1. Wet
2. Solution
3. Translucent
4. Dense
5. Three-Dimensional
6. Stable

Water is necessary for life

1. 70-95 percent of an organism is water.
2. Water is the medium for chemical and physical reactions.

Submersion Makes Life Easier

1. Terrestrial organisms must have systems to prevent drying and to circulate water.
2. Many small marine organisms rely on diffusion to keep them in equilibrium with their wet surroundings.

Diffusion Doesn't Require Work

1. Definition: Diffusion is the tendency for molecules to spread out.
2. It is caused by the random movements of molecules.
3. A substance will move from an area of high concentration to an area of low concentration.
4. Definition: Concentration is the amount of a given substance in a given amount of water.

Equilibrium is Uniformity with the Surroundings

1. Internal concentrations of salts, gases, and other substances will tend to match those of seawater.

Solvents and Solutes

1. Water is a solvent into which many substances can dissolve.
2. Dissolved substances such as salts and gases are called solutes.

Ionic Composition

1. Definition: Ionic composition is the relative amount of various dissolved salts (ions).
2. There are 10 major and 50 minor ions in seawater.
3. Sodium and chloride ions are the most abundant.

Salinity

1. Definition: Salinity is the total concentration of salts (total concentration of salts is symbolized: [salt]).
2. [salt] in seawater, for most of the oceans, is 32 to 37 parts per thousand (parts per thousand is symbolized: ppt).
3. The average is 35 ppt or 3.5 percent salt or 166 million tons/cubic mile.

Evaporation Predominates

1. If evaporation is greater than (>) rainfall, then salinity rises.
2. Definition: An evaporation basin is a region where desert lands surround the sea (ex. Red Sea [salt] = 42 ppt).

Rainfall Predominates

1. If evaporation is less than (<) rainfall, then salinity falls.
2. Runoff dilutes nearshore waters (ex. Baltic Sea [salt] = 5 ppt).

Dissolved Oxygen

1. Definition: Dissolved Oxygen (DO) is the oxygen in solution in seawater.
2. The average concentration of DO is 6 milliliters/liter (ml/l).

Oxygen Replacement

1. Oxygen is contributed from the atmosphere.
2. Oxygen is also released by algae and plants during photosynthesis.

Photosynthesis

1. Algae and plants produce oxygen as a byproduct of food production
2. The chemical process of photosynthesis is expressed as:
   6CO₂ + 6H₂O --> C₆H₁₂O₆ + 6O₂

Oxygen Depletion

1. Definition: Aerobes are organisms that use oxygen.
2. Oxygen is used by organisms for cellular respiration.
3. Large amounts of organic matter promote aerobic bacterial growth that can decrease DO.

Respiration

1. Aerobes use DO at a rate of 0.002-2.0 ml/g body weight/hr.
2. Aerobic respiration:
   C₆H₁₂O₆ + 6O₂ --> 6CO₂ + 6H₂O

Respiratory Surfaces

1. A respiratory surface must be thin and moist to promote diffusion.
2. Types of respiratory surfaces: body surface (DO from water), gills (DO from water), and lungs (Air).

Breathing Air

1. Air contains 20 times more oxygen than seawater.
2. Oxygen diffuses out of air faster than out of seawater.

Translucence

1. Definition: Translucence is a property of matter that allows light to pass through (transmitting) it while blocking (absorbing) only some of it.
2. Seawater is less translucent than air. It absorbs a greater percentage of the light passing through it.

Light Penetration Varies

1. Light penetration is dependent upon local conditions, such as wind, waves, suspended particles, plankton, etc.

Light Penetration in Clear Oceanic Waters

1. Approximately 35 percent of the light that enters the sea penetrates beyond 1 meter in depth.
2. Less than 1 percent penetrates beyond 100 meters.

Density

1. Definition: Density is the weight per unit volume often reported in grams/milliliter (g/ml).
2. The density of seawater is approximately 1g/ml which is relatively high.
3. Air has a density of approximately 0.001g/ml.

Air-Water Pressure Differences

1. Definition: Atmospheric pressure is the pressure created by the weight of the atmosphere bearing down upon everything beneath it.
2. The pressure of the atmosphere is about 14 pounds per square inch or 1 atmosphere (symbolized: atm) and varies about 1.4 pounds per square inch or 1/10 of an atmosphere.
3. Hydrostatic Pressure increases 14 pounds per square inch or 1 atm for every 10 meter increase in depth.

Pressure and the Ocean

1. About 88 percent of the ocean is greater than 1,000 meters deep with pressures of over 100 atm.
2. The average depth is 3,800 meters and the average pressure is 380 atm.
3. The maximum depth is about 11,000 meters and 1,100 atm of pressure.

Buoyancy is the Result of Relative Densities

1. Definition: Buoyancy is an upward force caused by the displacement of water.
2. If the density of an object is less than the density of seawater then the object will float.
3. If the density of an object is greater than the density of seawater then the object will sink.

Buoyancy Provides Support in Seawater

1. Many marine organisms lack skeletons and their bodies are supported by the water.
2. Marine organisms can reach very large sizes because their bodies are supported by the water.

Life in a Liquid

1. Due to the ocean's high density, life can be found throughout the liquid ocean environment and not just on the seafloor.
2. Many more organisms live in the water than in the air.

Swimming is Possible

1. It is easier for a fish to remain afloat than for a bird to remain aloft.

Division of the Living World is Different in the Oceans

1. Plankton
2. Nekton
3. Benthos

Plankton

1. Definition: Plankton are floaters.
2. They are important in marine food chains.
3. There is no terrestrial equivalent to plankton.

Nekton

1. Definition: Nekton are swimmers.
2. Many never rest on solid substrates.
3. Flying terrestrial organisms are similar but all terrestrial species must rest on solid ground.

Benthos

1. Definition: Benthos are organisms that live on or in solid substrates.
2. Most terrestrial organisms are equivalent to benthos.
3. Some marine benthos can venture up into the water.

Stability

1. Definition: Stability is the resistance to change.
2. Conditions in the ocean are relatively constant.

Sea Temperatures Change Slowly

1. Definition: Heat capacity is the amount of heat energy that must be gained or lost to bring about a change in temperature. It is often reported in calories/ degree centigrade.
2. Seawater has a high heat capacity.

Temperature

1. Average monthly sea surface temperature ranges from -1 degrees centigrade at the poles to 28 degrees centigrade at the equator.
2. Temperature decreases with depth down to 3 to 4 degrees centigrade at depths between 200 and 1,000 meters.

Changes are Minor when Compared to Land

1. Average monthly air temperature, over land, ranges from -45 degrees centigrade at the poles to 38 degrees centigrade at the equator.
2. Average Monthly Temperature Range:

Seawater Surface

polar	-1 degree centigrade
equatorial	28 degrees centigrade

Air

polar	-45 degrees centigrade
equatorial	38 degrees centigrade

Land Affects Sea Temperature

1. Fluctuations in sea temperature:

Average Change in Temperature

	Annual	Daily
Nearshore:	15 degrees centigrade	3 degrees centigrade
Offshore:	2 to 8 degrees centigrade	0.2 degrees centigrade