🌊 Chapter 14 – Ocean Water Movement
🌐 Introduction
The water of the ocean never remains calm; it is always in motion 🌊.
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.
🌊 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).
🌊 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.
🌊 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. ⚡
🌐 Ocean Currents
The continuous flow of water from one part of the ocean to another in a specific direction is called an ocean current. 🌊
⚡ Causes of Origin of Ocean Currents
Internal Oceanic Factors:
- Variation of temperature 🌡️
- Differences in sea level 🌊
- Density variations in water
External Factors:
- Air pressure and wind direction 🌬️
- Evaporation and precipitation ☔
Factors influencing direction and shape:
- Coastline direction & size 🏝️
- Shape of the ocean floor ⬇️
- Seasonal changes 🌦️
- Prevailing persistent winds 🌬️
⚡ 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 🌞
- 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. 🌡️
- Cause fog, humidity, and mild climates 🌫️
- Increase in plankton where cold and warm currents meet → rich fishing areas 🐟
⚡ 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.
🌊 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
🌞 Agulhas Warm Current
- In the south of Madagascar, the Mozambique Current and Madagascar Current join.
- This combined current is called the Agulhas Warm Current 🌡️
