Movements of Ocean Water Class 11 Geography

Introduction

• Ocean water is constantly changing and dynamic.
• Key physical characteristics include temperature, salinity, and density.
• External forces like the sun, moon, and winds significantly influence water movement.
• Types of Motion:
  1. Horizontal Motion: Includes ocean currents and waves.
  2. Vertical Motion: Refers to tides and water movement in the ocean.

Waves

• Waves represent energy moving across the ocean, not the water itself. Water particles move in small circles as waves pass.
• Wind generates waves by transferring energy to the water, which is then released at shorelines.
• Surface water movement has little effect on stagnant deep ocean water.
• As waves approach the beach, they slow down due to friction with the sea floor.
• Waves break when the water depth is less than half the wavelength.
• The largest waves occur in open oceans and grow larger as they absorb energy from the wind. Most waves are caused by wind pushing against the water. 
• Light breezes (up to two knots) create small ripples that develop into larger waves as wind speed increases, leading to whitecaps in breaking waves.
• Waves can travel thousands of kilometers before reaching the shore, where they break and dissolve as surf.

•  Steep waves are young and often formed by local winds, while slow waves come from far away, maybe even from another hemisphere.
• The tallest waves depend on wind strength, how long the wind blows, and the area it affects.
• Wind pushes the water, while gravity pulls down the wave crests. This causes the water to rise and fall, creating movement.
• The water underneath moves in a circular pattern, rising as the wave approaches and falling as it passes.

Tides

• Tides are the regular rise and fall of sea levels that happen once or twice a day, mainly because of the gravitational pull of the sun and moon. 
• Surges, on the other hand, are caused by weather factors like winds and changes in atmospheric pressure and happen irregularly. Studying tides can be complicated, as they vary greatly in frequency, magnitude, and height.
• The main reason for tides is the moon’s gravitational pull, with the sun playing a smaller role. 
• Centrifugal force helps balance gravity, creating two main tidal bulges: one toward the moon and another on the opposite side. The tide-generating force comes from the difference between these gravitational forces.
• Tidal bulges are taller on wide continental shelves but get lower when they reach mid-ocean islands. The shape of bays and estuaries can make tides stronger, especially in funnel-shaped bays. When tides flow between islands or into estuaries, they create tidal currents.

Tides of Bay of Fundy, Canada

The Bay of Fundy in Nova Scotia, Canada, has the highest tides in the world, with tidal bulges reaching 15 to 16 meters. There are two high tides and two low tides every day, roughly within a 24-hour period.

Types of Tides

Tides based on Frequency

Tides based on the Sun, Moon and the Earth Positions 

Additional Factors Influencing Tides

Tidal Terminology

Importance of Tides

• Tides are influenced by the positions of the Earth, Moon, and Sun, which allows for accurate predictions. 
• Tides can be forecasted well in advance due to the known positions of the Earth, Moon, and Sun.
• Tidal flows are essential for safe navigation, particularly in areas with shallow bars at harbor entrances that can hinder ship access.
• Tides assist in desilting sediments and cleaning polluted waters in river estuaries.
• Tides can be harnessed for electrical power generation. Countries like Canada, France, Russia, and China utilize tidal energy.
• A 3 MW tidal power project is currently underway in Durgaduani in Sunderbans of West Bengal.

Ocean Currents

• Rivers of water flowing within the ocean, following specific paths and directions.
• Ocean currents are driven by two main types of forces:

• The interaction of these forces creates large accumulations of water known as gyres, which form significant circular currents in every ocean basin.

Characteristics of Ocean Currents

• Currents are referred to by their "drift," which indicates the direction of movement.
• Water density affects vertical movement; higher salinity and colder water are denser, causing them to sink, while lighter water rises.
•  Form when cold water at the poles sinks and moves toward the equator.
• Originate from the equator and flow toward the poles, replacing sinking cold water.
• Surface currents are generally stronger, often exceeding 5 knots, while deeper currents are slower, typically less than 0.5 knots.
• Current speed is measured in knots, with stronger currents indicating higher speeds.

Types of Ocean Currents

Major Ocean Currents

• Wind and Coriolis Force: These elements are crucial in shaping major ocean currents.

• Atmospheric Circulation: The oceanic circulation pattern mirrors the Earth's atmospheric circulation.

• Middle Latitude Air Circulation: In the middle latitudes, air circulation is primarily anticyclonic, with this effect being more pronounced in the Southern Hemisphere than in the Northern Hemisphere.

Oceanic Circulation Patterns

• At higher latitudes, the oceanic circulation aligns with the cyclonic wind flow.
• Monsoon winds play a critical role in shaping current movements in affected regions.
• Warm currents from low latitudes tend to veer to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to the Coriolis force.
•  Oceanic circulation transports heat between latitude belts similarly to how the atmosphere does.
• Cold waters from the Arctic and Antarctic regions move toward warmer tropical and equatorial waters.
•  Conversely, warm waters from lower latitudes flow poleward.

Effects of Ocean Currents

• In tropical and subtropical latitudes (excluding regions near the equator), the west coasts are bordered by cool waters
• These areas have relatively low average temperatures with narrow daily and annual temperature ranges, often resulting in fog and generally arid conditions.
• The west coasts of continents in middle and higher latitudes are influenced by warm waters, creating a distinct marine climate.
• This results in cool summers and mild winters, with a narrow annual temperature range.
•  Warm currents flow along the east coasts of continents in tropical and subtropical regions, leading to warm and rainy climates.
• These areas are located on the western edges of subtropical anticyclones.
•  The interaction between warm and cold currents helps replenish oxygen in the water, promoting the growth of plankton, which is vital for fish populations.
•  The best fishing grounds in the world are primarily found in these mixing zones.