Oceans and Life

Chapter at a glance

The first Geography chapter of Part 2 explores human–ocean connections: the landforms of the ocean floor, how waves, tides and currents move, early warning systems for cyclones and tsunamis, marine resources and the Blue Economy, and the maritime zones and laws that govern the seas.

In Indian culture the ocean, Samudra, is seen as powerful and sacred and appears in many stories and rituals.

Submarine (ocean) relief

Like land, the ocean floor has mountains, valleys, plains and trenches. The Mariana Trench (Pacific) is the deepest place on Earth; the Mid-Ocean Ridge is the world’s longest mountain range; Mauna Kea (Hawai‘i), measured from its base, is taller than Mount Everest.

Bathymetry is the study and mapping of underwater topography.

Movement of ocean water

Waves

• The alternate rise and fall of the sea surface, mainly caused by wind; waves carry energy over long distances.
• Parts: crest (high point), trough (low point); wavelength is the horizontal distance between two crests or troughs.
• Waves are “coastal architects”. Erosion (hydraulic action, abrasion) turns a headland into crack → cave → arch → stack → stump. Deposition forms beaches.
• Tsunamis are giant waves caused mainly by undersea earthquakes; their run-up height can reach 30 m or more.

Tides

The rhythmic rise and fall of sea level, twice a day in most places: high tide (flood tide) and low tide (ebb tide).

Why tides matter:

• Navigation: high tide lets ships enter harbours. Tidal ranges in some ports are 4–5 m; the Gulf of Khambhat has about 12 m. Large crude carriers (VLCCs) wait for high tide to cross the shallow Singapore Strait.
• Tidal currents can reach 5–6 knots (about 9–11 km/h).
• Fishing: fish come closer to shore at high tide.
• Tidal energy: India’s coastline is 11,098.81 km; the main tidal energy sites are the Gulf of Kutch, Gulf of Khambhat and the Sundarbans.
• The Bhadkeshwar Mahadev Temple, Dwarka (Gujarat) can be reached only at low tide.

Ocean currents

Continuous streams of water flowing in definite directions, caused by winds, Earth’s rotation (Coriolis force), differences in temperature and salinity, and the shape of continents and basins. The Coriolis force deflects moving objects to the right in the Northern Hemisphere and to the left in the Southern.

• Warm currents (shown red) flow from warm regions; cold currents (shown blue) from cold regions.
• Gulf Stream (warm, from the Gulf of Mexico) keeps Norway’s waters ice-free at 60°–70° N.
• Labrador Current (cold, east coast of Canada) brings sea ice and icebergs to lower latitudes.
• Where warm and cold currents meet, nutrient-rich water creates fishing grounds.

Cyclones, tsunamis and early warning

Cyclones are large rotating storms caused by atmospheric disturbances over warm ocean water. Early Warning Systems detect hazards, predict them and issue timely warnings so people can evacuate.

• NCRMP (National Cyclone Risk Mitigation Project): cyclone shelters, stronger warning systems, better emergency response, and a Decision Support System for disaster authorities.
• SSEWS (Storm Surge Early Warning System) by INCOIS with IMD forecasts storm surges and coastal flooding.
• GEMINI (GAGAN-Enabled Mariner’s Instrument for Navigation and Information): a handheld device that receives GAGAN satellite data and sends it by Bluetooth to fishermen’s phones. Alerts come in nine regional languages, currently up to 50 nautical miles; an upgrade aims at two-way communication up to 300 nautical miles. Supported under PM Matsya Sampada Yojana.
• Naming cyclones: North Indian Ocean cyclones get names in order from a list of 169 names from 13 countries, e.g. Biparjoy (2023), Remal (2024).

Technology is not enough: public awareness and training help people respond correctly to warnings.

Marine resources and the Blue Economy

Materials and features of the ocean with intrinsic or economic value. Two groups: marine living resources (fish, seafood, biodiversity, coral reefs) and marine non-living resources (oil, natural gas, minerals, sand, gravel, tidal and wave “blue energy”).

• Food: fish is a major source of protein; fishing and aquaculture support livelihoods.
• Trade and tourism: about 90% of global trade by volume goes by sea.
• Culture: the śaṅkha (conch) and kapardikā (cowrie, once used as money) are linked to the Samudra Manthana story.

Maritime zones (UNCLOS)

1 nautical mile = exactly 1,852 m (about 6,076 ft), equal to one minute of latitude. Zones are measured from the baseline along the coast.

Innocent passage: foreign ships may cross territorial waters if they do not threaten peace, order or security, moving continuously (stopping only in emergencies). No fishing or military activity.

High-seas problems: overfishing, illegal fishing, resource conflicts and weak enforcement.

International maritime rules

• UNCLOS (UN Convention on the Law of the Sea) defines the zones and helps settle disputes.
• COLREGs: the “rules of the road at sea”, covering lookout, passing sides, give-way and stand-on vessels, safe speed, lights and sound signals.
• MARPOL: prevents pollution from ships.

Without these rules the oceans would be chaotic, with more pollution, collisions and disputes.

Questions to practise

1. How do ocean-floor features affect fishing, transport and underwater exploration?
2. Explain the difference between spring and neap tides with a diagram.
3. Describe the importance of marine resources for India.
4. A foreign ship sails through India’s territorial sea. Which principle allows this, and with what conditions? Innocent passage: continuous, peaceful movement, no fishing or military activity.
5. What rights does a country have in its EEZ? Special rights to explore and use resources (fish, oil, gas) up to 200 nautical miles; other ships may still pass.
6. Map work: mark five coastal states that need tsunami warnings, plus the Gulf of Kutch, Gulf of Khambhat and the Sundarbans.

Key takeaways

• Submarine relief (shelf, slope, plains, ridges, trenches, seamounts) shapes marine life, resources and exploration.
• Waves, tides and currents affect ecosystems, climate, fishing and navigation.
• Maritime zones: territorial waters, contiguous zone, EEZ, high seas, defined by UNCLOS.
• Sustainable use and cooperation (Blue Economy, SDG 14) protect the oceans for future generations.