๐ Chapter 14 – Ocean Water Movement
๐ Introduction
The water of the ocean never remains calm; it is always in motion ๐.
This continuous movement leads to the formation of waves, currents, and tides. Human life is affected by these in many ways. In this chapter, we will explore them in detail.
๐ Sea Waves
Sea waves are movements of water where water moves up and down at one place but does not travel horizontally; only energy flows from one place to another.
⚡ Characteristics of Waves
- Wave Crest & Trough: The highest point is the crest and the lowest point is the trough.
- Wave Height: Vertical distance between crest and trough.
- Wave Amplitude: Half of the wave height.
- Wave Period: Time interval between two successive crests or troughs passing a fixed point.
- Wave Length: Horizontal distance between two consecutive crests or troughs.
- Wave Speed: Rate at which a wave moves through water (measured in knots).
๐ Tide & Ebb
The sea level does not remain constant; it rises and falls twice a day.
- Tide (High Tide): Rise of sea level.
- Ebb (Low Tide): Fall of sea level.
Special Tides:
- On Purnima (Full Moon) and Amavasya (New Moon), tide height is 20% higher than normal.
⏱ Types of Tides
Based on Frequency:
- Semi-diurnal Tide: Two high and two low tides daily.
- Diurnal Tide: One high and one low tide daily.
- Mixed Tide: Combination of both types.
Based on Height:
- Spring Tide: High or large tide.
- Neap Tide: Low or small tide.
๐ Importance of Tides
- Helps ships enter rivers easily (e.g., Hooghly River, Kolkata).
- Fishermen use tides to go and return from the sea.
- Helps clean coastal pollution.
- Brings valuable items like conch shells, oysters, snails to the shore.
- Keeps sea water in motion, preventing freezing in cold regions.
- Tidal energy is used for electricity generation in many areas. ⚡
๐ Ocean Currents
The continuous flow of water from one part of the ocean to another in a specific direction is called an ocean current. ๐
⚡ Causes of Origin of Ocean Currents
Internal Oceanic Factors:
- Variation of temperature ๐ก️
- Differences in sea level ๐
- Density variations in water
External Factors:
- Air pressure and wind direction ๐ฌ️
- Evaporation and precipitation ☔
Factors influencing direction and shape:
- Coastline direction & size ๐️
- Shape of the ocean floor ⬇️
- Seasonal changes ๐ฆ️
- Prevailing persistent winds ๐ฌ️
⚡ Classification of Ocean Currents
Based on Depth:
- Surface Currents (Upper Currents): Top 10% of ocean water, found up to 400 m depth.
- Deep Currents: Form 90% of ocean water, flow due to density differences and gravity.
Based on Temperature:
- Warm Currents: Flow from warm areas to cold areas (equator → poles).
- Increase temperature of the regions they pass.
- Example: Gulf Stream ๐
- Cold Currents: Flow from cold areas to warm areas (poles → equator).
- Decrease temperature of the regions they pass.
- Example: Labrador Current ❄️
⚡ Effects of Ocean Currents
- Climate influence: Warm currents raise, cold currents lower land temperature. ๐ก️
- Cause fog, humidity, and mild climates ๐ซ️
- Increase in plankton where cold and warm currents meet → rich fishing areas ๐
⚡ Tidal Current
When a bay is connected to the open ocean by a narrow mouth, water enters during tide and exits during ebb.
- This movement of water in and out of the bay is called a tidal current.
๐ Sargasso Sea
- Calm water area between Gulf Stream, Canary, and North Equatorial Currents in the North Atlantic.
- Floating sea grass called Sargassum gives its name → Sargasso Sea.
- Area: ~11,000 sq. km
⚡ Difference Between Waves & Currents
๐ Agulhas Warm Current
- In the south of Madagascar, the Mozambique Current and Madagascar Current join.
- This combined current is called the Agulhas Warm Current ๐ก️
