98% of Antarctica's continental land mass is covered by ice up to 4.7 km thick. It is also the driest continent on earth. Most precipitation falls as snow. Except for the northern Peninsula, even summer daytime temperatures rarely exceed 0 °C.
To survive in these conditions, plants and microbes need to be able to withstand severe stresses. They endure repeated freezing and thawing and little fresh water. Antarctica also has a very small amount of environment that is ice-free.
The Antarctic can be divided into two distinct climate regions:
- The Maritime Antarctic — including much of the Antarctic Peninsula (the western side), and nearby islands
- Continental Antarctica — including the continental mass and parts of the Eastern Antarctic Peninsula.
The Maritime Antarctic generally receives more precipitation and has milder temperatures. This climate is more favourable for terrestrial plant life and microscopic animals.
Antarctic flora and their habitats
Lichens (200 species), bryophytes (over 50 species), algae (over 700 species) and fungi are all found in the Antarctic. Most of the algae are single-celled oceanic plants called phytoplankton.2 flowering plants (a grass and a small cushion-forming plant) are found on the northern and western parts of the Antarctic Peninsula.
Terrestrial plant life in Antarctica can occur on almost any exposed or ice-free rock, in lakes, and in snow and ice near the coast. Three specific types of habitats are common:
- 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.
Some specialised plant habitats also include snow banks and volcanic ground.
There are three main factors which determine the distribution of plant life in Antarctica:
- Climatic factors, e.g. frequency and duration of freeze/thaw cycling, temperature, availability of free water
- Edaphic factors (substrate characteristics e.g. soil type, underlying geology)
- Biotic factors (effects from other animals and plants).
Of these factors, the most important is the availability of water.
A number of fumarole communities exist on volcanic ground in Antarctica. Fumaroles are openings in the Earth’s surface, which emit steam and gas. Temperatures at fumaroles can reach 60°C only 10 cm below the surface. Plant colonies often thrive in these areas. Temperatures are much warmer, and steam and melting snow or ice helps create more free water.
Examples of these communities can be found in Continental and Maritime Antarctica. Mt Erebus is an active volcano that supports communities of soil microbes at altitudes over 3,000 m. Mt Melbourne is a dormant volcano with many fumaroles and areas of steam warmed or heated ground. Colonies are found on Deception Island in the South Shetland Islands, and on the South Sandwich Islands.
Impacts of climate change
The polar desert is a good indicator of climate change. The freeze/thaw balance controls many aspects in the environment. Small changes in the climate can have large effects.
In the Antarctic, it is thought that CO2, temperature and UV levels will all increase as a result of climate change. There will also be a change in water availability. A warmer climate will create more meltwater.
It may also increase the amount of habitat for plants, especially in coastal areas and on the Antarctic Peninsula. More availability would allow new plants to able to establish. This could be naturally or by accidental introduction from humans.
Changes will be more drastic in the marine environment. Climate change is likely to have profound effects on marine microbes. Increased ocean temperatures will likely cause changes in microbial distribution and abundance. Rising temperatures are likely to increase stratification, trapping marine microbes in near-surface waters. Here, they would have reduced ability to replenish nutrients, and greater exposure to solar UVB.
Increased CO2 in the ocean will also increase its acidity. Important organisms like Coccolithophorids and Pteropods could find it hard to exist in more acidic waters. Higher CO2 concentration is likely to cause changes in the marine microbial communities. Changes of these levels would have consequences for the entire Antarctic food web.
Climate change is expected to profoundly change the circulation of the oceans. The Southern Ocean is a key part of this system, because of its role in circumpolar transport of water. If the sinking of cold water off Greenland is interrupted by icecap meltwaters, circulation from the Atlantic will reduce. The formation of Antarctic Bottom Water will also reduce if coastal waters around Antarctica become warmer. These sinking waters carry oxygen from the surface to ocean’s abyssal depths. Interrupting this flow would profoundly impact bottom communities.
Because Antarctica is so isolated and difficult to access, sampling is infrequent. Much of the early sampling was not done in a systematic or scientific way. Even today, Antarctic flora researchers are few, compared to those in other parts of the world. In the past, this has led to some overlap between collections. Two separate collectors can give a single species of plant multiple names without realising.
Relatively little is known about Antarctic flora. New research is constantly updating our knowledge.