Antarctica is a continental land mass of around 14,000,000km2, 98% of which is covered by ice up to 4.7km thick. It is a polar desert and is the driest continent on earth. Most precipitation falls as snow, largely restricted to the region less than 300km from the Antarctic coast. The annual precipitation is approximately 200–500 mm. The Antarctic Peninsula receives about 900mm of precipitation a year while the Eastern Antarctic plateau may only receive around 50mm a year. Except for the northern Peninsula, even in summer daytime temperatures rarely exceed 0°C.
The Antarctic can be divided into two climatically distinct regions: The Maritime Antarctic — including much of the Antarctic Peninsula (principally the western side), and nearby islands — and Continental Antarctica — including the continental mass and parts of the Eastern Antarctic Peninsula. The Maritime Antarctic generally receives more precipitation (which may fall as rain in summer), has milder temperatures and is climatically more favourable for terrestrial plant life and microscopical animals.
There are lichens, (200 species) bryophytes (over 50 species of mosses and liverworts), fungi and over 700 species of algae found in the Antarctic. Most of the algae are single-celled oceanic plants called phytoplankton.
Two flowering plants (a grass and a small cushion-forming plant) are found on the northern and western parts of the Antarctic Peninsula.
Arctic versus Antarctic
The Arctic regions are generally of lower altitude (the highest is the Brooks Range in northern Alaska — 2800m), are less windy (around 36km/h on average), are more cloudy, and have higher precipitation. Except for the Greenland Icecap, continental glaciation is localised. Closeness of continental land masses has led to a commonality and higher diversity of the Arctic floras. Around 2000 lichens, 600–700 bryophytes and 900 flowering plants are known for the Arctic regions. There are even 5 flowering plants on Northern Ellesmere Island, Arctic Canada, at 83° N.
The Antarctic continent is higher (Vinson Massif – 5,140m) and the plateau ice cap rises up to 3,800m above sea level. It is also windier (around 54km per hour on average at coastal sites, but speeds of up to 252km per hour have been recorded). It is cold; the lowest temperatures recorded on earth (−89.4°C) was at Vostok Station on the Antarctic inland plateau. Temperatures at coastal continental localities may drop to as low as −41°C in mid winter. The ice plateau is generally less cloudy. The flora of the Antarctic consists of around 250 lichens, 100 mosses, 25–30 liverworts, around 700 terrestrial and aquatic algal species, an unknown number of (mostly microscopic) fungi, and two flowering plants.
Terrestrial plant life in Antarctica is restricted to three main habitat types.
- Permanent snow free areas with little precipitation.
- Areas with winter snow accumulation and essential water being provided from summer melt.
- Exposed nunataks and mountain peaks surrounded by permanent ice.
Typically though plant life occurs on almost any exposed or ice free rock, in lakes, and in the near-coastal snow and ice. Some examples of specialised plant habitats are snow banks and volcanic ground.
There are three main factors which determine the distribution of plant life in Antarctica.
- Climatic factors (frequency and duration of freeze/thaw cycling, temperature, availability of free water)
- Edaphic factors (substrate characteristics eg soil type, underlying geology)
- Biotic factors (effects from other animals and plants)
Of these factors, the most important is the availability of free water as aridity is the biggest determinant of plant distribution in Antarctica. To survive here, plants need to be able to withstand severe physiological stresses, such as repeated freezing and thawing, desiccation and changes to the cellular chemical environment.
A number of fumarole communities exist on volcanic ground in Antarctica. Fumaroles are openings in the earths surface, which emit steam and gas. Temperatures at fumaroles can reach 60°C only 10cm below the surface. Plant colonies often thrive in these areas because of the warmer temperatures and the limitless availability of free water from steam and melting snow or ice. Some examples of these communities can be found at two localities in Continental Antarctica; Mt Erebus (an active volcano which supports communities of soil microbes at altitudes over 3000m), Mt Melbourne (a dormant volcano with many fumaroles and areas of steam warmed or heated ground), and at two localities in the Maritime Antarctic; Deception Island in the South Shetland Islands (a volcano which last erupted in 1985) and the South Sandwich Islands. Mt Melbourne supports the only known occurrence of the moss Campylopus pyriformis (a European and Southern African species). Deception Island also supports small colonies of a number of mosses not otherwise found in the Antarctic region.
Climate change — terrestrial
Polar deserts are generally considered to be very good indicators of climate change because of the freeze/thaw balance which controls many aspects in the environment (such as available light, albedo, temperature and meltwater supply) and because desert systems are very responsive to changes in climate. In the Antarctic it is thought that as a result of climate change, CO2, temperature and UV levels will all increase. There will also be a change in water availability. For example, at Hudson Bay in the Arctic, it is predicted that if CO2 levels double then temperatures will rise by 7°C and soil moisture will decrease by 50%. Increased CO2, temperatures and UV is not expected to have a serious effect on plant life in the Antarctic. One effect of climate change will be to increase the amount of available habitat for colonisation, especially in coastal areas and on the Antarctic Peninsula. New plants may then be able to establish, either naturally or by accidental introduction from humans.
Climate change — marine
The situation will be very different in the marine environment where climate change is likely to have profound effects on marine microbes. Increased ocean temperatures are likely going to cause changes in microbial distribution and abundance, and change ocean currents. Increasing temperatures are also likely to increase stratification, trapping marine microbes in near-surface waters where they will experience reduced replenishment of nutrients and increasing exposure to solar UVB. In addition, increased CO2 in the ocean will increase its acidity. Organisms that make structures from calcium carbonate will find it increasingly difficult to deposit these structures in cold Antarctic waters, potentially excluding numerous organisms such as Coccolithophorids and Pteropods from Antarctic waters this century. Increased CO2 concentration is also likely to cause changes in the productivity and species composition of marine microbial communities with ramifications for the Antarctic food web.
Global warming is also expected to profoundly change the circulation in the world’s oceans, of which the Southern Ocean is a key component, due to its role in circumpolar transport of water as part of the global “conveyor belt” circulation. Circulation from the Atlantic will be reduced if the sinking of cold water off Greenland is interrupted by icecap meltwaters. Similarly, the formation of Antarctic Bottom Water will be reduced if coastal waters around Antarctica become warmer. These sinking waters carry oxygen from the surface to ocean’s abyssal depths, so interruption of the flow would be expected to profoundly impact bottom communities.
A degree of uncertainty does exist with the Antarctic flora though. Because the continent is so isolated and largely inaccessible, sampling can only be done infrequently. Much of the early sampling in particular, was not done in a systematic or scientific manner. Additionally the number of people working on the Antarctic flora compared to the flora of other regions is quite low. In the past this has led to some overlap between collections, where a single species of plant has been given two separate names by two different collectors, falsely increasing the number of recorded species. Comparatively little is known about the Antarctic flora, and it is constantly being updated.