Three major ocean basins that are interconnected: (1) Pacific; (2) Atlantic; (3) Indian. All three are interconnected in the Southern Ocean.

Average depth is 3.8 Km although it can be as deep as 11 km.

Variation in temperature is much less than over land thus acting as a moderating force. Temperature variation over land 146 degrees C and over the water 38 degrees C.

Oceans have a significant amount of dissolved salts the most important being gypsum, halite and carnalite. Average salt content is 3.5% by weight. Salt content is typically represented as parts per thousand, 35 %o.

Temperature and density variations within the oceans

Leads to vertical stratification.

• Pollution

Strong variations in salinity are observed across the oceans. The causes can be broken into processes that increase and decrease salinity.

Increase

Variations in density, temperature and salinity occur as a function of depth in the ocean as well. The primary effect is an increase with depth. The largest increases in each of the three occurs between the surface and 500 m. The changes in density, temperature and salinity over this region are entitled the pycncline, thermocline and halocline respectively.

There are three primary variables that control ocean circulation

These inputs result in changes in the following effects that control circulation

We now turn to smaller scale processes in the oceans that occur on the order of meters and kilometers. These local effects include the continuous waves and daily tides that you observe at the beech. Although the scale of the phenomena is local they are responsible for a large portion of the erosion experienced in the oceans.

Waves

We have already studied waves propagating from earthquakes in the solid earth. Now we turn to waves in the oceans generated by the interaction of surface winds with the water. Ocean waves will have an amplitude (height) and wavelength (distance from one peak to the next) just as seismic waves did. If the wavelength of the wave is L then the depth to which the wave penetrates is L/2. Waves result from the circular motion of individual water parcels.

When the depth of the wave (L/2), exceeds the depth of the water the wave will begin to change. This occurs when a wave approaches the shore. The height of the wave increases and its wavelength decreases. Eventually the height of the wave increases to a point where gravity causes the crest to collapse becoming a breaker and forming the surf.

A wave approaching the shore at an angle will begin to refract or bend laterally as it encounters the shallow water. This refraction results in waves approaching the beach at right angles. A secondary result of this bending is the development of a longshore current parallel to the shore.

A special kind of sea wave is generated by large earthquakes and is known as a tsunami. These waves have very long wavelengths (over 100 miles) and very fast velocities (590 miles/hour). They are generated by earthquakes and can travel across an entire ocean basin. In the open ocean their amplitude is small and unnoticeable. As they approach the shore and the water depth decreases, their amplitude grows rapidly (30 m) and can cause significant damage.

Tides

The sun and the moon are responsible for large gravitational forces on the earth. Because it is so much closer to the earth, the moon has the largest effect despite its much smaller mass than the sun. In additional to gravitational forces there are inertial forces resulting from the fact that the earth rotates about the sun and the moon rotates about the earth. The combination of gravitational and inertial forces result in the tides that we observe.

Tides from the moon are daily, yielding two high and two low tides every 24 hours. Superimposed on this cycle is the monthly (28 days) variation resulting from the combined interaction of the sun and the moon. The highest tides occur when the sun and the moon are either on the same or opposite sides of the earth. Thus one can see that the daily tides are dominant but become more complex as a result of these multiple interactions.

Finally we begin to explore the interactions between the oceans and the atmosphere. The weather phenomena known as El Nino is an example of one such interaction. It results from a change in surface winds and the effects of surface temperatures in the Pacific Ocean.