MOVEMENTS OF OCEAN WATER

1. Waves

• Waves are the energy, not the water as such which moves across the ocean surface.
• As a wave approaches the beach, it slows down this is due to the friction occurring between the dynamic water and the sea floor. The largest waves are found in the open oceans.
• Waves continue to grow larger as they move and absorb energy from the wind.
• The maximum wave height is determined by the strength of the wind i.e. how long it blows and the area over which it blows in a single direction.
• Waves travel because the wind pushes the water body in its course while gravity pulls the crests of the wave downward. The motion of the surface water seldom affects the stagnant deep bottom water of the oceans.
• Wave height –it is the vertical distance from the bottom of a trough to the top of a crest of a wave. Wave amplitude is one-half of the wave height.
• Wave period –it is merely the time interval between two successive crests or troughs as they pass a fixed point.
• Wavelength is the horizontal distance between two successive crests.
• Wave speed is the rate at which the wave moves through the water and is measured in knots.

2. Tides

• The moon's gravitational pull to a great extent and a lesser extent sun's gravitational pull.
• Centrifugal force, which is the force that acts to counterbalance gravity.
• Together the gravitational pull and the centrifugal force are responsible for creating two major tidal bulges on the earth.
• On the surface of the earth, the horizontal tide-generating forces are more important than the vertical forces in generating the tidal bulge.
• The tidal bulges on wide continental shelves have greater heights. when tidal bulges hit the mid–oceanic islands they become low.
• When the tide is channelled between islands or into bays and estuaries they are called tidal currents.
• The highest tides in the world occur in the Bay of Fundy in  Nova Scotia Canada.

Types of Tide 

Based on their frequency of occurrence

• Semi diurnal-two high tides and two low tides each day. successive high tides or low tides are approximately of the same height.
• Diurnal tide-there is only one high tide and one low tide during each day. the successive high and low tides are approximately the same height.
• Mixed tide tides having variations in height these tides occur along the west coast of North America and on many islands of the Pacific Ocean.

Based on their heights

• Spring Tide: When the sun moon and earth are in a straight line the height of the tide will be higher. They occur twice a month one during the full moon period and another during the new moon period.
• Neap Tide: At this time the sun and moon are at right angles to each other and the forces of the sun and moon counteract one another.The moon's attraction though more than twice as strong as the sun is diminished by the counteracting force of the sun's gravitation pull.
• Normally there is 7 day interval between the spring tide and the neap tide.
• Once in a month when the moon's orbit is closest to the earth( perigee) unusually high and low tides occur. During this time tidal range is greater than normal. Two weeks later when the moon is farthest from the earth( apogee) the moon's gravitational force is limited and the tidal ranges are less than their average heights.
• When the earth is closest to the sun( perihelion) around 3 January each year tidal ranges are much greater with unusually high and low tides.  When the earth is farthest from the sun (aphelion )around 4 July each year tidal ranges are much less than average.
• EBB- The time between the high tide and the low tide when the water level is falling.
• Flow or the time between the low tide and high tide, when the tide is rising.

Importance of Tide: Tidal flows are of great importance in navigation. Tides are also helpful in desilting the sediments and in removing polluted water from river estuaries. Tides used in generating power.

3. Ocean Currents

The streams of water that flow constantly on the ocean surface in definite directions are called ocean currents.

Characteristics of Ocean Currents

• Ocean currents are greatly influenced by the stresses exerted by the prevailing winds and Coriolis force.
• The air circulation over the oceans in the middle latitudes is mainly anticyclonic (more pronounced in the southern hemisphere than in the northern hemisphere)
• At higher latitudes where the wind flow is mostly cyclonic the oceanic circulation follows this pattern
• In regions of pronounced monsoonal flow  the monsoon winds influence the current movements
• Due to the Coriolis force the warm currents from low latitudes tend to move right in the northern hemisphere and to their left in the southern hemisphere
• The oceanic circulation transports heat from one latitude belt to another
• The cold waters of the Arctic and Antarctic circles move towards warm water in tropical and equatorial regions while the warm waters of the lower latitudes move polewards.

Ocean currents are influenced by two types of forces: Primary forces that initiate the movement of water and Secondary forces that influence the currents to flow. 

Primary Forces Influencing Current

1. Heating by the solar energy 
2. Wind
3. Gravity
4. Coriolis force
5. Tide
6. Thermohaline circulation –variation in temperature and salinity create density differences turn to affect ocean current

• Heating by solar energy causes water to expand.  That is why, near the equator, the ocean water is about 8 cm higher in level than in middle latitudes. this causes a very slight gradient and water tends to flow down the slope.
• Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water's surface affects the movement of the water body in its course.
• Gravity tends to pull the water down the pile and create gradient variation. The Coriolis force intervenes and causes the water to move to the right in the northern hemisphere and the left in the southern hemisphere. These large accumulations of water and the flow around them are called GYRES.
• Vertical mobility of ocean currents-differences in water density affect the vertical mobility of ocean currents .water with higher salinity is denser than water with low salinity and in the same way cold water is denser than warm water. Denser water tends to sink while relatively lighter water tends to rise.
• Cold water ocean currents occur when the cold water at the poles sinks slowly and moves towards the equator. warm water currents travel out from the equator along the surface flowing towards the pole to replace the sinking cold water. 

Types of Ocean Currents: Classified Based on their Depth and Temperature

• Surface currents- constitute  10 per cent of water in the ocean. These waters are upper 400 m of ocean.
• Deep water currents- constitute 90 per cent of the ocean. This water moves around the ocean basin due to variations in Density and Gravity.
• Deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.
• This started the Global Conveyor Belt a connected system of deep and surface currents that circulate for 1000 years
• This global set of ocean currents is a critical part of the earth's climate system as well as the ocean nutrient and carbon dioxide cycles.

Temperature

• Cold Currents:  These bring cold water into warm areas  these are unusually found on the west coast of continents in the low and middle latitudes( true in both hemispheres} and on the east coast in the higher latitudes in the northern hemisphere
• Warm Currents: Bring Warm Water in Cold areas observed on the east coast of continents in the low and middle latitudes in both hemispheres, in the northern hemisphere found on the west coast of continents in high latitudes.

Effects of Ocean Current

• Climate Conditions: The west coasts of the continent in the middle and higher latitudes are bordered by warm water which causes a distinct marine climate. Warm current flows parallel to the east coasts of the continent in the tropical and subtropical latitudes resulting in a warm and rainy climate. Eg:  The British Isles would have been extremely cold without the Warm North Atlantic Drift.  The hot climate of Peru is cooled by the cold Peru Current. 
• Fishing Grounds: Mixing of warm and cold current help to replenish the oxygen and favour the growth of plankton the primary food for a fish population the best fishing ground in the world exist mainly in these mixing zones.
• Desert Formation: Cold ocean currents have a direct effect on desert formation in west coast regions of tropical and subtropical continents.
• Rainfall: Winds blowing over warm currents pick up and carry moisture and bring rainfall like North  Atlantic Drift brings rainfall in areas located on the western coast of Europe. on the contrary cold currents do not bring rainfall and make the region cooler and drier eg the Kalahari desert hardly experiences rainfall due to the cold Benguela Current.
• Fog Formation: The meeting of warm and cool currents results in the formation of fog
• Trade and Commerce: Currents help ships to sail Many warm currents keep ports of Europe ice-free thereby helping in trade and commerce.
• Violent Storms: The meeting of warm and cold currents at times causes storms, Ocean Currents in the Arctic Ocean, Baffin Island and Current Cold, Labrador Current-Cold, Ocean Current in the Atlantic Ocean, Angola Current-Warm, Antilles Current-Warm, Benguela Current-Cold, Brazil Current-Cold, Cape Horn Current-Cold, Falkland Current-Cold, North Atlantic Current-Warm, South Atlantic Current-Cold, Ocean Current in the Indian Ocean, Aghulas Current-Warm, Leeuwin Current-Warm, Mozambique Current-Warm, Weat Australian Current-Cold, Ocean Current in Pacific Ocean, Alaska Current-Warm, Humboldt Current-Cold, Kamchatka Current-Cold, Kuroshio Current-Warm, North Pacific Current-Warm.