How do ocean currents and water masses differ in their impacts on marine life and coastal environment? Give suitable examples. UPSC 2019
Currents are distinct and generally horizontal flows of a mass of water in a fairly defined’ direction. Currents are formed due to the density of water rotation of the earth and planetary winds.
These currents form a clockwise pattern in the northern hemisphere and move in an anti-clockwise pattern in the southern hemisphere. The currents of the Indian Ocean are influenced by Monsoon winds.
The oceanic movement in the form of currents helps in the dispersal of marine life. Ocean currents are an important abiotic factor that significantly influences the food webs and reproduction of marine organisms and the marine ecosystems that they inhabit. Even fish and mammals living in the ocean may have their destinations and food supply affected by currents.
Water masses are formed as the result of climatic effects in specific regions. Within the ocean, distinct water masses with physical properties that are different from the surrounding water form and circulate, much like air masses in the atmosphere.
Several important water masses help to drive the thermohaline circulation. North Atlantic Deep Water (NADW), the biggest water mass in the oceans, forms in the North Atlantic and runs down the coast of Canada, eastward into the Atlantic, and south past the tip of South America.
NADW forms in the area where the North Atlantic Drift (the northern extension of the Gulf Stream) ends, so it helps to pull the Gulf Stream northward. If the NADW were to slow down or stop forming, as has happened in the past, this could weaken the Gulf Stream and the North Atlantic Drift and cool the climate of northwest Europe.
Another cold water mass, Antarctic Bottom Water (AABW), is the densest water mass in the oceans. It forms when cold, salty water sinks into the seas surrounding Antarctica, carrying oxygen and nutrients with it, and flows northward along the sea floor underneath the North Atlantic Deep Water, displacing the waters above it and helping to propel the Thermohaline Circulation.
This circulation pattern is not constant or permanent. Studies of Earth’s climate history have linked changes in the strength of the thermohaline circulation to broader climate changes. At times when the conveyor belt slowed down, temperatures in the Northern Hemisphere fell; when the circulation intensified, temperatures in the region rose.