Daily Static Quiz Prelims Practice 2027
- Thermohaline circulation is driven primarily by differences in water temperature and salinity, which affect water density.
- The sinking of dense, cold and saline water in the North Atlantic near Greenland is a key driver of the global thermohaline circulation, often called the "global conveyor belt."
- Thermohaline circulation operates independently of surface wind-driven currents and has no influence on global climate.
Statement 1 is correct — thermohaline circulation is driven by density differences arising from variations in temperature (thermo) and salinity (haline) of seawater. Statement 2 is correct — in the North Atlantic near Greenland, cold, salty water becomes dense and sinks, initiating the deep-water flow that drives the global conveyor belt linking surface and deep-ocean circulation. Statement 3 is incorrect — thermohaline circulation interacts with wind-driven surface currents and strongly influences global climate, which is why its disruption (e.g. from Arctic ice melt) is a major climate-change concern.
- A. Benguela Current 1. Warm current
- B. Brazil Current 2. Cold current
- C. Oyashio Current 3. Cold current
- D. East Australian Current 4. Warm current
The general rule is that western boundary currents are warm while eastern boundary currents are cold. The Benguela Current is cold (eastern boundary of the South Atlantic gyre, off southwest Africa) and the Oyashio is cold (flowing south from the Arctic past Kamchatka and Japan's northeast coast), while the Brazil Current (western South Atlantic) and the East Australian Current (western South Pacific) are both warm — giving A-2, B-1, C-3, D-4.
Option (c) is correct — coastal upwelling occurs when wind-driven Ekman transport pushes surface water offshore, drawing cold, nutrient-rich water up from depth, as seen off Peru, California and Namibia. Upwelling is a rising (not sinking) of deep water, so (a) is wrong; these nutrient-rich zones actually support highly productive fisheries, so (b) is wrong; and upwelling occurs in both hemispheres wherever winds favour offshore transport, so (d) is wrong.
Option (b) is correct — the California Current is a cold eastern-boundary current flowing south along the west coast of North America. The Canary Current flows off northwest Africa/Iberia (not eastern North America); the Falkland Current flows along the east coast of South America carrying cold Antarctic water northward (not the west); and the Somali Current flows along the east coast of Africa with seasonal monsoon reversal (not the west).
- The Somali Current is unique among major ocean currents for reversing its direction of flow with the seasonal monsoon.
- During the Southwest Monsoon, the Somali Current flows from south to north, aided by strong offshore winds.
- The reversal of the Somali Current is unrelated to the Indian monsoon system and is driven purely by lunar tidal forces.
Statement 1 is correct — the Somali Current is one of the few currents that completely reverses direction with the seasonal monsoon. Statement 2 is correct — during the Southwest Monsoon (June–September) strong winds drive it northeastward from south to north, also triggering intense coastal upwelling. Statement 3 is incorrect — the reversal is caused by the seasonal reversal of monsoon winds, not lunar tidal forces, making the Somali Current a classic example of ocean-atmosphere coupling in the Indian monsoon system.
