Thermohaline circulation

The ocean has a giant loop.

It works like a big belt. This belt moves water around the world.

Warm water moves to cold places. This water carries heat. It helps keep the Earth's weather steady.

In cold areas, the water changes. It gets very salty. This makes the water heavy. So, the water sinks deep down.

Deep water flows through the ocean. It moves very slowly. Some water stays deep for a long time.

This big loop is very important. It moves heat and food. It helps all life in the sea.

The ocean has a giant loop. Many people call it the global conveyor belt. This loop moves water and heat around the world.

The way this works depends on density. Density is how heavy water is for its size. Two main things change density. These are temperature and salinity, which means saltiness. Cold water is heavy. Salty water is also heavy. When water is both cold and salty, it sinks deep down.

In the North Atlantic, water gets very salty. This happens because of evaporation. Evaporation is when water turns into gas and leaves the ocean. This leaves the salt behind. The heavy water sinks to the bottom. It flows south through the deep ocean.

In the Southern Ocean, near Antarctica, it happens again. Strong winds blow ice away. The water gets very cold. As sea ice forms, it leaves salt in the water. This is called brine rejection. The salty brine sinks and flows north. This helps move heat and food across the globe. This loop helps keep our climate steady.

The ocean has a giant, moving system called thermohaline circulation. This system acts like a huge conveyor belt for the entire planet.

It moves heat and mass, like dissolved gases, around the globe. This movement is very important for our climate. The name comes from two words: "thermo" for temperature and "haline" for salt. Together, these two things decide how heavy or dense the seawater is.

This system works because of changes in water density. When water gets cold, it becomes denser and sinks. When water gets saltier, it also becomes denser and sinks. In the North Atlantic, wind and evaporation leave salt behind in the water. This cold, salty water sinks deep into the ocean floor. It then flows south through the deep ocean basins.

In the Southern Ocean, a process called brine rejection happens. As sea ice forms, it leaves salty brine behind. This heavy brine sinks and creates Antarctic Bottom Water.

Scientists have studied these ocean movements for a long time. In 1908, Johan Sandström proved that temperature can drive deep currents. He showed that currents happen when heating occurs deeper than cooling. Later, in the 1920s, researchers added the role of salt to this idea. In 1960, Henry Stommel and Arnold B. Arons established the idea of this circulation. They showed how different water masses move through the deep sea. This helped us understand how the whole ocean works together.

There are many important facts about this global system. The North Atlantic Deep Water (NADW) is one main driver. Another driver is the Antarctic Bottom Water (AABW). The oldest water in this loop can take 1,000 years to move. This water eventually rises back up in the North Pacific. Scientists use the UK-US RAPID programme to measure these currents. This program has been collecting data since 2004.

It helps us see how the Atlantic part of the belt is moving.

You can think of this circulation like a giant heater for Earth. It carries warmth from the equator toward the cold poles. This helps keep the temperature of our world steady. However, melting ice can add fresh water to the salty ocean. This makes the water less dense, so it might not sink as well. If the circulation slows down, it could change the weather. It might cause more droughts in some places or colder winters in Europe.

Thermohaline circulation is a massive, global system of ocean currents. It is often called the "global conveyor belt" or the ocean conveyor belt. This name was coined by the climate scientist Wallace Smith Broecker. The term "thermohaline" comes from two different factors: "thermo," meaning temperature, and "haline," meaning salt content. Together, these two factors determine the density of seawater. Because density changes how water moves, this circulation acts as a giant engine for the planet. It transports heat, energy, and mass, such as dissolved gases and solids, around the entire Earth.

The mechanism of this circulation relies on density gradients. Water becomes denser as it gets colder or saltier. In the North Atlantic, high winds and evaporation play a major role. Evaporation removes fresh water and leaves salt behind, making the surface water very salty. This region is also quite cool. The combination of high salinity and low temperature makes the water heavy enough to sink. This sinking water forms the North Atlantic Deep Water (NADW). It then flows south through deep ocean basins.

In the Southern Ocean, a different process drives deep water formation. Strong katabatic winds blow across the Antarctic ice shelves. These winds push newly formed sea ice away from the coast, creating open areas called polynyas. In these open areas, the ocean loses heat to the cold air. As sea ice forms, it undergoes a process called brine rejection. The ice crystals prefer to freeze pure water, leaving behind a very salty, cold liquid called brine. This heavy brine sinks to the bottom, creating Antarctic Bottom Water (AABW). This water is even denser than the NADW, so it flows beneath it.

This global system is divided into two major limbs. The first is the Atlantic Meridional Overturning Circulation (AMOC), which is centered in the North Atlantic. The second is the Southern Ocean Meridional Circulation (SMOC), located near Antarctica. Because 90% of humans live in the Northern Hemisphere, scientists have researched the AMOC extensively. However, the SMOC is just as important for the global climate. These two systems are connected through extensive mixing between ocean basins. This mixing reduces density differences and turns the oceans into one single, connected system.

Research into these deep currents has a long history. In the 19th century, oceanographers began suggesting that heat could drive deep currents. In 1908, Johan Sandström proved this at a research station in Bornö. He showed that currents occur when heating happens at a greater depth than cooling. In the 1920s, scientists expanded this by adding the role of salinity. Later, in 1960, Henry Stommel and Arnold B. Arons established the modern understanding of this circulation. They identified how distinct water masses move through the abyss.

The scale of this circulation is immense. The oldest waters in the system can take approximately 1,000 years to complete their journey. These old waters eventually rise to the surface through a process called upwelling. While most upwelling happens in the Southern Ocean, some scientists believe the bulk occurs in the North Pacific. To track these movements, the UK-US RAPID programme has been collecting data since 2004. It uses current meters and subsea cables to measure the strength of the AMOC at 26.5°N.

Changes to this circulation could significantly impact Earth's climate. Climate change is causing ice sheets to melt, which adds fresh water to the ocean. This fresh water dilutes the salt, making the water less dense and harder to sink. If the circulation slows down or collapses, it could reach a "tipping point." A collapse of the AMOC could cause much lower temperatures in Europe and faster sea level rise on the North American east coast. It could also lead to more droughts and fewer nutrients for marine ecosystems.