Oceans and Life

Class 09 Social Science

Oceans cover most of our planet and conceal many secrets beneath their waters. Just as land has mountains, valleys, and plains, the ocean floor, too, has several landforms, together known as submarine relief or ocean relief.

These include underwater mountains, valleys, plateaus, and trenches. The Mariana Trench in the Pacific Ocean is the deepest place on Earth, while the Mid-Ocean Ridge is the world’s longest mountain range, hidden beneath the ocean. Some underwater mountains like Mauna Kea (Hawai‘i) are even taller than Mount Everest.

Movement of Ocean Water

The water in the oceans is constantly in motion. Waves, tides, and currents are not merely movements of ocean water; they help shape the Earth’s surface, support marine life, aid fishing and travel, and even influence climate.

Waves

When the surface of the ocean rises and falls alternately, it is called a wave. Waves are primarily caused by winds blowing across the water. They carry energy across the oceans over long distances.

Waves are often called coastal architects as they shape the shoreline through erosion and sediment transport. In addition to erosional landforms, waves also form depositional features such as beaches.

During storms, strong winds can generate huge waves that may cause significant damage along coastlines. The giant waves majorly caused by underwater earthquakes are called tsunamis, which can be extremely destructive. On reaching the shore, tsunamis may attain a maximum vertical height above sea level, known as the run-up height, of up to 30 metres, or even more in extreme cases.

Tides

Tides are the rhythmic rise and fall of ocean water that occur twice a day in most parts of the world. When the water rises to its highest level and covers much of the shore, it is called high tide (flood tide). When the water falls to its lowest level and moves away from the shore, it is called low tide (ebb tide).

High tides are important for navigation because they raise the water level near the shore, allowing ships to enter harbours more easily. In ports and coastal areas, tidal information is essential, as tidal ranges in some ports can reach 4–5 metres. The Gulf of Khambhat has one of the highest tidal ranges, at about 12 metres. Before a ship berths at a port, it must check both the water depth and the tidal range to ensure safe docking, especially during low tide.

Some sea channels, such as the Singapore Strait, contain shallow areas. Hence, ships such as Very Large Crude Carriers (VLCCs) passing through these regions often wait for hours to transit only during high tide to ensure sufficient water depth and avoid running aground.

Tidal changes also generate strong currents because large volumes of water flow in and out of coastal areas. These tidal currents can reach speeds of 5-6 knots (about 9-11 km/h).

Ocean Currents

Ocean currents are continuous streams of water that flow across the ocean surface in definite directions. They are caused by factors, such as winds, the Earth’s rotation (Coriolis force), differences in temperature and salinity, and the shape of continents and ocean basins.

Ocean currents may be warm or cold depending on the direction from which the water flows. Currents flowing from warmer regions are called warm currents, while those flowing from colder regions are called cold currents. On maps, warm currents are usually shown in red and cold currents in blue.

The Gulf Stream, a warm current originating in the Gulf of Mexico in the Atlantic Ocean, flows towards Norway and keeps its waters relatively warm. As a result, sea ice does not form easily in the Norwegian region despite its high latitude (60°-70°). In contrast, the Labrador Current, a cold current flowing along the east coast of Canada, carries freezing water and supports the formation of sea ice and icebergs even at lower latitudes.

Cyclones and Tsunamis

Oceans and seas can give rise to sudden natural hazards such as cyclones, which are large rotating storms, and tsunamis, which are giant waves caused by earthquakes. To protect people from such dangers, scientists have developed Early Warning Systems that work like giant alarm systems for coastal areas. To reduce risks, people, communities, and governments must act in advance. Early Warning Systems help detect cyclones and tsunamis, predict disasters, and issue timely warnings so that people can evacuate and stay safe.

India has several Cyclone Warning Services and Marine Weather Services that monitor storms along both the eastern and western coasts. For early warning systems to be effective, they must function continuously. India uses advanced technologies to predict cyclones at an early stage, which has significantly reduced the loss of human and animal lives.

The Government of India has launched the National Cyclone Risk Mitigation Project (NCRMP) to build cyclone shelters, strengthen warning systems, and improve emergency response mechanisms. The project focuses on cyclone-prone States and Union Territories and includes a Decision Support System (DSS) for disaster management authorities. The Indian National Centre for Ocean Information Services (INCOIS), in collaboration with the India Meteorological Department (IMD), has also established the Storm Surge Early Warning System (SSEWS) for the Indian coasts. Its main objective is to protect coastal communities by forecasting cyclone-induced storm surges and the extent of coastal inundation.