Previous Year Question
With reference to the “EL-NINO”, which of the following statement/s is/are correct?
(1) El-Nino involves appearance of warm current off the coast of Peru in eastern pacific.
(2) This warm current increase the temperature of water on the Peruvian coast by 10°C there by increasing the amount of Plankton in the sea.
Select the correct answer using the code given below -
Only 2
Both 1 and 2
Only 1
Neither 1 nor 2
Correct Answer: C
Detailed Solution
Statement 1 is correct. During El Niño, sea-surface temperatures become warmer than normal across the central and eastern equatorial Pacific. Unusually warm surface water also develops in the eastern Pacific near Peru and Ecuador. This is associated with weakening of the normal easterly trade winds and changes in ocean-atmosphere circulation.
Under normal conditions, cold, nutrient-rich deep water upwells near the Peruvian coast. This water brings nutrients such as nitrates and phosphates towards the surface, supporting the growth of phytoplankton, which in turn sustains a rich marine food chain and major fisheries.
Statement 2 is incorrect. During El Niño, the thermocline becomes deeper in the eastern Pacific and coastal/equatorial upwelling weakens. Consequently, the supply of cold nutrient-rich water to the surface decreases. As a result, phytoplankton and primary productivity decrease rather than increase, which can also adversely affect fisheries.
The fixed 10°C rise mentioned in Statement 2 is also not the standard definition of El Niño. NOAA defines El Niño in terms of above-normal sea-surface temperatures in the central/eastern tropical Pacific; the actual magnitude of warming varies with the event and region.