The great ocean conveyor belt of currents is responsible for the transfer of heat throughout the Earth’s oceans. This ocean water phenomenon is a result of the temperature difference in the ocean waters between the warm, salty surface water, and the less salty cold water in the ocean depths.
The surface cold water at the Polar Regions is saltier than deeper water due to both evaporation and the formation of sea ice, which squeezes out ice from the forming ice. This increases surface water density and causes it to sink to the ocean depths.
The pumping effect causes the cold water at the ocean depth to flow horizontally towards the tropics where it can displace lighter and warmer water to complete the current loop. This motion of oceanic water is evident in equatorial waters, namely the Indian and Pacific oceans, due to variations in both water temperature and salinity; hence, the name thermohaline circulation.
The YouTube video “The great ocean conveyor” by oneoceanonline, shows an animation of the motion of warm ocean water at the equatorial region towards the poles. As this water cools, it becomes denser and sinks to the deep ocean before returning to the equator.
One of the vital benefits of the great ocean conveyor is its ability to deliver life sustaining oxygen to the ocean depths. Oxygen gets mixed with the ocean water through the turning action of waves, currents and tides on the surface. This motion is also responsible for the delivery of a warm climate that prevents the formation of sea ice in various parts of the northern hemisphere where the conveyor passes, such as Iceland and the southern region of Greenland. It also provides the British Isles and Scandinavia with warmer temperatures than other landmasses at similar latitudes.
The region of the Southern Hemisphere where the ocean conveyor passes has no landmass, which allows the water to flow all around the world, resulting in the Antarctic Circumpolar Current. Consequently, the surface and deep waters flow eastwards around Antarctica, forming a link between waters from multiple oceans. This causes the cold waters from the Indian and Pacific oceans to force themselves below the Atlantic waters, where the latter can join the surface circulation in its Northward flow. The warm water forms part of the wind driven surface currents that return to the northern hemisphere where the cycle begins again in the region around Greenland.
The ocean conveyor is a product of two factors, salinity and temperature. As such, reducing salinity of the North Atlantic surface water may reduce the pumping effect to supplement the flow of cold deep ocean currents, causing the ocean conveyor belt to slow down or cease. This phenomenon is said to have occurred in the period between 1400 and 1800 AD. This period is known as the Little Ice Age, when the Northern Europe’s climate was observed to be significantly colder than usual.
Scientists suggest that an increase in temperatures due the greenhouse effect is likely to result in melting of the polar ice, creating the dilemma of the possible implications with regard to the conveyor belt currents. In addition to this, there is likely to be an increase in more fresh water in the Atlantic Ocean due to additional precipitation on land masses such as river run-off from storms and melted snow.
An increase in fresh water from melting glaciers and sea ice in the waters around Greenland would reduce the salinity and consequently the density of deep cold waters, inhibiting the southward flow of deep ocean currents. This would, in turn, slow the conveyor.