Waves, Ocean Currents and Tides – UPSC World Geography Notes

The intricate and dynamic motion of ocean water is orchestrated by various factors, including wind, temperature, salinity, the Earth’s rotation, and the geography of ocean basins. This fluid choreography gives rise to Ocean Currents, tides, and Waves, representing the primary expressions of water movement within the vast expanses of the world’s oceans. For further insights into this fascinating subject, continue reading.

Shifting our focus from land to the hydrosphere in our Geography notes series, we now delve into the realm of water. In the preceding article, we delved into the topography of the ocean floor.

This comprehensive post aims to explore the intricate movements of ocean water, encompassing waves, tides, and ocean currents. We trust that these notes will prove immensely beneficial for efficient learning and last-minute revisions.

Movements of ocean water

You’re well aware that ocean water is constantly in motion. Various types of movements occur, influenced by different physical characteristics such as temperature, salinity, and density. Additionally, external forces like the sun, moon, and winds play a role in shaping the dynamics of ocean water.

The primary movements of ocean waters can be categorized into three major types:

  • Wave Motion
  • Tidal Movements
  • Ocean Currents

Waves and ocean currents signify horizontal shifts in ocean water, whereas tides represent a vertical motion within the ocean.

Waves

  • Waves: Oscillatory movements causing the rise and fall of water’s surface.
  • Horizontal movements of ocean water.
  • Energy, not water itself, moves across the ocean surface, sourced from the wind.
  • Size and strength of waves depend on factors like wind speed, duration, and fetch (the distance over which the wind blows).
  • In a wave, the movement of each water particle is circular.
  • Two main parts of a wave: crest (raised part) and trough (low point).

Tides

  • Periodical rise and fall of sea levels, occurring once or twice a day.
  • Caused by combined gravitational forces of the sun, moon, and the Earth’s rotation.
  • Vertical movements of water, distinct from meteorological effects like winds and atmospheric pressure changes.
  • Note: Meteorologically induced water movements are termed surges and lack regularity compared to tides.
  • Moon’s gravitational pull, particularly effective on Earth, is a primary factor in tidal occurrences.
  • Additional forces include the sun’s gravitational pull and centrifugal force due to the Earth’s rotation.
  • The Bay of Fundi in Canada experiences the world’s highest tides.
  • Tidal movements channeled between islands or into bays and estuaries are termed Tidal Currents.
  • Regular interval between two high or low tides is 12 hours and 25 minutes.

Flow Tide and Ebb Tide

Flow Tide (Flood Tide):

  • A rising tide or incoming tide leading to a high tide.
  • The duration between a low tide and a high tide (i.e., the rising time).

Ebb Tide:

  • The receding or outgoing tide.
  • The duration between high tide and low tide when water flows away from the shore.

Types of Tides

A. Tides based on Frequency:

  • Semi-diurnal Tide: Most common tidal pattern with two high tides and two low tides daily.
  • Diurnal Tides: Only one high tide and one low tide each day.
  • Mixed Tide: Tides with variations in height, often observed along the west coast of North America.

B. Tides based on Sun, Moon, and Earth’s Positions:

  • Spring Tides: Occur when the sun, moon, and earth align, resulting in higher-than-normal tide heights. These happen twice a month, during the full moon (Poornima) and the new moon (Amavasya).
  • Neap Tides: Approximately seven days after a spring tide, the sun and moon form a right angle concerning the earth, leading to counteracting gravitational forces. Tides during this period are lower than normal, known as neap tides. They occur twice a month, during the first quarter moon and the last quarter moon.

Magnitude of Tides

Perigee:

  • The point in the moon’s orbit closest to Earth.
  • Period characterized by unusually high and low tides.

Apogee:

  • The point in the moon’s orbit farthest from Earth.
  • Tidal ranges significantly less than average during this period.

Perihelion:

  • Earth’s position closest to the sun (around January 3rd).
  • Occurrence marked by unusual high and low tides.

Aphelion:

  • Earth’s position farthest from the sun (around July 4th).
  • Tidal ranges considerably less than average during this period.

Tidal Bore

When a wave or waves of water, generated by the leading edge of the incoming tide, travel up a river or narrow bay against the direction of the river or bay’s current, it is termed a tidal bore. Indian rivers such as the Ganges, Brahmaputra, Indus, etc., showcase instances of tidal bores.

Inter-Tidal Zone


The intertidal zone, also known as the foreshore and seashore, occasionally referred to as the littoral zone, encompasses the area above water at low tide and underwater at high tide (i.e., the region between the tide marks).

Effects of tides

Tides serve as a crucial connection between the port and the open sea. Notably, several major ports worldwide, such as London port on the River Thames and Kolkata port on the River Hugli, are situated on rivers away from the sea coast.

The tidal current plays a significant role in clearing away river sediments and impeding the growth of the delta. This process contributes to an increase in water depth, facilitating the safe navigation of ships to the ports. Moreover, tidal energy serves as a potential source for electricity production.

Ocean Currents

  • Ocean currents are horizontal flows of water covering substantial distances.
  • Resemble rivers within the ocean.
  • Formation influenced by factors like winds, density differences (temperature and salinity variations), gravity, and events such as earthquakes.
  • The direction of ocean current movement is primarily influenced by the rotation of the Earth.
  • In the northern hemisphere, most ocean currents move clockwise due to the Coriolis force.
  • In the southern hemisphere, ocean currents move anti-clockwise under the influence of the Coriolis force.

Gyre, Drift, and Stream

Any extensive system of rotating ocean currents, particularly associated with significant wind movements, is termed a Gyre—a phenomenon induced by the Coriolis force.

  • When ocean water advances under the influence of prevailing wind, it is referred to as Drift. The term “drift” is also utilized to denote the speed of an ocean current, measured in knots (e.g., North Atlantic Drift).
  • A large mass of ocean water moving in a defined path, akin to a sizable river on land, is identified as a Stream. Streams typically exhibit higher speeds compared to drifts (e.g., Gulf Stream).
  • Ocean eddies represent swirling, rotating water masses occurring within ocean currents. These eddies can significantly impact local oceanic and atmospheric conditions.

Types of Ocean Currents

Warm Ocean Currents:

  • Flow from equatorial regions toward poles, possessing a higher surface temperature, known as warm currents.
  • Transport warm waters to cold regions.
  • Typically observed on the east coast of continents in lower and middle latitudes in both hemispheres.
  • In the northern hemisphere, they are also present on the west coast of continents in higher latitudes (e.g., Alaska and Norwegian Currents).

Cold Ocean Currents:

  • Flow from polar regions toward the equator, characterized by a lower surface temperature, termed cold currents.
  • Bring cold waters into warm areas.
  • Commonly found on the west coast of continents in low and middle latitudes in both hemispheres.
  • In the northern hemisphere, they are also found on the east coast in higher latitudes (e.g., Labrador, East Greenland, and Oyashio currents).

Ocean Currents Classification:

  • Surface Currents: Constitute about 10% of ocean water, occupying the upper 400m in the ocean or the Ekman Layer. This layer of ocean water moves due to wind stress, known as Ekman Transport.
  • Deep Water Currents: Comprise about 90% of ocean water, moving around the ocean basin due to variations in density and gravity.

Factors influencing the origin and nature of ocean currents

Difference in Density:

  • Seawater density varies based on temperature and salinity.
  • Density increases with higher salinity and decreases with lower salinity.
  • Density decreases with higher temperature and increases with lower temperature.
  • Variations in temperature and salinity cause water to move, known as Thermohaline Circulation.

Thermohaline Circulation:

  • In polar regions, lower temperatures result in high-density water sinking to the bottom, moving towards less dense middle and lower latitudes (equatorial regions).
  • Upwelling occurs in warm regions, pushing less dense, warm water towards the poles.
  • In equatorial regions, high temperatures cause water expansion, elevating water levels above middle and upper latitudes. This gradient leads to water movement from equatorial to middle and upper latitudes.

The Earth’s Rotation:

  • Earth’s rotation induces the Coriolis force, deflecting air to the right in the northern hemisphere and to the left in the southern hemisphere.
  • Ocean water is also influenced by the Coriolis force, adhering to Ferrel’s Law.
  • In the northern hemisphere, ocean currents move in a clockwise (rightward) direction, while in the southern hemisphere, they move in an anti-clockwise (leftward) direction. (Note: In the Indian Ocean, due to the impact of the Asian monsoon, northern hemisphere currents may not consistently follow this pattern.)

The Winds:

  • Winds such as trade winds and westerlies propel ocean water in a steady flow before them.
  • Changes in the wind direction lead to corresponding changes in the current direction.

Conclusion

  • A vital aspect of Earth’s climate system, influences weather patterns, marine ecosystems, and global climate regulation.
  • Continuous scientific study and monitoring to comprehend and assess the impacts of these processes on our planet.

FAQs for Waves, Ocean Currents and Tides

Q1: Which forces influence the movement of ocean water?

A1: The movement of ocean water is influenced by various forces, including wind, temperature, salinity, the Earth’s rotation, and geographical features of ocean basins. These forces collectively drive phenomena like ocean currents, tides, and waves.

Q2: What is the movement of ocean water?

A2: The movement of ocean water refers to the dynamic and complex processes wherein water bodies exhibit horizontal and vertical motions. Ocean currents, tides, and waves are primary manifestations of ocean water movement, driven by factors such as wind, temperature, salinity, the Earth’s rotation, and the geography of ocean basins.

Q3: Which of the ocean movements is useful to the fisherman?

A3: Ocean currents, particularly those carrying nutrient-rich waters, are beneficial to fishermen. These currents enhance marine productivity, attracting various marine life and creating favorable conditions for fishing. Fishermen often leverage these ocean movements to locate and catch fish more effectively.

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