Previous Year Question
In the context of ecosystem productivity, marine upwelling zones are important as they increase the marine productivity by bringing the
decomposer microorganisms to the surface.
nutrients to the surface.
bottom-dwelling organisms to the surface.
Which of the statement(s) given above is/are correct?
1 and 2 only
2 only
2 and 3 only
3 only
Correct Answer: B
Detailed Solution
Upwelling is the process in which cold, nutrient-rich water rises from the depths of the ocean towards the surface.
This process generally occurs when winds and Ekman transport move surface water away from a coast or an oceanic region.
Water from the depths rises to replace the displaced surface water.
Deep ocean water contains large quantities of nutrients such as nitrate, phosphate and silicate.
These nutrients accumulate because of the decomposition and remineralisation of dead organisms and organic matter at depth.
Statement 1 is incorrect: The ecological importance of upwelling does not arise from bringing decomposer microorganisms to the surface.
Decomposer microorganisms occur in different parts of seawater and sediments, but their transport to the surface is not the principal basis of productivity in an upwelling zone.
Statement 2 is correct: Upwelling transports nutrients accumulated at depth to the sunlit upper layer of the ocean.
In the presence of light, phytoplankton use these nutrients for rapid photosynthesis and primary production.
Greater phytoplankton abundance supports the entire marine food web, including zooplankton, small fish, large fish and seabirds.
For this reason, many of the world’s major fishing grounds are associated with upwelling zones.
The coasts associated with the Peru or Humboldt Current, California Current, Canary Current and Benguela Current are major upwelling regions.
Powerful seasonal upwelling also occurs in the Arabian Sea near Somalia and the Arabian Peninsula during the southwest monsoon.
Statement 3 is incorrect: Bottom-dwelling organisms are adapted to the seabed environment, and bringing them to the surface is not the reason for productivity in upwelling zones.
Sudden transport of bottom-dwelling organisms to the surface may even cause their death because conditions of temperature, pressure and light differ between the surface and the seabed.
Upwelled water is generally cold and rich in nutrients and may sometimes contain comparatively less dissolved oxygen.
Therefore, upwelling zones increase marine productivity primarily by bringing nutrients to the surface. Hence, only statement 2 is correct.