Ch 13. Movemets of Ocean Water

Question 1

What is an Ocean current ?

Answer 1

Ocean currents are the constant flow of huge amounts of water in a certain direction.

Question 2

What causes Waves in the Ocean ?

Answer 2

Wind provides energy to the waves and triggers waves to travel in the ocean water and the energy is released on coastlines.

Waves travel because the wind pushes the body of water in its course and gravity pulls the crests of the waves in downward direction. The falling water pushes the former troughs in upward direction and the wave moves to a new spot.

Question 3

Why does the Ocean wave slow down when it approaches the beach ?

Answer 3

As a wave move towards the beach region, it slows down because of the friction occurring between the dynamic water and the seafloor. And the wave breaks, when the extent of depth of water is less than half the wavelength of the wave.

Question 4

What are Crests and Troughs of a Wave ? (Oceanography)

Answer 4

The highest and lowest points of a wave are known as the crest and trough respectively.

Crest - Highest point
Trough - Lowest point

Question 5

What is the ‘Height’ of a wave ? (Oceanography)

Answer 5

Wave height is the vertical distance from the base of a trough to the top of a crest.

Question 6

What is the ‘Amplitude’ of a wave ? (Oceanography)

Answer 6

It is calculated as one-half of the wave height.

Question 7

What is a Wave period ? (Oceanography)

Answer 7

It is simply the time interval between two successive wave crests or troughs as they pass a fixed point.

Question 8

What is the ‘Wavelength’ of a wave ? (Oceanography)

Answer 8

It is calculated as the horizontal distance between the two consecutive crests.

Question 9

What is the ‘Speed’ of a wave ? (Oceanography)

Answer 9

It is related with rate at which the wave travels through the water and is measured in knots (The distance the wave travels in a given amount of time).

Question 10

What is the ‘Frequency’ of a wave ? (Oceanography)

Answer 10

It is the number of waves passing a given point during a one-second time interval.

Question 11

What is a Tide ?

Answer 11

The periodical (once or twice in a day) rise and fall in the sea level, mainly because of the attraction of the Sun and the Moon, is known as a tide.

Question 12

What is an Ocean surge ?

Answer 12

Movements of water caused by meteorological effects (winds and atmospheric pressure changes) are called surges. Surges are not regular like tides.

Question 13

How does Tides occur ? (Vertical tide generating forces)

Answer 13

The gravitational pull of Moon to a great extent and to a lesser degree, the Sun’s gravitational pull, are the main causes for the occurrence of tides in ocean water. Another important factor is centrifugal force, which is the force that acts to counterbalance gravity.

Together, the centrifugal force and gravitational pull are responsible for establishing the two major tidal bulges on the earth.

Question 14

What are Horizontal tide generating forces ?

Answer 14

The tidal bulges on broad continental shelves have more height. When tidal bulges hit the islands of mid-oceanic region, they become low.

Various shape of bays and estuaries along a shoreline can also amplify the intensity of tides. Funnel-shaped bays greatly modify tidal magnitudes. (Ex: Bay of Fundy Highest tidal range)

Question 15

What is a Tidal current ?

Answer 15

When tide is channeled between the islands or into bays and estuaries, they are known as tidal currents.

Question 16

What are Semi-diurnal tides ?

Answer 16

Two high tides and two low
tides each day. The successive low or high tides are almost of the same height.

Question 17

What are Diurnal tides ?

Answer 17

There is only one low tide and one high tide during each day. The consecutive low and high tides are approximately of the same altitude.

Question 18

What are Mixed tides ? Where do they occur ?

Answer 18

Tides having variations in height are called as mixed tides. Generally, these tides take places along the west coast of North America and on many islands of the Pacific Ocean.

Question 19

What are Spring tides ?

Answer 19

When the earth, Moon and Sun are in a straight line, the tide height will be higher.

These are known as spring tides and they happen twice a month, one on the new Moon period and another during full Moon period.

Question 20

What are Neap tides ?

Answer 20

When the Moon and Sun are at right angles to each other and the forces of the Moon and Sun have a tendency to counteract one another, Neap tides are formed.

Question 21

How Perigee & Apogee and Perihelion & Aphelion affect the magnitude of the tides ?

Answer 21

Perigee, Perihelion - unusually low and high tides take place. At this time, the tidal range (height difference between low tide and high tide) is greater than normal.

Apogee, Aphelion - gravitational force of Moon is limited and the ranges of tide are less than their average heights.

Question 22

What is an Ebb ?

Answer 22

The time gap between the high tide and low tide, when the water level is falling, is termed as the ebb.

Question 23

What is a Flow or Flood in terms of Oceanic tides

Answer 23

The time between the low and high tide, when the tide is escalating, is known as the flow or flood.

Question 24

List few usages of the Tides in daily life

Answer 24

1. Navigation
2. Fishing
3. Desilting - in removing polluted water and desilting the sediments from river estuaries.
4. Weather
5. Tidal Energy
6. Tidal zone foods

Question 25

What is a Tidal Bore ? What are conditions required for it ?

Answer 25

A tidal bore is a condition where the flow of water from the river into the ocean reverses and the tide pushes water up the river. The Indian rivers like the Ganges, Brahmaputra, Indus, etc exhibits tidal bores.

Conditions required -
1. The river where a tidal bore appears must not be too deep.

2. The mouth of the river, needs to be comparatively shallow and fairly wide compared to the inland part of the river to create a sort of funneling effect.
3. The estuary (the mouth of the river) acts as the wide part of the funnel, channeling water into the narrower river, where the water rises to compensate for this influx of volume.
4. The name ‘bore’ is due to the sound the tidal current makes when it travels through narrow channels.

Question 26

Coriolis force is the only force that is acting on the direct of ocean currents in the Indian Ocean. True or False ?

Answer 26

False.

In the Indian Ocean region, the direction of flow of the current changes with the change in the direction of monsoon wind movement (force of wind is stronger than the Coriolis force)

Question 27

What forces are responsible for the formation of Ocean currents ?

Answer 27

1. Heating by solar energy
2. Wind
3. Gravity
4. Coriolis force
5. Salinity differences

Question 28

What is a Gyre ?

Answer 28

In the ocean, huge accumulations of water and the flow around them are known as Gyres. These create large circular currents in all the ocean basins.

Question 29

The only sea in the world which has no land boundary and is located entirely in the midst of an ocean is ?

Answer 29

Sargasso Sea

It is surrounded by four ocean currents. These ocean currents form a clockwise-circulating gyre that surrounds the Sargasso Sea much like a terrestrial coastline would. This vast patch of ocean named for a genus of free-floating seaweed know as Sargassum.

Question 30

What are Surface currents or Wind driven currents ?

Answer 30

Currents in the upper water of the ocean (upto a depth of 400 meter) are called Surface currents.

These comprise close to around 10% of all the water in the ocean. It is also called Wind-Driven Currents. The Surface Currents are a result of the Wind-stress and are modified by Coriolis force. Hence Surface currents mimic Atmospheric Wind Circulations.

Question 31

What are Thermohaline currents ?

Answer 31

Deep water currents.

Question 32

What are Cold currents ?

Answer 32

Those that flow from Polar Regions to equatorward have a lower surface temperature and are called cold currents (from higher latitudes to lower latitudes).

Generally found on the west coast of the continents near the low and middle latitude regions (in both the hemispheres) and on the east coast near the higher latitudes in the Northern Hemisphere of the earth.

Cold currents flow in the anti-clockwise direction in the northern hemisphere and in the clockwise direction in the southern hemisphere of the earth.

Question 33

What are Warm currents ?

Answer 33

Those that move from equatorial areas towards pole, have a higher surface temperature and are called warm currents.

These currents are usually observed on the east coast of continents in the low and middle latitudes (true in both hemispheres) and in the northern hemisphere they are found on the west coasts of continents in high latitude areas.

Warm currents move in the anti-clockwise direction in the southern hemisphere and in the clockwise direction in the northern hemisphere of the earth.

Question 34

Mention the Currents found in the Atlantic Ocean

Answer 34

North Atlantic Ocean:
● Cayenne current
● North Equatorial ocean current
● Florida current
● Gulf Stream
● North Atlantic Drift
● Canary current
● Labrador current
● E. Greenland current
● Norwegian current

● Equatorial counter current

South Atlantic Ocean:
● South equatorial current
● Brazillian current
● Falkland current
● South Atlantic ocean current
● Benguela current

Question 35

Mention the Currents found in the Pacific Ocean

Answer 35

North Pacific Ocean:
● North Equatorial Current
● Kuroshio Current
● North Pacific Drift
● California Current
● Alaskan or Bering Current
● Oyashio or Okhotsk Current

● Counter Equatorial Current

South Pacific Ocean:
● South Equatorial Current
● East Australian Current
● South Pacific Current
● Peruvian or Humboldt Current

Question 36

Mention the Currents found in the Indian Ocean

Answer 36

● North Equatorial Current
● South Equatorial Current
● Somali Current
● Agulhas or Mozambique Current
● Madagascar Current
● South Indian Ocean Current
● West Australian Current
● South West Monsoon Drift
● North-East Monsoon Drift

Question 37

How does warm ocean current affect a coatal area ?

Answer 37

It causes precipitation

Question 38

How does cold ocean current affect a coatal area ?

Answer 38

Results in the desert formation

Question 39

How does the blending of warm and cold ocean currents affect the coastal area ?

Answer 39

Develops rich fishing ground

Eg. eastern coast of Canada(Grand Banks around Newfoundland) and NE coast of Japan

Question 40

What is Upwelling of the ocean water ?

Answer 40

Movement of cold, deep, often nutrient- rich water to the surface mixed layer.

It brings water enriched with nutrients that are important for primary productivity that ultimately helps productive marine ecosystems

Question 41

What is Downwelling of the ocean water ?

Answer 41

Downwelling process happens when surface waters come together (converge), pressing the surface water in downward direction.

These movements are very crucial in delivering Oxygen to depth, stirring the ocean. Areas of downwelling have low productivity because of the nutrients get used up and they are not continuously resupplied by the nutrient-rich cold water, from below the surface.

Question 42

What is a Tsunami ?

Answer 42

“Tsunami” is a Japanese word which means “harbor wave,”. Unlike the normal Ocean waves which form due to winds or tides, the tsunami waves are formed due to the underwater activities like earthquake, landslide, volcano eruption, etc.