Oceanography: UPSC Previous Year Questions (Geography)

Explanation

The annual range of temperature is the difference between the highest and lowest temperatures recorded in a particular place or region over the course of a year.

Statement 1 is incorrect: The annual range of temperature (the difference between the highest and lowest average monthly temperatures) is generally smaller in the Pacific Ocean compared to the Atlantic Ocean. This is primarily due to the Pacific’s larger size and greater thermal inertia. The vastness of the Pacific allows for more heat absorption and distribution, moderating temperature extremes. Atlantic’s relatively smaller size and its greater contact with Arctic waters leads to more pronounced seasonal temperature variations. Also the Atlantic Ocean is narrower and more enclosed, allowing for greater temperature variability.

Statement 2 is correct: The Northern Hemisphere has a greater annual range of temperature than the Southern Hemisphere. This is primarily due to the larger landmasses in the Northern Hemisphere, which heat up and cool down more quickly compared to the predominantly oceanic Southern Hemisphere. In the Southern Hemisphere, the presence of vast oceans helps stabilize temperatures.

Explanation

Statement 1 is correct: The Horse Latitudes are sub-tropical regions located at approximately 30° to 35° North and South latitudes. These are high-pressure zones characterized by calm winds and minimal precipitation. The name "Horse Latitudes" is believed to have originated from the historical practice of sailors throwing horses overboard to conserve water when ships were stranded in these calm regions.

Statement 2 is incorrect: The Horse Latitudes are high-pres-sure belts, not low-pressure belts. These regions are associated with the subtropical high-pressure zones, where air from the equator descends, creating stable and dry conditions. The high-pressure conditions result from the descending air of the Hadley cells, which suppresses cloud formation and leads to arid climates. Many of the world’s major deserts, such as the Sahara and the Australian Outback, are situated under the Horse latitudes. Low-pressure belts, on the other hand, are found near the equator (Intertropical Convergence Zone) and at higher latitudes (subpolar lows).

Explanation

The Diamantina Trench is a deep-sea trench located in the southeastern Indian Ocean, off the coast of Western Australia. It is part of the Diamantina Fracture Zone, a complex series of deep troughs and ridges. The trench was formed due to seafloor spreading and tectonic activity in the Indian Ocean basin. It is not associated with a subduction zone, unlike many other deep-sea trenches such as the Mariana Trench in the Pacific Ocean.

Explanation

Statement 1 is incorrect: While some ocean currents are slow-moving others like the Gulf Stream, can move swiftly, reaching speeds of up to 5.6 miles per hour (9 kilometers per hour). Additionally, ocean currents are not limited to surface movements as there are also deep-water currents driven by differences in water density.

Statement 2 is correct: Ocean currents play a significant role in maintaining the Earth’s heat balance by transporting warm water from the equator to the poles and cold water from the poles to the equator. This helps regulate global temperatures.

Statement 3 is correct: Prevailing winds, such as the trade winds and westerlies, are a primary force driving ocean currents. These winds create friction on the ocean’s surface, causing water to move.

Statement 4 is correct: The configuration of the ocean, such as the shape of ocean basins, land masses, and coastlines, significantly influences the direction, speed, and path of ocean currents. For example, the Gulf Stream is influenced by the shape of the North American coastline, and the Antarctic Circumpolar Current is shaped by the absence of landmasses in the Southern Ocean.

Explanation

Assertion (A) is true: Neap tides occur when the gravitational forces of the Moon and the Sun are perpendicular to each other (i.e., during the first and third quarters of the lunar cycle). Since the Sun’s gravitational force partially cancels out the Moon’s gravitational effect, the difference between high tide and low tide is minimal. As a result, the high tide is lower than normal, and the low tide is higher than normal. Reason (R) is false: Neap tides occur during the first and third quarter phases of the Moon, not during the new moon. Spring tides, on the other hand, occur during the full moon and new moon when the Sun, Earth, and Moon are aligned, causing a higher-than-normal tidal range.

Explanation

Option (a) is correct: Red tides occur due to the excessive growth of dinoflagellates, which are single-celled organisms containing pigments that cause the water to appear reddish or brownish. These blooms can be found in estuaries, coastal areas, and even open ocean waters. Red tides can be dangerous to marine life and humans due to the toxins produced by the dinoflagellates, which can contaminate seafood and pose health risks when consumed.

Option (b), (c) and (d) are incorrect:

Sea tides refers to the regular rise and fall of sea levels due to gravitational forces exerted by the moon and the sun, not to algal blooms. Black tides are typically associated with oil spills in marine environments, leading to a dark discoloration of the water. Sea flowers is not a standard term used in marine science to describe algal blooms.

Explanation

Option (b) is correct: The Indian Ocean exhibits a unique phenomenon called the monsoon drift, where seasonal wind reversals, driven by the monsoon system, significantly influence ocean currents. During the northeast monsoon (November-March), winds originate from the northeast, pushing the North Equatorial Current southwestward and westward across the Equator. In contrast, the southwest monsoon (May-September) brings winds from the southwest, causing a reversal in current direction. This cyclical shift in wind patterns directly impacts the flow of ocean currents, making the Indian Ocean distinct from other major oceans.

Option (a), (c) and (d) are incorrect:

As the reversal of ocean currents in the Indian Ocean is caused by seasonal monsoon winds and not the ocean’s size. As the Indian Ocean is not landlocked though it is bordered by Asia, Africa, Australia, and the Indian subcontinent. It is because salinity variations do not primarily cause the reversal of currents.

Explanation

Assertion (A) is true: Mangroves are specialised for-est ecosystems found in the tropical and subtropical regions of the world especially along coastlines where saltwater and freshwater meet. They are specially adapted to thrive in saline, waterlogged soils where few other plants can survive. Reason (R) is true: Mangroves play a critical role in stabilizing shorelines by trapping sediments with their dense root systems, reducing erosion, and protecting coastal areas from storm surges and sea-level rise. They act as natural barriers, mitigating the impact of waves and tides, and preventing seawater from en-croaching further inland. Reason (R) correctly explains Assertion (A): Assertion (A) describes mangroves as specialized ecosystems in tropical and subtropical coastal regions and Reason (R) explains why these ecosystems are specialized i.e. their ability to stabilize shorelines and protect against sea encroachment.