The Antarctic Ecosystem Part 1

Antarctica (the continent at the South Pole).

The Southern Ocean (also called the Antarctic Ocean) surrounds the continent (1 mark). It lies in high southern latitudes, mainly south of the Antarctic Circle at about 66.5°S, encircling the pole at roughly 90°S (1 mark).

1. It is extremely COLD — the coldest continent on Earth, with inland annual means near −50°C and the world-record low of −89.2°C. 2. It is very DRY — most areas receive under 50mm of precipitation a year, making it a polar DESERT. 3. It is very WINDY — strong, persistent katabatic winds blow downhill off the ice plateau.

Antarctica is at very HIGH latitude around the South Pole, so the Sun is always low in the sky (or below the horizon for months); the Sun's energy is spread over a large area and passes through more atmosphere, so heating per square metre is weak (point + development). The surface is covered by white snow and ice with a high ALBEDO that reflects about 80% of incoming solar radiation back to space, so little is absorbed to warm the ground. The continent is also very HIGH — averaging around 2,500m — and temperature falls with altitude. Finally, its huge continental interior is far from the moderating warmth of the oceans, allowing extreme cooling.

The Antarctic ecosystem has low biodiversity mainly because of its extreme climate. Temperatures near −50°C inland are below the tolerance of most organisms, so few species can survive and reproduce; on land there are almost no flowering plants, only hardy mosses, lichens and tiny invertebrates. The polar-desert climate, with under 50mm of precipitation a year and most water locked up as ice, leaves little liquid water, so plant growth at the base of any food web is severely limited. Months of 24-hour winter DARKNESS stop photosynthesis for part of the year, meaning primary production is squeezed into a short summer phytoplankton bloom; few species can cope with this extreme seasonality. As a result, energy flows through SHORT, simple food chains dominated by krill rather than a complex web, so there are fewer niches and therefore fewer species. The continent's ISOLATION, ringed by the vast Southern Ocean and far from other land, also makes it very difficult for new species to colonise.

The climate of Antarctica shapes almost every feature of its ecosystem. First, the extreme COLD (inland means near −50°C, record low −89.2°C) makes the land almost lifeless: only mosses, lichens and a few invertebrates survive, so terrestrial biodiversity is very low and there are almost no plants. Because the environment is a polar DESERT (<50mm precipitation a year, with water frozen as ice), there is little liquid water on land to support plant growth, which is why the productive part of the ecosystem is the surrounding OCEAN rather than the continent.

Second, the seasonal climate controls how energy enters the food web. In summer the 24-hour daylight and nutrient-rich, partly ice-free Southern Ocean trigger a massive PHYTOPLANKTON bloom; these primary producers support huge swarms of KRILL, the keystone species. In winter, by contrast, 24-hour darkness halts photosynthesis, so production collapses and the whole system slows. This strong seasonality means the ecosystem depends on a short, intense growing season.

Third, the cold drives the structure of the food web and the adaptations within it. Energy flows through SHORT, simple chains (phytoplankton → krill → penguins/seals/fish → whales/orcas) with few species but very large populations of the survivors. To cope with the cold, animals show adaptations such as blubber, dense fur or waterproof feathers, huddling and counter-current heat exchange — features that exist precisely because of the climate.

Overall, the climate is the dominant control on the Antarctic ecosystem: the cold and dryness keep land biodiversity extremely low, while the seasonal light and the cold ocean concentrate life into a productive but simple, krill-based marine food web. To a large extent, then, the unusual character of the ecosystem — low biodiversity, marine focus and dependence on one keystone species — is a direct response to the extreme climate.