BLUE PLANET: OCEANS AND CLIMATE
The existence of the vast ocean is the main defining characteristic of our planet, mak ing earth unique in the solar system and the only Blue Planet. Although water is not uncommon in the universe, oceans are probably extremely rare. Other planets in the so
lar system have evidence of ice, ancient water basins and valleys, or even subsurface liquid water, but planet earth is the only one which has liquid surface water; probably due to our
How inappropriate to call this planet earth when it is quite clearly Ocean. Arthur C. Clarke
privileged position in respect to the sun: not close enough to evaporate and escape, nor far enough to freeze. Water is also linked to the origin of life, in which early organic molecules rested protected from temperature swings and from the sun’s destructive ultraviolet radiation, and where they could move freely to combine and evolve. This successful combination of water and life changed the composition of the atmosphere by releasing oxygen and extra water vapour, and shaped our landscape, through ero sion, weathering and sedimentation, in a continuous interchange of water between the ocean, the land and the atmosphere.
Water moves in a continuous cycle that begins and ends in the ocean. This hydrologic cycle is powered by solar radiation, which provides energy for evaporation. Then precipitation, transpiration from plants, runoff into streams and infiltration to ground water reservoirs complete the cycle, which will start over again when most of the initial evaporated water reaches the ocean. Although during the cycle, water can be present in different states as ice, liquid or vapor, the total water content of the ocean has remained fairly constant since its formation, with an average residence time of approximately 3,000 years. At the moment, 97.25% of the water in planet earth is in the form of liquid salty water in the oceans, with only 2.05% forming ice covers and glaciers, 0.68% groundwater, 0.01%
rivers and lakes, and 0.001% in the atmosphere (Campy and MaCaire, 2003).
Oceans have been influencing the climate and the ecology of the planet since the very beginning of life on earth. Over time, both the physical oceans and living organisms have contrib- uted to the cycling of carbon. Plankton in marine ecosystems produces more organic material than is needed to maintain the food chain. The excess carbon slowly accumulates on the sea bed during geological time (biological pump) (Longhurst, 1991; Siegenthaler and Sarmiento, 1993; Raven and Falkowski, 1999). With that process, sediment and fossilized carbonate plankton have changed the shape of our coasts.
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