The Great Conveyor: Thermohaline Circulation

If "thermos" means heat and "halos" means salt, then the term describes a process driven by those two specific variables.

If surface currents are moved by the atmosphere, then deep currents must have a different driver. If differences in temperature and salinity change the density of water, then thermohaline circulation is the resulting density-driven movement.

If water travels in a continuous loop around the entire planet, then it functions like a moving transport system. If it moves materials globally, then it is known as the Global Conveyor Belt.

If cold water molecules pack tighter than warm ones, then cooling increases density. If salt adds mass to a volume of water, then increasing salinity through brine rejection or evaporation also increases density.

If salt cannot fit into the crystal structure of freezing ice, then it must be excluded. If the excluded salt enters the liquid water nearby, then that water becomes extremely salty and dense.

If surface currents move at several kilometers per hour, they are relatively fast. If the deep-sea conveyor moves only a few centimeters per second, then the thermohaline circulation is significantly slower.

If surface water becomes denser than the water beneath it, then gravity will pull it toward the seafloor. If this vertical movement goes downward, then it is defined as downwelling.

If water sinks in the cold North Atlantic, then it must rise elsewhere to complete the loop. If the "end" of the deep path occurs where water warms and thins, then upwelling happens in the Indian and North Pacific.

If cold water sinks in the north, then a "vacuum" is created at the surface. If warm water from the tropics flows north to fill that space, then it brings heat that warms the European climate.

If fresh water is less dense than salt water, then it will float on the surface. If a layer of fresh meltwater prevents the North Atlantic water from becoming dense enough to sink, then the thermohaline circulation "engine" will stall.

If the deep currents move at a very slow rate and the path spans the entire globe, then it takes a vast amount of time to return to the start. If researchers track this, then the average time is about 1,000 years.

If surface water is in contact with the atmosphere, it absorbs oxygen. If that water sinks during thermohaline circulation, then it delivers that life-sustaining oxygen to the deep-sea floor.

If salinity is a measure of salt concentration, then removing water (evaporation/freezing) increases it. If adding water (rain/rivers) dilutes it, then those four factors control the "haline" component.

If density is defined as the amount of matter in a given space, then the standard physical formula is mass divided by volume. If salt adds mass and cooling reduces volume, then the density increases.

If "thermo" refers to heat and "cline" refers to a gradient or slope, then the area of the water column with a sharp temperature drop is the thermocline.

If the sun's heat is strongest at the equator, then it causes high rates of evaporation. If water evaporates and leaves salt behind, then the equatorial surface water becomes saltier and ready to travel toward the poles.

If the conveyor stops moving heat and air, then northern regions will cool and the deep sea will suffocate. If the deep nutrients are never brought back to the surface, then marine life will suffer; however, rotation and the moon are unrelated to ocean currents.

If water sinks in the Atlantic and doesn't reach the surface again until it hits the Pacific centuries later, then it has been "isolated" from the air for a very long time.

If the top 100 to 200 meters of the ocean are constantly stirred by the wind and waves, then the temperature and salinity are uniform. If this occurs, then it is called the surface mixed layer.

If the circulation moves massive amounts of heat around the planet and stores carbon dioxide in the deep sea, then it prevents the Earth from having extreme temperature swings. If it maintains this balance, then its primary role is climate regulation.