Q 1 – What are waves?
Ans. Waves are oscillatory movements in water, manifested by an alternate rise and fall of the sea surface. In other words, waves are actually the energy, not the water as such, which moves across the ocean surface. Water particles only travel in a small circle as a wave passes. 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 wind pushes the water body in its course while gravity pulls the crests of the waves downward. The falling water pushes the former troughs upward, and the wave moves to a new position. The actual motion of the water beneath the waves is circular. It indicates that things are earned up and forward as the wave approaches, and down and back as it passes.
Q 2 – Where do waves in the ocean get their energy from?
Ans. Wind provides energy to the waves. Wind causes waves to travel in the ocean and the energy is released on shorelines. The motion of the surface water seldom affects the stagnant deep bottom water of the oceans. As a wave approaches the beach, it slows down. This is due to the friction occurring between the dynamic water and the seafloor. Waves continue to grow larger as they move and absorb energy from the wind. Most of the waves are caused by the wind driving against water. When a breeze of two knots or less blows over calm water, small ripples form and grow as the wind speed increases until white caps appear in the breaking waves.
Q 3 – What are tides?
Ans. The periodical rise and fall of the sea level, once or twice a day, mainly due to the attraction of the sun and the moon, is called a tide. Tides vary in their frequency, direction and movement from place to place and also from time to time.
Q 4 – How are tides caused?
Ans. Tides are caused by:
- The moon’s gravitational pull to a great extent
- The sun’s gravitational pull to some extent are the major causes for the occurrence of tides.
- Another factor is centrifugal force, which is the force that acts to counter balance the gravity.
Together, the gravitational pull and the centrifugal force are responsible for creating the two major tidal bulges on the earth. On the side of the earth facing the moon, a tidal bulge occurs while on the opposite side though the gravitational attraction of the moon is less as it is farther away, the centrifugal force causes tidal bulge on the other side. The ‘tide-generating’ force is the difference between these two forces; i.e. the gravitational attraction of the moon and the centrifugal force.
Q 5 – How are tides related to navigation?
Ans. Since tides are caused by the earth- moon-sun positions which are known accurately, the tides can be predicted well in advance. This helps the navigators and fishermen plan their activities. Tidal flows are of great importance in navigation. Tidal heights are very important, especially harbours near rivers and within estuaries having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the harbour. Kolkata port on Hugli river is an example for it.
Q 6 – How do currents affect the temperature? How does it affect the temperature of coastal areas in the N. W. Europe?
Ans. Impact of currents on temperature varies depending on whether currents are warm or cold.
1. Cold currents: Cold currents bring cold water into warm water areas. These currents are usually found on the west coast of the continents in the low and middle latitudes (true in both hemispheres) and on the east coast in the higher latitudes in the Northern Hemisphere.
2. Warm currents: Warm currents bring warm water into cold water areas and are usually observed on the east coast of continents in the low and middle latitudes (true in both hemispheres). In the northern hemisphere they are found on the west coasts of continents in high latitudes.
In North West Europe, warm currents exist. They increase the temperature in coastal areas of N. W. Europe.
Q 7 – What are the causes of currents?
Ans. Ocean currents are like river flow in oceans. They are caused by two types of forces namely:
- Primary forces that initiate the movement of water;
- Secondary forces that influence the currents to flow.
Primary Forces: The primary forces that influence the currents are:
- Heating by solar energy: Heating by solar energy causes the water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope.
- Wind: Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course.
- Gravity: Gravity tends to pull the water down the pile and create gradient variation.
- Coriolis force: The Coriolis force intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere. These large accumulations of water and the flow around them are called Gyres. These produce large circular currents in all the ocean basins.
Q 8 – Which forces influence the movement of ocean water?
Ans. The external forces like of the sun, moon and the winds influence the movement of ocean water.
Q 9 – What types of movements take place in ocean water.
Ans. The horizontal and vertical motions are common in ocean water bodies. The horizontal motion refers to the ocean currents and waves. The vertical motion refers to tides.
Q 10 – Explain different types of vertical movement in the ocean water.
Ans. The vertical motion refers to the rise and fall of water in the oceans and seas. Due to attraction of the sun and the moon, the ocean water is raised up and falls down twice a day. The upwelling of cold water from subsurface and the sinking of surface water are also forms of vertical motion of ocean water.
Q 11 – How are ripples formed?
Ans. When a breeze of two knots or less blows over calm water, small ripples form and grow as the wind speed increases until white caps appear in the breaking waves.
Q 12 – How do steep and steady waves form?
Ans. Steep waves are fairly young ones and are probably formed by local wind. Slow and steady waves originate from far away places, possibly from another hemisphere.
Q 13 – What factors cause tides?
Ans. The moon’s gravitational pull to a great extent and to a lesser extent the sun’s gravitational pull, are the major causes for the occurrence of tides. Another factor is centrifugal force, which is the force that acts to counter balance the gravity. Together, the gravitational pull and the centrifugal force are responsible for creating the two major tidal bulges on the earth
Q 14 – Where does highest tide occur in the world?
Ans. The highest tides in the world occur in the Bay ofFundy in Nova Scotia, Canada.
Q 15 – What are Semi-diurnal tides?
Ans. The most common tidal pattern, featuring two high tides and two low tides each day. The successive high or low tides are approximately of the same height.
Q 16 – What are Diurnal tides?
Ans. There is only one high tide and one low tide during each day. The successive high and low tides are approximately of the same height.
Q 17 – What is a Mixed tide?
Ans. Tides having variations in height are known as mixed tides. These tides generally occur along the west coast of North America and on many islands of the Pacific Ocean.
Q 18 – What are Spring tides?
Ans. The position of both the sun and the moon in relation to the earth has direct bearing on tide height. When the sun, the moon and the earth are in a straight line, the height of the tide will be higher. These are called spring tides.
Q 19 – What are neap tides?
Ans. When the sun and moon are at right angles to each other and the forces of the sun and moon tend to counteract one another. The moon’s attraction, though more than twice as strong as the sun’s, is diminished by the counteracting force of the sun’s gravitational pull. These are called neap tides.
Q 20 – Define ocean currents.
Ans. Ocean currents are the continuous flow of huge amount of water in a definite direction. Ocean currents are like river flow in oceans. They represent a regular volume of water in a definite path and direction.
Q 21 – How are fishing and oceanic currents related?
Ans. The mixing of warm and cold currents help to replenish the oxygen and favour the growth of planktons, the primary food for fish population. The best fishing grounds of the world exist mainly in these mixing zones.
Q 22 – How do ocean currents affect the climate? Explain.
Ans. Effects of currents influenced by temperature.
- Warm currents makes the place warmer where as the cold currents makes the place colder. Example, Warm currents of Koroshio makes the southern Japan less cold in winter whereas the cold current of Koroshio makes the winter longer and severe in north Japan.
- Winds passing over warm currents absorbs lot of moisture and cause heavy rainfall in coastal areas. On the other hand winds passing over long currents do not get any warm currents as such, they make the climate of coastal areas dry. This is the reason why hot deserts are located near the coastal areas from where the cold current passes.
- The places where cold current and warm current near the coastal areas are found in abundance are rich fishing ground. For example, Newfoundland, the east coast of North America where Labrador current and Gulf stream meet.
Q 23 – Explain different types of ocean currents.
Ans. On the basis of depth:
- Surface currents constitute aboutlO percent of all the water in the ocean. These water are the upper 400 m of the ocean.
- Deep water currents make up the other 90 percent of the ocean water.
Deep waters sink into the deep ocean basins at high latitudes, where the . temperatures- are cold enough to cause the density to increase.
On the basis of temperature:
- Cold currents: Cold currents bring cold water into warm water areas. These currents are usually found on the west coast of the continents in the low and middle latitudes and on the east coast in the higher latitudes in the northern hemisphere;
- Warm currents: Warm currents bring warm water into cold water areas and are usually observed on the east coast of continents in the low and middle latitudes. In the northern hemisphere they are found on the west coasts of continents in high latitudes.
Q 24 – How do ocean currents get affected by winds and Coriolis force?
Ans. Wind: Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course
The Coriolis force: The coroilis intervenes and cause the water to move to the right in the northern hemisphere and to the left in the southern hemisphere.
Q 25 – In how many categories can tides be classified on the basis of their height and frequency?
Ans.
- Semi-diurnal tide: It is the most common tidal pattern, featuring two high tides and two low tides each day. The successive high 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 of the same height.
- Mixed tide: Tides having variations in height are known as mixed tides. These tides generally occur along the west coast of North America and on many islands of the Pacific Ocean.
- Spring tides: The position of both the sun and the moon in relation to the earth has direct bearing on tide height. When the sun, the moon and the earth are in a straight line, the height of the tide will be higher. These are called spring tides.
- Neap tides: Wlien the sun and moon are at right angles to each other and the forces of the sun and moon tend to counteract one another. The moon’s attraction, though more than twice as strong as the sun’s, is diminished by the counteracting force of the sun’s gravitational pull. These are called neap tides.
Q 26 – White the characteristics of waves in the oceanic water.
Ans. Characteristics of waves in the oceanic water are given below:
- The highest and lowest points of a wave are called the crest and trough.
- Wave height 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 is merely the time interval between two successive wave crests.
- 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.
- Wave frequency is the number of waves passing a given point during a one- second time interval.
Q 27 – Explain how do heating of solar energy, wind, gravitation and coriolis force affect the ocean currents.
Ans. Heating by solar energy: Heating by solar energy causes the water to expand, that is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope
- Wind: Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course.
- Gravity: Gravity tends to pull the water down the pile and create gradient variation.
- The Coriolis force: The coriolis intervenes and cause the water to move to the right in the northern hemisphere and to the left in the southern hemisphere.
Q 28 – How is the movement of currents influenced by prevailing winds? Give examples.
Ans. The prevailing winds, or winds that usually blow in the same direction, influence ocean currents because the wind causes friction on the water surface causing the water to move in the same direction as the wind. Some prevailing winds are called “trade winds” because merchants on sailboats used these regular winds to sail across the Indian Ocean or Atlantic Ocean to trade their goods. The wind made sailing to some places very easy and other places very difficult. Some of these regular winds change direction during certain months. This is called monsoon. Monsoon winds blow one direction from May to October, then change directions from November to April, which allowed the merchants to sail home in Monsoon areas of the world. The monsoon winds mainly effects South Asia (India). Indian traders sailed west to Africa in the summer and east back to India in the winter.
Q 29 – Why some currents are warm or cold?
Ans. There are several warm ocean currents that move warm water away from the equator. These currents of water have warm air above the water. The warm air raises the temperature of the land it touches. These areas enjoy a much warmer climate than other places at the same latitude. Areas such as England would be much colder without the warm Gulf Stream. Warm ocean currents flow on the eastern side of a continents. They only reach the western side in high latitude areas. Another characteristic is that they flow away from the equator. Warm currents have higher temperatures, so they are less dense than cold water. Usually warm water has a higher salinity, but it remains less dense than cold water, so cold water is heavier and flows under warm water. The water is warmed on the surface, so warm currents flow across the surface of the ocean. As a warm current cools down, it drops down and becomes a cold water currents.
Q 30 – What are under currents?
Ans. Under currents deep in the ocean flow in the opposite direction from the surface current above them. They replace the surface waters that are moving out. A major under current circles the globe at about 30 mph. The main under current is called the Great Conveyor Belt. It is truly like an underwater river. In fact, under currents are called “submarine rivers”.
Q 31 – What is inner space?
Ans. The world of oceans and seas is referred to as “inner space,”
Q 32 – What are the important mechanisms by which ocean currents are generated?
Ans. The important mechanisms are:
- The drag of winds over the ocean surface, and
- Unequal forces set up by differences in water density.
Q 33 – Classify the ocean currents.
Ans. The ocean currents may broadly be classified into cold currents and warm currents.
Q 34 – Give the other name of tropical easterlies.
Ans. Tropical easterlies are also known as trade winds.
Q 35 – Name the force that changes the direction of water drift in oceans.
Ans. The Coriolis force changes the direction of water drift in oceans.
Q 36 – What kind of currents results due to differences in water density?
Ans. Differences in water density set currents in a motion described as thermocline currents.
Q 37 – What is ‘gyre’?
Ans. Due to the Coriolis effect, the moving water turns and follows an elliptical path and it is known as a gyre.
Q 38 – Which current flows as Kuroshio current after reaching the coasts of Taiwan and Japan?
Ans. The North equatorial current flows as Kuroshio current after reaching the coasts of Taiwan and Japan.
Q 39 – Name the northern and southern branches of North Pacific current.
Ans. Alaska and California currents respectively.
Q 40 – Define waves.
Ans. Waves are oscillatory movements in water, where its particles move in a vertical plane, up and down.
Q 41 – What are the progressive waves?
Ans. Ocean waves produced by winds are called progressive waves.
Q 42 – What is the difference between flood tide and ebb tide?
Ans. Rise of sea level is called the flood tide and fall is called ebb tide.
Q 43 – Which is the birthplace of common eels?
Ans. The Sargasso in the western North Atlantic is surrounded by the Florida current. It is often windless and is clocked with seaweed. It is the birthplace of common eels.
Q 44 – Up to what depth in water, the photosynthesis is possible for plants?
Ans. The sunlight penetrates water up to 900 metres, but only in the top 100 metres is there enough light for plants to do photosynthesis.
Q 45 – When do the tides attain maximum height?
Ans. Twice a month, when the earth, the moon and the sun are in a straight line.
Q 46 – At what interval of time do the tides occur on each meridian and why?
Ans. Each meridian has a high and a low tide at an interval of 12 hrs. and 26 minutes, due to rotation of the earth
Q 47 – Name two types of waves.
Ans.
- Transverse waves, and
- Longitudinal waves.
Q 48 – What is the main cause of the tide?
Ans. The gravitational interaction of the earth, the moon and the sun is the main cause of tide.
Q 49 – What are the main processes of cooling of ocean water?
Ans. Back radiation of heat from the sea surface, convection and evaporation.
Q 50 – What are ocean currents?
Ans. The ocean currents are the regular movement of the surface of the water in a particular direction.
Q 51 – When does spring tide occur?
Ans. Springtide occurs in the first and last quarter of the moon and sun are almost in a line.
Q 52 – Where does neap tide occur?
Ans. When the sun and the moon are at right angles at the earth’s centre, neap tide occurs in the first and the last quarter of the moon.
Q 53 – What is the drift?
Ans. The motion of the ocean water, generally at low velocity, as a result of surface friction from the prevailing winds.
Q 54 – What is salinity?
Ans. It is the degree to which water contains dissolved salts.
Q 55 – Describe the types of ocean currents and their flow mechanism.
Ans. Ocean currents are of two types: warm and cold currents. The main currents flow from the low latitudes in tropical zones towards high latitudes in the temperate and sub-polar zones. The cold currents flow from high latitudes to low latitudes.
Q 56 – Give reasons why the height of tidal waves varies from place to place?
Ans. The height of the tidal waves varies from place to place because of the following reasons:
- The relative position of the moon and the sun with respect to the earth,
- Distribution of land and ocean on the earth’s surface, and
- Irregularities in the configuration of oceans.
Q 57 – What are tides?
Ans. Tides are periodic rise and fall in the level of water in seas and oceans caused by the differential attraction of the moon and the sun. Twice a day, about every 12 hrs and 26 minutes, the sea level rises and falls. The rise of sea level is called the flood tide and the fall is called the ebb tide.
Q 58 – What is a tidal bore?
Ans. The tidal waves follow the direction of the moon. In certain inland seas, where tidal waves reach from different directions, one can find a number of high tides and low tides. When such waves enter a gulf or river mouths, the tidal crests look like a vertical wall of water rushing upstream, which is known as the tidal bore
Q 59 – Discuss the impact of prevailing winds on the motion of currents.
Ans. Air flowing over the water surface exerts a dragging force upon that surface, setting the surface water layer in motion. Prevailing winds, such as the tropical easterlies (trade winds), blowing from east to west, and the middle-latitude westerlies, blowing from west to east, exert a one-way drag on sea surface over a vast expanse of oceans. This drag produces a system of drift currents.
Q 60 – Explain how differences in water density set currents in motion?
Ans. Differences in water density can also set currents in motion These are described as thermocline currents. A surface water layer in one place may be less dense because it is warmer, or lower in density than the water layer in adjacent place that is colder or has a higher density. The water then moves gently from the region of less to the higher density.
Q 61 – Why the circulation of currents in the Indian ocean is different from the Atlantic and the Pacific oceans?
Ans. The circulation of currents in the Indian ocean is characteristically different from the Atlantic and Pacific oceans because the Indian ocean is landlocked in the north. The circulation pattern in the northern portion of the Indian ocean changes its direction in response to the seasonal rhythm of the monsoons. There is a clear reversal of currents between winter and summer.
Q 62 – Describe the mechanism of origin of sea waves.
Ans. It is commonly believed that the waves are generated due to friction on water surface caused by winds. The height of sea waves depends on:
- The wind speed,
- The duration of wind from a particular direction, and
- The fetch or the expanse of water surface over which the wind blows.
Q 63 – Distinguish between progressive and oscillatory waves.
Ans. The ocean waves produced by winds rapidly through the water are called progressive waves, whereas in oscillatory waves each wave passes a fixed reference point, and the water particles travel through a vertical cycle of motion and return approximately to their original position.
Q 64 – Discuss the properties of waves.
Ans. Waves are oscillatory movements in water, where its particles move in a vertical plane, up and down. The upper part of the wave is called the crest, and the lower part is called the trough. Each wave has a wavelength, velocity, height and wave period. The distance between two successive crests or two successive troughs is the wavelength. The time taken by a wavelength to pass a fixed point is known as the wave period. The vertical distance between a trough and a crest is called the wave height. The ratio of wavelength to the wave period gives the velocity of the wave.
Q 65 – What are the disadvantages of tides?
Ans. Tides are sometimes harmful to ships and boats.
- Tides check the formation of deltas.
- Marshes are formed due to accumulation of tidal water.
- Tides also hinder fishing.
Q 66 – Why does the temperature of seawater decrease with depth?
Ans. The temperature of seawater is the same as that of the surface water up to a height of 100 metres. The surface of seawater receives, maximum insolation. As the rays penetrate the water, the heat is reduced by scattering, reflection and diffusion.
Q 67 – How can the velocity of the ocean currents be measured?
Ans. The ocean currents flow like extensive rivers in the ocean. The rate of flow and the width of the currents, however, are not uniform. The Gulf stream, for example, is 80 km. wide and 1.6 km. deep. The Florida current has a velocity of 10 km. per hour on the surface and 3.5 km. at a depth of 200 m.
Q 68 – Write a short note on the vertical circulation of ocean water.
Ans. Besides the horizontal movement, the vertical circulation of ocean water is also an important phenomenon. Ocean surface is marked with sinking and upwelling caused by wind action, evaporation of surface water, the addition of surface water by rainfall and changes in density due to cooling or warming of the surface layer. A most important cause of the sinking of ocean water on a large scale is cooling of the surface layer by loss of heat to the overlying atmosphere in high latitudes.
During long winters, much heat is lost to space than is gained by solar ^ radiation, thereby the relatively warm surface waters brought polewards v by ocean currents are drilled and increased in density. This water, generally close to the freezing point, sinks to the ocean floor, causing vertical circulation of the water.
Q 69 – Describe the currents of the Pacific ocean in brief.
Ans. The important currents of the Pacific ocean are North equatorial, Kuroshio current, Alaska current, California current, Oyashio current, Okhotsk current, South equatorial current, South. Pacific current and Peru current.
The North equatorial current from the west coast of Central America reaches the Philippine Island, flowing from east to west in the north Pacific ocean.
Turning northward, the North equatorial current flows along Taiwan and Japan to form Kuroshio current. The currents are influenced by the westerlies from the south-east coast of Japan and tend to flow from west to east as North Pacific current. The current gets bifurcated into the northern and southern branches, called Alaska and California currents respectively after reaching the west coast of N&rth America.
The Alaska current flows anti-clockwise above the coast of British Columbia and Alaska, whereas the California current flows along the coast of California. The cold current, the Oyashio, flows in the North Pacific. Another cold current, named Okhotsk flows in the north Pacific and merges with Oyashio current, which finally sinks beneath the warmer waters of the Kuroshio
The South equatorial current flows in the south Pacific ocean. It flows southward as the East Australian current before meeting the South Pacific current near Tasmania, which flows west to east. Near the south-western coast of South America, it turns north as the Peru Current. It is a cold current that feeds the South equatorial, thus completing the circle.
Q 70 – Distinguish between swash and backwash.
Ans. When ocean waves arrive at the coast of a continent or island, they encounter shallow Water. The configuration of coast interferes with the progress of the waives. Waves in shallow water are modified into ellipses that become progressively flattered as the coast is approached, As the steeping waves continue to travel shoreward, encountering still shallower water, the crest height increases sharply and the forward slope of the wave becomes greatly steepened. At a critical point, the ‘ waveform disintegrates into a mass of turbulent water called the breaker. Thereafter, it becomes a landward moving sheet of highly turbulent water known as the swash or uprush.
The water then begins to pour seaward down the slope in a reverse flow termed as backwash or back rush. Thus, backwash is the seaward flow of a body of water down the slope after a wave has broken on the beach, in contrast to swash. It may also be called the drag of a recording wave.
Q 71 – Write a short note on a spring tide and neap tide.
Ans. Tides are the periodic rise and fall in the level of water in seas and oceans caused by the differential attraction of the moon and the sun. Twice a day, about every 12 hrs and 26 minutes, the sea level rises and falls.
Tides do not rise to the same height every day. The relative position of the moon and the sun with respect to the earth is responsible for this variation in the height of tides. On the full moon and the new moon, the moon and the sun are almost in line with the earth, and hence, they exert their combined puli. Therefore, on these two days, tides are the highest and are known as spring tides.
On half-moon, the sun and the moon make a right angle at the earth’s centre. The pulls of the moon and the sun partly cancel each other out. as a result of which there are usually low tides called neap tides. This happens on the first and the last quarter of the lunar month when due to their right angular position to the attraction1 and centrifugal forces of the sun and the moon do not combine. This reduces the height of the tides to the minimum.
Q 72 – If there were no ocean currents, what would have happened to the world? Discuss.
Ans. The oceans contain about 3% of the total water on earth. This water is always available for evaporation into the atmosphere and its subsequent precipitation on the land and the seas.
The general movement of a mass of ocean water in a fairly defined direction over great distances is called the ocean current. Current ranges in scale from ocean-wide flow system to local currents of small extent and can be generated by several mechanisms.’ Ocean currents are broad of two types: warm and cold currents. The warm currents flow from the low latitudes in tropical zones towards the high latitudes in the temperate and polar zones. The cold currents flow from high latitudes to low latitudes.
Water has an exceptionally great capacity for absorbing heat. The circulation of ocean water through currents helps in distribution of heat received in low latitudes to certain areas of high latitudes. In this way, the oceans modify the climate of the earth. Without ocean currents, this modification of climate would not have been possible.
The distribution of rich fishing grounds in the oceans and seas depends upon the circulation of water of the oceans as they bring nutrients to the surface in some areas. This process of bringing nutrients – both mineral and organic to the surface through the upwelling of water and its circulation is known as the ploughing action of the seas. Ocean currents aid in these processes. The absence of ocean currents would have hampered this process.
Ocean surface is marked with sinking (surges) and upwelling (swells) caused by wind action, evaporation of surface water, the addition of surface water by rainfall and changes in density due to cooling or warming of the surface layer. A most important cause of the sinking of ocean water on a large scale is cooling of the surface layer by loss of heat to the overlying atmosphere in high altitudes.
During long winters, much heat is lost to space, than is gained by solar radiation, thereby relatively warm surface waters brought poleward by ocean currents are chilled and increased in density. This water may be close to the freezing point and, therefore, sinks to the ocean floor. Without ocean currents, all the above activities of the ocean water would not have taken place.