Antarctic Cold Arid Zone: Climate, Soils and Vegetation

After reading this article you will learn about Antarctic Cold Arid Zone:- 1. Subject-Matter of Antarctic Cold Arid Zone 2. Climate of Antarctic Cold Arid Zone 3. Soils 4. Terrestrial Vegetation 5. Fauna of Terrestrial. 

Subject-Matter of Antarctic Cold Arid Zone:

The Antarctic continent is dominated by a massive ice sheet. Some 86% of the world’s ice is found in the Antarctic ice cap and another 10% on Greenland, leaving only 4% of the world supply of ice in the form of mountain glaciers. If this amount of ice were to melt, the level of the world ocean would rise some 50 m or more enough to drown the majority of the world’s cities.

Antarctic covers an area of approximately 13-9 million sq. km., one tenth of the Earth’s land surface. It averages 1600 m in thickness and at points exceeds 4500 m. The Antarctic continent, some 14 x 10⁶ km² in area, ranges in height from spa-level to more than 4 km, with a mean altitude exceeding 2 km.

Although there is much variation in continental features-including exposed mountain chains, ‘dry’ valleys, and coastal ‘oases’ more than 95% of the total area is covered by snow and ice.

The continent is very cold, windy and over much of its area, very dry, it has a profound effect on Southern Hemisphere weather systems, but as yet or understanding of the climate and is complex short term and long term variations are poor.

Climate of Antarctic Cold Arid Zone:

The climate of Antarctic today, is dominated by three features – the water of southern ocean, the variable sea-ice cover, and the continental ice sheet. The cold area varies from about 3 x 10⁶ km² in summer to 19 x 10⁶ km² in winter, but the cover is not uniform; in September the concentration has been found to be between 15 and 85% over half the total area, and more than 85% over the other half.

Sea-ice thickness also varies, over the ocean in winter it is still largely unknown, but it is known to vary from about 0-3 m in latitudes 60-65°S in early winter to between 2 and 3 m in latitude 75° S in the late spring – early summer period.

Mean cloudiness over the oceans is high, it is a little lower over the continental coastline and there is a marked gradient in cloud amount in the area of steep ice slopes. The surface air temperature differences between summer and winter averaged around the latitude circles of 50, 55, 60 and 65°S, are 3-6, 4-3, 6-5 and 11 -8°C respectively the large difference at 65°S reflecting the effects of the sea-ice cover.

The mean diurnal temperature variation is generally small on the sub-Antarctic. islands, being about 2-3°C in summer and 1°C or less in winter.

The world’s lowest temperature of -89-6°C has been recorded in Antarctica. The snow and ice severely limit the availability of liquid water in most of the habitats. Radiation intensity at the surface is very low at all times, and during the period when the sun is above the horizon some 90% of the incoming radiation is reflected from the snow and ice.

Winds are a predominant factor in the weather of the polar deserts. Winds of a high velocity are enough to move snow and produce blizzard conditions. A slight increase in wind velocity brings a substantial increase in blowing snow.

Strong gravity winds develop, which blow off the landmasses. These winds, Katabatic winds, are the flow of cold, dense air mass down a topographic slope due to the force of gravity. They result from the extreme cooling of the air over the ice. The Katabatic winds produce ripples in the snow surface called sastrugi.

Soils of Antarctic Cold Arid Zone:

Ice-free areas occupy some 2% of the Antarctic continent and occur in the Antarctic peninsula, along the Trans – Antarctic mountains, and in other scattered coastal situation, where ice sheets have retreated.

The climate of Antarctica in most of the part is cold and arid. So far as soil formation is concerned, the most important features are the low temperatures, which result in a very slow rate of chemical processes, a very low level of biological activity, and more importantly a very low level of moisture availability.

Since moisture is only, available for chemical processes when it exists in a liquid form, the length of time during which soil temperature are above freezing point is particularly relevant.

In regions where soil temperature rarely rises above freezing, soil moisture is almost completely absent and chemical weathering processes are minimal, while in regions where there is more pronounced thawing, the soils may be quite wet, and leaching and chemical weathering are more evident.

The biological activity is confined to a very few micro-organisms, and in the most extreme situations the soil may be practically sterile. The rates of weathering and soil formation in cold deserts are extremely slow and the soils are consequently extremely fragile with respect to environmental changes.

Soil moisture status is largely a function of climate and is dependent on soil temperature. In those regions where temperatures are lowest, snowfall is minimal because of low humidity, and little thawing takes place of snow or of ice within soil profiles.

In the warmer coastal situations where humidity is greater, there is generally more snowfall and the higher temperatures result in the presence of more ice or water within the soil.

The soils are immature with little incorporation of organic matter, and deficit in certain mineral nutrients, notably available nitrogen, in areas beyond marine influence. Site aspect at high latitudes has a major effect on radiation receipt, whilst lack of winter snow cover can expose plants to both lethal winter temperatures and inadequate free water in summer.

Relationship with Soils of the Hot Arid Zone:

The desert-like nature of Antarctica has long been recognized and the soils described as cold desert soils. There are close relationships in many soil properties between soils from cold and hot desert areas.

They are parallel with respect to salts (including nitrate-occurrences), the disintegration of surface rocks, the type of lichens and algae found on and in rocks, the formation of surface soil crusts, and the presence of pale coloured horizons and red colours in old soils.

Terrestrial Vegetation of Antarctic Cold Arid Zone:

The continent may be highest in the world, and contains some of the world’s ice, but its tiny proportion of bare ground puts it at the bottom of the table for biological diversity in terrestrial habitats. Diversity is restricted to the cryptogams.

Cryptogams are subjected to the most severe environmental stresses of any of the Antarctic flora and fauna and may show physiological or biochemical characteristics necessary for survival in more temperate climates.

Ecology has highlighted the ability of many species to survive harsh conditions either by super cooling or by anhydrobiosis. Much remains to be covered about the nature of these mechanisms, the triggers that control in and their significance in species survival.

In a land covered by ice, water is generally very scarce. Yet in some localised areas lake and pools are important features. They range from the very line, never unfrozen lakes of Victoria Land through to the oligotrophic saline on Signy Island, free of ice for nearly three months.

Some are shallow and freeze to the bottom, others are deep and provide a protected and buffered environment for life. Because their flora and fauna are limited and may remain as sealed systems for much of the year.

The Antarctica has an almost wholly cryptogamic flora. Yet the fossil record indicates that, parts of the continent were more richly vegetated during the Late palaeozoic, the Late cretaceous and Tertiary periods. The Tertiary flora disappeared as the climate deteriorated with the Pleistocene glaciation educing continuous ice cover over the continent.

The communities are grouped in two formations defined by the dominance of flowering plants or cryptrogams, while the eight sub-formations of the cryptogannc group are differentiated by the growth form of community dominants.

Classification of Vegetation in the Antarctic Cold Arid Zone:

Antarctic herb tundra formation:

Grass and cushion chamaeophyte sub-formation.

Antarctic cryptogam tundra formation:

Crustaceous lichen sub-formation

Fruticose and foliose lichen sub-formation

Short moss turf sub-formation

Tall moss turf sub-formation

Bryophyte carpet and mat sub-formation

Moss hummock sub-formation

Alga sub-formation

Snow alga sub-formation

Deschampsia Antarctica, a grass, forms low mats and Colobanthus quitensis (Caryophyllaceae) occurs in compact cushions up to 25 cm wide. Both are most frequent at low altitudes as occasional components of essentially cryptogamic communities on level ground, or more typically on the warmer sites of north or west facing slopes.

D. Antarctica is the more widespread, and usually the more abundant species. Plants may coalesce to form continuous swards several metre wide on rock ledges and stony ground. C. quitensis and mosses such as Drepanocladus uncinatus are also abundant in some of these occasional stands of phanerogamic vegetation Poa flabellata.

Show Algae sub-formation:

During the main period of thaw in mid to late summer, first snow coloured red, green or occasionally yellow by aggregations of unicellular algae, including species of Chlamydomonas, Raphidonema and Ochromonas.

Fauna of Terrestrial Antarctic Cold Arid Zone:

Invertebrates:

The terrestrial animal life of the Antarctica is dominated by the invertebrates, represented by several groups from protozoans – nematodes to insects and mites. Other groups important to warmer geographical regions are missing or poorly represented. The tardigrades are minute animals, less than one millimetre in length, related to the arthropods. Rotifers are often found associated with the tardigrades.

Like them they live partly in fresh water, but several species inhabit moist terrestrial habitats. The echytraeuls are a family of small, white worms related to earthworms also occur in sub Antarctic islands.

67 species of insects have been recorded, but only twenty two of them are free-living, the remaining ones being parasites on warm- id animals. Approximately seventy species of mites are known from the continent. Antarctic mites mostly belong to the soft-bodied prostigmatid and the hard-shelled cryptostigmatid beetle mites.

Phytoplankton:

The Antarctic phytoplankton population in general, is dominated by is with small numbers of dinoflagellates and silico-flagellates. Very few species viz., Thalassiosira Antarctica, Porosira glacialis and Nitzschia cylindru are bipolar in distribution.

Phaeocystis poucheti is one of the few known-diatom algae which may ceedingly plentiful in warm and temperate waters as well as in Antarctica and Arctic seas. Slilico-flagellates are unicellular chtvsophycean algae. Only one species coflagellate, Dictyocha (Distephanus) speculum, is generally abundant arctic waters. It is a good indicator of cold water.

Ice Algae:

Tie groups of micro-flora known to be present in the pack-ice include is, chrysophyceans, dinoflagellates and green flagellates.

Zooplankton:

The dominant organism among Antarctic zooplankton is the shrimp- like Antarctic krill, Euphausia superba, which in the past supported enorumous stocks of Whales.

Krill:

Krill are relatively large and occur in swarms of great abundance. Of the eleven species of krill found in the Antarctic, the most important are tusia superba, E. frigida, E. crystallarophias, Thysanoessa macrura and entini.

These euphausiids are distributed as follows: in water north of itarctic convergence, E. valentini; in the pack-ice, E. crystallarophias, the open waters south of the convergence, dense patcnes of the larger s of E. frigida and E. superba.

Krill occur in large swarms, dense enough to dis-colour surface water, swarms can extend to depths of 40 to 50 m; although concentrations suitable for commercial catch are found between 1 and 10 m. In 76, the West German traveller, Weser, averaged 8 to 12 tones of krill per hour of towing time, with a maximum catch of 35 tons in 8 minutes.

The swarming habits of krill make it easy for baleen whales to feed on animals, with blue whales preferring adolescent krill and fin whales favouring adults. The existence of large stocks of krill in the Antarctic has been known any years, but interest in their commercial exploitation arose in the 1960s with the decline of whaling in the southern ocean.