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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
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.
BLUE PLANET:
OCEANS AND CLIMATE
How inappropriate to call this planet earth
when it is quite clearly Ocean.
Arthur C. Clarke
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.
