice,[5] or to designate drift ice zone in which the floes are densely packed.[5][6][7] The overall sea ice cover is termed the ice canopy from the perspective of submarine navigation.[6][7]
Classification based on age
Another classification used by scientists to describe sea ice is based on age, that is, on its development stages. These stages are: new ice, nilas, young ice, first-year and old.[5][6][7]
New ice, nilas and young ice
Nilas in Baffin Bay
New ice is a general term used for recently frozen sea water that does not yet make up solid ice. It may consist of frazil ice (plates or spicules of ice suspended in water), slush (water saturated snow), or shuga (spongy white ice lumps a few centimeters across). Other terms, such as grease ice and pancake ice, are used for ice crystal accumulations under the action of wind and waves.[citation needed] When sea ice begins to form on a beach with a light swell, ice eggs up to the size of a football can be created.[8]
Nilas designates a sea ice crust up to 10 centimetres (3.9 in) in thickness. It bends without breaking around waves and swells. Nilas can be further subdivided into dark nilas – up to 5 cm (2.0 in) in thickness and very dark and light nilas – over 5 cm (2.0 in) in thickness and lighter in color.
Young ice is a transition stage between nilas and first-year ice and ranges in thickness from 10 cm (3.9 in) to 30 cm (12 in), Young ice can be further subdivided into grey ice – 10 cm (3.9 in) to 15 cm (5.9 in) in thickness and grey-white ice – 15 cm (5.9 in) to 30 cm (12 in) in thickness. Young ice is not as flexible as nilas, but tends to break under wave action. Under compression, it will either raft (at the grey ice stage) or ridge (at the grey-white ice stage).
First-year sea ice
Distinction between 1st year sea ice (FY), 2nd year (SY), multiyear (MY) and old ice
First-year sea ice is ice that is thicker than young ice but has no more than one year growth. In other words, it is ice that grows in the fall and winter (after it has gone through the new ice – nilas – young ice stages and grows further) but does not survive the spring and summer months (it melts away). The thickness of this ice typically ranges from 0.3 m (0.98 ft) to 2 m (6.6 ft).[5][6][7] First-year ice may be further divided into thin (30 cm (0.98 ft) to 70 cm (2.3 ft)), medium (70 cm (2.3 ft) to 120 cm (3.9 ft)) and thick (>120 cm (3.9 ft)).[6][7]
Old sea ice
Old sea ice is sea ice that has survived at least one melting season (i.e. one summer). For this reason, this ice is generally thicker than first-year sea ice. Old ice is commonly divided into two types: second-year ice, which has survived one melting season and multiyear ice, which has survived more than one. (In some sources,[5] old ice is more than two years old.) Multi-year ice is much more common in the Arctic than it is in the Antarctic.[5][9] The thickness of old sea ice typically ranges from 2 to 4 m.[10] The reason for this is that sea ice in the south drifts into warmer waters where it melts. In the Arctic, much of the sea ice is land-locked.
Driving forces
While fast ice is relatively stable (because it is attached to the shoreline or the seabed), drift (or pack) ice undergoes relatively complex deformation processes that ultimately give rise to sea ice's typically wide variety of landscapes. Wind is the main driving force, along with ocean currents.[1][5] The Coriolis force and sea ice surface tilt have also been invoked.[5] These driving forces induce a state of stress within the drift ice zone. An ice floe converging toward another and pushing against it will generate a state of compression at the boundary between both. The ice cover may also undergo a state of tension, resulting in divergence and fissure opening. If two floes drift sideways past each other while remaining in contact, this will create a state of shear.
Deformation
Sea ice deformation results from the interaction between ice floes, as they are driven against each other. The result may be of three types of features:[6][7] 1) Rafted ice, when one piece is overriding another; 2) Pressure ridges, a line of broken ice forced downward (to make up the keel) and upward (to make the sail); and 3) Hummock, a hillock of broken ice that forms an uneven surface. A shear ridge is a pressure ridge that formed under shear – it tends to be more linear than a ridge induced only by compression.[6][7] A new ridge is a recent feature – it is sharp-crested, with its side sloping at an angle exceeding 40 degrees. In contrast, a weathered ridge is one with a rounded crest and with sides sloping at less than 40 degrees.[6][7] Stamukhi are yet another type of pile-up but these are grounded and are therefore relatively stationary. They result from the interaction between fast ice and the drifting pack ice.
Level ice is sea ice that has not been affected by deformation and is therefore relatively flat.[6][7]
Leads and polynyas
Leads and polynyas are areas of open water that occur within sea ice expanses even though air temperatures are below freezing and provide a direct interaction between the ocean and the atmosphere, which is important for the wildlife. Leads are narrow and linear – they vary in width from meter to km scale. During the winter, the water in leads quickly freezes up. They are also used for navigation purposes – even when refrozen, the ice in leads is thinner, allowing icebreakers access to an easier sail path and submarines to surface more easily. Polynyas are more uniform in size than leads and are also larger – two types are recognized: 1) Sensible-heat polynyas, caused by the upwelling of warmer water and 2) Latent-heat polynyas, resulting from persistent winds from the coastline.[5]
Aerial view showing an expanse of drift ice offshore Labrador (Eastern Canada) displaying floes of various sizes loosely packed, with open water in several networks of leads. (Scale not available.)
Aerial view showing an expanse of drift ice offshore Labrador (Eastern Canada) displaying floes of various sizes loosely packed, with open water in several networks of leads. (Scale not available.)
Aerial view showing an expanse of drift ice in southeastern Greenland, comprising loosely packed floes of various sizes, with a lead developing in the centre.(Scale not available.)
Aerial view showing an expanse of drift ice in southeastern Greenland, comprising loosely packed floes of various sizes, with a lead developing in the centre.(Scale not available.)
Aerial view showing an expanse of drift ice consisting mostly of water. (Scale not available.)
Aerial view showing an expanse of drift ice consisting mostly of water. (Scale not available.)
Close-up view inside a drift ice zone: several small rounded floes are separated from each other by slush or grease ice. (Bird at lower right for scale.)
Close-up view inside a drift ice zone: several small rounded floes are separated from each other by slush or grease ice. (Bird at lower right for scale.)
Example of hummocky ice: an accumulation of ice blocks, here about 20 to 30 cm (7.9 to 11.8 in) in thickness (with a thin snow cover).
Example of hummocky ice: an accumulation of ice blocks, here about 20 to 30 cm (7.9 to 11.8 in) in thickness (with a thin snow cover).
Field example of a pressure ridge. Only the sail (the part of the ridge above the ice surface) is shown in this photograph – the keel is more difficult to document.
Field example of a pressure ridge. Only the sail (the part of the ridge above the ice surface) is shown in this photograph – the keel is more difficult to document.
Aerial view of the Chukchi Sea between Chukotka and Alaska, displaying a pattern of leads. Much of the open water inside those leads is already covered by new ice (indicated by a slightly lighter blue color)(scale not available).
Aerial view of the Chukchi Sea between Chukotka and Alaska, displaying a pattern of leads. Much of the open water inside those leads is already covered by new ice (indicated by a slightly lighter blue color)(scale not available).
Formation
Main article: Sea ice growth processes
Satellite image of sea ice forming near St. Matthew Island in the Bering Sea
Only the top layer of water needs to cool to the freezing point.[11] Convection of the surface layer involves the top 100–150 m (330–490 ft), down to the pycnocline of increased density.
In calm water, the first sea ice to form on the surface is a skim of separate crystals which initially are in the form of tiny discs, floating flat on the surface and of diameter less than 0.3 cm (0.12 in). Each disc has its c-axis vertical and grows outwards laterally. At a certain point such a disc shape becomes unstable and the growing isolated crystals take on a hexagonal, stellar form, with long fragile arms stretching out over the surface. These crystals also have their c-axis vertical. The dendritic arms are very fragile and soon break off, leaving a mixture of discs and arm fragments. With any kind of turbulence in the water, these fragments break up further into random-shaped small crystals which form a suspension of increasing density in the surface water, an ice type called frazil or grease ice. In quiet conditions the frazil crystals soon freeze together to form a continuous thin sheet of young ice; in its early stages, when it is still transparent – that is the ice called nilas. Once nilas has formed, a quite different growth process occurs, in which water freezes on to the bottom of the existing ice sheet, a process called congelation growth. This growth process yields first-year ice.
In rough water, fresh sea ice is formed by the cooling of the ocean as heat is lost into the atmosphere. The uppermost layer of the ocean is supercooled to slightly below the freezing point, at which time tiny ice platelets (frazil ice) form. With time, this process leads to a mushy surface layer, known as grease ice. Frazil ice formation may also be started by snowfall, rather than supercooling. Waves and wind then act to compress these ice particles into larger plates, of several meters in diameter, called pancake ice. These float on the ocean surface and collide with one another, forming upturned edges. In time, the pancake ice plates may themselves be rafted over one another or frozen together into a more solid ice cover, known as consolidated pancake ice. Such ice has a very rough appearance on top and bottom.
If sufficient snow falls on sea ice to depress the freeboard below sea level, sea water will flow in and a layer of ice will form of mixed snow/sea water. This is particularly common around Antarctica.
Russian scientist Vladimir Vize (1886–1954) devoted his life to study the Arctic ice pack and developed the Scientific Prediction of Ice Conditions Theory, for which he was widely acclaimed in academic circles. He applied this theory in the field in the Kara Sea, which led to the discovery of Vize Island.
Yearly freeze and melt cycle
Seasonal variation and annual decrease of Arctic sea ice volume as estimated by measurement backed numerical modelling[12]
Volume of arctic sea ice over time using a polar coordinate system draw method (time goes counter clockwise; one cycle per year)
The annual freeze and melt cycle is set by the annual cycle of solar insolation and of ocean and atmospheric temperature and of variability in this annual cycle.
In the Arctic, the area of ocean covered by sea ice increases over winter from a minimum in September to a maximum in March or sometimes February, before melting over the summer. In the Antarctic, where the seasons are reversed, the annual minimum is typically in February and the annual maximum in September or October and the presence of sea ice abutting the calving fronts of ice shelves has been shown to influence glacier flow and potentially the stability of the Antarctic ice sheet.[13][14]
The growth and melt rate are also affected by the state of the ice itself. During growth, the ice thickening due to freezing (as opposed to dynamics) is itself dependent on the thickness, so that the ice growth slows as the ice thickens.[5] Likewise, during melt, thinner sea ice melts faster. This leads to different behaviour between multiyear and first year ice. In addition, melt ponds on the ice surface during the melt season lower the albedo such that more solar radiation is absorbed, leading to a feedback where melt is accelerated. The presence of melt ponds is affected by the permeability of the sea ice (i.e. whether meltwater can drain) and the topography of the sea ice surface (i.e. the presence of natural basins for the melt ponds to form in). First year ice is flatter than multiyear ice due to the lack of dynamic ridging, so ponds tend to have greater area. They also have lower albedo since they are on thinner ice, which blocks less of the solar radiation from reaching the dark ocean below.[15]
Physical properties
Sea ice is a composite material made up of pure ice, liquid brine, air, and salt. The volumetric fractions of these components—ice, brine, and air—determine the key physical properties of sea ice, including thermal conductivity, heat capacity, latent heat, density, elastic modulus, and mechanical strength.[16] Brine volume fraction depends on sea-ice salinity and temperature, while sea-ice salinity mainly depends on ice age and thickness. During the ice growth period, its bulk brine volume is typically below 5%.[17] Air volume fraction during ice growth period is typically around 1–2 %, but may substantially increase upon ice warming.[18] Air volume of sea ice in can be as high as 15 % in summer[19] and 4 % in autumn.[20] Both brine and air volumes influence sea-ice density values, which are typically around 840–910 kg/m3 for first-year ice. Sea-ice density is a significant source of errors in sea-ice thickness retrieval using radar and laser satellite altimetry, resulting in uncertainties of 0.3–0.4 m.[21]
Monitoring and observations
Main article: Measurement of sea ice
See also: Arctic sea ice decline, Arctic sea ice decline § Ice-free summer, and Antarctic sea ice
Changes in sea ice conditions are best demonstrated by the rate of melting over time. A composite record of Arctic ice demonstrates that the floes' retreat began around 1900, experiencing more rapid melting beginning within the past 50 years.[22] Satellite study of sea ice began in 1979 and became a much more reliable measure of long-term changes in sea ice. In comparison to the extended record, the sea-ice extent in the polar region by September 2007 was only half the recorded mass that had been estimated to exist within the 1950–1970 period.[23]
Arctic sea ice extent ice hit an all-time low in September 2012, when the ice was determined to cover only 24% of the Arctic Ocean, offsetting the previous low of 29% in 2007. Predictions of when the first "ice free" Arctic summer might occur vary.
Antarctic sea ice extent gradually increased in the period of satellite observations, which began in 1979, until a rapid decline in southern hemisphere spring of 2016.
Effects of climate change
As ice melts, the liquid water collects in depressions on the surface and deepens them, forming these melt ponds in the Arctic. These freshwater ponds are separated from the salty sea below and around it, until breaks in the ice merge the two.
Further information: Effects of climate change on oceans
Sea ice provides an ecosystem for various polar species, particularly the polar bear, whose environment is being threatened as global warming causes the ice to melt more as the Earth's temperature gets warmer. Furthermore, the sea ice itself functions to help keep polar climates cool, since the ice exists in expansive enough amounts to maintain a cold environment. At this, sea ice's relationship with global warming is cyclical; the ice helps to maintain cool climates, but as the global temperature increases, the ice melts and is less effective in keeping those climates cold. The bright, shiny surface (albedo) of the ice also serves a role in maintaining cooler polar temperatures by reflecting much of the sunlight that hits it back into space. As the sea ice melts, its surface area shrinks, diminishing the size of the reflective surface and therefore causing the earth to absorb more of the sun's heat. As the ice melts it lowers the albedo thus causing more heat to be absorbed by the Earth and further increase the amount of melting ice.[24] Though the size of the ice floes is affected by the seasons, even a small change in global temperature can greatly affect the amount of sea ice and due to the shrinking reflective surface that keeps the ocean cool, this sparks a cycle of ice shrinking and temperatures warming. As a result, the polar regions are the most susceptible places to climate change on the planet.[5]
Furthermore, sea ice affects the movement of ocean waters. In the freezing process, much of the salt in ocean water is squeezed out of the frozen crystal formations, though some remains frozen in the ice. This salt becomes trapped beneath the sea ice, creating a higher concentration of salt in the water beneath ice floes. This concentration of salt contributes to the salinated water's density and this cold, denser water sinks to the bottom of the ocean. This cold water moves along the ocean floor towards the equator, while warmer water on the ocean surface moves in the direction of the poles. This is referred to as "conveyor belt motion" and is a regularly occurring process.[5]
Change in extent of the Arctic Sea ice between April and August, in 2013
Change in extent of the Arctic Sea ice between April and August, in 2013
Sea ice off Baffin Island
Sea ice off Baffin Island
Sea ice imitates the shoreline along the Kamchatka Peninsula.
Sea ice imitates the shoreline along the Kamchatka Peninsula.
Clear view of the Antarctic Peninsula, the Larsen Ice Shelf and the sea ice-covered waters around the region
Clear view of the Antarctic Peninsula, the Larsen Ice Shelf and the sea ice-covered waters around the region
The Earth showing the annual minimum sea ice with a graph overlay showing the annual minimum sea ice area in millions of square kilometers
Modelling
In order to gain a better understanding about the variability, numerical sea ice models are used to perform sensitivity studies. The two main ingredients are the ice dynamics and the thermodynamical properties (see Sea ice emissivity modelling, Sea ice growth processes and Sea ice thickness). There are many sea ice model computer codes available for doing this, including the CICE numerical suite.
Many global climate models (GCMs) have sea ice implemented in their numerical simulation scheme in order to capture the ice–albedo feedback correctly. Examples include:
The Louvain-la-Neuve Sea Ice Model is a numerical model of sea ice designed for climate studies and operational oceanography developed at Université catholique de Louvain. It is coupled to the ocean general circulation model OPA (Ocean Parallélisé) and is freely available as a part of the Nucleus for European Modeling of the Ocean.
The MIT General Circulation Model is a global circulation model developed at Massachusetts Institute of Technology includes a package for sea-ice. The code is freely available there.
The University Corporation for Atmospheric Research develops the Community Sea Ice Model.
CICE is run by the Los Alamos National Laboratory. The project is open source and designed as a component of GCM, although it provides a standalone mode.
The Finite-Element Sea-Ice Ocean Model developed at Alfred Wegener Institute uses an unstructured grid.
The neXt Generation Sea-Ice model (neXtSIM) is a Lagrangian model using an adaptive and unstructured triangular mesh and includes a new and unique class of rheological model called Maxwell-Elasto-Brittle to treat the ice dynamics. This model is developed at the Nansen Center in Bergen, Norway.
The Coupled Model Intercomparison Project offers a standard protocol for studying the output of coupled atmosphere-ocean general circulation models. The coupling takes place at the atmosphere-ocean interface where the sea ice may occur.
G. Glacial Hydrology:
Surface melt, surface lakes, moulins, drainage and subglacial lakes, & Jökulhlaups
Surface Melt:
-Its rate is contributed by increased solar radiation and rainfall
Glacial hydrology: Study of the water that acts in and around glaciers. Glacier ice is permeable with microscopic passages which allow water through. The rate of percolation depends on salinity, pressure and temperature, but in shorter time frames it is too slow to be considered and rendered impermeable. Regardless, water is still able to build up both within and underneath a glacier simply by seeping in.
Proglacial Hydrology: Proglacial actions happen ahead of or downslope from a glacier and often remain once the glacier has disappeared. All proglacial hydrologic features are derived primarily from glacial meltwater. Proglacial lakes come in various shapes and sizes and have drastically different formation methods.
Ice-dammed Lakes: Glacier ice blocking off meltwater flow. Streams are also very common, running down valleys and plains, cutting into outwash and ground moraine.
Paternoster lakes: When a stream or multiple streams link two or more tarns.
Streams may be straight or braided:
Straight streams: Single-channel waterways
Braided streams: Many temporary islands separating the water flow known as braid bars, aits, or eyots.
Supraglacial Hydrology: Happen on the surface of a glacier. The water here is almost exclusively from surface melt during the ablation season. This water will often form supraglacial channels (supraglacial rivers & streams). When the water drains off the terminus, it becomes a "normal" river or stream.
The meltwater itself comes from firn, not the ice itself. On larger ice sheets where there is no downhill or uphill, large supraglacial lakes will form.
Supraglacial lakes: These lakes can grow very large in size, sometimes kilometers in diameter, and will sometimes last multiple years. However, the increased absorption of sunlight from the darker water can cause additional melting, which, in extreme cases, can lead to the disintegration of an ice sheet or ice shelf.
On the surface: Supraglacial lakes form on the ice surface.
In front of the ice: Proglacial lakes form in front of the ice.
Underneath the ice: Subglacial lakes form underneath the ice
Englacial Hydrology: Fractures and pores in glaciers such as crevasses are the primary way in which water enters a glacier.
Drainage mechanisms:
Hydrofractures: Cracks that can form below lakes on top of glaciers, draining the lakes and sending water to the base of the ice sheet.
Subglacial drainage channels: Connected to subglacial lakes beneath the Antarctic Ice Sheet.
Glacier-dammed lakes can drain catastrophically in outburst floods, also known as jökulhlaups.
Moulins: are also notable as many supraglacial streams will drain into them entirely.
Sustained by melting of the ice walls that contain them—otherwise, the internal pressure of the glacier would close them up. Aside from transporting water from the surface to the base of a glacier, englacial hydrologic features do not have many significant impacts on glacier dynamics, and are rather a consequence of varying melting and environmental conditions.
Englacial channels: Will also form within glaciers, always running roughly parallel with the direction of flow. They are one of the ways eskers can form.
Subglacial Hydrology: Subglacial actions happen underneath a glacier. These are the most important form of glacial hydrology as meltwater has a large impact on glacier flow.
Subglacial lakes: Bodies of freshwater that are contained deep within the layers of ice sheets. The largest known subglacial lake is Lake Vostok, located beneath the East Antarctic Ice Sheet. It is beneath more than 3 kilometers of ice, is 230 km in length, has an area of 14000 square kilometers, and a volume of about 2000 cubic kilometers.
Subglacial lakes are very abundant. The water underneath the ice remains liquid due to geothermal heating and pressure-melting.Subglacial lakes do not necessarily conform to the underlying topography, being able to form on hills in some cases. The water can also affect or create ice streams, significantly increasing the movement speed of the overlying ice.
Subglacial channels: Water channels under glaciers which are roughly parallel to the flow direction. They are one of the ways in which eskers can form.
Marginal Hydrology: Occurs near the edges (margins) of a glacier. It is more applicable to mountain glaciers. Marginal channels form with one part of their bed as rock and the other as ice. When they deposit sediments, they may form kame terraces. They also can plunge down into crevasses and moulins, creating potholes.
Postglacial Hydrology: Postglacial actions come after a glacier has left the region or disappeared entirely. Proglacial and postglacial hydrology have similar features, especially as some proglacial features outlast the glacier, but they should not be confused.
Surface Lakes:
Tarns : Lakes which form in cirques. Also called corrie lochs or simply cirque lakes, they are generally small compared to the size of the cirque they are in, but occasionally can push beyond the cirque lip. When multiple tarns are linked by single or braided streams, they become paternoster lakes.
Misfit streams:They are streams or rivers that run through a valley that they themselves did not create and thus, are disproportionate to the valley. Many U-Shaped valleys will have misfit streams running through them both during and after glaciation and are often an important source of freshwater for drinking and irrigation.
Moraine-dammed lakes: Where a lake is created behind a moraine. Overdeepend U-shaped valley basins can often form finger lakes, which can be hundreds of meters deep. They are also capped off by moraines. The extreme elevation changes can also lead to the formation of gorges as rivers and streams cut into the sides of the glacial valley.
Moulins/Mill/Glacier Mills: Narrow, near-vertical tubes within a glacier which start at the surface. Found in a flat section within the transverse crevasses but vary in depth though are no more than 10 meters wide. They carry meltwater down to the base which can lubricate the glacier as it slides along. Characteristics of mountain glaciers.
These water currents can plunge into the bedrock to create a hollowed-out region that may go by names of giant’s kettle, giant’s cauldron, pothole, glacial pothole, moulin pothole, and glacier mill cavity. This feature is created when debris from the falling water erodes the bedrock under it to involve the swirling motion to create the cylindrical shape of the pothole.
Jökulhlaups (Icelandic): glacial outburst floods that occur when a lake fed by glacial meltwater breaches its dam and drains catastrophically.
To occur, the lake water levels must reach a critical point such that the lake causes its ice dam to float, overtops its dam, or carves large meltwater channels beneath the glacier ice that allow for rapid drainage.
Volcanic activity beneath the glacier can also trigger its occurrence
H. Global Connections of Glaciation:
i. Atmosphere
effects of greenhouse gasses, insolation, and aerosols on glaciation (ie amplified melting due to changes in albedo, release of gasses from glacial melting)
ii. Oceans
sea level change and ice sheet variation (thickness and extent)
iii. Lithosphere
Isostatic effects on Earth’s crust
iv. Planetary/orbital influence on glaciation
(ie. Milankovitch cycles)
Milankovitch Cycles:
i. Role in producing climate activity
ii. Role in dating
In the 1920s, Serbian geophysicist and astronomer Milutin Milankovitch proposed that natural variations in three parameters of the earth's orbit caused fluctuations in the amount of incoming solar radiation, resulting in glacial periods:
1. Eccentricity - the variation in the circularity of Earth's orbital path.
2. Obliquity - (Axial Tilt) the variation in the degree of the tilt of Earth's rotational axis.
3. Precession - (Axial Precession) the variation in the direction of the tilt of Earth's rotational axis.
Eccentricity
Eccentricity is one of the three major cycles, with a period of approximately 100,000 years. Eccentricity is a measure of how elliptical (or non-circular) the orbit is. The lowest eccentricity is 5.5 E-5, nearly a perfect circle, while the highest is mildly elliptical at 0.0679. There are various components to the eccentricity cycle, with some running at 413 Ka, 95 Ka, and 125 Ka, all coming together to form a cycle of approximately 100 Ka. The current eccentricity is 0.017 and declining. The primary causes of eccentric variations are the gravitational effects of Jupiter and Saturn.
During a more eccentric orbit the perihelion (the point farthest from the sun) gets farther from the sun while the aphelion (the point nearest to the sun) gets closer. The semi-major axis (the orbit's longest "radius") does not change, nor does the orbital period (via Kepler's 3rd Law). Since the semi-major axis does not change size, the semi-minor axis (the orbit's shortest "radius") shrinks during times of higher eccentricity. This means that the magnitude of seasonal changes is greater. The difference between the amount of solar radiation at the perihelion and aphelion is greater as well. While in the current eccentricity, Earth receives approximately 6% more radiation at the perihelion than at the aphelion. During the times of peak eccentricity, the difference can be as high as 25%.
Eccentricity also varies season length. Earth will move faster at its perihelion, spending less time there. The perihelion currently occurs around 3 January while the aphelion is usually on 4 July, meaning autumn and winter are shorter in the northern hemisphere and longer in the southern. A less eccentric orbit will even out season lengths more. However, due to axial precession and apsidal precession, the date which coincides with the apsides will gradually change over time, making certain seasons longer and shorter depending on the hemisphere.
So, does high eccentricity or low eccentricity favor glaciation? Technically speaking, high eccentricity does cause a lower annual amount of insolation, meaning it is the preferred condition for glaciation. However, this value is very small. At 0.167% less annual insolation, this comes out to give us a total change of about 0.12 degrees Celsius. The effects of eccentricity are relatively small compared to those of obliquity and axial precession and do not have as large of an impact of seasonal climate variations. However, when put into conjunction with axial precession, the effects of eccentricity can be quickly amplified.
Obliquity
Obliquity is also one of the three major Milankovitch cycles, with a period of 40-41 Ka. Obliquity is the measure of the axial tilt relative to "vertical" position (the line perpendicular to the orbital plane) and varies between 22.1 to 24.5 degrees. The current axial tilt is 23.44 degrees and declining. An increased amount of axial tilt increases the seasonal variations in insolation with more occurring during the summer and less during the winter. This means higher latitudes will receive more annual solar radiation while the equator will receive less. Period of greater tilt experience more intense seasons. The currently decreasing tilt will create milder seasons and an overall cooling trend.
Lesser axial tilts favor glaciation because the milder summers at the poles preserve more of the ice each year, allowing for the ice sheets to expand. Additionally, milder seasons may cause an increase in moisture, allowing for greater annual snowfall and thus favoring glaciation.
Axial Precession
Axial Precession, often just Precession, is the last of the three main Milankovitch cycles. It has a period of approximately 26,000 years, with certain sub-cycles varying between 20 and 29 thousand years. Axial precession means the movement of the direction that the axis of rotation points. This means that Polaris will no longer be the north star (or pole star). In other words, when the Earth is at its aphelion, it will no longer be summer for the northern hemisphere. Axial precession is caused by tidal forces from the sun and moon, in roughly equal amounts. If we take the current situation of the southern hemisphere's summer coinciding with the aphelion, the solar radiation from both the axial tilt and the proximity to the sun are both at their peaks during that time. The opposite is also true for their winters. This means to a more extreme variation of solar radiation in the southern hemisphere. In the northern hemisphere, axial tilt and distance from the sun have their effects working against each other, resulting in less extreme variations. In approximately 13 thousand years, the direction in which the Earth points will have flipped: the north pole will be pointed towards the sun at Earth's perihelion.
Apsidal Precession & Precession of the Equinoxes
Later in the 20th century, various other scientists proposed other orbital variations as other possible contributors to the Milankovitch cycle. One of these is Apsidal Precession, or the precession of the semi-major axis. If axial tilt, the cause of the seasons, stays fixed during this time, apsidal precession will create a similar effect to that of axial precession. Halfway through one cycle, the location of the aphelion and perihelion will be switched, meaning the northern hemisphere will have summer coinciding with the perihelion. Apsidal precession itself does not have a specific period in which it favors or disfavors glaciation, rather, it depends on how it coincides with the 3 major Milankovitch Cycles, either amplifying or diminishing their effects.
When apsidal and axial precession are combined, we see the trend of the solstices and equinoxes "rotating" around in the orbit. This combined cycle becomes known as the Precession of the Equinoxes.
Problems with the Milankovitch Theory
The Milankovitch Cycle Theory is a good general explanation for the cyclical glaciation we see in our climate history. However, it is not without its issues, and five main examples have been introduced to show that the Milankovitch Theory is not a perfect predictor of long term climate cycles.
It is important to note that the solutions to all five problems outlined here are generally accepted to be internal changes within the Earth's atmosphere, such as the large release or absorption of greenhouse gases. Such an event would provide enough pressure to the climate to alter it in a way that does not match what the Milankovitch Theory would predict.
100,000-year Problem and Transition Problem
In theory, obliquity should have the greatest effect on the climate by affecting insolation at high latitudes. This would suggest a ~40,000-year period for glacial periods. However, research has shown that the glacial periods in the past 1 million years are dictated primarily on a 100,000-year cycle, matching eccentricity. Eccentricity variations have a significantly smaller impact on insolation than precession or obliquity and should have produced the weakest effects.
There are several theories which attempt to explain the problem. Internal oscillations of the climate, such as atmospheric composition, can often override the power of astronomical alignment. There is also the argument that, since axial precession relies substantially on eccentricity, eccentricity can easily dominate the precession cycle.
The Transition Problem is an extension to the 100,000-year Problem, and deals with the fact that, between 1 and 3 million years ago, glacial cycles indeed lined up more with the 40-41-thousand year cycle of obliquity rather than eccentricity. This time 1 million years ago is known as the Mid-Pleistocene Transition. The problem has partially been addressed as changes in atmospheric composition, namely the decline of carbon dioxide.
One commonly accepted solution to the 100,000-year Problem and Transition Problem is the difference between the polar environments of Antarctica and the Arctic. More specifically, Antarctica is able to generate more sea ice at a faster rate than the Arctic. This leads to a higher overall albedo in the southern hemisphere, leading to increased cooling, and a net imbalance in the internal climate control of the regions. During the periods of high eccentricity of the Pleistocene, the southern hemisphere experienced winter at the aphelion, much like it does today. This allowed for a much more dramatic growth in sea ice in the southern hemisphere, and, with it's positive feedback loop, continuously made the planet colder. Such conditions were to be expected only every 100,000 years, leading to the more visible 100,000-year cycle observed through much of the Pleistocene.
400,000-year Problem (Marine Isotope Stage 11 Problem)
In addition to the basic 100 thousand year cycle, eccentricity variations also have a strong 400k year cycle. Every 400,000 years, rather than rebound up to nearly 0.05, eccentricity stays well below the mark, around 0.02. Our present-day eccentricity is actually right after one of these stunted peaks in eccentricity, which matches the end of the Last Glacial Period & Pleistocene Glaciation. Since high eccentricity favors glaciation more, approximately 400,000 years ago should also be marked by a glaciation, albeit a weaker and less pronounced one. The time period from 400,000 years ago corresponds directly with Marine Isotope Stage 11. However, Marine Isotope Stage 11 was an interglacial period. In fact, it was the longest and warmest interglacial in the last 500,000 years. This peculiar problem where an expected mild glacial period is actually the most extreme interglacial recently observed in the entire Pleistocene is still lacking a proper explanation. As with many of these other problems, it is often partially attributed to internal changes on Earth, rather than it's orbital parameters.
Marine Isotope Stage 5 Problem
The MIS 5 Problem refers to the timing of the interglacial dating from 130 to 80 thousand years ago that appears to have begun 10 thousand years in advance of the orbital alignments hypothesized to have caused it. Once again, internal changes on Earth are hypothesized to have brought this earlier interglacial, rather than the Milankovitch Cycles. MIS 5 was also the last major interglacial prior to the end of the Pleistocene glaciation and entrance into the Holocene Epoch, the current epoch.
Effect exceeds cause
Very often, climate behavior is much more intense than calculations show they should be. Various internal characteristics of climate systems are believed to be sensitive to the insolation changes, causing amplification (positive feedback) and dampening reponses (negative feedback), leading to skewed data compared to what is expected based solely on orbital parameters.
Oxygen Isotope Analysis
There are 3 stable isotopes of oxygen, 16O, 17O, and 18O. There is approximately 1 atom of 18O for every 500 atoms of the most abundant isotope, 16O. 17O is very rare compared to the others and is generally ignored.
Water molecules containing the light isotope, 16O, are more active, evaporating slightly more readily than molecules containing the heavy 18O. Thus, the 18O/16O ratio in water vapor is smaller than in ocean water—oxygen in water vapor is "lighter". Similarly, when the vapor condenses, 18O does so more readily, leaving the vapor depleted in 18O. This leaves snows precipitated onto glaciers "lighter" than the ocean water. The depletion is even more noticeable at colder temperatures (as well as the reverse), making winter snow isotopically lighter than summer snows.
Similarly, oxygen isotope analysis can also be used on the calcite of oceanic core samples to find ancient ocean temperature change, and therefore climate change. Since the calcite is formed within the water, the 18O/16O ratios in calcite will increase with colder temperatures and decrease with warmer temperatures. This means calcite formed in cold periods will be isotopically heavier than those formed in warm periods.
It is important not to confuse an isotope analysis of ice versus that of calcite. It is easiest to remember that cold oceans produce heavier calcite and lighter ice, or that warm oceans produce lighter calcite and heavier ice.
Temperature and climate change are cyclical when plotted on a graph of temperature vs. time. Temperature coordinates are measured by deviation from today's annual mean temperature, taken as zero. Ratios are converted to a percent difference from the ratio found in the Standard Mean Ocean Water (SMOW). Either form of the graph appears as a waveform with overtones. Half of a period correlates to a Marine Isotopic Stage (MIS). It indicates a glacial (below 0) or interglacial (above 0). Earth has experienced 102 MIS's; early Pleistocene stages were shallow and frequent while the latest were the most intense and widespread.
v. History of ice on earth and its evidence
(ie drop stones, striations, sedimentary deposits)
vi. Neoproterozoic snowball Earth
vii. Late Paleozoic ice ages
viii. Eocene Oligocene Transition and the impact of opening oceanic seaways (ie Drake Passage)
ix. Pleistocene Northern Hemisphere glaciation
(ie Laurentide Ice Sheet retreat and melting history)
Laurentide Ice Sheet:
The Laurentide Ice Sheet was a historical ice sheet that covered most of North America during the Pleistocene glaciation. It was 4-5 kilometers thick in many areas but was perforated by many nunataks over hills and mountains near its fringes. It greatly shaped the appearance of modern-day North America, leaving behind moraines, eskers, and till everywhere. The Great Lakes were deepened under the forces of the Laurentide Ice Sheet, reaching their present-day form. It mostly disappeared at the end of the Pleistocene glaciation 11.7 Ka ago, but left numerous large ice caps and glaciers in its former ranges, mostly in Canada.
Retreat and Melting History
Impact on River Drainage
Oceanic Circulation
x. Recent records of cryospheric change
(ie Larsen B, Thwaites Glacier, Amundsen Sea Embayment)
Notable Glaciers
Hubbard Glacier: Hubbard Glacier is a tidewater valley glacier located in Alaska and Canada and the largest glacier in North America. In the past, it has created and released several glacial lakes, creating disastrous floods, including the second-largest glacial lake outburst flood (GLOF) ever recorded. It routinely calves off giant chunks of ice into Disenchantment Bay near the base of the Alaskan Panhandle.
Lambert Glacier: Lambert Glacier is an outlet glacier on Antarctica and is the largest glacier in the world excluding ice fields, ice caps, and ice sheets. It drains approximately 8% of the Antarctic Ice Sheet by volume.
Siachen Glacier: Siachen Glacier is a valley glacier located in the eastern Karakoram range between India and Pakistan. The glacier is part of the ongoing Indian-Pakistani conflict in Kashmir. At 76 kilometers long, it is the second-longest non-polar glacier in the world. The whole Himalayan region, including bordering ranges, is sometimes called the "Third Pole" due to its extreme temperatures being comparable to those of the Arctic and Antarctic.
Vatnajokull: Vatnajokull is an ice cap in Iceland. It is the largest glacier in Iceland, covering more than 9% of the land area of the nation, and second-largest by area in Europe. It is known particularly for its jökulhlaups, or glacial outburst floods, triggered by the volcanic activity of the island.
Larsen B: Larsen B was an ice shelf attached to the Antarctic Peninsula. From around 31 January to 7 March 2002, approximately 3,250 square kilometers of Larsen B's floating ice broke off from the continent. After the collapse of 2002, there was still a sizable portion remaining in the south which has since disappeared. Prior to its collapse, Larsen B had been stable for thousands of years, at least since the last ice age. During the decades leading up to its collapse, warm water currents were eating away at the underside of the shelf. It was shown to be unstable since at least 1995, with smaller, but still alarmingly large chunks being calved off from the main ice shelf, most notably one in 1998. The collapse in 2002 was further caused by ponds of meltwater which had formed during the 24-hour exposure to the sun during the Antarctic summer. The water flowed into cracks in the ice, wedged it apart, and disintegrated the ice shelf.
Patagonian Ice Fields: The North and South Patagonian Ice Fields, technically separate ice fields, are among the largest in the world and cover much of the Andes Mountains in Argentina and Chile. The South Patagonian is the larger of the two. During the Last Glacial Period, the two were joined together as one and covered almost all of southern Chile. Much like the other glaciers listed here, they have become an important site for research on climate change and global warming.
Greenland Ice Sheet: The Greenland Ice Sheet covers about 80% of the surface of Greenland and is second in size only to the Antarctic Ice Sheet. It is surrounded by several small glaciers and ice caps. With an average thickness of 2.1 km, a complete melt of the Greenland Ice Sheet would cause 7-8 meters of sea-level rise.
Antarctic Ice Sheets: The East and West Antarctic Ice Sheets comprise the vast majority of ice in Antarctica and the majority of ice in the world. They both have dozens of outlet glaciers on their fringes and are separated by the Transantarctic Mountains. The East Antarctic Ice Sheet is by far the larger of the two, having 9 times the volume of the West Antarctic Ice Sheet and containing about 4/5ths of all the world's ice. The East Antarctic Ice Sheet is about 2.2 km thick on average, while the West is only 1.3 km thick. Most of the West Antarctic Ice Sheet actually sits below sea level, which has left it more susceptible to melting and collapse. The ice shelves that buttress it are also at risk. The collapse of the West Antarctic Ice Sheet would cause a rise in sea level of 6 meters; the collapse of the East Antarctic Ice Sheet would cause a rise of over 55 meters.
Laurentide Ice Sheet: The Laurentide Ice Sheet was a historical ice sheet that covered most of North America during the Pleistocene glaciation. It was 4-5 kilometers thick in many areas but was perforated by many nunataks over hills and mountains near its fringes. It greatly shaped the appearance of modern-day North America, leaving behind moraines, eskers, and till everywhere. The Great Lakes were deepened under the forces of the Laurentide Ice Sheet, reaching their present-day form. It mostly disappeared at the end of the Pleistocene glaciation 11.7 Ka ago, but left numerous large ice caps and glaciers in its former ranges, mostly in Canada.
In addition to global modeling, various regional models deal with sea ice. Regional models are employed for seasonal forecasting experiments and for process studies.
Ecology
Main article: Sympagic ecology
Sea ice is part of the Earth's biosphere. When sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids, which in turn provide food for animals such as krill and specialised fish like the bald notothen, fed upon in turn by larger animals such as emperor penguins and minke whales.[25]
A decline of seasonal sea ice puts the survival of Arctic species such as ringed seals and polar bears at risk.[26][27][28]
Extraterrestrial presence
Other element and compounds have been speculated to exist as oceans and seas on extraterrestrial planets. Scientists notably suspect the existence of "icebergs" of solid diamond and corresponding seas of liquid carbon on the ice giants, Neptune and Uranus. This is due to extreme pressure and heat at the core, that would turn carbon into a supercritical fluid.[29][30]