The chemistry of the Atlantic Ocean is also changing in terms of its salinity, or salt content. A number of factors contribute to the salinity profile of the Atlantic Ocean. Evaporation, for example, is responsible for surface salinity being greater than the salinity of deeper water. When evaporation exceeds precipitation, salinity at the ocean surface increases. This has implications for movement of water and mixing of upper water with lower water. Melting of Arctic and Greenland ice because of warming sea and air temperatures, and increased precipitation over the ocean and neighboring continents, would be expected to have a freshening effect on the Atlantic, because these sources are low in salt. Changes in circulation, stronger winds, and changes in precipitation would be expected to increase salinity of surface waters near the tropics.
Measurements along the western basins of the Atlantic indicate significant freshening of high latitude water in both the Northern and Southern Hemispheres, and increased salinity in low latitudes during the latter half of the 20th century. The changing distribution of fresh and saline waters throughout the Atlantic and other oceans may be indicative of significant changes in the global hydrological cycle. The salinity of the Atlantic Ocean is also of particular interest because of its role in the thermohaline circulation (THC). The THC, along with prevailing winds produced by the Coriolis effect (circulation of large bodies of fluids such as air and water caused by the rotation of the planet), is the driving force behind the Atlantic meridional overturning circulation (AMOC).
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