Definition and importance of the cryosphere
The cryosphere consists of ice sheets and glaciers, together with sea ice, lake ice, ground ice (permafrost) and snow cover.
Mass and energy are constantly exchanged between the cryosphere and other major components of Earth systems: the hydrosphere, lithosphere, atmosphere and biosphere.
Glaciers are very visible and sensitive barometers of climate change because they constantly grow/advance and shrink/retreat in response to changes in temperature and precipitation.
Cryosphere:
The parts of the Earth’s crust and atmosphere subject to temperatures below 0 °C for at least part of each year.
Ice sheet
Complete submergence of regional topography; forms a gently sloping dome of ice several kilometres thick in the centre
10-100,000km2
Eg Greenland Antarctica
Ice cap
Smaller version of ice sheet occupying upland areas; outlet glaciers and ice sheets drain both ice sheets and ice caps
3-10,000km2
Vatnajökull
(Iceland)
Ice field
Ice covering an upland area, but not thick enough to bury topography; many do not extend beyond highland source
10-10,000km 2
Patagonia (Chile)
Columbia (Canada)
Valley glacier
Glacier confined between valley walls and terminating in a narrow tongue; forms from ice caps/sheets or cirques; may terminate in sea as a tidewater glacier
3-1500
Athabasca (Canada)
Piedmont glacier
Valley glacier which extends beyond the end of a mountain valley into a flatter area and spreads out like a fan
3-1000
Malaspina (Alaska)
Cirque glacier
Smaller glacier occupying a hollow on the mountain side - carves out a corrie or cirque; smaller version is known as a niche glacier
0.5-8
Cwm Idwal
Ice shelf
Large area of floating glacier ice extending from the coast where several glaciers have reached the sea and come together to form one mass or whole.
10-100,000
Ronne and
Ross Ice Shelf (Antarctica)
Warm based (temperate or wet) glaciers,
- occur in high altitude areas outside the polar region, such as in the Alps and sub-Arctic areas.
- The temperature of the surface layer fluctuates above and below melting point, depending on the time of year, whereas the temperature of the rest of the ice, extending downwards to the base, is close to melting point.
- Because of increased pressure of overlying ice, water exists as a liquid at temperatures below 0°C, causing the basal ice to melt continuously.
- The effects of pressure, geothermal energy and percolation of meltwater all contribute to prevent the glacier freezing to its bed.
- The glacier has lots of debris in its basal layers, and significant subglacial depositional features.
Cold based (polar) glaciers,
- occur in high latitudes, particularly in Antarctica and Greenland.
- As the average temperature of the ice is usually well below 0°C, as a result of the extreme surface temperature (as low as -20-30°C), the accumulation of heat from geothermal soruces is not great enough to raise the temperature of the base of the glaceir to 0°C even though the ice may be up to 500 m thick.
- There is relatively little surface melt in the very short and cool polar summer, so little meltwater percolates downwards.
- The glacier is permanently frozen to its bed, so there is no debris-rich basal layer.
A further subdivision is the hybrid polythermal glacier,
whereby the underneath is warm (wet) based and the margin cold based. Many large glaciers are cold based in their upper regions and warm based lower down, when they extend into warmer climate zones - this is a common occurrence in Svalbard, Norway.
Surging glaciers or ice streams
may occur within warm based, cold based or polythermal glaciers, and may have rates of flow of up to 100 m per day (examples include the Greenland outlet glaciers, which average 30 m per day) with huge amounts of calving (ice breaking off at the edges).
Present and past distribution of ice cover
- At present glacial ice covers over ten per cent of the Earth’s land area, and 75 per cent of the world’s freshwater is locked up in this ice cover, about 1.8 per cent of all the water (fresh, brackish or salt) on Earth.
present day:
* About 85 per cent of all current glacier ice is contained in Antarctica (shared between the West and East Antarctic Ice Sheets).
* The Greenland Ice Sheet is the second largest accumulation of glacier ice, with 10 per cent of the Earth’s total ice cover.
* The remaining ice cover is distributed among ice caps such as Vatnajökull (Iceland) and northern Canada and Alaska, highland ice fields and many smaller glaciers in high altitude areas (Himalayas, Rockies, Cascades, Andes, European Alps, etc.).
* There are even glaciers above 4000 m in Ecuador in the High Andes, Mount Kilimanjaro in Tanzania and in Indonesia in Equatorial regions!
A number of factors influence the distribution of ice cover.
- In high latitudes, the Sun’s rays hit the ground at a lower angle so the solar energy received has to heat a larger area.
- High altitudes are impacted by the environmental lapse rate (ELR) whereby temperature declines by 1 °C for every 100 m.
- aspect, which can determine the amount of snow falling and settling.
- In mountainous areas, aspect and relief combine to affect the distribution of cirque glaciers.
In the northern hemisphere, north- and east-facing slopes are both more sheltered and shadier, and thus more conducive to snow accumulation.
Pleistocene ice sheets and glaciers in both the northern and southern hemispheres, the following differences emerge:
- Ice cover at the Pleistocene maximum was more than three times greater than the present day.
- The Antarctica and Greenland ice sheets only covered a slightly greater area than they do today.
- The major extensions were two ice sheets in North America (Laurentide and Cordilleran) and the Scandinavian Ice Sheet in Europe - these all grew to thicknesses of 3000-4000 m and transformed the landscape of North America and Europe respectively.
- Other significant extensions included all of southern South America, South Island New Zealand, Siberia and the Himalayas.
Diagram of Past and present distribution of ice cover
