UPSC CSE Prelims
Oceanography Previous Year Questions (PYQs)
Showing solved Previous Year Questions for Chapter: Oceanography
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Which of the following is/are correct inference/inferences from isothermal maps in the month of January?.
- The isotherms deviate to the north over the ocean and to the south over the continent.
- The presence of cold ocean currents, Gulf Stream and North Atlantic Drift make the North Atlantic Ocean colder and the isotherms bend towards the north.
Select the answer using the code given below :
Detailed Explanation:
Answer: Option 1 — 1 only
In January (Northern Hemisphere winter), continents cool down faster than oceans due to differential heating. This causes isotherms to deviate northward over the warmer oceans and southward over the colder continents. Statement 2 is incorrect because the Gulf Stream and North Atlantic Drift are warm ocean currents, not cold, and they actually make the North Atlantic warmer, causing isotherms to bend northward.
✅ Statement 1 (Isotherm Deviation) – Correct: In January, isotherms deviate northward over oceans (which remain warmer) and southward over continents (which are colder) in the Northern Hemisphere due to differential heating and cooling rates of land and water.
❌ Statement 2 (Gulf Stream and North Atlantic Drift) – Incorrect: The Gulf Stream and North Atlantic Drift are warm ocean currents, not cold; they carry warm tropical water northward, making the North Atlantic relatively warmer and causing isotherms to bend northward, not making it colder.
📝 Short Notes: Isotherms and Ocean Currents
- Isotherms: Lines on a map connecting points of equal temperature, used to understand temperature distribution patterns across different regions and seasons.
- January Isotherm Pattern (Northern Hemisphere): During winter, continents are colder than oceans because land loses heat faster than water. Isotherms bend equatorward (southward) over continents and poleward (northward) over oceans.
- July Isotherm Pattern (Northern Hemisphere): During summer, continents are warmer than oceans. Isotherms bend poleward (northward) over continents and equatorward (southward) over oceans.
- Gulf Stream: A powerful warm ocean current originating in the Gulf of Mexico, flowing along the eastern coast of North America and across the Atlantic towards Europe, significantly warming Western Europe's climate.
- North Atlantic Drift: The extension of the Gulf Stream that continues eastward across the North Atlantic, bringing warm water and mild temperatures to Northwestern Europe, including the British Isles and Scandinavia.
- Effect of Ocean Currents on Isotherms: Warm currents like the Gulf Stream cause isotherms to bend poleward (northward in Northern Hemisphere), while cold currents like the Labrador Current cause isotherms to bend equatorward (southward in Northern Hemisphere).
- Differential Heating: Water has a higher specific heat capacity than land, meaning oceans heat up and cool down more slowly than continents, creating seasonal temperature contrasts that influence isotherm patterns.
Consider the following statements :
- The Red Sea receives very little precipitation in any form.
- No water enters the Red Sea from rivers.
Which of the statements given above is/are correct?
Detailed Explanation:
Answer: Option 3 — Both 1 and 2
The Red Sea is located in an arid desert region characterized by extremely high temperatures and low humidity, resulting in minimal precipitation. Additionally, no major rivers flow into the Red Sea; its water primarily comes from the inflow of saltier water from the Gulf of Aden through the Bab el-Mandeb Strait.
✅ Statement 1 (Low Precipitation) – Correct: The Red Sea receives very little precipitation due to its location in a desert region with high temperatures and low humidity.
✅ Statement 2 (No River Inflow) – Correct: No major rivers flow into the Red Sea; water enters primarily from the Gulf of Aden through the Bab el-Mandeb Strait.
📝 Short Notes: Red Sea - Oceanographic Features
- Location: The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa (Egypt, Sudan, Eritrea, Djibouti) and Asia (Saudi Arabia, Yemen), connected to the Arabian Sea via the Gulf of Aden through the Bab el-Mandeb Strait.
- Climate: Located in an arid desert belt with extremely high temperatures, low humidity, and minimal rainfall (less than 100 mm annually), making it one of the driest regions globally.
- River Inflow: Unlike most seas, the Red Sea has no significant river drainage into it, which is a unique oceanographic characteristic contributing to its high salinity.
- High Salinity: The Red Sea has one of the highest salinities among world oceans (around 40-41 ppt) due to high evaporation rates, low precipitation, and absence of freshwater inflow from rivers.
- Water Exchange: Water enters from the Gulf of Aden (saltier, denser water) and exits as surface water, creating a unique circulation pattern that maintains the Red Sea's salinity and temperature.
- Temperature: Surface water temperatures range from 20°C in winter to over 30°C in summer, making it one of the warmest seas in the world.
- Strategic Importance: The Red Sea is crucial for international maritime trade as it connects to the Suez Canal in the north, serving as a vital shipping route between Europe and Asia.
Which one of the following is the best example of repeated falls in sea level, giving rise to present-day extensive marshland?
Detailed Explanation:
Answer: Option 4 — Rann of Kutch
The Rann of Kutch is the best example of repeated falls in sea level giving rise to extensive marshland. Geological evidence indicates that this vast salt marsh in Gujarat was once a shallow extension of the Arabian Sea, but tectonic movements and climatic changes led to repeated sea level recessions, depositing saline materials and creating the present-day seasonal marshland. During monsoons, it fills with water forming a shallow lake, and in summer, it dries into extensive white salt flats.
Why other options are incorrect:
Option 1 – Bhitarkanika Mangroves: This is a deltaic mangrove ecosystem in Odisha formed by river sediment deposition, not by repeated sea level falls.
Option 2 – Marakkanam Salt Pans: These are coastal salt production areas in Tamil Nadu, created through human intervention for salt extraction, not natural sea level regression.
Option 3 – Naupada Swamp: This is a freshwater wetland ecosystem in Andhra Pradesh, unrelated to sea level changes.
📝 Short Notes: Rann of Kutch Formation
- Location: Northwestern Gujarat, extending into Pakistan; part of the Thar Desert region
- Types: Great Rann (larger, northern) and Little Rann (smaller, southern)
- Geological History: Once part of the Arabian Sea; tectonic uplift and sea level fluctuations during Pleistocene era isolated it from the sea
- Seasonal Transformation: Flooded during monsoon (June-September); dries into salt-encrusted desert in summer
- Ecological Significance: Home to Wild Ass Sanctuary in Little Rann; breeding ground for flamingos; unique halophytic (salt-tolerant) vegetation
- Economic Importance: Major salt production area; traditional salt farming by Agariya community
- Cultural Heritage: Famous for Rann Utsav festival; traditional handicrafts of Kutchi communities
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"Biorock technology" is talked about in which one of the following situations?
Detailed Explanation:
Answer: Option 1 — Restoration of damaged coral reefs
Biorock technology (also known as mineral accretion technology) uses low-voltage direct electrical current passed through seawater to precipitate dissolved minerals, creating a limestone-like structure on submerged metal frames. This creates an ideal substrate for coral larvae to settle and grow, accelerating coral reef restoration by 3-5 times compared to natural growth rates. The technology also makes corals more resilient to environmental stresses like ocean warming and acidification, making it a valuable tool for marine ecosystem restoration.
📝 Short Notes: Biorock Technology
- Principle: Electrolysis of seawater using low-voltage DC current (1.2-6 volts) causes precipitation of calcium carbonate and magnesium hydroxide on cathode structures
- Structure: Metal frames (usually steel) are placed underwater and connected to a low-voltage power source (solar panels or tidal energy)
- Benefits for Coral Restoration: Accelerated coral growth (3-5x faster), increased coral survival rates (up to 50x higher), enhanced resistance to bleaching and diseases
- Applications: Coral reef restoration, artificial reef creation, shoreline protection, mariculture support
- Developers: Pioneered by architect Wolf Hilbertz and marine biologist Thomas Goreau in the 1970s
- Global Examples: Projects in Maldives, Indonesia, Thailand, Seychelles, and other tropical regions with degraded coral reefs
- India Context: Potential application in Gulf of Mannar, Lakshadweep, and Andaman & Nicobar Islands for coral restoration
Consider the following statements:
- In the tropical zone, the western sections of the oceans are warmer than the eastern sections owing to the influence of trade winds.
- In the temperate zone, westerlies make the eastern sections of oceans warmer than the western sections.
Which of the statements given above is/are correct?
Detailed Explanation:
Answer: Option 3 — Both 1 and 2
Both statements correctly describe the influence of prevailing winds on ocean temperature distribution. Trade winds in tropical zones and westerlies in temperate zones drive warm surface currents in their respective directions, creating distinct temperature patterns across ocean basins.
✅ Statement 1 – Correct: Trade winds (blowing east to west) in tropical zones push warm surface waters westward, making western sections of tropical oceans warmer than eastern sections (e.g., warm Western Pacific versus cool Eastern Pacific).
✅ Statement 2 – Correct: Westerlies (blowing west to east) in temperate zones drive warm waters eastward, making eastern sections warmer than western sections (e.g., warm North Atlantic Drift warming Western Europe).
📝 Short Notes: Ocean Temperature Distribution and Wind Patterns
| Zone | Prevailing Wind | Wind Direction | Warm Ocean Section | Example |
|---|---|---|---|---|
| Tropical Zone (0°-30°) | Trade Winds | East to West | Western sections warmer | Warm West Pacific vs. Cool Peru Current (East Pacific) |
| Temperate Zone (30°-60°) | Westerlies | West to East | Eastern sections warmer | Gulf Stream/North Atlantic Drift warming Western Europe |
- Trade Winds mechanism: Push warm equatorial waters westward, causing warm water accumulation on western ocean boundaries and upwelling of cold water on eastern boundaries
- Westerlies mechanism: Drive warm currents from west to east, transferring heat from lower latitudes to higher latitudes on eastern ocean sides
- Western boundary currents: In tropical zones (e.g., Gulf Stream, Kuroshio) are warm, narrow, and fast-flowing
- Eastern boundary currents: In tropical zones (e.g., California Current, Peru Current) are cold, wide, and slow-flowing
- Climate impact: These patterns significantly influence coastal climates, with western tropical coasts being warmer and wetter, while eastern tropical coasts are cooler and drier
With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct?
- OMT is measured up to a depth of 26°C isotherm which is 129 meters in the south-western Indian Ocean during January-March.
- OMT collected during January-March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.
Select the correct answer using the code given below:
Detailed Explanation:
Answer: Option 2 — 2 only
Ocean Mean Temperature (OMT) is measured up to the depth of the 26°C isotherm and serves as a reliable indicator of upper ocean heat content for monsoon prediction. Statement 1 is incorrect because the depth of the 26°C isotherm in the south-western Indian Ocean during January-March is approximately 59 meters, not 129 meters. Statement 2 is correct as OMT data collected during January-March can indeed be used to assess whether Indian Summer Monsoon Rainfall (ISMR) will be above or below the long-term mean.
❌ Statement 1 – Incorrect: The depth of 26°C isotherm is approximately 59 meters in the south-western Indian Ocean during January-March, not 129 meters.
✅ Statement 2 – Correct: OMT collected during January-March is used to predict whether ISMR will be above or below the long-term mean, making it a valuable forecasting tool.
📝 Short Notes: Ocean Mean Temperature (OMT)
- Definition: OMT is the average temperature of the ocean water column from the surface down to the depth of the 26°C isotherm (D26).
- Significance: OMT is a more stable and reliable indicator of upper ocean heat content compared to Sea Surface Temperature (SST) alone.
- Monsoon Prediction: Research by Indian Institute of Tropical Meteorology (IITM) shows that OMT data from January-March in the south-western Indian Ocean can predict Indian Summer Monsoon Rainfall with greater accuracy.
- Depth Measurement: The 26°C isotherm depth varies spatially and temporally; in the south-western Indian Ocean during January-March, it is approximately 59 meters.
- Advantage over SST: Unlike SST which can fluctuate rapidly due to surface processes, OMT represents the integrated heat content of the upper ocean layer.
- Predictive Value: Higher OMT values generally indicate favorable conditions for above-normal monsoon rainfall over India.
Consider the following statements -
- Most of the world's coral reefs are in tropical waters.
- More than one-third of the world's coral reefs are located in the territories of Australia, Indonesia and the Philippines.
- Coral reefs host far more number of animal phyla than those hosted by tropical rainforests.
Which of the statements given above is/are correct?
Detailed Explanation:
Answer: Option 4 — 1, 2 and 3
All three statements about coral reefs are correct. Coral reefs are predominantly found in tropical waters where conditions are optimal for their growth. The distribution of coral reefs is highly concentrated, with Australia, Indonesia, and the Philippines together hosting more than one-third of the world's coral reefs. Remarkably, coral reefs exhibit exceptional biodiversity not just in terms of species numbers but also in phyletic diversity, hosting 32 out of 34 animal phyla compared to only 9 phyla in tropical rainforests.
✅ Statement 1 – Correct: Coral reefs primarily thrive in warm, shallow, clear tropical waters between 30°N and 30°S latitudes, where sea surface temperatures typically remain between 20°C and 30°C.
✅ Statement 2 – Correct: These three countries (Australia, Indonesia, and the Philippines) account for over 40% of the world's coral reef area, with Indonesia holding approximately 18%, Australia 17%, and the Philippines 9%.
✅ Statement 3 – Correct: While rainforests have a higher number of species, coral reefs have greater phyletic diversity, hosting 32 of the 34 recognized animal phyla compared to only about 9 phyla found in tropical rainforests.
📝 Short Notes: Coral Reefs
- Definition: Coral reefs are underwater structures made from calcium carbonate secreted by corals, which are marine invertebrates belonging to the class Anthozoa.
- Geographic Distribution: Found primarily in tropical and subtropical waters between 30°N and 30°S latitudes, covering less than 0.1% of the ocean floor but supporting 25% of marine species.
- Optimal Conditions: Require warm water (20-30°C), shallow depth (less than 50m for sunlight penetration), clear water with low turbidity, normal salinity (32-42 ppt), and minimal pollution.
- Major Coral Reef Regions: Great Barrier Reef (Australia - largest), Coral Triangle (Indonesia, Philippines, Malaysia, Papua New Guinea), Caribbean Sea, Red Sea, and Indian Ocean islands.
- Biodiversity Hotspots: Host 32 out of 34 animal phyla (highest phyletic diversity on Earth), support over 4,000 fish species, 800 coral species, and countless invertebrates.
- Ecological Importance: Provide coastal protection from waves and storms, support fisheries, generate tourism revenue, and are sources of medicinal compounds.
- Threats: Climate change and ocean warming (causing coral bleaching), ocean acidification, overfishing, pollution, destructive fishing practices, and coastal development.
At one of the places in India if you stand on the seashore and watch the sea, you will find that the sea water recedes from the shoreline a few kilometres and comes back to the shore, twice a day, and you can actually walk on the sea floor when the water recedes. This unique phenomenon is seen at -
Detailed Explanation:
Answer: Option 3 — Chandipur
Chandipur Beach in Balasore district of Odisha is famous for its unique phenomenon where the sea recedes up to 2-5 kilometers during low tide, exposing the sea floor for several hours. This extraordinary tidal behavior occurs twice daily due to the beach's exceptionally shallow gradient and flat sea bed, allowing visitors to literally walk on the sea floor. The water returns during high tide, making it one of the most distinctive coastal features in India.
Tides occur in oceans and seas due to which among the following?
- Gravitational Force of the Sun
- Gravitational Force of the Moon
- Centrifugal force of the Earth
Select the correct answer using the code given below
Detailed Explanation:
✅ Statement 1 – Correct: The Sun's gravitational force contributes to tidal generation, producing a tidal force approximately 46% as strong as the Moon's despite its greater mass but larger distance.
✅ Statement 2 – Correct: The Moon's gravitational pull is the primary cause of tides, creating a tidal bulge on the side of Earth facing the Moon due to stronger gravitational attraction on ocean water.
✅ Statement 3 – Correct: Centrifugal force from the Earth-Moon system's rotation around their common barycenter creates a second tidal bulge on the side of Earth opposite to the Moon.
What explains the eastward flow of the equatorial counter-current?
Detailed Explanation:
The North and South Equatorial Currents flow westward due to Trade Winds, causing water to accumulate on the western sides of ocean basins and creating a higher sea level in the west.
This convergence and water pile-up generates a pressure gradient that drives the Equatorial Counter-Current to flow eastward between the two equatorial currents in the Doldrums region (where surface winds are weak), restoring oceanic equilibrium.
Which of the following have coral reefs?
- Andaman and Nicobar Islands
- Gulf of Kutch
- Gulf of Mannar
- Sunderbans
Select the correct answer using the code given below.
Detailed Explanation:
✅ Statement 1 – Correct: Andaman and Nicobar Islands have extensive fringing coral reefs along their coasts, forming one of India's richest marine biodiversity zones.
✅ Statement 2 – Correct: Gulf of Kutch contains coral reefs in the northern Arabian Sea, declared as India's first Marine National Park in 1982.
✅ Statement 3 – Correct: Gulf of Mannar between India and Sri Lanka hosts 21 islands with fringing coral reefs, recognized as a Marine Biosphere Reserve.
❌ Statement 4 – Incorrect: Sundarbans is a mangrove delta ecosystem with brackish water and muddy substrate, unsuitable for coral reef formation which requires clear saline water.
The most important fishing grounds of the world are found in the regions where:
Detailed Explanation:
The world's most productive fishing grounds are located where warm and cold oceanic currents converge. This mixing creates nutrient-rich waters and ideal conditions for phytoplankton growth, which forms the base of the marine food chain.
Grand Banks (Newfoundland): Cold Labrador Current meets warm Gulf Stream, creating one of the world's richest fishing zones.
North-West Pacific (Japan): Cold Oyashio Current meets warm Kuroshio Current, supporting highly productive fisheries.
Consider the following factors:
- Rotation of the Earth
- Air pressure and wind
- The density of ocean water
- Revolution of the Earth
Which of the above factors influence the ocean currents?
Detailed Explanation:
✅ Statement 1 – Correct: Rotation of the Earth causes the Coriolis effect, which deflects ocean currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
✅ Statement 2 – Correct: Air pressure and wind generate wind-driven currents by exerting friction on the ocean surface; prevailing winds like Trade Winds and Westerlies drive major surface currents.
✅ Statement 3 – Correct: Density of ocean water, determined by temperature and salinity, drives thermohaline circulation (deep ocean currents).
❌ Statement 4 – Incorrect: Revolution of the Earth (orbit around the Sun) causes seasonal changes but does not directly influence ocean currents.