Ocean Waves, Currents & Tides

1. Ocean Waves

Waves are oscillatory movements in water, manifested by an alternating rise (crest) and fall (trough) of the sea surface. Water particles travel in a circular motion rather than moving forward horizontally; it is the energy that moves across the ocean surface.

• Mechanism: Formed primarily by the friction of wind blowing over the water's surface. The size of the wave depends on wind speed, duration, and the "fetch" (the uninterrupted distance over which the wind blows).
• Breaking Waves: As waves approach the shallow shore, friction with the bottom slows the lower part of the wave, causing the crest to pitch forward and break (surf).

2. Ocean Currents

Ocean currents are continuous, directed, large-scale movements of seawater, acting like massive rivers within the ocean. They dramatically influence global climate, shipping, and marine ecosystems.

Causes and Modifying Factors

1. Primary Forces (Initiation):
   • Heating by Solar Energy: Causes water to expand and rise at the equator, creating a very gentle slope towards the poles, driving surface water poleward.
   • Wind: Planetary winds (Trades, Westerlies) drag surface water along (drifts).
   • Gravity: Pulls water down the slope.
   • Coriolis Force: Deflects currents to the right in the NH and left in the SH, creating massive circular patterns called Gyres.
2. Secondary Forces (Modification):
   • Differences in water density (driven by temperature and salinity variations) fuel deep-ocean thermohaline circulation over thousands of years.

Types of Currents

• Warm Currents: Originate near the equator and flow towards poles (e.g., Gulf Stream, Kuroshio). They warm coastal climates and bring rain.
• Cold Currents: Originate in polar/high altitudes and flow towards the equator (e.g., Peru/Humboldt, California, Benguela). They lead to extreme desiccation, contributing to the formation of hot coastal deserts (Atacama, Namib) on the western margins of continents.

Convergence Zones

Where cold and warm currents meet (e.g., mixing of Gulf Stream and Labrador current near Newfoundland), dense fogs occur, making navigation hazardous. However, these zones promote massive upwelling of nutrients, creating the world's richest fishing grounds.

3. Tides

Tides are the regular, periodic rise and fall of the sea level occurring mostly twice a day.

• Cause: The gravitational pull exerted mostly by the Moon (being closer) and partly by the Sun, combined with the Earth's centrifugal force.
• Mechanism: The moon pulls water towards it creating a bulge on the near side. Simultaneously, centrifugal force causes an equal bulge on the exact opposite side of the Earth (high tides).

Types of Tides based on Lunar Phase

1. Spring Tides (High amplitude): Occur during the Full Moon and New Moon when the Sun, Earth, and Moon align (Syzygy). The combined gravitational pull produces exceptionally high and low tides.
2. Neap Tides (Low amplitude): Occur during the first and third quarter moons when the Sun and Moon are at right angles (Quadrature). Their gravitational pulls partially cancel each other out, resulting in lower-than-usual high tides.

Importance of Tides

• Prevents the freezing of water in high-latitude ports (e.g., London).
• Clears river estuaries of silt, aiding navigation (Hooghly river).
• Tremendous potential for generating tidal electricity (e.g., Gulf of Khambhat).