The Ocean is arguably the largest habitat on the planet, and it houses an astounding array of life, from microbes to whales. Oceanography is the branch of Earth science that studies the Earth's oceans. It is the systematic sci entific study of the oceans and deep sea with the goal of understanding their processes and phenomena. The relationship of oceans with other aspects of the Earth's environment is also highlighted in oceanographic studies. Biology, chemistry, geology and physics together make oceanography a richly interdisciplinary science. Although they contain most of the Earth's water and carbon and surface heat, and much of its biomass, the oceans do not operate alone. Together with the atmosphere, continents and ice-cover, they form a working platform, driven mostly by energy from the Sun.

Earth science has four main components: hydrosphere, solid earth, atmosphere and biosphere. Water at the Earth's surface or near it, is termed the hydrosphere. It includes oceans, water vapor, ground water, lakes, rivers, and polar icecaps. The water distribution in the hydrosphere is as follows: oceans—97.54 percent, icecaps—1.81 percent, groundwater—0.63 percent, others—0.02 percent. It is obvious that we live on a water planet.

Oceanography is studied in order to understand how oceans operate and how they interact with other aspects of the Earth system. Again, oceans are a vast source of food for the world's population. The oceans hold an enormous reservoir of minerals and they also hold reservoirs of fossil fuels or the potential for harnessing forces for energy development.

The study of oceanography may be divided into four branches: biological oceanography, chemical oceanography, geological oceanography and physical oceanography. Biological oceanography is the study of marine organisms and productivity, life cycles, and ecosystems. Biological oceanography spans studies of all levels of biological organization, from that of single genes, to organisms, to their population dynamics. It includes studies on how organisms interact with, and contribute to, essential global processes.

Chemical oceanography deals with water chemistry and biogeochemical cycling. It is the study of everything about the chemistry of the ocean and is based on the distribution and dynamics of elements, isotopes, atoms, and molecules. This ranges from fundamental physical, thermodynamic and kinetic chemistry to two-way interactions of ocean chemistry with biological, geological, and physical processes. It encompasses both inorganic and organic chemistry. Chemical oceanography includes processes that occur on a wide range of spatial and temporal scales; from global to regional to local to microscopic spatial dimensions and tim-escales from geological epochs to glacial-interglacial to millennial, decadal, interannual, seasonal, diurnal, and all the way to microsecond time scales. Geological oceanography is the study of the geology of the ocean floor including plate tectonics, ocean basin geology, and ocean history, while physical oceanography studies the ocean's physical attributes including temperature-salinity structure, water properties, mixing, waves, tides, and currents. Physical oceanography studies the physics of the ocean, the kinds of motions of water, the speed, and the direction of the water. Physical oceanography is the study of the fluid motions of the ocean. Its goal is to understand the processes at all time- and space-scales, to simulate these processes, and to make predictions if possible. Physical oceanographers are also interested in determining how much heat enters the ocean and where the heat is transferred.

These diverse topics reflect many basic disciplines (biology, chemistry, geology, meteorology, and physics) that oceanographers utilize to further knowledge of the world ocean and understanding of processes within it. Oceanography is born out of scientific curiosity and aids in the understanding of marine resources and their impact on humans and global climate changes. The aim of oceanography is an understanding of the oceanic circulation and the distribution of heat in it, appreciation of the interaction of oceans with the atmosphere, and the role they play in maintaining our climate.

Origin of the ocean basins is traced to many theories. In the cosmic school of thought, it is believed that the moon blew out of the Earth, only to be caught by the Earth's gravity as a natural satellite. The hole is said to be located in the region of the Pacific Ocean. This idea was popular until the evidence supporting the theory of plate tectonics gained support. In the plate tectonics theory, oceans are produced as diverging plates open the space between them. Triple junction theory states that a crack begins on a continental plate, joining cracks from three different directions, until a series of these cracks eventually separates the plate and produces a proto-ocean.

The supercontinent Cycle theory notes that the breaking apart of Pangaea has occurred several times with the production of supercontinents over and over, and with oceans breaking up the spaces between them. The most viable hypothesis for explaining the origin of the ocean water is that it is from the interior of the Earth. Earth's distance from the Sun and its mass were obviously crucial in the formation of the oceans.

The major oceans are Pacific, Atlantic, Indian, and Artic oceans. The Pacific Ocean is the largest and deepest, and covers 50 percent of the surface area of the world's oceans. Marine environments could be classified by light and location. Inhabitants of marine zones include planktons, nektons, and benthos. Water is found everywhere on Earth and is the only known substance that can naturally exist as a gas, liquid, and a solid, within the relatively small range of temperatures and pressures found at the Earth's surface. Oceans contain nearly 98 percent of all the water on or near the surface of the Earth. The residence time of ocean water is about 37,000 years. Changes to the coastal environment occur from the movement of ocean waters against the shore. Surface ocean currents are broad, slow, drifts of surface water, set in motion by the prevailing winds, but rarely causing erosion deeper than 164-328 ft. (50-100 m.). The gases that make up the oceans were trapped within the Earth as it formed. The major trapped volatile was water; others included nitrogen and carbon (IV) oxide. Seventy-one percent of Earth's surface is covered by water, and 29 percent of the surface area is land.

As a result of different water masses, the ocean can be viewed as stratified, with layers of water extending great distances with similar temperatures, or salinities, or most of water properties. There is unequal warming of the ocean; this leads to heat transfer, changes in density, and ultimately, movement of water masses via the thermohaline circulation process. Ocean and atmosphere form a coupled system. The coupling occurs through exchange processes at the interface. Ocean and atmosphere are coupled in climate models and circulation models; the computer models become the meeting point for observations, theory, and prediction. These exchange processes determine the energy and mass budgets of the ocean. Quantities exchanged between the ocean and the atmosphere in the energy budget are radiative energy and momentum, while in the mass budget quantities include evaporation, condensation, precipitation, and river run-off. The ocean plays a role in the climate system, which is complementary, and of comparable importance to that of the atmosphere. It transports heat in amounts comparable with atmospheric transport. It absorbs and releases carbon (IV) oxide. When it is heated, the ocean responds by storing some of the heat and by increased evaporation. Because the heat is mixed for some distance by the wind, temperature rises much less than it does on dry land under the same heating conditions. The evaporation has profound effects on the atmosphere and on climate.

When the ocean is cooled, it responds by generating vertical convective motions, which resup-ply heat to the surface. Thus, the temperature drop is much less than over land under the same cooling conditions. The overall result is that for the two-thirds of the Earth's surface covered by icefree ocean, the temperature over the whole ocean ranges only from 28 degrees F (minus 2 degrees C, the freezing point of salt water) to 86 degrees F (30 degrees C), and at any one place by hardly more than 1.8 degrees F (1 degrees C) during the course of a day and 10.8 degrees (10 degrees C) during the course of a year. The relatively slow response of the ocean to heating and cooling results in the oceanic annual cycle being delayed, relative to that in continental regions.

The ocean plays a key, but frequently understated, role in determining the Earth's climate. Indeed, any possibility of predicting the evolution of climate beyond a few weeks demands that ocean behavior also be taken into account. With respect to sensitivity and contribution to long-term climate change, there is reason to believe that the ocean is now changing, in response to climate changes over the past few hundred years. It can be expected to change further as anthropogenic influences become increasingly marked. The effect of the ocean on the atmosphere could be either to moderate or to intensify these changes; it will certainly modify them.

The oceanic environment places unique demands on instrumentation that are not easily met by standard laboratory equipment. As a consequence, the development and manufacturing of oceanographic instrumentation developed into a specialized activity. Available equipment for observing the ocean and marine life include research vessels, moorings, satellites, submersibles, towed vehicles, floats, and drifters. Reversing thermometers are used to measure hydrographic properties. Nansen and Niskin bottles, CTDs, multiple water sample devices, thermosalino-graphs, remote sensors current meters, wave measurements, tide gauges, remote sensors and shear probes are all employed for measuring the dynamic properties of the ocean. The first international organization of oceanography was created in 1902, as the International Council for the exploration of the sea.

Scientific graduates have directly applied their training in teaching positions on M.Sc and Ph.D courses, in industrial research laboratories; in government research laboratories, including the Water Boards and in environmental protection agencies. Other Oceanography graduates apply their knowledge in a wide range of jobs within business and industry and in the military. Oceanography is a relatively young discipline, shaped by a continual flow of exciting discoveries. Oceanographers continue to help us understand the precarious balance of oceans, the atmosphere, ice, solid earth, and living organ-isms—the Earth system that affects our lives and the future of our planet.

sEE ALsO: Current; Oceanic Changes; Salinity.

BIBLIOGRApHY. S.P. Lund, An Introduction to the Study of the World's Oceans (University of Southern California, 1995); M. Tomczak, The Place of Physical Oceanography in Science (University of Minnesota, 1999).

Akan Bassey Williams

Covenant University

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