Movements of Ocean Water

1. Understand the dynamic nature of ocean waters and their movements.
2. Explore horizontal and vertical motions like currents, waves, and tides.
3. Comprehend the causes and effects of oceanic phenomena such as waves, tides, and currents.
4. Investigate the characteristics, types, and significance of ocean waves and tides.
5. Examine how ocean currents affect global climate and marine life.

Movement of Ocean Water

Ocean water is constantly moving, influenced by various factors like temperature, salinity, density, and external forces such as the sun, moon, and wind. These forces lead to horizontal and vertical movements in water bodies. Horizontal motion pertains to ocean currents and waves, while vertical motion refers to tides.

Ocean currents, which are the continuous flow of vast amounts of water in a defined direction, move water from one location to another. In contrast, waves, though they involve horizontal movement, do not shift the water body itself; rather, wave trains progress across the water surface. Vertical motions occur when water rises and falls, largely influenced by gravitational attraction from the sun and the moon. Additional forms of vertical movement include the upwelling of cold water from deep ocean levels and the sinking of surface water.

Waves

Waves represent the energy moving across the ocean’s surface, not the water itself. Wind energy transfers to the waves, and as waves approach shorelines, they release this energy. The deep ocean water remains largely unaffected by surface waves, which diminish in speed as they approach the shore due to friction with the sea floor. When the water depth becomes less than half the wave’s wavelength, the wave breaks, producing surf along the shore.

Characteristics of Waves:

1. Wave Crest and Trough: The crest is the highest point, and the trough is the lowest point of a wave.
2. Wave Height: The vertical distance from the trough to the crest.
3. Wave Amplitude: One-half of the wave height.
4. Wave Period: The time between two successive wave crests or troughs.
5. Wavelength: The horizontal distance between two successive crests.
6. Wave Speed: The rate at which a wave moves, typically measured in knots.
7. Wave Frequency: The number of waves passing a point in one second.

Waves typically gain size as wind transfers energy to the water. Steep waves are often newly formed by local winds, while slow, steady waves may originate from distant regions, potentially from another hemisphere. The maximum height of a wave depends on the wind strength, duration, and the area over which the wind blows.

Tides

Tides are the periodic rise and fall of sea levels caused mainly by the gravitational pull of the moon and, to a lesser extent, the sun. Meteorological forces, such as wind and atmospheric pressure changes, can also affect tides, known as surges, but these are irregular. Tides can vary significantly based on location, time, and the specific interactions between gravitational forces and other external factors.

Types of Tides:

1. Semi-diurnal Tide: The most common type, with two high and two low tides each day, of roughly equal height.
2. Diurnal Tide: One high and one low tide per day, with consistent heights.
3. Mixed Tide: A variation in height between successive tides, often found along the west coast of North America.

Tides Based on Sun, Moon, and Earth Positions:

• Spring Tides: When the sun, moon, and earth align, causing higher-than-usual tides. These occur during the full moon and new moon.
• Neap Tides: Occur when the sun and moon are at right angles to each other, causing the forces to counteract each other, leading to lower high tides.

During a perigee, when the moon is closest to Earth, tides are particularly high and low. Conversely, during an apogee, when the moon is farthest from Earth, the tidal range is reduced.

Perihelion and aphelion describe Earth’s proximity to the sun. Around January 3rd (perihelion), tidal ranges are higher than average, while on July 4th (aphelion), the range decreases.

Importance of Tides:

Tides, due to their predictability, assist navigators and fishermen in planning their activities. Tidal flows also help in navigation, particularly near shallow bars in harbors. Tidal energy is harnessed in several regions, such as Canada, France, and China, for power generation.

Ocean Currents

Ocean currents behave like rivers within the ocean, moving water in regular paths and directions. These currents are influenced by primary forces that initiate water movement and secondary forces that guide its flow. Key forces include solar heating, wind, gravity, and the Coriolis effect.

1. Solar heating causes water to expand, especially near the equator, resulting in a higher water level and a slight gradient.
2. Wind transfers its energy to water, moving it in the direction of the wind.
3. Gravity pulls water down gradients.
4. The Coriolis effect causes water to move to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, forming large circular gyres in ocean basins.

Characteristics of Ocean Currents:

1. Drift: Currents are described by their drift, with stronger currents near the surface.
2. Density: Ocean water density depends on its salinity and temperature. Higher salinity or colder water is denser and tends to sink, while lighter water rises.

Types of Ocean Currents:

1. Surface Currents: Representing 10% of ocean water, these flow in the upper 400 meters.
2. Deep Water Currents: Making up 90% of the ocean, these move due to density variations.

Currents are also categorized as warm or cold. Warm currents move from equatorial regions towards the poles, while cold currents flow from polar regions towards the equator.

Major Ocean Currents:

Ocean currents follow global wind patterns and are affected by the Coriolis force. The movement of warm water from lower latitudes towards the poles and cold water from polar regions towards the equator is vital for global heat distribution. The interaction between warm and cold currents, particularly in regions like the North Atlantic, influences marine climates and ecosystems.

Important Note: The mixing of warm and cold currents enhances oxygen levels and supports plankton growth, crucial for marine life.

Effects of Ocean Currents

Ocean currents play a significant role in climate regulation. On the west coasts of continents, cold currents create arid conditions, while on the east coasts, warm currents lead to rainy and humid climates. In regions where cold and warm currents meet, the resulting upwelling boosts nutrient levels, leading to rich fishing grounds.

MCQ:

What is the period between high and low tides when the water level falls called?
Answer: Ebb