Ocean circulation

Publication - March 25, 2008
The Great Ocean Conveyor Belt slowly circulates the world’s water around the globe. Ocean water is always moving because of tides and waves. The ocean conveyor (or thermohaline circulation) is powered by differences in water temperature and salinity. A well-known part of the conveyor, the Gulf Stream, gives Europe its relatively mild climate.

How it works

Warm salty water from the Gulf Stream is cooled when it reaches the North Atlantic. It becomes denser and sinks to deeper layers of the ocean, pumping cold water south in the deep ocean, past Africa into the South Atlantic. Salt rejected as sea ice forms also increases the density of these waters and contributes to the process.

The dense, cooled water becomes part of the ocean conveyor and eventually returns to the surface in the Indian and Pacific oceans. As warm water returns to the Atlantic, the current moves pole-wards as the Atlantic Gulf Stream and North Atlantic Drift, warming northwestern Europe substantially.

Aside from keeping Europe warm, and playing an important role in the global climate, the conveyor provides an upwelling of bottom ocean nutrients, and increases the oceanic absorption of carbon dioxide.

What could go wrong

Studies warn of evidence of a slower conveyor circulation over the Scotland-Greenland deep ocean ridge. While the conveyor appears to have operated fairly reliably over the past several thousand years, changes to the conveyor circulation are associated with abrupt climate change.

In short, dilution of the ocean’s salinity — from meting Arctic ice (such as the Greenland ice sheet) and/or increased precipitation — could switch off, slow down or divert the conveyor. This dramatic cooling would mean a massive disruption to European agriculture and climate, and affect other sea currents and temperatures around the globe.