Antarctica originally formed part of the southern supercontinent, Gondwana, and its fossil record shows that the continent hosted cool temperate and even subtropical forests, dinosaurs, early mammals, and many other biota, despite lying at high southern paleolatitudes for over 100 My. The Antarctica of today is a continent of extremes, inspiring awe, trepidation, and superlatives from those privileged to experience it. It is certainly a forbidding place, more than twice the area of Australia, distant and isolated from other southern continents, with around 0.2 percent of its area ever exposed from permanent ice and snow and covered on average with ice more than 2 kilometers thick. In winter, the surface of an area of ocean of approximately the same size as the continent freezes around it, and throughout the year ice is one of the major drivers of physical and biological processes in the Southern Ocean. Antarctica is also distinct among the Earth’s continents, being the only one not to have ever had a natural human population, and only being discovered and explored over the last one to two centuries. Even now, the human population is limited to the temporary residents of national research stations (about five thousand in summer and one thousand in winter), augmented by thirty to forty thousand mostly ship-based tourist visitors in the austral summer. At least to human perception, the environments of the polar regions are challenging to life. Organisms that live on land in Antarctica today must survive chronic, highly variable and extreme environmental stresses, in particular low temperatures, desiccation, high winds, and a harsh radiation climate. At latitudes beyond the Antarctic Circle, extreme seasonality is driven by the sun remaining permanently below the horizon for up to several months during winter and, conversely, above the horizon in summer. In winter terrestrial habitats experience extremely low air temperatures, typically −40 to −60°C or lower (the lowest instrumentally recorded temperature on Earth is −89.2°C, at Vostok Station on the Antarctic polar plateau). As well as its extreme climate, parts of Antarctica, in particular the Antarctic Peninsula region, have been facing rates of regional climate change in recent decades that are the most rapid in the Southern Hemisphere, as well as the consequences of the anthropogenically caused stratospheric ozone hole. These provide both further challenges to the organisms native to the continent and its surrounding oceans, and a test-bed or proxy for understanding the consequences of change for organisms and ecosystems globally. Terrestrial ecosystems and biodiversity, the primary focus of this chapter, are generally depauperate, primarily comprised of cryptic and microscopic groups that are often overlooked except by specialists. Antarctic marine ecosystems, in contrast and despite also facing extreme seasonality and chronic exposure to near-freezing temperatures, can be highly diverse and comprise considerable biomass, possibly second only to tropical coral reefs.
The multi-seasonal NO<sub>y</sub> budget in coastal Antarctica and its link with surface snow and ice core nitrate: results from the CHABLIS campaign