The ocean waters are constantly moving from winds that create waves and the pulling of gravity, which causes the tides. One of the most significant features in the ocean is the thermohaline circulation, commonly referred to as the great ocean conveyor belt. This massive, continuous loop of flow plays a critical role in determining the climate of the world. The two mechanisms that make this conveyor belt work are heat and salt.

The great conveyor belt plays a major part in distributing the Sun's heat around the globe after it has been absorbed by the ocean. In fact, if it wasn't for this flow, the equator would be much hotter, the poles would be much colder, and western Europe would not enjoy as warm a climate as it currently does.

The ocean conveyor belt does not move fast, but it is enormous. It carries 100 times as much water as the Amazon River. The mechanism that drives it is the differences in density. It is the ratios of salt and temperature that determine the density. When water is cold and salty, it is denser and sinks. When it is warm and fresh, it is less dense and rises to the surface.

The conveyor belt literally travels the world. In general, in a continuous loop, it transfers warm water from the Pacific Ocean to the

Atlantic as a shallow current, then returns cold water from the Atlantic to the Pacific as a deep current that flows farther south. Specifically, as it travels past the north of Australia, it is a warm current. It travels around the southern tip of Africa, then moves up into the Atlantic Ocean. At this point, it turns into the Gulf Stream, which is a very warm, north-flowing current critical for providing warmth to western Europe and the northeast coast of the United States. After it passes western Europe and heads to the Arctic, the surface water evaporates and the water cools down, releasing its heat into the atmosphere. It is this released heat that western Europe enjoys as part of their moderate climate.

At this point, the water becomes very cold and increases in salinity, becoming very dense. As its density increases, it begins to sink. The cold, dense water sinks thousands of feet below the surface of the ocean. It is now at extremely deep depths and slowly moves southward through the deep ocean abyss in the Atlantic. It flows to the Southern Hemisphere south of Australia and heads north again, until it eventually mixes upward to the surface of the ocean and starts the process all over. This entire conveyor belt cycle takes about 1,000 years to complete.

Scientists at Argonne National Laboratory (ANL) have been actively researching how long it takes water to move through this conveyor system by tracking levels of the radioactive argon-39 isotope in the Earth's ocean circulation. They are interested in tracking changes in ocean circulation, because scientists have long believed that this system plays an important role in climate moderation. According to Ernst Rehm, a physicist at ANL, "We have some idea that if the 'conveyor belt' stops, then the warm water that is brought to Europe will stop. We have some idea that this may cause an ice age in Europe."

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