Exploring the Oceans
The oceans cover over 70% of Earth’s surface, yet we know more about the moon than we do about the deep sea. Exploring oceans helps us understand not just marine life, but also climate systems, resource potential, and plate tectonics. From underwater volcanoes to deep trenches, the oceans have complex landscapes shaped by millions of years of geological activity.
Relief of the Ocean Floor
Though it may look flat from above, the ocean floor has a variety of landforms just like continents. These include:
1. Continental Shelf
- The shallow, submerged margin of the continent, extending from the coastline.
- Rich in marine life, oil, and gas resources.
- Example: The North Sea shelf near Europe is important for oil drilling.
2. Continental Slope
- A steep descent beyond the shelf leading to deeper parts of the ocean.
- This marks the true edge of the continent.
3. Deep Sea Plain (Abyssal Plain)
- Flat, featureless, and deep regions of the ocean floor.
- Covered with fine sediments.
- Example: The Atlantic abyssal plains.
4. Ocean Deeps (Trenches)
- The deepest parts of the ocean, often near subduction zones.
- Example: Mariana Trench (over 11,000 m deep) in the Pacific Ocean.
Deposits of the Ocean Floor
Over time, materials like shells, plankton skeletons, volcanic ash, and sediments settle on the ocean floor.
1. Muds
- Transported by rivers and deposited into oceans.
- Rich in organic matter and clay particles.
2. Oozes
- Formed from the remains of microscopic marine organisms.
- Two types:
- Calcareous ooze – made of calcium carbonate (found in warm regions)
- Siliceous ooze – made of silica (found in colder regions)
3. Clays
- Very fine particles carried far by currents and winds.
- Found in deep ocean basins.
- Red clays are common in the Pacific.
Salinity of Oceans
Salinity is the amount of salt dissolved in ocean water, usually measured in parts per thousand (ppt). The average ocean salinity is 35 ppt.
Influencing factors:
- Evaporation (increases salinity)
- Precipitation and river inflow (reduces salinity)
- Freezing of sea water (leaves behind salt, increasing salinity)
Examples:
- High salinity: Red Sea, due to high evaporation and little river input
- Low salinity: Baltic Sea, due to fresh river inflow and less evaporation
Temperature of Ocean Water
Ocean temperatures vary with latitude, depth, and currents.
- Surface temperatures are highest at the equator (around 25–30°C) and lowest near the poles (around 0°C or below).
- Depth: As you go deeper, sunlight fades and the water gets colder.
There’s a zone called the thermocline where temperature drops rapidly with depth.
Movements of Ocean Currents
Ocean currents are large masses of water moving like rivers within the oceans.
Factors that drive ocean currents:
1. Planetary Winds
- Trade winds and westerlies push surface waters, creating currents.
- Example: North-East Trade Winds drive the North Equatorial Current.
2. Temperature and Salinity
- Warm water is lighter and rises, cold salty water is denser and sinks, creating movement.
3. Earth’s Rotation (Coriolis Effect)
- Causes currents to deflect right in the Northern Hemisphere and left in the Southern Hemisphere.
Circulation of the Atlantic Ocean
- North Equatorial Current flows westward.
- Near the Caribbean, it splits into the Gulf Stream (warm, northward) and the Florida Current.
- Gulf Stream warms Western Europe and merges with North Atlantic Drift.
- Returns south via the Canary Current (cold).
- In the south: Brazil Current (warm), Benguela Current (cold).
Key Feature: Strong northward heat transfer due to Gulf Stream.
Circulation of the Pacific Ocean
- Largest and deepest ocean with complex current systems.
- North Equatorial Current and South Equatorial Current move westward.
- Deflected north as the Kuroshio (Japan) Current (warm) and south as East Australia Current.
- Oyashio Current (cold) moves south from the Arctic and meets the Kuroshio near Japan.
- Peru (Humboldt) Current is cold and moves northward along the South American coast.
Note: Pacific currents are influenced by El Niño–La Niña cycles.
Circulation of the Indian Ocean
The Indian Ocean is unique because it is landlocked to the north, and currents change with the monsoons.
- Summer Monsoon (June–September):
- Winds blow from the southwest, causing the Southwest Monsoon Drift (northward flow).
- Winter Monsoon (October–March):
- Winds blow from the northeast, creating the Northeast Monsoon Drift (southwestward flow).
- Agulhas Current: Warm, flows along southeast Africa.
- West Australian Current: Cold, flows northward along Australia’s west coast.
