Ocean Currents, Tides, Coral Reefs, Continental Shelf & EEZ

Oceanography questions appear regularly in Kerala PSC Geography sections. Focus areas include identification of warm vs. cold currents, tide types, and EEZ limits.

1. Ocean Currents — Overview

Feature	Detail
Definition	Large-scale continuous movement of ocean water in a definite direction
Caused by	Wind, temperature differences, salinity differences, Earth’s rotation (Coriolis effect), shape of coastlines
Coriolis effect	Deflects currents to the right in Northern Hemisphere, to the left in Southern Hemisphere
Warm currents	Flow from equator towards poles; raise temperature of coast
Cold currents	Flow from poles towards equator; lower temperature of coast

2. Major Warm Currents

Current	Ocean	Region
Gulf Stream	Atlantic	East coast of North America towards Europe
North Atlantic Drift	Atlantic	Extension of Gulf Stream towards NW Europe
Brazilian Current	Atlantic	East coast of South America
Mozambique Current	Indian	East coast of Africa
Agulhas Current	Indian	SE coast of Africa
Kuroshio (Japan Current)	Pacific	East coast of Japan
North Equatorial Current	All three oceans	Flows westward near equator
South Equatorial Current	All three oceans	Flows westward near equator
Alaska Current	Pacific	Southern coast of Alaska

3. Major Cold Currents

Current	Ocean	Region
Labrador Current	Atlantic	East coast of Canada
Canary Current	Atlantic	NW coast of Africa
Benguela Current	Atlantic	SW coast of Africa
Falkland Current	Atlantic	East coast of southern South America
Oyashio (Kamchatka Current)	Pacific	East coast of Russia/Japan
California Current	Pacific	West coast of North America
Peru (Humboldt) Current	Pacific	West coast of South America
West Wind Drift (Antarctic Circumpolar)	Southern Ocean	Circles Antarctica (largest ocean current by volume)

4. Effects of Ocean Currents

Effect	Example
Warming of coasts	Gulf Stream keeps Western Europe warm despite high latitude
Cooling of coasts	Peru Current keeps Peru/Chile coast cool and dry
Fog formation	Warm and cold current meeting — Grand Banks (Labrador + Gulf Stream)
Rich fishing grounds	Where warm and cold currents meet — Grand Banks, coast of Japan
Desert formation	Cold currents along west coasts — Atacama (Peru Current), Namib (Benguela Current)
El Nino	Warming of eastern Pacific; weakening of Peru Current; global weather disruption
La Nina	Opposite of El Nino; strengthening of cold conditions in eastern Pacific

5. Tides

Concept	Detail
Definition	Periodic rise and fall of sea level caused by gravitational pull of Moon and Sun
Primary cause	Moon’s gravitational pull (Moon is closer, so stronger tidal effect than Sun)
Sun’s tidal force	About 46% of Moon’s tidal force
Tidal cycle	Approximately 12 hours 25 minutes between successive high tides
High tide	Water level rises to maximum
Low tide	Water level falls to minimum

Types of Tides

Type	Cause	Occurrence
Spring tide	Sun, Moon, and Earth in a line (syzygy)	Full Moon and New Moon days; highest tidal range
Neap tide	Sun and Moon at right angles to Earth (quadrature)	First and Third Quarter Moon; lowest tidal range
Perigean tide	Moon closest to Earth (perigee)	Extra-high spring tides
Apogean tide	Moon farthest from Earth (apogee)	Lower than normal spring tides

Importance of Tides

• Navigation: ships enter/leave harbours during high tide
• Fishing: tidal zones rich in marine life
• Tidal energy: potential renewable energy source (e.g., Gulf of Kutch in India)
• Cleaning: tides flush out river mouths and harbours

6. Coral Reefs

Feature	Detail
Formed by	Coral polyps (tiny marine organisms) that secrete calcium carbonate
Require	Warm water (20-30 degrees C), shallow depth (less than 50m), clear saline water, adequate sunlight
Cannot grow in	Fresh water, deep water, muddy/polluted water, cold water

Types of Coral Reefs

Type	Description	Example
Fringing reef	Attached to shore; no lagoon or narrow lagoon	Reefs along coast of South Florida
Barrier reef	Separated from coast by wide, deep lagoon	Great Barrier Reef (Australia) — largest in the world
Atoll	Ring-shaped reef enclosing a lagoon; no central island	Lakshadweep Islands, Maldives

Coral Reefs in India

Location	Type
Gulf of Kutch	Fringing reef
Gulf of Mannar	Fringing reef
Andaman and Nicobar Islands	Fringing reef
Lakshadweep Islands	Atolls
Palk Bay	Patchy reef

7. Continental Shelf, Slope, and Ocean Floor

Zone	Depth	Description
Continental Shelf	0 to about 200 m	Gentle slope; extension of continent underwater; richest fishing and mineral zone
Continental Slope	200 m to about 3,000 m	Steep descent from shelf to ocean floor
Continental Rise	3,000 m to about 5,000 m	Gradual slope at base of continental slope
Abyssal Plain	3,000 m to 6,000 m	Flat, deep ocean floor
Ocean Trenches	Beyond 6,000 m	Deepest parts; Mariana Trench = 11,034 m (deepest point — Challenger Deep)
Mid-Ocean Ridges	Variable	Underwater mountain chains; Mid-Atlantic Ridge is longest

8. Exclusive Economic Zone (EEZ)

Concept	Detail
Defined by	UNCLOS (United Nations Convention on the Law of the Sea), 1982
Territorial Sea	Up to 12 nautical miles from baseline
Contiguous Zone	12 to 24 nautical miles
EEZ	Up to 200 nautical miles from baseline
Rights in EEZ	Sovereign rights over natural resources (fishing, mining, oil/gas); not full sovereignty
High Seas	Beyond 200 nautical miles; open to all nations
Continental Shelf claim	Can extend up to 350 nautical miles if geological criteria met
India’s EEZ	Approximately 2.02 million sq km

9. PSC Quick Revision — One-Liners

• Gulf Stream warms Western Europe; Labrador Current cools eastern Canada
• Warm and cold currents meeting = fog and rich fishing grounds
• Spring tides occur during Full Moon and New Moon
• Neap tides occur during Quarter Moon phases
• Great Barrier Reef (Australia) is the largest coral reef system
• Lakshadweep Islands are coral atolls
• Mariana Trench (Challenger Deep) = deepest point in the ocean (11,034 m)
• EEZ extends up to 200 nautical miles under UNCLOS
• India’s EEZ is approximately 2.02 million sq km
• Peru (Humboldt) Current is a cold current along South America’s west coast
• El Nino = warming of eastern Pacific Ocean