Water surrounds all marine organisms. It constitutes the greater part of their bodies. It is also the medium in which various chemical reactions take place, both internally and externally.

The water molecule itself is very simple. Each molecule of water is composed of two hydrogen atoms and one oxygen atom. The hydrogen atoms bond to the oxygen atom asymmetricaly by sharing electrons. Each hydrogen atoms shares its only electron with the oxygen atom. The oxygen atoms receives the two electrons needed to complete its outer shell, making it a stable molecule.)

Important interactions take place becuase of the electron sharing. The oxygen atoms tends to draw the electrons provided by the Hydrogen atoms closer to its nucleus, thereby creating an electrical separation and a polar molecule. The polar nature results in the hydrogen end (which acts a positive charge because it is lacking an electron) attracting the oxygen end (with a negative charge because it now possesses an abundance of electrons) of other adjacent water molecules. This forms weak Hydrogen Bonds (6% as strong as the electron sharing bonds) between adjacent water molecules which are easily broken and reformed.

If water had not been not polar, it would be a gas at room temperature and have an exceptionally low freezing point, making life impossible.

At the air-water interface, the polar nature of water allows it to form a 'skin' over the water surface, strong enough to support small objects. This phenomenon is known as surface tension, and water has the highest surface tension of all common liquids.

Water has a great capacity to hold heat energy, with the highest heat of vaporization of most common substances (thus a high boiling point - allowing it to be liquid on the surface of the relatively warm Earth). When water evaporates, it absorbs considerable amounts of heat. Water has a high latent heat of fusion; when ice is formed, considerable amounts of heat energy is released. Water therefore performs the act of a buffer against temperature changes and keeps the earths climate from rapidly alternating.

When water freezes, it becomes less dense, that is why ice floats (if it were not so, the oceans would be frozen solid)

Water is a universal solvent with the capability of dissolving more substances than any other liquid (due, once again, to its polar characteristics and hydrogen bonding). When salts are dissolved in water, they turn into their ions. This allows for many free radicals to be available to the chemistry of life.

Water is very dense (800 times more dense than air). The density allows large and small organisms to float along effortlessly for long periods of time (compared to land, where terrestrial organisms must fight gravity with each step in order to move around.)

Water absorbs light rays very quickly (all light is absorbed by 600 feet beneath the surface of the oceans). Water absorbs light differentially. The red end of the light spectrum is absorbed first within the shallow water while the blue and green rays penetrate the deepest. This is important for plants because different plants use different parts of the light spectrum for photosynthesis, and the differential absorption can determine the vertical distribution of marine plants).

SALINITY

Seawater is pure water plus dissolved solids and gases.

The dissolved solids come from 'weathering' processes of the continental land masses (rocks being dissolved by rain water and flowing out to sea with the rivers).

The gases are obtained from the atmosphere.

As water is a universal solvent, many different compounds are dissolved in it. A 1kg sample of saltwater contains 35 g of dissolved compounds, including inorganic salts, organic compounds from living organisms, and dissolved gasses. The solid substances are known as 'salts' and their total amount in the water is refered to by a term known as Salinity (expressed as parts per thousand - ^o/_oo).

Salinity of the oceans generally range from 34 ^o/_ooto 37^o/_oo. Variations from place to place are due to factors such as rainfall, evaporation, biological activity and radioactive decay. Salinities are higher in the tropics due to high evaporation rates. Fresh supplies of salts are now being added to the oceans from the rivers at roughly the same rate that they are being removed by various physical, chemical and biological processes.

Inorganic salts compose most of the solid matter of the 'salts' (99.28%)

The remaining .72% of the 'salts' are organic salts crucial to life. These include phosphates, nitrates, (both nutrients required for photosynthesis) and silicon dioxide (required by diatoms to construct their glass skeletons).

In contrast to the other salts, the nitrates and phosphates vary in concentration due to biological activity. In surface waters, where plants are actively in the process of photosynthesis, the nitrates and phosphates can be in short supply, limiting the amount of biological activity that can take place.


TEMPERATURE

Temperature is a very important physical factor in the marine environment. It limits the distribution and ranges of ocean life by affecting the density, salinity, and concentration of dissolved gasses in the oceans, as well as influencing the metabolic rates and reproductive cycles of marine organisms.

The seasonal range of temperature in the ocean is affected by latitude , depth, and proximity to the shore. Marine temperatures change gradually because of the heat capacity of water. In the abyssal zone, water temperatures are remarkably stable and remain virtually constant throughout the year. Similarly, in equatorial and polar marine regions, ocean temperatures change very little with season.

Because the surface of the ocean is heated by sunlight, the depths are cooler. There is a minimum of vertical mixing, because the warm water cannot displace the dense, colder deep water.

Transmission of light in "pure" fresh or salt water.

In shallow waters, however, situations occur in which an oxygen deficiency transpires. If the sea bed is densely populated the bottom 10 to 15 cm of water usually has a reduced oxygen content.


CARBON DIOXIDE

All life depends on the photosynthesis of plant matter, and the primary ingredients of this synthesis are carbon dioxide and water, thus there is sufficient carbon dioxide in the water. Bicarbonates, which create favourable conditions for carbon dioxide retention, are contained within the sea. Even though carbon dioxide is in equilibrium with atmospheric carbon dioxide, it is constantly replenished through the respiration of animals. Thus no carbon deficiency occurs.


HYDROSTATIC PRESSURE

The pressure to which organisms are subjected, especially in deep waters, is called hydrostatic pressure which increases with an atmosphere for every ten meters increased in depth. Life exists at depths of up to 10 900 m at a pressure of over 1000 atmospheres, but no special adaption to depth has been detected. Marine animals without any gas filled cavities are usually unaffected by depth and pressure because liquids are only slightly compressible, and because the cells of these organisms are entirely fluid-filled or filled with semi-fluid protoplasma. Pressure, in some cases, is also necessary for the full development of organisms.


WEIGHT AND BUOYANCY

The density of the ocean water enables many creatures to float that would otherwise sink in fresh water. In close connection to buoyancy is the viscosity (resistance to friction) of water, which varies inversely with the temperature (warm is less viscous than cold water - in tropical surface waters a body will sink twice as fast as it would in polar waters.

Many adaptations on the side of the organisms have developed to make them neutrally buoyant.

The arrangement of bodily fluid so that it comprises of ions which are lighter than those of sea water.

The secretion of buoyancy substances.

The storing of fat in the body, either as drops of oil(coelenterates and copepods), or in the liver(sharks).

By increasing the body surface by means of appendages or the secretion of mucilage with the purpose of creating maximum friction and thereby delaying sinking.

MOTION

The oceans are constantly moving. Its movement ranges from strong currents such as the Gulf Stream, down to small swirls or eddies.

Motion, in short is caused by energy from the Sun, and the rotation of the Earth.

The Sun drives oceanic circulation in two primary ways:

Circulation of the atmosphere (winds). Energy is transferred from atmospheric winds to the upper layers of the ocean through frictional coupling between the ocean and the atmosphere at the sea-surface.

Causing variations in the temperature and salinity of seawater, which in turn control its density. Changes in temperature are caused by fluxes of heat across the air-sea boundary. Changes in salinity are brought about by the addition or removal of freshwater (mainly through evaporation and precipitation, but also, in polar regions, by the freezing and melting of ice). If surface water becomes more dense than underlying waters, an unstable situation develops and the denser surface water sinks. This vertical, density driven circulation is known as thermohaline circulation.

The rotation of the Earth contributes to ocean circulation patterns:

The frictional coupling between the oceans waters and the solid Earth is very weak.The same is true for air masses.

Only very close to the surface of the Earth is frictional coupling significant.

In the extreme case of a projectile moving above the surface of the Earth, the frictional coupling is effectively zero.

The Earth rotates at a constant rate.

Consider this: A is missile fired due north from a launch pad at the equator.

When it departs from the launch pad, the missile is moving eastwards at the same velocity as the surface of the Earth , as well as moving northwards at its firing velocity. Initially, because it has the same eastwards velocity as the surface of the Earth, the missile appears to travel in a straight line; however, as the eastward velocity at the surface of the earth is greatest at the Equator and decreases towards the poles, as the missile travels north, the eastward velocity of the Earth below the missile becomes less and less.

As a result, in relation to the Earth, the missile is moving not only northwards but also eastwards, at a progressively greater rate. The apparent deflection of objects which move over the surface of the Earth without being frictionally bounds to it (such as missiles, or water and air), is explained in terms of an apparent force known as the Coriolis force.

1. The magnitude of the Coriolis force increases from zero at the Equator to a maximum at the poles.

2. The Coriolis force acts at right angles to the direction of motion, so as to cause a deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Because a missile is moving so fast, the amount that the Earth has 'turned beneath" it during its short flight is small. Winds and ocean currents, on the other hand, are slow moving, and are therefore significantly affected by the Coriolis force.

Consider an ocean current flowing at 1 knot at 45 degrees north latitude. The mater will travel about 1800 meters in an hour, and during that hour the Coriolis force will have deflected it about 300m from its original path!

The Coriolis force therefore has a significant effect on deflecting ocean currents.





Ecology

Abiotic Factors