CUET UG Geography: Physical Geography - Oceanography, Ocean Currents, Tides, Marine Resources

Must-Know

• Ocean currents are continuous flows of water in a definite direction; the Gulf Stream is a warm western boundary current in the North Atlantic.
• The Coriolis effect deflects ocean currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to Earth’s rotation.
• Ekman transport causes net movement of water at 90° to the wind direction in the Northern Hemisphere due to Coriolis and frictional forces.
• The Sverdrup (Sv) is the unit for measuring ocean current volume transport; 1 Sv = 10? m³/s.
• The North Atlantic Drift is an extension of the Gulf Stream that moderates climate in Western Europe.
• Cold currents originate in high latitudes and flow toward the equator, e.g., the Labrador Current flows southward along Canada’s east coast.
• Warm currents originate near the equator and move toward poles, e.g., the Kuroshio Current flows northeastward from the Philippines.
• Upwelling brings cold, nutrient-rich water to the surface, supporting high biological productivity, e.g., along the Peruvian coast due to the Humboldt Current.
• Downwelling occurs when surface water sinks due to convergence or cooling, reducing nutrient availability in surface layers.
• Tides are periodic rise and fall of sea levels caused by gravitational pull of the Moon and Sun and Earth’s rotation.
• The Moon contributes about 68% of tidal force, while the Sun contributes 32%, due to proximity despite smaller mass.
• Spring tides occur during full moon and new moon when Sun, Moon, and Earth are aligned (syzygy), causing higher high tides and lower low tides.
• Neap tides occur during first and third quarter moons when Sun and Moon are at right angles (quadrature), resulting in minimal tidal range.
• Diurnal tide has one high and one low tide per day; common in the Gulf of Mexico.
• Semidiurnal tide has two high and two low tides of nearly equal height each day; observed along the Atlantic coast of the USA.
• Mixed tides show unequal high and low tides daily; typical of the Pacific coast of the USA.
• The Bay of Fundy (Canada) has the highest tidal range in the world—up to 17 meters—due to resonance and funnel-shaped coastline.
• Tidal energy is harnessed using tidal barrages; the Rance Tidal Power Station in France is the first major tidal plant (commissioned 1966).
• Exclusive Economic Zone (EEZ) extends up to 200 nautical miles from a country’s baseline; India declared its EEZ in 1976 under the Territorial Waters, Continental Shelf, EEZ and Maritime Zones Act.
• Continental shelf resources include petroleum, natural gas, and sand/gravel; Mumbai High is India’s largest offshore oil field located on the continental shelf.

Difficulty Level

Intermediate — requires understanding of interlinked physical processes (currents, tides, resource distribution) and specific examples from NCERT, but no complex calculations.

Common CUET Traps

• Trap: Confusing spring tides with seasonal spring; students think they occur only in spring season. Avoid: Spring tides occur twice monthly during new and full moons, regardless of season.
• Trap: Assuming all western boundary currents are warm; some like the Somali Current reverse seasonally. Avoid: The Somali Current flows northward and warm during southwest monsoon but becomes cold due to upwelling.
• Trap: Believing tidal energy is widely used in India. Avoid: India has no operational tidal power plant; projects like in the Gulf of Kutch are in planning or pilot stage—verify from NCERT.

Practice MCQs

1. Which ocean current is responsible for the relatively mild climate of Western Europe despite its high latitude?
   A. Labrador Current
   B. Canary Current
   C. North Atlantic Drift
   D. Benguela Current
   Answer: C
   Explanation: The North Atlantic Drift, a warm extension of the Gulf Stream, transports heat to Western Europe.
   Why others fail: The Labrador Current is cold and cools eastern Canada, making it a distractor for regions with cold climates.

2. During which lunar phase do neap tides occur?
   A. Full moon
   B. New moon
   C. First quarter
   D. Waxing gibbous
   Answer: C
   Explanation: Neap tides occur during the first and third quarter moons when the Sun and Moon are at right angles.
   Why others fail: Full moon causes spring tides, which are more prominent and often misremembered as the only significant tide.

3. What is the primary reason for upwelling along the Peruvian coast?
   A. Convergence of warm currents
   B. Offshore wind-driven Ekman transport
   C. High evaporation rates
   D. Subsidence of warm surface water
   Answer: B
   Explanation: Southeast trade winds cause offshore Ekman transport, leading to cold, nutrient-rich water rising.
   Why others fail: Convergence causes downwelling, not upwelling—students confuse convergence with divergence.

4. Which of the following best describes a semidiurnal tidal pattern?
   A. One high tide and one low tide per day
   B. Two high tides and two low tides of unequal height per day
   C. Two high tides and two low tides of approximately equal height per day
   D. Irregular tides with no predictable pattern
   Answer: C
   Explanation: Semidiurnal tides feature two nearly equal high and low tides daily, common on the U.S. Atlantic coast.
   Why others fail: Mixed tides (option B) are common on the Pacific coast and often confused with semidiurnal.

5. India’s Exclusive Economic Zone (EEZ) extends up to how many nautical miles from its baseline?
   A. 12 nautical miles
   B. 24 nautical miles
   C. 200 nautical miles
   D. 350 nautical miles
   Answer: C
   Explanation: The EEZ extends 200 nautical miles from the baseline as per UNCLOS and India’s 1976 maritime law.
   Why others fail: 12 nautical miles is the territorial sea limit, a common confusion with EEZ.

Last-Minute Revision

• Gulf Stream-warm, western Atlantic, originates near Florida.
• Labrador Current-cold, flows south, meets Gulf Stream near Newfoundland.
• Kuroshio Current-warm, western Pacific, analogous to Gulf Stream.
• Humboldt (Peru) Current-cold, causes upwelling, supports rich fisheries.
• Coriolis effect-deflects currents right (NH), left (SH).
• Ekman spiral-net water movement at 90° to wind.
• Sverdrup (Sv) = 10? m³/s — unit of ocean transport.
• Upwelling-cold, nutrient-rich water rises; boosts primary productivity.
• Downwelling-surface water sinks; reduces surface nutrients.
• Tides caused by Moon’s gravity > Sun’s due to proximity.
• Spring tides = new + full moon = maximum tidal range.
• Neap tides = first + third quarter = minimum tidal range.
• Diurnal tide = 1 high + 1 low per day (e.g., Gulf of Mexico).
• Semidiurnal = 2 nearly equal highs/lows per day (e.g., U.S. Atlantic coast).
• Mixed tide = 2 unequal highs/lows per day (e.g., U.S. Pacific coast).
• Bay of Fundy — highest tidal range (~17 m).
• Tidal energy: Rance (France) — first major plant (1966).
• India’s EEZ — 200 nautical miles, declared 1976.
• Mumbai High — major offshore oil field on continental shelf.
• Somali Current — unique: warm in summer, cold in winter due to monsoon reversal.