UPSC CSE Prelims
Ocean Temperature and Salinity Previous Year Questions (PYQs)
Practice solved questions for Ocean Temperature and Salinity with detailed step-by-step solutions, key insights, and trend analysis for UPSC CSE PRELIMS.
Solved Previous Year Questions
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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.
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.
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