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Day 4 – Q 2.What is upwelling and downwelling? How do they affect coastal regions? Examine.

2. What is upwelling and downwelling? How do they affect coastal regions? Examine.  

अपवेलिंग तथा डाउनवेलिंग क्या है? वे तटीय क्षेत्रों को कैसे प्रभावित करते हैं? जांच करें।


  • This question has broadly two parts. One part is about concepts upwelling and downwelling, second part is about their effects on coastal regions.
  • Give a short introduction to the topic, then start explaining the concepts, then their effects on coastal areas and lastly, conclude your answer.


  • In some coastal areas of the ocean the combination of persistent winds, Earth’s rotation (the Coriolis effect), and restrictions on lateral movements of water caused by shorelines and shallow bottoms induces upward and downward water movements.
  • The Coriolis effect plus the frictional coupling of wind and water (Ekman transport) cause net movement of surface water at about 90 degrees to the right of the wind direction in the Northern Hemisphere and to the left of the wind direction in the Southern Hemisphere.



  • Upwelling occurs where water from the deeper parts of the ocean is allowed to travel upwards to the surface.
  • Upwelling generally found along the equator due to diverging surface waters, around Antarctica between the East Wind Drift and West Wind drift, and along coastlines where the wind blows in such a way that Ekman Transport pushes water away from the coast.
  • It is most common along the west coast of continents (eastern sides of ocean basins).


  • Downwelling is the vertical movement of surface water to deeper parts of the ocean.  
  • Downwelling occurs in areas where waters converge and “pile up” such as in the North Atlantic where several surface currents meet and along the outermost boundary of the Southern Ocean where cold Antarctic water sinks below warmer South Pacific and South Atlantic waters.

This figure below shows how Ekman transport, aided by the wind and the coriolis effect, creates areas of upwelling and downwelling in coastal locations of the Southern hemisphere.

Effects of Upwelling and downwelling on coastal region

  • Upwelling and downwelling influence sea-surface temperature and biological productivity.
  • In Upwelling Deep ocean water is generally very cold and nutrient rich. Therefore, in areas of upwelling we often find very productive waters.
  • This nutrient rich water transport into the surface waters where sunlight, also required for phytoplankton growth (photic zone), is present, results in rapid growth of phytoplankton populations.
  • Since phytoplankton form the base of marine food webs, the world’s most productive fisheries are located in areas of coastal upwelling that bring cold nutrient rich waters to the surface.
  • On the other hand, in zones of coastal downwelling, the surface layer of warm, nutrient-deficient water thickens as water sinks.
  • Downwelling reduces biological productivity and transports heat, dissolved materials, and surface waters rich in dissolved oxygen to greater depths.
  • Dissolved oxygen is critical for living organisms in the deep ocean.
  • In extreme cases, nutrient-deficient waters coupled with over-fishing cause fisheries to collapse bringing about severe, extended economic impacts.
  • Coastal upwelling and downwelling also influence weather and climate.
  • Along the northern and central California coast, upwelling lowers sea surface temperatures and increases the frequency of summer fogs.
  • Upwelling cold water inhibits formation of tropical cyclones, because tropical cyclones derive their energy from warm surface waters.


  • Upwelling and downwelling illustrate mass continuity in the ocean; that is, water is a continuous fluid so that a change in distribution of water in one area is accompanied by a compensating change in water distribution in another area.
  • Coastal climate and economy of the coastal areas is mostly affected by these oceanic phenomena.

Best Answer: Ivjyot Oberoi

chiranjeev bishwas

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