The world’s biomes are divided into several levels of classification categories.

Aquatic biomes are those in water of some sort. We subdivide these into fresh water, marine (salt water) and brackish.

Fresh water biomes include lakes, ponds, rivers, streams, and stagnant water. They are subdivided based on whether the water is moving or stagnant, and on the basis of size.

Marine biomes are subdivided based upon water depth and sunlight penetration. One of the richest biomes in the world is the neritic biome, which is found along the continental shelves. This biome is very rich in biodiversity.

Brackish biomes are those where fresh water meets salt water, as in a river delta. They are characterized by intermediate salinity levels which change throughout the year.

Terrestrial biomes are those based on land. The primary subdivision of terrestrial biomes is based on latitude—distance from the equator. Within these primary categories, subdivisions are made based upon amount of precipitation and distribution of that precipitation throughout the year.

Tropical biomes are found in the region between the Topic of Cancer and the Tropic of Capricorn. These are the regions of the planet which get consistent amounts of very direct sunlight throughout the year. Any seasonality is the result of variations in rainfall, not in incident sunlight or day length. There are several categories of tropical biome, ranging from the wettest, tropical rain forest, to the driest, tropical desert. Rain forests are usually found around the equatorial region; deserts are usually found to the north and the south of that region.

Temperate biomes are found between the Tropic of Cancer and the Arctic Circle, and between the Tropic of Capricorn and the Antarctic Circle. They are characterized by distinct seasons, with long-day summers and short-day winters, with appropriate weather fluctuation throughout the year. Again, these biomes are subcategorized based upon yearly rainfall, from the temperate rain forest (wettest) to the temperate desert (driest). Temperate rain forests are typically found along the windward sides of mountain ranges which receive incoming air flow from the ocean. Temperate deserts are usually found in the “rain shadows” of mountain ranges. Toward the dry end of the spectrum we find the great grasslands, like the North American prairies.

Arctic biomes are found above the Arctic Circle and below the Antarctic Circle. They are characterized by extreme fluctuation in day-length throughout the year, including winter days in which the sun never rises above the horizon and summer days in which the sun never dips below the horizon. B. Biosphere refers to all of the parts of our planet which can support life. Our notion of the biosphere is expanding as we continue to explore new regions of our planet, but even the expanded biosphere is just a thin life-containing bubble on the surface of our world. It extends a mile or so up into the atmosphere and, at present, a couple of miles into the surface of the planet.

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Updated 25 September 2004