How do ocean currents and water masses differ in their impacts on marine life and coastal environment? Give suitable examples. (UPSC IAS Mains 2019 General Studies Paper – 1)
Ocean currents (surface or deep ocean currents) are streams of water flowing constantly in definite path and direction, for example, Gulf Stream (warm current) and Labrador current (cold current). Water masses are the extensive homogeneous body of immense volume of ocean water in terms of temperature and salinity. These are generally characterised by the downwelling of denser cold water and upwelling of less dense water, for example, the North Atlantic Deep-water mass in the Norwegian Sea.
Impacts of ocean currents
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- On marine life
- Ocean currents act as distributing agents of nutrients, oxygen and other elements necessary for the existence and survival of fishes and zooplanktons.
- They also transport planktons from one area to the other area. For example, Gulf Stream carries planktons from the Mexican Gulf to the coasts of Newfoundland and north-western Europe. Many significant fishing grounds of the world are developed in these areas.
- Mixing of warm and cold ocean currents bring rich nutrients which support marine organisms. For example, seas north of Japan is a rich fishing ground due to the mixing of warm Kuroshio and cold Kurile currents.
- Sometimes, a few ocean currents destroy planktons. For example, El Nino current destroys planktons off the Peruvian coasts resulting into mass deaths of fishes.
- On coastal environment
- Ocean currents maintain the horizontal heat balance of the earth. The warm currents transport warm waters of the tropics to colder areas of temperate and polar zones. Cold currents on the other hand bring cold waters of the high latitudes to the areas of low latitudes.
- Surface ocean currents also modify the weather conditions of the coastal areas. The ideal and favourable European type of climate of the western coasts of Europe is due to the moderating effects of the North Atlantic warm currents.
- Cold currents also intensify the desert-like conditions in the coastal areas, exemplified by the presence of some deserts in the western edges of continents, e.g., Namib Desert in Africa.
- The convergence of warm and cold currents causes foggy conditions, e.g., near Newfoundland due to convergence of warm Gulf Stream and cold Labrador current.
Impacts of water masses
- Downwelling of water masses
- It transports oxygen downward which is much needed by the marine organisms.
- This process discourages enrichment of seawater by bringing nutrients, and hence the areas of downwelling of water masses are not conducive to marine life and hence they are the areas of low marine productivity.
- Upwelling of water masses
- It is beneficial to the rich marine life because dissolved oxygen and nutrients are brought to the surface through upwelling. For example, the upwelling of nutrient rich cold water off the coast of Peru has made the region one of the richest fishing grounds.
Global warming is disrupting the sinking of cold, salty water as a result of increased melting of glaciers and sea ice. This could slow or even stop the circulation of ocean waters, which could result in potentially drastic impact on marine life and coastal environment. Thus, arresting global warming is the need of the hour.
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